The present invention relates to an evaluation apparatus and an evaluation method of a sheet type cell, which can be applied to evaluation of a secondary cell based on an operation principal of forming a new energy level in a band gap and capturing an electron by utilizing a photoexcited structural change of a metal oxide, for example. The term “evaluation” in this description is a term which includes “test”, “inspection”, and “measurement”.
The conventional secondary cells are chemical type cells in which electricity is stored and an electric current is extracted with movement of ions (electrically charged matter) through a chemical reaction. On the other hand, solar cells and atomic cells are known as physical type cells. Recently, a technology of secondary cells using lithium has been developed (see Patent Document 1).
Patent Document 1: Japanese Patent Laid-Open 2002-42863
None of the physical type cells is rechargeable and capable of forming a secondary cell.
In the chemical type secondary cells, as a chemical reaction is used, a charge/discharge performance is lowered, and a life is shortened. If electrolytes are used here, there always exists a risk of leakage.
In lithium ion secondary cells, reliability is reduced because of overcharging and charging/discharging, and there is a risk of fire when a short circuit occurs between electrodes. Possibility of the fire because of the short circuit is reduced by polymerizing or solidifying the electrolytes, but in the existent secondary cells there is a limitation of energy density from 500 to 800 Wh/L. Combinations of metal lithium of a negative electrode and various positive electrodes have been tested to obtain larger capacity. However, the risk of short circuit between the electrodes cannot be avoided because the electrolytes are used. Also, because rare metals such as lithium are used, there are problems of a material cost and procurement.
Therefore, the applicant is researching and developing sheet type (parallel plate type) secondary cells without causing a risk of leakage, generation of heat, or fire etc. due to a short circuit between electrodes and without elements that shorten the life in normal usage, while having higher energy density compared to the conventional chemical type cells. However, in the present circumstances, the sheet type cells are rarely available on the market, and how to evaluate sheet type cells is far from being established.
Therefore, an evaluation apparatus and evaluation method for sheet type cells appropriate for evaluation of sheet type cells are desired.
In order to solve the above described problems, a first aspect of the present invention is an evaluation method of a sheet type cell for evaluating the sheet type cell in which a storage layer is sandwiched by layers of a positive electrode and a negative electrode, the evaluation method including the step of bringing an electrode probe into contact with a measuring part on an outer surface of at least one of the positive electrode and the negative electrode, and measuring quantity of electricity at the measurement part, so as to evaluate the sheet type cell.
A second aspect of the present invention is an evaluation apparatus of a sheet type cell for evaluating the sheet type cell in which a storage layer is sandwiched by layers of a positive electrode and a negative electrode, the evaluation apparatus including an electrode probe that is brought into contact with a measuring part on an outer surface of at least one of the positive electrode and the negative electrode, and a measurement evaluation unit that measures quantity of electricity at the measurement part via the electrode probe, so as to evaluate the sheet type cell.
According to the present invention, a sheet type cell in which a storage layer is sandwiched between layers of a positive electrode and a negative electrode can be evaluated.
An embodiment of an evaluation apparatus and an evaluation method of a sheet type cell according to the present invention is described below by referring to the attached drawings.
(A-1) Explanation of a Sheet Type Cell which can be an Object to be Evaluated
A sheet type cell to be evaluated is not limited to the one which is implemented as a secondary cell, but may be the one which is implemented as a primary cell. Hereinafter, explanation is given supposing that the sheet type cell is a secondary cell. Also, any sheet type (parallel plate type) cell may be an object to be evaluated. For example, as shown in
Hereinafter, a sheet type cell having a storage layer in which a photoexcited structural change is used (hereinafter also referred to as a quantum cell), which may be the object to be evaluated, is briefly described. The storage layer in the quantum cell is referred to as a charging layer, in view of its characteristics.
The charging layer stores electrons with a charging operation, releases the charged electrons with a discharging operation, and keeps the electrons (storage of electricity) in a state without charging/discharging. The charging layer is formed by applying a technology of photoexcited structural change.
The photoexcited structural change is a phenomenon (technology) found out by Akira Nakazawa, who is the inventor of International Patent application JP2006/322011. That is, Akira Nakazawa found out that, when effective excitation energy is applied to an insulation-coated translucent metal oxide which is a semiconductor having a band gap as same as or more than a predetermined number, a lot of energy levels with no electrons are generated in the band gap. The quantum cell is charged by capturing electrons in these energy levels, and discharged by releasing the captured electrons.
