Precursor having porous isolation layer, positive electrode material, and preparation therefor and use thereof

Abstract

Provided in the present application are a precursor having a porous isolation layer, a positive electrode material, and the preparation therefor and the use thereof. The precursor comprises an inner core, a porous isolation layer covering the inner core, and an outer shell covering the porous isolation layer. The porosity of the porous isolation layer is higher than the porosities of the inner core and the outer shell. The precursor provided by the present application has the porous isolation layer, which blocks the propagation of micro-cracks and provides more space for release of stress built-up by volume expansion / contraction during deep charge and discharge processes, thereby ensuring that a positive electrode material prepared by the precursor has a stable structure and shape during cycle processes, and improving the cycle performance of batteries containing the positive electrode material prepared from the precursor.

Description

Precursor with porous isolation layer, positive electrode material and preparation and application thereof TECHNICAL FIELD

[0001] The present application belongs to the technical field of batteries, and relates to a precursor with a porous isolation layer, in particular to a precursor with a porous isolation layer, a positive electrode material and preparation and application thereof. BACKGROUND

[0002] With the rapid growth of demand for lithium ion batteries in consumer electronics, power batteries and energy storage fields, the price of lithium resources has been running high for a long time, and the supply has become increasingly tight, which has a profound impact on the normal development of the industry. The limited reserves and uneven distribution of lithium resources make it difficult for lithium ion batteries to meet the rapidly growing application demand. Compared with lithium resources, sodium resources are abundant in the earth's crust and oceans, widely distributed and low in cost, and sodium ion batteries have broad application potential in small power and large-scale energy storage. In addition, although the energy density is relatively low, sodium ion batteries have certain advantages in cost, safety, rate performance and low-temperature performance. Under this background, as an alternative to lithium ion batteries, the development of sodium ion batteries has very important economic value and strategic significance.

[0003] Sodium ion battery transition metal layered oxide positive electrode materials have excellent comprehensive performance and outstanding commercial prospects. Currently, the generation of microcracks during charging and discharging is a major technical challenge for the industrialization of sodium ion battery positive electrode materials. During the charging and discharging cycle, due to the embedding and extraction of Na + of large radius, the shrinkage in the c-axis direction causes uneven stress distribution within the secondary particles. When the stress accumulation exceeds the yield limit of the particles, cracks are generated between the grain boundaries. With the cycle, the cracks gradually extend from the inside to the surface of the secondary particles, and even make the particles pulverize. The formation of microcracks allows the electrolyte to enter the particle interior, and then a new solid-liquid side reaction interface is formed in the particle interior, which not only consumes the electrolyte and active material, but also forms an electron and ion isolated region in the particle interior, further increasing the impedance and deteriorating the electrochemical performance of the material.

[0004] CN112928250A discloses a nickel-cobalt-manganese ternary material, a precursor thereof and a preparation method and application thereof. The composition of the nickel-cobalt-manganese ternary material precursor is represented by Ni x Co y Mn (1-x-y) (OH)2, wherein 0.30 < x < 0.85, 0.05 < y < 0.35, and 0 < x + y < 1; the nickel-cobalt-manganese ternary material precursor comprises, from the inside to the outside, a core, a dense layer, a dense layer connecting layer and an outer shell, the core and the dense layer connecting layer both have a loose structure, and the dense layer and the outer shell both have a dense structure.

[0005] CN111732132A discloses a nickel-cobalt-manganese core-shell structure precursor and a preparation method thereof. The inner core of the precursor is dense and has pores; the outer shell is loose, and the primary particles are arranged radially on the inner core. The precursor structure is beneficial to the diffusion of Li ions and the infiltration of electrolyte in the lithium mixing sintering process, and provides a rapid migration channel for Li ions in the charging and discharging process, and meets the requirements of tap density and porous structure.

[0006] The precursors of the positive electrode materials disclosed in the prior art have certain defects. The batteries containing the positive electrode materials prepared from the precursors are prone to produce microcracks in the charging and discharging process. The microcracks can cause the pulverization of the positive electrode materials, increase the solid-liquid reaction interface, and also form an area isolated from electrons and ions, thereby reducing the electrochemical performance of the batteries. Therefore, it is crucial to develop and design a new type of precursor, a positive electrode material and a preparation method. SUMMARY

[0007] 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.

[0008] In view of the deficiencies in the prior art, the purpose of the present application is to provide a precursor with a porous isolation layer, a positive electrode material and a preparation and application. The precursor with a porous isolation layer provided by the present application has a porous isolation layer. The porous isolation layer blocks the propagation of microcracks, provides more space to release the stress accumulated by volume expansion / contraction in the deep charging and discharging process, ensures that the positive electrode material prepared from the precursor has a stable structure and appearance in the cycling process, and improves the cycling performance of the battery containing the positive electrode material prepared from the precursor.

[0009] To achieve this purpose, the following technical solutions are adopted in the present application:

[0010] In a first aspect, the present application provides a precursor with a porous isolation layer. The precursor includes an inner core, a porous isolation layer coated outside the inner core, and an outer shell coated outside the porous isolation layer. The porosity of the porous isolation layer is higher than the porosities of the inner core and the outer shell.

