Preparation method of sacrificial anode additive

Abstract

The invention belongs to the technical field of batteries, and relates to a preparation method of a sacrificial anode additive. The preparation method comprises the following steps: dissolving a lithium salt in water, then adding a carbon-based conductive agent, and uniformly dispersing to obtain a mixture A; adding a carbonic acid compound or air into the mixture A to obtain a mixture B; and carrying out solid-liquid separation on the mixture B, collecting a solid, washing and drying to obtain a target product, namely the sacrificial anode additive. According to the preparation method, uniformity and nanocrystallization of the material can be achieved, the preparation time is greatly shortened, the preparation efficiency is high, and large-scale mass production can be achieved; the prepared positive electrode additive comprises nanoscale lithium carbonate and a carbon-based conductive agent, and has high initial charge capacity.

Description

Technical Field

[0001] The invention belongs to the technical field of batteries and relates to a method for preparing a sacrificial positive electrode additive. Background Art

[0002] In order to meet the growing energy demand of modern society, higher demands are placed on rechargeable lithium-ion batteries with high energy density. The capacity of lithium-ion batteries depends on the transmission of active lithium between the positive and negative electrodes. During the first charge and discharge process, the formation of the SEI film consumes active lithium ions from the positive electrode, resulting in low initial coulombic efficiency, affecting the improvement of battery specific capacity and limiting the application of materials. Therefore, it is crucial to develop high-safety, low-cost lithium supplementation technology to improve the energy density and cycle life of lithium-ion batteries for the development of lithium-ion batteries.

[0003] Existing lithium replenishment technologies can be roughly divided into negative electrode replenishment and positive electrode replenishment. Negative electrode replenishment is simple and efficient, but due to the safety risks and process difficulties of metallic lithium itself, negative electrode replenishment technology is still not widely used. Compared with negative electrode replenishment, positive electrode replenishment is to add a small amount of high-capacity lithium replenishment material during the positive electrode slurry process. During the charging process, Li + It can be separated from high-capacity materials to replenish the irreversible capacity loss of the first charge and discharge, and lithium replenishment can be completed without additional process improvements. Therefore, its process is simple, the cost is low, and it is more suitable for the current lithium-ion battery manufacturing process. It is hailed as the most promising lithium replenishment technology.

[0004] At present, the most common lithium supplements are lithium-rich materials, organic lithium salts and lithium-containing compounds. These additives have their own advantages in positive electrode lithium supplementation, but they also have some defects. Among them, 1) lithium-rich compounds include Li2NiO2, Li2CuO2, Li2CoO2, Li5FeO4, Li6CoO4, etc. However, these compounds are unstable in the air. For example, the surface of Li2NiO2 will react with carbon dioxide and water in the air to generate lithium carbonate and lithium hydroxide. Li2CuO2 and Li2CoO2 are usually LiOH and Li2CO3 in the preparation process, and LiOH is also unstable in the air; Li5FeO4, Li6CoO4 and other materials have high irreversible capacity, but poor environmental stability; in addition, most of these materials have high decomposition voltage and are incompatible with most positive electrode materials, and the decomposition products not only increase the electrode mass, but also the decomposition products (such as Co3O4, etc.) will have an adverse effect on the battery. 2) Organic lithium salts: added to the battery system as a lithium replenishing material to replenish the active lithium ion consumption in the first cycle. For example, Professor T. Brousse (Safe and recyclable lithium-ion capacitors using sacrificial organic lithium salt, Nat. Mater., 2018, 17, 167-173) studied 3,4-dihydroxybenzonitrile dilithium salt (Li2DHBN) as a lithium replenisher. During the first charge process, this compound can irreversibly provide lithium ions to the graphite electrode without causing any side effects on the subsequent charging and discharging of the lithium ion capacitor. However, its irreversible capacity is low and its lithium replenishment capacity is limited. 3) Lithium-containing binary compounds: This type of additive has a high theoretical specific capacity and can replenish lithium in small amounts. The lithium replenishment effect is higher than that of lithium-rich compounds, such as Li2O2, Li3ON, Li2O, Li3N, Li2S and other small molecule lithium-containing compounds. The disadvantage is that Li2O2 and Li2O need to be at 4.77V (vs Li / Li + ) can only work under high voltage. High voltage will cause the electrolyte to decompose, and these binary lithium compounds have poor stability and are easy to produce gas, which affects battery performance and poses a safety hazard.

[0005] Although the industry, academia and research circles have conducted a lot of research on lithium-supplementing materials, the performance of lithium-supplementing materials still has a lot of room for improvement. Therefore, it is of great significance to develop a positive electrode lithium-supplementing material with high specific capacity, high stability, simple preparation process and easy mass production. Summary of the invention

[0006] The present invention aims at the shortcomings of positive electrode lithium supplement additives in the prior art and provides a method for preparing a sacrificial positive electrode additive. The sacrificial positive electrode additive is prepared by a liquid phase nano-processing method, which greatly shortens the preparation time. The prepared additive has uniform chemical composition and particle size and high first charge specific capacity.

