Phosphorus-aluminum inorganic adhesive for lithium-sulfur battery and preparation method thereof

Abstract

The application provides a phosphorus-aluminum inorganic adhesive for a lithium-sulfur battery and a preparation method thereof. The phosphorus-aluminum inorganic adhesive with a viscosity of 10-500 mPa.s and a solid content of 30-80% is prepared through a hydrothermal reaction of a phosphoric acid or hydrogen phosphate solution and an aluminum compound. The product has the characteristics of good strength, high-temperature resistance, and flame resistance. Compared with a traditional organic adhesive, the phosphorus-aluminum inorganic adhesive significantly reduces the use amount of the lithium-sulfur battery, increases the adhesion of the electrode material and the current collector, limits the diffusion of lithium polysulfide, enhances the transport capacity of lithium ions, and prolongs the cycle life of the battery. More importantly, the phosphorus-aluminum adhesive has excellent flame resistance, and when applied to the lithium-sulfur battery, the flame resistance of the battery can be improved, the use safety of the battery is improved, and the phosphorus-aluminum adhesive is expected to become a new type of environmentally-friendly flame-resistant lithium-sulfur battery adhesive.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of lithium-sulfur battery adhesives, and particularly relates to a preparation method of a phosphorus-aluminum inorganic adhesive for lithium-sulfur batteries with excellent flame retardant properties and application thereof. BACKGROUND

[0002] Commercialization of lithium batteries has been more than thirty years, and currently, intercalation chemical reaction lithium batteries encounter bottlenecks, and the problem of low energy storage capacity of traditional intercalation type lithium batteries needs to be solved. Conversion type lithium batteries can effectively improve the energy density of lithium batteries. As a typical conversion type battery, lithium-sulfur batteries are expected to become the ideal next generation lithium battery system due to their high theoretical energy density, low raw material price and environmental friendly ability. Currently, the key problem limiting the application of lithium-sulfur batteries is that polysulfides generated in the reaction process are easily dissolved in the electrolyte, thereby causing low cycle performance and shortening the service life of the battery. Adhesives with polar functional groups can bind polysulfides and improve the cycle performance of lithium-sulfur batteries. The adhesives reported in the prior art are mostly organic adhesives. Since organic matter basically does not provide conductive ability, it is necessary to reduce the proportion of adhesives in the battery, and more importantly, the safety performance of the battery has always been a subject of criticism, so it is necessary to design a lithium-sulfur battery adhesive with flame retardant ability.

[0003] Based on this, the present application provides a phosphorus-aluminum inorganic adhesive for lithium-sulfur batteries and a preparation method thereof. The phosphorus-aluminum (AP) adhesive is an inorganic polymer. Compared with the traditional commercial lithium-sulfur battery adhesive polyvinylidene fluoride (PVDF), the phosphorus-aluminum adhesive does not need to be dissolved in toxic N-methyl pyrrolidone (NMP) or N,N-dimethylformamide (DMF) and other toxic solvents. The phosphorus-aluminum adhesive has good electronic and ionic conduction performance, thereby providing better electrochemical performance for the battery. Compared with the S / C positive electrode based on organic adhesive, the weight proportion of the S / C positive electrode based on the phosphorus-aluminum adhesive is significantly reduced. In addition, the S / C electrode based on the phosphorus-aluminum adhesive also has excellent flame retardant performance. The present application utilizes a hydrothermal reaction to synthesize the AP adhesive from aluminum compounds, phosphoric acid or hydrogen phosphate by a hydrothermal method, and applies the AP adhesive to the S / C positive electrode of the lithium-sulfur battery. Compared with the S / C positive electrode of the organic adhesive, the AP adhesive can realize low weight proportion. The S / C positive electrode applying the material has excellent flame retardant ability, and the corresponding S / C lithium-sulfur battery can have a coulombic efficiency of about 99%. SUMMARY

[0004] The present application aims to provide a phosphorus aluminum inorganic adhesive for lithium-sulfur batteries and a preparation method thereof. A multifunctional adhesive with flame retardant performance, effective absorption of polysulfides, fast ion diffusion, inhibition of positive electrode volume change, and rich polar functional groups is prepared by hydrothermal reaction. Specifically, an aqueous inorganic phosphorus aluminum adhesive prepared from aluminum compounds and phosphoric acid or hydrogen phosphate is designed for sulfur cathodes in lithium-sulfur batteries.

