CN114497533A - In-situ spinel modified low-cobalt spherical lithium-rich manganese-based positive electrode material and preparation method thereof - Google Patents

In-situ spinel modified low-cobalt spherical lithium-rich manganese-based positive electrode material and preparation method thereof Download PDF

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CN114497533A
CN114497533A CN202210101401.0A CN202210101401A CN114497533A CN 114497533 A CN114497533 A CN 114497533A CN 202210101401 A CN202210101401 A CN 202210101401A CN 114497533 A CN114497533 A CN 114497533A
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lithium
cobalt
lmnca
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李星
刘鑫慧
晋一夫
付正
王明珊
陈俊臣
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Southwest Petroleum University
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Abstract

The invention belongs to the technical field of anode electrode materials, and discloses an in-situ spinel modified low-cobalt spherical lithium-rich manganese-based anode material and a preparation method thereof. The material consists of LMNCA and distorted spinel phase, and the chemical formula of the LMNCA is aLi2MnO3·bLiNixCoyAlzO2. The preparation method of the material comprises the following steps: (1) adding nickel sulfate, cobalt sulfate, manganese sulfate and aluminum nitrate into water to form a mixed solution; (2) under the protection gas, reacting the mixed solution, a sodium carbonate aqueous solution and a diluted ammonia aqueous solution to obtain a precipitate; (3) filtering the precipitate, and drying the precipitate in a vacuum environment to obtain a precursor;(4) grinding and mixing the precursor and lithium carbonate, and calcining twice in the air or oxygen atmosphere to obtain the low-cobalt spherical lithium-rich manganese-based positive electrode material. The preparation method is simple and convenient, the cost is low, and the prepared anode material has excellent cycling stability.

Description

In-situ spinel modified low-cobalt spherical lithium-rich manganese-based positive electrode material and preparation method thereof
Technical Field
The invention relates to the technical field of anode electrode materials, in particular to an in-situ spinel modified low-cobalt spherical lithium-rich manganese-based anode material and a preparation method thereof.
Background
Lithium-rich manganese-based positive electrode material xLi2MnO3·(1-x)LiMO2(M ═ Ni, Co, Mn, etc., 0<x<1) The lithium ion battery has the characteristics of high specific capacity, wide voltage window, low cost and the like, gradually receives wide attention, and becomes a hotspot of research of people. With LiCoO2Compared with the layered positive electrode material, the positive electrode material such as the ternary positive electrode material of NCM and NCA, the lithium-rich manganese-based positive electrode material has higher specific capacity ((>250mAh/g) higher working voltage(s) ((m)>4.8V). Due to the shortage of resources and the problem of environmental pollution, low-cobalt or cobalt-free cathode materials have become the direction of development and application of cathode materials.
The low-cobalt type lithium-rich manganese-based positive electrode material has the high specific capacity and the high working voltage of the lithium-rich manganese-based positive electrode material, and the utilization rate of cobalt is reduced. However, there are many disadvantages to such positive electrode materials, which limit their practical applications. For example, the first coulombic efficiency is low due to the first irreversible activation process [ Journal of Materials Chemistry,2007,17(30):3112-](ii) a Or due to the migration of transition metal ions from the transition metal layer to the lithium layer during cycling, resulting in structural changes that reduce cycling stability and cause voltage drop during cycling [ Chemistry of Materials 2015,27(4): 1381-1390; nano Letters,2014,14(5):2628-](ii) a Or due to Li2MnO3The phases have lower ionic/electronic conductivity, resulting in a lithium-rich manganese-based positive electrode material with poor rate capability. In addition, cobalt has the function of stabilizing a lattice structure, the content of cobalt in the low-cobalt lithium-rich manganese-based cathode material is reduced, and the content of nickel is increased, so that structural damage is more likely to occur in the circulating process, and the performance of the material is reduced.
