Uniform-pore ternary cathode material prepared by dual-frequency cavitation induction and application thereof

Abstract

The application belongs to the technical field of batteries and relates to a uniform-pore ternary positive electrode material prepared by double-frequency cavitation induction and application. The application optimizes the porosity and equivalent pore diameter of the secondary particles of the ternary positive electrode material, controls the uniformity of the pore distribution and pore size of the secondary particles in the ternary positive electrode material, and simultaneously makes the secondary particles have suitable stacking gaps, so that the battery prepared from the uniform-pore ternary positive electrode material has excellent cycle performance.

Description

Technical Field

[0001] This invention belongs to the field of battery technology and relates to a cathode material, particularly a uniformly porous ternary cathode material prepared by dual-frequency cavitation induction and its application. Background Technology

[0002] Ternary cathode materials, as layered transition metal oxides, possess significant advantages in high-performance applications due to their high specific capacity, stable voltage platform, high energy density, and excellent power density, particularly excelling in the field of electric vehicles requiring long driving range. Their unique layered structure allows lithium ions to diffuse efficiently in two-dimensional channels, endowing the material with superior rate performance. However, during repeated charge-discharge cycles, ternary cathode materials undergo complex phase transitions. With the insertion and extraction of lithium ions, the ordered layered crystal structure gradually transforms into a disordered structure. This is accompanied by anisotropic internal stress generated by crystal expansion and contraction. This internal stress causes grain boundary cracks to form along the grain boundaries within the material. As the number of cycles increases, these cracks gradually expand, eventually leading to the fragmentation of the material particles. After fragmentation, the contact area between the material and the electrolyte significantly increases, promoting interfacial side reactions and accelerating the loss of active materials. Ultimately, this results in poor cycle stability of the ternary cathode material, leading to a significant decline in overall performance after prolonged charge-discharge cycles. During repeated charge-discharge cycles, mechanical compression also occurs between particles along with crystal expansion and contraction, causing breakage of the binder / conductive network, which also affects battery performance.

[0003] To address these issues, researchers have improved the stability of layered structures through bulk doping, or utilized the porosity generated by the primary particle stacking within the ternary material itself to alleviate the pressure caused by crystal expansion, suppress internal stress, and reduce grain boundary cracks. This porosity arises from the natural stacking of primary particles; the area and distribution of these pores are randomly generated. Excessively large or concentrated pore areas can lead to a decrease in the material's mechanical strength, causing it to crack directly during electrode pressing. Conversely, pore areas that are too small cannot effectively alleviate the pressure caused by crystal expansion.

[0004] Therefore, there is a need to provide a ternary cathode material with suitable pore area, pore distribution, and excellent packing pores. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a uniformly porous ternary cathode material and its application. By optimizing the porosity and equivalent pore size of the ternary cathode material, the present invention controls the uniformity of pore distribution and pore size within the secondary particles of the ternary cathode material, as well as the appropriate packing gaps between the secondary particles, thereby enabling the ternary cathode material to possess excellent cycle performance.

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

[0007] In a first aspect, the present invention provides a uniformly porous ternary cathode material, wherein the uniformly porous ternary cathode material, after being pressed under 5T pressure, has a porosity of 0.0500 cm⁻¹. 3 / g≤V 堆 ≤0.0950cm 3 / g;

[0008] in, C D The compaction density of the uniformly porous ternary cathode material after being pressed under 5 tons (T) of pressure is expressed in g / cm³. 3 ρ represents the true density of the uniformly porous ternary cathode material, in g / cm³. 3 V g The total pore volume of the uniformly porous ternary cathode material is expressed in cm³. 3 / g.

[0009] C D The compaction density of the uniformly porous ternary cathode material after being pressed under 5T pressure is expressed in g / cm³. 3 ; corresponding C D The reciprocal of the number, in cm. 3 / g reflects the volume of the uniformly porous ternary cathode material, including closed pores, interparticle pores, and open pores per unit mass after pressing; ρ is the true density of the uniformly porous ternary cathode material, in g / cm³. 3 ; corresponding It is the reciprocal of ρ, and the unit is cm. 3 / g reflects the volume of the uniformly porous ternary cathode material and the closed pores in the material per unit mass. V g The total pore volume of the ternary cathode material reflects the open pore volume of the uniformly porous ternary cathode material with a measurable pore diameter <195.6 nm, and is expressed in cm³. 3 / g.

