Lithium supplement agent and preparation method and application thereof

Abstract

The invention provides a lithium supplement agent and a preparation method and application thereof.The lithium supplement agent comprises an inner core and a shell layer located on the surface of the inner core, the inner core comprises a lithium supplement material, the shell layer comprises a first shell layer and a second shell layer located on the surface of the side, deviating from the inner core, of the first shell layer, the first shell layer comprises a conductive polymer, and the second shell layer comprises a second shell layer located on the surface of the side, deviating from the inner core, of the first shell layer. The second shell layer comprises a carbon material, the roundness of the lithium supplement agent is 0.80-1, the shell layers of the lithium supplement agent are compact and have good conductivity, erosion of moisture and carbon dioxide in air to an inner core can be effectively inhibited, and the air stability of the lithium supplement agent is improved. In addition, the lithium supplement agent has good conductivity and relatively high roundness, so that the existence of dendritic crystals on the surface of the lithium supplement material is reduced, and the electrochemical performance such as the cycle performance of the lithium ion battery can be improved.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and particularly to a lithium supplement agent, a preparation method thereof, and an application thereof. Background Art

[0002] During the charge and discharge process of lithium-ion batteries, there are problems such as the formation of a solid electrolyte interface membrane (SEI) during the first charging process, the exfoliation of negative electrode material particles, and the irreversible deposition of lithium metal. The occurrence of these problems consumes active lithium ions in the positive electrode material, resulting in a reduction in the actual available energy density of lithium-ion batteries. Currently, the energy density of lithium-ion batteries has approached its theoretical upper limit, and lithium supplement materials have become the focus of current research because they can supplement lithium ions into lithium-ion batteries and compensate for lithium loss.

[0003] However, existing lithium supplement materials generally have problems such as poor stability, low roundness, and poor conductivity, resulting in poor electrochemical performance such as the cycle performance of the battery, which urgently needs to be solved. Summary of the Invention

[0004] The present invention provides a lithium supplement agent, a preparation method thereof, and an application thereof. The lithium supplement agent has properties such as good air stability, conductivity, and high roundness, which are beneficial to improving the electrochemical performance such as the cycle performance of the battery.

[0005] One aspect of the present invention provides a lithium supplement agent, including a core and a shell layer located on the surface of the core. The core includes a lithium supplement material, and the shell layer includes a first shell layer and a second shell layer located on the surface of the first shell layer facing away from the core. The first shell layer includes a conductive polymer, and the second shell layer includes a carbon material. The roundness of the lithium supplement agent is 0.80 - 1.

[0006] According to an embodiment of the present invention, the lithium supplement agent satisfies: 10 ≤ a * b ≤ 25, where a is the roundness of the lithium supplement agent, and b is the thickness of the shell layer, with the unit in nm.

[0007] According to an embodiment of the present invention, the thickness of the shell layer is 15 nm - 30 nm.

[0008] According to an embodiment of the present invention, the thickness of the first shell layer is 10 nm - 20 nm; and / or, the thickness of the second shell layer is 5 nm - 10 nm.

[0009] According to an embodiment of the present invention, the lithium supplement agent satisfies: the difference in carbon content between any two parts of the lithium supplement agent is less than or equal to 0.1%, and the difference in mass between any two parts of the lithium supplement agent is less than or equal to 0.1 g.

[0010] According to an embodiment of the present invention, the particle size distribution width of the lithium supplement agent satisfies 1.21 ≤ (D90 -D 10 ) / D 50 ≤10.56。

[0011] According to an embodiment of the present invention, the lithium supplement material includes a lithium-rich oxide, and the lithium-rich oxide includes lithium ferrite; and / or, the conductive polymer includes one or more of polystyrene, polyaniline, polyphenylene sulfide, polypyrrole, polyacetylene, polythiophene, polydioxythiophene, polyethylene oxide, polyvinyl alcohol, and polyacrylic acid.

[0012] Another aspect of the present invention also provides a method for preparing the above lithium supplement agent, including the following steps: coating the conductive polymer on the surface of the lithium supplement material to form the first shell layer on the surface of the lithium supplement material, obtaining an intermediate; coating the carbon material on the surface of the intermediate to form the second shell layer on the surface of the first shell layer facing away from the lithium supplement material, obtaining the lithium supplement agent; the mass ratio of the conductive polymer to the lithium supplement material is 1% to 5%.

[0013] According to an embodiment of the present invention, the process of coating the conductive polymer on the surface of the lithium supplement material includes: performing microwave drying on the raw material system including the lithium supplement material and the conductive polymer to form the first shell layer on the surface of the lithium supplement material, obtaining the intermediate; preferably, the power of the microwave drying is 500W to 650W; preferably, the time of the microwave drying is 30min to 60min.

[0014] According to an embodiment of the present invention, the process of coating the carbon material on the surface of the intermediate includes: depositing the carbon material on the surface of the intermediate by chemical vapor deposition to form the second shell layer on the surface of the first shell layer facing away from the lithium supplement material, obtaining the lithium supplement agent.

[0015] According to an embodiment of the present invention, in the process of depositing the carbon material on the surface of the intermediate by vapor deposition, the mass ratio of the carbon source used to the intermediate is 0.5 to 5, preferably 1 to 4; and / or, the temperature for depositing the carbon material is 500 to 1100 °C; and / or, the time for depositing the carbon material is 3 to 12h.

[0016] Another aspect of the present invention also provides a positive electrode sheet, including a positive electrode active material layer, and the positive electrode active material layer includes the above lithium supplement agent or a lithium supplement agent prepared according to the preparation method of the above lithium supplement agent.

[0017] According to an embodiment of the present invention, the positive electrode active material layer includes a positive electrode active material, and the mass ratio of the lithium supplement agent to the positive electrode active material is 0.5% to 10%.

[0018] Another aspect of the present invention provides a battery including the above-mentioned positive electrode sheet.

[0019] The lithium supplement agent in the present invention includes a core and a shell layer located on the surface of the core. The core includes a lithium supplement material. The shell layer includes a first shell layer and a second shell layer located on the surface of the first shell layer facing away from the core. The first shell layer includes a conductive polymer, and the second shell layer includes a carbon material. The roundness of the lithium supplement agent is 0.80-1. The shell layer of the lithium supplement agent is dense and has good conductivity, which can effectively inhibit the erosion of moisture and carbon dioxide in the air on the core, while improving the air stability of the lithium supplement agent and taking into account the improvement of the conductivity of the lithium supplement agent. In addition, within the indicated roundness range of the lithium supplement agent, the presence of dendrites on the surface of the lithium supplement material is reduced, the surface is smooth, and it can be fully mixed with the electrolyte, which is beneficial to the infiltration of the electrolyte and improves the electrochemical performance such as the cycle performance of the lithium-ion battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a scanning electron microscope image of the lithium supplement agent in Embodiment 1 of the present invention;

[0021] Figure 2 It is a schematic structural diagram of the lithium supplement agent according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0022] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0023] In related technologies, problems such as poor stability, low roundness, and poor conductivity generally exist in lithium supplement materials, resulting in poor electrochemical performance such as the cycle performance of the battery, which urgently needs to be solved.

