A lithium titanium phosphate lanthanum lithium-coated magnesium-doped lithium cobalt oxide cathode material and its preparation method

Abstract

This invention discloses a lithium titanium lanthanum lithium-coated magnesium-doped lithium cobalt oxide cathode material and its preparation method. The cathode material uses lithium cobalt oxide particles as a matrix, with lithium titanium lanthanum lithium-coated ...

Description

Technical Field

[0001] This invention belongs to the field of battery materials technology, and particularly relates to a lithium titanium phosphate lanthanum lithium-coated magnesium-doped lithium cobalt oxide cathode material and its preparation method. Background Technology

[0002] Lithium cobalt oxide materials have poor thermal stability and pose safety hazards when overcharged. Furthermore, operating voltages exceeding 4.2V cause lithium cobalt oxide to transform from a hexagonal to a monoclinic crystal system; deep delithiation under high voltage also leads to Co... 3+ Oxidized to Co 4+ Co 4+ The LiCoO2 material is prone to side reactions with the electrolyte, which leads to a decrease in its electrochemical performance. These problems limit the further application of LiCoO2.

[0003] To address the aforementioned issues, current research primarily focuses on modifying lithium cobalt oxide cathode materials through doping or surface coating. However, simple doping or coating alone cannot fully meet the requirements for high-capacity, high-specific-energy, and long-cycle applications of cathode materials. Especially during long charge-discharge cycles under high-voltage conditions, a series of phase transitions leading to structural deterioration results in a severe decline in capacity retention and structural stability. The phase transitions during lithium insertion / extraction in lithium cobalt oxide cause significant anisotropic expansion and contraction of the unit cell along the c-axis and a-axis, generating non-uniform stress within the crystal nucleus and deteriorating structural stability, thus causing a degradation in the performance of lithium cobalt oxide cathode materials.

[0004] Furthermore, as the charging voltage increases, the instability of the bulk phase, surface, and interface of LCO materials becomes significantly aggravated, which will greatly damage electrochemical performance and increase safety risks. Therefore, in order to ensure stable long-term cycling of lithium cobalt oxide under high voltage conditions, it is urgent to develop a method that is simple to modify, conducive to large-scale promotion, and produces lithium cobalt oxide cathode materials with good stability and excellent electrochemical performance. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the deficiencies and defects mentioned in the background art above, and to provide a lithium titanium lanthanum lithium coated magnesium-doped lithium cobalt oxide cathode material and its preparation method.

[0006] To solve the above-mentioned technical problems, the technical solution proposed by this invention is as follows:

[0007] A magnesium-doped lithium cobalt oxide cathode material coated with lithium lanthanum titanium phosphate is disclosed. The cathode material uses lithium cobalt oxide particles as the matrix, with lithium lanthanum titanium phosphate uniformly coated on the surface of the lithium cobalt oxide particles, and magnesium doping inside the lithium cobalt oxide particles.

[0008] Lithium titanium phosphate (LFP) is a NASICON-type fast ion conductor with an olivine structure, possessing a robust polyanionic framework and high ionic conductivity. This LFP material, synthesized using a phosphate structure, is uniformly coated onto the surface of lithium cobalt oxide with a nanometer-scale coating thickness. This method ensures uniform coating without affecting the capacity of the lithium cobalt oxide cathode material.

[0009] Stronger Mg-O bonds and Mg in the Li layer 2+ The pillar effect of Mg doping can stabilize the crystal structure to a large extent; the fast ion conductor lithium titanium phosphate coating protects the material interface and improves ionic conductivity. At the same time, magnesium doping occupies lithium sites, and the lithium ions after the raw materials are replaced are reused on the surface. In other words, by utilizing the residual lithium on the surface, a three-dimensional conductive coating layer of NASICON-type fast ion conductor is constructed on the particle surface, promoting rapid lithium ion conduction.

[0010] Preferably, the chemical formula of the lithium titanium phosphate-coated magnesium-doped lithium cobalt oxide cathode material is Mg-LiCoO2@Li 1+ x La x Ti 2-x (PO4)3, wherein 0.2 < x < 0.5, the coating amount of the lithium titanium phosphate is less than 2.0 wt% of the magnesium-doped lithium cobalt oxide particles, and the magnesium doping content is less than 1.0 mol% of the cobalt content in the cathode material.

[0011] If the coating amount is too small, the impact on the material is minimal, and a uniform coating layer cannot be completely formed on the particle surface. If the coating amount is too large, the coating formed on the material surface will be too thick, affecting the contact between the cathode material and the electrolyte.

[0012] Under the same technical concept, the present invention also provides a method for preparing a magnesium-doped lithium cobalt oxide cathode material coated with lithium lanthanum titanium phosphate, comprising the following steps:

[0013] (1) Mix cobalt source and lithium source evenly and sinter to prepare lithium cobalt oxide precursor material;

[0014] (2) The lithium cobalt oxide precursor material obtained in step (1) is mixed with a magnesium source and sintered twice to obtain magnesium-doped lithium cobalt oxide particles.

