A high-temperature-resistant lithium cobalt oxide positive electrode material, a preparation method and application thereof

Abstract

The application 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 base body and a coating layer coated on the surface of the lithium cobalt oxide base body; the lithium cobalt oxide base body is doped with Mg, Ti and La; the coating layer is a fast ion coating layer of a Li-Gd-Ti-O4 spinel phase; during preparation, body phase doping is carried out through a high-temperature solid phase method, Mg, Ti and La are doped in the lithium cobalt oxide base body, and the lattice structure thermal stability of the lithium cobalt oxide under high voltage (4.4V) is improved; and the solid phase method is adopted to form the fast ion coating layer of the Li-Gd-Ti-O4 spinel phase on the surface of the lithium cobalt oxide base body; through multiple mechanisms such as lattice stability of rare earth ions, interface blocking effect of composite oxides, lithium ion conductivity regulation and the like, the comprehensive performance of the lithium cobalt oxide positive electrode material is improved, especially capacity, cycle stability, thermal stability and high-voltage resistance and the like.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a high-temperature-resistant lithium cobalt oxide cathode material and a preparation method and application thereof. BACKGROUND

[0002] As a commonly used lithium ion battery cathode material, lithium cobalt oxide is widely used in various portable electronic devices such as notebook computers, mobile phones and tablet computers due to its high volume energy density. With the popularization of 5G and the development trend of lightweight and thin portable electronic devices, the market has higher requirements for the energy density of batteries. Increasing the charging voltage of lithium cobalt oxide can provide higher specific capacity and energy density.

[0003] However, under high cut-off voltage, lithium cobalt oxide will face the following problems: (1) irreversible evolution of bulk structure: H1-3 phase transition occurs, i.e. the layered structure is converted to other phases, which destroys the lattice regularity, affects the lithium ion insertion / extraction channel, and reduces the cycle stability of the battery; (2) interface deterioration problem: the surface structure collapses into a rock salt phase at high temperature, blocking the transmission of lithium ions, and the decomposition of electrolyte generates unstable CEI film, hindering conduction and forming a vicious cycle, which becomes more serious when running at higher temperatures (such as 45℃).

[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, which changes the physical and chemical state of the surface of lithium cobalt oxide, stabilizes the morphology and crystal structure of the material. However, there is a clear phase interface between the traditional coating layer and the lithium cobalt oxide bulk material, and stress and strain accumulation cracking easily occurs at the interface during charging and discharging, which has the risk of sudden deterioration of battery performance; and the conductivity of the coating layer is generally poor, and too thick will affect the conductivity of the material, hindering the conduction of lithium ions and electrons. For example: coating lithium cobalt oxide with conventional oxides, the interface cracks due to stress during high-voltage cycling, the internal resistance of the battery rises sharply, and the capacity decays rapidly. Moreover, the coating material has no electrochemical activity, and excessive coating will greatly reduce the specific capacity of lithium cobalt oxide. SUMMARY

[0005] The purpose of the present application is to provide a high-temperature-resistant lithium cobalt oxide cathode material and a preparation method and application thereof, which aims to solve the problem that the current lithium cobalt oxide cathode material has poor stability at high voltage and high temperature and is difficult to balance high capacity and cycle stability.

[0006] In order to achieve the above object, the present application adopts the following technical scheme: In a first aspect, the present application provides a high-temperature-resistant lithium cobalt oxide cathode material, comprising a lithium cobalt oxide base and a coating layer coated on the surface of the lithium cobalt oxide base, wherein the lithium cobalt oxide base 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] The inventors have found through a large number of experiments that doping Mg, Ti and La in the lithium cobalt oxide base can improve the lattice structure thermal stability of lithium cobalt oxide at high voltage (4.4V), and coating a fast ion coating layer of Li-Gd-Ti-O4 spinel phase on the surface of the lithium cobalt oxide base can improve the comprehensive performance of lithium cobalt oxide through multiple mechanisms such as lattice stabilization of rare earth ions, interface barrier effect of composite oxides and lithium ion conductivity regulation, especially capacity, cycle stability, thermal stability and high voltage resistance, etc., to ultimately obtain a high-temperature-resistant lithium cobalt oxide cathode material.

[0008] Specifically, La 3+ has an ionic radius of about 1.03 Å, Gd 3+ has an ionic radius of about 0.94 Å, has good spatial adaptability to the doped sites in the lithium cobalt oxide lattice (such as part of Li + vacancies, Co 3+ substitution sites), can effectively embed into the lattice without causing excessive lattice distortion. Moreover, the 4f orbit of La 3+ is completely empty, and the 4f orbit of Gd 3+ is half full, both of which are in a stable state of electronic structure, and in the lithium cobalt oxide lattice, they can stabilize the Co 3+ / Co 4+ redox pair through charge compensation and electron cloud shielding effect, and inhibit the dissolution of cobalt and the lattice phase transition at high voltage. In addition, in the coating layer (Li-Gd-Ti-O4 spinel phase), Gd, as a rare earth element, can promote the formation and stability of the spinel phase by virtue of its own ionic properties. La doped in the base cooperates with the surface Gd to construct a gradient structure of "lattice stabilization-interface protection" from the bulk phase to the surface.

