Homopore ternary positive electrode material prepared by dual-frequency cavitation induction and application thereof

Abstract

The invention belongs to the technical field of batteries, and relates to a uniform-pore ternary positive electrode material prepared by dual-frequency cavitation induction and application, and the uniform-pore ternary positive electrode material is prepared by optimizing the porosity and equivalent pore size in secondary particles of the ternary positive electrode material and controlling the pore distribution and pore size uniformity in the secondary particles in the ternary positive electrode material. And meanwhile, proper accumulation gaps exist among secondary particles, so that a battery prepared from the uniform-hole ternary positive electrode material has excellent cycle performance.

Description

Technical Field

[0001] The present invention belongs to the technical field of batteries and relates to a positive electrode material, in particular to a homogeneous pore ternary positive electrode material prepared by dual-frequency cavitation induction and its application. Background Art

[0002] Ternary cathode materials, layered transition metal oxides, hold significant advantages in high-performance applications due to their high specific capacity, stable voltage platform, high energy density, and excellent power density, particularly in electric vehicles, where long-range driving is crucial. Their unique layered structure allows efficient lithium ion diffusion within two-dimensional channels, endowing the material with exceptional rate performance. However, during repeated charge and discharge cycles, ternary cathode materials undergo complex phase transitions. As lithium ions are intercalated and deintercalated, the ordered layered crystal structure gradually transforms into a disordered structure. This is accompanied by crystal expansion and contraction, generating anisotropic internal stresses. These stresses cause grain boundary cracks to form along the grain boundaries within the material. With increasing cycle counts, these cracks gradually expand and eventually lead to particle pulverization. This pulverization significantly increases the contact area with the electrolyte, promoting interfacial side reactions and accelerating the loss of active materials. Ultimately, this leads to poor cycling stability and a significant decrease in overall performance after prolonged charge and discharge cycles. During repeated charge and discharge cycles, the expansion and contraction of the crystals also mechanically squeezes the particles, causing a break in the binder / conductive network and compromising battery performance.

[0003] To address these issues, researchers have used bulk doping to improve the stability of the layered structure, or utilized the pores created by the accumulation of primary particles within the ternary material itself to alleviate the pressure caused by crystal expansion, inhibit the generation of internal stress, and reduce the occurrence of grain boundary cracks. The existence of these pores arises from the natural accumulation of primary particles, and the area and distribution of the pores are random. Excessively large pores or concentrated distributions can reduce the mechanical strength of the material, leading to direct rupture during the electrode pressing process. Pore areas that are too small cannot effectively alleviate the pressure caused by crystal expansion.

[0004] To this end, it is necessary to provide a ternary positive electrode material with suitable pore area, pore distribution, and excellent stacking pores. Summary of the Invention

[0005] In view of the shortcomings of the existing technology, the purpose of the present invention is to provide a uniformly porous ternary positive electrode material and its application. The present invention optimizes the porosity and equivalent pore size of the ternary positive electrode material, controls the uniformity of the pore distribution and pore size inside the secondary particles in the ternary positive electrode material, and the appropriate stacking gaps between the secondary particles, so that the ternary positive electrode material has excellent cycle performance.

[0006] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0007] In the first aspect, the present invention provides a uniformly porous ternary positive electrode material, wherein the uniformly porous ternary positive electrode material has a stacking gap of 0.0500 cm after being pressed at 5T pressure. 3 / g≤V 堆 ≤0.0950cm 3 / g;

[0008] in, C D The compacted density of the uniformly porous ternary cathode material after being pressed at a pressure of 5 tons (T) is expressed in g / cm 3 ; ρ is the true density of the uniformly porous ternary cathode material, in g / cm 3 ; V g is the total pore volume of the homoporous ternary cathode material, in cm 3 / g.

[0009] C D is the compaction density of the uniformly porous ternary cathode material after being pressed at 5T, in g / cm 3 ; corresponding C D The reciprocal of the unit is cm 3 / g, which reflects the volume of the uniformly porous ternary positive electrode material, the closed pores in the material, the accumulated pores between particles, and the open pores of the material under unit mass after the uniformly porous ternary positive electrode material is pressed; ρ is the true density of the uniformly porous ternary positive electrode material, in g / cm 3 ; corresponding is the reciprocal of ρ, in cm 3 / g, reflecting the volume of the uniformly porous ternary positive electrode material and the closed pores in the material under unit mass. g is the total pore volume of the ternary cathode material, reflecting the open pore volume of the uniformly porous ternary cathode material with a pore diameter of <195.6 nm, in cm 3 / g.

