Positive electrode lithium supplement additive, preparation method thereof and application

Abstract

The present invention relates to the field of lithium-ion battery technology, and more specifically to a positive electrode lithium supplement additive, its preparation method, and its application. The present invention provides a positive electrode lithium supplement additive, which is a porous material with a core-shell structure. The core material is submicron lithium oxide, and the shell material is nanoscale carbon nanotubes. Nitrogen and Li3N are adsorbed in the gaps between the core-shell structure and between the carbon nanotube layers. The additive provided by the present invention can effectively reduce the interfacial impedance of the positive electrode material through the interaction of material structure and composition, while also improving the battery's initial charge and discharge efficiency, as well as the battery's capacity, cycle performance, and lifespan, and reducing the cell expansion rate, resulting in a battery with superior performance.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion batteries, and in particular to a positive electrode lithium supplement additive and a preparation method and application thereof. Background Art

[0002] Lithium-ion batteries include positive electrode materials, negative electrode materials, and electrolytes. The negative electrode materials are mainly silicon-based, carbon-based, and silicon-carbon-based. The electrolyte is usually composed of cyclic and linear carbonate solvents and solvated lithium salts. The electrolyte will undergo irreversible decomposition at low potentials (0.8-2.0V vs. Li / Li+), eventually leading to the formation of a very thin SEI film on the electrode surface. SEI has a very important impact on battery performance and will continue to form as the cycle progresses. However, a large amount of lithium consumption mainly occurs in the first cycle, resulting in a decrease in the first irreversible coulombic efficiency and a significant reduction in battery performance.

[0003] Pre-lithiation can effectively prevent the collapse of the electrode structure and the shedding of electrode materials during the subsequent charge and discharge cycles of the battery, helping to improve the battery's cycle performance. It can also lead to the formation of the SEI film in advance. Through artificial control, a more stable SEI film can be formed, which helps reduce electrolyte consumption, reduce the loss of active ions in the positive electrode material, and improve the initial coulombic efficiency of lithium-ion batteries.

[0004] Existing lithium replenishment technologies are mainly divided into negative electrode replenishment and positive electrode replenishment. The most commonly used negative electrode replenishment methods currently include lithium powder doping, ultra-thin lithium strip rolling, polymer-coated metal lithium for pre-lithiation, and chemical pre-lithiation of the negative electrode by reacting metal lithium with a chelating agent. Negative electrode pre-lithiation can significantly improve the initial Coulombic efficiency of the negative electrode material, thereby improving the energy efficiency of the battery. However, the use of metal lithium brings certain safety issues, and the negative electrode replenishment technology is cumbersome, has high environmental requirements, and is relatively expensive. After replenishment, a layer of metal lithium will remain on the surface of the negative electrode. Symmetrical chain carbonates such as dimethyl carbonate (DMC) and diethyl carbonate (DEC) and acid esters such as propyl propionate (PP) will react with the metal lithium. When the lithium sheet enters the above solution, the solution will change color and the metal lithium will dissolve, resulting in an uneven SEI film, consuming active lithium, and increasing battery impedance. Therefore, although there are many technologies related to negative electrode replenishment, they are still rarely used in actual production.

[0005] Positive electrode lithium replenishment typically involves adding a small amount of a positive electrode lithium replenishment additive during the positive electrode slurry preparation process. Existing positive electrode lithium replenishment additives, such as Li5FeO4, can provide a lithium source during the first charge, compensating for the lithium consumed in forming the SEI film and improving the initial coulombic efficiency. However, existing positive electrode lithium replenishment additives have low pre-lithiation efficiency, resulting in limited improvement in initial charge and discharge efficiency. Furthermore, they often increase the impedance of the positive electrode material, reducing its specific capacity. Summary of the Invention

[0006] In order to overcome the defects of existing positive electrode lithium replenishing additives in improving the initial charge and discharge efficiency of the battery, increasing the impedance of the positive electrode material and reducing the specific capacity of the material, a positive electrode lithium replenishing additive and its preparation method and application are provided.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] A positive electrode lithium supplement additive, comprising a porous material and a core-shell structure, wherein the core material is submicron lithium oxide, and the shell material is nanoscale carbon nanotubes; nitrogen and Li3N are adsorbed in the spaces between the core-shell structure and between the carbon nanotube layers. It is understood that the additive material of the present invention comprises a core of submicron lithium oxide, with spaces between the core and shell, and the shell material is nanoscale carbon nanotubes; nitrogen and Li3N are adsorbed in the spaces between the core-shell structure and between the carbon nanotube layers.

[0009] Preferably, the lithium oxide accounts for 30.76%-66.67% of the mass of the additive, the carbon nanotubes account for 33.33%-69.24% of the mass of the additive, the nitrogen accounts for 0.7%-1.5% of the volume of the additive, and the Li3N accounts for 0.01%-0.05% of the mass of the additive.