[0007] The first object of the present invention is achieved by the following technical solutions:

[0008] A method for preparing a sacrificial positive electrode additive comprises the following steps:

[0009] S1. dissolving lithium salt in water, and then adding a carbon-based conductive agent to disperse uniformly to obtain a mixture A;

[0010] S2. adding a carbonate compound or air to the mixture A to obtain a mixture B;

[0011] S3. The mixture B is subjected to solid-liquid separation, and the solid is collected, washed, and dried to obtain the target product, a sacrificial positive electrode additive.

[0012] Preferably, the lithium salt is a water-soluble lithium salt.

[0013] Preferably, the lithium salt is selected from one or more of lithium nitrate, lithium chlorate, lithium hydroxide, lithium hydroxide hydrate, lithium acetate, lithium acetate hydrate, lithium chloride, and lithium chloride hydrate.

[0014] More preferably, the lithium salt is selected from lithium hydroxide and / or lithium acetate.

[0015] Preferably, the carbon-based conductive agent is selected from one or more of Ketjen black, acetylene black, Super P, Super S, graphene, carbon nanotubes, conductive graphite, and carbon fiber.

[0016] Preferably, the carbon-based conductive agent is selected from one or more of Ketjen black, Super P, graphene, and carbon nanotubes.

[0017] More preferably, the carbon-based conductive agent is Ketjen black.

[0018] More preferably, the specific surface area of ​​the carbon-based conductive agent is ≥45m 2 / g.

[0019] Preferably, in step S1, the carbon-based conductive agent and the auxiliary agent are added and dispersed evenly.

[0020] Preferably, the auxiliary agent is one or more of ethanol, isopropanol, ethylene glycol, and a surfactant; the surfactant may be polyvinyl pyrrolidone PVP, polyethylene glycol PEG, Tween-80, Tween-20, and the like.

[0021] More preferably, the auxiliary agent is one or more of ethanol and ethylene glycol.

[0022] Step S1 of the present invention can be assisted by stirring, ultrasound, shearing, emulsification and other means to evenly disperse the carbon-based conductive agent, because the carbon-based conductive agent used generally has a large specific surface area, and these means are conducive to the wetting and dispersion of the carbon-based conductive agent.

[0023] Preferably, the carbonic acid compound is selected from one of bicarbonate, carbonate and carbon dioxide.

[0024] Bicarbonate is composed of bicarbonate ions (HCO3 - ) is a compound formed by combining with metal ions or ammonium ions, preferably, the bicarbonate is one or more of ammonium bicarbonate, sodium bicarbonate, calcium bicarbonate, potassium bicarbonate, and magnesium bicarbonate.

[0025] Carbonate is composed of carbonate ions (CO3 2- ) is a compound formed by combining with metal ions or ammonium ions, preferably, the carbonate is one or more of ammonium carbonate, sodium carbonate, and potassium carbonate.

[0026] When the carbonate compound used in step S2 is carbon dioxide, preferably, the reaction endpoint is when the pH value of the mixture B is 7 to 12. Carbon dioxide gas reacts chemically with lithium salt to produce nano-scale carbonate in situ, and excess carbon dioxide gas may react with carbonate to produce acid carbonate. Therefore, the present invention determines the reaction endpoint based on the relationship between the amount of carbon dioxide gas introduced and the pH value of the solution, and the pH value is 7 to 12.

[0027] More preferably, the reaction endpoint is when the pH value of the mixture B is 8 to 11.5.

[0028] When the carbonic acid compound used in step S2 is bicarbonate or carbonate, preferably, the carbonic acid compound is added in the form of an aqueous solution, that is, the carbonic acid compound is dissolved in water to form a carbonic acid compound aqueous solution, and the carbonic acid compound aqueous solution is added to the mixture A.

[0029] In step S2 of the present invention, air containing carbon dioxide gas may also be introduced into mixture A. Carbon dioxide in the air reacts chemically with lithium salt to produce nano-scale lithium carbonate in situ. Similarly, when air is introduced into mixture A, the reaction end point is that the pH value of mixture B is 7 to 12.

[0030] The method of solid-liquid separation in step S3 is not limited, and centrifugal separation, pressure filtration, suction filtration, membrane separation and other methods and corresponding equipment commonly used in the industry can be adopted; the method of drying in step S3 is also not limited, and air drying, freeze drying, vacuum drying and other methods and corresponding equipment can be adopted.

[0031] Mixture A includes lithium salt, carbon-based conductive agent and water, carbonate compound is added to mixture A, lithium salt in mixture A reacts with carbonate compound to generate lithium carbonate, lithium carbonate is insoluble in water, precipitates out, raw materials and by-products soluble in water are removed by solid-liquid separation, and the obtained solid is lithium carbonate and carbon-based conductive agent. Therefore, the sacrificial positive electrode additive obtained by the preparation method includes lithium carbonate and carbon-based conductive agent.

