Modified separator for lithium-sulfur battery and preparation process thereof

Abstract

The application discloses a modified diaphragm for lithium-sulfur batteries and a preparation process thereof. The modified diaphragm comprises a base diaphragm and a composite layer arranged on the surface of the base diaphragm. The composite layer is doped with nano metal oxide and cobalt nonasulfide. The application sets the composite layer on the base diaphragm. The composite layer is made of metal sulfide and metal oxide. The metal sulfide cobalt nonasulfide is arranged in an array on the surface of the base diaphragm. Since the metal sulfide has porosity and polarity, and the metal oxide has adsorption and catalytic properties, the two are combined. The physical barrier and chemical adsorption of the metal sulfide are utilized, the catalytic effect of the metal oxide is fully exerted, the mechanical stability is improved, the shuttle effect of polysulfide is effectively prevented, the prepared composite layer inhibits the shuttle effect, and the Coulomb efficiency and cycle life of the lithium-sulfur battery are improved.

Description

Technical Field

[0001] This invention relates to the field of battery separator technology, specifically to a modified separator for lithium-sulfur batteries and its preparation process. Background Technology

[0002] With the continuous miniaturization of electronic devices and the rapid development of mobile communication devices, portable electronic information products, electric vehicles, and energy storage power stations, traditional lithium-ion batteries using transition metal oxides such as lithium cobalt oxide (LiCoO2), lithium manganese oxide (LiMn2O4), and lithium nickel oxide (LiNiO2) as cathode materials can no longer meet the overall development needs, especially the requirements for high specific capacity and high energy density. Therefore, it is urgent to develop high-capacity lithium batteries that meet the needs of the information age. The theoretical specific capacity of lithium-sulfur batteries is nearly ten times that of current commercial lithium-ion batteries, and sulfur reserves are very abundant, with a very safe and stable supply chain. In existing technologies, lithium-sulfur batteries use metallic lithium as the negative electrode and sulfur or sulfur composite materials as the positive electrode. During charging and discharging, elemental sulfur is reduced to long-chain polysulfides Li₂Sx (4 < x < 8), which migrate in the electrolyte, causing a shuttle effect. Subsequently, elemental sulfur is further reduced to short-chain polysulfides, eventually forming insulating and insoluble Li₂S₂ / Li₂S. The insoluble Li₂S₂ / Li₂S deposits on the surface of the metallic lithium electrode, directly leading to the loss of active material and severely affecting the battery's coulombic efficiency and cycle life. Ultimately, the dendritic lithium formed by uneven dissolution and deposition, as well as the volume expansion during the formation of lithium sulfides, will lead to a rapid decay of discharge capacity. Traditional separators are mainly made of polypropylene (PP), polyethylene (PE), or their composites PP / PE / PP. Although these membranes are inexpensive and flexible, they have poor hydrophilicity, low ionic conductivity, and cannot inhibit the dissolution and diffusion of polysulfides in the electrolyte. Therefore, we propose a modified separator for lithium-sulfur batteries and its preparation process. Summary of the Invention

[0003] The purpose of this invention is to provide a modified separator for lithium-sulfur batteries and its preparation process, so as to solve the problems mentioned in the background art.

[0004] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a modified separator for lithium-sulfur batteries, the modified separator comprising a base film and a composite layer disposed on the surface of the base film, the composite layer being doped with nano-metal oxides and cobalt octasulfide.

[0005] Furthermore, the cobalt octasulfide is prepared by reacting cobalt nitrate, dimethylimidazole, and sulfur chloride.

[0006] Furthermore, the nano-metal oxide is one or more of Al2O3, RuO2, MnO, CeO2, and TiO2.

[0007] Furthermore, the base membrane is a single-layer or multi-layer wet-process membrane.

[0008] In the above technical solution, a composite layer is set on the base film prepared by wet method. The composite layer is made of metal sulfide and nano metal oxide, and the metal sulfide cobalt octasulfide is arranged in an array on the surface of the base film.

[0009] Among them, metal sulfides are porous and polar, and can adsorb lithium polysulfides through a physicochemical synergistic effect. Compared with ordinary membranes, the cobalt octasulfide array has a larger specific surface area, grows in situ on the surface of the base film, and has higher mechanical stability. The cobalt octasulfide has a hollow structure, which can effectively prevent the shuttle effect of polysulfides. Through the dual effects of physical barrier and chemical adsorption, it can simultaneously suppress the lithium polysulfide shuttle effect.

