Ultrahigh-nickel ternary single-crystal positive electrode material as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of preparation of energy materials, and particularly relates to an ultrahigh-nickel ternary single-crystal positive electrode material as well as a preparation method and application thereof. A transition metal salt solution and a mixed solution of a precipitant and a complexing agent are mixed in a micro-channel reactor for a co-precipitation reaction, a transition metal hydroxide precursor with the particle size being 60-200 nm is obtained, the transition metal hydroxide precursor and a lithium salt are mixed according to the molar ratio of 1: 1-2.5 and pressed at 5-50 Bar, an obtained blank is calcined for 1-15 h at the temperature of 850-900 DEG C in the oxygen atmosphere, and the lithium ion battery positive electrode material is obtained. The ultrahigh-nickel ternary single-crystal positive electrode material is obtained. According to the method, the large-size and uniform-crystal ultra-high-nickel ternary single-crystal positive electrode material can be prepared, the problem of structure defects induced in the high-temperature lithiation process can be effectively solved, and the problems of molten salt residue pollution caused by a molten salt method, corrosion to equipment and high cost can also be solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of energy material preparation, and specifically relates to an ultra-high nickel ternary single crystal positive electrode material and a preparation method and application thereof. Background Art

[0002] Ultra-high nickel layered oxide LiNi 1-x-y Co x Mn y O2 (1-xy ≥ 0.9, NCM) has a high discharge specific capacity and energy density and is considered to be one of the most promising cathode materials. However, as the proportion of nickel increases, its capacity attenuation and safety risk issues become more prominent. Single crystal structure is an effective strategy to improve the cycle stability of cathode materials. Compared with polycrystalline NCM, the single crystal structure can avoid the formation of intergranular cracks caused by anisotropic stress, thereby reducing side reactions between the cathode and the electrolyte, enhancing interfacial stability, and effectively preventing the irreversible phase transition of the cathode material from layered to rock salt phase.

[0003] It is worth noting that single crystals of different particle sizes are the key to achieving the optimal match between battery performance and application scenarios. For example, small-sized particles (0.5-3μm) shorten the ion diffusion path, enabling fast-charging power batteries and low-temperature, high-power equipment; large-sized particles (3-8μm) increase the tap density and inhibit side reactions, meeting the energy storage system's requirements for long life and high safety. At the same time, through multi-scale composite design, it breaks the limitation of single performance, takes into account both energy and power density, and promotes the development of lithium battery technology towards scenario customization and high performance, providing underlying material solutions for electric vehicles, energy storage power stations and special equipment.

[0004] The industrial production of high nickel ternary cathode materials usually follows a two-stage process of "precursor synthesis-mixed lithium calcination". The synthesis of the precursor is based on the transition metal sulfate-NaOH-NH4OH reaction system. The key lies in the precise control of the precipitation-complexation dynamic balance to achieve orderly co-precipitation of multi-ion ions and obtain a precursor with consistent element ratio and feed ratio, uniform element distribution and controllable particle size. The high temperature solid phase lithiation process is to make the lithium salt and the precursor Ni 1-x-y Co x Mn y(OH)2 is a key step in the full reaction. Compared with polycrystalline structures, the preparation of single-crystal NCM requires a higher temperature to promote the growth of single-crystal structure, but too high lithiation temperature is prone to produce oxygen defects and cause problems such as Li / Ni mixing, reducing structural stability and deteriorating electrochemical performance. In addition, lithiation temperature is also a key parameter for regulating the particle size of single-crystal NCM. As reported in the prior art, when the lithiation temperature is increased from 920°C to 970°C, the particle size of the obtained NCM532 single crystal can be increased from 1.9μm to 4.7μm. However, due to the instability of Ni, the ultra-high nickel ternary positive electrode is more sensitive to temperature. For example, when sintered at 900°C, the I in X-ray diffraction is 003 / I 104 The intensity ratio is <1.2, indicating that the cations are severely disordered.

[0005] The molten salt synthesis technology developed in recent years has provided a new strategy for the preparation of low-temperature single crystals. For example, the single crystal NCM920404 positive electrode material with a particle size of 3 to 4 μm was obtained by using the LiCl-NaCl molten salt method at a lithiation temperature of 825 ° C. However, the molten salt synthesis method requires a large amount of lithium salt to promote crystal growth, which will introduce impurity ions (such as Li + / Na + 、H + / Li + ), reducing the material capacity. The subsequent washing and re-sintering processes increase costs and weaken the particle surface, leading to the formation of a NiO-like rock salt phase. Furthermore, the reuse of lithium salts requires refining, making them unsuitable for industrial-scale production. Furthermore, in the molten salt synthesis method, oxygen has difficulty dissolving into the molten salt, hindering the oxidation of the transition metal, resulting in uneven crystal growth and making the preparation of large single crystal particles difficult. Summary of the Invention

[0006] In view of this, the purpose of the present invention is to provide an ultra-high nickel ternary single crystal positive electrode material and its preparation method and application. This method can prepare large-sized, crystal-uniform ultra-high nickel ternary single crystal positive electrode materials, which can effectively avoid the structural defects induced by the high-temperature lithiation process and the problem of molten salt residual pollution caused by the molten salt method.

