Retrieval method for novel electrode active material

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 carried out. For example, in the automobile industry, development of batteries for use in electric vehicles or hybrid vehicles is underway. Silicon is also 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. On the other hand, silicon electrode active materials have a problem of large expansion during charging. It is known that the expansion during charging can be suppressed by using a silicon clathrate electrode active material as the silicon electrode active material.

[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 the expansion of silicon clathrate electrode active materials during charging. In response to this demand, technology has 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 crystal phase, containing Na element, Si element, and M element which is a metal element having an ionic radius larger than that of Si element, and the ratio of M element to the total of Si element and M element is 0.1 atm% or more and 5 atm% or less.

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

[0007] For example, Non-Patent Document 1 discloses a method for calculating the energy when lithium ions are 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] In Non-Patent Document 1, the calculation is performed only from the viewpoint of the energy when lithium ions are inserted, targeting silicon that does not have a space in the crystal structure. In contrast, there is a need to develop a method for searching for new electrode active materials by optionally combining with machine learning, targeting materials that have a space in the crystal structure, such as silicon clathrate.

[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 or not a bond contained in the crystal structure is broken in the relaxed structure; and calculating a relationship between the predetermined amount of the arranged lithium ions and an expansion rate of the crystal structure due to the relaxation when it is determined that the bonds included in the crystal structure are not broken; A method for searching for a new electrode active material, comprising causing a computer to execute a process including the steps of: Effect 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 in the crystal. [Brief description 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 PREFERRED EMBODIMENTS

[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 has 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 a 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 be broken in the relaxed structure; and, if it is determined that the bonds contained in the crystal structure will not be broken, calculating the relationship between the predetermined amount of arranged lithium ions and the expansion coefficient 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 in which lithium ions can be arranged. For example, when the electrode active material is a negative electrode active material, the crystal structure may be a silicon clathrate that may be substituted with a specific element, and a Li 2 B 3 PO 8 An example of the specific element is aluminum.

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

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

[0022] The "predetermined amount" means an amount at which the capacity shows a predetermined value when the amount of lithium ions inserted is converted into the capacity of the battery. Here, the "predetermined value" may be 100mAh / g or more, 300mAh / g or more, 500mAh / g or more, 600mAh / g or more, 700mAh / g or more, 800mAh / g or more, or 900mAh / g or more, and may be 2000mAh / g or less, 1700mAh / g or less, 1500mAh / g or less, 1300mAh / g or less, 1200mAh / g or less, or 1100mAh / 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 may be arranged simultaneously, 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] As software for first-principles calculations, VASP from MedeA Inc. can be used.

[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 for changing the position of each atom in the molecular structure model so that the energy of the entire molecular structure model in the structure before lithium ions are arranged is set as an initial value and this energy becomes a minimum value.

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

[0028] The disclosed method includes having a computer execute a process to determine whether bonds contained in the crystal 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 will break 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 processing of the present disclosure and the expansion coefficient of the structure, thereby predicting a crystal structure with a small expansion coefficient, etc., in an optional step of the method of the present disclosure. EXAMPLES

[0033] Computer Processing Example 1 From the structure database, silicon clathrate (Si 34 ) crystal structure information was obtained, and structural information of an insertion structure was generated in which lithium ions were randomly arranged one atom at a time in the space within the crystal structure until the capacity exceeded 1000mAh / g. Then, based on first-principles calculations, the energy of the entire molecular structure model in the structure before the lithium ions were set as an initial value, and the position of each atom in the molecular structure model in the structure after the lithium ions were arranged was changed so that this energy would take a minimum value, thereby generating structural information of a relaxed structure in which the crystal structure was relaxed. Then, a process was performed to determine whether the length of the Si-Si bond contained in the relaxed structure was within a range in which the bond could be maintained. If the length of the bond was within a range in which the bond could be maintained, that is, if the bond was not broken, a process was performed to calculate the relationship between the amount of lithium ions arranged, i.e., the capacity, and the expansion rate of the crystal structure due to relaxation. The expansion rate means the rate of increase in volume due to the arrangement of lithium ions when the volume before the lithium ions were set to 100%.

[0034] Example 2 Silicon clathrate (Si clathrate) is a material in which one atom (approximately 3%) of 34 silicon atoms is replaced by aluminum. 33 Al 1The same processing as in Comparative Example 1 was performed by a computer, except that information on the crystal structure of (a) was obtained, and that in the process of determining whether or not a 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 a determination subject.

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

[0036] "result" In both of 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 rate of the crystal structure due to relaxation, calculated by the treatment in Examples 1 and 2, is shown in FIG. 1. As shown in FIG. 1, in the crystal structure evaluated in Example 2, the region where the change in the expansion rate with increasing capacity is small, that is, the non-expansion region, was up to about 450 mAh / g. In contrast, in the crystal structure evaluated in Example 1, the non-expansion region was up to about 410 mAh / g. Note that, for example, in the capacity of about 450 mAh / g, the reason why multiple volume expansion rates are shown in Example 2 is due to the fact that there is a difference in the volume expansion rate in crystal structures with different aluminum substitution positions. Furthermore, it was confirmed that in the region of higher capacity than the non-expansion region, the crystal structure evaluated in Example 2 had a smaller expansion rate than the crystal structure evaluated in Example 1. The evaluation results in these examples showed the same tendency as the actual evaluation results, and therefore, it was recognized that the method of the present disclosure is useful as a method for searching for 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 or not a bond contained in the crystal structure is broken in the relaxed structure; and calculating a relationship between the predetermined amount of the arranged lithium ions and an expansion rate of the crystal structure due to the relaxation when it is determined that the bonds included in the crystal structure are not broken; 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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