Electrolyte Containing Organotin Additive for Metal-Sulfur Secondary Battery and Metal-Sulfur Secondary Battery Containing the Same

Abstract

The present invention discloses an electrolyte containing an organotin additive for a metal-sulfur secondary battery and a metal-sulfur secondary battery containing the electrolyte. The electrolyte containing the organotin additive comprises a metal salt, an organic solvent and an organotin additive; the organotin additive is one or more of dimethyldichlorotin, dipropyldichlorotin, dibutyldichlorotin, tributyltin chloride, butyltin trichloride, phenyltin trichloride. The present invention provides a metal-sulfur secondary battery comprising the electrolyte containing the organotin additive. The organotin additive in the electrolyte of the present invention can act on both the positive electrode and the negative electrode simultaneously. On the positive electrode side, it has good adsorption and catalytic effects on sulfur and sulfides, can effectively inhibit the shuttle effect of polysulfides, and improve the cycle performance of the battery; on the negative electrode side, a protective layer can be formed, which can effectively protect the negative electrode of the battery and ensure the stability of the negative electrode structure.

Description

Technical Field

[0001] The present invention belongs to the technical field of secondary batteries, and particularly relates to an electrolyte for a metal-sulfur secondary battery and a metal-sulfur secondary battery containing the electrolyte. Background Art

[0002] The most advanced lithium-ion batteries are approaching their specific energy limits and cannot meet the growing energy demands, especially for electric vehicles. Therefore, there is an urgent need to develop new lithium batteries for energy storage and conversion devices. Metal-sulfur secondary batteries have become the main focus of academic and industrial energy storage research due to their high theoretical capacity, high energy density, and low cost. However, metal-sulfur secondary batteries are generally affected by the following aspects. Inherent drawbacks, including the low electronic conductivity of sulfur and polysulfide intermediates, polysulfide dissolution and shuttle effect, volume expansion of elemental sulfur during charge and discharge, and side reactions originating from metal anodes and organic liquid electrolytes, have seriously hindered the commercialization of metal-sulfur secondary batteries.

[0003] Catalysis has recently been introduced into metal-sulfur secondary batteries, and the accelerated conversion of soluble polysulfides has attracted great interest among scholars, providing a new idea for solving the shuttle effect. Heterogeneous catalysts such as metals and metal oxides / sulfides / nitrides and their heterostructures have been designed to achieve strong adsorption and rapid catalytic conversion of polysulfides. However, due to heterogeneous catalysis, the catalytic adsorption only occurs on the surface of the matrix material, polysulfides migrate to the catalyst surface through slow diffusion, and the catalyst will be covered by elemental sulfur, so the catalytic effect has not been fully utilized. Additives dissolved in the electrolyte can undergo homogeneous catalysis, adsorb polysulfides in the electrolyte and accelerate their conversion at the homogeneous interface, which should be able to better solve the shuttle problem.

[0004] CN 113937357 A discloses an electrolyte for a metal-sulfur secondary battery. The electrolyte includes a metal salt, an organic solvent, and a cerium(IV)-based additive; the cerium(IV)-based additive is one or more of cerium(IV) nitrate, cerium(IV) fluoride, cerium(IV) chloride, cerium(IV) iodide, ammonium cerium(IV) nitrate, and cerium(IV) trifluoromethanesulfonate. The cerium(IV)-based additive in this electrolyte can effectively protect the negative electrode of the battery and ensure the stability of the negative electrode structure; this additive can also act on the positive electrode, having good adsorption and catalytic effects on sulfur and sulfides, and can effectively inhibit the shuttle effect of polysulfides and improve the cycle performance of the battery. Through further research, it is found that the action mechanism of the cerium(IV)-based additive is mainly that the additive dissociates into cerium(IV) ions in the electrolyte, and the cerium(IV) ions have adsorption and catalytic effects on polysulfides, which can accelerate the conversion of polysulfides and improve the utilization rate of polysulfides; at the same time, the cerium(IV) ions can also react with the metal negative electrode to form an artificial SEI layer to protect the stability of the metal negative electrode. However, since cerium belongs to rare earth metals, the cerium-based additive is relatively expensive and is not economical in industrial production.

[0005] The present invention provides a simple method to solve the problem of dissolution and shuttle of polysulfides existing in the sulfur positive electrode and provide protection for the Li negative electrode, improving the electrochemical performance of the metal-sulfur secondary battery, which has important significance for promoting its commercial application. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide an electrolyte containing an organotin additive for a metal-sulfur secondary battery and a metal-sulfur secondary battery containing this electrolyte. The organotin compounds as electrolyte additives have high solubility, low price, simple composition, and environmental friendliness, and significantly improve the rate performance and cycle performance of the metal-sulfur secondary battery.

