Porous ternary metal oxide, preparation method thereof and application of porous ternary metal oxide in preparation of lithium-sulfur battery diaphragm

Abstract

The invention discloses a porous ternary metal oxide, a preparation method thereof and application of the porous ternary metal oxide in preparation of a lithium-sulfur battery diaphragm, and belongs to the technical field of lithium-sulfur batteries. According to the technical scheme, the preparation method comprises the following steps: completely dissolving Zn (CH3COO) 2 and Ga (NO3) 3xH2O in deionized water at room temperature to obtain a mixed solution, adding citric acid monohydrate serving as a chelating agent into the mixed solution, uniformly stirring, raising the temperature to 60-90 DEG C, continuously stirring to form semitransparent sol, drying the semitransparent sol to obtain foamed yellow xerogel, and drying the foamed yellow xerogel to obtain the ZnO / Ga / ZnO composite material. The yellow xerogel is smashed and calcined at the temperature of 400 DEG C to 600 DEG C, and the porous ternary metal oxide ZnGa2O4 is obtained. The invention is applied to the aspect of lithium-sulfur batteries, and solves the problems of shuttle effect of lithium polysulfide, low utilization rate of sulfur and low reaction rate in the existing lithium-sulfur batteries.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-sulfur batteries, and particularly relates to a porous ternary metal oxide, a preparation method thereof, and an application thereof in the preparation of a lithium-sulfur battery separator. Background Art

[0002] The urgency of environmental protection is driving the accelerated construction of a global clean energy system, and at the same time, higher requirements are also put forward for energy storage technologies. In this context, lithium-sulfur batteries show great application potential due to their unique energy storage mechanism. This system realizes energy storage through the reversible reaction of metallic lithium and elemental sulfur. The core of its electrochemical performance depends on the redox conversion of polysulfides (LiPSs, including S 8 2- to S 2 2- and other different chain-length structures). However, the "shuttle effect" of dissolved polysulfides in the electrolyte leads to irreversible loss of active substances and attenuation of cycle performance, becoming the key bottleneck restricting its practical application.

[0003] To address this challenge, the scientific research community has developed various immobilization strategies such as composite cathode construction, polysulfide adsorption, solid electrolytes, and electrolyte additives. Although these methods can partially inhibit the escape of polysulfides from the cathode, it is found that uneven lithium deposition on the lithium anode side will trigger dendrite growth, significantly increasing the risk of short circuit. At the same time, the problem of "dead sulfur" accumulation formed at the interface of the polypropylene (PP) separator during charge and discharge also seriously affects the battery performance. In response to these new problems, separator modification technology has gradually become a research hotspot - by constructing functional layers such as carbon nanotubes, graphene, nitrides, or sulfides on the surface of traditional separators to form a synergistic effect of physical barrier and chemical adsorption. However, existing modified materials still face two core challenges: firstly, it is difficult to significantly improve the density and selectivity of polar adsorption sites; secondly, the problem of sluggish kinetics of polysulfide conversion reactions has not been effectively solved. Therefore, developing a new functional material system with both strong chemical adsorption ability and high catalytic activity has become an important research direction for breaking through the technical bottleneck of lithium-sulfur batteries.

[0004] Using porous materials as separators can improve the conduction efficiency of lithium ions and the overall performance of the battery. However, many modification methods involve multi-step synthesis processes, increasing the complexity of production. Moreover, the auxiliaries required for some separator modification processes are relatively expensive, thus increasing the manufacturing cost of the battery. At the same time, to a certain extent, the modification of the separator will have a certain impact on the transport rates of lithium and sulfur, thereby restricting the battery performance. Some modifiers will cause problems such as battery safety and stability, such as thermal runaway and short circuit. Summary of the Invention

[0005] In view of the deficiencies of the existing technologies, the technical problem to be solved by the present invention is to solve the problems of the shuttle effect of polysulfide lithium, low sulfur utilization rate and low reaction rate in the existing lithium-sulfur batteries, and to provide a porous ternary metal oxide, a preparation method thereof and an application thereof in the preparation of a lithium-sulfur battery separator, which can greatly improve the capacity, cycle performance and rate performance of the lithium-sulfur battery.

