FR3138575A1 - METHOD FOR PREPARING AN ACTIVE MATERIAL FOR HIGH CAPACITY BATTERY, AND ITS USE - Google Patents

Abstract

The present invention relates in particular to a method for preparing an active material for a high-capacity battery, and a method for preparing a lithium-ion battery. The preparation method comprises the following steps: mixing an iron hydroxide colloid with a carbon source, and spray drying the resulting mixture to obtain a carbon-doped nano iron oxide; mixing the nano-iron oxide with a lithium source, and sintering in an inert atmosphere to obtain a sintered material; mixing the sintered material, an organic polymer and an organic solvent, wet grinding, and spray drying a resulting ground material under a protective atmosphere to obtain a dry material; and sintering the dry material in an inert atmosphere to obtain the battery active material. Figure for abstract: figure 1

Description

METHOD FOR PREPARING AN ACTIVE MATERIAL FOR HIGH CAPACITY BATTERY, AND ITS USE

The present disclosure belongs to the technical field of materials for lithium-ion batteries (“ lithium-ion battery ” in English, or LIB), and relates in particular to a process for preparing an active material for a high-capacity battery, and to a process preparation of a lithium-ion battery.

At present, new energy vehicles require power batteries to have increasing travel range, which puts forward advanced requirements for the recycling capacity of power battery materials. It is well known that, when an LIB is charged and discharged for the first time, due to the formation of a solid electrolyte interface (SEI) film, Lithium ions cannot be 100% returned to a positive electrode and some lithium ions will be lost, so the first charge and discharge capacity and cycling capacity of the LIB cannot be fully deployed. In order to solve the above problem, some ultra-high capacity substances are usually added to cathode material for improvement.

Li ₅ FeO ₄ has an ultra-high theoretical capacity, and so adding Li ₅ FeO ₄ in a specified amount to a cathode material can effectively reduce the loss of lithium ions during the first charge and discharge. Current synthesis processes for Li ₅ FeO ₄ still face some problems. For example, a synthesized material has a large particle size, resulting in a long lithium ion migration path, relatively low capacity, and low stability and electrical conductivity. Considering the above problems, a particle size of a material is generally reduced by reducing a particle size of iron oxide, but it is difficult to make the iron oxide exhibit a particle size on a nanoscale. In addition, nanoscale iron oxide on the market is expensive, its supply is low, and it has no cost advantage. In addition, among current carbon coating technologies, there is a technology in which a low molecular weight organic gaseous material is used for vapor coating on a surface of a material, which can improve the electrical conductivity and the stability of the material to a certain extent. However, steam coating has high requirements for safe production and equipment, which is not conducive to industrialization.

The present disclosure is intended to resolve at least one of the technical problems existing in the prior art. For this reason, the present disclosure provides a method for preparing an active material for a high-capacity battery, and a method for preparing a lithium-ion battery.

According to one aspect of the present disclosure, a method for preparing an active material for a high capacity battery is provided, comprising the following steps consisting of:

S1: mixing an iron hydroxide colloid with at least one carbon source, and spray-drying the resulting mixture to obtain a carbon-doped nano-iron oxide;

S2: mixing the nano-iron oxide with at least one lithium source, and sintering under an inert atmosphere to obtain a sintered material;

S3: mixing the sintered material, at least one organic polymer, and at least one organic solvent, wet grinding under a protective atmosphere, and spray drying the resulting ground material under a protective atmosphere to obtain a dry material; And

S4: sintering the dry material under an inert atmosphere to obtain the active battery material.

In some embodiments of the present disclosure, in step S1, the iron hydroxide colloid is prepared as follows: adding, preferably slowly, an iron salt solution to water, preferably hot, under heating and stirring, and keeps the resulting mixture warm for a specified period of time to obtain the iron hydroxide colloid. Iron hydroxide colloid is prepared by heating a solution of iron salt in water to allow a hydrolysis reaction. In addition, water is deionized water with an impurity content of 1000 ppm or less; in addition, the iron salt solution has a concentration of 0.1 mol/L to 12 mol/L; further, the iron salt solution is heated to 80°C or higher; and furthermore, once the addition is complete, the mixture is kept warm for 10 min or more.