[0007] In order to achieve the above object, the present invention provides the following technical solutions:

[0008] The present invention provides a method for preparing an ultra-high nickel ternary single crystal positive electrode material, comprising the following steps:

[0009] A transition metal salt solution and a mixed solution of a precipitant and a complexing agent are mixed in a microchannel reactor to perform a coprecipitation reaction, followed by solid-liquid separation to obtain a transition metal hydroxide precursor; the transition metal salt solution comprises a cobalt salt, a nickel salt, a manganese salt, and water; and the particle size of the transition metal hydroxide precursor is 60 to 200 nm;

[0010] The transition metal hydroxide precursor and lithium salt are mixed and pressed, and the obtained green body is calcined in an oxygen atmosphere to obtain an ultra-high nickel ternary single crystal positive electrode material;

[0011] The molar ratio of the transition metal hydroxide precursor to the lithium salt is 1:1 to 2.5; the pressing pressure is 5 to 50 Bar;

[0012] The calcination includes a gradient temperature increase stage, a constant temperature stage and a gradient temperature decrease stage; the temperature of the constant temperature stage is 850-900° C., and the holding time is 1-15 hours.

[0013] Preferably, the molar ratio of nickel in the nickel salt, cobalt in the cobalt salt and manganese in the manganese salt is 90-94:3-5:3-5; and the total metal concentration in the transition metal salt solution is 0.75-1.25 mol / L.

[0014] Preferably, the precipitant includes one or more of sodium hydroxide, sodium carbonate, sodium bicarbonate, lithium hydroxide and potassium hydroxide; the complexing agent includes one or more of ammonia water, ammonium bicarbonate, ammonium chloride, citric acid and ethylenediaminetetraacetic acid; the concentration of the complexing agent in the mixed solution of the precipitant and the complexing agent is 1.5-2.5 mol / L, and the concentration of the precipitant is 1.5-2 mol / L.

[0015] Preferably, the flow rates of the transition metal salt solution and the mixed solution of the precipitant and the complexing agent are independently 20 to 70 mL / min.

[0016] Preferably, the lithium salt includes lithium hydroxide and / or lithium nitrate.

[0017] Preferably, the gradient heating stage includes a first heating stage, a second heating stage and a third heating stage in sequence; the constant temperature of the first heating stage is 150-300°C, and the insulation time is 2-6h; the constant temperature of the second heating stage is 400-600°C, and the insulation time is 2-6h; the constant temperature of the third heating stage is 700-800°C, and the insulation time is 2-6h; the heating rate in the gradient heating stage is 1-5°C / min.

[0018] Preferably, the gradient cooling stage includes a first cooling stage and a second cooling stage in sequence; the constant temperature of the first cooling stage is 725-800°C, and the insulation time is 1-5h; the cooling rate to the constant temperature of the first cooling stage is 1-5°C / min; the second cooling stage is cooled to room temperature at a cooling rate of 1-5°C / min.

[0019] Preferably, the holding time of the pressing is 1 to 30 minutes.

[0020] The present invention also provides an ultra-high nickel ternary single crystal positive electrode material prepared by the preparation method described in the above technical solution, the chemical formula of which is LiNi 1-x-y Co x Mn y O2, 0.9≤1-xy≤0.94, particle size is 1.3~4μm.

[0021] The present invention also provides the use of the ultra-high nickel ternary single crystal positive electrode material described in the above technical solution in lithium-ion batteries.

[0022] The present invention provides a method for preparing an ultra-high nickel ternary single crystal positive electrode material, comprising the following steps: mixing a transition metal salt solution and a mixed solution of a precipitant and a complexing agent in a microchannel reactor to carry out a coprecipitation reaction, and performing solid-liquid separation to obtain a transition metal hydroxide precursor; the transition metal salt solution comprises a cobalt salt, a nickel salt, a manganese salt and water; the particle size of the transition metal hydroxide precursor is 60-200 nm; the transition metal hydroxide precursor and a lithium salt are mixed and pressed, and the obtained green body is calcined in an oxygen atmosphere to obtain an ultra-high nickel ternary single crystal positive electrode material; the molar ratio of the transition metal hydroxide precursor to the lithium salt is 1:1-2.5; the pressing pressure is 5-50 Bar; the calcination comprises a gradient heating stage, a constant temperature stage and a gradient cooling stage; the temperature of the constant temperature stage is 850-900°C, and the holding time is 1-15 hours. The microchannel synthesis technology used in the present invention has efficient mixing, efficient mass transfer and heat transfer and unique confinement effect, ensures that the coprecipitation reaction generates a small size, a transition metal hydroxide precursor with uniform morphology, increases the uniformity of the reaction in the subsequent lithiation process, and the high specific surface area brought by the small size enables the precursor and the lithium salt to be better contacted, promotes the homogeneous lithiation reaction, increases the uniformity of the lithium salt distribution, reduces the appearance of local inhomogeneous lithium salts, ensures a shorter lithium ion diffusion path in the lithiation process, accelerates topological lithiation, ensures that there is better Li / O diffusion during topological lithiation, makes it obtain a single crystal structure with a perfect layered structure at low temperatures, reduces the Li / O loss and Li / Ni mixed row caused by thermal driving force. In addition, the precursor and lithium salt mixed system are suppressed, promote the contact (or gap) between the precursor and the lithium salt particles, promote grain fusion and growth process in the subsequent lithiation process, and then obtain a large-scale ultra-high nickel ternary single crystal positive electrode material. The present invention can obtain large-sized ultra-high nickel ternary single crystal positive electrode materials without the need for high temperature and high molten salt ratio, effectively avoiding the structural defects induced by the high-temperature lithiation process, and also avoiding the molten salt residual pollution caused by the molten salt method, as well as the corrosion to equipment and high cost problems. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figures 1 to 4Scanning electron microscope (SEM) images of the ultra-high nickel ternary single crystal positive electrode materials prepared in Example 1, Example 2, Example 3 and Example 7, respectively;

