Charge / discharge characteristics 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-discharge characteristics.

Background Art

[0002] In recent years, the use of rechargeable secondary batteries has been increasing in many fields such as electronic devices, automobiles, and renewable energy. Such secondary batteries are used as power sources with relatively small capacities for relatively small devices such as communication devices and home appliances, or may also be used as power sources with relatively large capacities for transportation, household, or industrial use, and their usage environments are diverse. In order to obtain a battery that can be stably charged and discharged in various environments for each application, the characteristics of the active material used in the battery electrodes may be evaluated. As a method for such evaluation, a method for evaluating the discharge characteristics of an active material using an optical microscope and a micromanipulator is known (Japanese Patent No. 5743011).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In Patent Document 1, a glass separator coated with an electrode material (active material) is fixed in an electrolytic solution, and while observing the image of 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 set to 10 to 20000 nm, but in recent years, the active material particles have been miniaturized, and it may become difficult to observe them with an optical microscope. Further, in Cited Document 1, evaluation of the charging characteristics of the active material is not mentioned.

[0005] In light of the circumstances described above, this 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 aspect of the present disclosure, which solves the above problems, is a method for evaluating the charge-discharge characteristics of an active material used in the positive or negative electrode of a battery, comprising the steps of: placing the active material in contact with an electrolytic material in contact with a counter electrode member; connecting the probe of a probe microscope and the electrodes of a charger / discharger to the counter electrode member; bringing the probe into contact with the active material placed in the electrolytic material; 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. [Effects of the Invention]

[0007] The method for evaluating the charge-discharge characteristics of active materials described herein can evaluate the charge-discharge characteristics of minute active materials used as electrode materials for secondary batteries. [Brief explanation of the drawing]

[0008] [Figure 1] Figure 1 is a schematic front perspective view showing a measurement unit used in a method for evaluating the charge-discharge characteristics of an active material, which is one embodiment of the present disclosure. [Figure 2] Figure 2 is a graph showing the charge-discharge rate of a single particle of the negative electrode active material. [Figure 3] Figure 3 is a graph showing the voltage change when a single particle of the positive electrode active material is charged and discharged. [Modes for carrying out the invention]

[0009] [Description of Embodiments in this Disclosure] First, the embodiments of this disclosure will be listed and described.

[0010] (1) A method for evaluating the charge-discharge characteristics of an active material according to one aspect of the present disclosure is a method for evaluating the charge-discharge characteristics of an active material used in the positive or negative electrode of a battery, comprising the steps of: placing the active material in contact with an electrolytic material in contact with a counter electrode member; connecting the probe of a probe microscope and the electrodes of a charger / discharger to the counter electrode member; bringing the probe into contact with the active material placed in the electrolytic material; 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.

[0011] The method for evaluating the charge-discharge characteristics of the active material (hereinafter also simply referred to as the "evaluation method") uses a probe microscope, allowing for easy observation and contact of the probe even if the active material consists of minute particles. Furthermore, since the probe that contacts the active material and the counter electrode member that contacts the electrolytic material on which the active material is located serve as electrodes for charging and discharging the active material, at least one of the voltage and current between the active material and the counter electrode member, which change due to charging and discharging, can be easily measured. For this reason, the charge-discharge characteristics of the active material can be easily evaluated.

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

[0013] (3) In (2) above, the active material may be active material particles or aggregates formed by assembling or compacting the above-mentioned aggregates. That is, this evaluation method is suitable for the charge-discharge characteristics of the active material, whether it be active material particles or aggregates formed by assembling or compacting the above-mentioned aggregates.

[0014] [Details of the embodiments of this disclosure] The embodiments of this disclosure will be described in detail below with reference to the drawings.

[0015] [Method for evaluating the charge-discharge characteristics of active materials] A method for evaluating the charge-discharge characteristics of an active material according to one aspect of the present disclosure is a method for evaluating the charge-discharge characteristics of an active material used in the positive or negative electrode of a battery, comprising the steps of: placing the active material in contact with an electrolytic material in contact with a counter electrode member; connecting the probe of a probe microscope and the electrodes of a charger / discharger to the counter electrode member; bringing the probe into contact with the active material placed in the electrolytic material; 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> The evaluation method is performed using a measurement unit 1, which includes, for example, a counter electrode member 10, an electrolytic material 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, as shown in Figure 1. Preferably, the charger / discharger 40 is capable of measuring at least one of voltage and current, or the measurement unit 1 may further include at least one of a voltage meter and a current meter (hereinafter collectively referred to as the measuring instrument). Note that in Figure 1, the probe microscope, voltage meter, and current meter are not shown except for the probe 30.