[0007] To solve the above technical problems, the present invention adopts the following technical solutions:

[0008] In the first aspect, the present invention provides an electrolyte for a metal-sulfur secondary battery. The electrolyte includes a metal salt, an organic solvent, and an organotin additive; the organotin additive is one or more of dimethyldichlorotin, dipropyldichlorotin, dibutyldichlorotin, tributylchlorotin, butyltrichlorotin, and phenyltrichlorotin; the concentration of the metal salt in the electrolyte is 0.5 - 2.0 mol / L, and the addition amount of the organotin additive is 0.5 - 2 wt% of the total mass of the metal salt and the organic solvent; the water content in the electrolyte is below 100 ppm.

[0009] Preferably, in the electrolyte, the organotin additive is 1 wt%.

[0010] Preferably, the electrolyte is composed of a metal salt, an organic solvent, and an organotin additive.

[0011] The metal-sulfur secondary battery of the present invention includes a lithium-sulfur battery, a room-temperature sodium-sulfur battery, a potassium-sulfur battery, and a magnesium-sulfur battery. In the electrolyte for the metal-sulfur secondary battery, the metal salt and the organic solvent can be selected conventionally. Specifically, the metal salt in the electrolyte can be selected from one or more of lithium hexafluorophosphate, lithium perchlorate, lithium bis(trifluoromethanesulfonyl)imide, sodium hexafluorophosphate, sodium perchlorate, sodium bis(trifluoromethanesulfonyl)imide, potassium hexafluorophosphate, potassium perchlorate, potassium bis(trifluoromethanesulfonyl)imide, magnesium(II) hexafluorophosphate, magnesium(II) perchlorate, magnesium(II) bis(trifluoromethanesulfonyl)imide, and the selected metal salt should correspond to the metal negative electrode. The organic solvent in the electrolyte can be selected from one or more of diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, ethylene carbonate, propylene carbonate, diethyl carbonate, dimethyl carbonate, fluoroethylene carbonate, dimethyl trisulfide, dimethyl disulfide, dimethyl sulfide (DME), 1,3-dioxolane (DOL), 1,3-dioxane, dimethyl sulfoxide, ethyl methyl sulfone, sulfolane, isopropyl methyl sulfone, dimethyl sulfoxide, tetrahydrofuran.

[0012] In a second aspect, the present invention provides a metal-sulfur secondary battery, which includes a positive electrode, a negative electrode, a separator, and an electrolyte located between the positive electrode and the negative electrode. The electrolyte includes a metal salt, an organic solvent, and an organotin additive; the organotin additive is one or more of dimethyldichlorotin, dipropyldichlorotin, dibutyldichlorotin, tributyltin chloride, butyltrichlorotin, phenyltrichlorotin; the concentration of the metal salt in the electrolyte is 0.5 - 2.0 mol / L, and the addition amount of the organotin additive is 0.1 - 3 wt% of the total mass of the metal salt and the organic solvent; the water content in the electrolyte is below 100 ppm.

[0013] Details regarding the electrolyte are as described in the first aspect and will not be elaborated here.

[0014] In the metal-sulfur secondary battery of the present invention, the positive electrode, the negative electrode, and the separator can all be selected conventionally.

[0015] Specifically, the material of the negative electrode can be any one of metallic lithium, metallic sodium, metallic potassium, metallic magnesium, lithium alloy, sodium alloy, potassium alloy, magnesium alloy. The lithium alloy is Li x M 1 , where M 1 = Si, Sn, or Al; the aluminum alloy is Na y M 2 , where M 2= Sn, Au or Sb; the potassium alloy is K z M 3 , where M 3 = Si, Sn or Al; the magnesium alloy is Mg t M 4 , where M 4 = Si, Sn or Al; the values of x, y, z, and t are each greater than 0 and less than 1. The shape of the negative electrode (such as sheet or foil) can be prepared as needed.

[0016] The positive electrode is obtained by coating a composite of a sulfur-containing active material, a binder, and a conductive agent on a current collector. The sulfur-containing active material can be selected from one of elemental sulfur, sulfur-carbon composite, sulfonated polyacrylonitrile, metal sulfide, composite of elemental sulfur and sulfonated polyacrylonitrile, and composite of elemental sulfur and metal sulfide. The binder can be polyvinylidene fluoride. The positive electrode conductive agent can be conductive carbon black. In the composite of the sulfur-containing active material, the binder, and the conductive agent, the mass ratio of the sulfur-containing active material, the binder, and the conductive agent is 7:2:1.