[0010] Nanoscale metal oxides, with their nanoscale size, large specific surface area, and excellent adsorption properties, can catalyze reduction reactions. Batteries made with separators modified with pure metal oxides have low discharge capacity, leading to low energy density. Combining metal oxides as auxiliary materials with a cobalt octasulfide array utilizes their physical barrier and chemical adsorption effects while fully leveraging the catalytic activity of the metal oxides. The resulting composite layer suppresses the shuttle effect, improving the coulombic efficiency and cycle life of lithium-sulfur batteries.

[0011] A process for preparing a modified separator for lithium-sulfur batteries includes the following steps:

[0012] (1) Dissolve cobalt nitrate and dimethylimidazole in a solvent and react them. After the reaction is complete, a precursor is formed. Add a binder to obtain the precursor slurry.

[0013] (2) The precursor slurry is coated onto the surface of the base membrane to form a precursor coating, and the membrane A is obtained.

[0014] (3) Take diaphragm A and use atomic layer deposition technology to deposit a nano metal oxide layer on the surface of the precursor coating to obtain diaphragm B;

[0015] (4) Take diaphragm B, vulcanize it to obtain a composite layer, and then prepare a modified diaphragm.

[0016] Furthermore, this includes the following steps:

[0017] (1) Dissolve cobalt nitrate and dimethylimidazole in deionized water and react them at 30-80°C for 5-12 hours. After the reaction is complete, a precursor is formed. Add a binder to obtain the precursor slurry.

[0018] (2) The precursor slurry is coated on the surface of the base membrane and dried at 60-80°C for 1-2 hours to form a precursor coating and obtain membrane A.

[0019] (3) Take diaphragm A and deposit it on the surface of the precursor coating using metal chloride and deionized water as reaction sources to form a nano metal oxide layer. The deposition process parameters are: reaction temperature is 40-80℃, and atomic layer deposition cycle is 20-50 weeks to obtain diaphragm B.

[0020] (4) Take diaphragm B and place it in a carbon disulfide solution containing 2-5% sulfur chloride for sulfidation to obtain a composite layer and prepare a modified diaphragm.

[0021] Furthermore, the molar ratio of cobalt nitrate to dimethylimidazole is (1:1) to (1:3).

[0022] Furthermore, the adhesive is one or more of styrene-butadiene rubber, polyacrylic acid, and polyvinylidene fluoride.

[0023] In the above technical solution, cobalt nitrate and dimethylimidazole are reacted to generate cobalt dimethylimidazole, and a precursor of cobalt octasulfide is prepared. The precursor slurry is mixed with a binder to prepare a precursor slurry, which is coated on the surface of the base film. After drying, a membrane containing a metal skeleton cobalt dimethylimidazole (ZIF-67) layer is formed. The membrane is placed in an atomic layer deposition instrument and metal oxide is deposited on the surface of the precursor coating using metal chloride and deionized water as reaction sources. The precursor reacts with sulfur chloride to obtain the product cobalt octasulfide. Due to the uniform dispersion of the precursor in the precursor slurry, the metal sulfide cobalt octasulfide is arrayed on the surface of the membrane, forming a composite layer modified by nano-metal oxide-cobalt octasulfide array, thus realizing the above technical solution.

[0024] This invention incorporates the preparation step of nano-metal oxides into the preparation step of metal sulfides, enabling the metal sulfide cobalt octasulfide to fully contact the nano-metal oxides while adhering to the surface of the base film. This enhances the synergistic effect of the metal sulfide cobalt octasulfide and the nano-metal oxides, thereby improving the coulombic efficiency and cycle life of lithium-sulfur batteries.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0026] The modified separator for lithium-sulfur batteries of the present invention and its preparation process involve setting a composite layer on a base membrane. The composite layer is made of metal sulfides and metal oxides. The metal sulfides, cobalt octasulfide and cobalt 9, are arrayed on the surface of the base membrane. Since the metal sulfides are porous and polar, and the metal oxides have adsorption and catalytic properties, the combination of the two utilizes the physical barrier and chemical adsorption of the metal sulfides to fully exert the catalytic effect of the metal oxides, improves mechanical stability, and effectively prevents the shuttle effect of polysulfides. As a result, the composite layer suppresses the shuttle effect and improves the coulombic efficiency and cycle life of the lithium-sulfur battery. Detailed Implementation

[0027] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] The polyethylene film prepared by the wet-process was used as the base film in the following experiments.