[0009] In a second aspect, the present application provides a preparation method of a high-temperature-resistant lithium cobalt oxide cathode material, comprising the following steps: uniformly mixing aluminum-doped tricobalt tetroxide, lithium carbonate, a magnesium dopant, a titanium dopant and a lanthanum dopant to obtain a passing mixture; performing primary sintering on the passing mixture, naturally cooling, and crushing to obtain a lithium cobalt oxide base; mixing the lithium cobalt oxide base, lithium carbonate, nano-cobaltous hydroxide, a gadolinium coating agent and a titanium coating agent to obtain a lithium cobalt oxide base with a dense coating on the surface; performing secondary sintering on the lithium cobalt oxide base with a dense coating on the surface, naturally cooling, and sieving to obtain a high-temperature-resistant lithium cobalt oxide cathode material.

[0010] Preferably, in the said pass mixture, the molar ratio of Li and Co is 1.03-1.05, the adding amount of the said magnesium dopant is 0.135-0.825wt%, the adding amount of the said titanium dopant is 0.055-0.165wt%, and the adding amount of the said lanthanum dopant is 0.105-0.655wt%. Among them, the adding amount of the magnesium dopant, the titanium dopant and the lanthanum dopant respectively refers to the mass percentage of the total amount of the pass mixture.

[0011] The inventors found that doping Mg, Ti and La in the lithium cobaltate matrix can balance the lattice stress, achieve charge compensation and functional reinforcement. Moreover, the excess or deficiency of a certain element in the doping elements will trigger a chain of problems such as "structure collapse-dynamics obstruction-accelerated side reactions". Specifically, when Mg is excessive, it will excessively occupy Li sites, leading to Li + extraction channel blockage, rapid decline in rate performance, excessive lattice compression, abnormal thermal expansion coefficient, and easy cracking during high-temperature cycling; when Mg is insufficient, the layered structure is weak in stability, H1-3 phase transition (layered → mixed phase) easily occurs at high temperature, Co dissolution is accelerated, and the interface side reaction increases, resulting in rapid rise of internal resistance. 4+ When Ti is excessive, it triggers serious lattice distortion and disordered electron cloud distribution, which in turn reduces electronic conductivity, and promotes the generation of spinel phase (inactive phase), resulting in obvious capacity loss; when Ti is insufficient, electronic transmission is not optimized, electrode polarization is severe at high temperature and high voltage, and charge and discharge efficiency is low; Co 3+ dissolution is weakly inhibited, electrolyte corrosion is accelerated, and cycle life is shortened. When La is excessive, large-radius La 3+ excessive embedding in the lattice, splitting the layered structure, and a large number of bulk defects, accelerating oxygen loss and Co dissolution at high temperature; when La is insufficient, the interface protection is weak, the electrolyte directly corrodes the surface of lithium cobaltate at high temperature, the CEI film is unstable (easy to crack and peel off), the byproduct (such as Li2CO3, LiF) accumulates, the internal resistance continues to rise, and the cycle life is greatly reduced.

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

[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 lithium cobalt oxide substrate with dense surface coating, the added amount of lithium carbonate is 1-2wt%, the added amount of nano cobaltous hydroxide is 3-5wt%, the added amount of titanium coating agent is 0.35-1.05wt%, and the added amount of gadolinium coating agent is 0.1-0.7wt%. Among them, the added amount of lithium carbonate, nano cobaltous hydroxide, titanium coating agent and gadolinium coating agent refers to the mass percentage of the total amount of lithium cobalt oxide substrate with dense surface coating.

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

[0016] Preferably, the primary sintering is divided into two stages. The first stage is to keep the temperature at 750-850℃ for 6h, and the second stage is to keep the temperature at 1000-1050℃ for 10h. Specifically, the first stage (750-850℃, 6h) helps the lithium cobalt oxide to form a layered structure, promotes the solid solution of doping elements (Ti, Mg, La, etc.), controls the initial growth of crystal grains, and abnormal temperature will cause uneven doping, disorderly grain nucleation, and damage to the structural regularity. The second stage (1000-1050℃, 10h) perfects the crystal lattice, eliminates defects, promotes the dense growth of crystal grains, realizes the deep and uniform solid solution of doping elements, and improper temperature will cause difficulty in repairing lattice defects, excessive grain growth or impurity phase generation, and damage to the layered structure. The inventors found that reasonable segmented sintering can guarantee the integrity of the crystal lattice and the uniformity of doping, which is beneficial to the Li + The embedded / exited active sites provide sufficient sites, inhibit irreversible phase transition, and thus improve the capacity and cycle stability; temperature out of control reduces active sites and accelerates lattice collapse, resulting in capacity decay and shortened life. In addition, the regular structure and uniform doping can inhibit Co dissolution and oxygen loss at high temperature, and can withstand Li + The embedded / exited active sites provide sufficient sites, inhibit irreversible phase transition, and thus improve the capacity and cycle stability; temperature out of control reduces active sites and accelerates lattice collapse, resulting in capacity decay and shortened life. In addition, the regular structure and uniform doping can inhibit Co dissolution and oxygen loss at high temperature, and can withstand Li