[0010] Therefore, V 堆 It is the accumulated pore volume after 5T pressure pressing, reflecting the rearrangement of secondary particle morphology and particle size distribution and the inter-particle bite. Repeated charge and discharge process is accompanied by the expansion and contraction of crystals, and mechanical compression will also occur between particles, causing the breakage of binder and / or conductive network, thus affecting the cycle stability of the battery. 堆 The size of V is related to the size of the gap between particles, that is, the ability of particles to cope with mechanical extrusion. 堆 The larger the V is, the more conducive it is to the relaxation of the mechanical extrusion force between the positive electrode material particles, but too large a V 堆 Will reduce the capacity density of the material; on the contrary, V 堆The smaller the gap, the greater the capacity density of the material, but it cannot effectively alleviate the mechanical compression between the positive electrode material particles, further causing the breakage of the binder and / or conductive network in the battery pole piece, thereby affecting its cycle stability. Therefore, the stacking gap in the present invention meets the requirement of 0.0500cm 3 / g≤V 堆 ≤0.0950cm 3 / g, preferably 0.0600cm 3 / g≤V 堆 ≤0.0950cm 3 / g, more preferably 0.0700cm 3 / g≤V 堆 ≤0.0950cm 3 / g.

[0011] For example, C D The value range meets 3.3g / cm 3 ~3.9g / cm 3 , for example, it can be 3.3g / cm 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 , but not limited to the listed values, the remaining values ​​not listed in the numerical range are also applicable.

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

[0013] The uniformly porous ternary positive electrode material has a pore structure;

[0014] The structural stability parameters of the homoporous ternary cathode material satisfy:

[0015] in, The porosity and pore area are obtained from the cross-sectional scanning electron micrograph of the secondary particles. Porosity = the total area of ​​the pore region in the secondary particle region / the total cross-sectional area of ​​the secondary particle region. is the average porosity of the secondary particles, is the average of the pore areas in the cross-sectional SEM image of the secondary particles,

[0016]

[0017] The porosity is the ratio of the sum of the pore areas of the secondary particles of the homogeneous ternary cathode material to the cross-sectional area, reflecting the ratio of the pore volume inside the secondary particles; The average pore size reflecting the pore size of the homoporous ternary positive electrode material.

[0018] Due to the anisotropic internal stress generated by the expansion / contraction of the crystal during the charge and discharge process, the internal stress will cause grain boundary cracks to form along the grain boundaries inside the material. As the number of cycles increases, the cracks gradually expand and eventually lead to the crushing of the material particles. Therefore, This shows that the ternary positive electrode material has a certain amount of pores and pore size. The appropriate amount of pores and the appropriate average pore area can relieve the pressure caused by crystal expansion, inhibit the generation of internal stress, and avoid the decrease in the material's tap density caused by excessive pores.

[0019] In the present invention, the structural stability parameter of the homoporous ternary cathode material is satisfy: For example, it can be 0.0002 μm, 0.0005 μm, 0.0008 μm, 0.0010 μm, 0.0015 μm, 0.0020 μm, 0.0025 μm, 0.0030 μm or 0.0035 μm, but it is not limited to the listed values. Other values ​​not listed in the numerical range are also applicable. Preferably More preferably

[0020] Preferably, the cyclic stability parameter γ of the homoporous ternary cathode material satisfies:

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

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

[0023] In the present invention, the value range of γ satisfies 0.1×10 -8 cm 4 / g~2×10 -8 cm 4 / g, for example, it can 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 is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

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

[0025] S1, mixing a precipitant solution, a complexing agent solution, and a transition metal salt solution in parallel, and performing a first coprecipitation reaction under dual-frequency ultrasound; then adding acetic acid and acetonitrile, and performing a second coprecipitation reaction under single-frequency ultrasound. After aging, the obtained solid product is subjected to supercritical fluid drying to obtain a ternary precursor;

[0026] The dual-frequency ultrasound includes performing a first frequency ultrasound and a second frequency ultrasound simultaneously; 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; and perform a first sintering on the mixture to obtain the uniformly porous ternary positive electrode material described in the first aspect.

[0029] Uniformly porous ternary cathode materials are synthesized by sintering a ternary precursor with a lithium salt. The sintering process primarily achieves lithium ion insertion and lattice structure reorganization, rather than destroying the precursor's macroscopic morphology. This means the ternary cathode material inherits the morphological characteristics of the ternary precursor. A combination of dual-frequency and single-frequency ultrasound is used during the coprecipitation process to produce the uniformly porous ternary cathode material that meets the requirements of this invention.