[0011] The precursor with a porous isolation layer provided by the present application has a porous isolation layer. The porous isolation layer blocks the propagation of microcracks, provides more space to release the stress accumulated by volume expansion / contraction in the deep charging and discharging process, ensures that the positive electrode material prepared from the precursor has a stable structure and appearance in the cycling process, and improves the cycling performance of the battery containing the positive electrode material prepared from the precursor.

[0012] In one embodiment, the porosity of the inner core is 2-4%, for example, it can be 2%, 2.2%, 2.4%, 2.6%, 2.8%, 3%, 3.2%, 3.4%, 3.6%, 3.8% or 4%, but not limited to the listed values, other values not listed in the range are also applicable.

[0013] In one embodiment, the porosity of the outer shell is 2-4%, for example, it can be 2%, 2.2%, 2.4%, 2.6%, 2.8%, 3%, 3.2%, 3.4%, 3.6%, 3.8% or 4%, but not limited to the listed values, other values not listed in the range are also applicable.

[0014] In one embodiment, the porosity of the porous isolation layer is 5-10%, for example, it can be 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5% or 10%, but not limited to the listed values, other values not listed in the range are also applicable.

[0015] In one embodiment, the thickness of the porous isolation layer is 1-3 μm, for example, it can be 1 μm, 1.5 μm, 1.8 μm, 2 μm, 2.2 μm, 2.5 μm, 2.8 μm or 3 μm, but not limited to the listed values, other values not listed in the range are also applicable.

[0016] In one embodiment, the inner core is composed of NiFeMn(OH)2with a layered structure;

[0017] In one embodiment, the outer shell is composed of NiFeMn(OH)2with a layered structure;

[0018] In one embodiment, the components in the porous isolation layer include NiFeMn(OH)2with a layered structure, and further include any one of Zn(OH)2with an amorphous structure, Cu(OH)2with an orthorhombic system (Cmc21) or Ti(OH)4with an amorphous structure, or a combination of at least two of them.

[0019] In a second aspect, the application provides a preparation method of the precursor of the first aspect, the preparation method comprising:

[0020] (1) adding a first mixed salt solution, a precipitant solution and a complexing agent solution into a reaction base solution in parallel to perform a co-precipitation reaction to obtain a mixed solution containing a first precipitate;

[0021] (2) adding a second mixed salt solution, a precipitant solution and a complexing agent solution into the mixed solution containing the first precipitate obtained in step (1) in parallel flow to perform a co-precipitation reaction to obtain a mixed solution containing a second precipitate;

[0022] The second mixed salt solution comprises a doped metal ion and all the metal ions in the first mixed salt solution.

[0023] (3) adding the first mixed salt solution, the precipitant solution and the complexing agent solution into the mixed solution containing the second precipitate obtained in step (2) in parallel flow to perform a co-precipitation reaction to obtain the precursor.

[0024] The inner core obtained in step (1) has high density and good crystallinity; the second mixed salt solution in step (2) further comprises a doped metal ion, which produces more dislocations and crystal plane defects in the crystal growth process during the precipitation process, and a porous isolation layer with high porosity is obtained; and the outer shell obtained in step (3) has high density and good crystallinity. The precursor prepared by the preparation method has high density of the inner core and the outer shell and low density of the porous isolation layer between the inner core and the outer shell, which relieves the micro-cracks caused by the embedding and extraction of sodium ions during the charging and discharging process, and significantly improves the cycle performance of the positive electrode material prepared from the precursor.

[0025] The preparation method provided by the application has simple preparation process and strong universality. Only the feeding pipe of the mixed salt solution needs to be replaced during the production process, which is simple to operate and avoids additional processes, thereby avoiding the addition of additional dopants and having high-efficiency large-scale production prospects.

[0026] In one embodiment, the doped metal ion in step (2) satisfies a first condition and / or a second condition.

[0027] The first condition is that the difference between the precipitation constant of the doped metal ion and the precipitation constant of all the metal ions in the first mixed salt solution is not less than 10 3 .

[0028] The second condition is that the crystal structure of the substance formed after the precipitation of the doped metal ion is different from the crystal structure of the substance formed after the precipitation of all the metal ions in the first mixed salt solution.

[0029] In the first condition, the difference between the precipitation constant of the doped metal ion and the precipitation constant of all the metal ions in the first mixed salt solution is not less than 1×10 3 , i.e., the difference between the precipitation constant of the doped metal ion and the precipitation constant of Ni ion, Fe ion and Mn ion is not less than 1×10 3 , for example, 1×10 3 , 1.1×103 1.2 x 10 3 1.3 x 10 3 1.4 x 10 3 1.5 x 10 3 1.6 x 10 3 1.7 x 10 3 1.8 x 10 3 1.9 x 10 3 2 x 10 3 2.5 x 10 3 or 3 x 10 3 but are not limited to the recited values, other non-recited values within the range are also applicable.

