Charge / discharge characteristic evaluation method

Abstract

To provide a charge / discharge characteristic evaluation method for an active material which can evaluate a charge / discharge characteristic of a minute active material used as an electrode material of a secondary battery.SOLUTION: A charge / discharge characteristic evaluation method for an active material according to an aspect of the present disclosure is a method for evaluating a charge / discharge characteristic of an active material used for a positive electrode or a negative electrode of a battery. The method comprises: a step of arranging an active material in an electrolytic substance contacting a counter electrode member; a step of connecting an electrode of a charge / discharge device to a probe of a probe microscope and the counter electrode member; a step of bringing the probe into contact with the active material arranged in the electrolytic substance; a step of charging / discharging the active material in contact with the probe by the charge / discharge device; and a step of measuring at least one of a voltage and a current between the active material and the counter electrode member that change due to the charging / discharging.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a method for evaluating charge and discharge characteristics. [Background technology]

[0002] In recent years, the use of rechargeable secondary batteries has increased in a wide range of fields, including electronic devices, automobiles, and renewable energy. These secondary batteries are used in a variety of environments, including as relatively small-capacity power sources for relatively small devices such as communication devices and home appliances, as well as relatively large-capacity power sources for transportation, household use, and industrial applications. One way to obtain batteries that can be reliably charged and discharged in a variety of environments for various applications is to evaluate the characteristics of the active materials used in the battery electrodes. One known method for such evaluation is to evaluate the discharge characteristics of active materials using an optical microscope and a micromanipulator (Japanese Patent Publication No. 5743011). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 5743011 Summary of the Invention [Problem to be solved by the invention]

[0004] In Patent Document 1, a glass separator onto which an electrode material (active material) has been sprayed is fixed in an electrolyte solution, and while viewing images from a CCD camera attached to a microscope, a micromanipulator is operated to bring the tip of a probe into contact with a single particle of the active material to establish electrical contact, thereby measuring the discharge capacity of the single particle. The average particle diameter of the single particle is said to be 10 to 20,000 nm, but in recent years, efforts have been made to miniaturize active material particles, making observation with an optical microscope sometimes difficult. Furthermore, Patent Document 1 does not mention evaluating the charging characteristics of the active material.

[0005] In view of the above-mentioned circumstances, the present disclosure aims to provide a method for evaluating the charge-discharge characteristics of an active material that can easily evaluate the charge-discharge characteristics of a minute active material used as an electrode material for a secondary battery. [Means for solving the problem]

[0006] A method for evaluating the charge / discharge characteristics of an active material according to one embodiment of the present disclosure that solves the above-described problems is a method for evaluating the charge / discharge characteristics of an active material used in a positive electrode or a negative electrode of a battery, and includes the steps of: placing the active material in an electrolyte that is in contact with a counter electrode member; connecting an electrode of a charger / discharger to a probe of a probe microscope and the counter electrode member; abutting the probe against the active material placed in the electrolyte; charging and discharging the active material that the probe is in contact with using the charger / discharger; and measuring at least one of the voltage and current between the active material and the counter electrode member that change due to charging and discharging. [Effects of the Invention]

[0007] The method for evaluating the charge-discharge characteristics of an active material according to the present disclosure can evaluate the charge-discharge characteristics of minute active materials used as electrode materials for secondary batteries. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic front perspective view showing a measurement unit used in a method for evaluating charge-discharge characteristics of an active material according to one embodiment of the present disclosure. [Figure 2] FIG. 2 is a graph showing the charge / discharge rate of a single particle of the negative electrode active material. [Figure 3] FIG. 3 is a graph showing the voltage change when a single particle of the positive electrode active material is charged and discharged. DETAILED DESCRIPTION OF THE INVENTION

[0009] [Description of the embodiments of the present disclosure] First, embodiments of the present disclosure will be listed and described.

[0010] (1) A method for evaluating the charge-discharge characteristics of an active material according to one embodiment of the present disclosure is a method for evaluating the charge-discharge characteristics of an active material used in a positive electrode or a negative electrode of a battery, and includes the steps of: placing the active material in an electrolyte in contact with a counter electrode member; connecting an electrode of a charger / discharger to a probe of a probe microscope and the counter electrode member; bringing the probe into contact with the active material placed in the electrolyte; charging and discharging the active material in contact with the probe using the charger / discharger; and measuring at least one of the voltage and current between the active material and the counter electrode member, which change due to charging and discharging.

