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

Abstract

The application discloses a high-voltage lithium cobalt oxide positive active material and a preparation method and application thereof, the preparation method selects existing LiCoO2 as a precursor, PVP as a surfactant, and the two are added into anhydrous ethanol and uniformly mixed; phytic acid is used as a dopant to provide phosphorus elements and is dissolved in anhydrous ethanol; then the ethanol solution in which the phytic acid is dissolved is slowly added into a LiCoO2 / PVP / ethanol mixed solution. After being uniformly mixed, centrifugation / washing / drying are carried out to obtain a solid powder, the solid powder is pre-sintered in an argon atmosphere, and then high-temperature sintering is carried out in an air atmosphere, so that a P-doped modified LiCoO2 positive electrode material is finally obtained. The preparation method is green and safe, is suitable for large-scale industrial production, and the cyclic stability of the LiCoO2 positive electrode material after doping P is significantly improved at a high voltage of 4.5 V.

Description

Technical Field

[0001] This invention relates to the field of high-performance cathode materials for lithium-ion batteries, and in particular to a high-voltage lithium cobalt oxide cathode active material, its preparation method, and its application. Background Technology

[0002] With the continued rapid development of portable electronic devices and electric vehicles, human society has placed more stringent demands on the widely used lithium-ion battery system, and the positive electrode active material plays a dominant role in the performance of lithium-ion batteries. Therefore, the research and development of high-performance lithium-ion battery positive electrode materials with characteristics such as high specific capacity, high energy density, and long cycle stability is of great significance to promoting social development.

[0003] LiCoO2 (lithium cobalt oxide) was one of the earliest commercially produced and widely used cathode materials for lithium-ion batteries. It is widely used due to its advantages such as a wide operating voltage range, high theoretical specific capacity, high energy density, and mature processing technology. However, the actual specific capacity of lithium cobalt oxide is only about 140 mAh / g, only 50% of its theoretical specific capacity (274 mAh / g). Increasing the operating voltage can significantly improve the specific capacity of LiCoO2, but under high voltage conditions (>4.5V), excessive lithium ions will "deintercalate and reintercalate," causing the crystal structure of LiCoO2 to change from a hexagonal system to a monoclinic system without electrochemical properties. Simultaneously, the asymmetric lattice contraction and expansion of the material severely damages its structural stability, leading to a sharp deterioration in its cycle performance and coulombic efficiency under high voltage. Summary of the Invention

[0004] This invention provides a high-voltage lithium cobalt oxide cathode active material, its preparation method, and its application, which overcomes the defects of existing technologies such as poor cycle performance and coulombic efficiency under high voltage.

[0005] To achieve the above objectives, this invention proposes a method for preparing a high-voltage lithium cobalt oxide cathode active material, comprising the following steps:

[0006] S1: Add LiCoO2 and PVP to anhydrous ethanol and stir until completely dissolved;

[0007] S2: Dissolve phytic acid in anhydrous ethanol and stir until completely dissolved;

[0008] S3: Add the ethanol solution containing phytic acid dropwise to the LiCoO2 / PVP / ethanol mixed solution obtained in step S1, and stir to mix evenly;

[0009] S4: The mixture obtained in S3 is centrifuged, dried, and then pre-sintered in an inert atmosphere, followed by sintering in an air atmosphere to obtain phosphorus-doped modified LiCoO2 cathode active material.

[0010] To achieve the above objectives, the present invention also proposes a high-voltage lithium cobalt oxide cathode active material, which is prepared by the preparation method described above; the cathode active material is a phosphorus-doped LiCoO2 cathode material, which is composed of phosphorus-doped lithium cobalt oxide particles.

[0011] To achieve the above objectives, the present invention also proposes an application of a high-voltage lithium cobalt oxide positive electrode active material, which applies the positive electrode active material prepared by the above preparation method or the above-described positive electrode active material to a lithium-ion battery.

