METHOD OF PREPARING MOF-COATED MONOCRYSTAL TERNARY POSITIVE ELECTRODE MATERIAL

Abstract

The present invention provides a method of preparing an MOF-coated monocrystal ternary positive electrode material. Firstly, a solution A of nickel, cobalt and manganese metal salts, an ammonia complexing agent solution and a caustic soda liquid are added to a reactor for reaction to obtain a precursor core; then, an organic carboxylate is dissolved in an amount of an organic solvent to obtain a solution B; the solution B and a manganese metal salt solution with a given concentration are added to the reactor and aged to obtain an MOF-coated core-shell structure precursor; the core-shell structure precursor is pre-sintered at a low temperature to obtain a nickel-cobalt-manganese oxide with monocrystal structure; the nickel-cobalt-manganese oxide with monocrystal structure is uniformly mixed with LiOH.H.sub.2O in a mortar and then calcined at a high temperature to obtain an MOF-coated monocrystal ternary positive electrode material.

Claims

1. A method of preparing an MOF-coated monocrystal ternary positive electrode material, comprising following steps: at step 1, preparing a solution A of nickel, cobalt and manganese metal salts according to a molar ratio of x:y:1-x-y, wherein x represents a ratio of nickel, y represents a ratio of cobalt and 1-x-y represents a ratio of manganese; and preparing an ammonia complexing agent solution and a caustic soda liquid; at step 2, adding the solution A of nickel, cobalt and manganese metal salts, the ammonia complexing agent solution and the caustic soda liquid to a reactor at a feeding speed to obtain a sphere-like precursor core; at step 3, dissolving an organic carboxylate in an amount of an organic solvent to obtain a solution B with a given concentration; adding the solution B and a manganese metal salt solution with a given concentration to the reactor yielding the precursor core in the step 1 at a feeding speed, and aging to obtain an MOF-coated core-shell structure precursor, wherein a structural formula of the core-shell structure precursor is MOF-Ni.sub.xCo.sub.yMn.sub.1-x-y(OH).sub.2, a core of the core-shell structure precursor is a nickel-cobalt-manganese hydroxide, and a shell uses an Mn-based metal organic framework synthesized by coordination using Mn and an organic matter carboxylate; and at step 4, presintering the core-shell structure precursor obtained in the step 3 at a low temperature to obtain a nickel-cobalt-manganese oxide with monocrystal structure; uniformly mixing the nickel-cobalt-manganese oxide with monocrystal structure and LiOH.H.sub.2O in a mortar according to a stoichiometric ratio to obtain a mixture and calcining the mixture under an atmosphere of oxygen at a high temperature to obtain the MOF-coated monocrystal ternary positive electrode material, in the step 1, a range of the molar ratios is 0.6≤x≤0.98 and 0.01≤y≤0.2, in the step 4, the presintering at the low-temperature refers to calcining for 3-6 h at a temperature of 300-600° C.; in the step 4, the calcination at the high temperature refers to calcining for 10-20 h at a temperature of 700-800° C.

2. The method of preparing the MOF-coated monocrystal ternary positive electrode material of claim 1, wherein the caustic soda liquid is any one or a combination of several of sodium hydroxide, sodium carbonate and potassium hydroxide.

3. The method of preparing the MOF-coated monocrystal ternary positive electrode material of claim 1, wherein in the step 2, a reaction temperature of the reactor is 40-70° C. with a reaction time being 60-120 h.

4. The method of preparing the MOF-coated monocrystal ternary positive electrode material of claim 1, wherein the precursor core obtained in the step 2 is Ni.sub.xCo.sub.yMn.sub.1-x-y(OH).sub.2 and an average particle size of the precursor core is 3-8 μm.

5. The method of preparing the MOF-coated monocrystal ternary positive electrode material of claim 1, wherein in the step 3, a particle size of the core-shell structure precursor MOF-Ni.sub.xCo.sub.yMn.sub.1-x-y(OH).sub.2 is 4-9 μm.

6. The method of preparing the MOF-coated monocrystal ternary positive electrode material of claim 1, wherein in the step 2, a concentration of the solution A is 2-5 mol/L, a feeding rate of the solution A is 6-9 L/h, the ammonia complexing agent solution is an ammonia with a concentration of 7-14 g/L, a feeding rate of the ammonia is 1-1.5 L/h, a feeding rate of the caustic soda liquid is 2.5-3.5 L/h, and a stirring speed of the reactor is 250-500 r/min.