[0024] Figures 5-7 The scanning electron microscope (SEM) images of the ultra-high nickel ternary single crystal positive electrode materials prepared in Comparative Example 1, Comparative Example 2 and Comparative Example 3 are shown respectively;

[0025] Figure 8 This is a scanning electron microscope (SEM) image of the ultra-high nickel ternary single crystal positive electrode material prepared in Example 4;

[0026] Figure 9 This is a scanning electron microscope (SEM) image of the ultra-high nickel ternary single crystal positive electrode material prepared in Comparative Example 4;

[0027] Figure 10 The discharge capacity results of the battery assembled with the ultra-high nickel ternary single crystal positive electrode material prepared in Examples 1 to 3 and the battery assembled with the commercial single crystal positive electrode SC-NCM9055 are shown;

[0028] Figures 11-14 The XRD powder diffraction patterns of the ultra-high nickel ternary single crystal positive electrode materials prepared in Comparative Example 1 and Examples 1 to 3 are shown respectively. DETAILED DESCRIPTION

[0029] The present invention provides a method for preparing an ultra-high nickel ternary single crystal positive electrode material, comprising the following steps:

[0030] A transition metal salt solution and a mixed solution of a precipitant and a complexing agent are mixed in a microchannel reactor to perform a coprecipitation reaction, followed by solid-liquid separation to obtain a transition metal hydroxide precursor; the transition metal salt solution comprises a cobalt salt, a nickel salt, a manganese salt, and water; and the particle size of the transition metal hydroxide precursor is 60 to 200 nm;

[0031] The transition metal hydroxide precursor and lithium salt are mixed and pressed, and the obtained green body is calcined in an oxygen atmosphere to obtain an ultra-high nickel ternary single crystal positive electrode material;

[0032] The molar ratio of the transition metal hydroxide precursor to the lithium salt is 1:1 to 2.5; the pressing pressure is 5 to 50 Bar;

[0033] The calcination includes a gradient temperature increase stage, a constant temperature stage and a gradient temperature decrease stage; the temperature of the constant temperature stage is 850-900° C., and the holding time is 1-15 hours.

[0034] Unless otherwise specified, the present invention has no special requirements on the sources of the raw materials used, and commercially available products known to those skilled in the art can be used.

[0035] The invention mixes a transition metal salt solution with a mixed solution of a precipitant and a complexing agent in a microchannel reactor to carry out a coprecipitation reaction, and separates the solid and the liquid to obtain a transition metal hydroxide precursor.

[0036] As an embodiment, the transition metal salt solution includes a cobalt salt, a nickel salt, a manganese salt and water; the cobalt salt includes one or more of cobalt sulfate, cobalt chloride, cobalt nitrate and cobalt acetate, and in a specific embodiment, it is cobalt sulfate; the nickel salt includes one or more of nickel sulfate, nickel chloride, nickel nitrate and nickel acetate, and in a specific embodiment, it is nickel sulfate; the manganese salt includes one or more of manganese sulfate, manganese chloride, manganese nitrate and manganese acetate, and in a specific embodiment, it is manganese sulfate; the molar ratio of nickel in the nickel salt, cobalt in the cobalt salt and manganese in the manganese salt is 90-94:3-5:3-5, and in a specific embodiment, it is 90:5:5 or 94:3:3; the total metal concentration in the transition metal salt solution is 0.75-1.25 mol / L, and in a specific embodiment, it is 1 mol / L.

[0037] As an embodiment, the precipitant includes one or more of sodium hydroxide, sodium carbonate, sodium bicarbonate, lithium hydroxide and potassium hydroxide, and in a specific embodiment, it is sodium hydroxide; the complexing agent includes one or more of ammonia water, ammonium bicarbonate, ammonium chloride, citric acid and ethylenediaminetetraacetic acid (EDTA), and in a specific embodiment, it is ammonia water; the concentration of the complexing agent in the mixed solution of the precipitant and the complexing agent is 1.5-2.5 mol / L, and in a specific embodiment, it is 2 mol / L, and the concentration of the precipitant is 1.5-2 mol / L, and in a specific embodiment, it is 1.85 mol / L.

[0038] The present invention uses a precipitant to adjust the pH value of the coprecipitation reaction, provides hydroxide ions during the reaction, and precipitates the transition metal ions into hydroxides, thereby affecting the type of precursor. The complexing agent can control the release rate of the transition metal ions, regulate grain growth, inhibit the hydrolysis of metal ions, and promote the uniform distribution of elements. As an embodiment, the temperature of the coprecipitation reaction is 25 to 75°C, and 50°C in a specific embodiment; the flow rate of the transition metal salt solution and the mixed solution of the precipitant and the complexing agent is independently 20 to 70 mL / min, and 50 mL / min in a specific embodiment; the present invention has no special limitation on the time of the coprecipitation reaction, and the coprecipitation reaction time well known in the art can be used. The present invention starts to collect the product of the coprecipitation reaction 1 minute after solids appear at the outlet of the microchannel reactor.

