Composite lithium supplement agent, preparation method thereof and composite active material

Abstract

The invention relates to the technical field of lithium ion batteries, and discloses a composite lithium supplement agent, a preparation method thereof and a composite active material. The composite lithium supplement agent comprises a positive electrode lithium supplement agent; the chemical plating layer at least coats part of the surface of the positive electrode lithium supplement agent, the chemical plating layer comprises a transition metal boride and a particle additive, and the particle additive comprises at least one of titanium dioxide and aluminum oxide. The composite lithium supplement agent is mixed with a positive electrode active material, and lithium ions can be timely and rapidly supplemented, so that the charge-discharge cycle performance and overcharge resistance of the positive electrode active material are improved.

Description

Technical Field

[0001] This application relates to the field of lithium-ion battery technology, specifically to composite lithium replenishing agents and their preparation methods, and composite active materials. Background Technology

[0002] As a crucial energy storage technology, improving the energy density and cycle life of lithium-ion batteries has always been a key research focus. However, during the initial charge and discharge cycle of a lithium-ion battery, the positive electrode active material (such as lithium iron phosphate LiFePO4) suffers irreversible lithium loss due to the formation of the solid electrolyte interphase (SEI) film and electrolyte decomposition, leading to a reduction in battery capacity. To compensate for this loss, positive electrode lithium replenishing agents (such as Li5FeO4) have been introduced into lithium-ion battery systems. These agents are mostly lithium-rich compounds that can compensate for the irreversible lithium loss during SEI formation and cycling, thereby improving the battery's initial efficiency and cycle life while remaining compatible with existing manufacturing processes.

[0003] However, the industrialization of cathode lithium supplements still faces numerous challenges. Adding lithium supplements to the cathode active material layer can lead to residues after decomposition that may damage the electrode structure of lithium-ion batteries, and some binary lithium supplements can release gases (CO, N2) that could affect battery safety. Furthermore, during the generation and preparation process or within the lithium-ion battery environment, cathode lithium supplements can undergo side reactions with air, electrolyte, binders, etc., further increasing the risk of gas generation within the battery. Therefore, the performance and design of cathode lithium supplements need to be optimized.

[0004] It should be noted that the above statements are only used to provide background information related to this application and do not necessarily constitute prior art. Summary of the Invention

[0005] In a first aspect of this application, a composite lithium replenishing agent is proposed, comprising: a positive electrode lithium replenishing agent; and a chemical plating layer, wherein the chemical plating layer at least covers a portion of the surface of the positive electrode lithium replenishing agent, the chemical plating layer comprising a transition metal boride and a particulate additive, wherein the particulate additive comprises at least one of titanium dioxide and aluminum oxide.

[0006] In some embodiments, the transition metal boride includes M x B, wherein M is selected from at least one of Co and Ni, and x is 3-7; and / or, the transition metal boride includes M. y FeB, where M is selected from Co or Ni, and y is 4-9.

[0007] In some embodiments, the particle size of the particulate additive is 20nm-50nm, the mass percentage of the particulate additive in the composite lithium supplement is 0.1wt%-5wt%; and / or, in the chemical plating layer, the thickness of the transition metal boride is 10nm-50nm.

[0008] In some embodiments, the particle size of the positive electrode lithium replenishing agent is 1 μm-15 μm; and / or, the particle size ratio of the positive electrode lithium replenishing agent to the particulate additive is (50-750): 1.

[0009] In some embodiments, the resistivity of the transition metal borides is 3 μΩ·cm to 10 μΩ·cm.

[0010] In some embodiments, the positive electrode lithium replenishing agent includes at least one of Li5FeO4, Li2O, Li6CoO4, and Li2NiO2.

[0011] In a second aspect of this application, a method for preparing a composite lithium replenishing agent is proposed, comprising: chemically plating a positive electrode lithium replenishing agent with a chemical plating solution to obtain the composite lithium replenishing agent, wherein the chemical plating solution comprises a transition metal source, a boron source, a complexing agent, a particulate additive, and a solvent; the boron source comprises at least one of sodium borohydride and dimethylamine borane.