[0006] To solve the above technical problem, the technical solution adopted by the present invention is as follows: On the one hand, the present invention provides a preparation method of a porous ternary metal oxide, comprising: at room temperature, completely dissolving Zn(CH 3 COO) 2 and Ga(NO 3 ) 3 ⋅xH 2 O in deionized water to obtain a mixed solution, adding citric acid monohydrate as a chelating agent to the mixed solution and stirring evenly, then raising the temperature to 60-90 °C and continuously stirring to form a translucent sol, drying the translucent sol to obtain a foamy yellow xerogel, crushing the yellow xerogel and calcining it at 400-600 °C to obtain the porous ternary metal oxide ZnGa 2 O 4 .

[0007] Preferably, the molar ratio of Zn in Zn(CH 3 COO) 2 to Ga in Ga(NO 3 ) 3 ⋅xH 2 O is 1-2:1-2.

[0008] Preferably, the molar ratio of the sum of Zn in Zn(CH 3 COO) 2 and Ga in Ga(NO 3 ) 3 ⋅xH 2 O to the molar amount of citric acid monohydrate is 1-2:1-2.

[0009] Preferably, citric acid monohydrate is added as a chelating agent to the mixed solution and stirred for 0.5-3.0 h.

[0010] Preferably, the temperature is raised to 60-90 °C and continuously stirred for 5-10 h to form a translucent sol.

[0011] Preferably, the yellow xerogel is crushed in a crucible and transferred to a muffle furnace, and calcined at 400-600 °C for 2-6 hours at a heating rate of 2 °C / min.

[0012] On the other hand, the present invention provides a porous ternary metal oxide, which is prepared by the preparation method of the porous ternary metal oxide described in any of the above technical solutions.

[0013] The present invention also provides the application of the above porous ternary metal oxide in the preparation of a lithium-sulfur battery separator.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention provides a preparation method of a porous ternary metal oxide, which has the characteristics of simple process and is expected to realize large-scale industrialized batch production; the porous ternary metal oxide ZnGa prepared therefrom 2 O 4 has abundant voids, which can provide transmission channels for lithium ions and electrons. In addition, the abundant polar oxygen in the ternary metal oxide can effectively adsorb polysulfides and the metal oxide has high catalytic performance, which can effectively improve the electrochemical performance of the lithium-sulfur battery; compared with the traditional commercial separator, the separator modified with the porous ternary metal oxide greatly improves the capacity, cycle performance and rate performance of the lithium-sulfur battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 is an XRD schematic diagram of the porous ternary metal oxide ZnGa 2 O 4 provided in Example 1 of the present invention; Figure 2 is an SEM schematic diagram of the porous ternary metal oxide ZnGa 2 O 4 provided in Example 1 of the present invention; Figure 3 is a TEM schematic diagram of the porous ternary metal oxide ZnGa 2 O 4 provided in Example 1 of the present invention; Figure 4 is a photo of the separator modified with the porous ternary metal oxide ZnGa 2 O 4 provided in Example 1 of the present invention; Figure 5 is a comparison of the cycle performance of the porous ZnGa 2 O 4 modified separator and the commercial separator at 1 C; Figure 6 is a comparison of the rate performance of the porous ZnGa 2 O 4 modified separator and the commercial separator; Figure 7 is the porous ZnGa provided in Example 1 of the present invention2 O 4 Resistance value performance comparison between the modified separator and the commercial separator; Figure 8 SEM image of Comparative Example 2 of the present invention. Detailed implementation manners

[0016] The technical solutions in the specific embodiments of the present invention will be described in detail and completely below. Obviously, the described embodiments are only partial specific implementation manners of the overall technical solution of the present invention, rather than all implementation manners. Based on the overall concept of the present invention, all other embodiments obtained by those of ordinary skill in the art fall within the protection scope of the present invention.

[0017] On the one hand, the present invention provides a preparation method of a porous ternary metal oxide, including: at room temperature, completely dissolving Zn(CH 3 COO) 2 and Ga(NO 3 ) 3 ⋅xH 2 O in deionized water to obtain a mixed solution, adding citric acid monohydrate as a chelating agent to the mixed solution and stirring evenly, then raising the temperature to 60-90 °C and continuously stirring to form a translucent sol, drying the translucent sol to obtain a foamy yellow xerogel, crushing the yellow xerogel and calcining it at 400-600 °C to obtain a porous ternary metal oxide ZnGa 2 O 4 . Among them, the abundant polar oxygen in the ternary metal oxide can effectively adsorb polysulfides and the metal oxide has high catalytic performance, which can effectively improve the electrochemical performance of the lithium-sulfur battery. The porous ternary metal oxide with a porous structure has abundant voids that can provide transmission channels for lithium ions and electrons. The present invention uses a simple and large-scale production method of water bath stirring combined with calcination to obtain a porous ternary metal oxide for the related process technology of modifying the separator of a lithium-sulfur battery. Compared with the traditional commercial separator, the separator modified with the porous ternary metal oxide greatly improves the capacity, cycle performance and rate performance of the lithium-sulfur battery.