According to the analysis of the existing documents, the cubic close-packed structure of the spinel phase has better structural compatibility with the lithium-rich manganese-based anode material, the surface modification of the spinel phase can protect the main structure of the anode material, reduce the side reaction of the interface, stabilize the lattice oxygen, and be beneficial to improving the cycle stability of the lithium-rich manganese-based anode material and prolonging the cycle life. In addition, the spinel phase has a three-dimensional lithium ion diffusion channel, so that the diffusion kinetic performance can be improved, and lithium ions can be diffused more quickly. However, the prior art does not describe whether the modification method for in-situ constructing the spinel phase structure is suitable for the low-cobalt type lithium-rich manganese-based cathode material by reducing the lithium content to form lithium vacancies.
Therefore, how to apply the modification method of forming lithium vacancy by reducing the lithium content and constructing the spinel phase structure in situ to the low-cobalt lithium-rich manganese-based cathode material so as to improve the stability of the low-cobalt lithium-rich manganese-based cathode material in the circulation process becomes a problem to be solved by the technical staff in the field.
Disclosure of Invention
In view of the above, the invention provides an in-situ spinel modified low-cobalt spherical lithium-rich manganese-based positive electrode material and a preparation method thereof, so that a lithium vacancy is formed in an LMNCA in situ and a spinel phase is constructed, the formed spinel phase is favorable for stabilizing a lattice structure of the LMNCA, the side reaction of an interface is slowed down, the cycle stability of the LMNCA is improved, and the problems of structural damage and poor cycle stability of the low-cobalt lithium-rich manganese-based positive electrode material in the cycle are effectively solved.
In order to achieve the purpose, the invention adopts the following technical scheme:
the invention provides an in-situ spinel modified low-cobalt spherical lithium-rich manganese-based positive electrode material, which consists of LMNCA and a distorted spinel phase;
the chemical formula of the LMNCA is aLi2MnO3·bLiNixCoyAlzO2；
Wherein 0 < a, b < 1, and a + b ═ 1; 0 < x, y, z < 1, x + y + z being 1 and x > 2(y + z).
The distorted spinel phase is formed in situ in the bulk phase of the LMNCA.
The twisted spinel phase accounts for 0.01-24.84% of the total mass of the lithium-rich manganese-based positive electrode material.
The invention also provides a preparation method of the low-cobalt spherical lithium-rich manganese-based positive electrode material, which comprises the following steps:
(1) adding nickel sulfate, cobalt sulfate, manganese sulfate and aluminum nitrate into water to form a mixed solution;
(2) under the protection gas, reacting the mixed solution, a sodium carbonate aqueous solution and a diluted ammonia aqueous solution to obtain a precipitate;
(3) filtering the precipitate, and drying the precipitate in a vacuum environment to obtain a precursor;
(4) grinding and mixing the precursor and lithium carbonate, and calcining twice in the air or oxygen atmosphere to obtain the low-cobalt spherical lithium-rich manganese-based positive electrode material.
The mass ratio of the nickel sulfate to the cobalt sulfate to the manganese sulfate to the aluminum nitrate is (10-12): (2-4): (12-15): 1.
the concentration of the mixed solution is 1.5-4 mol/L, the concentration of the sodium carbonate aqueous solution is 1.5-4 mol/L, and the concentration of the dilute ammonia aqueous solution is 0.15-0.4 mol/L.
The protective gas is one of nitrogen, argon, helium and neon; the volume ratio of the mixed solution to the sodium carbonate aqueous solution to the dilute ammonia aqueous solution is (1-2): (1-2): (2-4).
The reaction temperature of the step (2) is 45-70 ℃, the reaction time is 16-25 h, and the pH value of the reaction is 7.5-8.0.
The suction filtration times are 2-5 times, and the drying temperature is 100-120 ℃.
The mass ratio of the precursor to the lithium carbonate is 5: (1.90-2.55);
the first calcining temperature is 400-600 ℃, and the first calcining time is 4-6 h;
the second calcination temperature is 800-1000 ℃, and the second calcination time is 10-15 h.
