A deep-sea high-safety lithium ion battery composite diaphragm and a preparation method thereof

Abstract

The application relates to a deep-sea high-safety lithium ion battery composite diaphragm with a large magnification and a preparation method, which comprises the following steps: adding sodium p-toluenesulfinate and pyrrole into a nano-conductive agent dispersion liquid, uniformly stirring to obtain a mixed liquid A; under the conditions of an ice water bath and stirring, adding (NH4)2S2O8 solution into the mixed liquid A drop by drop to obtain a mixed liquid B; the mixed liquid B is subjected to solid-liquid separation, washing and drying to obtain a modified nano-conductive agent; the modified nano-conductive agent is uniformly sprayed on the surface of a diaphragm substrate to obtain a lithium ion battery composite diaphragm. Under the action of (NH4)2S2O8, the sodium p-toluenesulfinate and the pyrrole form a polymer containing N-H functional groups and nitrogen-containing heterocyclic structures and are coated on the surface of the nano-conductive agent, so that the modified nano-conductive agent with an inorganic-organic core-shell structure is obtained; the composite diaphragm obtained by compounding the diaphragm substrate has good wettability and high tensile strength, and the magnification capacity is excellent.

Description

Technical Field

[0001] The present invention relates to the field of battery separators, and in particular to a deep-sea high-rate and high-safety lithium-ion battery composite separator and a preparation method thereof. Background Art

[0002] As a core component of lithium-ion batteries, the performance of the separator is directly related to the battery's electrochemical performance and safety. Common separators based on meta-aramid (PMIA), cellulose, polyvinylidene fluoride (PVDF), polyimide (PI), polyacrylonitrile (PAN), and polyethylene terephthalate (PET) have varying advantages and disadvantages and can be applied to lithium-ion batteries in various operating environments at atmospheric pressure.

[0003] However, in the field of deep-sea manned / unmanned submersibles at 10,000 meters, the pressure is 100 MPa or even higher, requiring high-rate discharge. In response to the requirements of high-rate discharge in deep-sea environments, the electrolyte membrane must meet the requirements of wettability, thermal stability, pressure shrinkage resistance, high ionic conductivity, mechanical properties, chemical stability, and non-reaction with electrode materials and electrolytes.

[0004] Among them, electrochemical performance and safety are the most critical factors in the deep-sea high-rate discharge environment. Conventional diaphragms cannot meet the requirements of voltage resistance and high-rate discharge at the same time. This is mainly because the high-rate discharge process under high pressure will produce local heat accumulation, thereby accelerating the Li + The local reaction rate decreases, forming lithium dendrites. Due to its poor thermal stability, commercial polyolefin separators cannot solve the above problems. Summary of the Invention

[0005] The purpose of the present invention is to overcome the above technical deficiencies, provide a deep-sea high-rate and high-safety lithium-ion battery composite diaphragm and preparation method, and solve the technical problem of poor high-rate discharge performance of the diaphragm in the prior art under pressure-resistant environment.

[0006] In order to achieve the above technical objectives, the technical solution provided by the present invention is:

[0007] In a first aspect, the present invention provides a method for preparing a composite diaphragm for a deep-sea high-rate and high-safety lithium-ion battery, comprising the following steps:

[0008] S1, adding sodium p-toluenesulfinate and pyrrole to the nano-conductive agent dispersion, and stirring to obtain a mixed solution A;

[0009] S2, adding (NH4)2S2O8 solution dropwise to the mixed solution A under ice-water bath and stirring to obtain mixed solution B;

[0010] S3, the mixed solution B is subjected to solid-liquid separation, washing and drying to obtain a modified nano-conductive agent;

[0011] S4, spraying the modified nano-conductive agent evenly on the surface of the diaphragm substrate to obtain a lithium-ion battery composite diaphragm.

[0012] In a second aspect, the present invention provides a lithium-ion battery composite separator prepared by the above preparation method.

[0013] Compared with the prior art, the present invention has the following beneficial effects:

