Precursor with core-shell structure, and preparation method therefor and use thereof

Abstract

Disclosed in the present application are a precursor with a core-shell structure, and a preparation method therefor and the use thereof. The precursor with a core-shell structure comprises a porous nickel-rich core and a manganese-rich or aluminum-containing shell that coats the surface of the core, wherein primary crystal grains forming the core are of a thin needle shape, and primary crystal grains forming the shell are of a thick block shape. By means of the method of the present application, during a coprecipitation reaction process, an internal loose and porous structure is manufactured by means of micro-oxidation, and a core-shell structure is formed; and a positive electrode material prepared from the precursor has improved rate capability, cycling performance and safety performance. By means of the method of the present application, a precursor having an internal porous structure can be formed without needing to add an extra pore-forming agent or a specific organic additive, thereby effectively avoiding the problem of reduced product performance due to impurity residues or increased cost due to subsequent impurity removal; and the preparation method is simple, and is easily applied to mass production.

Description

A core-shell structure precursor, a preparation method and application thereof TECHNICAL FIELD

[0001] The present application belongs to the field of lithium ion battery materials, and particularly relates to a core-shell structure precursor, a preparation method and application thereof. BACKGROUND

[0002] Lithium ion batteries (LIBs) are currently the most promising electric vehicle (EV) energy storage technology and have been widely used. In lithium ion batteries, the performance of the positive electrode material directly determines the performance of the lithium ion battery. Among them, high-nickel ternary materials have become the main research direction of long-range power batteries at present because of their high energy density and low cost, but the high-nickel ternary materials with conventional dense structures cannot meet the requirements of battery manufacturers for high output power, high cycle characteristics and high stability of power batteries.

[0003] Compared with the agglomerated dense structure, the ternary positive electrode material with an internal porous or even hollow structure has high output power and high cycle characteristics. This is because the material with this special structure has a larger hollow part in the center of the secondary particle, which can expand the contact area between the material and the electrolyte by the way of the electrolyte immersed in the hollow part, shorten the Li + diffusion path, thereby reducing the internal resistance of the battery and improving the output performance. In addition, due to the high internal porosity of this structure, the structure stress caused by the volume change of the positive electrode material during the charging and discharging process of the battery can be buffered, thereby stabilizing the structure and improving the cycle performance.

[0004] The morphology structure and physical property indexes of the positive electrode material will be inherited to a great extent from the precursor, and therefore, in order to comprehensively improve the output power, cycle characteristics and stability of the positive electrode material, a porous core-shell structure precursor can be prepared. In the related art, the method for preparing the porous precursor material either adds a pore-forming agent or a surfactant, or introduces a specific organic substance, so as to be carbonized in the subsequent sintering process to form a porous structure. CN106410157B discloses a high-rate long-life positive electrode material and a preparation method thereof, which uses a macromolecular PEG as a surfactant to obtain a porous structure precursor. CN112047397A discloses a preparation method of a porous ternary precursor, which needs to add a hydroxyethyl sulfone sulfate organic additive in the implementation process, and a porous precursor is prepared through a special process. However, in actual industrial production, customers have very strict requirements for impurities of products, and after adding the above-mentioned substances, higher requirements are put forward for subsequent impurity removal, which increases the process and cost. At the same time, the addition of other substances increases the production process and auxiliary materials, and the product manufacturing cost is further increased.

[0005] In addition, the nickel content in the high-nickel ternary material is high. Although the high nickel content increases the capacity of the battery, excessive nickel causes serious lithium-nickel mixing after lithium mixing sintering, and the unstable structure of the micron-sized spherical secondary particles during the cycle causes the particles to crack. Such cracking will lead to poor connection and electrical contact between the grains and the grains, resulting in rapid increase in impedance. At the same time, the electrolyte will penetrate into the secondary particles along the cracks, causing further side reactions and irreversible phase changes.

[0006] Therefore, it is a technical problem to be solved to provide a porous precursor material and a preparation method thereof, avoid the use of additives, and have good structural stability.

[0007] SUMMARY

[0008] The following is a summary of the subject matter described in detail herein. This summary is not intended to limit the scope of protection of the claims.

[0009] The present application provides a core-shell structure precursor and a preparation method and application thereof.

[0010] In a first aspect, the present application provides a core-shell structure precursor, which comprises a porous nickel-rich inner core and a manganese-rich or aluminum-containing outer shell coated on the surface of the inner core; the primary grains constituting the inner core are thin and needle-shaped; and the primary grains constituting the outer shell are thick and block-shaped.

[0011] The inner core of the core-shell structure precursor of the present application is a loose and porous nickel-rich inner core (such as nickel-cobalt-manganese hydroxide) with thin and needle-shaped primary grains, which can provide high capacity; and the outer shell is a dense structure with thick and block-shaped primary grains (such as nickel-manganese hydroxide, nickel-cobalt-manganese hydroxide or nickel-cobalt-aluminum hydroxide), which can provide high stability and safety, and improve the cycle performance. In addition, the positive electrode material prepared by using the precursor has a porous or even hollow structure in the inner core part when mixed with lithium and sintered, which can buffer the structural stress caused by the volume change of the positive electrode material during the charging and discharging process of the battery, and is not prone to micro-cracks, thereby stabilizing the structure and improving the rate performance of the positive electrode material.

[0012] The following is an optional embodiment of the present application, but is not a limitation on the technical solutions provided by the present application. Through the following optional embodiment, the technical purpose and beneficial effects of the present application can be better achieved and realized.

[0013] In one embodiment, the outer shell is a dense outer shell. The relatively dense outer shell can prevent excessive erosion of the electrolyte, improve the safety of the positive electrode material prepared therefrom, and further improve the safety performance of the battery.

[0014] In one embodiment, the particle size D50 of the core-shell structure precursor is 3-15 μm, for example 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 6 μm, 7 μm, 7.5 μm, 8 μm, 9 μm, 9.5 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm or 15 μm, etc.

