Lithium-deficient coated lithium cobalt oxide cathode material and preparation method thereof

Abstract

The application provides a lithium-deficient coated lithium cobaltate battery positive electrode material and a preparation method thereof. The material is a core-shell structure, which comprises a doped lithium cobaltate core material in the core-shell structure and a coating layer formed on the surface of the doped lithium cobaltate core material. 1‑a Mg a O2, wherein 0.001<=a<=0.005; the coating layer comprises Li x CoO2, yttrium oxide and lanthanum oxide; the content of the coating layer is 2%-6% of the lithium-deficient coated lithium cobaltate battery positive electrode material. The surface nano Co3O4 of the lithium-deficient coated lithium cobaltate battery positive electrode material reacts with excess Li to generate a lithium-deficient Li x CoO2 in a spinel structure, and the coating layer coats the lithium-deficient Li x CoO2 (x<1) and a composite metal oxide coating layer of yttrium oxide and lanthanum oxide, which has more stable mechanical properties and smaller volume change, inhibits the release of O atoms in the structure at high voltage, and at the same time, the coating layer reduces the direct contact of the material with the electrolyte, inhibits the side reaction and electrolyte corrosion, and significantly improves the capacity and cycle performance.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, specifically to a lithium cobalt oxide battery cathode material with a lithium-deficient coating layer and its preparation method. Background Technology

[0002] Lithium-ion batteries are among the most widely used energy storage devices. Compared to traditional lead-acid batteries, they offer higher energy density, longer cycle life, and are pollution-free and memory-effect-free during use, making them popular with consumers. Lithium cobalt oxide is primarily used in lithium-ion batteries for small portable electronic devices, such as mobile phones, laptops, smartwatches, and Bluetooth headsets.

[0003] Lithium cobalt oxide has a relatively low theoretical specific capacity, approximately 274 mAh / g, while the specific capacity in practical applications is generally around 140~160 mAh / g. As the requirements for battery energy density continue to increase, lithium cobalt oxide can only achieve this by continuously increasing the charge and discharge voltage to further improve the specific capacity. However, at higher voltages, lithium cobalt oxide is prone to structural changes and thermal runaway, resulting in a significant reduction in safety performance and cycle life. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the existing technology and provide a lithium-deficient coating layer for lithium cobalt oxide battery cathode material and its preparation method.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: a lithium-deficient coating layer for a lithium cobalt oxide battery cathode material, wherein the lithium-deficient coating layer for a lithium cobalt oxide battery cathode material has a core-shell structure, including a doped lithium cobalt oxide core material inside the core-shell structure and a coating layer formed on the surface of the doped lithium cobalt oxide core material;

[0006] The chemical formula of the doped lithium cobalt oxide core material is: LiCo 1-a Mg a O2, where 0.001≤a≤0.005;

[0007] The coating layer includes Li x CoO2, yttrium oxide, and lanthanum oxide;

[0008] The content of the coating layer is 2% to 6% of the lithium-deficient coating layer coating lithium cobalt oxide battery cathode material.

[0009] The lithium cobalt oxide cathode material described above, coated with a lithium-deficient coating layer, has a core-shell structure. This structure includes a doped lithium cobalt oxide core material within the core-shell structure and a coating layer formed on the surface of the doped lithium cobalt oxide core material. The lithium cobalt oxide is a single-crystal structure, and its surface nano-Co3O4 reacts with excess Li to form a spinel-structured lithium-deficient Li. xCoO2, or lanthanum oxide, possesses good thermal stability. By improving the crystal structure of the cathode material, its structural stability during charge and discharge processes is enhanced, thereby extending the battery's lifespan. Furthermore, lanthanum ions have a large ionic radius and strong redox reactivity, which can improve the material's energy density and ionic conductivity. Yttrium oxide exhibits good thermal and chemical stability, effectively preventing oxidation and corrosion of the material at high temperatures. It improves the electronic conductivity of the cathode material by reducing the work function, and its high dielectric constant can increase the battery's energy density. The coating layer encapsulates lithium-deficient Li... x The composite metal oxide coating of CoO2 (x<1), yttrium oxide, and lanthanum oxide works together to improve the crystal structure of the cathode material, resulting in better thermal and chemical stability, more stable mechanical properties, and smaller volume changes. It also suppresses the precipitation of O atoms in the structure under high voltage. At the same time, the coating reduces the direct contact between the material and the electrolyte, suppressing side reactions and electrolyte corrosion, and significantly improving capacity and cycle performance.

