Method for improving performance of single-crystal nmc622 positive electrode material

Abstract

The application relates to a method for improving the performance of single-crystal NMC622 positive electrode materials, which comprises the following steps: mixing transition metal compounds of a nickel source, a cobalt source and a manganese source with a lithium source according to a stoichiometric ratio, performing ball milling treatment to obtain a precursor mixture; wherein the ball milling speed during the ball milling treatment is 300-600 rpm, the ball-to-material ratio is 5:1-20:1, and the ball milling time is 10-24 h; S2, performing high-temperature solid-phase sintering on the precursor mixture in an oxygen-containing atmosphere to obtain single-crystal LiNi 0.6 Mn 0.2 Co 0.2 O2 positive electrode materials; wherein the sintering temperature is 850-920 DEG C, and the holding time is 10-20 h. Compared with the prior art, the single-crystal NMC622 positive electrode material prepared by the application has excellent electrochemical performance.

Description

Technical Field

[0001] This invention belongs to the field of battery materials technology and relates to a method for improving the performance of single-crystal NMC622 cathode material. Background Technology

[0002] Single-crystal high-nickel ternary layered oxides have become ideal cathode materials for next-generation lithium-ion batteries due to their high energy density, long cycle life, and excellent safety. Among various ternary cathode material systems, single-crystal LiNi... 0.6 Mn 0.2 Co 0.2 O2 (NMC622) cathode material has a moderate nickel content, possessing the advantages of low- and medium-nickel cathode materials such as NMC111, NMC442, and NMC532, which are easy to synthesize, have good structural stability, and good cycle stability. It also has the advantages of high capacity and low cost of nickel-rich cathode materials such as NMC721 and NMC811. Therefore, it has always been regarded as an important candidate material to meet the requirements of high energy and long life of lithium-ion batteries.

[0003] All-dry solid-phase synthesis (ASDSS) is a green method for preparing single-crystal NMC622 materials. Compared to the two-step process of "co-precipitation liquid phase + solid-phase sintering," this method mechanically mixes transition metal compounds with lithium sources through a simplified ball milling step, skipping the complex precursor preparation process and greatly simplifying the process. It also avoids the wastewater problems generated by liquid-phase reactions and reduces the handling of by-products after material preparation. However, in all-dry solid-phase synthesis, due to the strong metal-oxygen bonds in transition metal oxides and the inability of non-atomic-level mechanical mixing to achieve close contact between components, the distribution of transition metal elements is often uneven. Therefore, interdiffusion between elements becomes difficult during sintering, resulting in a slow lithiation process. This means that single-crystal cathode materials often need to be synthesized at higher sintering temperatures and longer holding times. However, excessively high sintering temperatures and excessively long holding times can easily lead to increased lithium / oxygen loss, forming a large number of oxygen vacancies, which in turn affects the orderliness of the material's layered structure and electrochemical performance.

[0004] For example, Obrovac et al. (doi: 10.1149 / 1945-7111 / abbcb1) prepared single-crystal LiNi using oxide precursors at 940℃. 0.6 Mn 0.2 Co 0.2 The O2 material has a discharge specific capacity of only 162 mAh g at 0.05C. -1 . Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing dry solid-state synthesis technologies, such as slow lithiation processes, and to provide a method to improve the performance of single-crystal NMC622 cathode materials. The aim is to synthesize single-crystal NMC622 cathode materials with ordered hierarchical structures and excellent electrochemical performance under relatively mild sintering conditions by reducing the metal-oxygen bond energy of transition metal oxides, reducing element diffusion resistance, and promoting high-temperature lithiation reaction kinetics in dry solid-state synthesis.

[0006] The objective of this invention can be achieved through the following technical solutions: One of the technical solutions of the present invention is to provide a method for improving the performance of single-crystal NMC622 cathode material, comprising the following steps: S1. The transition metal compounds of nickel source, cobalt source, and manganese source are mixed with lithium source in stoichiometric ratio and ball milled to obtain precursor mixture; wherein the ball milling speed is 300-600 rpm, the ball-to-material ratio is 5:1-20:1, and the ball milling time is 10-24 h. S2. The precursor mixture obtained in step S1 is subjected to high-temperature solid-state sintering in an oxygen-containing atmosphere to obtain single-crystal LiNi. 0.6 Mn 0.2 Co 0.2 O2 cathode material; wherein the sintering temperature is 850~920℃ and the holding time is 10~20h.

