CN115818736A - Hollow lithium nickel manganese oxide positive electrode material and preparation method and application thereof - Google Patents
Hollow lithium nickel manganese oxide positive electrode material and preparation method and application thereof Download PDFInfo
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Abstract
The invention provides a hollow lithium nickel manganese oxide positive electrode material and a preparation method and application thereof, wherein the preparation method of the positive electrode material comprises the following steps: s1, providing manganese dioxide microspheres; s2, mixing and soaking the manganese dioxide microspheres, a nickel source and a lithium source in a solvent, removing the solvent to obtain a precursor, and sintering to obtain the hollow spherical lithium nickel manganese oxide cathode material. Manganese carbonate particles can be prepared by a carbonate precipitation method, and then the material can be prepared by regulating and controlling the diffusion rate of nickel-manganese ions in sintering through dipping and calcining. The lithium nickel manganese oxide material prepared by the method has uniform particle size, the sintered material has a hollow structure, and the material has a concentration gradient of manganese ions in the radial direction, so that the dissolution of the manganese ions is reduced; the design of the hollow structure is beneficial to the infiltration of electrolyte, can support high-rate charge and discharge, simultaneously buffers the volume effect of the material in the charge and discharge process, and further improves the stability of the applied lithium ion battery.
Description
Technical Field
The invention belongs to the technical field of material chemistry, and particularly relates to a hollow lithium nickel manganese oxide positive electrode material, a preparation method thereof and a corresponding lithium ion battery.
Background
Electric power is used as a clean energy source, and the proportion of all energy sources is heavier and heavier. Accordingly, the demand of the society for secondary batteries is also increasing. Lithium ion secondary batteries using lithium iron phosphate as the positive electrode have energy density approaching the theoretical limit, and ternary batteries also enter a high nickel system. The methods for increasing the energy density of the battery are generally two, one is to increase the specific capacity of the electrode material, and the other is to increase the working voltage of the battery system. Among electrode materials, lithium nickel manganese oxide material has a discharge voltage close to 4.7V, and can greatly improve the energy density of a battery, so that the lithium nickel manganese oxide material is more and more concerned by researchers.
LiNi, a widely studied positive electrode material for lithium ion batteries 0.5 Mn 1.5 O 4 The (LNMO) material still has some problems to be solved, such as slow diffusion of lithium ions, low rate capability and Mn formation in the discharge process 3+ Ions and the initiation of the Taylor effect lead to structural collapse, manganese ion dissolution, specific capacity reduction caused by nickel-lithium mixed discharge in the charging and discharging processes, and the like. In order to solve the above problems, it is possible to develop a technology such as shortening the diffusion path of lithium ions by controlling the particle size of LNMO and/or preparing a cathode material having a hollow structure.
For example, chinese patent publication No. CN 103746108A describes a method for preparing a lithium ion battery cathode material doped with a hollow lithium nickel manganese oxide structure, which includes several steps of preparing carbon spheres, preparing magnesium-doped hollow lithium nickel manganese oxide, and coating the magnesium-doped hollow lithium nickel manganese oxide. However, the preparation method utilizes the carbon spheres as sacrificial templates, and is complicated and difficult to prepare.
Disclosure of Invention
In order to solve the technical problems, the invention provides a hollow lithium nickel manganese oxide positive electrode material and a preparation method and application thereof.
The invention provides a preparation method of a hollow lithium nickel manganese oxide positive electrode material, which comprises the following steps:
s1, providing manganese dioxide microspheres;
s2, mixing and soaking the manganese dioxide microspheres, a nickel source and a lithium source in a solvent, removing the solvent to obtain a precursor, and sintering to obtain the hollow spherical lithium nickel manganese oxide cathode material.
Preferably, the manganese dioxide microspheres of step S1 are obtained as follows:
manganese sulfate monohydrate is precipitated by carbonate to obtain manganese carbonate microspheres;
and calcining the obtained manganese carbonate microspheres at 300-700 ℃ in an air atmosphere to obtain manganese dioxide microspheres.
Preferably, the manganese carbonate microspheres are obtained by precipitation reaction of manganese sulfate monohydrate and ammonium bicarbonate, and the molar ratio of the manganese sulfate monohydrate to the ammonium bicarbonate is 1: 5-1: 40.
Preferably, the precipitation reaction is carried out in a mixed solvent of ethanol and water, and the volume ratio of the added ethanol to the added water is 50: 1-5: 1.
Preferably, the concentration of manganese ions in the precipitation reaction is between 0.2M and 1M; the calcining time of the manganese carbonate microspheres is 2-10h.