[0010] Preferably, the Li in the coating layer x The ratio of CoO2, yttrium oxide, and lanthanum oxide is 10:(0.5~2):(0.5~2).

[0011] Preferably, the coating layer comprises Li x CoO2, niobium oxide, yttrium oxide, and lanthanum oxide.

[0012] The inventors discovered through research that the coating layer encapsulates lithium-deficient Li x In the composite metal oxide coating layer of CoO2 (x<1) and niobium oxide, yttrium oxide, and lanthanum oxide, the lithium-deficient LixCoO2 (x<1) has a spinel structure, exhibits small volume changes during delithiation, and possesses better structural stability. It maintains the mechanical integrity of the core-shell cathode material structure during cycling. Furthermore, Li vacancies provide more ion transport channels, improving battery capacity and rate performance. Niobium oxide has a stable crystal structure and a unique lithium-ion intercalation mechanism (intercalation reaction), enabling rapid charge and discharge and improving rate performance; its volume expansion rate is less than 2%, significantly enhancing battery safety. Lanthanum oxide has good thermal stability; by improving the crystal structure of the cathode material, its structural stability during charge and discharge is enhanced, thereby extending battery life. Additionally, lanthanum ions have a large ionic radius and strong redox reactivity, which can improve the material's energy density and ionic conductivity. Yttrium oxide has good thermal and chemical stability, effectively preventing oxidation and corrosion at high temperatures. It improves the electronic conductivity of the cathode material by reducing the work function, and its high dielectric constant can increase the battery's energy density.

[0013] A coating layer combining lithium-deficient LixCoO2 (x<1) with a composite metal oxide is employed. Firstly, nano-Co3O4 fully reacts to absorb surface Li, forming a relatively stable coating layer with more Li ion channels. Then, the relatively stable crystal structure of the composite metal further enhances the material's thermal stability, while simultaneously improving ionic and electronic conductivity and energy density. The synergistic effect of the multi-layer coating enhances the surface structural and chemical stability of the cathode material, preventing decomposition, corrosion, or structural damage under high voltage, and improving the contact and compatibility between the cathode material and the electrolyte, thereby increasing the battery's cycle life and safety performance. Secondly, by increasing the oxygen vacancy concentration and surface activity in the cathode material, the electronic and ionic conductivity of the cathode material are improved, thus increasing the battery's capacity and rate performance. The improved ionic and electronic conductivity, reduced volume change, and more stable crystal structure, along with enhanced surface activity and stability, combined with the reduced direct contact between the material and the electrolyte, suppress side reactions and electrolyte corrosion, significantly improve capacity and cycle performance.

[0014] Preferably, the Li in the coating layer x The ratio of CoO2, niobium oxide, yttrium oxide and lanthanum oxide is 10:(0.5~2):(0.5~2):(0.5~2).

[0015] Preferably, the Li in the coating layer x The source material for CoO2 is nano-Co3O4.

[0016] Preferably, the content of the coating layer is 2.0% to 4.5% of the lithium-deficient coating layer coating the positive electrode material of the lithium cobalt oxide battery.

[0017] Preferably, the Li in the coating layer x The ratio of CoO2, niobium oxide, yttrium oxide and lanthanum oxide is 10: (0.8~1.2): (1.2~1.5): (1.0~1.5).

[0018] The inventors discovered through research that the coating layer encapsulates lithium-deficient Li x When the content of the composite metal oxide coating of CoO2 (x<1) and niobium oxide, yttrium oxide and lanthanum oxide meets the above requirements, it has better cycle performance.