[0007] In this invention, by precisely controlling the ball milling time, the particle size, elemental distribution uniformity, and lattice strain of the transition metal oxide precursor are effectively controlled. Continuous collisions between particles during ball milling introduce moderate defects such as dislocations and vacancies into the oxide lattice, reducing the metal-oxygen bond energy and increasing the powder surface energy. This reduces the diffusion resistance of elements during solid-state sintering and significantly promotes the kinetics of the lithiation reaction. When the ball milling time is too short, the elemental distribution is uneven and the particle size is large; when the ball milling time is too long, excessive loss of lattice oxygen, decreased crystallinity, and increased electrostatic repulsion occur. The preferred ball milling time range of this invention is 16–20 h, with the precursor milled for 18 h exhibiting the smallest particle size distribution (D0). 50 The oxide lattice exhibits the most uniform elemental distribution (1.0 μm) and the optimal lattice strain (0.08%) and the minimum cell parameters. This indicates that moderate defects are formed in the oxide lattice to reduce the metal-oxygen bond energy, providing optimal kinetic conditions for subsequent sintering. This reduces the diffusion resistance of elements during solid-state sintering, promotes the kinetics of high-temperature lithiation reaction, and synthesizes a single-crystal cathode material with an ordered layered structure and excellent electrochemical performance under relatively mild sintering conditions.

[0008] In some specific embodiments, in step S1, the nickel source is selected from one or more of nickel oxide, nickel hydroxide, nickel carbonate, and nickel oxalate; The cobalt source is selected from one or more of cobalt tetroxide, cobalt monoxide, cobalt hydroxide, and cobalt carbonate; The manganese source is selected from one or more of manganese dioxide, manganese trioxide, manganese tetroxide, and manganese carbonate; The lithium source is selected from one or more of lithium carbonate, lithium hydroxide, lithium nitrate, and lithium acetate.

[0009] In some specific embodiments, in step S1, the milling media are zirconia balls or stainless steel balls.

[0010] In some specific embodiments, in step S2, the oxygen volume in the oxygen-containing atmosphere is greater than 0% and less than or equal to 100%, and the gas flow rate is 0.5 to 5 L / min.

[0011] In some specific embodiments, in step S2, the temperature is raised to 450-550°C at a rate of 2-5°C / min during sintering, and held for 2-4 hours for pre-sintering; then the temperature is raised to 850-920°C at a rate of 2-5°C / min, and held for 10-20 hours for high-temperature sintering, followed by natural cooling to room temperature.

[0012] This invention employs a segmented sintering method. The pre-sintering stage effectively removes moisture and volatile components from the material and initially promotes solid-state reactions between the components, laying the foundation for the subsequent high-temperature lithiation process. After sintering, the product can be pulverized and sieved to obtain uniformly sized single-crystal cathode material.

[0013] The second technical solution of the present invention is to provide a single-crystal NMC622 cathode material, which is prepared by one of the above technical solutions.

[0014] In some specific embodiments, the single-crystal NMC622 cathode material has at least one of the following characteristics: (1) Single crystal particle D 50 The particle size is 2–4 μm; (2) I (003) / I (104) Peak intensity ratio greater than 1.2; (3) The initial discharge specific capacity is not less than 170 mAh g in the voltage range of 2.7 to 4.5V and at a 1C rate. -1 After 100 cycles, the capacity retention rate is no less than 85%.

[0015] The third technical solution of the present invention is to provide an application of the single-crystal NMC622 cathode material as described in the second technical solution above in the preparation of lithium-ion batteries.

[0016] The fourth technical solution of the present invention is to provide a lithium-ion positive electrode sheet, comprising the single-crystal NMC622 positive electrode material as described in the second technical solution above.

[0017] The fifth technical solution of the present invention is to provide a lithium-ion battery, including the lithium-ion positive electrode sheet as described in the fourth technical solution above.