[0012] In some embodiments, the method further includes: before the chemical plating process, performing a surface ball milling treatment on the positive electrode lithium replenishing agent, wherein the rotation speed of the surface ball milling treatment is 100 rpm to 600 rpm, and the surface ball milling treatment time is 10 min to 60 min.

[0013] In some embodiments, the temperature of the electroless plating treatment is 30°C-60°C, and the time of the electroless plating treatment is 1 min-10 min.

[0014] In some embodiments, the transition metal source comprises a soluble salt of a transition metal, and the concentration of the transition metal source is 0.1 mol / L to 0.5 mol / L.

[0015] In some embodiments, the complexing agent includes at least one selected from ethylenediamine, diethylenetriaminepentacarboxylic acid, ethylenediaminetetraacetic acid, sodium ethylenediaminetetramethylene phosphate, and triethanolamine, and the concentration of the complexing agent is 0.01 mol / L to 0.1 mol / L.

[0016] In some embodiments, the particulate additive includes at least one of titanium dioxide and aluminum oxide, and the concentration of the particulate additive is 0.01 mol / L to 0.05 mol / L.

[0017] In a third aspect of this application, a composite active material is proposed, comprising: a positive electrode active material; a composite lithium supplement agent proposed in this application or a composite lithium supplement agent prepared by the method proposed in this application.

[0018] The beneficial effects of the technical solution proposed in this application include at least the following: The composite lithium replenisher proposed in this application possesses high lithium-ion transport performance, which can replenish the lithium element loss in the positive electrode active material during the charging and discharging process of lithium-ion batteries, thereby improving the energy density and actual usable capacity of lithium-ion batteries. Simultaneously, the chemical coating structure of this composite lithium replenisher has the ability to absorb and convert reactive oxygen species generated during the lithium replenishment process, which can suppress and mitigate phenomena such as decomposition and gas generation that may occur during lithium replenishment. Therefore, when this composite lithium replenisher is mixed with the positive electrode active material, it can provide timely and rapid lithium-ion replenishment, thereby improving the charge-discharge cycle performance and overcharge resistance of the positive electrode active material. Attached Figure Description

[0019] The above and / or additional aspects and advantages of this application will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which: Figure 1 This is a schematic diagram of the structure of a composite lithium supplement agent according to an embodiment of this application.

[0020] Explanation of reference numerals in the attached figures: 11 positive electrode lithium supplement; 33 particulate additive; 22 transition metal boride. Detailed Implementation

[0021] The embodiments of this application are described in detail below, with examples of these embodiments shown in the accompanying drawings. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0022] Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used in this application is for the purpose of describing particular embodiments only and is not intended to limit this application; unless otherwise stated, the values ​​of the parameters mentioned in this application can be measured using various measurement methods commonly used in the art (e.g., they can be tested according to the methods given in the embodiments of this application).

[0023] The terms “comprising” and “having”, and any variations thereof, in the specification and claims of this application are open-ended expressions, meaning they include what is specified in this application but do not exclude other aspects.

[0024] In the description of this application, all figures disclosed herein, whether or not the words "approximately" or "about" are used, are approximate values. Each figure may vary by less than 10% or by a difference that is considered reasonable by one of the art, such as 1%, 2%, 3%, 4%, or 5%.

[0025] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0026] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0027] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0028] In related technologies, the modification methods of positive electrode lithium replenishment agents mainly include several directions such as surface coating, element doping, composite structure design and liquid positive electrode lithium replenishment agents.

[0029] Surface coating involves constructing an inorganic oxide or conductive polymer protective layer (such as Al2O3 or polypyrrole) on the surface of the positive electrode lithium supplement to isolate water and oxygen contact. However, the insulating surface coating layer can hinder the effective transport of lithium ions, and the polymer in the surface coating layer has poor high-temperature resistance, which can worsen the decomposition and gas generation of the positive electrode lithium supplement. Elemental doping can be achieved by introducing Mg.2 + F - Adjusting the crystal structure of the positive electrode lithium supplement to reduce its lithium release voltage is one approach, but this method is complex and has limited voltage control, still facing the problem of mismatch with the operating voltage of the positive electrode active material. Composite structure design utilizes the addition of carbon materials or metal nanoparticles to improve the conductivity of the positive electrode lithium supplement, but the high-temperature processing during preparation can easily cause the loss of active lithium in the positive electrode lithium supplement, and the added metals may catalyze electrolyte decomposition. While liquid positive electrode lithium supplements can avoid the insufficient stability problem of solid positive electrode lithium supplements, they may cause problems such as electrode corrosion and continuous gas generation in lithium-ion batteries due to uncontrollable side reactions.

