Modeling method
Patent Information
- Application Number
- JP2024051778
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2024-03-27
- Publication Date
- 2025-10-09
Smart Images
Figure 2025150731000001_ABST
Abstract
Description
[Technical Field]
[0001] The present invention relates to a modeling method. [Background technology]
[0002] Polycarbon sulfide, in which sulfur is bonded to a carbon skeleton, has been proposed as an electrode active material for next-generation lithium-ion batteries. Polycarbon sulfide is generally obtained by calcining a mixture of carbon material and sulfur. To evaluate, analyze, and predict the battery properties of calcined polycarbon sulfide, it is necessary to understand its chemical structure.
[0003] However, while analytical results based on existing analytical methods can provide a partial chemical structure, they do not necessarily allow the chemical structure of polycarbon sulfides to be determined. Therefore, it is necessary to estimate the chemical structure by utilizing simulations. For example, in Non-Patent Document 1, a simulation was performed using the ReaxFF force field based on reactive force field molecular dynamics to estimate the chemical structure of SPAN (sulfurized polyacrylonitrile), a type of polycarbon sulfide. [Prior art documents] [Non-patent literature]
[0004] [Non-Patent Document 1] SP Beltran and PB Balbuena, “Sulfurized Polyacrylonitrile (SPAN): Changes in Mechanical Properties during Electrochemical Lithiation”, J. Phys. Chem. C, 125, 13185-13194, 2021. Summary of the Invention [Problem to be solved by the invention]
[0005] However, Non-Patent Document 1 uses the chemical structure of SPAN after calcination, which has already been experimentally estimated, as the initial structure, and therefore suffers from a lack of versatility. In other words, it cannot be applied to materials whose chemical structure after calcination is not fully understood. Meanwhile, in principle, it is possible to model the chemical structure of polycarbonate sulfide by performing a first-principles molecular dynamics calculation at high temperature for a long period of time on a system containing all of the calcined raw materials. However, this approach is not realistic in terms of the calculation scale and calculation time. A method for modeling the chemical structure of polycarbonate sulfide has not yet been established, and there is a need for a more versatile modeling method that is more accurate and enables simulations within a realistic time frame.
[0006] An object of the present invention is to provide a modeling method for simulating, within a realistic time frame, a stable structural model of an electrode active material containing carbon atoms and sulfur atoms obtained through calcination. [Means for solving the problem]
[0007] The present invention relates to the following modeling method. A modeling method for creating a stable structural model of an electrode active material containing carbon atoms and sulfur atoms obtained through calcination by simulating a chemical reaction that progresses during calcination for a low molecular model unit, comprising: (1) determining the atomic ratio of elements constituting the electrode active material; (2) creating a low molecular model unit, which is a precursor of the electrode active material, from the atomic ratio; and (3) performing molecular dynamics calculations capable of handling chemical reactions on at least one of the low molecular model units; A modeling method comprising: [Effects of the Invention]
[0008] According to the present invention, it is possible to provide a modeling method for simulating, within a realistic time period, a stable structural model of an electrode active material containing carbon atoms and sulfur atoms obtained through calcination. [Brief explanation of the drawings]
[0009] [Figure 1] 1 is a flowchart of a modeling method according to one embodiment of the present invention. [Figure 2] 1 is a flowchart of a modeling method according to one embodiment of the present invention. [Figure 3] 1 shows chemical structural formulas of low molecular model units in an embodiment of the present invention. [Figure 4] In the embodiment of the present invention, 12 molecules of low molecular model units are arranged in a simulation box of ReaxFF. [Figure 5] In the embodiment of the present invention, the chemical structural formula after performing a reaction force field molecular dynamics calculation on 12 molecules of a low molecular model unit is shown. [Figure 6] In the examples of the present invention, the chemical structural formula after a reaction force field molecular dynamics calculation is performed is shown, and the chemical structural formula after a semi-empirical first-principles molecular dynamics calculation is also shown. [Figure 7] These are partial structures related to cyclization, condensed ring formation, and crosslinking of carbon atoms extracted from Figure 6. [Figure 8] These are partial structures (thiophene skeletons and thiophene fused rings) related to the cyclization and condensation of sulfur atoms extracted from Figure 6. DETAILED DESCRIPTION OF THE INVENTION
[0010] A modeling method according to one embodiment of the present invention is a modeling method for creating a stable structural model of an electrode active material containing carbon and sulfur atoms obtained through calcination by simulating chemical reactions that proceed during calcination for low-molecular-weight model units, and includes the steps of: (1) determining the atomic ratio of elements constituting the electrode active material; (2) creating a low-molecular-weight model unit, which is a precursor of the electrode active material, from the atomic ratio; and (3) performing molecular dynamics calculations capable of handling chemical reactions for at least one of the low-molecular-weight model units.