[0012] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0013] 1. The high-voltage lithium cobalt oxide cathode active material provided by this invention has a small amount of phosphorus (P) uniformly incorporated into its surface to enhance structural strength and stability during cycling. Currently, commercially produced LiCoO2 materials have a specific capacity of only about 50% of their theoretical capacity. When the charging cut-off voltage is increased to obtain higher capacity, severe irreversible structural changes occur, leading to a sharp deterioration in cycle performance and significantly limiting their application range. The main reason for this is that under high-voltage operating conditions, oxygen (O) elements in LiCoO2 detach from the crystal lattice, causing the collapse of its layered structure. To address the shortcomings of existing technologies, the cathode active material prepared by the method provided in this invention has P elements uniformly incorporated into the surface lattice of the modified lithium cobalt oxide. The P elements occupy Co element positions and form stronger ionic bonds with O elements, preventing the detachment of O elements from the lithium cobalt oxide material during cycling. Furthermore, the P elements support the layered structure, thereby stabilizing the LiCoO2 structure. Therefore, the cathode active material prepared by the method provided in this invention can significantly improve its cycle performance and coulombic efficiency under high voltage.

[0014] 2. Existing phosphorus doping processes generally utilize the high-temperature decomposition of phosphates such as sodium hypophosphite to generate phosphine, which is then used as the phosphorus source for doping. However, phosphine is highly toxic, posing safety hazards during the preparation process and hindering large-scale production. The present invention provides a method for preparing high-voltage lithium cobalt oxide cathode active materials. Firstly, anhydrous ethanol is selected as the solvent, commercially available large-scale LiCoO2 is used as the modified matrix, and PVP (polyvinylpyrrolidone) is used as the surfactant; phytic acid (C6H... 18 O 24P6 is used as a dopant to provide the phosphorus source, dissolved in anhydrous ethanol to obtain a solution. Then, the ethanol solution of phytic acid is slowly added dropwise to the LiCoO2 / PVP / ethanol mixed solution for uniform mixing. During the mixing process, PVP exhibits high surface activity, effectively improving the surface state of LiCoO2, allowing for uniform adsorption of phytic acid on the LiCoO2 surface. Furthermore, two sintering processes—pre-sintering under argon atmosphere and sintering under air atmosphere—ensure that the phytic acid adsorbed on the LiCoO2 surface incorporates phosphorus into the lithium cobalt oxide surface lattice, resulting in a structurally stable LiCoO2 cathode active material with excellent high-voltage cycle performance. The preparation method provided by this invention is green and environmentally friendly, suitable for large-scale commercial production. The prepared cathode material exhibits excellent structural stability, long-term cycle stability under high voltage, and high coulombic efficiency. Using this cathode material in lithium-ion batteries can enable lithium-ion batteries to have high actual specific capacity and energy density, excellent long-term cycle performance under high voltage, and high coulombic efficiency. Attached Figure Description

[0015] 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 only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0016] Figure 1 The XRD patterns of the doped P-LCO prepared in Example 1 and commercial P-LCO are shown below.

[0017] Figure 2 {111} crystal plane spectra of the doped P-LCO prepared in Example 1 and commercial P-LCO;

[0018] Figure 3 Here is a SEM image of the P-LCO doped material prepared in Example 1 at 500 nm.

[0019] Figure 4 The image shows a TEM image of the doped P-LCO obtained in Example 1 at 2 μm.

[0020] Figure 5 Here is an HRTEM image of the doped P-LCO obtained in Example 1 at 5 nm.

[0021] Figure 6 EDS image of P-LCO doped obtained in Example 1;

[0022] Figure 7 Image showing the elemental distribution of doped P-LCO obtained in Example 1;

[0023] Figure 8 The graph shows the cycle performance of the lithium-ion battery with P-LCO doped as the positive electrode prepared in Example 1.

[0024] Figure 9 The diagram shows the median voltage of a lithium-ion battery using the doped P-LCO obtained in Example 1 as the positive electrode.

[0025] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0026] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0027] Furthermore, the technical solutions of the various embodiments of the present invention can be combined with each other, but only if they are feasible for those skilled in the art. If the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention.

[0028] Unless otherwise specified, all medicines / reagents used are commercially available.

[0029] This invention proposes a method for preparing a high-voltage lithium cobalt oxide cathode active material, comprising the following steps:

[0030] S1: Add LiCoO2 and PVP to anhydrous ethanol and stir until completely dissolved.

[0031] S2: Dissolve phytic acid in anhydrous ethanol and stir until completely dissolved.

[0032] S3: Add the ethanol solution containing phytic acid dropwise to the LiCoO2 / PVP / ethanol mixed solution obtained in step S1, and stir to mix evenly.