[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 include, for example, a known electrode mixture and a current collector. The electrode mixture may include, for example, a coated sheet containing an active material and having voids for the liquid electrolyte 20 to permeate, and may also include a conductive additive such as acetylene black and a binder such as polyvinylidene fluoride. The current collector may be, for example, 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 a secondary battery, and may be in a liquid state or a solid state. Examples of the liquid electrolyte include those containing a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. Examples of the solid electrolyte include materials (various solid electrolytes) having ion conductivity and being solid at normal temperature.

[0019] When the electrolyte 20 is in a liquid state, it may be put into a container (tank) 50 together with the counter electrode member 10 (see FIG. 1), or the above electrolyte may be dropped onto the flat counter electrode member. When the electrolyte is in a solid state, the electrolyte and the counter electrode member may be arranged so that they have a contact point.

[0020] When the electrolyte 20 is in a liquid state, the active material E may be arranged such that part or all of it is submerged in the electrolyte 20 and the active material E and the counter electrode member 10 do not contact each other. A non-conductive member may be arranged as a separator between them so that the active material E and the counter electrode member 10 do not contact each other in the electrolyte 20. When the electrolyte is in a solid state, the electrolyte and the active material may have a contact point, and they may be arranged such that the active material and the counter electrode member do not contact each other.

[0021] The container 50 is not particularly limited and may be formed of a conductive member or a non-conductive member. If the container 50 is formed of a conductive member, the counter electrode member 10 may be arranged to contact the container 50, and one electrode of the charger 40 and the above measuring instrument may be connected. If the container 50 is formed of a non-conductive member, the above one electrode may be connected to the counter electrode member 10. That is, the connection between the above one electrode and the counter electrode member 10 may be a direct connection or an indirect connection as long as electricity can conduct.

[0022] The probe microscope described above 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 instrument, and is configured to function as an electrode for charging and discharging the active material E and for measuring voltage and current.

[0023] <Active material> The active material E is not particularly limited as long as it is an electrode material used in the positive or negative electrode of a secondary battery. Examples include carbon-based materials and lithium titanate, which are negative electrode active materials for lithium-ion batteries, and lithium-containing metal oxides and lithium oxoate compounds, which are positive electrode active materials for lithium-ion batteries. Alternatively, the active material E may be a known or unknown substance used to evaluate its usability as an electrode material.

[0024] Furthermore, the active material E may be obtained by disassembling a secondary battery, or it may be in its raw material state before being used in a secondary battery.

[0025] The active material E that the probe 30 contacts 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 assembling or compacting active material particles or the above masses. That is, the active material E may be a single particle, a mass formed by artificially assembling multiple single particles by applying an external force, an aggregate formed by spontaneously (unartificially) assembling multiple single particles, a mass or aggregate formed by artificially or unartificially assembling multiple such masses or aggregates, or two or more of the above single particles, masses, and aggregates may be assembled artificially or unartificially, one or more of each. Figure 1 shows a single particle of active material E. Note that Figure 1 is a schematic diagram for explanatory purposes, and the shape and scale of each component (member) do not accurately reflect the actual ones.

[0026] The upper limit of the average particle diameter of the aggregate in contact with the 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 aggregate 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% volume cumulative standard (D50 value) measured by a laser scattering particle size distribution device.

[0027] The upper limit of the average particle diameter of the aggregate that the probe 30 contacts is not particularly limited and may be 200 μm or 100 μm. The lower limit of the average particle diameter of the aggregate 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 particles in 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 particles is not particularly limited and may be 0.01 μm or 0.1 μm.

[0029] <Placement process> In the placement process, the active material E is placed on the electrolytic material 20 that is in contact with the counter electrode member 10. That is, the placement process includes the steps of bringing the electrolytic material 20 into contact with the counter electrode member 10 and placing the active material E on the electrolytic material 20 that is in contact with the counter electrode member 10.

