JP5045420B2 - Electrode evaluation method and evaluation apparatus - Google Patents

Description

  The present invention relates to a method for evaluating an electrode of a power storage device, and more particularly to a method and apparatus for measuring and evaluating characteristics as a single electrode.

An electrode for an electricity storage device such as an electrochemical capacitor is composed of a positive electrode and a negative electrode, and the characteristics of the device appear by combining the characteristics of a single electrode. For this reason, various negative electrodes and positive electrodes have been studied, and high capacity and high withstand voltage have appeared. For example, Patent Document 1 (WO 2006/054747) discloses an electric double layer capacitor having a large capacity and high reliability.
WO2006 / 054747

  Generally, in order to select and design an electrode and use it to obtain the highest capacity as an electricity storage device, for example, the amount of positive and negative electrodes is changed at present, and the total capacity, charge / discharge efficiency, voltage holding characteristics, etc. By examining the results, the most appropriate positive / negative electrode ratio is determined. In a state where the positive electrode and the negative electrode are combined, it can be comprehensively determined, but it is difficult to determine the performance of each single electrode and the direction of improvement.

  Conventionally, as a method for evaluating a single electrode, there is a method using a third electrode (reference electrode). However, it is difficult to actually incorporate the third electrode into the electricity storage device, and it is almost impossible to install the third electrode in a simple two-pole cell or coin battery structure. In addition, as another method of evaluating a single electrode, there is a method of measuring metal lithium as a counter electrode, but there are limited devices that can be measured, and the problem that metal lithium is not responsive and cannot be evaluated at a high rate. There is.

  In view of these problems, an object of the present invention is to provide a method and an apparatus for simply evaluating a single electrode.

  The present invention relates to the following matters.

1. An evaluation method of an electrode used in an electricity storage device having a positive electrode, a negative electrode, and an electrolyte solution,
Producing a bipolar cell having at least an electrode to be evaluated, a reference electrode using a material having a known potential-electrical quantity characteristic, and an electrolyte;
A step of measuring voltage-electrical quantity characteristics using the produced bipolar cell;
And a step of obtaining a single electrode potential-electric quantity characteristic of the electrode under evaluation based on the measured voltage-electric quantity characteristic and the potential-electric quantity characteristic of the reference electrode. .

  2. 2. The electrode evaluation method according to 1 above, wherein the material constituting the reference electrode is activated carbon.

  3. 3. The electrode evaluation method according to 2 above, wherein the material constituting the reference electrode is activated carbon fiber.

  4). 4. The electrode evaluation method according to any one of the above items 1 to 3, wherein the reference electrode is set so that a capacity ratio between the reference electrode and the electrode to be evaluated is 1 or more.

  5). 5. The electrode evaluation method according to claim 4, wherein the reference electrode is set so that a capacity ratio between the reference electrode and the electrode to be evaluated is 2 or more.

  6). 6. The measurement electrode according to any one of 1 to 5 above, wherein a reference electrode is used in which the potential change amount of the reference electrode is 20% or less of the maximum voltage of the bipolar cell in the measurement conditions of the prepared bipolar cell. Electrode evaluation method.

  7). 6. The electrode evaluation according to 4 or 5 above, wherein the material constituting the reference electrode has an electric quantity characteristic per unit mass measured with respect to an electric potential, and a capacity ratio is determined by adjusting an amount used. Method.

  8). 8. The electrode evaluation method as described in 7 above, wherein the material constituting the reference electrode is activated carbon fiber whose electric quantity characteristic per unit mass with respect to the potential is measured, and the capacity ratio is determined by adjusting the number of sheets. .

  9. 9. The electrode evaluation method according to any one of 1 to 8, wherein a potential-differential capacity characteristic is obtained as the potential-electric quantity characteristic of the electrode to be evaluated.

  10. 10. The electrode evaluation method according to any one of 1 to 9, wherein an irreversible reaction amount is obtained as the potential-electric quantity characteristic of the electrode to be evaluated.

  11. 11. The electrode evaluation method according to any one of 1 to 10 above, wherein the voltage-electrical quantity characteristic is measured by a constant current method.

  12 11. The electrode evaluation method as described in any one of 1 to 10 above, wherein the voltage-electric quantity characteristic is measured by a constant potential method.

13. An apparatus for evaluating unipolar potential characteristics of an electricity storage device,
(A) a bipolar electrode unit comprising at least a reference electrode using a material having a known potential-electrical quantity characteristic and an electrolyte, and capable of forming a bipolar cell together with the electrode to be evaluated; and (b) incorporating the electrode to be evaluated. An electrode evaluation apparatus comprising a measuring unit for measuring voltage-electricity characteristics of a bipolar cell.

  14 (C) means for calculating a single electrode potential-electric quantity characteristic of the electrode to be evaluated based on the measured voltage-electric quantity characteristic of the bipolar cell and the potential-electric quantity characteristic of the reference electrode; 14. The electrode evaluation apparatus as described in 13 above, comprising:

  15. 15. The electrode evaluation apparatus as described in 13 or 14 above, wherein the material constituting the reference electrode is activated carbon.

  16. 16. The electrode evaluation apparatus according to 15 above, wherein the material constituting the reference electrode is activated carbon fiber.

  17. 17. The electrode evaluation apparatus according to any one of 13 to 16, wherein the reference electrode is set so that a capacitance ratio between the reference electrode and the electrode to be evaluated is 1 or more.

  18. 18. The electrode evaluation apparatus according to claim 17, wherein the reference electrode is set so that a capacity ratio between the reference electrode and the electrode to be evaluated is 2 or more.