[0015] In one embodiment, the ratio of the particle size of the core-shell structure precursor to the shell thickness is (2.5-21):1, for example 2.5:1, 3:1, 3.5:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, 11:1, 12:1, 13:1, 14:1, 15:1, 16:1, 17:1, 18:1, 19:1, 20:1 or 21:1, etc., optionally (3-15):1.

[0016] In one embodiment, the inner core is a hydroxide of nickel-cobalt-manganese, and the molar ratio of metal ions is Ni:Co:Mn=x1:y1:z1, wherein x1≥0.6, 0.02≤y1≤0.2, 0.05≤z1≤0.2, and x1+y1+z1=1. Specifically, x1 may, for example, be 0.6, 0.65, 0.7, 0.75, 0.8 or 0.85, etc., y1 may, for example, be 0.02, 0.03, 0.05, 0.06, 0.08, 0.1, 0.12, 0.15, 0.16, 0.18 or 0.2, etc., and z1 may, for example, be 0.05, 0.06, 0.08, 0.09, 0.1, 0.12, 0.13, 0.14, 0.15, 0.17, 0.18 or 0.2, etc.

[0017] In one embodiment, the shell is a hydroxide of nickel-manganese, a hydroxide of nickel-cobalt-manganese or a hydroxide of nickel-cobalt-aluminum.

[0018] In one embodiment, when the shell is a hydroxide of nickel-manganese or a hydroxide of nickel-cobalt-manganese, the molar ratio of metal ions is Ni:Co:Mn=x2:y2:z2, wherein x2≥0.4, 0≤y2≤0.2, 0.2≤z2≤0.6, x2+y2+z2=1, and x1>x2, z1<z2. Specifically, x2 may, for example, be 0.4, 0.45, 0.5, 0.55 or 0.58, etc., y2 may, for example, be 0, 0.02, 0.05, 0.08, 0.1, 0.12, 0.15, 0.17 or 0.2, etc., and z2 may, for example, be 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55 or 0.6, etc.

[0019] In one embodiment, when the shell is a nickel-cobalt-aluminum hydroxide, the molar ratio of metal ions is Ni:Co:Al=x3:y3:z3, wherein x3≥0.6, 0.02≤y3≤0.2, 0.02≤z3≤0.2, and x3+y3+z3=1. Specifically, x3may be, for example, 0.6, 0.65, 0.7, 0.75, 0.8, or 0.85, etc., y3may be, for example, 0.02, 0.04, 0.05, 0.06, 0.08, 0.1, 0.13, 0.16, 0.18, or 0.2, etc., and z3may be, for example, 0.02, 0.03, 0.04, 0.06, 0.08, 0.1, 0.11, 0.13, 0.15, 0.17, 0.18, or 0.2, etc.

[0020] In the core-shell structure precursor of the present application, the inner core is a nickel-cobalt-manganese hydroxide with high nickel content and low manganese content, which can provide high capacity; and the shell is a nickel-manganese hydroxide, a nickel-cobalt-manganese hydroxide, or an aluminum-containing nickel-cobalt-aluminum hydroxide with low nickel content and high manganese content, which can provide high stability, so that the positive electrode material prepared using the precursor has good safety, thereby improving the safety performance of the battery.

[0021] In a second aspect, the present application provides a preparation method of the core-shell structure precursor according to the first aspect, which comprises the following steps:

[0022] Providing a core layer metal salt solution, a shell layer metal salt solution, a precipitant solution, and a complexing agent solution, ready for use;

[0023] Passing the core layer metal salt solution, the precipitant solution, and the complexing agent solution into the reactor containing the bottom liquid in parallel flow, first performing a stage I reaction under an inert atmosphere, then performing a stage II reaction under a micro-oxidizing atmosphere, stopping the feeding when the preset particle size is reached, and obtaining a core layer precipitate;

[0024] Passing the shell layer metal salt solution, the precipitant solution, and the complexing agent solution into the reactor in parallel flow, performing a stage III reaction under an inert atmosphere, so that the shell layer metal salt is precipitated on the core layer precipitate, stopping the reaction when the target particle size is reached, and obtaining a slurry containing the core-shell structure precursor.

[0025] The method of the present application utilizes micro-oxidation to manufacture an internal loose porous structure during the co-precipitation reaction. The method can form a precursor with an internal porous structure without the need for additional pore-forming agents or specific organic additives, effectively avoiding the problems of performance degradation of the product or increased cost of subsequent impurity removal caused by impurity residues.

[0026] The preparation method of the present application is simple, the entire process only needs to modify the gas path of the atmosphere supply unit (such as the mixed gas path of air and nitrogen), does not need other organic additives, does not need to additionally increase the impurity removal process, is fully compatible with the existing production line, and is easy to scale up.

[0027] In one embodiment, the core layer metal salt solution is a sulfate solution containing nickel, cobalt and manganese.

[0028] In one embodiment, the concentration of total metal ions in the core layer metal salt solution is 1-3 mol / L, such as 1 mol / L, 1.2 mol / L, 1.3 mol / L, 1.5 mol / L, 1.7 mol / L, 1.8 mol / L, 2 mol / L, 2.3 mol / L, 2.6 mol / L, 2.8 mol / L or 3 mol / L, etc.

[0029] In one embodiment, the shell layer metal salt solution is a sulfate solution containing nickel and manganese, or a sulfate solution containing nickel, cobalt and manganese, or a combination of a sulfate solution containing nickel and cobalt and a sodium metaaluminate solution.

[0030] In one embodiment, the concentration of total metal ions in the shell layer metal salt solution is 1-3 mol / L, such as 1 mol / L, 1.2 mol / L, 1.3 mol / L, 1.5 mol / L, 1.7 mol / L, 1.8 mol / L, 2 mol / L, 2.3 mol / L, 2.6 mol / L, 2.8 mol / L or 3 mol / L, etc.

[0031] In one embodiment, the precipitant solution is a sodium hydroxide solution with a mass concentration of 20-40%, such as 20%, 22%, 24%, 25%, 27%, 30%, 32%, 35%, 38% or 40%, etc.

