High-temperature-resistant lithium cobalt oxide positive electrode material as well as preparation method and application thereof

Abstract

The invention relates to the technical field of batteries, in particular to a high-temperature-resistant lithium cobalt oxide positive electrode material and a preparation method and application thereof.The high-temperature-resistant lithium cobalt oxide positive electrode material comprises a lithium cobalt oxide matrix and a coating layer coating the surface of the lithium cobalt oxide matrix, the lithium cobalt oxide matrix is doped with Mg, Ti and La, and the coating layer is a fast ion coating layer of a Li-Gd-Ti-O4 spinel phase. Bulk phase doping is carried out through a high-temperature solid-phase method, Mg, Ti and La are doped in a lithium cobalt oxide matrix, and the lattice structure thermal stability of lithium cobalt oxide under high voltage (4.4 V) is improved; a fast ion coating layer of a Li-Gd-Ti-O4 spinel phase is formed on the surface of a lithium cobalt oxide matrix by adopting a solid phase method, and the comprehensive performance of the lithium cobalt oxide positive electrode material is improved through multiple mechanisms such as the lattice stabilization effect of rare earth ions, the interface barrier effect of composite oxide and lithium ion conductivity regulation and control; particularly, the capacity, the cycling stability, the thermal stability, the high-voltage tolerance and the like are realized.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to a high-temperature resistant lithium cobalt oxide positive electrode material, a preparation method thereof, and applications thereof. Background Art

[0002] Lithium cobalt oxide, a commonly used cathode material for lithium-ion batteries, is widely used in various portable electronic devices such as laptops, mobile phones, and tablets due to its high volume-to-energy density. With the promotion of 5G and the trend towards lighter and thinner portable electronic devices, the market has placed higher demands on battery energy density. Increasing the charging voltage of lithium cobalt oxide can provide higher specific capacity and energy density.

[0003] However, at high cut-off voltages, lithium cobalt oxide faces the following problems: (1) Irreversible evolution of the bulk structure: H1-3 phase transition occurs, that is, the layered structure transforms to other phases, destroying the lattice regularity, affecting the insertion / extraction channels of lithium ions, and reducing the battery cycle stability; (2) Interface deterioration problem: At high temperatures, the surface structure collapses into a rock salt phase, blocking the transmission of lithium ions, and the electrolyte decomposes to form an unstable CEI film, which hinders conduction and forms a vicious cycle. Especially when operating at higher temperatures (such as 45°C), the above-mentioned interface problems become more serious.

[0004] In order to solve the above problems, researchers have modified lithium cobalt oxide through surface coating and bulk doping to improve its stability at high voltage and high temperature. Surface coating technology is one of the effective modification methods. It stabilizes the morphology and crystal structure of the material by changing the physical and chemical state of the lithium cobalt oxide surface. However, there is a clear phase interface between the traditional coating layer and the lithium cobalt oxide bulk material. During charging and discharging, the interface is prone to stress and strain accumulation and cracking, which poses a hidden danger of sudden deterioration of battery performance. In addition, the conductivity of the coating layer is generally poor. If it is too thick, it will affect the conductivity of the material and hinder the conduction of lithium ions and electrons. For example: when lithium cobalt oxide is coated with conventional oxides, during high voltage cycling, the interface will crack due to stress, the internal resistance of the battery will rise sharply, and the capacity will decay rapidly. In addition, most coating materials are electrochemically inactive, and too high a coating amount will significantly reduce the discharge capacity of lithium cobalt oxide. Summary of the Invention

[0005] The purpose of the present invention is to provide a high-temperature resistant lithium cobalt oxide positive electrode material and its preparation method and application, aiming to solve the problem that the current lithium cobalt oxide positive electrode material has poor stability under high voltage and high temperature and is difficult to achieve both high capacity and cycle stability.

[0006] In order to achieve the above-mentioned objectives, the present invention adopts the following technical solutions: In the first aspect, the present invention proposes a high-temperature resistant lithium cobalt oxide positive electrode material, comprising a lithium cobalt oxide matrix and a coating layer coated on the surface of the lithium cobalt oxide matrix, the lithium cobalt oxide matrix is ​​doped with Mg, Ti and La, and the coating layer is a fast ion coating layer of Li-Gd-Ti-O4 spinel phase.

[0007] After a large number of experiments, the inventors found that doping Mg, Ti and La into the lithium cobalt oxide matrix can improve the thermal stability of the lattice structure of lithium cobalt oxide at high voltage (4.4V), and form a fast ion coating layer of Li-Gd-Ti-O4 spinel phase on the surface of the lithium cobalt oxide matrix. The comprehensive performance of lithium cobalt oxide, especially capacity, cycle stability, thermal stability and high voltage tolerance, can be improved through multiple mechanisms such as the lattice stabilization of rare earth ions, the interface barrier effect of composite oxides and the regulation of lithium ion conductivity, ultimately obtaining a high-temperature resistant lithium cobalt oxide positive electrode material.