  According to the present invention, it is possible to easily evaluate a single electrode in a device configuration that is close to reality.

  The electrode to be evaluated evaluated according to the present invention is a positive electrode or a negative electrode used for a bipolar cell type electricity storage device. Preferably, an electrode composed of a carbon material such as activated carbon, graphite, or graphite material (a carbon material having a larger interplanar spacing than graphite), in which charging / discharging is caused by ion adsorption, caused by intercalation, Any of a combination of both may be used.

  In an electricity storage device having a positive electrode and a negative electrode, as the battery is charged, the positive electrode shifts to a high potential and the negative electrode shifts to a low potential. Each electric potential is determined by each electric quantity. The voltage between the electrodes of a normal device is obtained by subtracting the potential of the negative electrode from the potential of the positive electrode. In observation from the outside (measurement of charge amount and voltage), what kind of potential changes the single electrode changes due to charging? Cannot be judged.

  Therefore, in the present invention, a reference electrode whose potential-electrical quantity characteristics have already been evaluated as a counter electrode is used to produce an electricity storage device structure in combination with an electrode to be evaluated, its charge / discharge characteristics are measured, and the characteristics of the reference electrode are obtained. By correcting based on this, the characteristics of the electrode under evaluation as a single electrode can be obtained.

FIG. 5 shows a typical example in which the positive electrode is evaluated using the reference electrode on the negative electrode side (see Examples described later). A curve (b) shows an actually measured voltage-electric quantity characteristic curve between the positive electrode and the negative electrode. Here, the potential of the negative electrode reference electrode (vs. the standard hydrogen electrode potential) -electric quantity characteristic has been measured and calculated as shown by the line (a). here,
Voltage = positive electrode potential−negative electrode potential (= reference electrode potential), therefore
Positive electrode potential = voltage + negative electrode potential (= reference electrode potential) (Formula 1)
Thus, the characteristic line (a) is added to the characteristic curve (b) with respect to the potential on the horizontal axis in FIG.

When using the reference electrode on the positive electrode side and evaluating the negative electrode,
Voltage = positive electrode potential (= reference electrode potential) −negative electrode potential, therefore
Negative electrode potential = positive electrode potential (= reference electrode potential) −voltage (Formula 2)
Thus, the characteristics of the negative electrode potential can be evaluated.

  If the characteristics of the reference electrode are known by measuring and / or calculating in advance, the characteristics of the single electrode of the electrode to be evaluated are evaluated by measuring the characteristics of the bipolar cell that is close to the actual usage pattern. be able to.

  The reference electrode is preferably one in which charging / discharging is performed by ion adsorption / desorption. That is, in the electrode by ion adsorption / desorption, since the linearity of the potential-electric quantity characteristic is high, the potential-electric quantity characteristic of the reference electrode is approximated as a straight line in the calculation by the formula (1) or the formula (2). Therefore, in addition to simple calculation, the characteristics of the evaluation electrode can be qualitatively understood without performing calculation. Here, if charging / discharging of the reference electrode is accompanied by intercalation or the like, the potential does not change linearly depending on the amount of charge, so the influence of the reference electrode appears strongly in the voltage characteristics of the bipolar cell, As a result, it becomes difficult to see the characteristics of the electrode to be evaluated.

  Also, if the limit capacity of the reference electrode is small when the amount of electricity charged until reaching the decomposition potential is the limit capacity, when proceeding with charging, the reference electrode side first reaches the limit capacity and the reaction current is carried, The linearity of the potential-electric quantity characteristic on the reference electrode side is lowered, and the characteristic calculation of the electrode to be evaluated becomes complicated.

Therefore, the limit capacity of the reference electrode is preferably equal to or more than the capacity that does not reach the limit capacity even if the charge electricity amount of the electrode to be evaluated is inserted.
Capacity ratio = (reference electrode limit capacity) / (evaluated electrode limit capacity)
The capacity ratio defined by is preferably 1 or more. Taking a certain margin, the capacity ratio is more preferably 2 or more.

  In addition, the larger the capacitance ratio, the greater the slope of the potential-electric quantity characteristic of the reference electrode. That is, in FIG. 5, the inclination of the potential-electric quantity characteristic line (a) of the reference electrode stands more vertically (the line (a) of FIG. 5 is also sufficiently inclined). When the characteristics of the electrode to be evaluated are calculated according to the formula (1) or the formula (2), the voltage and potential of the electrode to be evaluated can be determined while maintaining the shape of the voltage-electric quantity characteristic curve measured by the bipolar cell. Corresponds to the shifted shape. For this reason, the conversion is very simple and the characteristics of the electrode to be evaluated can be easily grasped immediately from the voltage-electric quantity characteristic curve shape of the bipolar cell. Therefore, the capacity ratio is more preferably 5 or more.

  In the measurement conditions of the produced bipolar cell, the potential change amount of the reference electrode is preferably 20% or less, more preferably 10% or less, of the maximum voltage of the bipolar cell.

For this reason, as the material for the reference electrode, a material having a particularly large ion adsorption amount per weight is preferable, and activated carbon is preferable. The activated carbon may be powdered normal activated carbon, more preferably activated carbon fiber. Activated carbon fibers are those fibers themselves have properties of activated carbon, as the surface area, preferably those having more than 800 m ² / g, are typically used. For 1500~2000m ² / g.