[0030] The crystal structure of the substance formed after the doping metal ion is precipitated in the second condition of the application is different from the crystal structure of the substance formed after all the metal ions in the first mixed salt solution are precipitated, that is, the crystal structure of the substance formed after the doping metal ion is precipitated is different from the crystal structure of the substance formed after the Ni ion, the Fe ion and the Mn ion are precipitated alone or co-precipitated.

[0031] If the precipitation constant of the doping metal ion and the metal ion in the first mixed salt solution is small, and the crystal structure of the precipitate after precipitation is consistent, then the crystallization growth process is more sufficient, and a structure with high density and good crystallinity will be obtained after co-precipitation; if the precipitation constant of the doping metal ion and the metal ion in the first mixed salt solution has a certain gap, or the crystal structure of the precipitate after precipitation is inconsistent, then more dislocations and crystal plane defects will be produced in the crystallization growth process, and a structure with high porosity will be obtained.

[0032] The doping metal ion in the second mixed salt solution in step (2) of the preparation method described in the application meets the first condition and / or the second condition, and more dislocations and crystal plane defects will be produced in the crystallization growth process of the precipitate in step (2), so that a porous isolation layer with high porosity is formed outside the core.

[0033] In one embodiment, the addition speed of the second mixed salt solution, the precipitant solution and the complexing agent solution in step (2) is higher than the addition speed of the first mixed salt solution, the precipitant solution and the complexing agent solution in steps (1) and (3).

[0034] The preparation method provided in the application improves the flow rate of the metal salt solution, the precipitant and the complexing agent in step (2) for preparing the porous isolation layer, thereby improving the growth speed of the precipitate crystal, disturbing the ordered lattice structure arrangement mode, and promoting the generation of the porous isolation layer.

[0035] In one embodiment, the second mixed salt solution in step (2) is added at a rate of 40 to 80 L / h, for example, it can be 40 L / h, 45 h, 50 h, 55 h, 60 h, 65 h, 70 h, 75 / h or 80 h, but not limited to the listed values, other values not listed in the range of values are also applicable.

[0036] In one embodiment, the precipitant solution in step (2) is added at a rate of 15 to 25 L / h, for example, it can be 15 L / h, 16 L / h, 17 L / h, 18 L / h, 19 L / h, 20 L / h, 21 L / h, 22 L / h, 23 L / h, 24 L / h or 25 L / h, but not limited to the listed values, other values not listed in the range of values are also applicable.

[0037] In one embodiment, the complexing agent solution in step (2) is added at a rate of 2 to 4 L / h, for example, it can be 2 L / h, 2.2 L / h, 2.4 L / h, 2.6 L / h, 2.8 L / h, 3 L / h, 3.2 L / h, 3.4 L / h, 3.6 L / h, 3.8 L / h or 4 L / h, but not limited to the listed values, other values not listed in the range of values are also applicable.

[0038] In one embodiment, the first mixed salt solution in step (1) and step (3) is added at a rate of 10 to 40 L / h, for example, it can be 10 L / h, 12 L / h, 15 L / h, 17 L / h, 20 L / h, 22 L / h, 25 L / h, 27 L / h, 30 L / h, 32 L / h, 35 L / h, 37 L / h or 40 L / h, but not limited to the listed values, other values not listed in the range of values are also applicable.

[0039] In one embodiment, the precipitant solution in step (1) and step (3) is added at a rate of 5 to 15 L / h, for example, it can be 5 L / h, 6 L / h, 7 L / h, 8 L / h, 9 L / h, 10 L / h, 11 L / h, 12 L / h, 13 L / h, 14 L / h or 15 L / h, but not limited to the listed values, other values not listed in the range of values are also applicable.

[0040] In one embodiment, the complexing agent solution in step (1) and step (3) is added at a rate of 0.5 to 1.5 L / h, for example, it can be 0.5 L / h, 0.6 L / h, 0.7 L / h, 0.8 L / h, 0.9 L / h, 1 L / h, 1.1 L / h, 1.2 L / h, 1.3 L / h, 1.4 L / h or 1.5 L / h, but not limited to the listed values, other values not listed in the range of values are also applicable.

[0041] In one embodiment, the temperature for performing the co-precipitation reaction in steps (1)-(3) is 50-70 °C, and the stirring speed is 200-400 rpm, and the pH is 9-11.

[0042] The temperature for performing the co-precipitation reaction in steps (1)-(3) is 50-70 °C, for example, it can be 50 °C, 52 °C, 54 °C, 56 °C, 58 °C, 60 °C, 62 °C, 64 °C, 66 °C, 68 °C, or 70 °C, but is not limited to the listed values, and other values not listed in this range are also applicable.

[0043] The stirring speed for performing the co-precipitation reaction in steps (1)-(3) is 200-400 rpm, for example, it can be 200 rpm, 220 rpm, 240 rpm, 260 rpm, 280 rpm, 300 rpm, 320 rpm, 340 rpm, 360 rpm, 380 rpm, or 400 rpm, but is not limited to the listed values, and other values not listed in this range are also applicable.