[0011] In this modeling method, (a) small molecule model units are created from the elemental analysis results (e.g., ratios of CSH) of the electrode active material and used as the initial structure. This allows for more efficient modeling of electrode active materials with unspecified chemical structures than first-principles molecular dynamics calculations, which are a fundamental approach. Furthermore, (b) molecular dynamics calculations that can handle chemical reactions are performed on the small molecule model units, enabling large-scale, highly accurate simulations of chemical reactions while suppressing side reactions. Therefore, this method can be applied to electrode active materials with unspecified chemical structures, and it is possible to track reactions between small molecule model units and simulate chemical reactions with high accuracy. Therefore, it is believed to achieve the excellent effect of significantly reducing calculation time and enabling stable structural models of electrode active materials to be modeled within a realistic time frame.
[0012] The step (3) preferably includes: (3-1) performing a reaction force field molecular dynamics calculation on at least one of the small molecule model units; and (3-2) further performing a semi-empirical first-principles molecular dynamics calculation.
[0013] In the process of performing molecular dynamics calculations that can handle chemical reactions, the calculation time can be further reduced by taking two steps: first, promoting the chemical reaction of small molecule model units using a reaction force field molecular dynamics calculation, and then performing a more accurate semi-empirical first-principles molecular dynamics calculation. Note that the reaction force field molecular dynamics calculation is a method that can handle larger systems, although it is less accurate than the semi-empirical first-principles molecular dynamics calculation, while the semi-empirical first-principles molecular dynamics calculation is a method that can perform calculations for longer periods of time, although it is less accurate than the first-principles molecular dynamics calculation.
[0014] The total number of atoms constituting at least one low molecular model unit used in the step (3) is preferably 100 or more and 9,999 or less.
[0015] By setting the total number of atoms to a predetermined value or more, appropriate calculations can be ensured, while by setting the total number of atoms to a predetermined value or less, it is possible to prevent the calculation scale from becoming too large and making it impossible to achieve a realistic calculation time.
[0016] The electrode active material preferably contains a carbon-sulfur structure.
[0017] This is because the carbon-sulfur structure is one of the preferred embodiments of the electrode active material containing carbon atoms and sulfur atoms obtained through calcination, which is the subject of this modeling method.
[0018] The electrode active material is preferably a positive electrode active material.
[0019] <Definition> In this specification, the term "modeling method" refers to a method for creating a stable structural model of an electrode active material containing carbon atoms and sulfur atoms obtained through calcination by simulating the chemical reactions that proceed during calcination.
[0020] The "stable structural model" is a chemical structure estimated from molecular dynamics calculations that can handle chemical reactions for an electrode active material containing carbon atoms and sulfur atoms obtained through calcination.
[0021] A "small molecule model unit" is a single chemical structural formula or multiple chemical structural formulas used as the target (i.e., precursor) for performing calculations in molecular dynamics calculations that can handle chemical reactions. In other words, a small molecule model unit may consist of a single chemical structural formula or multiple chemical structural formulas. A small molecule model unit is its smallest unit, i.e., a single chemical structural formula or multiple chemical structural formulas is counted as one set.
[0022] In this specification, the term "simulation" is synonymous with calculation in molecular dynamics.
[0023] "Molecular dynamics calculation" is the execution of a calculation program that reproduces the movement of atoms and molecules in a computer, and is also called molecular dynamics simulation. First, (a) the initial arrangement of atoms is determined, then (b) the forces acting on one atom from other atoms are calculated, and then (c) how the atom will move when subjected to these forces is calculated. By repeating steps (b) and (c) for the new atomic arrangement obtained in this way, the movement of the atoms is reproduced. Forces acting on atoms include the force of chemical bonds when atoms form molecules, electrostatic forces due to atoms being positively or negatively charged, and forces acting between molecules. In this embodiment, a molecular dynamics calculation that can handle chemical reactions is performed.
