Battery material evaluation method

Abstract

To provide a battery material evaluation method that can evaluate an increase or decrease ratio of an abundance of a phase of interest in a battery material by a simple method.SOLUTION: A battery material evaluation method comprises: a step of XRD-measuring constituent components of a predetermined phase in a state (1) of a battery material; a step of XRD-measuring the constituent components of the predetermined phase in a state (2) of the battery material; a step of calculating a peak height A(1) and a peak height A(2) of a fitting curve obtained by fitting, with a Gaussian function, predetermined 2θ value peaks obtained by the XRD measurement of the constituent components of the predetermined phase in the state (1) and the state (2) of the battery material; and a step of relatively evaluating an increase rate or a decrease rate of the content of the constituent components of the predetermined phase in the state (2) of the battery material with respect to the content of the constituent components of the predetermined phase in the state (1) of the battery material by comparing the peak height A(1) and the peak height A(2) of the fitting curve.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a method for evaluating battery materials. [Background technology]

[0002] In recent years, with the rapid spread of information-related devices and communication devices such as personal computers, video cameras, and mobile phones, the development of batteries to be used as power sources for these devices has become important. Lithium-ion batteries have also attracted attention from the viewpoint of their high energy density. There is also a demand for improved energy density and battery characteristics for lithium secondary batteries in large-scale applications such as vehicle-mounted power sources and load leveling.

[0003] The quality of battery materials may change due to exposure to air during the manufacturing process or storage. Battery materials generally contain a main phase and a subphase, and some of the components that make up the subphase contain impurities. Conventionally, the content of components contained in these phases can be calculated from the integrated value of the X-ray diffraction peak obtained by XRD measurement (Patent Document 1, etc.). For this reason, XRD measurement is often used to evaluate the amount of each component when multiple phases are present. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2021-034205 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in order to accurately quantify battery materials using XRD measurements, it is necessary to analyze the peaks of interest using dedicated analysis software. Therefore, without analysis software, it was difficult to evaluate the amount of the phase of interest using the XRD measurement results. Therefore, it was difficult to evaluate the extent to which impurities were generated in the battery material due to exposure to the atmosphere, i.e., the increase or decrease in the amount of the phase of interest.

[0006] The present invention has been made to solve the above-mentioned problems, and aims to provide a method for evaluating a battery material that can easily evaluate the rate of increase or decrease in the amount of a phase of interest in a battery material. [Means for solving the problem]

[0007] The present invention, which has been completed based on the above findings, is defined in the following items 1 to 5. 1. A step of measuring the components of a predetermined phase in the battery material state (1) by XRD; A step of subjecting the constituent components of the predetermined phase in the state (2) of the battery material to XRD measurement; A step of fitting a peak at a predetermined 2θ value obtained by XRD measurement of a component of a predetermined phase in the battery material state (1) and the battery material state (2) with a Gaussian function, and calculating a peak height A(1) of the obtained fitting curve and a peak height A(2) of the fitting curve; a step of relatively evaluating an increase or decrease rate of the content of a component of a predetermined phase in the state (2) of the battery material relative to the content of the component of the predetermined phase in the state (1) of the battery material by comparing a peak height A(1) of the fitting curve with a peak height A(2) of the fitting curve; A method for evaluating battery materials, comprising: 2. The method for evaluating a battery material according to 1 above, wherein the predetermined phase is an impurity phase. 3. A method for evaluating a battery material as described in 2 above, comprising: relatively evaluating the rate of increase or decrease in the content of the constituent components of the impurity phase in the battery material state (2) relative to the content of the constituent components of the impurity phase in the battery material state (1), and then quantitatively evaluating the degree of deterioration of the battery material based on the rate of increase or decrease. 4. The method for evaluating a battery material according to any one of 1 to 3 above, wherein the battery material is a positive electrode active material, a negative electrode active material, or a solid electrolyte of an all-solid-state lithium ion battery. 5. The method for evaluating a battery material according to any one of 1 to 3 above, wherein the battery material is a positive electrode active material or a negative electrode active material of a liquid lithium ion battery. Effect of the Invention

[0008] According to the present invention, it is possible to provide a method for evaluating a battery material that can easily evaluate the rate of increase or decrease in the amount of a phase of interest in the battery material. [Brief description of the drawings]

