Preparation method and application of high-nickel positive electrode material with core-shell structure

Abstract

According to the preparation method and the application of the high-nickel positive electrode material with the core-shell structure, the deep charge-discharge specific capacity and the cycling stability of the layered positive electrode material are remarkably improved by controlling the calcination condition of the high-nickel positive electrode material in an oxygen-free environment, regulating and controlling the oxygen vacancy on the surface of the material and synthesizing the sample with the core-shell structure. Meanwhile, the method is simple, effective and low in cost, and the prepared material is good in morphology uniformity and suitable for large-scale production.

Description

Technical Field

[0001] The present invention relates to a preparation method and application of a high-nickel cathode material with a core-shell structure, belonging to the technical field of lithium-ion batteries. Background Art

[0002] The two major problems of energy and environment faced globally continuously stimulate the development of green and renewable energy. Among them, lithium-ion batteries, as electrochemical energy storage devices, are also extremely important. Lithium-ion batteries are widely used in portable electronic devices, electric vehicles, and large-scale energy storage systems. The cruising range and battery service life of electric vehicles, which people are very concerned about, are directly related to the electrochemical performance of lithium-ion batteries, especially the cathode part. As one of the most promising cathode materials, high-nickel layered oxides have been widely studied for their high theoretical specific capacity, fast electron / ion transport rate, high output voltage, and relatively low cost. However, due to its high Ni content, high-nickel materials face inherent challenges such as cation mixing, structural degradation, and microcrack generation, resulting in rapid capacity decay during cycling, which hinders its practical application in lithium-ion batteries. In order to achieve the wide application of high-nickel cathode materials with high power and stability, scientific researchers have developed various strategies to optimize high-nickel cathode materials. The existing modification methods mainly include structural doping, surface coating, morphological integration, and concentration gradient control. However, these methods do not completely solve all the problems mentioned above because each optimization strategy has certain limitations. Especially when further exerting the capacity advantage of high-nickel cathode materials and increasing the charging cut-off voltage, the effects of the above modification measures are greatly reduced. Therefore, new modification technologies must be developed to optimize the high-nickel cathode material system.

[0003] Constructing a core-shell structure is a common method to stabilize electrode materials. However, constructing a core-shell structure on high-nickel cathode materials often has complex methods, high costs, and poor morphological uniformity of the prepared materials, making it difficult to commercialize. Therefore, the existing means cannot meet the requirements for the performance of high-nickel cathode materials. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide a preparation method and application of a high-nickel cathode material with a core-shell structure.

[0005] To achieve the above purpose, the technical solution of the present invention is as follows:

[0006] A high-nickel cathode material with a core-shell structure, characterized in that: the material is prepared by the following method, and the method steps are as follows:

[0007] (1) Put ordinary high-nickel layered cathode powder into a crucible, and then put the crucible into a heating device for calcination in an oxygen-free environment;

[0008] (2) cooling after calcination to obtain a high nickel cathode material with a core-shell structure in a crucible;

[0009] Among them, the ordinary high nickel layered positive electrode material is calcined in an oxygen-free environment, and the unstable oxygen on the surface of the material will be 4+ The valence state decreases and overflows, forming oxygen vacancies, which causes the surface structure of the material to gradually transition from layered structure to spinel structure and rock salt structure, and then form a surface shell.

[0010] Preferably, in step (1), the common high nickel layered cathode powder is LiNi x A y M 1-x-y O2, where A is Co or Fe, M is Mn or W or Al, 0.6 <x<1,0≤y≤0.4,0≤1-x-y≤0.4。

[0011] Preferably, in step (1), the oxygen-free environment includes a vacuum environment and an inert gas environment.

[0012] Preferably, in step (1), the calcination temperature is 100°C to 600°C, and the calcination time is 2h to 15h; the preferred conditions are a calcination temperature of 150°C to 300°C, and a calcination time of 3h to 7h; and the calcination temperature is 200°C, and the calcination time is 5h, and the obtained positive electrode material has the best performance.

[0013] Preferably, in step (1), the heating rate is 2°C / min to 15°C / min, and in step (2), the cooling rate is 1°C / min to 10°C / min.

[0014] Preferably, when in step (1), the calcination environment is an inert gas, the heating device is a tubular furnace, and the inert gas flow rate is 50 CFM to 300 CFM.

[0015] Preferably, the particle diameter of the high-nickel positive electrode material with a core-shell structure is 1 μm to 15 μm, wherein the core part inside the particle is a layered structure, and the shell layer outside the particle is a layered-spinel mixed structure or a spinel structure or a spinel rock salt mixed structure or a rock salt structure, and the specific shell structure is determined by the calcination temperature and calcination time.