[0008] Specifically, La 3+ The ionic radius is about 1.03Å, Gd 3+ The ionic radius is about 0.94Å, which is similar to the dopants in the lithium cobalt oxide lattice (such as some Li + Vacancy, Co 3+ The spatial adaptability of La substitution sites is good, and it can be effectively embedded in the lattice without causing excessive lattice distortion. 3+ The 4f orbital is completely empty ( ), Gd 3+ The 4f orbital is half full ( ), are all electronically stable states. In the lithium cobalt oxide lattice, they can stabilize Co through charge compensation and electron cloud shielding effects. 3+ / Co 4+ The redox pair inhibits cobalt dissolution and lattice phase transitions under high voltage. Furthermore, in the coating layer (Li-Gd-Ti-O4 spinel phase), Gd, as a rare earth element, promotes the formation and stability of the spinel phase through its inherent ionic properties. La doping in the matrix, synergistically with surface Gd, creates a gradient structure from the bulk to the surface that combines lattice stability with interface protection.

[0009] In a second aspect, the present invention proposes a method for preparing a high-temperature resistant lithium cobalt oxide positive electrode material, comprising the following steps: uniformly mixing aluminum-doped cobalt tetroxide, lithium carbonate, a magnesium dopant, a titanium dopant and a lanthanum dopant to obtain a qualified mixture; sintering the qualified mixture once, cooling it naturally, and crushing it to obtain a lithium cobalt oxide matrix; mixing the lithium cobalt oxide matrix, lithium carbonate, nano-cobaltous hydroxide, a gadolinium coating agent and a titanium coating agent to obtain a lithium cobalt oxide matrix with a densely coated surface; and subjecting the lithium cobalt oxide matrix with a densely coated surface to a secondary sintering, cooling it naturally, and sieving it to obtain a high-temperature resistant lithium cobalt oxide positive electrode material.

[0010] Preferably, in the qualified mixture, the molar ratio of Li to Co is 1.03 to 1.05, the amount of the magnesium dopant added is 0.135 to 0.825 wt %, the amount of the titanium dopant added is 0.055 to 0.165 wt %, and the amount of the lanthanum dopant added is 0.105 to 0.655 wt %. The amounts of the magnesium dopant, titanium dopant, and lanthanum dopant added refer to their respective mass percentages of the total qualified mixture.

[0011] The inventors found that doping Mg, Ti and La in the lithium cobalt oxide matrix can balance the lattice stress, achieve charge compensation and enhance the function. In addition, the excess or deficiency of one of the doping elements will lead to a series of problems such as "structural collapse - kinetic hindrance - intensified side reactions". Specifically, when Mg is excessive, it will excessively occupy the Li site, resulting in Li + The deintercalation channel is blocked, the rate performance drops sharply, the lattice is over-compressed, the thermal expansion coefficient is abnormal, and high-temperature cycles are prone to cracking; when Mg is insufficient, the layered structure is unstable, and H1-3 phase transition (layered → mixed phase) is prone to occur at high temperatures, Co dissolution is aggravated, interface side reactions increase, and internal resistance rises rapidly. When Ti is excessive, high-valent Ti 4+ It causes serious lattice distortion and disordered electron cloud distribution, which in turn reduces electronic conductivity and promotes the formation of spinel phase (inactive phase), resulting in significant capacity loss. When Ti is insufficient, electron transport optimization is insufficient, electrode polarization is severe under high temperature and high voltage, and charge and discharge efficiency is low. 3+ Dissolution inhibition is weak, electrolyte corrosion is aggravated, and cycle life is shortened. When La is excessive, large radius La 3+ Excessive embedding in the lattice cracks the layered structure, causing a surge in bulk defects, and accelerating oxygen loss and Co dissolution at high temperatures. When La is insufficient, the interface protection is weak, the electrolyte directly corrodes the lithium cobalt oxide surface at high temperatures, the CEI film is unstable (easy to crack and peel off), side reaction products (such as Li2CO3, LiF) accumulate, the internal resistance continues to rise, and the cycle life is greatly reduced.

[0012] Preferably, the aluminum content in the aluminum-doped cobalt tetroxide is 0.4 wt%.

[0013] Preferably, the magnesium dopant is nano-magnesium oxide, the titanium dopant is nano-titanium oxide, and the lanthanum dopant is nano-lanthanum oxide.

[0014] Preferably, in the densely coated lithium cobalt oxide matrix, the amount of lithium carbonate added is 1-2 wt %, the amount of nano-cobaltous hydroxide added is 3-5 wt %, the amount of titanium coating agent added is 0.35-1.05 wt %, and the amount of gadolinium coating agent added is 0.1-0.7 wt %. The amounts of lithium carbonate, nano-cobaltous hydroxide, titanium coating agent, and gadolinium coating agent added refer to their respective mass percentages relative to the total amount of the densely coated lithium cobalt oxide matrix.

[0015] Preferably, the titanium coating agent is nano-titanium oxide, and the gadolinium coating agent is nano-gadolinium oxide.