[0024] "Molecular dynamics calculations that can handle chemical reactions" refers to molecular dynamics calculations that can handle bonds between atoms, bond recombinations, etc. Examples of molecular dynamics calculations that can handle chemical reactions include first-principles molecular dynamics calculations, reaction force field molecular dynamics calculations, and semi-empirical first-principles molecular dynamics calculations.
[0025] "First-principles molecular dynamics calculations" are a method of calculating atomic interactions based on quantum mechanics, taking into account all interactions between atomic nuclei and electrons, without using any empirical parameters obtained from experiments, and using only the type of atom and the number of electrons as input parameters. This method does not require other information such as experimental data, and in principle, can obtain reliable data regardless of the state of the system. However, the enormous amount of calculation required limits the size of the system that can be calculated.
[0026] "Reactive force field molecular dynamics calculations" are molecular dynamics calculations that deal with chemical reactions, and are performed using a "force field that can handle chemical reactions," which allows the forces and energies acting on atoms required for the calculation to be expressed in empirical formulas, i.e., simple functional forms. Force fields that can handle chemical reactions include reactive force fields and machine learning force fields. While the disadvantages are that an appropriate force field is required and accuracy is low, the advantage is that it can handle large-scale systems.
[0027] "Semi-empirical first-principles molecular dynamics calculation" is a calculation method positioned intermediate between reaction force field molecular dynamics calculation and first-principles molecular dynamics calculation. It is a method that introduces empirical parameters such as the tight binding method and semi-empirical molecular orbital method, and although it is less accurate than first-principles molecular dynamics calculation, it is possible to perform simulations for longer periods of time.
[0028] <Modeling method> The modeling method of this embodiment will be described. This modeling method creates a stable structural model of an electrode active material containing carbon and sulfur atoms obtained through calcination by simulating chemical reactions that proceed during calcination for low-molecular-weight model units, and includes predetermined steps. Each step of this modeling method will be described below.
[0029] 1. Modeling method according to one embodiment 1 is a flowchart showing steps of a modeling method according to one embodiment of the present invention. Step S110 corresponds to step (1), step S120 corresponds to step (2), and step S130 corresponds to step (3).
[0030] The modeling method of this embodiment is a modeling method for creating a stable structure model of an electrode active material containing carbon and sulfur atoms obtained through calcination, and more specifically, the electrode active material preferably contains a carbon-sulfur structure containing carbon and sulfur atoms as constituent atoms. The electrode active material is either a positive electrode active material or a negative electrode active material. The calcination is preferably performed in a non-oxidizing atmosphere.
[0031] The electrode active material containing carbon atoms and sulfur atoms is typically obtained by calcining a raw material containing an organic compound as a carbon atom source and sulfur as a sulfur atom source. Examples of the organic compound include unsaturated chain hydrocarbon monomers, polymers of unsaturated chain hydrocarbon monomers, and condensates of substituted aromatic hydrocarbons with sulfur chloride. The organic compound may also contain heteroatoms such as nitrogen atoms and sulfur atoms. The organic compounds can be used alone or in combination of two or more.
[0032] (Process (1)) Step (1) is a step of determining the atomic ratio of elements constituting the electrode active material. Any existing method may be used to determine the atomic ratio. For example, the atomic ratio can be calculated using the atomic weight of each element measured by elemental analysis from the mass of each element. In addition, for sulfur, the atomic ratio may be calculated using the atomic weight of sulfur measured by ion chromatography.
[0033] (Process (2)) Step (2) is a step of preparing a low molecular model unit, which is a precursor of an electrode active material, from the atomic ratio determined in Step (1). This step can be carried out in the following order: Step (2-1), Step (2-2), and Step (2-3).
[0034] [Process (2-1)] Step (2-1) focuses on the atomic ratio of carbon atoms to sulfur atoms among the atomic ratios of elements constituting the electrode active material, approximates the atomic ratio of carbon atoms to sulfur atoms with natural numbers less than 10, N (carbon) and M (sulfur), and arranges N carbon atoms in a linear chain.