[0010] Therefore, V 堆 This refers to the pore volume after 5T pressure pressing, reflecting the rearrangement of secondary particle morphology and size distribution, as well as the interlocking of particles. Repeated charge-discharge processes involve crystal expansion and contraction, and mechanical compression between particles can occur, causing breakage of the binder and / or conductive network, thus affecting the battery's cycle stability. V 堆 The size of V is related to the size of the gaps between particles, that is, the ability of particles to cope with mechanical compression. 堆 The larger the V, the better it is for relaxing the mechanical extrusion pressure between cathode material particles, but an excessively large V... 堆 It will reduce the bulk density of the material; conversely, V 堆A smaller void space will relatively increase the capacity density of the material, but it cannot effectively alleviate the mechanical compression between the cathode material particles, further causing the breakage of the binder and / or conductive network in the battery electrode, thus affecting its cycle stability. Therefore, the packing void space in this invention satisfies 0.0500 cm. 3 / g≤V 堆 ≤0.0950cm 3 / g, preferably 0.0600cm 3 / g≤V 堆 ≤0.0950cm 3 / g, further preferably 0.0700cm 3 / g≤V 堆 ≤0.0950cm 3 / g.

[0011] For example, C D The value range satisfies 3.3 g / cm³. 3 ~3.9g / cm 3 For example, it could be 3.3 g / cm³ 3 3.4g / cm 3 3.5g / cm 3 3.6g / cm 3 3.7g / cm 3 3.8g / cm 3 Or 3.9g / cm 3 However, this does not limit the listed values; any other unlisted values ​​within the range are also applicable.

[0012] Preferably, the uniformly porous ternary cathode material comprises secondary particles formed by primary particle stacking;

[0013] The uniformly porous ternary cathode material has a porous structure;

[0014] Structural stability parameters of the uniformly porous ternary cathode material satisfy:

[0015] in, Porosity and pore area were obtained from cross-sectional scanning electron microscopy images of the secondary particles. Porosity = total area of ​​pore regions in the secondary particle region / total cross-sectional area of ​​the secondary particle region. The average porosity of the secondary particles is... This represents the average area of ​​each pore in the cross-sectional scanning electron microscope image of the secondary particle.

[0016]

[0017] Porosity is the ratio of the sum of the pore areas in the secondary particles of the uniformly porous ternary cathode material to the cross-sectional area, reflecting the proportion of pores contained in the secondary particles. The average pore diameter reflects the pore size in the uniformly porous ternary cathode material.

[0018] Due to the anisotropic internal stress generated by the expansion / contraction of the crystal during charging and discharging, the internal stress causes grain boundary cracks to form along the grain boundaries within the material. With increasing cycle count, these cracks gradually propagate and eventually lead to the fragmentation of the material particles. Therefore, This indicates that the ternary cathode material possesses a certain amount of porosity and pore size. Appropriate porosity and an appropriate average pore area can alleviate the pressure caused by crystal expansion, suppress the generation of internal stress, and at the same time avoid the decrease in material tap density caused by excessive porosity.

[0019] In this invention, the structural stability parameters of the uniformly porous ternary cathode material satisfy: For example, the values ​​could be 0.0002μm, 0.0005μm, 0.0008μm, 0.0010μm, 0.0015μm, 0.0020μm, 0.0025μm, 0.0030μm, or 0.0035μm, but are not limited to the listed values. Other unlisted values ​​within the range are also applicable, preferably... Further preferred

[0020] Preferably, the cycle stability parameter γ of the uniformly porous ternary cathode material satisfies:

[0021] 0.1×10 -8 cm 4 / g≤γ≤2×10 -8 cm 4 / g,

[0022] The cycle stability parameter γ described in this invention reflects the mechanical properties inside and between secondary particles. When this value is within a certain range, the internal structure of the secondary particles is stable and the relaxation between secondary particles is appropriate, so that the uniformly porous ternary cathode material maintains good cycle performance and better tap density.

[0023] In this invention, the value range of γ satisfies 0.1 × 10⁻⁶. -8 cm 4 / g~2×10 -8 cm 4 / g, for example, could be 0.1×10 - 8 cm 4 / g, 0.3×10 -8 cm 4 / g, 0.5×10 -8 cm 4 / g, 0.6×10 -8 cm 4 / g, 0.8×10 -8 cm 4 / g, 1×10 -8 cm 4 / g, 1.2×10 -8 cm 4 / g, 1.5×10 -8 cm 4 / g, 1.6×10 -8 cm 4 / g, 1.8×10 -8 cm 4 / g or 2×10 -8 cm 4 / g, but not limited to the listed values, the same applies to any other unlisted values ​​within the range.

[0024] Secondly, the present invention provides a method for preparing a uniformly porous ternary cathode material, the method comprising the following steps:

[0025] S1. A first coprecipitation reaction was carried out under dual-frequency ultrasound conditions by mixing a precipitant solution, a complexing agent solution, and a transition metal salt solution in parallel flow. Then, acetic acid and acetonitrile were added, and a second coprecipitation reaction was carried out under single-frequency ultrasound conditions. After aging, the resulting solid product was dried with supercritical fluid to obtain a ternary precursor.

[0026] The dual-frequency ultrasound includes simultaneously performing a first frequency ultrasound and a second frequency ultrasound; the ultrasonic frequency of the first frequency ultrasound is 20KHz to 40KHz, and the ultrasonic frequency of the second frequency ultrasound is 40KHz to 60KHz.

[0027] The ultrasonic frequency of the single-frequency ultrasound is 40KHz to 60KHz.