[0009] [Figure 1] This shows XRD data (lower graph) and a fitting curve (upper graph) created by fitting the XRD data with a Gaussian function. [Diagram 2] 1 shows an XRD chart (left graph) according to an embodiment, XRD data (lower right graph) near the 2θ value peak corresponding to Li2CO3 in the XRD chart, and a fitting curve (upper right graph) created by fitting the XRD data with a Gaussian function. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Next, the embodiments of the present invention will be described in detail with reference to the drawings. It should be understood that the present invention is not limited to the following embodiments, and that appropriate changes and improvements in the design may be made based on the ordinary knowledge of those skilled in the art without departing from the spirit of the present invention.

[0011] <Evaluation methods for battery materials> The method for evaluating a battery material according to an embodiment of the present invention evaluates the increase or decrease rate of the amount of a target phase in a simple manner. The battery material is not particularly limited as long as it is a material having multiple phases, such as a main phase and a subphase. As such a battery material, for example, a positive electrode active material, a negative electrode active material, or a solid electrolyte of an all-solid-state lithium ion battery, or a positive electrode active material or a negative electrode active material of a liquid lithium ion battery, which will be described in detail later, can be used.

[0012] (Process 1) In the evaluation method of a battery material according to an embodiment of the present invention, first, the components of a predetermined phase in the battery material state (1) are measured by XRD. The battery material state (1) is a reference state for evaluation of the battery material in the battery material state (2) described below, and may be, for example, the state immediately after the battery material is produced, or the state after a predetermined period of time has elapsed since the battery material was produced.

[0013] The "predetermined phase" of the battery material may be any of a plurality of phases including a main phase and a subphase constituting the battery material. The main phase is a phase that occupies more than 50% of the volume of a plurality of phases constituting the battery material, and the subphase is a phase that exists in the portion excluding the main phase. For example, when the battery material is a solid electrolyte of an all-solid-state lithium-ion battery, the main phase is a phase composed of the elemental species of the main raw material LiGeVO, and the other impurity phases, for example, composed of Li2CO3 generated by exposure to the atmosphere, are the subphases, and any of these may be selected as the "predetermined phase."

[0014] The XRD measurement of the components of a predetermined phase is carried out, for example, by analyzing by powder X-ray diffraction method: XRD (θ / 2θ method) under the following conditions. X-ray diffraction equipment: Rigaku SmartLab ·Light source: CuKα line Voltage: 40kV ·Current: 30mA The conditions for the XRD measurement are not limited to those described above and can be appropriately adjusted depending on the type of battery material. However, the conditions for the XRD measurement performed for the battery material state (1) must be the same as the conditions for the XRD measurement performed for the battery material state (2) described below.

[0015] (Process 2) Next, the components of the predetermined phase in the battery material state (2) are measured by XRD. The battery material state (2) is preferably one that has been left for a certain period of time by exposure to the atmosphere or the like, or one whose composition has been changed by heat treatment or the like, compared to the battery material state (1) described above. That is, the battery material state (2) is preferably one in which the predetermined phase has undergone some compositional change compared to the battery material state (1). Furthermore, the "predetermined phase" in step 2 indicates the same phase as the "predetermined phase" in step 1.

[0016] Moreover, the conditions for the XRD measurement carried out for the battery material in state (2) must be the same as the conditions for the XRD measurement carried out for the battery material in state (1), as described above.

[0017] (Step 3) Next, a peak at a predetermined 2θ value obtained by XRD measurement of a component of a predetermined phase in the state (1) of the battery material is fitted with a Gaussian function, and the height A(1) of the peak of the obtained fitting curve is calculated. More specifically, as shown in the lower graph of FIG. 1, first, attention is paid to the data of the peak at the 2θ value (XRD data) corresponding to the component of the predetermined phase obtained by XRD measurement. This XRD data is raw data, and is depicted by dots as shown in the lower graph of FIG. 1. This XRD data is fitted with a Gaussian function to obtain a fitting curve (an approximation curve for a Gaussian distribution) as shown in the upper graph of FIG. 1.

[0018] The Gaussian function f(x) is a function shown in the following formula (1). In formula (1), σ is the standard deviation, μ is the average value, and d is the background. A is a constant obtained as a result of fitting with the Gaussian function, and represents the peak height of the fitting curve shown in the upper graph of FIG. 1.