[0017] Preferably, the secondary sintering is at 890-950℃ for 9h. It should be noted that the suitable range of 890-950℃ can improve the crystallinity, optimize the lattice regularity, and reduce defects; sintering at too low or too high temperature will increase lattice defects, and even cause phase transition. And the suitable sintering temperature can make the thickness of the coating layer uniform and dense; improper temperature will make the coating layer uneven and discontinuous, and cannot effectively protect the lithium cobaltate matrix. Within this sintering temperature range, the grains grow moderately, the particle size is uniform, and the morphology is regular; while at extreme temperature, the grain size is uneven, easy to agglomerate, and the morphology is irregular, with large internal stress. In terms of performance, the suitable sintering temperature can guarantee high capacity and cycle stability, improve thermal stability and high-voltage resistance, and make the material have good electrical conductivity and mechanical properties.

[0018] In a third aspect, the application provides a use of the high-temperature-resistant lithium cobaltate cathode material as described above in a lithium ion battery. Specifically, the high-temperature-resistant lithium cobaltate cathode material can be used in 4.4V notebook battery replacement.

[0019] The high-temperature-resistant lithium cobaltate cathode material of the application is composed of a lithium cobaltate matrix and a dense and uniform coating layer coated on the surface of the lithium cobaltate matrix. During preparation, body doping is carried out by high-temperature solid-phase method, Mg, Ti and La are doped in the lithium cobaltate matrix, which can improve the thermal stability of the lattice structure of lithium cobaltate 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 cobaltate matrix by solid-phase method, which improves the comprehensive performance of the lithium cobaltate cathode material through multiple mechanisms such as lattice stabilization of rare earth ions, interface barrier effect of composite oxides, and lithium ion conductivity regulation, especially capacity, cycle stability, thermal stability and high-voltage resistance, etc., solving the problems of poor stability of current lithium cobaltate cathode material at high voltage and high temperature, and difficulty in balancing high capacity and cycle stability. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 is a scanning electron microscope image of the surface-dense-coated lithium cobaltate matrix prepared in Example 2;

[0021] Figure 2 is a scanning electron microscope image of the high-temperature-resistant lithium cobaltate cathode material prepared in Example 2;

[0022] Figure 3 is a comparison chart of battery cycle retention rate corresponding to Example 2 and Comparative Example 1. DETAILED DESCRIPTION

[0023] The application will be described in further detail below with reference to specific embodiments and the accompanying drawings of the specification, but the embodiments of the application are not limited thereto.

[0024] Example 1

[0025] Aluminum-doped tricobalt tetraoxide (containing 0.4wt% Al) and lithium carbonate (purity≥99.9%) were weighed according to the Li / Co molar ratio of 1.03, and 0.110wt% nano-titanium oxide, 0.480wt% nano-magnesium oxide and 0.430wt% nano-lanthanum oxide were added and mixed uniformly to obtain the qualified mixture;

[0026] The qualified mixture was loaded into a 4kg mullite box and cut into pieces and punched, and was placed into a muffle furnace. The air flow was adjusted to 30L / min, and the temperature was raised to the first platform of 750~850℃ at a heating rate of 2.5℃ / min, and was kept for 6h. Then the temperature was raised to the second platform of 1000~1050℃ and was kept for 10h for high-temperature sintering. After sintering, the muffle furnace was naturally cooled to below 50℃, and was taken out. Mechanical pulverizer was used for crushing and depolymerization to obtain the lithium cobalt oxide matrix;

[0027] The lithium cobalt oxide matrix, 1.5wt% lithium carbonate (purity≥99.9%), 4wt% nano-cobaltous hydroxide, 0.4wt% nano-gadolinium oxide and 0.4wt% nano-titanium oxide were mixed in a high-speed mixer for 30min to obtain the lithium cobalt oxide matrix with a dense coated surface;

[0028] The lithium cobalt oxide matrix with a dense coated surface was loaded into a 4kg mullite box and cut into pieces and punched, and was placed into a muffle furnace. The air flow was adjusted to 30L / min, and the temperature was raised to 890~950℃ at a heating rate of 2.5℃ / min and was kept for 9h for high-temperature sintering. After sintering, the muffle furnace was naturally cooled to below 50℃, and was taken out. A 325 mesh sieve disc was used for sieving to obtain the high-temperature-resistant lithium cobalt oxide positive electrode material.