[0028] S2. Prepare a mixed slurry containing lithium salt and the ternary precursor; spray dry the mixed slurry to obtain a mixture; subject the mixture to a first sintering to obtain the uniformly porous ternary cathode material described in the first aspect.

[0029] The uniformly porous ternary cathode material is synthesized by sintering a ternary precursor with a lithium salt. The sintering process mainly achieves lithium-ion intercalation and lattice structure reorganization, rather than destroying the macroscopic morphological framework of the precursor. That is, the ternary cathode material inherits the morphological characteristics of the ternary precursor. A combination of dual-frequency and single-frequency ultrasound is used in the co-precipitation process to obtain the uniformly porous ternary cathode material that meets the requirements of this invention.

[0030] The preparation method provided by this invention firstly performs a first coprecipitation reaction under dual-frequency ultrasound, which improves the porosity and pore size uniformity of the product. The first frequency ultrasound generates cavitation bubbles, and the collapse of these bubbles leads to local supersaturation, promoting the primary nucleation formation of the coprecipitation reaction and accelerating its progress. At the same time, the presence of cavitation bubbles obstructs the crystal growth process, increasing the pore area in the coprecipitated product and making the pore size distribution more uniform. The second frequency ultrasound generates an ultrasonic jet, which is beneficial for the thorough mixing and uniform dispersion of the precipitant solution, complexing agent solution, and transition metal salt solution at the microscopic level, increasing the particle size uniformity of the ternary precursor.

[0031] Following dual-frequency ultrasound, the second coprecipitation reaction process employs single-frequency ultrasound. By using high-frequency ultrasound in the latter half of the process, cavitation bubbles generated by low-frequency ultrasound during the reaction are avoided, thereby reducing the number of pores near the surface of the ternary precursor and improving compaction density. Furthermore, the combined application of dual-frequency and single-frequency ultrasound ensures uniform particle distribution and orderly crystal growth, which is beneficial for optimizing particle rearrangement and interlocking.

[0032] The single-frequency ultrasound combined with the addition of acetic acid and acetonitrile in the second coprecipitation reaction can reduce the formation of crystal nuclei, allowing the preceding crystal to continue growing and reducing the problems of incomplete crystal growth, poor structure, and poor stress resistance caused by the new crystal nuclei formed in the second coprecipitation reaction. Taking ammonia water as the complexing agent solution as an example, acetonitrile can disperse metal ammonia complex ions to a certain extent, reduce the competition between the solvent and hydrogen bond donors, enhance the stability of metal ammonia complex ions, and avoid the formation of new crystal nuclei due to the concentration of metal ions; at the same time, it does not affect the transfer of unsaturated transition metal electrons from the (010) plane to the metal ammonia complex ions, promoting the growth of the crystal in the

[010] direction; the acetate ions of acetic acid coordinate with the surface metal sites, weakening the metal-hydroxyl bond (M-OH), reducing the deprotonation energy barrier, enhancing the deprotonation effect of the (001) crystal plane -OH, and enhancing the growth in the

[001] direction.

[0033] The solid product is dried using supercritical fluid drying, which avoids the shrinkage and rupture of the pore structure caused by the surface tension generated during solvent evaporation in traditional drying methods, increases the formation of closed pores, and maximizes the preservation of the uniformity and integrity of the pore structure in the ternary precursor.

[0034] Preferably, the complexing agent solution includes ammonia. As a further preferred technical solution, during the first coprecipitation reaction and the second coprecipitation reaction, the concentration of ammonia in the system is 0.05 mol / L to 1 mol / L, for example, it can be 0.05 mol / L, 0.1 mol / L, 0.3 mol / L, 0.5 mol / L, 0.6 mol / L, 0.8 mol / L or 1 mol / L, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable, preferably 0.3 mol / L to 0.8 mol / L.

[0035] Preferably, the precipitant solution includes a sodium hydroxide solution. As a further preferred technical solution, the concentration of the sodium hydroxide solution is 3 mol / L to 10 mol / L, for example, it can be 3 mol / L, 4 mol / L, 5 mol / L, 6 mol / L, 8 mol / L or 10 mol / L, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0036] Preferably, the transition metal salt in the transition metal salt solution includes nickel salt, cobalt salt and manganese salt, and the concentration of the transition metal salt in the transition metal salt solution is 1 mol / L to 3 mol / L, for example, it can be 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L or 3 mol / L, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0037] Preferably, in the transition metal salt solution, the molar ratio of nickel, cobalt and manganese is (5-95):(1-9):(1-5).

[0038] Preferably, the nickel salt includes at least one of nickel sulfate and its hydrate; the cobalt salt includes at least one of cobalt sulfate and its hydrate; and the manganese salt includes at least one of manganese sulfate and its hydrate.

[0039] Preferably, the coprecipitation reaction is carried out in a protective atmosphere, the gas used in the protective atmosphere including nitrogen and / or an inert gas; the inert gas includes any one or at least two combinations of helium, neon or argon, typical but non-limiting combinations include a combination of helium and neon, a combination of neon and argon, a combination of helium and argon, or a combination of helium, neon and argon.