[0017] The separator can be a glass fiber membrane, a polyethylene microporous membrane, a polypropylene microporous membrane, or an ethylene-propylene copolymer microporous membrane.

[0018] The metal-sulfur secondary battery of the present invention can be assembled into a button cell, a soft package cell, or a cylindrical cell.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0020] (1) In previous work, the application of common additives in metal-sulfur secondary batteries usually only modifies one aspect of the positive electrode or the negative electrode, and it is difficult to improve the overall performance of the battery. In the metal-sulfur secondary battery of the present invention, the organotin additive, as a bifunctional additive, can be uniformly dissolved in the electrolyte solvent. Its unique structure can prevent the dissociation of anions and cations caused by solvation, can complex with polysulfide lithium, has an adsorption effect on polysulfide, can capture the polysulfide dissolved in the electrolyte, and can catalyze the conversion of polysulfide. Therefore, on the positive electrode side, it can promote the rapid conversion of sulfur and polysulfide, and carry out homogeneous catalysis with polysulfide, improve the utilization rate of the catalyst, alleviate the capacity attenuation of the battery, and extend the battery life; at the same time, the organotin metal compound has reactivity with Li metal and can in-situ generate a SEI layer to protect the Li negative electrode. The formation of the SEI layer reduces the corrosion of the electrolyte and soluble polysulfide on the Li metal, inhibits the formation of Li dendrites, and promotes the rapid and uniform deintercalation and intercalation of Li ions, obtaining a metal-sulfur secondary battery with more excellent cycle performance and rate performance.

[0021] (2) The metal-sulfur secondary battery provided by the present invention selects an organotin compound as an electrolyte additive, which has high solubility, low price, simple composition, environmental friendliness, and significantly improves the cycling performance of the metal-sulfur secondary battery, showing great application prospects. Description of the Drawings

[0022] Figure 1 Cycling performance and Coulomb efficiency of the lithium-sulfur battery in Example 1 of the present invention.

[0023] Figure 2 Cycling performance and Coulomb efficiency of the lithium-sulfur battery in Example 10 of the present invention.

[0024] Figure 3 Cycling performance and Coulomb efficiency of the lithium-sulfur battery in Example 11 of the present invention.

[0025] Figure 4 Cycling performance and Coulomb efficiency of the lithium-sulfur battery in Comparative Example 1 of the present invention.

[0026] Figure 5 Optical photograph of the polysulfide deposition experiment in Example 1 of the present invention.

[0027] Figure 6 XPS spectrum of the Cl 2p orbital of the precipitate in Example 1 of the present invention.

[0028] Figure 7 XPS spectrum of the Sn 3d orbital of the precipitate in Example 1 of the present invention.

[0029] Figure 8 SEM image of the SEI film formed on the sodium negative electrode side before cycling of the lithium-sulfur battery obtained in Example 1.

[0030] Figure 9 XRD pattern of the SEI film formed on the sodium negative electrode side before cycling of the lithium-sulfur battery obtained in Example 1.

[0031] Figure 10 SEM image of the surface of the sodium negative electrode side after 50 cycles of the lithium-sulfur battery obtained in Comparative Example 1.

[0032] Figure 11 SEM image of the surface of the sodium negative electrode side after 50 cycles of the lithium-sulfur battery obtained in Example 1.

[0033] Figure 12 XPS spectrum of Sn 3d on the surface of the lithium negative electrode in Example 1 of the present invention.

[0034] Figure 13 XPS spectrum of C1s on the surface of the lithium negative electrode in Example 1 of the present invention.

[0035] Figure 14This is the XPS spectrum of Cl 2p on the lithium anode surface in Example 1 of the present invention.

[0036] Figure 15 This is the cycling performance and Coulomb efficiency of the lithium-sulfur battery in Comparative Example 5 of the present invention. Detailed implementation manners

[0037] The present invention will be further described below in conjunction with examples and drawings.

[0038] The metal-sulfur secondary battery of the present invention includes an electrolyte, a negative electrode, a positive electrode, and a separator. The positive electrode of the present invention is a composite of a sulfur-containing active material, a binder, and a conductive agent coated on a current collector; the positive electrode current collector is a carbon-coated aluminum foil commonly used in the art, purchased from Shenzhen Kejing.

[0039] For Comparative Examples 1-4 and Examples 1-11 of the present invention, the sulfur-containing active material used is a sulfur-carbon composite material commonly used in metal-sulfur secondary batteries. The specific operation is as follows: 0.8 g of sublimed sulfur is mixed with 1.2 g of porous carbon (purchased from Kuraray, Japan), and ball-milled at a rotation speed of 500 rpm for 1 h to obtain a uniformly mixed powder; the ball-milled mixture is transferred to a tube furnace and heated at 155 °C for 10 h in an argon atmosphere to obtain an S / C composite material.

