High-temperature-resistant lithium battery diaphragm and preparation method thereof

Abstract

The invention discloses a high-temperature-resistant lithium battery diaphragm, and relates to the technical field of lithium battery diaphragms.The high-temperature-resistant lithium battery diaphragm is prepared from, by weight, polyethylene, polypropylene, nano-hydroxyapatite super-long nanowires, a silane coupling agent, a catalyst and ceramic particles, and the total weight of all the raw materials is 100 parts. Through an elaborately designed raw material formula and a preparation process, high thermal stability and mechanical strength of the diaphragm are realized, and the requirements of a high-performance lithium battery are met. The nanoscale inorganic filler in the diaphragm not only improves the heat resistance of the diaphragm, but also keeps good ion transmission performance. And by adding the silane coupling agent and the catalyst, the binding force between the inorganic filler and the polyolefin matrix is further enhanced, and a three-dimensional network structure is formed through a grafting reaction, so that the high-temperature resistance and safety of the diaphragm are remarkably improved. The invention also provides a corresponding preparation method, which ensures the uniformity and consistency of the diaphragm.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium battery separators, and in particular relates to a high temperature resistant lithium battery separator and a preparation method thereof. Background Art

[0002] In the structure of lithium batteries, the diaphragm is one of the key internal components. The performance of the diaphragm determines the interface structure and internal resistance of the battery, and directly affects the battery's capacity, cycle and safety performance. A diaphragm with excellent performance plays an important role in improving the overall performance of the battery. The main function of the diaphragm is to separate the positive and negative electrodes of the battery to prevent the two electrodes from contacting and short-circuiting. In addition, it also has the function of allowing electrolyte ions to pass through. The diaphragm material is non-conductive, and its physical and chemical properties have a great influence on the performance of the battery. Different types of batteries use different diaphragms. For lithium battery series, since the electrolyte is an organic solvent system, a diaphragm material resistant to organic solvents is required, and a high-strength thin-film polyolefin porous membrane is generally used. However, traditional lithium battery diaphragms are easy to melt at high temperatures, posing a safety hazard. Therefore, the development of diaphragms with high thermal stability is crucial to improving the safety of lithium batteries. Summary of the invention

[0003] To achieve the above-mentioned purpose, the technical scheme of the present invention is as follows: a high temperature resistant lithium battery separator, wherein the battery separator is made of the following raw materials in parts by weight: polyethylene, polypropylene, nano-hydroxyapatite ultra-long nanowires, silane coupling agent, catalyst and ceramic particles, and the total weight of each raw material is 100 parts.

[0004] As an improvement of the present invention, the total weight of the polyethylene and the polypropylene is 90-95 parts.

[0005] As an improvement of the present invention, the content of the nano-hydroxyapatite ultra-long nanowires is 2-5 parts.

[0006] As an improvement of the present invention, the ceramic particles contain one or more of Al2O3, SiO2 or Mg(OH)2, and the content thereof is 2-10 parts.

[0007] As an improvement of the present invention, the content of the silane coupling agent is 0.5-5 parts.

[0008] As an improvement of the present invention, the catalyst content is 0.5-5 parts.

[0009] As an improvement of the present invention, the method comprises the following steps: Step S1, prepare 70 parts of polyethylene as the main matrix material; prepare 10 parts of polypropylene, prepare 5 parts of nano-hydroxyapatite ultra-long nanowires as a reinforcing material, prepare 10 parts of ceramic particles as a high temperature resistant material, such as Al2O3, SiO2 or Mg(OH)2, as a high temperature resistant material, prepare 3 parts of silane coupling agent, and prepare 2 parts of catalyst content; The silane coupling agent is used to enhance the bonding force between the inorganic filler and the polyolefin matrix, and the catalyst is used to promote the reaction between the silane coupling agent and the polyolefin matrix.

[0010] Step S2, using a high shear mixer to evenly mix polyethylene, polypropylene, nano-hydroxyapatite ultra-long nanowires and ceramic particles; adding a silane coupling agent and a catalyst in sequence; the catalyst is a copper catalyst.

[0011] Step S3, melting the mixed raw materials at a temperature of 200-300°C, using a three-layer co-extrusion device, wherein the middle layer contains nanowires and ceramic particles, and the inner and outer layers are pure polyolefin materials, and the parameters of the extruder are adjusted to ensure that the materials are fully melted and evenly distributed; Step S4, biaxially stretching the coextruded film material to form a microporous structure; Step S5, heat setting the stretched film material at a temperature of 120-180°C; Step S6, the heat-set film material is cooled by a cooling roller, and the cooled film material is wound on a winder to form a finished battery separator; Step S7, performing necessary post-processing on the rolled battery separator.

