Lithium-sulfur battery preparation method and lithium-sulfur battery

Abstract

This invention provides a method for preparing a lithium-sulfur battery and a lithium-sulfur battery. The method includes: determining the minimum barrier efficiency required for the separator in the lithium-sulfur battery to resist polysulfides; determining the minimum charge density corresponding to the minimum barrier efficiency based on the minimum barrier efficiency and the correlation between the barrier efficiency and the surface charge density of the modification layer; determining the ion type and concentration of the large-volume negatively charged ions to be added to the modification layer preparation solution based on the minimum charge density, to prepare the modification layer preparation solution; generating a modification layer on the surface of a substrate using the modification layer preparation solution to obtain a separator, and using the separator to prepare the lithium-sulfur battery. In the separator of the lithium-sulfur battery, since the modification layer is generated by the modification layer preparation solution, and the modification layer preparation solution contains large-volume negatively charged ions, the surface of the modification layer is negatively charged, thus forming like-charge repulsion with the polysulfides, thereby reducing the shuttle effect of the polysulfides.

Description

Technical Field

[0001] This invention relates to the field of lithium-sulfur battery technology, specifically to a method for preparing lithium-sulfur batteries and lithium-sulfur batteries themselves. Background Technology

[0002] Lithium-sulfur batteries have attracted significant attention from both industry and science due to their high theoretical specific capacity and energy density. The structure of a lithium-sulfur battery typically includes a positive electrode, a negative electrode, and a separator between them. In practical applications, the "shuttle effect" of polysulfides often occurs in lithium-sulfur batteries, which can affect their performance. Therefore, there is a need for lithium-sulfur batteries that can effectively block the shuttle effect. Summary of the Invention

[0003] The purpose of this invention is to provide a method for preparing a lithium-sulfur battery and a lithium-sulfur battery, in order to solve the problem that the existing lithium-sulfur batteries have poor blocking effect on the shuttle effect of polysulfides.

[0004] The first aspect of this invention provides a method for preparing a lithium-sulfur battery, the method comprising:

[0005] Determine the minimum barrier efficiency required for polysulfides in the separator of the lithium-sulfur battery to be prepared;

[0006] Based on the minimum blocking efficiency and the correlation between the blocking efficiency and the surface charge density of the modified layer, the minimum charge density corresponding to the minimum blocking efficiency is determined.

[0007] Based on the minimum charge density, determine the ion type and concentration of the large-volume negatively charged ions to be added to the modification layer preparation solution in order to prepare the modified layer preparation solution.

[0008] The modified layer is generated on the surface of the substrate by the modified layer preparation solution to obtain the separator, and the lithium-sulfur battery to be prepared is prepared using the separator.

[0009] Preferably, the method further includes determining the correlation between blocking efficiency and surface charge density of the modified layer in the following manner:

[0010] A diaphragm control group and multiple diaphragm samples were obtained. The diaphragm control group included a substrate, and the diaphragm samples included a substrate and a modification layer disposed on the surface of the substrate. The modification layer of each diaphragm sample had a different surface charge density.

[0011] The obtained membrane control group was assembled into a control group lithium-sulfur battery, and each membrane sample was assembled into a test lithium-sulfur battery.

[0012] The blocking efficiency of the control group lithium-sulfur battery and each lithium-sulfur battery under test was tested for polysulfides.

[0013] Based on the blocking efficiency of the control group lithium-sulfur batteries against polysulfides, the blocking efficiency of each lithium-sulfur battery under test against polysulfides, and the surface charge density of the modified layer of the separator sample in each lithium-sulfur battery under test, the correlation between the blocking efficiency and the surface charge density of the modified layer was determined.

[0014] Preferably, the method further includes:

[0015] The surface potential of the modified layer of each membrane sample was measured in advance using a Zeta potentiometer, and the surface charge density of the modified layer of each membrane sample was calculated based on the measured surface potential.

[0016] Preferably, the blocking efficiency of the control group lithium-sulfur battery and each lithium-sulfur battery to be tested against polysulfides is tested. Specifically, the control group lithium-sulfur battery and each lithium-sulfur battery to be tested are used as the current lithium-sulfur battery, and the blocking efficiency of the current lithium-sulfur battery against polysulfides is determined by the following method:

[0017] Under the target test conditions, the target operating time of the current lithium-sulfur battery will be determined.

[0018] For the current lithium-sulfur battery after the target operating time, determine the concentration of polysulfides in the electrolyte on both sides of the separator in the current lithium-sulfur battery;

[0019] The polysulfide blocking efficiency of the current lithium-sulfur battery is determined based on the concentration of polysulfides in the electrolyte on both sides of the separator in the current lithium-sulfur battery.