[0018] In a preferred embodiment, the molar dosage ratio of Zn in Zn(CH 3 COO) 2 to Ga in Ga(NO 3 ) 3 ⋅xH 2 O is 1-2∶1-2. Optionally, the molar ratio of Zn(CH 3 COO) 2 and Ga(NO 3 ) 3 ⋅xH 2 O is 1∶2, 2:1, 1∶1.

[0019] In a preferred embodiment, the sum of the molar amounts of Zn in Zn(CH 3 COO) 2 and Ga in Ga(NO 3 ) 3 ⋅xH 2 O and the molar amount of citric acid monohydrate is in a ratio of 1 - 2:1 - 2. Optionally, the sum of the molar amounts of Zn in Zn(CH 3 COO) 2 and Ga in Ga(NO 3 ) 3 ⋅xH 2 O and the molar amount of citric acid monohydrate can also be 1:1, 1:2, or 2:1.

[0020] In a preferred embodiment, citric acid monohydrate is added as a chelating agent to the mixed solution and stirred for 0.5 - 3.0 h. Optionally, the stirring time can also be 1.0 h, 1.5 h, 2.0 h, 2.5 h, or any point value within this range.

[0021] In a preferred embodiment, the temperature is raised to 60 - 90 °C and continuously stirred for 5 - 10 h to form a translucent sol. It can be understood that the temperature can also be 70 °C, 80 °C, or any point value within this range, and the continuous stirring time can also be 6 h, 7 h, 8 h, 9 h, or any point value within this range.

[0022] In a preferred embodiment, the yellow dry gel is crushed in a crucible and transferred to a muffle furnace, and calcined at 400 - 600 °C for 2 - 6 h at a heating rate of 2 °C / min. The temperature can also be 450 °C, 500 °C, 550 °C, or any point value within this range, and the calcination time can also be 3 h, 4 h, 5 h, or any point value within this range.

[0023] The above preparation method is simple and convenient and can achieve large-scale production. A ternary porous metal oxide can be obtained through a one-step water bath method and a calcination process. The porous structure of the ternary porous metal oxide obtained by this method improves the conduction rate of lithium ions in the separator, thereby improving the charge and discharge efficiency of the battery, the high adsorption and catalytic performance of the ternary oxide, and solving the problem that traditional lithium-sulfur batteries cannot inhibit the shuttle effect of LiPSs generated during the charge and discharge process.

[0024] On the other hand, the present invention provides a porous ternary metal oxide prepared by the preparation method of the porous ternary metal oxide described in any of the above technical solutions. This porous ternary metal oxide can improve the capacity, cycle performance, and rate performance of the battery.

[0025] The present invention also provides an application of the above-mentioned porous ternary metal oxide in preparing a separator for a lithium-sulfur battery.

[0026] In order to introduce the porous ternary metal oxide, its preparation method and its application in preparing a separator for a lithium-sulfur battery provided by the embodiments of the present invention more clearly and in detail, the following will be described in conjunction with specific embodiments.

[0027] Example 1 At room temperature, a certain amount of Zn(CH 3 COO) 2 and Ga(NO 3 ) 3 ⋅xH 2 O (the molar dosage ratio of Zn in Zn(CH 3 COO) 2 to Ga in Ga(NO 3 ) 3 ⋅xH 2 O is 1:2) was completely dissolved in 30 mL of deionized water. Then, a certain amount of citric acid monohydrate was used as a chelating agent (the molar dosage sum of Zn in Zn(CH 3 COO) 2 to Ga in Ga(NO 3 ) 3 ⋅xH 2 O and the molar dosage of citric acid monohydrate was 1:1) was added to the above homogeneous solution and stirred for 0.5 hours. Then the temperature was raised to 90 °C and continuously stirred for 5 hours to form a translucent sol. Subsequently, the dry gel was dried overnight at 120 °C to obtain a foamy yellow dry gel. Finally, the dry gel was crushed in a crucible and transferred to a muffle furnace, and calcined at 500 °C for 4 hours at a heating rate of 2 °C / min. After cooling to room temperature, the obtained porous ternary metal oxide ZnGa 2 O 4 .