[0039] The present invention uses microchannel synthesis technology with efficient mixing, efficient mass and heat transfer, and a unique confinement effect to ensure the generation of small-sized transition metal hydroxide precursors. In addition, the transition metal hydroxide precursor material has a uniform morphology, which increases the uniformity of the reaction in the subsequent lithiation process. The high specific surface area brought by the small size enables better contact between the precursor and the lithium salt, increases the uniformity of the lithium salt distribution, and reduces the occurrence of locally uneven lithium salts. In addition, due to the small particle size of the nano-sized precursor, the lithium ion diffusion path during the lithiation process is correspondingly reduced, which is more conducive to the occurrence of topological lithiation.

[0040] As an embodiment, the solid-liquid separation is centrifugal separation; the rotation speed of the centrifugal separation is 200-500 rpm, specifically 300-400 rpm, and the time is 30-60 min, specifically 40-50 min.

[0041] As an embodiment, after the solid-liquid separation, the method further comprises: washing, filtering, and drying the solid obtained from the solid-liquid separation in sequence to obtain the transition metal hydroxide precursor; the reagent used for the washing is deionized water; the number of washings is 5 to 20, and in a specific embodiment, 8 to 15 times, and filtering is performed after each washing; the pH value of the reagent after washing is 6.5 to 8, and in a specific embodiment, 7; the drying temperature is 60 to 100° C., and in a specific embodiment, 70 to 80° C., and the drying time is 10 to 20 hours, and in a specific embodiment, 12 hours; the drying is vacuum drying; the vacuum degree of the vacuum drying is -0.6 to -1 MPa, and in a specific embodiment, -0.8 MPa. Drying in a vacuum environment can accelerate drying and isolate air.

[0042] As an embodiment, the chemical formula of the transition metal hydroxide precursor is LiNi 1-x-y Co x Mn y (OH)2, 0.9≤1-xy≤0.94, in the specific embodiment, LiNi 0.9 Co 0.05 Mn 0.05 (OH)2, particle size 60-200 nm, specifically 100-150 nm.

[0043] After obtaining the transition metal hydroxide precursor, the present invention mixes the transition metal hydroxide precursor and lithium salt and presses them to obtain a green body.

[0044] As an embodiment, before the mixing, the process further comprises: ball milling the transition metal hydroxide precursor; the ball milling is dry milling; the equipment used for the ball milling is a planetary ball mill; the ball milling speed is 200 to 500 rpm, and in a specific embodiment, it is 300 rpm; the ball milling time is 30 to 120 minutes, and in a specific embodiment, it is 60 minutes; the diameter of the grinding balls used for the ball milling is 5 to 10 mm, and in a specific embodiment, it is 10 mm, 8 mm, and 5 mm, and the material is zirconium dioxide; the ball-to-material ratio of the ball milling is 0.75 to 1:1 to 1.5, and in a specific embodiment, it is 1:1.5; the particle size of the transition metal hydroxide precursor after the ball milling is 60 to 200 nm, and in a specific embodiment, it is 100 to 150 nm. The present invention uses ball milling to break up the soft agglomeration between the transition metal hydroxide precursor nanoparticles, reduce precursor agglomeration, and ensure that it is more evenly mixed with the lithium salt.

[0045] As an embodiment, the lithium salt includes lithium hydroxide and / or lithium nitrate, specifically lithium hydroxide and lithium nitrate; the molar ratio of the lithium hydroxide and lithium nitrate is 3 to 6:4 to 7, specifically 0.4:0.6 in the embodiment; the particle size of the lithium salt is 1 to 3 μm, specifically 2 μm in the embodiment; the molar ratio of the transition metal hydroxide precursor to the lithium salt is 1:1 to 2.5, specifically 1:1.05, 1:1.1, 1:1.5 or 1:2.0 in the embodiment.

[0046] In one embodiment, the transition metal hydroxide precursor and the lithium salt are mixed under ball milling conditions; the parameters of the ball milling are as described above and are not further described here. The purpose of mixed ball milling is to uniformly mix the transition metal hydroxide precursor and the lithium salt, improve experimental reproducibility compared to hand milling, and no longer affect particle size.

[0047] As an embodiment, the pressing pressure is 5 to 50 Bar, specifically 10 to 30 Bar, and the holding time is 1 to 30 min, specifically 5 to 10 min. The specific steps of the pressing are: placing the mixture obtained by mixing the transition metal hydroxide precursor and the lithium salt into a pressing mold for pressing. The present invention does not specifically limit the material and size of the pressing mold, and a pressing mold of a material and size well known in the art can be used.

[0048] The present invention compresses a highly mixed system of precursors and lithium salts, adjusting the contact (or gaps) between the precursor and lithium salt particles by varying the static pressure, promoting grain fusion and growth during the subsequent lithiation process. Ultra-high nickel ternary single crystal cathode materials of varying particle sizes can be obtained through simple static pressure adjustment. During the pressing process, as the pressure increases, the particle size of the ultra-high nickel ternary single crystal cathode material increases and then decreases. The Li / Ni intermixing and the 003 and 104 peak intensity ratios in the crystal structure increase and then decrease. Electrochemical performance shows that as the pressure increases, the capacity decreases and then increases, but the cycling performance increases and then decreases.