[0030] The preparation method provided by the present invention first performs a first coprecipitation reaction under dual-frequency ultrasound conditions, thereby improving the porosity and pore size uniformity of the product; the first-frequency ultrasound generates cavitation bubbles, the cavitation bubbles burst to cause local supersaturation, promotes the primary nucleation formation of the coprecipitation reaction, and accelerates the coprecipitation reaction; at the same time, the presence of the cavitation bubbles causes obstruction in the crystallization growth process, increases the pore area in the coprecipitation product, and makes the pore size distribution more uniform; the second-frequency ultrasound generates an ultrasonic jet, which is conducive to the full mixing and uniform dispersion of the precipitant solution, the complexing agent solution and the transition metal salt solution at the microscopic level, thereby increasing the particle size uniformity of the ternary precursor.

[0031] After dual-frequency ultrasound, the second coprecipitation reaction uses single-frequency ultrasound. By using a single high-frequency ultrasound in the second half of the reaction, cavitation bubbles generated by low-frequency ultrasound are avoided. This reduces the number of pores near the surface of the ternary precursor, which helps to increase the compaction density. Furthermore, the combined application of dual-frequency and single-frequency ultrasound ensures uniform particle distribution and orderly crystal growth, which helps optimize particle rearrangement and inter-particle interlocking.

[0032] The addition of acetic acid and acetonitrile to the single-frequency ultrasound during the second coprecipitation reaction can reduce nucleation, allowing the previous crystal to continue growing, and reducing the problem of imperfect crystal growth, poor structure, and poor stress resistance caused by the new nuclei formed in the second coprecipitation reaction. Taking ammonia as the complexing agent solution as an example, acetonitrile can disperse the metal ammine complex ions to a certain extent, reducing competition between the solvent and hydrogen bond donors, enhancing the stability of the metal ammine complex ions, and preventing the formation of new 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 ammine complex ions, promoting crystal growth in the

[010] direction. The acetate group of acetic acid coordinates with the surface metal sites, weakening the metal-hydroxyl bond (M-OH), reducing the deprotonation energy barrier, enhancing the deprotonation of the -OH on the (001) crystal plane, and enhancing 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 surface tension generated when the solvent evaporates in the traditional drying method, increases the production of closed pores, and maximizes the uniformity and integrity of the pore structure in the ternary precursor.

[0034] Preferably, the complexing agent solution includes ammonia water. As a further preferred technical solution, during the first coprecipitation reaction and the second coprecipitation reaction, the ammonia water concentration 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. The remaining values ​​not listed in the numerical 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, 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 values ​​not listed within the numerical 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, and other values ​​not listed within the numerical 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, and the gas used in the protective atmosphere includes nitrogen and / or an inert gas; the inert gas includes any one or a combination of at least two of helium, neon or argon, and 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 the present 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, and other values ​​not listed within the numerical 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. The remaining unlisted values ​​within the numerical range are also applicable, preferably 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 the present 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, and other values ​​not listed within the numerical 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. The remaining unlisted values ​​within the numerical range are also applicable, preferably 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 the present 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, and other values ​​not listed within the numerical 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 values ​​not listed within the numerical range are also applicable, preferably 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°C-70°C.

[0047] In the present invention, the pH value of the first coprecipitation reaction is regulated 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 values ​​not listed within the numerical range are also applicable, preferably 11.1 to 11.5.

[0048] The temperature of the first coprecipitation reaction is 40°C to 70°C, for example, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C or 70°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

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

[0050] In the present invention, the pH value of the second coprecipitation reaction is regulated 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 values ​​not listed within the numerical range are also applicable, preferably 11.1 to 11.5.

[0051] The temperature of the second coprecipitation reaction is 40°C to 70°C, for example, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C or 70°C, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0052] Preferably, the total time of 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, and the remaining unlisted values ​​within the numerical 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, and the remaining unlisted values ​​within the numerical 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, and other values ​​not listed within the numerical range are also applicable.

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

[0056] In the present invention, when the second coprecipitation reaction is carried out, the precipitant solution, the complexing agent solution and the transition metal salt solution are continuously introduced, so the volume of the reaction solution continues to increase, and the corresponding amount of acetonitrile added also increases accordingly.