[0029] Example 2

[0030] Aluminum-doped tricobalt tetraoxide (containing 0.4wt% Al) and lithium carbonate (purity≥99.9%) were weighed according to the Li / Co molar ratio of 1.03, and 0.110wt% nano-titanium oxide, 0.480wt% nano-magnesium oxide and 0.430wt% nano-lanthanum oxide were added and mixed uniformly to obtain the qualified mixture;

[0031] The qualified mixture was loaded into a 4kg mullite box and cut into pieces and punched, and was placed into a muffle furnace. The air flow was adjusted to 30L / min, and the temperature was raised to the first platform of 750~850℃ at a heating rate of 2.5℃ / min, and was kept for 6h. Then the temperature was raised to the second platform of 1000~1050℃ and was kept for 10h for high-temperature sintering. After sintering, the muffle furnace was naturally cooled to below 50℃, and was taken out. Mechanical pulverizer was used for crushing and depolymerization to obtain the lithium cobalt oxide matrix;

[0032] The lithium cobaltate matrix, 1.5wt% lithium carbonate (purity ≥ 99.9%), 4wt% nano-cobalt hydroxide, 0.4wt% nano-gadolinium oxide and 0.4wt% nano-titanium oxide are mixed in a high-speed mixer for 30min to obtain a lithium cobaltate matrix with a dense coating on the surface (the scanning electron microscope image is shown in Figure 1

[0033] The lithium cobaltate matrix with a dense coating on the surface is loaded into a 4kg mullite box and cut into pieces and punched, and is placed into a muffle furnace. The air flow is adjusted to 30L / min, and the temperature of the muffle furnace is raised to 890~950℃ at a heating rate of 2.5℃ / min, and is kept for 9h for high-temperature sintering. After sintering is completed, the muffle furnace is naturally cooled to below 50℃, and is taken out. A 325 mesh sieve plate is used for sieving to obtain a high-temperature-resistant lithium cobaltate positive electrode material (the scanning electron microscope image is shown in Figure 2

[0034] Example 3

[0035] Aluminum-doped tricobalt tetroxide (containing 0.4wt% Al) and lithium carbonate (purity ≥ 99.9%) are weighed according to a Li / Co molar ratio of 1.05, and 0.110wt% nano-titanium oxide, 0.480wt% nano-magnesium oxide and 0.430wt% nano-lanthanum oxide are added and uniformly mixed to obtain a qualified mixture.

[0036] The qualified mixture is loaded into a 4kg mullite box and cut into pieces and punched, and is placed into a muffle furnace. The air flow is adjusted to 30L / min, and the temperature of the muffle furnace is raised to a first platform of 750~850℃ at a heating rate of 2.5℃ / min, and is kept for 6h. Then the temperature is raised to a second platform of 1000~1050℃ and is kept for 10h for high-temperature sintering. After sintering is completed, the muffle furnace is naturally cooled to below 50℃, and is taken out. A mechanical pulverizer is used for crushing and depolymerization to obtain a lithium cobaltate matrix.

[0037] The lithium cobaltate matrix, 1.5wt% lithium carbonate (purity ≥ 99.9%), 4wt% nano-cobalt hydroxide, 0.4wt% nano-gadolinium oxide and 0.4wt% nano-titanium oxide are mixed in a high-speed mixer for 30min to obtain a lithium cobaltate matrix with a dense coating on the surface.

[0038] The lithium cobaltate matrix with a dense coating on the surface is loaded into a 4kg mullite box and cut into pieces and punched, and is placed into a muffle furnace. The air flow is adjusted to 30L / min, and the temperature of the muffle furnace is raised to 890~950℃ at a heating rate of 2.5℃ / min, and is kept for 9h for high-temperature sintering. After sintering is completed, the muffle furnace is naturally cooled to below 50℃, and is taken out. A 325 mesh sieve plate is used for sieving to obtain a high-temperature-resistant lithium cobaltate positive electrode material.

[0039] Example 4 ​​

[0040] Aluminum-doped tricobalt tetraoxide (containing 0.4wt% Al) and lithium carbonate (purity≥99.9%) were weighed according to the Li / Co molar ratio of 1.04, and 0.055wt% nano-titanium oxide, 0.135wt% nano-magnesium oxide and 0.105wt% nano-lanthanum oxide were added and mixed uniformly to obtain the qualified mixture;

[0041] The qualified mixture was loaded into a 4kg mullite box and cut into pieces and punched, and was placed into a muffle furnace. The air flow was adjusted to 30L / min, and the temperature was raised to the first platform of 750-850℃ at a heating rate of 2.5℃ / min, and was kept for 6h. Then the temperature was raised to the second platform of 1000-1050℃ and was kept for 10h for high-temperature sintering. After sintering, the muffle furnace was naturally cooled to below 50℃, and was taken out. Mechanical pulverizer was used for crushing and depolymerization to obtain the lithium cobalt oxide matrix;

[0042] The lithium cobalt oxide matrix, 1.5wt% lithium carbonate (purity≥99.9%), 4wt% nano-cobaltous hydroxide, 0.4wt% nano-gadolinium oxide and 0.4wt% nano-titanium oxide were mixed in a high-speed mixer for 30min to obtain the lithium cobalt oxide matrix with a dense coated surface;

[0043] The lithium cobalt oxide matrix with a dense coated surface was loaded into a 4kg mullite box and cut into pieces and punched, and was placed into a muffle furnace. The air flow was adjusted to 30L / min, and the temperature was raised to 890-950℃ at a heating rate of 2.5℃ / min and was kept for 9h for high-temperature sintering. After sintering, the muffle furnace was naturally cooled to below 50℃, and was taken out. A 325 mesh sieve disc was used for sieving to obtain the high-temperature-resistant lithium cobalt oxide positive electrode material.

