A single-crystal ternary material, a preparation method and application thereof

Abstract

The application provides a single-crystal ternary material and a preparation method and application thereof, and the preparation method comprises the following steps: (1) mixing lithium salt, nickel salt, cobalt salt, M salt and a molten salt to obtain a mixed solution; the molten salt comprises any one or a combination of at least two of KNO3, NaNO3, KCl, NaCl, K2SO4 and Na2SO4, and the M salt comprises manganese salt and / or aluminum salt; (2) performing spray pyrolysis on the mixed solution to obtain a single-crystal precursor; and (3) sintering the single-crystal precursor to obtain the single-crystal ternary material. By using the molten salt assisted spray pyrolysis method, the single-crystal precursor with high uniformity and dispersion can be simply and quickly prepared, and the lithium salt is added in the preparation process of the precursor, so that the traditional solid-phase mixing and grinding process of lithiumation is omitted, the lithiumation speed is accelerated, and finally, the single-crystal ternary material with better electrochemical performance is prepared by using a short process, lower energy consumption and cost.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, and relates to a single-crystal ternary material, its preparation method, and its application. Background Technology

[0002] Currently, most nickel-cobalt-manganese ternary cathode materials on the market are polycrystalline, consisting of secondary microspheres formed by the aggregation of primary micro-nano-scale particles. This type of material is generally formed during the co-precipitation synthesis of ternary precursors. During battery cycling, this structure is prone to cracking along the gaps between primary particles due to uneven volume expansion of different grains, which is one reason for the rapid capacity decay of lithium-ion batteries. Monocrystalline ternary materials, on the other hand, are obtained by high-temperature crystallization growth of primary particles. They do not exhibit particle aggregation or microcracks, possess better mechanical properties, and hardly generate microcracks during charge-discharge cycles. Achieving a monocrystalline structure is one of the effective methods to improve the discharge voltage of ternary materials, and the cycle stability of monocrystalline materials is also superior to that of polycrystalline materials.

[0003] Patent CN114940519A discloses a method for preparing a high-nickel single-crystal lithium nickel cobalt manganese oxide ternary cathode material. This ternary material undergoes a two-stage high-temperature, long-time (600℃-24h + 900℃-24h) sintering process to obtain the single-crystal ternary cathode material. The research paper by He Kangyu et al., "Preparation of LiNi by Molten Salt Method," further supports this method. 0.8 Co 0.1 M 0.1 The results of "O2 Single Crystals and Their Electrochemical Properties" (Materials Reports, 2021, 35(12): 12027-12031) show that: spherical Ni synthesized by co-precipitation 0.8 Co 0.1 M 0.1 (OH)2 is used as a precursor, with the addition of excess lithium carbonate (n(Ni) 0.8 Co 0.1 M 0.1 (OH)2):n(Li)=1:1.3) and with increasing sintering temperature, the secondary particles of the original spherical precursor agglomeration can be sintered and dispersed to form NCM811 particles with single crystal morphology.

[0004] As reported in patents and literature, the preparation of single-crystal ternary materials generally requires high sintering temperatures and times, as well as excessively high lithium salt ratios. This results in high energy consumption, significant lithium salt volatilization losses during sintering, and excessive residual alkali on the material surface, leading to a decrease in capacity. Furthermore, to avoid the re-agglomeration of single-crystal particles during high-temperature, long-duration sintering, the calcination process is usually divided into multiple stages, making the preparation process complex and lengthy. Therefore, developing a low-energy-consumption, short-process, and high-performance method for preparing single-crystal ternary materials has become an urgent problem to be solved. Summary of the Invention

[0005] To address the problems existing in the prior art, the present invention aims to provide a single-crystal ternary material, its preparation method, and its applications. This invention employs a molten salt-assisted spray pyrolysis method to simply and rapidly prepare a highly uniformly dispersed single-crystal precursor. Simultaneously, lithium salt is added during the precursor preparation process, eliminating the need for solid-phase mixing and grinding in traditional lithiation processes, thus accelerating the lithiation rate. Ultimately, a single-crystal ternary material with superior electrochemical performance is prepared using a simplified process with lower energy consumption and cost.