In the quantum cell, the positive electrode 4 includes an electrode main body layer and a p-type metal oxide semiconductor layer formed to be in contact with the charging layer 2. The p-type metal oxide semiconductor layer is provided to prevent injection of electrons from the electrode main body layer to the charging layer 2.
The electrode main body layers of the negative electrode 3 and the positive electrode 4 are simply required to be formed as conductive layers.
The charging layer 2 is formed in a way where insulation-coated n-type metal oxide semiconductor particles adhere to the negative electrode 3 in a thin film shape, and is transformed to be capable of storing electrons with a photoexcited structural change caused at the n-type metal oxide semiconductor by ultraviolet irradiation.
(A-2) Evaluation Methods for Sheet Type Cells to be Evaluated as an Extension of Prior Arts and their Problems
As described above,
It is intended that the evaluation method and the evaluation apparatus according to this embodiment, which will be described in detail later, are mainly applied to inspection during a production process. The inspection can be conducted by the evaluation method and the evaluation apparatus according to this embodiment without attaching the negative electrode terminal 5 and the positive electrode terminal 6, and the inspection can also be conducted after attaching the negative electrode terminal 5 and the positive electrode terminal 6.
It may be possible to conduct inspection for detecting a charging/discharging characteristic of the secondary cell device 10, to which the negative electrode terminals 5 and the positive electrode terminal 6 are attached, similarly to the inspection of other secondary cells.
For example, as shown in
The secondary cell device 10 (that is, the sheet type cell 1) has a layer structure, and is practically formed in a plate shape. When there is an abnormality in the charging/discharging characteristics in such a layer structure, it is necessary to disassemble (or break) the sheet type cell 1 as the object, so as to analyze and examine its inner part unless its cause appears on the surface or on the outer part. When the defect is in the inner part, the inner part can be hardly examined optically, unless the electrode is transparent, and special means using X-rays, β-rays or the like is required in order to examine the inner part nondestructively. In other words, it is difficult to identify the abnormal part, and the special means and the like are required for the identification.
The evaluation apparatus and the evaluation method according to this embodiment are made in view of the above-described circumstances.
(A-3) Evaluation According to this Embodiment
The evaluation method according to this embodiment is to measure an electric characteristic value (a voltage, for example) by bringing the probe into contact with an arbitrary part on the surface of the positive electrode 4 of the sheet type cell 1, and to identify the abnormal part from the measurement result, if there is the abnormality such as the defect. A requirement for this embodiment is to probe the surface of the positive electrode 4, and this embodiment is applicable when probing can be made on the arbitrary part on the positive electrode 4 of the sheet type cell 1. Here, the probing means that the probe is electrically brought into contact with a contact part.
Hereinafter, an explanation will be given to the case where the evaluation is made by bringing the probe into contact with the arbitrary part on the surface of the positive electrode 4 of the sheet type cell 1 and measuring the electric characteristic value, as illustrated in the flowchart of
In addition to the voltage source (or the current source) 11, the current source 12, the switch 13, and the voltage meter 14 that are described above, an evaluation apparatus 20 according to this embodiment includes a first probe 21 that is brought into contact with the negative electrode 3, a second probe 22 that is brought into contact with the arbitrary part on the positive electrode 4, a probe moving mechanism 23 that moves the probes 21 and 22 and brings them into a contact state or a non-contact state, and a control unit (that is formed by a personal computer, for example) 24 that allows power supply of the voltage source 11, current extraction by the current source 12, switching of the switch 13, acquisition of a measurement value from the voltage meter 14, movement control of the probe moving mechanism 23, and the like.
It is to be noted that the negative electrode 3 has an area where a storage layer 2 and the like are not provided thereon so as to enable the connection of the negative electrode terminal, for example (refer to
Although
In the inspection of the charging/discharging characteristic, the control unit 24 first allows the voltage source (or the current source) 11 to be connected to the negative electrode 3 and the positive electrode 4 via the switch 13, and allows the time to pass so that a voltage between both ends becomes constant, so as to attain the fully charged state, as represented in
The inspection of the charging/discharging characteristic may be made on only one spot (gravity center of a contour, for example) that is arbitrarily selected on the positive electrode 4, or may be made respectively on a plurality of spots on the positive electrode 4. In the latter case, the sheet type cell 1 to be evaluated may be determined as normal when all the spots are evaluated as normal.