[0029] Example 1

[0030] (1) Dissolve cobalt nitrate and dimethylimidazole in deionized water, with a molar ratio of 1:1. Place the mixture at 30°C for 5 hours. Once the reaction is complete, a precursor is formed. Add a binder, which is styrene-butadiene rubber, to obtain the precursor slurry.

[0031] (2) The precursor slurry is coated onto the surface of the base membrane and dried at 60°C for 0.5 hours to form a precursor coating and obtain membrane A.

[0032] (3) Take diaphragm A and place it in an atomic deposition apparatus. Use 0.01 mol / L aluminum chloride and deionized water as reaction sources to deposit on the surface of the precursor coating to form a nano metal oxide layer, wherein the nano metal oxide is Al2O3. Deposition process parameters: reaction temperature is 40℃, atomic layer deposition cycle is 20 weeks, and diaphragm B is obtained.

[0033] (4) Take diaphragm B and place it in a carbon disulfide solution containing 2% sulfur chloride for sulfidation to obtain a composite layer and prepare a modified diaphragm.

[0034] Example 2

[0035] (1) Dissolve cobalt nitrate and dimethylimidazole in deionized water, with a molar ratio of cobalt nitrate to dimethylimidazole of 1:1. Place the mixture at 55°C for 8.5 hours. Once the reaction is complete, a precursor is formed. Add a binder, which is polyacrylic acid, to obtain a precursor slurry.

[0036] (2) The precursor slurry is coated on the surface of the base membrane and dried at 70°C for 1 hour to form a precursor coating and obtain membrane A.

[0037] (3) Take diaphragm A and place it in an atomic deposition apparatus. Use 0.01 mol / L ruthenium chloride and deionized water as reaction sources to deposit on the surface of the precursor coating to form a nano metal oxide layer, wherein the nano metal oxide is RuO2. The deposition process parameters are: reaction temperature is 60℃, atomic layer deposition cycle is 35 weeks, and diaphragm B is obtained.

[0038] (4) Take diaphragm B and place it in a carbon disulfide solution containing 3.5% sulfur chloride to perform sulfidation, thereby obtaining a composite layer and preparing a modified diaphragm.

[0039] Example 3

[0040] (1) Dissolve cobalt nitrate and dimethylimidazole in deionized water, with a molar ratio of 1:1. Place the mixture at 80°C for 12 hours. Once the reaction is complete, a precursor is formed. Add a binder, which is polyvinylidene fluoride, to obtain the precursor slurry.

[0041] (2) The precursor slurry is coated on the surface of the base membrane and dried at 80°C for 1 hour to form a precursor coating and obtain membrane A.

[0042] (3) Take diaphragm A and place it in an atomic deposition apparatus. Use 0.01 mol / L manganese chloride and deionized water as reaction sources to deposit on the surface of the precursor coating to form a nano metal oxide layer, wherein the nano metal oxide is MnO. Deposition process parameters: reaction temperature is 80℃, atomic layer deposition cycle is 50 weeks, and diaphragm B is obtained.

[0043] (4) Take diaphragm B and place it in a carbon disulfide solution containing 5% sulfur chloride for sulfidation to obtain a composite layer and prepare a modified diaphragm.

[0044] Example 4

[0045] (1) Dissolve cobalt nitrate and dimethylimidazole in deionized water. The molar ratio of cobalt nitrate to dimethylimidazole is 1:2. The mixture is placed at 80°C for 12 hours. After the reaction is completed, a precursor is formed. A binder is added. The binder is styrene-butadiene rubber. The precursor slurry is then prepared.

[0046] (2) The precursor slurry is coated on the surface of the base membrane and dried at 80°C for 1 hour to form a precursor coating and obtain membrane A.

[0047] (3) Take diaphragm A and place it in an atomic deposition apparatus. Use 0.01 mol / L cerium chloride and deionized water as the reaction source to deposit on the surface of the precursor coating to form a nano metal oxide layer, wherein the nano metal oxide is CeO2. The deposition process parameters are: reaction temperature is 80℃, atomic layer deposition cycle is 50 weeks, and diaphragm B is obtained.

[0048] (4) Take diaphragm B and place it in a carbon disulfide solution containing 5% sulfur chloride for sulfidation to obtain a composite layer and prepare a modified diaphragm.

[0049] Example 5

[0050] (1) Cobalt nitrate and dimethylimidazole were dissolved in deionized water at a molar ratio of 1:3. The mixture was placed at 80°C for 12 hours. After the reaction was completed, a precursor was formed. A binder was added, which was styrene-butadiene rubber, to obtain the precursor slurry.