[0019] This invention also provides a method for preparing the lithium cobalt oxide battery cathode material coated with any of the lithium-deficient coating layers described above, the method comprising the following steps:

[0020] (1) LiCo was obtained by mixing cobalt tetroxide, lithium carbonate and magnesium salt in a certain proportion and sintering at 950~1100℃ in an oxygen-containing atmosphere. 1-a Mg aO2 material particles;

[0021] (2) The LiCo obtained in step (1) 1-a Mg a O2 material particles are mixed with nano-Co3O4 and oxides of other materials forming the coating layer, and then sintered at 800~900℃ in an oxygen-containing atmosphere to obtain lithium-deficient coating layer coated lithium cobalt oxide battery cathode material.

[0022] The above-mentioned method for preparing lithium cobalt oxide battery cathode materials with lithium-deficient coating is simple and practical, and can be mass-produced. It provides a simple and short-time high-temperature sintering process for preparing high-voltage lithium cobalt oxide materials.

[0023] Preferably, in step (1), the particle size Dv50 of cobalt tetroxide is 9.5~11 μm, the Li / Co molar ratio of cobalt tetroxide to lithium carbonate is 1.05~1.07:1, and the lithium carbonate is a single crystal structure.

[0024] Preferably, in step (2), the LiCo obtained in step (1) 1-a Mg a The O2 material particles were controlled to have a Dv50 of 12~14μm for sintering in step (2).

[0025] Preferably, the sintering time in step (1) is 6 to 8 hours, and the sintering time in step (2) is 6 to 9 hours.

[0026] The beneficial effects of this invention are as follows: This invention provides a lithium-deficient coating layer for lithium cobalt oxide batteries and its preparation method. The lithium cobalt oxide cathode material of this invention has a core-shell structure, including a doped lithium cobalt oxide core material inside the core-shell structure and a coating layer formed on the surface of the doped lithium cobalt oxide core material. The lithium cobalt oxide has a single crystal structure, and its surface nano-Co3O4 reacts with excess Li to generate a spinel-structured lithium-deficient Li. x CoO2, coating layer encapsulating lithium-deficient Li x The composite metal oxide coating of CoO2 (x<1), yttrium oxide, and lanthanum oxide has more stable mechanical properties and smaller volume changes, suppresses the precipitation of O atoms in the structure under high voltage, and at the same time reduces the direct contact between the material and the electrolyte, suppresses side reactions and electrolyte corrosion, and significantly improves capacity and cycle performance. Attached Figure Description

[0027] Figure 1 This is a SEM image of the lithium cobalt oxide battery cathode material coated with a lithium-deficient coating layer according to an embodiment of the present invention.

[0028] Figure 2 This is a TEM image of the lithium cobalt oxide battery cathode material coated with a lithium-deficient coating layer according to an embodiment of the present invention. Detailed Implementation

[0029] To better illustrate the purpose, technical solution, and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments.

[0030] Example 1

[0031] As an embodiment of the present invention, a lithium-deficient coating layer coated lithium cobalt oxide battery cathode material is a core-shell structure, including a doped lithium cobalt oxide core material inside the core-shell structure and a coating layer formed on the surface of the doped lithium cobalt oxide core material.

[0032] The chemical formula of the doped lithium cobalt oxide core material is: LiCo 1-a Mg a O2, where a = 0.003;

[0033] The coating layer includes Li x CoO2, yttrium oxide, and lanthanum oxide;

[0034] The content of the coating layer is 3.0% of the lithium-deficient coating layer coating of the lithium cobalt oxide battery cathode material;

[0035] Li in the coating layer x The ratio of CoO2, yttrium oxide, and lanthanum oxide is 10:1.2:1.2.

[0036] The preparation method of the lithium cobalt oxide battery cathode material with a lithium-deficient coating layer in this embodiment includes the following steps:

[0037] (1) Cobalt tetroxide with a Dv50 of 10.5 μm, lithium carbonate, and magnesium salt were mixed in a certain proportion and sintered at 1050 °C in an oxygen-containing atmosphere for 7 hours to obtain LiCo. 1-a Mg a O2 material particles; Dv50 particle size of 13.63 μm obtained by air jet milling; Li / Co molar ratio of cobalt tetroxide to lithium carbonate is 1.05~1.07:1, and lithium carbonate is a single crystal structure;

[0038] (2) The LiCo obtained in step (1) 1-a Mg a O2 material particles were mixed with nano-Co3O4 and oxides of other materials forming the coating layer, and then sintered at 880°C in an oxygen-containing atmosphere for 8 hours to obtain lithium-deficient coating layer coated lithium cobalt oxide battery cathode material.

