Multi-site doped positive electrode material and preparation method thereof

Abstract

The invention provides a multi-site doped positive electrode material and a preparation method thereof. The positive electrode material comprises Br and K as doping elements. In the high-temperature lithiation process of a precursor and a lithium source, Br and K are introduced as doping elements, Br doping can motivate a large amount of oxygen-related anion oxidation reduction behaviors in a layered structure, the capacity of the positive electrode material is improved, irreversible loss of lattice oxygen can be effectively inhibited in the high-voltage cycle process, and the performance of the positive electrode material is improved. And good cycling stability and safety are ensured.

Description

Technical Field

[0001] The present invention relates to the field of lithium batteries, and in particular to a multi-site doped positive electrode material and a preparation method thereof. Background Art

[0002] As one of the four core materials of lithium-ion batteries, cathode materials are the decisive factor in the electrochemical performance of lithium-ion batteries. x Co y Mn 1-x-y O2 (NCM, x ≥ 0.6) has attracted extensive attention due to its high specific capacity and excellent rate performance, and is considered to be one of the most promising cathode materials for the next generation of lithium-ion batteries. However, the poor cycle stability, poor thermal stability and low safety performance of nickel-rich ternary cathode materials limit their large-scale application in electric vehicles and hybrid vehicles. For example: 1. Cation mixing. The ionic radii of Ni2+ and Li+ are similar. During high-temperature calcination and cycling, they will occupy lithium ion vacancies, thereby causing changes in the crystal structure and resulting in rapid attenuation of the material capacity; 2. Poor cycle stability. Intergranular cracks are the main reason for the poor cycle stability of the electrode. The H2→H3 phase transition of the material will cause intergranular cracks, and the cracks will become more obvious as the Ni content increases; 3. Lattice oxygen release. Lattice oxygen is easily over-oxidized to gaseous oxygen molecules under high voltage conditions. The formation of oxygen molecules will lead to serious capacity loss. Lithium-rich oxide cathodes usually suffer from severe lattice oxygen release, causing serious safety hazards; 4. Surface residual alkali. Nickel-rich ternary materials easily react with H2O and CO2 in the air to generate LiOH and Li2CO3 on the surface of the material, which react with LiPF6 in the electrolyte to generate HF, corroding the electrode. The presence of Li2CO3 and the escaped oxygen atoms in the NCM material react with the electrolyte to generate CO2, reducing the safety performance of the battery.

[0003] Therefore, the research on nickel-rich ternary cathode materials NCM is of great significance to the improvement of the current lithium-ion battery system. With the continuous improvement of material preparation methods, the electrochemical performance of nickel-rich ternary cathode materials has been significantly improved. Summary of the invention

[0004] Ion doping and surface coating are widely used methods. Through ion doping, the crystal structure is stabilized and the structural collapse during the cycle is prevented, thereby achieving the purpose of improving the stability of the cathode material, but it is necessary to screen suitable dopants. Surface coating can effectively isolate the interface side reactions between the electrolyte and the electrode material, but the thickness of the coating layer and the coating uniformity are difficult to control. The present invention aims to solve one of the technical problems in the related art at least to a certain extent. To this end, one purpose of the present invention is to propose an ion doping technology that enables the material to have high capacity, long cycle, and high voltage stability. The lithium ion nickel-rich layered oxide of the present invention is prepared by multi-site doping and tempering treatment, and has the advantages of high capacity, long cycle, and high safety. Br and K are introduced as doping elements during the high-temperature lithiation process of the precursor and the lithium source. Br doping can stimulate a large amount of oxygen-related anion redox behavior in the layered structure, improve the capacity of the positive electrode material, and effectively inhibit the irreversible loss of lattice oxygen during high-voltage cycling, ensuring its good cycle stability and safety. In addition, during the doping process, Br + Will Ni 2+ Oxidized to Ni 3+ , avoid Ni 2+ The formation of rock salt phase. K has more extranuclear electrons and can generate a more influential electromagnetic field. + and Ni 2+ There is a large electromagnetic force between them, which will increase Ni 2+ The migration barrier to Li vacancies inhibits the mixing of Li / Ni and the dissolution of TM, and improves the stability of the crystal structure. At the same time, the larger ionic radius of K can widen the lattice spacing and improve its reaction kinetics. Finally, through high-temperature tempering treatment, the surface of the material is remelted and recrystallized, which can further improve the uniformity of element doping on the one hand, and effectively reduce the surface residual alkali of nickel-rich materials on the other hand.