[0033] S4: The mixture obtained in S3 is centrifuged, dried, and then pre-sintered in an inert atmosphere, followed by sintering in an air atmosphere to obtain phosphorus-doped modified LiCoO2 cathode active material.

[0034] After centrifugation, remove the supernatant and then dry.

[0035] Lithium cobalt oxide is one of the most mature cathode materials in commercial lithium-ion batteries, but its actual specific capacity is only 140 mAh g. -1Around [amount], which is only the theoretical capacity (274mAh g). -1 Approximately 50% of the capacity. Increasing the battery's operating voltage can significantly improve the specific capacity and energy density of the LiCoO2 cathode material. However, traditional lithium cobalt oxide cathode materials cannot operate directly above 4.5V. Charging under high voltage conditions leads to excessive lithium-ion "deintercalation" accompanied by the continuous extraction of oxygen elements from the crystal lattice, causing irreversible structural changes and resulting in rapid deterioration of the material's discharge capacity and cycle performance. To address these problems, this invention creatively utilizes phytic acid (C6H4O3)... 18 O 24 Phosphorus-doped lithium cobalt oxide was prepared using P6 as a phosphorus source to improve its cycling performance under high voltage.

[0036] Preferably, in step S1, the mass ratio of LiCoO2 to PVP is 1:1.5 to 2.5; the volume of anhydrous ethanol is 200 to 300 mL. A mass ratio of lithium cobalt oxide to PVP of 1:2 is optimal. Too little PVP will result in insufficient surface improvement of LiCoO2 and inability to uniformly adsorb dopants; while too much PVP will not only be wasteful but also reduce its own activity, leading to poor wetting and dispersion effects on the lithium cobalt oxide surface. An appropriate amount of PVP is beneficial for the uniform adsorption of dopants on the LiCoO2 surface, which is conducive to uniform doping in subsequent steps.

[0037] Preferably, in step S1, the stirring temperature is room temperature (~25°C) and the stirring time is 0.5~1 hour. The stirring time is preferably 1 hour to facilitate sufficient contact between LiCoO2 and PVP.

[0038] Preferably, in step S2, the volume fraction of phytic acid in the ethanol solution containing phytic acid is 2-3%. Considering the amount of lithium cobalt oxide used, the volume fraction of phytic acid is preferably 2.5%, because phytic acid provides the P source as a dopant. Too little phytic acid will result in a smaller amount of dopant element in the subsequent doping process, which will not significantly improve the cycling performance of lithium cobalt oxide under high voltage; while too much phytic acid will result in a larger amount of dopant element in the subsequent doping process, thereby causing a large distortion of the lithium cobalt oxide crystal structure, which is not conducive to its structural stability. Therefore, an appropriate amount of phytic acid can make the amount of dopant element in the subsequent doping process more moderate, improving its structural stability and cycling stability under high voltage without changing the crystal structure of the LiCoO2 cathode material.

[0039] Preferably, in step S2, the stirring temperature is room temperature (~25°C) and the stirring time is 0.5~1 hour. The stirring time is preferably 1 hour to facilitate the complete dissolution of phytic acid in ethanol.

[0040] Preferably, in step S3, the dropping rate is 3-5 mL / min; the stirring temperature is 60°C, and the stirring time is 0.5-1 h. The dropping rate is preferably 3 mL / min, and the stirring time is preferably 1 h, to ensure sufficient contact between LiCoO2 and phytic acid and to allow for uniform adsorption of phytic acid on its surface.

[0041] Preferably, in step S4, the centrifugation speed is 7500 r / min, the time is 3-5 min, and the number of centrifugations is 1-3; the drying temperature is 60-80℃, and the time is 4-5 h. The number of centrifugations is preferably 3 to thoroughly wash away residual PVP and unadsorbed phytic acid; the drying time is preferably 1 h to ensure no residual ethanol.

[0042] Preferably, in step S4, the pre-sintering process specifically includes:

[0043] In an argon atmosphere, the sintering temperature was increased from room temperature to 650°C at a heating rate of 2°C / min and held for 2 hours.

[0044] The sintering process is specifically as follows:

[0045] In an air atmosphere, the sintering temperature was increased from room temperature to 750°C at a heating rate of 5°C / min, and held at that temperature for 5 hours.

[0046] Pre-sintering in an argon atmosphere followed by sintering in an air atmosphere is beneficial for the uniform and sufficient doping of P element in the LiCoO2 lattice.

