A lithium cobalt oxide positive electrode material and its preparation method and application

Abstract

The present invention provides a lithium cobalt oxide positive electrode material and its preparation method and application. The preparation method comprises the following steps: (1) mixing a cobalt salt and a transition metal oxide, and subjecting the mixture to a primary calcination treatment to obtain a modified single-crystal cobalt oxide precursor; (2) mixing the modified single-crystal cobalt oxide precursor obtained in step (1) with a first lithium source, subjecting the mixture to a secondary calcination treatment, adding a second lithium source, and subjecting the mixture to a third calcination treatment to obtain the lithium cobalt oxide positive electrode material. The present invention prepares a doped single-crystal cobalt oxide precursor by thermally decomposing a cobalt salt, which helps improve the electrochemical properties of lithium cobalt oxide. Since lithium cobalt oxide rapidly degrades at higher charging voltages, doping with trace elements can effectively inhibit the structural collapse of the material caused by deep discharge, and can be used to stabilize the structure of the lithium cobalt oxide positive electrode material, thereby increasing the charging voltage of lithium cobalt oxide and improving the cycle life of high-voltage lithium cobalt oxide batteries.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion batteries and relates to a lithium cobalt oxide positive electrode material and a preparation method and application thereof. Background Art

[0002] Due to the rapid upgrade requirements of portable electronics, electric vehicles, and grid energy storage, high-energy-density lithium-ion batteries will be an important development direction in the energy storage field. Currently, the energy density of lithium-ion batteries is mainly limited by the cathode material. To further improve the energy density of batteries, it is crucial to develop high-voltage, high-capacity cathode materials. Among the various cathode materials, lithium cobalt oxide cathode materials have attracted widespread attention due to their high theoretical specific capacity, extremely high compaction density, and good rate performance. As a result, lithium cobalt oxide occupies a large share of the 3C and other consumer electronics markets.

[0003] However, on the one hand, with the increasing demand for 3C products, the price of cobalt is also rising. On the other hand, although increasing the charge cut-off voltage can further increase the capacity of lithium cobalt oxide and obtain more lithium ions, when the charge cut-off voltage is ≥4.5V, lithium cobalt oxide will face the huge challenges of structural collapse and harmful cathode / electrolyte interface reactions. To address this problem, researchers have also developed various strategies, such as electrolyte additives, doping during lithium cobalt oxide synthesis, and coating of lithium cobalt oxide, to stabilize the material structure and thus suppress the irreversible phase transition of lithium cobalt oxide at high voltage. However, although researchers have used various means to improve the electrochemical performance of lithium cobalt oxide as a positive electrode material, irreversible phase transition and interface instability of lithium cobalt oxide at high voltage still occur. In addition, the treatment methods for lithium cobalt oxide modification are complex and costly, and the high cost of lithium cobalt oxide material synthesis has not been solved. Therefore, it is particularly important to reduce the cost of lithium cobalt oxide by controlling the synthesis of precursors while synthesizing positive electrode materials with high electrochemical performance.

[0004] CN108110248A discloses a lithium cobalt oxide lithium ion battery positive electrode material, the positive electrode material matrix chemical formula is Li x Co 1-y M y O2, where 0.95≤x≤1.08, 0.01≤y≤0.05. The surface of the positive electrode material has an inner and outer coating structure, the inner coating structure being a Li2ZrO3 coating layer and the outer coating structure being a carbon nanotube coating layer. The mass of the Li2ZrO3 is 0.1%-5% of the mass of the lithium cobalt oxide matrix, and the mass of the carbon nanotubes is 0.1%-1% of the mass of the lithium cobalt oxide matrix. The preparation method of the lithium cobalt oxide battery positive electrode material is complex and costly.

[0005] CN113224386A discloses a lithium cobalt oxide battery electrolyte additive combination product, comprising a triazine-containing compound, a negative electrode reducing agent, a fluorinated solvent, a phosphate ester, and an auxiliary lithium salt. The triazine-containing compound is used as an electrolyte additive to isolate the lithium cobalt oxide from the electrolyte, thereby inhibiting electrolyte decomposition. However, with increased cycling, the lithium cobalt oxide undergoes irreversible phase changes, leading to the dissolution of large amounts of transition metals, which significantly reduces battery performance.