[0035] [Process (2-2)] Step (2-2) is a step of bonding M sulfur atoms with single bonds to carbon atoms other than the terminals of the linear N-carbon chain obtained in step (2-1), and further bonding the remaining atoms excluding hydrogen to the non-terminal atoms based on the atomic ratio. In this case, the bonding positions of the sulfur atoms are N-2 positions excluding the terminal carbon atoms of the carbon chain, and the number of bonding sulfur atoms is M. Therefore, the number of bonding positions of the basic skeleton (BS) formed by bonding sulfur atoms is N-2 C M This becomes:
[0036] For example, when N=5 and M=2, the number of basic skeletons is 5-2 This becomes C2, and specifically there are three types as follows. BS(1):-CCC(S)-C(S)-C- BS(2):-CC(S)-CC(S)-C- BS(3):-CC(S)-C(S)-CC-
[0037] Also, when N=7 and M=4, the number of basic skeletons is 7-2 This is C4, and there are five specific ways to do this: BS(1):-CCC(S)-C(S)-C(S)-C(S)-C- BS(2):-CC(S)-CC(S)-C(S)-C(S)-C- BS(3):-CC(S)-C(S)-CC(S)-C(S)-C- BS(4):-CC(S)-C(S)-C(S)-CC(S)-C- BS(5):-CC(S)-C(S)-C(S)-C(S)-CC-
[0038] obtained above N-2 C MFor each atom other than carbon, sulfur, and hydrogen among the elements constituting the electrode active material in the basic skeleton, the number of atoms corresponding to the above N and M is determined. The number of atoms is rounded to one decimal place. If the number of atoms is 1 or greater, the closest natural number is determined. Atoms (atoms other than carbon, sulfur, and hydrogen) are bonded to atoms other than the terminal carbon atoms of the basic skeleton in the same number as the natural number. The priority of the bonding positions is determined in order of molecular stability of the low molecular model unit after bonding with hydrogen atoms in the following step (2-3).
[0039] If the number of atoms is less than 1, the number of basic skeletons ( N-2 C M ), if one or more atoms to be bonded can be recognized in at least one basic skeleton, then, in accordance with the number, those atoms (atoms other than carbon, sulfur, and hydrogen) are bonded to atoms other than the terminal carbon atoms of the basic skeleton. The priority of the basic skeletons to be bonded is determined in order of molecular stability of the low molecular model unit after bonding of hydrogen atoms in the step (2-3) below. Here, "if one or more atoms to be bonded can be recognized" means that the number of atoms (atoms other than carbon, sulfur, and hydrogen) calculated to be bonded to at least one basic skeleton is 0.5 or more. If the number is less than 0.5, then those atoms are not bonded to the carbon skeleton.
[0040] [Process (2-3)] Step (2-3) is carried out by using the hydroxybenzoate obtained in step (2-2). N-2 C MThis is a process of obtaining a low-molecular-weight model unit by bonding hydrogen atoms to the remaining bonds of a basic skeleton. In this case, first, one hydrogen atom is bonded to each carbon atom at both ends of each basic skeleton. This is because this is the minimum required to finally complete each basic skeleton as a molecule. The number of hydrogen atoms bonded to the remaining bonds of each other basic skeleton is made to approach the atomic ratio of hydrogen atoms in the electrode active material. Then, if the number of hydrogen atoms to be bonded is fewer than the number of bonds, double or triple bonds can be introduced into the basic skeleton. However, just because the number of hydrogen atoms is small, double or triple bonds should not be introduced without consideration for the stability of the final molecule obtained.
[0041] At this stage, any basic skeletons that would significantly reduce the stability of the molecules obtained by bonding hydrogen atoms can be eliminated in advance, resulting in a set of low-molecular-weight model units consisting of a single chemical structure or multiple chemical structures, which can be used in subsequent steps.
[0042] (Step (3)) Step (3) is a step of performing molecular dynamics calculations capable of handling chemical reactions for at least one of the low molecular model units, i.e., at least one set. A molecular dynamics calculation capable of handling chemical reactions is performed for at least one set of low molecular model units obtained in step (2). In carrying out this step, at least one set of low molecular model units may be used as the precursor to be calculated, but two or more sets of low molecular model units may also be used. Increasing the number of sets of low molecular model units used improves the calculation accuracy, but increases the calculation scale (number of atoms handled) and calculation time. On the other hand, if the calculation scale is too small, the calculation accuracy decreases, and there is a possibility that a stable structural model of the desired electrode active material cannot be obtained. Those skilled in the art can appropriately determine the number of low molecular model units to be used based on the relationship between calculation accuracy and calculation scale.