Preferably, the nickel source of step S2 is one or more of nickel oxide, nickel acetate, nickel sulfate and nickel nitrate, and the lithium source is one or more of lithium hydroxide, lithium carbonate and lithium chloride.
Preferably, the step S2 specifically includes:
putting the manganese dioxide microspheres, a nickel source and a lithium source together in ethanol according to a stoichiometric ratio, performing ultrasonic dispersion, heating to remove ethanol to obtain a precursor, grinding, and sintering to obtain a hollow spherical lithium nickel manganese oxide cathode material; the heating temperature is preferably 40 ℃ to 80 ℃.
Preferably, the sintering of the step S2 is carried out at a constant temperature of 600-900 ℃, and the time is preferably 2-20h.
The invention provides a hollow lithium nickel manganese oxide positive electrode material which is prepared by the preparation method, has a hollow spherical structure and a radial concentration gradient of manganese ions, and has an adjustable size of 0.5-5 mu m.
The invention provides a lithium ion battery which comprises the hollow lithium nickel manganese oxide positive electrode material.
The invention mainly provides a hollow lithium nickel manganese oxide positive electrode material and a preparation method thereof, which can be prepared by simple precipitation-impregnation-calcination process steps without an additional template. The size of the lithium nickel manganese oxide material prepared by the method is adjustable between 0.5 and 5 mu m, and the lithium nickel manganese oxide material has the advantages of uniform particle size, obvious hollow structure, manganese ion concentration gradient in the radial direction of particles and the like. The uniform particle size distribution of the electrolyte enables the prepared battery to have higher consistency; the obvious hollow structure can shorten the diffusion distance of lithium ions in the electrode material, improve the rate capability, relieve the volume change caused by the release and the insertion of the lithium ions and maintain the cycle performance of the battery; the radial concentration gradient of the manganese ions can reduce the concentration of the manganese ions on the surface of the material, slow down the dissolution of the manganese ions and improve the electrochemical stability of the material. The preparation method provided by the invention is simple, is easy for large-scale production, and can provide technical support for the preparation of the high-voltage anode of the lithium ion battery.
Drawings
FIG. 1 is a corresponding 5 μm-scale SEM photograph of the LNMO material prepared in example 1;
FIG. 2 is a corresponding 1 μm-scale SEM photograph of the LNMO material prepared in example 1;
figure 3 is a XRD spectrum corresponding to LNMO prepared at two concentrations for example 1 and example 2.
Detailed Description
The technical solutions in the embodiments of the present application are clearly and completely described below, and it is obvious that the described embodiments are only a part of the embodiments of the present application, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.
The invention provides a preparation method of a hollow lithium nickel manganese oxide positive electrode material, which comprises the following steps:
s1, providing manganese dioxide microspheres;
s2, mixing and soaking the manganese dioxide microspheres, a nickel source and a lithium source in a solvent, removing the solvent to obtain a precursor, and sintering to obtain the hollow spherical lithium nickel manganese oxide cathode material.
The method for preparing the lithium nickel manganese oxide lithium ion cathode material with the hollow structure provided by the invention does not need to use soft and hard templates, the preparation process is simple, and the prepared material is hollow spherical lithium nickel manganese oxide, which is beneficial to improving the stability of a corresponding lithium ion battery.
The preparation method mainly comprises the steps of manganese carbonate microsphere preparation, manganese dioxide microsphere preparation, dipping process and final sintering process, and can be used for preparing the lithium nickel manganese oxide cathode material with a hollow structure by regulating and controlling Kirkendall effect.
In the embodiment of the invention, manganese carbonate microsphere particles are prepared by carbonate precipitation, and the specific process comprises the following steps: dissolving a certain amount of manganese sulfate monohydrate in water (usually deionized water), adding a certain amount of ethanol after completely dissolving, adding an ammonium bicarbonate aqueous solution with a proper concentration, and continuously stirring for a period of time at room temperature; the obtained mixture solution can be centrifugally separated, washed by water and dried to obtain the manganese carbonate microspheres.
In a preferred embodiment of the invention, the molar ratio of manganese sulfate monohydrate to ammonium bicarbonate is between 1: 5 and 1: 40, further between 1: 6 and 1: 30. The preferred volume ratio of the addition amount of the ethanol to the deionized water is 50: 1-5: 1, and the more preferred volume ratio is 45: 1-4: 1. The concentration of manganese ions in the precipitation reaction can be between 0.2M and 1.0M; the room temperature is well known to those skilled in the art, e.g., 10 to 35 ℃; stirring and centrifugation, etc., are also conventional in the art. Wherein the particle size range of the manganese carbonate microspheres obtained by separation is between 1.2 and 6.0 mu m.