[0006] The above schemes have the problem that the preparation method is complicated or the lithium cobalt oxide undergoes irreversible phase change after the battery is prepared, resulting in the dissolution of a large amount of transition metals, which greatly reduces the battery performance. Therefore, it is very necessary to develop a lithium cobalt oxide positive electrode material with a simple preparation method that can avoid the irreversible phase change of lithium cobalt oxide, inhibit the dissolution of a large amount of transition metals, and thus improve the battery performance. Summary of the Invention

[0007] The purpose of the present invention is to provide a lithium cobalt oxide positive electrode material and its preparation method and application. The present invention prepares a doped single crystal cobalt tetroxide precursor by thermal decomposition of cobalt salt, which helps to improve the electrochemical performance of lithium cobalt oxide. Since lithium cobalt oxide will undergo irreversible phase change at a higher charging voltage, and the dissolution of transition metals exacerbates the oxidative decomposition of the electrolyte, all of which will lead to poor battery performance. Doping with trace elements can effectively inhibit the structural collapse of the material caused by deep discharge, and can be used to stabilize the structure of the lithium cobalt oxide positive electrode material, increase the charging voltage of lithium cobalt oxide, thereby obtaining higher energy and improving the cycle life of high-voltage lithium cobalt oxide batteries.

[0008] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0009] In a first aspect, the present invention provides a method for preparing a lithium cobalt oxide positive electrode material, the preparation method comprising the following steps:

[0010] (1) mixing a cobalt salt and a transition metal oxide, and subjecting the mixture to a calcination treatment to obtain a modified single crystal cobalt trioxide precursor;

[0011] (2) The modified cobalt trioxide precursor obtained in step (1) is mixed with a first lithium source, and after a second calcination treatment, a second lithium source is added, and the lithium cobalt oxide positive electrode material is obtained after a third calcination treatment.

[0012] The present invention adopts low-cost cobalt salts and transition metal oxides in the process of preparing the modified single-crystal cobalt tetroxide precursor to prepare the Al-doped single-crystal cobalt tetroxide precursor, which not only reduces the cost of raw materials but also achieves a good doping effect, so that the synthesized lithium cobalt oxide has better suppression of the occurrence of irreversible phase change at high voltage, and the synthesized dense lithium cobalt oxide has a better crystal structure and a cleaner surface with fewer cracks, which not only improves the reversibility of lithium cobalt oxide in long cycles, but also reduces transition metal dissolution, reduces interface side reactions, and improves interface stability.

[0013] Preferably, the cobalt salt in step (1) is a cobalt-containing sulfide.

[0014] Preferably, the cobalt salt includes any one of cobalt sulfate, cobalt sulfate heptahydrate, cobalt oxalate, cobalt carbonate or cobaltous sulfate, or a combination of at least two thereof.

[0015] Preferably, the transition metal oxide in step (1) comprises any one of manganese oxide, calcium oxide, iron oxide, aluminum oxide, magnesium oxide, titanium oxide or zinc oxide, or a combination of at least two thereof.

[0016] Preferably, the mass ratio of the cobalt salt to the transition metal oxide in step (1) is 1:(0.005-0.010), for example: 1:0.005, 1:0.006, 1:0.008 or 1:0.010, etc.

[0017] Preferably, the mixing method comprises ball milling.

[0018] Preferably, the ball milling time is 10 to 120 min, for example, 10 min, 20 min, 50 min, 80 min or 120 min, etc., preferably 15 to 40 min.

[0019] Preferably, the temperature of the primary calcination in step (1) is 800-950°C, for example, 800°C, 850°C, 880°C, 900°C or 950°C.

[0020] Preferably, the primary calcination time is 4 to 10 hours, for example, 4 hours, 5 hours, 6 hours, 8 hours or 10 hours, etc., preferably 5 to 7 hours.

[0021] Preferably, in step (2), the first lithium source and the second lithium source independently comprise tetralithium citrate, lithium nitrate, lithium carbonate and / or lithium hydroxide.

[0022] Preferably, the mass ratio of the first lithium source to the second lithium source is 1:(0.005-0.05), for example: 1:0.005, 1:0.008, 1:0.01, 1:0.02 or 1:0.05, etc.