[0040] In this invention, the ultrasonic frequency of the first frequency ultrasound is 20KHz to 40KHz, for example, it can be 20KHz, 25KHz, 30KHz, 35KHz or 40KHz, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0041] Preferably, the ultrasonic power of the first frequency ultrasound is 80W / L to 120W / L, for example, it can be 80W / L, 90W / L, 100W / L, 110W / L or 120W / L, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable. Preferably, it is 95W / L to 120W / L, where W / L means that for every 1L of solution in the reaction system, the corresponding ultrasonic power is increased.

[0042] In this invention, the ultrasonic frequency of the second frequency ultrasound is 40KHz to 60KHz, for example, it can be 40KHz, 45KHz, 50KHz, 55KHz or 60KHz, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0043] Preferably, the ultrasonic power of the second frequency ultrasound is 35W / L to 60W / L, for example, it can be 35W / L, 40W / L, 45W / L, 50W / L, 55W / L or 60W / L, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable. Preferably, it is 40W / L to 60W / L, where W / L means that for every 1L of solution in the reaction system, the corresponding ultrasonic power is increased.

[0044] In this invention, the ultrasonic frequency of the single-frequency ultrasound is 40KHz to 60KHz, for example, it can be 40KHz, 45KHz, 50KHz, 55KHz or 60KHz, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0045] Preferably, the ultrasonic power of the single-frequency ultrasound is 35W / L to 60W / L, for example, it can be 35W / L, 40W / L, 45W / L, 50W / L, 55W / L or 60W / L, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable. Preferably, it is 40W / L to 60W / L, where W / L means that for every 1L of solution in the reaction system, the corresponding ultrasonic power is increased.

[0046] Preferably, the pH value of the first coprecipitation reaction is 11-12, and the temperature is 40℃-70℃.

[0047] In this invention, the pH value of the first coprecipitation reaction is controlled by the flow rate of the precipitant solution, and is 11 to 12. For example, it can be 11, 11.2, 11.5, 11.6, 11.8 or 12, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable, preferably 11.1 to 11.5.

[0048] The temperature of the first coprecipitation reaction is 40℃ to 70℃, for example, it can be 40℃, 45℃, 50℃, 55℃, 60℃, 65℃ or 70℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0049] Preferably, the pH value of the second coprecipitation reaction is 11-12, and the temperature is 40℃-70℃.

[0050] In this invention, the pH value of the second coprecipitation reaction is controlled by the flow rate of the precipitant solution, and is 11 to 12. For example, it can be 11, 11.2, 11.5, 11.6, 11.8 or 12, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable, preferably 11.1 to 11.5.

[0051] The temperature of the second coprecipitation reaction is 40℃~70℃, for example, it can be 40℃, 45℃, 50℃, 55℃, 60℃, 65℃ or 70℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0052] Preferably, the total time for the first coprecipitation reaction and the second coprecipitation reaction is 3h to 25h, for example, it can be 3h, 5h, 8h, 10h, 12h, 15h, 16h, 20h or 25h, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0053] Preferably, the time ratio of the first coprecipitation reaction to the second coprecipitation reaction is (14-17):(3-6), for example, it can be 14:6, 15:5, 16:4 or 17:3, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0054] Preferably, the amount of acetic acid added is such that its concentration in the reaction system is 0.1 mol / L to 0.15 mol / L, for example, 0.1 mmol / L, 0.12 mmol / L, 0.13 mmol / L, 0.14 mmol / L or 0.15 mmol / L, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0055] Preferably, the amount of acetonitrile added is 3% to 8% of the volume of the reaction solution, for example, it can be 3%, 4%, 5%, 6%, 7% or 8%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0056] In this invention, during the second coprecipitation reaction, the precipitant solution, complexing agent solution, and transition metal salt solution are continuously introduced, so the volume of the reaction solution continuously increases, and the corresponding amount of acetonitrile added also increases accordingly.

[0057] Preferably, the supercritical fluid drying includes supercritical carbon dioxide fluid drying at a temperature of 35°C to 50°C and a pressure of 8 MPa to 11 MPa.

[0058] The temperature for drying supercritical fluids is 35℃ to 50℃, for example, it can be 35℃, 40℃, 45℃ or 50℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0059] The pressure for supercritical fluid drying is 8 MPa to 11 MPa, for example, it can be 8 MPa, 9 MPa, 10 MPa or 11 MPa, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0060] During the sintering process, lithium elements are lost. In order to compensate for the loss of lithium, the preferred embodiment of the present invention requires that the amount of lithium salt be excessive.