[0030] In summary, existing technologies for improving cathode lithium replenishment agents generally suffer from drawbacks, such as an imbalance between the agent's stability and electrochemical performance, poor compatibility between lithium release voltage and cathode active materials, and difficulty in completely resolving gas generation issues. Consequently, the cycle performance and storage performance of lithium-ion batteries require further improvement. Furthermore, the preparation process relies on high-cost techniques (such as atomic layer deposition and chemical vapor deposition), hindering large-scale application. Therefore, the composite lithium replenishment agent proposed in this application combines high-efficiency lithium replenishment, low-voltage activation for compatibility with cathode active materials, and good interfacial stability in lithium-ion batteries, effectively improving their cycle performance and storage performance. The proposed composite lithium replenishment agent preparation method also boasts advantages such as simple preparation process and reasonable cost.

[0031] In a first aspect of this application, a composite lithium replenishing agent is proposed, comprising: a positive electrode lithium replenishing agent; and a chemical plating layer, wherein the chemical plating layer at least covers a portion of the surface of the positive electrode lithium replenishing agent, the chemical plating layer comprising a transition metal boride and a particulate additive, wherein the particulate additive comprises at least one of titanium dioxide and aluminum oxide.

[0032] The composite lithium replenisher proposed in this application has an outer chemical plating layer for the positive electrode lithium replenisher, which is composed of a transition metal boride and particulate additives. The transition metal boride is a chemically inert amorphous compound that serves as the main body of the chemical plating layer, encapsulating the positive electrode lithium replenisher. Utilizing its chemical inertness, the transition metal boride, encapsulating the positive electrode lithium replenisher, acts as a physical barrier to effectively prevent the positive electrode lithium replenisher from contacting H2O / CO2, and also isolates the positive electrode lithium replenisher from direct contact with the electrolyte, reducing the reaction between the positive electrode lithium replenisher and the electrolyte, suppressing side reactions, and thus reducing problems such as gas generation that threaten the safety performance of lithium-ion batteries. Furthermore, as an amorphous compound, the transition metal boride has a high degree of atomic disorder, so its chemical properties are less affected by defects such as grain boundaries and dislocations, greatly reducing problems such as intergranular corrosion, pitting corrosion, and stress corrosion cracking that may occur in crystalline materials.

[0033] Furthermore, particulate additives, by adhering to the transition metal borides on the electroless plating layer, can further optimize the small number of microcrystalline regions within the transition metal borides. These microcrystalline regions of the transition metal borides are relatively unstable and hinder ion transport. The addition of nanoparticles from the particulate additives can refine the grains of these microcrystalline regions, weakening their crystallinity and improving lithium-ion transport performance. It also converts some microcrystalline regions into amorphous regions, increasing the proportion of amorphous regions and thus enhancing the stability and ion transport properties of the electroless plating layer.

[0034] Furthermore, the transition metal ions in the transition metal borides can catalyze the conversion of active oxygen generated by the positive electrode lithium replenisher during battery formation, thereby effectively controlling the decomposition and gas production of the positive electrode lithium replenisher. The composite particulate additives titanium dioxide and / or aluminum oxide in the chemical plating layer can synergistically and selectively absorb residual active oxygen, reducing side reactions between residual active oxygen and the electrolyte. Moreover, the high electronic conductivity of the transition metal borides enhances the conductivity of the lithium replenisher particle surface, which is beneficial for reducing the lithium release voltage of the composite lithium replenisher.