[0049] After obtaining the green body, the present invention calcines the green body in an oxygen atmosphere to obtain an ultra-high nickel ternary single crystal positive electrode material.

[0050] In one embodiment, the calcination is performed in a tubular furnace, wherein the volume fraction of oxygen in the oxygen atmosphere is 100%. The present invention uses pure oxygen as the calcination atmosphere, and introduces pure oxygen for a period of time before calcination to remove air from the tubular furnace.

[0051] The calcination includes a gradient heating stage, a constant temperature stage and a gradient cooling stage; the gradient heating stage includes a first heating stage, a second heating stage and a third heating stage in sequence; the constant temperature of the first heating stage is 150-300°C, 200°C in a specific embodiment, and the holding time is 2-6h, 3h in a specific embodiment; the constant temperature of the second heating stage is 400-600°C, 500°C in a specific embodiment, and the holding time is 2-6h, 3h in a specific embodiment; the constant temperature of the third heating stage is 700-800°C, 775°C in a specific embodiment, and the holding time is 2-6h, 3h in a specific embodiment; the heating rate in the gradient heating stage is 1-5°C / min, 2°C / min in a specific embodiment; the constant temperature of the constant temperature stage is 100-150°C / min, 200°C / min in a specific embodiment, and the holding time is 2-6h, 3h in a specific embodiment. The temperature is 850-900°C, 850°C in a specific embodiment, and the holding time is 1-15h, 1h, 3h, 5h, 7h or 10h in a specific embodiment; the heating rate for heating to the temperature of the constant temperature stage is 1-5°C / min, 2°C / min in a specific embodiment; the gradient cooling stage includes a first cooling stage and a second cooling stage in sequence; the constant temperature of the first cooling stage is 725-800°C, 775°C in a specific embodiment, and the holding time is 1-5h, 3h in a specific embodiment; the cooling rate for cooling to the constant temperature of the first cooling stage is 1-5°C / min, 2°C / min in a specific embodiment; the second cooling stage is cooled to room temperature at a cooling rate of 1-5°C / min, 2°C / min in a specific embodiment.

[0052] During the calcination process, the transition metal hydroxide precursor undergoes lithiation. The high specific surface area brought about by the smaller size of the precursor allows the lithium salt and the precursor to be in more complete contact, reducing local uneven distribution of the lithium salt and ensuring better Li / O diffusion during topological lithiation. The small size also ensures a shorter lithium ion diffusion path during the lithiation process, accelerating topological lithiation.

[0053] When preparing single crystals from traditional micron-sized precursors, it is necessary to first perform topological lithiation of the micron precursor, then continue to increase the temperature to cause the precursor to crack under high temperature conditions, and then further fuse the cracked small pieces of material to generate the final single crystal positive electrode material. In this process, although the continuous high temperature will generate a layered structure more quickly, it will also cause the original Li / O in the surface layer of the material to detach from the structure due to the higher temperature, resulting in loss. The high driving force provided by the higher temperature will cause the Li / Ni in the material to mix, affecting the orderliness and interlayer spacing of the positive electrode material, and ultimately affecting the Li + The present invention uses a small-sized, highly active precursor synthesized through microchannel technology and a method of mixing lithium salts by ball milling to obtain a highly mixed reaction system of the precursor and lithium salt. This improves the solid-solid contact between the precursor and the lithium salt, promotes homogeneous lithiation, and easily obtains a single crystal structure with a well-defined layered structure at low temperatures, thereby reducing Li / O loss and Li / Ni mixing caused by thermal driving forces.

[0054] As an embodiment, after the calcination, the process further includes: washing and re-firing the calcined product in sequence to obtain an ultra-high nickel ternary single crystal positive electrode material; the reagent used for the water washing is deionized water; the number of water washings is 1 to 3 times, and 2 times in a specific embodiment; the re-firing temperature is 400 to 700°C, and 600°C in a specific embodiment, and the holding time is 3 to 8 hours, and 5 hours in a specific embodiment; the heating rate for heating to the re-firing temperature is 1 to 5°C / min, and 2°C / min in a specific embodiment.

[0055] The present invention also provides an ultra-high nickel ternary single crystal positive electrode material prepared by the preparation method described in the above technical solution, the chemical formula of which is LiNi 1-x-y Co x Mn y O2, 0.9≤1-xy≤0.94, particle size is 1.3~4μm.

[0056] As an embodiment, the chemical formula of the ultra-high nickel ternary single crystal positive electrode material is LiNi 0.9 Co 0.05 Mn 0.05O2, particle size is 1.37μm, 1.45μm, 1.64μm, 1.91μm, 2.47μm, 2.82μm or 3.26μm.

[0057] The present invention also provides the use of the ultra-high nickel ternary single crystal positive electrode material described in the above technical solution in lithium-ion batteries.

[0058] The present invention does not specifically limit the application of the ultra-high nickel ternary single crystal positive electrode material in lithium-ion batteries, and any application method well known in the art may be used.

[0059] The technical solutions of the present invention will be described clearly and completely below in conjunction with the embodiments of the present invention, but they should not be understood as limiting the scope of protection of the present invention.

