Search method for new electrode active materials

Abstract

To provide a method for retrieving a novel electrode active material subjected to a crystal structure including a space.SOLUTION: A method for retrieving a novel electrode active material causes a computer to execute processing including: acquiring information of a target crystal structure from a structure database; generating structure information of an insertion structure in which a predetermined amount of lithium ions is disposed in a space inside of the crystal structure; generating structure information of relaxation structure in which the crystal structure is relaxed on the basis of first principal calculation; determining whether or not a bond included in the crystal structure is cut in the relaxation structure; and calculating a relation between the predetermined amount of disposed lithium ions and an expansion coefficient of the crystal structure depending on the relaxation in a case where it is determined that the bond included in the crystal structure is not cut.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a method for searching for new electrode active materials. [Background technology]

[0002] In recent years, the development of batteries has been actively pursued. For example, in the automotive industry, development of batteries for use in electric vehicles or hybrid vehicles is progressing. Silicon is known as an electrode active material for batteries, particularly lithium-ion batteries.

[0003] Silicon electrode active materials have a large theoretical capacity and are effective in increasing the energy density of batteries. However, they suffer from the problem of large expansion during charging. It is known that the use of silicon clathrate electrode active materials as silicon electrode active materials can suppress expansion during charging.

[0004] Although silicon clathrate electrode active materials can suppress expansion during charging compared to ordinary silicon electrode active materials, there is a demand for further suppression of silicon clathrate electrode active materials' expansion during charging. In response to this demand, technologies have been developed to suppress expansion during charging by replacing silicon in silicon clathrate with specific elements.

[0005] For example, Patent Document 1 discloses an active material having a silicon clathrate-type crystalline phase, containing Na, Si, and M, a metal element having an ionic radius larger than that of Si, and the ratio of M to the total of Si and M is 0.1 atm % or more and 5 atm % or less.

[0006] Meanwhile, studies are being conducted to search for substances that can be used as electrode active materials for lithium ion batteries by performing predetermined calculations.

[0007] For example, Non-Patent Document 1 discloses a method for calculating the energy required for lithium ions to be inserted into silicon based on first principles. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Patent Publication No. 2021-018981 [Non-patent literature]

[0009] [Non-Patent Document 1] Maria KY Chan et al., J. Am. Chem. Soc. 2012, 134, 14362-14374 Summary of the Invention [Problem to be solved by the invention]

[0010] Non-Patent Document 1 focuses on silicon, which does not have voids in its crystal structure, and performs calculations solely from the perspective of the energy required for lithium ion insertion. In contrast, there is a need to develop a method for searching for novel electrode active materials, optionally in combination with machine learning, for materials that have voids in their crystal structure, such as silicon clathrates.

[0011] An object of the present disclosure is to provide a method for searching for novel electrode active materials that target crystal structures having spaces. [Means for solving the problem]

[0012] The present inventors have found that the above problems can be solved by the following means. <Aspect 1> Obtaining target crystal structure information from a structure database; generating structural information of an insertion structure in which lithium ions are arranged in a space within the crystal structure up to a predetermined amount; generating structural information of a relaxed structure obtained by relaxing the crystal structure based on first-principles calculations; determining whether bonds contained in the crystalline structure are broken in the relaxed structure; and When it is determined that the bond included in the crystal structure is not broken, calculating the relationship between the predetermined amount of the arranged lithium ions and the expansion rate of the crystal structure due to the relaxation; A method for searching for a new electrode active material, comprising causing a computer to execute a process including the steps of: [Effects of the Invention]

[0013] According to the present disclosure, it is possible to provide a method for searching for novel electrode active materials that target structures having spaces within the crystal. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a graph showing the relationship between the volume of a crystal structure and the expansion rate of the crystal structure due to relaxation. DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, embodiments of the present disclosure will be described in detail. Note that the present disclosure is not limited to the following embodiments, and various modifications can be made within the scope of the present disclosure.

[0016] <<Method for searching for new electrode active materials>> The disclosed method for searching for new electrode active materials involves having a computer execute processes including: acquiring information on a target crystal structure from a structure database; generating structural information on an insertion structure in which lithium ions are arranged in the space within the crystal structure up to a predetermined amount; generating structural information on a relaxed structure in which the crystal structure is relaxed based on first-principles calculations; determining whether or not bonds contained in the crystal structure will break in the relaxed structure; and, if it is determined that the bonds contained in the crystal structure will not break, calculating the relationship between the predetermined amount of arranged lithium ions and the expansion rate of the crystal structure due to relaxation.

[0017] In the present disclosure, the "electrode active material" can be used as either a "positive electrode active material" or a "negative electrode active material", and is particularly used as a "negative electrode active material".

[0018] The method of the present disclosure includes causing a computer to execute a process for obtaining information on a target crystal structure from a structure database.

[0019] The crystal structure is not particularly limited as long as it has a space within it where lithium ions can be arranged. For example, when the electrode active material is a negative electrode active material, examples of the crystal structure include silicon clathrate, which may be substituted with a specific element, and Li2B3PO8. Examples of the specific element include aluminum.

[0020] An example of the process of acquiring information is the process of saving information stored on a network or on the cloud to a terminal such as a personal computer.

[0021] The disclosed method includes causing a computer to execute a process for generating structural information about an insertion structure in which lithium ions are arranged in spaces within a crystal structure up to a predetermined amount.

[0022] The "predetermined amount" means an amount at which the capacity of the battery exhibits a predetermined value when the amount of lithium ions inserted is converted into battery capacity. Here, the "predetermined value" may be 100 mAh / g or more, 300 mAh / g or more, 500 mAh / g or more, 600 mAh / g or more, 700 mAh / g or more, 800 mAh / g or more, or 900 mAh / g or more, or may be 2000 mAh / g or less, 1700 mAh / g or less, 1500 mAh / g or less, 1300 mAh / g or less, 1200 mAh / g or less, or 1100 mAh / g or less.