[0015] (3) Dissolve lithium source, lanthanum source, titanium source and phosphorus source to prepare lithium titanium lanthanum phosphate, and add magnesium-doped lithium cobalt oxide cathode material obtained in step (2) to it. Stir, heat, evaporate, grind and sinter to obtain lithium titanium lanthanum phosphate coated with magnesium-doped lithium cobalt oxide cathode material.

[0016] The method for synthesizing cathode materials firstly involves magnesium doping, which can regulate the defects and their distribution within lithium cobalt oxide particles, thereby suppressing the structural phase transition that leads to the degradation of the electrochemical performance of lithium cobalt oxide materials during high-voltage charging and discharging. Secondly, by coating the surface with lithium lanthanum titanium phosphate, which has high structural and electrochemical stability, a uniform interface layer with excellent ionic and electronic conductivity is constructed. Finally, by combining the dual-modified lithium cobalt oxide materials, the surface stability problem of lithium cobalt oxide materials during high-voltage charging is effectively solved.

[0017] Preferably, step (1) includes the following steps: mixing the cobalt source and the lithium source evenly and sintering them once, wherein the molar ratio of cobalt in the cobalt source to lithium in the lithium source is 1:(1.02-1.10); the cobalt source is one or more of cobalt oxide, cobalt carbonate, and cobalt acetate, and the lithium source is lithium hydroxide and / or lithium carbonate.

[0018] Lithium volatilizes during the calcination process, therefore the lithium in the lithium source must be in excess of the cobalt in the cobalt source, and this excess must be controlled within an appropriate range after sintering. If the excess is too small, the excess lithium source will not be enough to compensate for the amount of lithium volatilized during sintering; if the excess is too large, it is easy to leave residues in the product, which will further form residual lithium and affect performance.

[0019] Preferably, the cobalt source and lithium source are mixed by ball milling for 3-8 hours; the first calcination is a low-temperature calcination, with the temperature increased to 550-650°C at a rate of 1-10°C / min, and sintered for 4-6 hours in an air or oxygen atmosphere.

[0020] The primary process of sintering involves the decomposition and mutual reaction of cobalt and lithium sources. If the sintering temperature is too low or the time is too short, the cobalt and lithium sources cannot be completely decomposed. If the temperature is too high or the time is too long, side reactions will occur in addition to the decomposition and reaction of the cobalt and lithium sources. Furthermore, excessively high temperatures and long times will increase energy consumption.

[0021] Preferably, in step (2), the molar amount of magnesium in the magnesium source is less than 1% of the molar amount of cobalt in the lithium cobalt oxide precursor, and the magnesium source is one or more of magnesium oxide, magnesium carbonate, and magnesium hydroxide.

[0022] If too little magnesium is added, it will not have a significant impact on the stable structure of lithium cobalt oxide and will not be able to control defects. If too much magnesium is added, it will reduce the capacity of the doped material.

[0023] Preferably, in step (2), the lithium cobalt oxide precursor material is mixed with the magnesium source by ball milling or grinding, and the secondary calcination is carried out at a rate of 1-10℃ / min to 800-1000℃, more preferably 850-950℃, and sintered for 8-12 hours in an air or oxygen atmosphere.

[0024] The precursor formed after the first sintering of lithium cobalt oxide is introduced with a magnesium source during the second sintering process, allowing magnesium to enter the bulk phase under high temperature conditions. The second sintering process mainly involves the growth of lithium cobalt oxide particles after magnesium doping enters the bulk phase, while simultaneously regulating the internal defects and distribution of the particles. If the sintering temperature is too low or the time is too short, the growth and development of lithium cobalt oxide particles will be incomplete, and the magnesium doping effect will be unsatisfactory. If the temperature is too high or the time is too long, side reactions will occur, causing severe volatilization of reactants and resulting in deviations in the chemical formula. Furthermore, excessively high temperatures and long times will increase energy consumption.

[0025] Preferably, the preparation of lithium titanium lanthanum phosphate in step (3) specifically involves: adding a phosphorus source to an organic solvent, then dissolving a lithium source and a lanthanum source therein, and finally adding a titanium source. The preparation process is carried out in an anhydrous environment. The lithium source is one or more of lithium nitrate, lithium acetate, and lithium hydroxide. The lanthanum source is one or more of lanthanum nitrate, lanthanum chloride, and lanthanum oxide. The titanium source is tetrabutyl titanate, and the phosphorus source is phosphoric acid. The solvent is anhydrous ethanol, ethylene glycol, or other organic solvents.

