Preparation and application of surface-modified cobalt-free lithium-rich manganese-based oxide positive electrode material

Abstract

The invention relates to the technical field of lithium ion batteries, and discloses preparation and application of a surface-modified cobalt-free lithium-rich manganese-based oxide cathode material.The preparation method comprises the steps that a nickel source and a manganese source are weighed according to the required stoichiometric ratio and added into deionized water, a co-precipitation method is adopted to obtain an evenly-mixed precursor Mn0. 6Ni0. 2 (CO3) 0. 8, and the precursor Mn0. 6Ni0. 2 (CO3) 0. 8 is prepared; and synthesizing the cobalt-free lithium-rich manganese-based oxide positive electrode material by using a high-temperature solid-phase method. An iron source is adopted as a coating raw material, the cobalt-free lithium-rich manganese-based oxide positive electrode material containing an iron oxide coating is synthesized by utilizing a hydrothermal method, in the annealing process after high temperature, iron oxide reacts with residual lithium on the surface of the cobalt-free lithium-rich manganese-based oxide positive electrode material, and a surface coating is generated on the surface in situ. The prepared surface-modified cobalt-free lithium-rich manganese-based oxide positive electrode material is applied to a lithium ion battery, the specific capacity is large, the rate capability is excellent, the performance is stable, and the capacity fading is obviously slowed down in the charge-discharge cycle process.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion batteries, and in particular to the preparation and application of a surface-modified cobalt-free lithium-rich manganese-based oxide positive electrode material. Background Art

[0002] With the widespread use of new energy vehicles, the diversified development of energy storage technology, and the accelerated update and iteration of IoT smart terminals, lithium-ion batteries have been widely used in mobile devices and consumer electronics markets. However, cathode materials are the key factor in improving the energy density of lithium-ion batteries. 2 MnO 3 (1-x)LiTMO 2 (TM=Ni, Mn) due to its high reversible capacity (>250 mAh g -1 ) and energy density (>1000Wh kg -1 ) and a higher operating voltage (4.8 V), however, its low first coulombic efficiency, severe voltage decay and poor rate performance restrict the development of this material.

[0003] By Li 2 MnO 3 -MO 2 -LiTMO 2 The ternary phase diagram analysis shows that the cobalt-free lithium-rich manganese-based oxide cathode material can obtain excess capacity when charged to greater than 4.4V, and the capacity comes from the redox reaction of oxygen anions. At present, it is usually necessary to charge the material to a high voltage (≥4.8 V) during the first charge and discharge cycle to activate the oxygen anions to provide capacity. However, this will cause irreversible phase changes on the surface of the material, loss of lattice oxygen and dissolution of transition metal ions, further causing continuous interface side reactions on the surface, reduced initial coulomb efficiency, irreversible capacity decay, and continuous voltage decay.

[0004] In summary, the current problems limiting the application of cobalt-free lithium-rich manganese-based oxide positive electrode materials are mainly due to the unique redox process of cobalt-free lithium-rich manganese-based oxide positive electrode materials. During the cycle process, this material causes serious irreversible release of lattice oxygen and dissolution of transition metal ions, which aggravates the corrosion of the electrolyte on the material surface, and then leads to the deterioration of the material structure, ultimately affecting the battery's poor cycle stability and serious voltage and capacity attenuation.

[0005] Therefore, the present invention proposes a surface modification method for a cobalt-free lithium-rich manganese-based oxide positive electrode material to solve the above problems. Summary of the invention

[0006] In view of the deficiencies in the prior art, the present invention provides a surface modification method for a cobalt-free lithium-rich manganese-based oxide positive electrode material to solve the problems of capacity loss and voltage decay caused by irreversible precipitation of lattice oxygen in the cobalt-free lithium-rich manganese-based oxide positive electrode material during high-voltage charge and discharge cycles. Technical Solution