The evaluation configuration as shown in
As shown in
Vm1={(Rc+R2)×V1+R1×V2}/(R1+Rc+R2) (1)
Vm2={(Rc+R1)×V2+R2×V1}/(R1+Rc+R2) (2)
The charge voltage measurement operation at the two spots, as described above, makes it possible to find out the characteristics and the abnormality of the electromotive voltages and the internal resistances at the measurement spots. When, for example, the respective layers of the sheet type cell 1 are formed normally and uniformly, the measurement voltages Vm1 and Vm2 at the arbitrary two spots m1 and m2 are almost equal to each other, and have the values according to the equivalent resistance Rc at the stable time, as is clear from the expression (1) and the expression (2). The positive electrode 4 is usually formed by a uniform metal film and the equivalent resistance Rc is stable. However, when there is a crack or the like between the measurement spots m1 and m2, for example, the value of the equivalent resistance Rc is increased equivalently, which causes abnormal values in the measurement voltages Vm1 and Vm2. In addition, when the charging layer 2 is generated differently between the arbitrary two spots m1 and m2, and when the electromotive voltages V1 and V2 are significantly different from each other, a significant difference is also caused between the measurement voltages Vm1 and Vm2. It is to be noted that, when the sheet type cell is in a completely broken state (dead state), the measurement voltages Vm1 and Vm2 become zero equally (the measurement voltages Vm1 and Vm2 become equal to each other).
It is to be noted that when the expression (1) and the expression (2) can be rearranged with respect to the electromotive voltages V1 and V2, and the rearranged expressions are applied, it is clear that the electromotive voltages V1 and V2 can be calculated from the measurement voltages Vm1 and Vm2 at the two spots. This means that the states of the charge voltages V1 and V2 can be figured out from the measurement voltages Vm1 and Vm2.
Here, when the substrate 7 is not provided on the negative electrode 3 side, and when electrical probing is made similarly to the positive electrode 4, the principle of operation similar to the above can also be applied (refer to
When the evaluation of the charging/discharging characteristic at each of the arbitrary spots, and the evaluation based on the relationship of the measurement voltages of the electromotive voltages (charge voltages) at the plurality of spots, as described above, are made at the multiple spots, it is possible to perform the characteristic evaluation and the abnormality detection over the entire surface of the sheet type cell 1. This embodiment aims at the multi-spot inspection as described above.
Hereinafter, it is demonstrated from a simulation result that the evaluation of the sheet type cell 1 can be made from the measurement voltages (Vm1 and Vm2) at the arbitrary parts, with reference to
It is assumed that the sheet type cell 1 to be evaluated is equally divided into N-pieces in the vertical direction and is equally divided into M-pieces in the horizontal direction, as shown in
In
By applying the equivalent circuit (circuit model) of the element as described above, the simulation for identifying the abnormal part in the sheet type cell 1 is performed.
The above description focuses on the charge voltage VBS and explains the calculation result when there is no abnormality in the internal resistances RBS of the respective elements of the storage layer 2. As is clear from the above-described expression (1) and the expression (2), when the internal resistances RBS of the respective elements of the storage layer 2 (corresponding to R1 and R2 in the respective expressions) have the abnormality, it affects the voltage (measurement voltage) on the upper surface of the respective elements of the positive electrode 4, similarly to the above.
An actual prototype of the quantum cell having the size of 30 mm×30 mm is used as the sheet type cell 1, divided lengthwise and widthwise into 6×6 pieces, and subjected to the voltage measurement. As this prototype has a fault of a dead short circuit (internal resistance is 0Ω) and has a small power capacity, the voltage is measured by giving a voltage of about 1 V from the outside and probing the respective elements.
In addition, when a distance and an electric potential difference between the measured two spots are made clear, it is possible to calculate a current flowing therebetween.
Methods exemplified below may be adopted as an output method of the inspection result according to the evaluation apparatus of this embodiment, for example.
The measurement value and a measurement process value (a difference from the average value of the measurement values, for example) for each of the elements are displayed or printed out as it is. The measurement value and the measurement process value for each of the elements are converted into scales where the measurement value and the measurement process value belong, so as to obtain a greyscale image as those displayed in
(A-4) Effect of Embodiment
According to the above-described embodiment, the evaluation is made by bringing the probe into contact with the positive electrode and by measuring the quantity of electricity. Accordingly, it is possible to easily evaluate the sheet type cell to be evaluated without destruction, and to identify the abnormal part, if any.
