Preparation method of ultra-high nickel high-cycle cobalt-free positive electrode material

Abstract

The application discloses a preparation method of a superhigh-nickel high-cycle cobalt-free positive electrode material, and comprises the following steps: S1, a nickel source, a manganese source, a complexing agent and a precipitant are prepared into a reaction solution to perform a coprecipitation reaction, so that slurry is obtained; and centrifugation, washing and drying are performed to obtain nickel-manganese hydroxide; S2, the nickel-manganese hydroxide is uniformly mixed with a lithium source and a dopant to obtain a mixture, and first sintering is performed; the oxygen concentration in a sintering atmosphere is 86%-88%, and the sintering temperature is 650 DEG C-800 DEG C; S3, the sintered material is crushed, pickled and dried; and S4, the dried material is uniformly mixed with a coating agent, and second sintering is performed. The application adjusts the cationic disordering of the material and controls the cationic disordering degree within a certain range; the internal and external lattice distortions are relatively uniform; the cycle performance is good; the capacity attenuation is more uniform; and therefore, the cycle performance of the positive electrode material is optimal.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium ion batteries, and particularly relates to a cobalt-free positive electrode material with ultrahigh nickel and high cycle and a preparation method thereof. BACKGROUND

[0002] With the popularity and continuous promotion of new energy vehicles, lithium ion batteries as power sources have developed rapidly, and the performance requirements of lithium batteries have also been continuously improved. As a commonly used lithium battery positive electrode material, the ternary positive electrode material has the advantages of high energy density and good cycle performance. However, due to the scarcity and strategic value of cobalt, the price of cobalt is high, which makes the cost of the ternary material higher than that of other lithium battery positive electrode materials. At the same time, the exploitation of cobalt pollutes the environment more seriously. Therefore, the development of cobalt-free positive electrode materials is of great significance.

[0003] In the ternary positive electrode material, cobalt can prevent cation mixing (mixing of Ni 2+ and Li + ), inhibit phase transition during charging and discharging, and improve the stability of the layered structure of the material. However, in the cobalt-free positive electrode material, the addition of cobalt is reduced, and the problem of cation mixing is more obvious. Cation mixing can form a spinel structure, which is further converted into a rock salt structure during the charging and discharging process, resulting in poor stability of the layered structure, and thus the rate performance and cycle performance of the cobalt-free positive electrode material are reduced. SUMMARY

[0004] The purpose of the present application is to solve the problems of poor cycle and rapid capacity decay of the cobalt-free positive electrode material in the prior art, and to improve the cycle performance of the cobalt-free positive electrode material by controlling the degree of cation mixing and coating lithium aluminum hydride.

[0005] To achieve the above-mentioned purpose, the technical scheme adopted by the present application is a preparation method of a cobalt-free positive electrode material with ultrahigh nickel and high cycle, comprising the following steps:

[0006] S1. Preparing a reaction solution by mixing a nickel source, a manganese source, a complexing agent and a precipitating agent to perform a co-precipitation reaction to obtain a slurry; and performing centrifugation, washing and drying to obtain a nickel-manganese hydroxide;

[0007] S2. Uniformly mixing the nickel-manganese hydroxide with a lithium source and a dopant to obtain a mixture, and performing a first sintering; mixing pure oxygen and air at the same pressure according to a certain proportion of flow to obtain a sintering atmosphere for the first sintering, the oxygen concentration in the sintering atmosphere is 86%-88%, the sintering temperature is 650-800℃, and the sintering time is 8-12h;

[0008] S3. Crushing the sintered material, acid washing and drying;

[0009] S4, mixing the dried material obtained in step S3 with a coating agent, and performing a second sintering, the temperature of the second sintering being 350-500°C, the time being 6-10h, and the sintering atmosphere being air.

[0010] Preferably, in step S1, the pH value of the reaction solution is 10.0-12.2.

[0011] Preferably, in step S1, the chemical formula of the nickel-manganese hydroxide is Ni x Mn 1-x (OH)2, 0.95≤x≤0.99.

[0012] Preferably, in step S1, during the co-precipitation reaction, the reaction temperature is 45-60°C, the reaction time is 30-60h, and the stirring speed is 500-1200r / min.

[0013] Preferably, in step S2, the dopant is any one or several of ZrO2, TiO2, Al2O3, WO3, and MgO.

[0014] Preferably, in step S2, the molar ratio of Li in the lithium source to the total metal (Ni+Co+Mn) is (1.05-1.15):1.

[0015] Preferably, in step S2, the molar ratio of the dopant to the nickel-manganese hydroxide is 0.1%-0.5%.

[0016] Preferably, the lithium source can be lithium hydroxide or lithium carbonate.