[0006] To achieve this objective, the present invention employs the following technical solution:

[0007] In a first aspect, the present invention provides a method for preparing a single-crystal ternary material, the method comprising:

[0008] (1) Mix lithium salt, nickel salt, cobalt salt, M salt and molten salt to obtain a mixed solution;

[0009] The molten salt includes any one or a combination of at least two of KNO3, NaNO3, KCl, NaCl, K2SO4 and Na2SO4, and the M salt includes manganese salt and / or aluminum salt.

[0010] (2) The mixed solution described in step (1) is subjected to spray pyrolysis to obtain a single-crystal precursor;

[0011] (3) The single-crystal precursor described in step (2) is sintered to obtain a single-crystal ternary material.

[0012] In this invention, lithium salt and specific molten salt are added during the preparation of the precursor mixed solution. These molten salts are difficult to generate corresponding oxides through thermal decomposition. Therefore, they surround the nickel cobalt manganese / lithium aluminate grains in the form of salts, promoting "directional growth" of the grains during the grain growth stage and preventing multiple crystal nuclei from fusing and growing to form polycrystalline structures. These molten salts are removed by water washing, thereby enabling the nickel cobalt manganese / lithium aluminate precursor to form highly dispersed single crystal particles, i.e., single-crystal precursors. At the same time, by adding lithium salt to the mixed solution prepared from the precursor in advance, lithium ions and transition metal ions can be mixed uniformly at the molecular level. This not only eliminates the solid-phase mixing and grinding steps before the traditional lithiation process, but also eliminates the path for lithium ions to diffuse from the precursor surface to the bulk phase, further accelerating the lithiation speed. Moreover, the resulting ternary material has a low residual lithium (alkali) content on the surface. The above-mentioned molten salt-assisted spray pyrolysis method can easily and quickly prepare highly uniformly dispersed single-crystal precursors, significantly reducing the temperature and time required for subsequent lithiation processes, reducing lithium volatilization losses, preventing the formation of single-crystal agglomerates, reducing lithium-nickel mixing, and enabling ternary materials to exhibit better electrochemical performance.

[0013] The present invention has a simple preparation process, low energy consumption and low lithium source consumption, and significantly reduced cost; the prepared single-crystal ternary material can effectively avoid the formation of intergranular cracks during charge-discharge cycles, and realize the construction of long-life ternary lithium-ion batteries.

[0014] In this invention, the molten salt includes any one or a combination of at least two of KNO3, NaNO3, KCl, NaCl, K2SO4, and Na2SO4. For example, it can be a combination of KNO3 and NaNO3, K2SO4 and Na2SO4, KCl, NaCl, and K2SO4, NaNO3, KCl, NaCl, K2SO4, and Na2SO4, or a combination of KNO3, NaNO3, KCl, NaCl, K2SO4, and Na2SO4, etc. In this invention, different molten salts can also control the morphology of the material particles. For example, single crystal particles formed in KCl molten salt are spherical, while single crystal particles formed in NaCl molten salt are perfect octahedrons.

[0015] It should be noted that the molten salt in this invention can also be LiCl and / or Li2SO4, but from the perspective of cost and low ratio of lithium salt, KNO3, NaNO3, KCl, NaCl, K2SO4 and Na2SO4 have lower costs and do not require a high ratio of lithium salt. When an excess of molten salt is used, it can significantly reduce industrial production costs.

[0016] Preferably, the lithium salt comprises lithium nitrate.

[0017] Preferably, the nickel salt comprises nickel nitrate.

[0018] Preferably, the cobalt salt comprises cobalt nitrate.

[0019] Preferably, the manganese salt includes manganese nitrate.

[0020] Preferably, the aluminum salt includes aluminum nitrate.

[0021] Preferably, the molar ratio of the total metal elements in the nickel salt, cobalt salt, and M salt in step (1) to the metal elements in the molten salt is 1:(2-3), for example, it can be 1:2, 1:2.1, 1:2.2, 1:2.3, 1:2.4, 1:2.5, 1:2.6, 1:2.7, 1:2.8, 1:2.9, or 1:3, etc., and more preferably 1:2.5. When the molten salt content is too high, it will affect the electrochemical performance of the single-crystal ternary material; when the molten salt content is too low, it is not conducive to fully dispersing in the material to guide the formation of single crystals, and it is easy to produce a structure of local single crystal and local polycrystalline.