[0010] Preferably, the particle size of the lithium oxide is 0.1-0.5 μm, and the particle size of the carbon nanotube is 10-15 nm.

[0011] The submicron lithium oxide is obtained by calcining micron-sized lithium carbonate with a particle size of 2-5 μm. Optionally, the calcination temperature is 1200-1600° C., the heating rate is 3-5° C. / min, and the calcination time is 6-10 hours.

[0012] The present invention also provides a method for preparing the above-mentioned positive electrode lithium supplement additive, comprising the following steps:

[0013] 1) mixing nano-sized carbon nanotubes, a polar organic solvent, a dispersant, and a non-polar organic solvent, ball-milling the mixture, then adding micron-sized lithium carbonate, continuing the ball-milling, and drying the mixture to obtain a dried mixture;

[0014] 2) calcining the dried mixture under a high-pressure nitrogen atmosphere, wherein the nitrogen pressure is not less than 70 kPa, to obtain the positive electrode lithium supplement additive.

[0015] Preferably, the mass ratio of the nano-scale carbon nanotubes, polar organic solvent, dispersant and non-polar organic solvent is (8-12):100:(0.4-1):(0.8-1.4);

[0016] Optionally, the mass ratio of the nano-scale carbon nanotubes, polar organic solvent, dispersant and non-polar organic solvent is 10:100:0.6:1.0;

[0017] The mass ratio of the nano-scale carbon nanotubes and micron-scale lithium carbonate is (0.2-0.9):1. The present invention can further ensure that the battery using the additive material has more excellent performance and reduces battery impedance by controlling the mass ratio of the nano-scale carbon nanotubes and micron-scale lithium carbonate to (0.2-0.9):1. If the carbon nanotubes account for too much, the content of Li on the carbon nanotube layer is too little, the number of lithium ions provided during the deintercalation of metallic lithium is reduced, and the pre-lithiation effect is greatly reduced; if the carbon nanotubes account for too little, the content of Li on the carbon nanotube layer is too much, and the number of lithium ions provided during the deintercalation of metallic lithium increases sharply, which will increase the thickness of the battery SEI film, increase the battery impedance, and affect the performance of the battery; preferably, the mass ratio of the nano-scale carbon nanotubes and micron-scale lithium carbonate is 0.6:1.

[0018] Preferably, the ball milling temperature is 21-29°C, the ball milling time is 2-6 hours, and the continued ball milling time does not exceed 8 hours. Optionally, the continued ball milling time is 1-8 hours. The present invention controls the ball milling temperature to 21-29°C and the ball milling time to 2-6 hours. While ensuring that the carbon nanotubes are uniformly dispersed in the slurry, it also avoids the destruction of the carbon nanotube structure due to excessive grinding time. The carbon atoms at the broken parts will irreversibly react with Li+, resulting in poor electrochemical performance of the lithium-ion battery.

[0019] The drying temperature is 80-100°C and the drying time is 8-10h;

[0020] The calcination temperature is 1200-1600°C, the heating rate is 3-5°C / min, and the calcination time is 6-10h; preferably, the calcination temperature is 1400°C and the calcination time is 8h. The present invention is conducive to the decomposition of Li2CO3 to generate Li2O and CO2 at high temperature by controlling the calcination temperature and calcination time, which is conducive to improving the diffusion of metal Li atoms into the carbon nanotube material layer and enhancing the adhesion with metal Li. The generation of gas makes the lithium-ion battery positive electrode lithium supplement additive have a porous and loose structural feature, which is conducive to shortening the Li+ ion migration path and interface impedance, facilitating the migration of Li+ ions to continuously supplement the lithium source for the lithium-ion battery, thereby promoting the first effect of the lithium-ion battery.

[0021] The nitrogen pressure is 70-74 kPa;

[0022] The particle size of the nano-scale carbon nanotubes is 10-15 nm, and the particle size of the micron-scale lithium carbonate is 2-5 μm;

[0023] After the calcination is completed, the calcined material is further crushed, ground and sieved;

[0024] The present invention does not specifically limit the types of the polar organic solvent, dispersant, and non-polar organic solvent. Preferably, the polar organic solvent is N-methylpyrrolidone, the dispersant is polyvinylpyrrolidone, and the non-polar organic solvent is toluene. The polyvinylpyrrolidone and toluene used in the present invention can promote uniform dispersion of carbon nanotubes and prevent carbon nanotube agglomeration.

[0025] The present invention does not impose any specific limitation on the ball milling medium, and any conventional ball milling medium in the art can achieve the purpose of the present invention. Optionally, the ball milling medium can be 1.0-1.2 mm zirconium silicate beads or zirconium oxide beads.