[0007] To achieve the above object, the present invention provides the following technical solution: a method for preparing a surface-modified cobalt-free lithium-rich manganese-based oxide positive electrode material, comprising the following steps: Step 1: Weigh the nickel source and the manganese source according to the required stoichiometric ratio, and dissolve them in deionized water to obtain a uniformly mixed solution; Step 2: adding the above solution and the precipitant solution into a reactor for reaction, adding a complexing agent to regulate the precipitation of the metal salt, then heating and fully stirring, filtering, drying, grinding and screening to obtain a precursor powder of a cobalt-free lithium-rich manganese-based oxide positive electrode material; Step 3: Mix and grind the above-mentioned precursor powder with a lithium source, and sinter the mixture at a high temperature to obtain an unmodified cobalt-free lithium-rich manganese-based oxide positive electrode material; Step 4: Add the positive electrode material to the solvent for ultrasonic dispersion, then add the iron source and stir thoroughly for hydrothermal reaction, anneal after the reaction, and grind to obtain a surface modified cobalt-free lithium-rich manganese-based oxide positive electrode material.

[0008] Wherein, the chemical formula of the positive electrode material is xLi 2 MnO 3 (1-x)LiTMO 2 (TM=Ni,Mn),0 <x<1 Preferably, the stoichiometric ratio of the substances in step 1 is Li / TM=(1.1-1.5):1.

[0009] Preferably, the nickel source and manganese source in step 1 are selected from one or a combination of sulfate, nitrate, acetate, oxalate and chloride.

[0010] Preferably, the complexing agent in step 2 is one or more of citric acid, oxalic acid, ethylenediaminetetraacetic acid, ammonia water, and urea; the precipitating agent is one or more of carbonic acid, carbonate, bicarbonate, hydroxide, and oxalate; the solubility of the precursor solution is 0.1-10 mol / L, and the solubility of the complexing agent in the precursor solution is 0.05-5 mol / L.

[0011] Preferably, the heating temperature of the water bath in step 2 is 20-70° C., the stirring is performed by magnetic stirring, the rotation speed is 100-1500 rpm, and the stirring time is 6-20 h.

[0012] Preferably, the lithium source in step three is one or more of lithium hydroxide, lithium carbonate, lithium nitrate, and lithium acetate; the specific operation of high temperature sintering in step three is to add the obtained precursor powder to the lithium source and grind it evenly, place it in a corundum boat and send it into a muffle furnace, heat it from room temperature to 600°C-1000°C at a heating rate of 1°C / min-10°C / min, keep it warm for 2-24 hours, and then cool it naturally.

[0013] Preferably, the solvent in step 4 is any one of deionized water, ethanol, chloroform, oleic acid, N-methylformamide, and dimethyl sulfoxide; the iron source is one or more of ferrous acetate, ferrous chloride, ferrous sulfate, ferrous nitrate, ferrous oxalate, and ferrous carbonate, wherein the amount of the iron source is 0.2%-20% of the total mass of the positive electrode material.

[0014] Preferably, in step 4, the ultrasonic treatment temperature is 10-80°C, and the ultrasonic time is 0.1-5h; the hydrothermal reaction temperature is 90-200°C, and the reaction time is 2-10h; and the sintering is performed by raising the temperature to 300-1000°C at a heating rate of 1-10°C / min, keeping the temperature for 2-8 hours, and then cooling naturally.

[0015] Preferably, the cobalt-free lithium-rich manganese-based oxide positive electrode material obtained above is coated with lithium iron oxide in situ on its surface. The presence of the coating can effectively alleviate the interface side reaction between the electrolyte and the surface of the electrode material, which is beneficial to improve the electrochemical performance of the cobalt-free lithium-rich manganese-based oxide positive electrode material. The cobalt-free lithium-rich manganese-based oxide positive electrode material is xLi 2 MnO 3 (1-x)LiTMO 2 A layered material composed of 0<x<1, wherein TM is at least one of Mn, Ni, Al, Ti, Zr, Fe, Cr, Mo, W, Ge, Pd, and Pt.

[0016] Under high temperature calcination in an inert atmosphere, the iron-containing oxide reacts with the residual lithium on the surface of the material to form a surface coating of lithium iron oxide. In order to prove that the modification process will not affect the main phase of the material, the present invention sets up an unmodified original cobalt-free lithium-rich manganese-based oxide positive electrode material as a comparative case to prove that the method adopted by the present invention can play a positive effect.