[0022] Preferably, the molar ratio of the total metal elements in the nickel salt, cobalt salt, and M salt in step (1) to the lithium in the lithium salt is 1:(1~1.1), for example, it can be 1:1, 1:1.01, 1:1.02, 1:1.03, 1:1.04, 1:1.05, 1:1.06, 1:1.07, 1:1.08, 1:1.09, or 1:1, etc., and more preferably 1:2.5. In this invention, a single-crystal ternary material with excellent electrochemical performance can be generated without requiring a high lithium salt content.

[0023] Preferably, the total concentration of metal ions in the mixed solution in step (1) is 50 to 400 g / L, for example, it can be 50 g / L, 100 g / L, 150 g / L, 200 g / L, 250 g / L, 300 g / L, 350 g / L or 400 g / L, etc., preferably 200 to 300 g / L.

[0024] As a preferred technical solution of the preparation method of the present invention, the temperature of spray pyrolysis in step (2) is 600-800℃, for example, it can be 600℃, 620℃, 640℃, 660℃, 680℃, 700℃, 720℃, 740℃, 760℃, 780℃ or 800℃, etc., preferably 650-700℃.

[0025] Preferably, the spray pyrolysis time in step (2) is 1 to 60 seconds, for example, it can be 1 second, 5 seconds, 10 seconds, 15 seconds, 20 seconds, 25 seconds, 30 seconds, 35 seconds, 40 seconds, 45 seconds, 50 seconds, 55 seconds or 60 seconds, and preferably 10 to 30 seconds.

[0026] It should be noted that spray pyrolysis equipment generally includes an atomizing device and a pyrolysis furnace. The mixed solution is sprayed into the pyrolysis furnace through the atomizing device at a certain feed rate, and the pyrolysis products are collected by a dust collection device.

[0027] In some embodiments, the atomizing device includes any one of single-fluid atomization, dual-fluid atomization, pressure atomization, ultrasonic atomization, or electrostatic atomization, preferably dual-fluid atomization.

[0028] Preferably, the feeding rate is 0.1 to 500 L / h, for example, it can be 0.1 L / h, 1 L / h, 5 L / h, 10 L / h, 50 L / h, 100 L / h, 200 L / h, 300 L / h, 400 L / h, or 500 L / h, etc.; the feeding rate is directly related to the size of the equipment. In pilot-scale equipment, the feeding rate is preferably 100 to 300 L / h; in small-scale equipment, the feeding rate is preferably 0.1 to 5 L / h.

[0029] It should be noted that the temperature of spray pyrolysis in this invention refers to the temperature inside the pyrolysis furnace, and the time of spray pyrolysis refers to the residence time of the material inside the pyrolysis furnace.

[0030] Preferably, the average particle size of the single-crystal precursor in step (2) is 3 to 5 μm, for example, it can be 3 μm, 4 μm, 5 μm, etc.

[0031] Preferably, after the spray pyrolysis in step (2) and before the sintering in step (3), a washing, filtering and drying step is performed. The spray pyrolysis yields a powder product with uniform particle size, which is washed and filtered with solvent to remove excess molten salt ions. After drying, a single-crystal precursor of nickel cobalt manganese / lithium aluminate is obtained.

[0032] Preferably, the solvent used for washing includes water.

[0033] Preferably, the sintering temperature in step (3) is 700 to 900°C, for example, it can be 700°C, 720°C, 740°C, 760°C, 780°C, 800°C, 820°C, 840°C, 860°C, 880°C or 900°C.

[0034] Preferably, the sintering time in step (3) is 4 to 8 hours, for example, it can be 4 hours, 4.5 hours, 5 hours, 5.5 hours, 6 hours, 6.5 hours, 7 hours, 7.5 hours or 8 hours.

[0035] Preferably, the gas in the sintering atmosphere in step (3) includes oxygen, for example, sintering can be performed in an air or oxygen atmosphere.