[0026] The present invention also provides a lithium ion battery positive electrode material, comprising a positive electrode active substance, the positive electrode lithium replenishing additive described above, a conductive agent and a binder, wherein the amount of the positive electrode lithium replenishing additive accounts for 0.1%-10% of the total mass of the positive electrode material.

[0027] The present invention does not specifically limit the composition of the positive electrode active material. Optionally, the positive electrode active material is selected from one or more of lithium cobalt oxide positive electrode material, lithium nickel manganese cobalt oxide positive electrode material, lithium nickel manganese aluminum oxide positive electrode material, lithium manganese oxide positive electrode material, lithium nickel manganese oxide positive electrode material, lithium iron phosphate positive electrode material, lithium manganese phosphate positive electrode material, and lithium iron manganese phosphate positive electrode material, but is not limited to the types listed above. Other positive electrode active materials containing transition metals commonly used in the art are also applicable to the present invention.

[0028] The present invention does not specifically limit the types of the conductive agent and the binder. Optionally, the conductive agent is one or more of Super P, acetylene black, Ketjen black, conductive graphite, and graphene.

[0029] The binder is one or more of PVDF (polyvinylidene fluoride), LA132, LA133, CMC (carboxymethyl cellulose), and SBR (styrene-butadiene rubber), wherein LA132 and LA133 are conventional commercially available binders in the art.

[0030] The present invention also provides a lithium-ion battery comprising a positive electrode containing the aforementioned lithium-ion battery positive electrode material. The lithium-ion battery also includes a negative electrode material, which includes, but is not limited to, one or more of graphite, silicon-carbon, and silicon-oxygen. Silicon-carbon, silicon-oxygen, and other negative electrode materials with low initial coulombic efficiency are preferred.

[0031] Beneficial effects of the present invention:

[0032] 1. The positive electrode lithium supplement additive provided by the present invention is a porous material with a core-shell structure. Its core material is submicron lithium oxide and its shell material is nanoscale carbon nanotubes. Nitrogen and Li3N are adsorbed in the gaps between the core-shell structure and between the carbon nanotube layers. Nano-scale carbon nanotubes are used as shell materials. Their excellent electrical conductivity is conducive to reducing the interfacial impedance of the positive electrode material. The porous structure of the additive is conducive to the adsorption and stratification of metallic Li, which facilitates the migration of Li+ ions to continuously replenish the lithium source for the lithium-ion battery, thereby promoting the first effect of the lithium-ion battery. At the same time, the nano-scale carbon nanotube shell material increases the surface activity of submicron-scale Li2O, reduces its Gibbs free energy, and promotes the migration of Li+ ions. The interlayer structure of the carbon nanotube provides an attachment site for metallic lithium, allowing more metallic lithium to diffuse and embed into the interlayer structure of the carbon nanotube under high temperature. At the same time, nitrogen and Li3N are adsorbed in the gaps between the core-shell structure and between the carbon nanotube layers. During the use of the lithium-ion battery, the lithium between the carbon nanotube layers is first deintercalated, and the submicron-scale Li2O core is deintercalated last to replenish The metallic lithium between the carbon nanotube layers continuously provides Li+ ions for the lithium-ion battery. At the same time, Li3N can achieve an electrochemical reaction between 0.01V and 4.5V under the catalytic action of the metal in the positive electrode material, and promote the formation of a dense CEI thin film layer between the positive electrode and the electrolyte. In actual work, the nitrogen between the layers easily reacts with the lithium element to obtain lithium nitride, further replenishing the consumed lithium nitride and continuously exerting a catalytic effect. At the same time, the additive material obtained by the present invention has a high positive electrode potential during the charging process. The higher potential will promote Li+ to enter the negative electrode side and enter the negative electrode material at a lower potential, thereby achieving pre-lithiation of a variety of negative electrode materials. At the same time, submicron lithium oxide and nanoscale carbon nanotubes enable uniform and dense contact between them and the electrode material particles, greatly improving the efficiency of the pre-lithiation process. The present invention adopts a specific core-shell structure, wherein the core material is submicron lithium oxide and the shell material is nanoscale carbon nanotubes; nitrogen and Li3N are adsorbed in the gaps between the core-shell structure and between the carbon nanotube layers. Through the interaction between the material structure and components, the impedance of the positive electrode material can be effectively reduced, while the initial charge and discharge efficiency of the battery, as well as the battery capacity, cycle performance, and life can be improved, the expansion rate of the battery core can be reduced, and the battery has more excellent performance.