[0043] The number of atoms handled in this step, i.e., the total number of atoms constituting all of the low-molecular-weight model units subjected to this step, is preferably 100 or more and 9999 or less. The lower limit of the number of atoms handled is more preferably 130 or more, even more preferably 150 or more, even more preferably 180 or more, and even more preferably 200 or more. On the other hand, the number of atoms handled is more preferably 5000 or less, even more preferably 4000 or less, even more preferably 3000 or less, even more preferably 2000 or less, and even more preferably 1500 or less.
[0044] A molecular dynamics calculation capable of handling chemical reactions is a molecular dynamics calculation capable of handling bonds between atoms, bond recombinations, etc., and specifically includes first-principles molecular dynamics calculation, reaction force field molecular dynamics calculation, semi-empirical first-principles molecular dynamics calculation, etc. As a molecular dynamics calculation capable of handling chemical reactions, at least one selected from the group consisting of first-principles molecular dynamics calculation, reaction force field molecular dynamics calculation, and semi-empirical first-principles molecular dynamics calculation can be used. Of these, a combination of a reaction force field molecular dynamics calculation and a semi-empirical first-principles molecular dynamics calculation is preferred, and it is even more preferred to perform both calculations in this order.
[0045] For the reaction force field molecular dynamics calculation and the semi-empirical first-principles molecular dynamics calculation, the explanation in the section "2. Modeling Methods According to Other Embodiments" below can be referred to.
[0046] In molecular dynamics calculations that can handle chemical reactions, the chemical reactions to be simulated are those that occur in low-molecular-weight model units during calcination, which is preferably assumed to be carried out in a non-oxidizing atmosphere.
[0047] 2. Modeling Method According to Another Embodiment FIG. 2 is a flowchart illustrating steps of a modeling method according to another embodiment of the present invention. Step S210 corresponds to step (1), step S220 corresponds to step (2), step S230 corresponds to step (3), step S2301 corresponds to step (3-1), and step S2302 corresponds to step (3-2). This embodiment is characterized in that step (3) includes step (3-1) of performing a reaction force field molecular dynamics calculation for at least one small molecule model unit, and further step (3-2) of performing a semi-empirical first-principles molecular dynamics calculation. The above explanation applies to step (1) and step (2). Furthermore, steps (3-1) and (3-2) are described below, and the explanation of step (3) in the above embodiment applies unless otherwise specified. Furthermore, the following explanations regarding the steps (3-1) and (3-2) can also be applied to the explanation of the step (3) in the above embodiment, unless there is a particular contradiction.
[0048] (Process (3-1)) Step (3-1) is a step of performing a reaction force field molecular dynamics calculation on at least one of the low molecular model units.
[0049] A reactive force field molecular dynamics calculation is a molecular dynamics calculation performed using a force field that can handle chemical reactions. Here, a force field that can handle chemical reactions can be any force field that can handle atomic bonds, bond recombinations, etc., and can be used without any particular restrictions. Examples of such force fields include reactive force fields and machine learning force fields. An example of a reactive force field is ReaxFF, and commercially available software such as LAMPS and AMS can be used. Furthermore, an example of a machine learning force field is commercially available software such as DeepMD and Matlantis.
[0050] As the low molecular model unit, at least one set of the low molecular model units obtained in the step (2) may be used, or two or more sets of low molecular model units may be used. The number of atoms that can be handled in this step can be referenced from the explanation for step (3) in the above embodiment.
[0051] ReaxFF is a preferred reaction force field. ReaxFF is a reactive molecular dynamics calculation program that uses both the relationship between bond distance and bond order and the relationship between bond order and bond energy in calculations, and can provide a reaction force field that describes bond cleavage and creation. The parameters of the reaction force field in ReaxFF are determined from quantum chemical calculation data, enabling highly accurate description of chemical reactions while maintaining a calculation speed comparable to that of conventional classical molecular dynamics simulations. ReaxFF supports many elements and can be suitably applied to simulations of the sintering reaction of electrode active materials containing carbon and sulfur atoms according to this embodiment.
[0052] In a simulation using ReaxFF, the temperature conditions can be set appropriately taking into consideration the type and number of atoms used, the type of reaction, etc. Because the atoms used in this step are primarily carbon atoms and sulfur atoms, the number of atoms is, for example, the same as that described in step (3) above, and the reaction is a calcination reaction, a temperature profile can be considered in which the temperature is raised to a predetermined temperature and then lowered. The temperature reached during the temperature increase is preferably 2000 K or higher and 3000 K or lower, more preferably 2000 K or higher and 2700 K or lower, and even more preferably 2000 K or higher and 2500 K or lower. A preferred temperature is 2300 K, for example. Meanwhile, the temperature lowered is a temperature near room temperature, for example, about 300 K.
