A core-shell positive electrode precursor and its preparation method and application

Abstract

The present invention provides a core-shell positive electrode precursor and a preparation method and application thereof. The preparation method first prepares a nickel-cobalt-manganese primary particle cluster inner core by reverse feeding, then uses the inner core as a seed crystal, and then in-situ grows a nickel-cobalt-manganese single crystal coating layer as an outer shell on the outside of the seed crystal by forward feeding, so that a core-shell positive electrode precursor for a lithium-ion battery can be prepared simply and efficiently; the prepared core-shell positive electrode precursor, on the one hand, can be used as a buffer layer for material deformation due to the porous and fluffy inner core, thereby reducing the generation of internal stress and providing space for lithium ion storage; on the other hand, the nickel-cobalt-manganese single crystal coating layer reduces the cracking of the material based on the consistent contraction and expansion of the single crystal material, inhibits the side reaction with the electrolyte, reduces the polarization overpotential of lithium ion diffusion, and the in-situ grown nickel-cobalt-manganese single crystal serves as a strong and stable primary particle, thereby enhancing the mechanical-thermal stability of the electrode.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion batteries, and in particular to positive electrode materials for lithium ion batteries, and in particular to a core-shell positive electrode precursor and a preparation method and application thereof. Background Art

[0002] At present, the market size of lithium-ion batteries has grown significantly in the past two decades. They have a fairly high energy density and stable discharge in a wide temperature range. The rapid growth of mobile device applications has encouraged the continuous development of lithium-ion battery technology. At present, the positive electrode materials of lithium-ion batteries used in the market are mainly polycrystalline ternary positive electrode materials, which have a large number of grain boundaries. During the battery charging and discharging process, the stress generated by the anisotropic contraction and expansion of the primary particles makes the contact between the primary particles loose, resulting in secondary particles prone to grain boundary cracking and breakage. In addition, the side reactions on the surface of the positive electrode material and the electrolyte interface increase rapidly, resulting in an increase in battery impedance and a rapid decline in performance.

[0003] Compared with polycrystalline ternary cathode materials, single crystal types can effectively deal with the problem of grain boundary crushing and the performance degradation caused by it. Compared with commercial polycrystalline ternary materials, single crystal ternary materials have better cycle stability at both room temperature and high temperature, and are safer. However, single crystal ternary cathode materials still have the technical problem of low lithium ion capacity, which makes the rate performance of single crystal ternary lithium batteries low. It is particularly urgent to find electrode materials with large capacity and high energy density.

[0004] Nickel-cobalt-manganese ternary cathode material is a common ternary lithium battery cathode material. During the battery charging and discharging process, nickel-cobalt-manganese oxide particles continuously experience lithium insertion and extraction. Due to the continuous contraction and expansion of the material, this reciprocating volume change will produce a large amount of uneven residual stress inside the material, causing cracks inside the particles. In addition, the electrolyte erodes the material, and a large number of side reactions occur on the surface of the material, causing structural collapse and dissolution of the cathode material. This affects the ion transfer rate, which is manifested as an increase in the internal resistance and a decrease in capacity of the battery after a long cycle.

[0005] In summary, there is a need to develop a new type of core-shell cathode precursor and a preparation method thereof, and then apply it to obtain a new type of cathode material, in order to avoid cracks in the cathode material due to strain, and to avoid the falling off and breakage of the cathode material. Summary of the invention

[0006] In view of the problems existing in the prior art, the present invention provides a core-shell positive electrode precursor and a preparation method and application thereof. The preparation method first prepares a nickel-cobalt-manganese primary particle cluster inner core by reverse feeding, then uses this as a crystal seed, and then grows a nickel-cobalt-manganese single crystal coating layer as an outer shell in situ on the outside of the crystal seed by forward feeding, so that a core-shell positive electrode precursor for a lithium-ion battery can be prepared simply and efficiently; the prepared core-shell positive electrode precursor, on the one hand, can be used as a buffer layer for material deformation due to the porous and fluffy inner core, thereby reducing the generation of internal stress and providing space for lithium ion storage; on the other hand, the nickel-cobalt-manganese single crystal coating layer reduces the cracking of the material based on the consistent shrinkage and expansion of the single crystal material, inhibits the side reaction with the electrolyte, and reduces the polarization overpotential of lithium ion diffusion; the in-situ grown nickel-cobalt-manganese single crystal acts as a strong and stable primary particle, thereby enhancing the mechanical-thermal stability of the electrode.

[0007] To achieve this object, the present invention adopts the following technical solutions:

[0008] One of the purposes of the present invention is to provide a method for preparing a core-shell cathode precursor, the preparation method comprising the following steps:

[0009] (1) preparing a nickel-cobalt-manganese ternary metal salt solution as solution A, preparing an inorganic strong base solution as solution B, and preparing a chelating agent solution as solution C;

[0010] (2) Solution A is used as a primary base solution, and solution B and solution C are injected simultaneously to perform a coprecipitation;

[0011] (3) After a solid-liquid separation, the solid product is freeze-dried to obtain seed crystals;

[0012] (4) Mixing the seed crystals with water to obtain a secondary bottom solution, injecting solution A, solution B and solution C simultaneously to perform secondary co-precipitation, and sequentially performing secondary solid-liquid separation, drying and calcination to obtain a core-shell positive electrode precursor.