[0044] Example 5

[0045] Aluminum-doped tricobalt tetraoxide (containing 0.4wt% Al) and lithium carbonate (purity≥99.9%) were weighed according to the Li / Co molar ratio of 1.04, and 0.055wt% nano-titanium oxide, 0.135wt% nano-magnesium oxide and 0.105wt% nano-lanthanum oxide were added and mixed uniformly to obtain the qualified mixture;

[0046] The qualified mixture was loaded into a 4kg mullite box and cut into pieces and punched, and was placed into a muffle furnace. The air flow was adjusted to 30L / min, and the temperature was raised to the first platform of 750-850℃ at a heating rate of 2.5℃ / min, and was kept for 6h. Then the temperature was raised to the second platform of 1000-1050℃ and was kept for 10h for high-temperature sintering. After sintering, the muffle furnace was naturally cooled to below 50℃, and was taken out. Mechanical pulverizer was used for crushing and depolymerization to obtain the lithium cobalt oxide matrix;

[0047] The lithium cobaltate base, 1.5wt% lithium carbonate (purity ≥ 99.9%), 4wt% nano cobalt hydroxide, 0.4wt% nano gadolinium oxide and 0.4wt% nano titanium oxide are mixed in a high-speed mixer for 30 minutes to obtain a lithium cobaltate base with a dense coated surface;

[0048] The lithium cobaltate base with a dense coated surface is loaded into a 4kg mullite box and cut into blocks and punched, and is placed into a muffle furnace. The air flow is adjusted to 30L / min, and the temperature of the muffle furnace is raised to 890~950℃ at a heating rate of 2.5℃ / min, and is kept for 9h for high-temperature sintering. After sintering is completed, the muffle furnace is naturally cooled to below 50℃, and is taken out. A 325 mesh sieve plate is used for sieving to obtain a high-temperature-resistant lithium cobaltate positive electrode material.

[0049] Example 6

[0050] Aluminum-doped tricobalt tetroxide (containing 0.4wt% Al) and lithium carbonate (purity ≥ 99.9%) are weighed according to a Li / Co molar ratio of 1.04, and 0.110wt% nano titanium oxide, 0.480wt% nano magnesium oxide and 0.430wt% nano lanthanum oxide are added and uniformly mixed to obtain a passable mixture.

[0051] The passable mixture is loaded into a 4kg mullite box and cut into blocks and punched, and is placed into a muffle furnace. The air flow is adjusted to 30L / min, and the temperature of the muffle furnace is raised to a first platform of 750~850℃ at a heating rate of 2.5℃ / min, and is kept for 6h. Then the temperature is raised to a second platform of 1000~1050℃ and is kept for 10h for high-temperature sintering. After sintering is completed, the muffle furnace is naturally cooled to below 50℃, and is taken out. A mechanical pulverizer is used for crushing and depolymerization to obtain a lithium cobaltate base.

[0052] The lithium cobaltate base, 1.5wt% lithium carbonate (purity ≥ 99.9%), 4wt% nano cobalt hydroxide, 0.1wt% nano gadolinium oxide and 0.35wt% nano titanium oxide are mixed in a high-speed mixer for 30 minutes to obtain a lithium cobaltate base with a dense coated surface;

[0053] The lithium cobaltate base with a dense coated surface is loaded into a 4kg mullite box and cut into blocks and punched, and is placed into a muffle furnace. The air flow is adjusted to 30L / min, and the temperature of the muffle furnace is raised to 890~950℃ at a heating rate of 2.5℃ / min, and is kept for 9h for high-temperature sintering. After sintering is completed, the muffle furnace is naturally cooled to below 50℃, and is taken out. A 325 mesh sieve plate is used for sieving to obtain a high-temperature-resistant lithium cobaltate positive electrode material.

