阅读说明：本技术 一种淀粉改性包覆磷酸铁制备锂离子电池正极材料的方法 (Method for preparing lithium ion battery anode material by using starch modified coated iron phosphate ) 是由 杨建文 郑家炜 徐月姬 刘鑫鑫 吴金梅 肖顺华 黄斌 于 2021-07-28 设计创作，主要内容包括：本发明公开了一种淀粉改性包覆磷酸铁制备锂离子电池正极材料的方法。(1)将磷酸铁和碳酸锂研磨,加入蒸馏水,搅拌分散液,磷酸铁和碳酸锂的摩尔比为2:1；(2)在分散液中加入淀粉和淀粉改性剂,水浴加热,恒温搅拌,干燥,得磷酸铁改性淀粉包覆前驱体,其中：淀粉和淀粉改性剂质量比为1～4︰1；(3)将磷酸铁改性淀粉包覆前驱体,在氩气气氛下经过预烧和焙烧反应,得到LiFePO-(4)/C复合正极材料。本发明借助分子增韧改性提高磷酸铁颗粒表面淀粉糊成膜的均匀性、柔韧性和稳定性,通过碳热还原固相反应,制得颗粒尺寸、分散性和电化学性能良好的LiFePO-(4)/C复合正极材料。(The invention discloses a method for preparing a lithium ion battery anode material by using starch modified coated iron phosphate. (1) Grinding iron phosphate and lithium carbonate, adding distilled water, and stirring the dispersion liquid, wherein the molar ratio of the iron phosphate to the lithium carbonate is 2: 1; (2) adding starch and a starch modifier into the dispersion liquid, heating in a water bath, stirring at a constant temperature, and drying to obtain an iron phosphate modified starch coated precursor, wherein: the mass ratio of the starch to the starch modifier is 1-4: 1; (3) the iron phosphate modified starch is coated on the precursor, and the LiFePO is obtained by pre-sintering and roasting reaction under the argon atmosphere 4 the/C composite cathode material. The invention improves the uniformity, flexibility and stability of starch paste film forming on the surfaces of iron phosphate particles by virtue of molecular toughening modification, and prepares LiFePO with good particle size, dispersibility and electrochemical properties through carbothermic reduction solid-phase reaction 4 the/C composite cathode material.)

1. A method for preparing a lithium ion battery anode material by using starch modified coated iron phosphate is characterized by comprising the following specific steps:

(1) respectively weighing 0.3809-3.8085 g of iron phosphate and 0.1000-1.0000 g of lithium carbonate in an agate mortar, grinding for 20-30 minutes, transferring into a beaker, adding 10-100 mL of distilled water, stirring and dispersing to obtain a dispersion liquid, wherein the molar ratio of the iron phosphate to the lithium carbonate is 2: 1;

(2) adding 0.1082-1.0820 g of starch and 0.0216-1.0820 g of starch modifier into the dispersion liquid obtained in the step (1), heating in a water bath to 60-100 ℃, stirring at a constant temperature to form light yellow viscous slurry, and then drying in a 120 ℃ forced air drying oven for more than 12 hours to obtain an iron phosphate modified starch coated precursor, wherein: the mass ratio of the starch to the starch modifier is 1-4: 1;

(3) grinding the iron phosphate modified starch coated precursor obtained in the step (2) by using an agate mortar for 10-30 minutes, transferring the iron phosphate modified starch coated precursor into a porcelain ark, placing the porcelain ark into a vacuum tube furnace, heating to 360-400 ℃ at a heating rate of 2-4 ℃/min under an argon atmosphere, presintering for 1-3 hours, then heating to 600-800 ℃ at the same heating rate, preserving heat for 2-20 hours, then naturally cooling to room temperature, discharging, grinding for 10-20 minutes to obtain LiFePO₄a/C composite positive electrode material;

the starch is one or more of soluble starch, amylose, amylopectin, modified starch, dextrin and starch derivatives;

the starch modifier is a compound capable of eliminating or reducing the action of hydrogen bonds in starch chains, namely water, urea, glycerol and glycol, and one or more of organic matter modifiers and inorganic matter modifiers having a plasticizing effect on starch.