[0013] The preparation method of the present invention uses solution A as a primary base liquid, and injects solution B and solution C at the same time. With the addition of solution B and solution C, a cluster floc of primary particles is formed by reaction in the reactor, that is, the inner core of the nickel-cobalt-manganese primary particle cluster is first prepared by reverse feeding, and then used as a crystal seed, and then a nickel-cobalt-manganese single crystal coating layer is in situ grown on the outside of the crystal seed as an outer shell by forward feeding, so that a core-shell positive electrode precursor for a lithium-ion battery can be prepared simply and efficiently; moreover, the first coprecipitation and the second coprecipitation use the same nickel-cobalt-manganese ternary metal salt solution, so that the composition of the nickel-cobalt-manganese primary particle cluster inner core and the nickel-cobalt-manganese single crystal coating layer are the same, and the in situ grown nickel-cobalt-manganese single crystal coating layer and the inner core of the nickel-cobalt-manganese primary particle cluster are tightly and firmly bonded.

[0014] The core-shell positive electrode precursor prepared by the preparation method of the present invention, on the one hand, can be used as a buffer layer for material deformation due to the porous and fluffy inner core, thereby reducing the generation of internal stress and providing space for lithium ion storage; on the other hand, the nickel-cobalt-manganese single crystal coating layer reduces the cracking of the material based on the consistent shrinkage and expansion of the single crystal material, inhibits the side reaction with the electrolyte, reduces the polarization overpotential of lithium ion diffusion, and the in-situ grown nickel-cobalt-manganese single crystals serve as strong and stable primary particles, thereby enhancing the mechanical-thermal stability of the electrode.

[0015] It should be noted that in the preparation method of the present invention, the hydroxide generated by coprecipitation can be completely decomposed into oxides through calcination, which can stabilize the sample structure, improve the crystallization of the shell layer, and prevent the structure from being destroyed during the subsequent mixed lithium sintering process.

[0016] As a preferred technical solution of the present invention, the molar ratio of Ni:Co:Mn in the nickel-cobalt-manganese ternary metal salt solution in step (1) is 0.8:x:y; wherein 0<x<0.2, 0.8+x+y=1.

[0017] Preferably, the concentration of the nickel-cobalt-manganese ternary metal salt solution in step (1) is 1.5 to 2 mol / L, for example, 1.5 mol / L, 1.6 mol / L, 1.7 mol / L, 1.8 mol / L, 1.9 mol / L or 2 mol / L, but is not limited to the listed values, and other values ​​not listed within the above numerical range are also applicable.

[0018] Preferably, the nickel-cobalt-manganese ternary metal salt solution in step (1) comprises any one of sulfate, nitrate or chloride, or a combination of at least two of them.

[0019] As a preferred technical solution of the present invention, the inorganic strong alkali solution in step (1) is a sodium hydroxide solution or a potassium hydroxide solution.

[0020] Preferably, the concentration of the inorganic strong base solution in step (1) is 8 to 10 mol / L, for example 8 mol / L, 8.3 mol / L, 8.5 mol / L, 8.7 mol / L, 9 mol / L, 9.2 mol / L, 9.5 mol / L, 9.8 mol / L or 10 mol / L, etc., but is not limited to the listed values, and other values ​​not listed within the above numerical range are also applicable.

[0021] Preferably, the chelating agent solution in step (1) is aqueous ammonia or oxalic acid solution.

[0022] Preferably, the concentration of the chelating agent solution in step (1) is 4.5-5.5 mol / L, for example, 4.5 mol / L, 4.6 mol / L, 4.7 mol / L, 4.8 mol / L, 4.9 mol / L, 5 mol / L, 5.1 mol / L, 5.2 mol / L, 5.3 mol / L, 5.4 mol / L or 5.5 mol / L, but is not limited to the listed values, and other values ​​not listed within the above numerical range are also applicable.

[0023] As a preferred technical solution of the present invention, in step (2), the injection speed ratio of solution B to solution C is 3.5 to 4.5:1, for example, 3.5:1, 3.6:1, 3.7:1, 3.8:1, 3.9:1, 4:1, 4.1:1, 4.2:1, 4.3:1, 4.4:1 or 4.5:1, but is not limited to the listed values, and other values ​​not listed within the above numerical range are also applicable.

[0024] Preferably, the temperature of the one coprecipitation in step (2) is 35-45°C, for example, 35°C, 36°C, 37°C, 38°C, 39°C, 40°C, 41°C, 42°C, 43°C, 44°C or 45°C, etc., but is not limited to the listed values, and other values ​​not listed within the above numerical range are also applicable.