[0061] Preferably, the total molar ratio of the transition metal elements in the ternary precursor to the molar ratio of lithium in the lithium salt is 1:1 to 1:1.1, for example, it can be 1:1, 1:1.02, 1:1.05, 1:1.08 or 1:1.1, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0062] Preferably, the lithium salt includes any one or a combination of at least two of lithium hydroxide, lithium carbonate, or lithium chloride. Typical but non-limiting combinations include combinations of lithium hydroxide and lithium carbonate, combinations of lithium hydroxide and lithium chloride, combinations of lithium carbonate and lithium chloride, or combinations of lithium hydroxide, lithium carbonate, and lithium chloride.

[0063] Preferably, the solid content of the mixed slurry is 25wt% to 35wt%, for example, it can be 25wt%, 28wt%, 30wt%, 32wt% or 35wt%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0064] Preferably, the solvent for the mixed slurry is deionized water.

[0065] Preferably, the first sintering includes pre-firing at 450°C to 550°C for 5 to 8 hours in an oxygen-containing atmosphere, followed by main firing at 750°C to 850°C for 12 to 15 hours.

[0066] Optionally, the gas used in the oxygen-containing atmosphere includes air and / or oxygen.

[0067] The preheating temperature is 450℃~550℃, for example, it can be 450℃, 480℃, 500℃, 520℃ or 550℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0068] The preheating time is 5h to 8h, for example, it can be 5h, 6h, 7h or 8h, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0069] The temperature of the main firing is 750℃~850℃, for example, it can be 750℃, 780℃, 800℃, 820℃ or 850℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0070] The main cooking time is 12h to 15h, for example, it can be 12h, 13h, 14h or 15h, but it is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0071] Preferably, the preparation method further includes: mixing the coating agent with the uniformly porous ternary cathode material, and performing a second sintering.

[0072] This invention uses a coating agent to isolate the uniformly porous ternary cathode material from the electrolyte, preventing side reactions between the two and preventing the destruction and collapse of the crystal structure of the uniformly porous ternary cathode material, which is beneficial to improving its electrochemical performance.

[0073] Preferably, the elements in the coating agent include any one or a combination of at least two of silicon, titanium, phosphorus, sulfur, fluorine, magnesium, aluminum, germanium, bismuth, strontium, lanthanum, yttrium, or thallium.

[0074] Preferably, the mass of the coating agent is 0.8wt% to 1.2wt% of the uniformly porous ternary cathode material, for example, it can be 0.8wt%, 0.9wt%, 1wt%, 1.1wt% or 1.2wt%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0075] Preferably, the second sintering temperature is 580℃~620℃, and the time is 6h~10h.

[0076] The second sintering temperature is 580℃~620℃, for example, it can be 580℃, 590℃, 600℃, 610℃ or 620℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0077] The second sintering time is 6h to 10h, for example, it can be 6h, 7h, 8h, 9h or 10h, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0078] It should be noted that the uniformly porous ternary cathode material prepared by dual-frequency cavitation induction in this application refers to the uniformly porous ternary cathode material prepared by the dual-frequency cavitation induction method of this invention. However, those skilled in the art will understand that the uniformly porous ternary cathode material of this invention is not limited to the preparation method of this invention; the preparation method of this invention is merely an example. As mentioned above, dual-frequency cavitation induction refers to the use of dual-frequency ultrasound. The first frequency ultrasound generates cavitation bubbles, and the collapse of the cavitation bubbles leads to local supersaturation, promoting the primary nucleation formation of the co-precipitation reaction and accelerating the co-precipitation reaction. Uniform porosity refers to the relatively uniform pore size within the secondary particles of the ternary cathode material.

[0079] Thirdly, the present invention provides a battery comprising the uniformly porous ternary cathode material described in the first aspect, or the uniformly porous ternary cathode material prepared by the preparation method described in the second aspect.

[0080] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0081] Compared with the prior art, the present invention has at least the following beneficial effects:

[0082] (1) This invention optimizes the porosity and equivalent pore size inside the secondary particles of the ternary cathode material, controls the uniformity of pore distribution and pore size inside the secondary particles of the ternary cathode material, and at the same time makes the secondary particles have suitable packing gaps, so that the ternary cathode material has excellent cycle performance.

[0083] (2) The preparation method provided by the present invention first carries out the first coprecipitation reaction under dual-frequency ultrasound, which improves the porosity and pore size uniformity of the product; after dual-frequency ultrasound, the second coprecipitation reaction process adopts single-frequency ultrasound. By selecting high-frequency ultrasound in the second half of the process, cavitation bubbles generated by low-frequency ultrasound during the reaction process are avoided, thereby reducing the number of pores near the surface of the ternary precursor, which is beneficial to improving the compaction density; the method of using a combination of dual-frequency ultrasound and single-frequency ultrasound makes the particle distribution uniform and the crystal grows in an orderly manner, which is beneficial to optimizing the rearrangement of particles and the interlocking between particles;

[0084] (3) The solid product is dried by supercritical fluid drying, which avoids the shrinkage and rupture of the pore structure caused by the surface tension generated during solvent evaporation in the traditional drying method, increases the generation of closed pores, and preserves the uniformity and integrity of the pore structure in the ternary precursor to the maximum extent. Attached Figure Description

[0085] Figure 1This is a SEM cross-sectional view of the secondary particles of the uniformly porous ternary cathode material obtained in Example 1;

[0086] Figure 2 The X-ray diffraction pattern of the uniformly porous ternary cathode material obtained in Example 1 is shown. Detailed Implementation

[0087] 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.