[0018] Compared with the prior art, the present invention has the following advantages: (1) This invention targets the medium-nickel NMC622 system. By precisely controlling the ball milling time (10–24 h, preferably 16–20 h, optimal 18 h), the particle size and element distribution uniformity of the transition metal oxide precursor are optimized. A moderate lattice strain (optimal value 0.08%) is introduced into the oxide lattice, effectively reducing the metal-oxygen bond energy and increasing the powder surface energy. This significantly reduces the diffusion resistance of elements during solid-state sintering and promotes the kinetics of high-temperature lithiation. Compared with the prior art, this invention can achieve efficient lithiation under relatively mild sintering conditions (850–920 °C, holding time 10–20 h), avoiding the lithium / oxygen loss problem caused by excessively high sintering temperature and excessively long holding time.

[0019] (2) The single-crystal NMC622 cathode material prepared by this invention has unique structural characteristics: the I(003) / I(104) peak intensity ratio in the X-ray diffraction (XRD) pattern is greater than 1.2, indicating that the layered structure has high order and low Li / Ni mixing degree; the single-crystal particles D 50 The particle size is 2~4 μm, the morphology is highly dispersed and the crystal faces are clear; this structural feature is a unique product attribute directly given by the ball milling-sintering process optimized in this invention.

[0020] (3) The single-crystal NMC622 cathode material prepared by this invention has excellent electrochemical performance: the discharge specific capacity can reach 179 mAh / g in the voltage range of 2.7 to 4.5V and at a 1C rate, and the capacity retention rate is as high as 93% after 100 cycles; at a 7C ultra-high rate, the discharge specific capacity can still reach 132 mAh / g. The cathode material (BM18h) of this invention was matched with commercial graphite anodes to assemble soft-pack full cells for testing. After 500 cycles at a 1C rate and 2.7 to 4.5V, the capacity retention rate was still as high as 91%, which is significantly better than the co-precipitation method comparison sample (80%), showing excellent prospects for practical application. Attached Figure Description

[0021] Figure 1 XRD patterns of transition metal oxide precursors (NiO, Mn2O3, Co3O4) under different ball milling times.

[0022] Figure 2This is a SEM image of the precursor mixture after ball milling for 18 hours.

[0023] Figure 3 XRD patterns of NMC622 cathode materials prepared under different ball milling times.

[0024] Figure 4 SEM image of NMC622 cathode material obtained by ball milling for 18 hours.

[0025] Figure 5 HRTEM image of NMC622 cathode material prepared by ball milling for 18 hours.

[0026] Figure 6 This is a performance comparison chart of the NMC622 cathode material (AD-NMC622) prepared by the present invention and the cathode material (CP-NMC622) prepared by the co-precipitation method in a pouch full cell after 500 cycles at 1C rate. Detailed Implementation

[0027] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0028] Unless otherwise specified, the materials and processes described in the following embodiments or examples are conventional materials and processes used in the art to achieve the corresponding functions.

[0029] Example 1: This embodiment provides a method for preparing a single-crystal NMC622 cathode material, including the following steps: (1) Accurately weigh 30g of raw material powders of lithium carbonate (Li2CO3), nickel oxide (NiO), manganese dioxide (MnO2) and cobalt tetroxide (Co3O4) according to the stoichiometric ratio of Li: Ni: Mn: Co = 1.03:0.6:0.2:0.2, place them in a planetary ball mill jar, and add zirconium oxide grinding balls at a ball-to-material ratio of 10:1; (2) The precursor mixture was obtained by ball milling at 400 rpm for 10 h on a planetary ball mill. (3) The precursor mixture was transferred to a corundum crucible and placed in a tube furnace for segmented sintering in an oxygen atmosphere (gas flow rate of 2L / min): the temperature was raised to 500℃ at a heating rate of 3℃ / min and held for 3h for pre-sintering; then the temperature was raised to 900℃ at a heating rate of 3℃ / min and held for 15h for high-temperature sintering; and then naturally cooled to room temperature. (4) The sintered product is taken out, crushed and sieved to obtain single crystal NMC622 cathode material, denoted as BM10h.