[0020] Preferably, the correlation between the blocking efficiency and the surface charge density of the modified layer is determined based on the blocking efficiency of the control group lithium-sulfur battery against polysulfides, the blocking efficiency of each lithium-sulfur battery under test against polysulfides, and the surface charge density of the modified layer of the separator sample in each lithium-sulfur battery under test. Specifically, this includes:

[0021] The blocking efficiency of each lithium-sulfur battery to be tested against polysulfides was subtracted from the blocking efficiency of the control group lithium-sulfur battery against polysulfides to obtain the increased blocking efficiency of each lithium-sulfur battery against polysulfides due to the modification layer.

[0022] Using the increased polysulfide blocking efficiency due to the modification layer in each lithium-sulfur battery under test as the dependent variable and the surface charge density of the modification layer in the corresponding separator sample of the lithium-sulfur battery under test as the independent variable, curve fitting was performed to generate the correlation between blocking efficiency and surface charge density of the modification layer.

[0023] Preferably, the method further includes:

[0024] The modified layer preparation solution was prepared by dispersing cellulose nanocrystals in a dispersion solution by ultrasonic vibration.

[0025] Preferably, the membrane is obtained by forming a modified layer on the surface of the substrate using the modified layer preparation solution, specifically including:

[0026] The modified layer preparation solution is injected into a quartz cell with microchannels and self-assembled into a film on the substrate surface under the action of gravity. The substrate including the film is then transferred to a freeze dryer or evaporator for curing and cleaning to obtain the diaphragm.

[0027] Preferably, determining the minimum barrier efficiency required for polysulfides in the separator of the lithium-sulfur battery to be prepared specifically includes:

[0028] Determine the type and rated voltage of the electrolyte to be used in the lithium-sulfur battery to be prepared;

[0029] The minimum blocking efficiency is determined based on the electrolyte type, the rated voltage, and a preset rule, wherein the preset rule is used to determine the minimum blocking efficiency corresponding to various types of electrolytes and rated voltages.

[0030] Preferably, the type and concentration of negatively charged ions to be added to the modification layer preparation solution are determined based on the minimum charge density, specifically including:

[0031] When the minimum charge density is less than a first threshold, the ion type of the bulky negatively charged ion is selected as a bulky negatively charged ion with a valence of -1, and the corresponding ion concentration is determined based on the difference between the first threshold and the minimum charge density; or,

[0032] When the minimum charge density is greater than the second threshold, the ion type of the bulky negatively charged ion is selected as a bulky negatively charged ion with a -2 valence, and the corresponding ion concentration is determined based on the difference between the minimum charge density and the second threshold, wherein the second threshold is greater than the first threshold; or,

[0033] When the minimum charge density is between the first threshold and the second threshold, the ion type of the bulk negatively charged ions is selected such that the molar number of bulk negatively charged ions with -1 valence and bulk negatively charged ions with -2 valence each account for half, and the corresponding ion concentration is determined according to the difference between the minimum charge density and the first threshold and the second threshold.

[0034] A second aspect of the present invention provides a lithium-sulfur battery, which is prepared by the method provided in the present invention.

[0035] The lithium-sulfur battery preparation method provided in this invention includes: first, determining the minimum barrier efficiency required by the separator for polysulfides in the lithium-sulfur battery to be prepared; then, determining the minimum charge density corresponding to the minimum barrier efficiency based on the minimum barrier efficiency and the correlation between the barrier efficiency and the surface charge density of the modification layer; then, determining the ion type and concentration of the large-volume negatively charged ions to be added to the modification layer preparation solution based on the minimum charge density, thereby preparing the modification layer preparation solution; then, generating a modification layer on the surface of the substrate using the modification layer preparation solution to obtain the separator; and finally, preparing the lithium-sulfur battery using the separator. In the separator of the lithium-sulfur battery to be prepared, since the modification layer is generated on the surface of the substrate using the modification layer preparation solution, and the modification layer preparation solution contains large-volume negatively charged ions, the surface of the modification layer is negatively charged, thereby forming like-charge repulsion with the polysulfides. Through this like-charge repulsion, the shuttle effect of the polysulfides can be reduced. Attached Figure Description

[0036] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments of the present invention will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0037] Figure 1 A schematic diagram of the specific structure of a lithium-sulfur battery provided in an embodiment of the present invention;

[0038] Figure 2 A schematic diagram of the specific structure of a lithium-sulfur battery provided for another embodiment of the present invention;

[0039] Figure 3 A schematic diagram of the specific process for preparing a lithium-sulfur battery, provided for another embodiment of the present invention;

[0040] Figure 4 This is a schematic diagram illustrating the specific process for determining the correlation between blocking efficiency and surface charge density of the modification layer, provided as an embodiment of the present invention. Detailed Implementation

[0041] The technical solutions of the embodiments of the present invention will now be described with reference to the accompanying drawings. In the description of the present invention, the terms "first," "second," etc., are used only for distinguishing descriptions and should not be construed as indicating or implying relative importance or order.