[0026] The phosphorus source is a phosphoric acid solution. First, an easily dispersed phosphoric acid source is added. Then, the lithium and lanthanum sources are added as solid particles. Finally, an easily hydrolyzable titanium source is added to ensure the smooth preparation of lithium titanium lanthanum phosphate.

[0027] Preferably, after adding magnesium-doped lithium cobalt oxide particles in step (3), the solid-liquid ratio is adjusted to 1:(10-50); if the solid content is too high or too low, it will affect the uniformity of the coating layer formed subsequently.

[0028] The stirring is carried out at room temperature, with a rotation speed of 300-500 r / min, for 6-8 hours. The synthesis of the reactants is controlled under room temperature conditions, and a homogeneous coating layer is formed in the solution. Too low a temperature or too short a time is not conducive to the synthesis of the coating layer, while too high a temperature or too long a time will cause the solvent to evaporate, resulting in incomplete coating formation and coating process.

[0029] The heating process involves raising the temperature to 70-80°C after stirring at room temperature; the evaporation process involves heating and stirring until the solvent evaporates; after the reaction is complete and the initial coating is achieved, the solution needs to be evaporated to dryness and the coating material needs to be evenly coated on the surface of the particles. The evaporation temperature should be moderate. If the temperature is too low, the evaporation time will be too long and side reactions may occur. If the temperature is too high, the evaporation process will be too fast and the coating will be uneven.

[0030] The grinding process involves re-grinding the product after it has been evaporated to dryness. The product may exhibit agglomeration after evaporation, and grinding further disperses the particles evenly.

[0031] Preferably, the sintering process involves heating to 500-700°C at a rate of 1-10°C / min and sintering for 5-10 hours in an air or oxygen atmosphere. This sintering process primarily involves the uniform dispersion and reinforcement of the lithium lanthanum titanium phosphate coating. If the temperature is too low or the time is too short, the coating will not be effectively dispersed and reinforced. If the temperature is too high or the time is too long, the coating will decompose and damage the material structure.

[0032] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0033] (1) The magnesium-doped lithium cobalt oxide cathode material coated with lithium lanthanum titanium phosphate obtained in this invention has the following advantages: First, magnesium doping can regulate the defects and their distribution inside the lithium cobalt oxide particles, thereby suppressing the structural phase transition that causes the electrochemical performance of the lithium cobalt oxide material to decay during high-voltage charging and discharging. Second, the surface is coated with lithium lanthanum titanium phosphate, which has high structural and electrochemical stability, to construct a uniform interface layer with excellent ionic and electronic conductivity. Finally, magnesium doping occupies lithium sites, and the lithium ions after the raw materials are replaced are reused on the surface. In other words, by utilizing the residual lithium on the surface, a three-dimensional conductive coating layer of NASICON-type fast ion conductor is constructed on the particle surface to promote the rapid conduction of lithium ions. By combining the dual-modified lithium cobalt oxide material, the surface stability problem of lithium cobalt oxide material during high-voltage charging is effectively solved.

[0034] (2) The synthesis method of the materials solicited in this invention involves the synergistic modification of lithium cobalt oxide by magnesium doping and lithium titanium phosphate coating. Doping is performed by forming a precursor after the lithium cobalt oxide is sintered at low temperature once. During the second sintering process, a magnesium source is introduced to allow magnesium to enter the bulk phase under high temperature conditions. After the magnesium doping enters the bulk phase, the lithium cobalt oxide particles grow, while controlling the internal defects and distribution of the particles. Coating is performed by uniformly dispersing the magnesium-doped lithium cobalt oxide cathode material in an organic solution, and then introducing a lithium source, lanthanum source, titanium source, and phosphorus source to grow a layer of lithium titanium phosphate coating on the surface of the material. Finally, the material is treated at low temperature to obtain the lithium titanium phosphate coated magnesium-doped lithium cobalt oxide cathode material. The resulting lithium titanium phosphate coating layer is uniformly dispersed and firm, which can improve the stability of the lithium cobalt oxide particles. Attached Figure Description

[0035] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0036] Figure 1 This is the XRD pattern of the magnesium-doped lithium cobalt oxide cathode material coated with lithium lanthanum titanium phosphate in Example 1 of the present invention.

[0037] Figure 2 This is a SEM image of the magnesium-doped lithium cobalt oxide cathode material coated with lithium lanthanum titanium phosphate in Example 1 of this invention.

[0038] Figure 3 The figures show the charge-discharge cycle curves and charge-discharge coulomb curves of the battery assembled using the magnesium-doped lithium cobalt oxide cathode material coated with titanium lanthanum lithium in Example 1 of this invention and its preparation method.

[0039] Figure 4 The figures show the charge-discharge cycle curves and charge-discharge coulomb curves of the battery assembled using the magnesium-doped lithium cobalt oxide cathode material coated with titanium lanthanum lithium in Example 2 of this invention and its preparation method.

