阅读说明：本技术 一种六氟锆酸锂和碳共包覆磷酸铁锂复合材料、其制备方法和用途 (Lithium hexafluorozirconate and carbon co-coated lithium iron phosphate composite material, and preparation method and application thereof ) 是由 杨帆 王张健 杨顺毅 吴小珍 杨才德 于 2018-06-20 设计创作，主要内容包括：本发明公开了一种六氟锆酸锂和碳共包覆磷酸铁锂复合材料、其制备方法和用途。所述复合材料包括：磷酸铁锂内核,以及包覆在所述内核表面的包覆层,所述包覆层由六氟锆酸锂和热解碳组成,所述复合材料中包括至少两个不同的粒度范围的复合材料颗粒。本发明的方法包括：1)将锂源、磷铁源、碳源和六氟锆酸锂制浆、研磨活化；2)利用喷雾干燥机造出至少两个粒度范围的球体；(3)烧结,得到六氟锆酸锂和碳共包覆磷酸铁锂的复合材料。本发明的方法可明显提升材料的压实密度,而且采用该复合材料作为正极活性物质制成的全电池具有优异的首圈容量、循环性能和低温性能。(The invention discloses a lithium hexafluorozirconate and carbon co-coated lithium iron phosphate composite material, a preparation method and application thereof. The composite material comprises: the lithium iron phosphate composite material comprises a lithium iron phosphate core and a coating layer coated on the surface of the core, wherein the coating layer is composed of lithium hexafluorozirconate and pyrolytic carbon, and the composite material comprises at least two composite material particles with different particle size ranges. The method of the invention comprises the following steps: 1) pulping, grinding and activating a lithium source, a ferrophosphorus source, a carbon source and lithium hexafluorozirconate; 2) producing spheres with at least two particle size ranges by using a spray dryer; (3) and sintering to obtain the lithium hexafluorozirconate and carbon co-coated lithium iron phosphate composite material. The method can obviously improve the compaction density of the material, and the full battery prepared by adopting the composite material as the positive active substance has excellent first-turn capacity, cycle performance and low-temperature performance.)

1. A lithium hexafluorozirconate and carbon co-coated lithium iron phosphate composite, comprising: the lithium iron phosphate core comprises a lithium iron phosphate core and a coating layer coated on the surface of the core, wherein the coating layer consists of lithium hexafluorozirconate and pyrolytic carbon;

wherein the composite material comprises composite particles of at least two different particle size ranges.

2. The composite material of claim 1, wherein the composite material comprises large particles and small particles of different particle size ranges;

preferably, the large particles have a particle size ranging from 7 μm to 20 μm, and the small particles have a particle size ranging from 500nm to 5 μm;

preferably, the mass ratio of the large particles to the small particles is 4:6 to 6: 4.

3. The composite material according to claim 1 or 2, characterized in that it is a spherical particle;

preferably, the crystal form of the lithium iron phosphate is olivine;

preferably, the mass percent of the lithium iron phosphate is 96-98% based on 100% of the total mass of the composite material;

preferably, the mass percent of the lithium hexafluorozirconate is 0.1-1% based on 100% of the total mass of the composite material;

preferably, the mass percent of the pyrolytic carbon is 1-3.9% based on 100% of the total mass of the composite material.

4. A method of preparing a lithium hexafluorozirconate and carbon co-coated lithium iron phosphate composite as claimed in any one of claims 1 to 3, comprising the steps of:

(1) adding a lithium source, a ferrophosphorus source and a coating material source into a grinding tank, and adding a dispersing agent to adjust the solid content to obtain precursor slurry;

(2) grinding the precursor slurry until the particle size of the precursor slurry is in a nanometer level so as to activate the lithium iron phosphate reaction raw material and the coating material source;

(3) utilizing a spray dryer to manufacture spheres with at least two particle size ranges;

(4) collecting the powder obtained in the step (3), and sintering to obtain a lithium hexafluorozirconate and carbon co-coated lithium iron phosphate composite material;

wherein the coating material source comprises a carbon source and lithium hexafluorozirconate.