[0016] Preferably, the one-time sintering is divided into two stages, the first stage: keeping warm at 750~850℃ for 6h; the second stage: keeping warm at 1000~1050℃ for 10h. Specifically, the first stage (750~850℃, keeping warm for 6h) helps lithium cobalt oxide to initially form a layered structure, promotes the solid solution of doping elements (Ti, Mg, La, etc.), and controls the initial growth of grains. Abnormal temperature will cause uneven doping, disordered grain nucleation, and destroy the regularity of the structure; the second stage (1000~1050℃, keeping warm for 10h) improves the lattice, eliminates defects, promotes the densification growth of grains, and realizes deep and uniform solid solution of doping elements. Improper temperature will make lattice defects difficult to repair, excessive grain growth or impurity phase generation, and damage the layered structure. The inventors found that reasonable segmented sintering can ensure the integrity of the lattice and uniform doping, which is beneficial for Li + Insertion / extraction provides sufficient sites to inhibit irreversible phase transition, thereby improving capacity and cycle stability; temperature runaway reduces active sites, accelerates lattice collapse, causes capacity decay, and shortens life. In addition, regular structure and uniform doping can inhibit Co dissolution and oxygen loss at high temperatures, and withstand Li + Stress relief enhances thermal stability and high-voltage tolerance; sintering anomalies, on the other hand, amplify defects, reduce the material's stability at high temperatures and high voltages, and accelerate failure. Furthermore, adjusting the sintering temperature can control particle morphology, forming uniform and regular particles, improving crystallinity and reducing defects, thereby enhancing conductivity, reducing electrode internal resistance, and improving battery consistency and rate performance.

[0017] Preferably, the secondary sintering is to keep the temperature at 890~950℃ for 9h. It should be noted that the appropriate range of 890~950℃ can improve the crystallinity, optimize the lattice regularity and reduce defects; sintering temperature that is too low or too high will increase lattice defects and even induce phase change. And the appropriate sintering temperature can make the coating layer uniform and dense; inappropriate temperature will make the coating layer uneven and discontinuous, and cannot effectively protect the lithium cobalt oxide matrix. In this sintering temperature range, the grains grow moderately, with uniform particle size and regular morphology; when the temperature is extreme, the grain size is uneven, easy to agglomerate, irregular morphology, and large internal stress. In terms of performance, the appropriate sintering temperature can ensure high capacity and cycle stability, improve thermal stability and high voltage tolerance, and make the material have good conductivity and excellent mechanical properties.

[0018] In a third aspect, the present invention provides an application of the high-temperature-resistant lithium cobalt oxide cathode material described above in a lithium-ion battery. Specifically, the high-temperature-resistant lithium cobalt oxide cathode material can be used in a 4.4V laptop replacement battery.

[0019] The beneficial effects of the present invention are as follows: the high-temperature resistant lithium cobalt oxide positive electrode material of the present invention is composed of a lithium cobalt oxide matrix and a dense and uniform coating layer coated on the surface of the lithium cobalt oxide matrix. During preparation, bulk doping is performed by a high-temperature solid-phase method, and Mg, Ti and La are doped into the lithium cobalt oxide matrix, which can improve the thermal stability of the lattice structure of lithium cobalt oxide at high voltage (4.4V); and a fast ion coating layer of Li-Gd-Ti-O4 spinel phase is formed on the surface of the lithium cobalt oxide matrix by a solid-phase method. Through multiple mechanisms such as the lattice stabilization effect of rare earth ions, the interface barrier effect of composite oxides, and the regulation of lithium ion conductivity, the comprehensive performance of the lithium cobalt oxide positive electrode material, especially the capacity, cycle stability, thermal stability and high voltage tolerance, is improved, thereby solving the problem that the current lithium cobalt oxide positive electrode material has poor stability at high voltage and high temperature and is difficult to achieve both high capacity and cycle stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a scanning electron microscope image of the densely coated lithium cobalt oxide substrate prepared in Example 2; Figure 2 is a scanning electron microscope image of the high-temperature resistant lithium cobalt oxide positive electrode material prepared in Example 2; Figure 3 It is a comparison chart of the battery cycle retention rates corresponding to Example 2 and Comparative Example 1. DETAILED DESCRIPTION

[0021] The present invention will be described in further detail below with reference to specific implementation methods and the accompanying drawings, but the implementation methods of the present invention are not limited thereto.

[0022] Example 1 Weigh aluminum-doped cobalt tetroxide (containing 0.4 wt% Al) and lithium carbonate (purity ≥ 99.9%) at a Li / Co molar ratio of 1.03, add 0.110 wt% nano-titanium oxide, 0.480 wt% nano-magnesium oxide, and 0.430 wt% nano-lanthanum oxide, and mix well to obtain a qualified mixture; The qualified mixed material was put into a mullite sagger (4 kg), cut into pieces and punched, and placed in a muffle furnace. The air flow rate was adjusted to 30 L / min. The temperature of the muffle furnace was raised to the first platform of 750-850°C at a heating rate of 2.5°C / min and kept warm for 6 hours. The temperature was then raised to the second platform of 1000-1050°C and kept warm for 10 hours for high-temperature sintering. After the sintering was completed, the muffle furnace was naturally cooled to below 50°C, taken out, and crushed and depolymerized using a mechanical crusher to obtain a lithium cobalt oxide matrix. A lithium cobalt oxide matrix, 1.5 wt% lithium carbonate (purity ≥ 99.9%), 4 wt% nano-cobaltous hydroxide, 0.4 wt% nano-gadolinium oxide, and 0.4 wt% nano-titanium oxide were mixed in a high-speed mixer for 30 minutes to obtain a lithium cobalt oxide matrix with a dense surface coating; The lithium cobalt oxide substrate with dense surface coating was packed into a mullite sagger (4 kg), cut into pieces and punched, and placed in a muffle furnace. The air flow rate was adjusted to 30 L / min, and the temperature of the muffle furnace was raised to 890-950°C at a heating rate of 2.5°C / min and kept warm for 9 hours for high-temperature sintering. After the sintering was completed, the muffle furnace was naturally cooled to below 50°C, taken out, and sieved with a 325-mesh sieve to obtain a high-temperature resistant lithium cobalt oxide positive electrode material.