[0053] The reaction time can be set appropriately taking into consideration the points considered when setting the temperature conditions and the temperature conditions. The time is preferably, for example, in the range of 100 picoseconds or more and 4000 picoseconds or less. A time of 100 picoseconds or more can improve the calculation accuracy, and a time of 4000 picoseconds or less can prevent the calculation scale from expanding and the calculation time from becoming longer. The time condition is more preferably 200 picoseconds or more, and even more preferably 400 picoseconds or more. The time condition is more preferably 2000 picoseconds or less, and even more preferably 1000 picoseconds or less.
[0054] The time required for the calculation is, for example, preferably 100 hours or less, more preferably 50 hours or less, even more preferably 30 hours or less, even more preferably 10 hours or less, and even more preferably 6 hours or less. The time required is usually at least about 2 hours.
[0055] In the simulation, it is preferably assumed that the firing is carried out in a non-oxidizing atmosphere.
[0056] (Process (3-2)) Step (3-2) is a step of further performing semi-empirical first-principles molecular dynamics calculations on the calculation results of step (3-1).
[0057] The chemical structure of the product obtained in step (3-1) is subjected to semi-empirical first-principles molecular dynamics calculations, using a tight-binding method or the like.
[0058] The calculation conditions include, for example, a temperature in the range of 2000 K or higher and 3000 K or lower and a time in the range of 10 picoseconds or higher and 200 picoseconds or lower. The temperature is more preferably 2200 K or higher, and even more preferably 2400 K or higher. The temperature is more preferably 2800 K or lower, and even more preferably 2600 K or lower. The time is more preferably 30 picoseconds or higher, and even more preferably 50 picoseconds or higher. The time is more preferably 150 picoseconds or lower, and even more preferably 100 picoseconds or lower. The temperature and time conditions are appropriately set taking into consideration the calculation accuracy and the time required for the calculation. The time required for the calculation is preferably within 30 days, more preferably within 20 days, even more preferably within 15 days, and even more preferably within 10 days.
[0059] In the simulation, it is preferably assumed that the firing is carried out in a non-oxidizing atmosphere. [Example]
[0060] The present invention will be described in more detail below with reference to examples, although the present invention is not limited to the following examples.
[0061] Example 1 A reference [A. Yamano et al., "Rubber-Derived Sulfur Composite Cathode Material for Li-S / Li-ion Battery", Electrochemistry, 90(7), 077003 (2022)] examines the chemical structure of a rubber-derived sulfur composite for use in the cathode of Li-S / Li-ion batteries, synthesized by vulcanizing butadiene rubber and a large amount of sulfur, based on analytical results such as Raman spectroscopy. The authors estimate that the rubber-derived sulfur composite has a thienoacene or thienoacene-like chain as its primary structure. In this example, the chemical structure of the rubber-derived sulfur composite is modeled based on the elemental ratio information of the rubber-derived sulfur composite shown in the reference.
[0062] Step (1): Calculating the atomic ratio Based on the results of elemental analysis in the reference (Table 1 in the reference), the mass ratios of the elements that make up the rubber-derived sulfur complex are confirmed to be 58.6% by weight of sulfur atoms, 40.87% by weight of carbon atoms, 0.15% by weight of hydrogen atoms, and 0.05% by weight of nitrogen atoms. Here, the atomic weight of carbon is 12.01, that of sulfur is 32.07, that of hydrogen is 1.01, and that of nitrogen is 14.01, and the atomic weight ratios are calculated. If the number of sulfur atoms is 4, the atomic ratios of the other atoms are as shown in the table below.
[0063] [Table 1]
[0064] From the above, the atomic ratio of carbon atoms to sulfur atoms, expressed as natural numbers less than 10, is obtained as number of carbon atoms:number of sulfur atoms=7:4.
[0065] Step (2): A step of preparing a precursor low molecular model unit Based on the above atomic ratio, a low molecular model unit was prepared according to the following steps.