[0032] Preferably, the mass ratio of lithium carbonate to the carbon-based conductive agent is 0.1 to 20:1, more preferably 0.5 to 10:1, and even more preferably 1 to 5:1.

[0033] The amounts of the lithium salt, carbonate compound and carbon-based conductive agent added in the present invention are not particularly limited, as long as the mass ratio of lithium carbonate produced by the reaction of the lithium salt and carbonate compound to the carbon-based conductive agent is within a suitable range.

[0034] Preferably, the lithium carbonate has a nanoparticle size with an average particle size of 1 to 800 nm; more preferably, the average particle size is 1 to 500 nm; and even more preferably, the average particle size is 1 to 200 nm.

[0035] Preferably, the carbon-based conductive agent is nanoparticles with an average particle size of 1 to 500 nm; more preferably, the average particle size is 1 to 300 nm; and even more preferably, the average particle size is 1 to 100 nm.

[0036] Another object of the present invention is achieved by the following technical solutions:

[0037] A sacrificial positive electrode additive comprises lithium carbonate and a carbon-based conductive agent, and the sacrificial positive electrode additive is prepared by the above-mentioned preparation method.

[0038] Preferably, the mass ratio of lithium carbonate to the carbon-based conductive agent is 0.1 to 20:1, more preferably 0.5 to 10:1, and even more preferably 1 to 5:1.

[0039] Preferably, the lithium carbonate has a nanoparticle size with an average particle size of 1 to 800 nm; more preferably, the average particle size is 1 to 500 nm; and even more preferably, the average particle size is 1 to 200 nm.

[0040] Preferably, the carbon-based conductive agent is nanoparticles with an average particle size of 1 to 500 nm; more preferably, the average particle size is 1 to 300 nm; and even more preferably, the average particle size is 1 to 100 nm.

[0041] The third object of the present invention is achieved by the following technical solutions:

[0042] A positive electrode of a lithium ion battery comprises a current collector and a positive electrode material coated on the current collector, wherein the positive electrode material contains 0.5 to 20 wt % of a sacrificial positive electrode additive.

[0043] Preferably, the positive electrode material contains 1 to 10 wt % of the sacrificial positive electrode additive.

[0044] Preferably, the positive electrode material includes a sacrificial positive electrode additive, a positive electrode active material and a binder.

[0045] More preferably, the positive electrode material also includes a conductive agent.

[0046] Preferably, in the positive electrode material, the content of the sacrificial positive electrode additive is 0.5-20wt%, the content of the positive electrode active material is 60-90wt%, and the conductive agent is added according to actual conditions. If the conductive agent is added, the content of the conductive agent is 0<≤15wt%, and the content of the binder is 2-15wt%.

[0047] There is no particular limitation on the positive electrode active material, which may be exemplified by nickel, cobalt and manganese oxides; there is no particular limitation on the conductive agent, which may be exemplified by conductive carbon black, graphite, nano-carbon fiber, etc.; there is no particular limitation on the binder, which may be exemplified by polyvinylidene fluoride, polytetrafluoroethylene, styrene-butadiene rubber, hydroxymethyl cellulose, etc.

[0048] Compared with the prior art, the present invention has the following beneficial effects:

[0049] 1. The present invention is the first to prepare sacrificial positive electrode additives by liquid phase nano-crystallization method, which can simultaneously achieve uniform mixing and self-assembly of active components and auxiliary components. Therefore, the prepared additives have uniform chemical composition and particle size, and the material is nano-scale, with high electrochemical activity, high initial charge capacity and conversion rate;

[0050] 2. Compared with the ball milling method, the liquid phase nano-processing method of the present invention greatly shortens the preparation time, has high preparation efficiency, has simple requirements on equipment, and is easy to realize industrial-scale production;

[0051] 3. The positive electrode additive prepared by the present invention includes nano-scale lithium carbonate and a carbon-based conductive agent, which has a high initial charging capacity and a high utilization rate as a positive electrode lithium supplement additive, and can evenly play a role in supplementing active lithium ions in the battery system. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 The first charge and discharge curves of the sacrificial positive electrode additives of Example 1 and Example 2;

[0053] Figure 2 The SEM images of the sacrificial positive electrode additive prepared in Example 2 and the lithium supplement additive prepared in Comparative Example 1 are shown in FIG. Figure 2(a) is a SEM image of the sacrificial cathode additive prepared in Example 2. Figure 2 (b) is a SEM image of the lithium supplement additive prepared in Comparative Example 1;

[0054] Figure 3 The charge and discharge curves of samples NCM523@Li and NCM523 in the application example. DETAILED DESCRIPTION

[0055] The technical scheme of the present invention is further described below by specific examples and accompanying drawings. It should be understood that the specific examples described herein are only used to help understand the present invention and are not intended for specific limitations of the present invention. The accompanying drawings used herein are only for better illustrating the disclosure of the present invention and do not have a limiting effect on the scope of protection. If not otherwise specified, the raw materials used in the embodiments of the present invention are all commonly used raw materials in the art, and the methods used in the embodiments are all conventional methods in the art.