[0040] The sulfur-containing active material in Example 12 is elemental sulfur.

[0041] The sulfur-containing active material in Example 13 is a SPAN composite material. The specific preparation method is as follows: 1.75 g of sublimed sulfur and 1 g of polyacrylonitrile sulfide (purchased from Shanghai Macklin) are mixed and ball-milled at a rotation speed of 300 rpm for 4 h to obtain a uniformly mixed powder; the ball-milled mixture is transferred to a tube furnace and heated at 350 °C for 6 h in an argon atmosphere to obtain a SPAN composite material.

[0042] The sulfur-containing active material in Example 14 is an S / CoS2 composite material. The specific preparation method is as follows: 1.2 g of cobalt tetroxide (purchased from Sigma, USA) and 2.25 g of thioacetamide (TAA) are refluxed at 90 °C for 10 minutes, and the precipitate is collected using a centrifuge. After drying, it is heated at 350 °C for 2 h in an argon atmosphere to obtain a CoS2 sulfur host. Subsequently, 0.4 g of CoS2 and 1.6 g of sublimed sulfur are mixed and heated at 155 °C for 10 h in an argon atmosphere to obtain an S / CoS2 composite material.

[0043] Preparation of the positive electrode: The sulfur-containing active material, polyvinylidene fluoride, and conductive carbon black are mixed and ground according to a mass ratio of 7:1:2, and mixed evenly in N-methylpyrrolidone (NMP) to obtain a slurry. 2 ml of the slurry with a concentration of 0.2 g / ml is uniformly coated on 60 cm 2Coated on carbonized aluminum foil, dried at 60 °C for 12 h, then cut into electrodes with a diameter of 12 mm and placed in a glove box for use.

[0044] In the comparative examples and examples of the present invention, the electrolyte is dehydrated by adding molecular sieves, and its water content is below 100 ppm.

[0045] Examples 1-14

[0046] Electrolyte preparation:

[0047] According to Table 1, a mixture of two or more of 1,3-dioxolane (DOL), 1,3-dioxane, diethylene glycol dimethyl ether (DME), triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, ethylene carbonate, propylene carbonate, diethyl carbonate, dimethyl carbonate, fluoroethylene carbonate, dimethyl trisulfide, dimethyl disulfide, dimethyl sulfide, dimethyl sulfoxide, ethyl methyl sulfone, sulfolane, isopropyl methyl sulfone, dimethyl sulfoxide, tetrahydrofuran is used as the organic solvent. An organotin additive with a mass of 0.1-3% of the total mass of the metal salt and the organic solvent is added, the metal salt is added, and the concentration of the metal salt in the electrolyte is 1.0 mol / L (M). After stirring well, the electrolyte for the metal-sulfur secondary battery is obtained.

[0048] A polypropylene microporous membrane of type Celgard 2400 or a glass fiber membrane of Whatman GF / D is selected as the separator. The positive electrode material, the separator, the metal sheet and the above electrolyte (the dosage of the electrolyte is 30 μl) are assembled into a metal-sulfur secondary battery in a glove box filled with argon (the contents of O2 and H2O are both < 0.1 ppm).

[0049] Using dimethyltin dichloride as the electrolyte additive, different metal-sulfur secondary battery systems are assembled to obtain Examples 1-4; using different organotin compounds as the electrolyte additive, lithium-sulfur batteries are assembled to obtain Examples 5-9; using different concentrations of dimethyltin dichloride as the electrolyte additive, lithium-sulfur batteries are assembled to obtain Examples 10-11; using different sulfur materials as the positive electrode active material, lithium-sulfur batteries are assembled to obtain Examples 12-14.

[0050] Comparative Example 1

[0051] As shown in Table 1, the electrolyte prepared without adding an organotin additive, that is, the electrolyte containing an organic solvent and a lithium salt, is used as Comparative Example 1. The specific operation is as follows: In a glove box filled with argon, a mixture of ethylene glycol dimethyl ether (DME) and 1,3-dioxolane (DOL) with a volume ratio of 1:1 is used as the organic solvent, the lithium salt is added, and the concentration of the lithium salt in the electrolyte is 1.0 M. After stirring well, the electrolyte for the lithium-sulfur battery is obtained.

[0052] The polypropylene microporous membrane of model Celgard 2400 was selected as the separator, and the positive electrode material, separator, lithium metal sheet and the above electrolyte (the dosage of the electrolyte was 30 μl) were assembled into a lithium-sulfur battery in a glove box filled with argon (the contents of O2 and H2O were both < 0.1 ppm).