[0023] Preferably, the molar ratio of the cobalt element in the modified cobalt trioxide precursor to the lithium element in the first lithium source is 1:(1-1.1), for example, 1:1, 1:1.02, 1:1.05, 1:1.08 or 1:1.1.

[0024] Preferably, grinding treatment is performed before the secondary calcination treatment in step (2).

[0025] Preferably, the grinding treatment time is 0.1 to 2 hours, for example, 0.1 hour, 0.4 hours, 0.1 hour, 1.5 hours or 2 hours, etc., preferably 0.2 to 1 hour.

[0026] Preferably, the temperature of the secondary calcination treatment is 700-900°C, for example, 700°C, 720°C, 830°C, 850°C or 900°C, and preferably 800-870°C.

[0027] Preferably, the secondary calcination time is 5 to 12 hours, for example, 5 hours, 6 hours, 8 hours, 10 hours or 12 hours, etc., preferably 6 to 10 hours.

[0028] Preferably, the temperature of the three calcination treatments in step (2) is 800-950°C, for example, 800°C, 850°C, 900°C, 920°C or 950°C, etc., preferably 880-920°C.

[0029] Preferably, the time for the three calcination treatments is 8 to 15 hours, for example, 8 hours, 9 hours, 10 hours, 11 hours or 15 hours, etc., preferably 8 to 12 hours.

[0030] In a second aspect, the present invention provides a lithium cobalt oxide positive electrode material, which is prepared by the method described in the first aspect.

[0031] In a third aspect, the present invention provides a lithium cobalt oxide positive electrode, wherein the lithium cobalt oxide positive electrode comprises the lithium cobalt oxide positive electrode material as described in the second aspect.

[0032] In a fourth aspect, the present invention provides a lithium cobalt oxide battery, comprising the lithium cobalt oxide positive electrode as described in the third aspect.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] (1) The method of the present invention has low raw material cost and simple process, and the synthesized dense lithium cobalt oxide has a better crystal structure, a cleaner surface and fewer cracks. It not only improves the reversibility of lithium cobalt oxide in long cycles, but also reduces transition metal dissolution, reduces interfacial side reactions, and improves interface stability.

[0035] (2) The present invention uses relatively low-cost cobalt salts and transition metal oxides as raw materials to prepare the modified cobalt tetroxide precursor. The processing method is also simple, and the generated tail gas can be used for the production of sulfuric acid, further reducing production costs.

[0036] (3) The lithium cobalt oxide synthesized in the present invention has excellent electrochemical properties. The lithium cobalt oxide positive electrode material of the present invention has a capacity retention rate of up to 80.12% after 200 cycles at a high cut-off voltage of 4.5 V and a rate of 0.5 C. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 This is an SEM image of the lithium cobalt oxide positive electrode material described in Example 1 of the present invention.

[0038] Figure 2 This is an enlarged SEM image of the lithium cobalt oxide positive electrode material described in Example 1 of the present invention.

[0039] Figure 3 This is an SEM image of the lithium cobalt oxide positive electrode material described in Comparative Example 3.

[0040] Figure 4 This is an enlarged SEM image of the lithium cobalt oxide positive electrode material described in Comparative Example 3.

[0041] Figure 5 3 is a comparison chart of the EIS of the lithium cobalt oxide positive electrode materials described in Example 1 and Comparative Examples 1-3 after cycling.

[0042] Figure 6 It is a comparison chart of the cycle performance of batteries made from the lithium cobalt oxide positive electrode materials described in Example 1 and Comparative Examples 1-3.

[0043] Figure 7 This is a comparison chart of the rate performance of batteries made with the lithium cobalt oxide positive electrode materials described in Example 1 and Comparative Examples 1-3. DETAILED DESCRIPTION

[0044] The technical solution of the present invention is further described below by way of specific embodiments. It should be understood by those skilled in the art that the embodiments are merely to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0045] Example 1

[0046] This embodiment provides a lithium cobalt oxide positive electrode material, and the preparation method of the lithium cobalt oxide positive electrode material is as follows:

[0047] 0.1285 g of commercially available alumina powder and 45 g of cobalt sulfate heptahydrate were ball-milled and mixed evenly. After calcining at 890° C. in a tube furnace for 6 h, the product was taken out, and cobalt trioxide and lithium carbonate were evenly mixed according to the stoichiometric ratio. The mixture was calcined at 850° C. in a muffle furnace for 6 h, and 1 wt% of lithium carbonate was added. The mixture was calcined at 900° C. in a muffle furnace for 10 h to obtain the lithium cobalt oxide positive electrode material.