The principle applied by the invention is as follows: manganese sulfate, nickel sulfate, cobalt sulfate, aluminum sulfate, sodium carbonate and ammonia water are used as raw materials, a coprecipitation method is adopted to prepare a low-cobalt precursor with a spherical shape, the addition amount of lithium salt is reduced during sintering and oxidation of mixed lithium salt, in-situ formation of lithium vacancies in LMNCA is realized, a spinel phase is constructed, the formed spinel phase is beneficial to stabilizing the lattice structure of LMNCA, the side reaction of an interface is slowed down, and the cycle stability of LMNCA is improved.
According to the technical scheme, compared with the prior art, the invention has the following beneficial effects:
(1) the raw materials are easy to obtain, the cost is low, and a large amount of target materials can be synthesized at one time;
(2) the spinel phase is generated in situ, the compatibility with the raw material structure is good, the material structure can be stabilized, and the cycle stability is improved;
(3) the process for modification by reducing the addition amount of lithium salt during sintering is simple and convenient, and is suitable for large-scale production.
Drawings
Fig. 1 is SEM images of low cobalt spherical lithium manganese rich positive electrode material precursors in example 1 and comparative example 1 of the present invention.
Fig. 2 is an SEM image of a low-cobalt spherical lithium manganese rich positive electrode material (LMNCA-103) in comparative example 1 of the present invention.
Fig. 3 is an SEM image of an in situ spinel modified low cobalt spherical lithium manganese rich cathode material (LMNCA-90) in example 1 of the present invention.
Fig. 4 is an SEM image of an in situ spinel modified low cobalt spherical lithium manganese rich cathode material (LMNCA-85) in example 1 of the present invention.
FIG. 5 shows X-ray diffraction patterns of in-situ spinel-modified low-cobalt spherical lithium-manganese-rich positive electrode material (LMNCA-90, LMNCA-85) in example 1 and low-cobalt spherical lithium-manganese-rich positive electrode material (LMNCA-103) in comparative example 1.
FIG. 6 is a graph showing the cycle performance test of the in-situ spinel-modified low-cobalt spherical lithium-manganese-rich positive electrode material (LMNCA-90, LMNCA-85) in example 1 of the present invention and the low-cobalt spherical lithium-manganese-rich positive electrode material (LMNCA-103) in comparative example 1.
FIG. 7 is a graph showing the rate capability test of in-situ spinel-modified low-cobalt spherical lithium-manganese-rich cathode material (LMNCA-90, LMNCA-85) in example 1 and low-cobalt spherical lithium-manganese-rich cathode material (LMNCA-103) in comparative example 1.
FIG. 8 is a graph of the morphology of the low cobalt spherical lithium manganese rich positive electrode material (LMNCA-103) in comparative example 1 after 300 cycles.
Fig. 9 is a morphology of the in-situ spinel modified low-cobalt spherical lithium-manganese-rich cathode material (LMNCA-90) of example 1 after 300 cycles.
Fig. 10 is a morphology of the spinel-modified low-cobalt spherical lithium-manganese-rich cathode material (LMNCA-85) in situ of example 1 after 300 cycles.
Detailed Description
The invention provides an in-situ spinel modified low-cobalt spherical lithium-rich manganese-based positive electrode material, which consists of LMNCA and a distorted spinel phase;
the chemical formula of the LMNCA is aLi2MnO3·bLiNixCoyAlzO2；
Wherein 0 < a, b < 1, and a + b ═ 1; 0 < x, y, z < 1, x + y + z equal to 1 and x > 2(y + z).
Preferably, a is 0.4, b is 0.6; x is 0.8, y is 0.15, and z is 0.05.
Preferably, the distorted spinel phase accounts for 10-15% of the total mass of the lithium-rich manganese-based positive electrode material.