[0024] Specifically, lithium supplement materials generally have poor air stability and are prone to react with moisture and carbon dioxide in the air to generate residual alkali components such as lithium hydroxide, which affects the performance and processing of lithium-ion batteries. For example, during the preparation of the positive electrode sheet, a lithium supplement material is added to the positive electrode slurry used to form the positive electrode coating, and then the positive electrode slurry is coated on the positive electrode current collector to form a positive electrode coating on the surface of the positive electrode current collector, achieving positive electrode lithium supplementation for the positive electrode. However, the lithium supplement material is prone to react with moisture and carbon dioxide in the air to generate residual alkali components such as lithium hydroxide on its surface, which not only affects the function of the lithium supplement material and the performance of the positive electrode sheet, but also easily causes the phenomenon of slurry gelling in the coating process. Especially when the content of residual alkali components such as lithium hydroxide on the surface of the lithium supplement material accumulates to a relatively high level, it is easy to cause a more serious slurry gel phenomenon in the positive electrode slurry, even resulting in the inability to perform coating, and is not conducive to the performance of electrochemical properties such as the cycle performance of lithium-ion batteries.

[0025] According to the research of the inventors, if the lithium supplement material is coated, the stability and other properties of the lithium supplement material can be improved to a certain extent. However, the roundness of the coated lithium supplement material is usually poor, which easily causes micro-dendrites on the surface of the lithium supplement material, resulting in irregular particles of the lithium supplement material, increasing the contact area with the electrolyte, intensifying the side reaction of the electrolyte, causing serious gas generation in the battery, and increasing the contact resistance between the particles of the lithium supplement material, which is not conducive to electron conduction in the battery. At the same time, the formation of the coating layer on the surface of the lithium supplement agent will also affect the conductivity and other properties of the coated lithium supplement material to a certain extent, affecting the function of the lithium supplement material.

[0026] In view of this, an embodiment of the present invention provides a lithium supplement agent, which includes a core and a shell layer located on the surface of the core. The core includes a lithium supplement material, and the shell layer includes a first shell layer and a second shell layer located on the surface of the first shell layer facing away from the core. The first shell layer includes a conductive polymer, and the second shell layer includes a carbon material. The roundness of the lithium supplement agent is 0.80 - 1.

[0027] In the above system, the shell layer of the lithium supplement agent contains both a first shell layer including a conductive polymer and a second shell layer including a carbon material (as Figure 2 shown), making the shell layer of the lithium supplement agent relatively dense and having good conductivity, which can effectively inhibit the erosion of moisture and carbon dioxide in the air on the core, while improving the air stability of the lithium supplement agent, taking into account the improvement of the conductivity of the lithium supplement agent. In addition, the lithium supplement agent has high roundness, reducing the presence of dendrites on the surface of the lithium supplement material, with a smooth surface, which is beneficial to reducing the contact area between the lithium supplement agent and the electrolyte, inhibiting the occurrence of side reactions of the electrolyte and gas generation in the battery, and can reduce the contact resistance between the particles of the lithium supplement material, which is beneficial to electron conduction in the battery, taking into account the improvement of the electronic conductivity of the lithium supplement agent, the capacity of the lithium-ion battery, and the electrochemical properties such as cycle performance.

[0028] According to the research of the inventors, when using a conductive polymer to coat the lithium supplement material, the roundness is relatively low. Therefore, modifying the first shell layer with the second shell layer is beneficial to improving the roundness of the lithium supplement agent, reducing the existence of dendrites on the surface of the lithium supplement material, further inhibiting the erosion of moisture and carbon dioxide in the air on the core, and enhancing the air stability of the lithium supplement agent. In addition, the conductive polymer and the carbon material have good electrical conductivity, which is beneficial to improving the electrical conductivity of the lithium supplement agent, reducing the electrochemical impedance of the battery, and concurrently enhancing the electrochemical properties such as the capacity and cycle performance of the battery.

[0029] Generally, the roundness of the lithium supplement agent is less than 0.8. For example, when the roundness (a) of the lithium supplement agent satisfies 0.7 ≤ a < 0.8, the morphology of the lithium supplement agent is slightly irregular (such as oval or slightly concave-convex particles). When 0.6 ≤ a < 0.7, the morphology of the lithium supplement agent is significantly irregular (such as polyhedral, sheet-like or dendritic particles). When a < 0.6, the morphology of the lithium supplement agent is highly irregular (such as fragmented, porous or fibrous). The lithium supplement agent of the present invention is granular, and specifically can be a spheroid or a sphere (or an ideal sphere), that is, the lithium supplement agent particles are spheroid particles (0.8 ≤ a < 1) or sphere particles (a is 1).

[0030] Specifically, the roundness of the lithium supplement agent can be 0.80, 0.81, 0.82, 0.83, 0.84, 0.85, 0.86, 0.87, 0.88, 0.89, 0.90, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, 1 or the range composed of any two of them.

[0031] The roundness of the lithium supplement agent in the embodiments of the present application can be measured by conventional testing methods in the art. For example, a scanning electron microscope (SEM) can be used to scan and photograph the lithium supplement agent to obtain a picture with a magnification of 1k times, and the picture is imported into the SEM image analysis software (Metis) for roundness calculation to obtain the roundness of the lithium supplement agent.

[0032] In some embodiments, the lithium supplement agent satisfies 10 ≤ a * b ≤ 25, where a is the roundness of the lithium supplement agent, b is the thickness of the shell layer, and a * b is the product of the roundness of the lithium supplement agent and the thickness of the shell layer. When a * b is not less than 10, while maintaining a high roundness, the shell layer of the lithium supplement agent has a relatively high thickness, which is beneficial to further inhibiting the erosion of moisture and carbon dioxide in the air on the core, and concurrently enhancing the electrical conductivity, air stability of the lithium supplement agent, and electrochemical properties such as the battery capacity and cycle performance. At the same time, when a * b is not greater than 25, it is beneficial to improving the lithium ion transmission rate in the lithium supplement agent and further enhancing the electrochemical properties such as the battery capacity.

[0033] Specifically, according to the research of the inventors, the material and thickness of the coating layer will affect the properties of the lithium supplement agent such as roundness. For example, if the coating layer is too thick, the lithium ion transmission rate in the lithium supplement agent will decrease, affecting the electrochemical properties such as the cycle performance of the battery. If the coating layer is too thin, the roundness will be small, dendrites will be generated on the surface of the lithium supplement material, exacerbating the erosion of moisture and carbon dioxide in the air on the core, and reducing the air stability of the lithium supplement agent. For the coating material, when the lithium supplement material is coated with a conductive polymer, the roundness of the lithium supplement agent is usually low. In the embodiments of the present invention, by sequentially coating the surface of the lithium supplement material with a first shell layer (including a conductive polymer) and a second shell layer (including a carbon material), the thickness of the coating layer (shell layer) of the lithium supplement agent and the roundness of the lithium supplement agent can be balanced, which is more conducive to the lithium supplement agent having a thinner coating layer while significantly improving the roundness of the lithium supplement agent, thereby taking into account the improvement of the ion transport ability of the lithium supplement agent and reducing the interfacial side reactions.

[0034] Specifically, a*b can be 10, 12, 15, 18, 20, 23, 25 or the range composed of any two of them.