(B-1) According to the above-described embodiment, the explanation is given to the case where the evaluation is made by measuring the voltage at the arbitrary two spots on the sheet type cell 1 to be evaluated (refer to
Im={Rc//Ri/(R1+Rc//Ri+R2)}×{(V1−V2)/Ri} (3)
where Rc//Ri=Rc×Ri/(Rc+Ri)
When the internal resistance value Ri of the ammeter 32 is known, the measurement current value Im, the internal resistances R1 and R2, and the electromotive voltages (charge voltages) V1 and V2 at the respective spots m1 and m2 are associated with each other, as represented in the expression (3). In other words, a characteristic test and internal inspection are made possible by measuring the voltage. Particularly, when the highly sensitive ammeter, such as a galvanometer, is applied, it is possible to accurately find out the direction of a current flowing on the surface of the positive electrode 4.
(B-2)
The probe 30 is brought into contact with the measurement part, and probes 31-N, 31-E, 31-S, and 31-W are respectively brought into contact with spots in four directions, each having an equal distance from the contact spot of the probe 30 as the center. Base ends of the probes 31-N, 31-E, 31-S, and 31-W are connected to a probe selection circuit 34. The probe selection circuit 34 selects only one probe out of the probes 31-N, 31-E, 31-S, and 31-W under the control of the control unit 24. One end of the ammeter (galvanometer, for example) 32 is connected to a base end of the probe 30, and the other end of the ammeter 32 is connected to a common terminal of the probe selection circuit 34. The control unit 24 allows the probes 31-N, 31-E, 31-S, and 31-W to be selected alternatively and cyclically, so as to measure a current flowing between the probe 30 and any of the surrounding probes 31-N, 31-E, 31-S, and 31-W and, from the current measurement value, to find out the direction of a current flowing through the spot of the center probe 30 in the most probable manner.
In order to prevent an error current value from entering the current measurement value due to a difference between an electric potential of each of the probes 30, 31-N, 31-E, 31-S, and 31-W and an electric potential of a surrounding member or the like, it is desirable that a predetermined electric potential Vref2 (an ideal electric potential that the probe 30 may have, for example) is applied to a surrounding member 35 or the like of the probes 30, 31-N, 31-E, 31-S, and 31-W via a buffer amplifier 36 or the like, so as to prevent the current (error current) due to the difference with the electric potential of the surrounding member 35, which should not be measured, from flowing to the ammeter 32. In other words, it is desirable to perform guarding.
It is also possible to enhance spatial resolution further by increasing the number of the directions than that of the configuration of
(B-3) According to the explanation of the principle of the evaluation operation of the above-described embodiment, the explanation is given to the voltage measurement after the charging (refer to
(B-4) Such inconvenience that the original difference in the voltages at the respective measurement parts is difficult to be detected as the electromotive voltages become uniform over time may be avoided by the voltage measurement with a load connected, instead of the voltage measurement immediately after the full charge as described above. Namely, when a known load (a current source or a constant resistance) 40 is connected to the sheet type cell 1, as shown in
(B-5) Moreover, as it is possible to find out the part in the sheet type cell 1 where the measured voltage is abnormal (the defect, for example) by the moving function of the probe or the sheet type cell 1, or by the multi-probe, automatic detection and automatic repair are possible by inputting its location information (identification information of the defect may be added thereto) into a repair apparatus (a laser repair device, for example) 50 (
(B-6)
In an evaluation apparatus 60 as shown in
The voltage after subtracting the predetermined voltage Vref1 is measured in order to use a dynamic range of the voltage meter 14 effectively and to improve measurement resolution. When the voltage is measured at the plurality of parts, calibration may be made at the respective parts by the predetermined voltage Vref1, so as to minimize an error due to a positional difference between the measurement parts.
Although not shown in
In the example of
In the example of
(B-7) The evaluation configuration based on the voltage measurement as shown in
For example, the voltage (electric potential) may be measured at many parts by using the multi-probe, and the current measurement that can identify the direction and the like may be applied to the part where the measurement electric potential is determined to be abnormal, so as to search for the abnormal part with higher accuracy.
(B-8) In the above-described embodiment, the explanation is given to the case where the sheet type cell 1 functioning as a secondary cell having the configuration as shown in
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