[0025] Preferably, the stirring rate of the co-precipitation in step (2) is 60 to 100 rpm, for example, 60 rpm, 65 rpm, 70 rpm, 75 rpm, 80 rpm, 85 rpm, 90 rpm, 95 rpm or 100 rpm, but is not limited to the listed values, and other values ​​not listed within the above numerical range are also applicable.

[0026] Preferably, the first solid-liquid separation in step (3) is filtration.

[0027] Preferably, the freeze-drying temperature in step (3) is -30 to -40°C, for example, -30°C, -31°C, -32°C, -33°C, -34°C, -35°C, -36°C, -37°C, -38°C, -39°C or -40°C, and the time is 300-400min, for example, 300min, 310min, 330min, 350min, 370min, 390min or 400min, but is not limited to the listed values, and other values ​​not listed within the above numerical range are also applicable.

[0028] As a preferred technical solution of the present invention, the solid content of the secondary base liquid in step (4) is 80-150 g / L, for example 80 g / L, 90 g / L, 100 g / L, 110 g / L, 120 g / L, 130 g / L, 140 g / L or 150 g / L, etc., but is not limited to the listed values, and other values ​​not listed within the above numerical range are also applicable.

[0029] Preferably, in step (4), the injection flow rate of the solution A is 20 to 40 L / h, for example, 20 L / h, 21 L / h, 23 L / h, 25 L / h, 27 L / h, 30 L / h, 32 L / h, 35 L / h, 38 L / h or 40 L / h, the injection amount molar ratio of the solution C to the solution A is 1.5 to 2.5:1, for example, 1.5:1, 1.6:1, 1.7:1, 1.8:1, 1.9:1, 2:1, 2.1:1, 2.2:1, 2.3:1, 2.4:1 or 2.5:1, and the injection control system pH of the solution B is 10 to 12, for example, 10, 10.5, 11, 11.5 or 12, but is not limited to the listed values, and other values ​​not listed within the above numerical range are also applicable.

[0030] Preferably, the temperature of the secondary coprecipitation in step (4) is 50-70°C, for example, 50°C, 55°C, 60°C, 65°C or 70°C, but is not limited to the listed values, and other values ​​not listed within the above numerical range are also applicable.

[0031] Preferably, the stirring rate of the secondary co-precipitation in step (4) is 200-400 rpm, for example, 200 rpm, 220 rpm, 250 rpm, 280 rpm, 300 rpm, 320 rpm, 350 rpm, 380 rpm or 400 rpm, but is not limited to the listed values, and other values ​​not listed within the above numerical range are also applicable.

[0032] Preferably, nitrogen is introduced as protective gas in both the first coprecipitation in step (2) and the second coprecipitation in step (4).

[0033] As a preferred technical solution of the present invention, the secondary solid-liquid separation in step (4) includes centrifugal washing.

[0034] Preferably, the drying in step (4) comprises drying in an oven.

[0035] Preferably, the drying temperature is 100-150°C, for example 100°C, 110°C, 120°C, 130°C, 140°C or 150°C, but is not limited to the listed values, and other unlisted values ​​within the above numerical range are also applicable.

[0036] Preferably, the calcination in step (4) is carried out under a nitrogen atmosphere.

[0037] Preferably, the calcination temperature in step (4) is 400-600°C, for example, 400°C, 430°C, 450°C, 480°C, 500°C, 520°C, 550°C, 570°C or 600°C, but is not limited to the listed values, and other values ​​not listed within the above numerical range are also applicable.

[0038] Preferably, the calcination time in step (4) is 2 to 3 h, for example, 2 h, 2.1 h, 2.3 h, 2.5 h, 2.7 h, 2.9 h or 3 h, but is not limited to the listed values, and other values ​​not listed within the above numerical range are also applicable.

[0039] As a preferred technical solution of the present invention, the preparation method comprises the following steps:

[0040] (1) preparing a nickel-cobalt-manganese ternary metal salt solution as solution A, wherein the molar ratio of Ni:Co:Mn in the nickel-cobalt-manganese ternary metal salt solution is 0.8:x:y; wherein 0<x<0.2, 0.8+x+y=1; the concentration of the nickel-cobalt-manganese ternary metal salt solution is 1.5-2 mol / L; and the nickel-cobalt-manganese ternary metal salt solution comprises any one of sulfate, nitrate or chloride, or a combination of at least two of them;

[0041] Prepare an inorganic strong alkali solution as solution B; the inorganic strong alkali solution is a sodium hydroxide solution or a potassium hydroxide solution, and the concentration of the inorganic strong alkali solution is 8 to 10 mol / L;

[0042] A chelating agent solution is prepared as solution C; the chelating agent solution is ammonia water or oxalic acid solution, and the concentration of the chelating agent solution is 4.5-5.5 mol / L;

[0043] (2) using solution A as a primary base liquid, introducing nitrogen as a protective gas, and injecting solution B and solution C at the same time, controlling the injection speed ratio of solution B to solution C to be 3.5-4.5:1, maintaining the temperature at 35-45° C., and stirring at a rate of 60-100 rpm, to perform a coprecipitation;