[0016] Preferably, the shell thickness of the high-nickel positive electrode material with a core-shell structure is 2nm to 10nm, and the positive electrode material performance is best when the shell thickness is 3nm to 5nm.

[0017] A lithium-ion battery, wherein the positive electrode material of the battery adopts the high-nickel positive electrode material with a core-shell structure described in the present invention.

[0018] Beneficial effects

[0019] The present invention provides a high-nickel cathode material with a core-shell structure. By using a simple method of calcining ordinary high-nickel cathode materials in an oxygen-free environment and utilizing the instability of high-valent nickel ions on the material surface, a stable shell structure is in-situ generated on the surface of the high-nickel cathode material. The obtained high-nickel cathode material with a core-shell structure not only does not affect the transport of interfacial lithium ions, but also inhibits the anisotropic phase transformation of the cathode material during deep charge and discharge, thereby significantly improving the specific capacity and cycle stability of the high-nickel cathode material at a high charging cut-off voltage.

[0020] The present invention provides a high-nickel cathode material with a core-shell structure. By using finished products of ordinary high-nickel cathode materials and controlling the temperature and time for secondary calcination in an oxygen-free environment, a stable shell structure is obtained in-situ on its surface, realizing the improvement of high-voltage electrochemical performance. The method is simple and effective, with low cost, and the prepared material has good morphological uniformity, being suitable for large-scale production. Description of the Drawings

[0021] Figure 1 XRD (X-ray diffraction) data of the high-nickel cathode materials prepared in Example 1, Example 2, and Comparative Example 1.

[0022] Figure 2 XRD refinement data graph of the high-nickel cathode material prepared in Example 2.

[0023] Figure 3 HRTEM (High-resolution transmission electron microscopy) images of the high-nickel cathode materials prepared in Example 1, Example 2, and Comparative Example 1.

[0024] Figure 4 Electrochemical cycling performance graphs of the batteries assembled in Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3. Detailed Description of the Invention

[0025] The present invention will be further described in detail below in conjunction with specific embodiments.

[0026] In the following examples or comparative examples:

[0027] Button Battery Assembly and Electrochemical Performance Test: At room temperature, the electrochemical performance test was carried out using CR2025 button batteries. The working electrode was prepared as follows: First, the materials obtained in the examples or comparative examples were mixed with acetylene black, and a polyvinylidene fluoride (PVDF) / N-methyl-2-pyrrolidone (NMP) solution was added dropwise to the mixed sample so that the mass ratio of the materials obtained in the examples or comparative examples, acetylene black, and PVDF was 8:1:1 to obtain a uniform slurry; then, the obtained slurry was evenly scraped onto aluminum foil and vacuum dried at 100 °C for 12 h to remove the solvent; finally, a small round piece with a diameter of 1.1 cm was pressed from the aluminum foil coated with the sample as the positive electrode, a lithium sheet as the negative electrode material, 1.0 M LiPF6 carbonate electrolyte (ethylene carbonate (EC): diethyl carbonate (DEC): dimethyl carbonate (DMC) volume ratio of 1:1:1), and the charge and discharge test was completed under a Blue Electric battery test system. The test voltage range was 3.0 - 4.6 V, the test temperature was room temperature, and the test current density was 1 C (1 C = 200 mA / g).

[0028] Example 1

[0029] The ordinary LiNi 0.9 Co 0.05 Mn 0.05 O2 material was loosely spread out in a crucible, and then the crucible was placed in a tubular furnace with argon gas passing through. First, it was heated at 30 °C for 1 h to remove the air in the tube, and then the temperature was raised to 200 °C and calcined for 5 h. The heating rate was 5 °C / min. Argon gas was passed through throughout the process, and the gas flow rate was 200 CFM. Finally, it was cooled to room temperature at a rate of 2 °C / min to obtain a high-nickel cathode material with a core-shell structure, namely NCM925.

[0030] The XRD test results of the prepared high-nickel cathode material are as Figure 1 shown. The results show that the main structure of the obtained high-nickel material is still the R-3m layered structure.

[0031] The HRTEM test diagram of the prepared high-nickel cathode material is as Figure 3 shown. The results show that a layered-spinel mixed-phase shell layer is in-situ formed on the surface layer of the obtained high-nickel material.

[0032] The electrochemical cycling results of the assembled battery are as Figure 4 shown. It can be seen from the figure that in Example 1, in the voltage range of 3.0 - 4.6 V, after 150 cycles at 1 C, the capacity retention rate is 83.6%.