[0032] In one embodiment, the complexing agent solution is an aqueous ammonia solution with a mass concentration of 10-30%, such as 10%, 12%, 13%, 14%, 15%, 17%, 18%, 20%, 23%, 26% or 30%, etc.

[0033] In one embodiment, the preparation method of the bottom solution comprises: mixing and stirring water, a complexing agent solution and a precipitant solution under an inert atmosphere, the complexing agent solution being aqueous ammonia, and the stirring speed being 200-600 rpm, such as 200 rpm, 220 rpm, 240 rpm, 260 rpm, 280 rpm, 300 rpm, 350 rpm, 400 rpm, 450 rpm, 500 rpm, 550 rpm or 600 rpm, etc.

[0034] The kind of the gas in the inert atmosphere is not limited in the present application, and can be at least one of nitrogen, helium or argon.

[0035] In one embodiment, the pH value of the bottom liquid is 11.3-12.8, for example, can be 11.3, 11.5, 11.6, 11.8, 11.9, 12.0, 12.1, 12.3, 12.5, 12.6 or 12.8, etc.; the ammonia concentration is 2-12 g / L, for example, can be 2 g / L, 4 g / L, 5 g / L, 6 g / L, 8 g / L, 9 g / L, 10 g / L, 11 g / L or 12 g / L, etc.

[0036] The present application does not limit the amount of the bottom liquid added into the reactor, for example, can be 1 / 4-2 / 3 of the total volume of the reactor.

[0037] As an optional technical solution of the preparation method of the core-shell structure precursor described in the present application, the reaction temperature of the stage I, stage II and stage III is within 40-80℃, for example, can be 40℃, 45℃, 50℃, 55℃, 60℃, 65℃, 70℃, 75℃ or 80℃, etc. The co-precipitation crystallization reaction occurs in each stage, and the temperature of each stage can be the same or different, as long as it is within the above range.

[0038] In one embodiment, the precipitation crystallization reaction temperature of each stage is maintained within the above temperature range by using a mold temperature machine, and the temperature is maintained constant ±2℃.

[0039] In one embodiment, during the reaction process of the stage I and stage II, the ammonia concentration of the reaction system is 2-12 g / L, for example, can be 2 g / L, 4 g / L, 5 g / L, 6 g / L, 8 g / L, 9 g / L, 10 g / L, 11 g / L or 12 g / L, etc.; the stirring speed of the reaction system is 200-600 rpm, for example, can be 200 rpm, 220 rpm, 240 rpm, 260 rpm, 280 rpm, 300 rpm, 350 rpm, 400 rpm, 450 rpm, 500 rpm, 550 rpm or 600 rpm, etc.

[0040] In one embodiment, the stage I is the nucleation stage of the core layer precipitate, the pH value of the reaction system is 11.3-12.8, for example, can be 11.3, 11.4, 11.5, 11.6, 11.8, 11.9, 12.0, 12.2, 12.3, 12.5, 12.6, 12.7 or 12.8, etc.; the reaction time is 4-10 h, for example, can be 4 h, 4.2 h, 4.5 h, 4.7 h, 5 h, 5.3 h, 5.6 h, 5.8 h, 6 h, 6.5 h, 7 h, 7.5 h, 8 h, 8.5 h, 9 h, 9.5 h or 10 h, etc.

[0041] In one embodiment, the gas in the inert atmosphere during the stage I reaction includes at least one of nitrogen, helium and argon.

[0042] In one embodiment, the stage II is a pH decreasing and growth stage of the core layer precipitate, and the pH value of the reaction system is 10.8-11.4, for example, 10.8, 10.9, 11.0, 11.1, 11.2, 11.3 or 11.4, etc.

[0043] In one embodiment, the gas in the micro-oxidizing atmosphere during the stage II reaction includes a protective gas and air, and the volume ratio of the protective gas to air is (1-32):1, for example, 1:1, 3:1, 5:1, 7:1, 8:1, 10:1, 12:1, 15:1, 17:1, 18:1, 20:1, 22:1, 24:1, 25:1, 27:1, 28:1, 30:1 or 32:1, etc., and more preferably (4-10):1.

[0044] In one embodiment, the protective gas includes at least one of nitrogen, helium and argon.

[0045] In the method of the present application, the flow rate of the core layer metal salt solution in the stage I and stage II is not specifically limited, and varies with the volume of the reactor.

[0046] As an alternative technical solution of the method for preparing the core-shell structure precursor described in the present application, the stage III is a growth stage of the core layer precipitate, and compared with the stage I and stage II, the flow rate of the shell layer metal salt solution in the stage III is controlled to be less than that of the core layer metal salt solution, the stirring speed is reduced, the pH value is reduced, and the ammonia concentration is increased, so as to promote the full growth of the primary grains and make the outer shell dense.

[0047] In one embodiment, the pH value is reduced and the ammonia concentration is increased by adjusting the flow rate of the precipitant solution and the complexing agent solution.

[0048] In the method of the present application, by only adjusting the atmosphere, the pH value of the reaction system, the stirring speed and the ammonia concentration in different reaction stages, the core-shell structure precursor with a loose and porous internal structure, thin and needle-like primary grains in the internal structure and a relatively dense outer shell and thick and blocky primary grains in the outer shell can be prepared, which makes the fine primary particles in the internal core shrink outward during the lithium mixing and sintering, so that the internal structure presents a porous or even hollow structure, thereby improving the rate performance of the positive electrode material.

[0049] In one embodiment, the feeding flow rate of the shell layer metal salt solution is Q2, the feeding flow rate of the core layer metal salt solution in the stage I and the stage II is Q1, Q2:Q1=(0.3-0.8):1, for example, 0.3:1, 0.4:1, 0.5:1, 0.6:1, 0.7:1 or 0.8:1, etc., optionally (0.5-0.6):1.

[0050] In one embodiment, in the stage III, the stirring speed is 150-500 rpm, for example, 150 rpm, 175 rpm, 200 rpm, 220 rpm, 240 rpm, 260 rpm, 280 rpm, 300 rpm, 350 rpm, 400 rpm, 450 rpm or 500 rpm, etc.