[0044] (3) After filtering, freeze-drying the solid product at -30 to -40°C for 300 to 400 minutes to obtain seed crystals;

[0045] (4) Mixing the seed crystals with water to obtain a secondary bottom liquid with a solid content of 80 to 150 g / L, introducing nitrogen as a protective gas, and injecting solution A, solution B and solution C at the same time, controlling the injection flow rate of solution A to be 20 to 40 L / h, the injection amount molar ratio of solution C to solution A to be 1.5 to 2.5:1, and the injection of solution B to regulate the reaction pH of the system to be 10 to 12, maintaining the temperature at 50 to 70° C., stirring at a rate of 200 to 400 rpm, and performing secondary coprecipitation, pumping the reaction solution into a centrifuge for centrifugal washing, drying the obtained solid product in an oven, and calcining it in an atmosphere furnace under a nitrogen atmosphere, the calcination temperature being 400 to 600° C., and the calcination time being 2 to 3 h, to obtain a core-shell positive electrode precursor.

[0046] The second object of the present invention is to provide a core-shell positive electrode precursor prepared by the preparation method described in the first object, wherein the core-shell positive electrode precursor comprises a nickel-cobalt-manganese primary particle cluster core, and a nickel-cobalt-manganese single crystal coating layer grown in situ on the outside of the nickel-cobalt-manganese primary particle cluster core; the nickel-cobalt-manganese primary particle cluster core and the nickel-cobalt-manganese single crystal coating layer have the same composition, and both are nickel-cobalt-manganese oxide.

[0047] The core-shell positive electrode precursor of the present invention, on the one hand, provides an internal buffer space for the expansion and contraction of the material through the internal porous core, thereby reducing the shedding and breakage of the positive electrode material caused by the volume change of the material outside. On the other hand, the prepared nickel cobalt manganese oxide single crystal shell inhibits the side reaction of the particles with the electrolyte, thereby reducing the cracks caused by the material strain during the charge and discharge process.

[0048] As a preferred technical solution of the present invention, the composition of the nickel-cobalt-manganese oxide is Ni 0.8 Co x Mn y O; wherein, 0<x<0.2, 0.8+x+y=1.

[0049] Preferably, the D50 particle size of the inner core of the nickel-cobalt-manganese primary particle cluster is 2 to 4 μm, for example, 2 μm, 2.3 μm, 2.5 μm, 2.7 μm, 3 μm, 3.3 μm, 3.5 μm, 3.8 μm or 4 μm, but is not limited to the listed values, and other unlisted values ​​within the above numerical range are also applicable.

[0050] Preferably, the thickness of the nickel-cobalt-manganese single crystal coating layer is 1 to 2 μm, for example, 1 μm, 1.1 μm, 1.3 μm, 1.5 μm, 1.7 μm, 1.9 μm or 2 μm, but is not limited to the listed values, and other unlisted values ​​within the above numerical range are also applicable.

[0051] The third object of the present invention is to provide an application of a core-shell positive electrode precursor, wherein the core-shell positive electrode precursor is mixed with a lithium source and applied to the preparation of a positive electrode material for a lithium-ion battery;

[0052] The core-shell positive electrode precursor is the core-shell positive electrode precursor described in the second purpose, or the core-shell positive electrode precursor is the core-shell positive electrode precursor prepared by the preparation method described in the first purpose.

[0053] Compared with the prior art solutions, the present invention has at least the following beneficial effects:

[0054] (1) The preparation method of the present invention uses solution A as a primary base solution, and injects solution B and solution C at the same time. With the addition of solution B and solution C, a cluster of primary particles is formed in the reactor by reaction, that is, the core of the nickel-cobalt-manganese primary particle cluster is first prepared by reverse feeding, and then used as a seed crystal, and then the nickel-cobalt-manganese single crystal coating layer is in situ grown on the outside of the seed crystal by forward feeding as an outer shell, which can be used to prepare a core-shell positive electrode precursor for lithium-ion batteries in a simple and efficient manner;

[0055] (2) The primary coprecipitation and the secondary coprecipitation of the preparation method of the present invention use the same nickel-cobalt-manganese ternary metal salt solution, so that the composition of the nickel-cobalt-manganese primary particle cluster core and the nickel-cobalt-manganese single crystal coating layer are the same, and the in-situ grown nickel-cobalt-manganese single crystal coating layer is tightly and firmly bonded to the nickel-cobalt-manganese primary particle cluster core;

[0056] (3) The core-shell positive electrode precursor prepared by the preparation method of the present invention, on the one hand, can be used as a buffer layer for material deformation due to the porous and fluffy inner core, reducing the generation of internal stress and providing space for lithium ion storage. On the other hand, the nickel-cobalt-manganese single crystal coating layer reduces the cracking of the material based on the consistent shrinkage and expansion of the single crystal material, inhibits the side reaction with the electrolyte, and reduces the polarization overpotential of lithium ion diffusion. The in-situ grown nickel-cobalt-manganese single crystals serve as strong and stable primary particles, which enhances the mechanical-thermal stability of the electrode. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] Figure 1 is a SEM image of the core-shell positive electrode precursor prepared in Example 1 of the present invention;

[0058] Figure 2 This is a cross-sectional SEM image of the core-shell positive electrode precursor prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0059] The technical solution of the present invention is further described below with reference to the accompanying drawings and through specific implementation methods.