After obtaining the manganese carbonate microspheres, the embodiment of the present invention performs a preparation step of manganese dioxide microspheres. Specifically, the manganese carbonate material prepared in the above steps is calcined for several hours at 300-700 ℃ in the air atmosphere, so as to obtain the manganese dioxide microspheres.
In some embodiments of the invention, the temperature of the calcination may be from 350 ℃ to 600 ℃, and further may be from 400 ℃ to 590 ℃. The manganese carbonate microspheres are preferably calcined for 2-10 hours, and more preferably for 3-8 hours. Further, the particle size of the obtained manganese dioxide microspheres is between 1.3 and 5.5 microns.
Then, in the embodiment of the present invention, hollow structure LNMO (LiNi) is performed o.5 Mn 1.5 O 4 ) And (4) preparing the material. In the specific embodiment of the invention, a certain amount of manganese dioxide microspheres are weighed, a certain amount of nickel source and a certain amount of lithium source are respectively weighed according to the stoichiometric ratio, and are jointly placed in a proper amount of ethanol for ultrasonic dispersion. And slowly heating until the ethanol is completely evaporated to obtain a precursor of a mixture of the three materials, uniformly grinding, placing in a high-temperature furnace, preferably performing solid-phase reaction at 600-900 ℃, and calcining at constant temperature for a period of time to obtain the LNMO with a hollow structure, namely the hollow spherical lithium nickel manganese oxide cathode material.
In the embodiment of the invention, the nickel source can be one or more of nickel oxide, nickel acetate, nickel sulfate and nickel nitrate; the lithium source may be one or more of lithium hydroxide, lithium carbonate, and lithium chloride. The solvent involved in the impregnation process is preferably ethanol; the temperature for heating to remove the solvent is preferably 40 to 80 ℃, more preferably 50 to 70 ℃. The temperature of the final sintering process in the embodiment of the invention is 600-900 ℃ constant temperature, which can also be called as a calcining process; the calcination is preferably carried out at a temperature of 610 to 880 ℃, more preferably at a temperature of 680 to 780 ℃, for example, at a temperature of 750 ℃ for a period of preferably 2 to 20 hours, further preferably 3 to 15 hours, or the like. According to the embodiment of the invention, the cathode material can be prepared by the steps of dipping and calcining and controlling the diffusion rate of nickel and manganese ions in sintering by controlling the temperature of dipping and calcining, wherein certain concentration gradient exists in the radial distribution of the manganese ions in the material particles.
According to the embodiment of the invention, the lithium nickel manganese oxide cathode material with a hollow structure is prepared without a template by a precipitation-impregnation-calcination method, and the method is simple and easy to implement.
The invention provides a hollow lithium nickel manganese oxide positive electrode material which is prepared by the preparation method, and the lithium nickel manganese oxide material is LNMO (LiNi) with a hollow structure 0.5 Mn 1.5 O 4 ) And has a radial concentration gradient of manganese ions; the lithium ion battery anode material is used as an anode material for preparing a lithium ion battery, and can improve the stability of the battery and the like.
Correspondingly, the invention provides a lithium ion battery which comprises the hollow lithium nickel manganese oxide cathode material.
In the embodiment of the invention, the lithium nickel manganese oxide material prepared by the method has uniform particle size, and the size of the lithium nickel manganese oxide material is adjustable between 0.5 and 5 microns, such as between 1.5 and 5 microns; moreover, because the diffusion rates of different ions are different, the sintered material is a hollow structure, the wall thickness of the hollow structure is about 100-200 nm, and meanwhile, the different diffusion rates also cause the radial concentration gradient of manganese ions in the material, so that the dissolution of the manganese ions is weakened. The design of the hollow structure is beneficial to the infiltration of electrolyte, can support high-rate charge and discharge, simultaneously buffers the volume effect of the material in the charge and discharge process, and further improves the stability of the battery.
The embodiment of the invention can uniformly mix the prepared anode LNMO material with the conductive agent and the binder, prepare slurry after adding N-methylpyrrolidone (NMP), and coat the pole piece. The electrolyte can be prepared from a solution of PC/DEC/DOL in a volume ratio of 1: 1, containing 2.5M LiFSI and 0.3M LiPO 2 F 2 The negative electrode is prepared by using a silicon-carbon negative electrode with the silicon content of 5 percent, and the lithium ion battery is assembled and prepared after the standardized process treatment.