In some embodiments of the present disclosure, in step S1, the hot water has a temperature of 80°C or more, particularly 80°C to 100°C. Advantageously, the iron salt solution and the water are heated to a temperature of 80°C or more, in particular from 80°C to 100°C.

In certain embodiments of the present disclosure, in step S1, the carbon source(s) are selected from carbon nanotube (CNT), conductive carbon black, graphite powder, polyethyleneimine (PEI), glucose, polyvinyl alcohol (PVA) and their mixtures. In addition, the carbon source has a volume particle size Dv50 ranging from 0.5 µm to 3 µm.

In some embodiments of the present disclosure, in step S1, spray drying is carried out at a temperature ranging from 180°C to 250°C.

In some embodiments of the present disclosure, in step S1, during spray drying, the mixture is to be stirred at a rotational speed of 100 rpm to 500 rpm.

In certain embodiments of the present disclosure, in step S1, the carbon source(s) were added in an amount ranging from 5% to 30% by weight, relative to the mass of the nano-iron oxide obtained. .

In some embodiments of the present disclosure, in step S1, the nano-iron oxide has a Brunauer–Emmett–Teller (BET) specific surface area ranging from 28 m ² /g to 58 m ² /g and a size of particle volume Dv50 ranging from 100 nm to 700 nm.

In certain embodiments of the present disclosure, in step S2, the lithium source(s) are selected from lithium hydroxide monohydrate, anhydrous lithium hydroxide, lithium oxide and mixtures thereof, and a molar ratio between the lithium in lithium source and iron in nano-iron oxide ranges from 5.0 to 5.8.

In certain embodiments of the present disclosure, in step S2, sintering is carried out at a temperature ranging from 600°C to 900°C. Additionally, sintering is carried out for 8 h to 36 h.

In certain embodiments of the present disclosure, in step S3, the organic polymer(s) are chosen from polypyrroles (PPy), polythiophenes (PT), polyacetylenes (PA), polyphenylenes, polyphenylacetylenes (PPA) and their mixtures. In addition, the organic polymer(s) were added in an amount ranging from 0.1% to 3% by weight of the theoretical mass of the active battery material obtained.

In certain embodiments of the present disclosure, in step S3, the organic solvent(s) are chosen from triethanolamine (TEA), N-methylpyrrolidone (NMP), 2-hydroxyethylamine, glycerol, ether di -n-pentyl (DNPE) and mixtures thereof. Compared with low flash point organic solvents such as methanol and ethanol, the organic solvent adopted in the present disclosure has a relatively higher flash point, which ensures the uniform progress of spray drying.

In some embodiments of the present disclosure, in step S3, the wet grinding is carried out as follows: adding the sintered material to the organic solvent, performing coarse wet crushing under a protective atmosphere, and carrying out sand grinding (“ sand-grinding ” in English) during which the organic polymer is added to obtain the crushed material. In addition, the coarse wet crushing is carried out at a rotation speed ranging from 400 rpm to 800 rpm, and a material obtained after the coarse wet crushing has a particle size Dv50 of 20 or less. μm. In addition, sand grinding is carried out at a rotation speed ranging from 2000 rpm to 3000 rpm.

In some embodiments of the present disclosure, in step S3, the ground material has a volume particle size Dv50 ranging from 0.5 μm to 3 μm.

In some embodiments of the present disclosure, in step S3, spray drying is carried out at a temperature ranging from 150°C to 220°C.

In certain embodiments of the present disclosure, in step S4, the sintering is carried out at a temperature ranging from 200°C to 600°C, more preferably from 400°C to 600°C. And according to a particular embodiment, in step S4, the sintering is carried out at a temperature ranging from 200°C to 400°C. In addition, the sintering is advantageously carried out for 2 h to 10 h.

In some embodiments of the present disclosure, in step S4, a material obtained after sintering is sieved, and the obtained battery active material has a volume particle size Dv50 ranging from 2 μm to 8 μm.

The present disclosure also relates to a method for preparing a lithium-ion battery (LIB) comprising at least steps S1 to S4 according to the invention.