[0060] To better illustrate the present invention and facilitate understanding of the technical solution of the present invention, typical but non-limiting embodiments of the present invention are as follows:

[0061] Example 1

[0062] This embodiment provides a method for preparing a core-shell positive electrode precursor, the preparation method comprising the following steps:

[0063] (1) preparing a nickel-cobalt-manganese ternary metal salt solution as solution A, wherein the molar ratio of Ni:Co:Mn in the nickel-cobalt-manganese ternary metal salt solution is 0.8:0.1:0.1; the concentration of the nickel-cobalt-manganese ternary metal salt solution is 1.8 mol / L; and the nickel-cobalt-manganese ternary metal salt solution is a sulfate solution;

[0064] An inorganic strong alkali solution is prepared as solution B; the inorganic strong alkali solution is a sodium hydroxide solution with a concentration of 8 mol / L;

[0065] A chelating agent solution is prepared as solution C; the chelating agent solution is 5 mol / L ammonia water;

[0066] (2) adding solution A as a primary bottom liquid into the reactor, introducing nitrogen as a protective gas, and injecting solution B and solution C at the same time, controlling the injection flow rate of solution B to be 10 L / h, and the injection flow rate of solution C to be 2.5 L / h, that is, controlling the injection speed ratio of solution B to solution C to be 4:1, maintaining the temperature at 35° C., and stirring at a rate of 60 rpm, performing a coprecipitation to generate a primary particle cluster flocculent;

[0067] (3) After filtering, the solid product was freeze-dried at -30°C for 360 min to obtain seed crystals;

[0068] (4) Mixing the seed crystal with water to obtain a secondary bottom liquid with a solid content of 80 g / L, introducing nitrogen as a protective gas, and injecting solution A, solution B and solution C at the same time, controlling the injection flow rate of solution A to be 20 L / h, the injection flow rate of solution C to be 14.5 L / h, the injection amount molar ratio of solution C to solution A to be 2:1, and the injection of solution B to control the reaction pH of the system to be 10, maintaining the temperature at 50°C, stirring at a rate of 200 rpm, and performing secondary co-precipitation, pumping the reaction solution into a centrifuge for centrifugal washing, drying the obtained solid product in an oven at 120°C, and calcining in an atmosphere furnace under a nitrogen atmosphere, the calcination temperature is 400°C, and the calcination time is 2h to obtain a core-shell positive electrode precursor.

[0069] Figure 1 The SEM image of the core-shell cathode precursor prepared in Example 1 is shown. It can be seen that the sample particle size is between 4 and 5 μm, and there are no cracks or fine powders, indicating that the core-shell cathode precursor is successfully prepared.

[0070] Figure 2 The cross-sectional SEM image of the core-shell cathode precursor prepared in Example 1 shows that the diameter of the core of the sample is about 2 μm and the thickness of the shell is about 1 μm. The core is porous and flocculent and is tightly connected to the shell, which is beneficial to the conductivity and ion transport of the material. The shell is a dense single crystal shell, which is beneficial to improving the strain resistance of the material.

[0071] Example 2

[0072] This embodiment provides a method for preparing a core-shell positive electrode precursor, the preparation method comprising the following steps:

[0073] (1) preparing a nickel-cobalt-manganese ternary metal salt solution as solution A, wherein the molar ratio of Ni:Co:Mn in the nickel-cobalt-manganese ternary metal salt solution is 0.8:0.1:0.1; the concentration of the nickel-cobalt-manganese ternary metal salt solution is 1.5 mol / L; and the nickel-cobalt-manganese ternary metal salt solution is a sulfate solution;

[0074] An inorganic strong alkali solution is prepared as solution B; the inorganic strong alkali solution is a sodium hydroxide solution with a concentration of 8 mol / L;

[0075] A chelating agent solution is prepared as solution C; the chelating agent solution is ammonia water with a concentration of 4.5 mol / L;

[0076] (2) adding solution A as a primary bottom liquid into the reactor, introducing nitrogen as a protective gas, and injecting solution B and solution C at the same time, controlling the injection flow rate of solution B to be 7 L / h, and the injection flow rate of solution C to be 2 L / h, that is, controlling the injection speed ratio of solution B to solution C to be 3.5:1, maintaining the temperature at 40° C., and stirring at a rate of 80 rpm, performing a coprecipitation to generate primary particle cluster floccules;

[0077] (3) After filtering, the solid product was freeze-dried at -35°C for 300 min to obtain seed crystals;

[0078] (4) Mixing the seed crystal with water to obtain a secondary bottom liquid with a solid content of 100 g / L, introducing nitrogen as a protective gas, and injecting solution A, solution B and solution C at the same time, controlling the injection flow rate of solution A to be 30 L / h, the injection flow rate of solution C to be 20 L / h, the injection amount molar ratio of solution C to solution A to be 2:1, and the injection rate of solution B to be regulated by the reaction system pH to be 11, maintaining the temperature at 60°C, stirring at a rate of 300 rpm, and performing secondary co-precipitation, pumping the reaction solution into a centrifuge for centrifugal washing, drying the obtained solid product in an oven at 120°C, and calcining in an atmosphere furnace under a nitrogen atmosphere, the calcination temperature is 500°C, and the calcination time is 2.5 h to obtain a core-shell positive electrode precursor.