[0053] Comparative Example 2

[0054] As shown in Table 1, the electrolyte prepared without adding an organotin additive, that is, the electrolyte containing an organic solvent and a sodium salt, was used as Comparative Example 2. The specific operation was as follows: In a glove box filled with argon, a mixed solution of propylene carbonate (PC) and ethylene carbonate (EC) with a volume ratio of 1:1 was used as the organic solvent, and a sodium salt was added to make the concentration of the sodium salt in the electrolyte 1.0 M, and it was stirred evenly to obtain the electrolyte of the room-temperature sodium-sulfur battery.

[0055] The glass fiber membrane of model Whatman GF / D was selected as the separator, and the positive electrode material, separator, sodium metal sheet and the above electrolyte (the dosage of the electrolyte was 30 μl) were assembled into a room-temperature sodium-sulfur battery in a glove box filled with argon (the contents of O2 and H2O were both < 0.1 ppm).

[0056] Comparative Example 3

[0057] As shown in Table 1, the electrolyte prepared without adding an organotin additive, that is, the electrolyte containing an organic solvent and a potassium salt, was used as Comparative Example 3. The specific operation was as follows: In a glove box filled with argon, a mixed solution of propylene carbonate (PC) and ethylene carbonate (EC) with a volume ratio of 1:1 was used as the organic solvent, and a potassium salt was added to make the concentration of the potassium salt in the electrolyte 1.0 M, and it was stirred evenly to obtain the electrolyte of the potassium-sulfur battery.

[0058] The glass fiber membrane of model Whatman GF / D was selected as the separator, and the positive electrode material, separator, potassium metal sheet and the above electrolyte (the dosage of the electrolyte was 30 μl) were assembled into a potassium-sulfur battery in a glove box filled with argon (the contents of O2 and H2O were both < 0.1 ppm).

[0059] Comparative Example 4

[0060] As shown in Table 1, the electrolyte prepared without adding an organotin additive, that is, the electrolyte containing an organic solvent and a magnesium salt, was used as Comparative Example 4. The specific operation was as follows: In a glove box filled with argon, a mixed solution of ethylene glycol dimethyl ether (DME) and 1,3-dioxolane (DOL) with a volume ratio of 1:1 was used as the organic solvent, and a magnesium salt was added to make the concentration of the magnesium salt in the electrolyte 1.0 M, and it was stirred evenly to obtain the electrolyte of the magnesium-sulfur battery.

[0061] Select a glass fiber membrane of Whatman GF / D as the separator, and assemble a magnesium-sulfur battery with the positive electrode material, the separator, a magnesium metal sheet, and the above electrolyte (the dosage of the electrolyte is 30 μl) in a glove box filled with argon (the contents of O2 and H2O are both < 0.1 ppm).

[0062] Comparative Example 5

[0063] As shown in Table 1, an electrolyte is prepared with an inorganic tin salt SnCl4 as an additive, that is, an electrolyte containing an organic solvent, SnCl4, and a lithium salt is used as Comparative Example 5. The specific operation is as follows: In a glove box filled with argon, a mixed solution of ethylene glycol dimethyl ether (DME) and 1,3-dioxolane (DOL) with a volume ratio of 1:1 is used as the organic solvent, and a lithium salt and SnCl4 are added, and the concentrations of the lithium salt and SnCl4 in the electrolyte are 1.0 M and 1%, respectively, and stirred evenly to obtain a lithium-sulfur battery electrolyte.

[0064] Select a polypropylene microporous membrane of Celgard 2400 as the separator, and assemble a lithium-sulfur battery with the positive electrode material, the separator, a lithium metal sheet, and the above electrolyte (the dosage of the electrolyte is 30 μl) in a glove box filled with argon (the contents of O2 and H2O are both < 0.1 ppm).

[0065] After the batteries prepared in Examples 1-14 and Comparative Examples 1-4 are placed in a constant temperature and humidity chamber at 25 °C and left standing for 12 h, charge-discharge cycle tests are carried out on a blue electric test charge-discharge tester. The test conditions are constant current charge and discharge at 0.5 C (1 C = 1675 mAh / g) for 300 cycles.

[0066] Table 1 Specific components and cycle performance of the batteries in Examples 1-11 and Comparative Examples 1-4

[0067]

[0068]

[0069] Table 2 Specific components and cycle performance of the batteries in Examples 12-14

[0070]

[0071]

[0072] Comparative analysis of Examples 1-4 and Comparative Examples 1-4 shows that: in the metal-sulfur batteries of Comparative Examples 1-4, after 300 cycles, only a relatively low discharge specific capacity was obtained, which can be attributed to the fact that during the test, a large amount of sulfur dissolved into the electrolyte and passed through the separator to reach the surface of the metal negative electrode, resulting in the loss of active substances. However, the specific capacities of the first cycle and the 300th cycle in the metal-sulfur secondary batteries of Examples 1-4 are much higher than those of Comparative Examples 1-4, and the discharge specific capacity of the 300th cycle still maintains a relatively high value, indicating that after using the Sn(CH3)2Cl2 additive, the battery has better cycling performance, and the Sn(CH3)2Cl2 electrolyte additive has good compatibility with different metal-sulfur secondary battery systems.