[0060] Example 1

[0061] (1)Ni 0.9 Co 0.05 Mn 0.05 Preparation of (OH)2 precursor

[0062] CoSO4·7H2O, MnSO4·4H2O, and NiSO4·6H2O were placed in a 5L beaker and dissolved in a portion of deionized water. After mechanical stirring until the solids dissolved, the remaining deionized water was added to 5L to prepare a transition metal salt solution A with a total metal concentration of 1 mol / L, wherein the molar ratio of Ni, Co, and Mn was 90:5:5; a mixed solution B of a precipitant and a complexing agent was then prepared with ammonia water and NaOH, wherein the ammonia concentration was 2 mol / L and the NaOH concentration was 1.85 mol / L, which served as the complexing agent and precipitant, respectively, in the coprecipitation reaction process. The mixture was thoroughly mixed and set aside;

[0063] The transition metal salt solution A and the mixed solution B of the precipitant and the complexing agent were pumped into the microchannel reactor at the same flow rate of 50 mL / min using the injection pump of the microchannel reactor (the temperature was controlled at 50 ° C by a water bath) to complete rapid mixing and co-precipitation reaction. After solid appeared at the outlet for 1 minute, the product was collected at the outlet. The collected product was centrifuged at 400 rpm for 40 minutes. The obtained solid was washed with deionized water and filtered 8 times until the pH value of the solution after washing was 7. It was then dried in a vacuum oven at 80 ° C and -0.8 MPa vacuum for 12 hours to obtain Ni 0.9 Co 0.05 Mn 0.05 (OH)2 precursor (particle size 100 nm);

[0064] (2)LiNi 0.9 Co 0.05 Mn 0.05 O2 production

[0065] The Ni 0.9 Co 0.05 Mn 0.05 (OH)2 precursor was used as the lithiation precursor and was ball milled in a planetary ball mill. The ball milling time was 60 min, the rotation speed was 300 rpm, and the zirconium dioxide grinding balls used were 1 grinding ball with a diameter of 10 mm, 2 grinding balls with a diameter of 8 mm, and 4 grinding balls with a diameter of 5 mm. The ball-to-material ratio was 1:1.5. After ball milling, Ni 0.9 Co 0.05 Mn 0.05 The particle size of the (OH)2 precursor is 100 nm;

[0066] After ball milling, Ni 0.9 Co 0.05 Mn 0.05 The (OH)2 precursor and lithium salt (LiOH·H2O and LiNO3 with a molar ratio of 0.4:0.6) were mixed in a ball mill at a molar ratio of 1:1.1 and loaded into a ball mill for ball milling. The ball milling time was 60 min, the rotation speed was 300 rpm, and the zirconium dioxide grinding balls used were 1 grinding ball with a diameter of 10 mm, 2 grinding balls with a diameter of 8 mm and 4 grinding balls with a diameter of 5 mm, and the ball-to-material ratio was 1:1.5. The mixed powder was then placed in a pressing mold and pressed at a pressure of 20 Bar for 5 min. The resulting green body was placed in a tubular furnace with pure oxygen to exhaust the internal air. The calcination was carried out in an oxygen atmosphere (oxygen volume fraction of 100%). The calcination conditions were as follows: first, the material was kept at 200°C for 3 hours, then at 500°C for 3 hours, then the material was heated to 775°C for 3 hours, then heated to 850°C for 1 hour, and the heating rate of the whole process was 2°C / min. The material was then cooled to 775°C at a rate of 2°C / min and kept for 3 hours. The material was then cooled to room temperature at a rate of 2°C / min, washed twice with deionized water to remove excess lithium salt, and heated to 600°C at a rate of 2°C / min for 5 hours to obtain an ultra-high nickel ternary single crystal positive electrode material (LiNi 0.9 Co 0.05 Mn 0.05 O2, particle size 1.45 μm).

[0067] Example 2

[0068] The difference from Example 1 is that after ball milling, Ni 0.9 Co 0.05 Mn 0.05 The molar ratio of (OH)2 precursor to lithium salt (LiOH·H2O and LiNO3 with a molar ratio of 0.4:0.6) is 1:1.1, the pressing pressure is 30 Bar, and the rest of the contents are the same as Example 1. The particle size of the obtained ultra-high nickel ternary single crystal positive electrode material is 1.91 μm.

[0069] Example 3

[0070] The difference from Example 1 is that the pressing pressure is 40 Bar, and the rest of the contents are the same as Example 1. The particle size of the obtained ultra-high nickel ternary single crystal positive electrode material is 1.64 μm.

[0071] Example 4

[0072] The difference from Example 1 is that after ball milling, Ni 0.9 Co 0.05 Mn 0.05 The molar ratio of (OH)2 precursor to lithium salt (LiOH·H2O and LiNO3 with a molar ratio of 0.4:0.6) is 1:1.05, the pressing pressure is 30 Bar, and the rest of the contents are the same as Example 1. The particle size of the obtained ultra-high nickel ternary single crystal positive electrode material is 1.37 μm.

[0073] Example 5

[0074] The difference from Example 1 is that the pressing pressure is 30 Bar, and the temperature is kept at 850°C for 3 hours. The rest of the contents are the same as Example 1. The particle size of the obtained ultra-high nickel ternary single crystal positive electrode material is 2.47 μm.