[0056] In the following examples and comparative examples:

[0057] The raw materials used are: commercial Ketjen-black KB (Ketjen-black EC-600JD) purchased from Lion of Japan, branched chain morphology, its particles are about 30-40nm, Ketjen-black specific surface area is 1726m 2 / g; Commercial Super P (full name Super Pli, brand TIMCAL) was purchased from Kasma Mall, with a particle size of 40-50nm and a specific surface area of ​​54m 2 / g. Lithium sheets were purchased from Zhongli Industrial Co., Ltd.

[0058] Button cell production and testing: PVDF is used as a binder and NMP as a solvent. The additive, Super P and PVDF are mixed in a mass ratio of 2:1:2, and then evenly coated on aluminum foil, dried in an oven at 80°C for 12 hours, compacted by a roller press, and punched into a 14mm diameter disc for the battery pole. CR2032 batteries are used, the electrolyte is 1mol / L LiPF6 (EC:DMC=3:7), Celgard325 is used as a diaphragm, and the half-cell is assembled in an argon-filled glove box in the order of positive electrode shell-positive electrode-diaphragm-negative electrode (lithium sheet)-gasket-shrapnel-negative electrode shell, where the water and oxygen concentrations in the glove box are below 0.5ppm.

[0059] At 28°C, the lithium-supplemented material half-cell was tested in a voltage window of 2.8 to 4.6 V, with a charging rate of 0.05C.

[0060] Unless otherwise specified, batteries containing different lithium supplement materials were prepared and evaluated according to the above method.

[0061] SEM test: tested using S4800 electron scanning microscope.

[0062] Example 1

[0063] The method for preparing the sacrificial positive electrode additive of this embodiment comprises the following steps:

[0064] S1. Add 27.5 g of lithium acetate (dihydrate) into about 100 ml of pure water. After it is completely dissolved, add 2.3 g of Ketjen black and stir to disperse evenly to obtain a mixture A.

[0065] S2, dissolving 21.3 g of ammonium bicarbonate in 50 ml of pure water to obtain an ammonium bicarbonate solution, and adding all of the ammonium bicarbonate solution to mixture A to obtain mixture B;

[0066] S3. The mixture B was centrifuged at a speed of 5000 rpm for 5 min to separate the solid and the liquid to obtain a solid. The solid was washed with water three times, dried at 80° C. for 2 hours, and sieved to obtain the target product, a sacrificial positive electrode additive.

[0067] The sacrificial positive electrode additive prepared in this embodiment includes lithium carbonate and Ketjen black, and the mass ratio of lithium carbonate to Ketjen black is about 4.3:1. The sacrificial positive electrode additive prepared in this embodiment is nanometer-level.

[0068] In this embodiment, the chemical changes that may occur can be represented by the chemical equation: 2LiAC+2NH4HCO3=Li2CO3+2NH4AC+CO2+H2O. During the air drying process, the residual ammonium bicarbonate begins to decompose at about 36°C and completes the decomposition at 60°C. It decomposes by heat to generate ammonia, carbon dioxide and water, which are discharged during the drying process.

[0069] The sacrificial positive electrode additive of Example 1 was used to make a battery pole piece, and a metal lithium sheet was used as a counter electrode to assemble a button-type half-cell, and the first cycle charge and discharge test was carried out. Figure 1 The first charge and discharge curve of the sacrificial cathode additive of Example 1 is shown. The charge capacity of the first cycle is 640 mAh g -1 .

[0070] Example 2

[0071] The method for preparing the sacrificial positive electrode additive of this embodiment comprises the following steps:

[0072] S1. 10 g of lithium hydroxide (monohydrate) was put into 120 ml of pure water. After it was completely dissolved, 4.5 g of Ketjen Black was added and stirred to disperse evenly to obtain a mixture A.

[0073] S2, continuously introducing carbon dioxide gas into mixture A until the pH reaches 9, to obtain mixture B;

[0074] S3. Mixture B was centrifuged at a speed of 5000 rpm for 5 min to obtain a solid, which was washed with water three times, dried at 80° C. with forced air for 6 hours, and sieved to obtain the target product, a sacrificial positive electrode additive.

[0075] The sacrificial positive electrode additive prepared in this embodiment includes lithium carbonate and Ketjen black, and the mass ratio of lithium carbonate to Ketjen black is about 2:1. Figure 2 As shown in (a), the sacrificial positive electrode additive prepared in this embodiment is nanometer-level and has uniform particle size.