[0044] The pH for performing the co-precipitation reaction in steps (1)-(3) is 9-11, for example, it can be 9, 9.2, 9.4, 9.6, 9.8, 10, 10.2, 10.4, 10.6, 10.8, or 11, but is not limited to the listed values, and other values not listed in this range are also applicable.

[0045] In one embodiment, the first mixed salt solution in steps (1) and (3) is a nickel-iron-manganese mixed salt solution; the doping metal ions in step (2) include any one or a combination of at least two of Zn ions, Cu ions, or Ti ions, and a typical but non-limiting combination includes a combination of Zn ions and Cu ions, a combination of Cu ions and Ti ions, or a combination of Zn ions, Cu ions, and Ti ions.

[0046] In one embodiment, the total concentration of metal ions in the first mixed salt solution in steps (1)-(3) is 0.5-2.0 mol / L, for example, it can be 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1 mol / L, 1.1 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L, 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 in this range are also applicable.

[0047] In one embodiment, the mole amount of the doping metal ion is no more than 5%, such as 1%, 2%, 3%, 4%, or 5%, but not limited to the listed values, and other values not listed in the range are also applicable, based on 100% of the mole amount of all metal ions in the second mixed salt solution of step (2).

[0048] In one embodiment, the nickel salt, the iron salt, and the manganese salt in the first mixed salt solution of steps (1) and (3) each independently comprises any one or a combination of at least two of a sulfate salt, a nitrate salt, or a chloride, typically but not limited to a combination of a sulfate salt and a nitrate salt, a combination of a nitrate salt and a chloride, or a combination of a sulfate salt, a nitrate salt, and a chloride; and the doping metal ion salt in the second mixed salt solution of step (2) comprises any one or a combination of at least two of a sulfate salt, a nitrate salt, or a chloride, typically but not limited to a combination of a sulfate salt and a nitrate salt, a combination of a nitrate salt and a chloride, or a combination of a sulfate salt, a nitrate salt, and a chloride.

[0049] In one embodiment, the precipitant solution in steps (1) to (3) comprises a NaOH solution and / or a KOH solution.

[0050] In one embodiment, the concentration of the precipitant solution in steps (1) to (3) is 6 to 10 mol / L, such as 6 mol / L, 6.5 mol / L, 7 mol / L, 7.5 mol / L, 8 mol / L, 8.5 mol / L, 9 mol / L, 9.5 mol / L, or 10 mol / L, but not limited to the listed values, and other values not listed in the range are also applicable.

[0051] In one embodiment, the complexing agent solution in steps (1) to (3) comprises an ammonia solution and / or a sodium citrate solution.

[0052] In one embodiment, the concentration of the complexing agent solution in steps (1) to (3) is 0.2 to 1 mol / L, such as 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, or 1 mol / L, but not limited to the listed values, and other values not listed in the range are also applicable.

[0053] In one embodiment, steps (1) to (3) are each performed in a protective atmosphere.

[0054] In one embodiment, the first precipitate obtained in step (1) has a D50 particle size of 4-6 μm, for example, 4 μm, 4.2 μm, 4.4 μm, 4.6 μm, 4.8 μm, 5 μm, 5.2 μm, 5.4 μm, 5.6 μm, 5.8 μm or 6 μm, but not limited to the listed values, and other values not listed in the range are also applicable.

[0055] In one embodiment, the second precipitate obtained in step (2) has a D50 particle size of 6-8 μm, for example, 6 μm, 6.2 μm, 6.4 μm, 6.6 μm, 6.8 μm, 7 μm, 7.2 μm, 7.4 μm, 7.6 μm, 7.8 μm or 8 μm, but not limited to the listed values, and other values not listed in the range are also applicable.

[0056] The difference between the D50 particle size of the second precipitate and the D50 particle size of the first precipitate is the thickness of the porous isolation layer.

[0057] In one embodiment, the precursor obtained in step (3) has a D50 particle size of 8-10 μm, for example, 8 μm, 8.2 μm, 8.4 μm, 8.6 μm, 8.8 μm, 9 μm, 9.2 μm, 9.4 μm, 9.6 μm, 9.8 μm or 10 μm, but not limited to the listed values, and other values not listed in the range are also applicable.

[0058] In one embodiment, the co-precipitation reaction in step (3) is followed by sequentially performing centrifugation, washing, drying and demagnetization.

[0059] In a third aspect, the application provides a positive electrode material, which is prepared from the precursor of the first aspect.

[0060] In a fourth aspect, a preparation process of the positive electrode material of the third aspect, the preparation process comprises:

[0061] Mixing the precursor and a sodium source, and sintering to obtain the positive electrode material.

[0062] In one embodiment, the sodium source comprises Na2CO3 and / or NaOH.

[0063] In one embodiment, the sintering temperature is 800-900 °C, and the time is 10-20 h.

[0064] The sintering temperature in the present application is 800-900 DEG C, for example, it can be 800 DEG C, 810 DEG C, 820 DEG C, 830 DEG C, 840 DEG C, 850 DEG C, 860 DEG C, 870 DEG C, 880 DEG C, 890 DEG C or 900 DEG C, but not limited to the listed values, other values not listed in the range are also applicable.