[0005] In the first aspect of the present invention, the present invention proposes a positive electrode material. According to an embodiment of the present invention, the positive electrode material includes Br and K as doping elements. Br doping can stimulate a large amount of oxygen-related anion redox behavior in the layered structure, improve the capacity of the positive electrode material, and effectively inhibit the irreversible loss of lattice oxygen during high voltage cycling, ensuring its good cycle stability and safety. In addition, during the doping process, Br + Will Ni 2+ Oxidized to Ni 3+ , avoid Ni 2+ The formation of rock salt phase. K has more extranuclear electrons and can generate a more influential electromagnetic field. + and Ni 2+ There is a large electromagnetic force between them, which will increase Ni 2+The migration barrier to Li vacancies inhibits the mixing of Li / Ni and the dissolution of TM, and improves the stability of the crystal structure. At the same time, the larger ionic radius of K can widen the lattice spacing and improve its reaction kinetics. Finally, through high-temperature tempering treatment, the surface of the material is remelted and recrystallized, which can further improve the uniformity of element doping on the one hand, and effectively reduce the surface residual alkali of nickel-rich materials on the other hand.

[0006] According to an embodiment of the present invention, the positive electrode material may further include at least one of the following additional technical features:

[0007] According to an embodiment of the present invention, the doping element is provided by KBr.

[0008] According to an embodiment of the present invention, the positive electrode material further includes a hydroxide precursor and a lithium source.

[0009] According to an embodiment of the present invention, the hydroxide precursor is Ni 0.9 Co 0.05 Mn 0.05 (OH)2.

[0010] According to an embodiment of the present invention, the lithium source is LiOH·H2O.

[0011] According to an embodiment of the present invention, the molar ratio of Li element to Ni element, Co element and Mn element is 1.03:1.

[0012] According to an embodiment of the present invention, the mass ratio of the KBr to the hydroxide precursor and the lithium source mixture is 0.1%.

[0013] In another aspect of the present invention, the present invention also provides a method for preparing a positive electrode material. According to an embodiment of the present invention, the method comprises:

[0014] 1) mixing a hydroxide precursor, a lithium source and KBr to obtain a mixture;

[0015] 2) subjecting the mixture to a first sintering treatment to obtain a first-stage lithium battery positive electrode material;

[0016] 3) The first-stage lithium battery positive electrode material is subjected to a second sintering treatment to obtain the positive electrode material.

[0017] According to an embodiment of the present invention, the above method may further include at least one of the following additional technical features:

[0018] According to an embodiment of the present invention, the hydroxide precursor is Ni 0.9 Co 0.05 Mn 0.05 (OH)2.

[0019] According to an embodiment of the present invention, the lithium source is LiOH·H2O.

[0020] According to an embodiment of the present invention, the molar ratio of Li element to Ni element, Co element and Mn element is 1.03:1.

[0021] According to an embodiment of the present invention, the mass ratio of the KBr to the hydroxide precursor and the lithium source mixture is 0.1%.

[0022] According to an embodiment of the present invention, the mixing process is performed in a high-speed mixer.

[0023] According to an embodiment of the present invention, the rotating speed of the mixer is 500 r / min.

[0024] According to an embodiment of the present invention, the mixing time is 30 minutes.

[0025] According to an embodiment of the present invention, the first sintering treatment is performed at a heating rate of 3° C. / min, heating to 730° C. and keeping the temperature for 15 hours.

[0026] According to an embodiment of the present invention, the first sintering process further includes cooling the product of the first sintering process to room temperature.

[0027] According to an embodiment of the present invention, the second sintering treatment is performed at a heating rate of 3°C / min, heating to 650°C and keeping the temperature for 10 hours.

[0028] In yet another aspect of the present invention, the present invention further provides a battery. According to an embodiment of the present invention, the battery comprises the positive electrode material described above or the positive electrode material obtained according to the method described above. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The above and / or additional aspects and advantages of the present invention will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which:

[0030] Figure 1 This is the SEM image of the prepared nickel-rich cathode material;

[0031] Figure 2 This is a comparison chart of the first charge and discharge curves of the positive electrode materials prepared in Example 1 and Comparative Example 1. DETAILED DESCRIPTION

[0032] The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, but should not be construed as limiting the present invention.

[0033] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In the description of the present invention, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0034] The present invention is described below with reference to specific embodiments. It should be noted that these embodiments are merely illustrative and do not limit the present invention in any way.