5. The method of claim 4, wherein the lithium source of step (1) comprises any one of lithium carbonate, lithium acetate, lithium hydroxide, lithium chloride, or lithium nitrate, or a combination of at least two thereof;

preferably, the ferrophosphorus source in step (1) comprises any one of anhydrous ferric phosphate, ferric phosphate dihydrate or hydrated ammonium ferric phosphate or a combination of at least two of the foregoing;

preferably, in the coating material source in the step (1), the carbon source is any one or a combination of at least two of glucose, sucrose, polyethylene glycol, polyvinyl alcohol or phytic acid;

preferably, the dispersant in step (1) comprises any one or a combination of at least two of water, ethanol or acetone, wherein the water is preferably deionized water and/or pure water;

preferably, the solid content is adjusted to 15 to 45 percent in the step (1);

preferably, the molar ratio of the lithium source, the ferrophosphorus source, the carbon source and the lithium hexafluorozirconate is Li, Fe, C, Zr (1.01-1.05): 1, (1.0-1.4): 0.001-0.1.

6. The method according to claim 4 or 5, characterized in that step (2) is ground until the particle size of the precursor slurry is between 50nm and 500nm, preferably between 130nm and 180 nm;

preferably, the inlet temperature of the spray drying in the step (3) is 180-360 ℃;

preferably, the outlet temperature of the spray drying in the step (3) is 60-120 ℃;

preferably, the method for producing the spheres with at least two particle size ranges in the step (3) is as follows: spray drying is carried out by adopting a multi-pipe air inlet and multi-pipe feeding mode;

preferably, the spray drying is carried out in the step (3) by a two-tube air inlet and two-tube feeding mode, so that spheres with two particle size ranges of large and small are produced;

preferably, the spray drying is carried out in the step (3) by a two-pipe air inlet and two-pipe feeding mode, wherein the feeding amount of one air inlet pipe and the feeding pipe matched with the air inlet pipe for spray granulation is respectively 10 NL/min-30 NL/min and 1 ml/min-8 ml/min, and the air inlet amount of the other air inlet pipe and the feeding pipe matched with the air inlet pipe for spray granulation are respectively 50 NL/min-100 NL/min and 10 ml/min-20 ml/min;

preferably, the spray drying is carried out in the step (3) by a two-pipe air inlet and two-pipe feeding mode, wherein the air inflow of one air inlet pipe and the feeding amount of the feeding pipe matched with the air inlet pipe for spray granulation are respectively 20 NL/min-25 NL/min and 2 ml/min-4 ml/min, and the air inflow of the other air inlet pipe and the feeding amount of the feeding pipe matched with the air inlet pipe for spray granulation are respectively 50 NL/min-60 NL/min and 15 ml/min-18 ml/min.

7. The method according to any one of claims 4 to 6, wherein the sintering of step (4) is performed under an inert atmosphere comprising any one of a nitrogen atmosphere, an argon atmosphere, a helium atmosphere, a neon atmosphere, a krypton atmosphere, or a xenon atmosphere, or a combination of at least two atmospheres;

preferably, the sintering of step (4) is carried out in a controlled temperature electric furnace;

preferably, the sintering temperature in the step (4) is 600-800 ℃;

preferably, the sintering time in the step (4) is 2 to 24 hours, preferably 8 to 12 hours.

8. A method according to any of claims 4-7, characterized in that the method comprises the steps of:

(1) adding a lithium source, a ferrophosphorus source, a carbon source and lithium hexafluorozirconate into a grinding tank according to the molar ratio of Li to Fe to C to Zr (1.01-1.05) to 1 (1.0-1.4) to (0.001-0.1), and adding a dispersing agent to adjust the solid content to obtain precursor slurry;

(2) grinding the precursor slurry until the particle size of the precursor slurry is 50-500 nm so as to activate the lithium iron phosphate reaction raw material, the carbon source and the lithium hexafluorozirconate;

(3) spray drying is carried out by utilizing a spray dryer in a mode of feeding materials through two pipes of air inlet and two pipes of air inlet, spheres with at least two particle size ranges are manufactured, and the specific parameters are as follows:

the air inflow of one air inlet pipe and the feeding amount of the feeding pipe matched with the air inlet pipe for spray granulation are respectively 10 NL/min-30 NL/min and 1 ml/min-8 ml/min, and the air inflow of the other air inlet pipe and the feeding amount of the feeding pipe matched with the air inlet pipe for spray granulation are respectively 50 NL/min-100 NL/min and 10 ml/min-20 ml/min;

the inlet temperature of spray drying is 180-360 ℃, and the outlet temperature is 60-120 ℃;

(4) collecting the powder obtained in the step (3), and sintering the powder for 2 to 24 hours at the temperature of 600 to 800 ℃ in an inert atmosphere to obtain the lithium hexafluorozirconate and carbon co-coated lithium iron phosphate composite material;

the inert atmosphere comprises any one of a nitrogen atmosphere, an argon atmosphere, a helium atmosphere, a neon atmosphere, a krypton atmosphere or a xenon atmosphere or a combination of at least two of the atmospheres.