[0017] Preferably, during the first and second sintering processes, the temperature is raised at a rate of 1.5°C / min, and after the sintering is completed, the temperature is allowed to decrease naturally.

[0018] Preferably, in step S3, the sintered material is crushed, and during the crushing process, the particle size of the material is controlled to be D50=2-5μm and Dmin>1μm.

[0019] Preferably, in step S3, the washing agent used for the acid washing of the crushed material is one or any combination of carbonic acid, nitric acid, acetic acid, hydrochloric acid, and hypochlorous acid.

[0020] Preferably, the concentration of the washing agent used for the acid washing is 0.1-0.4mol / L.

[0021] Preferably, the mass ratio of the washing agent to the material used for the acid washing is 0.4-0.8:1.

[0022] Preferably, the acid washing time is 0.5-2h.

[0023] Preferably, the drying temperature is 100-150℃.

[0024] Preferably, the vacuum degree of the drying process is -0.09mpa.

[0025] Preferably, in the step S4, the dried material is mixed with the coating agent uniformly, and a second sintering is performed to form a coating layer on the surface of the cobalt-free positive electrode material, the material of the coating agent including lithium aluminum hydride.

[0026] Preferably, the molar amount of the coating agent is 0.1%-0.5% of the dried material.

[0027] The beneficial effects of the present application are: in the layered positive electrode material, the cationic disordering represents the structural defects of the material, so the lowest cationic disorder is usually pursued when the material is synthesized, but the applicant found that the influence of the degree of cationic disordering in the ultra-high nickel cobalt-free positive electrode material is not single. In the ultra-high nickel cobalt-free positive electrode material, the cationic disordering will cause the capacity attenuation, but the too low degree of cationic disordering will cause the heterogeneous phase separation, i.e. the core-shell structure, in the process of multiple charge and discharge. The appropriate cationic disordering is beneficial to improve the cycle performance and rate performance of the material. Therefore, in the present application, the cationic disordering of the material is adjusted, pure oxygen and air are mixed at the same pressure according to a certain proportion of flow, and then are introduced into the atmosphere furnace to achieve the effect of controlling the oxygen concentration (the oxygen concentration is 86%-88%), which not only adjusts the degree of cationic disordering, but also avoids the problem that the change of sintering temperature will cause the change of particle size, specific surface area, residual lithium and other physical indicators when the sintering temperature is usually adjusted to adjust the degree of cationic disordering. In the present application, the ultra-high nickel cobalt-free positive electrode material is controlled at a certain degree of cationic disordering, the lattice distortion inside and outside is relatively uniform, so the cycle performance is good, and the capacity attenuation is more uniform, so that the cycle performance of the positive electrode material reaches the best. BRIEF DESCRIPTION OF DRAWINGS

[0028] Table 1 is the capacity retention rate of each example and comparative example under the condition of 2.75-4.2V, 1 C after 200 cycles;

[0029] Figure 1 SEM image of the cobalt-free positive electrode material prepared in Example 1;

[0030] Figure 2 Cycle performance graph of the cobalt-free positive electrode material prepared in Example 1 and Comparative Example 1 and Comparative Example 2 under the condition of 2.75-4.2V, 1 C;

[0031] Figure 3 XRD graph of the cobalt-free positive electrode material prepared in Example 1 and Comparative Example 1;

[0032] Figure 4The XRD pattern of the cobalt-free positive electrode material prepared for Comparative Example 1 and Comparative Example 1. DETAILED DESCRIPTION

[0033] In order to make the person skilled in the art better understand the present application, the technical solutions of the present application will be described clearly and completely in combination with the embodiments of the present application below. The embodiments are not all the embodiments. Based on the embodiments in the present application, other embodiments obtained by the person skilled in the art without creative labor should belong to the protection scope of the present application.

[0034] In Examples 1-3, Comparative Example 1 and Comparative Example 2, the preparation method of the nickel-manganese hydroxide is as follows:

[0035] S1: nickel sulfate and manganese sulfate are prepared into a mixed salt solution with a molar ratio of 0.95:0.05, the concentration of the mixed salt solution is 2 mol / L, the mixed salt solution is passed into a reaction kettle in a co-current manner at a flow rate of 1.5 L / h, and 10 mol / L ammonia solution at a flow rate of 0.1 L / h and 5 mol / L sodium hydroxide solution at a flow rate of 0.9 L / h, the stirring speed is 600 r / min, the pH value in the reaction kettle is controlled at 12.2, and the reaction is carried out at a temperature of 45℃ for 36 hours, and then the concentrated slurry is centrifuged, washed and dried to obtain nickel-manganese hydroxide (Ni 0.95 Mn 0.05 (OH)2).