[0030] Example 2: This embodiment provides a method for preparing a single-crystal NMC622 cathode material. The preparation steps are basically the same as those in Example 1, except that the ball milling time in step (2) is adjusted to 14 hours.

[0031] The resulting sample was denoted as BM14h.

[0032] Example 3: This embodiment provides a method for preparing a single-crystal NMC622 cathode material. The preparation steps are basically the same as those in Example 1, except that the ball milling time in step (2) is adjusted to 18h.

[0033] The resulting sample was denoted as BM18h.

[0034] Example 4: This embodiment provides a method for preparing a single-crystal NMC622 cathode material. The preparation steps are basically the same as those in Example 1, except that the ball milling time in step (2) is adjusted to 20h.

[0035] The resulting sample is denoted as BM20h.

[0036] Example 5: This embodiment provides a method for preparing a single-crystal NMC622 cathode material. The preparation steps are basically the same as those in Example 1, except that the ball milling time in step (2) is adjusted to 24 hours.

[0037] The resulting sample was denoted as BM24h.

[0038] Example 6: This embodiment provides a method for preparing a single-crystal NMC622 cathode material. The preparation steps are basically the same as those in Example 3, except that the lithium source in step (1) is replaced with lithium hydroxide (LiOH·H2O), while other raw materials remain unchanged.

[0039] The resulting sample was denoted as BM18h-L.

[0040] Example 7: This embodiment provides a method for preparing a single-crystal NMC622 cathode material. The preparation steps are basically the same as those in Example 3, except that the ball milling speed in step (2) is adjusted to 600 rpm.

[0041] The resulting sample is denoted as BM18h-H.

[0042] Example 8: This embodiment provides a method for preparing a single-crystal NMC622 cathode material. The preparation steps are basically the same as those in Example 3, except that the high-temperature sintering temperature in step (3) is adjusted to 920°C and the holding time is adjusted to 12h.

[0043] The obtained sample was designated BM18h-920.

[0044] Comparative Example 1: This comparative example provides a method for preparing a single-crystal NMC622 cathode material. The preparation steps are the same as those in Example 1, except that: in step (2), ball milling is not performed, and the raw material powder is simply mixed manually.

[0045] The resulting sample is denoted as BM0h.

[0046] Comparative Example 2: This comparative example provides a method for preparing a single-crystal NMC622 cathode material. The preparation steps are basically the same as those in Example 1, except that the ball milling time in step (2) is adjusted to 4 hours.

[0047] The resulting sample is denoted as BM4h.

[0048] Comparative Example 3: This comparative example provides a method for preparing a single-crystal NMC622 cathode material. The preparation steps are basically the same as those in Example 1, except that the ball milling time in step (2) is adjusted to 36 hours.

[0049] The resulting sample was designated BM36h.

[0050] Comparative Example 4: This comparative example provides a method for preparing a single-crystal NMC622 cathode material. The preparation steps are basically the same as those in Example 3, except that the high-temperature sintering temperature in step (3) is adjusted to 750°C and the holding time is still 15h.

[0051] The obtained sample was designated BM18h-750.

[0052] Comparative Example 5: This comparative example provides a single-crystal NMC622 cathode material prepared by co-precipitation method, the preparation steps of which are as follows: Transition metal hydroxide precursor (Ni0.6Mn0.2Co0.2(OH)2) was prepared by conventional coprecipitation method.