[0073] Taking Sn(CH3)2Cl2 as an example, the effect of the additive on polysulfide lithium was investigated by adding the additive to a 20 mM Li2S6 solution. As can be seen from Figure 5 it, after adding the additive, the solution changed from the original dark brown to light yellow and yellow precipitates formed at the bottom of the solution. This indicates that the additive has a certain adsorption effect on Li2S6 in the solution. The composition of the precipitate was investigated by X-ray photoelectron spectroscopy (XPS) experiments. Figure 6 And Figure 7 show the Sn 3d spectra and Cl 2p spectra of Sn(CH3)2Cl2 and Sn(CH3)2Cl2-Li2S6. It can be seen that the 5d orbit of the Sn element in Sn(CH3)2Cl2 is split into 5d 5 / 2 and 5d 3 / 2 , and their peaks are located at 487.28 eV and 495.68 eV respectively; the 2p orbit of the Cl element is split into 2p 3 / 2 and 2p 1 / 2 , and their peaks are located at 198.68 eV and 200.28 eV respectively. In the precipitate adsorbed with Li2S6, the peaks of Sn and Cl in Sn(CH3)2Cl2 changed respectively. It can be clearly seen from the figure that after adsorption, the 5d 5 / 2 and 5d 3 / 2 orbits of Sn shifted in the direction of lower binding energy. Among them, the peak of Sn 5d 5 / 2 became 486.88 eV, and the peak of Sn 5d 3 / 2 became 495.18 eV. The peaks of Sn5d 5 / 2 and 5d 3 / 2 decreased by 0.4 eV and 0.5 eV respectively. The peak of the Cl element in the precipitate shifted in the direction of higher binding energy. Among them, the peak of Cl 2p 3 / 2 became 199.08 eV, while the peak of Cl 2p 1 / 2The peak value becomes 200.78 eV, with its peak values increasing by 0.4 eV and 0.5 eV respectively. The peak positions of Sn and Cl elements shift in opposite directions. This may be because according to the Lewis acid-base theory, the lone pair electrons on sulfur tend to transfer to the empty orbitals of Sn with lower energy, while the lone pair electrons on Cl tend to transfer to the empty orbitals of Li, thereby strengthening the interaction between dimethyldichlorotin and Li2S6, reducing the shuttle effect of polysulfides, and improving the electrochemical performance of sulfur.

[0074] Comparative analysis of Example 1, Examples 5-9 and Comparative Example 1 was carried out. The examples and the comparative example were assembled into lithium-sulfur batteries for comparative analysis. Under a discharge rate of 0.5C, the specific capacities of the first week and the 300th cycle of Examples 5-9 were significantly better than those of Comparative Example 1, indicating that the organotin additives of the present invention are all well applicable to lithium-sulfur batteries and can significantly improve the cycling performance of lithium-sulfur batteries. Comparative analysis of Example 1 and Examples 12-14 showed that when lithium-sulfur batteries were assembled with different cathode active materials for testing, it was found that the specific capacities of the 300th cycle of the 4 examples had no obvious difference, indicating that the organotin additives of the present invention are applicable to different cathode active materials.

[0075] Comparative analysis of Example 1, Examples 10-11 and Comparative Example 1 was carried out. Combining the results, it was found that the addition of Sn(CH3)2Cl2 has a positive effect on the cycling performance of lithium-sulfur batteries, and the addition of different contents of Sn(CH3)2Cl2 can improve the reversible capacity of the battery to varying degrees. When the addition amount of Sn(CH3)2Cl2 is 1%, the battery shows the best reversible capacity and cycling stability.

[0076] The capacity improvement amplitude of adding 0.5% is less than that of adding 1 wt%. This may be because at a lower concentration, the number of additive molecules is limited and insufficient to play a role in the overall performance of the battery.