[0028] Comparative Example 1 At room temperature, a certain amount of Zn(CH 3 COO) 2 and Ga(NO 3 ) 3 ⋅xH 2 O (the molar dosage ratio of Zn in Zn(CH 3 COO) 2 to Ga in Ga(NO 3 ) 3 ⋅xH 2 O is 1:3) was completely dissolved in 30 mL of deionized water. Then, a certain amount of citric acid monohydrate was used as a chelating agent (Zn(CH 3 COO)2 The sum of the molar amounts of Zn in and Ga(NO 3 ) 3 ⋅xH 2 O and the molar amount of citric acid monohydrate were added to the above homogeneous solution at a ratio of 1:1) and stirred for 0.5 h. Then the temperature was raised to 90 °C and continuously stirred for 5 h to form a translucent sol. Subsequently, the dry gel was dried overnight at 120 °C to obtain a foamy yellow dry gel. Finally, the dry gel was crushed in a crucible and transferred to a muffle furnace, and calcined at 500 °C for 4 h at a heating rate of 2 °C / min. After cooling to room temperature, a ternary metal oxide with impurities (non-pure phase) was obtained.

[0029] Comparative Example 2 At room temperature, a certain amount of Zn(CH 3 COO) 2 and Ga(NO 3 ) 3 ⋅xH 2 O (the molar ratio of Zn in Zn(CH 3 COO) 2 to Ga in Ga(NO 3 ) 3 ⋅xH 2 O was 1:2) was completely dissolved in 30 mL of deionized water. Then, a certain amount of citric acid monohydrate was used as a chelating agent (the sum of the molar amounts of Zn in Zn(CH 3 COO) 2 and Ga in Ga(NO 3 ) 3 ⋅xH 2 O and the molar amount of citric acid monohydrate were added to the above homogeneous solution at a ratio of 1:1) and stirred for 0.5 h. Then the temperature was raised to 90 °C and continuously stirred for 5 h to form a translucent sol. Subsequently, the dry gel was dried overnight at 120 °C to obtain a foamy yellow dry gel. Finally, the dry gel was crushed in a crucible and transferred to a muffle furnace, and calcined at 800 °C for 4 h at a heating rate of 2 °C / min. After cooling to room temperature, a ternary metal oxide ZnGa with a non-porous structure was obtained 2 O 4 .

[0030] Performance Test The porous ternary metal oxide ZnGa 2 O 4 prepared in Example 1 was subjected to XRD, SEM, and TEM tests, and the results obtained are as Figure 1-3 shown.

[0031] From Figure 1It can be found that the prepared porous ternary metal oxide corresponds to cubic ZnGa 2 O 4 (PDF#38-1240); From Figure 2 It can be found that the surface morphology of the prepared ternary metal oxide ZnGa 2 O 4 is mainly a nanoporous morphology; From Figure 3 It can be found that the prepared ternary metal oxide ZnGa 2 O 4 is a porous structure composed of nanoparticles; Using the porous ternary metal oxide ZnGa 2 O 4 to modify the separator, the ternary metal oxide ZnGa 2 O 4 modified separator is prepared by a simple coating process. First, 80 mg of ZnGa 2 O 4 powder, 10 mg of conductive carbon black (Super P) and 10 mg of polyvinylidene fluoride (PVDF) are dispersed in N-methylpyrrolidone (NMP), stirred for 12 hours, and then the homogeneous slurry is coated on a commercial separator of type Celgard 2500 and dried in a vacuum drying oven at 60 °C for 12 hours. Finally, the commercial separator modified by the ternary metal oxide ZnGa 2 O 4 is cut into discs with a diameter of 19 mm.

[0032] Preparation of the cathode material for the lithium-sulfur battery: The carbon / sulfur composite material (carbon nanotubes / sulfur) is made by the melting method. Carbon nanotubes (CNTs) and sublimed sulfur are mixed in a mass ratio of 3:7 into a hydrothermal reactor and heated at 155 °C for 10 hours. Subsequently, 80 mg of the carbon / sulfur composite material, 10 mg of Super P and 10 mg of PVDF are dispersed in NMP, stirred for 12 hours, the slurry is evenly coated on aluminum foil, and dried under vacuum conditions at 60 °C for 12 hours. Finally, the cathode sheet is cut into discs with a diameter of 12 mm to obtain the cathode material.