[0017] Compared with the prior art, the present invention provides a method for preparing a surface-modified cobalt-free lithium-rich manganese-based oxide positive electrode material, which has the following beneficial effects: 1. The preparation method of the surface-modified cobalt-free lithium-rich manganese-based oxide positive electrode material has low raw material cost, simple process, and good electrochemical properties. The discharge capacity is as high as 270.4 mAh / g at a small current density, and can reach a discharge capacity of 240.4 mAh / g even at a high current density. After 100 cycles at a high current density, its reversible discharge capacity can still reach 215.8 mAh / g, and it shows excellent rate performance.

[0018] 2. A method for preparing the surface-modified cobalt-free lithium-rich manganese-based oxide positive electrode material. The present invention provides an in-situ construction of a coating on the surface of the cobalt-free lithium-rich manganese-based oxide positive electrode material, which matches traditional electrolyte materials and negative electrode materials and can be widely used in secondary lithium-ion batteries, as well as electric vehicles and portable electronic devices.

[0019] The co-precipitation method and high-temperature solid-phase sintering method are applied to the preparation of positive electrode materials, which have the advantages of uniform particles, regular morphology, environmentally friendly raw materials and short reaction time; an in-situ coating is constructed on the surface of the cobalt-free lithium-rich manganese-based oxide positive electrode material, which can effectively inhibit the corrosion of the electrolyte on the material surface, reduce interfacial side reactions, and at the same time reduce the presence of residual lithium on the material surface, because the residual lithium will react with the electrolyte to generate HF, which will corrode the material and cause the dissolution of transition metals, thereby causing structural phase changes. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Mn prepared by coprecipitation method in Example 1 0.6 Ni 0.2 (CO 3 ) 0.8 Precursor ( Figure 1 a), Cobalt-free lithium-rich manganese-based oxide positive electrode material without surface modification (1b), SEM image of the cobalt-free lithium-rich manganese-based oxide positive electrode material obtained after surface modification (1c); Figure 2 This is the XRD pattern of the cobalt-free lithium-rich manganese-based oxide positive electrode material obtained after surface modification in Example 2; Figure 3 This is a comparison diagram of the first charge and discharge curves of the cobalt-free lithium-rich manganese-based oxide positive electrode material obtained after surface modification in Example 3 and the cobalt-free lithium-rich manganese-based oxide positive electrode material without surface modification; Figure 4 This is a rate performance diagram of the cobalt-free lithium-rich manganese-based oxide positive electrode material obtained after surface modification in Example 3. DETAILED DESCRIPTION

[0021] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention. Example

[0022] Weigh MnSO in a molar ratio of 3:1 4 、NiSO 4 The salt was dissolved in deionized water to prepare a 2 mol / L mixed solution; the concentration of ammonia water complexing agent was 1.2 mol / L, and the precipitant was 2 mol / L Na 2 CO 3 solution; the mixed solution and Na 2 CO 3 The solution was simultaneously added dropwise to a vigorously stirred reactor, to which an appropriate amount of complexing agent solution was pre-added, and the pH value was controlled at the same time, and the water bath heating temperature was 50°C; after the addition was completed, the reaction was allowed to proceed for 16 hours; the reaction product was filtered, washed, and dried in a vacuum oven at 90°C for 12 hours to obtain a precursor, and then Li 1.2 Mn 0.6 Ni 0.2 O 2 Weigh 5% excess Li 2 CO 3 As a lithium source, the mixture was fully ground and placed in a muffle furnace, kept at 500 ° C for 5 h, then heated to 900 ° C for calcination for 10 h, and cooled to room temperature to obtain a cobalt-free lithium-rich manganese-based oxide positive electrode material Li 1.2 Mn 0.6 Ni 0.2 O 2 A certain amount of cobalt-free lithium-rich manganese-based oxide cathode material was weighed and ultrasonically dispersed in ethanol for 1 h, and then a certain amount of urea and 1g FeSO 4 Add to the ethanol solution containing the cobalt-free lithium-rich manganese-based oxide positive electrode material and stir for 1 hour. The solution is subjected to a hydrothermal reaction at 160°C for 7 hours, filtered after the reaction, and the obtained sample is calcined at 300°C for 2 hours under Ar atmosphere, and then continued to be heated to 700°C for 6 hours to obtain a modified cobalt-free lithium-rich manganese-based oxide positive electrode material with a lithium iron oxide coating on the surface. Example