[0075] Example 6

[0076] The difference from Example 1 is that the pressing pressure is 30 Bar, and the temperature is kept at 850°C for 7 hours. The rest of the contents are the same as Example 1. The particle size of the obtained ultra-high nickel ternary single crystal positive electrode material is 2.82 μm.

[0077] Example 7

[0078] The difference from Example 1 is that the pressing pressure is 30 Bar, and the temperature is kept at 850°C for 10 hours. The rest of the contents are the same as Example 1. The particle size of the obtained ultra-high nickel ternary single crystal positive electrode material is 3.26 μm.

[0079] Comparative Example 1

[0080] The difference from Example 1 is that after ball milling, Ni 0.9 Co 0.05 Mn 0.05 The molar ratio of (OH)2 precursor to lithium salt (LiOH·H2O and LiNO3 with a molar ratio of 0.4:0.6) is 1:1.05. No pressing is performed and it is directly calcined. The rest of the contents are the same as in Example 1. The particle size of the obtained ultra-high nickel ternary single crystal positive electrode material is 0.9μm.

[0081] Comparative Example 2

[0082] The difference from Example 1 is that no pressing is performed and calcination is performed directly. The rest of the contents are the same as Example 1. The particle size of the obtained ultra-high nickel ternary single crystal positive electrode material is 1.18 μm.

[0083] Comparative Example 3

[0084] The difference from Example 1 is that after ball milling, Ni 0.9 Co 0.05 Mn 0.05 The molar ratio of the (OH)2 precursor to the lithium salt (LiOH·H2O and LiNO3 with a molar ratio of 0.4:0.6) is 1:2.0. No pressing is performed and the material is directly calcined. The rest of the contents are the same as in Example 1. The particle size of the obtained ultra-high nickel ternary single crystal positive electrode material is 1.45 μm.

[0085] Comparative Example 4

[0086] The difference from Example 1 is that commercial Ni 0.9 Co 0.05 Mn 0.05 The particle size of the (OH)2 precursor is 4 μm, and it is mixed with lithium salt (LiOH·H2O and LiNO3 with a molar ratio of 0.4:0.6) at a molar ratio of 1:1.05. The pressing pressure is 30 Bar, and the rest of the contents are the same as in Example 1.

[0087] Performance Testing

[0088] Figures 1 to 4 The scanning electron microscope (SEM) images of the ultra-high nickel ternary single crystal positive electrode materials prepared in Example 1, Example 2, Example 3 and Example 7 are respectively.

[0089] like Figures 1 to 3 As shown, for Ni 0.9 Co 0.05 Mn 0.05 After the pressure change of the mixed system of (OH)2 precursor and lithium salt, the corresponding change of grain size occurs. Figure 1 、 Figure 2 and Figure 3 The grain sizes are 1.45μm, 1.91μm and 1.64μm respectively, which shows that with the increase of pressure, the growth of grains is promoted, but when the pressure is too high, the growth of grains is not obvious, indicating that there is an optimal pressure condition under the condition of keeping at 850℃ for 1h to promote the increase of grain size, reducing the application of high temperature and long time.

[0090] like Figure 4 As shown in FIG, by increasing the sintering time at 850°C, it was found that after calcination at 30 Bar pressure, 1.1 lithium content, and 10 h, the grain size further increased to 3.26 μm.

[0091] (2) Figures 5-7 The scanning electron microscope (SEM) images of the ultra-high nickel ternary single crystal positive electrode materials prepared in Comparative Example 1, Comparative Example 2 and Comparative Example 3 are respectively.

[0092] from Figures 5-7 It can be seen that by comparing the effects of different lithium loadings on grain size when the pressure treatment is removed and the temperature is kept at 850°C for 1 hour, it is found that when the lithium loading increases from 1.05 to 1.1 and 2.0, the grain size changes from 0.9μm to 1.18μm and 1.45μm. The comparison shows that without pressure treatment, the increase in grain size requires more lithium salt to achieve, while after pressure treatment, the increase in interfacial contact between the precursor particles leads to a significantly faster growth of the grain size.

[0093] (3) Figure 8 This is a scanning electron microscope (SEM) image of the ultra-high nickel ternary single crystal positive electrode material prepared in Example 4. Figure 9 This is a scanning electron microscope (SEM) image of the ultra-high nickel ternary single crystal positive electrode material prepared in Comparative Example 4.

[0094] pass Figure 8 and Figure 9 By comparison, it was found that the nano-sized precursor particles in Example 4 obtained single-crystalline positive electrode materials after sintering at 850°C for 1 hour, while the micron-sized precursor particles in Comparative Example 2 still showed a polycrystalline morphology after sintering. This is because the smaller size of the nano-precursor particles overcomes the lithiation heterogeneity during the sintering process, and better interface fusion promotes faster material transfer during the single crystal growth process, so that the precursor particles generate single-crystalline positive electrode materials and increase the grain size.

[0095] However, due to the existence of lithiation heterogeneity, the micron-sized precursor undergoes an uneven lithiation process during the particle growth process, which limits the material transfer and interface fusion during the subsequent particle growth process, so that the primary particles cannot grow quickly enough to overcome the van der Waals force that causes agglomeration and fall off, and single crystal materials cannot be generated. Although the external pressure increases the contact of the precursor-lithium salt system and accelerates material transfer, the intrinsic diffusion kinetic disadvantage of the long-distance transmission path cannot be compensated by shortening the contact distance through pressure, resulting in slow grain growth. If effective single crystallization is to be achieved, it is necessary to rely on extending the holding time or increasing the sintering temperature to enhance the driving force of atomic migration. However, such conditions are prone to cause lithium volatilization, intensify the irreversible transformation of the layered structure to the rock salt phase, and increase interfacial side reactions, which significantly affect the electrochemical properties of the material.