[0076] The sacrificial positive electrode additive of Example 2 was used to make a battery pole piece, and a metal lithium sheet was used as a counter electrode to assemble a button-type half-cell, and the first cycle charge and discharge test was carried out. Figure 1 The first charge and discharge curve of the sacrificial cathode additive of Example 2 is shown. The charge capacity of the first cycle is 1040 mAh g -1 .

[0077] The charging specific capacity of the sample in Example 2 is higher than that in Example 1. This is because the carbon content in the sample in Example 2 is higher than that in Example 1. The more suitable carbon content ratio activates the electrochemical activity of the carbonate component. This is also confirmed by the fact that the charging platform voltage (3.8V) of the sample in Example 2 is lower than that in Example 1 (about 3.9V).

[0078] Example 3

[0079] The method for preparing the sacrificial positive electrode additive of this embodiment comprises the following steps:

[0080] S1. 6 g of lithium hydroxide (anhydrous) was put into 100 ml of pure water. After it was completely dissolved, 1.8 g of Ketjen black and 1 g of PVP were added and sheared and dispersed uniformly to obtain a mixture A.

[0081] S2, dissolving 19 g of ammonium bicarbonate in 50 ml of pure water to obtain an ammonium bicarbonate solution, and adding all of the ammonium bicarbonate solution to mixture A to obtain mixture B;

[0082] S3. The mixture B is filtered to obtain a solid, which is washed three times with water, dried at 80° C. for 2 hours, and vacuum dried at 100° C. for 4 hours, and sieved to obtain the target product, a sacrificial positive electrode additive.

[0083] The PVP added in the preparation process can be used as a super dispersant, which can effectively promote the infiltration and dispersion of Ketjen black in water.

[0084] The sacrificial positive electrode additive prepared in this embodiment includes lithium carbonate and Ketjen black, and the mass ratio of lithium carbonate to Ketjen black is about 4.9:1. The sacrificial positive electrode additive prepared in this embodiment is nanometer-level.

[0085] The sacrificial positive electrode additive of Example 3 was used to make a battery pole piece, and a metal lithium sheet was used as a counter electrode to assemble a button-type half-cell. The first cycle charge and discharge test was carried out. The first cycle charge capacity of the sacrificial positive electrode additive of Example 3 was 604 mAh·g -1 .

[0086] Example 4

[0087] The method for preparing the sacrificial positive electrode additive of this embodiment comprises the following steps:

[0088] S1. 10 g of lithium hydroxide (monohydrate) was put into 100 ml of pure water. After it was completely dissolved, 3.6 g of Ketjen black and 5 ml of ethanol were added and dispersed evenly with an emulsifier to obtain a mixture A.

[0089] S2, dissolving 19.5 g of ammonium bicarbonate in 50 ml of pure water to obtain an ammonium bicarbonate solution, and adding all of the ammonium bicarbonate solution to mixture A to obtain mixture B;

[0090] S3. Mixture B was centrifuged at a speed of 5000 rpm for 5 min to obtain a solid, which was washed 3 times with water, dried at 80° C. for 2 hours, and vacuum dried at 100° C. for 6 hours, and sieved to obtain the target product, a sacrificial positive electrode additive.

[0091] The ethanol added in the preparation process is miscible with water, and lithium hydroxide is only slightly soluble in ethanol. After the addition of ethanol, it has a certain anti-solvent effect in the solution, which is conducive to the formation of a large number of nano-carbonate crystals and promotes the nano-sizing of the sample.

[0092] The sacrificial positive electrode additive prepared in this embodiment includes lithium carbonate and Ketjen black, and the mass ratio of lithium carbonate to Ketjen black is about 2.5:1. The sacrificial positive electrode additive prepared in this embodiment is nanometer-level.

[0093] The sacrificial positive electrode additive of Example 4 was used to make a battery pole piece, and a metal lithium sheet was used as a counter electrode to assemble a button-type half-cell. The first cycle charge and discharge test was carried out. The first cycle charge specific capacity of the sacrificial positive electrode additive of Example 4 was 721 mAh·g -1 .

[0094] Example 5

[0095] The difference between Example 5 and Example 2 is that step S1 of Example 5 is: 10g lithium hydroxide (monohydrate) is put into 120ml pure water, and after it is completely dissolved, 3.5g Ketjen Black and 1g Super P are added, and stirred and dispersed evenly to obtain a mixture A; the other steps are the same as Example 2.

[0096] The sacrificial positive electrode additive prepared in this embodiment includes lithium carbonate, Ketjen black and Super P. The mass ratio of lithium carbonate to carbon-based conductive agent (the sum of Ketjen black and Super P) is about 2:1. The sacrificial positive electrode additive prepared in this embodiment is nanometer-level.