[0005] To achieve the above-mentioned purpose, the present application adopts the following technical solutions:

[0006] A phosphorus aluminum inorganic adhesive for lithium-sulfur batteries, and a preparation method thereof, comprising the following steps:

[0007] (1) Using a phosphoric acid solution or a hydrogen phosphate solution and an aluminum compound as raw materials, the phosphorus aluminum elements are in proportion, and the solid content of the adhesive is designed;

[0008] (2) The phosphoric acid solution or the hydrogen phosphate solution is heated in a water bath, the aluminum compound is slowly added, and the reaction is carried out for a period of time to obtain a phosphorus aluminum inorganic adhesive (AP adhesive) for lithium-sulfur batteries after cooling;

[0009] (3) Sulfur powder and conductive carbon black are mixed and ground in a certain proportion, and an S / C composite is prepared by calcination;

[0010] (4) The S / C composite and the AP adhesive are mixed and ground in a certain proportion to form a slurry, which is then coated on a carbon-coated aluminum foil and dried as a working electrode.

[0011] In step (1), the hydrogen phosphate includes one of soluble monohydrogen phosphate and soluble dihydrogen phosphate; the aluminum compound includes one of aluminum hydroxide, aluminum sulfate, aluminum oxide, and aluminum nitride; the phosphorus aluminum ratio is the molar ratio of phosphorus element to aluminum element, ranging from 1.9 to 4.1; and the solid content of the adhesive is 30%-80%.

[0012] In step (2), the water bath temperature is 60-140℃; the reaction time is 15-240 min; and the viscosity of the phosphorus aluminum inorganic adhesive is 10-500 mPa·s.

[0013] In step (3), the conductive carbon black is selected from one or more of mixtures of Ketjen black, acetylene black, Super-P, Super-S, 350G, KS-6, KS-15, SFG-6, and SFG-15; in the S / C composite, the sulfur content is 40-85wt%, and the conductive carbon black content is 15-60wt%; and the calcination is carried out in a 150-200℃ oven for 10-24 h under a nitrogen atmosphere.

[0014] The working electrode of step (4) has a S / C composite content of 85-99wt%, and an AP adhesive content of 1-15wt% (preferably 2wt%); and the drying conditions are: drying in a vacuum drying oven at 60-110℃ for 10-24h.

[0015] The prepared S / C positive electrode based on the phosphorus-aluminum adhesive is applied to a lithium-sulfur battery to test its electrochemical performance.

[0016] The electrochemical test includes: (1) half-cell test: a 15.6mm Li foil as the negative electrode, and the S / C composite with different binders as the positive electrode, to assemble a CR2016 button cell in an argon atmosphere glove box. 1molL -1 LiTFSI added with 1.0% LiNO3 in DOL / DME as the electrolyte, and the electrolyte amount is 40 μL; (2) full-cell test: lithium deposition on copper-coated carbon cloth as the negative electrode, and the S / C composite with different binders as the positive electrode, to assemble a CR2032 button cell in an argon atmosphere glove box. 1molL -1 LiPF6 added with 5.0% FEC in EC / DMC (1:1) as the electrolyte, and the electrolyte amount is 20 μL mg −1 of active material sulfur.

[0017] The electrolyte salt is selected from the following lithium salts: lithium tetrafluoroborate (LiBF4), lithium hexafluorophosphate (LiPF6), lithium perchlorate (LiClO4), lithium bis(oxalato)borate (LiBOB), lithium difluoro(oxalato)borate (LiDFOB), lithium bis(difluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiOTf), etc., and the electrolyte is selected from an organic solvent or a mixture of organic solvents, and the organic solvents include ethylene carbonate (EC), 1,3-dioxolane (DOL), propylene carbonate (PC), dimethyl carbonate (DMC), tetramethyl sulfoxide (TMS), ethylene glycol dimethyl ether (DME), diethylene glycol dimethyl ether (G2), tetraethylene glycol dimethyl ether (TEGDME, G4), fluoroethylene carbonate (FEC), and tetrahydrofuran (THF), etc.