Wherein the conductive agent can be one or more of Super P Super conductive carbon, carbon nanotube (CNT dispersion liquid), large-particle size conductive carbon (KS 6) and the like, the binder is polyvinylidene fluoride (PVDF), and the mass ratio of the conductive agent is 0.8-2.5%, specifically 0.8%,1.0% and 1.2%1.4%,1.6%,1.8%,2.0%,2.2%,2.5%, etc.; the addition proportion of the binder is 1.5% -2.8%, specifically 1.5%,1.8%,2.0%,2.4%,2.8%. Common solvents for lithium battery electrolytes are mainly carbonate organic solvents, including Propylene Carbonate (PC), diethyl carbonate (DEC), ethylene Carbonate (EC), ethyl Methyl Carbonate (EMC) and the like; there are also other types of organic solvents, such as 1, 3-Dioxolane (DOL). The organic solvent is generally used as a main component of the electrolyte by mixing a high dielectric constant solvent and a low viscosity solvent, and the solvent mixture of the electrolyte is a volume ratio. Common electrolyte lithium salts include lithium perchlorate, lithium hexafluorophosphate, lithium tetrafluoroborate and the like, and imide lithium salts such as lithium bis (trifluoromethylsulfonyl) imide, which is called LiFSI for short, can be adopted in the invention; lithium difluorophosphate (LiPO) 2 F 2 ) As an electrolyte additive, the electrolyte is also beneficial to the stability of the battery.
In addition, in some embodiments of the invention, the electrolyte may be PC/DEC/DOL, EC/DEC; the electrolyte LiFSI concentration can be 0.7-2.5M, and lithium difluorophosphate (LiP 0) 2 F 2 ) Is added below 0.3M; the present invention is not particularly limited to the assembly process of the lithium ion battery.
In summary, the embodiment of the invention provides a lithium nickel manganese oxide lithium ion cathode material with a hollow structure and a preparation method thereof. The method of the invention does not need to use a template, and is simple and convenient to prepare. Moreover, the lithium nickel manganese oxide material prepared by the method has uniform particle size which can be between 0.5 and 5 mu m, the wall thickness of the hollow structure is between about 100 and 200nm, and the material has a manganese ion concentration gradient in the radial direction. The lithium nickel manganese oxide cathode material provided by the invention is used in a lithium ion battery, can weaken the dissolution of manganese ions, has a hollow structure which is beneficial to the infiltration of electrolyte, can support high-rate charge and discharge, simultaneously buffers the volume effect of the material in the charge and discharge process, and further improves the stability of the battery.
In order to better understand the technical content of the invention, specific examples are provided below to further illustrate the invention. Wherein, the raw materials used in the embodiment of the invention are commercially available.
Example 1:
(1) 100g of manganese sulfate monohydrate is dissolved in deionized water, after the manganese sulfate monohydrate is completely dissolved, 20mL of ethanol is added, the concentration of manganese ions is 0.2M, then 0.1M ammonium bicarbonate aqueous solution is added, and stirring is continued for 2 hours at room temperature. And (4) centrifugally separating the obtained mixture solution, washing with water, and drying to obtain the manganese carbonate microspheres.
(2) And (2) calcining the manganese carbonate material prepared in the step (1) for 2 hours at 500 ℃ in an air atmosphere to obtain the manganese dioxide microspheres.
(3) Weighing a certain amount of manganese dioxide microspheres, respectively weighing a certain amount of nickel nitrate and lithium carbonate according to a stoichiometric ratio, and placing the nickel nitrate and the lithium carbonate together in a proper amount of ethanol for ultrasonic dispersion. Slowly heating to 55 ℃ until the ethanol is completely evaporated to obtain a precursor of a mixture of the three materials, uniformly grinding, placing in a high-temperature furnace, carrying out solid-phase reaction at 750 ℃, and calcining at constant temperature for 6 hours to obtain the LNMO with a hollow structure.
(4) And (3) preparing slurry by taking the prepared hollow LNMO material as a positive electrode active material, assembling the lithium ion battery, and testing the electrochemical performance of the lithium ion battery. The method comprises the following specific steps: uniformly mixing the prepared anode LNMO material with SuperP super conductive carbon, CNT conductive liquid and binder PVDF according to the mass ratio of 93:2:2.5, adding 120 parts by mass of NMP, and uniformly coating; the electrolyte solution contains 2.5M LiFSI and 0.3M LiPO in a ratio of PC/DEC/DOL of 1: 1 2 F 2 The negative electrode of the solution is prepared by using a silicon-carbon negative electrode with the silicon content of 5 percent, and the lithium ion battery is assembled and prepared after the standardized process treatment.