[0035] The composite lithium replenisher proposed in this application possesses high lithium-ion transport performance, which can replenish the lithium element loss in the positive electrode active material during the charge and discharge process of lithium-ion batteries, thereby improving the energy density and actual usable capacity of lithium-ion batteries. Simultaneously, the chemical coating structure of this composite lithium replenisher has the ability to absorb and convert reactive oxygen species generated by the composite lithium replenisher, which can suppress and mitigate phenomena such as decomposition and gas generation that may occur during lithium replenishment. Therefore, when this composite lithium replenisher is mixed with the positive electrode active material, it can provide timely and rapid lithium-ion replenishment and can achieve activation and adaptation of the positive electrode active material at lower voltages, contributing to improved charge-discharge cycle performance and storage performance of the positive electrode active material.

[0036] In some embodiments, the transition metal boride includes M x B, wherein M is selected from at least one of Co and Ni, and x is 3-7; and / or, the transition metal boride includes M. y FeB, where M is selected from Co or Ni, and y is 4-9. The aforementioned transition metal borides possess good electrical conductivity, and their amorphous structure exhibits a certain density. Therefore, they can enhance the conductivity of the lithium replenishment agent particle surface and effectively encapsulate and protect the positive electrode lithium replenishment agent in the composite lithium replenishment agent.

[0037] In some embodiments, the particle size of the particulate additive is 20nm-50nm, and the mass percentage of the particulate additive in the composite lithium replenisher is 0.1wt%-5wt%; and / or, in the electroless plating layer, the thickness of the transition metal boride is 10nm-50nm. The thickness of the transition metal boride is the same as the thickness of the transition metal boride on the surface of the positive electrode lithium replenisher. The particulate additive is mixed in the layered transition metal boride to jointly form the electroless plating layer. The surface of the electroless plating layer has undulations due to the composite of the particulate additive. The aforementioned particle size range of the particulate additive in the electroless plating layer can form an electroless plating layer with good active oxygen conversion performance with the transition metal boride. Furthermore, the aforementioned addition amount and particle size of the particulate additive can effectively control the crystallization degree of the transition metal boride and effectively adsorb residual active oxygen components. Therefore, it is beneficial to form an electroless plating layer with stable and high lithium-ion transport performance, thereby improving the lithium replenishment effect and efficiency of the composite lithium replenisher.

[0038] As an example, the particle size of the particulate additive is 20nm, 25nm, 30nm, 35nm, 40nm, 45nm or 50nm.

[0039] As an example, the thickness of the transition metal boride is 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm or 50 nm.

[0040] In some embodiments, the particle size of the positive electrode lithium replenisher is 1 μm-15 μm; and / or, the particle size ratio of the positive electrode lithium replenisher to the particulate additive is (50-750):1. Thus, a nanoscale electroless coating is formed on the surface of the positive electrode lithium replenisher within the aforementioned particle size range. This electroless coating achieves a good barrier coating effect and also helps the composite lithium replenisher maintain a high lithium element content and lithium-ion transport capacity. Therefore, it is beneficial to achieve a high lithium replenishment amount with a certain amount of composite lithium replenisher and improve the lithium-ion transport capacity of the composite lithium replenisher, thereby improving the lithium replenishment effect.

[0041] As an example, the particle size of the positive electrode lithium replenishing agent is 1μm, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm or 15μm.

[0042] As an example, the particle size ratio of the positive electrode lithium supplement to the particulate additive is 50:1, 60:1, 70:1, 80:1, 90:1, 100:1, 150:1, 200:1, 300:1, 400:1 or 500:1.

[0043] In some embodiments, the resistivity of the transition metal borides is 3 μΩ·cm to 10 μΩ·cm. Therefore, the surface of the composite lithium supplement has high conductivity, and during the lithium release process, the transition metal ions can play a certain catalytic role, which is beneficial to reducing the lithium release voltage of the composite lithium supplement.

[0044] In some embodiments, the positive electrode lithium replenishing agent includes at least one selected from Li5FeO4, Li2O, Li6CoO4, and Li2NiO2. The aforementioned positive electrode lithium replenishing agent has a high lithium-ion ratio, and with the same amount of composite lithium replenishing agent added, it can release more lithium ions to compensate for lithium-ion losses during lithium-ion battery cycling.

[0045] In a second aspect of this application, a method for preparing a composite lithium replenishing agent is proposed, comprising: chemically plating a positive electrode lithium replenishing agent with a chemical plating solution to obtain the composite lithium replenishing agent, wherein the chemical plating solution comprises a transition metal source, a boron source, a complexing agent, a particulate additive, and a solvent; the boron source comprises at least one of sodium borohydride and dimethylamine borane.