[0035] Example 1

[0036] 1. Weigh the hydroxide precursor Ni 0.9 Co 0.05 Mn 0.05 (OH)2 and lithium source LiOH·H2O and dopant KBr, wherein the molar ratio of Li / (Ni+Co+Mn) is 1.03, and the mass ratio of dopant KBr to the mixture of precursor and lithium source is 0.1%, and they are mixed uniformly by a high-speed mixer, the mixer speed is 500r / min, and the mixing time is 30min to obtain a uniformly mixed mixture;

[0037] 2. The mixture is sintered at high temperature in an oxygen atmosphere in a box-type atmosphere furnace. The sintering system is to increase the temperature to 730°C at a heating rate of 3°C / min and keep the temperature for 15 hours. After the sintering is completed, the mixture is cooled to room temperature with the furnace to obtain the first stage lithium battery positive electrode material;

[0038] 3. The first stage lithium battery positive electrode material is sintered at high temperature in an oxygen atmosphere in a box-type atmosphere furnace. The sintering temperature is 650°C, the sintering time is 10h, and the heating rate is 3°C / min. The material is then cooled in the furnace and sieved to obtain the final product, the lithium battery positive electrode material.

[0039] Example 2

[0040] 1. Weigh the hydroxide precursor Ni 0.9 Co 0.05 Mn 0.05 (OH)2 and lithium source LiOH·H2O and dopant KBr, wherein the molar ratio of Li / (Ni+Co+Mn) is 1.03, and the mass ratio of dopant KBr to the mixture of precursor and lithium source is 0.1%, and they are mixed uniformly by a high-speed mixer, the mixer speed is 500r / min, and the mixing time is 30min to obtain a uniformly mixed mixture;

[0041] 2. The mixture is sintered at high temperature in an oxygen atmosphere in a box-type atmosphere furnace. The sintering system is to increase the temperature to 730°C at a heating rate of 3°C / min and keep the temperature for 15 hours. After the sintering is completed, the mixture is cooled to room temperature with the furnace to obtain the first stage lithium battery positive electrode material;

[0042] 3. The first stage lithium battery positive electrode material is sintered at high temperature in an oxygen atmosphere in a box-type atmosphere furnace. The sintering temperature is 750°C, the sintering time is 10 hours, and the heating rate is 3°C / min. The material is then cooled in the furnace and sieved to obtain the final product, the lithium battery positive electrode material.

[0043] Comparative Example 1

[0044] 1. Weigh the hydroxide precursor Ni 0.9 Co 0.05 Mn 0.05 (OH)2 and lithium source LiOH·H2O and dopant KBr, wherein the molar ratio of Li / (Ni+Co+Mn) is 1.03, and the mass ratio of dopant KBr to the mixture of precursor and lithium source is 0.1%, and they are mixed uniformly by a high-speed mixer, the mixer speed is 500r / min, and the mixing time is 30min to obtain a uniformly mixed mixture;

[0045] 2. The mixture was sintered at high temperature in an oxygen atmosphere in a box-type atmosphere furnace. The sintering system was to increase the temperature to 730°C at a heating rate of 3°C / min and keep the temperature for 15 hours. After the sintering was completed, the mixture was cooled to room temperature with the furnace to obtain the first-stage lithium battery positive electrode material.

[0046] Comparative Example 2

[0047] 1. Weigh the hydroxide precursor Ni 0.9 Co 0.05 Mn 0.05 (OH)2 and lithium source LiOH·H2O, wherein the molar ratio of Li / (Ni+Co+Mn) is 1.03, are mixed uniformly by a high-speed mixer, the mixer speed is 500r / min, the mixing time is 30min, and a uniformly mixed mixture is obtained;

[0048] 2. The mixture is sintered at high temperature in an oxygen atmosphere in a box-type atmosphere furnace. The sintering system is to increase the temperature to 730°C at a heating rate of 3°C / min and keep the temperature for 15 hours. After the sintering is completed, the mixture is cooled to room temperature with the furnace to obtain the first stage lithium battery positive electrode material;

[0049] 3. The first stage lithium battery positive electrode material is sintered at high temperature in an oxygen atmosphere in a box-type atmosphere furnace. The sintering temperature is 650°C, the sintering time is 10h, and the heating rate is 3°C / min. The material is then cooled in the furnace and sieved to obtain the final product, the lithium battery positive electrode material.