9. A positive electrode sheet, characterized in that it comprises the lithium hexafluorozirconate composite described in any one of claims 1 to 3 and carbon-co-coated lithium iron phosphate as a positive electrode material;

preferably, the positive electrode sheet further comprises a foil, a binder and a conductive agent.

10. A lithium ion battery, characterized in that the lithium ion battery comprises the positive electrode sheet according to claim 9;

preferably, the lithium ion battery further comprises a negative electrode sheet, a separator and an electrolyte.

Technical Field

The invention relates to the field of lithium ion battery positive electrode materials, and relates to a lithium hexafluorozirconate and carbon co-coated lithium iron phosphate composite material, a preparation method and application thereof, in particular to a lithium hexafluorozirconate and carbon co-coated lithium iron phosphate composite material with high compaction density and good electrochemical performance, a preparation method thereof and application as a lithium ion positive electrode material.

Background

As a cathode material that has been commercialized, a lithium iron phosphate material has problems of low electron conductivity and low ion transfer rate. Lithium iron phosphate power batteries also need further optimization due to low actual energy density.

At present, carbon coating has become a main means for improving the electrochemical performance of lithium iron phosphate cathode materials in industry. However, the coated carbon layer reduces the overall compacted density of the material, resulting in a lower volumetric energy density of the lithium iron phosphate battery. In addition, the inactive lithium sites in the graphite cathode can cause the lithium iron phosphate cathode material to lose a part of lithium ions in the charging and discharging process, so that the first-circle capacity of the full battery is reduced, and the normal performance of the battery is influenced. Among the technical means disclosed, there have been few researches for the targeted solution of the above-mentioned problems.

CN 106252635 a discloses graphene-coated lithium iron phosphate and a preparation method thereof, the method comprising: s1, mixing deionized water and graphene oxide to prepare a graphene oxide dispersion liquid, and mixing the graphene oxide dispersion liquid with a nitrogen source to obtain a mixture A; s2, mixing deionized water with a lithium source, a phosphorus source and an iron source to prepare a lithium source dispersion liquid, a phosphorus source dispersion liquid and an iron source dispersion liquid, sequentially adding the prepared lithium source dispersion liquid, phosphorus source dispersion liquid and iron source dispersion liquid into the mixture A, and stirring to obtain a mixture B; s3, drying the mixture B to obtain a nitrogen-doped graphene-coated lithium iron phosphate precursor; s4, preheating and sintering the nitrogen-doped graphene-coated lithium iron phosphate precursor to obtain the nitrogen-doped graphene-coated lithium iron phosphate cathode material. However, the surface coating of the pure nitrogen-doped graphene has the problems of high cost, difficulty in dispersion of the graphene and difficulty in uniform coating, so that the coating effect is not ideal, the volumetric specific energy of the product is reduced, and the electrochemical performance of the lithium iron phosphate is affected finally, which limits the application of the lithium iron phosphate in coating of electrode materials.

CN 014766956 a discloses a preparation method of a nickel-coated lithium iron phosphate positive electrode material, in which nickel is uniformly coated on the surface of the lithium iron phosphate material in an electroplating manner, so as to improve the capacity and cycle performance of the material. However, the coating means only solves the problem of poor electrochemical performance of the material per se, but does not effectively solve the problems of low first efficiency, poor low-temperature performance, low first-cycle capacity and the like of the battery in the charging and discharging processes.

Therefore, it is of great significance to seek a reasonable technical means to improve the pole piece compaction density, the first-turn capacity, the cycle performance and the low-temperature performance of the lithium iron phosphate material.

Disclosure of Invention

In view of the above problems in the prior art, the present invention aims to provide a lithium hexafluorozirconate and carbon co-coated lithium iron phosphate composite material, a preparation method and applications thereof, and in particular, to provide a lithium hexafluorozirconate and carbon co-coated lithium iron phosphate composite material with high compaction density and good electrochemical performance, a preparation method thereof and applications thereof as a lithium ion positive electrode material.