The invention also provides a preparation method of the low-cobalt spherical lithium-rich manganese-based positive electrode material, which comprises the following steps:
(1) adding nickel sulfate, cobalt sulfate, manganese sulfate and aluminum nitrate into water to form a mixed solution;
(2) under the protection gas, reacting the mixed solution, a sodium carbonate aqueous solution and a diluted ammonia aqueous solution to obtain a precipitate;
(3) filtering the precipitate, and drying the precipitate in a vacuum environment to obtain a precursor;
(4) grinding and mixing the precursor and lithium carbonate, and calcining twice in the air or oxygen atmosphere to obtain the low-cobalt spherical lithium-rich manganese-based positive electrode material.
Preferably, the mass ratio of the nickel sulfate to the cobalt sulfate to the manganese sulfate to the aluminum nitrate is 11.1:2.2:13.5: 1.
Preferably, the concentration of the mixed solution is 2-3 mol/L, the concentration of the sodium carbonate aqueous solution is 2-3 mol/L, and the concentration of the dilute ammonia aqueous solution is 0.2-0.3 mol/L.
Preferably, the protective gas is nitrogen; the volume ratio of the mixed solution to the sodium carbonate aqueous solution to the dilute ammonia aqueous solution is 1: 1:2.
preferably, the reaction temperature in the step (2) is 55-60 ℃, the reaction time is 18-22 h, and the pH value of the reaction is 7.7.
Preferably, the suction filtration times are 3 times, and the drying temperature is 110 ℃.
Preferably, the mass ratio of the precursor to the lithium carbonate is 5: (1.91-2.45);
the first calcining temperature is 450 ℃, and the first calcining time is 5 hours;
the second calcination temperature is 850 ℃, and the second calcination time is 12 h.
Preferably, the water used in the present invention is deoxygenated water.
The technical solutions in the embodiments of the present invention will be clearly and completely described below, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, 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 invention.
Example 1
The preparation method of the spherical low-cobalt spherical lithium-rich manganese-based anode material modified by the in-situ spinel comprises the following specific steps:
adding nickel sulfate, cobalt sulfate, manganese sulfate and aluminum nitrate into deoxygenated water according to the mass ratio of 11.1:2.2:13.5:1 to prepare a mixed solution of 2 mol/L; dissolving sodium carbonate in deoxidized water to prepare 2mol/L sodium carbonate aqueous solution; dissolving a proper amount of strong ammonia water in deoxidized water to prepare a 0.2mol/L weak ammonia water solution; under the nitrogen atmosphere, slowly adding 50ml of mixed solution, 50ml of sodium carbonate solution and 100ml of diluted ammonia water solution into a reaction kettle with the pH value of 7.7 at the same time, maintaining the temperature of 55 ℃ and rapidly stirring, reacting for 20 hours, filtering the precipitate for 3 times, and drying at the temperature of 110 ℃ in a vacuum environment to obtain the spherical low-cobalt lithium-rich manganese material precursor. Taking 5g of precursor, respectively adding 2.55g (LMNCA-100), 2.42g (LMNCA-95), 2.3g (LMNCA-90), 2.17g (LMNCA-85), 2.04g (LMNCA-80) and 1.91g (LMNCA-75) of lithium carbonate, adding a proper amount of absolute ethyl alcohol, uniformly mixing, drying the ethyl alcohol by distillation, putting the mixed material into a corundum crucible, and sintering for 5 hours at 450 ℃ in an air atmosphere; and then sintering for 12h at 850 ℃ in a pure oxygen atmosphere to obtain the in-situ spinel modified spherical low-cobalt lithium-rich manganese-based cathode material with different lithium contents.
Wherein LMNCA-100 represents the lithium content in the material as a theoretical metering value; LMNCA-95 represents a lithium content in the material of 95% of theoretical stoichiometric; LMNCA-90 indicates that the lithium content in the material is 90% of the theoretical stoichiometric value; LMNCA-85 represents the lithium content in the material as 85% of the theoretical stoichiometric value; LMNCA-80 represents the lithium content of the material as 80% of the theoretical stoichiometric value; LMNCA-75 represents a 75% theoretical stoichiometric lithium content in the material.