[0039] Example 2

[0040] As an embodiment of the present invention, this embodiment is a lithium-deficient coating layer for a lithium cobalt oxide battery cathode material. The only difference between this embodiment and Embodiment 1 is that the coating layer includes Li... xCoO2, yttrium oxide, and lanthanum oxide; Li in the coating layer x The ratio of CoO2, yttrium oxide, and lanthanum oxide is 10:0.8:1.5.

[0041] Example 3

[0042] As a lithium-deficient coating layer for lithium cobalt oxide battery cathode material according to an embodiment of the present invention, the only difference between this embodiment and Embodiment 1 is that the lithium-deficient coating layer includes Li x CoO2, niobium oxide, yttrium oxide, and lanthanum oxide; Li in the coating layer x The ratio of CoO2, niobium oxide, yttrium oxide, and lanthanum oxide is 10:0.8:1.2:1.5.

[0043] Example 4

[0044] As an embodiment of the present invention, the only difference between this embodiment and embodiment 3 is that the content of the coating layer is 2.0% of the lithium-deficient coating layer coated lithium cobalt oxide battery cathode material.

[0045] Example 5

[0046] As an embodiment of the present invention, the only difference between this embodiment and embodiment 3 is that the content of the coating layer is 2.5% of the lithium-deficient coating layer coated lithium cobalt oxide battery cathode material.

[0047] Example 6

[0048] As an embodiment of the present invention, the only difference between this embodiment and embodiment 3 is that the content of the coating layer is 4.5% of the lithium-deficient coating layer of the lithium cobalt oxide battery cathode material.

[0049] Example 7

[0050] As an embodiment of the present invention, the only difference between this embodiment and embodiment 3 is that the content of the coating layer is 5.5% of the lithium-deficient coating layer coated lithium cobalt oxide battery cathode material.

[0051] Example 8

[0052] As a lithium-deficient coating layer for lithium cobalt oxide battery cathode material according to an embodiment of the present invention, the only difference between this embodiment and Embodiment 3 is that the Li in the coating layer... x The ratio of CoO2, niobium oxide, yttrium oxide, and lanthanum oxide is 10:0.5:0.5:2.0.

[0053] Example 9

[0054] As a lithium-deficient coating layer for lithium cobalt oxide battery cathode material according to an embodiment of the present invention, the only difference between this embodiment and Embodiment 3 is that the Li in the coating layer... x The ratio of CoO2, niobium oxide, yttrium oxide, and lanthanum oxide is 10:0.5:0.5:0.5.

[0055] Example 10

[0056] As a lithium-deficient coating layer for lithium cobalt oxide battery cathode material according to an embodiment of the present invention, the only difference between this embodiment and Embodiment 3 is that the Li in the coating layer... x The ratio of CoO2, niobium oxide, yttrium oxide, and lanthanum oxide is 10:2.0:0.5:0.5.

[0057] Example 11

[0058] As a lithium-deficient coating layer for lithium cobalt oxide battery cathode material according to an embodiment of the present invention, the only difference between this embodiment and Embodiment 3 is that the Li in the coating layer... x The ratio of CoO2, niobium oxide, yttrium oxide, and lanthanum oxide is 10:1.0:1.2:1.0.

[0059] Example 12

[0060] As a lithium-deficient coating layer for lithium cobalt oxide battery cathode material according to an embodiment of the present invention, the only difference between this embodiment and Embodiment 3 is that the Li in the coating layer... x The ratio of CoO2, niobium oxide, yttrium oxide, and lanthanum oxide is 10:1.2:1.2:1.5.