[0023] Example 2 Weigh aluminum-doped cobalt tetroxide (containing 0.4 wt% Al) and lithium carbonate (purity ≥ 99.9%) at a Li / Co molar ratio of 1.04, add 0.110 wt% nano-titanium oxide, 0.480 wt% nano-magnesium oxide, and 0.430 wt% nano-lanthanum oxide, and mix well to obtain a qualified mixture; The qualified mixed material was put into a mullite sagger (4 kg), cut into pieces and punched, and placed in a muffle furnace. The air flow rate was adjusted to 30 L / min. The temperature of the muffle furnace was raised to the first platform of 750-850°C at a heating rate of 2.5°C / min and kept warm for 6 hours. The temperature was then raised to the second platform of 1000-1050°C and kept warm for 10 hours for high-temperature sintering. After the sintering was completed, the muffle furnace was naturally cooled to below 50°C, taken out, and crushed and depolymerized using a mechanical crusher to obtain a lithium cobalt oxide matrix. The lithium cobalt oxide matrix, 1.5wt% lithium carbonate (purity ≥ 99.9%), 4wt% nano-cobalt hydroxide, 0.4wt% nano-gadolinium oxide and 0.4wt% nano-titanium oxide were mixed in a high-speed mixer for 30 minutes to obtain a lithium cobalt oxide matrix with a dense surface coating (SEM image as shown in FIG. Figure 1 shown); The lithium cobalt oxide substrate with dense surface coating was packed into a mullite sagger with 4 kg, cut into pieces and punched, and placed in a muffle furnace. The air flow rate was adjusted to 30 L / min, and the temperature of the muffle furnace was raised to 890-950 ° C at a heating rate of 2.5 ° C / min and kept at this temperature for 9 hours for high temperature sintering. After the sintering was completed, the muffle furnace was naturally cooled to below 50 ° C, taken out, and sieved with a 325 mesh sieve to obtain a high temperature resistant lithium cobalt oxide positive electrode material (Scanning electron microscope image as shown in FIG). Figure 2 shown).

[0024] Example 3 Weigh aluminum-doped cobalt tetroxide (containing 0.4 wt% Al) and lithium carbonate (purity ≥ 99.9%) at a Li / Co molar ratio of 1.05, add 0.110 wt% nano-titanium oxide, 0.480 wt% nano-magnesium oxide, and 0.430 wt% nano-lanthanum oxide, and mix well to obtain a qualified mixture; The qualified mixed material was put into a mullite sagger (4 kg), cut into pieces and punched, and placed in a muffle furnace. The air flow rate was adjusted to 30 L / min. The temperature of the muffle furnace was raised to the first platform of 750-850°C at a heating rate of 2.5°C / min and kept warm for 6 hours. The temperature was then raised to the second platform of 1000-1050°C and kept warm for 10 hours for high-temperature sintering. After the sintering was completed, the muffle furnace was naturally cooled to below 50°C, taken out, and crushed and depolymerized using a mechanical crusher to obtain a lithium cobalt oxide matrix. A lithium cobalt oxide matrix, 1.5 wt% lithium carbonate (purity ≥ 99.9%), 4 wt% nano-cobaltous hydroxide, 0.4 wt% nano-gadolinium oxide, and 0.4 wt% nano-titanium oxide were mixed in a high-speed mixer for 30 minutes to obtain a lithium cobalt oxide matrix with a dense surface coating; The lithium cobalt oxide substrate with dense surface coating was packed into a mullite sagger (4 kg), cut into pieces and punched, and placed in a muffle furnace. The air flow rate was adjusted to 30 L / min, and the temperature of the muffle furnace was raised to 890-950°C at a heating rate of 2.5°C / min and kept warm for 9 hours for high-temperature sintering. After the sintering was completed, the muffle furnace was naturally cooled to below 50°C, taken out, and sieved with a 325-mesh sieve to obtain a high-temperature resistant lithium cobalt oxide positive electrode material.

[0025] Example 4 Weigh aluminum-doped cobalt tetroxide (containing 0.4 wt% Al) and lithium carbonate (purity ≥ 99.9%) at a Li / Co molar ratio of 1.04, add 0.055 wt% nano-titanium oxide, 0.135 wt% nano-magnesium oxide, and 0.105 wt% nano-lanthanum oxide, and mix well to obtain a qualified mixture; The qualified mixed material was put into a mullite sagger (4 kg), cut into pieces and punched, and placed in a muffle furnace. The air flow rate was adjusted to 30 L / min. The temperature of the muffle furnace was raised to the first platform of 750-850°C at a heating rate of 2.5°C / min and kept warm for 6 hours. The temperature was then raised to the second platform of 1000-1050°C and kept warm for 10 hours for high-temperature sintering. After the sintering was completed, the muffle furnace was naturally cooled to below 50°C, taken out, and crushed and depolymerized using a mechanical crusher to obtain a lithium cobalt oxide matrix. A lithium cobalt oxide matrix, 1.5 wt% lithium carbonate (purity ≥ 99.9%), 4 wt% nano-cobaltous hydroxide, 0.4 wt% nano-gadolinium oxide, and 0.4 wt% nano-titanium oxide were mixed in a high-speed mixer for 30 minutes to obtain a lithium cobalt oxide matrix with a dense surface coating; The lithium cobalt oxide substrate with dense surface coating was packed into a mullite sagger (4 kg), cut into pieces and punched, and placed in a muffle furnace. The air flow rate was adjusted to 30 L / min, and the temperature of the muffle furnace was raised to 890-950°C at a heating rate of 2.5°C / min and kept warm for 9 hours for high-temperature sintering. After the sintering was completed, the muffle furnace was naturally cooled to below 50°C, taken out, and sieved with a 325-mesh sieve to obtain a high-temperature resistant lithium cobalt oxide positive electrode material.