[0077] When the additive concentration of 2% is added, the viscosity of the electrolyte will increase, resulting in poor wetting ability of the electrolyte for the separator and the cathode material, insufficient contact between the electrolyte and the cathode material, and hindered lithium ion migration. After cycling for a certain number of weeks, the contact area between the cathode and the electrolyte becomes larger and the capacity gradually increases; and the dissolution of the additive in the electrolyte requires the participation of ether solvents in the electrolyte for coordination. Therefore, a part of the solvents that form coordination with lithium ions in the electrolyte will combine with the additive. The number of solvents around lithium ions decreases, resulting in a decrease in the migration ability of lithium ions in the electrolyte, an increase in the internal resistance of the electrolyte, an increase in the polarization of the battery, and a decrease in the capacity.

[0078] It is shown that the optimal addition amount of the organotin additive of the present invention is set to 1%.

[0079] Comparing Example 1, Comparative Example 1 and Comparative Example 5, it can be found from the combined results that inorganic tin salts do not have adsorption and catalytic activity for polysulfides. This is because in the electrolyte, inorganic tin salts will undergo solvation and dissociate into tin ions and inorganic salt ions. The tin ions and inorganic salt ions are surrounded by solvents on the outside. Therefore, the microstructure of inorganic tin salts in the solution is that the tin ions and inorganic salt ions are separated from each other. Separate tin ions and inorganic salt ions cannot form a complex structure with polysulfides, so there is no adsorption and catalytic effect.

[0080] Figure 8 and Figure 9 These are the SEM and XRD diagrams of the SEI film formed on the sodium negative electrode side before the cycle of the lithium-sulfur battery obtained in Example 1. Figure 8 It shows that: after adding the additive, a uniform and flat protective layer grew on the surface of the lithium sheet. To explore the composition of the SEI layer, XRD technology was used to analyze the material composition of the surface SEI layer. From Figure 9 it can be seen that three peaks with strong intensity belong to metallic lithium, corresponding to Li (JCPDS no. 00-001-1131). By analyzing the remaining peaks of XRD and combining the information of the Sn, C, and Cl elements contained in the additive composition, the main components of the SEI layer are Li2SnO3, Li 13 Sn5 and LiCl.

[0081] Figure 10 and Figure 11 These are the SEM diagrams of the surface of the sodium negative electrode side of the lithium-sulfur batteries obtained in Comparative Example 1 and Example 1 after 50 cycles respectively. After 50 cycles, it can be seen that when using the unmodified electrolyte, the layered structure of Li metal is damaged and there are blocky protrusions on the surface. This may be because the formation of Li dendrites continuously damages the surface SEI layer, resulting in grooved cracks. The exposed dendrites continuously consume Li metal and the electrolyte, and a highly stable SEI layer cannot be formed. Li ions cannot be deposited uniformly, which exacerbates the growth of lithium dendrites. After adding the additive, the surface of Li metal is relatively flat, indicating that the addition of the additive plays a protective role for the Li negative electrode, hinders the corrosion of Li metal by the electrolyte and polysulfide, and inhibits the formation of Li dendrites.

[0082] Figure 12 This is the Sn 3d spectrum, in which the Sn 3d orbitals are split into Sn 3d 3 / 2 and Sn 3d 5 / 2, 486.3 eV and 494.5 eV correspond to the formation of Li2SnO3. Generally, Li2SnO3 is used as a negative electrode material and has good lithiophilicity, which enables Li ions to not only transport at grain boundaries but also migrate in the material phase in the SEI layer, promoting the insertion and extraction of Li ions at the interface. 483.9 eV and 492.8 correspond to Li 13 Sn5. Li 13 Sn5 has high electronic conductivity, and the density of states value at the Fermi level corresponds to 4.17 states / eV. Therefore, the high conductivity of the alloy phase easily leads to the formation of a stable SEI film and promotes electron transfer, thereby improving the cycling performance.

[0083] Figure 13 is the C1s spectrum, in which there are four peaks with peak values of 289.71, 288.53 eV, 286.22 eV, and 284.8 eV, which are attributed to Li2CO3, C═O, C - O - C, and C - C / C - H bonds respectively. The formation of Li2CO3, C - O, and C═O is attributed to the side reaction between the ether solvent and the lithium foil. The presence of the C - C / C - H peak may be because the ether solvent participates in the reaction between the additive and Li metal as a reactant. Since O atoms participate in the formation of Li2SnO3, the remaining alkyl groups will be lithiated to form alkyl lithium. And the C - C / C - H signal is strong, indicating that the generated alkyl lithium is one of the main components of the SEI layer.

[0084] Figure 14 is the Cl 2p spectrum, in which the 2p orbital splits into Cl 2p 1 / 2 and Cl 2p 3 / 2 , corresponding to the formation of LiCl. The formation of LiCl provides sufficient hardness (6.5 GPa) and a low Li ion diffusion barrier (0.09 eV) for the SEI layer, which can prevent the growth of lithium dendrites and promote the transport of Li ions.