[0048] The SEM image of the lithium cobalt oxide positive electrode material is as follows Figure 1-2 shown.

[0049] Comparative Example 1

[0050] The only difference between this comparative example and Example 1 is that no alumina is added, and other conditions and parameters are exactly the same as those in Example 1.

[0051] Comparative Example 2

[0052] The only difference between this comparative example and Example 1 is that no aluminum oxide is added, and commercially available cobalt trioxide is directly used as a precursor to prepare the lithium cobalt oxide positive electrode material. Other conditions and parameters are exactly the same as those in Example 1.

[0053] Comparative Example 3

[0054] The only difference between this comparative example and Example 1 is that commercially available cobalt trioxide is directly used as a precursor to prepare the lithium cobalt oxide positive electrode material, and an amount of aluminum oxide equal to that in Example 1 is added during the sintering process. Other conditions and parameters are exactly the same as those in Example 1.

[0055] The SEM image of the prepared lithium cobalt oxide positive electrode material is as follows Figure 3-4 shown.

[0056] Performance testing:

[0057] The lithium cobalt oxide positive electrode materials obtained in Example 1 and Comparative Examples 1-3 were respectively mixed with the conductive agent AB, the binder PVDF, and the solvent NMP and evenly coated on a 15 μm aluminum foil. The mixture was vacuum-dried at 85°C for 12 h. The dried positive electrode sheet was punched into a circular electrode sheet with a diameter of 12 mm using a sheet punching machine. The treated lithium cobalt oxide positive electrode sheet and the electrolyte system were used to assemble a 2025 button battery with a sandwich structure for graphite (full battery) or lithium metal positive electrode (half battery) using a Celgard PP separator. The battery was subjected to performance testing. The cycle performance comparison of the battery is shown in the figure below. Figure 6 As shown by Figure 6 It can be seen that the lithium cobalt oxide positive electrode material described in Example 1 has a capacity retention rate of 80.12% after 200 cycles at a high cut-off voltage of 4.5V and a rate of 0.5C. The rate performance comparison of the battery is shown in the figure below. Figure 7 shown.

[0058] By comparing Example 1 and Comparative Example 1, it can be seen that the present invention can effectively inhibit the structural collapse of the material caused by deep discharge by doping a trace amount of transition metal oxide in the process of preparing the cobalt trioxide precursor, and can be used to stabilize the structure of the lithium cobalt oxide positive electrode material, thereby increasing the charging voltage of lithium cobalt oxide and improving the cycle life of high-voltage lithium cobalt oxide batteries.

[0059] From the comparison between Example 1 and Comparative Example 2, it can be seen that the cost of commercial cobalt tetroxide is relatively high, and the price and cost of the selected modification materials are also relatively high. The modification method is generally costly and requires relatively expensive experimental equipment and demanding experimental conditions. The present invention uses lower-cost cobalt salts and transition metal oxides, the processing method is also quite simple, and the performance of the obtained lithium cobalt oxide positive electrode material is significantly improved. At the same time, the tail gas can be used for the production of sulfuric acid to further reduce production costs.

[0060] By comparison between Example 1 and Comparative Example 3, it can be seen that when commercial cobalt oxide is used to prepare lithium cobaltate positive electrode material, even after adding transition metal oxide, the performance of the obtained lithium cobaltate positive electrode material is still inferior to the lithium cobaltate positive electrode material prepared by the method described in the present application, because the doped cobalt oxide precursor prepared by the method of the present invention is single crystalline, and the single crystalline cobalt oxide precursor helps to improve the electrochemical properties of lithium cobaltate.