[0014] The present invention uses sodium p-toluenesulfinate and pyrrole as raw materials. Under the action of (NH4)2S2O8, sodium p-toluenesulfinate and pyrrole can form a high molecular polymer containing NH functional groups and nitrogen-containing heterocyclic structures. The NH functional groups have adhesiveness, which can make the prepared polymer coated on the surface of the nano-conductive agent, thereby obtaining a modified nano-conductive agent with an inorganic-organic core-shell structure; by compounding the modified nano-conductive agent with a diaphragm matrix, the modified nano-conductive agent strengthens the diaphragm matrix. At the same time, the core-shell structure of the modified nano-conductive agent avoids the short circuit risk caused by the conductivity of the internal conductive agent and retains the hydrophilicity of the external polymer surface containing multiple NH groups. Therefore, the composite diaphragm obtained by the present invention has good wettability and high tensile strength, which promotes low interface resistance and high Li + The electrical conductivity helps to obtain excellent rate capacity and high safety. The composite diaphragm of the present invention disperses local heat sources, avoiding the violent growth of lithium dendrites caused by local heat accumulation, thereby effectively improving the safety of lithium-ion batteries and meeting the application requirements of high deep-sea pressure and high rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is a battery cycle curve diagram of a conventional PP-based diaphragm and the composite diaphragm obtained in the present invention at 100 MPa;

[0016] Figure 2 This is the pressure test result of the composite diaphragm of the present invention. DETAILED DESCRIPTION

[0017] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0018] The present invention provides a deep-sea high-rate and high-safety lithium-ion battery composite diaphragm and a preparation method. The high-rate discharge performance of the diaphragm under a pressure-resistant environment is improved by a modification method. Specifically, by modifying the lithium-ion battery diaphragm, high lithium ion conductivity and lithium ion transfer number are achieved, lithium dendrite growth is effectively reduced, and the high-rate discharge process of the lithium-ion battery at 100MPa is safe and stable.

[0019] In a first aspect, the present invention provides a method for preparing a composite diaphragm for a deep-sea high-rate and high-safety lithium-ion battery, comprising the following steps:

[0020] S1, adding sodium p-toluenesulfinate and pyrrole to the nano-conductive agent dispersion, and stirring to obtain a mixed solution A;

[0021] S2, adding (NH4)2S2O8 solution dropwise to the mixed solution A under ice-water bath and stirring to obtain mixed solution B;

[0022] S3, the mixed solution B is subjected to solid-liquid separation, washing and drying to obtain a modified nano-conductive agent;

[0023] S4, spraying the modified nano-conductive agent evenly on the surface of the diaphragm substrate to obtain a lithium-ion battery composite diaphragm.

[0024] Preferably, in step S1, the nano-conductive agent includes nitrogen-doped carbon nanotubes (NCNTs), which are commonly available in the market, and the nitrogen doping amount is 10 to 30 at %.

[0025] Preferably, in step S1, the concentration of the nano-conductive agent dispersion is 0.6-1.6 mg / mL.

[0026] Further preferably, the specific preparation steps of the nano-conductive agent dispersion include: adding the nano-conductive agent to deionized water, first performing ultrasonic treatment for 1.5 to 2.5 hours; then stirring at a speed of 800 to 1000 rpm for 30 to 40 minutes in a water bath at 0 to 3°C to obtain the nano-conductive agent dispersion.

[0027] Preferably, in step S1, the mass ratio of the nano-conductive agent to sodium p-toluenesulfinate is 1:(5-7); the ratio of the nano-conductive agent to pyrrole is (60-80) mg:(60-80) μL.

[0028] Preferably, the ratio of the nano-conductive agent in step S1 to the (NH4)2S2O8 in step S2 is (60-80) mg: (1-1.2) mmol.

[0029] Further preferably, in step S2, the concentration of the (NH4)2S2O8 solution is 0.1 mol / L, and the ratio of the nano-conductive agent to the (NH4)2S2O8 solution is (60-80) mg: (10-12) mL.

[0030] Preferably, in step S2, stirring is performed for 3.5 to 4.5 hours. The present invention controls the polymerization reaction by the stirring time to avoid polymerization failure and failure to obtain the target polymer.

[0031] Preferably, in step S3, washing is performed by washing with deionized water for 3 to 5 times; and drying is performed by vacuum drying at 60 to 70° C. for 10 to 14 hours.

[0032] Preferably, in step S4, the spraying is performed by electrostatic spraying; the spraying amount of the modified nano-conductive agent is 2-10 mg / cm 2 ; The diaphragm matrix adopts PP diaphragm.

[0033] In a second aspect, the present invention provides a lithium-ion battery composite separator prepared by the above preparation method.

