Lithium cobalt oxide composite positive electrode material and preparation method thereof

Abstract

The invention discloses a lithium cobalt oxide composite positive electrode material and a preparation method thereof, and relates to the technical field of lithium ion batteries, according to the lithium cobalt oxide composite positive electrode material prepared by the system, lithium cobalt oxide microspheres are modified in an Al < 3 + > + Ti < 4 + > co-doping mode, Al < 3 + > can stabilize a layered structure, and Ti < 4 + > can stabilize the layered structure; the stability of the material in the charge-discharge cycle process is improved, the problems of structural collapse and the like are reduced, so that the service life of the material is prolonged, a lithium ion diffusion channel can be effectively widened by introducing Ti < 4 + >, rapid transmission of lithium ions in the charge-discharge process of the battery is facilitated, the charge-discharge efficiency of the battery can be improved, and the service life of the material is prolonged. Further, the electrochemical performance of the battery is improved, so that the performance of the battery under different multiplying powers is more excellent.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion batteries, and more specifically, to a lithium cobaltate composite cathode material and a preparation method thereof. Background Art

[0002] With the rapid development of modern technology, the demand for high-performance batteries in various electronic devices such as smart phones, tablet computers, and electric vehicles is increasing day by day. Lithium-ion batteries have occupied a dominant position in many energy storage fields due to their advantages such as high energy density, long cycle life, and no memory effect. As a key component of lithium-ion batteries, the performance of the cathode material plays a crucial role in the performance of the entire battery.

[0003] Among many cathode materials, lithium cobaltate (LiCoO₂) materials are widely used in lithium-ion batteries for consumer electronics and other fields due to their high working voltage, good charge-discharge platform, and easy synthesis. However, with the continuous improvement of battery performance requirements, traditional lithium cobaltate materials gradually expose some limitations, which restrict their further development in high-performance battery applications.

[0004] During the charge-discharge cycle of the battery, the layered structure of traditional lithium cobaltate materials is prone to collapse. This is because when lithium ions are repeatedly inserted and removed, stress will be generated on the lattice structure of the material. Under the long-term action, the originally stable layered structure is damaged, resulting in a rapid attenuation of the battery capacity and a shortening of the cycle life, unable to meet the needs of long-term stable use of electronic devices.

[0005] The diffusion rate of lithium ions in traditional lithium cobaltate materials is relatively slow, which becomes one of the key factors restricting the improvement of battery charge-discharge efficiency. In the case of high-current charge-discharge (high-rate charge-discharge), lithium ions cannot be transmitted inside the electrode material in time, resulting in an aggravation of battery polarization, a significant reduction in the chargeable and dischargeable capacity, making it difficult for the battery to adapt to high-performance usage scenarios such as fast charging, restricting the further shortening of the charging time of electronic devices and their application in some occasions where rapid energy replenishment is required.

[0006] The electronic conductivity of traditional lithium cobaltate materials is relatively low, usually at a level of about 10 -4 S / cm. During high-rate charge-discharge, the transmission speed of electrons in the electrode material cannot keep up with the transmission demand of lithium ions, affecting the overall rate performance of the battery, resulting in the actual available capacity of the battery being much lower than the theoretical capacity at high rates, unable to fully exert the energy storage potential of the battery, and difficult to meet application scenarios with high requirements for high-rate charge-discharge performance such as fast charging of electric vehicles.

[0007] In the working environment of lithium-ion batteries, the electrolyte comes into contact with the cathode material. Traditional lithium cobaltate materials lack an effective protection mechanism and are vulnerable to corrosion by components such as HF in the electrolyte. This corrosion damages the surface structure of the material, further affecting its electrochemical performance, exacerbating the attenuation of battery capacity and the deterioration of performance, and reducing the service life and overall performance stability of the battery.