Example 2
The preparation method of the spherical low-cobalt spherical lithium-rich manganese-based anode material modified by the in-situ spinel comprises the following specific steps:
adding nickel sulfate, cobalt sulfate, manganese sulfate and aluminum nitrate into deoxygenated water according to the mass ratio of 11:3:13:1 to prepare a mixed solution of 3 mol/L; dissolving sodium carbonate in deoxidized water to prepare 3mol/L sodium carbonate aqueous solution; dissolving a proper amount of strong ammonia water in deoxidized water to prepare a 0.3mol/L dilute ammonia water solution; under the nitrogen atmosphere, slowly adding 50ml of mixed solution, 50ml of sodium carbonate solution and 100ml of diluted ammonia water solution into a reaction kettle with the pH value of 7.8 at the same time, maintaining the temperature of 60 ℃ and rapidly stirring, reacting for 22h, filtering the precipitate for 3 times, and drying at the temperature of 115 ℃ in a vacuum environment to obtain the spherical low-cobalt lithium-rich manganese material precursor. Taking 5g of the precursor, adding 2.17g (LMNCA-85) of lithium carbonate, adding a proper amount of absolute ethyl alcohol, uniformly mixing, evaporating the ethyl alcohol to dryness, putting the mixed material into a corundum crucible, and sintering for 5.5 hours at 500 ℃ in an air atmosphere; and then sintering for 13h at 900 ℃ in a pure oxygen atmosphere to obtain the in-situ spinel modified spherical low-cobalt type lithium-rich manganese-based cathode material.
Example 3
The preparation method of the spherical low-cobalt spherical lithium-rich manganese-based anode material modified by the in-situ spinel comprises the following specific steps:
adding nickel sulfate, cobalt sulfate, manganese sulfate and aluminum nitrate into deoxygenated water according to the mass ratio of 11.1:2.2:13.5:1 to prepare a mixed solution of 2.5 mol/L; dissolving sodium carbonate in deoxidized water to prepare 2.5mol/L sodium carbonate aqueous solution; dissolving a proper amount of strong ammonia water in deoxidized water to prepare a 0.25mol/L dilute ammonia water solution; under the nitrogen atmosphere, slowly adding 50ml of mixed solution, 50ml of sodium carbonate solution and 100ml of diluted ammonia water solution into a reaction kettle with the pH value of 7.9 at the same time, maintaining the temperature of 63 ℃ and rapidly stirring, reacting for 22h, filtering the precipitate for 3 times, and drying at 105 ℃ in a vacuum environment to obtain the spherical low-cobalt lithium-rich manganese material precursor. Taking 5g of the precursor, adding 2.42g (LMNCA-95) of lithium carbonate, adding a proper amount of absolute ethyl alcohol, uniformly mixing, evaporating the ethyl alcohol to dryness, putting the mixed material into a corundum crucible, and sintering for 4.5 hours at 550 ℃ in an air atmosphere; and then sintering for 10h at 950 ℃ in a pure oxygen atmosphere to obtain the in-situ spinel modified spherical low-cobalt type lithium-rich manganese-based cathode material.