[0088] Example 1

[0089] This embodiment provides a uniformly porous ternary cathode material, the preparation method of which includes the following steps:

[0090] (1) Nickel sulfate, cobalt sulfate and manganese sulfate were mixed in a molar ratio of 8:1:1 to obtain a transition metal salt solution with a concentration of 1.8 mol / L. The transition metal salt solution, 5 mol / L sodium hydroxide solution and ammonia water were added to the reactor in parallel. The first coprecipitation reaction was carried out for 15 h under the conditions of dual-frequency sonication, temperature of 50℃, pH value of 11.4 and ammonia concentration of 0.6 mol / L. Then acetic acid and acetonitrile were added. The second coprecipitation reaction was carried out for 3 h under the conditions of single-frequency sonication, temperature of 50℃, pH value of 11.4 and ammonia concentration of 0.6 mol / L. After aging for 1.5 h, the product was filtered and washed to obtain a solid product. The obtained solid product was dried by supercritical fluid to obtain a ternary precursor.

[0091] The dual-frequency ultrasound includes simultaneously performing a first frequency ultrasound and a second frequency ultrasound; the first frequency ultrasound has an ultrasonic frequency of 30KHz and an ultrasonic power of 105W / L; the second frequency ultrasound has an ultrasonic frequency of 50KHz and an ultrasonic power of 45W / L.

[0092] The single-frequency ultrasound has an ultrasonic frequency of 50KHz and an ultrasonic power of 45W / L.

[0093] The concentration of acetic acid added in the reaction solution is 0.13 mmol / L, and the amount of acetonitrile added is 6% of the volume of the reaction solution.

[0094] The supercritical fluid drying is supercritical carbon dioxide fluid drying at a temperature of 45°C and a pressure of 9 MPa.

[0095] (2) The lithium hydroxide pulverized by air jet milling is mixed with the ternary precursor and deionized water at a speed of 1800 rpm for 3 hours to obtain a mixed slurry with a solid content of 30 wt%; the mixed slurry is spray dried (outlet temperature is 300℃) to obtain a mixture; the mixture is subjected to a first sintering to obtain the ternary intermediate;

[0096] The total molar ratio of transition metal elements in the ternary precursor to the molar ratio of lithium in the lithium hydroxide is 1:1.1; the first sintering includes pre-firing at 500°C for 6 hours in an oxygen atmosphere, followed by main firing at 800°C for 13 hours.

[0097] (3) Mix titanium dioxide with the ternary intermediate and sinter at 600°C for 8 hours to obtain a ternary cathode material; the mass of the titanium dioxide is 1 wt% of the ternary intermediate.

[0098] The SEM cross-sectional image of the secondary particles of the ternary cathode material obtained in this embodiment is shown below. Figure 1 As shown, the X-ray diffraction pattern is as follows: Figure 2 As shown.

[0099] In the preparation methods of Examples 2 to 11 and Comparative Examples 1 to 2, except for the process parameters in Tables 1 to 3, the rest are the same as in Example 1.

[0100] The preparation methods of the transition metal salt solution in Examples 2 to 11 and Comparative Examples 1 to 2, the ammonia concentration, pH value and time of the first coprecipitation reaction, and the ammonia concentration, pH value and time of the second coprecipitation reaction are shown in Table 1.

[0101] In the preparation methods of Examples 2 to 11 and Comparative Examples 1 to 2, the ultrasonic frequency and power of the first frequency ultrasound, the ultrasonic frequency and power of the second frequency ultrasound, the ultrasonic frequency and power of the single frequency ultrasound, and the amounts of acetonitrile and acetic acid added are shown in Table 2.

[0102] The preparation methods of Examples 2 to 11 and Comparative Examples 1 to 2, the temperature and pressure of supercritical fluid drying, and the pre-calcination and main calcination are shown in Table 3.

[0103] Table 1

[0104]

[0105] Table 2

[0106]

[0107]

[0108] Table 3

[0109]

[0110]

[0111] Performance Characterization

[0112] The ternary cathode materials of the above embodiments and comparative examples were tested, including:

[0113] (1) Morphological characterization: The cross-sectional image of the ternary cathode material was obtained by scanning electron microscopy.

[0114] (2) The calculation involved cutting the ternary cathode material with a focused ion beam (FIB) to obtain high-resolution cross-sectional scanning electron microscope (SEM) images of individual secondary particles. The microstructure of the sample was observed using SEM to ensure that primary particles, secondary particles, and pore structures could be clearly distinguished. The obtained SEM images were then quantitatively analyzed using ImageJ software.