[0036] Example 1

[0037] S2: the nickel-manganese hydroxide, lithium hydroxide and dopant are prepared into a mixture with a molar ratio of 1:1.08:0.004, the dopant is a mixture of WO3 and MgO with a molar ratio of 1:1, the prepared mixture is uniformly mixed using a high-speed mixer, the mixed mixture is placed in an atmosphere with an oxygen concentration of 86% (pure oxygen and air are mixed at the same pressure according to a certain proportion of flow to obtain the sintering atmosphere for the first sintering), and then the mixture is calcined at a constant temperature of 730℃ for 8 hours and naturally cooled to room temperature;

[0038] S3: the sintered mixture is crushed using a mechanical crusher, the mixture is cleaned using 0.2 mol / L dilute hydrochloric acid at a dilute hydrochloric acid to mixture mass ratio of 0.4:1 for 1 hour, the temperature is maintained at 45℃, the acid-washed mixture is pressure-filtered, and then vacuum dried at 120℃ and -0.09mpa for 5 hours;

[0039] S4: the dried mixture and lithium aluminum hydride are prepared into a mixture with a molar ratio of 1:0.001, the mixture is uniformly mixed using a high-speed mixer, the mixed mixture is placed in an air atmosphere, and then the mixture is calcined at a constant temperature of 420℃ for 6 hours and naturally cooled to room temperature.

[0040] Example 2

[0041] S2: The nickel-manganese hydroxide, lithium hydroxide, and dopant were prepared in a molar ratio of 1:1.06:0.004, and the dopant was a mixture of WO3 and MgO in a molar ratio of 1:2. The prepared material was uniformly mixed using a high-speed mixer, and the mixed material was placed in an atmosphere with an oxygen concentration of 86% (pure oxygen and air were mixed at the same pressure according to a certain proportion of flow rate to serve as the sintering atmosphere for the first sintering) and calcined at a constant temperature of 690°C for 12 hours, and then naturally cooled to room temperature.

[0042] S3: The sintered material was crushed using a mechanical crusher, and the material was cleaned with 0.2 mol / L dilute hydrochloric acid at a dilute hydrochloric acid to material mass ratio of 0.4:1 for 1 hour while maintaining a temperature of 45°C. After the acid cleaning, the material was vacuum dried at 120°C and -0.09 mpa for 5 hours.

[0043] S4: The dried material and lithium aluminum hydride were prepared in a molar ratio of 1:0.002, uniformly mixed using a high-speed mixer, and placed in an air atmosphere and calcined at a constant temperature of 420°C for 6 hours, and then naturally cooled to room temperature.

[0044] Example 3

[0045] S2: The nickel-manganese hydroxide, lithium hydroxide, and dopant were prepared in a molar ratio of 1:1.09:0.002, and the dopant was a mixture of WO3 and MgO in a molar ratio of 1:1. The prepared material was uniformly mixed using a high-speed mixer, and the mixed material was placed in an atmosphere with an oxygen concentration of 88% (pure oxygen and air were mixed at the same pressure according to a certain proportion of flow rate to serve as the sintering atmosphere for the first sintering) and calcined at a constant temperature of 780°C for 8 hours, and then naturally cooled to room temperature.

[0046] S3: The sintered material was crushed using a mechanical crusher, and the material was cleaned with 0.2 mol / L dilute acetic acid at a dilute acetic acid to material mass ratio of 0.4:1 for 1 hour while maintaining a temperature of 45°C. After the acid cleaning, the material was vacuum dried at 120°C and -0.09 mpa for 5 hours.

[0047] S4: The dried material and lithium aluminum hydride were prepared in a molar ratio of 1:0.001, uniformly mixed using a high-speed mixer, and placed in an air atmosphere and calcined at a constant temperature of 420°C for 6 hours, and then naturally cooled to room temperature.

[0048] Comparative Example 1

[0049] S2: The nickel-manganese hydroxide and lithium source lithium hydroxide, dopant were prepared in a molar ratio of 1:1.08:0.004, the dopant was a mixture of WO3 and MgO in a molar ratio of 1:1, the prepared material was uniformly mixed using a high-speed mixer, the mixed material was placed in an atmosphere with an oxygen concentration of >95%, and calcined at a constant temperature of 730°C for 8 hours, and naturally cooled to room temperature;

[0050] S3: The sintered material was crushed using a mechanical crusher, and the material was cleaned with 0.2 mol / L dilute hydrochloric acid at a ratio of dilute hydrochloric acid to material mass of 0.4:1 for 1 hour, maintaining a temperature of 45°C, the pickled material was pressure filtered, and vacuum dried at 120°C and -0.09 mpa for 5 hours;

[0051] S4: The dried material and lithium aluminum hydride were prepared in a molar ratio of 1:0.001, uniformly mixed using a high-speed mixer, and the mixed material was placed in an air atmosphere, calcined at a constant temperature of 420°C for 6 hours, and naturally cooled to room temperature.