[0040] Figure 5 The figures show the charge-discharge cycle curves and charge-discharge coulomb curves of the battery assembled using the magnesium-doped lithium cobalt oxide cathode material coated with titanium lanthanum lithium in Example 3 of this invention and its preparation method.

[0041] Figure 6 This is a SEM image of the lithium cobalt oxide cathode material of Comparative Example 1 of this invention.

[0042] Figure 7 This is a SEM image of magnesium-doped lithium cobalt oxide, which is the comparative example 2 of this invention.

[0043] Figure 8 This is a SEM image of magnesium-doped lithium cobalt oxide, which is the comparative example of this invention. Detailed Implementation

[0044] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0045] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0046] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0047] Example 1:

[0048] A magnesium-doped lithium cobalt oxide cathode material coated with lithium titanium lanthanum phosphate is disclosed, wherein lithium cobalt oxide particles are used as the matrix, lithium titanium lanthanum phosphate is uniformly coated on the surface of the lithium cobalt oxide particles, and magnesium is doped inside the lithium cobalt oxide particles.

[0049] The chemical formula is Mg-LiCoO2@Li 1.3 La 0.3 Ti 1.7The coating amount of (PO4)3, lanthanum titanium phosphate lithium is 0.6 wt% of the magnesium-doped lithium cobalt oxide particles, and the magnesium doping content is 1 mol% of the cobalt content in the cathode material.

[0050] Its preparation method includes the following steps:

[0051] (1) Weigh 0.79271g (0.01073mol) Li2CO3 and 1.6402g (0.0068mol) Co3O4, place them in a ball mill jar, and mix and grind for 5h. In an oxygen atmosphere, heat to 600℃ at a rate of 5℃ / min and hold for 5h, then cool to room temperature to obtain lithium cobalt oxide precursor material.

[0052] (2) Weigh 0.008236g (0.204mmol) MgO and add it to 2g (0.020435mol) of the lithium cobalt oxide precursor material obtained in step (2). Grind for 0.5h and then sinter at 900℃ for 10h at the first stage heating rate to obtain magnesium-doped lithium cobalt oxide cathode material.

[0053] (3) Dissolve 0.0048 mL (0.0917 mmol) of H3PO4 in 30 mL of anhydrous ethanol, then add 0.00274 g (0.03974 mmol) of LiNO3 and 0.003971 g (0.00917 mmol) of La(NO3)3·6H2O, and finally weigh out 0.017686 mL (0.051969 mmol) of C 16 H 36 After mixing O4Ti evenly, add 2g (0.020435mmol) of the magnesium-doped lithium cobalt oxide cathode material obtained in step (2), stir at room temperature for 6h, heat to 80℃ until dry, take out and grind for 0.5h, heat to 600℃ at a rate of 5℃ / min in an oxygen atmosphere and hold for 6h, cool down to room temperature to obtain the magnesium-doped lithium cobalt oxide cathode material coated with lithium titanium lanthanum lithium.

[0054] like Figure 1 As shown, the characteristic peaks of the lithium titanium phosphate-coated magnesium-doped lithium cobalt oxide cathode material in this embodiment match those of the LiCoO2 (PDF#75-0532) on the PDF card, and no impurity phase is generated.

[0055] like Figure 2 As shown in the SEM image of the magnesium-doped lithium cobalt oxide cathode material coated with lithium lanthanum titanium phosphate in this embodiment, there is a clear coating on the surface.

[0056] Battery Assembly: Weigh 0.08g of the lithium titanium phosphate lanthanum lithium-coated magnesium-doped lithium cobalt oxide positive electrode material obtained in this embodiment, add 0.01g of acetylene black as a conductive agent and 0.01g of PVDF polyvinylidene fluoride as a binder, and mix and grind with N-methylpyrrolidone as a solvent to form a positive electrode material; coat the obtained positive electrode material onto the surface of aluminum foil to form an electrode sheet; in a sealed glove box filled with argon gas, use the electrode sheet as the positive electrode, a lithium metal sheet as the negative electrode, a microporous polypropylene membrane as the separator, and 1mol / L LiPF6 / EC:DMC:DEC (volume ratio 1:1:1) as the electrolyte to assemble a CR2025 coin cell, and perform charge and discharge performance tests.

[0057] like Figure 3 As shown, the battery assembled from the titanium lanthanum lithium-coated magnesium-doped lithium cobalt oxide cathode material and its preparation method obtained in this embodiment exhibits the following characteristics: Initial discharge specific capacity: 192.6 mAh / g; initial charge specific capacity: 200.4 mAh / g; initial charge-discharge coulombic efficiency: 96.15% at a charge-discharge voltage of 2.7-4.5V and a current density of 0.1C (1C = 200 mA / g). At a 1C current density, the initial discharge specific capacity: 191.6 mAh / g; initial charge specific capacity: 195.2 mAh / g; initial charge-discharge coulombic efficiency: 98.2%. After 100 cycles at a 1C current density, the discharge specific capacity remains as high as 181.8 mAh / g, with a capacity retention rate of 94.89%. This demonstrates that the method of coating magnesium-doped lithium cobalt oxide cathode material with titanium lanthanum lithium-coated magnesium-doped lithium-cobalt oxide in this embodiment facilitates lithium-ion transport during charge-discharge, resulting in stable discharge specific capacity, charge-discharge performance, and coulombic efficiency, and good cycle performance.