  As an initial step for carrying out the present invention, first, a reference electrode material is prepared, a part thereof is taken, and the potential-electric quantity characteristic of the reference electrode material is measured. In detail, as in Reference Example 1 to be described later, a three-electrode cell to which a reference electrode is added and an electrolyte system used for evaluation are used to measure potential-electric quantity characteristics. By converting this per unit mass, the characteristics of the reference electrode material are obtained. In particular, when performing rate characteristic evaluation, accurate evaluation is possible by measuring the DCIR (DC voltage drop) of the reference electrode at the evaluation current and performing IR (voltage drop) correction of the reference electrode potential. . In addition, it is preferable to perform evaluation of this reference electrode material in the range which can consider that material is the same. Generally, variation in material characteristics is small within the same production lot. If there is a non-negligible variation in material characteristics for each production lot, it is preferable to evaluate the characteristics for each production lot, and this is not necessary if it is known that the characteristics are stable. Evaluation may be performed as appropriate depending on variations in material characteristics.

  Next, a predetermined amount of the reference electrode material, that is, a volume ratio of 1 or more, preferably 2 or more, more preferably 5 or more with respect to the electrode to be evaluated is taken. It is possible to easily evaluate the characteristics of a large number of electrodes to be evaluated by assembling an electricity storage device (bipolar cell) and measuring the characteristics.

  As the reference electrode material, it is preferable that the electrode is easily manufactured and the fluctuation and variation in electrode characteristics are small due to the manufacture of the electrode. When using activated carbon powder, it is necessary to harden the activated carbon together with the binder, and there is a possibility that variation may occur depending on the operation between the measured electrode and the electrode used for evaluation. On the other hand, activated carbon fibers, especially those in the form of cloth (woven fabric, non-woven fabric), can be cut into a predetermined shape and an electrode can be configured using a predetermined number of sheets, so fluctuations and variations are small and capacity adjustment is also possible. It can be done very simply.

  As described above, according to the present invention, it is possible to measure the potential-electric quantity characteristic of a single electrode, in addition to the potential-differential capacity characteristic.

By the way, in the measurement of the capacity characteristic and / or the differential capacity characteristic, the operation of the potential or voltage is usually measured with dV / dt constant, and the current at that time is measured to differentiate from the relationship of i · dt / dV = C. The capacity is being measured. However, in this case, since the current value changes while moving ΔV, the voltage change ΔV _R = iR due to the resistance changes when the resistor R is present. The potential of will also change. Therefore, by obtaining the dt / dV to the i constant, can be constant [Delta] V _R, can be measured accurately differentiation capacity by measuring by [Delta] V _R is negligible current.

  Moreover, in this invention, the irreversible reaction in an electrode to be evaluated can be evaluated. For example, when an electrode to be evaluated that intercalates from a potential at the positive electrode is used and a reference electrode having a relatively low capacity ratio of 2 to 5 according to the present invention is used as the negative electrode, charging is performed within a potential at which no reaction occurs at the positive electrode. When the same amount of electricity is discharged, both the positive and negative electrodes return to the original potential, and when recharging is performed, charging starts at the same potential. At this time, since the negative electrode is charged with the same amount of electricity, the negative electrode potential when the positive electrode starts to be charged does not change, and thus the observed charge start voltage does not change. On the other hand, if an irreversible reaction occurs at the electrode to be measured, for example, if an irreversible reaction such as solvent decomposition occurs at the positive electrode, the total amount of electricity charged to the positive electrode and the amount of electricity used for the reaction current at the positive electrode Will be used to charge the negative electrode. When discharging in this state, when the positive electrode returns to the original potential, the negative electrode remains charged by the reaction current at the positive electrode. That is, the negative electrode potential is low. Since the next charge starts from this state, when the positive electrode reaches an intercalating potential, the negative electrode starts at a low potential from the beginning and shifts negatively by the same amount of electricity. That is, the intercalation start voltage observed in the bipolar cell is shifted to the higher voltage. The amount of electricity used for the reaction can be obtained from this shift amount.

  In addition, when a reference electrode with a capacity ratio of 5 or more is used, the cycle can be repeated to measure the charge / discharge curve and observe the situation where the start voltage of intercalation does not change, so that no reaction occurs at the positive electrode. The potential can also be obtained.

  As described above, in the present invention, by using a predetermined reference electrode, it is possible to easily evaluate the unipolar characteristics of the electrode to be evaluated, which is very useful in designing an electricity storage device. I understood it.

  Furthermore, the present invention relates to an electrode evaluation apparatus used in the above method, and (a) at least a reference electrode using a material having a known potential-electric quantity characteristic and an electrolytic solution, and two electrodes together with an electrode to be evaluated. A bipolar cell part that can constitute the cell; and (b) a measurement part that measures voltage-electricity characteristics of the bipolar cell incorporating the electrode to be evaluated.

  The selection of the reference electrode and the electrolytic solution is as described above, and other necessary bipolar cell members are known. The measuring unit for the voltage-electric quantity characteristic of the bipolar cell can also use a known device, preferably at least in the case of constant current method, galvanostat, electrometer and recorder, in the case of constant potential method. Equipped with a potential sweep device such as a potentiostat and a function generator, and a recorder. It is also preferable that the recorder has at least one of a clocking function, a calculation function, and a display function. With these functions, for example, the amount of electricity stored in the device can be easily calculated and displayed.

  The electrode evaluation apparatus according to the present invention preferably further includes (c) a single electrode of the electrode to be evaluated based on the measured voltage-electricity characteristic of the two-pole cell and the potential-electricity characteristic of the reference electrode. There is further provided a means for calculating the potential-electric quantity characteristic of. The calculation method in the calculation means is as already described. This calculation means can also serve as the calculation function of the voltage-electric quantity characteristic measuring device of the bipolar cell. Further, these calculation means, timing function, calculation function, display function, etc. can exist as a hardware configuration of a dedicated or general-purpose computer and / or as a logical configuration by software.