According to a preferred embodiment of the present disclosure, the present disclosure has at least the following beneficial effects:

1. The present disclosure adopts iron hydroxide colloid as the iron source. Compared to iron hydroxide prepared by a direct reaction between an iron source and an alkaline liquor, followed by precipitation, the iron hydroxide colloid has better dispersibility and results in more iron oxide particles. small, which is conducive to the subsequent preparation of small particle Li ₅ FeO ₄ ; and the iron hydroxide material prepared by a direct reaction between an iron source and an alkaline liquor is prone to agglomeration and has a large particle size and high platform tension. Additionally, in the present disclosure, at least one conductive carbon source is introduced into the iron hydroxide colloid, which can not only block the melt growth of the material during sintering to ensure that the Synthesized particles have a small particle size, but also help improve the electrical conductivity of the material.

2. In the present disclosure, the Li ₅ FeO ₄ block synthesized by sintering is wet milled in an organic solvent and under a protective atmosphere to effectively reduce a particle size of the material, which can prevent the material from deterioration in the air and is conducive to shortening a lithium ion migration path, thus improving the capacity of the material. The organic polymer is added during sand grinding to form a nano-carbon coating layer on a surface of the material. The organic polymer used in the present disclosure has a larger molecular chain than a general low molecular weight organic material and can thus form a relatively dense coating layer on the surface of the material, and in order to ensure a coating effect, a thickness of the coating layer can be regulated, which can further improve the stability and electrical conductivity of the material. Compared to steam coating, the present disclosure has lower equipment requirements and higher safety.

The high-capacity battery active material synthesized by the present disclosure involves a simple synthesis process, low processing cost, and high yield, and can be easily industrialized.

The present disclosure is described in more detail below with reference to the accompanying drawings and examples.

There is a schematic diagram illustrating a synthesis process of Example 1 of the present disclosure;

There is a scanning electron microscopy (SEM) image of iron oxide synthesized in Example 1;

There is an SEM image of Li ₅ FeO ₄ synthesized in Example 1;

There is a transmission electron microscopy (TEM) image of Li ₅ FeO ₄ synthesized in Example 1;

There represents a charge-discharge curve of Li ₅ FeO ₄ synthesized in Example 1;

There is a SEM image of Li ₅ FeO ₄ synthesized in Comparative Example 1;

There represents a charge-discharge curve of Li ₅ FeO ₄ synthesized in Comparative Example 1;

There is a SEM image of Li ₅ FeO ₄ synthesized in Comparative Example 2; And

There represents a charge-discharge curve of Li ₅ FeO ₄ synthesized in Comparative Example 2.

The concept of the present disclosure and the technical effects produced thereby will be described clearly and completely below with reference to the examples, so as to enable a full understanding of the objectives, characteristics and effects of the present disclosure. Clearly, the examples described are only some rather than all of the examples in the present disclosure. All other examples obtained by those skilled in the art based on the examples of the present disclosure without creative efforts are within the scope of protection of the present disclosure.

Example 1

In this example, a high capacity battery active material Li ₅ FeO ₄ was synthesized, as shown in Figure ; and a specific synthesis process was as follows:

(1) Under heating at 90 °C and stirring at 80 rpm, 3 L of iron chloride solution having a concentration of 5 mol/L was slowly added to deionized water, and a resulting mixture was kept warm for 20 min to obtain a colloidal solution of iron hydroxide; and a graphite powder with Dv50 of 1.5 μm was added as a carbon source in an amount of 6.5% of a theoretical mass of the final product nano-iron oxide, and a resulting mixture was further stirred at 300 rpm, then spray-dried at 200 °C to obtain carbon-doped nano-iron oxide. A morphology of nano-iron oxide was represented on the , and the nano-iron oxide was determined to have a Dv50 particle size of 560 nm and a BET surface area of 42 m ² /g.

(2) Nano iron oxide and lithium hydroxide were mixed at a high rotation speed of 600 rpm for 40 min in a high-speed mixer with a molar ratio between lithium and iron of 5 ,3 to obtain a homogeneous material, and the homogeneous material was subjected to high-temperature sintering at 680 °C for 25 h under a nitrogen atmosphere to obtain a sintered block material.