[0023] Weigh MnSO in a molar ratio of 3:1 4 、NiSO 4 The salt was dissolved in deionized water to prepare a 2 mol / L mixed solution; the concentration of ammonia water complexing agent was 0.6 mol / L, and the precipitant was 2 mol / L Na 2 CO3 solution; the mixed solution and Na 2 CO 3 The solution was simultaneously added dropwise to a vigorously stirred reactor, to which an appropriate amount of complexing agent solution was pre-added, and the pH value was controlled at the same time. The water bath heating temperature was 50°C. After the addition was completed, the reaction was allowed to proceed for 16 hours. The reaction product was filtered, washed, and dried in a vacuum oven at 90°C for 12 hours to obtain a precursor, and then the precursor was prepared according to the Li 1.2 Mn 0.6 Ni 0.2 O 2 Weigh 5% excess Li 2 CO 3 As a lithium source, the mixture was fully mixed and placed in a muffle furnace, kept at 500 ° C for 5 h, then heated to 900 ° C for 10 h, and cooled to room temperature to obtain a cobalt-free lithium-rich manganese-based oxide positive electrode material Li 1.2 Mn 0.6 Ni 0.2 O 2 A certain amount of cobalt-free lithium-rich manganese-based oxide cathode material was weighed and ultrasonically dispersed in ethanol for 1 h, and then a certain amount of urea and 1g FeSO 4 Add to the above ethanol solution containing the cobalt-free lithium-rich manganese-based oxide positive electrode material and stir for 1 hour. Carry out hydrothermal reaction at 160°C for 7 hours, filter after the reaction, and calcine the obtained sample at 300°C for 2 hours under Ar atmosphere, and continue to heat to 700°C for 6 hours to obtain a modified cobalt-free lithium-rich manganese-based oxide positive electrode material with a lithium iron oxide coating on the surface. Example

[0024] Weigh MnSO in a molar ratio of 3:1 4 、NiSO 4 The salt was dissolved in deionized water to prepare a 2 mol / L mixed solution; the concentration of ammonia water complexing agent was 1.2 mol / L, and the precipitant was 2 mol / L Na 2 CO 3 solution; the mixed solution and the NaOH solution were simultaneously added dropwise to a vigorously stirred reactor by a peristaltic pump, an appropriate amount of complexing agent solution was added to the reactor in advance, and the pH value was controlled at the same time, and the water bath heating temperature was 50°C; after the addition was completed, the reaction was carried out for 16 hours; the reaction product was filtered, washed, and dried in a vacuum oven at 90°C for 12 hours to obtain a precursor, and then Li 1.2 Mn 0.6 Ni 0.2 O 2 An excess of 5% LiOH was weighed as a lithium source, mixed thoroughly and placed in a muffle furnace, kept at 500°C for 5 hours, then raised to 900°C for calcination for 10 hours, and cooled to room temperature to obtain a cobalt-free lithium-rich manganese-based oxide positive electrode material Li 1.2 Mn 0.6Ni 0.2 O 2 A certain amount of cobalt-free lithium-rich manganese-based oxide cathode material was weighed and ultrasonically dispersed in ethanol for 1 h, and then a certain amount of urea and 1g FeSO 4 Add to the ethanol solution containing the cobalt-free lithium-rich manganese-based oxide positive electrode material and stir for 1 hour. The solution is subjected to a hydrothermal reaction at 160°C for 7 hours, filtered after the reaction, and the obtained sample is calcined at 300°C for 2 hours under an Ar atmosphere, and then further heated to 700°C for 6 hours to obtain a modified cobalt-free lithium-rich manganese-based oxide positive electrode material with a lithium iron oxide coating on the surface. Example