[0054] Example 7

[0055] Aluminum-doped cobalt trioxide (containing 0.4wt% Al) and lithium carbonate (purity≥99.9%) were weighed according to a Li / Co molar ratio of 1.04, and 0.110wt% nano-titanium oxide, 0.480wt% nano-magnesium oxide and 0.430wt% nano-lanthanum oxide were added and mixed uniformly to obtain a qualified mixture;

[0056] The qualified mixture was loaded into a 4kg mullite box and cut into pieces and punched, and was placed into a muffle furnace. The air flow was adjusted to 30L / min, and the temperature was raised to a first platform of 750~850℃ at a heating rate of 2.5℃ / min, and was kept for 6h. Then the temperature was raised to a second platform of 1000~1050℃ and was kept for 10h for high-temperature sintering. After sintering, the muffle furnace was naturally cooled to below 50℃, and was taken out. Mechanical pulverizer was used for crushing and depolymerization to obtain a lithium cobaltate matrix;

[0057] The lithium cobaltate matrix, 1.5wt% lithium carbonate (purity≥99.9%), 4wt% nano-cobaltous hydroxide, 0.7wt% nano-gadolinium oxide and 1.05wt% nano-titanium oxide were mixed in a high-speed mixer for 30min to obtain a lithium cobaltate matrix with a dense coated surface;

[0058] The lithium cobaltate matrix with a dense coated surface was loaded into a 4kg mullite box and cut into pieces and punched, and was placed into a muffle furnace. The air flow was adjusted to 30L / min, and the temperature was raised to 890~950℃ at a heating rate of 2.5℃ / min and was kept for 9h for high-temperature sintering. After sintering, the muffle furnace was naturally cooled to below 50℃, and was taken out. A 325 mesh sieve disc was used for sieving to obtain a high-temperature-resistant lithium cobaltate positive electrode material.

[0059] Comparative Example 1

[0060] Different from Example 2, no nano-titanium oxide was added in the qualified mixture of the present comparative example.

[0061] The rest were the same as Example 2, which will not be repeated here.

[0062] Comparative Example 2

[0063] Different from Example 2, the addition amount of nano-titanium oxide in the qualified mixture of the present comparative example was 2.0wt%.

[0064] The rest were the same as Example 2, which will not be repeated here.

[0065] Comparative Example 3

[0066] Different from Example 2, no nano-magnesium oxide was added in the qualified mixture of the present comparative example.

[0067] The rest were the same as Example 2, which will not be repeated here.

[0068] Comparative Example 4

[0069] Different from Example 2, the addition amount of nano-magnesium oxide in the qualified mixture of this comparative example is 2.0wt%.

[0070] The rest is the same as Example 2, which will not be repeated here.

[0071] Comparative Example 5

[0072] Different from Example 2, no nano-lanthanum oxide is added in the qualified mixture of this comparative example.

[0073] The rest is the same as Example 2, which will not be repeated here.

[0074] Comparative Example 6

[0075] Different from Example 2, the addition amount of nano-lanthanum oxide in the qualified mixture of this comparative example is 2.0wt%.

[0076] The rest is the same as Example 2, which will not be repeated here.

[0077] Comparative Example 7

[0078] Different from Example 2, the addition amount of lithium carbonate in the surface-densely-coated lithium cobalt oxide matrix of this comparative example is 0.5wt%.

[0079] The rest is the same as Example 2, which will not be repeated here.

[0080] Comparative Example 8

[0081] Different from Example 2, the addition amount of lithium carbonate in the surface-densely-coated lithium cobalt oxide matrix of this comparative example is 3.0wt%.

[0082] The rest is the same as Example 2, which will not be repeated here.

[0083] Comparative Example 9

[0084] Different from Example 2, no nano-titanium oxide is added in the surface-densely-coated lithium cobalt oxide matrix of this comparative example.

[0085] The rest is the same as Example 2, which will not be repeated here.

[0086] Comparative Example 10

[0087] Different from Example 2, the addition amount of nano-titanium oxide in the surface-densely-coated lithium cobalt oxide matrix of this comparative example is 2.0wt%.

[0088] The rest is the same as Example 2, which will not be repeated here.

[0089] Comparative Example 11

[0090] Unlike Example 2, the surface of the lithium cobalt oxide matrix of this comparative example was not doped with nanometer gadolinium oxide.

[0091] The rest was the same as Example 2, which will not be repeated here.

[0092] Comparative Example 12

[0093] Unlike Example 2, the amount of nanometer gadolinium oxide added to the surface of the lithium cobalt oxide matrix of this comparative example was 1.0 wt%.

[0094] The rest was the same as Example 2, which will not be repeated here.

[0095] Comparative Example 13

[0096] Unlike Example 2, the lithium cobalt oxide matrix of this comparative example was doped with 4.0 wt% cobalt hydroxide instead of 4.0 wt% cobalt carbonate.

[0097] The rest was the same as Example 2, which will not be repeated here.

[0098] Comparative Example 14

[0099] Unlike Example 2, the amount of nanometer cobalt hydroxide added to the surface of the lithium cobalt oxide matrix of this comparative example was 2.0 wt%.

[0100] The rest was the same as Example 2, which will not be repeated here.

[0101] Comparative Example 15

[0102] Unlike Example 2, the amount of nanometer cobalt hydroxide added to the surface of the lithium cobalt oxide matrix of this comparative example was 6.0 wt%.

[0103] The rest was the same as Example 2, which will not be repeated here.