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

[0058] The temperature of supercritical fluid drying is 35°C to 50°C, for example, 35°C, 40°C, 45°C or 50°C, but is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0059] The pressure of supercritical fluid drying is 8 MPa to 11 MPa, for example, 8 MPa, 9 MPa, 10 MPa or 11 MPa, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0060] There is a loss of lithium element during the sintering process. In order to compensate for the loss of lithium due to ignition, the preferred embodiment of the present invention requires that the amount of lithium salt used be excessive.

[0061] Preferably, the molar ratio of the total molar amount of the transition metal elements in the ternary precursor to the 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, and the other unlisted values ​​within the numerical 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 a combination of lithium hydroxide and lithium carbonate, a combination of lithium hydroxide and lithium chloride, a combination of lithium carbonate and lithium chloride, or a combination 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, and the remaining values ​​not listed within the numerical range are also applicable.

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

[0065] Preferably, the first sintering comprises pre-sintering at 450° C. to 550° C. for 5 to 8 hours in an oxygen-containing atmosphere, and then performing main sintering 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 pre-calcination temperature is 450° C. to 550° C., for example, 450° C., 480° C., 500° C., 520° C. or 550° C., but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0068] The pre-burning time is 5 hours to 8 hours, for example, 5 hours, 6 hours, 7 hours or 8 hours, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0069] The main firing temperature is 750°C to 850°C, for example, it can be 750°C, 780°C, 800°C, 820°C or 850°C, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0070] The main burning time is 12 hours to 15 hours, for example, it can be 12 hours, 13 hours, 14 hours or 15 hours, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

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

[0072] The present invention isolates the uniform porous ternary cathode material from the electrolyte by using a coating agent, thereby preventing side reactions between the two and preventing the destruction and collapse of the crystal structure of the uniform 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 positive electrode material, for example, it can be 0.8wt%, 0.9wt%, 1wt%, 1.1wt% or 1.2wt%, but is not limited to the listed values, and the remaining unlisted values ​​within the numerical range are also applicable.

[0075] Preferably, the second sintering temperature is 580° C. to 620° C., and the time is 6 hours to 10 hours.

[0076] The temperature of the second sintering is 580° C. to 620° C., for example, 580° C., 590° C., 600° C., 610° C. or 620° C., but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0077] The second sintering time is 6 hours to 10 hours, for example, 6 hours, 7 hours, 8 hours, 9 hours or 10 hours, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0078] It should be noted that the homogeneous pore ternary positive electrode material prepared by dual-frequency cavitation induction in this application refers to the homogeneous pore ternary positive electrode material of the present invention that can be prepared by the dual-frequency cavitation induction method of the present invention, but those skilled in the art will know that the homogeneous pore ternary positive electrode material of the present invention is not limited to the preparation method of the present invention, and the preparation method of the present invention is only an example. As mentioned above, dual-frequency cavitation induction refers to the use of dual-frequency ultrasound, the first frequency ultrasound produces cavitation bubbles, the rupture of cavitation bubbles leads to local supersaturation, promotes the primary nucleation formation of the co-precipitation reaction, and accelerates the co-precipitation reaction. Uniform pore refers to the relatively uniform pore size of the secondary particles in the ternary positive electrode material.

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

[0080] The numerical range described in the present invention includes not only the point values ​​listed above, but also any point values ​​between the above numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists 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) The present invention optimizes the porosity and equivalent pore size inside the secondary particles of the ternary cathode material, controls the uniformity of the pore distribution and pore size inside the secondary particles in the ternary cathode material, and simultaneously provides suitable stacking gaps between the secondary particles, so that the ternary cathode material has excellent cycle performance;

[0083] (2) The preparation method provided by the present invention first performs a first coprecipitation reaction under the condition of dual-frequency ultrasound, thereby improving the porosity and pore size uniformity of the product; after the dual-frequency ultrasound, the second coprecipitation reaction process adopts single-frequency ultrasound, and a separate high-frequency ultrasound is selected in the second half to avoid the cavitation bubbles generated by low-frequency ultrasound during the reaction process, thereby reducing the number of pores near the surface of the ternary precursor, which is beneficial to improving the compaction density; the use of a mixed application of dual-frequency ultrasound and single-frequency ultrasound makes the particles evenly distributed and the crystals grow in an orderly manner, which is beneficial to optimizing the rearrangement of the particles and the bite between the 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 when the solvent evaporates in the traditional drying method, increases the production of closed pores, and maximizes the uniformity and integrity of the pore structure in the ternary precursor. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0086] Figure 2 This is the X-ray diffraction pattern of the uniformly porous ternary positive electrode material obtained in Example 1. DETAILED DESCRIPTION

[0087] The technical solution of the present invention is further described below by way of specific embodiments. It should be understood by those skilled in the art that the embodiments are merely to help understand the present invention and should not be regarded as specific limitations of the present invention.