[0046] The method for preparing composite lithium supplements proposed in this application involves depositing a chemical plating layer on the surface of the positive electrode lithium supplement using a chemical plating solution. The prepared chemical plating layer exhibits high thickness uniformity and a tight bond between the chemical plating layer and the positive electrode lithium supplement, which helps reduce defects such as gaps caused by uneven thickness in the chemical plating layer. Furthermore, it allows for the relatively dispersed and uniform composite of particulate additives within the prepared chemical plating layer. The uniformly coated nanoscale chemical plating layer effectively isolates the positive electrode lithium supplement from air contact, thereby improving the air stability of the composite lithium supplement. This ensures the composite lithium supplement is relatively stable during storage and / or lithium-ion battery cycling, and prevents side reactions between the electrolyte and lithium supplement residues, thus reducing the occurrence of gas generation and other side reactions. Moreover, the reaction conditions of this method are mild, having minimal impact on the performance of the positive electrode lithium supplement. The thickness of the prepared chemical plating layer can also be controlled by adjusting the chemical plating treatment time and temperature. Therefore, the method for preparing composite lithium supplements proposed in this application can produce composite lithium supplements with high chemical stability through a relatively simple and easily controllable process. The process has low energy consumption, low equipment requirements, and is suitable for large-scale production.

[0047] In some embodiments, the method further includes: before the chemical plating process, performing a surface ball milling treatment on the positive electrode lithium replenishing agent, wherein the rotation speed of the surface ball milling treatment is 100 rpm to 600 rpm, and the surface ball milling treatment time is 10 min to 60 min.

[0048] Surface ball milling breaks the chemical bonds on the surface of the cathode lithium supplement material, creating numerous active sites on the particle surface. These active sites are exposed to the preparation environment during the process and react with trace amounts of water or oxygen to form hydroxyl (-OH) groups, resulting in hydroxylation of the active particles. The hydroxylated cathode lithium supplement surface exhibits strong hydrophilicity, which facilitates the uniform spreading of the electroless plating solution on the cathode lithium supplement surface and provides active sites for subsequent electroless plating reactions. These active sites allow for rapid initiation of the autocatalytic reaction in the electroless plating solution, thus promoting the formation of a uniformly thick electroless plating layer with a consistent distribution of transition metal borides and particulate additives.

[0049] In some embodiments, after surface ball milling, ultrasonic cleaning is performed using anhydrous ethanol for 10-30 minutes. This helps to remove impurities from the surface of the positive electrode lithium replenisher.

[0050] In some embodiments, the prepared composite lithium supplement is post-treated, which includes: centrifugation washing with ethanol 3-5 times, followed by vacuum drying at 60°C-100°C for 6-12 hours. This helps to remove impurities adhering to the surface of the composite lithium supplement.

[0051] In some embodiments, the temperature of the electroless plating treatment is 30°C-60°C, and the treatment time is 1 min-10 min. Therefore, by adjusting the time and temperature of the electroless plating treatment, the thickness of the prepared electroless plating layer can be controlled.

[0052] In some embodiments, the transition metal source comprises a soluble salt of a transition metal, and the concentration of the transition metal source is 0.1 mol / L to 0.5 mol / L. When the concentration of the transition metal source is within the aforementioned range, the transition metal source can be well and uniformly reduced and deposited on the surface of the positive electrode lithium supplement by the boron source within the target temperature range.

[0053] As an example, the concentration of the transition metal source is 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, or 0.5 mol / L.

[0054] In some embodiments, the complexing agent includes at least one selected from ethylenediamine, diethylenetriaminepentacarboxylic acid, ethylenediaminetetraacetic acid, sodium ethylenediaminetetramethylene phosphate, and triethanolamine, and the concentration of the complexing agent is 0.01 mol / L to 0.1 mol / L. Therefore, the addition of the aforementioned complexing agent can improve the stability of transition metal ions in the electroless plating solution, which is beneficial for the autocatalytic reaction between transition metal ions and boron elements on the surface of the positive electrode lithium supplement during the electroless plating process to form a uniformly thick electroless plating layer.