[0051] In one embodiment, compared with the stage II, the stirring speed in the stage III is lower by 40-120 rpm, for example, 40 rpm, 45 rpm, 50 rpm, 60 rpm, 70 rpm, 80 rpm, 90 rpm, 100 rpm, 110 rpm or 120 rpm, etc., optionally, the stirring speed is lower by 50-100 rpm; the pH value of the reaction system is lower by 0.3-0.8, for example, 0.3, 0.4, 0.5, 0.6, 0.7 or 0.8, etc.; the ammonia concentration is higher by 1-6 g / L, for example, 1 g / L, 1.2 g / L, 1.3 g / L, 1.5 g / L, 1.6 g / L, 1.8 g / L, 2 g / L, 2.3 g / L, 2.6 g / L, 2.8 g / L, 3 g / L, 3.5 g / L, 4 g / L, 4.5 g / L, 5 g / L, 5.5 g / L or 6 g / L, etc., optionally, the ammonia concentration is higher by 1-3 g / L.

[0052] In one embodiment, the slurry containing the core-shell structure precursor is sequentially subjected to aging, separation, washing and drying to obtain the core-shell structure precursor powder.

[0053] The separation method in the method of the present application is not limited, for example, it can be filtration or centrifugation.

[0054] In the method of the present application, the impurity ions (for example, Na + and SO4 2- ) adsorbed in the co-precipitation process can be removed by washing, thereby effectively removing the impurities inside the precursor particles and improving the cycle performance of the positive electrode material.

[0055] In a third aspect, the present application provides a positive electrode material, which is prepared by using the core-shell structure precursor of the first aspect.

[0056] The core-shell structure precursor of the application is further used to prepare the positive electrode material, and the rate performance, cycle performance and safety performance of the positive electrode material are improved.

[0057] In a fourth aspect, the application provides a lithium ion battery comprising the positive electrode material of the third aspect.

[0058] The numerical ranges described herein include all the points within the range, and the application does not list all the specific point values in the range due to the length of the article and for the sake of simplicity.

[0059] Compared with the related art, the application has the following beneficial effects.

[0060] (1) The inner core of the core-shell structure precursor of the application is a loose porous nickel-rich inner core (such as nickel-cobalt-manganese hydroxide) with thin and thin needle-shaped primary grains, which can provide high capacity; and the outer shell is a dense structure with thick block-shaped primary grains (such as manganese-rich nickel-manganese hydroxide, nickel-cobalt-manganese hydroxide or aluminum-containing nickel-cobalt-aluminum hydroxide), which can provide high stability and safety, and improve the cycle performance. In addition, the positive electrode material prepared by using the precursor has a porous or even hollow structure in the inner core part when mixed with lithium and sintered, which can buffer the structural stress caused by the volume change of the positive electrode material during the charging and discharging process of the battery, and is not easy to produce micro-cracks, which can stabilize the structure and improve the rate performance of the positive electrode material.

[0061] (2) The method of the application uses micro-oxidation to manufacture a loose porous structure in the pH environment of co-precipitation, which can form a precursor with an internal porous structure without adding a pore-forming agent or a specific organic additive, effectively avoiding the problem of performance degradation caused by impurity residues, or the problem of increased cost of subsequent impurity removal.

[0062] (3) The preparation method of the application is simple, and the entire process flow only needs to modify the gas path (such as the mixed gas path of air and nitrogen) of the atmosphere supply unit, without other organic additives, and does not need to add additional impurity removal processes, which is fully compatible with the existing production line and easy to scale up.

[0063] Other aspects can be understood after reading and understanding the description of the drawings and the detailed description. BRIEF DESCRIPTION OF DRAWINGS

[0064] Figure 1 is a schematic diagram of a co-precipitation reaction device in the application;

[0065] Wherein, 1 is a core layer metal salt solution, 2 is a first shell layer metal salt solution, 3 is a second shell layer metal salt solution, 4 is a sodium hydroxide solution, and 5 is an ammonia solution.

[0066] Figure 2 is the Ni 0.84 Co 0.05 Mn 0.11 (OH)2@Ni 0.6 Co 0.05 Mn 0.35 The electron microscope pictures of the core-shell structure precursor of (OH)2. DETAILED DESCRIPTION

[0067] The technical solutions of the present application are further illustrated below in conjunction with the drawings and through specific embodiments.

[0068] The specific embodiments described herein are only used to explain the present application and do not limit the present application.

[0069] In the embodiments of the present application, the pH value, temperature, ammonia concentration and the like fluctuate during the reaction process, and therefore the above parameters are presented as a small range in each embodiment.

[0070] The schematic diagram of the co-precipitation reaction device used in the preparation of the core-shell structure precursor in the embodiments of the present application is shown in Figure 1; wherein 1 is a core layer metal salt solution, 2 is a first shell layer metal salt solution, 3 is a second shell layer metal salt solution, 4 is a sodium hydroxide solution, and 5 is an ammonia solution; wherein the types of the first shell layer metal salt solution and the second shell layer metal salt solution are different, and taking Example 3 as an example, the first shell layer metal salt solution is a nickel-manganese-containing sulfate salt solution, and the second shell layer metal salt solution is a sodium metaaluminate solution.