Example 2:
(1) 100g of manganese sulfate monohydrate is dissolved in deionized water, after the manganese sulfate monohydrate is completely dissolved, 20mL of ethanol is added, the concentration of manganese ions is 1.0M, then 0.5M ammonium bicarbonate aqueous solution is added, and stirring is continued for 2 hours at room temperature. And (4) centrifugally separating the obtained mixture solution, washing with water, and drying to obtain the manganese carbonate microspheres.
(2) And (2) calcining the manganese carbonate material prepared in the step (1) for 2 hours at 550 ℃ in an air atmosphere to obtain manganese dioxide microspheres.
(3) Weighing a certain amount of manganese dioxide microspheres, respectively weighing a certain amount of nickel nitrate and lithium chloride according to a stoichiometric ratio, and placing the nickel nitrate and the lithium chloride together in a proper amount of ethanol for ultrasonic dispersion. Slowly heating to 55 ℃ until the ethanol is completely evaporated to obtain a precursor of a mixture of the three materials, uniformly grinding, placing the precursor in a high-temperature furnace for solid-phase reaction at 750 ℃, and calcining at constant temperature for 6 hours to obtain the LNMO with a hollow structure.
(4) And (3) preparing slurry by taking the prepared hollow LNMO material as a positive electrode active material, assembling the lithium ion battery, and testing the electrochemical performance of the lithium ion battery. The method specifically comprises the following steps: uniformly mixing the prepared anode LNMO material with SuperP super conductive carbon, CNT conductive liquid and binder PVDF according to the mass ratio of 93:2:2.5, adding 120 parts by mass of NMP, and uniformly coating; the electrolyte solution contains 2.5M LiFSI and 0.3M LiPO in a ratio of PC/DEC/DOL of 1: 1 2 F 2 The negative electrode of the solution is prepared by using a silicon-carbon negative electrode with the silicon content of 5 percent, and the lithium ion battery is assembled and prepared after the standardized process treatment.
FIGS. 1 and 2 are Scanning Electron Microscope (SEM) photographs of hollow LNMO material prepared in example 1, with different dimensions; FIG. 3 is an X-ray diffraction (XRD) pattern corresponding to LNMO prepared at two concentrations in example 1 and example 2. According to the attached drawings, the size of the hollow LNMO material prepared by the embodiment of the invention is adjustable between 1.5 and 5 micrometers, the particle size is uniform, and the hollow structure is obvious. The manganese ion concentration gradient exists in the radial direction of the material particles, and can be obtained through the EDX linear distribution result of the cross section.
Example 3:
(1) 100g of manganese sulfate monohydrate is dissolved in deionized water, after the manganese sulfate monohydrate is completely dissolved, 20mL of ethanol is added, the concentration of manganese ions is 1.0M, then 0.5M ammonium bicarbonate aqueous solution is added, and the mixture is continuously stirred for 2 hours at room temperature. And (4) centrifugally separating the obtained mixture solution, washing with water, and drying to obtain the manganese carbonate microspheres.
(2) And (2) calcining the manganese carbonate material prepared in the step (1) for 2 hours at 550 ℃ in an air atmosphere to obtain manganese dioxide microspheres.
(3) Weighing a certain amount of manganese dioxide microspheres, respectively weighing a certain amount of nickel nitrate and lithium chloride according to a stoichiometric ratio, and placing the nickel nitrate and the lithium chloride together in a proper amount of ethanol for ultrasonic dispersion. Slowly heating to 55 ℃ until the ethanol is completely evaporated to obtain a precursor of a mixture of the three materials, uniformly grinding, placing in a high-temperature furnace, carrying out solid-phase reaction at 750 ℃, and calcining at constant temperature for 6 hours to obtain the LNMO with a hollow structure.
(4) And (3) preparing slurry by taking the prepared hollow LNMO material as a positive electrode active material, assembling the lithium ion battery, and testing the electrochemical performance of the lithium ion battery. The method specifically comprises the following steps: and mixing the prepared anode LNMO material with SuperP super conductive carbon, CNT conductive liquid and binder PVDF according to a ratio of 93:2:2.5:2.5, adding 120 parts by mass of NMP, and uniformly coating; the electrolyte solution contains 0.7M LiFSI and 0.3M LiPO in a ratio of PC/DEC/DOL of 1: 1 2 F 2 The negative electrode of the solution is prepared by using a silicon-carbon negative electrode with the silicon content of 5 percent, and the lithium ion battery is assembled and prepared after the standardized process treatment.