[0035] In some embodiments, the thickness of the shell layer is 15nm - 30nm, such as 15nm, 18nm, 20nm, 23nm, 25nm, 28nm, 30nm or the range composed of any two of them. When the thickness of the shell layer is not less than 15nm, it is beneficial to inhibit the erosion of moisture and carbon dioxide in the air on the core and improve the air stability of the lithium supplement agent. In addition, when the thickness of the shell layer is not less than 15nm, it is also beneficial to reduce the electrochemical impedance of the lithium supplement agent, taking into account the improvement of the conductivity of the lithium supplement agent and the electrochemical properties such as the capacity and cycle performance of the battery. At the same time, when the thickness of the shell layer is not more than 30nm, it is beneficial to improve the lithium ion transmission rate in the lithium supplement agent and further improve the electrochemical properties such as the capacity of the battery. Therefore, by controlling the shell layer thickness within 15nm - 30nm, it is beneficial to take into account the improvement of the conductivity, air stability, lithium ion transmission rate, and electrochemical properties such as the capacity and cycle performance of the lithium supplement agent.

[0036] The thickness of the first shell layer in the embodiments of the present application can be measured through the following process: Grind the lithium supplement agent with an ion milling machine, put the ground lithium supplement agent into a field emission scanning electron microscope (FE-SEM) for single-particle cross-section scanning, take the scanning results of at least 10 particles, calculate the thickness of the first shell layer of at least 10 particles according to the scale, and take the average value to obtain the thickness of the first shell layer, where the thickness of the first shell layer of each particle is the average value of its maximum thickness and minimum thickness.

[0037] The thickness of the second shell layer in the embodiments of the present application can be measured through the following process: Grind the lithium supplement agent with an ion milling machine, put the obtained ground lithium supplement agent into a field emission scanning electron microscope (FE-SEM) for single-particle cross-section scanning, take the scanning results of at least 10 particles, calculate the thickness of the second shell layer of at least 10 particles according to the scale, take the average value thereof to obtain the thickness of the second shell layer, where the thickness of the second shell layer of each particle is the average value of its maximum thickness and minimum thickness.

[0038] In the embodiments of the present invention, the thickness of the shell layer (for example, 15 nm to 30 nm) refers to the total thickness of the shell layer on the surface of the lithium supplement agent. For example, when the shell layer on the surface of the lithium supplement agent includes the above-mentioned first shell layer and second shell layer, the thickness of the shell layer refers to the sum of the thickness of the first shell layer and the thickness of the second shell layer.

[0039] In some embodiments, the thickness of the first shell layer is greater than or equal to the thickness of the second shell layer. According to the research of the inventors, the first shell layer plays a role in coating the lithium supplement material. Controlling the thickness of the first shell layer to be greater than or equal to the thickness of the second shell layer is beneficial to the uniform coating of the lithium supplement material and avoids the problem that the first shell layer deteriorates due to too small a thickness, thereby causing the first shell layer to be damaged. At the same time, the second shell layer plays a role in modifying the first shell layer, which is further beneficial to improving the surface uniformity of the lithium supplement material. Controlling the thickness of the first shell layer to be greater than or equal to the thickness of the second shell layer is also beneficial to the insertion and extraction of lithium ions and improves the electrochemical performance such as the battery cycle performance.

[0040] In some embodiments, the thickness of the first shell layer is 10 nm - 20 nm, such as 10 nm, 11 nm, 12 nm, 13 nm, 14 nm, 15 nm, 16 nm, 17 nm, 18 nm, 19 nm, 20 nm or the range composed of any two of them, which is beneficial to improving the conductivity and ion transport ability of the lithium supplement agent, taking into account the improvement of the electronic conductivity and battery capacity of the lithium supplement agent. In addition, it is also beneficial to inhibit the erosion of moisture and carbon dioxide in the air on the core and improve the air stability of the lithium supplement agent.

[0041] In some embodiments, the thickness of the second shell layer is 5 nm - 10 nm, such as 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, 10 nm or the range composed of any two of them, which is beneficial to further improving the conductivity and lithium ion transport ability of the lithium supplement agent, thereby taking into account the improvement of the electronic conductivity and battery capacity of the lithium supplement agent. In addition, it is also beneficial to inhibit the erosion of moisture and carbon dioxide in the air on the core and improve the air stability of the lithium supplement agent.

[0042] In some embodiments, the carbon content of the lithium supplement agent (i.e., the mass percentage of the carbon material in the lithium supplement agent) is 1.0 wt% to 1.5 wt%, such as 1.0 wt%, 1.1 wt%, 1.2 wt%, 1.3 wt%, 1.4 wt%, 1.5 wt% or the range composed of any two of them, which is beneficial to improving the conductivity of the lithium supplement agent, accelerating the transmission of lithium ions, and improving the electrochemical properties such as the capacity of the battery.

[0043] In some embodiments, the lithium supplement agent satisfies that the difference in carbon content between any two parts of the lithium supplement agent is less than or equal to 0.1%, and the difference in mass between any two parts of the lithium supplement agent is less than or equal to 0.1 g. In the above system, the carbon material on the surface of the lithium supplement agent is evenly distributed, which is beneficial to reducing the existence of dendrites on the surface of the lithium supplement material and improving the electrochemical properties such as the capacity and cycle performance of the lithium ion battery.

[0044] Specifically, the difference in carbon content between any two parts of the lithium supplement agent can be less than or equal to 0.1%, less than or equal to 0.09%, less than or equal to 0.08%, less than or equal to 0.07%, less than or equal to 0.06%, less than or equal to 0.05%, less than or equal to 0.04%, less than or equal to 0.03%, less than or equal to 0.02% or the range composed of any two of them, and the difference in mass between any two parts of the lithium supplement agent can be less than or equal to 0.1 g, less than or equal to 0.08 g, less than or equal to 0.05 g, less than or equal to 0.03 g, less than or equal to 0.01 g or the range composed of any two of them.

[0045] The microscopic state of the lithium supplement agent in the embodiments of the present invention is granular, and the macroscopic state is powdery. The difference in carbon content between any two parts of the lithium supplement agent is the difference in carbon content between any two parts of the lithium supplement agent powder, which can be measured through the following process: Take three parts of powder from the lithium supplement agent powder and use a carbon-sulfur analyzer (Sichuan Sains HCS-801 high-frequency infrared carbon-sulfur analyzer) to test the carbon content, and obtain three carbon content values. Take the difference between the maximum value and the minimum value as the difference in carbon content between any two parts of the lithium supplement agent, where the difference in mass between any two parts of the three parts of powder is less than or equal to 0.1 g.

[0046] In some embodiments, the lithium supplement material includes a lithium-rich compound, the lithium-rich compound includes a lithium-rich oxide, and the lithium-rich oxide includes lithium ferrite (Li5FeO4). According to the research of the inventors, the lithium ion content in lithium ferrite is high, and 1 mol of lithium ferrite can release 4 mol of lithium ions during discharge, which is more beneficial to supplementing lithium ions into the battery, compensating for lithium loss, and facilitating the capacity of the battery.