In order to achieve the purpose, the invention adopts the following technical scheme:

in a first aspect, the present invention provides a lithium hexafluorozirconate and carbon co-coated lithium iron phosphate composite, characterized in that the composite comprises: the lithium iron phosphate core comprises a lithium iron phosphate core and a coating layer coated on the surface of the core, wherein the coating layer consists of lithium hexafluorozirconate and pyrolytic carbon;

wherein the composite material comprises composite particles of at least two different particle size ranges.

The composite material comprises at least two composite material particles with different particle size ranges, the particles with different sizes are naturally mixed, the small balls fill the gaps of the large balls, the space utilization rate of active substances is optimized, the pole piece compaction density of the material is improved, and the volume energy density of the material is indirectly improved. F in lithium hexafluorozirconate^-The strong electronegativity allows lithium hexafluorozirconate and a carbon source to form an Fe-F-C bond on the surface of the positive electrode material so as to provide new Li⁺A storage location. These new Li sites will store additional active Li⁺During the first charging cycle, the active Li sites and SEI interface film of the negative electrode are filled in one step to reduce the Li content in the positive electrode material⁺Loss in the charging and discharging process improves the capacity of the first circle of the full battery.

As a preferred technical scheme of the composite material, the composite material comprises large particles and small particles with different particle size ranges.

Preferably, the large particles have a particle size in the range of 7 μm to 20 μm, such as 7 μm, 8 μm, 10 μm, 11.5 μm, 12 μm, 14 μm, 15 μm, 17 μm, 18 μm, or 20 μm, etc.; the small particles have a particle size in the range of 500nm to 5 μm, for example, 500nm, 750nm, 1 μm, 2 μm, 3 μm, 3.5 μm, 4 μm or 5 μm.

Preferably, the mass ratio of large particles to small particles is from 4:6 to 6:4, such as 4:6, 4.2:5.8, 4.5:5.5, 5.7:4.3 or 6:4, and the like.

According to the scheme, the granularity and the mass ratio of the large particles to the small particles are matched, so that the compaction density of the pole piece can be better improved, and the electrochemical performance of the material can be improved.

The composite material is spherical particles.

Preferably, the crystal form of the lithium iron phosphate is olivine.

Preferably, the mass percentage of the lithium iron phosphate is 96% to 98%, for example, 96%, 96.5%, 97%, 97.5%, 98%, or the like, based on 100% of the total mass of the composite material.

Preferably, the mass percent of the lithium hexafluorozirconate is 0.1% to 1%, for example, 0.1%, 0.2%, 0.3%, 0.4%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, or the like, based on 100% of the total mass of the composite.

Preferably, the pyrolytic carbon is present in an amount of 1% to 3.9% by mass, for example 1%, 1.5%, 2%, 2.2%, 2.4%, 2.5%, 2.7%, 3.0%, 3.3%, 3.5%, 3.6%, 3.8%, 3.9%, or the like, based on 100% by mass of the total composite material.

In a second aspect, the present invention provides a method for preparing a lithium hexafluorozirconate and carbon co-coated lithium iron phosphate composite as described in the first aspect, characterized in that the method comprises the steps of:

(1) adding a lithium source, a ferrophosphorus source and a coating material source into a grinding tank, and adding a dispersing agent to adjust the solid content to obtain precursor slurry;

(2) grinding the precursor slurry until the particle size of the precursor slurry is in a nanometer level so as to activate the lithium iron phosphate reaction raw material and the coating material source;

(3) utilizing a spray dryer to manufacture spheres with at least two particle size ranges;

(4) collecting the powder obtained in the step (3), and sintering to obtain a lithium hexafluorozirconate and carbon co-coated lithium iron phosphate composite material;

wherein the coating material source comprises a carbon source and lithium hexafluorozirconate.

The method of the invention firstly adjusts the precursor slurry to proper viscosity to grind and realize the activation of the raw material and the coating treatment source, then utilizes a spray dryer to atomize and form large and small spheres with at least two particle size ranges, takes the large spheres as the main body and small spheres as the assistance, naturally mixes the large and small spheres in the atomizing process, optimizes the space utilization rate of active substances in a mode of filling gaps between the large spheres by the small spheres to improve the pole piece compaction density of the material, and indirectly improves the volume energy density of the material. Using F in the calcination process^-The strong electronegativity enables the activated lithium hexafluorozirconate and a carbon source to form Fe-F-C bonds on the surface layer of the positive electrode material so as to provide new Li⁺A storage location. These new Li sites will store additional active Li⁺In the process of first circle charging, the active Li sites and the SEI interface film of the negative electrode can be filled in one step, so that the loss of the positive electrode material Li + in the process of charging and discharging is reduced, and the full electricity is improvedThe first circle capacity of the pool.