[0058] Example 2:

[0059] A lithium titanium lanthanum lithium-coated magnesium-doped lithium cobalt oxide cathode material is disclosed, wherein lithium cobalt oxide particles are used as the matrix, lithium titanium lanthanum lithium-coated lithium cobalt oxide particles are uniformly coated on the surface of the lithium cobalt oxide particles, and magnesium elements are doped inside the lithium cobalt oxide particles.

[0060] The chemical formula is Mg-LiCoO2@Li 1.3 La 0.3 Ti 1.7 The coating amount of (PO4)3, lanthanum titanium phosphate lithium is 0.9 wt% of the magnesium-doped lithium cobalt oxide particles, and the magnesium doping content is 1 mol% of the cobalt content in the cathode material.

[0061] The preparation method includes the following steps:

[0062] (1) Weigh 0.79271g (0.01073mol) Li2CO3 and 1.6402g (0.0068mol) Co3O4, place them in a ball mill jar, and mix and grind for 5h. In an oxygen atmosphere, heat to 600℃ at a rate of 5℃ / min and hold for 5h, then cool to room temperature to obtain lithium cobalt oxide precursor material.

[0063] (2) Weigh 0.008236g (0.204mmol) MgO and add it to 2g (0.020435mol) of the lithium cobalt oxide precursor material obtained in step (2). Grind for 0.5h and then sinter at 900℃ for 10h at the first stage heating rate to obtain magnesium-doped lithium cobalt oxide cathode material.

[0064] (3) Dissolve 0.0072 mL (0.13756 mmol) of H3PO4 in 35 mL of anhydrous ethanol, then add 0.00411 g (0.059612 mmol) of LiNO3 and 0.0059567 g (0.013757 mmol) of La(NO3)3·6H2O, and finally weigh 0.026529 mL (0.077954 mmol) of C 16 H 36 After mixing O4Ti evenly, add 2g (0.020435mmol) of the magnesium-doped lithium cobalt oxide cathode material obtained in step (2), stir at room temperature for 6h, heat to 80℃ until dry, take out and grind for 0.5h, heat to 600℃ at a rate of 5℃ / min in an oxygen atmosphere and hold for 6h, cool down to room temperature to obtain the magnesium-doped lithium cobalt oxide cathode material coated with lithium titanium lanthanum lithium.

[0065] Testing revealed that the characteristic peaks of the lithium titanium phosphate lanthanum lithium-coated magnesium-doped lithium cobalt oxide cathode material in this embodiment match those of the LiCoO2 (PDF#75-0532) data from the PDF card, and no impurity phases were generated.

[0066] The SEM image of the magnesium-doped lithium cobalt oxide cathode material coated with lithium lanthanum titanium phosphate in this embodiment shows a distinct coating layer on the surface.

[0067] Battery assembly: Same as in Example 1.

[0068] like Figure 4As shown, the battery assembled from the titanium lanthanum lithium-coated magnesium-doped lithium cobalt oxide cathode material and its preparation method obtained in this embodiment exhibits the following characteristics: initial discharge specific capacity of 195.5 mAh / g, charging specific capacity of 204.6 mAh / g, and initial charge-discharge coulombic efficiency of 95.57% at a charge-discharge voltage of 2.7-4.5V and a current density of 0.1C (1C = 200 mA / g). At a 1C current density, the initial discharge specific capacity is 184.2 mAh / g, the charging specific capacity is 195.5 mAh / g, and the initial charge-discharge coulombic efficiency is 97.96%. After 100 cycles at a 1C current density, the discharge specific capacity remains as high as 175.3 mAh / g, with a capacity retention rate of 95.17%. This demonstrates that the method of coating magnesium-doped lithium cobalt oxide cathode material with titanium lanthanum lithium-coated magnesium-doped lithium-cobalt oxide in this embodiment facilitates lithium-ion transport during charge-discharge, resulting in stable discharge specific capacity, charge-discharge performance, and coulombic efficiency, as well as good cycle performance.

[0069] Example 3:

[0070] A lithium titanium lanthanum lithium-coated magnesium-doped lithium cobalt oxide cathode material is disclosed, wherein lithium cobalt oxide particles are used as the matrix, lithium titanium lanthanum lithium-coated lithium cobalt oxide particles are uniformly coated on the surface of the lithium cobalt oxide particles, and magnesium elements are doped inside the lithium cobalt oxide particles.