Comparative example 1
The preparation method of the unmodified low-cobalt spherical lithium-rich manganese-based positive electrode material comprises the following specific steps:
adding nickel sulfate, cobalt sulfate, manganese sulfate and aluminum nitrate into deoxygenated water according to the mass ratio of 11.1:2.2:13.5:1 to prepare a mixed solution of 2 mol/L; dissolving sodium carbonate in deoxidized water to prepare 2mol/L sodium carbonate aqueous solution; dissolving a proper amount of strong ammonia water in deoxidized water to prepare a 0.2mol/L dilute ammonia water solution; under the nitrogen atmosphere, slowly adding 50ml of mixed solution, 50ml of sodium carbonate solution and 100ml of diluted ammonia water solution into a reaction kettle with the pH value of 7.7 at the same time, maintaining the temperature of 55 ℃ and rapidly stirring, reacting for 20 hours, filtering the precipitate for 3 times, and drying at the temperature of 110 ℃ in a vacuum environment to obtain the spherical low-cobalt lithium-rich manganese material precursor. Taking 5g of the precursor, adding 2.63g (LMNCA-103) of lithium carbonate, adding a proper amount of absolute ethyl alcohol, uniformly mixing, evaporating the ethyl alcohol to dryness, putting the mixed material into a corundum crucible, and sintering for 5 hours at 450 ℃ in an air atmosphere; and then sintering for 12h at 850 ℃ in a pure oxygen atmosphere to obtain the unmodified low-cobalt spherical lithium-rich manganese-based positive electrode material.
Wherein LMNCA-103 represents that the lithium content in the material is 103% of the theoretical amount.
Electrochemical performance test of example 1:
assembling the button cell: 0.4g of the positive electrode material prepared in example 1 was weighed, 0.05g of acetylene black as a conductive agent and 0.05g of pvdf as a binder were added, uniformly ground and mixed in an agate mortar to prepare an electrode slurry, the electrode slurry was uniformly coated on an aluminum foil, and the electrode slurry was dried at 65 ℃ for 12 hours in a vacuum environment to prepare an electrode sheet. In a glove box, the electrode is taken as a positive electrode, metal lithium is taken as a negative electrode, Celgard2500 is taken as a diaphragm, and 1.2mol/L LiPF6EMC (volume ratio 3:7) is used as electrolyte, and the CR2032 button cell is assembled.
And carrying out constant-current charge-discharge long-cycle test and constant-current charge-discharge multiplying power performance test at the temperature of 30 ℃, wherein the test voltage range is 2.0V-4.8V. In the long-cycle test, the activation is carried out at the multiplying power of C/10 in the first 3 circles, then the constant-current charging is carried out at the multiplying power of C/5, and the discharging is carried out at the multiplying power of C/3. In the rate performance test, the charge and discharge rates are respectively 5 times of C/10, C/5, C/3, C/2, 1C, 2C and 3C, and then the cycle returns to C/10 for 5 times. The result shows that the modified LMNCA-85 and LMNCA-90 have better electrochemical performance.
The first discharge specific capacity of the LMNCA-85 material under the condition of C/10 is 233 mAh/g; the first discharge specific capacity of the LMNCA-90 material under C/10 is 219 mAh/g. After 200 cycles, the capacity retention rate of LMNCA-85 is 90.6%; the capacity retention of LMNCA-90 was 85.2%.
The discharge capacities of LMNCA-85 at the multiplying power of C/10, C/5, C/3, C/2, 1C, 2C and 3C are 230mAh/g, 213mAh/g, 199mAh/g, 187mAh/g, 165mAh/g, 140mAh/g and 123mAh/g respectively. The discharge capacities of LMNCA-90 at the rates of C/10, C/5, C/3, C/2, 1C, 2C and 3C are 240mAh/g, 226mAh/g, 212mAh/g, 198mAh/g, 171mAh/g, 143mAh/g and 124mAh/g, respectively.
The tap density of the LMNCA-85 material is 1.74g/cm3The LMNCA-90 material has a tap density of 1.731g/cm3。
Electrochemical performance test of comparative example 1:
assembling the button cell: 0.4g of the positive electrode material prepared in comparative example 1 was weighed, 0.05g of acetylene black as a conductive agent and 0.05g of PVDF as a binder were added, uniformly ground and mixed in an agate mortar to prepare electrode slurry, the electrode slurry was uniformly coated on an aluminum foil, and the electrode sheet was prepared after drying for 12 hours in a vacuum environment at 65 ℃. In a glove box, the electrode is taken as a positive electrode, metal lithium is taken as a negative electrode, Celgard2500 is taken as a diaphragm, and 1.2mol/L LiPF6EMC (volume ratio 3:7) is used as electrolyte, and the CR2032 button cell is assembled.