[0033] 2. The preparation method of the positive electrode lithium supplement additive provided by the present invention comprises the following steps: mixing nano-scale carbon nanotubes, polar organic solvents, dispersants and non-polar organic solvents, ball milling, adding micron-scale lithium carbonate, continuing ball milling, drying, and obtaining a dried mixture; and then calcining the dried mixture under a high-pressure nitrogen atmosphere to obtain the positive electrode lithium supplement additive. The present invention ball mills nano-scale carbon nanotubes and micron-scale lithium carbonate to form a nano-scale carbon nanotube-coated micron-scale lithium carbonate mixture, and then calcining it under high-pressure nitrogen. Li2CO3 decomposes at high temperature to generate Li2O and CO2. The generation of gas is conducive to opening the shell material pathway, reducing the core material Li + The migration impedance during the battery charge and discharge process makes the additive have a porous structural feature; moreover, the carbon nanotubes are short-range ordered at the microscopic level, which is conducive to the adsorption and stratification of metallic Li, and is conducive to the rapid migration of Li+ into the electrolyte to participate in the charge and discharge process, thereby promoting the initial effect of the lithium-ion battery. In addition, the material is calcined under a high-pressure nitrogen atmosphere, which can promote the diffusion of some Li atoms into the carbon nanotube layers; at the same time, the formation of a porous shell structure will promote the entry of high-pressure nitrogen into the core-shell structure, which is conducive to the formation of gaps between the core-shell structure and the adsorption of N2 and Li3N between the carbon nanotube layers. At the same time, during the calcination process, micron-sized lithium carbonate will form submicron-sized lithium oxide. The reduction in size will form a certain gap between the lithium oxide core structure and the carbon nanotube layer coated on the outer surface, allowing Li+ to migrate rapidly, thereby improving battery performance. The additive material prepared by the method of the present invention has a specific core-shell structure, wherein the core material is submicron lithium oxide and the shell material is nanoscale carbon nanotubes; nitrogen and Li3N are adsorbed in the gaps between the core-shell structure and between the carbon nanotube layers. Through the interaction between the material structure and components, the impedance of the positive electrode material can be effectively reduced, while the initial charge and discharge efficiency of the battery, as well as the battery capacity, cycle performance, and life can be improved, the battery core expansion rate is reduced, and the battery has more excellent performance.

[0034] At the same time, the method provided by the present invention does not require changes to the original production process and has low cost. The prepared material not only avoids the direct use of metallic lithium, but also has significantly improved safety and reliability compared with previous negative electrode lithium supplementation. It can also provide a lithium source during the first charge to compensate for the lithium consumed by the negative electrode material to form the SEI film, thereby improving the initial coulombic efficiency and battery capacity of the lithium-ion battery, and has important significance for the commercial application of carbon-based negative electrode materials, silicon-based negative electrode materials, and silicon-carbon negative electrode materials. DETAILED DESCRIPTION

[0035] The following examples are provided for a better understanding of the present invention and are not intended to limit the best mode of implementation. They do not limit the content and scope of protection of the present invention. Any product identical or similar to the present invention obtained by anyone under the guidance of the present invention or by combining the features of the present invention with other prior arts shall fall within the scope of protection of the present invention.

[0036] If no specific experimental steps or conditions are specified in the examples, the conventional experimental steps or conditions described in the literature in this field can be used. If the manufacturer of the reagents or instruments is not specified, they are all commercially available conventional reagents.

[0037] Example 1

[0038] This embodiment provides a method for preparing a positive electrode lithium supplement additive, comprising the following steps:

[0039] 1) adding 10 g of carbon nanotubes (particle size of 12 nm) to 100 g of N-methylpyrrolidone, and adding 0.6 g of polyvinylpyrrolidone and 1.0 g of toluene, and ball milling the mixed slurry using a high-energy ball mill at a ball milling temperature of 25° C. for 4 hours, using zirconium oxide beads with a diameter of 1.0-1.2 mm as the ball milling medium, and then adding lithium carbonate (lithium carbonate particle size of 3 μm, carbon nanotubes and lithium carbonate mass ratio of 0.9:1), and continuing ball milling for 6 hours to fully mix the lithium carbonate in the above slurry. After the ball milling, the slurry is placed in a blast drying oven at 90° C. for 9 hours to obtain a dried mixed material;

[0040] 2) The dried mixture is placed in a tubular heating furnace and calcined in a high-pressure nitrogen atmosphere (nitrogen pressure of 70 kPa), the calcination temperature is 1400 ° C, the heating rate is 3 ° C / min, and the calcination time is 8 h. After the calcination, the material is crushed, ground, sieved, and vacuum stored to obtain the positive electrode lithium supplement additive. The obtained positive electrode lithium supplement additive is a porous material having a core-shell structure, wherein the core material is lithium oxide with a particle size of 0.2 μm, and the shell material is carbon nanotubes with a particle size of 12 nm. Nitrogen and Li3N are adsorbed in the gaps between the core-shell structure and the interlayers of the carbon nanotubes, wherein lithium oxide accounts for 37.657% of the mass of the additive, carbon nanotubes account for 62.325% of the mass of the additive, nitrogen accounts for 0.842% of the volume of the additive, and Li3N accounts for 0.018% of the mass of the additive.