[0053] The specific steps are as follows: (1) Weigh out nickel sulfate (NiSO4·6H2O), cobalt sulfate (CoSO4·7H2O) and manganese sulfate (MnSO4·H2O) according to the molar ratio of Ni:Co:Mn=0.6:0.2:0.2, dissolve them in deionized water, and prepare a mixed salt solution with a total metal ion concentration of 2 mol / L; (2) Prepare a 4 mol / L sodium hydroxide (NaOH) solution as a precipitant and a 2 mol / L ammonia (NH3·H2O) solution as a complexing agent. (3) Add an appropriate amount of deionized water to the reactor as the base liquid, introduce nitrogen gas to remove air, heat the base liquid to 50-60℃ and keep it constant, and adjust the stirring speed to 400-600 rpm. (4) The mixed salt solution, sodium hydroxide solution and ammonia solution are added to the reaction vessel in parallel using a peristaltic pump. The pH value of the reaction system is strictly controlled to be 10.5 to 11.5, and the molar ratio of ammonia to metal salt is controlled to be between 0.5 and 1.0. (5) The reaction was continuously stirred for 12–24 h under a nitrogen atmosphere to co-precipitate metal ions to form Ni. 0.6 Mn 0.2 Co 0.2 (OH)2 precursor; (6) After the reaction is complete, the resulting slurry is filtered and washed repeatedly with deionized water until the filtrate is neutral (pH≈7) to remove residual sulfate ions and sodium ions; (7) The washed precursor was vacuum dried at 100-120°C for 10-24 h to obtain spherical or near-spherical Ni. 0.6 Mn 0.2 Co 0.2 (OH)2 precursor powder.

[0054] After washing and drying, it is mixed with lithium carbonate in stoichiometric ratio and sintered at 900℃ for 15 hours in an oxygen atmosphere to obtain co-precipitated single-crystal NMC622 cathode material, denoted as CP.

[0055] The samples prepared in the above embodiments and comparative examples were characterized and tested as follows: (1) The particle size distribution of the precursor mixture and the final product was tested using a laser particle size analyzer (Malvern Mastersizer 3000).

[0056] (2) Phase analysis of the precursor mixture and the final product was performed using an X-ray diffractometer (XRD, Cu Kα radiation source). The scanning range was 10° to 80° and the scanning rate was 2° / min. The lattice parameters and lattice strain were calculated using the Rietveld refinement method.

[0057] like Figure 1 The figure shows the XRD patterns of transition metal oxide precursors (NiO, Mn2O3, Co3O4) after different ball milling times. All diffraction peaks correspond to the three oxides mentioned above. After ball milling, the diffraction peaks shifted significantly, indicating a change in lattice parameters. Combined with the lattice strain data in Table 1, the precursors reached the optimal lattice strain state (0.08%) after 18 hours of ball milling, indicating that moderate defects were formed in the oxide lattice at this time, which is beneficial for reducing the metal-oxygen bond energy and accelerating element interdiffusion and lithiation reaction kinetics.

[0058] like Figure 3 The image shows the XRD patterns of NMC622 cathode materials prepared under different ball milling times. All samples can be indexed as hexagonal α-NaFeO2 structures with space group R-3m. The XRD refinement results show that with increasing ball milling time, the a / c axis parameters and cell volume first increase and then decrease. The BM18h sample has the largest a-axis (2.875 Å), c-axis (14.254 Å), and cell volume (102.03 Å). 3 ), which means a larger Li + Transmission channels. Meanwhile, BM18h has the lowest Li / Ni mixing value (1.72%) and the highest Ni3+ / Ni2+ ratio (1.76), indicating that its layered structure is the most ordered.

[0059] (3) The microstructure of the precursor mixture and the final product was observed using a scanning electron microscope (SEM).

[0060] like Figure 2 The image shown is a SEM image of the precursor mixture after ball milling for 18 hours. It can be seen that the precursor particles are fine and uniform, with no obvious agglomeration, which is beneficial for element diffusion and oxidation reactions during the subsequent solid-state sintering process.

[0061] like Figure 4 The image shown is a SEM image of the NMC622 cathode material prepared in Example 3 (BM18h). As can be seen from the image, the obtained material exhibits a highly dispersed single-crystal morphology with clear crystal faces and uniform particle size (D). 50 (≈2.8 μm), consistent with the morphology description in Table 2.

[0062] (4) The uniformity of the distribution of Ni, Mn and Co elements in the precursor mixture was analyzed by energy dispersive X-ray spectroscopy (EDS).

[0063] (5) The lattice fringes and microstructure of the cathode product were observed using a high-resolution transmission electron microscope (HRTEM).

[0064] like Figure 5The image shown is an HRTEM image of the BM18h sample. Clearly discernible lattice fringes and regular diffraction spots confirm a highly ordered layered structure. The interplanar spacing of the (003) crystal planes is 0.48 nm, and there is no impurity accumulation or contamination layer on the surface, confirming that atomic-level homogeneous mixing was successfully achieved using the ADSPS method of this invention.