[0097] The sacrificial positive electrode additive of Example 5 was used to make a battery electrode, and a metal lithium sheet was used as a counter electrode to assemble a button-type half-cell for the first cycle charge and discharge test. The first cycle charge capacity of the sacrificial positive electrode additive of Example 5 was 523 mAh·g -1 .

[0098] Example 6

[0099] The difference between Example 6 and Example 3 is that step S1 of Example 6 is: 6 g of lithium hydroxide (anhydrous) is put into 100 ml of pure water, and after it is completely dissolved, 1.8 g of Ketjen black and 5 ml of ethylene glycol are added, and the mixture is sheared and dispersed evenly to obtain a mixture A; the other steps are the same as Example 3.

[0100] The sacrificial positive electrode additive prepared in this embodiment includes lithium carbonate and Ketjen black, and the mass ratio of lithium carbonate to Ketjen black is about 4.9:1. The sacrificial positive electrode additive prepared in this embodiment is nanometer-level.

[0101] The sacrificial positive electrode additive of Example 6 was used to make a battery pole piece, and a metal lithium sheet was used as a counter electrode to assemble a button-type half-cell. The first cycle charge and discharge test was carried out. The first cycle charge capacity of the sacrificial positive electrode additive of Example 6 was 675 mAh·g -1 .

[0102] Example 7

[0103] The difference between Example 7 and Example 3 is that step S1 of Example 7 is: 10.5 g of lithium chloride is put into 100 ml of pure water, and after it is completely dissolved, 1.8 g of Ketjen black and 1 g of PVP are added, and the mixture is sheared and dispersed evenly to obtain a mixture A; the other steps are the same as those of Example 3.

[0104] The sacrificial positive electrode additive prepared in this embodiment includes lithium carbonate and Ketjen black, and the mass ratio of lithium carbonate to Ketjen black is about 4.9:1. The sacrificial positive electrode additive prepared in this embodiment is nanometer-level.

[0105] The sacrificial positive electrode additive of Example 7 was used to make a battery pole piece, and a metal lithium sheet was used as a counter electrode to assemble a button-type half-cell. The first cycle charge and discharge test was carried out. The first cycle charge capacity of the sacrificial positive electrode additive of Example 7 was 655 mAh·g -1 .

[0106] Example 8

[0107] The difference between Example 8 and Example 2 is that step S2 of Example 8 is: continuously introducing carbon dioxide gas into mixture A until the pH value is 12 to obtain mixture B; the other steps are the same as those of Example 2.

[0108] The sacrificial positive electrode additives prepared in this embodiment include lithium carbonate and Ketjen black, both of which are nanometer-level.

[0109] The sacrificial positive electrode additive of Example 8 was used to make a battery electrode, and a metal lithium sheet was used as a counter electrode to assemble a button-type half-cell for the first cycle charge and discharge test. The first cycle charge capacity of the sacrificial positive electrode additive of Example 8 was 489 mAh·g -1 , which is lower than the charging specific capacity of Example 2. The reason is that the pH value of Example 8 is slightly higher than that of Example 2, the lithium ions participating in the reaction in the solution are relatively small, and the amount of lithium carbonate generated is small.

[0110] Example 9

[0111] The difference between Example 9 and Example 2 is that step S2 of Example 9 is: dissolving 13.1 g of sodium carbonate in 50 ml of pure water to obtain a sodium carbonate solution, and adding all of the sodium carbonate solution to mixture A to obtain mixture B; the other steps are the same as in Example 2.

[0112] The sacrificial positive electrode additive prepared in this embodiment includes lithium carbonate and Ketjen black, and the mass ratio of lithium carbonate to Ketjen black is about 2.0:1. The sacrificial positive electrode additive prepared in this embodiment is nanometer-level.

[0113] The sacrificial positive electrode additive of Example 9 was used to make a battery pole piece, and a metal lithium sheet was used as a counter electrode to assemble a button-type half-cell. The first cycle charge and discharge test was carried out. The first cycle charge capacity of the sacrificial positive electrode additive of Example 9 was 566 mAh·g -1 ,, lower than that of Example 2. The reason may be that the sodium carbonate particles generated by the rapid reaction of sodium carbonate are larger, which limits its activity.

[0114] Example 10

[0115] The difference between Example 10 and Example 2 is that step S2 of Example 10 is: dissolving 21.1 g of sodium bicarbonate in 80 ml of pure water to obtain a sodium bicarbonate solution, and adding all of the sodium bicarbonate solution to mixture A to obtain mixture B; the other steps are the same as in Example 2.

[0116] The sacrificial positive electrode additive prepared in this embodiment includes lithium carbonate and Ketjen black, and the mass ratio of lithium carbonate to Ketjen black is about 2.0:1. The sacrificial positive electrode additive prepared in this embodiment is nanometer-level.