[0041] Example 2

[0042] This embodiment provides a method for preparing a positive electrode lithium supplement additive, comprising the following steps:

[0043] 1) adding 8 g of carbon nanotubes (particle size of 13 nm) to 100 g of N-methylpyrrolidone, and adding 0.4 g of polyvinylpyrrolidone and 1.4 g of toluene, and ball milling the mixed slurry using a high-energy ball mill at a ball milling temperature of 25° C. for 4 h, using zirconium oxide beads with a diameter of 1.0-1.2 mm as the ball milling medium, and then adding lithium carbonate (lithium carbonate particle size of 3 μm, carbon nanotubes and lithium carbonate mass ratio of 0.8:1), and continuing ball milling for 6 h to fully mix the lithium carbonate in the above slurry. After the ball milling, the slurry is placed in a blast drying oven at 85° C. for 9 h to obtain a dried mixed material;

[0044] 2) The dried mixture is placed in a tubular heating furnace and calcined in a high-pressure nitrogen atmosphere (nitrogen pressure of 71 kPa), the calcination temperature is 1300 ° C, the heating rate is 4 ° C / min, and the calcination time is 9 h. After the calcination, the material is crushed, ground, sieved, and vacuum stored to obtain the positive electrode lithium supplement additive. The obtained positive electrode lithium supplement additive is a porous material having a core-shell structure, wherein the core material is lithium oxide with a particle size of 0.2 μm, and the shell material is carbon nanotubes with a particle size of 13 nm. Nitrogen and Li3N are adsorbed in the gaps between the core-shell structure and the interlayers of the carbon nanotubes, wherein lithium oxide accounts for 42.840% of the mass of the additive, carbon nanotubes account for 57.129% of the mass of the additive, nitrogen accounts for 0.891% of the volume of the additive, and Li3N accounts for 0.031% of the mass of the additive.

[0045] Example 3

[0046] This embodiment provides a method for preparing a positive electrode lithium supplement additive, comprising the following steps:

[0047] 1) adding 12 g of carbon nanotubes (particle size of 14 nm) to 100 g of N-methylpyrrolidone, and adding 1 g of polyvinylpyrrolidone and 0.8 g of toluene, and ball milling the mixed slurry using a high-energy ball mill at a ball milling temperature of 25° C. for 4 h. The ball milling medium is zirconia beads with a diameter of 1.0-1.2 mm. Then, lithium carbonate (lithium carbonate particle size of 3 μm, mass ratio of carbon nanotubes to lithium carbonate of 0.8:1) is added, and ball milling is continued for 6 h to fully mix the lithium carbonate in the above slurry. After the ball milling is completed, the slurry is placed in a blast drying oven at 100° C. for 8 h to obtain a dried mixed material;

[0048] 2) The dried mixture is placed in a tubular heating furnace and calcined in a high-pressure nitrogen atmosphere (nitrogen pressure of 72 kPa), the calcination temperature is 1600 ° C, the heating rate is 3 ° C / min, and the calcination time is 6 h. After the calcination, the material is crushed, ground, sieved, and vacuum stored to obtain the positive electrode lithium supplement additive. The obtained positive electrode lithium supplement additive is a porous material having a core-shell structure, wherein the core material is lithium oxide with a particle size of 0.2 μm, and the shell material is carbon nanotubes with a particle size of 14 nm. Nitrogen and Li3N are adsorbed in the gaps between the core-shell structure and the interlayers of the carbon nanotubes, wherein lithium oxide accounts for 40.712% of the mass of the additive, carbon nanotubes account for 59.251% of the mass of the additive, nitrogen accounts for 0.843% of the volume of the additive, and Li3N accounts for 0.037% of the mass of the additive.

[0049] Example 4

[0050] This embodiment provides a method for preparing a positive electrode lithium supplement additive, which differs from Example 1 in that the mass ratio of carbon nanotubes to lithium carbonate in step 1) is 0.6:1.

[0051] The prepared positive electrode lithium supplement additive is a porous material with a core-shell structure. The core material is lithium oxide with a particle size of 0.2 μm, and the shell material is carbon nanotubes with a particle size of 12 nm. Nitrogen and Li3N are adsorbed in the gaps between the core-shell structure and between the carbon nanotube layers. Among them, lithium oxide accounts for 50.345% of the mass of the additive, carbon nanotubes account for 49.613% of the mass of the additive, nitrogen accounts for 0.957% of the volume of the additive, and Li3N accounts for 0.042% of the mass of the additive.

[0052] Example 5

[0053] This embodiment provides a method for preparing a positive electrode lithium supplement additive, which differs from Example 1 in that the mass ratio of carbon nanotubes to lithium carbonate in step 1) is 0.4:1.