[0026] Example 5 Weigh aluminum-doped cobalt tetroxide (containing 0.4 wt% Al) and lithium carbonate (purity ≥ 99.9%) at a Li / Co molar ratio of 1.04, add 0.165 wt% nano-titanium oxide, 0.825 wt% nano-magnesium oxide, and 0.655 wt% nano-lanthanum oxide, and mix well to obtain a qualified mixture; The qualified mixed material was put into a mullite sagger (4 kg), cut into pieces and punched, and placed in a muffle furnace. The air flow rate was adjusted to 30 L / min. The temperature of the muffle furnace was raised to the first platform of 750-850°C at a heating rate of 2.5°C / min and kept warm for 6 hours. The temperature was then raised to the second platform of 1000-1050°C and kept warm for 10 hours for high-temperature sintering. After the sintering was completed, the muffle furnace was naturally cooled to below 50°C, taken out, and crushed and depolymerized using a mechanical crusher to obtain a lithium cobalt oxide matrix. A lithium cobalt oxide matrix, 1.5 wt% lithium carbonate (purity ≥ 99.9%), 4 wt% nano-cobaltous hydroxide, 0.4 wt% nano-gadolinium oxide, and 0.4 wt% nano-titanium oxide were mixed in a high-speed mixer for 30 minutes to obtain a lithium cobalt oxide matrix with a dense surface coating; The lithium cobalt oxide substrate with dense surface coating was packed into a mullite sagger (4 kg), cut into pieces and punched, and placed in a muffle furnace. The air flow rate was adjusted to 30 L / min, and the temperature of the muffle furnace was raised to 890-950°C at a heating rate of 2.5°C / min and kept warm for 9 hours for high-temperature sintering. After the sintering was completed, the muffle furnace was naturally cooled to below 50°C, taken out, and sieved with a 325-mesh sieve to obtain a high-temperature resistant lithium cobalt oxide positive electrode material.

[0027] Example 6 Weigh aluminum-doped cobalt tetroxide (containing 0.4 wt% Al) and lithium carbonate (purity ≥ 99.9%) at a Li / Co molar ratio of 1.04, add 0.110 wt% nano-titanium oxide, 0.480 wt% nano-magnesium oxide, and 0.430 wt% nano-lanthanum oxide, and mix well to obtain a qualified mixture; The qualified mixed material was put into a mullite sagger (4 kg), cut into pieces and punched, and placed in a muffle furnace. The air flow rate was adjusted to 30 L / min. The temperature of the muffle furnace was raised to the first platform of 750-850°C at a heating rate of 2.5°C / min and kept warm for 6 hours. The temperature was then raised to the second platform of 1000-1050°C and kept warm for 10 hours for high-temperature sintering. After the sintering was completed, the muffle furnace was naturally cooled to below 50°C, taken out, and crushed and depolymerized using a mechanical crusher to obtain a lithium cobalt oxide matrix. A lithium cobalt oxide matrix, 1.5 wt% lithium carbonate (purity ≥ 99.9%), 4 wt% nano-cobaltous hydroxide, 0.1 wt% nano-gadolinium oxide, and 0.35 wt% nano-titanium oxide were mixed in a high-speed mixer for 30 minutes to obtain a lithium cobalt oxide matrix with a dense surface coating; The lithium cobalt oxide substrate with dense surface coating was packed into a mullite sagger (4 kg), cut into pieces and punched, and placed in a muffle furnace. The air flow rate was adjusted to 30 L / min, and the temperature of the muffle furnace was raised to 890-950°C at a heating rate of 2.5°C / min and kept warm for 9 hours for high-temperature sintering. After the sintering was completed, the muffle furnace was naturally cooled to below 50°C, taken out, and sieved with a 325-mesh sieve to obtain a high-temperature resistant lithium cobalt oxide positive electrode material.