[0071] The chemical formula is Mg-LiCoO2@Li 1.2 La 0.2 Ti 1.8 The coating amount of (PO4)3, lanthanum titanium phosphate lithium is 0.3 wt% of magnesium-doped lithium cobalt oxide particles, and the magnesium doping content is 1.2 mol% of the cobalt content in the cathode material.

[0072] The preparation method includes the following steps:

[0073] (1) Weigh 0.40013g (0.0054mol) Li2CO3 and 0.8201g (0.0034mol) Co3O4, place them in a ball mill jar, and mix and grind for 5h. In an oxygen atmosphere, heat to 600℃ at a rate of 5℃ / min and hold for 5h, then cool to room temperature to obtain lithium cobalt oxide precursor material.

[0074] (2) Weigh 0.00494g (0.12mmol) MgO and add it to 1g (0.01022mol) of the lithium cobalt oxide precursor material obtained in step (2). Grind for 0.5h and then sinter at 900℃ for 10h at the first stage heating rate to obtain magnesium-doped lithium cobalt oxide cathode material.

[0075] (3) Dissolve 0.0024 mL (0.046049 mmol) of H3PO4 in 25 mL of anhydrous ethanol, then add 0.00127 g (0.018419 mmol) of LiNO3 and 0.001329 g (0.000307 mmol) of La(NO3)3·6H2O, and finally weigh 0.009403 mL (0.047049 mmol) of C 16 H 36 After mixing O4Ti evenly, add 1g (0.01022mol) of the magnesium-doped lithium cobalt oxide cathode material obtained in step (2), stir at room temperature for 6h, heat to 80℃ until dry, take out and grind for 0.5h, heat to 600℃ at a rate of 5℃ / min in an oxygen atmosphere and hold for 6h, cool down to room temperature to obtain the magnesium-doped lithium cobalt oxide cathode material coated with lithium titanium lanthanum lithium.

[0076] Testing revealed that the characteristic peaks of the lithium titanium phosphate lanthanum lithium-coated magnesium-doped lithium cobalt oxide cathode material in this embodiment match those of the LiCoO2 (PDF#75-0532) data from the PDF card, and no impurity phases were generated.

[0077] The SEM image of the magnesium-doped lithium cobalt oxide cathode material coated with lithium lanthanum titanium phosphate in this embodiment shows a distinct coating layer on the surface.

[0078] Battery assembly: Same as in Example 1.

[0079] like Figure 5 As shown, the battery assembled from the titanium lanthanum lithium-coated magnesium-doped lithium cobalt oxide cathode material and its preparation method obtained in this embodiment exhibits the following characteristics: Initial discharge specific capacity of 188.5 mAh / g, initial charge specific capacity of 197.4 mAh / g, and initial charge-discharge coulombic efficiency of 95.49% at a charge-discharge voltage of 2.7-4.5V and a current density of 0.1C (1C = 200 mA / g). At a 1C current density, the initial discharge specific capacity is 182.2 mAh / g, the initial charge specific capacity is 185.5 mAh / g, and the initial charge-discharge coulombic efficiency is 98.24%. After 100 cycles at a 1C current density, the discharge specific capacity remains as high as 173 mAh / g, with a capacity retention rate of 94.95%. This demonstrates that the method of coating magnesium-doped lithium cobalt oxide cathode material with titanium lanthanum lithium-coated magnesium-doped lithium-cobalt oxide in this embodiment facilitates lithium-ion transport during charge-discharge processes, resulting in stable discharge specific capacity, charge-discharge performance, and coulombic efficiency, as well as good cycle performance.

[0080] Comparative Example 1:

[0081] A method for preparing a lithium cobalt oxide cathode material includes the following steps:

[0082] (1) Weigh 0.79271g (0.01073mol) Li2CO3 and 1.6402g (0.0068mol) Co3O4, place them in a ball mill jar, and mix and grind for 5h.

[0083] (2) The uniformly mixed material obtained in step (1) is heated to 600°C at a rate of 5°C / min and held for 5 hours in an oxygen atmosphere. After cooling to room temperature, the material is taken out and ground for 30 minutes. Then, it is heated to 900°C at the first stage heating rate and sintered for 10 hours to obtain the lithium cobalt oxide cathode material.

[0084] Testing showed that the characteristic peaks of the lithium cobalt oxide cathode material in this embodiment matched those of the LiCoO2 (PDF#75-0532) PDF card, and no impurity phases were generated.

[0085] like Figure 6 The image shown is a SEM image of the lithium cobalt oxide cathode material in this embodiment.

[0086] Battery assembly: Same as in Example 1.