[0042] As mentioned earlier, in order to enhance the membrane's ability to block polysulfides generated by the "shuttle effect," a modification layer is often applied to the membrane's surface. However, the application of this modification layer increases the difficulty of manufacturing lithium-sulfur batteries. For example, during the formation of the modification layer, it is often difficult to select suitable negatively charged ions and determine their concentration, leading to increased manufacturing complexity.

[0043] In view of this, embodiments of the present invention provide a method for preparing a lithium-sulfur battery and a lithium-sulfur battery thereof. Here, a brief description of the structure of the lithium-sulfur battery prepared by this method can be given first, such as... Figure 1 The diagram shown is a schematic representation of the specific structure of a lithium-sulfur battery 1 provided in an embodiment of the present invention. In addition to a positive electrode 11 and a negative electrode 12, the lithium-sulfur battery 1 also includes a separator 13 disposed between the positive electrode 11 and the negative electrode 12. In practical applications, the active material of the positive electrode 11 of the lithium-sulfur battery 1 is sulfur, and the active material of the negative electrode 12 can be metallic lithium.

[0044] In the structure of the lithium-sulfur battery 1, electrolyte is included between the separator 13 and the positive electrode 11, and between the separator 13 and the negative electrode 12. In addition, the lithium-sulfur battery 1 may also include other components such as battery pack, but this is not limited here.

[0045] It is important to note that this can be combined with, for example Figure 1 As shown, the separator 13 may further include a substrate 131 and a modifying layer 132, wherein the modifying layer 132 is disposed on the surface of the substrate 131, for example, the modifying layer 132 may be disposed in the substrate 131, close to the surface of the positive electrode 11. Of course, it can also be as follows... Figure 2 As shown, the modification layer 132 is disposed in the substrate 131, close to the surface of the negative electrode 12.

[0046] The separator 13 and the substrate 131 can be further explained here. The main function of the substrate 131 is to provide rigid support, and considering the application scenario of lithium-sulfur batteries, the substrate 131 also needs to have a certain degree of ion permeability. Considering these requirements for the substrate 131, in practical applications, the substrate 131 can be prepared using a polyethylene porous membrane or a polypropylene porous membrane. Furthermore, the thickness of the substrate 131 can be, for example, 5~25μm (i.e., micrometers), such as 5μm, 10μm, 15μm, 20μm, 25μm, or other thicknesses between 5μm and 25μm.

[0047] It should be further explained that the focus of the present invention is the structure of the diaphragm 13, that is, a modification layer 132 is provided on the surface of the substrate 131, thereby mainly suppressing the "shuttle effect" through the modification layer 132, that is, suppressing polysulfides from shuttling between the positive electrode 11 and the negative electrode 12 through the diaphragm 13.

[0048] Based on the functional requirements of the modification layer 132, the inventors of this invention analyzed polysulfides and found that polysulfides mainly carry negative charges. Therefore, this invention utilizes the principle of repulsion between like charges to set a negative charge on the surface of the modification layer 132. In other words, the surface of the modification layer 132 in this invention carries a negative charge. In this way, when polysulfides approach the modification layer 132, they can be repelled by the negative charge on the surface of the modification layer 132, thereby reducing the possibility of polysulfides penetrating the diaphragm 13 and at least partially suppressing the "shuttle effect" of polysulfides.

[0049] The modification layer 132 can be made of cellulose nanocrystals (CNCs), which are nanoscale cellulose extracted from natural fibers. These nanocrystals not only possess the characteristics of nanoparticles but also exhibit unique strength and optical properties, showing broad application prospects. Cellulose nanocrystals can be obtained by acid hydrolysis and ultra-high pressure treatment of natural cellulose raw materials, and their morphology is nanoscale rod-shaped or fibrous crystals.

[0050] In practical applications, the cellulose nanocrystals can be dispersed in a dispersion solution by ultrasonic vibration to prepare the modified layer preparation solution. This dispersion solution can be water or an organic solvent. However, since the prepared modified layer 132 needs to be negatively charged, the modified layer preparation solution needs to be modified. Specifically, specific negatively charged ions (at a specific concentration) can be added to the modified layer preparation solution to improve the ability of the prepared modified layer 132 to suppress the "shuttle effect." This invention requires determining the ion type and concentration of these negatively charged ions to formulate the modified layer preparation solution.