Reference Example 1 Evaluation of Reference Electrode Material As schematically shown in FIG. 1, activated carbon fiber cloth (ACC-5092-10, surface area 800 m ² / g, both of positive electrode 1 and negative electrode 2 using a tripolar screw cell. Nippon Kainol Co., Ltd.) is used, and one piece of activated carbon fiber cloth is stacked on the negative electrode 2 and two pieces of activated carbon fiber cloth are stacked on the positive electrode 1 so that the negative electrode capacity / positive electrode capacity ratio is 0.5, and the separator 3 is interposed therebetween. Then, the positive electrode side current collector 4 a and the negative electrode side current collector 4 b were pressed by applying pressure from both sides, the electrolyte solution 6 was immersed, and a capacitor was assembled using an Ag / AgCl electrode as the reference electrode 5.

  ACD-01 A charge / discharge cycle was performed at a voltage of 0 V to 1.5 V using a charge / discharge test apparatus (Asuka Electronics Co., Ltd.). Separately from the charge / discharge operation, voltage terminals were connected to the reference electrode and the positive electrode and the reference electrode and the negative electrode, respectively, using the other two channels, and the voltage was monitored. A stable potential at the 10th cycle was confirmed. The measurement conditions are as follows.

(1) Cell: Tripolar screw cell;
(2) Positive electrode (C): Activated carbon fiber cloth 88.7 mg (16 mmφ) × 2 sheets [ACC-5092-10 Nippon Kainol Co., Ltd.];
(3) Negative electrode (A): Activated carbon fiber cloth 43.1 mg (16 mmφ) × 1 sheet [ACC-5092-10 Nippon Kainol Co., Ltd.];
(4) Reference electrode: Ag / AgCl [EE009 (manufactured by CYPRESS SYSTEMS)];
(5) Separator: Glass fiber filter paper GF / C [Whatman];
(6) Electrolytic solution: 1.5M TEMA · BF ₄ [PC] (triethylmethylammonium tetrafluoroborate, propylene carbonate solution);
(7) Charging / discharging conditions: CCCV charging (1.0 mA, 1.5 V, CV 2 min), CC discharging (1.0 mA, 0 V), rest (2 min).

  FIG. 2 shows the relationship between the positive and negative electrode potentials converted to the standard hydrogen electrode standard (hereinafter referred to as vs. NHE) at the 10th cycle and the quantity of electricity.

  By converting this per unit mass, the characteristics of the activated carbon fiber cloth as a single negative electrode and the single positive electrode are as shown in FIGS. 3 and 4, respectively. The characteristics of the reference electrode using this activated carbon fiber cloth can be obtained by mass conversion using the graph of FIG. 3 or FIG.

<Example 1> Evaluation of electrode to be evaluated (positive electrode) The activated carbon fiber cloth whose characteristics were measured in Reference Example 1 was used as a reference electrode on the negative electrode side, and the positive electrode was evaluated. The positive electrode to be evaluated is acetylene black manufactured by Electrochemical Co., Ltd. with respect to 100 parts of graphite Timrex KS-6 (002 interlayer distance 0.3357 nm, average particle diameter 3.4 μm, surface area 20 m ² / g) manufactured by TIMCAL as an active material. (Abbreviated as AB) After 8 parts of powders are mixed, an aqueous solution in which 1.5 parts of carboxymethyl cellulose (CMC; binder) manufactured by Daicel Chemical Industries, Ltd. and 200 parts of water are mixed is added and mixed. Finally, 2 parts of an acrylic resin binder and 33 parts of water were added and mixed gently to prepare a slurry, and an electrode having a thickness of 50 microns was prepared on an aluminum foil. Each material and measurement conditions are summarized below.

(1) Positive electrode (C): KS-6: 6.37 mg (16 mmφ) [CMC (1.3%), acrylic resin binder (1.8%), AB (7.2%) / etched Al];
(2) Negative electrode (A): Activated carbon fiber cloth: 188.6 mg (16 mmφ) × 4 sheets [ACC-5092-10 Nippon Kainol Co., Ltd.];
(3) Separator: Glass fiber filter paper GF / C [Whatman];
(4) Electrolytic solution: 1.5M TEMA · BF ₄ [PC];
(5) Charging / discharging conditions: CCCV charging (1.0 mA, 2.1 V, CV 2 min), CC discharging (1.0 mA, 0 V), rest (2 min), 10 cycles. [ACD-01 Charge / Discharge Test Equipment Asuka Electronics Co., Ltd.]

  FIG. 5 shows measured voltage-electricity characteristics after 10 cycles (curve (b)), characteristics of the negative reference electrode (line (a)), and characteristics of the electrode to be evaluated (curve (c) )). As is apparent from this graph, the characteristics of the negative reference electrode (line (a)) have good linearity and are steep, so that the shape is determined from the actually measured voltage-electric quantity characteristics (curve (b)). The characteristic (curve (c)) of the positive electrode to be evaluated can be obtained without largely changing. Therefore, the electrode to be evaluated can be easily evaluated.

  FIG. 6 shows the cell voltage-evaluated electrode reference differential capacity characteristics at this time (upper side: charging, lower side: discharging). FIG. 7 shows the potential-differential capacity (per weight) characteristic during charging of the electrode to be evaluated (positive electrode). Comparing FIG. 6 and FIG. 7, the shapes of the differential capacity characteristics at the time of charging are similar, and the unipolar characteristics can be immediately understood from FIG. 6 alone.