[0036] Generally speaking, Ni 0.8 Co 0.1 M 0.1 When (OH)₂ is used as the precursor (particle size approximately 10 μm), and x ≥ 0.8 (i.e., the subscript of Ni / content), an oxygen atmosphere is required to avoid the formation of impurity phases (low-valence NiO) on the surface of high-nickel materials. The sintering temperature is generally 700–800℃, and the sintering time is generally 20–25 h. When x < 0.8, an air atmosphere is generally used, with a sintering temperature of 800–900℃ and a sintering time of 10–15 h. However, this invention uses a single-crystal precursor (particle size < 5 μm), and lithium ions are pre-uniformly dispersed within the precursor material, significantly accelerating the lithiation rate and shortening the sintering time to 4–8 h. The short sintering process greatly reduces lithium volatilization loss, thus eliminating the need for excessive lithium source addition, resulting in a lower residual alkali on the surface of the ternary material. Furthermore, short sintering does not cause agglomeration of the single-crystal precursor particles, helping to maintain the highly dispersed single-crystal morphology of the ternary material.

[0037] As a preferred embodiment of the preparation method of the present invention, the preparation method includes:

[0038] (1) Mix a lithium salt, a nickel salt, a cobalt salt, an M salt and a molten salt to obtain a mixed solution;

[0039] Among them, the molten salt includes any one or a combination of at least two of KNO3, NaNO3, KCl, NaCl, K2SO4 and Na2SO4, the M salt includes a manganese salt and / or an aluminum salt, and the sum of the metal elements in the nickel salt, cobalt salt and M salt and the molar ratio of the metal elements in the molten salt is 1:(2-3), the sum of the metal elements in the nickel salt, cobalt salt and M salt and the molar ratio of lithium in the lithium salt is 1:(1-1.1), and the total concentration of metal ions in the mixed solution is 50-400 g / L;

[0040] (2) Perform spray pyrolysis on the mixed solution in step (1), the temperature of the spray pyrolysis is 600-800 °C, the time is 1-60 s, and after the spray pyrolysis, wash, filter and dry the obtained product to obtain a single crystal type precursor, and the average particle size of the single crystal type precursor is 3-5 μm;

[0041] (3) Sinter the single crystal type precursor in step (2) at 700-900 °C for 4-8 h to obtain a single crystal type ternary material.

[0042] In a second aspect, the present invention provides a single crystal type ternary material, and the single crystal type ternary material is prepared by using the preparation method described in the first aspect.

[0043] The single crystal type ternary material prepared by the present invention effectively avoids the formation of intergranular cracks during the charge and discharge cycle, realizes the construction of a long-life ternary lithium ion battery, and has excellent electrochemical performance.

[0044] Preferably, the single crystal type ternary material includes Li a Ni x Co y M 1-x-y O2, where 1≤a≤1.1, for example, it can be 1, 1.02, 1.04, 1.06, 1.08 or 1.1, etc., 0<x<1, for example, it can be 0.1, 0.2, 0.5, 0.8 or 0.9, etc., 0<y<1, for example, it can be 0.1, 0.2, 0.5, 0.8 or 0.9, etc., 0<x + y<1, for example, it can be 0.1, 0.2, 0.5, 0.8 or 0.9, etc., and M includes Mn and / or Al.

[0045] In a third aspect, the present invention provides a lithium ion battery, and the positive electrode of the lithium ion battery includes the single crystal type ternary material described in the second aspect.

[0046] The lithium-ion battery prepared using the single-crystal ternary material described in this invention has high initial discharge capacity, initial coulombic efficiency, and cycle capacity retention.

[0047] Compared with the prior art, the present invention has the following beneficial effects:

[0048] (1) The present invention uses a molten salt-assisted spray pyrolysis method, which can easily and quickly prepare highly uniformly dispersed single crystal precursors, significantly reduce the temperature and time required for subsequent lithiation processes, reduce lithium volatilization losses, avoid the formation of single crystal particles to form agglomerates, reduce the degree of lithium-nickel mixing, and enable ternary materials to exhibit better electrochemical performance.