[0066] [Process (2-1)] In the above atomic ratio, carbon atoms corresponding to the number of carbon atoms are arranged in a straight chain to obtain the following carbon chain. L-C7:-CCCCCCC-
[0067] [Process (2-2)] Sulfur atoms corresponding to the number of sulfur atoms in the above atomic ratio are bonded to carbon atoms other than the terminal carbon of the carbon chain L-C7 via single bonds. There are five possible bonding positions for sulfur atoms in the carbon chain L-C7, excluding the terminal carbon. Meanwhile, the number of sulfur atoms is four. Therefore, the number of the basic skeleton of the carbon chain L-C7S4 to which sulfur atoms are bonded is 5C4, and specifically, the following five possibilities are possible. Note that the only remaining atom excluding hydrogen atoms is a nitrogen atom, and since the number of nitrogen atoms is 0.0 according to Table 1 above, the bond is omitted. BS(1):-CCC(S)-C(S)-C(S)-C(S)-C- BS(2):-CC(S)-CC(S)-C(S)-C(S)-C- BS(3):-CC(S)-C(S)-CC(S)-C(S)-C- BS(4):-CC(S)-C(S)-C(S)-CC(S)-C- BS(5):-CC(S)-C(S)-C(S)-C(S)-CC-
[0068] [Process (2-3)] Hydrogen atoms are attached to the remaining bonds of the five basic skeletons. In this case, first, one hydrogen atom is attached to each carbon atom at both ends of each basic skeleton. This results in the following five carbon chains: L-C7S4H2. L-C7S4H2(1):-CH-CC(S)-C(S)-C(S)-C(S)-CH- L-C7S4H2(2):-CH-C(S)-CC(S)-C(S)-C(S)-CH- L-C7S4H2(3):-CH-C(S)-C(S)-CC(S)-C(S)-CH- L-C7S4H2(4):-CH-C(S)-C(S)-C(S)-CC(S)-CH- L-C7S4H2(5):-CH-C(S)-C(S)-C(S)-C(S)-C-CH-
[0069] Since the ratio of hydrogen atoms to the total number of atoms is 0.3 as shown in Table 1, the introduction of additional hydrogen atoms should be minimized. Therefore, the chemical structural formulas of the five carbon chains L-C7S4H2 are completed, taking into consideration the introduction of double and triple bonds. At this time, unstable structures are eliminated, taking into consideration the stability of the final molecule. In this case, the same chemical structural formulas shown below, obtained from L-C7S4H2(1) and L-C7S4H2(5) above, in which the sulfur atoms bonded to each other are consecutive and located in the center of the carbon chain, were considered stable. Therefore, the chemical structural formula shown below was selected as the low-molecular-weight model unit (C7S4H6) to be subjected to the following steps.
[0070] [ka]
[0071] The low molecular model unit is shown in Figure 3. In Figure 3, black represents carbon atoms, gray represents sulfur atoms, and white represents hydrogen atoms (the same applies below). The low molecular model unit is made up of 17 atoms.
[0072] Step (3): A step of performing molecular dynamics calculations that can handle chemical reactions Each of the small molecule model units was considered as one set, and molecular dynamics calculations capable of handling chemical reactions were performed on 12 sets of these. Specifically, as shown below, first, a reaction force field molecular dynamics calculation was performed, and then a semi-empirical first-principles molecular dynamics calculation was performed. A total of 204 atoms were used in the calculations.
[0073] Step (3-1): A step of performing a reaction force field molecular dynamics calculation Using ReaxFF, 12 sets of the small molecule model units (total number of atoms: 204) were placed in a simulation box (Figure 4), and reactive force field molecular dynamics calculations were performed. The ReaxFF simulations were performed under a temperature profile of 2300 K followed by a temperature drop to 300 K, with a reaction time of 500 picoseconds (calculation time: 6 hours). The calcination was performed in a non-oxidizing atmosphere. This temperature profile facilitates chemical reactions (condensation, cyclization, crosslinking, etc.) between the small molecule models, even in short simulation times. The chemical structural formulas of the products obtained after the simulation, including those resulting from side reactions, are shown in Figure 5. This shows that the small molecules in the initial structure reacted with each other, resulting in condensation and crosslinking. However, due to the high temperature at which the simulation was performed and the dependence of the ReaxFF simulation results on the selected parameters, the structural model after the simulation contains numerous radicals and localized chemically unstable structures.