[0051] The organic solvent can be one or more of the following: ethanol, acetone, diethyl ether, benzene, toluene, chloroform, amine compounds (such as N,N-dimethylformamide, dimethylacetamide, etc.), dimethyl sulfoxide, dimethylpyrrolidone, polylactic acid, polyethylene, polypropylene, polystyrene, ionic liquids, etc.; and the solid content (i.e., the content of cellulose nanocrystals) in the dispersion can be 0.1% to 30%, for example, 0.1%, 1%, 5%, 10%, 15%, 20%, 25%, or 30%. Furthermore, during the aforementioned ultrasonic process, the temperature can be 20–80°C, and the duration can be 20–120 minutes.

[0052] like Figure 3 The diagram shown is a schematic flowchart of the lithium-sulfur battery preparation method provided in an embodiment of the present invention. The method includes the following steps:

[0053] Step S21: Determine the minimum barrier efficiency required for polysulfides in the separator of the lithium-sulfur battery to be prepared.

[0054] The lithium-sulfur battery to be prepared is the lithium-sulfur battery that needs to be prepared by the method provided in the embodiments of the present invention. The specific structure of the lithium-sulfur battery to be prepared can be referred to... Figure 1 and Figure 2 As shown, its structure will not be explained here.

[0055] As mentioned above, in this embodiment of the invention, negative charges are loaded onto the surface of the modified layer of the separator, thereby suppressing the "shuttle effect" through the principle of like charges repelling each other. Therefore, a minimum blocking efficiency for polysulfides can be set, ensuring that the blocking efficiency of the separator in the lithium-sulfur battery to be prepared is greater than this minimum blocking efficiency. This ensures that the prepared lithium-sulfur battery meets practical requirements. The blocking efficiency quantifies the polysulfide blocking effect; specifically, a higher blocking efficiency indicates a better polysulfide blocking effect, and vice versa. How to determine the polysulfide blocking efficiency will be explained later.

[0056] At this point, in step S21, it is necessary to determine the minimum barrier efficiency required by the separator for polysulfides in the lithium-sulfur battery to be prepared. In practical applications, considering that the electrolyte type and rated voltage of the lithium-sulfur battery have a major impact on the generation and shuttle of polysulfides, step S21 of this invention requires determining the electrolyte type and rated voltage of the lithium-sulfur battery to be prepared before determining the minimum barrier efficiency. Specifically, to determine the electrolyte type and rated voltage of the lithium-sulfur battery to be prepared, the electrolyte type can be determined first. Specifically, the electrolyte type can usually be classified according to the solvent. For example, the electrolyte type can include aqueous electrolyte, organic electrolyte, ionic liquid, etc. In this invention, for the lithium-sulfur battery to be prepared, the selected electrolyte type can be determined based on factors such as the temperature of the application scenario and the required conductivity.

[0057] In addition, the rated voltage of the lithium-sulfur battery to be prepared can be determined based on the application scenario of the lithium-sulfur battery to be prepared, such as the required rated power output and the voltage required by the electrical equipment.

[0058] After obtaining the type of electrolyte and rated voltage of the lithium-sulfur battery to be prepared, the minimum blocking efficiency of the separator against polysulfides can be determined based on the electrolyte type, the rated voltage, and preset rules. The preset rules can be used to determine the minimum blocking efficiency corresponding to various types of electrolytes and rated voltages.

[0059] In practical applications, the preset rule can be a mapping table that records various types of electrolytes and rated voltages, as well as their corresponding minimum blocking efficiencies. After obtaining the type of electrolyte and rated voltage to be used in the lithium-sulfur battery to be prepared, the mapping table can be consulted to obtain the corresponding minimum blocking efficiency.

[0060] In practical applications, the mapping table can be pre-generated in the following way: for example, multiple lithium-sulfur batteries are obtained, all of which contain electrolytes of the target type and have rated voltages of the target rated voltage. The target type of electrolyte can be any type of electrolyte, and the target rated voltage can be any voltage value. The difference between these lithium-sulfur batteries is that the barrier efficiency of their separators against polysulfides is different.

[0061] Then, under the same test conditions, these lithium-sulfur batteries were subjected to volt-ampere cycle tests. After reaching the target number of charge-discharge cycles (e.g., 1000 cycles), the performance degradation value of these lithium-sulfur batteries was measured (this performance degradation value can be characterized by voltage degradation value; for example, a 10% voltage degradation can be taken as the performance degradation value). Based on the performance degradation values ​​of these lithium-sulfur batteries, the minimum barrier efficiency corresponding to the target type of electrolyte and the target rated voltage was obtained. At this point, the higher the barrier efficiency, the less pronounced the polysulfide shuttle effect, and the smaller the corresponding performance degradation value of the lithium-sulfur battery. Conversely, the lower the barrier efficiency, the more pronounced the polysulfide shuttle effect, and the larger the corresponding performance degradation value of the lithium-sulfur battery. Therefore, this minimum barrier efficiency essentially reflects the highest tolerance for performance degradation value under the conditions of the target type of electrolyte and the target rated voltage; that is, the maximum tolerable performance degradation value under N charge-discharge cycles.