[0104] Performance Test

[0105] The lithium cobaltate prepared in Examples 1-7 and Comparative Examples 1-15 was used as a 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, mixed uniformly with dispersant N-methyl pyrrolidone (NMP) to form a slurry, coated on a current collector aluminum foil, and then dried at 120°C for 2h, and cut into a circular positive electrode sheet with a diameter of 1.56cm2. A lithium metal sheet was used as a negative electrode, combined with a separator, the above positive electrode sheet and LiPF6 (EC:DEC=1:1) electrolyte to assemble a 2032 type button cell in a glove box. Constant current charge and discharge test was performed on a new battery test system. 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 for 50 weeks. The test results are shown in Table 1 and Figure 3

[0106]

[0107] As can be seen from Table 1, the battery prepared using the lithium cobaltate positive electrode material of Examples 1-7 of the present application has not only high capacity, but also good cycle stability at high temperature and high cut-off voltage, and the battery prepared using the lithium cobaltate positive electrode material of Example 2 has the best performance.

[0108] As can be seen from the comparison of Example 2 and Comparative Examples 1, 3 and 5, when one of Ti, Mg and La is missing in the doping mixture, the performance will be poor. Specifically, in Comparative Example 1, Ti is missing in the doping element, the lattice phase transition is intensified during the charge and discharge process, the structure collapse speed is accelerated during the cycle, and the cycle is deteriorated; in Comparative Example 3, Mg is missing in the doping element, the Li + diffusion channel cannot be expanded, the ion migration resistance is reduced, the Li + migration activation energy is increased, the high temperature performance and the capacity retention rate at high rate are decreased; in Comparative Example 5, La is missing in the doping element, the side reaction between the electrolyte and the active material is increased, the SEI film is continuously broken / reproduced, the impedance is irreversibly increased, the interface side reaction is more severe at high temperature, the thermal stability is decreased, and the cycle is deteriorated.

[0109] As can be seen from the comparison of Example 2 and Comparative Examples 2, 4 and 6, when the addition amount of each dopant in the doping mixture is too high, the performance will be poor. Specifically, in Comparative Example 2, Ti is excessive, the high voltage Ti 4+ induces serious lattice distortion, the electron cloud distribution is disordered, and the electronic conductivity is reduced, and at the same time, the spinel phase (non-active phase) is generated, and the capacity loss is obvious; in Comparative Example 4, Mg is excessive, the Li + deintercalation channel is blocked, and at the same time, the lattice is excessively compressed, the thermal expansion coefficient is abnormal, and the cycle is easy to crack at high temperature, and the cycle is deteriorated; in Comparative Example 6, La is excessive, the large radius La​3+ Over-embedded in the lattice, cracking the layered structure, the body defects are increasing, oxygen loss and Co dissolution are accelerated at high temperature, and the cycle life is shortened.

[0110] From the comparison of 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 the local composition deviation caused by uneven distribution of lithium source during mixing (such as local lithium excess or deficiency), and can improve the consistency of the material. Specifically, when lithium is insufficient, it will cause the lack of lithium site in the lattice, forming a "cobalt-rich phase", increasing the risk of cobalt dissolution during charging and discharging, and reducing the cycle stability and safety; when lithium is excessive, it is easy to cause surface Li enrichment, uncontrollable side reactions (such as the formation of thick SEI film), leading to cycle deterioration.

[0111] From the comparison of Example 2 and Comparative Examples 9-10, it can be seen that when TiO2 is not added or is added in excess during the coating process, the battery performance will deteriorate accordingly. The inventors found that if no titanium coating agent TiO2 is added, the lithium cobaltate material may be more prone to redox reaction with the electrolyte, leading to thickening of the interface film and accumulation of by-products, which will also lead to a decrease in mechanical stability, and more easily cause cracks or peeling due to volume expansion during charging and discharging, further reducing the cycle life; if the titanium coating agent TiO2 is excessive, a large amount of non-active spinel phase will be generated, blocking the Li + transport channel, at the same time, TiO2 will agglomerate to cause uneven surface coating, local thermal stress concentration, and easy to cause structure collapse at high temperature, ultimately leading to cycle performance deterioration.

[0112] From the comparison of Example 2 and Comparative Examples 11-12, it can be seen that when Gd2O3 is not added or is added in excess during the coating process, the battery performance will decrease. The inventors found that if no gadolinium coating agent Gd2O3 is added, a Li-Co-Ti-O solid solution structure will be formed on the surface of the material, leading to a decrease in electrical conductivity and an increase in polarization during charging and discharging, reducing the energy efficiency of the battery, and at the same time, the lattice constant may shrink, causing the Li + diffusion channel to narrow; the absence of Gd causes the Gd-Ti structure optimization effect to disappear, causing lattice distortion and leading to local structure collapse, ultimately leading to cycle performance deterioration; if too much Gd element is coated, rare earth ions are excessively enriched on the surface, forming a thick and dense "insulating layer", hindering the Li + electron conduction, leading to a sharp decline in rate performance; at the same time, excessive Gd 3+ will cause excessive distortion of the surface lattice, thermal stress concentration, and easy to crack during high-temperature cycling, ultimately leading to cycle performance deterioration.