(3) The sintered block material was placed in a crusher with rollers at an interval of 1.5 mm, a solvent 2-hydroxyethylamine was added, and the sintered block material was subjected to coarse crushing by way wet at a rotational speed of 650 rpm in a nitrogen atmosphere until a crushed material has a Dv50 particle size of 12 μm; the crushed material was subjected to high-speed sand grinding for 1.5 h at a rotation speed of 2,600 rpm until a resulting material had a particle size of 0.9 μm, during which PT was added in an amount of 1% of a theoretical mass of the material finally synthesized; and the material obtained after sand grinding was spray-dried at 220°C in a nitrogen atmosphere to obtain a dry material.

(4) The dry material was subjected to low-temperature sintering at 520 °C for 10 h, and a resulting sintered material was sieved through a 400 mesh screen to obtain a high-capacity battery active material Li ₅ FeO ₄ . A particle size Dv50 of the high-capacity battery active material was determined to be 4 μm.

Characterization test: As shown in the , the Li ₅ FeO ₄ material synthesized by the above method had major particle uniformity and a large coating layer, indicating a major coating effect.

Example 2

In this example, an active material for a high-capacity battery Li ₅ FeO ₄ was synthesized; and a specific synthesis process was as follows:

(1) Under heating at 90 °C and stirring at 80 rpm, 3 L of iron chloride solution having a concentration of 5 mol/L was slowly added to deionized water, and a resulting mixture was kept warm for 20 min to obtain a colloidal solution of iron hydroxide; and a CNT was added as a carbon source in an amount of 6.5% of a theoretical mass of the final product nano-iron oxide, and a resulting mixture was further stirred at 300 rpm and then dried by spraying at 200 °C to obtain a nano-iron oxide doped with carbon.

(2) Nano iron oxide and lithium hydroxide were mixed at a high rotation speed of 600 rpm for 40 min in a high-speed mixer with a molar ratio between lithium and iron of 5 ,3 to obtain a homogeneous material, and the homogeneous material was subjected to high-temperature sintering at 680 °C for 25 h under a nitrogen atmosphere to obtain a sintered block material.

(3) The sintered block material was placed in a crusher with rollers at an interval of 1.5mm, NMP solvent was added, and the sintered block material was subjected to coarse wet crushing at a rotation speed of 650 rpm in a nitrogen atmosphere; a crushed material was subjected to high-speed sand grinding for 1.5 h at a rotation speed of 2,600 rpm until a resulting material had a particle size of 0.9 μm, during which polyphenylene was added in an amount of 1% of a theoretical mass of the material finally synthesized; and the material obtained after sand grinding was spray-dried at 220°C in a nitrogen atmosphere to obtain a dry material.

(4) The dry material was subjected to low-temperature sintering at 550 °C for 10 h, and a resulting sintered material was sieved through a 400 mesh screen to obtain a high-capacity battery active material Li ₅ FeO ₄ .

Comparative Example 1

In this comparative example, carbon-free Li ₅ FeO ₄ was synthesized, which was different from Example 1 in that the carbon source and organic polymer were not added; and a specific synthesis process was as follows:

(1) Under heating at 90 °C and stirring at 80 rpm, 3 L of iron chloride solution having a concentration of 5 mol/L was slowly added to deionized water, and a resulting mixture was kept warm for 20 min to obtain a colloidal solution of iron hydroxide; and a resulting mixture was spray-dried at 200 °C to obtain a nano-oxide. The nano-iron oxide was determined to have a Dv50 particle size of 890 nm and a BET surface area of 31 m ² /g.

(2) Nano iron oxide and lithium hydroxide were mixed at a high rotation speed of 600 rpm for 40 min in a high-speed mixer with a molar ratio between lithium and iron of 5 ,3 to obtain a homogeneous material, and the homogeneous material was subjected to high-temperature sintering at 680 °C for 25 h under a nitrogen atmosphere to obtain a sintered block material.