[0115] Calculation: Using ImageJ, the area of ​​the pore region and non-pore region of the cross-section of the ternary cathode material is calculated using SEM, and the total area A of the pore region is obtained. pores The total cross-sectional area A of the secondary particle region total , For each embodiment or comparative example, SEM images of 25 secondary particles were selected for porosity calculation, and the average value was taken to obtain...

[0116] Calculation: Using ImageJ, calculate the total area of ​​all visible pores in the SEM image of the ternary cathode material cross-section, and obtain the average value. Then, apply the formula... Calculations were performed, where n represents the number of visible pores in the corresponding secondary particle; for each embodiment or comparative example, SEM images of 25 secondary particles were selected to calculate the pore area, and the average value was taken to obtain... According to the formula get

[0117] Structural stability parameters Calculation: Based on and According to the formula Obtain the corresponding structural stability parameters

[0118] (3) Compacted density C D True density ρ, total pore volume V g , deposited porosity V 堆Calculation of γ:

[0119] Compacted density C D Calculation: According to GB / T 24533-2009 "Graphite Anode Materials for Lithium-ion Batteries", the ternary cathode material was pressed under a pressure of 5T using a compaction density meter, and its corresponding compaction density was recorded.

[0120] Calculation of true density ρ: The true density ρ of the ternary cathode material was obtained by testing with a Bestar physical adsorption instrument-TD according to GB / T 24586-2009 "Determination of apparent density, true density and porosity of iron ore".

[0121] Total pore volume V g Calculation: According to the static capacity method, the total pore volume Vg of the cathode material was tested using a BSD-660SA6B6 (P / P0 = 0.990, pore diameter < 195.6 nm).

[0122] Accumulated porosity V 堆 Calculation: Based on the compaction density C obtained from the test. D True density ρ, total pore volume V g According to the formula Obtain the corresponding product data V 堆 ;

[0123] Calculation of γ: Based on the obtained V 堆 And β, according to the formula Obtain the data γ for the corresponding product;

[0124] The physical properties of the ternary cathode materials in each embodiment and comparative example are shown in Table 4.

[0125] (4) Electrochemical performance test: The ternary cathode material, acetylene black and polyvinylidene fluoride were uniformly mixed in N-methylpyrrolidone in a mass ratio of 90:5:5, then coated on aluminum foil, dried in a vacuum drying oven, and then pressed into a cathode sheet with a diameter of 12 mm in an argon glove box.

[0126] In a glove box, a coin cell is assembled from a positive electrode, a polypropylene porous membrane, a negative lithium electrode, and an electrolyte. The electrolyte contains LiPF6 as the solvent, with a concentration of 1 mol / L, and the solvent is EC (ethylene carbonate) and DMC (dimethyl carbonate) in a volume ratio of 1:1.

[0127] The LAND battery testing system was used to perform constant current charge-discharge tests on coin cells to examine the electrochemical performance of ternary cathode materials, such as cycle stability and rate performance. The test voltage was 2.8V-4.25V and the test current density was 1C. The results are shown in Table 5.

[0128] Table 4

[0129]

[0130] Table 5

[0131]

[0132]

[0133] As can be seen from Tables 4 and 5, the V of the products provided in Examples 1 to 11 堆 Within the range specified in this invention, it exhibits superior discharge specific capacity and cycle performance at 1C.

[0134] Furthermore, compared with Examples 1 to 3, the products provided in Examples 4 to 5 and Example 7 have higher structural stability parameters. If the values ​​are too high or too low, it will affect the electrochemical performance to some extent. The product structure stability parameters provided in Example 4... Relatively large, specifically manifested as High; Examples 5 and 7 provide structural stability parameters for the product. Relatively small, specifically manifested as The relatively small value of the element affects its electrochemical performance.

[0135] Compared with Examples 1 to 3, the structural stability parameters of the product provided in Example 6 are... Both the cyclic stability parameter γ and the cyclic stability parameter are relatively too large, specifically manifested as follows: An excessively large value can negatively impact the performance of its electrochemical properties.

[0136] Compared with Examples 1 to 3, the structural stability parameters of the product provided in Example 8 are... The value is too large and exceeds the preferred range of this invention, but the cyclic stability parameter γ is within the preferred range, specifically manifested as follows: and If the value is too large, it will affect the performance of its electrochemical properties; compared with Example 6, the difference is that the cycle stability parameter γ does not exceed the range, and the cycle performance of the product provided in Example 8 is better than that in Example 6.

[0137] Compared with Examples 1 to 3, the structural stability parameters of the product provided in Example 9 are... If the value is too small, the cycle stability parameter γ will also be smaller, specifically manifested as follows: and If the value is too small, it will affect the performance of its electrochemical properties.

[0138] Compared with the embodiments, the products provided in Comparative Examples 1 to 2, V 堆 Not within 0.0500cm 3 / g≤V堆 ≤0.0950cm 3 Within the range of / g, the electrochemical performance of ternary cathode materials is poor.