[0065] Tables 1 and 2 below show the statistics for the above test items.

[0066] Table 1. Particle size and lattice strain of precursor mixtures at different ball milling times

[0067] As shown in Table 1, the particle size of the precursor mixture first decreases and then increases with increasing ball milling time. The particle size reaches its minimum value (D) after 18 hours of ball milling. 50 =1.0 μm), while the lattice strain also reaches its minimum value (0.08%), resulting in optimal elemental uniformity. When the ball milling time is too short (e.g., 0 h, 4 h), the particle size is large and the elemental distribution is uneven; when the ball milling time is too long (e.g., 36 h), due to cold welding and agglomeration of powder particles, the particle size increases, and the lattice strain also increases significantly. The variation law of precursor structure with ball milling time is similar to... Figure 1 The XRD results were consistent. Continuous collisions between particles during ball milling introduce lattice defects, but excessive ball milling leads to lattice oxygen loss, decreased crystallinity, and increased electrostatic repulsion.

[0068] Table 2. Structural and morphological characteristics of single-crystal NMC622 cathode materials prepared under different ball milling times.

[0069] As shown in Table 2, the XRD pattern of the BM18h sample obtained by ball milling for 18 h is shown in Table 2. (003) / I (104) The peak intensity ratio reached 1.52, significantly higher than the industry-standard threshold of 1.2, indicating extremely high order in its layered structure and extremely low Li / Ni mixing. The single-crystal morphology of the BM18h sample is as follows: Figure 4 As shown. Meanwhile, the single-crystal particles D of the BM18h sample... 50 The particles have a diameter of 2.8 μm and exhibit highly dispersed morphology with clear crystal faces. These structural features are directly attributed to the optimal lattice strain and uniform elemental distribution of the precursor achieved by precisely controlling the ball milling time in this invention, further demonstrating the controllability of the microstructure of the product by the process of this invention.

[0070] (6) Electrochemical performance testing: The prepared positive electrode material was mixed with conductive agent Super P and binder polyvinylidene fluoride (PVDF) at a mass ratio of 8:1:1. An appropriate amount of N-methylpyrrolidone (NMP) was added to form a slurry, which was uniformly coated on aluminum foil. After vacuum drying at 120℃ for 12h, it was punched into a circular electrode sheet with a diameter of 12mm. Using lithium metal sheet as counter electrode, Celgard2400 polypropylene membrane as separator, and 1mol / L LiPF6 / ethylene carbonate (EC) + dimethyl carbonate (DMC) + ethyl methyl carbonate (EMC) (volume ratio of 1:1:1) as electrolyte, CR2032 coin cell half-cells were assembled in an argon glove box. Constant current charge-discharge test was performed using a LAND battery testing system, with a voltage range of 2.7~4.5V (vs. Li / Li + 1C = 200mAh g -1 ).

[0071] Table 3 Electrochemical performance of single-crystal NMC622 cathode materials prepared under different ball milling times (coin half-cell, 2.7–4.5 V)

[0072] As shown in Table 3, the BM18h sample has a strength of 179 mAh g at 1C rate. -1 The discharge specific capacity of the sample reached 93% after 100 cycles, exhibiting the best overall performance, comparable to the co-precipitation method (CP) sample, but with a simpler and more environmentally friendly process. Samples with excessively short or long ball milling times showed significantly poorer electrochemical performance due to low layered structure order and unsatisfactory single-crystal morphology. Comparative Example 4 (BM18h-750) showed a significant performance decline due to insufficient lithiation caused by an excessively low sintering temperature. Furthermore, the BM18h sample still achieved a discharge specific capacity of 132 mAh g⁻¹ at an ultra-high rate of 7C. -1 It exhibits excellent rate performance.

[0073] To evaluate the practical application performance of the material of this invention, BM18h samples and CP samples prepared by the co-precipitation method were assembled into pouch cells for testing. The assembly conditions of the pouch cells were as follows: commercial graphite was used as the negative electrode, and the positive electrode size was 4.1 × 6.3 cm. 2 The negative electrode plate measures 4.3 × 6.5 cm. 2 The capacity ratio (N / P ratio) of the negative electrode to the positive electrode is 1.1; the electrolyte is 1.2 M LiPF6 dissolved in a mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) (volume ratio 1:1), with 2 wt.% of vinylene carbonate (VC) added as an additive; and the separator is Celgard 2400.