Example 4:
(1) 100g of manganese sulfate monohydrate is dissolved in deionized water, after the manganese sulfate monohydrate is completely dissolved, 20mL of ethanol is added, the concentration of manganese ions is 1.0M, then 0.5M ammonium bicarbonate aqueous solution is added, and the mixture is continuously stirred for 2 hours at room temperature. And (4) centrifugally separating the obtained mixture solution, washing with water, and drying to obtain the manganese carbonate microspheres.
(2) And (2) calcining the manganese carbonate material prepared in the step (1) for 2 hours at 550 ℃ in an air atmosphere to obtain the manganese dioxide microspheres.
(3) Weighing a certain amount of manganese dioxide microspheres, respectively weighing a certain amount of nickel source and lithium source according to a stoichiometric ratio, and placing the nickel source and the lithium source together in a proper amount of ethanol for ultrasonic dispersion. Slowly heating to 55 ℃ until the ethanol is completely evaporated to obtain a precursor of a mixture of the three materials, uniformly grinding, placing the precursor in a high-temperature furnace, performing solid-phase reaction at 750 ℃, and calcining at constant temperature for 6 hours to obtain the LNMO with a hollow structure.
(4) And (3) preparing slurry by taking the prepared hollow LNMO material as a positive electrode active material, assembling the lithium ion battery, and testing the electrochemical performance of the lithium ion battery. The method specifically comprises the following steps: uniformly mixing the prepared anode LNMO material with SuperP super conductive carbon, CNT conductive liquid and binder PVDF according to the mass ratio of 93:2:2.5, adding 120 parts by mass of NMP, and uniformly coating; the electrolyte is a solution containing 2.5M LiFSI with the ratio of PC/DEC/DOL of 1: 1, the cathode is prepared by a silicon-carbon cathode with the silicon content of 5%, and the lithium ion battery is assembled after standardized process treatment.
Example 5:
(1) 100g of manganese sulfate monohydrate is dissolved in deionized water, after the manganese sulfate monohydrate is completely dissolved, 20mL of ethanol is added, the concentration of manganese ions is 0.2M, then 0.1M ammonium bicarbonate aqueous solution is added, and stirring is continued for 2 hours at room temperature. And (4) centrifugally separating the obtained mixture solution, washing with water, and drying to obtain the manganese carbonate microspheres.
(2) And (2) calcining the manganese carbonate material prepared in the step (1) for 2 hours at 550 ℃ in an air atmosphere to obtain manganese dioxide microspheres.
(3) Weighing a certain amount of manganese dioxide microspheres, respectively weighing a certain amount of nickel nitrate and lithium chloride according to a stoichiometric ratio, and placing the nickel nitrate and the lithium chloride together in a proper amount of ethanol for ultrasonic dispersion. Slowly heating to 55 ℃ until the ethanol is completely evaporated to obtain a precursor of a mixture of the three materials, uniformly grinding, placing in a high-temperature furnace, carrying out solid-phase reaction at 750 ℃, and calcining at constant temperature for 6 hours to obtain the LNMO with a hollow structure.
(4) And (3) preparing slurry by taking the prepared hollow LNMO material as a positive electrode active material, assembling the lithium ion battery, and testing the electrochemical performance of the lithium ion battery. The method specifically comprises the following steps: uniformly mixing the prepared anode LNMO material with SuperP super conductive carbon, CNT conductive liquid and binder PVDF according to the mass ratio of 93:2:2.5, adding 120 parts by mass of NMP, and uniformly coating; the electrolyte solution contains 0.7M LiFSI and 0.3M LiPO in a ratio of PC/DEC/DOL of 1: 1 2 F 2 The negative electrode is prepared by using a silicon-carbon negative electrode with the silicon content of 5 percent, and the lithium ion battery is assembled and prepared after the standardized process treatmentAnd (4) a pool.
Example 6:
(1) 100g of manganese sulfate monohydrate is dissolved in deionized water, after the manganese sulfate monohydrate is completely dissolved, 20mL of ethanol is added, the concentration of manganese ions is 0.2M, then 0.1M ammonium bicarbonate aqueous solution is added, and stirring is continued for 2 hours at room temperature. And (4) centrifugally separating the obtained mixture solution, washing with water, and drying to obtain the manganese carbonate microspheres.
(2) And (2) calcining the manganese carbonate material prepared in the step (1) for 2 hours at 550 ℃ in an air atmosphere to obtain manganese dioxide microspheres.