[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 are mixed in a molar ratio of 8:1:1 to obtain a transition metal salt solution with a transition metal salt concentration of 1.8 mol / L; the transition metal salt solution, 5 mol / L sodium hydroxide solution and ammonia water are added to a reactor in parallel, and a first coprecipitation reaction is carried out for 15 hours under the conditions of dual-frequency ultrasound, temperature of 50°C, pH value of 11.4 and ammonia concentration of 0.6 mol / L; then acetic acid and acetonitrile are added, and a second coprecipitation reaction is carried out for 3 hours under the conditions of single-frequency ultrasound, temperature of 50°C, pH value of 11.4 and ammonia concentration of 0.6 mol / L; the mixture is aged for 1.5 hours, and then filtered and washed to obtain a solid product; the obtained solid product is dried by supercritical fluid to obtain a ternary precursor;

[0091] The dual-frequency ultrasound includes simultaneous first-frequency ultrasound and 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 ultrasonic frequency of the single-frequency ultrasound is 50KHz, and the ultrasonic power is 45W / L;

[0093] The concentration of the 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, the temperature is 45°C and the pressure is 9MPa;

[0095] (2) mixing the jet milled lithium hydroxide 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%; spray drying the mixed slurry (at an outlet temperature of 300° C.) to obtain a mixture; and subjecting the mixture to a first sintering to obtain the ternary intermediate;

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

[0097] (3) Mixing titanium dioxide and the ternary intermediate, and performing a second sintering at 600° C. for 8 h to obtain a ternary positive electrode material; the mass of the titanium dioxide is 1 wt % of the ternary intermediate.

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

[0100] In the preparation methods of Examples 2 to 11 and Comparative Examples 1 to 2, the preparation of the transition metal salt solution, 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 ultrasonic power of the first frequency ultrasound, the ultrasonic frequency and ultrasonic power of the second frequency ultrasound, the ultrasonic frequency and ultrasonic power of the single frequency ultrasound, and the added amounts of acetonitrile and acetic acid are as 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 conditions of pre-firing and main firing 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) Morphology characterization: The cross-section of the ternary cathode material was tested using a scanning electron microscope.

[0114] (2) Calculation: The ternary cathode material was cut using a focused ion beam (FIB) to obtain high-resolution cross-sectional scanning electron microscope (SEM) images of single secondary particles. The microstructure of the sample was observed by SEM to ensure that the primary particles, secondary particles and pore structure could be clearly distinguished. The acquired SEM images were quantitatively analyzed using ImageJ software.

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

[0116] Calculation: Use ImageJ to calculate the total area of ​​each visible hole in the SEM of the cross section of the ternary cathode material and calculate the average value. According to the formula Calculation is performed, where n is the number of visible pores of the corresponding secondary particles; 25 SEM images of secondary particles are selected for pore area calculation in each embodiment or comparative example, and the average value is taken to obtain According to the formula get

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

[0118] (3) Compacted density C D , true density ρ, total pore volume V g 、Accumulated pore V 堆Calculation of and γ:

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

[0120] Calculation of true density ρ: The ternary cathode material is tested using the Bester physical adsorption instrument-TD according to GB / T 24586-2009 "Determination of apparent density, true density and porosity of iron ore" to obtain the corresponding true density ρ;

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

[0122] Stacked Porosity V 堆 Calculation: Based on the compaction density C obtained by testing D , true density ρ, total pore volume V g , according to the formula Get the data V of the corresponding product 堆 ;

[0123] Calculation of γ: According to the obtained V 堆 and β, by the formula Get the data γ of the corresponding product;

[0124] The physical properties of the ternary cathode materials of various embodiments and comparative examples are shown in Table 4.

[0125] (4) Electrochemical performance test: The ternary positive electrode material, acetylene black and polyvinylidene fluoride were uniformly mixed in N-methylpyrrolidone at a mass ratio of 90:5:5, then coated on aluminum foil and placed in a vacuum drying oven for drying. After drying, a positive electrode sheet with a diameter of 12 mm was pressed using a tablet press in an argon glove box.