[0028] Example 7 Weigh aluminum-doped cobalt tetroxide (containing 0.4 wt% Al) and lithium carbonate (purity ≥ 99.9%) at a Li / Co molar ratio of 1.04, add 0.110 wt% nano-titanium oxide, 0.480 wt% nano-magnesium oxide, and 0.430 wt% nano-lanthanum oxide, and mix well to obtain a qualified mixture; The qualified mixed material was put into a mullite sagger (4 kg), cut into pieces and punched, and placed in a muffle furnace. The air flow rate was adjusted to 30 L / min. The temperature of the muffle furnace was raised to the first platform of 750-850°C at a heating rate of 2.5°C / min and kept warm for 6 hours. The temperature was then raised to the second platform of 1000-1050°C and kept warm for 10 hours for high-temperature sintering. After the sintering was completed, the muffle furnace was naturally cooled to below 50°C, taken out, and crushed and depolymerized using a mechanical crusher to obtain a lithium cobalt oxide matrix. A lithium cobalt oxide matrix, 1.5 wt% lithium carbonate (purity ≥ 99.9%), 4 wt% nano-cobaltous hydroxide, 0.7 wt% nano-gadolinium oxide, and 1.05 wt% nano-titanium oxide were mixed in a high-speed mixer for 30 minutes to obtain a lithium cobalt oxide matrix with a dense surface coating; The lithium cobalt oxide substrate with dense surface coating was packed into a mullite sagger (4 kg), cut into pieces and punched, and placed in a muffle furnace. The air flow rate was adjusted to 30 L / min, and the temperature of the muffle furnace was raised to 890-950°C at a heating rate of 2.5°C / min and kept warm for 9 hours for high-temperature sintering. After the sintering was completed, the muffle furnace was naturally cooled to below 50°C, taken out, and sieved with a 325-mesh sieve to obtain a high-temperature resistant lithium cobalt oxide positive electrode material.

[0029] Comparative Example 1 Different from Example 2, nano titanium oxide was not added to the qualified mixture of this comparative example.

[0030] The rest are the same as in Example 2 and will not be described again here.

[0031] Comparative Example 2 The difference from Example 2 is that the addition amount of nano-titanium oxide in the qualified mixture of this comparative example is 2.0 wt %.

[0032] The rest are the same as in Example 2 and will not be described again here.

[0033] Comparative Example 3 Different from Example 2, nano magnesium oxide was not added to the qualified mixture of this comparative example.

[0034] The rest are the same as in Example 2 and will not be described again here.

[0035] Comparative Example 4 The difference from Example 2 is that the amount of nano-magnesium oxide added to the qualified mixture of this comparative example is 2.0 wt %.

[0036] The rest are the same as in Example 2 and will not be described again here.

[0037] Comparative Example 5 Different from Example 2, no nano-lanthanum oxide was added to the qualified mixture of this comparative example.

[0038] The rest are the same as in Example 2 and will not be described again here.

[0039] Comparative Example 6 The difference from Example 2 is that the amount of nano-lanthanum oxide added to the qualified mixture of this comparative example is 2.0 wt %.

[0040] The rest are the same as in Example 2 and will not be described again here.

[0041] Comparative Example 7 Different from Example 2, the amount of lithium carbonate added to the lithium cobalt oxide matrix with a dense surface coating in this comparative example is 0.5 wt %.

[0042] The rest are the same as in Example 2 and will not be described again here.

[0043] Comparative Example 8 Different from Example 2, the amount of lithium carbonate added to the densely coated lithium cobalt oxide matrix in this comparative example is 3.0 wt %.

[0044] The rest are the same as in Example 2 and will not be described again here.

[0045] Comparative Example 9 Different from Example 2, nano-titanium oxide is not added to the lithium cobalt oxide matrix with densely coated surface in this comparative example.

[0046] The rest are the same as in Example 2 and will not be described again here.

[0047] Comparative Example 10 Different from Example 2, the amount of nano-titanium oxide added to the densely coated lithium cobalt oxide matrix in this comparative example is 2.0 wt %.

[0048] The rest are the same as in Example 2 and will not be described again here.

[0049] Comparative Example 11 Different from Example 2, nano-gadolinium oxide is not added to the lithium cobalt oxide matrix with dense surface coating in this comparative example.

[0050] The rest are the same as in Example 2 and will not be described again here.

[0051] Comparative Example 12 Different from Example 2, the amount of nano-gadolinium oxide added to the densely coated lithium cobalt oxide matrix in this comparative example is 1.0 wt %.

[0052] The rest are the same as in Example 2 and will not be described again here.

[0053] Comparative Example 13 Different from Example 2, in this comparative example, 4.0 wt % of cobaltous hydroxide in the densely coated lithium cobaltate substrate is replaced with 4.0 wt % of cobalt carbonate.

[0054] The rest are the same as in Example 2 and will not be described again here.

[0055] Comparative Example 14 Different from Example 2, the amount of nano-cobaltous hydroxide added to the densely coated lithium cobaltate matrix in this comparative example is 2.0 wt %.

[0056] The rest are the same as in Example 2 and will not be described again here.

[0057] Comparative Example 15 Different from Example 2, the amount of nano-cobaltous hydroxide added to the densely coated lithium cobaltate matrix in this comparative example is 6.0 wt %.

[0058] The rest are the same as in Example 2 and will not be described again here.

[0059] Performance Testing The lithium cobalt oxide prepared in Examples 1 to 7 and Comparative Examples 1 to 15 was used as the positive electrode material, and the positive electrode material, conductive agent acetylene black and binder PVDF were weighed in a mass ratio of 92:4:4. After being mixed evenly with dispersant N-methylpyrrolidone (NMP) to form a slurry, it was coated on the current collector aluminum foil, and then dried at 120°C for 2 hours and cut into 1.56 cm2 circular positive electrode sheets. The metal lithium sheet was used as the negative electrode, combined with the separator, the above-mentioned positive electrode sheet, and LiPF6 (EC:DEC=1:1) electrolyte, and assembled into a 2032 type button battery in a glove box. The constant current charge and discharge test was carried out on the Xinwei battery test system for performance testing. Test conditions: voltage range 3.0-4.4V, 0.1C charge and discharge for 1 week; transferred to a 45°C constant temperature box, voltage range 3.0-4.4V, 1C charge and discharge cycle for 50 weeks. The test results are shown in Tables 1 and Figure 3 shown.