[0008] To overcome the problems of the above-mentioned traditional lithium cobaltate materials, researchers have carried out a series of improvement efforts. Some studies have attempted to improve the performance of lithium cobaltate materials through single-element doping. For example, certain metal ions are doped to enhance structural stability or increase the lithium-ion diffusion rate, etc. However, single-element doping can often only improve certain aspects of performance and cannot simultaneously take into account the comprehensive improvement of multiple aspects of performance such as structural stability, lithium-ion diffusion, and electron transport, making it difficult to fully meet the strict requirements of high-performance batteries for cathode materials. There are also some technologies that use coating methods to protect and optimize the performance of lithium cobaltate materials. For example, simple inorganic or organic materials are used for coating to improve the compatibility between the material and the electrolyte or enhance electron conductivity, etc. However, these coating methods often have relatively single functions, or the structural design of the coating layer is not reasonable enough to form a synergistic effect and cannot effectively solve the above-mentioned multiple key performance problems at the same time. For example, while improving the electron transport ability, it is necessary to take into account inhibiting electrolyte corrosion, etc.

[0009] In summary, although the existing technology has made certain progress in improving the performance of lithium cobaltate cathode materials, there are still many deficiencies and it is difficult to meet the urgent needs of current and future high-performance lithium-ion batteries for the comprehensive improvement of multiple aspects of cathode material performance. Therefore, it is necessary to develop a new lithium cobaltate composite cathode material and the corresponding preparation method to overcome the limitations of the existing technology and achieve further optimization and improvement of the performance of lithium-ion batteries. Summary of the Invention

[0010] Aiming at the deficiencies of the existing technology, the purpose of the present invention is to provide a lithium cobaltate composite cathode material and its preparation method.

[0011] To achieve the above purpose, the present invention provides the following technical solutions:

[0012] A lithium cobaltate composite cathode material, the lithium cobaltate composite cathode material is a lithium cobaltate microsphere with a double-layer coating structure. The inner layer of the double-layer coating structure is an ion conductor for inhibiting electrolyte corrosion, and the outer layer is an electron conductor. The lithium cobaltate microsphere is co-doped with Al 3+ +Ti 4+ to stabilize the layered structure, and Ti 3+ to broaden the lithium-ion diffusion channel. 4+

[0013] Further, a preparation method of a lithium cobalt oxide composite cathode material is as follows:

[0014] Step 1: Prepare a lithium cobalt oxide precursor and a dopant;

[0015] Step 2: Perform ball milling and mixing treatment on the lithium cobalt oxide precursor and the dopant, and mix to obtain a precursor;

[0016] Step 3: Perform staged calcination on the precursor to obtain lithium cobalt oxide microspheres;

[0017] Step 4: Gradiently coat the lithium cobalt oxide microspheres to obtain a lithium cobalt oxide composite cathode material.

[0018] Further, the lithium cobalt oxide precursor uses high-purity Li3PO4 and Co3O4, with a molar ratio of 1.05:1, and the excess lithium compensates for high-temperature volatilization.

[0019] Further, the dopant uses Al2O3 nanopowder and TiO2 nanopowder. The Al2O3 nanopowder has a particle size of 50 nm and a purity of ≥99.9%, and is used to provide Al 3+ , the TiO2 nanopowder is anatase type, with a particle size of 30 nm and a purity of ≥99.5%, and is used to provide Ti 4+ , doping ratio: Al:Ti:Co = 1:1:98, total doping amount 2%.

[0020] Further, the staged calcination includes a low-temperature pre-crystallization step and a medium-temperature doping and curing step (450 °C). The equipment used for the staged calcination is a tube furnace;

[0021] The heating program of the low-temperature pre-crystallization step: Raise the temperature to 300 °C at 5 °C / min and hold for 4 h;

[0022] The heating program of the medium-temperature doping and curing step: Continue to raise the temperature to 450 °C (2 °C / min) and hold for 8 h.