[0049] (2) In this invention, lithium salt is added to the raw material solution (mixed solution) prepared by the precursor in advance. Lithium ions and transition metal ions can be mixed uniformly at the molecular level. This not only eliminates the solid phase mixing and grinding step before the traditional lithiation process, but also eliminates the path of lithium ions diffusing from the precursor surface to the bulk phase, further accelerating the lithiation speed. Moreover, the residual lithium (alkali) on the surface of the obtained single crystal ternary material is low.

[0050] (3) The single-crystal ternary material prepared by the present invention effectively avoids the formation of intergranular cracks during charge-discharge cycles, thereby realizing the construction of long-life ternary lithium-ion batteries.

[0051] (4) The preparation process of this invention is simple, energy consumption is low and lithium source consumption is low, and the cost is significantly reduced. Attached Figure Description

[0052] Figure 1 This is a schematic diagram of the process for preparing single-crystal ternary materials in a specific embodiment of the present invention.

[0053] Figure 2 The single-crystal ternary material Li prepared in Example 1 of this invention 1.02 Ni 0.8 Co 0.1 Mn 0.1 X-ray diffraction (XRD) pattern of O2.

[0054] Figure 3 The single-crystal ternary material Li prepared in Example 1 of this invention 1.02 Ni 0.8 Co 0.1 Mn 0.1 Scanning electron microscope (SEM) image of O2. Detailed Implementation

[0055] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0056] Example 1

[0057] This embodiment provides a method for preparing a single-crystal ternary material, the flowchart of which is shown below. Figure 1 As shown, it includes:

[0058] (1) Dissolve lithium nitrate, nickel nitrate, cobalt nitrate, manganese nitrate and potassium nitrate (molten salt) in water at a molar ratio of 1.05:0.8:0.1:0.1:2.5 to prepare a mixed solution of 250 g / L (based on the total concentration of metal ions);

[0059] (2) Spray pyrolysis: The mixed solution is sprayed into the pyrolysis furnace at a feed rate of 200 L / h through a two-fluid atomizing device, and the reaction is held at 650℃ for 20s. The pyrolysis product (powder product) is then collected by a dust collection device. The product is washed and filtered with deionized water to remove excess potassium ions and nitrate ions. After drying, a single-crystal precursor of lithium nickel cobalt manganese oxide is obtained.

[0060] (3) The above-mentioned single-crystal precursor was sintered at 750°C for 6 hours in an oxygen atmosphere to obtain the single-crystal ternary material Li. 1.02 Ni 0.8 Co 0.1 Mn 0.1 O2.

[0061] Figure 2 The single-crystal ternary material Li prepared in this embodiment 1.02 Ni 0.8 Co 0.1 Mn 0.1 The X-ray diffraction (XRD) spectrum of O2 shows that the crystal structure of the prepared ternary material conforms to the layered LiNiO2 structure (PDF#09-0063). The (006) / (102) and (108) / (110) peaks are clearly split, indicating that the layered structure has good crystallinity. Furthermore, the peak height ratio of (003) / (104) is 1.34, which is significantly greater than 1.2, indicating that the lithium-nickel mixing degree of the prepared ternary material is relatively low.

[0062] Figure 3 The single-crystal ternary material Li prepared in this embodiment 1.02 Ni 0.8 Co 0.1 Mn 0.1 The scanning electron microscope (SEM) image of O2 shows that the prepared ternary material does indeed exhibit a single-crystal particle morphology, with a grain size between 1 and 2 μm, relatively obvious grain boundaries, no agglomeration, and good dispersion.

[0063] Example 2

[0064] This embodiment provides a method for preparing a single-crystal ternary material, the flowchart of which is shown below. Figure 1 As shown, it includes:

[0065] (1) Dissolve lithium nitrate, nickel nitrate, cobalt nitrate, manganese nitrate and sodium nitrate (molten salt) in water at a molar ratio of 1:0.6:0.2:0.2:2 to prepare a mixed solution of 200 g / L (based on the total concentration of metal ions);

[0066] (2) Spray pyrolysis: The mixed solution is sprayed into the pyrolysis furnace at a feed rate of 250 L / h through a two-fluid atomizing device, and the reaction is held at 700℃ for 10 s. The pyrolysis product (powder product) is then collected by a dust collection device. The product is washed and filtered with deionized water to remove excess potassium ions and nitrate ions. After drying, a single-crystal precursor of lithium nickel cobalt manganese oxide is obtained.