[0033] Electrochemical testing of the lithium-sulfur battery: The electrolyte uses 1.0 M LiTFSI and 5 wt% of LiNO 3Dissolved in 1,3-dioxolane (DOL) / 1,2-dimethoxyethane (DME) with a volume ratio of 1:1. The button cells of model CR2032 were assembled in a glove box where the oxygen and water contents were both less than 0.01 ppm. The static charge-discharge tests of the current were carried out on a Neware test system, where the voltage window was 1.7 - 2.8 V, and the C-rate mode was adopted (1C = 1675 mAh g -1 ). The resistance tests were carried out on a Shanghai Zhenhua electrochemical workstation.

[0034] For the porous ternary metal oxide ZnGa prepared by Example 1 2 O 4 The photo of the modified separator is as shown in Figure 4 It can be found from Figure 4 that the prepared ternary metal oxide ZnGa 2 O 4 can be tightly loaded on the surface of the modified commercial separator and is not easy to fall off.

[0035] The porous ZnGa 2 O 4 modified separator provided by Example 1 of the present invention was compared with the commercial separator in terms of cycle performance and rate performance. The results are as shown in Figure 5 , 6 It can be found from Figure 5 that the commercial separator can provide an initial discharge specific capacity of 614.2 mAh g -1 and maintain a discharge specific capacity of 335.6 mAh g -1 after 300 cycles. Compared with the commercial separator, the porous ZnGa 2 O 4 modified separator can provide a high discharge specific capacity of up to 723.4 mAh g -1 after 300 cycles. It can be found from Figure 6 that the separator modified by porous ZnGa 2 O 4 still maintains high rate performance. For example, when the current density is as high as 5 C, the modified commercial separator can provide a discharge specific capacity of up to 698.4 mAh g -1 , which is much higher than that of the commercial separator (433.3 mAh g -1 ). As shown in Figure 7 , compared with the commercial separator, the porous ZnGa 2 O 4 modified separator has a lower resistance value, so it is more conducive to the transmission of electrons and ions.

[0036] Figure 8 SEM images of Comparative Example 2 are shown, and comparing them with Figure 2Comparison reveals that: the sample mainly exhibits a nanoparticle structure and has no obvious porous structure.

Claims

1. A method for preparing a porous ternary metal oxide, characterized in that: include: At room temperature, Zn(CH3COO)2 and Ga(NO3)3⋅xH2O are completely dissolved in deionized water to obtain a mixed solution, citric acid monohydrate is added to the mixed solution as a chelating agent and stirred evenly, then the temperature is raised to 60-90°C and stirred continuously to form a translucent sol, the translucent sol is dried to obtain a foamy yellow dry gel, the yellow dry gel is crushed and calcined at 400-600°C to obtain a porous ternary metal oxide ZnGa2O4.

2. The method for preparing the porous ternary metal oxide according to claim 1, characterized in that: The molar ratio of Zn in Zn(CH3COO)2 to Ga in Ga(NO3)3⋅xH2O is 1-2:1-2.

3. The method for preparing the porous ternary metal oxide according to claim 1, characterized in that: The molar ratio of the sum of the molar amounts of Zn in Zn(CH3COO)2 and Ga in Ga(NO3)3⋅xH2O to the molar amount of citric acid monohydrate is 1-2:1-2.

4. The method for preparing a porous ternary metal oxide according to claim 1, characterized in that: Citric acid monohydrate was added to the mixed solution as a chelating agent and stirred for 0.5-3.0 h.

5. The method for preparing a porous ternary metal oxide according to claim 1, characterized in that: The temperature was raised to 60-90°C and stirring was continued for 5-10 h to form a translucent sol.

6. The method for preparing a porous ternary metal oxide according to claim 1, characterized in that: The yellow xerogel was crushed in a crucible and transferred to a muffle furnace and calcined at 400-600°C for 2-6 hours at a heating rate of 2°C / min.

7. A porous ternary metal oxide, characterized in that: The porous ternary metal oxide is prepared by the preparation method of any one of claims 1 to 6.

8. Use of the porous ternary metal oxide according to claim 7 in preparing a lithium-sulfur battery separator.

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