[0055] As an example, the concentration of the complexing agent is 0.01 mol / L, 0.02 mol / L, 0.03 mol / L, 0.04 mol / L, 0.05 mol / L, 0.06 mol / L, 0.07 mol / L, 0.08 mol / L, 0.09 mol / L, or 0.1 mol / L.

[0056] In some embodiments, the particulate additive includes at least one of titanium dioxide and aluminum oxide, and the concentration of the particulate additive is 0.01 mol / L to 0.05 mol / L. The concentration of the particulate additive within the aforementioned range facilitates more uniform embedding of the particulate additive within the transition metal boride to form the chemical plating layer on the surface of the positive electrode lithium supplement.

[0057] As an example, the concentration of the particulate additive is 0.01 mol / L, 0.02 mol / L, 0.03 mol / L, 0.04 mol / L, or 0.05 mol / L.

[0058] In a third aspect of this application, a composite active material is proposed, comprising: a positive electrode active material; a composite lithium supplement agent proposed in this application or a composite lithium supplement agent prepared by the method proposed in this application.

[0059] In some embodiments, the mixing ratio of the positive electrode active material to the composite lithium replenisher is 1:(1wt%-5wt%); and / or, the positive electrode active material includes at least one of ternary positive electrode material and lithium iron phosphate positive electrode material. Thus, the composite lithium replenisher can promptly replenish sufficient lithium ions to compensate for the irreversible lithium loss of the positive electrode active material and provide supplementary lithium ions for the formation of the negative electrode SEI film. This helps reduce the irreversible phase transition in the positive electrode active material caused by lithium ion loss, thereby improving the reversible capacity of the positive electrode active material.

[0060] As an example, the mixing ratio of the positive electrode active material to the composite lithium supplement is 1:1wt%, 1:2wt%, 1:3wt%, 1:4wt%, or 1:5wt%.

[0061] In a fourth aspect, this application proposes a positive electrode sheet, comprising: the composite active material proposed in this application; and a current collector, wherein the composite active material is disposed on at least one side of the current collector. Thus, the lithium replenishment agent proposed in this application can rapidly and timely replenish lithium-ion losses, optimize the electrode interface state of the positive electrode sheet to a certain extent, and indirectly improve the cycle performance of the battery.

[0062] In a fifth aspect, this application proposes a battery comprising the composite active material or the composite lithium replenishing agent proposed in this application. Therefore, the battery can have superior cycle performance.

[0063] In a sixth aspect of this application, an electrical device is provided, including the battery proposed in this application.

[0064] The following specific embodiments illustrate the solution of this application. It should be noted that these embodiments are for illustrative purposes only and should not be considered as limiting the scope of this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0065] Example 1 Ni-B / TiO2-coated Li5FeO4 cathode lithium supplement Surface ball milling treatment: Select Li5FeO4 raw material with a purity ≥99.9% (particle size D) 50 =3±0.2μm), surface activation treatment was carried out using a planetary ball mill: 3.00g of Li5FeO4 and 100mL of anhydrous ethanol were added to a zirconium oxide ball mill jar and ball milled at 300rpm for 30min. Then, the mixture was vacuum filtered through a 0.22μm nylon filter membrane to obtain positive electrode lithium supplement particles with surface hydroxylation.

[0066] Preparation of electroless plating solution: The electroless plating solution was prepared in an argon glove box (oxygen content <0.1ppm), comprising: anhydrous nickel nitrate (Ni(NO3)2, 0.300mol / L); sodium borohydride (NaBH4) 0.100 mol / L; complexing agent ethylenediamine (C2H8N2) 0.050mol / L; and ethanol solution. The solution was stirred at 800rpm for 30min using a magnetic stirrer, and the pH was adjusted to 9.5±0.2 using 0.1M NaOH solution.

[0067] Chemical plating treatment: The surface-milled Li5FeO4 particles were uniformly dispersed in 200 mL of chemical plating solution and transferred to a constant temperature water bath reactor (PTFE liner). The reaction temperature was set at 30 ± 1 °C and the mechanical stirring speed was 500 rpm. After stirring for 30 s, titanium dioxide (TiO2) powder with a particle size of 30 nm was added again. The mixing ratio of the positive electrode active material to the composite lithium supplement was 1:1 wt%, and the chemical plating treatment time was 2 min.