Technical Field

The invention belongs to the technical field of lithium ion battery materials, and particularly relates to a method for preparing a lithium ion battery anode material by using starch modified coated iron phosphate.

Background

The lithium ion battery has the advantages of high energy density, high working voltage, long cycle life, no memory effect and the like, and is widely applied to a plurality of fields of daily electronic products, electric automobiles, energy storage and the like. The positive electrode material is the key for determining the performance of the lithium ion battery and is important for the development of the lithium ion battery. Currently, lithium cobaltate (LiCoO) is the mainstream positive electrode material₂) Lithium manganate (LiMn)₂O₄) Ternary material (NCM/NCA) and lithium iron phosphate (LiFePO)₄) And the like. Wherein the olivine structure LiFePO₄The positive electrode material has larger specific discharge capacity (170mAh g)^-1) The lithium ion battery positive electrode material has the advantages of excellent cycle performance, good thermal stability, low price, rich raw materials, environmental protection and the like, and is considered to have great potential. However, LiFePO₄Li of (2)⁺The diffusion rate and the electronic conductivity thereof are extremely low, which greatly influences the exertion of the electrochemical performance thereof. Surface carbon coating enables improvement of electron conductivity and Li⁺The improvement of the ion transport property has become to improve the LiFePO₄One of the effective means for the electrochemical performance of the positive electrode material.

Starch is an abundant and cheap natural carbon source material, and has been researched to be used for LiFePO₄And modifying the positive electrode material by carbon coating. However, starch has poor molecular chain flexibility, strong intermolecular force and great molecular chain rigidity, so that starch has poor film forming property, and a starch film is brittle and hard, is easy to break and fall off and is used as carbon-coated LiFePO₄The composite material particles obtained from the raw materials are seriously agglomerated, and the specific capacity, the circulation, the multiplying power and other performances of the composite material are not ideal enough. Thus, LiFePO₄the/C industryStarch is rarely used as a carbon source material in the chemical process. With the rapid development of the application of the lithium iron phosphate battery in the fields of electric automobiles and energy storage, the natural and cheap starch is used as a modified material of the iron phosphate, and the method has practical significance for the low-cost manufacture of the high-energy lithium iron phosphate cathode material.

Disclosure of Invention

The invention aims to enhance the flexibility of starch molecules through chemical modification, improve the dispersion uniformity of iron phosphate particles in starch slurry and the integrity of surface film formation so as to inhibit LiFePO in the subsequent pyrolysis and carbon reduction processes₄Agglomeration and overgrowth of/C particles.

The method comprises the following specific steps:

(1) respectively weighing 0.3809-3.8085 g of iron phosphate and 0.1000-1.0000 g of lithium carbonate in an agate mortar, grinding for 20-30 minutes, transferring into a beaker, adding 10-100 mL of distilled water, stirring and dispersing to obtain a dispersion liquid, wherein the molar ratio of the iron phosphate to the lithium carbonate is 2: 1.

(2) Adding 0.1082-1.0820 g of starch and 0.0216-1.0820 g of starch modifier into the dispersion liquid obtained in the step (1), heating in a water bath to 60-100 ℃, stirring at a constant temperature to form light yellow viscous slurry, and then drying in a 120 ℃ forced air drying oven for more than 12 hours to obtain an iron phosphate modified starch coated precursor, wherein: the mass ratio of the starch to the starch modifier is 1-4: 1.

(3) Grinding the iron phosphate modified starch coated precursor obtained in the step (2) by using an agate mortar for 10-30 minutes, transferring the iron phosphate modified starch coated precursor into a porcelain ark, placing the porcelain ark into a vacuum tube furnace, heating to 360-400 ℃ at a heating rate of 2-4 ℃/min under an argon atmosphere, presintering for 1-3 hours, then heating to 600-800 ℃ at the same heating rate, preserving heat for 2-20 hours, then naturally cooling to room temperature, discharging, grinding for 10-20 minutes to obtain LiFePO₄the/C composite cathode material.

The starch is one or more of soluble starch, amylose, amylopectin, modified starch, dextrin and starch derivatives.

The starch modifier is a compound capable of eliminating or reducing the action of hydrogen bonds in starch chains, namely water, urea, glycerol and glycol, and one or more of organic matter modifiers and inorganic matter modifiers having a plasticizing effect on starch.