[0018] Compared with existing battery adhesives, the present application has the following advantages:

[0019] (1) The present application selects aluminum hydroxide and phosphoric acid as raw materials to prepare inorganic adhesives, both of which contain a large amount of oxygen-containing functional groups. The prepared inorganic adhesives rich in polar groups provide strong adhesion to the current collector, promote the diffusion of lithium ions, and adsorb lithium polysulfide to inhibit the shuttle effect.

[0020] (2) The phosphoric aluminum adhesive also contains a large amount of phosphoric acid or aluminum hydroxide, both of which are good flame retardants and can provide flame retardancy for the sulfur electrode, significantly improving the safety of the lithium-sulfur battery.

[0021] (3) The present application has the possibility of ultra-low dosage. Although a poor adhesive content (2wt%) is used, the lithium-sulfur battery based on the phosphoric aluminum adhesive still exhibits excellent cycle performance. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 SEM image of S / C cathode based on 2wt% AP inorganic glue obtained in Example 1;

[0023] Figure 2 Specific burning time (calculation method: burning time divided by the mass of sulfur) of sulfur cathodes with different adhesives obtained in Example 1;

[0024] Figure 3 Cycle performance of CR2016 button cells based on different AP adhesive contents in Example 1 at 0.5 coulomb charge;

[0025] Figure 4 CR2016 button cells of lithium-sulfur batteries S / C cathodes based on AP adhesive and PVDF, PAA, CMC organic adhesive obtained in Example 1, adhesive content is 2wt%, electrochemical test, discharge specific capacity at 0.5 coulomb charge;

[0026] Figure 5 CR2032 full battery system of S / C cathode based on 2wt% AP adhesive obtained in Example 2, cycle performance at 0.2 coulomb and 0.5 coulomb charge. DETAILED DESCRIPTION

[0027] In order to further illustrate the present application, specific examples are given below, so that the skilled person can better understand the present application. The examples described are only preferred embodiments of the present application, and any equivalent changes and modifications made within the scope of the patent application of the present application shall be included in the scope of the present application. The reagent model number involved in the examples does not represent a limitation to this model number. If the reagents are not explicitly marked in the examples, they should be considered as conventional products that can be purchased in the market.

[0028] Example 1

[0029] (1) 300 g of phosphoric acid (solid content 85%) was diluted with 163.64 mL of deionized water, and the diluted phosphoric acid solution (concentration 55 wt%) was added to a round-bottom flask. 50 g of aluminum hydroxide powder was first added, and magnetic stirring was performed at 85°C for 20 min. Then, 36.91 g of aluminum hydroxide powder was added, and stirring was performed at 110°C for 20 min. Thus, a phosphorus-aluminum adhesive with a phosphorus-aluminum molar ratio of 2.33 was prepared.

[0030] (2) Commercial sulfur powder, Ketjen black (Ketjen black 600), and conductive agent (super P) were mixed in a mass ratio of 4:1:1, and ground for 60 min. The mixture was placed in an oven at 160°C for 15 h to prepare an S / C composite. The S / C composite was mixed with 1 wt%, 2 wt%, and 10 wt% of the AP adhesive to prepare a slurry. The slurry was coated on a carbon-coated aluminum foil, and after drying, an S / C positive electrode disc with a diameter of 12 mm was prepared. Figure 1 The SEM image of the 2 wt% AP adhesive S / C positive electrode is shown in FIG. 6, indicating that a thick and uniform Li2S is deposited on the electrode.

[0031] (3) A slurry was prepared by mixing the S / C composite with 2 wt% of an organic adhesive (PVDF, PAA, or CMC), and then the slurry was coated on a carbon-coated aluminum foil. After drying, an S / C positive electrode disc with a diameter of 12 mm was prepared, and the flame retardant performance was tested. The test results are shown in FIG. 7. Figure 2 The AP adhesive S / C positive electrode had the lowest specific burning time (489 s / g), indicating that it had excellent flame retardant performance.