[0126] In a glove box, a positive electrode sheet, a polypropylene porous separator, a negative electrode lithium sheet and an electrolyte were assembled into a button cell; the solvent in the electrolyte was LiPF6 with a concentration of 1 mol / L, and the solvent was EC (ethylene carbonate) and DMC (dimethyl carbonate) in a volume ratio of 1:1.

[0127] The LAND battery test system was used to perform constant current charge and discharge tests on button batteries to examine the electrochemical properties of the ternary cathode material, 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 to 5, the V of the products provided by Examples 1 to 11 is 堆 Within the scope specified in the present invention, the discharge specific capacity and cycle performance at 1C are excellent.

[0134] Furthermore, compared with Examples 1 to 3, the products provided in Examples 4 to 5 and 7 have structural stability parameters of If the value is too large or too small, it will affect the electrochemical performance to a certain extent. Relatively large, specifically High; Example 5, Example 7 provide structural stability parameters of the product Relatively small, specifically is relatively too small, which affects its electrochemical performance.

[0135] Compared with Examples 1 to 3, the structural stability parameters of the product provided by Example 6 are and the cyclic stability parameter γ are relatively too large, specifically is relatively too large, which affects its electrochemical performance.

[0136] Compared with Examples 1 to 3, the structural stability parameters of the product provided in Example 8 are Too large and beyond the preferred range of the present invention, but the cyclic stability parameter γ is within the preferred range, specifically and 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 by Example 8 is better than that of Example 6.

[0137] Compared with Examples 1 to 3, the structural stability parameters of the product provided by Example 9 are If it is too small, the cyclic stability parameter γ will also be smaller, which is specifically expressed as and If it is too small, its electrochemical performance will be affected.

[0138] Compared with the embodiment, the products provided in Comparative Examples 1 and 2 have V 堆 Not within 0.0500cm 3 / g≤V堆 ≤0.0950cm 3 / g range, resulting in poor electrochemical performance of the ternary positive electrode material.

[0139] The applicant declares that the above is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the scope of protection and disclosure of the present invention.

Claims

1. A uniformly porous ternary cathode material, characterized in that: After the uniformly porous ternary cathode material is pressed at 5T pressure, the stacking gap meets 0.0500cm 3 / g≤V 堆 ≤0.0950cm 3 / g; in, C D is the compaction density of the uniformly porous ternary cathode material after being pressed at 5T, in g / cm 3 ; ρ is the true density of the uniformly porous ternary cathode material, in g / cm 3 ; V g is the total pore volume of the homoporous ternary cathode material, in cm 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 accumulation of primary particles; The uniformly porous ternary cathode material has a porous structure; The structural stability parameters of the homoporous ternary cathode material satisfy: in, The porosity and pore area are obtained from the cross-sectional scanning electron micrograph of the secondary particles. Porosity = the total area of ​​the pore region in the secondary particle region / the total cross-sectional area of ​​the secondary particle region. is the average porosity of the secondary particles, is the average of the pore areas in the cross-sectional SEM image of the secondary particles, And / or, the cycle stability parameter γ of the homoporous ternary cathode material satisfies: 0.1×10 -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 comprises the following steps: S1, mixing a precipitant solution, a complexing agent solution, and a transition metal salt solution in parallel, and performing a first coprecipitation reaction under dual-frequency ultrasound; then adding acetic acid and acetonitrile, and performing a second coprecipitation reaction under single-frequency ultrasound. After aging, the obtained solid product is subjected to supercritical fluid drying to obtain a ternary precursor; The dual-frequency ultrasound includes performing a first frequency ultrasound and a second frequency ultrasound simultaneously; 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 a lithium salt and the ternary precursor; spray-dry the mixed slurry to obtain a mixture; and subject the mixture to a first sintering to obtain the uniformly porous ternary positive electrode 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 11-12, and the temperature is 40°C-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°C-70°C.

6. The preparation method according to claim 3, characterized in that The total time of 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, with 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 molar ratio of the total molar amount of the transition metal element in the ternary precursor to the lithium in the lithium salt is 1:1 to 1:1.1; and / or, the solid content of the mixed slurry is 25 wt% to 35 wt%; And / or, the first sintering includes pre-sintering at 450° C. to 550° C. for 5 to 8 hours in an oxygen-containing atmosphere, and then performing main sintering 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 comprises: mixing the coating agent with the uniformly porous ternary positive electrode 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 0.8 wt% to 1.2 wt% of the uniformly porous ternary positive electrode material; And / or, the second sintering temperature is 580° C. to 620° C., and the time is 6 hours to 10 hours.

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

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