[0051] (2) The precursor slurry is coated on the surface of the base membrane and dried at 80°C for 1 hour to form a precursor coating and obtain membrane A.

[0052] (3) Take diaphragm A and place it in an atomic deposition apparatus. Use 0.01 mol / L titanium chloride and deionized water as reaction sources to deposit on the surface of the precursor coating to form a nano metal oxide layer, wherein the nano metal oxide is TiO2. Deposition process parameters: reaction temperature is 80℃, atomic layer deposition cycle is 50 weeks, and diaphragm B is obtained.

[0053] (4) Take diaphragm B and place it in a carbon disulfide solution containing 5% sulfur chloride for sulfidation to obtain a composite layer and prepare a modified diaphragm.

[0054] Comparative Example 1

[0055] The base film was placed in an atomic deposition apparatus and deposited on the surface of the precursor coating using 0.01 mol / L manganese chloride and deionized water as the reaction source to form a nano-metal oxide layer, wherein the nano-metal oxide is MnO. The deposition process parameters were: reaction temperature of 80℃ and atomic layer deposition cycle of 50 cycles, to obtain the battery separator.

[0056] Comparative Example 2

[0057] (1) Dissolve cobalt nitrate and dimethylimidazole in deionized water, with a molar ratio of 1:1. Place the mixture at 80°C for 12 hours. Once the reaction is complete, a precursor is formed. Add a binder, which is styrene-butadiene rubber, to obtain the precursor slurry.

[0058] (2) The precursor slurry is coated on the surface of the base membrane and dried at 80°C for 2 hours to form a precursor coating and obtain membrane A.

[0059] (3) Take diaphragm A and place it in a carbon disulfide solution containing 5% sulfur chloride to carry out sulfidation to obtain a modified diaphragm.

[0060] Comparative Example 3

[0061] (1) Dissolve cobalt nitrate and dimethylimidazole in deionized water, with a molar ratio of 1:1. Place the mixture at 80°C for 12 hours. Once the reaction is complete, a precursor is formed. Add a binder, which is styrene-butadiene rubber, to obtain the precursor slurry.

[0062] (2) The precursor slurry is coated on the surface of the base membrane and dried at 80°C for 2 hours to form a precursor coating and obtain membrane A.

[0063] (3) Take diaphragm A and place it in a carbon disulfide solution containing 5% sulfur chloride to carry out sulfidation to obtain diaphragm B;

[0064] (4) Obtain membrane B and place it in an atomic deposition apparatus. Use 0.01 mol / L manganese chloride and deionized water as reaction sources to deposit on the surface of the precursor coating to form a nano metal oxide layer, wherein the nano metal oxide is MnO. The deposition process parameters are: reaction temperature is 80℃, atomic layer deposition cycle is 50 weeks, and a nano metal oxide and cobalt octasulfide modified membrane is obtained, thus preparing the modified membrane.

[0065] Comparative Example 4

[0066] (1) Take the base film and place it in an atomic deposition apparatus. Use 0.01 mol / L manganese chloride and deionized water as the reaction source to deposit on the surface of the precursor coating to form a nano metal oxide layer, wherein the nano metal oxide is MnO. The deposition process parameters are: reaction temperature is 80℃, atomic layer deposition cycle is 50 weeks, and a nano metal oxide and cobalt octasulfide modified diaphragm is obtained, thus diaphragm A is prepared.

[0067] (2) Cobalt nitrate and dimethylimidazole were dissolved in deionized water at a molar ratio of 1:1. The mixture was placed at 80°C for 12 hours. After the reaction was completed, a precursor was formed. A binder was added, which was styrene-butadiene rubber, to obtain the precursor slurry.

[0068] (3) The precursor slurry is coated on the surface of diaphragm A and dried at 80°C for 2 hours to form a precursor coating, thus obtaining diaphragm B.

[0069] (4) Take diaphragm B and place it in a carbon disulfide solution containing 5% sulfur chloride for sulfidation to obtain a modified diaphragm; Comparative Example 5

[0070] The base film is used as the battery separator.

[0071] experiment

[0072] Using the separators obtained in Examples 1-5 and Comparative Examples 1-5, and with 70 wt% sulfur powder, 15 wt% superconducting carbon black, and 15 wt% polyvinylidene fluoride as the positive electrode and lithium metal as the negative electrode, a lithium-sulfur battery was prepared using 1.85 mol / L LiCF3SO3 / DOL,DME (volume ratio 1:1).

