A method for preparing a lithium ion battery separator using secondary aluminum dross

Abstract

The application relates to a method for preparing a lithium ion battery diaphragm by using secondary aluminum ash, and belongs to the diaphragm material field. The method is to convert aluminum components such as elemental aluminum, aluminum oxide, aluminum nitride, aluminum carbide and magnesium aluminum spinel in the secondary aluminum ash into sodium metaaluminate under high temperature by using an alkaline auxiliary agent such as sodium carbonate or sodium hydroxide. Then, the sodium metaaluminate is uniformly mixed with powdered instant sodium silicate, a binder and a pore-forming agent, is formed into a shape by die pressing, and is calcined at high temperature to obtain a porous zeolite phase ceramic diaphragm. The ceramic diaphragm has excellent thermal stability, high porosity and good electrolyte affinity, effectively improves ion conductivity, and improves the capacity retention rate of the battery during large-current charging and discharging and long-time operation.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion battery separators, and relates to a preparation method of a lithium-ion battery separator with high temperature resistance and suitable for large current charge and discharge. Background Art

[0002] A battery separator is a layer of separator material between the positive and negative electrodes of a battery. Its main function is to isolate the positive and negative electrodes and insulate electrons, but it allows ions in the electrolyte to freely transfer between the positive and negative electrodes, thus completing the battery reaction. Currently, the commercially available lithium-ion battery separator materials are mainly porous polyolefins such as polyethylene (PE) or polypropylene (PP), etc. Although polyolefin separators have many advantages for lithium-ion batteries, the melting points of polyolefin separators are relatively low. The melting points of polyethylene and polypropylene are 130°C and 150°C respectively. When the temperature exceeds this value, the separator will melt, causing the battery to short-circuit. In practical applications, the battery may quickly heat up to 200°C. Especially for large-capacity batteries used in large-scale battery energy storage power stations supporting wind energy and photovoltaic power generation, the large current charge and discharge are more likely to cause fluctuations in the battery temperature, thus facing more severe safety problems. To solve this problem, researchers use inorganic particles such as Al2O3, SiO2, ZrO2, etc. to coat the surface of the polyolefin separator to make a composite separator, and utilize the high heat resistance of the inorganic particles to improve the thermal stability of the composite separator. However, there are still organic materials (polyolefin matrix or organic binder) in the coated separator, and these organic materials still have problems of thermal degradation and thermal shrinkage, resulting in serious safety problems for the battery in an overheated environment. Therefore, some scholars have proposed to use nano-Al2O3 and SiO2 to prepare pure inorganic separators by high-temperature calcination. This kind of inorganic separator has incomparable thermal stability, but the low porosity, ionic conductivity and poor electrolyte affinity of the separator are not conducive to the improvement of battery performance. Therefore, on the basis of retaining the high heat resistance advantage of the inorganic separator, finding new raw materials and new methods to improve the porosity, ionic conductivity and electrolyte affinity of the inorganic separator and obtaining a new type of porous inorganic separator has become a new research idea.

[0003] Aluminum ash is a solid product produced during the production of metallic aluminum or aluminum alloy, which is composed of metallic aluminum, aluminum oxide and other compounds, and is divided into primary aluminum ash and secondary aluminum ash. Metallic aluminum is extracted from primary aluminum ash to obtain secondary aluminum ash. Due to the use of inorganic salt additives in this process, the composition of secondary aluminum ash becomes more complex. The metallic aluminum and aluminum nitride in it can generate hydrogen and ammonia when encountering water or getting damp. Currently, the utilization of secondary aluminum ash mainly involves recovering aluminum oxide, sodium chloride, potassium chloride from secondary aluminum ash, and using secondary aluminum ash as raw materials to prepare low-value-added products such as building materials, water purifying agents, refractory materials, etc. There is no report on the research of using secondary aluminum ash for the preparation of high-value-added products such as lithium-ion battery separators. Summary of the Invention:

[0004] The purpose of this invention is to eliminate the battery safety hazards caused by the poor thermal stability of lithium-ion battery separators, improve the battery's capacity retention rate during high-current charging and discharging and long-term operation, and fully utilize the various components in secondary aluminum ash to achieve high-value-added applications of solid waste. To this end, secondary aluminum ash is used as a key raw material. First, it is mixed with an alkaline additive and calcined in a muffle furnace to obtain a calcined product. Then, the calcined product is mixed evenly with powdered fast-dissolving sodium silicate, a binder, and a pore-forming agent, molded into a green body, and calcined again to obtain a porous ceramic separator for lithium-ion batteries.