7. The method of preparing the MOF-coated monocrystal ternary positive electrode material of claim 1, wherein in the step 3, the organic carboxylate is any one or a combination of several of 5-hydroxyisophthalic acid, trimesic acid, and 1,2,4,5-benzenetetracarboxylic acid.

8. The method of preparing the MOF-coated monocrystal ternary positive electrode material of claim 1, wherein in the step 3, the organic solvent is an alcohol organic solvent and a concentration of the obtained solution B is 1.5-2.5 mol/L.

9. The method of preparing the MOF-coated monocrystal ternary positive electrode material of claim 1, wherein in the step 3, a reaction condition in the reactor is as follows: a temperature of 25-40° C., a stirring speed of 300-400 r/min, a time of 3-6 h and an aging time of 2-5 h.

10. The method of preparing the MOF-coated monocrystal ternary positive electrode material of claim 1, wherein in the step 3, in the core of the MOF-Ni.sub.xCo.sub.yMn.sub.1-x-y(OH).sub.2 precursor, a molar percent of nickel to total metals is 70-90%, a molar percent of cobalt to total metals is 5-20% and a molar percent of manganese to total metals is 10-30%.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] FIG. 1 is a SEM diagram illustrating an MOF-coated core-shell structure precursor obtained according to a first embodiment of the present invention.

[0021] FIG. 2 is a sectional SEM diagram illustrating an MOF-coated core-shell structure precursor obtained according to a first embodiment of the present invention.

[0022] FIG. 3 is an EDS diagram illustrating a core-shell structure precursor obtained according to a first embodiment of the present invention, where the interior of the spheres represents a metal Ni element and the exterior of the spheres represents a metal Mn element.

[0023] FIG. 4 is an MOF-coated monocrystal ternary positive electrode material obtained according to a first embodiment of the present invention.

[0024] FIG. 5 is a SEM diagram illustrating an MOF-coated core-shell structure precursor obtained according to a second embodiment of the present invention.

[0025] FIG. 6 is a sectional SEM diagram illustrating an MOF-coated core-shell structure precursor obtained according to a second embodiment of the present invention.

[0026] FIG. 7 is an MOF-coated monocrystal ternary positive electrode material obtained according to a second embodiment of the present invention.

[0027] FIG. 8 is a SEM diagram illustrating an MOF-coated core-shell structure precursor obtained according to a third embodiment of the present invention.

[0028] FIG. 9 is a sectional SEM diagram illustrating an MOF-coated core-shell structure precursor obtained according to a third embodiment of the present invention.

[0029] FIG. 10 is an MOF-coated monocrystal ternary positive electrode material obtained according to a third embodiment of the present invention.

DESCRIPTION OF THE EMBODIMENTS

Embodiment 1

[0030] At step 1, a nickel-cobalt-manganese salt solution of a metal molar ratio of 82:8:10 (a metal concentration is 2 mol/L) was added to a reactor by using a metering pump at a flow rate of 6 L/h, and meanwhile, ammonia of 12 g/L and sodium hydroxide of 3 mol/L were added to the reactor at the flow rates of 1 L/h and 2.5 L/h respectively, where during a reaction process, pH value of the system was adjusted to be between 10.5 and 12.0 by controlling the flow rates of ammonia and sodium hydroxide. Nitrogen was introduced into the sealed reactor at the flow rate of 2 L/h. The stirring speed of a stirring paddle was 400 r/min and a reaction temperature of the system was 62° C. During the reaction, a particle size of the particles in the reactor was detected by using a laser particle sizer at an interval of one hour. By observing the morphology of primary particles and secondary particles of process samples, the primary particles were controlled to be flake-shaped homogeneously-agglomerated spherical particles. When the average particle size of the spherical particles reached 3.0 μm, feeding was stopped to obtain a nickel-cobalt-manganese hydroxide Ni.sub.0.82Co.sub.0.08Mn.sub.0.1(OH).sub.2.