[0061] Example 13

[0062] As a lithium-deficient coating layer for lithium cobalt oxide battery cathode material according to an embodiment of the present invention, the only difference between this embodiment and Embodiment 3 is that the Li in the coating layer... x The ratio of CoO2, niobium oxide, yttrium oxide, and lanthanum oxide is 10:0.8:1.2:1.0.

[0063] Comparative Example 1

[0064] As a comparative example of the present invention, a lithium-deficient coating layer for a lithium cobalt oxide battery cathode material differs from Example 3 only in that:

[0065] The coating layer includes Li x CoO2, yttrium oxide.

[0066] Comparative Example 2

[0067] As a comparative example of the present invention, a lithium-deficient coating layer for a lithium cobalt oxide battery cathode material differs from Example 3 only in that:

[0068] The coating layer includes Li x CoO2, niobium oxide.

[0069] Comparative Example 3

[0070] As a comparative example of the present invention, a lithium-deficient coating layer for a lithium cobalt oxide battery cathode material differs from Example 3 only in that:

[0071] The coating layer includes Li x CoO2, lanthanum oxide.

[0072] Comparative Example 4

[0073] As a comparative example of the present invention, a lithium-deficient coating layer for a lithium cobalt oxide battery cathode material differs from Example 3 only in that:

[0074] The coating layer includes niobium oxide, lanthanum oxide, and yttrium oxide.

[0075] Experimental methods

[0076] I. Material Characterization

[0077] (a) Types of covering layers

[0078] ICP tests were performed on samples from Examples 1, 3, and Comparative Examples 1-4. The test results are shown in Table 1 below:

[0079] Table 1. Main elemental contents of lithium cobalt oxide battery cathode materials with lithium-deficient coating.

[0080]

[0081] Figure 1 The image shown is a SEM image of Example 3, illustrating that the core material has a single-crystal morphology. Figure 2 The image shown is a high-magnification transmission electron microscope (TEM) image from Example 3 of this invention. The results indicate that a dense coating layer has formed on the surface of the core structure. Table 1 shows the elemental analysis of the main elements present in the lithium-deficient coating layer covering the cathode material of the lithium cobalt oxide battery. Figure 2 It can be seen that the samples of Example 1, Example 3, and Comparative Examples 1-4 formed different types of coating layers.

[0082] II. Material Performance Testing

[0083] The positive electrode material, conductive agent acetylene black, and binder polyvinylidene fluoride were weighed in a mass ratio of 90%:5%:5%. An appropriate amount of N-methylpyrrolidone was added and the mixture was stirred into a slurry by centrifugation. The slurry was then uniformly coated onto a 20 μm thick aluminum foil to form a 150 μm thick electrode sheet. After drying the electrode sheet at 150℃ for 8 hours, it was pressed to a thickness of 80 μm with a pressure of 5 MPa and then cut into circular positive electrode sheets with a diameter of Φ = 13.5 mm.

[0084] Using a prepared circular positive electrode as the positive electrode and a lithium metal sheet as the negative electrode, and 1 mol / L LiPF6 / EC+DMC (volume ratio 1:1, produced in Zhangjiagang, battery grade) as the electrolyte, and a Celgard 2400 membrane as the separator, the cells were assembled and sealed into CR2032 coin cell half-cells in a vacuum glove box filled with dry argon gas. The battery's electrical performance was tested at voltages of 3.0–4.48 V.

[0085] The experimental results are shown in Table 2.

[0086]

[0087] As shown in Table 2, the lithium cobalt oxide cathode material coated with the lithium-deficient coating layer of the present invention has a core-shell structure, including a doped lithium cobalt oxide core material inside the core-shell structure and a coating layer formed on the surface of the doped lithium cobalt oxide core material. The lithium cobalt oxide has a single crystal structure, and its surface nano-Co3O4 reacts with excess Li to generate a spinel-structured lithium-deficient Li. x CoO2, coating layer encapsulating lithium-deficient Li x The composite metal oxide coating of CoO2 (x<1), yttrium oxide, and lanthanum oxide can enhance the surface structural stability and chemical stability of the cathode material, improve the contact and compatibility between the cathode material and the electrolyte, thereby improving the cycle life and safety performance of the battery. On the other hand, it can improve the electronic conductivity and ionic conductivity of the cathode material, thereby improving the capacity and rate performance of the battery.