[0062] For example, when a company is producing and designing lithium-sulfur batteries, after selecting the target type of electrolyte and the target rated voltage, it can set the maximum tolerance for the performance degradation of the lithium-sulfur battery (e.g., a maximum performance degradation of 30% under 1000 charge-discharge cycles) based on the application scenario of its products. Then, through the series of tests mentioned above, the corresponding minimum blocking efficiency can be obtained.

[0063] Step S22: Determine the minimum charge density corresponding to the minimum blocking efficiency based on the minimum blocking efficiency and the correlation between the blocking efficiency and the surface charge density of the modified layer.

[0064] Since the principle of this invention is to improve the blocking efficiency of polysulfides by utilizing the repulsion between the negative charge on the surface of the modification layer and the polysulfides, there is a correlation between the charge density on the surface of the modification layer and the blocking efficiency of polysulfides. Therefore, in this invention, the correlation between the blocking efficiency and the charge density on the surface of the modification layer can be determined in advance, and then in step S22, the minimum charge density corresponding to the minimum blocking efficiency can be determined based on the minimum blocking efficiency and the correlation.

[0065] In practical applications, such as Figure 4 As shown, the relationship between blocking efficiency and surface charge density of the modification layer can typically be determined in advance using the following methods. Specifically, this method may include the following steps:

[0066] Step S221: Obtain a diaphragm control group and multiple diaphragm samples, wherein the diaphragm control group includes a substrate, and the diaphragm samples include a substrate and a modification layer disposed on the surface of the substrate.

[0067] In other words, the control group of diaphragms only has a matrix but no modification layer, while the diaphragm samples have both a matrix and a modification layer, and the modification layers of each diaphragm sample have different surface charge densities.

[0068] The method provided in this invention can obtain the surface charge density of the modified layer in the following way: for example, the surface potential of the modified layer of each membrane sample can be measured in advance using a Zeta potentiometer, and then the surface charge density of the modified layer of the corresponding membrane sample can be calculated based on the measured surface potential. For example, the surface charge density of the modified layer can be calculated according to E=σ / ε0. In this calculation formula, E is the surface potential of the modified layer, σ is the surface charge density of the modified layer, and ε0 is the vacuum dielectric constant. The specific value of ε0 can be obtained by querying, and will not be explained here.

[0069] Step S222: Assemble the obtained membrane control group into a control group lithium-sulfur battery, and assemble each membrane sample into a test lithium-sulfur battery.

[0070] To improve accuracy, the control group lithium-sulfur batteries and each tested lithium-sulfur battery were identical except for the separator inside the battery; other parts, including the positive electrode, negative electrode, and electrolyte, were the same.

[0071] Step S223: Test the blocking efficiency of the control group lithium-sulfur battery and each lithium-sulfur battery under test for polysulfides.

[0072] It is important to note that the blocking efficiency in this invention is a quantification of the blocking effect on polysulfides. Specifically, the blocking efficiency against polysulfides can be measured as follows: The control group lithium-sulfur battery and each lithium-sulfur battery under test can be used as the current lithium-sulfur battery. The blocking efficiency against polysulfides of the current lithium-sulfur battery can be determined as follows: Under target test conditions (such as target temperature and target pressure), the current lithium-sulfur battery can be operated for a target duration (such as 100 hours, 500 hours, etc.). Then, for the current lithium-sulfur battery after operating for the target duration, the blocking efficiency against polysulfides can be determined. The concentration of polysulfides in the electrolyte on both sides of the membrane in the battery can be measured by collecting electrolyte samples from both sides of the current lithium-sulfur battery membrane and then measuring the concentration of polysulfides in the electrolyte on both sides of the current lithium-sulfur battery membrane using methods such as spectrophotometry or others. After obtaining the concentration of polysulfides in the electrolyte on both sides of the membrane, the blocking efficiency of the current lithium-sulfur battery against polysulfides can be determined based on the concentration of polysulfides in the electrolyte on both sides of the current lithium-sulfur battery membrane. For example, the blocking efficiency of the current lithium-sulfur battery against polysulfides can be characterized by the concentration difference or concentration ratio of polysulfides on both sides.

[0073] Step S224: Based on the blocking efficiency of the control group lithium-sulfur battery against polysulfides, the blocking efficiency of each lithium-sulfur battery under test against polysulfides, and the surface charge density of the modified layer of the separator sample in each lithium-sulfur battery under test, determine the correlation between the blocking efficiency and the surface charge density of the modified layer.