[0071] Example 1

[0072] The present embodiment provides a preparation method of a core-shell structure precursor, comprising the following steps:

[0073] Step S1, a core layer metal salt solution (a nickel-cobalt-manganese-containing sulfate salt solution) and a shell layer metal salt solution (a nickel-cobalt-manganese-containing sulfate salt solution) are respectively prepared according to the molecular formula Ni 0.84 Co 0.05 Mn 0.11 (OH)2and Ni 0.6 Co 0.05 Mn 0.35 (OH)2, and the total metal ion concentration is 2 mol / L; a sodium hydroxide solution with a mass fraction of 32% is prepared; an ammonia solution with a mass fraction of 16% and a concentrated ammonia solution with a mass fraction of 22% are respectively prepared;

[0074] Step S2, 40 L of pure water is added to a 100 L reaction kettle, and nitrogen gas is introduced as a protective gas; the 22% concentrated ammonia solution and the sodium hydroxide solution are added, the bottom liquid pH value is adjusted to 12.2, the ammonia concentration is adjusted to 4-5 g / L, the temperature is maintained at 60±1℃, and the stirring speed is 500 rpm;

[0075] Step S3, the prepared core layer metal salt solution, sodium hydroxide solution and 16% ammonia solution were added into the reactor at a uniform speed and current, with a flow rate of 4L / h, 1L / h and 0.4L / h respectively, to carry out the reaction of stage I and stage II. In stage I, pure nitrogen was introduced as the reaction atmosphere, the stirring speed was 420 rpm, the pH of the reaction system was controlled at 11.8-12.2 by gradually adjusting the flow rate of liquid alkali and ammonia, the ammonia concentration was controlled at 4-5 g / L, and the reaction was carried out for 6 h; in stage II, the mixed gas with a volume ratio of nitrogen: air = 5: 1 was introduced as the reaction atmosphere, the stirring speed was 420 rpm, the pH of the reaction system was gradually decreased and finally controlled at 11.3 ± 0.1 by gradually adjusting the flow rate of sodium hydroxide solution and ammonia, the ammonia concentration was controlled at 4-5 g / L, and the reaction was carried out until the particle size D50 of the secondary particles reached 3 μm, and the feeding was stopped.

[0076] Step S4, pure nitrogen was used as the reaction atmosphere, the stirring speed was changed to 360 rpm, the metal salt solution was switched to the shell layer metal salt solution, the flow rates of the shell layer salt solution, sodium hydroxide solution and ammonia solution were reduced to 1 / 2 of those at the end of stage II, and the pH of the reaction system was gradually decreased and finally controlled at 10.8 ± 0.1 by gradually adjusting the flow rate of liquid alkali and ammonia, the ammonia concentration was controlled at 6-7 g / L, and the reaction was carried out until the particle size D50 of the secondary particles reached the target particle size of 5.0 μm, and the feeding was stopped.

[0077] Step S5, the core-shell structure precursor slurry obtained in step S4 was allowed to stand and precipitate, the supernatant was removed, and sodium hydroxide solution was added for aging. After aging for 8 h, the supernatant was removed, and the remaining material was pumped into a centrifuge for multiple alkali washing and water washing. The water-washed material was dried, screened and demagnetized to obtain a Ni 0.84 Co 0.05 Mn 0.11 (OH)2@Ni 0.6 Co 0.05 Mn 0.35 (OH)2core-shell structure precursor with a particle size D50 of 5.04 μm and a shell thickness of 0.97 μm. The scanning electron microscope image of the cross section is shown in FIG. 2. As can be seen from the figure, the inner core of the precursor is loose and porous, and the primary grains are thin and needle-like in morphology, and the diameter of the spherical particles is about 4 μm; the outer shell is dense in structure, and the primary grains are thick and blocky in morphology, and the thickness of the shell is about 1 μm.

[0078] Example 2

[0079] The present embodiment provides a preparation method of a core-shell structure precursor, comprising the following steps:

[0080] Step S1, a core-shell structure precursor was prepared according to the following steps: 0.9 Co 0.05 Mn 0.05(OH)2and Ni 0.4 Mn 0.6 The core layer metal salt solution (sulfate solution containing nickel, cobalt and manganese) and the shell layer metal salt solution (sulfate solution containing nickel and manganese) were prepared respectively with a total metal ion concentration of 2 mol / L; a 32% sodium hydroxide solution was prepared; a 16% ammonia solution and a 22% concentrated ammonia solution were prepared respectively;

[0081] In step S2, 40 L of pure water was added to a 100 L reactor, and nitrogen was introduced as a protective gas; 22% concentrated ammonia solution and sodium hydroxide solution were added to adjust the pH of the bottom liquid to 12.4±0.1, the ammonia concentration to 10±0.5 g / L, and the temperature to 70±1℃, with a stirring speed of 360 rpm;

[0082] In step S3, the prepared core layer metal salt solution, sodium hydroxide solution and 16% ammonia solution were added to the reactor at a flow rate of 4.2 L / h, 1.05 L / h and 0.84 L / h respectively in a uniform and parallel manner to carry out the phase I and phase II reactions. In phase I, pure nitrogen was introduced as the reaction atmosphere, the stirring speed was 320 rpm, and the pH of the reaction system was controlled at 11.9-12.1 and the ammonia concentration was controlled at 10±0.5 g / L by gradually adjusting the flow rates of liquid alkali and ammonia, and the reaction was carried out for 10 h; in phase II, a mixture of nitrogen and air with a volume ratio of 2:1 was introduced as the reaction atmosphere, the stirring speed was 320 rpm, and the pH of the reaction system was gradually decreased and finally controlled at 11.2±0.1 and the ammonia concentration was controlled at 10±0.5 g / L by gradually adjusting the flow rates of sodium hydroxide solution and ammonia, and the reaction was carried out until the particle size D50 of the secondary particles reached 7 μm, and the feeding was stopped;

[0083] In step S4, pure nitrogen was used as the reaction atmosphere, the stirring speed was changed to 280 rpm, the metal salt solution was switched to the shell layer metal salt solution, and the flow rates of the shell layer salt solution, sodium hydroxide solution and ammonia solution were reduced to 0.7 times those at the end of phase II, and the pH of the reaction system was gradually decreased and finally controlled at 10.7±0.1 and the ammonia concentration was controlled at 12±0.5 g / L by gradually adjusting the flow rates of liquid alkali and ammonia, and the reaction was carried out until the particle size D50 of the secondary particles reached the target particle size of 7.5 μm, and the feeding was stopped;

[0084] In step S5, the core-shell structure precursor slurry obtained in step S4 was allowed to settle and precipitate, the supernatant was removed, and sodium hydroxide solution was added for aging; after aging for 6 h, the supernatant was removed, and the remaining material was pumped into a centrifuge for multiple alkali washing and water washing; the water-washed material was dried, screened and demagnetized to obtain a D50 of 7.53 μm, a shell layer of 0.52 μm and a porous interior Ni 0.9 Co 0.05 Mn 0.05(OH)2@Ni 0.4 Mn 0.6 (OH)2core-shell structure precursor.