[0023] Further, the gradient coating of the lithium cobalt oxide microspheres includes an inner layer Li3PO4 coating method and an outer layer carbon nanotube coating method;

[0024] Inner layer Li3PO4 coating method: Chemical vapor deposition (CVD) + liquid phase assistance; Immerse the calcined material in a 0.1 M Li3PO4 precursor solution (LiOH + H3PO4), and perform ultrasonic dispersion; Transfer to a CVD furnace, and introduce Ar gas at 250 °C to thermally decompose Li3PO4 and deposit it evenly; Thickness: ~10 nm, coverage rate above 95%;

[0025] Outer carbon nanotube coating method: catalytic chemical vapor deposition; Mix the Li3PO4-coated microspheres with ferrocene and place them in a quartz tube; Introduce a C2H2 / Ar mixed gas and react at 600 °C for 1 h for in-situ growth of CNTs; Morphology: form a three-dimensional intertwined network with a thickness of ~20 nm.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] The lithium cobaltate composite cathode material prepared by the present invention, by adopting the co-doping method of Al 3+ +Ti 4+ modifies the lithium cobaltate microspheres. Among them, Al 3+ can stabilize the layered structure, help improve the stability of the material during charge and discharge cycling, reduce the occurrence of problems such as structural collapse, thereby extending the service life of the material. The introduction of Ti 4+ can effectively broaden the lithium ion diffusion channels, which is very beneficial for the rapid transmission of lithium ions during the charge and discharge of the battery, can improve the charge and discharge efficiency of the battery, and further improve the electrochemical performance of the battery, making the battery perform more excellently at different rates. The outer layer is coated with a carbon nanotube (CNT) network to form an electron conductor layer. The carbon nanotubes in-situ grown by catalytic chemical vapor deposition (CCVD) present a three-dimensional intertwined network shape. The electronic conductivity increases significantly from 10 -4 S / cm to 10 -2 S / cm, greatly improving the electron transport ability of the material. During fast charging at a high rate (such as 5C), the capacity can reach 80% of the theoretical value, which is greatly improved compared with traditional materials (less than 50%), enabling the battery to adapt to the use scenario of fast charging and meeting the demand for fast charging of modern electronic devices, etc. The inner layer of the double-layer coating structure is coated with an ion conductor Li3PO4, which can effectively inhibit the direct contact between the electrolyte and lithium cobaltate, reduce HF corrosion, further improve the stability of the material in the electrolyte environment, and reduce the risk of material performance degradation caused by electrolyte corrosion. Specific embodiments

[0028] Example 1: A lithium cobaltate composite cathode material, the lithium cobaltate composite cathode material is a lithium cobaltate microsphere with a double-layer coating structure. The inner layer of the double-layer coating structure is an ion conductor (such as Li3PO4) for inhibiting electrolyte corrosion, and the outer layer is an electron conductor (such as a carbon nanotube network) for improving the rate performance. The lithium cobaltate microspheres are co-doped with Al 3+ +Ti 4+ Al 3+ stabilizes the layered structure, and Ti 4+ broadens the lithium ion diffusion channels.

[0029] Example 2: A preparation method of a lithium cobaltate composite cathode material, which is applied to the lithium cobaltate composite cathode material described in Claim 1, and the method steps are as follows:

[0030] Step 1: Prepare a lithium cobaltate precursor and a dopant.

[0031] The lithium cobaltate precursor uses high-purity Li3PO4 and Co3O4, with a molar ratio of 1.05:1, and the excess lithium compensates for high-temperature volatilization.

[0032] The dopant uses Al2O3 nanopowder and TiO2 nanopowder. The Al2O3 nanopowder has a particle size of 50 nm and a purity of ≥99.9%, and is used to provide Al 3+ , the TiO2 nanopowder is anatase type, with a particle size of 30 nm and a purity of ≥99.5%, and is used to provide Ti 4+ , doping ratio: Al:Ti:Co = 1:1:98 (atomic ratio), and the total doping amount is 2%.

[0033] Step 2: Perform ball milling and mixing treatment on the lithium cobaltate precursor and the dopant, and mix them to obtain a precursor.

[0034] The ball milling and mixing treatment is used to ensure the uniform dispersion of Al2O3 / TiO2 in the precursor. The ball milling and mixing treatment uses a planetary ball mill (zirconia balls, ball-to-material ratio of 10:1), uses absolute ethanol (to prevent agglomeration), rotates at 300 rpm, for 6 h, in a vacuum environment (to avoid oxidation).