[0074] Step (3-2): A step of performing semi-empirical first-principles molecular dynamics calculations Semiempirical first-principles molecular dynamics calculations were performed on the chemical structure of the product obtained from the ReaxFF simulation. The tight-binding method was used for the semiempirical first-principles molecular dynamics calculations. The semiempirical first-principles molecular dynamics calculations were performed at 2500 K for 75 picoseconds (calculation time: 10 days). Furthermore, calcination was performed in a non-oxidizing atmosphere. These calculations enabled us to obtain the chemical structure of the product with even greater accuracy (Figure 6). These calculations allowed us to extract substructures that are believed to have undergone cyclization, condensation, and crosslinking from the chemical structure in Figure 6 (Figures 7 and 8). Figure 7 shows the extracted substructures related to carbon atom cyclization, condensation, and crosslinking. Figure 8 shows the extracted substructures related to sulfur atom cyclization and condensation (thiophene skeleton and thiophene-fused ring). These calculations are believed to have further stabilized the chemical structure.
[0075] <Consideration> The chemical structure obtained by the above calculation (Figure 6) has the following three characteristics: first, five- and six-membered carbon rings are formed, second, a thiophene skeleton is formed, and third, a fused ring structure is formed.
[0076] According to the reference cited above, the chemical structure of the rubber-derived sulfur complex obtained by vulcanization of butadiene rubber with a large amount of sulfur is estimated to have the following thienoacene or thienoacene-like chain as its main structure (Figure 3 in the reference). Comparing this with the calculation results above, it can be said that the chemical structures of both are similar to each other. In particular, it is noteworthy that this modeling method was able to predict the formation of thiophene skeletons and thiophene fused rings.
[0077] [ka]
[0078] Furthermore, considering that the "thienoacene" estimated in the above reference is merely an ideal chemical structure, and that in reality carbonized and crosslinked structures are expected to coexist, the chemical structure obtained by this calculation (FIG. 6) is considered to reflect a more realistic structure. Therefore, the modeling method according to this embodiment is considered to be an excellent method.
[0079] <Embodiment> The following describes a preferred embodiment.
[0080] [1] A modeling method for creating a stable structural model of an electrode active material containing carbon atoms and sulfur atoms obtained through calcination by simulating a chemical reaction that progresses during calcination for a low-molecular-weight model unit, (1) determining the atomic ratio of elements constituting the electrode active material; (2) creating a low molecular model unit, which is a precursor of the electrode active material, from the atomic ratio; and (3) performing molecular dynamics calculations capable of handling chemical reactions on at least one of the low molecular model units; A modeling method comprising: [2] The step (3) (3-1) performing a reaction force field molecular dynamics calculation on at least one of the small molecule model units; and (3-2) Further, a step of performing semi-empirical first-principles molecular dynamics calculations The modeling method according to [1] above, comprising: [3] The modeling method according to [1] or [2], wherein the total number of atoms constituting at least one low-molecular-weight model unit used in step (3) is 100 or more and 9,999 or less, preferably 130 or more and 5,000 or less, more preferably 150 or more and 4,000 or less, even more preferably 180 or more and 3,000 or less, even more preferably 200 or more and 2,000 or less, and even more preferably 200 or more and 1,500 or less. [4] The modeling method according to any one of [1] to [3], wherein the electrode active material contains a carbon-sulfur structure. [5] The modeling method according to any one of [1] to [4], wherein the electrode active material is a positive electrode active material. [Explanation of symbols]
[0081] S110 Process (1) S120 process (2) S130 process (3) S210 Process (1) S220 Process (2) S230 Process (3) S2301 Process (3-1) S2302 Process (3-2)
Claims
1. A modeling method for creating a stable structural model of an electrode active material containing carbon atoms and sulfur atoms obtained through calcination by simulating a chemical reaction that progresses during calcination for a low molecular model unit, comprising: (1) determining the atomic ratio of elements constituting the electrode active material; (2) creating a low molecular model unit, which is a precursor of the electrode active material, from the atomic ratio; and (3) A step of performing molecular dynamics calculations capable of handling chemical reactions on at least one of the low molecular model units. A modeling method comprising:
2. The step (3) (3-1) performing a reaction force field molecular dynamics calculation on at least one of the small molecule model units; and (3-2) Further, a step of performing semi-empirical first-principles molecular dynamics calculations The modeling method of claim 1 , comprising:
3. 3. The modeling method according to claim 1, wherein the total number of atoms constituting at least one low-molecular-weight model unit used in step (3) is 100 or more and 9,999 or less.
4. 3. The modeling method according to claim 1, wherein the electrode active material comprises a carbon-sulfur structure.
5. The modeling method according to claim 1 or 2, wherein the electrode active material is a positive electrode active material.