As a preferable technical scheme of the method of the invention, the lithium source in the step (1) comprises any one or a combination of at least two of lithium carbonate, lithium acetate, lithium hydroxide, lithium chloride or lithium nitrate.

Preferably, the ferrophosphorus source in step (1) includes any one or a combination of at least two of anhydrous ferric phosphate, ferric phosphate dihydrate or hydrated ammonium ferric phosphate, but is not limited to the above-listed ferrophosphorus sources, and other ferrophosphorus sources that can provide both elemental phosphorus and elemental iron can also be used in the present invention.

Preferably, in the coating material source in step (1), the carbon source is any one or a combination of at least two of glucose, sucrose, polyethylene glycol, polyvinyl alcohol or phytic acid. The carbon sources selected by the method are all organic carbon sources, and compared with inorganic carbon sources, the organic carbon sources can form more defect sites in the carbonization process, thereby being beneficial to forming new Li⁺A storage location.

Preferably, the dispersant in step (1) comprises any one or a combination of at least two of water, ethanol or acetone, and the water is preferably deionized water and/or pure water.

Preferably, step (1) adjusts the solid content to 15% to 45%, for example, 15%, 17%, 22%, 30%, 33%, 36%, 38%, 40%, 42.5%, or 45%, etc., within which sand mill clogging can be avoided, slurry can be sufficiently dispersed and ground, and actual productivity can be secured.

Preferably, the molar ratio of the lithium source, the ferrophosphorus source, the carbon source and the lithium hexafluorozirconate is Li: Fe: C: Zr (1.01 to 1.05):1 (1.0 to 1.4): 0.001 to 0.1, for example, 1.01:1:1.4:0.1, 1.05:1:1.1:0.005, 1.03:1:1.3:0.1 or 1.02:1:1.1: 0.008.

Preferably, the step (2) is carried out until the particle size of the precursor slurry is in the range of 50nm to 500nm, such as 50nm, 75nm, 85nm, 100nm, 120nm, 145nm, 160nm, 180nm, 200nm, 230nm, 265nm, 300nm, 350nm, 400nm, 450nm or 500nm, etc., preferably 130nm to 180 nm.

Preferably, the inlet temperature of the spray drying in step (3) is 180 ℃ to 360 ℃, such as 180 ℃, 200 ℃, 225 ℃, 270 ℃, 300 ℃, 320 ℃, 340 ℃ or 360 ℃, etc.

Preferably, the outlet temperature of said spray drying of step (3) is 60 ℃ to 120 ℃, such as 60 ℃, 70 ℃, 80 ℃, 95 ℃, 100 ℃, 110 ℃ or 120 ℃ and the like.

Preferably, the method for producing the spheres with at least two particle size ranges in the step (3) is as follows: spray drying is carried out by means of multi-pipe air inlet and multi-pipe air inlet. The invention can realize the preparation of spheres with different particle size ranges by controlling different air inlet speeds of the air inlet pipes and different feeding speeds of the feeding pipes.

For example, the multi-tube air inlet and multi-tube feeding mode of the invention can be carried out as follows:

the number of the spray drying air inlet pipes and the number of the feed pipes are at least 2, the air inlet pipes and the feed pipes need to be matched for use, one air inlet pipe corresponds to one feed pipe so as to form a spray drying unit group, and for at least 2 air inlet pipes, at least 2 different flow rates in the at least 2 air inlet pipes need to be ensured (the air inlet flow rate can be controlled by respectively installing gas flow meters on air inlet pipelines); for at least 2 feed pipes, it is necessary to ensure that there are at least 2 different feed volumes (which can be fed from the same barrel of slurry by connecting peristaltic pumps to the feed pipe lines).

In order to obtain particles (referred to as large particles and small particles for short) with two different particle size ranges, for example, for preparing small particles, the air inflow amount of at least 2 air inlet pipes can be in the range of 10 to 30NL/min, and the feeding amount of at least 2 feeding pipes corresponding to the at least 2 air inlet pipes one by one can be in the range of 1 to 8 ml/min. In order to prepare large particles, the air inflow range of at least 2 air inlet pipes is 50-100 NL/min, and the feeding amount range of the feeding pipes corresponding to the at least 2 air inlet pipes in a one-to-one mode is 10-20 ml/min. The air inflow of the at least 2 air inlet pipes is not completely the same but falls within the range of 10-30 NL/min, and the feeding amount of the corresponding at least 2 feeding pipes is not completely the same but falls within the range of 1-8 ml/min.