[0050] Preparation of button cells: The positive electrode materials prepared in the examples and comparative examples were used in button cells for electrochemical performance testing. The assembly process of the battery was as follows: the positive electrode material, polyvinylidene fluoride (PVDF) and conductive carbon black were mixed in a mass ratio of 8:1:1 and dissolved in N-methylpyrrolidone (NMP) solvent to prepare positive electrode slurry, so that there were no particles inside the slurry. The slurry was evenly coated on aluminum foil on a coating machine to make a pole piece. The coated pole piece was placed in a vacuum drying oven at a temperature of 120°C for vacuum drying for 12 hours, and the pole piece was taken out and rolled on a roller press for standby use. The electrode was cut into a circular electrode with a diameter of 12 mm using a cutting machine, placed in a vacuum drying oven and dried at 60°C for 12 hours, then taken out and weighed using an electronic balance. Finally, the positive electrode, lithium sheet, spring, gasket, positive electrode shell, negative electrode shell, diaphragm, and electrolyte were assembled into a CR2025 button half-cell in a glove box filled with argon. The electrolyte was 1M NaPF6 dissolved in a mixture of EC (ethylene carbonate) and DMC (dimethyl carbonate) (according to the volume ratio of EC: DMC = 1:1), and the metal lithium sheet was the counter electrode. The charge and discharge voltage range is 2.8-4.4V, the first charge and discharge rate is 0.1C, and the nominal specific capacity is 1C = 200mAh / g. The cycle performance test charge and discharge rate is 1C cycle 50 weeks.

[0051] The test results are compared in Table 1 below.

[0052] Table 1

[0053]

[0054]

[0055] From Table 1, the electrochemical performance of Examples 1 and 2 is significantly better than that of Comparative Examples 1 and 2. The nickel-rich positive electrode material co-doped with K-Br and tempered shows a higher discharge capacity (225.6 mAh / g) and a higher first coulomb efficiency (90.1%) and good cycle performance (97.5%), which is mainly attributed to the K-Br co-doping effect. Br doping inhibits the release of lattice oxygen during the cycle and improves the capacity. K doping inhibits Li / Ni mixing, stabilizes the crystal structure, improves cycle stability, and widens the lattice spacing. At the same time, after tempering, the uniformity of doping is further improved, and the surface residual alkali of the material is effectively reduced.

[0056] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0057] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A positive electrode material, It is characterized in that The positive electrode material includes Br and K as doping elements.

2. The positive electrode material according to claim 1, It is characterized in that The doping element is provided by KBr.

3. The positive electrode material according to claim 2, It is characterized in that The positive electrode material further includes a hydroxide precursor and a lithium source.

4. The positive electrode material according to claim 3, It is characterized in that The hydroxide precursor is Ni 0.9 Co 0.05 Mn 0.05 (OH) 2 .

5. The positive electrode material according to claim 3, It is characterized in that The lithium source is LiOH·H 2 O.

6. The positive electrode material according to claim 3, It is characterized in that The molar ratio of Li element to Ni element, Co element and Mn element is 1.03:

1.

7. The positive electrode material according to claim 3, It is characterized in that The mass ratio of the KBr to the hydroxide precursor and the lithium source mixture is 0.1%.

8. A method for preparing a positive electrode material, It is characterized in that include: 1) mixing a hydroxide precursor, a lithium source and KBr to obtain a mixture; 2) subjecting the mixture to a first sintering treatment to obtain a first-stage lithium battery positive electrode material; 3) The first-stage lithium battery positive electrode material is subjected to a second sintering treatment to obtain the positive electrode material.

9. The method according to claim 8, It is characterized in that The hydroxide precursor is Ni 0.9 Co 0.05 Mn 0.05 (OH) 2 ; Optionally, the lithium source is LiOH·H 2 O; Optionally, the molar ratio of Li element to Ni element, Co element and Mn element is 1.03:1; Optionally, the mass ratio of the KBr to the hydroxide precursor and the lithium source mixture is 0.1%; Optionally, the mixing process is carried out in a high-speed mixer; Optionally, the mixer has a rotation speed of 500 r / min; Optionally, the mixing time is 30 min; Optionally, the first sintering treatment is performed at a heating rate of 3°C / min, heating to 730°C, and keeping the temperature for 15 hours; Optionally, the first sintering process further comprises cooling the product of the first sintering process to room temperature; Optionally, the second sintering treatment is performed by heating the temperature to 650° C. at a heating rate of 3° C. / min and keeping the temperature for 10 hours.

10. A battery, It is characterized in that The battery comprises the positive electrode material according to any one of claims 1 to 7 or the positive electrode material obtained according to the method according to any one of claims 8 or 9.

Images