[0032] (4) CR2016 button cells were assembled using Celgard 2500 as the separator, 15.6 mm Li foil as the negative electrode, and the prepared S / C disc with a diameter of 12 mm as the positive electrode. 1 mol L -1 LiTFSI was added with 1.0% LiNO3 as the electrolyte in DOL / DME, and the amount of electrolyte was 40 μL. The above assembly was carried out in an argon atmosphere glove box, and the corresponding electrochemical performance was tested. The lithium-sulfur battery based on 2 wt% AP adhesive had better performance than the lithium-sulfur battery based on 1 wt% AP adhesive and had little difference from the lithium-sulfur battery based on 10 wt% AP adhesive. Figure 3 At a charge-discharge rate of 0.5C, the initial discharge capacity of the lithium-sulfur battery based on 2 wt% AP adhesive was 1190 mAh g -1 , which was better than that of the lithium-sulfur battery based on 2 wt% organic adhesive PVDF (maximum 482 mAh g -1 ), PAA (375 mAh g -1 ), and CMC (380 mAh g -1), 500 cycles, the lithium-sulfur battery with AP adhesive has a capacity retention of 660 mAh g -1 , while its specific capacity is still significantly higher than that of organic adhesive PVDF (386 mAh g -1 ), PAA (305 mAh g -1 ), CMC (106 mAh g -1 ) (see Table 1). Figure 4 Full-cell test shows that at 0.2C charge-discharge rate, the initial area capacity can reach 2.28 mAh cm -2 , and after 800 cycles, the area capacity still remains at 0.89 mAh cm -2 , with an average coulombic efficiency as high as 98.5%; at 0.5C charge-discharge rate, the initial area capacity reaches 1.75 mAh cm -2 , and after 600 cycles, the area capacity still remains at 1.07 mAh cm −2 , with an average coulombic efficiency remaining above 99% (see Table 2). Figure 5

[0033] Example 2

[0034] (1) 300 g of phosphoric acid (solid content 85%) was diluted with 163.64 mL of deionized water, and the diluted phosphoric acid solution (concentration 55 wt%) was added to a round-bottom flask. First, 50 g of aluminum hydroxide powder was added, and the mixture was stirred at 85°C for 20 min. Then, 36.91 g of aluminum hydroxide powder was added, and the mixture was stirred at 110°C for 20 min. In this way, a phosphorus-aluminum adhesive with a phosphorus-aluminum molar ratio of 2.33 was prepared.

[0035] (2) Commercial sulfur powder, Ketjen black (Ketjen black 600), and conductive agent (super P) were mixed in a mass ratio of 4:1:1 and ground for 60 min. Then, the mixture was placed in an oven at 160°C for 15 h to prepare an S / C composite. The S / C composite was mixed with 2 wt% of the phosphorus-aluminum adhesive to form a slurry, which was coated on a carbon-coated aluminum foil and dried to form S / C positive electrode discs with a diameter of 12 mm.

[0036] (3) Lithium was deposited on copper-plated carbon cloth as the negative electrode, and the S / C composite was used as the positive electrode to assemble CR2032 button cells. 1 mol L -1 LiPF6 was added to EC / DMC (1:1) with 5.0% FEC as the electrolyte, and the amount of electrolyte was 20 μL mg −1 of active sulfur. The above assembly was carried out in an argon glove box, and the corresponding electrochemical performance was tested.

[0037] Example 3 ​

[0038] (1) 300 g of phosphoric acid (solid content 85%) was diluted with 163.64 mL of deionized water, the diluted phosphoric acid solution (concentration 55 wt%) was added to a round bottom flask, 50 g of aluminum hydroxide powder was first added, stirred at 85 °C for 20 min, then 32.44 g of aluminum hydroxide powder was added, stirred at 110 °C for 20 min, to prepare a phosphorus-aluminum adhesive with a phosphorus-aluminum molar ratio of 2.80 for standby.

[0039] (2) Commercial sulfur powder, Ketjen black (Ketjen black 600) and conductive agent (KS-6) were mixed in a mass ratio of 3:1:1, ground for 60 min, and placed in a 150 °C oven for 16 h to prepare an S / C composite. An S / C positive electrode disc with a diameter of 12 mm was prepared by mixing 2 wt% AP adhesive with the S / C composite to make a slurry, coating the slurry on a carbon-coated aluminum foil, and drying.