[0031] At step 2, 5-hydroxyisophthalic acid was dissolved in an amount of ethanol to obtain a mixed solution with a concentration of 2 mol/L; the 5-hydroxyisophthalic acid solution of 2 mol/L and a manganese metal salt solution of 1.5 mol/L were added to the above reactor at a feeding speed to perform reaction for 4 h at the temperature of 40° C. at the stirring speed of 350 r/min and then perform aging for 2 h to obtain a core-shell structure precursor with a particle size being 5.0 μm and the shell being Mn-MOF monocrystal-coated (the structural formula is MOF-Ni.sub.0.82Co.sub.0.08Mn.sub.0.1(OH).sub.2), where the core of the precursor is high nickel, the shell is a pure manganese core-shell material, and the chemical formula of the Mn-MOF is Mn(C.sub.8H.sub.3O.sub.5).sub.2.2H.sub.2O.

[0032] At step 3, 5 Kg of MOF-Ni.sub.0.82Co.sub.0.08Mn.sub.0.1(OH).sub.2 precursor was calcined at the temperature of 350° C. to obtain a nickel-cobal-manganese oxide with monocrystal structure (the structural formula is Ni.sub.0.8Co.sub.0.05Mn.sub.0.15O.sub.1.5). The oxide and 4.5 Kg of LiOH.H.sub.2O were uniformly mixed in a Henshel mixer and then calcined for 10 h under the atmosphere of oxygen at the temperature of 700° C. and then pulverized and screened to finally obtain a nickel-cobalt-manganese positive electrode material with monocrystal structure. The positive electrode material was assembled to form a CR2025 button cell which was subjected to electrochemical property detection. The detection result showed that: with a current density of 0.1 C (17 mA/g) and a voltage range of 2.5-4.3V, the discharge capacity was 196.56 mA/g and the capacity retention rate of 1 C 50 cycles was 97.56%.

Embodiment 2

[0033] At step 1, a nickel-cobalt-manganese salt solution of a metal molar ratio of 75:13:12 (a metal concentration is 2 mol/L) was added to a reactor by using a metering pump at a flow rate of 6 L/h, and meanwhile, ammonia of 12 g/L and sodium hydroxide of 3 mol/L were added to the reactor at the flow rates of 1 L/h and 2.5 L/h respectively, where during a reaction process, pH value of the system was adjusted to be between 10.5 and 12.0 by controlling the flow rates of ammonia and sodium hydroxide. Nitrogen was introduced into the sealed reactor at the flow rate of 2 L/h. The stirring speed of a stirring paddle was 400 r/min and a reaction temperature of the system was 62° C. During the reaction, a particle size of the particles in the reactor was detected by using a laser particle sizer at an interval of one hour. By observing the morphology of primary particles and secondary particles of process samples, the primary particles were controlled to be flake-shaped homogeneously-agglomerated spherical particles. When the average particle size of the spherical particles reached 3.8 μm, feeding was stopped to obtain a nickel-cobalt-manganese hydroxide Ni.sub.0.75Co.sub.0.13Mn.sub.0.12(OH).sub.2.

[0034] At step 2, 5-hydroxyisophthalic acid was dissolved in an amount of ethanol to obtain a mixed solution with a concentration of 2 mol/L; the 5-hydroxyisophthalic acid solution of 2 mol/L and a manganese metal salt solution of 1.5 mol/L were added to the above reactor at a feeding speed to perform reaction for 4 h at the temperature of 40° C. at the stirring speed of 350 r/min and then perform aging for 2 h to obtain a core-shell structure precursor with a particle size being 5.5 μm and the shell being Mn-MOF monocrystal-coated (the structural formula is MOF-Ni.sub.0.75Co.sub.0.13Mn.sub.0.12(OH).sub.2), where the core of the precursor is high nickel, the shell is a pure manganese core-shell material, and the chemical formula of the Mn-MOF is Mn(C.sub.8H.sub.3O.sub.5).sub.2.2H.sub.2O.