<Example 2> Evaluation of electrode to be evaluated (negative electrode) The negative electrode was evaluated using the activated carbon fiber cloth whose characteristics were measured in Reference Example 1 as a reference electrode on the positive electrode side. The negative electrode to be evaluated was prepared in the same manner as the positive electrode of Example 1, except that the active material was changed to activated carbon RP-20 (average particle size 2 μm, surface area 1800 m ² / g) manufactured by Kuraray Chemical Co., Ltd. Each material and measurement conditions are summarized below.

(1) Positive electrode (C): Activated carbon fiber cloth: 183.2 mg (16 mmφ) × 4 sheets [ACC-5092-10 Nippon Kainol Co., Ltd.];
(2) Negative electrode (A): RP-20: 7.35 mg (16 mmφ) [CMC (1.3%), acrylic resin binder (1.8%), AB (7.2%) / etched Al;
(3) Separator: Glass fiber filter paper GF / C [Whatman];
(4) Electrolytic solution: 1.5M TEMA · BF ₄ [PC];
(5) Charging / discharging conditions: CCCV charging (1.0 mA, 2.1 V, CV 2 min), CC discharging (1.0 mA, 0 V), rest (2 min), 10 cycles. [ACD-01 Charge / Discharge Test Equipment Asuka Electronics Co., Ltd.]

  FIG. 8 shows the measured voltage-electricity characteristics (curve (b)) after 10 cycles, the characteristics of the positive reference electrode (line (a)) and the characteristics of the negative electrode to be evaluated (curve (c) )). As is clear from this graph, the characteristic of the positive electrode reference electrode (line (a)) has good linearity and is steep, so that the shape is determined from the actually measured voltage-electric quantity characteristic (curve (b)). The characteristic (curve (c)) of the negative electrode to be evaluated having a shape that is just inverted without greatly changing is obtained. Therefore, the electrode to be evaluated can be easily evaluated.

  FIG. 9 shows the cell voltage-evaluated electrode reference differential capacity characteristics at this time (upper side: charging, lower side: discharging). FIG. 10 shows the potential-differential capacity (per weight) characteristic during charging of the electrode under evaluation (negative electrode). The graph of FIG. 10 is similar to the shape of the differential capacity characteristic at the time of charging in FIG. 9 that is horizontally reversed, and it can be seen that the unipolar characteristic can be immediately understood from FIG.

Reference Example 2 Evaluation of reference electrode material 2
In Reference Example 1, the reference electrode material was evaluated using a three-pole screw cell. However, when the three-pole screw cell cannot be used, the natural potential measured using a general three-pole beaker cell and 2 From the voltage characteristics measured by the polar cell, the reference electrode material can be evaluated as follows.

(I) Theory A reference electrode material (for example, activated carbon fiber cloth) is used as a positive electrode and a negative electrode, stacked with a separator interposed between them, and an electrolyte solution is injected into the two-electrode cell (see FIG. 11A) is shown in FIG. ) Equivalent circuit diagram. When the positive and negative electrode capacities are C ₊ and C ₋ , respectively, the amount of electricity Q stored in the positive and negative electrodes is equal, and the voltage is divided into Q / C ₊ and Q / C ₋ . Here, when the positive and negative electrodes are the same material and have the same weight, it can be assumed that C ₊ ≈C _−, and the voltage is divided into half of the cell voltage from the natural potential of the electrode (hereinafter referred to as RP),
Positive electrode potential = R. P. + Cell voltage / 2
Negative electrode potential = R. P. -Cell voltage / 2
It becomes.

  That is, the reference electrode material R.I. P. If the voltage-electric quantity characteristics of the bipolar cell are obtained, a monopolar potential can be obtained. Specific description will be given below.

(Ii) Measurement of natural potential (RP) of reference electrode As shown in FIG. 12, an electrolyte solution (1.5M TEMA BF ₄ [PC]), activated carbon fiber cloth (ACC-5092-20, surface area 1800 m) in a container ² / g, Nippon Kainol Co., Ltd.) and an Ag / AgCl reference electrode to form a three-electrode cell, and the potential difference between the activated carbon fiber cloth and the reference electrode was measured with a potentiostat (Hokuto Denko Co., Ltd. HA-151). did. R.C. when activated carbon fiber is attached to the electrolyte. P. Table 1 shows the values.

  The average value of 0.392 V (vs. NHE) measured on 12 sheets was measured using an activated carbon fiber cloth ACC-5092-20 R.D. P. It was.

(Iii) Confirmation of reference electrode potential Activated carbon fiber cloth serving as a positive electrode was stacked through a separator, an electrolyte was injected, a two-pole screw cell was assembled, and measurement was performed under the following conditions.

(1) Positive electrode (C): Activated carbon fiber cloth: 30.5 mg (16 mmφ) × 1 sheet [ACC-5092-20 Nippon Kainol Co., Ltd.];
(2) Negative electrode (A): Activated carbon fiber cloth: 30.5 mg (16 mmφ) × 1 sheet [ACC-5092-20 Nippon Kainol Co., Ltd.];
(3) Separator: Glass fiber filter paper GF / C [Whatman];
(4) Electrolytic solution: 1.5M TEMA · BF ₄ [PC];
(5) Charging / discharging conditions: CC charging (1.0 mA, 1.0 V), CC discharging (1.0 mA, 0 V) 5 cycles. CCCV charge (1.0 mA, 1.0 V, CV 10 hours) [ACD-01 charge / discharge test equipment Asuka Electronics Co., Ltd.]