[0030] <Connecting process> In the connection step, the electrodes of the charger / discharger 40 are connected to the probe 30 and counter electrode member 10 of the probe microscope. The order of this connection step and the arrangement step described above 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] <Process of bringing into contact> In the contact step, the probe 30 is brought into contact with the active material E placed on the electrolytic material 20. Because this evaluation method uses a probe microscope, the probe 30 can be easily and reliably brought into contact with the active material E while observing the active material E. The probe microscope has a contact pressure feedback control that maintains contact between the probe and the object being observed, so it is possible to maintain contact between the probe 30 and the active material E while suppressing changes in the contact pressure of the probe 30 on the active material E. By bringing the probe 30, which is connected to the charger / discharger 40, into contact with the active material E, the active material E can be made into a state where it can be charged and discharged, and surface observation of the active material E can be performed at the same time.

[0032] <Charging and discharging process> In the charging and discharging process, the active material E in contact with the probe 30 is charged and discharged using the charger / discharger 40. The charger / discharger 40 is preferably capable of conducting 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 allow minute currents to pass through.

[0033] The voltage used in the above charging and discharging is not particularly limited and may be appropriately selected depending on the nature of the active material E. The upper limit of the voltage may be, for example, 10.0V, 8.5V, or 7.0V. The lower limit of the voltage may be, for example, -10.0V, -5.0V, or 0V. The current used in the above charging and discharging is not particularly limited and may be appropriately selected depending on the nature of the active material E. The upper limit of the current may be, for example, 10μA, 1μA, 100nA, or 10nA. The lower limit of the current may be, for example, 0.01pA, 0.1pA, or 1.0pA.

[0034] <Measurement process> In the measurement process, at least one of the voltage and current between the active material E and the counter electrode member 10, which change during charging and discharging, is measured. By measuring the voltage and current during charging and discharging, the charge-discharge characteristics of the active material E can be evaluated. Since this evaluation method uses a probe microscope probe 30 connected to a charge / discharge unit 40, the probe 30 can be easily brought into contact with, for example, single-particle active material E with a particle size of less than 10 μm to perform charging and discharging.

[0035] [Other embodiments] The above embodiments do not limit the configuration of the present invention. Accordingly, the above embodiments allow for the omission, substitution, or addition of components of each part of the above embodiments based on the description herein and common technical knowledge, and all such omissions, substitutions, or additions should be interpreted as falling within the scope of the present invention. [Examples]

[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] The charge rate was measured when a single particle of graphite negative electrode active material was placed on the electrolyte material 20 of measurement unit 1 and the unit was charged and discharged. The results are shown in Figure 2. Note that in Figure 2, the graph line for 1.0C (dashed line) overlaps with the graph line for 1.0C (second time).

[0038] Figure 2 shows that, particularly at low rates (0.5C, 1.0C), the discharge curve exhibits multiple plateaus at low voltages, suggesting a stage structure change characteristic of graphite. Furthermore, a decrease in capacity is observed as the rate increases, indicating a trend similar to that of typical rate characteristics.

[0039] [Example 2] The voltage was measured when a single particle of a positive electrode active material (NMC positive electrode active material) mainly composed of nickel, manganese, and cobalt was placed on the electrolyte 20 of measurement unit 1 and 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 presumed to be due to a side reaction occurring during charging, which led to a decrease in capacity during discharging.

[0041] Figures 2 and 3 suggest that this evaluation method allows for easy and accurate assessment of charge-discharge characteristics even for single-particle active materials. [Industrial applicability]

[0042] The evaluation method disclosed herein can evaluate the charge-discharge characteristics of active materials used in electrode materials for secondary batteries, and is therefore suitable for evaluating battery characteristics in battery development and manufacturing settings. [Explanation of symbols]

[0043] 1 Measurement 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 the positive or negative electrode of a battery, A step of placing an active material on the electrolytic material in contact with the counter electrode member, The process involves connecting the electrodes of a charger / discharger to the probe of a probe microscope and the counter electrode member, A step of bringing the probe into contact with the active material placed in the electrolytic material, A step of charging and discharging the active material in contact with the above probe using the above charger / discharger, A step of 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. Equipped with, A method for evaluating the charge-discharge characteristics of an active material, wherein the active material is a single active material particle or a mass formed by compacting multiple active material particles.

2. The method for evaluating the charge-discharge characteristics of an active material according to claim 1, wherein the active material is an aggregate formed by assembling or compacting active material particles or the aggregated bodies.

Images