[0034] The main mechanism of action and advantages of the present invention are:

[0035] The present invention uses sodium p-toluenesulfinate and pyrrole as raw materials, and under the oxidation of (NH4)2S2O8, initiates the polymerization of monomer pyrrole into polypyrrole, and sodium p-toluenesulfinate is used as a dopant in the polymer. By controlling the raw material ratio and temperature, a high molecular polymer containing NH functional groups and nitrogen-containing heterocyclic structures can be formed. The NH functional group has adhesion, which can make the prepared polymer coated on the surface of the nano-conductive agent to form an inorganic-organic structure with a core-shell structure, thereby obtaining a modified nano-conductive agent. The core-shell structure of the modified nano-conductive agent avoids the short circuit risk caused by the conductivity of the internal conductive agent and retains the hydrophilicity of the external polymer surface containing multiple NH groups; after the modified nano-conductive agent is sprayed on the surface of the diaphragm substrate, it can effectively play a reinforcing role. Therefore, the composite diaphragm obtained by the present invention has good wettability and high tensile strength, which promotes low interface resistance and high Li + The electrical conductivity further contributes to the excellent rate capacity and high safety. The composite diaphragm of the present invention disperses the local heat source, avoiding the violent growth of lithium dendrites caused by local heat accumulation, thereby further improving the safety of LIBs and meeting the application requirements of high deep-sea pressure and high rate.

[0036] The present invention is further described below through specific examples. Where specific techniques or conditions are not specified in the examples, the methods were followed according to those described in literature in the art or according to the product specifications. Reagents or instruments used, where the manufacturer is not specified, are commercially available conventional products. The nitrogen doping level of the nanoconductive agent NCNT is 20 at%.

[0037] Example 1

[0038] A method for preparing a deep-sea high-rate and high-safety lithium-ion battery composite diaphragm comprises the following steps:

[0039] S1, 70 mg of nano-conductive agent NCNT was added into 100 mL of deionized water, and ultrasonic treatment was performed for 2 hours, and then transferred to a low-temperature water bath at 0-3°C, and stirred at a speed of 1000 rpm for 30 min to obtain a nano-conductive agent dispersion liquid;

[0040] To the nano-conductive agent dispersion liquid, 420 mg of sodium toluene sulfinate and 70 μL of pyrrole were added, and stirred for 30 min to obtain a uniform mixture A;

[0041] S2, under the condition of ice water bath at 0°C and stirring, 10 mL of (NH4)2S2O8 solution with a concentration of 0.1 M was added dropwise into the mixture A, and stirred for 4 hours to obtain a mixture B;

[0042] S3, the mixture B was filtered, washed with deionized water for 4 times, and vacuum dried in an oven at 65°C for 12 hours to obtain a modified nano-conductive agent; the modified nano-conductive agent is formed by coating a high polymer on the nano-conductive agent, and the high polymer contains N-H functional groups and nitrogen heterocyclic structures;

[0043] S4, the modified nano-conductive agent was uniformly sprayed on the surface of the diaphragm substrate (PP diaphragm) by electrostatic spraying, and the spraying amount of the modified nano-conductive agent was 5 mg / cm 2 , to obtain a composite diaphragm.

[0044] Comparative Example 1

[0045] The diaphragm substrate in Example 1 was directly used, i.e. PP diaphragm.

[0046] Performance test

[0047] 1. The charge-discharge performance of the diaphragm was tested by assembling a button cell. The positive electrode material was lithium iron phosphate, the negative electrode material was lithium sheet, and the diaphragm of Example 1 and Comparative Example 1 was used to separate the two, and 100 microliters of 15wt% commercial lithium hexafluorophosphate electrolyte was added dropwise, and then fixed by a button positive and negative cell shell to obtain a button lithium ion battery. Then the charge-discharge performance was tested by a blue electric test system, and the discharge rate was 0.5 C. After 50 cycles, the discharge specific capacity of each battery was compared, and the results were shown in Figure 1 .

[0048] As Figure 1As shown, the battery assembled with the diaphragm before and after modification has a slightly higher discharge capacity of Example 1 than that of Comparative Example 1 at the initial stage of charge and discharge, and is between 140mAh / g and 150mAh / g. After 50 cycles, the capacity retention rate of Comparative Example 1 is 90.6%, and the capacity retention rate of Example 1 is 95.8%. This shows that the composite diaphragm prepared by modifying the nano-conductive agent has good wettability and liquid retention rate to the electrolyte, so that the battery has a higher capacity retention rate and better electrochemical performance. This is attributed to the fact that the modified coating is firmly coated on the surface of the diaphragm, and its particle size is appropriate, the particle size is uniform, and it has good retention of the electrolyte. Therefore, the present invention provides a composite diaphragm for lithium-ion batteries that can be used at 100MPa in the deep sea, with high rate, high safety, three-dimensional conductivity and high wettability.

[0049] 2. A 45Ah battery cell was prepared using lithium iron phosphate as the positive electrode material, spherical graphite as the negative electrode material, polylactic acid as the binder, dibutyl phthalate as the plasticizer, acetylene black as the conductive agent, and a dedicated electrolyte for the deep-sea 10,000-meter battery (Struggler). The composite separator obtained in Example 1 was used as the separator.