[0005] The objective of this invention is achieved through the following technical solution:

[0006] Secondary aluminum ash is thoroughly mixed with alkaline additives and heated in a muffle furnace at a rate of 5-10°C / min from room temperature to 900-1100°C, and held for 1-4 hours. The resulting calcined product is then mixed evenly with powdered fast-dissolving sodium silicate, binder, and pore-forming agent, and molded into a green body. After drying, the green body is heated in a muffle furnace at a rate of 3-7°C / min from room temperature to 1000-1200°C and held for 4-8 hours to obtain a lithium-ion battery separator with an all-ceramic matrix. The secondary aluminum ash is the ash residue after primary aluminum ash extraction, which is dry-milled, dried, and passed through a 200-mesh square-hole sieve to obtain secondary aluminum ash powder. Finally; the alkaline additive is sodium carbonate or sodium hydroxide; the mass ratio of secondary aluminum ash to alkaline additive is 1:0.5-2; the binder is one of hydroxyethyl cellulose, hydroxypropyl cellulose, and sodium carboxymethyl cellulose; the pore-forming agent is one of starch, glucose, and urea; the obtained calcined product is mixed with powdered fast-dissolving sodium silicate, binder, and pore-forming agent at a mass ratio of 50-80:40-60:0.1-1:30-40; the molding conditions are: molding pressure of 1-20 MPa, holding time of 0.1-5 minutes; the pore-forming agent is a powder sample that has passed through a 300-mesh square hole sieve.

[0007] Beneficial Effects: This invention uses secondary aluminum ash as the main raw material to prepare lithium-ion battery separators. It utilizes alkaline additives such as sodium carbonate or sodium hydroxide to transform the aluminum-containing components in the secondary aluminum ash, such as elemental aluminum, alumina, aluminum nitride, aluminum carbide, and magnesium aluminum spinel, into sodium aluminate at high temperatures. The sodium aluminate is then mixed with powdered, readily soluble sodium silicate, molded, and calcined at high temperatures, undergoing a zeolite phase transformation to become the main matrix phase of the ceramic. The sodium salts, fluoride salts, and small amounts of heavy metal ions in the secondary aluminum ash can be transformed into crystalline phases at high temperatures for stable solidification. The use of a pore-forming agent constructs a porous structure within the ceramic, ultimately obtaining a porous zeolite phase ceramic separator. Attached image description:

[0008] Figure 1 Optical photographs of porous ceramic diaphragms

[0009] Figure 2 Scanning electron microscope images of porous ceramic diaphragms

[0010] Figure 3 XRD patterns of porous ceramic membranes

[0011] Figure 4 Rate performance curves of lithium / lithium iron phosphate batteries using porous ceramic separators Detailed implementation method:

[0012] The present invention will be further described in detail with reference to the embodiments:

[0013] Secondary aluminum ash is thoroughly mixed with sodium carbonate or sodium hydroxide at a mass ratio of 1:0.5-2. The mixture is then heated in a muffle furnace at a rate of 5-10℃ / min from room temperature to 900-1100℃ and held for 1-4 hours. The resulting calcined product is then mixed uniformly with powdered fast-dissolving sodium silicate, a binder (one of hydroxyethyl cellulose, hydroxypropyl cellulose, or sodium carboxymethyl cellulose), and a pore-forming agent (one of starch, glucose, or urea) at a mass ratio of 50-80:40-60:0.1-1:30-40. The mixture is then molded into a green body at a molding pressure of 1-20 MPa and a holding time of 0.1-5 minutes. This green body is then heated in a muffle furnace at a rate of 3-7℃ / min from room temperature to 1000-1200℃ and held for 4-8 hours to obtain a porous ceramic diaphragm.

[0014] Example 1

[0015] Secondary aluminum ash and sodium carbonate were thoroughly mixed at a mass ratio of 1:0.5 and heated in a muffle furnace from room temperature to 1000°C at a heating rate of 7°C / min, and held at that temperature for 2 hours. The calcined product was then mixed with powdered fast-dissolving sodium silicate, hydroxyethyl cellulose, and starch at a mass ratio of 50:50:0.5:30 and molded into a green body at a molding pressure of 5 MPa and a holding time of 2 minutes. The green body was then heated in a muffle furnace from room temperature to 1000°C at a heating rate of 4°C / min and held at that temperature for 4 hours to obtain a porous ceramic diaphragm.

[0016] The porous ceramic membrane has a porosity of 54.3%, a liquid absorption rate of 203%, and an ionic conductivity of 1.9 mS / cm. -1 .

[0017] Example 2

[0018] Secondary aluminum ash and sodium hydroxide were thoroughly mixed at a mass ratio of 1:1 and heated in a muffle furnace from room temperature to 1000°C at a heating rate of 6°C / min, and held at that temperature for 3 hours. The calcined product was then mixed with powdered fast-dissolving sodium silicate, hydroxypropyl cellulose, and glucose at a mass ratio of 60:40:0.1:35. The mixture was then molded into a green body at a molding pressure of 2 MPa and a holding time of 5 minutes. This green body was then heated in a muffle furnace from room temperature to 1100°C at a heating rate of 7°C / min and held at that temperature for 5 hours to obtain a porous ceramic diaphragm.

[0019] The porous ceramic membrane has a porosity of 55.7%, a liquid absorption rate of 197%, and an ionic conductivity of 2.2 mS / cm. -1 .