[0088] Meanwhile, the coating layer encapsulates lithium-deficient Li. x The composite metal oxide coating of CoO2 (x<1) with niobium oxide, yttrium oxide and lanthanum oxide, in addition to the above performance advantages, further improves rate performance through the unique lithium-ion intercalation mechanism of niobium oxide.

[0089] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A lithium-deficient coating layer for lithium cobalt oxide battery cathode material, characterized in that, The lithium-deficient coating layer covers the lithium cobalt oxide battery cathode material with a core-shell structure, including a doped lithium cobalt oxide core material inside the core-shell structure and a coating layer formed on the surface of the doped lithium cobalt oxide core material. The chemical formula of the doped lithium cobalt oxide core material is: LiCo 1-a Mg a O2, where 0.001≤a≤0.005; The coating layer includes Li x CoO2, niobium oxide, yttrium oxide, and lanthanum oxide, where x < 1; Li in the coating layer x The ratio of CoO2, niobium oxide, yttrium oxide, and lanthanum oxide is 10:(0.5~2):(0.5~2):(0.5~2); The content of the coating layer is 2% to 6% of the lithium-deficient coating layer coated on the positive electrode material of the lithium cobalt oxide battery. The preparation method of the lithium-deficient coating layer-coated lithium cobalt oxide battery cathode material includes the following steps: (1) LiCo was obtained by mixing cobalt tetroxide, lithium carbonate and magnesium salt in a certain proportion and sintering at 950~1100℃ in an oxygen-containing atmosphere. 1-a Mg a O2 material particles; (2) The LiCo obtained in step (1) 1-a Mg a O2 material particles are mixed with nano-Co3O4 and oxides of other materials forming the coating layer, and then sintered at 800~900℃ in an oxygen-containing atmosphere to obtain lithium-deficient coating layer coated lithium cobalt oxide battery cathode material.

2. The lithium-deficient coating layer for lithium cobalt oxide battery cathode material according to claim 1, characterized in that, The content of the coating layer is 2.0% to 4.5% of the lithium-deficient coating layer coating of the lithium cobalt oxide battery cathode material.

3. The lithium-deficient coating layer for lithium cobalt oxide battery cathode material according to claim 1, characterized in that, Li in the coating layer x The ratio of CoO2, niobium oxide, yttrium oxide and lanthanum oxide is 10: (0.8~1.2): (1.2~1.5): (1.0~1.5).

4. The method for preparing the lithium cobalt oxide battery cathode material coated with a lithium-deficient coating layer as described in any one of claims 1 to 3, characterized in that, The method includes the following steps: (1) LiCo was obtained by mixing cobalt tetroxide, lithium carbonate and magnesium salt in a certain proportion and sintering at 950~1100℃ in an oxygen-containing atmosphere. 1-a Mg a O2 material particles; (2) The LiCo obtained in step (1) 1-a Mg a O2 material particles are mixed with nano-Co3O4 and oxides of other materials forming the coating layer, and then sintered at 800~900℃ in an oxygen-containing atmosphere to obtain lithium-deficient coating layer coated lithium cobalt oxide battery cathode material.

5. The method for preparing the lithium-deficient coating layer of the lithium cobalt oxide battery cathode material according to claim 4, characterized in that, In step (1), the particle size Dv50 of cobalt tetroxide is 9.5~11 μm, the Li / Co molar ratio of cobalt tetroxide to lithium carbonate is 1.05~1.07:1, and the lithium carbonate is a single crystal structure.

6. The method for preparing the lithium-deficient coating layer of the lithium cobalt oxide battery cathode material according to claim 4, characterized in that, In step (2), the LiCo obtained in step (1) 1-a Mg a The O2 material particles were controlled to have a Dv50 of 12~14μm for sintering in step (2).

7. The method for preparing the lithium-deficient coating layer of the lithium cobalt oxide battery cathode material according to claim 4, characterized in that, The sintering time for step (1) is 6 to 8 hours, and the sintering time for step (2) is 6 to 9 hours.

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