[0085] In this embodiment, an organotin material is used as an electrolyte additive, which can achieve the adsorption and catalysis of polysulfides in a metal - sulfur secondary battery, reducing capacity decay; the additive in - situ generates a metal protection layer with the metal negative electrode, reducing the occurrence of side reactions, and promoting the uniform deposition of metal ions, greatly improving the cycling performance and lifespan of the metal - sulfur secondary battery. This method directly adds an organotin electrolyte additive based on the existing common secondary battery electrolyte, which is simple and fast, and the additive has a low cost and is environmentally friendly.

[0086] The above content is a specific description of the content of the present invention in combination with preferred embodiments, but it cannot be determined that the specific implementation of the present invention is only limited to the described embodiments. For those skilled in the art who understand the present invention, without departing from the research idea of the present invention, several evolutions and substitutions can still be made, and these deductions and substitutions are all included within the scope defined by the claims of the present invention.

Claims

1. An electrolyte containing an organic tin additive for a metal-sulfur secondary battery, characterized in that: The electrolyte containing the organic tin additive comprises a metal salt, an organic solvent and an organic tin additive; the organic tin additive is one or more of dimethyltin dichloride, dipropyltin dichloride, dibutyltin dichloride, tributyltin chloride, butyltin trichloride and phenyltin trichloride; the concentration of the metal salt in the electrolyte is 0.5 to 2.0 mol / L, and the amount of the organic tin additive added is 0.1 to 3 wt% of the total mass of the metal salt and the organic solvent; the water content in the electrolyte is below 100 ppm; the metal salt in the electrolyte is selected from one or more of lithium perchlorate, lithium hexafluorophosphate, lithium bis(trifluoromethanesulfonylimide), sodium perchlorate, sodium hexafluorophosphate, sodium bis(trifluoromethanesulfonylimide), potassium perchlorate, potassium hexafluorophosphate, potassium bis(trifluoromethanesulfonylimide), magnesium perchlorate, magnesium hexafluorophosphate and magnesium bis(trifluoromethanesulfonylimide), and the selected metal salt should correspond to the metal negative electrode of the metal-sulfur secondary battery.

2. The electrolyte containing an organic tin additive according to claim 1, wherein: The electrolyte consists of metal salt, organic solvent and organic tin additive.

3. The electrolyte containing an organic tin additive according to claim 1, wherein: In the electrolyte, the addition amount of the organic tin additive is 1 wt% of the total mass of the metal salt and the organic solvent.

4. The electrolyte according to any one of claims 1 to 3, wherein: The organic solvent in the electrolyte is selected from one or more of 1,3-dioxolane, 1,3-dioxane, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, ethylene carbonate, propylene carbonate, diethyl carbonate, dimethyl carbonate, fluoroethylene carbonate, dimethyl trisulfide, dimethyl disulfide, dimethyl sulfide, dimethyl sulfoxide, ethyl methyl sulfone, cyclopentane, isopropyl methyl sulfone, dimethyl sulfoxide, and tetrahydrofuran.

5. A metal-sulfur secondary battery comprising a positive electrode, a negative electrode, a separator and an electrolyte located between the positive electrode and the negative electrode, characterized in that: The electrolyte is the electrolyte containing an organic tin additive according to any one of claims 1 to 3.

6. The metal-sulfur secondary battery according to claim 5, wherein: The material of the negative electrode is any one of metallic lithium, metallic sodium, metallic potassium, metallic magnesium, lithium alloy, sodium alloy, potassium alloy, and magnesium alloy. The lithium alloy is Li x M 1 , where M 1 =Si, Sn or Al; the sodium alloy is Na y M 2 , where M 2 =Sn, Au or Sb; the potassium alloy is K z M 3 , where M 3 =Si, Sn or Al; the magnesium alloy is Mg t M 4 , where M 4 =Si, Sn or Al; the values of x, y, z and t are respectively greater than 0 and less than 1.

7. The metal-sulfur secondary battery according to claim 5, wherein: The positive electrode is obtained by coating a composite of sulfur-containing active material, binder and conductive agent on a current collector.

8. The metal-sulfur secondary battery according to claim 7, wherein: The sulfur-containing active material is selected from one of elemental sulfur, sulfur-carbon composite, sulfurized polyacrylonitrile, composite of elemental sulfur and sulfurized polyacrylonitrile, and composite of elemental sulfur and metal sulfide; the binder is polyvinylidene fluoride; and the conductive agent is conductive carbon black.

9. The metal-sulfur secondary battery according to claim 5, wherein: The separator is a polyethylene microporous membrane, a glass fiber membrane, an ethylene propylene copolymer microporous membrane or a polypropylene microporous membrane.

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