[0079] Example 3

[0080] This embodiment provides a method for preparing a core-shell positive electrode precursor, the preparation method comprising the following steps:

[0081] (1) preparing a nickel-cobalt-manganese ternary metal salt solution as solution A, wherein the molar ratio of Ni:Co:Mn in the nickel-cobalt-manganese ternary metal salt solution is 0.8:0.1:0.1; the concentration of the nickel-cobalt-manganese ternary metal salt solution is 2 mol / L; and the nickel-cobalt-manganese ternary metal salt solution is a sulfate solution;

[0082] An inorganic strong alkali solution is prepared as solution B; the inorganic strong alkali solution is a sodium hydroxide solution with a concentration of 10 mol / L;

[0083] A chelating agent solution is prepared as solution C; the chelating agent solution is 5.5 mol / L ammonia water;

[0084] (2) adding solution A as a primary bottom liquid into the reactor, introducing nitrogen as a protective gas, and injecting solution B and solution C at the same time, controlling the injection flow rate of solution B to be 9 L / h, and the injection flow rate of solution C to be 2 L / h, that is, controlling the injection speed ratio of solution B to solution C to be 4.5:1, maintaining the temperature at 45° C., and stirring at a rate of 100 rpm, performing a coprecipitation to generate a primary particle cluster flocculent;

[0085] (3) After filtering, the solid product was freeze-dried at -40°C for 400 min to obtain seed crystals;

[0086] (4) Mixing the seed crystal with water to obtain a secondary bottom liquid with a solid content of 150 g / L, introducing nitrogen as a protective gas, and injecting solution A, solution B and solution C at the same time, controlling the injection flow rate of solution A to be 40 L / h, the injection flow rate of solution C to be 30 L / h, the injection amount molar ratio of solution C to solution A to be 2:1, and the injection rate of solution B to be regulated by the reaction system pH to be 12, maintaining the temperature at 70°C, stirring at a rate of 400 rpm, and performing secondary co-precipitation, pumping the reaction solution into a centrifuge for centrifugal washing, drying the obtained solid product in an oven at 120°C, and calcining in an atmosphere furnace under a nitrogen atmosphere, the calcination temperature is 600°C, and the calcination time is 3h to obtain a core-shell positive electrode precursor.

[0087] Example 4

[0088] The present embodiment provides a method for preparing a core-shell positive electrode precursor. Compared with Example 1, the only difference is that in step (2), solution B and solution C are injected simultaneously, the injection flow rate of solution B is controlled to be 9 L / h, and the injection flow rate of solution C is controlled to be 1.5 L / h, that is, the injection speed ratio of solution B to solution C is controlled to be 6:1.

[0089] Example 5

[0090] The present embodiment provides a method for preparing a core-shell positive electrode precursor. Compared with Example 1, the only difference is that in step (2), solution B and solution C are injected simultaneously, the injection flow rate of solution B is controlled to be 10 L / h, and the injection flow rate of solution C is controlled to be 5 L / h, that is, the injection speed ratio of solution B to solution C is controlled to be 2:1.

[0091] Example 6

[0092] This embodiment provides a method for preparing a core-shell positive electrode precursor. Compared with Example 1, the only difference is that in step (4), the injection of solution B regulates the reaction pH of the system to be 13.

[0093] Example 7

[0094] This embodiment provides a method for preparing a core-shell positive electrode precursor. Compared with Embodiment 1, the only difference is that in step (4), the calcination temperature is 350°C.

[0095] Comparative Example 1

[0096] This comparative example provides a method for preparing a positive electrode precursor. Compared with Example 1, the only difference is that the one-time coprecipitation to prepare the positive electrode precursor core in steps (2) and (3) is not performed. The specific contents are as follows:

[0097] Pure water, solution B and solution C are added into the reactor, the volume ratio of solution B to solution C is 4:1, the pH is adjusted to 10, and it is used as the base liquid to maintain the stability of the system. Nitrogen is introduced as a protective gas, and solution A, solution B and solution C are injected at the same time. The injection flow rate of solution A is controlled to be 20L / h, the injection flow rate of solution C is 14.5L / h, the injection amount molar ratio of solution C to solution A is 2:1, and the injection regulation system reaction pH is 10. The temperature is maintained at 50°C and the stirring rate is 200rpm. Co-precipitation is carried out, and the reaction solution is pumped into a centrifuge for centrifugal washing. The obtained solid product is dried at 120°C in an oven and calcined in a nitrogen atmosphere in an atmosphere furnace. The calcination temperature is 400°C and the calcination time is 2h to obtain a positive electrode precursor.