[0047] In some embodiments, the particle size distribution width (SPAN) of the lithium supplement agent satisfies 1.21 ≤ (D 90 -D10 ) / D 50 ≤10.56, where D 10 represents the particle size at which the cumulative volume of particles in the particle size distribution of the lithium supplement agent based on volume reaches 10% starting from the small particle size side, i.e., D v10 ; D 50 represents the particle size at which the cumulative volume of particles in the particle size distribution of the lithium supplement agent based on volume reaches 50% starting from the small particle size side, i.e., D v50 ; D 90 represents the particle size at which the cumulative volume of particles in the particle size distribution of the lithium supplement agent based on volume reaches 90% starting from the small particle size side, i.e., D v90 . For example, (D 90 -D 10 ) / D 50 can be 1.21, 1.25, 1.30, 1.50, 2.00, 2.20, 2.30, 2.40, 2.48, 2.50, 3.00, 3.50, 4.00, 4.50, 5.00, 5.50, 6.00, 6.50, 7.00, 7.50, 8.00, 9.00, 10.00, 10.50, 10.56 or the range composed of any two of them. In the above range, the particle size distribution width of the lithium supplement agent is narrow, the particle sizes of the lithium supplement agent are uniform, which is beneficial to the improvement of electrochemical properties such as the battery cycle performance.

[0048] In some embodiments, the conductive polymer includes one or more of styrene, polyaniline, polyphenylene sulfide, polypyrrole, polyacetylene, polythiophene, poly(3,4-ethylenedioxythiophene), poly(ethylene oxide) (PEO), poly(vinyl alcohol) (PVA), and poly(acrylic acid) (PAA).

[0049] The embodiment of the present invention also provides a preparation method of the above lithium supplement agent, including the following steps: coating a conductive polymer on the surface of the lithium supplement material to form a first shell layer on the surface of the lithium supplement material to obtain an intermediate; coating a carbon material on the surface of the intermediate to form a second shell layer on the surface of the first shell layer away from the lithium supplement material to obtain the lithium supplement agent; the mass ratio of the conductive polymer to the lithium supplement material is 1% - 5%, for example, 1%, 2%, 3%, 4%, 5% or the range composed of any two of them.

[0050] In some embodiments, the mass ratio of the conductive polymer to the lithium supplement material is 1% - 3%, for example, 1%, 1.5%, 2%, 2.5% or the range composed of any two of them, which is beneficial to further improving the battery capacity and taking into account the improvement of performance such as the battery cycle performance.

[0051] The mass percentage of free lithium in the lithium supplement prepared by the above method is less than or equal to 1%, for example, less than or equal to 0.1%, less than or equal to 0.09%, less than or equal to 0.08%, less than or equal to 0.07%, less than or equal to 0.06%, less than or equal to 0.05%, less than or equal to 0.04%, less than or equal to 0.03%, less than or equal to 0.02%, or the range composed of any two of them, which is beneficial to the performance of battery capacity and can avoid problems such as slurry gelation during the coating process caused by too high mass percentage of free lithium in the lithium supplement.

[0052] In the embodiments of the present invention, the lithium supplement material can be prepared by conventional methods in the art. For example, when the lithium supplement material is a lithium-rich compound, it can be prepared by sintering a mixture containing a lithium source and a non-lithium metal source.

[0053] Specifically, during implementation, the lithium source and the non-lithium metal source can be first mixed and then sintered at a high temperature under vacuum or inert gas protection to obtain the lithium supplement material.

[0054] Specifically, the high-temperature sintering can be carried out through the following process: heating from room temperature to 400°C to 550°C (hereinafter referred to as the first temperature), holding for 3h to 6h (hereinafter referred to as the first holding time), then heating to 750°C to 900°C (hereinafter referred to as the second temperature), and holding for 5 to 15h (hereinafter referred to as the second holding time).

[0055] Specifically, during implementation, the first temperature can be 400°C, 420°C, 450°C, 480°C, 500°C, 530°C, 550°C, or the range composed of any two of them; the first holding time can be 3h, 4h, 5h, 6h, or the range composed of any two of them; the second temperature can be 750°C, 800°C, 850°C, 900°C, or the range composed of any two of them; the second holding time can be 5h, 6h, 7h, 8h, 9h, 10h, 11h, 12h, 13h, 14h, 15h, or the range composed of any two of them.

[0056] Specifically, during implementation, the product obtained by high-temperature sintering can be cooled to room temperature with the furnace to obtain the lithium supplement material.

[0057] Exemplarily, the molar ratio of the lithium element in the lithium source to the metal element in the non-lithium metal source is (5 to 6):1, for example, 5:1, 5.2:1, 5.5:1, 5.8:1, 6:1, or the range composed of any two of them.

[0058] In specific implementation, the particle size of the lithium source can be in the micron range, and the lithium source can include one or more of lithium hydroxide (LiOH), lithium carbonate (Li2CO3), lithium oxide (Li2O), lithium peroxide (Li2O2), lithium nitrate (LiNO3), lithium sulfate (Li2SO4), lithium citrate (C6H5Li3O7), lithium oxalate (Li2C2O4), lithium ethoxide (C2H5OLi), and metallic lithium.

[0059] In addition, the particle size of the non-lithium metal source can be in the nanometer range. The non-lithium metal source refers to a metal source different from the lithium source and does not contain lithium element. The non-lithium metal source can include one or more of iron oxide (Fe2O3), iron tetroxide (Fe3O4), iron hydroxide (Fe(OH)3), and iron oxyhydroxide (FeO(OH)).

[0060] In some embodiments, the process of coating the surface of the lithium supplement material with a conductive polymer includes: subjecting a raw material system including the lithium supplement material and the conductive polymer to microwave drying to form a first shell layer on the surface of the lithium supplement material, thereby obtaining an intermediate.

[0061] In some embodiments, the power of the microwave drying is 500W - 650W, such as 500W, 550W, 600W, 650W, or a range composed of any two of them, and the time of the microwave drying is 30min - 60min, such as 30min, 40min, 50min, 60min, or a range composed of any two of them, which is beneficial to controlling the thickness of the first shell layer, taking into account the improvement of the air stability and electronic conductivity of the lithium supplement agent, and also taking into account the improvement of the capacity and cycle performance of the battery.

[0062] Specifically, the surface of the lithium supplement material can be coated with a conductive polymer by wet ball milling. That is, after mixing the lithium supplement material, the conductive polymer, and a solvent, wet ball milling is carried out, and then the obtained ball milling system is subjected to microwave drying (or microwave heating) to obtain an intermediate. In specific implementation, the process of mixing the lithium supplement material, the conductive polymer, and the solvent can include: adding the lithium supplement material to the solvent to disperse the lithium supplement material in the solvent, and then adding the conductive polymer thereto.

[0063] Among them, the solvent includes organic solvents, and the organic solvents include one or more of ethanol, tetrahydrofuran (THF), N-methylpyrrolidone (NMP), and dimethyl sulfoxide (DMSO).

[0064] In addition, the rotation speed of the wet ball milling is 200r / min - 700r / min, such as 200r / min, 300r / min, 400r / min, 500r / min, 600r / min, 700r / min, or a range composed of any two of them.

[0065] In addition, the time for wet ball milling is 1 h to 3 h, such as 1 h, 1.5 h, 2 h, 2.5 h, 3 h, or the range composed of any two of them.

[0066] In specific implementation, after the microwave drying is completed, the obtained dried product can be sieved once to obtain an intermediate; wherein, the mesh number of the sieve used for the first sieving is 300 mesh to 500 mesh, such as 300 mesh, 350 mesh, 400 mesh, 450 mesh, 500 mesh, or the range composed of any two of them.