[0054] The prepared positive electrode lithium supplement additive is a porous material with a core-shell structure. The core material is lithium oxide with a particle size of 0.2 μm, and the shell material is carbon nanotubes with a particle size of 12 nm. Nitrogen and Li3N are adsorbed in the gaps between the core-shell structure and between the carbon nanotube layers. Among them, lithium oxide accounts for 58.394% of the mass of the additive, carbon nanotubes account for 41.563% of the mass of the additive, nitrogen accounts for 0.984% of the volume of the additive, and Li3N accounts for 0.043% of the mass of the additive.

[0055] Example 6

[0056] This embodiment provides a method for preparing a positive electrode lithium supplement additive, which differs from Example 1 in that the mass ratio of carbon nanotubes to lithium carbonate in step 1) is 0.2:1.

[0057] The prepared positive electrode lithium supplement additive is a porous material with a core-shell structure. The core material is lithium oxide with a particle size of 0.2 μm, and the shell material is carbon nanotubes with a particle size of 12 nm. Nitrogen and Li3N are adsorbed in the gaps between the core-shell structure and between the carbon nanotube layers. Among them, lithium oxide accounts for 65.810% of the mass of the additive, carbon nanotubes account for 34.141% of the mass of the additive, nitrogen accounts for 1.108% of the volume of the additive, and Li3N accounts for 0.049% of the mass of the additive.

[0058] Comparative Example 1

[0059] The positive electrode lithium supplement additive provided in this comparative example is carbon nanotubes with a particle size of 12 nm.

[0060] Comparative Example 2

[0061] This comparative example provides a method for preparing a positive electrode lithium supplement additive, comprising the following steps:

[0062] 1) adding 10 g of carbon nanotubes (particle size 12 nm) to 100 g of N-methylpyrrolidone, 0.6 g of polyvinylpyrrolidone, and 1.0 g of toluene, and ball milling the mixed slurry in a high-energy ball mill at a ball milling temperature of 25° C. for 4 hours using zirconium oxide beads with a diameter of 1.0-1.2 mm. After the ball milling, the slurry was dried in a forced air drying oven at 90° C. for 9 hours to obtain a dried mixed material;

[0063] 2) The dried mixture is placed in a tubular heating furnace and calcined under a high-pressure nitrogen atmosphere (nitrogen pressure is 70 kPa) at a calcination temperature of 1400° C., a heating rate of 3° C. / min, and a calcination time of 8 h. After the calcination, the material is crushed, ground, sieved, and stored in a vacuum to obtain the positive electrode lithium supplement additive.

[0064] Comparative Example 3

[0065] This comparative example provides a method for preparing a positive electrode lithium supplement additive. Compared with Example 1, the difference is that in step 2), the dried mixed material is placed in a tubular heating furnace and calcined under a nitrogen atmosphere at atmospheric pressure. The calcination temperature is 1400°C, the heating rate is 3°C / min, and the calcination time is 8 hours. After the calcination, the material is crushed, ground, sieved, and vacuum-stored to obtain the positive electrode lithium supplement additive. The prepared positive electrode lithium supplement additive is a porous material with a core-shell structure. Its core material is lithium oxide with a particle size of 0.5 μm, and its shell material is carbon nanotubes with a particle size of 15 nm. The carbon nanotubes have undesorbed CO2 gas adsorbed between the layers, which increases the Li+ migration resistance and reduces the performance of the additive. The lithium oxide accounts for 30.76% of the mass of the additive, and the carbon nanotubes account for 69.24% of the mass of the additive. Nitrogen is tracely adsorbed on the surface of the carbon nanotube shell, and no Li3N is detected. This indicates that atmospheric nitrogen has difficulty promoting N2 molecules to enter the voids of the core-shell structure of the material to participate in the reaction.

[0066] Test Case

[0067] Lithium-ion battery manufacturing

[0068] 1) Preparation of positive electrode: LiNi 0.65 Mn 0.35 O2 material is used as the positive electrode active material. The positive electrode active material, the positive electrode lithium supplement additive provided in the above embodiment or comparative example, and polyvinylidene fluoride are homogenized in a mass ratio of 96%:2.5%:1.5% to prepare a slurry. The prepared slurry is evenly coated on a 12 μm thick aluminum foil with a double-sided coating weight of 50 mg / cm 2 , and then through drying, rolling, die cutting, punching into positive electrode sheets.

[0069] 2) Preparation of electrolyte

[0070] Dissolve an equal volume of ethylene carbonate in ethyl methyl carbonate, and then evenly dissolve an appropriate amount of LiPF6 in the mixed solvent to form a 1 mol / L electrolyte for later use.