[0019]

number

[0020] A known method can be used for fitting the Gaussian function. For example, the solver function of Microsoft Excel (registered trademark) (hereinafter also referred to as the Excel solver function) can be used to easily perform fitting the Gaussian function.

[0021] In addition, a peak at a predetermined 2θ value obtained by XRD measurement of a component of a predetermined phase in the battery material state (2) is fitted with a Gaussian function, and the peak height A(2) of the obtained fitting curve is calculated. Here, a fitting curve is obtained in the same manner as the fitting of the XRD data related to the battery material state (1) with a Gaussian function, and then the peak height A(2) is calculated. Note that the fitting using the Gaussian function related to the battery material state (2) and the calculation of the peak height A(2) of the fitting curve may be performed simultaneously with the fitting using the Gaussian function related to the battery material state (1) described above and the calculation of the peak height A(1) of the fitting curve.

[0022] (Step 4) Next, the peak height A(1) of the fitting curve is compared with the peak height A(2) of the fitting curve to relatively evaluate the increase or decrease rate of the content of the component of a specific phase in the battery material state (2) relative to the content of the component of a specific phase in the battery material state (1). The peak height A(1) of the fitting curve corresponds to the content of the component of a specific phase in the battery material state (1), and the peak height A(2) of the fitting curve corresponds to the content of the component of a specific phase in the battery material state (2). Therefore, if the peak height A(2) of the fitting curve is 10% higher than the peak height A(1) of the fitting curve, it can be evaluated that the content of the component of a specific phase in the battery material state (2) is similarly 10% higher than the content of the component of a specific phase in the battery material state (1). Conversely, when the peak height A(2) of the fitting curve is 10% lower than the peak height A(1) of the fitting curve, it can be evaluated that the content of a component of a specified phase in the battery material state (2) is similarly 10% lower than the content of the component of a specified phase in the battery material state (1).

[0023] As described above, the method for evaluating a battery material according to an embodiment of the present invention makes it possible to relatively evaluate, in a simple manner, the rate of increase or decrease in the content of a component of a predetermined phase in a battery material state (2) relative to the content of the component of a predetermined phase in a battery material state (1) by comparing the peak height A(1) of the fitting curve with the peak height A(2) of the fitting curve.

[0024] In addition, in addition to state (1) and state (2), the state of the battery material may be measured in a plurality of states, such as state (3), state (4), and state (5), which are further changed. For example, when state (3) and state (4) of the battery material are to be measured, the components of a specific phase in state (3) and state (4) of the battery material are subjected to XRD measurement in the same manner as described above, and the peaks of a specific 2θ value obtained by the XRD measurement are fitted with a Gaussian function, and the peak height A(3) of the fitting curve obtained and the peak height A(4) of the fitting curve are calculated. Then, by comparing the peak heights (3) and (4) of the fitting curve with the peak height A(1) of the fitting curve, the increase or decrease rate of the content of the component of the specific phase in the battery material in state (3) and state (4) relative to the content of the component of the specific phase in state (1) of the battery material can be relatively evaluated in a simple manner.

[0025] In addition, in the battery material evaluation method according to the embodiment of the present invention, when a predetermined phase is an impurity phase, the degree of deterioration of the battery material can be quantitatively evaluated by relatively evaluating the increase or decrease rate of the content of the components of the impurity phase in the battery material state (2) relative to the content of the components of the impurity phase in the battery material state (1). For example, when the battery material is a solid electrolyte of an all-solid-state lithium-ion battery, the phase composed of the elemental species of the main raw material LiGeVO is set as the main phase, and the other impurity phases, for example, the impurity phases composed of Li2CO3 generated by exposure to the atmosphere, are set as the "predetermined phase". At this time, the battery material state (1) is the solid electrolyte immediately after production, and the battery material state (2) is the solid electrolyte exposed to the atmosphere for a predetermined period of time. Then, in the above-mentioned step 4, when the height A(2) of the peak of the fitting curve is 10% higher than the height A(1), it can be evaluated that the content of the components of the impurity phase in the battery material state (2) is similarly 10% higher than the content of the components of the impurity phase in the battery material state (1), and it can be evaluated that the quality of the solid electrolyte has deteriorated by that amount. Conversely, if some processing is performed on a battery material in state (1) to change it to state (2) and the height A(2) of the peak of the fitting curve is 10% lower than the height A(1), it can be evaluated that the content of the constituent components of the impurity phase in the battery material in state (2) is similarly 10% lower than the content of the constituent components of the impurity phase in the battery material in state (1), and it can be evaluated that the quality of the solid electrolyte has been improved by that amount.