[0067] In some embodiments, the process of coating the carbon material on the surface of the intermediate includes: depositing the carbon material on the surface of the intermediate by chemical vapor deposition to form a second shell layer on the surface of the first shell layer facing away from the lithium supplementing material, thereby obtaining a lithium supplementing agent.

[0068] The present invention uses chemical vapor deposition (CVD) method to coat the carbon material and form the second shell layer. Compared with plasma enhanced chemical vapor deposition (PECVD), the process flow is simplified and the production cost is effectively reduced.

[0069] In some embodiments, during the process of depositing the carbon material on the surface of the intermediate by vapor deposition method, the mass ratio of the carbon source to the intermediate is 0.5 to 5, such as 0.5, 1, 2, 3, 4, 5, or the range composed of any two of them, which is beneficial to controlling the thickness of the second shell layer, modifying the first shell layer, more conducive to improving the roundness of the lithium supplementing agent, reducing dendrites on the surface of the lithium supplementing material, beneficial to inhibiting the erosion of moisture and carbon dioxide in the air on the inner core, improving the air stability of the lithium supplementing agent. In addition, it is also beneficial to improving the conductivity and lithium ion transmission ability of the lithium supplementing agent, and taking into account the improvement of electrochemical properties such as the capacity and cycle performance of the battery. Preferably, it is 1 to 4. In the above preparation process, the carbon material is formed by carbonizing the carbon source.

[0070] In some embodiments, the temperature for depositing the carbon material (or the temperature for carbonization treatment) is 500 to 1100 °C, such as 500 °C, 600 °C, 700 °C, 800 °C, 900 °C, 1000 °C, 1100 °C, or the range composed of any two of them.

[0071] In some embodiments, the time for depositing the carbon material (i.e., the time for introducing the carbon source, or the time for carbonization treatment) is 3 to 12 h, such as 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, or the range composed of any two of them.

[0072] In specific implementation, carbon materials can be deposited on the surface of the intermediate by CVD method under a protective gas. The protective gas is an inert gas, and the protective gas can include one or more of nitrogen and argon. The flow rate of the protective gas can be 100 sccm - 2000 sccm, such as 100 sccm, 200 sccm, 500 sccm, 800 sccm, 1000 sccm, 1500 sccm, 2000 sccm or the range composed of any two of them.

[0073] In the embodiment of the present invention, the process of depositing carbon materials on the surface of the intermediate by chemical vapor deposition method can be carried out by using conventional CVD equipment in the art. In specific implementation, the intermediate can be first added into the CVD equipment, the material can be lifted with a certain furnace tube rotation speed, and the protective gas can be introduced for gas washing, then it can be heated to the temperature of carbonization treatment at a certain heating rate, and then a carbon source can be introduced into the CVD equipment for carbonization treatment to obtain the lithium supplement agent.

[0074] Among them, the furnace tube rotation speed can be 5 r / min - 10 r / min, such as 5 r / min, 6 r / min, 7 r / min, 8 r / min, 9 r / min, 10 r / min or the range composed of any two of them.

[0075] Specifically, the heating rate can be 3 °C / min - 20 °C / min, such as 3 °C / min, 5 °C / min, 7 °C / min, 10 °C / min, 12 °C / min, 15 °C / min, 17 °C / min, 20 °C / min or the range composed of any two of them.

[0076] In addition, the carbon source includes organic gas, and the organic gas can include aliphatic hydrocarbons, and the aliphatic hydrocarbons can include one or more of methane, ethane, propane, butane, ethylene, propylene, butene, pentene, acetylene, propyne, and butyne.

[0077] In specific implementation, after the carbonization treatment is completed, the obtained carbonized product can be cooled, specifically by furnace cooling, to obtain the cooled carbonized product, and the cooled carbonized product is subjected to secondary sieving to obtain the lithium supplement agent; among them, the mesh number of the sieve used for secondary sieving is 400 mesh - 500 mesh, such as 400 mesh, 450 mesh, 500 mesh or the range composed of any two of them.

[0078] The embodiment of the present invention also provides a positive electrode sheet, which includes a positive electrode active material layer. The positive electrode active material layer includes the above-mentioned lithium supplement agent or the lithium supplement agent prepared according to the preparation method of the above-mentioned lithium supplement agent, and has the properties corresponding to the above-mentioned lithium supplement agent, which will not be elaborated here.

[0079] In some embodiments, the positive electrode active material layer includes a positive electrode active material, and the mass ratio of the lithium supplement agent to the positive electrode active material is 0.5% to 10%, such as 0.5%, 1%, 2%, 3%, 5%, 8%, 10%, or a range composed of any two of them.

[0080] Specifically, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer located on at least one surface of the positive electrode current collector. Specifically, the positive electrode active material layer can be provided on one surface of the positive electrode current collector, or positive electrode active material layers are respectively provided on opposite surfaces in the thickness direction of the positive electrode current collector.

[0081] Specifically, the positive electrode active material layer may include a positive electrode active material, a positive electrode conductive agent, a positive electrode binder, and the above-mentioned lithium supplement agent. Among them, the positive electrode active material, the positive electrode conductive agent, and the positive electrode binder can all be conventional materials in the art. For example, the positive electrode active material may include one or more of lithium iron phosphate, lithium cobaltate, lithium manganate, and positive electrode ternary materials. The positive electrode ternary materials may include nickel cobalt manganese ternary materials (NCM) and / or nickel cobalt aluminum ternary materials (NCA). The positive electrode conductive agent may include one or more of conductive carbon black (Super.P or SP), conductive graphite, carbon nanotubes (CNT), acetylene black, graphene, Ketjen black, and carbon fiber. The positive electrode binder may include one or more of polyvinylidene fluoride (PVDF), polyvinyl fluoride, polyethylene, polypropylene, polyvinyl alcohol, polyvinyl chloride, carboxylated polyvinyl chloride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, etc.

[0082] Embodiments of the present invention may use a conventional positive electrode current collector in the art. For example, the positive electrode current collector includes aluminum foil.

[0083] In the embodiments of the present invention, the positive electrode sheet can be prepared by a conventional method in the art, for example, by a coating method. Specifically, components for forming the positive electrode active material layer, such as the positive electrode active material, the positive electrode conductive agent, and the positive electrode binder, can be dispersed in a positive electrode solvent. The positive electrode solvent includes, for example, N-methylpyrrolidone (NMP), to form a positive electrode slurry, and then the positive electrode slurry is coated on the surface of the positive electrode current collector and processed through processes such as drying and rolling to obtain the positive electrode sheet. Among them, the processes such as coating, drying, and rolling involved are conventional operations for preparing the positive electrode sheet by the coating method, and no special limitations are imposed on them.

[0084] Embodiments of the present invention further provide a battery, including the above-mentioned positive electrode sheet, having properties corresponding to the above-mentioned positive electrode sheet, which will not be elaborated here.

[0085] The battery of the present invention can be a lithium-ion battery.

[0086] Generally, a battery includes a battery cell, an electrolyte, and a casing for encapsulating the battery cell. The electrolyte is injected into the battery cell within the casing. The battery cell includes a positive electrode sheet, a negative electrode sheet, and a separator located between the positive electrode sheet and the negative electrode sheet. Among them, the battery cell can be a wound battery cell and / or a stacked battery cell.