[0074] like Figure 6The figure shows a comparison of the cycling performance of a pouch cell (AD-NMC622) assembled with a graphite anode and a co-precipitation method control (CP-NMC622) at 1C rate and within the 2.7-4.5V voltage range. As can be seen from the figure, after 500 cycles, the full cell assembled with BM18h retains a capacity of 91%, while the co-precipitation method control only retains 80%. The cycling stability of BM18h is significantly better than that of the CP control, fully demonstrating that the single-crystal NMC622 cathode material prepared by the ADSPS method of this invention has excellent practical application prospects.

[0075] The above results fully demonstrate that the single-crystal NMC622 cathode material prepared by the all-dry solid-state synthesis method of the present invention has excellent practical application performance and industrialization promotion value.

[0076] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A method for improving the performance of single-crystal NMC622 cathode material, characterized in that, Includes the following steps: S1. The transition metal compounds of nickel source, cobalt source, and manganese source are mixed with lithium source in stoichiometric ratio and ball milled to obtain precursor mixture; wherein the ball milling speed is 300-600 rpm, the ball-to-material ratio is 5:1-20:1, and the ball milling time is 10-24 h. S2. The precursor mixture obtained in step S1 is subjected to high-temperature solid-state sintering in an oxygen-containing atmosphere to obtain single-crystal LiNi. 0.6 Mn 0.2 Co 0.2 O2 cathode material; wherein the sintering temperature is 850~920℃ and the holding time is 10~20h.

2. The method for improving the performance of single-crystal NMC622 cathode material according to claim 1, characterized in that, In step S1, the nickel source is selected from one or more of nickel oxide, nickel hydroxide, nickel carbonate, and nickel oxalate; The cobalt source is selected from one or more of cobalt tetroxide, cobalt monoxide, cobalt hydroxide, and cobalt carbonate; The manganese source is selected from one or more of manganese dioxide, manganese trioxide, manganese tetroxide, and manganese carbonate; The lithium source is selected from one or more of lithium carbonate, lithium hydroxide, lithium nitrate, and lithium acetate.

3. The method for improving the performance of single-crystal NMC622 cathode material according to claim 1, characterized in that, In step S1, the milling media are zirconia balls or stainless steel balls.

4. The method for improving the performance of single-crystal NMC622 cathode material according to claim 1, characterized in that, In step S2, the oxygen volume in the oxygen-containing atmosphere is greater than 0% and less than or equal to 100%, and the gas flow rate is 0.5 to 5 L / min.

5. The method for improving the performance of single-crystal NMC622 cathode material according to claim 1, characterized in that, In step S2, the temperature is raised to 450–550°C at a rate of 2–5°C / min and held for 2–4 hours for pre-firing; then the temperature is raised to 850–920°C at a rate of 2–5°C / min and held for 10–20 hours for high-temperature sintering, followed by natural cooling to room temperature.

6. A single-crystal NMC622 cathode material, characterized in that, Prepared by the method described in any one of claims 1 to 5.

7. The single-crystal NMC622 cathode material according to claim 6, characterized in that, The single-crystal NMC622 cathode material has at least one of the following characteristics: (1) Single crystal particle D 50 The particle size is 2–4 μm; (2) I (003) / I (104) Peak intensity ratio greater than 1.2; (3) The initial discharge specific capacity is not less than 170 mAh g in the voltage range of 2.7 to 4.5V and at a 1C rate. -1 After 100 cycles, the capacity retention rate is no less than 85%.

8. The application of the single-crystal NMC622 cathode material as described in claim 6 or 7 in the preparation of lithium-ion batteries.

9. A lithium-ion positive electrode, characterized in that, Including the single-crystal NMC622 cathode material as described in claim 6 or 7.

10. A lithium-ion battery, characterized in that, Including the single-crystal NMC622 cathode material as described in claim 6 or 7.

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