[0012] Based on the above technical features, in step S2, polyethylene, polypropylene, nano-hydroxyapatite ultra-long nanowires and ceramic particles are uniformly mixed using a high shear mixer to ensure that the nanowires and ceramic particles are evenly dispersed in the polyolefin matrix to avoid agglomeration.

[0013] As an improvement of the present invention, in step S4, the longitudinal stretching is performed at 100-200° C., and the transverse stretching ratio is about 5 times.

[0014] As an improvement of the present invention, the method also includes a step of detecting the thermal stability of the diaphragm, including: preparing a diaphragm sample and placing it in a testing device; applying certain conditions of pressing to the diaphragm sample to form a diaphragm / pole piece assembly; using a high-temperature hot needle to pierce the diaphragm assembly and measuring the thermal shrinkage area of ​​the diaphragm around the puncture hole; and judging the thermal stability of the diaphragm based on the size of the thermal shrinkage area.

[0015] Testing of the diaphragm also includes measuring the mechanical strength, ionic conductivity and chemical corrosion resistance of the diaphragm. The comprehensive performance of the diaphragm is verified through a series of tests including but not limited to differential scanning calorimetry (DSC), tensile testing, electrochemical impedance spectroscopy (EIS) and chemical stability testing.

[0016] As an improvement of the present invention, the pressing conditions include a pressure of 0.2-1.0 MPa and a temperature of 45-90°C.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: the present invention relates to a high temperature resistant lithium battery separator, which achieves high thermal stability and mechanical strength of the separator through a carefully designed raw material formula and preparation process, and meets the needs of high performance lithium batteries. The nanoscale inorganic filler in the separator not only improves the heat resistance of the separator, but also maintains good ion transmission performance. By adding silane coupling agents and catalysts, the bonding force between the inorganic filler and the polyolefin matrix is ​​further enhanced, and the high temperature resistance and safety of the separator are significantly improved. The present invention also provides a corresponding preparation method to ensure the uniformity and consistency of the separator. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 Flow chart of the preparation method in this embodiment. DETAILED DESCRIPTION

[0019] The present invention will be further explained below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the following specific embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention.

[0020] Example: Figure 1 As shown, this embodiment relates to a high temperature resistant lithium battery separator. Through a carefully designed raw material formula and preparation process, the high thermal stability and mechanical strength of the separator are achieved, meeting the needs of high performance lithium batteries. The nanoscale inorganic filler in the separator not only improves the heat resistance of the separator, but also maintains good ion transmission performance. By adding silane coupling agent and catalyst, the bonding force between the inorganic filler and the polyolefin matrix is ​​further enhanced, and the high temperature resistance and safety of the separator are significantly improved. The present invention also provides a corresponding preparation method to ensure the uniformity and consistency of the separator.

[0021] The embodiment is specifically a high temperature resistant lithium battery separator, which is made of the following raw materials in parts by weight: polyethylene, polypropylene, nano-hydroxyapatite ultra-long nanowires, silane coupling agent, catalyst and ceramic particles, and the total weight of each raw material is 100 parts.

[0022] Furthermore, the total weight of the polyethylene and the polypropylene is 90-95 parts.

[0023] Furthermore, the content of the nano-hydroxyapatite ultra-long nanowires is 2-5 parts.

[0024] Furthermore, the ceramic particles contain one or more of Al2O3, SiO2 or Mg(OH)2, and the content thereof is 2-10 parts.

[0025] Furthermore, the content of the silane coupling agent is 0.5-5 parts.

[0026] Furthermore, the catalyst content is 0.5-5 parts.

[0027] Furthermore, the method comprises the following steps: Step S1, prepare 70 parts of polyethylene as the main matrix material; prepare 10 parts of polypropylene, prepare 5 parts of nano-hydroxyapatite ultra-long nanowires as a reinforcing material, prepare 10 parts of ceramic particles as a high temperature resistant material, such as Al2O3, SiO2 or Mg(OH)2, as a high temperature resistant material, prepare 3 parts of silane coupling agent, and prepare 2 parts of catalyst content; The silane coupling agent is used to enhance the bonding force between the inorganic filler and the polyolefin matrix, and the catalyst is used to promote the reaction between the silane coupling agent and the polyolefin matrix.

[0028] Step S2, using a high shear mixer to evenly mix polyethylene, polypropylene, nano-hydroxyapatite ultra-long nanowires and ceramic particles; adding a silane coupling agent and a catalyst in sequence; the catalyst is a copper catalyst.