[0117] The sacrificial positive electrode additive of Example 10 was used to make a battery pole piece, and a metal lithium sheet was used as a counter electrode to assemble a button-type half-cell. The first cycle charge and discharge test was carried out. The first cycle charge capacity of the sacrificial positive electrode additive of Example 10 was 735 mAh·g -1 .

[0118] Embodiment 11

[0119] The difference between Example 11 and Example 2 is that step S1 of Example 11 is: 10 g lithium hydroxide (monohydrate) is put into 120 ml pure water, and after it is completely dissolved, 4.5 g Super P is added, and stirred and dispersed evenly to obtain a mixture A; the other steps are the same as Example 2.

[0120] The sacrificial cathode additive prepared in this embodiment includes lithium carbonate and Super P, and the mass ratio of lithium carbonate to Super P is about 2:1. The sacrificial cathode additive prepared in this embodiment is nanometer-level.

[0121] The sacrificial positive electrode additive of Example 11 was used to make a battery electrode, and a metal lithium sheet was used as a counter electrode to assemble a button-type half-cell for the first cycle charge and discharge test. The first cycle charge capacity of the sacrificial positive electrode additive of Example 11 was 586 mAh·g -1 .

[0122] Comparative Example 1

[0123] Comparative Example 1 The positive electrode additive was prepared by ball milling method, and the specific preparation method was as follows:

[0124] 4 g of commercial lithium carbonate (ACS, ≥99.5%, Shanghai Aladdin Biochemical Technology Co., Ltd., with a particle size of about 10 μm) and 2 g of Ketjen black and 200 g of anhydrous ethanol were weighed and placed in a ball mill. Zirconium balls were used as grinding materials, and small balls ( mm) and large balls ( The mass ratio of the ball to the powder was 2:1, and the weight ratio of the ball to the powder was 4:1. The ball was milled in a ball mill system at a speed of 500 rpm for 12 hours. After the ball milling, the ethanol was separated and removed using a high-speed desktop centrifuge at a speed of 5000 rpm for 5 minutes. The obtained powder was dried in an oven at 80°C for 24 hours and sieved to obtain the target lithium supplement material.

[0125] The lithium supplement material includes lithium carbonate and Ketjen black, and the mass ratio of lithium carbonate to Ketjen black is 2:1. Figure 2 As shown in (b), the lithium supplement material prepared in Comparative Example 1 is composed of irregular large micron-sized particles and nano-sized particles, and nano-sized particles exist on the surface of the large particles; compared with Example 2 ( Figure 2 (a)), the lithium supplement material prepared in Comparative Example 1 is not as uniform as that in Example 2 because the method in Example 2 is more likely to form nano-scale uniform particles, while the method in Comparative Example 1 is limited by process conditions and has some large particles.

[0126] The sacrificial positive electrode additive of comparative example 1 was used to make a battery electrode, and a metal lithium sheet was used as a counter electrode to assemble a button-type half-cell for the first cycle charge and discharge test. The first cycle charge capacity of the sacrificial positive electrode additive of comparative example 1 was 645 mAh g -1 .

[0127] The mass ratio of lithium carbonate and Ketjen black in Comparative Example 1 and Example 2 is the same. Example 2 uses the liquid phase nano-crystallization method of the present invention to prepare sacrificial positive electrode additives, and Comparative Example 1 uses the solid phase mixed ball milling method to prepare lithium supplement materials. The grinding method of Comparative Example 1 takes a long time, the mixing uniformity between the components is poor, and the particles are large, while the liquid phase nano-crystallization method of the present invention can greatly reduce the preparation time and has better mixing uniformity. Finally, the charging specific capacity of the first cycle of the lithium supplement material of Example 2 is significantly better than that of the lithium supplement material of Comparative Example 1.

[0128] Comparative Example 2

[0129] The difference between Comparative Example 2 and Example 2 is that step S1 of Comparative Example 2 is: 10 g of lithium hydroxide (monohydrate) is added into 120 ml of pure water to obtain mixture A; the other steps are the same as those of Example 2.

[0130] The sacrificial positive electrode additive prepared in Comparative Example 2 is nano lithium carbonate.

[0131] The nano lithium carbonate of comparative example 2 was used to make battery pole pieces, and the metal lithium sheet was used as the counter electrode to assemble into a button-type half-cell. The first cycle charge and discharge test was carried out. The first cycle charge specific capacity of the nano lithium carbonate of comparative example 2 was 11 mAh g -1 Therefore, the material without the addition of carbon-based conductive agent is basically inactive.

[0132] Application Examples

[0133] During the battery homogenization process, 5% by mass of the additive obtained in Example 1 was introduced into the positive electrode sheet, and assembled with the graphite electrode into a full battery, wherein the ratio of the additive in Example 1, NCM523, PVDF, and SP in the positive electrode sheet was 5:90:1.5:3.5, and the sample was labeled NCM523@Li. The corresponding positive electrode sheet without additives was assembled with the graphite electrode into a full battery, wherein the ratio of NCM523, PVDF, and SP was 95:2:3, and the sample was labeled NCM523.