[0074] After obtaining the polysulfide blocking efficiencies of the control group lithium-sulfur battery and each lithium-sulfur battery under test, the correlation between the blocking efficiency and the surface charge density of the modification layer can be determined based on the polysulfide blocking efficiencies of the control group lithium-sulfur battery, the polysulfide blocking efficiencies of each lithium-sulfur battery under test, and the surface charge density of the modification layer in the separator samples of each lithium-sulfur battery under test. Specifically, one method could be to first subtract the polysulfide blocking efficiency of the control group lithium-sulfur battery from the polysulfide blocking efficiency of each lithium-sulfur battery under test, obtaining the increased polysulfide blocking efficiency in each lithium-sulfur battery under test due to the modification layer (referred to as the additional blocking efficiency). For example, the polysulfide blocking efficiency of the control group lithium-sulfur battery can be denoted as η0; the polysulfide blocking efficiencies of each lithium-sulfur battery under test can be denoted as η1, η2, ..., η. n Where n is the number of lithium-sulfur batteries to be tested, and correspondingly, the surface charge density of the modified layer of the separator sample in each lithium-sulfur battery to be tested is denoted as ρ1, ρ2...ρ n At this point, the increased blocking efficiency against polysulfides due to the modification layer in each tested lithium-sulfur battery is calculated, denoted as η1-η0, η2-η0...η n-η0. Furthermore, the surface charge density of the modification layer of the separator sample in each lithium-sulfur battery under test can be combined to obtain the corresponding relationship table shown in Table 1.

[0075] Obviously, the correspondence table shown in Table 1 includes multiple sets of correspondence data between the newly added blocking efficiency and charge density. Then, the increased blocking efficiency against polysulfides due to the modification layer in each lithium-sulfur battery under test can be used as the dependent variable, and the surface charge density of the modification layer of the corresponding separator sample in the lithium-sulfur battery under test can be used as the independent variable. That is, curve fitting can be performed with the newly added blocking efficiency in Table 1 as the dependent variable and the charge density as the independent variable, thereby generating the correlation between the blocking efficiency and the surface charge density of the modification layer.

[0076] Table 1

[0077]

[0078] After generating the correlation between the blocking efficiency and the surface charge density of the modified layer in this way, in step S22, the minimum blocking efficiency can be incorporated into the correlation to calculate the charge density corresponding to the minimum blocking efficiency, which is the minimum charge density.

[0079] Step S23: Based on the minimum charge density, determine the ion type and concentration of the large-volume negatively charged ions to be added to the modified layer preparation solution, so as to prepare the modified layer preparation solution.

[0080] In this invention, the selected negatively charged ions are specifically large-volume negatively charged ions, including nitrate ions, sulfate ions, carbonate ions, bicarbonate ions, etc. These negative ions are composed of multiple atoms, and therefore are usually large in volume. In addition, the valence states of these large-volume negatively charged ions are usually not the same; for example, some large-volume negatively charged ions have a valence state of -1, while others have a valence state of -2.

[0081] In step S23 of this invention, the ion type (i.e., ion of a certain valence state) and ion concentration of the bulk negatively charged ions to be added in the modification layer preparation solution can be determined based on the minimum charge density. For example, when the minimum charge density is less than the first threshold, it means that only a relatively small charge density is needed. At this time, the ion type of the bulk negatively charged ion can be a bulk negatively charged ion with a valence of -1, such as an acid radical ion or a bicarbonate ion. Its ion concentration can be determined based on the difference between the first threshold and the minimum charge density. For example, the larger the difference, the greater the gap between the minimum charge density and the first threshold (meaning the minimum charge density is smaller), and therefore the smaller the ion concentration. Conversely, the smaller the difference, the smaller the gap between the minimum charge density and the first threshold, and therefore the larger the ion concentration.

[0082] When the minimum charge density is greater than the second threshold, it indicates that a relatively large charge density is required. In this case, the ion type of the large-volume negatively charged ion can be a -2 valence large-volume negatively charged ion, such as sulfate or carbonate ions. Its ion concentration can be determined based on the difference between the minimum charge density and the second threshold. For example, the larger the difference, the greater the gap between the minimum charge density and the first threshold (meaning the minimum charge density is also larger), and therefore the higher the ion concentration. Conversely, the smaller the difference, the smaller the gap between the minimum charge density and the first threshold, and therefore the lower the ion concentration. The second threshold is greater than the first threshold.

[0083] Of course, when the minimum charge density is between the first threshold and the second threshold, the ion type of the bulk negatively charged ion can be half -1 valence bulk negatively charged ions and half -2 valence bulk negatively charged ions (in moles). Similarly, the ion concentration can also be determined based on the difference between the minimum charge density and the first and second thresholds. For example, if the minimum charge density is closer to the second threshold, the ion concentration is also greater, and conversely, if the minimum charge density is closer to the first threshold, the ion concentration is also smaller.