[0029] Step S3, melting the mixed raw materials at a temperature of 200-300°C, using a three-layer co-extrusion device, wherein the middle layer contains nanowires and ceramic particles, and the inner and outer layers are pure polyolefin materials, and the parameters of the extruder are adjusted to ensure that the materials are fully melted and evenly distributed; Step S4, biaxially stretching the coextruded film material to form a microporous structure; Step S5, heat setting the stretched film material at a temperature of 120-180°C; Step S6, the heat-set film material is cooled by a cooling roller, and the cooled film material is wound on a winder to form a finished battery separator; Step S7, performing necessary post-processing on the rolled battery separator.

[0030] In step S2, polyethylene, polypropylene, nano-hydroxyapatite ultra-long nanowires and ceramic particles are uniformly mixed using a high shear mixer to ensure that the nanowires and ceramic particles are uniformly dispersed in the polyolefin matrix to avoid agglomeration.

[0031] Furthermore, in step S4, the longitudinal stretching is performed at 100-200° C., and the transverse stretching ratio is about 5 times.

[0032] Furthermore, the method also includes a step of detecting the thermal stability of the diaphragm, including: preparing a diaphragm sample and placing it in a testing device; applying certain conditions of pressing to the diaphragm sample to form a diaphragm / pole piece assembly; using a high-temperature hot needle to pierce the diaphragm assembly and measuring the thermal shrinkage area of ​​the diaphragm around the puncture hole; and judging the thermal stability of the diaphragm based on the size of the thermal shrinkage area.

[0033] Furthermore, the pressing conditions include a pressure of 0.2-1.0 MPa and a temperature of 45-90°C.

[0034] It should be noted that the above content only illustrates the technical idea of ​​the present invention and cannot be used to limit the protection scope of the present invention. For ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications all fall within the protection scope of the claims of the present invention.

Claims

1. A high temperature resistant lithium battery separator, characterized in that: The battery separator is made of the following raw materials in parts by weight: polyethylene, polypropylene, nano-hydroxyapatite ultra-long nanowires, silane coupling agent, catalyst and ceramic particles, and the total weight of each raw material is 100 parts.

2. A high temperature resistant lithium battery separator according to claim 1, characterized in that: The total weight of the polyethylene and the polypropylene is 90-95 parts.

3. A high temperature resistant lithium battery separator according to claim 2, characterized in that: The content of the nano-hydroxyapatite ultra-long nanowires is 2-5 parts.

4. A high temperature resistant lithium battery separator according to claim 3, characterized in that: The ceramic particles contain one or more of Al2O3, SiO2 or Mg(OH)2, and the content thereof is 2-10 parts.

5. A high temperature resistant lithium battery separator according to claim 4, characterized in that: The content of the silane coupling agent is 0.5-5 parts.

6. A high temperature resistant lithium battery separator according to claim 5, characterized in that: The catalyst content is 0.5-5 parts.

7. The method for preparing a high temperature resistant lithium battery separator according to claim 6, characterized in that: The method comprises the following steps: Step S1, prepare 70 parts of polyethylene as the main matrix material; prepare 10 parts of polypropylene, prepare 5 parts of nano-hydroxyapatite ultra-long nanowires as a reinforcing material, prepare 10 parts of ceramic particles as a high temperature resistant material, prepare 3 parts of silane coupling agent, and prepare 2 parts of catalyst content; Step S2, using a high shear mixer to mix polyethylene, polypropylene, nano-hydroxyapatite ultra-long nanowires and ceramic particles uniformly; Step S3, melting the mixed raw materials at a temperature of 200-300°C, using a three-layer co-extrusion device, wherein the middle layer contains nanowires and ceramic particles, and the inner and outer layers are pure polyolefin materials, and the parameters of the extruder are adjusted to ensure that the materials are fully melted and evenly distributed; Step S4, biaxially stretching the coextruded film material to form a microporous structure; Step S5, heat setting the stretched film material at a temperature of 120-180°C; Step S6, the heat-set film material is cooled by a cooling roller, and the cooled film material is wound on a winder to form a finished battery separator; Step S7, performing necessary post-processing on the rolled battery separator.

8. The method for preparing a high temperature resistant lithium battery separator according to claim 5, characterized in that: In the step S4, the longitudinal stretching is performed at 100-200° C., and the transverse stretching ratio is about 5 times.

9. The method for preparing a high temperature resistant lithium battery separator according to claim 7, characterized in that: The method also includes a step of detecting the thermal stability of the diaphragm, including: preparing a diaphragm sample and placing it in a testing device; applying certain conditions of pressing to the diaphragm sample to form a diaphragm / pole piece assembly; using a high-temperature hot needle to pierce the diaphragm assembly and measuring the thermal shrinkage area of ​​the diaphragm around the pierced hole; and judging the thermal stability of the diaphragm based on the size of the thermal shrinkage area.

10. The method for preparing a high temperature resistant lithium battery separator according to claim 9, characterized in that: The pressing conditions include a pressure of 0.2-1.0 MPa and a temperature of 45-90°C.

Images