[0096] (4) Figure 10 The discharge capacity results of the battery assembled with the ultra-high nickel ternary single crystal positive electrode material prepared in Examples 1 to 3 and the battery assembled with the commercial single crystal positive electrode SC-NCM9055 are shown in the figure. The test conditions are 25°C, 2.75~4.3V, and 1C.

[0097] like Figure 10As shown, the discharge capacity of the phone assembled with the ultra-high nickel ternary single crystal positive electrode material prepared by the present invention is better than that of the battery assembled with the commercial single crystal positive electrode, and it has the value of further exploration and promotion.

[0098] (5) Figures 11-14 The XRD powder diffraction patterns of the ultra-high nickel ternary single crystal positive electrode materials prepared in Comparative Example 1 and Examples 1 to 3 are shown respectively.

[0099] from Figures 11-14 It can be seen that the XRD structural analysis of the synthesized samples shows that the XRD powder diffraction spectra of the ultra-high nickel ternary single crystal positive electrode materials prepared in Comparative Example 1 and Examples 1 to 3 correspond to the standard spectra of high nickel ternary positive electrode materials (PDF#09-0063), and belong to α-NaFeO2 type layered metal oxide positive electrode materials.

[0100] Although the above embodiment describes the present invention in detail, it is only a part of the embodiments of the present invention rather than all the embodiments. People can also obtain other embodiments based on this embodiment without creativity, and these embodiments all fall within the scope of protection of the present invention.

Claims

1. A method for preparing an ultra-high nickel ternary single crystal positive electrode material, characterized in that: The following steps are involved: A transition metal salt solution and a mixed solution of a precipitant and a complexing agent are mixed in a microchannel reactor to perform a coprecipitation reaction, followed by solid-liquid separation to obtain a transition metal hydroxide precursor; the transition metal salt solution comprises a cobalt salt, a nickel salt, a manganese salt, and water; and the particle size of the transition metal hydroxide precursor is 60 to 200 nm; The transition metal hydroxide precursor and lithium salt are mixed and pressed, and the obtained green body is calcined in an oxygen atmosphere to obtain an ultra-high nickel ternary single crystal positive electrode material; The molar ratio of the transition metal hydroxide precursor to the lithium salt is 1:1 to 2.5; the pressing pressure is 5 to 50 Bar; The calcination includes a gradient temperature increase stage, a constant temperature stage and a gradient temperature decrease stage; the temperature of the constant temperature stage is 850-900° C., and the holding time is 1-15 hours.

2. The preparation method according to claim 1, characterized in that The molar ratio of nickel in the nickel salt, cobalt in the cobalt salt and manganese in the manganese salt is 90-94:3-5:3-5; and the total metal concentration in the transition metal salt solution is 0.75-1.25 mol / L.

3. The preparation method according to claim 1, characterized in that The precipitant includes one or more of sodium hydroxide, sodium carbonate, sodium bicarbonate, lithium hydroxide and potassium hydroxide; the complexing agent includes one or more of ammonia water, ammonium bicarbonate, ammonium chloride, citric acid and ethylenediaminetetraacetic acid; the concentration of the complexing agent in the mixed solution of the precipitant and the complexing agent is 1.5-2.5 mol / L, and the concentration of the precipitant is 1.5-2 mol / L.

4. The preparation method according to claim 1, 2 or 3, characterized in that: The flow rates of the transition metal salt solution and the mixed solution of the precipitant and the complexing agent are independently 20 to 70 mL / min.

5. The preparation method according to claim 1, characterized in that The lithium salt includes lithium hydroxide and / or lithium nitrate.

6. The preparation method according to claim 1, characterized in that The gradient heating stage includes a first heating stage, a second heating stage and a third heating stage in sequence; the constant temperature of the first heating stage is 150-300°C, and the insulation time is 2-6 hours; the constant temperature of the second heating stage is 400-600°C, and the insulation time is 2-6 hours; the constant temperature of the third heating stage is 700-800°C, and the insulation time is 2-6 hours; the heating rate in the gradient heating stage is 1-5°C / min.

7. The preparation method according to claim 1, characterized in that The gradient cooling stage includes a first cooling stage and a second cooling stage in sequence; the constant temperature in the first cooling stage is 725-800°C, and the insulation time is 1-5 hours; the cooling rate to the constant temperature of the first cooling stage is 1-5°C / min; the second cooling stage is cooled to room temperature at a cooling rate of 1-5°C / min.

8. The preparation method according to claim 1, characterized in that The holding time of the pressing is 1 to 30 minutes.

9. The ultra-high nickel ternary single crystal positive electrode material prepared by the preparation method according to any one of claims 1 to 8, characterized in that: The chemical formula is LiNi 1-x-y Co x Mn y O2, 0.9≤1-xy≤0.94, particle size is 1.3~4μm.

10. Use of the ultra-high nickel ternary single crystal positive electrode material according to claim 9 in lithium-ion batteries.

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