[0011] The method for evaluating the charge-discharge characteristics of an active material (hereinafter simply referred to as the "evaluation method") uses a probe microscope, so that even if the active material is a microparticle, the probe can be easily observed while being applied to the active material. Furthermore, the probe that is applied to the active material and the counter electrode member that is in contact with the electrolyte in which the active material is disposed are used as electrodes for charging and discharging the active material, so that at least one of the voltage and current between the active material and the counter electrode member, which change with charging and discharging, can be easily measured. This makes it easy to evaluate the charge-discharge characteristics of the active material.

[0012] (2) In the above (1), the active material may be a single active material particle or an aggregate formed by compacting multiple active material particles. That is, the evaluation method is suitable for evaluating the charge-discharge characteristics of a single-particle active material or an aggregate formed by compacting multiple active material particles.

[0013] (3) In the above (2), the active material may be an aggregate formed by aggregating or consolidating active material particles or the aggregates. That is, the evaluation method is suitable for evaluating the charge-discharge characteristics of an active material in the form of an aggregate formed by aggregating or consolidating active material particles or the aggregates.

[0014] [Details of the embodiments of the present disclosure] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings.

[0015] [Method for evaluating charge / discharge characteristics of active materials] A method for evaluating the charge-discharge characteristics of an active material according to one embodiment of the present disclosure is a method for evaluating the charge-discharge characteristics of an active material used in a positive electrode or a negative electrode of a battery, and includes the steps of: placing the active material in an electrolyte that is in contact with a counter electrode member; connecting an electrode of a charger / discharger to a probe of a probe microscope and the counter electrode member; bringing the probe into contact with the active material placed in the electrolyte; charging and discharging the active material in contact with the probe using the charger / discharger; and measuring at least one of the voltage and current between the active material and the counter electrode member that change due to charging and discharging.

[0016] <Measurement unit> 1, the evaluation method is carried out using a measurement unit 1 including a counter electrode member 10, an electrolyte 20 in contact with the counter electrode member 10, a probe 30 of a probe microscope that is brought into contact with the active material E, and a charger / discharger 40 for charging and discharging the active material E. The charger / discharger 40 is preferably capable of measuring at least one of voltage and current, or the measurement unit 1 may further include at least one of a voltage measuring device and a current measuring device (hereinafter, these will be collectively referred to as measuring devices). Note that in FIG. 1, the probe microscope, voltage measuring device, and current measuring device, excluding the probe 30, are not shown.

[0017] The counter electrode member 10 is configured to function as a negative electrode if the active material E is a positive electrode active material, and as a positive electrode if the active material E is a negative electrode active material. The counter electrode member 10 may, for example, include a known electrode mixture and a current collector. Examples of the electrode mixture include a coated sheet containing an active material and having voids for the liquid electrolyte (electrolyte solution) 20 to penetrate, and containing a conductive aid such as acetylene black and a binder such as polyvinylidene fluoride. Examples of the current collector include a metal foil, such as aluminum foil when used as a positive electrode and copper foil when used as a negative electrode.

[0018] The electrolyte 20 is not particularly limited and may be a known electrolyte used in secondary batteries, and may be in liquid or solid form. Examples of liquid electrolytes include those containing a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. Examples of solid electrolytes include materials (various solid electrolytes) that are ion-conductive and solid at room temperature.

[0019] When the electrolyte 20 is a liquid, it may be placed in a container (tank) 50 together with the counter electrode member 10 (see FIG. 1), or the electrolyte may be dropped onto a flat counter electrode member. When the electrolyte is a solid, the electrolyte and the counter electrode member may be arranged so as to have contact points.

[0020] When the electrolyte 20 is a liquid, the active material E is preferably arranged so that it is partially or completely submerged in the electrolyte 20 and so that the active material E and the counter electrode member 10 do not come into contact with each other. A non-conductive member may be arranged as a separator between the active material E and the counter electrode member 10 in the electrolyte 20 to prevent them from coming into contact with each other. When the electrolyte is a solid, the electrolyte and the active material are preferably arranged so that they have contact with each other and so that the active material and the counter electrode member do not come into contact with each other.