[0047] The present invention also proposes a high-voltage lithium cobalt oxide cathode active material, which is prepared by the preparation method described above; the cathode active material is a phosphorus-doped LiCoO2 cathode material, which is composed of phosphorus-doped lithium cobalt oxide particles.

[0048] This invention also proposes an application of a high-voltage lithium cobalt oxide cathode active material, which involves applying the cathode active material prepared by the above-described preparation method or the cathode active material described above to a lithium-ion battery.

[0049] Example 1

[0050] This embodiment provides a method for preparing a high-voltage lithium cobalt oxide cathode active material, including:

[0051] S1: Disperse 1.5g of commercially available ordinary LiCoO2 and 3g of surfactant PVP in 250mL of anhydrous ethanol and stir at room temperature (~25℃) for 30min;

[0052] S2: Add 1 mL of phytic acid to 40 mL of ethanol (volume fraction 2.5%) and stir at room temperature (~25℃) for 30 min;

[0053] S3: Add the ethanol solution of phytic acid obtained in step S2 dropwise to the LiCoO2 / PVP / ethanol mixed solution obtained in step S1 at a rate of 3 mL / min, and stir at 60 °C for 1 h.

[0054] S4: The mixture obtained in step S3 was washed with anhydrous ethanol and centrifuged three times at a speed of 7500 r / min for 3 min each time to obtain preliminarily modified LiCoO2 powder. It was then placed in a forced-air drying oven and dried at 60℃ for 1 h, and evaporated to dryness. The evaporated sample was placed in a ceramic crucible and then in a tube furnace. High-purity Ar gas was continuously introduced, and the temperature was increased to 650℃ at a rate of 2℃ / min under the Ar atmosphere and held for 2 h. After natural cooling, it was placed in a muffle furnace and heated to 750℃ at a rate of 5℃ / min under an air atmosphere and held for 5 h. After natural cooling, a high-voltage lithium cobalt oxide cathode active material was obtained.

[0055] Figure 1 The XRD patterns are those of the high-voltage lithium cobalt oxide cathode active material prepared in this embodiment and commercial lithium cobalt oxide. Figure 1 It can be seen that the prepared cathode material has an α-NaFeO2 type layered structure, and its crystal structure is consistent with that of commercial lithium cobalt oxide. The original structure was not destroyed by the doping treatment.

[0056] Figure 2 The image shows a comparison of the XRD peak positions of the high-voltage lithium cobalt oxide cathode active material prepared in this embodiment and the commercial lithium cobalt oxide {111} crystal plane. It can be seen that after doping treatment, the peak position is significantly shifted to the left, indicating that P replaces some Co sites and forms a stronger interionic bond with O, resulting in a smaller unit cell.

[0057] Figure 3 and Figure 4 The images shown are SEM and TEM images of the high-voltage lithium cobalt oxide cathode active material prepared in this embodiment. It can be seen that the particle size of the lithium cobalt oxide particles is about 4-5 micrometers, and they are composed of several lithium cobalt oxide nanoparticles.

[0058] Figure 5 The high-resolution TEM image of the high-voltage lithium cobalt oxide cathode active material prepared in this embodiment shows that the exposed crystal plane is {111}.

[0059] Figure 6 and Figure 7 The images show the EDS elemental energy spectrum and elemental distribution diagram of the high-voltage lithium cobalt oxide cathode active material prepared in this embodiment. It can be seen that the high-voltage lithium cobalt oxide prepared by doping treatment contains Co, O and P elements, and the three elements Co, O and P are uniformly distributed in the P-doped lithium cobalt oxide material.

[0060] The high-voltage lithium cobalt oxide cathode active material (P-LCO) prepared in this embodiment and commercially available P-LCO were used as cathodes in lithium-ion batteries, and charge-discharge cycle performance tests were conducted in the voltage range of 4.5V-3V; their cycle performance curves are shown below. Figure 8 As can be seen, at a charge / discharge current density of 1C, the initial discharge capacity of P-LCO is 192 mAh / g. After 155 charge / discharge cycles, its discharge capacity remains at 162 mAh / g, with a capacity retention of 84% and an average coulombic efficiency of 99.5%. This reveals that the P-doped lithium cobalt oxide possesses excellent cycle performance and high reversibility as a cathode for high-voltage lithium-ion batteries. In contrast, under the same test conditions, the initial discharge capacity of commercial LCO is 176 mAh / g. After 155 charge / discharge cycles, its discharge capacity decreases to 120 mAh / g, with a capacity retention of only 68% and an average coulombic efficiency of only 94.7%. This indicates that commercial LCO exhibits poor cycle performance and low reversibility at high voltages.