[0052] The positive electrode materials prepared in the above example 1, comparative examples 1 and 2 were made into soft pack batteries, and the specific preparation process was as follows: the prepared positive electrode material, super-p, CNT and PVDF were mixed into a uniform slurry in a mass ratio of 95:1:2:2, and N-methyl-2-pyrrolidone was added to uniformly coat on the aluminum foil; carbon powder, super-p, CMC and SBR were mixed into a uniform slurry in a mass ratio of 96:1:1:2, and N-methyl-2-pyrrolidone was added to uniformly coat on the aluminum foil. The coated pole piece was cut, scraped, dried, rolled, and then cut into the appropriate size, and then baked after welding the pole lug and pasting the adhesive paper to obtain the positive and negative electrode sheets. Through winding, flattening, packaging, and then baking, liquid injection, and sealing, a 604062 type soft pack battery was obtained.

[0053] The relevant electrochemical tests and characterization tests were carried out for example 1 and comparative examples 1 and 2. The specific results are shown in the table. Figures 1-4 The cation mixing of example 1 was higher, but the capacity decay was more uniform, the cation mixing of comparative example 1 was lower, but the cycle performance was poor, and the capacity decay was obvious. This is because the internal and external lattice distortions of comparative example 1 are different during charging and discharging, resulting in phase separation and forming a "core-shell" structure, greatly increasing the diffusion barrier of lithium ions in the crystal grains, leading to rapid capacity decay of the material. The cycle performance of example 1 is better because of the certain degree of cation mixing, and the internal and external lattice distortions are more uniform, so the capacity decay is more uniform.

[0054] The above is only a preferred embodiment of the present application, and the present application is not limited to the above-mentioned embodiment. As long as the same technical effects are achieved by the same means, it should belong to the protection scope of the present application. The technical solutions and embodiments within the protection scope of the present application can be variously modified and changed.

[0055] Table 1 Capacity retention rate at 2.75-4.2V, 1C, 200 cycles

[0056]

Claims

1. A method for preparing a cobalt-free cathode material with ultra-high nickel and high cycle life, characterized in that... Includes the following steps: S1. A reaction solution is prepared by mixing a nickel source, a manganese source, a complexing agent, and a precipitating agent to carry out a co-precipitation reaction, resulting in a slurry; the slurry is then centrifuged, washed, and dried to obtain nickel-manganese hydroxide; the pH value of the reaction solution is 10.0-12.2, and the chemical formula of the nickel-manganese hydroxide is Ni x Mn 1-x (OH)2, 0.95≤x≤0.99; During the coprecipitation reaction, the reaction temperature is 45℃-60℃, the reaction time is 30h-60h, and the stirring speed is 500r / min-1200r / min; S2. Nickel-manganese hydroxide is uniformly mixed with lithium source and dopant to obtain a mixture, and then subjected to the first sintering. Pure oxygen and air are mixed at the same pressure and at a certain flow rate to form the sintering atmosphere for the first sintering. The oxygen concentration in the sintering atmosphere is 86%-88%, the sintering temperature is 650℃-800℃, and the sintering time is 8h-12h. The molar ratio of Li to total metal (Ni + Co + Mn) in the lithium source is (1.05-1.15):

1. S3. Crush, pickle, and dry the sintered material; S4. Mix the dried material obtained in step S3 with the coating agent evenly, and perform a second sintering. The temperature of the second sintering is 350℃-500℃, the time is 6h-10h, and the sintering atmosphere is air.

2. The method for preparing the ultra-high nickel, high-cycle cobalt-free cathode material as described in claim 1, characterized in that, In step S2, the dopant is any one or more of ZrO2, TiO2, Al2O3, WO3, and MgO.

3. The method for preparing the ultra-high nickel, high-cycle cobalt-free cathode material as described in claim 1, characterized in that, In step S2, the molar ratio of the dopant to nickel manganese hydroxide is 0.1%-0.5%.

4. The preparation method of the ultra-high nickel, high-cycle cobalt-free cathode material as described in claim 1, characterized in that, The lithium source is lithium hydroxide or lithium carbonate; the coating agent is lithium aluminum hydride.

5. The method for preparing the ultra-high nickel, high-cycle cobalt-free cathode material as described in claim 1, characterized in that, In step S4, the molar amount of the coating agent is 0.1%-0.5% of the dried material.

6. The method for preparing the ultra-high nickel, high-cycle cobalt-free cathode material as described in claim 1, characterized in that, In step S3, when the sintered material is crushed, the particle size is controlled at D50 = 2μm-5μm and Dmin > 1μm.

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