[0035] At step 3, 5 Kg of MOF-Ni.sub.0.75Co.sub.0.13Mn.sub.0.12(OH).sub.2 precursor was calcined at the temperature of 350° C. to obtain a nickel-cobal-manganese oxide with monocrystal structure (the structural formula is Ni.sub.0.7Co.sub.0.1Mn.sub.0.2O.sub.1.5). The oxide and 4.5 Kg of LiOH.H.sub.2O were uniformly mixed in a Henshel mixer and then calcined for 10 h under the atmosphere of oxygen at the temperature of 700° C. and then pulverized and screened to finally obtain a nickel-cobalt-manganese positive electrode material with monocrystal structure. The positive electrode material was assembled to form a CR2025 button cell which was subjected to electrochemical property detection. The detection result showed that: with a current density of 0.1 C (17 mA/g) and a voltage range of 2.5-4.3V, the discharge capacity was 186.56 mA/g and the capacity retention rate of 1 C 50 cycles was 98.56%.

Embodiment 3

[0036] At step 1, a nickel-cobalt-manganese salt solution of a metal molar ratio of 90:5:5 (a metal concentration is 2 mol/L) was added to a reactor by using a metering pump at a flow rate of 6 L/h, and meanwhile, ammonia of 12 g/L and sodium hydroxide of 3 mol/L were added to the reactor at the flow rates of 1 L/h and 2.5 L/h respectively, where during a reaction process, pH value of the system was adjusted to be between 10.5 and 12.0 by controlling the flow rates of ammonia and sodium hydroxide. Nitrogen was introduced into the sealed reactor at the flow rate of 2 L/h. The stirring speed of a stirring paddle was 400 r/min and a reaction temperature of the system was 62° C. During the reaction, a particle size of the particles in the reactor was detected by using a laser particle sizer at an interval of one hour. By observing the morphology of primary particles and secondary particles of process samples, the primary particles were controlled to be flake-shaped homogeneously-agglomerated spherical particles. When the average particle size of the spherical particles reached 3.0 μm, feeding was stopped to obtain a nickel-cobalt-manganese hydroxide Ni.sub.0.9Co.sub.0.05Mn.sub.0.05(OH).sub.2.

[0037] At step 2, 5-hydroxyisophthalic acid was dissolved in an amount of ethanol to obtain a mixed solution with a concentration of 2 mol/L; the 5-hydroxyisophthalic acid solution of 2 mol/L and a manganese metal salt solution of 1.5 mol/L were added to the above reactor at a feeding speed to perform reaction for 4 h at the temperature of 40° C. at the stirring speed of 350 r/min and then perform aging for 2 h to obtain a core-shell structure precursor with a particle size being 4.5 μm and the shell being Mn-MOF monocrystal-coated (the structural formula is MOF-Ni.sub.0.9Co.sub.0.05Mn.sub.0.05(OH).sub.2), where the core of the precursor is high nickel, the shell is a pure manganese core-shell material, and the chemical formula of the Mn-MOF is Mn(C.sub.8H.sub.3O.sub.5).sub.2.2H.sub.2O.

[0038] At step 3, 5 Kg of MOF-Ni.sub.0.9Co.sub.0.05Mn.sub.0.05(OH).sub.2 precursor was calcined at the temperature of 350° C. to obtain a nickel-cobal-manganese oxide with monocrystal structure (the structural formula is Ni.sub.0.87Co.sub.0.03Mn.sub.0.1O.sub.1.5). The oxide and 4.5 Kg of LiOH.H.sub.2O were uniformly mixed in a Henshel mixer and then calcined for 10 h under the atmosphere of oxygen at the temperature of 700° C. and then pulverized and screened to finally obtain a nickel-cobalt-manganese positive electrode material with monocrystal structure. The positive electrode material was assembled to form a CR2025 button cell which was subjected to electrochemical property detection. The detection result showed that: with a current density of 0.1 C (17 mA/g) and a voltage range of 2.5-4.3V, the discharge capacity was 201.56 mA/g and the capacity retention rate of 1 C 50 cycles was 96.56%.

[0039] It should be noted that unless otherwise stated or defined clearly, the above reaction parameters and component ratios are merely illustrative and not used to limit the specific implementations of the present invention. Those skilled in the art may understand the specific meaning of the terms in the present invention based on actual situations.

[0040] The above are merely preferred embodiments of the present invention. It should be pointed out that those skilled in the art may make several improvements and replacements without departing from the technical principle of the present invention and these improvements and replacements are considered to be within the scope of protection of the present invention.