[0113] From the comparison of Example 2 and Comparative Example 13, it can be seen that cobalt hydroxide Co(OH)2 is replaced by cobalt carbonate CoCO3, the decomposition of CoCO3 will produce more CO2 gas release and the bubble escape speed is slow, which can lead to the formation of more pores in the sintered body, reducing the density of the material, directly leading to the capacity of the battery to reduce, if the gas remains between the particles, it can cause structural stress in the charging and discharging process, accelerate the material cracking, and cobalt hydroxide Co(OH)2 decomposition products are CoO and H2O, the gas is easy to discharge and no residue, which can avoid this problem.

[0114] From the comparison of Example 2 and Comparative Examples 14 and 15, it can be seen that the amount of cobalt hydroxide added will affect the cycle performance of the battery, because the coating layer containing cobalt hydroxide can improve the electronic conductivity and ion diffusion performance of lithium cobalt oxide, when the amount of cobalt hydroxide added is too small, the coating layer will also be relatively thin, and the too thin coating layer will weaken the electronic conductivity and ion diffusion performance, and will exacerbate the side reaction on the surface of the lithium cobalt oxide matrix, leading to deterioration of the cycle performance; and when the amount of cobalt hydroxide added is too much, the coating layer will correspondingly become thicker, and the too thick coating layer will hinder the transmission of electrons between lithium cobalt oxide particles, leading to a decrease in electronic conductivity, ion diffusion is hindered, and resistance increases, ultimately leading to deterioration of the cycle performance.

[0115] Based on the disclosure and teachings of the above description, those skilled in the art of the present application can also make changes and modifications to the above embodiments. Therefore, the present application is not limited to the above specific embodiments, and any obvious improvements, replacements or modifications made by those skilled in the art based on the present application shall fall within the scope of the present application. In addition, although some specific terms are used in the present specification, these terms are only for convenience of explanation and do not constitute any limitation on the present application.

Claims

1. A method for preparing a high-temperature-resistant lithium cobalt oxide cathode material, characterized in that, The method comprises the following steps: aluminum-doped tricobalt tetroxide, lithium carbonate, magnesium dopant, titanium dopant and lanthanum dopant are uniformly mixed to obtain a qualified mixture; the qualified mixture is subjected to primary sintering, naturally cooled, and crushed to obtain a lithium cobaltate matrix; the lithium cobaltate matrix, lithium carbonate, nano-cobaltous hydroxide, gadolinium coating agent and titanium coating agent are mixed to obtain a lithium cobaltate matrix with a compact coating on the surface; the lithium cobaltate matrix with a compact coating on the surface is subjected to secondary sintering, naturally cooled, and sieved to obtain a high-temperature-resistant lithium cobaltate positive electrode material; in the qualified mixture, the magnesium dopant is added in an amount of 0.135-0.825wt%, the titanium dopant is added in an amount of 0.055-0.165wt%, and the lanthanum dopant is added in an amount of 0.105-0.655wt%; in the lithium cobaltate matrix with a compact coating on the surface, the lithium carbonate is added in an amount of 1-2wt%, the nano-cobaltous hydroxide is added in an amount of 3-5wt%, the titanium coating agent is added in an amount of 0.35-1.05wt%, and the gadolinium coating agent is added in an amount of 0.1-0.7wt%.

2. The method for preparing the high-temperature resistant lithium cobalt oxide cathode material according to claim 1, characterized in that, in the qualified mixture, the molar ratio of Li to Co is 1.03-1.

05.

3. The method for preparing the high-temperature resistant lithium cobalt oxide cathode material according to claim 1, characterized in that, the aluminum content in the aluminum-doped tricobalt tetroxide is 0.4wt%.

4. The method for preparing the high-temperature resistant lithium cobalt oxide cathode material according to claim 1, 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.

5. The method for preparing the high-temperature resistant lithium cobalt oxide cathode material according to claim 1, characterized in that, the titanium coating agent is nano-titanium oxide, and the gadolinium coating agent is nano-gadolinium oxide.

6. The method for preparing the high-temperature resistant lithium cobalt oxide cathode material according to claim 1, characterized in that, the primary sintering is divided into two stages, the first stage: 750-850℃ for 6h; the second stage: 1000-1050℃ for 10h.

7. The method for preparing the high-temperature resistant lithium cobalt oxide cathode material according to claim 1, characterized in that, the secondary sintering is 890-950℃ for 9h.

8. The high-temperature resistant lithium cobalt oxide cathode material according to any one of claims 1-7, wherein the high-temperature resistant lithium cobalt oxide cathode material is prepared by the method of claim 7. the lithium cobaltate matrix doped with Mg, Ti and La, and the coating layer on the surface of the lithium cobaltate matrix, wherein the coating layer is a fast ion coating layer of Li-Gd-Ti-O4 spinel phase.

9. Use of the high-temperature-resistant lithium cobaltate positive electrode material in a lithium ion battery.

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