[0065] The sintering time in the present application is 10-20h, for example, it can be 10h, 11h, 12h, 13h, 14h, 15h, 16h, 17h, 18h, 19h or 20h, but not limited to the listed values, other values not listed in the range are also applicable.

[0066] Compared with the prior art, the present application has the following beneficial effects:

[0067] (1) The precursor provided by the present application has a porous isolation layer, which blocks the propagation of microcracks and provides more space to release the stress accumulated by volume expansion / contraction during deep charge and discharge process, ensuring that the positive electrode material prepared from the precursor has a stable structure and appearance during the cycle process, and improving the cycle performance of the battery containing the positive electrode material prepared from the precursor;

[0068] (2) The preparation method provided by the present application has prepared a precursor with high density of core and shell and low density of porous isolation layer between the core and the shell, which alleviates the generation of microcracks caused by sodium ion insertion and extraction during charging and discharging, and significantly improves the cycle performance of the positive electrode material prepared from the precursor;

[0069] (3) The preparation method provided by the present application has simple preparation process and strong universality, only the feeding pipe of mixed salt solution needs to be replaced during production, the operation is simple, and additional process is avoided, thereby avoiding the addition of additional dopant, and having high efficiency and large-scale production prospect.

[0070] Other aspects can be apparent after reading and understanding the drawings and detailed description. BRIEF DESCRIPTION OF DRAWINGS

[0071] The accompanying drawings are used to provide further understanding of the technical solutions herein, and constitute a part of the specification, and together with the embodiments of the present application, are used to explain the technical solutions herein, and do not constitute a limitation on the technical solutions herein.

[0072] Fig. 1 is a structure schematic diagram of the precursor with porous isolation layer provided by the embodiment 1 of the present application.

[0073] Fig. 2 is an EPMA diagram of the precursor with porous isolation layer provided by the embodiment 1 of the present application.

[0074] Wherein, 1 - inner core; 2 - porous isolation layer; 3 - outer shell. DETAILED DESCRIPTION

[0075] The technical solutions of the present application are further illustrated by specific embodiments. Those skilled in the art should understand that the embodiments are only to help understand the present application and should not be regarded as specific limitations of the present application.

[0076] Embodiment 1

[0077] The present embodiment provides a precursor with a porous isolation layer 2 as shown in FIG. 1 and FIG. 2, the precursor comprising an inner core 1 with a porosity of 3%, a porous isolation layer 2 with a porosity of 8% coated outside the inner core 1, and an outer shell 3 with a porosity of 3% coated outside the porous isolation layer 2, the porosity of the porous isolation layer 2 being higher than the porosities of the inner core 1 and the outer shell 3.

[0078] The inner core 1 is composed of NiFeMn(OH)2 with a layered structure;

[0079] The outer shell 3 is composed of NiFeMn(OH)2 with a layered structure;

[0080] The components in the porous isolation layer 2 include NiFeMn(OH)2 with a layered structure, and also include Zn(OH)2 with an amorphous structure.

[0081] The preparation method of the precursor is as follows:

[0082] (1) Under a nitrogen atmosphere, a nickel-iron-manganese mixed salt solution (molar ratio of nickel ions, iron ions and manganese ions is 1:1:1) with a total concentration of metal ions of 1 mol / L, a sodium hydroxide solution and ammonia water are added to the reaction bottom liquid in parallel, the addition speed of the nickel-iron-manganese mixed salt solution is 25 L / h, and a coprecipitation reaction is carried out at 60°C, a stirring speed of 300 rpm and a pH of 10, to obtain a mixed liquid containing a first precipitate with a D50 particle size of 6 μm;

[0083] (2) Under a nitrogen atmosphere, a second mixed salt solution with a total concentration of metal ions of 1 mol / L, a sodium hydroxide solution and ammonia water are added to the mixed liquid containing the first precipitate obtained in step (1) in parallel, the addition speed of the second mixed salt solution is 60 L / h, and a coprecipitation reaction is carried out at 60°C, a stirring speed of 300 rpm and a pH of 10, to obtain a mixed liquid containing a second precipitate with a D50 particle size of 7 μm;

[0084] The second mixed salt solution comprises zinc ions, and further comprises nickel ions, iron ions and manganese ions; the molar percentage of the zinc ions in the second mixed salt solution is 4%, and the molar ratio of the nickel ions, the iron ions and the manganese ions in the second mixed salt solution is 1:1:1; the amorphous structure of Zn(OH)2 formed after the zinc ions are precipitated is different from the crystal structure of the substance formed after all the metal ions in the first mixed salt solution are precipitated.

[0085] (3) Under a nitrogen atmosphere, a nickel-iron-manganese mixed salt solution (the molar ratio of nickel ions, iron ions and manganese ions is 1:1:1) with a total concentration of metal ions of 1 mol / L, a sodium hydroxide solution and ammonia water are added into the mixed solution containing the second precipitate obtained in step (2) in parallel flow, the addition speed of the nickel-iron-manganese mixed salt solution is 25 L / h, and a coprecipitation reaction is carried out at 60°C, a stirring speed of 300 rpm and a pH of 10 to obtain the precursor with a D50 particle size of 9 μm.