The cell voltage after this CCCV charge was 0.94V. Therefore, the unipolar potential is: positive electrode potential = R. P. + Cell voltage / 2
= 0.39 + (0.94 / 2) = +0.86 V
Negative electrode potential = R. P. -Cell voltage / 2
= 0.39- (0.94 / 2) =-0.08 V
Can be calculated.

  As a result of disassembling this cell and measuring the potential of the positive electrode and the negative electrode in a tripolar beaker cell, the positive electrode potential +0.88 V vs. NHE, negative electrode potential -0.06 Vvs. NHE was obtained, which almost coincided with the calculated value.

(Iv) Measurement of Electricity of Reference Electrode Activated carbon fiber cloth (ACC-5092-20, surface area 1800 m ² / g, Nippon Kainol Co., Ltd.) one by one with a separator interposed between the positive electrode and the negative electrode, and an electrolyte solution was injected Then, a two-pole screw cell was assembled and measured under the following conditions.

(1) Positive electrode (C): Activated carbon fiber cloth: 30.1 mg (16 mmφ) × 1 sheet [ACC-5092-20 Nippon Kainol Co., Ltd.];
(2) Negative electrode (A): Activated carbon fiber cloth: 30.1 mg (16 mmφ) × 1 sheet [ACC-5092-20 Nippon Kainol Co., Ltd.];
(3) Separator: Glass fiber filter paper GA-100 [Advantech Toyo Co., Ltd.];
(4) Electrolytic solution: 1.5M TEMA · BF ₄ [PC];
(5) Charging / discharging conditions: CC charging (1.0 mA, 1.0 V), CC discharging (1.0 mA, 0 V) [ACD-01 Charging / discharging test equipment Asuka Electronics Co., Ltd.]

  FIG. 13 shows the measurement results of the cell voltage at the 10th cycle—the positive reference electric quantity. This measurement result and the R.D. P. = 0.39 V, from the equation (i), the unipolar potential-electric quantity (per weight) characteristics of the negative electrode and the positive electrode can be obtained from the graphs of FIGS. 14 and 15, respectively.

Example 3 Evaluation Using Reference Electrode Surface Area 1800 m ² / g Activated Carbon Fiber Cloth A cell was prepared in the same manner as in Example 1 except that the activated carbon fiber cloth whose characteristics were measured in Reference Example 2 was used as the reference electrode on the negative electrode side. Then, the positive electrode was evaluated.

(1) Positive electrode (C): KS-6: 8.46 mg (16 mmφ) [CMC (1.3%), acrylic resin binder (1.8%), AB (7.2%) / etched Al];
(2) Negative electrode (A): Activated carbon fiber cloth: 188.6 mg (16 mmφ) × 4 sheets [ACC-5092-20 Nippon Kainol Co., Ltd.];
(3) Separator: Glass fiber filter paper GA-100 [Advantech Toyo Co., Ltd.];
(4) Electrolytic solution: 1.5M TEMA · BF ₄ [PC];
(5) Charge / discharge conditions: CC charge (1.0 mA, 2.2 V), CC discharge (1.0 mA, 0 V), rest (2 min), 10 cycles. [ACD-01 Charge / Discharge Test Equipment Asuka Electronics Co., Ltd.]

  FIG. 16 shows the measured voltage-electricity characteristics (curve (b)) after 10 cycles, the characteristics of the negative electrode reference (line (a)), and the characteristics of the positive electrode to be evaluated (curve (c) determined therefrom). )).

  FIG. 17 shows cell voltage-evaluated electrode reference differential capacity characteristics, and FIG. 18 shows potential-differential capacity (per weight) characteristics of the evaluated electrode (positive electrode) single electrode.

<Example 4> Evaluation of irreversible reaction amount A cell was prepared in the same manner as in Example 3 except that the volume ratio was reduced, and the irreversible reaction amount was evaluated.

(1) Positive electrode (C): KS-6: 6.70 mg (16 mmφ) [CMC (1.3%), acrylic resin binder (1.8%), AB (7.2%) / etched Al];
(2) Negative electrode (A): Activated carbon fiber cloth: 53.8 mg (16 mmφ) × 2 sheets [ACC-5092-20 Nippon Kainol Co., Ltd.];
(3) Separator: Glass fiber filter paper GA-100 [Advantech Toyo Co., Ltd.];
(4) Electrolytic solution: 1.5M TEMA · BF ₄ [PC];
(5) Charge / discharge conditions: CC charge (1.0 mA, 2.2 V), CC discharge (1.0 mA, 0 V), rest (2 min), 10 cycles. [ACD-01 Charge / Discharge Test Equipment Asuka Electronics Co., Ltd.]

  FIGS. 19 and 20 show the voltage-differential capacity characteristics of the cell and the potential-differential capacity (per weight) characteristics of the single electrode to be evaluated (positive electrode), respectively. Since the intercalation start potential of the electrode to be measured is constant from FIG. 20, it can be confirmed that the shift of the intercalation start voltage to the high voltage side in FIG. 19 is due to an irreversible reaction.

  When the intercalation voltage at which the differential capacity becomes 0.1 mAh / g / mV is obtained from FIG. 19, it becomes 1.797V (1 cycle), 1.894V (2 cycles), 1.956V (10 cycles) and 1 cycle. The intercalation voltage difference between two cycles is 0.101V, and the intercalation voltage difference between one cycle and 10 cycles is 0.163V. Accordingly, the amount of irreversible reaction in the first cycle is 0.093 mAh from the amount of electricity at which the reference electrode potential becomes 0.291 V (RP-0.101 V) and 0.229 V (RP-0.163 V). The amount of irreversible reaction up to the 10th cycle can be calculated as 0.173 mAh.