[0067] (3) The above-mentioned single-crystal precursor was sintered at 800°C for 4 hours in an oxygen atmosphere to obtain the single-crystal ternary material Li. 0.98 Ni 0.6 Co 0.2 Mn 0.2 O2.

[0068] Example 3

[0069] This embodiment provides a method for preparing a single-crystal ternary material, the flowchart of which is shown below. Figure 1 As shown, it includes:

[0070] (1) Dissolve lithium nitrate, nickel nitrate, cobalt nitrate, manganese nitrate and sodium chloride (molten salt) in water at a molar ratio of 1.1:0.8:0.1:0.1:3 to prepare a mixed solution of 300 g / L (based on the total concentration of metal ions);

[0071] (2) Spray pyrolysis: The mixed solution is sprayed into the pyrolysis furnace at a feed rate of 150 L / h through a two-fluid atomizing device and reacted at 650℃ for 30 s. The pyrolysis product (powder product) is then collected by a dust collection device. The product is washed and filtered with deionized water to remove excess potassium ions and nitrate ions. After drying, a single crystal precursor of lithium nickel cobalt manganese oxide is obtained.

[0072] (3) The above-mentioned single-crystal precursor was sintered at 700°C for 8 hours in an oxygen atmosphere to obtain the single-crystal ternary material Li. 1.05 Ni 0.8 Co 0.1 Mn 0.1 O2.

[0073] Example 4

[0074] Except for the molar ratio of lithium nitrate, nickel nitrate, cobalt nitrate, manganese nitrate and potassium nitrate (molten salt) in step (1) being 1.05:0.8:0.1:0.1:3.5, all other steps are the same as in Example 1.

[0075] Example 5

[0076] Except for the molar ratio of lithium nitrate, nickel nitrate, cobalt nitrate, manganese nitrate and potassium nitrate (molten salt) in step (1) being 1.05:0.8:0.1:0.1:1.5, all other steps are the same as in Example 1.

[0077] Example 6

[0078] Except for the spray pyrolysis temperature of 600°C in step (2), the rest are the same as in Example 1.

[0079] Example 7

[0080] Except for the spray pyrolysis temperature of 800°C in step (2), the rest is the same as in Example 1.

[0081] Example 8

[0082] Except for the sintering time of 3 hours in step (3), the rest is the same as in Example 1.

[0083] Example 9

[0084] Except for the sintering time of 10h in step (3), the rest is the same as in Example 1.

[0085] Comparative Example 1

[0086] Except for step (1) where molten salt is not added, everything else is the same as in Example 1.

[0087] Comparative Example 2

[0088] Except that lithium nitrate and molten salt are not added in step (1), the traditional co-precipitation method is used instead of spray pyrolysis to prepare the precursor in step (2). The precursor, lithium carbonate, and molten salt are then mixed and ground in the same proportion before the sintering operation in step (3) is performed. All other steps are the same as in Example 1.

[0089] Comparative Example 3

[0090] Except for the absence of lithium nitrate in step (1), after spray pyrolysis in step (2), the product of spray pyrolysis is ground and mixed with lithium nitrate before the sintering operation in step (3). The rest is the same as in Example 1.

[0091] The amount of lithium nitrate added in this comparative example is the same as in Example 1.

[0092] I. Preparation of Lithium-ion Batteries

[0093] The single-crystal ternary materials of Examples 1-9 and Comparative Examples 1-3 were mixed with the conductive agent Super P and the binder PVDF in a mass ratio of 8:1:1, and dissolved in N-methylpyrrolidone (NMP) to prepare a positive electrode slurry. The positive electrode slurry was coated onto aluminum foil, dried, and then cut into [size not specified]. The CR2016 coin cell lithium-ion battery is assembled by stacking and pressing the following components in sequence: a circular wafer as the positive electrode, a lithium metal sheet as the negative electrode, a polyethylene film as the separator, a 1M LiPF6 solute as the electrolyte, and a mixture of ethylene carbonate, dimethyl carbonate and diethyl carbonate in a volume ratio of 1:1:1.