[0086] Example 2

[0087] The present embodiment provides a precursor with a porous isolation layer 2, which comprises an inner core 1 with a porosity of 2%, a porous isolation layer 2 with a porosity of 5% coated outside the inner core 1, and an outer shell 3 with a porosity of 2% coated outside the porous isolation layer 2, the porosity of the porous isolation layer 2 being higher than the porosities of the inner core 1 and the outer shell 3.

[0088] The inner core 1 is composed of NiFeMn(OH)2 with a layered structure.

[0089] The outer shell 3 is composed of NiFeMn(OH)2 with a layered structure.

[0090] The components in the porous isolation layer 2 comprise NiFeMn(OH)2 with a layered structure, and further comprise Cu(OH)2 with an orthorhombic system (Cmc21).

[0091] The preparation method of the precursor is as follows:

[0092] (1) Under an argon atmosphere, a nickel-iron-manganese mixed salt solution (the molar ratio of nickel ions, iron ions and manganese ions is 1:1:1) with a total concentration of metal ions of 0.5 mol / L, a potassium hydroxide solution and a sodium citrate solution are added into a reaction bottom solution in parallel flow, the addition speed of the nickel-iron-manganese mixed salt solution is 10 L / h, and a coprecipitation reaction is carried out at 70°C, a stirring speed of 400 rpm and a pH of 11 to obtain a mixed solution containing a first precipitate with a D50 particle size of 5 μm.

[0093] (2) under an argon atmosphere, a second mixed salt solution with a total concentration of metal ions of 0.5 mol / L, a potassium hydroxide solution and a sodium citrate solution are added to the mixed solution containing the first precipitate obtained in step (1) in a concurrent manner, the second mixed salt solution is added at a speed of 40 L / h, and a co-precipitation reaction is carried out at 70℃, a stirring speed of 400 rpm and a pH of 11 to obtain a mixed solution containing a second precipitate with a D50 particle size of 6 μm;

[0094] The second mixed salt solution comprises copper ions, and further comprises nickel ions, iron ions and manganese ions; the molar percentage of the copper ions in the second mixed salt solution is 2% based on 100% of the total molar amount of all metal ions in the second mixed salt solution, and the molar ratio of the nickel ions, the iron ions and the manganese ions in the second mixed salt solution is 1:1:1; the copper ions form Cu(OH)2 with an orthorhombic crystal system (Cmc21) after precipitation, which is different from the crystal structure of the substance formed after the precipitation of all metal ions in the first mixed salt solution;

[0095] (3) under an argon atmosphere, a nickel-iron-manganese mixed salt solution (the molar ratio of nickel ions, iron ions and manganese ions is 1:1:1) with a total concentration of metal ions of 0.5 mol / L, a potassium hydroxide solution and a sodium citrate solution are added to the mixed solution containing the second precipitate obtained in step (2) in a concurrent manner, the nickel-iron-manganese mixed salt solution is added at a speed of 10 L / h, and a co-precipitation reaction is carried out at 70℃, a stirring speed of 400 rpm and a pH of 11 to obtain the precursor with a D50 particle size of 8 μm.

[0096] Example 3

[0097] The present embodiment provides a precursor with a porous isolation layer 2, which comprises an inner core 1 with a porosity of 4%, a porous isolation layer 2 coated outside the inner core 1 with a porosity of 10%, and an outer shell 3 coated outside the porous isolation layer 2 with a porosity of 4%, the porosity of the porous isolation layer 2 being higher than the porosities of the inner core 1 and the outer shell 3.

[0098] The inner core 1 is composed of NiFeMn(OH)2 with a layered structure;

[0099] The outer shell 3 is composed of NiFeMn(OH)2 with a layered structure;

[0100] The components in the porous isolation layer 2 comprise NiFeMn(OH)2 with a layered structure, and further comprise Ti(OH)4 with an amorphous structure.

[0101] The preparation method of the precursor is as follows:

[0102] (1) under an argon atmosphere, a mixed salt solution of nickel, iron and manganese with a total concentration of 2.0 mol / L (the molar ratio of nickel ions, iron ions and manganese ions is 1:1:1), a sodium hydroxide solution and ammonia water were added to the reaction liquid in parallel, the addition rate of the mixed salt solution was 40 L / h, and a coprecipitation reaction was carried out at 50℃, a stirring speed of 200 rpm and a pH of 9 to obtain a mixed liquid containing a first precipitate with a D50 particle size of 6 μm;

[0103] (2) under an argon atmosphere, a second mixed salt solution with a total concentration of 2.0 mol / L, a sodium hydroxide solution and ammonia water were added to the mixed liquid containing the first precipitate obtained in step (1) in parallel, the addition rate of the second mixed salt solution was 80 L / h, and a coprecipitation reaction was carried out at 50℃, a stirring speed of 200 rpm and a pH of 9 to obtain a mixed liquid containing a second precipitate with a D50 particle size of 7 μm;