<Example 5> Evaluation by a constant potential method (i) Measurement of electric quantity of reference electrode For each of the positive electrode and the negative electrode, activated carbon fiber cloth (ACC-5092-20, surface area 1800 m ² / g, Nippon Kainol Co., Ltd.) one by one, It piled up through the separator, the electrolyte solution was inject | poured, the bipolar battery cell was assembled, and the measurement was performed on the following conditions.

(1) Positive electrode (C): Activated carbon fiber cloth: 27.1 mg (16 mmφ) × 1 sheet [ACC-5092-20 Nippon Kainol Co., Ltd.];
(2) Negative electrode (A): Activated carbon fiber cloth: 27.1 mg (16 mmφ) × 1 sheet [ACC-5092-20 Nippon Kainol Co., Ltd.];
(3) Separator: Glass fiber filter paper GA-100 [Advantech Toyo Co., Ltd.];
(4) Electrolytic solution: 1.5M TEMA · BF ₄ [PC];
(5) Measuring apparatus: Potentiostat HA-151 [Hokuto Denko Co., Ltd.], simplified function generator HB-111 [Hokuto Denko Co., Ltd.];
Measurement conditions: Voltage 0-1.0V, sweep speed 1mV / sec

  FIG. 21 shows the measurement results of the cell voltage at the 10th cycle—the positive reference electric quantity. This measurement result and R.D. obtained in Reference Example 2 (ii). P. = 0.39 V, from the formula of Reference Example 2 (i), the unipolar potential-electric quantity (per weight) characteristics of the negative electrode and the positive electrode are as shown in FIGS. 22 and 23, respectively.

(Ii) Evaluation of electrode to be evaluated (positive electrode) A cell was prepared in the same manner as in Example 3, and the positive electrode was evaluated under the following conditions.

(1) Positive electrode (C): KS-6: 9.10 mg (16 mmφ) [CMC (1.3%), acrylic resin binder (1.8%), AB (7.2%) / etched Al];
(2) Negative electrode (A): Activated carbon fiber cloth: 107.3 mg (16 mmφ) × 4 sheets [ACC-5092-20 Nippon Kainol Co., Ltd.];
(3) Separator: Glass fiber filter paper GA-100 [Advantech Toyo Co., Ltd.];
(4) Electrolytic solution: 1.5M TEMA · BF ₄ [PC];
(5) Measuring apparatus: Potentiostat HA-151 [Hokuto Denko Co., Ltd.], simplified function generator HB-111 [Hokuto Denko Co., Ltd.];
Measurement conditions: Voltage 0-1.0V, sweep speed 1mV / sec

  FIG. 24 shows the actually measured voltage-electricity characteristics after 10 cycles (curve (b)), the characteristics of the negative reference electrode (line (a)), and the characteristics of the positive electrode to be evaluated (curve (c) )). FIG. 25 shows the cell voltage-evaluated electrode reference differential capacity characteristic, and FIG. 26 shows the potential-differential capacity (per weight) characteristic of the evaluated electrode (positive electrode) single electrode. In contrast to the constant current method (Example 3), the peak can be clearly observed, whereas in the constant potential method, the current increases at the peak position and the influence of IR drop appears, so the peak is broad. Broadening is improved by setting the sweep speed slower so that the current value at the peak time becomes the same as that in the constant current method, but the measurement takes a very long time.

It is a figure which shows the structure of a 3 pole screw cell typically. In the reference example 1, it is a graph which shows the electric quantity characteristic (vs. standard hydrogen electrode) of the activated carbon fiber cloth of the 10th cycle. In the reference example 1, it is a graph which shows the monopolar electric potential-electric quantity (per weight) characteristic of the negative electrode of activated carbon fiber cloth. In the reference example 1, it is a graph which shows the monopolar electric potential-electricity (per weight) characteristic of the positive electrode of activated carbon fiber cloth. In Example 1, it is a graph which shows the unipolar characteristic of the voltage-electrical quantity characteristic (b) measured using the reference electrode (negative electrode) and the to-be-evaluated electrode (positive electrode), and a positive electrode (c) and a negative electrode (a). . In Example 1, it is a graph which shows the voltage of a cell-to-be-evaluated electrode reference | standard differential capacitance characteristic. In Example 1, it is a graph which shows the electric potential-differential capacity | capacitance (per weight) characteristic at the time of charge of a to-be-evaluated electrode (positive electrode) single electrode. In Example 2, it is a graph which shows the unipolar characteristic of the voltage-electrical quantity characteristic (b) measured using the reference electrode (positive electrode) and the to-be-evaluated electrode (negative electrode), and a positive electrode (a) and a negative electrode (c). . In Example 2, it is a graph which shows the voltage of a cell-to-be-evaluated electrode reference | standard differential capacity | capacitance characteristic. In Example 2, it is a graph which shows the electric potential-differential capacity | capacitance (per weight) characteristic at the time of charge of a to-be-evaluated electrode (negative electrode) single electrode. (A) It is a figure which shows typically the structure of a 2 pole cell. (B) It is an equivalent circuit schematic of a two-pole cell. It is a figure which shows typically the structure of a 3 pole cell. In the reference example 2, it is a graph which shows the measurement result of the cell voltage-positive electrode reference | standard electric quantity of the 10th cycle of the 2 pole cell which uses activated carbon fiber cloth for positive / negative electrode. In the reference example 2, it is a graph which shows the monopolar electric potential-electricity (per weight) characteristic of the negative electrode of activated carbon fiber cloth. In the reference example 2, it is a graph which shows the monopolar electric potential-electricity (per weight) characteristic of the positive electrode of activated carbon fiber cloth. In Example 3, it is a graph which shows the unipolar characteristic of the voltage-electrical quantity characteristic (b) measured using the reference electrode (negative electrode) and the to-be-evaluated electrode (positive electrode), and a positive electrode (c) and a negative electrode (a). . In Example 3, it is a graph which shows the voltage of a cell-to-be-evaluated electrode reference | standard differential capacity | capacitance characteristic. In Example 3, it is a graph which shows the electric potential-differential capacity | capacitance (per weight) characteristic of the single electrode of the to-be-evaluated electrode (positive electrode). In Example 4, it is a graph which shows the result of having measured the voltage of the cell-to-be-evaluated electrode reference | standard differential capacitance characteristic. It is a graph which shows the electric potential-differential capacity | capacitance (per weight) characteristic of the to-be-evaluated electrode (positive electrode) of Example 4. In Example 5, it is a graph which shows the measurement result of the cell voltage-positive electrode reference | standard electric quantity of the 10th cycle of the bipolar cell which uses the activated carbon fiber cloth of reference electrode material for positive / negative electrode. In Example 5, it is a graph which shows the monopolar electric potential-electricity (per weight) characteristic of the negative electrode of activated carbon fiber cloth. In Example 5, it is a graph which shows the monopolar electric potential-electricity (per weight) characteristic of the positive electrode of activated carbon fiber cloth. In Example 5, it is a graph which shows the unipolar characteristic of the voltage-electrical quantity characteristic (b) measured using the reference electrode (negative electrode) and the to-be-evaluated electrode (positive electrode), and a positive electrode (c) and a negative electrode (a). . In Example 5, it is a graph which shows the voltage of a cell-to-be-evaluated electrode reference | standard differential capacity | capacitance characteristic. 6 is a graph showing single electrode potential-differential capacity (per weight) characteristics of an electrode to be evaluated (positive electrode) of Example 5.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Positive electrode 2 Negative electrode 3 Separator 4a Positive electrode side collector 4b Negative electrode side collector 5 Reference electrode 6 Electrolyte