(3) The sintered block material was placed in a crusher with rollers at an interval of 1.5 mm, a solvent 2-hydroxyethylamine was added, and the sintered block material was subjected to coarse crushing by way wet at a rotational speed of 650 rpm in a nitrogen atmosphere until a crushed material has a Dv50 particle size of 12 μm; the crushed material was subjected to high-speed sand grinding for 1.5 h at a rotational speed of 2600 rpm until a resulting material had a particle size of 1.2 μm; the material obtained after sand grinding was spray dried at 220°C in a nitrogen atmosphere to obtain a dry material; and the dry material was sieved through a 400 mesh screen to obtain Li ₅ FeO ₄ battery active material. A Dv50 particle size of the battery active material was determined to be 5.2 μm.

Characterization test: As shown in the , the Li ₅ FeO ₄ material synthesized by the above method had major particle uniformity.

The nano-iron oxide obtained in this comparative example has a larger particle size than the nano-iron oxide obtained in Example 1. The reason is that the graphite powder is introduced into the hydroxide colloid of iron in Example 1, so that the melt growth of the iron oxide can be blocked to allow a small particle size of the final product of Example 1.

Comparative Example 2

In this comparative example, a battery active material Li ₅ FeO ₄ was synthesized, which was different from Example 1 in that dry grinding was adopted; and a specific synthesis process was as follows:

(1) The nano-iron oxide of Example 1 and lithium hydroxide were mixed at a high rotation speed of 600 rpm for 40 min in a high-speed mixer with a molar ratio between lithium and iron of 5.3 to obtain a homogeneous material, and the homogeneous material was subjected to high-temperature sintering at 680 °C for 25 h under a nitrogen atmosphere to obtain a sintered block material.

(2) The sintered block material was placed in a mill with rollers at an interval of 1.5mm and subjected to airflow grinding, then PT was added in an amount of 1% of a theoretical mass of the finally synthesized material, and a resulting mixture was dry mixed and then sintered at 520 °C in a nitrogen atmosphere.

(3) A sintered material was sieved through a 400 mesh screen to obtain Li ₅ FeO ₄ battery active material. A Dv50 particle size of the battery active material was determined to be 8.2 μm.

Characterization test: As shown in the , the Li ₅ FeO ₄ material synthesized by the above method had a large particle size.

Comparative Example 3

In this comparative example, a Li ₅ FeO ₄ battery active material was synthesized, which was different from Example 1 in that a low molecular weight organic material was used instead of the polymer; and a specific synthesis process was as follows:

A sintered block material was prepared according to steps (1) and (2) of Example 1; the sintered block material was placed in a crusher with rollers at an interval of 1.5 mm, a solvent 2-hydroxyethylamine was added, and the sintered block material was subjected to coarse wet crushing at a rotation speed of 650 rpm in a nitrogen atmosphere until a crushed material has a Dv50 particle size of 12 μm; the crushed material was subjected to high-speed sand grinding for 1.5 h at a rotation speed of 2,600 rpm until a resulting material had a particle size of 0.9 μm, during which glucose was added in an amount of 1% of a theoretical mass of the material finally synthesized; the material obtained after sand grinding was spray dried at 220°C in a nitrogen atmosphere to obtain a dry material; And

the dry material was sintered at 550 °C for 10 h, and a resulting sintered material was sieved through a 400 mesh screen to obtain Li ₅ FeO ₄ battery active material.

Test Example

The Li₅FeO₄prepared in each of Examples 1 and 2 and Comparative Examples 1, 2 and 3 was manufactured into a button battery, including the steps of preparing suspension, coating, drying, pressing, assembling, and testing on a case: 1) suspension preparation: 4 g of a material was weighed and mixed with a conductive agent and a binder, where the material, conductive agent and binder were in a mass ratio of 8:1:1 , the binder was polyvinylidene fluoride (PVDF), and the conductive agent was conductive carbon; 2) coating: the mixture was coated on aluminum foil with a scraper; 3) drying: the coated electrode sheet was dried in a vacuum drying oven at 120 °C for 2 h; 4) pressing: the dried electrode sheet was pressed with a rolling machine; and 5) assembly: battery components such as a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte were assembled into the button battery. A specific capacitance was tested at a charging voltage of 4.25 V and a charging rate of 0.1 C. The test results are shown in Table 1. Sample No. Charging capacity, mAh/g Example 1 705 Example 2 698 Comparative Example 1 220 Comparative Example 2 545 Comparative Example 3 621