[0068] The composite lithium supplement was obtained by centrifuging at 12,000 rpm for 10 min using a high-speed centrifuge, washing three times each with deionized water and anhydrous ethanol, and finally drying in a vacuum drying oven at 80℃ for 10 h (vacuum degree ≤10 Pa); the thickness of the transition metal boride composite coating was 30 nm.

[0069] Example 2 Example 2 is the same as Example 1, except that the chemical plating time is 3 minutes and the thickness of the transition metal boride composite coating is 40 nm.

[0070] Example 3 Example 3 is consistent with Example 1, except that the electroless plating solution includes 0.300 mol / L anhydrous cobalt nitrate (Co(NO3)2), 0.100 mol / L sodium borohydride (NaBH4), and 0.050 mol / L complexing agent ethylenediamine (C2H8N2) to prepare a Co-B / TiO2 electroless plating layer; ethanol solution; electroless plating treatment time is 2 min; and the thickness of the transition metal boride composite coating is 25 nm.

[0071] Example 4 Example 4 is consistent with Example 1, except that the electroless plating solution includes anhydrous nickel nitrate (Ni(NO3)2, 0.200 mol / L), anhydrous cobalt nitrate (Co(NO3)2), 0.100 mol / L, sodium borohydride (NaBH4), and complexing agent ethylenediamine (C2H8N2), 0.050 mol / L, to prepare a Ni-Co-B / TiO2 electroless plating layer; the electroless plating treatment time is 2 min; and the thickness of the transition metal boride composite coating is 28 nm.

[0072] Comparative Example 1 Comparative Example 1 used Li5FeO4 lithium supplement (particle size D) 50 =3±0.2μm).

[0073] Comparative Example 2 Comparative Example 2 is the same as Example 1, except that no particulate additives were added to the composite lithium supplement, and the thickness of the transition metal boride composite coating is 30 nm.

[0074] Comparative Example 3 In Comparative Example 3, no Li5FeO4 lithium supplement was added to the positive electrode active material.

[0075] The implementation examples and comparative examples are shown in Table 1.

[0076] Table 1

[0077] Test method: 1. Electrochemical property testing The electrode system (working electrode: lithium iron phosphate powder or a mixture of lithium iron phosphate lithium supplement powder / acetylene black / polyvinylidene fluoride (PVDF) = 8:1:1; counter electrode: lithium sheet) was used to assemble CR2032 coin cells in a glove box. Cyclic voltammetry tests were performed using an electrochemical workstation.

[0078] Lithium release voltage: Under the same formation steps, the lower the lithium release voltage, the easier it is for lithium ions to be released from the lithium replenishing agent, and more lithium ions are replenished to the negative electrode, thus increasing the specific capacity. The specific capacity of Example 1 is increased by 1.2 mAh / g compared to Comparative Example 1.

[0079] 2. Ion diffusion coefficient test Li was calculated using galvanostatic intermittent titration (GITT). + Diffusion coefficient.

[0080]

[0081] Assemble lithium iron phosphate powder / lithium sheet half-cells (CR2032 type), charge to 100% SOC, and allow to stand until voltage stabilizes; pulse discharge with a small current of 0.05C for 15 min, followed by 45 min of rest to allow lithium ion diffusion equilibrium, cycle 40 times covering the full SOC range, maintain temperature at 25±0.5℃ throughout, and record voltage-time curves; based on Fick's second law, the lithium ion diffusion coefficient D... Li+ ; Where: ΔEs: Voltage recovery during the resting phase (minus ohmic voltage drop); ΔEt: Voltage change during the pulse discharge phase (minus ohmic voltage drop); Vm: Molar volume of lithium iron phosphate (44.8 cm³). 3 / mol); S: effective contact area of ​​electrode; τ: settling time; F: Faraday constant (96485 C / mol).

[0082] 3. Gas production test A 2Ah pouch cell (positive electrode: lithium iron phosphate (LFP) + 1wt% composite lithium replenishing agent; negative electrode: graphite) was prepared and stored at high temperature in a 60℃ constant temperature chamber for 28 days. After the storage period, the pouch cell temperature was allowed to return to room temperature, and the gas volume was monitored by the water displacement method.