[0071] 3) Negative electrode

[0072] The negative electrode sheet uses a silicon-carbon negative electrode material (the silicon-carbon negative electrode material contains 6.8wt% Si). The silicon-carbon negative electrode material, styrene-butadiene rubber, sodium carboxymethyl cellulose and conductive agent Super P (superconducting carbon black) are mixed in a mass ratio of 95wt%:2.2wt%:1.8wt%:1wt%. Deionized water is used for homogenization. The slurry viscosity is adjusted to 3000-5000cP (the test slurry temperature standard is 25±2°C) and the solid content is 50±2%. The prepared slurry is evenly coated on a 6μm thick copper foil, and the double-sided coating weight is 30mg / cm 2, and then through drying, rolling, die cutting, punching into negative electrode sheets.

[0073] 4) Isolation film: PET isolation film with a thickness of 16μm is used.

[0074] 5) Preparation of batteries:

[0075] The positive electrode sheet, separator, and negative electrode sheet are stacked in order and packaged into soft-pack batteries, which are then baked, injected with liquid, pre-charged, formed, and sealed to form battery cells.

[0076] Test Case

[0077] The electrochemical performance tests of the batteries prepared above were carried out as follows:

[0078] The test method for 1C initial discharge capacity is as follows: charge to 4.2V at a 1C rate of constant current and constant voltage, and then discharge to 2.7V at a 1C rate (the recorded discharge capacity is the 1C initial discharge capacity).

[0079] The initial charge and discharge efficiency (first efficiency) is tested as follows: discharge at a 1C rate to 2.7V, then charge at a 1C constant current and constant voltage rate to 4.2V (record the charge capacity C0), and then discharge at a 1C rate to 2.7V (record the discharge capacity C1). Initial charge and discharge efficiency / % = (C1 / C0) * 100%.

[0080] The test method for capacity retention is as follows: charge the battery to 4.2V at a constant current and constant voltage rate of 1C, then discharge it to 2.7V at a rate of 1C (record the discharge capacity C1), and after 200 cycles, record the discharge capacity C 200 ; Capacity retention rate / % = (C 200 / C1)*100%.

[0081] The DCIR test method is as follows: discharge at a constant current of 300A for 10 seconds and record the voltage change ΔV; DCIR = ΔV / I.

[0082] The test method for calendar life is as follows: Under a 55°C environment, the capacity retention (%) of the battery is tested at 100% SOC (4.2V) for 60 days.

[0083] The test method for the battery cell expansion rate is as follows: place the battery cell flat on a horizontal table, use a laser rangefinder to measure the horizontal height of the highest point in the center of the battery cell (i.e. H1), then charge it at a constant current and constant voltage rate of 1C to 4.2V, and then discharge it at a rate of 1C to 2.7V. After 200 cycles, place the battery cell flat on a horizontal table again, and use a laser rangefinder to measure the horizontal height of the highest point in the center of the battery cell (i.e. H2). The battery cell expansion rate after the cycle / % = ((H2-H1) / H1)*100%;

[0084] Place the battery cell flat on a horizontal table and use a laser rangefinder to measure the horizontal height of the highest point in the center of the battery cell (i.e., H1). Then, store the battery cell at 100% SOC (4.2V) at 55°C for 60 days. Place the battery cell flat on a horizontal table again and use a laser rangefinder to measure the horizontal height of the highest point in the center of the battery cell (i.e., H2). The battery cell expansion rate after storage / % = ((H2-H1) / H1)*100%.

[0085] The test results are shown in Table 1.

[0086] Table 1

[0087]

[0088] It can be seen from Comparative Examples 1 and 2 that when carbon nanotubes are ball-milled and subjected to high-temperature treatment alone, their performance in lithium-ion batteries deteriorates. By comparing Comparative Example 2 with Example 1, the lithium-ion battery positive electrode lithium supplement additive of the present invention is beneficial to the migration of Li+ ions and continuously replenishes the lithium source for the lithium-ion battery, thereby promoting the initial effect of the lithium-ion battery and improving the performance of the lithium-ion battery such as capacity. By comparing Comparative Example 3 with Example 1, the lithium-ion battery positive electrode lithium supplement additive of the present invention is obtained by calcining under a high-pressure nitrogen atmosphere, so that nitrogen and Li3N are adsorbed in the gaps between the core-shell structure and the carbon nanotube layers. Through the interaction of material structure and composition, the impedance of the positive electrode material can be effectively reduced, and at the same time, the initial charge and discharge efficiency of the battery, as well as the capacity, cycle performance, and life of the battery can be improved, the expansion rate of the battery cell can be reduced, and the battery has more excellent performance.

[0089] The lithium-ion battery positive electrode lithium supplement additive provided by the present invention can effectively promote the formation of the SEI film, improve the battery's initial efficiency, and reduce the battery impedance. The positive electrode lithium supplement additive can provide sufficient lithium ions. The surplus Li+ provided during the first charging process is obviously sufficient to compensate for the Li+ lost by the formation of the SET film on the negative electrode surface, which is conducive to the formation of a more uniform and dense SEI film, improves the initial efficiency, and can effectively reduce the impedance of the positive electrode material. At the same time, it can improve the battery's capacity, cycle performance, and lifespan, reduce the battery cell expansion rate, and provide the battery with more excellent performance.