[0061] in addition, Figure 9 By comparing the median discharge voltage of P-LCO and commercially available P-LCO during cycling, it is evident that P-doped LCO maintains a more stable discharge voltage at high voltages, while the discharge voltage of commercially available LCO decays rapidly at high voltages. This further illustrates the crucial role of P doping in the overall electrochemical performance of lithium-ion batteries.

[0062] Example 2

[0063] This embodiment provides a method for preparing a high-voltage lithium cobalt oxide cathode active material. Compared with Example 1, the volume fraction of phytic acid in step S2 of this embodiment is 2%, resulting in a high-voltage lithium cobalt oxide cathode active material. Other steps are the same as in Example 1.

[0064] The surface P element content of the high-voltage lithium cobalt oxide positive electrode active material prepared in this embodiment is not much different from that in Example 1, and the cycle performance under high voltage (~4.5V) is still significantly improved compared with ordinary lithium cobalt oxide.

[0065] Example 3

[0066] This embodiment provides a method for preparing a high-voltage lithium cobalt oxide cathode active material. Compared with Example 1, the volume fraction of phytic acid in step S2 of this embodiment is 3%, resulting in a high-voltage lithium cobalt oxide cathode active material. Other steps are the same as in Example 1.

[0067] The surface P element content of the high-voltage lithium cobalt oxide positive electrode active material prepared in this embodiment is not much different from that in Example 1, and the cycle performance under high voltage (~4.5V) is still significantly improved compared with ordinary lithium cobalt oxide.

[0068] The above description is merely a preferred embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural transformations made using the contents of the present invention's specification and drawings under the inventive concept of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. A method for producing a high-voltage lithium cobalt oxide cathode active material, characterized by, The method comprises the following steps: S1: adding LiCoO2 and PVP into anhydrous ethanol and stirring until completely dissolved; The mass ratio of LiCoO2 to PVP is 1:1.5-2.5; the volume of anhydrous ethanol is 200-300 mL; the stirring temperature is room temperature, and the stirring time is 0.5-1 h; S2: dissolving phytic acid in anhydrous ethanol and stirring until completely dissolved; The volume fraction of phytic acid in the phytic acid-dissolved ethanol solution is 2-3%; the stirring temperature is room temperature, and the stirring time is 0.5-1 h; S3: adding the phytic acid-dissolved ethanol solution into the LiCoO2 / PVP / ethanol mixed solution obtained in step S1 dropwise and stirring to mix uniformly; The dropwise adding rate is 3-5 mL / min; the stirring temperature is 60℃, and the stirring time is 0.5-1 h; S4: centrifuging and drying the mixed solution obtained in step S3, then pre-sintering under an inert atmosphere, and then sintering in an air atmosphere to obtain a phosphorus-doped modified LiCoO2 positive electrode active material.

2. The production method according to claim 1, wherein In step S4, the centrifuging is performed at a speed of 7500 r / min for 3-5 min, and the centrifuging is performed 1-3 times; the drying is performed at a temperature of 60-80℃ for 4-5 h.

3. The production method according to claim 1, wherein In step S4, the pre-sintering process specifically comprises: In an argon atmosphere, the sintering temperature is increased from room temperature to 650℃ at a temperature increasing rate of 2 ℃ / min, and the temperature is kept for 2 h; The sintering process specifically comprises: In an air atmosphere, the sintering temperature is increased from room temperature to 750℃ at a temperature increasing rate of 5 ℃ / min, and the temperature is kept for 5 h.

4. A high-voltage lithium cobalt oxide cathode active material, characterized by, The positive electrode active material is a phosphorus-doped LiCoO2 positive electrode material, which is composed of phosphorus-doped lithium cobalt oxide particles.

5. Use of a high-voltage lithium cobalt oxide cathode active material, characterized in that The positive electrode active material prepared by the preparation method of any one of claims 1-3 or the positive electrode active material of claim 4 is applied to a lithium ion battery.

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