The invention improves the uniformity, flexibility and stability of starch paste film forming on the surfaces of iron phosphate particles by virtue of molecular toughening modification, and prepares LiFePO with good particle size, dispersibility and electrochemical properties through carbothermic reduction solid-phase reaction₄the/C composite cathode material.

Drawings

FIG. 1 shows LiFePO prepared by the present invention₄An SEM photo of the morphology of the/C composite cathode material, wherein: a-example 1, b-example 2, c-example 3.

FIG. 2 shows LiFePO prepared by the present invention₄a/C composite positive electrode material cyclic voltammetry performance diagram, wherein: a-example 1, b-example 2, c-example 3.

FIG. 3 shows LiFePO prepared by the present invention₄The charge-discharge performance diagram of the/C composite positive electrode material is as follows: a-example 1, b-example 2, c-example 3.

Detailed Description

Example 1:

(1) 0.7617g of iron phosphate (battery grade, Jingxi Xiangtan electrochemical technology Co., Ltd.) and 0.2000g of lithium carbonate (analytical reagent, West Longscience Co., Ltd.) were weighed respectively in an agate mortar, ground for 20 minutes, transferred into a beaker, added with 20mL of distilled water, and stirred and dispersed to obtain a dispersion.

(2) And (2) adding 0.2164g of soluble starch (analytically pure, chemical reagent of national medicine group, Ltd.) into the dispersion liquid obtained in the step (1), heating in a water bath to 90 ℃, stirring at constant temperature to form light yellow viscous slurry, and then drying in a 120 ℃ forced air drying oven for more than 12 hours to obtain the iron phosphate modified starch coated precursor.

(3) Grinding the precursor coated with the iron phosphate modified starch obtained in the step (2) by using an agate mortar for 10 minutes, transferring the precursor into a porcelain ark, placing the porcelain ark into a vacuum tube furnace, heating the porcelain ark to 360 ℃ at a heating rate of 4 ℃/min under an argon atmosphere, presintering the porcelain ark for 2 hours, heating the porcelain ark to 650 ℃ at the same heating rate, preserving the heat for 15 hours, naturally cooling the porcelain ark to room temperature, discharging the porcelain ark, and grinding the porcelain ark for 10 minutes to obtain LiFePO₄the/C composite positive electrode material sample-a.

As can be seen from SEM pictures (see the attached figure 1-a in the specification), LiFePO prepared by coating iron phosphate with starch by direct gelatinization and pyrolysis₄The particle sizes of the/C cathode material (a) are different, and a more serious agglomeration phenomenon exists.

LiFePO prepared in the above way is mixed according to the mass ratio of 8:1:1₄Grinding 0.2000g of/C positive electrode material, 0.0250g of PVDF binder and 0.0250g of acetylene black conductive agent in an agate mortar until the materials are uniformly mixed, adding 1.5mL of N-methyl pyrrolidone (NMP), continuously grinding for 20 minutes, coating the mixture on an aluminum foil collector by using a 75-micrometer coater, drying the mixture overnight at 105 ℃ in a vacuum oven, punching the sheet, weighing the sheet to obtain LiFePO₄a/C electrode plate; with LiFePO₄The electrode plate of the electrode is used as a research electrode, the metal lithium plate is used as a reference electrode and a counter electrode, and the amount of the electrode plate is 1mol L^-1LiPF₆(EC + DMC) solution (volume ratio 1:1) as electrolyte, Celgard2500 membrane as diaphragm, in argon-filled glove box (water, oxygen content all)<0.1ppm) assembled CR2032 type coin cells and left for 4 hours to test the electrochemical performance of the cells. As can be seen from the cyclic voltammetry curve (see the attached figure 2-a of the specification), the oxidation peak and reduction peak currents are small, and the potential difference between the oxidation peak and the reduction peak slightly increases with the increase of the cycle number; as can be seen from the charge-discharge curve at its current density of 0.2C (see FIG. 3-a in the specification), the specific capacity of sample-a is about 133.9mAh g^-1。

Example 2:

(1) 0.7617g of iron phosphate (battery grade, Jingxi Xiangtan electrochemical technology Co., Ltd.) and 0.2000g of lithium carbonate (analytical reagent, West Longscience Co., Ltd.) were weighed respectively in an agate mortar, ground for 20 minutes, transferred into a beaker, added with 20mL of distilled water, and stirred and dispersed to obtain a dispersion.