In addition, the positions of the air inlet pipe, the feeding pipe and the nozzle interface do not influence the experimental effect. In order to ensure the productivity, the number of the air inlet pipes for preparing the small particles is less than or equal to that of the air inlet pipes for preparing the large particles, and the air inlet pipes and the feeding pipes are matched in a one-to-one mode for spray granulation, so that the number of the feeding pipes for preparing the small particles is less than or equal to that of the feeding pipes for preparing the large particles under the condition.

More specific but non-limiting examples are given to illustrate the preparation of large and small particles:

first turn on N₂Gas flowmeter and corresponding N₂A peristaltic pump of each feeding pipe regulates and controls the granularity to be a certain set granularity between 7 and 20 mu m; and recording parameters of the flow meter and the peristaltic pump after the granularity is stable. Then, turn off N₂A gas flow meter and corresponding peristaltic pump, and then the remaining N₁Gas flow meter and corresponding N₁The peristaltic pump of each feeding pipe regulates and controls a certain set granularity between 500 mu m and 5 mu m. After the particle size is stabilized, N is recorded before the gas flowmeter and the corresponding peristaltic pump are started₂A gas flow meter and a peristaltic pump (N)₁And N₂All positive integers).

More preferably, the spray drying in step (3) is carried out by means of two-pipe air inlet and two-pipe feeding, and spheres with two size ranges of large and small are produced, which are also realized by adjusting the air inlet speed of each air inlet pipe and the feeding speed of each feeding pipe.

Preferably, the spray drying in the step (3) is carried out by multi-pipe air inlet and multi-pipe feeding, wherein the feeding amount of one air inlet pipe and the feeding pipe matched with the air inlet pipe for spray granulation is respectively 10 NL/min-30 NL/min and 1 ml/min-8 ml/min, and the air inlet amount of the other air inlet pipe and the feeding pipe matched with the air inlet pipe for spray granulation are respectively 50 NL/min-100 NL/min and 10 ml/min-20 ml/min.

In the preferred technical proposal, the air input quantity of one air inlet pipe is 10 NL/min-30 NL/min, such as 10NL/min, 15NL/min, 17NL/min, 18NL/min, 20NL/min, 22NL/min, 25NL/min, 28NL/min or 30 NL/min; the intake air amount of the other intake pipe is 50NL/min to 100NL/min, for example, 50NL/min, 65NL/min, 80NL/min, 90NL/min, or 100 NL/min.

In the preferred technical scheme, the feeding amount of one feeding pipe is 1 ml/min-8 ml/min, such as 1ml/min, 2ml/min, 3ml/min, 5ml/min, 6ml/min or 8 ml/min; the feeding amount of the other feeding port is 10 ml/min-20 ml/min, such as 10ml/min, 12ml/min, 15ml/min, 17ml/min, 18ml/min, 19ml/min or 20 ml/min.

More preferably, in the step (3), the spray drying is carried out by feeding the mixture through two air inlets and two air pipes, wherein the air inflow of one air inlet pipe and the feeding amount of the feeding pipe matched with the air inlet pipe for spray granulation are respectively 20 NL/min-25 NL/min and 2 ml/min-4 ml/min, and the air inflow of the other air inlet pipe and the feeding amount of the feeding pipe matched with the air inlet pipe for spray granulation are respectively 50 NL/min-60 NL/min and 15 ml/min-18 ml/min.

In the method, in the spray drying process in the step (3), the temperature of the feeding hole, the temperature of the discharging hole, the feeding rate and the air input are all key parameters for controlling the atomization formation of the spheres with different particle size ranges, and the combination performance of the atomization granulation can also be influenced.

Preferably, the sintering of step (4) is performed under an inert atmosphere, which includes any one of a nitrogen atmosphere, an argon atmosphere, a helium atmosphere, a neon atmosphere, a krypton atmosphere, or a xenon atmosphere, or a combination of at least two atmospheres.

Preferably, the sintering in step (4) is performed in a controlled temperature electric furnace.