[0098] Comparative Example 2

[0099] This comparative example provides a method for preparing a core-shell positive electrode precursor. Compared with Example 1, the only difference is that the freeze-drying in step (3) is replaced by drying in an oven at 120°C.

[0100] The modified ternary precursor material prepared in the above embodiments and comparative examples was mixed with lithium hydroxide and sintered to obtain a positive electrode material, and the positive electrode material was prepared into a positive electrode sheet, and a lithium sheet, a lithium hexafluorophosphate electrolyte and a polyethylene separator were prepared into a lithium ion battery. The lithium ion battery was subjected to a charge and discharge test for 100 cycles at 25°C, with a voltage range of 2.75-4.6V and a current density of 1C.

[0101] The test results are shown in Table 1:

[0102] Table 1

[0103]

[0104]

[0105] From Table 1 we can see that:

[0106] The present invention can obtain a precursor material of a core-shell structure, thereby being able to obtain a battery with excellent electrochemical performance; it can be seen from Example 1 and Comparative Example 1 that the internal porous core can effectively inhibit the fragmentation caused by the volume deformation of the material during charge and discharge, thereby ensuring the cyclic stability of the material; it can be seen from Example 1 and Comparative Example 2 that the porous structure core can be better preserved by freeze drying compared with high-temperature drying; it can be seen from Example 1 and Example 4 that a high amount of alkali solution added during a single coprecipitation is not conducive to the synthesis of flocculent structure agglomerates; it can be seen from Example 1 and Example 5 that a high amount of complexing agent added during a single coprecipitation makes it difficult for the ternary metal salt to precipitate, which is not conducive to the electrochemical performance of the material; it can be seen from Example 1 and Example 6 and Example 7 that the pH and calcination temperature are not suitable when preparing the shell layer by secondary coprecipitation, which is not conducive to the formation of a single crystal structure.

[0107] The present invention illustrates the detailed structural features of the present invention through the above embodiments, but the present invention is not limited to the above detailed structural features, that is, it does not mean that the present invention must rely on the above detailed structural features to be implemented. Those skilled in the art should understand that any improvement of the present invention, equivalent replacement of the components selected by the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

[0108] The preferred embodiments of the present invention are described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, a variety of simple modifications can be made to the technical solution of the present invention, and these simple modifications all belong to the protection scope of the present invention.

[0109] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0110] In addition, various embodiments of the present invention may be arbitrarily combined, and as long as they do not violate the concept of the present invention, they should also be regarded as the contents disclosed by the present invention.

Claims

1. A method for preparing a core-shell cathode precursor, characterized in that: The preparation method comprises the following steps: (1) preparing a nickel-cobalt-manganese ternary metal salt solution as solution A, preparing an inorganic strong base solution as solution B, and preparing a chelating agent solution as solution C; wherein the concentration of the nickel-cobalt-manganese ternary metal salt solution is 1.5 to 2 mol / L; the concentration of the inorganic strong base solution is 8 to 10 mol / L; and the concentration of the chelating agent solution is 4.5 to 5.5 mol / L; (2) using solution A as a primary base solution and injecting solution B and solution C simultaneously to perform a co-precipitation; wherein the injection rate ratio of solution B to solution C is 3.5 to 4.5:1; (3) After a solid-liquid separation, the solid product is freeze-dried to obtain seed crystals; (4) Mixing the seed crystals with water to obtain a secondary bottom solution, injecting solution A, solution B and solution C simultaneously to perform secondary co-precipitation, and sequentially performing secondary solid-liquid separation, drying and calcination to obtain a core-shell positive electrode precursor.

2. The preparation method according to claim 1, characterized in that: The molar ratio of Ni:Co:Mn in the nickel-cobalt-manganese ternary metal salt solution in step (1) is 0.8:x:y; wherein 0<x<0.2, 0.8+x+y=1.

3. The preparation method according to claim 1, characterized in that: The nickel-cobalt-manganese ternary metal salt solution in step (1) includes any one of sulfate, nitrate or chloride, or a combination of at least two of them.

4. The preparation method according to claim 1, characterized in that: The inorganic strong alkali solution in step (1) is a sodium hydroxide solution or a potassium hydroxide solution.

5. The preparation method according to claim 1, characterized in that: The chelating agent solution in step (1) is aqueous ammonia or oxalic acid solution.

6. The preparation method according to claim 1, characterized in that: The temperature of the first coprecipitation in step (2) is 35-45°C.

7. The preparation method according to claim 1, characterized in that: The stirring rate of the coprecipitation in step (2) is 60-100 rpm.

8. The preparation method according to claim 1, characterized in that: The first solid-liquid separation in step (3) is filtration.

9. The preparation method according to claim 1, characterized in that: The freeze-drying temperature of step (3) is -30 to -40°C and the time is 300 to 400 minutes.

10. The preparation method according to claim 1, characterized in that: The solid content of the secondary base liquid in step (4) is 80 to 150 g / L.