[0035] Step 3: Perform segmented calcination on the precursor to obtain lithium cobaltate microspheres.

[0036] The segmented calcination includes a low-temperature pre-crystallization step (300 °C) and a medium-temperature doping and curing step (450 °C). The equipment used for the segmented calcination is a tube furnace (oxygen atmosphere, flow rate of 50 mL / min).

[0037] The heating program of the low-temperature pre-crystallization step (300 °C): heat up to 300 °C at 5 °C / min, hold for 4 h, function: promote the preliminary reaction of Li / Co to form LiCoO2 crystal nuclei, and avoid the segregation of Al / Ti at high temperatures.

[0038] The heating program of the medium-temperature doping and curing step (450 °C): continue to heat up to 450 °C (2 °C / min), hold for 8 h, mechanism: Al 3+ enters the Co site, enhances the Co-O bond energy, and stabilizes the layered structure; Ti 4+ introduces lattice vacancies and broadens the Li + diffusion channel; product: obtain Al / Ti co-doped LiCoO2 microspheres (particle size 3 - 5 μm).

[0039] Step 4: Gradiently coat the lithium cobaltate microspheres to obtain a lithium cobaltate composite cathode material.

[0040] The gradient-coated lithium cobalt oxide microspheres include an inner layer of Li3PO4 coating and an outer layer of carbon nanotube (CNT) coating (electronic conductor).

[0041] Method for inner layer Li3PO4 coating (ionic conductor): Chemical vapor deposition (CVD) + liquid-phase assistance; Immerse the calcined material in a 0.1M Li3PO4 precursor solution (LiOH + H3PO4), and disperse it by ultrasonic waves; Transfer it to a CVD furnace, introduce Ar gas at 250°C, and thermally decompose Li3PO4 and deposit it evenly; Thickness: ~10nm, coverage rate above 95%; Function: Inhibit direct contact between the electrolyte and lithium cobalt oxide, reduce HF corrosion.

[0042] Method for outer layer carbon nanotube (CNT) coating (electronic conductor): Catalytic chemical vapor deposition (CCVD); Mix the Li3PO4-coated microspheres with ferrocene (catalyst), and place them in a quartz tube; Introduce a C2H2 / Ar mixed gas (volume ratio 1:9), react at 600°C for 1h, and CNTs grow in-situ; Morphology: Form a three-dimensional intertwined network, thickness ~20nm; Function: Improve electronic conductivity (increase from 10 -4 S / cm to 10 -2 S / cm).

[0043] Key process control points

[0044] 1. Doping uniformity: Insufficient ball milling time will lead to local enrichment of Al / Ti, and the distribution needs to be verified by SEM-EDS mapping.

[0045] 2. Coating layer density: Too thick Li3PO4 coating will hinder Li + transport, which can be optimized by adjusting the CVD temperature and time.

[0046] 3. Calcination atmosphere: Oxygen atmosphere prevents Co 2+ from being generated, but it is necessary to avoid excessive oxygen partial pressure leading to Li volatilization.

[0047] Material characterization and performance

[0048] 1. Structure analysis:

[0049] XRD: After doping, the (003) peak shifts to a higher angle (the layer spacing shrinks, and the structure is more stable);

[0050] TEM: Clearly shows the double-layer coating interface (the inner layer of Li3PO4 is amorphous, and the outer layer of CNT is crystalline).

[0051] 2. Electrochemical performance:

[0052] The initial efficiency at 4.6V > 95%, and the capacity retention rate after 1000 cycles at 0.5C is 92%;

[0053] The 5C fast charging capacity reaches 80% of the theoretical value (less than 50% for traditional materials).

[0054] Industrial adaptability

[0055] 1. Equipment compatibility: Ball milling and CVD are both mature processes and can be directly connected to existing production lines.

[0056] 2. Cost control: Low-temperature calcination (<500 °C) reduces energy consumption, and the CNT dosage of less than 1 wt% saves costs.