[0085] Example 3

[0086] The present embodiment provides a preparation method of a core-shell structure precursor, comprising the following steps:

[0087] Step S1, according to the molecular formula Ni 0.8 Co 0.1 Mn 0.1 (OH)2and Ni 0.7 Co 0.15 Al 0.15 (OH)2and a shell layer metal salt solution (a sulfate solution containing nickel, cobalt and manganese) are prepared respectively, and the total metal ion concentration is 1 mol / L; a sodium hydroxide solution with a mass fraction of 32% is prepared; an ammonia solution with a mass fraction of 16% and a concentrated ammonia solution with a mass fraction of 22% are prepared respectively;

[0088] Step S2, 40 L of pure water is added to a 100 L reaction kettle, and nitrogen gas is introduced as a protective gas; 22% concentrated ammonia solution and sodium hydroxide solution are added, the bottom liquid pH value is adjusted to 12.0±0.1, the ammonia concentration is 7±0.5 g / L, the temperature is maintained at 45±1℃, and the stirring speed is 360 rpm;

[0089] Step S3, in a uniform and parallel flow manner, the prepared core layer metal salt solution, sodium hydroxide solution and 16% ammonia solution are added to the reaction kettle at a flow rate of 8 L / h, 1.6 L / h and 0.96 L / h respectively to carry out stage I and stage II reactions. Among them, stage I: pure nitrogen gas is introduced as the reaction atmosphere, the stirring speed is 300 rpm, the reaction system pH is controlled at 11.7-11.9 by gradually fine-tuning the liquid alkali and ammonia flow, the ammonia concentration is controlled at 7±0.5 g / L, and the reaction is carried out for 5 h; stage II: a mixed gas with a volume ratio of nitrogen:air=16:1 is introduced as the reaction atmosphere, the stirring speed is 300 rpm, the reaction system pH is gradually lowered and finally controlled at 10.8±0.1 by gradually fine-tuning the sodium hydroxide solution and ammonia flow, the ammonia concentration is controlled at 7±0.5 g / L, and the reaction is carried out until the particle size D50 of the secondary particles reaches 9.5 μm, and the feeding is stopped;

[0090] Step S4, using pure nitrogen as the reaction atmosphere, the rotation speed is changed to 240 rpm, the metal salt solution is switched to the shell metal salt solution, and the flow rates of the shell salt solution, the sodium hydroxide solution and the ammonia solution are reduced to 0.4 at the end of the stage II reaction, and then the flow rates of the liquid alkali and the ammonia solution are adjusted to gradually reduce the pH of the reaction system and finally control the pH at 10.5±0.1, and the ammonia concentration is controlled at 10 g / L, and the reaction is stopped when the particle size D50 of the secondary particles reaches the target particle size of 10.5 μm;

[0091] Step S5, the core-shell structure precursor slurry obtained in step S4 is allowed to stand and precipitate, the supernatant is pumped out, and the supernatant is pumped out, and the remaining material is pumped into a centrifuge for multiple alkali washing and water washing; the material after water washing is dried, screened and demagnetized, to obtain a Ni 0.8 Co 0.1 Mn 0.1 (OH)2@Ni 0.7 Co 0.15 Al 0.15 (OH)2core-shell structure precursor.

[0092] Example 4

[0093] The embodiment provides a preparation method of a core-shell structure precursor, and the difference between the preparation method and the embodiment 1 is that the reaction time of step S4 is changed, so that the particle size D50 of the secondary particles reaches the target particle size of 4.2 μm.

[0094] Example 5

[0095] The embodiment provides a preparation method of a core-shell structure precursor, and the difference between the preparation method and the embodiment 1 is that the reaction time of step S4 is changed, so that the particle size D50 of the secondary particles reaches the target particle size of 6.5 μm.

[0096] Example 6

[0097] The embodiment provides a preparation method of a core-shell structure precursor, and the difference between the preparation method and the embodiment 1 is that in step S3, the ratio of nitrogen to air is 32:1.

[0098] Example 7

[0099] The embodiment provides a preparation method of a core-shell structure precursor, and the difference between the preparation method and the embodiment 1 is that in step S3, the ratio of nitrogen to air is 1:1.

[0100] Example 8

[0101] The embodiment provides a preparation method of a core-shell structure precursor, which is different from the preparation method of the embodiment 1 in that the rotation speed is changed to 300 rpm in step S4.

[0102] Embodiment 9

[0103] The embodiment provides a preparation method of a core-shell structure precursor, which is different from the preparation method of the embodiment 1 in that the rotation speed is changed to 380 rpm in step S4.

[0104] Embodiment 10

[0105] The embodiment provides a preparation method of a core-shell structure precursor, which is different from the preparation method of the embodiment 1 in that the ammonia concentration is controlled to be 10±0.5 g / L in step S4.

[0106] Comparative example 1

[0107] The embodiment provides a preparation method of a precursor, which is different from the preparation method of the embodiment 1 in that the step S4 is not performed, and the prepared precursor does not contain a shell structure.

[0108] Comparative example 2

[0109] The embodiment provides a preparation method of a precursor, which is different from the preparation method of the embodiment 1 in that the mixed gas of nitrogen:air=5:1 in step S3 is replaced by nitrogen.

[0110] Application example 1

[0111] The application example provides a lithium ion battery, which comprises a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte.

[0112] The preparation method of the lithium ion battery provided by the application example comprises the following steps:

[0113] Preparation of a positive electrode material:

[0114] The core-shell structure precursor described in the embodiment 1 is mixed with lithium hydroxide in a molar ratio of 1:1.05. Then, the mixture is placed in an oxygen environment for sintering, and the sintering temperature is 820 DEG C, and the holding time is 18h, so that the reaction is complete and the required positive electrode material is obtained.