[0094] II. Performance Testing

[0095] The prepared lithium-ion batteries were subjected to electrochemical performance tests. The test voltage was 3.0–4.3V. The initial discharge specific capacity and initial coulombic efficiency were measured at 0.1C, and the capacity retention rate after 100 charge-discharge cycles was measured at 1C. The test results are shown in Table 1.

[0096] Table 1

[0097]

[0098]

[0099] As can be seen from Examples 1-9 above, the present invention can simply and quickly prepare highly uniformly dispersed single-crystal precursors by using molten salt-assisted spray pyrolysis. At the same time, lithium salts are added during the preparation of the precursors, eliminating the need for solid-phase mixing and grinding in the traditional lithiation process, thus accelerating the lithiation speed. Finally, a single-crystal ternary material with better electrochemical performance is prepared using a simplified process with lower energy consumption and cost.

[0100] A comparison of Examples 1 and Examples 4-5 shows that when the molar ratio of the total metal elements in nickel salt, cobalt salt, and M salt to the metal elements in molten salt is 1:(2-3), it can fully guide the formation of single crystals without affecting the material properties. In Example 4, the content of molten salt is too high, which leads to a decrease in the material's discharge specific capacity. In Example 5, the content of molten salt is too low, which leads to the formation of polycrystalline structures in the material, affecting the overall structural stability of the material and reducing the material's cycle stability. Therefore, compared with Examples 4 and 5, the crystal structure of Example 1 is more stable and singular, and the discharge capacity, coulombic efficiency, and retention rate after 100 cycles are higher.

[0101] A comparison of Examples 1 and 6-7 shows that the material performance is better when the spray pyrolysis temperature is in the range of 650-700℃. In Example 6, the spray pyrolysis temperature is too low, resulting in insufficient pyrolysis and more nitrate ions being trapped in the material, which affects the performance. In Example 7, the spray pyrolysis temperature is too high, which leads to further agglomeration of the formed single crystal particles and the formation of some polycrystalline particles. Therefore, compared with Examples 6-7, the overall battery performance of Example 1 is better.

[0102] A comparison of Examples 1 and 8-9 shows that the sintering time in this invention can be shortened to 4-8 hours. The short sintering process significantly reduces lithium volatilization loss, thus eliminating the need for excessive lithium source, resulting in lower residual alkali on the surface of the ternary material. Furthermore, short sintering does not cause agglomeration of precursor single-crystal particles, helping to maintain the highly dispersed single-crystal morphology of the ternary material. In Example 8, the sintering time was too short, resulting in lower orderliness of the layered crystal structure of the material, increasing the difficulty of lithium ion extraction and affecting capacity utilization. In Example 9, the sintering time was too long, leading to severe lithium volatilization loss and a reduction in effective reversible capacity. Therefore, compared to Examples 8-9, Example 1 has lower energy consumption and better battery performance.

[0103] A comparison of Example 1 and Comparative Examples 1-2 shows that spray pyrolysis and molten salt work synergistically in this invention. Using only one of these methods cannot yield the best single-crystal ternary material with optimal morphology and electrochemical performance. In Comparative Example 1, without molten salt, the "directional growth" of grains cannot be promoted during the grain growth stage. During spray pyrolysis, the crystal nuclei easily fuse and grow into polycrystalline structures. Comparative Example 2 uses a traditional co-precipitation method to prepare the precursor, resulting in severe particle agglomeration. Even with the presence of molten salt, the sintered ternary material remains polycrystalline, and the battery performance indicators are significantly reduced. Therefore, the molten salt-assisted spray pyrolysis method specific to this invention can easily and quickly prepare highly uniformly dispersed single-crystal precursors, enabling the single-crystal ternary material to exhibit superior electrochemical performance.