[0083] 4. Cyclic performance test 1C charge / discharge test (2.0V-3.75V, 25℃±1℃) was performed in the Blue Electric test system.

[0084] Test results: See Table 2.

[0085] Table 2

[0086] In the description of this application, it should be understood that the terms "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application.

[0087] In the description of this application, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. "First feature" and "second feature" may include one or more of the indicated feature.

[0088] In the description of this application, "multiple" means two or more.

[0089] In the description of this application, "A and / or B" can include any of the cases of A alone, B alone, or A and B, where A and B are merely examples and can be any technical feature connected by "and / or" in this application.

[0090] In this application, the order in which the steps are written does not imply a strict execution order and does not limit the implementation process. The specific execution order of each step should be determined by its function and possible internal logic. Unless otherwise specified, all steps in this application can be performed sequentially or randomly, preferably sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, if the method may also include step (c), it means that step (c) can be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0091] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A composite lithium supplement, characterized in that, include: Positive electrode lithium replenisher; A chemical plating layer, wherein the chemical plating layer at least covers a portion of the surface of the positive electrode lithium replenishing agent, the chemical plating layer comprising a transition metal boride and a particulate additive, the particulate additive comprising at least one of titanium dioxide and aluminum oxide.

2. The composite lithium supplement agent according to claim 1, characterized in that, The transition metal borides include M x B, wherein M is selected from at least one of Co and Ni, and x is 3-7; and / or, The transition metal borides include M y FeB, where M is selected from Co or Ni, and y is 4-9.

3. The composite lithium supplement agent according to claim 1, characterized in that, The particle size of the particulate additive is 20nm-50nm, and the mass percentage of the particulate additive in the composite lithium supplement is 0.1wt%-5wt%; and / or, In the chemical plating layer, the thickness of the transition metal boride is 10nm-50nm.

4. The composite lithium supplement agent according to claim 1, characterized in that, The positive electrode lithium replenishing agent has a particle size of 1μm-15μm; and / or, The particle size ratio of the positive electrode lithium supplement to the particulate additive is (50-750):

1.

5. The composite lithium supplement agent according to any one of claims 1-4, characterized in that, The resistivity of the transition metal borides is 3 μΩ·cm-10 μΩ·cm.

6. The composite lithium supplement agent according to any one of claims 1-4, characterized in that, The positive electrode lithium replenishing agent includes at least one of Li5FeO4, Li2O, Li6CoO4, and Li2NiO2.

7. A method for preparing the composite lithium supplement agent according to any one of claims 1-6, characterized in that, include: The composite lithium replenishing agent is obtained by electroless plating of the positive electrode with an electroless plating solution, wherein the electroless plating solution includes a transition metal source, a boron source, a complexing agent, a particulate additive, and a solvent. The boron source includes at least one of sodium borohydride and dimethylamine borane.

8. The method according to claim 7, characterized in that, Also includes: Before the chemical plating process, the positive electrode lithium replenishing agent is subjected to surface ball milling treatment. The surface ball milling treatment speed is 100rpm-600rpm and the surface ball milling treatment time is 10min-60min.

9. The method according to claim 7, characterized in that, At least one of the following conditions must be met: The temperature of the electroless plating treatment is 30℃-60℃, and the time of the electroless plating treatment is 1min-10min; The transition metal source includes a soluble salt of a transition metal, and the concentration of the transition metal source is 0.1 mol / L to 0.5 mol / L. The complexing agent includes at least one of ethylenediamine, diethylenetriaminepentacarboxylic acid, ethylenediaminetetraacetic acid, sodium ethylenediaminetetramethylene phosphate, and triethanolamine, and the concentration of the complexing agent is 0.01 mol / L to 0.1 mol / L; The particulate additive includes at least one of titanium dioxide and aluminum oxide, and the concentration of the particulate additive is 0.01 mol / L-0.05 mol / L.

10. A composite active material, characterized in that, include: Positive electrode active material; The composite lithium supplement as described in any one of claims 1-6 or the composite lithium supplement prepared by the method described in any one of claims 7-9.

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