And carrying out constant-current charge-discharge long-cycle test and constant-current charge-discharge multiplying power performance test at the temperature of 30 ℃, wherein the test voltage range is 2.0V-4.8V. In the long-cycle test, the activation is carried out at the multiplying power of C/10 in the first 3 circles, then the constant-current charging is carried out at the multiplying power of C/5, and the discharging is carried out at the multiplying power of C/3. In the rate performance test, the charge and discharge rates are respectively 5 times of C/10, C/5, C/3, C/2, 1C, 2C and 3C, and then the cycle returns to C/10 for 5 times.
The test results were as follows: the first discharge specific capacity of the LMNCA-103 material under C/10 is 160mAh/g, and after 200 cycles, the capacity retention rate of the LMNCA-103 material is 81.2%.
The discharge capacities of the LMNCA-103 material at the rates of C/10, C/5, C/3, C/2, 1C, 2C and 3C are 191mAh/g, 177mAh/g, 165mAh/g, 154mAh/g, 135mAh/g, 113mAh/g and 100mAh/g respectively.
The tap density of the LMNCA-103 material is 1.6875g/cm3。
The performance tests show that the cycle performance and rate capability of the in-situ spinel modified spherical low-cobalt lithium-rich manganese-based anode material prepared by the invention are obviously superior to those of an unmodified low-cobalt spherical lithium-rich manganese-based anode material.
In addition, as can be seen from the drawings 1-10 in the specification:
fig. 1 is SEM images of spherical low-cobalt lithium-rich manganese positive electrode material precursors in example 1 and comparative example 1 of the present invention, from which it can be observed that they have a spherical morphology.
Fig. 2 is an SEM image of the low-cobalt spherical lithium manganese rich positive electrode material (LMNCA-103) in comparative example 1 of the present invention, from which it can be observed that it retains the spherical morphology of the precursor but has a rougher surface.
Fig. 3 is an SEM image of the in-situ spinel-modified spherical lithium-manganese-rich cathode material with low cobalt (LMNCA-90) in example 1 of the present invention, which can be observed to retain the spherical morphology of the precursor and have a smoother surface.
Fig. 4 is an SEM image of the in-situ spinel-modified spherical lithium-manganese-rich cathode material with low cobalt (LMNCA-85) in example 1 of the present invention, which can be observed to retain the spherical morphology of the precursor and have a smoother surface.
FIG. 5 is an X-ray diffraction pattern of in-situ spinel-modified low-cobalt spherical lithium-manganese-rich positive electrode material (LMNCA-90, LMNCA-85) in example 1 and low-cobalt spherical lithium-manganese-rich positive electrode material (LMNCA-103) in comparative example 1, showing the presence of Li in all three materials2MnO3And LiMO2(M is a transition metal element) phase. Broadening of the (101) and (104) peaks of the modified LMNCA was observed, which is a phenomenon in which a spinel phase exists.
Fig. 6 is a cycle performance test chart of the in-situ spinel-modified low-cobalt spherical lithium manganese rich positive electrode material (LMNCA-90, LMNCA-85) in example 1 and the low-cobalt spherical lithium manganese rich positive electrode material (LMNCA-103) in comparative example 1, from which it can be found that the modified LMNCA discharge capacity and cycle stability are significantly better than those of the unmodified LMNCA material.
Fig. 7 is a graph showing the rate capability test of the low cobalt spherical lithium manganese rich positive electrode material (LMNCA-90, LMNCA-85) modified by spinel in situ in example 1 of the present invention and the low cobalt spherical lithium manganese rich positive electrode material (LMNCA-103) in comparative example 1, from which it can be found that the discharge capacity of the modified LMNCA is higher than that of the unmodified LMNCA material at a larger current.