[0084] In addition, to improve the effect, the added cation can be a small-volume metal ion, such as sodium or potassium ions. In practical applications, for example, when the required large-volume negatively charged ion is a -2 valence large-volume negatively charged ion, sodium sulfate, sodium carbonate, potassium sulfate, or potassium carbonate can be added to the modification layer preparation solution. When the required large-volume negatively charged ion is a -1 valence large-volume negatively charged ion, potassium nitrate, sodium nitrate, sodium bicarbonate, or potassium bicarbonate can be added to the modification layer preparation solution.

[0085] Step S24: A modified layer is generated on the surface of the substrate using the modified layer preparation solution to obtain a separator, and the lithium-sulfur battery to be prepared is prepared using the separator.

[0086] After obtaining the modified layer preparation solution through the above step S23, in this step S24, the modified layer preparation solution is mainly used to generate a modified layer on the surface of the substrate. Obviously, since the modified layer preparation solution includes large-volume negatively charged ions, while the cations are small-volume metal ions such as sodium ions or potassium ions, the surface of the generated modified layer is mainly composed of these large-volume negatively charged ions, thereby making the surface of the modified layer negatively charged and able to form like-charge repulsion with polysulfides.

[0087] In practical applications, step S24 can be implemented by first injecting the modified layer preparation solution into a quartz cell with microchannels, and then self-assembling it into a film on the substrate surface under the influence of gravity. The substrate, including the film, is then transferred to a freeze dryer or evaporator for curing and cleaning to obtain the separator. After obtaining the separator, it can be combined with a positive electrode, a negative electrode, and an electrolyte to assemble the lithium-sulfur battery to be prepared.

[0088] The lithium-sulfur battery preparation method provided in this invention includes: first, determining the minimum barrier efficiency required by the separator for polysulfides in the lithium-sulfur battery to be prepared; then, determining the minimum charge density corresponding to the minimum barrier efficiency based on the minimum barrier efficiency and the correlation between the barrier efficiency and the surface charge density of the modification layer; then, determining the ion type and concentration of the large-volume negatively charged ions to be added to the modification layer preparation solution based on the minimum charge density, thereby preparing the modification layer preparation solution; then, generating a modification layer on the surface of the substrate using the modification layer preparation solution to obtain the separator; and finally, preparing the lithium-sulfur battery using the separator. In the separator of the lithium-sulfur battery to be prepared, since the modification layer is generated on the surface of the substrate using the modification layer preparation solution, and the modification layer preparation solution contains large-volume negatively charged ions, the surface of the modification layer is negatively charged, thereby forming like-charge repulsion with the polysulfides. Through this like-charge repulsion, the shuttle effect of the polysulfides can be reduced.

[0089] In this embodiment of the invention, a lithium-sulfur battery can also be provided. This lithium-sulfur battery is prepared using the lithium-sulfur battery preparation method provided in this embodiment of the invention. Therefore, this lithium-sulfur battery can also solve the problems in the prior art, which will not be described further here.

[0090] In this embodiment of the invention, an electrical device may be further provided, which is equipped with the lithium-sulfur battery provided in this embodiment of the invention. For example, the electrical device may be a vehicle, a computer, a mobile phone, etc.

[0091] Although embodiments of the invention have been described in conjunction with the accompanying drawings, those skilled in the art can make various modifications and variations without departing from the spirit and scope of the invention, and such modifications and variations all fall within the scope defined by the appended claims.

Claims

1. A method of preparing a lithium-sulfur battery, characterized by, The method includes: Determine the minimum barrier efficiency required for polysulfides in the separator of the lithium-sulfur battery to be prepared; Based on the minimum blocking efficiency and the correlation between the blocking efficiency and the surface charge density of the modified layer, the minimum charge density corresponding to the minimum blocking efficiency is determined. Based on the minimum charge density, determine the ion type and concentration of the large-volume negatively charged ions to be added to the modification layer preparation solution in order to prepare the modified layer preparation solution. The modified layer is generated on the surface of the substrate by the modified layer preparation solution to obtain the separator, and the lithium-sulfur battery to be prepared is prepared using the separator; The method further includes determining the correlation between blocking efficiency and surface charge density of the modified layer in the following manner: A diaphragm control group and multiple diaphragm samples were obtained. The diaphragm control group included a substrate, and the diaphragm samples included a substrate and a modification layer disposed on the surface of the substrate. The modification layer of each diaphragm sample had a different surface charge density. The obtained membrane control group was assembled into a control group lithium-sulfur battery, and each membrane sample was assembled into a test lithium-sulfur battery. The blocking efficiency of the control group lithium-sulfur battery and each lithium-sulfur battery under test was tested for polysulfides. Based on the blocking efficiency of the control group lithium-sulfur battery against polysulfides, the blocking efficiency of each lithium-sulfur battery under test against polysulfides, and the surface charge density of the modified layer of the separator sample in each lithium-sulfur battery under test, the correlation between the blocking efficiency and the surface charge density of the modified layer is determined. Determine the minimum barrier efficiency required for polysulfides in the separator of the lithium-sulfur battery to be prepared, specifically including: Determine the type and rated voltage of the electrolyte to be used in the lithium-sulfur battery to be prepared; The minimum blocking efficiency is determined based on the electrolyte type, the rated voltage, and a preset rule, wherein the preset rule is used to determine the minimum blocking efficiency corresponding to various types of electrolytes and rated voltages.