Claims (18)

An evaluation method of an electrode used in an electricity storage device having a positive electrode, a negative electrode, and an electrolyte solution,
Producing a bipolar cell having at least an electrode to be evaluated, a reference electrode using a material having a known potential-electrical quantity characteristic, and an electrolyte;
A step of measuring voltage-electrical quantity characteristics using the produced bipolar cell;
And a step of obtaining a single electrode potential-electric quantity characteristic of the electrode under evaluation based on the measured voltage-electric quantity characteristic and the potential-electric quantity characteristic of the reference electrode. .   The electrode evaluation method according to claim 1, wherein the material constituting the reference electrode is activated carbon.   The electrode evaluation method according to claim 2, wherein the material constituting the reference electrode is activated carbon fiber.   The electrode evaluation method according to claim 1, wherein the reference electrode is set so that a capacitance ratio between the reference electrode and the electrode to be evaluated is 1 or more.   The electrode evaluation method according to claim 4, wherein the reference electrode is set so that a capacity ratio between the reference electrode and the electrode to be evaluated is 2 or more.   6. The reference electrode according to claim 1, wherein the reference electrode has a potential change amount of 20% or less of a maximum voltage of the bipolar cell under measurement conditions of the produced bipolar cell. Electrode evaluation method.   6. The electrode according to claim 4, wherein the material constituting the reference electrode has an electric quantity characteristic per unit mass measured with respect to an electric potential, and a capacity ratio is determined by adjusting an amount to be used. Evaluation methods.   8. The electrode evaluation according to claim 7, wherein the material constituting the reference electrode is an activated carbon fiber whose electric quantity characteristic per unit mass with respect to the potential is measured, and the capacity ratio is determined by adjusting the number of the electrodes. Method.   The electrode evaluation method according to claim 1, wherein a potential-differential capacity characteristic is obtained as the potential-electric quantity characteristic of the electrode to be evaluated.   The electrode evaluation method according to claim 1, wherein an irreversible reaction amount is obtained as a potential-electric quantity characteristic of the electrode to be evaluated.   The electrode evaluation method according to claim 1, wherein the voltage-electric quantity characteristic is measured by a constant current method.   The electrode evaluation method according to claim 1, wherein the voltage-electric quantity characteristic is measured by a constant potential method. An apparatus for evaluating unipolar potential characteristics of an electricity storage device,
(A) a bipolar electrode unit comprising at least a reference electrode using a material having a known potential-electrical quantity characteristic and an electrolyte, and capable of forming a bipolar cell together with the electrode to be evaluated; and (b) incorporating the electrode to be evaluated. An electrode evaluation apparatus comprising a measuring unit for measuring voltage-electricity characteristics of a bipolar cell.   (C) means for calculating a single electrode potential-electric quantity characteristic of the electrode to be evaluated based on the measured voltage-electric quantity characteristic of the bipolar cell and the potential-electric quantity characteristic of the reference electrode; The electrode evaluation apparatus according to claim 13, comprising:   The electrode evaluation apparatus according to claim 13 or 14, wherein the material constituting the reference electrode is activated carbon.   The electrode evaluation apparatus according to claim 15, wherein the material constituting the reference electrode is activated carbon fiber.   The electrode evaluation apparatus according to claim 13, wherein the reference electrode is set so that a capacitance ratio between the reference electrode and the electrode to be evaluated is 1 or more.   The electrode evaluation apparatus according to claim 17, wherein the reference electrode is set so that a capacitance ratio between the reference electrode and the electrode to be evaluated is 2 or more.

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