[0090] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will readily appreciate that other variations or modifications based on the above descriptions are possible. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain within the scope of protection of the present invention.

Claims

1. A positive electrode lithium supplement additive, characterized in that: The additive is a porous material with a core-shell structure, wherein the core material is submicron lithium oxide and the shell material is nano-scale carbon nanotubes; nitrogen and Li3N are adsorbed in the gaps between the core-shell structure and between the carbon nanotube layers; The preparation method of the positive electrode lithium supplement additive comprises the following steps: 1) mixing nano-sized carbon nanotubes, a polar organic solvent, a dispersant, and a non-polar organic solvent, ball-milling the mixture, then adding micron-sized lithium carbonate, continuing the ball-milling, and drying the mixture to obtain a dried mixture; 2) calcining the dried mixture under a high-pressure nitrogen atmosphere, wherein the nitrogen pressure is not less than 70 kPa, to obtain the positive electrode lithium supplement additive.

2. The positive electrode lithium supplement additive according to claim 1, characterized in that The lithium oxide accounts for 30.76%-66.67% of the additive mass.

3. The positive electrode lithium supplement additive according to claim 1, characterized in that The carbon nanotubes account for 33.33% to 69.24% of the additive mass.

4. The positive electrode lithium supplement additive according to claim 1, characterized in that The nitrogen gas accounts for 0.7% to 1.5% of the volume of the additive.

5. The positive electrode lithium supplement additive according to claim 1, characterized in that The Li3N accounts for 0.01%-0.05% of the mass of the additive.

6. The positive electrode lithium supplement additive according to claim 1, characterized in that The particle size of the lithium oxide is 0.1-0.5 μm, and the particle size of the carbon nanotube is 10-15 nm.

7. The positive electrode lithium supplement additive according to any one of claims 1 to 6, characterized in that: The submicron lithium oxide is obtained by calcining micron lithium carbonate with a particle size of 2-5 μm.

8. The method for preparing the positive electrode lithium supplement additive according to any one of claims 1 to 7, characterized in that: The steps include: 1) mixing nano-sized carbon nanotubes, a polar organic solvent, a dispersant, and a non-polar organic solvent, ball-milling the mixture, then adding micron-sized lithium carbonate, continuing the ball-milling, and drying the mixture to obtain a dried mixture; 2) calcining the dried mixture under a high-pressure nitrogen atmosphere, wherein the nitrogen pressure is not less than 70 kPa, to obtain the positive electrode lithium supplement additive.

9. The method for preparing the positive electrode lithium supplement additive according to claim 8, characterized in that: The mass ratio of the nano-scale carbon nanotubes, polar organic solvent, dispersant and non-polar organic solvent is (8-12):100:(0.4-1):(0.8-1.4); The mass ratio of the nano-scale carbon nanotubes to the micron-scale lithium carbonate is (0.2-0.9):

1.

10. The method for preparing the positive electrode lithium supplement additive according to claim 8 or 9, characterized in that: The ball milling temperature is 21-29°C, the ball milling time is 2-6 hours, and the ball milling time is not more than 8 hours; The drying temperature is 80-100°C and the drying time is 8-10h; The calcination temperature is 1200-1600°C, the heating rate is 3-5°C / min, and the calcination time is 6-10h; The nitrogen pressure is 70-74 kPa; The particle size of the nano-scale carbon nanotubes is 10-15 nm, and the particle size of the micron-scale lithium carbonate is 2-5 μm; After the calcination is completed, the calcined material is further crushed, ground and sieved; The polar organic solvent is N-methylpyrrolidone, the dispersant is polyvinylpyrrolidone, and the non-polar organic solvent is toluene.

11. A positive electrode material for a lithium ion battery, characterized in that: The invention comprises a positive electrode active material, the positive electrode lithium replenishing additive according to any one of claims 1 to 7, a conductive agent and a binder, wherein the amount of the positive electrode lithium replenishing additive accounts for 0.1% to 10% of the total mass of the positive electrode material.

12. The lithium-ion battery positive electrode material according to claim 11, characterized in that The positive electrode active material is selected from one or more of lithium cobalt oxide positive electrode material, lithium nickel manganese cobalt oxide positive electrode material, lithium nickel manganese aluminum oxide positive electrode material, lithium manganese oxide positive electrode material, lithium nickel manganese oxide positive electrode material, lithium iron phosphate positive electrode material, lithium manganese phosphate positive electrode material, and lithium iron manganese phosphate positive electrode material. 13 . A lithium ion battery comprising a positive electrode comprising the lithium ion battery positive electrode material according to claim 11 .

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