[0025] Weigh MnSO in a molar ratio of 3:1 4 、NiSO 4 The salt was dissolved in deionized water to prepare a 2 mol / L mixed solution; the concentration of ammonia water complexing agent was 1.2 mol / L, and the precipitant was 4 mol / L NaOH solution; the mixed solution and NaOH were pumped by a peristaltic pump. 2 CO 3 The solution was simultaneously added dropwise to a vigorously stirred reactor, to which an appropriate amount of complexing agent solution was pre-added, and the pH value was controlled, and the reactor was heated in a water bath at 50°C. After the addition was completed, the reaction was allowed to proceed for 16 hours. The reaction product was filtered, washed, and dried in a vacuum oven at 90°C for 12 hours to obtain a precursor, and then the precursor was prepared according to the Li 1.2 Mn 0.6 Ni 0.2 O 2 An excess of 5% LiOH was weighed as a lithium source, mixed thoroughly and placed in a muffle furnace. The mixture was heated at 500°C for 5 h at a heating rate of 5°C / min, then heated to 900°C for calcination for 10 h. After cooling to room temperature, a cobalt-free lithium-rich manganese-based positive electrode material Li 1.2 Mn 0.6 Ni 0.2 O 2 A certain amount of cobalt-free lithium-rich manganese-based material was weighed and ultrasonically dispersed in ethanol for 1 h, and then a certain amount of urea and 1.5 g FeSO 4 Add to the ethanol solution containing the cobalt-free lithium-rich manganese-based oxide positive electrode material and stir for 1 hour. The solution is subjected to a hydrothermal reaction at 160°C for 7 hours, filtered after the reaction, and the obtained sample is calcined at 300°C for 2 hours under an Ar atmosphere, and then further heated to 700°C for 6 hours to obtain a modified cobalt-free lithium-rich manganese-based oxide positive electrode material with a lithium iron oxide coating on the surface. Example

[0026] Weigh MnSO in a molar ratio of 3:1 4 、NiSO 4The salt was dissolved in deionized water to prepare a 2 mol / L mixed solution; the concentration of ammonia water complexing agent was 0.6 mol / L, and the precipitant was 4 mol / L NaOH solution; the mixed solution and NaOH were pumped by a peristaltic pump. 2 CO 3 The solution was simultaneously added dropwise to a vigorously stirred reactor, to which an appropriate amount of complexing agent solution was pre-added, and the pH value was controlled at the same time. The water bath heating temperature was 50°C. After the addition was completed, the reaction was allowed to proceed for 16 hours. The reaction product was filtered, washed, and dried in a vacuum oven at 90°C for 12 hours to obtain a precursor, and then the precursor was prepared according to the Li 1.2 Mn 0.6 Ni 0.2 O 2 An excess of 5% LiOH was weighed as a lithium source, mixed thoroughly and placed in a muffle furnace, kept at 500°C for 5 hours, then raised to 900°C for calcination for 10 hours, and cooled to room temperature to obtain a cobalt-free lithium-rich manganese-based oxide positive electrode material Li 1.2 Mn 0.6 Ni 0.2 O 2 A certain amount of cobalt-free lithium-rich manganese-based oxide cathode material was weighed and ultrasonically dispersed in ethanol for 1 h, and then a certain amount of urea and 1.5 g FeSO 4 Add to the ethanol solution containing the cobalt-free lithium-rich manganese-based oxide positive electrode material and stir for 1 hour. The solution is subjected to a hydrothermal reaction at 160°C for 7 hours, filtered after the reaction, and the obtained sample is calcined at 300°C for 2 hours under an Ar atmosphere, and then further heated to 700°C for 6 hours to obtain a modified cobalt-free lithium-rich manganese-based oxide positive electrode material with a lithium iron oxide coating on the surface.