[0104] The second mixed salt solution comprises titanium ions, and also comprises nickel ions, iron ions and manganese ions; the molar amount of the doping metal ions accounts for 5% of 100% of the molar amount of all metal ions in the second mixed salt solution, and the molar ratio of nickel ions, iron ions and manganese ions in the second mixed salt solution is 1:1:1; the titanium ions form Ti(OH)4 with an amorphous structure after precipitation, which is different from the crystal structure of the substance formed after the precipitation of all metal ions in the first mixed salt solution;

[0105] (3) under an argon atmosphere, a mixed salt solution of nickel, iron and manganese with a total concentration of 2.0 mol / L (the molar ratio of nickel ions, iron ions and manganese ions is 1:1:1), a sodium hydroxide solution and ammonia water were added to the mixed liquid containing the second precipitate obtained in step (2) in parallel, the addition rate of the mixed salt solution was 40 L / h, and a coprecipitation reaction was carried out at 50℃, a stirring speed of 200 rpm and a pH of 9 to obtain the precursor with a D50 particle size of 10 μm.

[0106] Example 4

[0107] This example provides a precursor with a porous isolation layer 2, wherein the porosity of the porous isolation layer 2 is 4%, i.e., the addition rate of the second mixed salt solution in step (2) of the preparation method of the precursor is 25 L / h, and the rest is the same as in Example 1.

[0108] Example 5

[0109] This example provides a precursor with a porous isolation layer 2, wherein the porosity of the porous isolation layer 2 is 15%, i.e., the addition rate of the second mixed salt solution in step (2) of the preparation method of the precursor is 100 L / h, and the rest is the same as in Example 1.

[0110] Example 6

[0111] This example provides a precursor with a porous isolation layer 2, which is the same as example 1 except that the thickness of the porous isolation layer 2 is 0.5 μm.

[0112] Example 7

[0113] This example provides a precursor with a porous isolation layer 2, which is the same as example 1 except that the thickness of the porous isolation layer 2 is 4 μm.

[0114] Comparative Example 1

[0115] This comparative example provides a precursor, which is the same as example 1 except that the porosity of the precursor is 3% from inside to outside and no special porous isolation layer 2 is constructed, i.e., the second mixed salt solution in step (2) is replaced by the nickel-iron-manganese mixed salt solution in step (1).

[0116] The precursors provided in the above examples and comparative examples are mixed with Na2CO3, sintered at 850°C for 15 h to obtain positive electrode materials; the prepared positive electrode materials, conductive carbon black and binder PVDF are weighed according to a mass ratio of 7.5:1.5:1, and the above materials are uniformly dispersed in N-methyl pyrrolidone (NMP) to prepare conductive slurry. Then, the conductive slurry is coated on an aluminum foil, dried at 70°C, cut and weighed. The battery type is a button cell, the model is CR2032, the separator is glass fiber, the negative electrode is a sodium metal sheet, and the electrolyte is 1M NaPF6 EC / DMC = 1:1. The half battery is assembled in the order of sodium metal sheet, separator, positive electrode sheet, gasket and spring sheet in an Ar-filled glove box. The specific capacity of the prepared CR2032 button-type half battery is tested in a voltage window of 2.0 to 4.1 V, the first cycle is tested according to 0.1C / 0.1C charge-discharge, and then 0.5C / 1C is cycled for 50 cycles. The cycle stability is represented by the percentage of the 50th cycle discharge capacity divided by the first cycle discharge capacity. The test results are shown in Table 1:

[0117] Table 1

[0118] From Table 1, it can be seen that:

[0119] (1) The positive electrode materials are prepared from the precursors prepared in examples 1-3 of the present application, and the sodium ion batteries prepared from the obtained positive electrode materials all exhibit high capacity retention rates after 300 cycles at 1C and 5C, and the batteries containing the positive electrode materials prepared from the precursors have excellent cycle performance;

[0120] (2) By comparing Example 1 with Examples 4 and 5, it can be seen that the porosity of the core 1 in the present application affects the performance of the precursor and the sodium-ion battery; when the porosity of the porous isolation layer 2 is too low, the capacity retention rate of 50 cycles will be low, because the porosity of the porous isolation layer 2 is similar to that of the core 1 and the shell 3, which cannot effectively block the propagation of micro-cracks, nor can it provide more space to release the stress accumulated in the volume expansion / contraction process, thereby it is difficult to improve the cycle performance of the battery containing the positive electrode material prepared from the precursor;

[0121] (3) By comparing Example 1 with Examples 6 and 7, it can be seen that the thickness of the porous isolation layer 2 in the present application affects the performance of the precursor and the sodium-ion battery; when the thickness of the porous isolation layer 2 is too small, the capacity retention rate of 50 cycles will be low, because the porous isolation layer 2 with too small thickness cannot effectively block the propagation of micro-cracks, nor can it provide more space to release the stress accumulated in the volume expansion / contraction process, thereby it is difficult to improve the cycle performance of the battery containing the positive electrode material prepared from the precursor; when the thickness of the porous isolation layer 2 is too large, the capacity retention rate will also decrease, because the too thick porous isolation layer 2 causes more active surfaces of the positive electrode material to contact with the electrolyte, the side reaction increases, and the cycle performance decreases;

[0122] (4) By comparing Example 1 with Comparative Example 1, it can be seen that the precursor provided in the present application has a porous isolation layer 2, the porosity of the porous isolation layer 2 is higher than that of the core 1 and the shell 3, the porous isolation layer 2 effectively blocks the propagation of micro-cracks, provides more space to release the stress accumulated in the volume expansion / contraction process, ensures that the positive electrode material prepared from the precursor has a stable structure and shape during the cycle process, and improves the cycle performance of the battery containing the positive electrode material prepared from the precursor.