[0134] The sample battery is tested for charge and discharge capacity and efficiency in the voltage window of 2.8 to 4.6 V. Figure 3 The NCM523 sample has a charge capacity of 204mAh g -1 The discharge capacity is 165mAh·g-1, and the first efficiency is about 80.87%; the charging capacity of the NCM523@Li battery sample is 249mAh·g -1 , the discharge capacity is 170mAh·g-1, and the first efficiency is 68%. During the first cycle of charging of the NCM523@Li full battery with additives, the additives decompose to provide additional active lithium ions, so the charging capacity of the NCM523@Li sample is about 45mAh·g higher than that of the NCM523 sample. -1 , the discharge capacity increased by 5 mAh g -1 This part of the capacity is provided by the additive. When the negative electrode uses graphite, the charging capacity is 45 mAh g higher. -1 Lithium ions replace the lithium ions in NCM523, making up for the consumption of lithium ions in the formation process of SEI film of graphite negative electrode and improving the energy density of the battery.

[0135] The various aspects, embodiments, and features of the present invention should be considered to be illustrative in all aspects and not limiting of the present invention, the scope of which is defined solely by the claims. Other embodiments, modifications, and uses will be apparent to those skilled in the art without departing from the spirit and scope of the claimed invention.

[0136] In the preparation method of the present invention, the order of each step is not limited to the order listed. For those skilled in the art, without creative work, the order of each step is also within the protection scope of the present invention. In addition, two or more steps or actions can be performed simultaneously.

[0137] Finally, it should be noted that the specific embodiments described herein are merely examples of the present invention, and are not intended to limit the implementation methods of the present invention. A person skilled in the art of the present invention may make various modifications or supplements to the specific embodiments described, or replace them in a similar manner. It is not necessary and impossible to provide all examples of all implementation methods here. However, these obvious changes or modifications derived from the essential spirit of the present invention still fall within the scope of protection of the present invention, and interpreting them as any additional limitation is contrary to the spirit of the present invention.

Claims

1. A method for preparing a sacrificial positive electrode additive, characterized in that: The preparation method comprises the following steps: S1. dissolving lithium salt in water, and then adding a carbon-based conductive agent to disperse uniformly to obtain a mixture A; S2. adding a carbonate compound or air to the mixture A to obtain a mixture B; S3. The mixture B is subjected to solid-liquid separation, and the solid is collected, washed, and dried to obtain the target product, a sacrificial positive electrode additive.

2. The preparation method according to claim 1, characterized in that: The lithium salt is selected from one or more of lithium nitrate, lithium chlorate, lithium hydroxide, lithium hydroxide hydrate, lithium acetate, lithium acetate hydrate, lithium chloride, and lithium chloride hydrate; The carbon-based conductive agent is selected from one or more of Ketjen black, acetylene black, Super P, Super S, graphene, carbon nanotubes, conductive graphite, and carbon fiber; The carbonate compound is selected from one of bicarbonate, carbonate and carbon dioxide.

3. The preparation method according to claim 1 or 2, characterized in that: The carbon-based conductive agent is Ketjen black.

4. The preparation method according to claim 1, characterized in that: In step S1, a carbon-based conductive agent and an auxiliary agent are added and dispersed uniformly; The auxiliary agent is one or more of ethanol, isopropanol, ethylene glycol and a surfactant.

5. The preparation method according to claim 2, characterized in that: The bicarbonate is one or more of ammonium bicarbonate, sodium bicarbonate, calcium bicarbonate, potassium bicarbonate, and magnesium bicarbonate; The carbonate is one or more of ammonium carbonate, sodium carbonate and potassium carbonate.

6. The preparation method according to claim 1 or 2, characterized in that: When the carbonate compound used in step S2 is carbon dioxide, the reaction end point is when the pH value of the mixture B is 7-12.

7. A sacrificial positive electrode additive, characterized in that: It comprises lithium carbonate and a carbon-based conductive agent, and the sacrificial positive electrode additive is prepared by the preparation method according to claim 1.

8. The sacrificial cathode additive according to claim 7, characterized in that: The mass ratio of lithium carbonate to carbon-based conductive agent is 0.1 to 20:1; The lithium carbonate has a nanoparticle size with an average particle size of 1 to 800 nm; the carbon-based conductive agent has a nanoparticle size with an average particle size of 1 to 500 nm.

9. A positive electrode of a lithium ion battery, characterized in that: The positive electrode comprises a current collector and a positive electrode material coated on the current collector, wherein the positive electrode material contains 0.5 to 20 wt % of the sacrificial positive electrode additive according to claim 7.

10. The positive electrode according to claim 9, characterized in that The positive electrode material contains 1 to 10 wt % of the sacrificial positive electrode additive.

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