(3) Weighing a certain amount of manganese dioxide microspheres, respectively weighing a certain amount of nickel nitrate and lithium chloride according to a stoichiometric ratio, and placing the nickel nitrate and the lithium chloride together in a proper amount of ethanol for ultrasonic dispersion. Slowly heating to 55 ℃ until the ethanol is completely evaporated to obtain a precursor of a mixture of the three materials, uniformly grinding, placing in a high-temperature furnace, carrying out solid-phase reaction at 750 ℃, and calcining at constant temperature for 6 hours to obtain the LNMO with a hollow structure.
(4) And (3) preparing slurry by taking the prepared LNMO material as a positive active material, assembling the lithium ion battery, and testing the electrochemical performance of the lithium ion battery. The method specifically comprises the following steps: uniformly mixing the prepared anode LNMO material with Super P Super conductive carbon, CNT conductive liquid and binder PVDF according to the mass ratio of 93:2:2.5, adding 120 parts by mass of NMP, and uniformly coating; the electrolyte solution has an EC/DEC ratio of 1: 1, and contains 2.5M LiFSI and 0.3M LiPO 2 F 2 The negative electrode of the solution is prepared by using a silicon-carbon negative electrode with the silicon content of 5 percent, and the lithium ion battery is assembled and prepared after the standardized process treatment.
Comparative example:
(1) 100g of manganese sulfate monohydrate and nickel nitrate with the same molar mass are dissolved in deionized water together, 20mL of ethanol is added after the manganese sulfate monohydrate and the nickel nitrate are completely dissolved, the concentration of manganese ions is 0.2M, then 0.1M ammonium bicarbonate aqueous solution is added, and the mixture is continuously stirred for 2 hours at room temperature. And centrifugally separating the obtained mixture solution, washing with water, and drying to obtain the manganese carbonate and nickel carbonate microspheres.
(2) And (2) calcining the manganese carbonate and nickel carbonate materials prepared in the step (1) for 2 hours at 550 ℃ in an air atmosphere to obtain preliminarily calcined materials.
(3) Weighing a certain amount of preliminary calcination material, weighing a certain amount of lithium carbonate according to a stoichiometric ratio, and placing the lithium carbonate and the lithium carbonate together in a proper amount of ethanol for ultrasonic dispersion. Slowly heating until the ethanol is completely evaporated to obtain a mixture precursor, uniformly grinding the mixture precursor, placing the mixture precursor in a high-temperature furnace, carrying out solid-phase reaction at the temperature of 750 ℃, and calcining at constant temperature for 6 hours to obtain the hollow LNMO.
(4) Uniformly mixing the prepared anode LNMO material and Super P Super conductive carbon, CNT conductive liquid and PVDF according to the mass ratio of 93:2:2.5, adding 120 parts by mass of NMP, and uniformly coating; the electrolyte solution has an EC/DEC ratio of 1: 1, and contains 2.5M LiFSI and 0.3M LiPO 2 F 2 The negative electrode of the solution is prepared by using a silicon-carbon negative electrode with the silicon content of 5 percent, and the lithium ion battery is assembled and prepared after the standardized process treatment.
The following are electrochemical performance test results of the lithium ion batteries of the examples; the test temperature was 25 ℃ and the current at-30 ℃ upon discharge was 0.5 ℃.
Table 1 electrochemical performance test results of the lithium ion batteries of the examples
The data of the comparative example show that the particle size distribution of the prepared LNMO can be regulated and controlled by adjusting the metal ion concentration in the first-step precipitation process (see D50 data), and the LNMO with smaller average particle size can provide higher specific capacity and better capacity retention rate under the same condition; meanwhile, the hollow structure of the LNMO can effectively promote the infiltration and diffusion of electrolyte and improve the electrochemical performance of the battery.
The preparation process of the comparative example is as follows: and (3) coprecipitating nickel and manganese ions to prepare a precursor, and then calcining. The EDX linear distribution of the cross section of the comparative example material shows that the element proportion distribution is uniform and the concentration gradient in the example is not formed, i.e. the comparative example material does not have the concentration gradient distribution of manganese ions in the radial direction. The comparative examples were found to have initial discharge capacities similar to those of the examples by comparing the data with those of the comparative examples, indicating that the preparation method does not affect the initial discharge capacities of the materials. However, the discharge capacity of the comparative example decays significantly faster than that of the examples during the cycling process, and the capacity retention rate is only 81.9% after 100 cycles, which shows that the preparation method in the examples has a non-negligible effect on improving the cycling stability of the material.