[0033] Example 2

[0034] The ordinary LiNi 0.9 Co 0.05 Mn0.05 The O2 material is loosely spread flat in a crucible, and then the crucible is placed in a tubular furnace with argon flowing through. It is first heated at 30°C for 1 h to remove the air in the tube, then heated to 300°C and calcined for 5 h at a heating rate of 5°C / min. Argon is continuously passed through the whole process, and the gas flow rate is 200 CFM. Finally, it is cooled to room temperature at a rate of 2°C / min to obtain a high-nickel cathode material with a core-shell structure, which is NCM935.

[0035] The XRD test results of the prepared high-nickel cathode material are as Figure 1 shown. The results show that the main structure of the obtained high-nickel material is still the R-3m layered structure.

[0036] The refined XRD test results of the prepared high-nickel cathode material are as Figure 2 shown. The results show that a small amount of spinel phase is generated in the material obtained after calcination at 300°C for 5 h in an argon atmosphere.

[0037] The HRTEM test images of the prepared high-nickel cathode material are as Figure 3 shown. The results show that a spinel phase shell layer is in-situ generated on the surface layer of the obtained high-nickel material.

[0038] Example 3

[0039] The ordinary LiNi 0.9 Co 0.05 Mn 0.05 O2 material is loosely spread flat in a crucible, and then the crucible is placed in a tubular furnace with argon flowing through. It is first heated at 30°C for 1 h to remove the air in the tube, then heated to 400°C and calcined for 5 h at a heating rate of 5°C / min. Argon is continuously passed through the whole process, and the gas flow rate is 200 CFM. Finally, it is cooled to room temperature at a rate of 2°C / min to obtain a high-nickel cathode material with a core-shell structure, which is NCM945.

[0040] The XRD test results of the prepared high-nickel cathode material are as Figure 1 shown. The results show that the main structure of the obtained high-nickel material is still the R-3m layered structure.

[0041] Example 4

[0042] The ordinary LiNi 0.9 Co 0.05 Mn 0.05The O2 material was loosely spread flat in a crucible, and then the crucible was placed in a tubular furnace with argon flowing through it. It was first heated at 30 °C for 1 h to remove the air in the tube, then heated to 500 °C and calcined for 5 h with a heating rate of 5 °C / min. Argon was continuously passed through the whole process with a gas flow rate of 200 CFM. Finally, it was cooled to room temperature at a rate of 2 °C / min to obtain a high-nickel cathode material with a core-shell structure, namely NCM955.

[0043] The XRD test results of the prepared high-nickel cathode material are as Figure 1 shown. The results indicate that the main structure of the obtained high-nickel material is still the R-3m layered structure.

[0044] Example 5

[0045] The ordinary LiNi 0.9 Co 0.05 Mn 0.05 O2 material was loosely spread flat in a crucible, and then the crucible was placed in a tubular furnace with argon flowing through it. It was first heated at 30 °C for 1 h to remove the air in the tube, then heated to 600 °C and calcined for 5 h with a heating rate of 5 °C / min. Argon was continuously passed through the whole process with a gas flow rate of 200 CFM. Finally, it was cooled to room temperature at a rate of 2 °C / min to obtain a high-nickel cathode material with a core-shell structure, namely NCM965.

[0046] The XRD test results of the prepared high-nickel cathode material are as Figure 1 shown. The results indicate that the main structure of the obtained high-nickel material is still the R-3m layered structure.

[0047] The XRD test refinement results of the prepared high-nickel cathode material are as Figure 2 shown. The results show that there is a little rock salt phase in the material obtained after calcination at 600 °C in an argon atmosphere for 5 h.

[0048] The HRTEM test image of the prepared high-nickel cathode material is as Figure 3 shown. The results indicate that a spinel rock salt phase shell is in-situ formed on the surface layer of the obtained high-nickel material.

[0049] Comparative Example 1

[0050] The ordinary LiNi 0.9 Co 0.05 Mn 0.05 [[ID= forty-four]]O2 material without any secondary treatment is NCM9 as Comparative Example 1.

[0051] The XRD test of Comparative Example 1 is as Figure 1 shown. The results show that the structure of Comparative Example 1 is the R-3m layered structure.

[0052] The XRD test refinement results of Comparative Example 1 are asFigure 2 As shown, there are no other structures in the overall surface material.

[0053] For the battery assembled in Comparative Example 1, within the voltage range of 3.0 - 4.6V and at a current density of 1C, after 150 cycles, the capacity retention rate is 69.1%, as Figure 4 shown.