[0060]

[0061] As can be seen from Table 1, the batteries prepared using the lithium cobalt oxide positive electrode materials of Examples 1 to 7 of the present invention not only have high capacity, but also have excellent cycle stability at high temperature and high cut-off voltage. The battery prepared using the lithium cobalt oxide positive electrode material of Example 2 has the best performance.

[0062] From the comparison between Example 2 and Comparative Examples 1, 3, and 5, it can be seen that when one of Ti, Mg, and La is missing from the qualified mixture, its performance will deteriorate. Specifically, the doping element in Comparative Example 1 lacks Ti, which intensifies the lattice phase transition during charge and discharge, resulting in accelerated structural collapse during the cycle and deterioration of the cycle; the doping element in Comparative Example 3 lacks Mg, which cannot expand the Li + Diffusion channel, reducing ion migration resistance, Li + The migration activation energy increases, and the high-temperature performance and capacity retention rate at high rates decrease. In Comparative Example 5, the doping element lacks La, the side reactions between the electrolyte and the active material increase, the SEI film continues to rupture / regenerate, the impedance increases irreversibly, the interface side reactions become more intense at high temperatures, the thermal stability decreases, and the cycle deteriorates.

[0063] From the comparison between Example 2 and Comparative Examples 2, 4, and 6, it can be seen that when the amount of each dopant added to the qualified mixture is too high, its performance will also deteriorate. Specifically, when the amount of Ti in Comparative Example 2 is excessive, the high-valence Ti 4+ It causes serious lattice distortion and disordered electron cloud distribution, which reduces the electronic conductivity and promotes the formation of spinel phase (inactive phase), resulting in obvious capacity loss. When Mg is excessive in comparative example 4, it excessively occupies the Li site, resulting in Li + The embedding and de-embedding channels are blocked, the lattice is over-compressed, the thermal expansion coefficient is abnormal, and the high temperature cycle is prone to cracking, resulting in cycle deterioration; when La is excessive in Comparative Example 6, the large radius La 3+ Excessive embedding in the lattice will crack the layered structure, causing a surge in bulk defects, accelerating oxygen loss and Co dissolution at high temperatures, and shortening the cycle life.

[0064] From the comparison between Example 2 and Comparative Examples 7-8, it can be seen that when Li2CO3 is added in a serious shortage or excess during the coating process, the battery performance will be poor. The inventors found that adding appropriate lithium carbonate during the coating process can avoid local composition deviations (such as local lithium excess or deficiency) caused by uneven distribution of lithium sources during qualified mixing, and can improve material consistency. Specifically, when lithium is insufficient, it will lead to the loss of lithium sites in the lattice, forming a "cobalt-rich phase", increasing the risk of cobalt dissolution during charging and discharging, and reducing cycle stability and safety; when lithium is excessive, it is easy to cause surface Li enrichment and runaway side reactions (such as the formation of a thick SEI film), leading to cycle deterioration.

[0065] From the comparison between Example 2 and Comparative Examples 9-10, it can be seen that if TiO2 is not added or added in excess during the coating process, the battery performance will deteriorate accordingly. The inventors found that if the titanium coating agent TiO2 is not added, the lithium cobalt oxide material may be more likely to undergo redox reaction with the electrolyte, resulting in thickening of the interface film and accumulation of by-products, which will also lead to a decrease in mechanical stability. During the charge and discharge process, it is more likely to crack or peel off due to volume expansion, further reducing the cycle life; if the titanium coating agent TiO2 is excessive, a large amount of inactive spinel phase will be generated, blocking the Li + The transmission channel and the first discharge capacity decrease. At the same time, TiO2 will agglomerate, resulting in uneven surface coating and local thermal stress concentration, which can easily cause structural collapse at high temperatures and ultimately lead to deterioration of cycle performance.

[0066] From the comparison between Example 2 and Comparative Examples 11-12, it can be seen that when Gd2O3 is not added or added in excess during the coating process, the battery performance will decline. The inventors found that if the gadolinium coating agent Gd2O3 is not added, a Li-Co-Ti-O solid solution structure will form on the surface of the material, resulting in a decrease in conductivity and an increase in polarization during charge and discharge, reducing the energy efficiency of the battery. At the same time, the lattice constant may shrink, resulting in Li + The diffusion channel becomes narrower; the lack of Gd will cause the Gd-Ti structure optimization effect to disappear, which will cause lattice distortion, resulting in local structural collapse, and ultimately lead to deterioration of cycle performance; if too much Gd is coated, rare earth ions will be over-enriched on the surface, forming a thick and dense "insulating layer", which will hinder Li + Electron conduction leads to a sharp decline in rate performance; at the same time, excess Gd 3+ It will cause excessive surface lattice distortion, thermal stress concentration, easy cracking during high-temperature cycling, and ultimately lead to deterioration of cycle performance.