11. The preparation method according to claim 1, characterized in that: In step (4), the injection flow rate of the solution A is 20 to 40 L / h, the injection amount molar ratio of the solution C to the solution A is 1.5 to 2.5:1, and the injection control system pH of the solution B is 10 to 12.

12. The preparation method according to claim 1, characterized in that: The temperature of the secondary coprecipitation in step (4) is 50-70°C.

13. The preparation method according to claim 1, characterized in that: The stirring rate of the secondary coprecipitation in step (4) is 200-400 rpm.

14. The preparation method according to claim 1, characterized in that: Nitrogen is introduced as protective gas during both the first coprecipitation in step (2) and the second coprecipitation in step (4).

15. The preparation method according to claim 1, characterized in that: The secondary solid-liquid separation in step (4) includes centrifugal washing.

16. The preparation method according to claim 1, characterized in that: The drying in step (4) includes drying in an oven; the drying temperature is 100-150°C.

17. The preparation method according to claim 1, characterized in that: The calcination in step (4) is carried out under a nitrogen atmosphere.

18. The preparation method according to claim 1, characterized in that: The calcination temperature in step (4) is 400-600°C.

19. The preparation method according to claim 1, characterized in that: The calcination time in step (4) is 2 to 3 hours.

20. The preparation method according to claim 1, characterized in that: The preparation method comprises the following steps: (1) preparing a nickel-cobalt-manganese ternary metal salt solution as solution A, wherein the molar ratio of Ni:Co:Mn in the nickel-cobalt-manganese ternary metal salt solution is 0.8:x:y; wherein 0<x<0.2, 0.8+x+y=1; the concentration of the nickel-cobalt-manganese ternary metal salt solution is 1.5-2 mol / L; and the nickel-cobalt-manganese ternary metal salt solution comprises any one of sulfate, nitrate or chloride, or a combination of at least two of them; Prepare an inorganic strong alkali solution as solution B; the inorganic strong alkali solution is a sodium hydroxide solution or a potassium hydroxide solution, and the concentration of the inorganic strong alkali solution is 8 to 10 mol / L; A chelating agent solution is prepared as solution C; the chelating agent solution is ammonia water or oxalic acid solution, and the concentration of the chelating agent solution is 4.5-5.5 mol / L; (2) using solution A as a primary base liquid, introducing nitrogen as a protective gas, and injecting solution B and solution C at the same time, controlling the injection speed ratio of solution B to solution C to be 3.5-4.5:1, maintaining the temperature at 35-45° C., and stirring at a rate of 60-100 rpm, to perform a coprecipitation; (3) After filtering, freeze-drying the solid product at -30 to -40°C for 300 to 400 minutes to obtain seed crystals; (4) Mixing the seed crystals with water to obtain a secondary bottom liquid with a solid content of 80 to 150 g / L, introducing nitrogen as a protective gas, and injecting solution A, solution B and solution C at the same time, controlling the injection flow rate of solution A to be 20 to 40 L / h, the injection amount molar ratio of solution C to solution A to be 1.5 to 2.5:1, and the injection of solution B to regulate the reaction pH of the system to be 10 to 12, maintaining the temperature at 50 to 70° C., stirring at a rate of 200 to 400 rpm, and performing secondary coprecipitation, pumping the reaction solution into a centrifuge for centrifugal washing, drying the obtained solid product in an oven, and calcining it in an atmosphere furnace under a nitrogen atmosphere, the calcination temperature being 400 to 600° C., and the calcination time being 2 to 3 h, to obtain a core-shell positive electrode precursor.

21. A core-shell cathode precursor prepared according to the preparation method according to any one of claims 1 to 20, characterized in that: The core-shell positive electrode precursor includes a nickel-cobalt-manganese primary particle cluster core and a nickel-cobalt-manganese single crystal coating layer grown in situ on the outside of the nickel-cobalt-manganese primary particle cluster core; the nickel-cobalt-manganese primary particle cluster core and the nickel-cobalt-manganese single crystal coating layer have the same composition and are both nickel-cobalt-manganese oxide.

22. The core-shell cathode precursor according to claim 21, characterized in that: The composition of the nickel-cobalt-manganese oxide is Ni 0.8 Co x Mn y O; wherein, 0<x<0.2, 0.8+x+y=1.

23. The core-shell cathode precursor according to claim 21, characterized in that: The D50 particle size of the inner core of the nickel-cobalt-manganese primary particle cluster is 2 to 4 μm.

24. The core-shell cathode precursor according to claim 21, characterized in that: The thickness of the nickel-cobalt-manganese single crystal coating layer is 1 to 2 μm.

25. An application of a core-shell cathode precursor, characterized in that: The core-shell cathode precursor is mixed with a lithium source and applied to the preparation of cathode materials for lithium-ion batteries; The core-shell positive electrode precursor is the core-shell positive electrode precursor according to any one of claims 21 to 24, or the core-shell positive electrode precursor is the core-shell positive electrode precursor prepared by the preparation method according to any one of claims 1 to 20.

Images