[0104] A comparison of Example 1 and Comparative Example 3 shows that in this invention, lithium salt is added to the raw material solution for precursor preparation in advance, allowing lithium ions and transition metal ions to mix uniformly at the molecular level. This not only eliminates the solid-phase mixing and grinding step before the traditional lithiation process but also eliminates the path for lithium ions to diffuse from the precursor surface to the bulk phase, further accelerating the lithiation speed. Furthermore, the resulting ternary material has a lower residual lithium (alkali) content on its surface. In contrast, Comparative Example 3 uses a traditional solid-phase grinding method with lithium salt and precursor. Under the same lithium salt content, its lithiation speed is slower, and the uniformity is poorer, resulting in a higher residual alkali on the material surface. The final material's discharge specific capacity and cycle performance are significantly worse than those of Example 1.

[0105] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for preparing a single-crystal ternary material, characterized in that, The preparation method includes: (1) Mix lithium salt, nickel salt, cobalt salt, M salt and molten salt to obtain a mixed solution; The molten salt includes any one or a combination of at least two of KNO3, NaNO3, KCl, NaCl, K2SO4 and Na2SO4, and the M salt includes manganese salt and / or aluminum salt. (2) The mixed solution in step (1) is subjected to spray pyrolysis to obtain a single-crystal precursor. The spray pyrolysis temperature is 600~800℃. (3) Sinter the single-crystal precursor described in step (2) to obtain a single-crystal ternary material; The sintering time in step (3) is 4~8h.

2. The preparation method according to claim 1, characterized in that, In step (1), the molar ratio of the total metal elements in the nickel salt, cobalt salt and M salt to the metal elements in the molten salt is 1:(2~3).

3. The preparation method according to claim 1, characterized in that, In step (1), the molar ratio of the total metal elements in the nickel salt, cobalt salt and M salt to the lithium in the lithium salt is 1:(1~1.1).

4. The preparation method according to claim 1, characterized in that, The total concentration of metal ions in the mixed solution in step (1) is 50~400g / L.

5. The preparation method according to claim 4, characterized in that, The total concentration of metal ions in the mixed solution in step (1) is 200~300g / L.

6. The preparation method according to claim 1, characterized in that, The spray pyrolysis temperature in step (2) is 650~700℃.

7. The preparation method according to claim 1, characterized in that, The spray pyrolysis time in step (2) is 1~60s.

8. The preparation method according to claim 1, characterized in that, The spray pyrolysis time in step (2) is 10~30s.

9. The preparation method according to claim 1, characterized in that, The average particle size of the single-crystal precursor in step (2) is 3~5μm.

10. The preparation method according to claim 1, characterized in that, After the spray pyrolysis in step (2) and before the sintering in step (3), washing, filtering and drying steps are also performed.

11. The preparation method according to claim 10, characterized in that, The solvent used for washing includes water.

12. The preparation method according to claim 1, characterized in that, The sintering temperature in step (3) is 700~900℃.

13. The preparation method according to claim 1, characterized in that, The gas in the sintering atmosphere in step (3) includes oxygen.

14. The preparation method according to claim 1, characterized in that, The preparation method includes: (1) Mix lithium salt, nickel salt, cobalt salt, M salt and molten salt to obtain a mixed solution; The molten salt comprises any one or a combination of at least two of KNO3, NaNO3, KCl, NaCl, K2SO4, and Na2SO4; the M salt comprises manganese salt and / or aluminum salt; the molar ratio of the sum of the metal elements in the nickel salt, cobalt salt, and M salt to the metal elements in the molten salt is 1:(2~3); the molar ratio of the sum of the metal elements in the nickel salt, cobalt salt, and M salt to the lithium in the lithium salt is 1:(1~1.1); and the total concentration of metal ions in the mixed solution is 50~400 g / L. (2) The mixed solution in step (1) is subjected to spray pyrolysis. The spray pyrolysis temperature is 600~800℃ and the time is 1~60s. After spray pyrolysis, the obtained product is washed, filtered and dried to obtain a single crystal precursor. The average particle size of the single crystal precursor is 3~5μm. (3) The single-crystal precursor described in step (2) is sintered at 700~900℃ for 4~8h to obtain a single-crystal ternary material.

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