[0050] Charge at a constant current of 0.2C at normal pressure, with a cut-off voltage of 3.65V. One hour after charging, perform a pressure test using a pressure cylinder. When the pressure in the pressure cylinder is increased to 100MPa, discharge at a constant current of 20C based on the rated capacity of the battery cell, with a cut-off voltage of 2.5V. One hour after pressure relief is complete, charge the battery cell at a constant current of 0.2C at normal pressure, and repeat this cycle five times.

[0051] The results are as follows Figure 2 As shown, the battery cells' five discharge capacities were 44.279Ah, 44.022Ah, 43.815Ah, 43.703Ah, and 43.38Ah, respectively. The cell capacity retention rates were 100%, 99.42%, 98.95%, 98.70%, and 97.97%, respectively, demonstrating minimal discharge capacity degradation. The test results demonstrate that the pressure-bearing discharge performance of the battery cells of the present invention is not significantly affected by full ocean depth pressure conditions, and that all materials meet the requirements for a 10,000-meter deep-sea environment.

[0052] The specific embodiments of the present invention described above do not limit the scope of protection of the present invention. Any other corresponding changes and modifications made based on the technical concept of the present invention should be included in the scope of protection of the claims of the present invention.

Claims

1. A method for preparing a deep-sea high-rate and high-safety lithium-ion battery composite diaphragm, characterized in that: The following steps are involved: S1, adding sodium p-toluenesulfinate and pyrrole to the nano-conductive agent dispersion, and stirring to obtain a mixed solution A; S2, adding (NH4)2S2O8 solution dropwise to the mixed solution A under ice-water bath and stirring conditions to obtain mixed solution B; S3, the mixed solution B is subjected to solid-liquid separation, washing and drying to obtain a modified nano-conductive agent; S4, spraying the modified nano-conductive agent evenly on the surface of the diaphragm substrate to obtain a lithium-ion battery composite diaphragm.

2. The method for preparing a deep-sea high-rate and high-safety lithium-ion battery composite diaphragm according to claim 1, characterized in that: In step S1, the nano-conductive agent includes nitrogen-doped carbon nanotubes.

3. The method for preparing a deep-sea high-rate and high-safety lithium-ion battery composite diaphragm according to claim 1, characterized in that: In step S1 , the concentration of the nano-conductive agent dispersion is 0.6-1.6 mg / mL.

4. The method for preparing a deep-sea high-rate and high-safety lithium-ion battery composite diaphragm according to claim 1, characterized in that: The specific preparation steps of the nano-conductive agent dispersion include: adding the nano-conductive agent to deionized water, first ultrasonically treating it for 1.5 to 2.5 hours; then stirring it at a speed of 800 to 1000 rpm for 30 to 40 minutes in a water bath at 0 to 3°C to obtain the nano-conductive agent dispersion.

5. The method for preparing a deep-sea high-rate and high-safety lithium-ion battery composite diaphragm according to claim 1, characterized in that: In step S1, the mass ratio of the nano-conductive agent to sodium p-toluenesulfinate is 1:(5-7); the ratio of the nano-conductive agent to pyrrole is (60-80) mg:(60-80) μL.

6. The method for preparing a deep-sea high-rate and high-safety lithium-ion battery composite diaphragm according to claim 1, characterized in that: The ratio of the nano-conductive agent in step S1 to the (NH4)2S2O8 in step S2 is (60-80) mg: (1-1.2) mmol.

7. The method for preparing a deep-sea high-rate and high-safety lithium-ion battery composite diaphragm according to claim 6, characterized in that: In step S2, the concentration of the (NH4)2S2O8 solution is 0.1 mol / L, and the ratio of the nano-conductive agent to the (NH4)2S2O8 solution is (60-80) mg: (10-12) mL; Stir for 3.5 to 4.5 hours to obtain mixed solution B.

8. The method for preparing a deep-sea high-rate and high-safety lithium-ion battery composite diaphragm according to claim 1, characterized in that: In step S3, washing is performed by washing with deionized water for 3 to 5 times; and drying is performed by vacuum drying at 60 to 70° C. for 10 to 14 hours.

9. The method for preparing a deep-sea high-rate and high-safety lithium-ion battery composite diaphragm according to claim 1, characterized in that: In step S4, the spraying is carried out by electrostatic spraying; the spraying amount of the modified nano conductive agent is 2 to 10 mg / cm 2 ; The diaphragm matrix adopts PP diaphragm.

10. A lithium-ion battery composite separator prepared by the preparation method according to any one of claims 1 to 9.

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