[0027] The specific embodiments described above have detailed descriptions of the objectives, technical solutions and beneficial effects of the present invention. It should be understood that the above descriptions are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. Preparation of a surface-modified cobalt-free lithium-rich manganese-based oxide positive electrode material, characterized in that: The following steps are involved: Step 1: Weigh the nickel source and the manganese source according to the required stoichiometric ratio, and dissolve them in deionized water to obtain a uniformly mixed solution; Step 2: adding the above solution and the precipitant solution into a reactor for reaction, adding a complexing agent to regulate the precipitation of the metal salt, then heating and fully stirring, filtering, drying, and grinding to obtain a precursor powder of a cobalt-free lithium-rich manganese-based oxide positive electrode material; Step 3: Mix and grind the above-mentioned precursor powder with a lithium source, and sinter the mixture at a high temperature to obtain an unmodified cobalt-free lithium-rich manganese-based oxide positive electrode material; Step 4: Add the positive electrode material to the solvent for ultrasonic dispersion, then add the iron source and stir thoroughly for hydrothermal reaction, anneal after the reaction, and grind to obtain a surface modified cobalt-free lithium-rich manganese-based oxide positive electrode material.

2. The method for preparing a surface-modified cobalt-free lithium-rich manganese-based oxide positive electrode material according to claim 1, characterized in that: in, The chemical formula of the precursor is Mn 0.6 Ni 0.2 (CO3) 0.8 The chemical formula of the positive electrode material is xLi2MnO3· (1-x)LiTMO2 (TM = Ni, Mn), 0 <x<1。 3. The method for preparing a surface-modified cobalt-free lithium-rich manganese-based oxide positive electrode material according to claim 1, characterized in that: The stoichiometric ratio of the materials in step 1 is Li / TM=(1.1-1.5):

1.

4. The method for preparing a surface-modified cobalt-free lithium-rich manganese-based oxide positive electrode material according to claim 1, characterized in that: In the step 1, the nickel source and the manganese source are selected from one or more of sulfate, nitrate, acetate, oxalate and chloride.

5. The method for preparing a surface-modified cobalt-free lithium-rich manganese-based oxide positive electrode material according to claim 1, characterized in that: The complexing agent used in the co-precipitation method in step 2 is one or more of citric acid, oxalic acid, ethylenediaminetetraacetic acid, ammonia water, and urea; the precipitating agent is one or more of carbonic acid, carbonate, bicarbonate, hydroxide, and oxalate; the solubility of the precursor solution is 0.1-10 mol / L, and the solubility of the complexing agent in the precursor solution is 0.05-5 mol / L.

6. The method for preparing a surface-modified cobalt-free lithium-rich manganese-based oxide positive electrode material according to claim 1, characterized in that: In the step 2, the heating temperature of the water bath is 20-70° C., the stirring is performed by magnetic stirring, the rotation speed is 100-1500 rpm, and the stirring time is 6-20 hours.

7. The method for preparing a surface-modified cobalt-free lithium-rich manganese-based oxide positive electrode material according to claim 1, characterized in that: The lithium source described in step three is one or more of lithium hydroxide, lithium carbonate, lithium nitrate, and lithium acetate; the specific operation of high temperature sintering in step three is to add the obtained precursor powder to the lithium source and grind it evenly, put it in a corundum boat and send it into a muffle furnace, heat it from room temperature to 600℃-1000℃ at a heating rate of 1℃ / min-10℃ / min, keep it warm for 2-24 hours, and then cool it naturally.

8. The method for preparing a surface-modified cobalt-free lithium-rich manganese-based oxide positive electrode material according to claim 1, characterized in that: The solvent in step 4 is any one of deionized water, ethanol, chloroform, oleic acid, N-methylformamide, and dimethyl sulfoxide; the iron source is one or more of ferrous acetate, ferrous chloride, ferrous sulfate, ferrous nitrate, ferrous oxalate, and ferrous carbonate, wherein the amount of the iron source is 0.2%-20% of the total mass of the positive electrode material.

9. The method for preparing a surface-modified positive electrode material according to claim 1, characterized in that: In the step 4, the ultrasonic treatment temperature is 10-80°C, and the ultrasonic time is 0.1-5h; the hydrothermal reaction temperature is 90-200°C, and the reaction time is 2-10h; and the sintering is to increase the temperature to 300-1000°C at a heating rate of 1-10°C / min, keep the temperature for 2-8h, and then cool naturally.

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