Preferably, the sintering temperature in step (4) is 600 ℃ to 800 ℃, such as 600 ℃, 650 ℃, 700 ℃, 720 ℃, 750 ℃, 775 ℃, 785 ℃, or 800 ℃, etc.

Preferably, the sintering time in step (4) is 2h to 24h, such as 2h, 3h, 4h, 5h, 6.5h, 8h, 10h, 12h, 15h, 18h, 20h, 22h or 24h, etc., preferably 8h to 12 h.

As a further preferred technical solution of the method of the present invention, the method comprises the steps of:

(1) adding a lithium source, a ferrophosphorus source, a carbon source and lithium hexafluorozirconate into a grinding tank according to the molar ratio of Li to Fe to C to Zr (1.01-1.05) to 1 (1.0-1.4) to (0.001-0.1), and adding a dispersing agent to adjust the solid content to obtain precursor slurry;

(2) grinding the precursor slurry until the particle size of the precursor slurry is 50-500 nm so as to activate the lithium iron phosphate reaction raw material, the carbon source and the lithium hexafluorozirconate;

(3) spray drying is carried out by utilizing a spray dryer in a mode of feeding materials through two pipes of air inlet and two pipes of air inlet, spheres with at least two particle size ranges are manufactured, and the specific parameters are as follows:

the air inflow of one air inlet pipe and the feeding amount of the feeding pipe matched with the air inlet pipe for spray granulation are respectively 10 NL/min-30 NL/min and 1/min-8 ml/min, and the air inflow of the other air inlet pipe and the feeding amount of the feeding pipe matched with the air inlet pipe for spray granulation are respectively 50 NL/min-100 NL/min and 10 ml/min-20 ml/min;

the inlet temperature of spray drying is 180-360 ℃, and the outlet temperature is 60-120 ℃;

(4) collecting the powder obtained in the step (3), and sintering the powder for 2 to 24 hours at the temperature of 600 to 800 ℃ in an inert atmosphere to obtain the lithium hexafluorozirconate and carbon co-coated lithium iron phosphate composite material;

the inert atmosphere comprises any one of a nitrogen atmosphere, an argon atmosphere, a helium atmosphere, a neon atmosphere, a krypton atmosphere or a xenon atmosphere or a combination of at least two of the atmospheres.

In a third aspect, the present invention provides a positive electrode sheet comprising the lithium hexafluorozirconate described in the first aspect and a carbon-co-coated lithium iron phosphate composite as a positive electrode material.

Preferably, the positive electrode sheet further comprises a foil, a binder and a conductive agent.

In a fourth aspect, the present invention provides a lithium ion battery comprising the positive electrode sheet according to the third aspect of the present invention;

preferably, the lithium ion battery further comprises a negative electrode sheet, a separator and an electrolyte.

The reagents and equipment used in the methods of the invention are commercially available and do not require special customization.

Compared with the prior art, the invention has the following beneficial effects:

(1) the invention provides a lithium hexafluorozirconate and carbon co-coated lithium iron phosphate composite material with a novel structure and a preparation method thereof, the method grinds precursor slurry of a lithium source, a ferrophosphorus source and a coating treatment source, can activate raw materials and a coating material, has a large atomization granulation process, and can improve the pole piece compaction density of the material by small sphere collocation; the coating material can form a 'Fe-F-C' bond on the surface layer of the lithium iron phosphate material to form new Li in the calcining process⁺The active site improves the first-turn capacity of the composite material in the charging and discharging process of the full battery; the preparation process of the composite material is simple, the energy consumption is low, no waste liquid is generated, and the prepared composite material has excellent electrochemical performance and is suitable for industrial production.

(2) The lithium hexafluorozirconate and carbon co-coated lithium iron phosphate composite material is used as a positive electrode material to prepare a positive electrode plate and assembled into a battery, and the compaction density of the electrode plate is high and is 2.53g/cm³The above; the first-turn capacity of the battery is high, the cycle performance and the low-temperature performance are good, the capacity retention rate of the battery is more than 95.3% after 1000 cycles, and the capacity retention rate of the battery is more than 75.0% at minus 20 ℃.

Drawings

FIG. 1 is a particle size distribution curve of an atomized and granulated powder of example 1.

Fig. 2 is an SEM image of the lithium hexafluorozirconate and carbon co-coated lithium iron phosphate composite prepared in example 1.

Detailed Description

The technical scheme of the invention is further explained by the specific implementation mode in combination with the attached drawings.