[0026] (Battery materials) As described above, the battery material is not particularly limited as long as it has multiple phases such as a main phase and a subphase. Examples of such battery materials include a positive electrode active material, a negative electrode active material, or a solid electrolyte of an all-solid-state lithium ion battery, or a positive electrode active material or a negative electrode active material of a liquid lithium ion battery.

[0027] The positive electrode active material of the all-solid-state lithium ion battery or the liquid lithium ion battery is not particularly limited, and known materials such as lithium metal composite oxides can be used. The composition of the positive electrode active material is, for example, the composition formula: Li a Ni b Mn c Co d M e O2 (wherein 1.00≦a≦1.08, 0≦b≦0.90, b+c+d+e=1.0, and M is one or more selected from Sc, Ti, V, Cr, Fe, Cu, Zn, Ga, Ge, Al, Bi, Sn, Mg, Ca, B, and Zr).

[0028] The negative electrode active material of the all-solid-state lithium ion battery or the liquid lithium ion battery is not particularly limited, and known materials can be used. The negative electrode active material can be, for example, a carbon material, specifically, artificial graphite, graphite carbon fiber, resin-sintered carbon, pyrolytic vapor-grown carbon, coke, mesocarbon microbeads (MCMB), furfuryl alcohol resin-sintered carbon, polyacene, pitch-based carbon fiber, vapor-grown carbon fiber, natural graphite, non-graphitizable carbon, or a mixture thereof.

[0029] The solid electrolyte of the all-solid-state lithium ion battery is not particularly limited, and any known solid electrolyte can be used. For example, the solid electrolyte has the composition formula: Li a A x M y O4 (wherein A is Ge, Si or Ti, M is V, P or As, 3.25≦a≦3.75, 0.30≦x≦0.75, and 0.25≦y≦0.70). The solid electrolyte may be, for example, represented by the composition formula: Li 7-3x-y A x La3Zr 2-y D y O 12 (wherein A is Al or Ga, D is Ta or Nb, 0≦x≦2.0, and 0≦y≦1.0), or the composition formula: Li 1+x Al x A 2-x It may be represented by the formula (PO4)3, where A is Ti or Ge, and 0≦x≦1.0. EXAMPLES

[0030] The following examples are provided to provide a better understanding of the present invention and its advantages, but the present invention is not limited to these examples.

[0031] <Example 1> The solid electrolyte in all-solid-state lithium-ion batteries is Li 3.5 Ge 0.5 V 0.5 O4 was used as the battery material to be evaluated. 3.5 Ge 0.5 V 0.5 When O4 is left in an air atmosphere, it reacts with water vapor in the air to produce LiOH. LiOH further reacts with carbon dioxide in the air to produce Li2CO3. This Li2CO3 forms an impurity phase in the solid electrolyte. In this example, the solid electrolyte Li 3.5 Ge 0.5 V 0.5 The rate of increase or decrease in the content of Li2CO3, an impurity phase that occurs in the solid electrolyte, was evaluated when O4 was left in an air atmosphere for a specified period of time.

[0032] First, Li 3.5 Ge 0.5 V 0.5 0.5g of O4 powder was weighed out, placed in a beaker as a sample, and left in a thermostatic chamber for 7 days. The temperature inside the thermostatic chamber was set to 30℃ and the relative humidity to 40%RH, which were conditions similar to the atmosphere. A total of eight samples were taken from the thermostatic chamber just before the test in the thermostatic chamber, and after 1 hour, 2 hours, 4 hours, 8 hours, 1 day, 3 days, and 7 days from the start of the test. They were lightly crushed using a mortar and pestle, and then each was measured by XRD.