[0073] The prepared lithium-sulfur battery was used as a sample. Constant current charge-discharge was performed at the same current density within a voltage range of 1.8–2.8 V to detect the electrochemical performance of the sample. The percentage of the first discharge capacity to the first charge capacity was recorded as the coulombic efficiency. The specific capacity (mass) and specific capacity (volume) of the sample were tested at the 1st, 5th, 15th, 50th, 100th, and 200th cycles. The following test results were recorded:

[0074]

[0075]

[0076]

[0077] Based on the data in the table above, the following conclusions can be clearly drawn:

[0078] The diaphragms obtained in Examples 1-5 were compared with those obtained in Comparative Examples 1-5. The test results show that...

[0079] 1. Compared with the separators obtained in Comparative Examples 1-5, the separators obtained in Examples 1-5 have higher initial specific capacity and areal capacity, and the decreasing trend is relatively slow with the increase of cycle number. The coulombic efficiency is also higher. This fully demonstrates that the separator prepared by the present invention improves the coulombic efficiency and cycle life of lithium-sulfur batteries.

[0080] 2. Comparing the separators obtained in Examples 3-5, their initial data on coulombic efficiency, specific capacity, and areal capacity showed no significant changes, and the decreasing trend gradually slowed down with the increase of cycle number. It can be seen that the change in the ratio between cobalt nitrate and dimethylimidazole can affect the cycle life of the battery.

[0081] 3. Comparing the separator obtained in Example 3 with the separators obtained in Comparative Examples 1-5, Comparative Example 1 is a separator modified with nano-metal oxides, and Comparative Example 2 is a separator modified with a cobalt octasulfide array. Compared with the separator obtained in Example 3, the specific capacity and areal capacity of Comparative Examples 1-2 decreased significantly during cycling, and the coulombic efficiency also decreased. It can be seen that modifying the separator only with nano-metal oxides or metal sulfides results in poor coulombic efficiency and cycle life of the lithium-sulfur battery. This fully demonstrates that the combined effect of nano-metal oxides and cobalt octasulfide in separator modification improves the coulombic efficiency and cycle life of the lithium-sulfur battery.

[0082] Comparative Example 3 reverses steps (3) and (4) in Example 3, and Comparative Example 4 moves step (3) forward. As can be seen from the data, the coulombic efficiency and cycle life of the lithium-sulfur batteries prepared in Comparative Examples 3-4 are worse than those in Example 3. Combined with Comparative Examples 1-2, it is fully demonstrated that the preparation process in this invention has a positive impact on the coulombic efficiency and cycle life of the prepared lithium-sulfur batteries.

[0083] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0084] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A process for the preparation of a modified separator for lithium-sulfur batteries, characterized in that, Includes the following steps: (1) Dissolve cobalt nitrate and dimethylimidazole in deionized water and react them at 30-80°C for 5-12 hours. After the reaction is complete, a precursor is formed. Add a binder to obtain the precursor slurry. (2) The precursor slurry is coated on the surface of the base membrane and dried at 60-80°C for 1-2 hours to form a precursor coating and obtain membrane A. (3) Take membrane A and deposit it on the surface of the precursor coating using metal chloride and deionized water as reaction sources to form a nano metal oxide layer. The deposition process parameters are: reaction temperature of 40-80℃ and atomic layer deposition cycle of 20-50 weeks to obtain membrane B; the nano metal oxide is one or more of Al2O3, RuO2, MnO, CeO2 and TiO2. (4) Take diaphragm B and place it in a carbon disulfide solution containing 2-5% sulfur chloride to perform sulfidation to obtain a composite layer and prepare a modified diaphragm.

2. The process for preparing a modified separator for lithium-sulfur batteries according to claim 1, characterized in that: The molar ratio of cobalt nitrate to dimethylimidazole is (1:1) to (1:3).

3. The process for preparing a modified separator for lithium-sulfur batteries according to claim 1, characterized in that: The adhesive is one or more of styrene-butadiene rubber, polyacrylic acid, and polyvinylidene fluoride.

4. The modified separator for lithium-sulfur batteries prepared according to the process of any one of claims 1 to 3, characterized by: The modified diaphragm includes a base membrane and a composite layer disposed on the surface of the base membrane, wherein the composite layer is doped with nano-metal oxides and cobalt octasulfide.

5. The modified separator for lithium-sulfur batteries according to claim 4, characterized in that: The base membrane is a single-layer or multi-layer wet-process membrane.

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