[0020] Example 3

[0021] Secondary aluminum ash and sodium hydroxide were thoroughly mixed at a mass ratio of 1:2 and heated in a muffle furnace from room temperature to 900°C at a heating rate of 5°C / min, and held at that temperature for 1 hour. The calcined product was then mixed with powdered fast-dissolving sodium silicate, sodium carboxymethyl cellulose, and urea at a mass ratio of 70:45:0.5:40. The mixture was then molded into a green body at a molding pressure of 10 MPa and a holding time of 2 minutes. This green body was then heated in a muffle furnace from room temperature to 1000°C at a heating rate of 3°C / min and held at that temperature for 7 hours to obtain a porous ceramic diaphragm.

[0022] The porous ceramic membrane has a porosity of 62.1%, a liquid absorption rate of 239%, and an ionic conductivity of 2.6 mS / cm. -1 .

[0023] Example 4

[0024] Secondary aluminum ash and sodium carbonate were thoroughly mixed at a mass ratio of 1:1.5 and heated in a muffle furnace from room temperature to 1100°C at a heating rate of 10°C / min, and held at that temperature for 4 hours. The calcined product was then mixed with powdered instant sodium silicate, hydroxypropyl cellulose, and starch at a mass ratio of 80:55:1:40 and molded into a green body at a molding pressure of 1 MPa and a holding time of 5 minutes. The green body was then heated in a muffle furnace from room temperature to 1200°C at a heating rate of 5°C / min and held at that temperature for 8 hours to obtain a porous ceramic diaphragm.

[0025] The porous ceramic membrane has a porosity of 60.9%, a liquid absorption rate of 227%, and an ionic conductivity of 2.0 mS / cm. -1 .

[0026] Example 5

[0027] Secondary aluminum ash and sodium hydroxide were thoroughly mixed at a mass ratio of 1:1.2 and heated in a muffle furnace from room temperature to 1100°C at a heating rate of 9°C / min, and held at that temperature for 2 hours. The calcined product was then mixed with powdered fast-dissolving sodium silicate, sodium carboxymethyl cellulose, and urea at a mass ratio of 65:60:1:32. The mixture was then molded into a green body at a molding pressure of 20 MPa and a holding time of 0.1 minutes. This green body was then heated in a muffle furnace from room temperature to 1100°C at a heating rate of 6°C / min and held at that temperature for 6 hours to obtain a porous ceramic diaphragm.

[0028] The porous ceramic membrane has a porosity of 49.4%, a liquid absorption rate of 180%, and an ionic conductivity of 1.8 mS / cm. -1 .

[0029] Example 6

[0030] Secondary aluminum ash and sodium hydroxide were thoroughly mixed at a mass ratio of 1:0.9 and heated in a muffle furnace from room temperature to 900°C at a heating rate of 8°C / min, and held at that temperature for 4 hours. The calcined product was then mixed with powdered fast-dissolving sodium silicate, hydroxyethyl cellulose, and glucose at a mass ratio of 55:60:0.2:35 and molded into a green body at a molding pressure of 4 MPa and a holding time of 5 minutes. The green body was then heated in a muffle furnace from room temperature to 1100°C at a heating rate of 7°C / min and held at that temperature for 4 hours to obtain a porous ceramic diaphragm.

[0031] The porous ceramic membrane has a porosity of 51.2%, a liquid absorption rate of 195%, and an ionic conductivity of 1.7 mS / cm. -1 .

Claims

1. A method for preparing a lithium ion battery separator using secondary aluminum dross, characterized by, The method comprises the following steps: The secondary aluminum ash is mixed with an alkaline additive, and then the mixture is heated in a muffle furnace at a temperature increasing rate of 5-10 DEG C / min from room temperature to 900-1100 DEG C, and is kept at the temperature for 1-4 hours; the obtained calcined product is mixed with powdered instant sodium silicate, a binder and a pore-forming agent, and then is molded into a green body; the green body is dried and then is heated in a muffle furnace at a temperature increasing rate of 3-7 DEG C / min from room temperature to 1000-1200 DEG C, and is kept at the temperature for 4-8 hours to obtain a lithium ion battery separator of a full ceramic matrix; the secondary aluminum ash is a residue after extracting elemental aluminum from primary aluminum ash, and is obtained by dry ball milling, drying and sieving through a 200-mesh square hole screen; the alkaline additive is sodium carbonate or sodium hydroxide; the mass ratio of the secondary aluminum ash to the alkaline additive is 1:0.5-2; the binder is one of hydroxyethyl cellulose, hydroxypropyl cellulose and sodium carboxymethyl cellulose; the pore-forming agent is one of starch, glucose and urea; and the obtained calcined product is mixed with the powdered instant sodium silicate, the binder and the pore-forming agent at a mass ratio of 50-80:40-60:0.1-1:30-40.

2. The method for preparing a lithium ion battery separator using secondary aluminum ash according to claim 1, characterized by, The molding pressure is 1-20 MPa, and the pressure keeping time is 0.1-5 min.

3. The method for preparing a lithium ion battery separator using secondary aluminum ash according to claim 1, characterized by, The pore-forming agent is a powder sample sieved through a 300-mesh square hole screen.

4. A lithium ion battery separator prepared using secondary aluminum dross, characterized by: The lithium ion battery separator is prepared by any one of the methods of claims 1-3.

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