[0087] In the embodiments of the present invention, a battery can be prepared by conventional methods in the art. For example, the positive electrode sheet, the separator, and the negative electrode sheet can be stacked alternately to obtain a stacked battery cell; or the positive electrode sheet, the separator, and the negative electrode sheet can be wound in sequence to obtain a wound battery cell. Then, the battery cell is placed in a casing, and after conventional processes such as liquid injection (i.e., injecting the electrolyte), encapsulation, standing, formation, and grading, the battery is obtained.

[0088] Specifically, the negative electrode sheet includes a negative electrode current collector and a negative electrode coating located on at least one surface of the negative electrode current collector. Specifically, a negative electrode coating can be provided on one surface of the negative electrode current collector, or negative electrode coatings can be respectively provided on opposite surfaces in the thickness direction of the negative electrode current collector.

[0089] Specifically, the negative electrode coating (negative electrode active material layer) can include a negative electrode active material, a negative electrode conductive agent, and a negative electrode binder, all of which can be conventional materials in the art. For example, the negative electrode active material can include one or more of artificial graphite and silicon carbon; the negative electrode conductive agent can include one or more of conductive carbon black (SP), carbon nanotubes (CNT), acetylene black, graphene, Ketjen black, and carbon fiber; the negative electrode binder can include one or more of sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, a polymer containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyvinyl alcohol, and sodium polyacrylate.

[0090] In the embodiments of the present invention, a conventional negative electrode current collector in the art can be used. For example, the negative electrode current collector includes copper foil.

[0091] In the embodiments of the present invention, the negative electrode sheet can be obtained by conventional methods in the art. For example, it can be obtained by a coating method. Specifically, components for forming the negative electrode coating such as the negative electrode active material, the negative electrode conductive agent, and the negative electrode binder can be dispersed in a negative electrode solvent. The negative electrode solvent includes water, for example, to prepare a negative electrode slurry, and then it is coated on the surface of the negative electrode current collector. After processes such as drying and rolling, the negative electrode sheet is obtained. Among them, the processes such as coating, drying, and rolling involved are conventional operations for preparing the negative electrode sheet by the coating method, and no special restrictions are imposed on this.

[0092] In the embodiments of the present invention, the separator is used to separate the positive electrode sheet and the negative electrode sheet to prevent the positive electrode sheet and the negative electrode sheet from contacting and short - circuiting. Conventional separators in the art can be used in the embodiments of the present invention. For example, the separator includes a polypropylene film (PP film), polyethylene (PE), a three - layer composite separator of polypropylene / polyethylene / polypropylene (PP / PE / PP three - layer composite separator), but is not limited thereto.

[0093] In the embodiments of the present invention, the electrolyte can be a non - aqueous electrolyte. The non - aqueous electrolyte generally includes a lithium salt, a carbonate solvent, and an additive. Among them, the carbonate solvent can include one or more of a cyclic carbonate solvent and a chain - like carbonate solvent, specifically including ethylene carbonate (EC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), propylene carbonate (PC), ethyl propionate (EP), fluoroethylene carbonate (FEC), etc.; the lithium salt can include one or more of lithium hexafluorophosphate (LiPF6), lithium perchlorate, etc.; the additive can include one or more of fluoroethylene carbonate, difluoroethylene carbonate, fluorocyclotriphosphazene, hexafluorocyclotriphosphazene, vinylene carbonate (VC), etc.

[0094] In the embodiments of the present invention, conventional housing materials in the art can be used to encapsulate the battery cell. The housing includes, for example, soft packaging materials such as aluminum - plastic films (the battery at this time is a soft - packaged battery), but is not limited thereto.

[0095] Hereinafter, the present invention will be further introduced through specific embodiments.

[0096] Example 1

[0097] 1. Preparation of the lithium supplement agent

[0098] After weighing LiOH and Fe2O3 according to the molar ratio of lithium to iron elements of 5.2:1 respectively, they are put into a steel mill for grinding and mixing, and then sintered to obtain the lithium - supplement material Li5FeO4.

[0099] Li5FeO4 is dispersed in tetrahydrofuran, and after stirring evenly, conductive polymer polystyrene is added thereto for wet ball - milling to obtain a ball - milling system. Among them, the addition amount of the conductive polymer (i.e., the mass ratio of the conductive polymer to Li5FeO4) is 1 wt%, the rotation speed of the wet ball - milling is 200 r / min, and the time of the wet ball - milling is 1 h.

[0100] After microwave drying the ball - milling system, a dried product is obtained. The dried product is sieved once to obtain an intermediate (Li5FeO4 coated with a conductive polymer). Among them, the power of the microwave drying is 500 W, the time of the microwave drying is 30 min; the mesh number of the sieve used for the first sieving is 300 meshes.

[0101] The intermediate was added to the CVD equipment, stirred at a speed of 5 r / min, and nitrogen was introduced as a protective gas. The flow rate of nitrogen was 100 sccm, and the temperature was raised to 500°C at a heating rate of 3°C / min, and then acetylene was introduced for carbonization treatment. After the carbonization treatment was completed, it was cooled with the furnace and passed through a 400-mesh sieve to obtain a lithium supplement. Among them, the amount of acetylene added was twice the amount of the intermediate added (that is, the mass ratio of acetylene to the intermediate was 2), and the time for acetylene to be introduced (carbonization treatment time) was 0.5h. The lithium supplement in Example 1 was tested by scanning electron microscopy, and the results are as follows: Figure 1 As shown, it can be seen that the lithium supplement in Example 1 is spherical particles.

[0102] 2. Preparation of batteries

[0103] (1) Preparation of positive electrode

[0104] The lithium supplement agent and lithium iron phosphate (positive electrode active material) are compounded as a mixed system, wherein the mass ratio of the lithium supplement agent to the positive electrode active material is 2%, and the mixed system is weighed according to the mass ratio of SP:PVDF=96:2:2, and then added into a double planetary mixer, and an appropriate amount of NMP is added and mixed to fully prepare a positive electrode slurry;

[0105] The positive electrode slurry is coated on the front and back surfaces of the aluminum foil, and after drying and rolling, a positive electrode coating is formed on the front and back surfaces of the aluminum foil to obtain a positive electrode sheet.

[0106] (2) Preparation of negative electrode sheet

[0107] The negative electrode active material is artificial graphite, which is weighed according to the mass ratio of negative electrode active material: CMC: SBR: SP = 94:1:2:3 and added into a double planetary mixer, and an appropriate amount of deionized water is added and mixed to fully form a negative electrode slurry; the negative electrode slurry is coated on the front and back surfaces of the copper foil, and after drying and rolling, a negative electrode coating is formed on the front and back surfaces of the copper foil to obtain a negative electrode sheet.

[0108] (3) Battery assembly

[0109] The positive electrode sheet, the separator (PP / PE / PP three-layer structure composite separator) and the negative electrode sheet are alternately stacked to assemble a laminated battery cell; the laminated battery cell is placed in an aluminum-plastic film, and the injection port is retained, and the above electrolyte is injected into it through the injection port, and then the injection port is closed, and aging, formation (cut-off voltage is 4.3V) and aging treatment are carried out in sequence to obtain a battery. The above-mentioned electrolyte is composed of LiPF6, EC, EMC, and FEC, wherein the mass ratio of EC to EMC is 7:3, the mass percentage of FEC in the electrolyte is 1%, and the concentration of LiPF6 in the electrolyte is 1mol / L.