[0021] The container 50 is not particularly limited, and may be formed of a conductive material or a non-conductive material. If the container 50 is formed of a conductive material, the counter electrode member 10 may be placed in contact with the container 50, and one electrode of the charger / discharger 40 and the measuring device may be connected thereto. If the container 50 is formed of a non-conductive material, the one electrode may be connected to the counter electrode member 10. That is, the connection between the one electrode and the counter electrode member 10 may be direct or indirect, as long as electrical conduction is achieved.

[0022] The probe microscope is not particularly limited, and a known probe microscope may be used. The charger / discharger 40 is not particularly limited, and a known charger / discharger may be used. The probe 30 of the probe microscope is connected to the charger / discharger 40 and the other electrode of the measuring device, and is configured to function as an electrode for charging / discharging the active material E and for measuring the voltage and current.

[0023] <Active material> The active material E is not particularly limited as long as it is an electrode material used for the positive or negative electrode of a secondary battery, and examples thereof include carbon-based materials and lithium titanate, which are negative electrode active materials for lithium ion batteries, lithium-containing metal oxides and lithium oxoacid salt compounds, which are positive electrode active materials for lithium ion batteries, etc. Alternatively, the active material E may be a known or unknown substance for which the possibility of use as an electrode material is to be evaluated.

[0024] Moreover, the active material E may be one extracted by disassembling a secondary battery, or may be one (in a material state) prior to being used in a secondary battery.

[0025] The active material E contacted by the probe 30 may be a single active material particle or a mass formed by compacting multiple active material particles. Alternatively, it may be an aggregate formed by consolidating or compacting active material particles or the masses. That is, the active material E may be a single particle, a mass formed by artificially applying an external force to multiple single particles, an aggregate formed by spontaneous (non-artificial) aggregation of multiple single particles, an artificial or non-artificial aggregation of multiple such masses or multiple such aggregates, or an artificial or non-artificial aggregation of two or more of the single particles, the masses, and the aggregates, each consisting of one or more of the single particles, the masses, and the aggregates. Figure 1 shows a single-particle active material E. Note that Figure 1 is a schematic diagram for illustrative purposes, and the shape and scale of each component (member) do not accurately reflect the actual components.

[0026] The upper limit of the average particle diameter of the aggregates that come into contact with probe 30 is not particularly limited and may be 1000 μm, 500 μm, or 200 μm. The lower limit of the average particle diameter of the aggregates is not particularly limited and may be 1.0 μm, 3.0 μm, or 5.0 μm. The average particle diameter refers to the value based on the 50% cumulative volume (D50 value) measured using a laser scattering particle size distribution analyzer.

[0027] The upper limit of the average particle size of the agglomerates that come into contact with the probe 30 is not particularly limited and may be 200 μm or 100 μm. The lower limit of the average particle size of the agglomerates is not particularly limited and may be 0.5 μm, 1.5 μm, or 3.0 μm.

[0028] The upper limit of the average particle diameter of the single particle that comes into contact with the probe 30 is not particularly limited and may be 100 μm or 50 μm. The lower limit of the average particle diameter of the single particle is not particularly limited and may be 0.01 μm or 0.1 μm.

[0029] <Placement process> In the disposing step, the active material E is disposed on the electrolyte 20 in contact with the counter electrode member 10. That is, the disposing step includes a procedure of bringing the electrolyte 20 into contact with the counter electrode member 10, and a procedure of disposing the active material E on the electrolyte 20 in contact with the counter electrode member 10.

[0030] <Connection process> In the connecting step, the electrodes of the charger / discharger 40 are connected to the probe 30 of the probe microscope and the counter electrode member 10. The order of this connecting step and the above-mentioned placing step does not matter. That is, the charger / discharger 40 may be connected to the counter electrode member 10 that is in contact with the electrolyte 20, or the counter electrode member 10 connected to the charger / discharger 40 may be brought into contact with the electrolyte 20.

[0031] <Contacting process> In the contacting step, probe 30 is contacted with active material E placed in electrolyte 20. This evaluation method uses a probe microscope, so it is possible to easily and reliably contact probe 30 with active material E while observing active material E. Probe microscopes have contact pressure feedback control that maintains contact (a state of contact) between the probe and the object being observed, so it is possible to maintain contact between probe 30 and active material E while suppressing changes in the contact pressure of probe 30 with active material E. By contacting probe 30, which is connected to charger / discharger 40, with active material E, it is possible to bring active material E into a state where it can be charged and discharged, and it is also possible to simultaneously observe the surface of active material E.