[0061] Depend on Figure 1-2 and Figure 3-4 By comparison, it can be seen that the lithium cobalt oxide positive electrode material prepared by the method of the present invention has a better layered structure, a more uniform particle size, a cleaner surface, fewer microcracks, and is more dense.

[0062] The EIS comparison diagrams of the lithium cobalt oxide positive electrode materials after cycling in Example 1, Comparative Example 1, Comparative Example 2 and Comparative Example 3 are shown in FIG. Figure 5 As shown by Figure 5 It can be seen that the lithium cobalt oxide of the present invention has better kinetic properties, and the formed CEI is thinner, which is more conducive to electrochemical performance.

[0063] The applicant declares that the above is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the scope of protection and disclosure of the present invention.

Claims

1. A method for preparing a lithium cobalt oxide positive electrode material, characterized in that: The preparation method comprises the following steps: (1) mixing a cobalt salt and a transition metal oxide, and subjecting the mixture to a calcination treatment to obtain a modified single crystal cobalt trioxide precursor; (2) mixing the modified single crystal cobalt trioxide precursor obtained in step (1) with a first lithium source, adding a second lithium source after a second calcination treatment, and performing a third calcination treatment to obtain the lithium cobalt oxide positive electrode material; The molar ratio of the cobalt element in the modified single crystal cobalt trioxide precursor to the lithium element in the first lithium source is 1:(1-1.1); The mass ratio of the first lithium source to the second lithium source is 1:(0.005-0.05); The cobalt salt in step (1) is any one of cobalt sulfate, cobalt sulfate heptahydrate or cobaltous sulfate, or a combination of at least two thereof; The temperature of the first calcination in step (1) is 800° C. to 950° C.; and the time of the first calcination is 4 to 10 hours.

2. The preparation method according to claim 1, wherein The transition metal oxide in step (1) includes any one of manganese oxide, zirconium oxide, iron oxide, aluminum oxide, magnesium oxide, titanium oxide or zinc oxide, or a combination of at least two thereof.

3. The preparation method according to claim 1, wherein The mass ratio of the cobalt salt to the transition metal oxide in step (1) is 1:(0.005-0.010).

4. The preparation method according to claim 1, wherein The mixing method includes ball milling.

5. The preparation method according to claim 4, wherein The ball milling time is 10 to 120 minutes.

6. The preparation method according to claim 5, wherein The ball milling time is 15 to 40 minutes.

7. The preparation method according to claim 1, wherein The time of the first calcination is 5 to 7 hours.

8. The preparation method according to claim 1, wherein In step (2), the first lithium source and the second lithium source independently comprise lithium nitrate, tetralithium citrate, lithium carbonate and / or lithium hydroxide.

9. The preparation method according to claim 1, wherein The grinding treatment is performed before the secondary calcination treatment in step (2).

10. The preparation method according to claim 9, characterized in that The grinding time is 0.1 to 2 hours.

11. The preparation method according to claim 10, characterized in that The grinding treatment time is 0.2 to 1 hour.

12. The preparation method according to claim 1, wherein The temperature of the secondary calcination treatment is 700-900°C.

13. The preparation method according to claim 1, wherein The temperature of the secondary calcination treatment is 800-870°C.

14. The preparation method according to claim 1, wherein The secondary calcination time is 5 to 12 hours.

15. The preparation method according to claim 14, wherein The secondary calcination time is 6 to 10 hours.

16. The preparation method according to claim 1, wherein The temperature of the three calcination treatments in step (2) is 800-950°C.

17. The preparation method according to claim 16, wherein The temperature of the three calcination treatments is 880-920°C.

18. The preparation method according to claim 1, wherein The time of the three calcination treatments is 8 to 15 hours.

19. The preparation method according to claim 18, characterized in that The time of the three calcination treatments is 8 to 12 hours.

20. A lithium cobalt oxide positive electrode material, characterized in that: The lithium cobalt oxide positive electrode material is prepared by the method according to any one of claims 1 to 19.

21. A lithium cobalt oxide positive electrode, characterized in that The lithium cobalt oxide positive electrode comprises the lithium cobalt oxide positive electrode material according to claim 20.

22. A lithium cobalt oxide battery, characterized in that: The lithium cobalt oxide battery comprises the lithium cobalt oxide positive electrode as claimed in claim 21.

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