In addition, according to examples 3 to 6 and the like, the higher concentration electrolyte provides higher coulombic efficiency, mainly because the higher concentration electrolyte contains more lithium salts, which can compensate lithium loss consumed by the SEI film in the charge and discharge processes, thereby improving the coulombic efficiency of the battery; liPO 2 F 2 The addition of (2) can improve the cycling stability of the battery; the use of the electrolyte EC/DEC is not beneficial to the development of low-temperature performance, and should be because the higher melting point of EC is, the viscosity is obviously increased at low temperature, and the diffusion of lithium ions is inhibited.
It is clear that the examples do not fully list the impact of the improvement of the technical parameters of the patent on the properties, and in fact the adjustment of the parameters in each step has a different impact on the final material properties.
The preparation method has the advantages that the LNMO positive electrode material with the hollow structure can be prepared by controlling the different diffusion rates of the nickel and manganese ions without using a sacrificial template, the particle size is uniform, the concentration gradient distribution of the manganese ions in the radial direction of the particles is beneficial to improving the stability of the corresponding lithium ion battery. The preparation method provided by the invention is simple, is easy for large-scale production, and can provide technical support for the preparation of the high-voltage anode of the lithium ion battery.
The description of the specific embodiments of the invention has been presented for purposes of illustration and description, and is not intended to limit the invention to the precise forms disclosed, for the purpose of explaining certain principles and practical applications of the invention, and many parameters may be varied in accordance with the above teachings. The scope of the invention is defined by the claims and their equivalents.
Claims (10)
1. The preparation method of the hollow lithium nickel manganese oxide cathode material is characterized by comprising the following steps of:
s1, providing manganese dioxide microspheres;
s2, mixing and soaking the manganese dioxide microspheres, a nickel source and a lithium source in a solvent, removing the solvent to obtain a precursor, and sintering to obtain the hollow spherical lithium nickel manganese oxide cathode material.
2. The preparation method of the hollow lithium nickel manganese oxide cathode material according to claim 1, wherein the manganese dioxide microspheres obtained in the step S1 are obtained in the following way:
manganese sulfate monohydrate is precipitated by carbonate to obtain manganese carbonate microspheres;
and calcining the obtained manganese carbonate microspheres at 300-700 ℃ in an air atmosphere to obtain manganese dioxide microspheres.
3. The preparation method of the hollow lithium nickel manganese manganate cathode material as claimed in claim 2, wherein the manganese carbonate microspheres are obtained by precipitation reaction of manganese sulfate monohydrate and ammonium bicarbonate, and the molar ratio of the manganese sulfate monohydrate to the ammonium bicarbonate is 1: 5-1: 40.
4. The method for preparing the hollow lithium nickel manganese oxide cathode material according to claim 3, wherein the precipitation reaction is carried out in a mixed solvent of ethanol and water, and the volume ratio of the added ethanol to the added water is 50: 1-5: 1.
5. The preparation method of the hollow lithium nickel manganese oxide cathode material according to claim 3, wherein the concentration of manganese ions in the precipitation reaction is between 0.2M and 1M; the calcining time of the manganese carbonate microspheres is 2-10h.
6. The preparation method of the hollow lithium nickel manganese oxide cathode material according to any one of claims 1 to 5, wherein the nickel source in step S2 is one or more of nickel oxide, nickel acetate, nickel sulfate and nickel nitrate, and the lithium source is one or more of lithium hydroxide, lithium carbonate and lithium chloride.
7. The preparation method of the hollow lithium nickel manganese oxide cathode material according to claim 6, wherein the step S2 specifically comprises the following steps:
putting the manganese dioxide microspheres, a nickel source and a lithium source together in ethanol according to a stoichiometric ratio, performing ultrasonic dispersion, heating to remove ethanol to obtain a precursor, grinding, and sintering to obtain a hollow spherical lithium nickel manganese oxide cathode material; the heating temperature is preferably 40 ℃ to 80 ℃.
8. The preparation method of the hollow lithium nickel manganese oxide cathode material according to claim 7, wherein the sintering in the step S2 is carried out at a constant temperature of 600-900 ℃, preferably for 2-20h.
9. A hollow lithium nickel manganese oxide cathode material obtained by the preparation method of any one of claims 1 to 8, which has a hollow spherical structure and a manganese ion radial concentration gradient, and the size of the hollow spherical structure is adjustable between 0.5 and 5 microns.
10. A lithium ion battery comprising the hollow lithium nickel manganese oxide positive electrode material of claim 9.
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