It can be seen from Table 1 that a load capacity of Comparative Example 3 is lower than that of Example 1. The reason is that the carbon coating material of Comparative Example 3 is an organic material of low molecular weight and, thus, a carbon coating layer formed is not as dense as that of Example 1, resulting in reduced capacity.

There represents a charge-discharge curve of Li ₅ FeO ₄ synthesized in Example 1, and it can be seen from the figure that the material has a capacity of up to 705 mAh/g.

There represents a charge-discharge curve of Li ₅ FeO ₄ synthesized in Comparative Example 1, and it appears from the figure that a capacity of the material is 220 mAh/g, which is significantly lower than a capacity of the material doped with carbon and coated in Example 1, indicating that carbon doping and coating can greatly improve the capacitance of the material.

There represents a charge-discharge curve of Li ₅ FeO ₄ synthesized in Comparative Example 2, and it can be seen from the figure that a capacity of the material is 545 mAh/g, which is approximately 160 mAh/g lower than the capacity of small particle Li ₅ FeO ₄ synthesized by wet milling in Example 1, indicating that wet milling can effectively reduce a particle size of a material to shorten a lithium ion migration path and improve a capacity of a material.

The examples of the present disclosure have been described in detail above with reference to the accompanying drawings, but the present disclosure is not limited thereto. Within the framework of the knowledge possessed by those skilled in the art, various modifications can be made without departing from the purpose of the present disclosure. Additionally, where there is no conflict, the examples in this disclosure and the features in the examples may be combined with one another.

Claims (10)

Process for preparing an active material for a battery, comprising the following steps:
step S1: mixing an iron hydroxide colloid with at least one carbon source, and spray-drying the resulting mixture to obtain a carbon-doped nano-iron oxide;
step S2: mixing said nano-iron oxide with at least one source of lithium, and sintering under an inert atmosphere to obtain a sintered material;
step S3: mixing said sintered material, at least one organic polymer and at least one organic solvent, wet grinding under a protective atmosphere, and spray drying the resulting ground material under a protective atmosphere to obtain a dry material; And
step S4: sintering said dry material under an inert atmosphere to obtain the active battery material. A preparation method according to claim 1, wherein, in step S1, the iron hydroxide colloid is prepared as follows: slowly adding an iron salt solution to water under heating and stirring , and keeps the resulting mixture warm for a specified period of time to obtain the iron hydroxide colloid. Preparation process according to claim 1 or 2, in which, in step S1, the carbon source(s) are chosen from carbon nanotube, conductive carbon black, graphite powder, polyethyleneimine, glucose, polyvinyl alcohol, and their mixtures. Preparation process according to any one of claims 1 to 3, wherein, in step S1, the spray drying is carried out at a temperature ranging from 180°C to 250°C. Preparation process according to any one of claims 1 to 4, in which, in step S1, the carbon source(s) were added in an amount ranging from 5% to 30% by weight, relative to to the mass of the nano-iron oxide obtained. Preparation process according to any one of claims 1 to 5, in which, in step S2, the sintering is carried out at a temperature ranging from 600 °C to 900 °C. Preparation process according to any one of claims 1 to 6, in which, in step S3, the organic polymer(s) are chosen from polypyrroles, polythiophenes, polyacetylenes, polyphenylenes, polyphenylacetylenes and mixtures thereof. Preparation method according to any one of claims 1 to 7, wherein, in step S3, the ground material has a particle size Dv50 ranging from 0.5 μm to 3 μm. Preparation process according to any one of claims 1 to 8, in which, in step S4, the sintering is carried out at a temperature ranging from 400 °C to 600 °C. Process for preparing a lithium-ion battery, comprising at least steps S1 to S4 as defined according to any one of claims 1 to 9.