[0032] <Charging and discharging process> In the charging / discharging step, the active material E in contact with the probe 30 is charged / discharged by a charger / discharger 40. The charger / discharger 40 is preferably capable of passing minute currents of nanoamperes [nA] or picoamperes [pA], and the wiring and terminals connecting the charger / discharger 40 to the counter electrode member 10 and the probe 30 are also preferably adjusted to pass minute currents.

[0033] The voltage during the charge and discharge is not particularly limited and may be appropriately selected depending on the embodiment of the active material E, etc. The upper limit of the voltage may be, for example, 10.0 V, 8.5 V, or 7.0 V. The lower limit of the voltage may be, for example, −10.0 V, −5.0 V, or 0 V. The current during the charge and discharge is not particularly limited and may be appropriately selected depending on the embodiment of the active material E, etc. The upper limit of the current may be, for example, 10 μA, 1 μA, 100 nA, or 10 nA. The lower limit of the current may be, for example, 0.01 pA, 0.1 pA, or 1.0 pA.

[0034] <Measurement process> In the measuring step, at least one of the voltage and current between the active material E and the counter electrode member 10, which change with charge and discharge, is measured. By measuring the voltage and current during charge and discharge, it is possible to evaluate the charge and discharge characteristics of the active material E. This evaluation method uses a probe 30 of a probe microscope connected to a charger / discharger 40, so that the probe 30 can be easily brought into contact with a single-particle active material E having a particle size of, for example, less than 10 μm to charge and discharge the material.

[0035] [Other embodiments] The above-described embodiments do not limit the configuration of the present invention. Therefore, the above-described embodiments may include omissions, substitutions, or additions of components based on the description in this specification and common general technical knowledge, and all of these should be construed as falling within the scope of the present invention. [Example]

[0036] The present disclosure will be described in more detail below with reference to examples, but the present disclosure is not limited to these examples.

[0037] [Example 1] A single particle of graphite negative electrode active material was placed in electrolyte 20 of measurement unit 1, and the charge rate was measured when charging and discharging. The results are shown in Figure 2. In Figure 2, the graph line for 1.0 C (dashed line) overlaps with the graph line for 1.0 C (second time).

[0038] Figure 2 shows that the discharge curves at low rates (0.5C, 1.0C) show multiple plateaus at low voltages, which is thought to indicate a stage structural change specific to graphite. As the rate increases, a decrease in capacity is also observed, which is thought to be a trend similar to that of general rate characteristics.

[0039] [Example 2] A single particle of a positive electrode active material (NMC positive electrode active material) primarily composed of nickel, manganese, and cobalt was placed in the electrolyte 20 of the measurement unit 1, and the voltage was measured when the material was charged and discharged at 6 pA. The particle size of the single particle was approximately 4.5 μm. The results are shown in Figure 3.

[0040] Figure 3 shows that there is a difference in capacity between charging and discharging. This is presumably due to a side reaction occurring during charging, which causes a decrease in capacity during discharging.

[0041] 2 and 3 suggest that this evaluation method makes it possible to easily and accurately evaluate the charge-discharge characteristics even of single-particle active materials. [Industrial Applicability]

[0042] The evaluation method of the present disclosure can evaluate the charge / discharge characteristics of active materials used in electrode materials for secondary batteries, and is therefore suitable for use in evaluating battery characteristics at battery development and manufacturing sites, etc. [Explanation of symbols]

[0043] 1 measuring unit 10 Counter electrode member 20 Electrolytes 30 probes 40 Charger / discharger 50 containers E active material

Claims

1. A method for evaluating the charge-discharge characteristics of an active material used in a positive electrode or a negative electrode of a battery, comprising: disposing an active material in an electrolyte in contact with a counter electrode member; connecting electrodes of a charger / discharger to the probe of the probe microscope and the counter electrode member; contacting the probe with an active material disposed in the electrolyte; a step of charging and discharging the active material in contact with the probe by the charger / discharger; measuring at least one of the voltage and current between the active material and the counter electrode member, which change due to charging and discharging; A method for evaluating the charge-discharge characteristics of an active material, comprising:

2. 2. The method for evaluating charge-discharge characteristics of an active material according to claim 1, wherein the active material is a single active material particle or a mass obtained by compacting a plurality of active material particles.

3. 3. The method for evaluating charge-discharge characteristics of an active material according to claim 2, wherein the active material is an aggregate obtained by aggregating or compressing active material particles or the lumps.

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