[0057] As described above, it is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution and inventive concept of the present invention, makes equivalent substitutions or changes, and all should be covered within the protection scope of the present invention.

[0058] The preferred embodiments of the present invention disclosed above are only used to help explain the present invention. The preferred embodiments do not describe all the details in detail, nor do they limit the present invention to only the specific embodiments. Obviously, many modifications and changes can be made according to the content of this specification. This specification selects and specifically describes these embodiments to better explain the principle and practical application of the present invention, so that those skilled in the art in the relevant technical field can understand and utilize the present invention well. The present invention is only limited by the claims and their full scope and equivalents.

Claims

1. A lithium cobalt oxide composite cathode material, characterized in that, The lithium cobaltate composite cathode material is a lithium cobaltate microsphere with a double-layer coating structure. The inner layer of the double-layer coating structure is an ion conductor for inhibiting electrolyte corrosion, and the outer layer is an electron conductor. The lithium cobaltate microsphere is co-doped with Al 3+ +Ti 4+ to stabilize the layered structure, and Ti 3+ to widen the lithium ion diffusion channels. 4+ ​ 2. A preparation method of a lithium cobalt oxide composite cathode material, which is applied to the lithium cobalt oxide composite cathode material described in claim 1, and is characterized in that, The method steps are as follows: Step 1: Prepare lithium cobalt oxide precursor and dopant; Step 2: Perform ball milling and mixing treatment on the lithium cobalt oxide precursor and dopant, and mix to obtain the precursor; Step 3: Perform segmented calcination on the precursor to obtain lithium cobalt oxide microspheres; Step 4: Gradiently coat the lithium cobalt oxide microspheres to obtain a lithium cobalt oxide composite cathode material.

3. The preparation method of a lithium cobalt oxide composite cathode material according to claim 2, characterized in that, The lithium cobalt oxide precursor uses high-purity Li3PO4 and Co3O4, with a molar ratio of 1.05:1, and lithium excess compensates for high-temperature volatilization.

4. The preparation method of a lithium cobalt oxide composite cathode material according to claim 2, characterized in that, The dopants are Al2O3 nanopowder and TiO2 nanopowder. The particle size of the Al2O3 nanopowder is 50 nm, and the purity is ≥99.9%, which is used to provide Al 3+ , and the TiO2 nanopowder is anatase type, with a particle size of 30 nm and a purity of ≥99.5%, which is used to provide Ti 4+ , doping ratio: Al:Ti:Co = 1:1:98, and the total doping amount is 2%.

5. The preparation method of a lithium cobalt oxide composite cathode material according to claim 2, characterized in that, The segmented calcination includes a low-temperature pre-crystallization step and a medium-temperature doping and curing step (450 °C), and the equipment used for segmented calcination is a tube furnace; The heating program of the low-temperature pre-crystallization step: heat up to 300 °C at 5 °C / min and hold for 4 h; The heating program of the medium-temperature doping and curing step: continue to heat up to 450 °C (2 °C / min) and hold for 8 h.

6. The preparation method of a lithium cobalt oxide composite cathode material according to claim 2, characterized in that, The gradient coating of lithium cobalt oxide microspheres includes an inner layer Li3PO4 coating method and an outer layer carbon nanotube coating method; Inner layer Li3PO4 coating method: chemical vapor deposition (CVD) + liquid-phase assistance; immerse the calcined material in a 0.1 M Li3PO4 precursor solution (LiOH + H3PO4), and perform ultrasonic dispersion; transfer to a CVD furnace, and introduce Ar gas at 250 °C to thermally decompose Li3PO4 and uniformly deposit it; thickness: ~10 nm, coverage rate above 95%; Outer layer carbon nanotube coating method: catalytic chemical vapor deposition; mix the Li3PO4-coated microspheres with ferrocene and place them in a quartz tube; introduce a C2H2 / Ar mixed gas and react at 600 °C for 1 h to in-situ grow CNTs; morphology: form a three-dimensional intertwined network, thickness ~20 nm.