[0123] The above merely provides a specific implementation of the present application, but the protection scope of the present application is not limited thereto, and those skilled in the art should understand that any changes or replacements within the technical scope disclosed in the present application, which can be easily thought of by those skilled in the art, all fall within the protection scope and disclosure scope of the present application.

Claims

1. A precursor with a porous isolation layer, comprising an inner core, a porous isolation layer coated outside the inner core, and an outer shell coated outside the porous isolation layer, the porosity of the porous isolation layer being higher than the porosities of the inner core and the outer shell.

2. The precursor of claim 1, wherein, The porosity of the inner core is 2-4%; Optionally, the porosity of the outer shell is 2-4%; Optionally, the porosity of the porous isolation layer is 5-10%; Optionally, the thickness of the porous isolation layer is 1-3μm.

3. The precursor of claim 1 or 2, wherein, The inner core is composed of NiFeMn(OH) 2 with a layered structure; Optionally, the outer shell is composed of NiFeMn(OH) 2 with a layered structure; Optionally, the components in the porous isolation layer include NiFeMn(OH) 2 with a layered structure, and also include any one or a combination of at least two of Zn(OH) 2 with an amorphous structure, Cu(OH) 2 with an orthorhombic structure (Cmc21), or Ti(OH) 4 with an amorphous structure. 4.A method for preparing the precursor of any one of claims 1-3, comprising: (1) adding a first mixed salt solution, a precipitant solution and a complexing agent solution into a reaction base solution in parallel to perform a co-precipitation reaction to obtain a mixed solution containing a first precipitate; (2) adding a second mixed salt solution, a precipitant solution and a complexing agent solution into the mixed solution containing the first precipitate obtained in step (1) in parallel to perform a co-precipitation reaction to obtain a mixed solution containing a second precipitate; The second mixed salt solution includes doped metal ions and all metal ions in the first mixed salt solution; (3) adding a first mixed salt solution, a precipitant solution and a complexing agent solution into the mixed solution containing the second precipitate obtained in step (2) in parallel to perform a co-precipitation reaction to obtain the precursor.

5. The production method according to claim 4, wherein The doped metal ions in step (2) satisfy a first condition and / or a second condition; The first condition is that the difference between the precipitation constant of the doped metal ion and the precipitation constant of all metal ions in the first mixed salt solution is not less than 1 x 10 3 ; The second condition is that the crystal structure of the substance formed after the doped metal ions are precipitated is different from the crystal structure of the substance formed after all metal ions in the first mixed salt solution are precipitated.

6. The production method according to claim 4 or 5, wherein, The adding speeds of the second mixed salt solution, the precipitant solution and the complexing agent solution in step (2) are all higher than the adding speeds of the first mixed salt solution, the precipitant solution and the complexing agent solution in steps (1) and (3) ; Optionally, the adding speed of the second mixed salt solution in step (2) is 40-80L / h; Optionally, the adding speed of the first mixed salt solution in steps (1) and (3) is 10-40L / h; Optionally, the temperature during the co-precipitation reaction in steps (1)-(3) is 50-70℃, the stirring speed is 200-400rpm, and the pH is 9-11.

7. The method of making according to any one of claims 4 to 6, wherein, The first mixed salt solution in steps (1) and (3) is a nickel-iron-manganese mixed salt solution; the doped metal ions in step (2) include any one or a combination of at least two of Zn ions, Cu ions or Ti ions; Optionally, the total concentration of metal ions in the first mixed salt solution in steps (1)-(3) is 0.5-2.0mol / L; Optionally, the molar amount of the doping metal ions is not more than 5% of the total molar amount of all metal ions in the second mixed salt solution of step (2); Optionally, steps (1)-(3) are all carried out in a protective atmosphere; Optionally, the D50 particle size of the first precipitate obtained in step (1) is 4-6 μm; Optionally, the D50 particle size of the second precipitate obtained in step (2) is 6-8 μm; Optionally, the D50 particle size of the precursor obtained in step (3) is 8-10 μm.

8. A cathode material prepared from the precursor of any one of claims 1-3.

9. A process for preparing the cathode material of claim 8, comprising: mixing the precursor with a sodium source, and sintering to obtain the cathode material.

10. The manufacturing process of claim 9, wherein, The sodium source comprises Na2CO3 and / or NaOH; Optionally, the sintering is carried out at a temperature of 800-900 °C for 10-20 h.

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