[0110] Example 2

[0111] The difference from Example 1 is that the addition amount of the conductive polymer is 2 wt%, and the remaining steps and conditions are the same as those in Example 1.

[0112] Example 3

[0113] The difference from Example 1 is that the addition amount of the conductive polymer is 3 wt%, and the remaining steps and conditions are the same as those in Example 1.

[0114] Example 4

[0115] The difference from Example 1 is that the addition amount of the conductive polymer is 4 wt%, and the remaining steps and conditions are the same as those in Example 1.

[0116] Example 5:

[0117] The difference from Example 1 is that the addition amount of the conductive polymer is 5 wt%, and the remaining steps and conditions are the same as those in Example 1.

[0118] Example 6

[0119] The difference from Example 1 is that the addition amount of the conductive polymer is 2 wt%, and the addition amount of acetylene is 0.5 times the addition amount of the intermediate, and the remaining steps and conditions are the same as those in Example 1.

[0120] Example 7

[0121] The difference from Example 1 is that the addition amount of the conductive polymer is 2 wt%, and the addition amount of acetylene is 1 time the addition amount of the intermediate, and the remaining steps and conditions are the same as those in Example 1.

[0122] Example 8

[0123] The difference from Example 1 is that the addition amount of the conductive polymer is 2 wt%, and the addition amount of acetylene is 3 times the addition amount of the intermediate, and the remaining steps and conditions are the same as those in Example 1.

[0124] Example 9

[0125] The difference from Example 1 is that the addition amount of the conductive polymer is 2 wt%, and the addition amount of acetylene is 4 times the addition amount of the intermediate, and the remaining steps and conditions are the same as those in Example 1.

[0126] Example 10

[0127] The difference from Example 1 is that the addition amount of the conductive polymer is 2 wt%, and the addition amount of acetylene is 5 times the addition amount of the intermediate, and the remaining steps and conditions are the same as those in Example 1.

[0128] Example 11

[0129] The difference from Example 1 is that the power of microwave drying is 650 W, the time of microwave drying is 60 min, and the remaining steps and conditions are the same as those in Example 1.

[0130] Example 12

[0131] The difference from Example 1 is that the power of microwave drying is 800 W, and the remaining steps and conditions are the same as those in Example 1.

[0132] Example 13

[0133] The difference from Example 1 is that the time of microwave drying is 120 min, and the remaining steps and conditions are the same as those in Example 1.

[0134] Example 14

[0135] The difference from Example 1 is that the temperature of carbonization treatment is 1100 °C, and the remaining steps and conditions are the same as those in Example 1.

[0136] Example 15

[0137] The difference from Example 1 is that the time of carbonization treatment is 3 h, and the remaining steps and conditions are the same as those in Example 1.

[0138] Comparative Example 1

[0139] The difference from Example 1 is that the addition amount of conductive polymer is 7 wt%, the addition amount of acetylene is 1.5 times the addition amount of intermediate, and the remaining steps and conditions are the same as those in Example 1.

[0140] Comparative Example 2

[0141] The difference from Example 2 is that in the preparation process of the lithium supplement agent:

[0142] LiOH and Fe2O3 were respectively weighed according to the molar ratio of lithium to iron elements of 5.2:1, put into a steel mill for grinding and mixing, and then sintered to obtain the lithium supplement material Li5FeO4; Li5FeO4 was added into a CVD device, stirred at a speed of 5 r / min, and nitrogen was introduced as a protective gas, the flow rate of nitrogen was 100 sccm, and the temperature was raised to 500 °C at a heating rate of 3 °C / min, and then acetylene was introduced for carbonization treatment. After the carbonization treatment was completed, it was cooled with the furnace and sieved through a 400-mesh sieve to obtain an intermediate product (carbon-coated Li5FeO4). Among them, the introduction time of acetylene (the time of carbonization treatment) was 0.5 h.

[0143] Disperse the intermediate product in tetrahydrofuran. After stirring evenly, add the conductive polymer poly(phenylene vinylenes) to it for wet ball milling to obtain a ball milling system. The rotation speed of the wet ball milling is 200 r / min, and the time of the wet ball milling is 1 h.

[0144] After microwave drying the ball milling system, sieve it through a 300-mesh sieve to obtain a lithium supplement agent. Among them, the power of the microwave drying is 500 W, and the time of the microwave drying is 30 min. Among them, the addition amount of the conductive polymer, the addition amount of the carbon source, and the addition amount of the lithium supplement material are the same as those in Example 2.

[0145] The remaining steps and conditions are the same as those in Example 2.

[0146] Summarize the addition amount of the conductive polymer (i.e., the mass ratio of the conductive polymer to Li5FeO4), the ratio of the addition amount of the carbon source to the addition amount of the intermediate in each example and comparative example in Table 1.

[0147] Perform performance tests on the lithium supplement agents and batteries in the examples and comparative examples through the following processes respectively. The results are shown in Table 1 and Table 2:

[0148] (1) Particle size distribution width (SPAN) test: Use Nano Measurer to detect the lithium supplement agents in each example and comparative example to obtain the particle size distribution width (SPAN) of the lithium supplement agents.

[0149] (2) Carbon content difference between any two parts of the lithium supplement agent: Take three parts of powder from the lithium supplement agent powder and use a carbon and sulfur analyzer (Sichuan Sains HCS-801 high-frequency infrared carbon and sulfur analyzer) to test the carbon content, measure three carbon content values, and take the difference between the maximum value and the minimum value as the carbon content difference (carbon content difference between any two parts of the lithium supplement agent). Among them, the mass difference between any two parts of the three parts of powder is less than or equal to 0.1 g.

[0150] (3) Powder impedance test: Use Keithley 2450 / 2460 SourceMeter to test the impedance of the compacted lithium supplement agent powder to obtain the powder impedance of the lithium supplement agent.

[0151] (4) Conductivity test: Use Keithley 2450 source meter to perform electronic conductivity test on the lithium supplement agent to obtain the electronic conductivity of the lithium supplement agent.

[0152] (5) Battery capacity test: Perform charge and discharge tests on the batteries in the examples and comparative examples: The test temperature is 25 °C, the voltage range is 2.8 V to 4.2 V, and the current density (or charge and discharge rate) is 0.1 C to obtain the first charge capacity.

[0153] (6) Air stability test: Under the conditions of a temperature of 25 °C and a humidity of 30% RH, the lithium supplement agents in each example and the comparative example were exposed to air for 24 h to obtain the lithium supplement agents after 24 h of exposure. Then, batteries were prepared with the lithium supplement agents after 24 h of exposure according to the battery preparation methods in the above examples and comparative examples, and charge-discharge tests were carried out: the test temperature was 25 °C, the voltage range was 2.8 V to 4.2 V, and the current density (or charge-discharge rate) was 0.1 C. The first charge-discharge capacity (charge capacity after 24 h of exposure) of the lithium supplement agent after 24 h of exposure was obtained. Air stability (i.e., capacity retention rate after 24 h of exposure) = charge capacity after 24 h of exposure / first charge-discharge capacity * 100%.