(2) Adding 0.2164g of soluble starch (analytically pure, chemical reagents of national medicine group, Inc.) and 0.2164g of urea (analytically pure, West Longsco science, Inc.) into the dispersion obtained in the step (1), heating in a water bath to 90 ℃, stirring at constant temperature to form light yellow viscous slurry, and then drying in a 120 ℃ forced air drying oven for more than 12 hours to obtain the precursor coated with the iron phosphate modified starch.

(3) Grinding the precursor coated with the iron phosphate modified starch obtained in the step (2) by using an agate mortar for 10 minutes, transferring the precursor into a porcelain ark, placing the porcelain ark into a vacuum tube furnace, heating the porcelain ark to 360 ℃ at a heating rate of 4 ℃/min under an argon atmosphere, presintering the porcelain ark for 2 hours, heating the porcelain ark to 650 ℃ at the same heating rate, preserving the heat for 15 hours, naturally cooling the porcelain ark to room temperature, discharging the porcelain ark, and grinding the porcelain ark for 20 minutes to obtain LiFePO₄sample/C composite positive electrode material-b.

LiFePO₄The chemical reagent, the electrode manufacturing method and the electrochemical performance testing method used for preparing the/C composite cathode material sample-b are the same as those in example 1, and as can be seen from an SEM photo (see the attached figure 1-b in the specification), particles of the sample-b are mainly spherical, the particle size is mainly concentrated in the range of 0.1-0.2 microns, but small particles with the particle size of about 0.05 microns and agglomerated large particles with irregular shapes exist; the current of the oxidation peak and the reduction peak in the cyclic voltammetry curve (see the attached figure 2-b of the specification) is slightly larger than that of the sample-a, and the potential difference of the oxidation peak and the reduction peak is slightly increased along with the increase of the cycle number; its specific capacity is about 147.7mAh g^-1(see FIG. 3-b of the specification).

Example 3:

(1) 0.7617g of iron phosphate (battery grade, Jingxi Xiangtan electrochemical technology Co., Ltd.) and 0.2000g of lithium carbonate (analytical reagent, West Longscience Co., Ltd.) were weighed respectively in an agate mortar, ground for 20 minutes, transferred into a beaker, added with 20mL of distilled water, and stirred and dispersed to obtain a dispersion.

(2) Adding 0.2164g of soluble starch (analytically pure, chemical reagents of national medicine group, Inc.) and 0.0722g of urea (analytically pure, West Longsco science, Inc.) into the dispersion obtained in the step (1), heating in a water bath to 90 ℃, stirring at constant temperature to form light yellow viscous slurry, and then drying in a 120 ℃ forced air drying oven for 12 hours to obtain the precursor coated with the iron phosphate modified starch.

(3) Grinding the precursor coated with the iron phosphate modified starch obtained in the step (2) by using an agate mortar for 20 minutes, transferring the precursor into a porcelain ark, placing the porcelain ark into a vacuum tube furnace, heating the porcelain ark to 360 ℃ at a heating rate of 4 ℃/min under an argon atmosphere, presintering the porcelain ark for 2 hours, and then heating the porcelain ark at the same heating rateKeeping the temperature for 15 hours at 650 ℃, then naturally cooling to room temperature, discharging, grinding for 20 minutes to obtain LiFePO₄the/C composite positive electrode material sample-C.

LiFePO₄The chemical reagents, the electrode manufacturing and the electrochemical performance testing method used for preparing the/C composite cathode material sample-C are the same as those in the example 1, and as can be seen from an SEM picture (see the attached figure 3-C in the specification), the particles of the sample-C are spherical, the particle size is mainly concentrated on about 0.15 mu m, and the dispersibility is good; the redox peak current in the cyclic voltammetry curve (see the attached figure 2-c in the specification) is larger than that of the sample-a and the sample-b, and the redox peak potential difference is slightly reduced along with the increase of the cycle number; its specific capacity is about 161.6mAh g^-1(see FIG. 3-c of the specification).