[0067] By comparing Example 2 and Comparative Example 13, it can be seen that when cobaltous hydroxide Co(OH)2 is replaced with cobalt carbonate CoCO3, the decomposition of CoCO3 will produce a larger amount of CO2 gas released and the bubble escape rate is slower, which may cause more pores to form inside the sintered body, reduce the density of the material, and directly lead to a decrease in the capacity of the battery. If the gas remains between the particles, it may cause structural stress during the charge and discharge process and accelerate the cracking of the material. The decomposition products of cobaltous hydroxide Co(OH)2 are CoO and H2O, and the gas is easy to discharge and there is no residue, which can avoid this problem.

[0068] By comparing Example 2 with Comparative Examples 14 and 15, it can be seen that the amount of cobaltous hydroxide added will affect the cycle performance of the battery, because the coating layer containing cobaltous hydroxide can improve the electronic conductivity and ion diffusion performance of lithium cobalt oxide. When the amount of cobaltous hydroxide added is too small, the coating layer will be correspondingly thinner, and an excessively thin coating layer will weaken the electronic conductivity and ion diffusion performance, and will aggravate the side reactions on the surface of the lithium cobalt oxide matrix, resulting in deterioration of the cycle performance; and when the amount of cobaltous hydroxide added is too much, the coating layer will become thicker, and an excessively thick coating layer will hinder the transmission of electrons between the lithium cobalt oxide particles, resulting in a decrease in electronic conductivity, hindered ion diffusion, increased resistance, and ultimately deterioration of the cycle performance.

[0069] Based on the disclosure and teachings of the above description, those skilled in the art will be able to make changes and modifications to the above embodiments. Therefore, the present invention is not limited to the above specific embodiments. Any obvious improvements, substitutions, or modifications made by those skilled in the art based on the present invention fall within the scope of protection of the present invention. In addition, although certain specific terms are used in this description, these terms are only for convenience of description and do not constitute any limitation to the present invention.

Claims

1. A high temperature resistant lithium cobalt oxide positive electrode material, characterized in that: The invention comprises a lithium cobalt oxide matrix and a coating layer coated on the surface of the lithium cobalt oxide matrix. The lithium cobalt oxide matrix is ​​doped with Mg, Ti and La. The coating layer is a fast ion coating layer of Li-Gd-Ti-O4 spinel phase.

2. A method for preparing a high-temperature resistant lithium cobalt oxide positive electrode material, characterized in that: The method comprises the following steps: uniformly mixing aluminum-doped cobalt tetroxide, lithium carbonate, a magnesium dopant, a titanium dopant and a lanthanum dopant to obtain a qualified mixed material; subjecting the qualified mixed material to a primary sintering, natural cooling, and crushing to obtain a lithium cobaltate matrix; mixing the lithium cobaltate matrix, lithium carbonate, nano-cobaltous hydroxide, a gadolinium coating agent and a titanium coating agent to obtain a lithium cobaltate matrix with a densely coated surface; subjecting the lithium cobaltate matrix with a densely coated surface to a secondary sintering, natural cooling, and sieving to obtain a high-temperature resistant lithium cobaltate positive electrode material.

3. The method for preparing a high temperature resistant lithium cobalt oxide positive electrode material according to claim 2, characterized in that: In the qualified mixture, the molar ratio of Li to Co is 1.03-1.05, the added amount of the magnesium dopant is 0.135-0.825 wt %, the added amount of the titanium dopant is 0.055-0.165 wt %, and the added amount of the lanthanum dopant is 0.105-0.655 wt %.

4. The method for preparing a high temperature resistant lithium cobalt oxide positive electrode material according to claim 2, characterized in that: The aluminum content in the aluminum-doped cobalt tetroxide is 0.4 wt %.

5. The method for preparing a high temperature resistant lithium cobalt oxide positive electrode material according to claim 2, characterized in that: The magnesium dopant is nano-magnesium oxide, the titanium dopant is nano-titanium oxide, and the lanthanum dopant is nano-lanthanum oxide.

6. The method for preparing a high temperature resistant lithium cobalt oxide positive electrode material according to claim 2, characterized in that: In the lithium cobalt oxide matrix with a dense surface coating, the addition amount of the lithium carbonate is 1-2wt%, the addition amount of the nano-cobaltous hydroxide is 3-5wt%, the addition amount of the titanium coating agent is 0.35-1.05wt%, and the addition amount of the gadolinium coating agent is 0.1-0.7wt%.

7. The method for preparing a high temperature resistant lithium cobalt oxide positive electrode material according to claim 2, characterized in that: The titanium coating agent is nano titanium oxide, and the gadolinium coating agent is nano gadolinium oxide.

8. The method for preparing a high temperature resistant lithium cobalt oxide positive electrode material according to claim 2, characterized in that: The primary sintering is divided into two stages: the first stage: keeping the temperature at 750-850° C. for 6 hours; the second stage: keeping the temperature at 1000-1050° C. for 10 hours.

9. The method for preparing a high temperature resistant lithium cobalt oxide positive electrode material according to claim 2, characterized in that: The secondary sintering is carried out at a temperature of 890-950° C. for 9 hours.

10. Use of the high-temperature resistant lithium cobalt oxide positive electrode material according to claim 1 in a lithium-ion battery.

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