[0054] Comparative Example 2

[0055] Spread the ordinary LiNi 0.9 Co 0.05 Mn 0.05 O2 material loosely on a crucible, then place the crucible in a tube furnace with oxygen flowing through. First, heat it at 30°C for 1h to remove the air in the tube, then raise the temperature to 200°C and calcine for 5h, with a heating rate of 5°C / min. Oxygen is continuously passed through the whole process, and the gas flow rate is 200CFM. Finally, cool it to room temperature at a rate of 2°C / min to obtain an oxygen-calcined sample, which is O2-NCM925.

[0056] The electrochemical cycling results of the assembled battery are as Figure 4 shown. It can be seen from the figure that for Comparative Example 2, within the voltage range of 3.0 - 4.6V and after 150 cycles at 1C, the capacity retention rate is 69.7%.

[0057] Comparative Example 3

[0058] Spread the ordinary LiNi 0.9 Co 0.05 Mn 0.05 O2 material loosely on a crucible, then place the crucible in a muffle furnace for calcination in an air environment. Raise the temperature to 200°C and calcine for 5h, with a heating rate of 5°C / min, and then cool it to room temperature at a rate of 2°C / min to obtain an air-calcined sample, which is Air-NCM925.

[0059] The electrochemical cycling results of the assembled battery are as Figure 4 shown. It can be seen from the figure that for Comparative Example 3, within the voltage range of 3.0 - 4.6V and after 150 cycles at 1C, the capacity retention rate is 75.8%.

[0060] In summary, the invention includes but is not limited to the above embodiments. Any equivalent replacement or partial improvement made under the spirit and principle of the present invention will be regarded as within the protection scope of the present invention.

Claims

1. A high-nickel cathode material with a core-shell structure, characterized in that: The said material is prepared by the following method, and the method steps are as follows: (1) Put ordinary high-nickel layered cathode powder into a crucible, and then put the crucible into a heating device for calcination in an oxygen-free environment; (2) After the calcination is completed, cool down, and a high-nickel cathode material with a core-shell structure is obtained in the crucible; Among them, when the ordinary high-nickel layered cathode material is calcined in an oxygen-free environment, the unstable oxygen on the material surface will overflow as the valence of unstable Ni4+ decreases, forming oxygen vacancies, so that the surface structure of the material gradually transitions from a layered structure to a spinel structure and a rock salt structure, and then a surface shell layer is formed.

2. The high-nickel cathode material with a core-shell structure as described in claim 1, wherein: In step (1), the ordinary high-nickel layered cathode powder is LiNi x A y M 1-x-y O2, where A is Co or Fe, M is Mn or W or Al, 0.6 < x < 1, 0 ≤ y ≤ 0.4, 0 ≤ 1 - x - y ≤ 0.

4.

3. A high-nickel cathode material with a core-shell structure as described in claim 1, characterized in that: In step (1), the said oxygen-free environment includes a vacuum environment and an inert gas environment.

4. A high-nickel cathode material with a core-shell structure as described in claim 1, characterized in that: In step (1), the calcination temperature is 100°C to 600°C, and the calcination time is 2h to 15h; preferably, the calcination temperature is 150°C to 300°C, and the calcination time is 3h to 7h; among them, when the calcination temperature is 200°C and the calcination time is 5h, the performance of the obtained cathode material is the best.

5. A high-nickel cathode material with a core-shell structure as described in claim 1, characterized in that: In step (1), the heating rate is 2°C / min to 15°C / min, and in step (2), the cooling rate is 1°C / min to 10°C / min.

6. The high-nickel cathode material with a core-shell structure as described in claim 1, characterized in that: When in step (1), the calcination environment is an inert gas, the heating device is a tube furnace, and the flow rate of the inert gas is 50CFM to 300CFM.

7. A high-nickel cathode material with a core-shell structure as described in claim 1, characterized in that: The particle diameter of the high-nickel cathode material with a core-shell structure is 1μm to 15μm. Among them, the core part inside the particle is a layered structure, and the outer shell layer of the particle is a layered-spinel mixed structure or a spinel structure or a spinel-rock salt mixed structure or a rock salt structure. The specific shell layer structure is determined by the calcination temperature and the calcination time.

8. A high-nickel cathode material with a core-shell structure as described in claim 1, characterized in that: The shell layer thickness of the high-nickel cathode material with a core-shell structure is 2nm to 10nm. Among them, when the shell layer thickness is 3nm to 5nm, the performance of the cathode material is the best.

9. A lithium-ion battery, characterized in that: The cathode material of the said battery adopts a high-nickel cathode material with a core-shell structure as described in any one of claims 1 to 8.

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