[0033] The XRD measurement was carried out by powder X-ray diffraction method: XRD (θ / 2θ method) under the following conditions. X-ray diffraction equipment: Rigaku SmartLab ·Light source: CuKα line Voltage: 40kV ·Current: 30mA The graph on the left side of Figure 2 shows the XRD chart of a sample at the start of the test that was not exposed to the air, the XRD chart of a sample that was exposed to the air in a constant temperature and humidity chamber for three days, and the XRD chart of a sample that was exposed to the air in a constant temperature and humidity chamber for seven days.

[0034] In the XRD chart obtained by XRD measurement of a total of eight samples immediately before the test in the constant temperature and humidity chamber, and 1 hour, 2 hours, 4 hours, 8 hours, 1 day, 3 days, and 7 days after the start of the test, a Gaussian function was fitted to the 2θ value peak corresponding to Li2CO3 that constitutes the impurity phase. The graph in the lower right of Figure 2 shows an XRD chart enlarged by superimposing the measurement results of three samples for the XRD data (raw data) near the 2θ value peak corresponding to Li2CO3 in the graph on the left of Figure 2. The graph in the upper right of Figure 2 is the fitting curve obtained by fitting this XRD data with a Gaussian function.

[0035] The Gaussian function: f(x) is a function shown in the following formula (1). In formula (1), σ is the standard deviation, μ is the average value, and d is the background. A is a constant obtained as a result of fitting with the Gaussian function, and represents the peak height of the fitting curve shown in the upper graph of Figure 1. The Gaussian function was fitted using the Solver function of Excel.

[0036]

number

[0037] In this manner, the peak height A of the fitting curve was calculated for a total of eight samples, immediately before the test in the constant temperature and humidity chamber (no exposure to air), and 1 hour, 2 hours, 4 hours, 8 hours, 1 day, 3 days, and 7 days after the start of the test. In addition, the increase rate (%) of the peak height A of the fitting curve relative to the sample immediately before the test was calculated. The evaluation results are shown in Table 1.

[0038] [Table 1]

[0039] According to Table 1, the peak height A of the fitting curve of the sample immediately before the test in the constant temperature and humidity chamber (without air exposure) is 181% higher than the peak height A (=41.4) of the fitting curve of the sample after 1 hour. Therefore, it can be seen that the powder of the solid electrolyte used in this example increases the impurity Li2CO3 by 1 hour of air exposure, and the content of Li2CO3 in the impurity phase increases by 181%. In addition, it was found that the content of Li2CO3 in the impurity phase increases by 264% after 2 hours, and the content of Li2CO3 in the impurity phase continues to increase with time, increasing by 866% after 7 days. As a result, it was confirmed that the content of impurities increases with time, and this made it possible to quantitatively evaluate the deterioration of the battery material. As described above, it can be seen that the method for evaluating a battery material according to the present invention makes it possible to evaluate, in a simple manner, the rate of increase or decrease in the amount of a phase of interest in a battery material.

Claims

1. A step of measuring the components of a predetermined phase in the battery material state (1) by XRD; A step of measuring the components of the predetermined phase in the state (2) of the battery material by XRD; A step of fitting a peak at a predetermined 2θ value obtained by XRD measurement of a component of a predetermined phase in the battery material state (1) and the battery material state (2) with a Gaussian function, and calculating a peak height A(1) of the fitting curve and a peak height A(2) of the fitting curve; a step of relatively evaluating an increase or decrease rate of a content of a component of a predetermined phase in the state (2) of the battery material relative to an content of a component of the predetermined phase in the state (1) of the battery material by comparing a peak height A(1) of the fitting curve with a peak height A(2) of the fitting curve; A method for evaluating battery materials, comprising:

2. The method for evaluating a battery material according to claim 1 , wherein the predetermined phase is an impurity phase.

3. 3. The method for evaluating a battery material according to claim 2, further comprising: relatively evaluating an increase or decrease rate of a content of a component of an impurity phase in a state (2) of the battery material relative to a content of the component of an impurity phase in a state (1) of the battery material; and quantitatively evaluating a degree of deterioration of the battery material based on the increase or decrease rate.

4. The method for evaluating a battery material according to any one of claims 1 to 3, wherein the battery material is a positive electrode active material, a negative electrode active material, or a solid electrolyte of an all-solid-state lithium ion battery.

5. The method for evaluating a battery material according to any one of claims 1 to 3, wherein the battery material is a positive electrode active material or a negative electrode active material of a liquid lithium ion battery.

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