[0115] Preparation of a positive electrode sheet:

[0116] The prepared positive electrode material, a conductive agent Super P and a binder PVDF are mixed in a mass ratio of 97:1:2. Then, the mixture is dispersed in NMP (N-methyl pyrrolidone) to form a uniform positive electrode slurry. Subsequently, the positive electrode slurry is uniformly coated on an aluminum foil, and after drying and rolling processes, a positive electrode sheet is finally obtained.

[0117] Preparation of the anode sheet:

[0118] The preparation process of the anode sheet involves mixing the negative active material, conductive agent, and binder in a certain proportion and dispersing them in a suitable solvent to form an anode slurry. Then, the anode slurry is coated on a copper foil, and after drying and rolling, the anode sheet is obtained. The specific type of negative active material, the selection of conductive agent and binder, and the mixing ratio can be adjusted according to actual needs.

[0119] Providing a separator and electrolyte:

[0120] The separator is an important component in lithium-ion batteries, used to isolate the positive and negative electrodes to prevent short circuits. In this application example, a porous polyolefin material can be used as a separator. The electrolyte is responsible for conducting ions between the positive and negative electrodes and is usually made by dissolving lithium salts in organic solvents. Depending on the performance requirements of the battery, the appropriate electrolyte formula can be selected.

[0121] Using the above positive sheet, negative sheet, separator, and electrolyte, the battery is assembled according to standard battery assembly processes, and finally a lithium-ion battery is obtained.

[0122] Application Example 2-10

[0123] This application example provides a lithium-ion battery, the difference between its preparation method and application example 1 is that the core-shell structure precursor of example 1 is replaced by the core-shell structure precursor of example 2-10.

[0124] Application Comparative Example 1-2

[0125] This application example provides a lithium-ion battery, the difference between its preparation method and application example 1 is that the core-shell structure precursor of example 1 is replaced by the core-shell structure precursor of comparative example 1-2.

[0126] Performance test:

[0127] (1) Rate performance test: The rate performance is an important indicator to measure the charging and discharging capacity of lithium-ion batteries at high current density. To test the rate performance of the lithium-ion battery in this application example, charging and discharging tests at different current densities can be used. The specific steps include: first, the battery is cycled at a small current density of 0.1C to stabilize the battery performance; then, gradually increase the current density, and record the charging and discharging capacity and voltage change of the battery at different current densities (including 0.2C, 0.5C, 1C, 2C and 5C). By comparing the performance data at different current densities, the rate performance of the battery can be evaluated, i.e. the charging and discharging capacity of the battery at high current density.

[0128] (2) Cycle performance test: Cycle performance is a key indicator for evaluating the long-term stability of lithium-ion batteries. To test the cycle performance of the lithium-ion battery in this application example, the battery can be subjected to continuous charge-discharge cycles under standard conditions. The specific steps include: setting appropriate charge-discharge voltage range (2.7-4.3V), current density (1C) and cycle number (100 cycles), and repeating the charge-discharge process of the battery. At the end of each cycle, record the discharge capacity, coulombic efficiency and other key parameters of the battery. By comparing the performance data of different cycle periods, the cycle stability of the battery can be evaluated, i.e. the performance degradation of the battery during long-term use.

[0129] The rate performance and cycle performance of the lithium-ion batteries of application examples 1-10 and application comparative examples 1-2 were tested, and the results are shown in Table 1.

[0130] Table 1

[0131] As can be seen from Table 1, the use of the core-shell precursor prepared by the application in the preparation of the positive electrode material for lithium-ion batteries can effectively improve the rate performance and cycle performance of the battery. The precursor used in application comparative example 1 is not a core-shell structure, resulting in poor cycle performance.

[0132] As can be seen from the comparison of application example 1 and application examples 4-5, the shell of the core-shell structure precursor used in application example 4 is thin, resulting in poor cycle performance, but the rate performance is slightly improved; the shell of the core-shell structure precursor used in application example 5 is thick, resulting in better cycle performance, but the rate performance is slightly reduced.

[0133] As can be seen from the comparison of application example 1 and application examples 6-7 and application comparative example 2, when preparing the core-shell structure precursor, the stage II of step S3 should be carried out in a micro-oxidizing atmosphere, and the volume ratio of nitrogen and air in the micro-oxidizing atmosphere has an optimal range. If there is too much nitrogen, the primary grains of the inner core will be coarse and the voids will be less, resulting in reduced rate performance but slightly improved cycle performance; if there is too much air, the primary grains of the inner core will be fine and the voids will be more, resulting in improved rate performance but reduced cycle performance.

[0134] As can be seen from the comparison of application example 1 and application examples 8-9, in the process of preparing the core-shell structure precursor, the difference between the rotation speed in step S4 and the rotation speed in step S3 has an optimal range. If the difference is too large, the primary grains of the shell will be coarse and tightly connected, which improves the protection of the inner core and improves the cycle performance, but is not conducive to the improvement of the rate performance; if the difference is too small, the primary grains of the shell will be fine and loose, which reduces the protection of the inner core and reduces the cycle performance, but is conducive to the improvement of the rate performance.

[0135] It can be known from the comparison between Application Example 1 and Application Example 10 that in the process of preparing the core-shell structure precursor, the ammonia concentration in step S4 should be greater than that in step S3, but the difference between the ammonia concentration in step S4 and that in step S3 should not be too large, otherwise the primary crystal grains of the outer shell will be extremely thick and closely connected, the protection of the inner core will be improved, which is beneficial to the improvement of the cycle performance, but is not conducive to the improvement of the rate performance.

[0136] The applicant declares that the detailed method of the present application is illustrated by the above examples, but the present application is not limited to the above detailed method, that is, the present application does not mean that it must rely on the above detailed method to be implemented. It should be understood by those skilled in the art that any improvement of the present application, equivalent replacement of each raw material of the product of the present application, addition of auxiliary ingredients, selection of specific methods, etc. fall within the protection scope and disclosure scope of the present application.