[0139] The applicant declares that 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 uniformly porous ternary cathode material, characterized in that, The uniformly porous ternary cathode material, after being pressed under 5T pressure, has a porosity of 0.0500 cm⁻¹. 3 / g≤V 堆 ≤0.0950cm 3 / g; in, C D The compaction density of the uniformly porous ternary cathode material after being pressed under 5T pressure is expressed in g / cm³. 3 ρ represents the true density of the uniformly porous ternary cathode material, in g / cm³. 3 V g The total pore volume of the uniformly porous ternary cathode material is expressed in cm³. 3 / g.

2. The uniformly porous ternary cathode material according to claim 1, characterized in that, The uniformly porous ternary cathode material comprises secondary particles formed by the stacking of primary particles. The uniformly porous ternary cathode material has a porous structure; Structural stability parameters of the uniformly porous ternary cathode material satisfy: in, Porosity and pore area were obtained from cross-sectional scanning electron microscopy images of the secondary particles. Porosity = total area of ​​pore regions in the secondary particle region / total cross-sectional area of ​​the secondary particle region. The average porosity of the secondary particles is... This represents the average area of ​​each pore in the cross-sectional scanning electron microscope image of the secondary particle. And / or, the cycle stability parameter γ of the uniformly porous ternary cathode material satisfies: 0.1 × 10⁻⁶ -8 cm 4 / g≤γ≤2×10 - 8 cm 4 / g, 3. A method for preparing a uniformly porous ternary cathode material, characterized in that, The preparation method includes the following steps: S1. A first coprecipitation reaction was carried out under dual-frequency ultrasound conditions by mixing a precipitant solution, a complexing agent solution, and a transition metal salt solution in parallel flow. Then, acetic acid and acetonitrile were added, and a second coprecipitation reaction was carried out under single-frequency ultrasound conditions. After aging, the resulting solid product was dried with supercritical fluid to obtain a ternary precursor. The dual-frequency ultrasound includes simultaneously performing a first frequency ultrasound and a second frequency ultrasound; the ultrasonic frequency of the first frequency ultrasound is 20KHz to 40KHz, and the ultrasonic frequency of the second frequency ultrasound is 40KHz to 60KHz. The ultrasonic frequency of the single-frequency ultrasound is 40KHz to 60KHz. S2. Prepare a mixed slurry containing lithium salt and the ternary precursor; spray dry the mixed slurry to obtain a mixture; the mixture is subjected to a first sintering to obtain the uniformly porous ternary cathode material according to any one of claims 1 to 2.

4. The preparation method according to claim 3, characterized in that, The ultrasonic power of the first frequency ultrasound is 80W / L to 120W / L; And / or, the ultrasonic power of the second frequency ultrasound is 35W / L to 60W / L; And / or, the pH value of the first coprecipitation reaction is 11 to 12, and the temperature is 40°C to 70°C.

5. The preparation method according to claim 3, characterized in that, The ultrasonic power of the single-frequency ultrasound is 35W / L to 60W / L; And / or, the pH value of the second coprecipitation reaction is 11-12, and the temperature is 40℃-70℃.

6. The preparation method according to claim 3, characterized in that, The total time for the first coprecipitation reaction and the second coprecipitation reaction is 3h to 25h; And / or, the time ratio of the first coprecipitation reaction to the second coprecipitation reaction is (14-17):(3-6).

7. The preparation method according to claim 3, characterized in that, The amount of acetic acid added is such that its concentration in the reaction system is 0.1 mol / L to 0.15 mol / L; And / or, the amount of acetonitrile added is 3% to 8% of the volume of the reaction solution; And / or, the supercritical fluid drying includes supercritical carbon dioxide fluid drying at a temperature of 35°C to 50°C and a pressure of 8 MPa to 11 MPa.

8. The preparation method according to claim 3, characterized in that, The total molar ratio of transition metal elements in the ternary precursor to the molar ratio of lithium in the lithium salt is 1:1 to 1:1.

1. And / or, the solid content of the mixed slurry is 25wt% to 35wt%; And / or, the first sintering includes pre-firing at 450°C to 550°C for 5 to 8 hours in an oxygen-containing atmosphere, followed by main firing at 750°C to 850°C for 12 to 15 hours.

9. The preparation method according to any one of claims 3 to 8, characterized in that, The preparation method further includes: mixing the coating agent with the uniformly porous ternary cathode material, and performing a second sintering; And / or, the elements in the coating agent include any one or a combination of at least two of silicon, titanium, phosphorus, sulfur, fluorine, magnesium, aluminum, germanium, bismuth, strontium, lanthanum, yttrium or thallium; And / or, the mass of the coating agent is 0.8wt% to 1.2wt% of the uniformly porous ternary cathode material; And / or, the second sintering temperature is 580℃~620℃, and the time is 6h~10h.

10. A battery, characterized in that, The battery comprises the uniformly porous ternary cathode material according to any one of claims 1 to 2, or the uniformly porous ternary cathode material prepared by the preparation method according to any one of claims 3 to 9.

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