[0023] The lithium ions may be arranged in the spaces within the crystal structure one atom at a time, or multiple atoms at the same time, and may be arranged regularly or randomly with a predetermined space within the crystal structure as the starting point.

[0024] The method disclosed herein includes causing a computer to execute a process for generating structural information of a relaxed structure obtained by relaxing a crystal structure based on first-principles calculations.

[0025] VASP from MedeA can be used as software for first-principles calculations.

[0026] An example of a process for generating structural information of a relaxed structure obtained by relaxing a crystal structure based on first-principles calculations is a process in which the energy of the entire molecular structure model in the structure before lithium ions are arranged is set as an initial value, and the position of each atom in the molecular structure model is changed so that this energy takes a minimum value.

[0027] The calculation conditions for the first-principles calculation may be set differently depending on the material, but for example, the exchange-correlation functional PBEsol and pseudopotential PAW may be used, with a cutoff energy of 600 eV.

[0028] The disclosed method includes causing a computer to perform a process to determine whether bonds contained in a crystalline structure are broken in the relaxed structure.

[0029] An example of the process for determining whether or not a bond contained in a crystal structure can be broken is a process for determining whether or not the length of the target bond is within a range in which the bond can be maintained.

[0030] The method disclosed herein includes, when it is determined that the bonds contained in the crystal structure are not broken, having a computer execute a process for calculating the relationship between a predetermined amount of arranged lithium ions and the expansion rate of the crystal structure due to relaxation.

[0031] In the present disclosure, the term "expansion rate" refers to the rate of increase in volume due to the arrangement of lithium ions, when the volume before the arrangement of lithium ions is taken as 100%.

[0032] The method of the present disclosure can be optionally combined with machine learning, for example, by having a computer learn the relationship between the crystal structure subjected to the process of the present disclosure and the expansion coefficient of that structure, thereby predicting a crystal structure with a small expansion coefficient, as an optional step in the method of the present disclosure. [Example]

[0033] Computer processing Example 1 From the structural database, silicon clathrate (Si clathrate) is known to be useful as an electrode active material for lithium-ion batteries. 34 We obtained information on the crystal structure of a lithium-ion-containing silicon nanotube (Sb), and then generated structural information for an insertion structure in which lithium ions were randomly arranged one atom at a time within the space within the crystal structure until a capacity of over 1000 mAh / g was achieved. Based on first-principles calculations, we set the energy of the entire molecular structure model before lithium ions were arranged as the initial value. We then adjusted the position of each atom in the molecular structure model after lithium ions were arranged so that this energy reached a minimum value, thereby generating structural information for a relaxed structure in which the crystal structure was relaxed. We then performed a process to determine whether the length of the Si-Si bond in the relaxed structure was within a range that could maintain the bond. If the bond length was within a range that could maintain the bond, i.e., if the bond was not broken, we ran a computer-generated process to calculate the relationship between the amount of lithium ions arranged, i.e., capacity, and the expansion rate of the crystal structure due to relaxation. The expansion rate refers to the percentage increase in volume due to the arrangement of lithium ions, with the volume before lithium ions being taken as 100%.

[0034] Example 2 Silicon clathrate (Si clathrate) is a silicon clathrate in which one atom (approximately 3%) of 34 silicon atoms is replaced by aluminum. 33 The same processing as in Comparative Example 1 was performed by a computer, except that information on the crystal structure of Si-Al (Si-Si bond length) was acquired, and that in the processing to determine whether or not the bond would be broken, not only the length of the Si-Si bond but also the length of the Si-Al bond was used as the object of determination.

[0035] The software used for the first-principles calculation was VASP from MedeA, Inc. Calculations were performed using the exchange-correlation functional PBEsol and the pseudopotential PAW with a cutoff energy of 600 eV.

[0036] "result" In both the crystal structures subjected to the treatments in Examples 1 and 2, the bonds within the structure were not broken up until the capacity exceeded 1000 mAh / g.

[0037] The relationship between the capacity and the expansion coefficient of the crystal structure due to relaxation, calculated by the processes in Examples 1 and 2, is shown in Figure 1. As shown in Figure 1, the crystal structure evaluated in Example 2 had a region where the change in expansion coefficient with increasing capacity was small, i.e., a no-expansion region, up to approximately 450 mAh / g. In contrast, the crystal structure evaluated in Example 1 had a no-expansion region up to approximately 410 mAh / g. Note that, for example, at capacities around 450 mAh / g, the multiple volume expansion coefficients shown in Example 2 are due to differences in volume expansion coefficients between crystal structures with different aluminum substitution positions. Furthermore, it was confirmed that the crystal structure evaluated in Example 2 had a smaller expansion coefficient than the crystal structure evaluated in Example 1 in the higher capacity region than the no-expansion region. The evaluation results in these examples showed the same tendency as the actual evaluation results, and therefore the method of the present disclosure was found to be useful for discovering electrode active materials for lithium-ion batteries.

Claims

[Claim 1] Obtaining target crystal structure information from a structure database; generating structural information of an insertion structure in which lithium ions are arranged in a space within the crystal structure up to a predetermined amount; generating structural information of a relaxed structure obtained by relaxing the crystal structure based on first-principles calculations; determining whether bonds contained in the crystalline structure are broken in the relaxed structure; and When it is determined that the bond included in the crystal structure is not broken, calculating the relationship between the predetermined amount of the arranged lithium ions and the expansion rate of the crystal structure due to the relaxation; A method for searching for a new electrode active material, comprising causing a computer to execute a process including the steps of:

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