Claims

1. A core-shell structure precursor, comprising a porous nickel-rich inner core and a manganese-rich or aluminum-containing outer shell coated on the surface of the inner core, and primary grains constituting the inner core are thin needle-shaped, and primary grains constituting the outer shell are thick block-shaped.

2. The core-shell structure precursor of claim 1, wherein, The outer shell is a dense outer shell.

3. The core-shell structure precursor according to claim 1 or 2, wherein The particle size D50 of the core-shell structure precursor is 3-15 μm. Optionally, the ratio of the particle size of the core-shell structure precursor to the thickness of the outer shell is (2.5-21) : 1, or (3-15) :

1.

4. The core-shell structure precursor according to any one of claims 1 to 3, wherein, The inner core is a nickel-cobalt-manganese hydroxide, and the molar ratio of metal ions is Ni:Co:Mn=x1:y1:z1, wherein x1≥0.6, 0.02≤y1≤0.2, 0.05≤z1≤0.2, and x1+y1+z1=1. Optionally, the outer shell is a nickel-manganese hydroxide, a nickel-cobalt-manganese hydroxide, or a nickel-cobalt-aluminum hydroxide. Optionally, when the outer shell is a nickel-manganese hydroxide or a nickel-cobalt-manganese hydroxide, the molar ratio of metal ions is Ni:Co:Mn=x2:y2:z2, wherein x2≥0.4, 0≤y2≤0.2, 0.2≤z2≤0.6, x2+y2+z2=1, and x1>x2, z1<z2. Optionally, when the outer shell is a nickel-cobalt-aluminum hydroxide, the molar ratio of metal ions is Ni:Co:Al=x3:y3:z3, wherein x3≥0.6, 0.02≤y3≤0.2, 0.02≤z3≤0.2, and x3+y3+z3=1. 5.A method for preparing the core-shell structure precursor of any one of claims 1-4, comprising the following steps: providing a core layer metal salt solution, a shell layer metal salt solution, a precipitant solution, and a complexing agent solution, ready for use; passing the core layer metal salt solution, the precipitant solution, and the complexing agent solution into a reactor containing a bottom liquid in parallel, first performing a stage I reaction under an inert atmosphere, and then performing a stage II reaction under a micro-oxidizing atmosphere stopping the feeding when a preset particle size is reached, to obtain a core layer precipitate; passing the shell layer metal salt solution, the precipitant solution, and the complexing agent solution into the reactor in parallel, performing a stage III reaction under an inert atmosphere, to precipitate the shell layer metal salt on the core layer precipitate, and stopping the reaction when a target particle size is reached, to obtain a slurry containing the core-shell structure precursor.

6. The method of producing a core-shell structure precursor according to claim 5, wherein, The core layer metal salt solution is a nickel-cobalt-manganese sulfate solution. Optionally, the concentration of total metal ions in the core layer metal salt solution is 1-3 mol / L. Optionally, the shell layer metal salt solution is a nickel-manganese sulfate solution, or a nickel-cobalt-manganese sulfate solution, or a combination of a nickel-cobalt sulfate solution and a sodium metaaluminate solution. Optionally, the concentration of total metal ions in the shell layer metal salt solution is 1-3 mol / L.

7. The method of producing a core-shell structure precursor according to any one of claims 5 or 6, wherein, The precipitant solution is a sodium hydroxide solution with a mass concentration of 20-40%. Optionally, the complexing agent solution is an ammonia solution with a mass concentration of 10-30%.

8. The method of producing a core-shell structure precursor according to any one of claims 5 to 7, wherein The preparation method of the base solution comprises: mixing and stirring water, a complexing agent solution and a precipitant solution under an inert atmosphere, the complexing agent solution being ammonia water, and the stirring speed being 200-600 rpm; Optionally, the pH value of the base solution is 11.3-12.8, and the ammonia concentration is 2-12 g / L.

9. The method of producing a core-shell structure precursor according to any one of claims 5 to 8, wherein, The reaction temperature of the stages I, II and III is in the range of 40-80℃. Optionally, during the reaction of the stages I and II, the ammonia concentration of the reaction system is 2-12 g / L, and the stirring speed of the reaction system is 200-600 rpm.

10. The method of producing a core-shell structure precursor according to any one of claims 5 to 9, wherein, The stage I is a nucleation stage of the core layer precipitate, the pH value of the reaction system is 11.3-12.8, and the reaction time is 4-10 h. Optionally, during the reaction of the stage I, the gas in the inert atmosphere comprises at least one of nitrogen, helium and argon.

11. The method of producing a core-shell structure precursor according to any one of claims 5 to 10, wherein, The stage II is a pH reduction and growth stage of the core layer precipitate, the pH value of the reaction system is 10.8-11.

4. Optionally, during the reaction of the stage II, the gas in the micro-oxidizing atmosphere comprises a protective gas and air, and the volume ratio of the protective gas to air is (1-32):1, optionally (4-10):

1. Optionally, the protective gas comprises at least one of nitrogen, helium and argon.

12. The method of producing a core-shell structure precursor according to any one of claims 5 to 11, wherein, The stage III is a growth stage of the core layer precipitate, compared with the stages I and II, the flow rate of the shell layer metal salt solution in the stage III is less than that of the core layer metal salt solution, the stirring speed is reduced, the pH value is reduced, and the ammonia concentration is increased, so as to promote the full growth of the primary crystal grains and make the shell dense. Optionally, the feeding flow rate of the shell layer metal salt solution is Q2, the feeding flow rate of the core layer metal salt solution in the stages I and II is Q1, and Q2:Q1=(0.3-0.8):1, optionally (0.5-0.6):

1. Optionally, in the stage III, the stirring speed is 150-500 rpm. Optionally, compared with the stage II, the stirring speed in the stage III is reduced by 40-120 rpm, optionally reduced by 50-100 rpm, the pH value of the reaction system is reduced by 0.3-0.8, and the ammonia concentration is increased by 1-6 g / L, optionally increased by 1-3 g / L.

13. A positive electrode material prepared by using the core-shell structure precursor according to any one of claims 1-4.

14. A lithium ion battery comprising the positive electrode material according to claim 13.

Images