[0040] (3) A CR2016 button cell was assembled using Celgard 2500 as the separator, 15.6 mm Li foil as the negative electrode, and the prepared S / C disc with a diameter of 12 mm as the positive electrode. 1 mol L -1 LiTFSI was added with 1.0% LiNO3 as electrolyte in DOL / DME, and the amount of electrolyte was 40 μL. The above assembly was carried out in an argon atmosphere glove box, and the corresponding electrochemical performance was tested.

[0041] Example 4

[0042] (1) 300 g of phosphoric acid (solid content 85%) was diluted with 163.64 mL of deionized water, the diluted phosphoric acid solution (concentration 55 wt%) was added to a round bottom flask, 50 g of aluminum hydroxide powder was first added, stirred at 85 °C for 20 min, then 32.44 g of aluminum hydroxide powder was added, stirred at 110 °C for 20 min, to prepare a phosphorus-aluminum adhesive with a phosphorus-aluminum molar ratio of 2.80 for standby.

[0043] (2) Commercial sulfur powder, Ketjen black (Ketjen black 300) and conductive agent (SFG-6) were mixed in a mass ratio of 4:1:2, ground for 60 min, and then placed in a 160 °C oven for 15 h to prepare an S / C composite. An S / C positive electrode disc with a diameter of 12 mm was prepared by mixing 2 wt% phosphorus-aluminum adhesive with the S / C composite to make a slurry, coating the slurry on a carbon-coated aluminum foil, and drying.

[0044] (3) Lithium was deposited on copper-coated carbon cloth as the negative electrode, and S / C composite was used as the positive electrode to assemble a CR2032 button cell. 1 mol L -1LiPF6in EC / DMC (1:1) with 5.0% FEC as electrolyte, electrolyte amount is 20 μL mg −1 active material sulfur. The above assembly is carried out in an argon atmosphere glove box, and the corresponding electrochemical performance is tested.

[0045] The above merely preferred embodiments of the present application, any equivalent changes and modifications made in the scope of the present application patent application, should be included in the scope of the present application.

Claims

1. The application of a phosphorus aluminum inorganic adhesive in lithium-sulfur batteries, characterized in that: The method of using the phosphorus aluminum inorganic adhesive in lithium-sulfur batteries includes the following steps: (1) Using a certain concentration of phosphoric acid solution or hydrogen phosphate solution and aluminum compound as raw materials, with phosphorus and aluminum elements in corresponding proportions, design the solid content of the adhesive; (2) Heat the phosphoric acid solution or hydrogen phosphate solution in a water bath, slowly add aluminum compound, react for a period of time, and then cool to obtain phosphoric aluminum inorganic adhesive; (3) Sulfur powder and conductive carbon black are mixed and ground in a certain proportion and then calcined to prepare S / C composite; (4) The S / C composite and phosphorus aluminum inorganic adhesive are mixed and ground in a certain proportion to form a slurry, which is then coated on carbon-coated aluminum foil and dried to serve as a working electrode. The hydrogen phosphate mentioned in step (1) includes one of soluble monohydrogen phosphate and soluble dihydrogen phosphate; the aluminum compound includes one of aluminum hydroxide, aluminum sulfate, aluminum oxide, and aluminum nitride; the phosphorus-aluminum ratio is the molar ratio of phosphorus to aluminum, ranging from 1.9 to 4.1; the solid content of the adhesive is 30% to 80%; The water bath temperature in step (2) is 60-140℃; the reaction time is 15-240 min; and the viscosity of the aluminum phosphate inorganic adhesive is 10-500 mPa·s. The conductive carbon black in step (3) is selected from one or more of Ketjen black, acetylene black, Super-P, Super-S, 350G, KS-6, KS-15, SFG-6, and SFG-15; the sulfur content in the S / C composite is 40-85wt%, and the conductive carbon black content is 15-60wt%; calcination is carried out in an oven at 150-200℃ for 10-24 h under a nitrogen atmosphere. The working electrode described in step (4) has an S / C composite content of 98 wt% and a phosphorus aluminum inorganic adhesive content of 2 wt%; the drying conditions are: drying in a vacuum drying oven at 60~110 ℃ for 10~24 h.

Images