2. The method for preparing a lithium-sulfur battery according to claim 1, characterized in that, The method further includes: The surface potential of the modified layer of each membrane sample was measured in advance using a Zeta potentiometer, and the surface charge density of the modified layer of each membrane sample was calculated based on the measured surface potential.

3. The method for preparing a lithium-sulfur battery according to claim 1, characterized in that, The blocking efficiency of the control group lithium-sulfur battery and each lithium-sulfur battery under test against polysulfides was tested. Specifically, the control group lithium-sulfur battery and each lithium-sulfur battery under test were used as the current lithium-sulfur battery, and the blocking efficiency of the current lithium-sulfur battery against polysulfides was determined by the following method: Under the target test conditions, the target operating time of the current lithium-sulfur battery will be determined. For the current lithium-sulfur battery after the target operating time, determine the concentration of polysulfides in the electrolyte on both sides of the separator in the current lithium-sulfur battery; The polysulfide blocking efficiency of the current lithium-sulfur battery is determined based on the concentration of polysulfides in the electrolyte on both sides of the separator in the current lithium-sulfur battery.

4. The method for preparing a lithium-sulfur battery according to claim 1, characterized in that, Based on the polysulfide blocking efficiency of the control group lithium-sulfur batteries, the polysulfide blocking efficiency of each tested lithium-sulfur battery, and the surface charge density of the modified layer of the separator sample in each tested lithium-sulfur battery, the correlation between the blocking efficiency and the surface charge density of the modified layer is determined, specifically including: The blocking efficiency of each lithium-sulfur battery to be tested against polysulfides was subtracted from the blocking efficiency of the control group lithium-sulfur battery against polysulfides to obtain the increased blocking efficiency of each lithium-sulfur battery against polysulfides due to the modification layer. Using the increased polysulfide blocking efficiency due to the modification layer in each lithium-sulfur battery under test as the dependent variable and the surface charge density of the modification layer in the corresponding separator sample of the lithium-sulfur battery under test as the independent variable, curve fitting was performed to generate the correlation between blocking efficiency and surface charge density of the modification layer.

5. The method for preparing a lithium-sulfur battery according to claim 1, characterized in that, The method further includes: The modified layer preparation solution was prepared by dispersing cellulose nanocrystals in a dispersion solution by ultrasonic vibration.

6. The method for preparing a lithium-sulfur battery according to claim 1, characterized in that, The membrane is obtained by generating a modified layer on the surface of the substrate using the modified layer preparation solution, specifically including: The modified layer preparation solution is injected into a quartz cell with microchannels and self-assembled into a film on the substrate surface under the action of gravity. The substrate including the film is then transferred to a freeze dryer or evaporator for curing and cleaning to obtain the diaphragm.

7. The method for preparing a lithium-sulfur battery according to claim 1, characterized in that, Based on the minimum charge density, the type and concentration of the large-volume negatively charged ions to be added to the modification layer preparation solution are determined, specifically including: When the minimum charge density is less than a first threshold, the ion type of the bulky negatively charged ion is selected as a bulky negatively charged ion with a valence of -1, and the corresponding ion concentration is determined based on the difference between the first threshold and the minimum charge density; or, When the minimum charge density is greater than the second threshold, the ion type of the bulky negatively charged ion is selected as a bulky negatively charged ion with a -2 valence, and the corresponding ion concentration is determined based on the difference between the minimum charge density and the second threshold, wherein the second threshold is greater than the first threshold; or, When the minimum charge density is between the first threshold and the second threshold, the ion type of the bulk negatively charged ions is selected such that the molar number of bulk negatively charged ions with -1 valence and bulk negatively charged ions with -2 valence each account for half, and the corresponding ion concentration is determined according to the difference between the minimum charge density and the first threshold and the second threshold.

8. A lithium-sulfur battery, characterized in that, The lithium-sulfur battery is prepared by the method described in any one of claims 1 to 7.

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