Fig. 8 is a morphology diagram of the low cobalt spherical lithium manganese rich cathode material (LMNCA-103) after 300 cycles in comparative example 1 of the present invention, from which it can be found that the modified LMNCA spherical particles are broken and the sphericity remains poor.
Fig. 9 is a morphology of the in-situ spinel modified low-cobalt spherical lithium manganese rich cathode material (LMNCA-90) of example 1 after 300 cycles, from which it can be seen that the modified LMNCA substantially maintained the previous spherical morphology with structural stability superior to the unmodified LMNCA material.
Fig. 10 is a morphology of the in-situ spinel modified low-cobalt spherical lithium manganese rich cathode material (LMNCA-85) of example 1 after 300 cycles, from which it can be seen that the modified LMNCA substantially maintained the previous spherical morphology with structural stability superior to the unmodified LMNCA material.
The embodiments in the present description are described in a progressive manner, each embodiment focuses on differences from other embodiments, and the same and similar parts among the embodiments are referred to each other.
The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims (10)

1. An in-situ spinel modified low-cobalt spherical lithium-rich manganese-based cathode material is characterized in that the material consists of LMNCA and a distorted spinel phase;
the chemical formula of the LMNCA is aLi2MnO3·bLiNixCoyAlzO2；
Wherein 0 < a, b < 1, and a + b ═ 1; 0 < x, y, z < 1, x + y + z being 1 and x > 2(y + z).
2. The spherical lithium-rich manganese-based positive electrode material of claim 1, wherein the distorted spinel phase is formed in situ in the bulk phase of LMNCA.
3. The low-cobalt spherical lithium-rich manganese-based positive electrode material as claimed in claim 2, wherein the distorted spinel phase accounts for 0.01-24.84% of the total mass of the lithium-rich manganese-based positive electrode material.
4. The preparation method of the low-cobalt spherical lithium-rich manganese-based positive electrode material as claimed in any one of claims 1 to 3, characterized by comprising the following steps:
(1) adding nickel sulfate, cobalt sulfate, manganese sulfate and aluminum nitrate into water to form a mixed solution;
(2) under the protection gas, reacting the mixed solution, a sodium carbonate aqueous solution and a diluted ammonia aqueous solution to obtain a precipitate;
(3) filtering the precipitate, and drying the precipitate in a vacuum environment to obtain a precursor;
(4) grinding and mixing the precursor and lithium carbonate, and calcining twice in the air or oxygen atmosphere to obtain the low-cobalt spherical lithium-rich manganese-based positive electrode material.
5. The preparation method according to claim 4, wherein the mass ratio of the nickel sulfate to the cobalt sulfate to the manganese sulfate to the aluminum nitrate is (10-12): (2-4): (12-15): 1.
6. the method according to claim 4 or 5, wherein the concentration of the mixed solution is 1.5 to 4mol/L, the concentration of the sodium carbonate aqueous solution is 1.5 to 4mol/L, and the concentration of the dilute ammonia aqueous solution is 0.15 to 0.4 mol/L.
7. The method of claim 4, wherein the protective gas is one of nitrogen, argon, helium, and neon; the volume ratio of the mixed solution to the sodium carbonate aqueous solution to the diluted ammonia aqueous solution is (1-2): (1-2): (2-4).
8. The preparation method according to claim 7, wherein the reaction temperature in the step (2) is 45-70 ℃, the reaction time is 16-25 h, and the pH value of the reaction is 7.5-8.0.
9. The preparation method according to claim 7 or 8, wherein the suction filtration is performed 2 to 5 times, and the drying temperature is 100 to 120 ℃.
10. The preparation method according to claim 4, wherein the mass ratio of the precursor to the lithium carbonate is 5: (1.90-2.55);
the first calcining temperature is 400-600 ℃, and the first calcining time is 4-6 h;
the second calcination temperature is 800-1000 ℃, and the second calcination time is 10-15 h.
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