[0154] (7) Cycle performance test: The batteries in the examples and the comparative example were subjected to cyclic charge-discharge tests: the test temperature was 25 °C, the voltage range was 2.8 V to 4.2 V, the current density (or charge-discharge rate) was 0.1 C, and cyclic charge-discharge was carried out for 100 cycles to obtain the capacity retention rate after 100 cycles.

[0155] (8) Tests on the thickness of the first shell layer, the thickness of the second shell layer, and the thickness of the shell layer: The lithium supplement agent was ground using an ion milling machine, and the ground lithium supplement agent was placed in a field emission scanning electron microscope (FE-SEM) for single-particle cross-section scanning. The scanning results of 10 particles were photographed, and the thicknesses of the first shell layer and the second shell layer of the 10 particles were calculated according to the scale. The average values were taken respectively to obtain the thickness of the first shell layer and the thickness of the second shell layer. Among them, the thickness of the first shell layer of each particle was the average value of its maximum thickness and minimum thickness, the thickness of the second shell layer of each particle was the average value of its maximum thickness and minimum thickness, and the shell layer thickness was equal to the sum of the thickness of the first shell layer and the thickness of the second shell layer.

[0156] (9) Roundness test

[0157] The lithium supplement agent was scanned and photographed using SEM at a magnification of 1k times. The picture was imported into SEM image analysis software (Metis) for roundness calculation to obtain the roundness of the lithium supplement agent.

[0158] Table 1

[0159]

[0160] Table 2

[0161]

[0162]

[0163] As can be seen from Table 1 and Table 2, compared with Comparative Example 1 and Comparative Example 2, the lithium supplement agents in Examples 1 to 15 include a core and a shell layer located on the surface of the core. The core includes a lithium supplement material, and the shell layer includes a first shell layer and a second shell layer located on the surface of the first shell layer facing away from the core. The first shell layer includes a conductive polymer, and the second shell layer includes a carbon material. The roundness of the lithium supplement agent is 0.80 to 1, which is beneficial to improving the conductivity and air stability of the lithium supplement agent and taking into account the improvement of electrochemical properties such as the capacity and cycle performance of the battery.

[0164] Compared with Example 4 and Example 5, Examples 1 to 3 further control the mass ratio of the conductive polymer to the lithium supplement material to be 1% to 3%, which is beneficial to improving the powder impedance and electronic conductivity of the lithium supplement agent while taking into account the improvement of properties such as the capacity and cycle performance of the battery.

[0165] Compared with Example 6 and Example 10, Examples 2, 9 to 10 further control the mass ratio of the carbon source to the intermediate to be 1 to 4, which is beneficial to improving the powder impedance and electronic conductivity of the lithium supplement agent while taking into account the improvement of properties such as the capacity and cycle performance of the battery.

[0166] Compared with Example 12 and Example 13, Examples 1 to 11, Example 14, and Example 15 further control the power of microwave drying to be 500W to 650W, the time of microwave drying to be 30min to 60min, and the thickness of the first shell layer to be 10nm - 20nm, which is beneficial to further taking into account the improvement of the air stability and electronic conductivity of the lithium supplement agent and the improvement of the capacity and cycle performance of the battery.

[0167] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A lithium supplement, characterized in that, It includes a core and a shell layer located on the surface of the core. The core includes a lithium supplement material, and the shell layer includes a first shell layer and a second shell layer located on the surface of the first shell layer facing away from the core. The first shell layer includes a conductive polymer, and the second shell layer includes a carbon material. The roundness of the lithium supplement agent is 0.80 - 1.

2. The lithium supplement according to claim 1, characterized in that The lithium supplement agent satisfies: 10 ≤ a * b ≤ 25, where a is the roundness of the lithium supplement agent and b is the thickness of the shell layer, with the unit in nm.

3. The lithium supplement agent according to claim 1, characterized in that, The thickness of the shell layer is 15 nm - 30 nm.

4. The lithium supplement according to claim 1, wherein The thickness of the first shell layer is 10 nm - 20 nm; and / or, the thickness of the second shell layer is 5 nm - 10 nm.

5. The lithium supplement according to claim 1, characterized in that, The lithium supplement agent satisfies: the difference in carbon content between any two parts of the lithium supplement agent is less than or equal to 0.1%, and the difference in mass between any two parts of the lithium supplement agent is less than or equal to 0.1 g.

6. The lithium supplement according to claim 1, wherein The particle size distribution width of the lithium supplement satisfies 1.21 ≤ (D 90 - D 10 ) / D 50 ≤ 10.

56.

7. The lithium supplement according to claim 1, wherein The lithium supplement material includes a lithium-rich oxide, and the lithium-rich oxide includes lithium ferrite; and / or, the conductive polymer includes one or more of polystyrene, polyaniline, polyphenylene sulfide, polypyrrole, polyacetylene, polythiophene, polydioxythiophene, polyethylene oxide, polyvinyl alcohol, and polyacrylic acid.

8. A method for preparing the lithium supplement agent according to any one of claims 1-7, characterized in that, It includes the following steps: Coat the conductive polymer on the surface of the lithium supplement material to form the first shell layer on the surface of the lithium supplement material, obtaining an intermediate; Coat the carbon material on the surface of the intermediate to form the second shell layer on the surface of the first shell layer facing away from the lithium supplement material, obtaining the lithium supplement agent; The mass ratio of the conductive polymer to the lithium supplement material is 1% - 5%.

9. The preparation method of the lithium supplement agent according to claim 8, wherein, The process of coating the conductive polymer on the surface of the lithium supplement material includes: subjecting the raw material system including the lithium supplement material and the conductive polymer to microwave drying to form the first shell layer on the surface of the lithium supplement material, obtaining an intermediate; Preferably, the power of the microwave drying is 500 W - 650 W; Preferably, the time of the microwave drying is 30 min - 60 min.

10. The preparation method of the lithium supplement agent according to claim 8, characterized in that, The process of coating the carbon material on the surface of the intermediate includes: Depositing the carbon material on the surface of the intermediate by chemical vapor deposition to form the second shell layer on the surface of the first shell layer facing away from the lithium supplement material, obtaining the lithium supplement agent.

11. The preparation method of the lithium supplement agent according to claim 10, wherein, During the process of depositing the carbon material on the surface of the intermediate by vapor deposition, the mass ratio of the carbon source used to the intermediate is 0.5 - 5, preferably 1 - 4; and / or, the temperature of depositing the carbon material is 500 - 1100 °C; and / or, the time of depositing the carbon material is 3 - 12 h.

12. A positive electrode sheet, characterized in that, It includes a positive electrode active material layer, and the positive electrode active material layer includes the lithium supplement agent according to any one of claims 1 - 7 or the lithium supplement agent prepared by the preparation method of the lithium supplement agent according to any one of claims 8 - 11.

13. The positive electrode sheet according to claim 12, characterized in that, The positive electrode active material layer includes a positive electrode active material, and the mass ratio of the lithium supplement agent to the positive electrode active material is 0.5% - 10%.

14. A battery, characterized in that, It includes the positive electrode sheet according to any one of claims 12 - 13.

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