[0087] Testing revealed that the lithium cobalt oxide cathode material and its preparation method obtained in this comparative example, when assembled into a battery, exhibited the following characteristics under charging / discharging voltages: 2.7-4.5V, 0.1C (1C = 200mA / g) current density: initial discharge specific capacity of 192 mAh / g, charging specific capacity of 203.8 mAh / g, and initial charge / discharge coulombic efficiency of 94.2%. At 1C current density, the initial discharge specific capacity was 185.5 mAh / g, and the charging specific capacity was 190.2 mAh / g. After 100 cycles at 1C current density, the discharge specific capacity decreased to 134 mAh / g, with a capacity retention rate of only 72.24%.

[0088] Comparative Example 2:

[0089] A method for preparing a magnesium-doped lithium cobalt oxide cathode material includes the following steps:

[0090] (1) Weigh 0.79271g (0.01073mol) Li2CO3 and 1.6402g (0.0068mol) Co3O4, place them in a ball mill jar, and mix and grind for 5h.

[0091] (2) The uniformly mixed material obtained in step (1) is heated to 600°C at a rate of 5°C / min and held for 5 hours in an oxygen atmosphere, and then cooled to room temperature to obtain lithium cobalt oxide precursor material.

[0092] (3) Weigh 0.008236g (0.000204mol) MgO and add it to 2g (0.020435mol) of the lithium cobalt oxide precursor material obtained in step (2). Grind for 0.5h and then sinter at 900℃ for 10h at the first stage heating rate to obtain magnesium-doped lithium cobalt oxide cathode material.

[0093] Testing showed that the characteristic peaks of the lithium cobalt oxide cathode material in this embodiment matched those of the LiCoO2 (PDF#75-0532) PDF card, and no impurity phases were generated.

[0094] like Figure 7 The image shown is a SEM image of the magnesium-doped lithium cobalt oxide cathode material in this embodiment.

[0095] Battery assembly: Same as in Example 1.

[0096] Testing revealed that the battery assembled from the magnesium-doped lithium cobalt oxide cathode material and its preparation method obtained in this comparative example exhibited the following characteristics: Initial discharge specific capacity of 190.6 mAh / g and initial charge specific capacity of 203.1 mAh / g at a charge / discharge voltage of 2.7-4.5V and a current density of 0.1C (1C = 200 mA / g), with an initial charge / discharge coulombic efficiency of 93.85%. At a 1C current density, the initial discharge specific capacity was 181.6 mAh / g, and the initial charge specific capacity was 186.3 mAh / g. After 100 cycles at a 1C current density, the discharge specific capacity decreased to 152.3 mAh / g, with a capacity retention rate of 83.87%.

[0097] Comparative Example 3:

[0098] A method for preparing a magnesium-doped lithium cobalt oxide cathode material includes the following steps:

[0099] (1) Weigh 0.40013g (0.005415mol) Li2CO3 and 0.82011g (0.0034057mol) Co3O4, place them in a ball mill jar, and mix and grind for 5h.

[0100] (2) The uniformly mixed material obtained in step (1) is heated to 600°C at a rate of 5°C / min and held for 5 hours in an oxygen atmosphere, and then cooled to room temperature to obtain lithium cobalt oxide precursor material.

[0101] (3) Weigh 0.00494g (0.00012mol) MgO and add it to 1g (0.01022mol) of the lithium cobalt oxide precursor material obtained in step (2). Grind for 0.5h and then sinter at 900℃ for 10h at the first stage heating rate to obtain magnesium-doped lithium cobalt oxide cathode material.

[0102] Testing showed that the characteristic peaks of the lithium cobalt oxide cathode material in this embodiment matched those of the LiCoO2 (PDF#75-0532) PDF card, and no impurity phases were generated.

[0103] like Figure 8 The image shown is a SEM image of the magnesium-doped lithium cobalt oxide cathode material in this embodiment.

[0104] Battery assembly: Same as in Example 1.

[0105] Testing revealed that the battery assembled from the magnesium-doped lithium cobalt oxide cathode material and its preparation method obtained in this comparative example exhibited the following characteristics: Initial discharge specific capacity of 182 mAh / g and initial charge specific capacity of 193.2 mAh / g at a charge / discharge voltage of 2.7-4.5V and a current density of 0.1C (1C = 200 mA / g), with an initial charge / discharge coulombic efficiency of 94.2%. At a 1C current density, the initial discharge specific capacity was 181.1 mAh / g, and the initial charge specific capacity was 186.4 mAh / g. After 100 cycles at a 1C current density, the discharge specific capacity decreased to 146.2 mAh / g, with a capacity retention rate of 80.73%.

Claims

1. A lithium titanium phosphate lanthanum lithium-coated magnesium-doped lithium cobalt oxide cathode material, characterized in that, The cathode material uses lithium cobalt oxide particles as the matrix, and lithium titanium lanthanum lithium phosphate is uniformly coated on the surface of the lithium cobalt oxide particles. Magnesium ions are doped inside the lithium cobalt oxide particles. The chemical formula of the lithium titanium lanthanum phosphate-coated magnesium-doped lithium cobalt oxide cathode material is Mg-LiCoO2@Li 1+x La x Ti 2-x (PO4)3, wherein 0.2 < x < 0.5, the coating amount of the titanium lanthanum lithium phosphate is less than 2.0 wt% of the magnesium-doped lithium cobalt oxide particles, and the magnesium doping content is less than or equal to 1.2 mol% of the cobalt content in the cathode material; the titanium lanthanum lithium phosphate coated magnesium-doped lithium cobalt oxide cathode material is prepared by the following preparation method: (1) the cobalt source and the lithium source are mixed evenly and sintered to prepare the lithium cobalt oxide precursor material; (2) the lithium cobalt oxide precursor material obtained in step (1) is mixed with the magnesium source and sintered twice to obtain magnesium-doped lithium cobalt oxide particles; (3) the lithium source, lanthanum source, titanium source and phosphorus source are dissolved to prepare titanium lanthanum lithium phosphate, and the magnesium-doped lithium cobalt oxide cathode material obtained in step (2) is added to it, stirred, heated, evaporated, ground and sintered to obtain the titanium lanthanum lithium phosphate coated magnesium-doped lithium cobalt oxide cathode material.

2. A method for preparing the magnesium-doped lithium cobalt oxide cathode material coated with lithium lanthanum titanium phosphate as described in claim 1, characterized in that, Includes the following steps: (1) Mix cobalt source and lithium source evenly and sinter to prepare lithium cobalt oxide precursor material; (2) The lithium cobalt oxide precursor material obtained in step (1) is mixed with a magnesium source and sintered twice to obtain magnesium-doped lithium cobalt oxide particles. (3) Dissolve lithium source, lanthanum source, titanium source and phosphorus source to prepare lithium titanium lanthanum phosphate, and add magnesium-doped lithium cobalt oxide cathode material obtained in step (2) to it. Stir, heat, evaporate, grind and sinter to obtain lithium titanium lanthanum phosphate coated with magnesium-doped lithium cobalt oxide cathode material.

3. The preparation method according to claim 2, characterized in that, Step (1) includes the following steps: mixing cobalt source and lithium source evenly and sintering once, wherein the molar ratio of cobalt in cobalt source to lithium in lithium source is 1:(1.02-1.10); wherein the cobalt source is one or more of cobalt oxide, cobalt carbonate, and cobalt acetate, and the lithium source is lithium hydroxide and / or lithium carbonate.

4. The preparation method according to claim 3, characterized in that, The cobalt source and lithium source are mixed by ball milling for 3-8 hours; the first sintering is a low-temperature calcination, with the temperature increased to 550-650℃ at a rate of 1-10℃ / min, and sintered for 4-6 hours in an air or oxygen atmosphere.

5. The preparation method according to claim 2, characterized in that, In step (2), the molar amount of magnesium in the magnesium source is less than 1% of the molar amount of cobalt in the lithium cobalt oxide precursor, and the magnesium source is one or more of magnesium oxide, magnesium carbonate, and magnesium hydroxide.

6. The preparation method according to claim 2, characterized in that, In step (2), the lithium cobalt oxide precursor material is mixed with the magnesium source by ball milling or grinding, and the secondary sintering is carried out at a rate of 1-10℃ / min to 800-1000℃ for 8-12 h in an air or oxygen atmosphere.

7. The preparation method according to claim 2, characterized in that, The preparation of lithium titanium lanthanum phosphate in step (3) is as follows: a phosphorus source is added to an organic solvent, then a lithium source and a lanthanum source are dissolved in it, and finally a titanium source is added. The preparation process is carried out in an anhydrous environment. The lithium source is one or more of lithium nitrate, lithium acetate, and lithium hydroxide. The lanthanum source is one or more of lanthanum nitrate, lanthanum chloride, and lanthanum oxide. The titanium source is tetrabutyl titanate, and the phosphorus source is phosphoric acid. The solvent is one or more of anhydrous ethanol and ethylene glycol.

8. The preparation method according to claim 2, characterized in that, After adding magnesium-doped lithium cobalt oxide particles in step (3), the solid-liquid ratio is adjusted to 1:(10-50); the stirring is carried out at room temperature with a rotation speed of 300-500 r / min for 6-8 h; the heating is carried out after stirring at room temperature, and the temperature is raised to 70-80℃ during stirring; the evaporation is carried out by heating and stirring until the solvent evaporates; the grinding is carried out by grinding the dried product again.

9. The preparation method according to claim 2, characterized in that, The sintering described in step (3) involves heating to 500-700℃ at a rate of 1-10℃ / min and sintering for 5-10 hours in an air or oxygen atmosphere.

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