A secondary battery capable of detecting uneven electrode reaction.

Abstract

In a secondary battery in which an active material layer coated on the positive electrode current collector foil and an active material layer coated on the negative electrode current collector foil face each other with an electrolyte layer (an electrolyte layer with a separator interposed or a solid electrolyte layer) in between, the degree of reaction unevenness in the thickness direction of the active material layer is detected. [Solution] A secondary battery 1 having an active material layer 3 coated on a positive electrode current collector foil 2 and an active material layer 5 coated on a negative electrode current collector foil 4 facing each other with an electrolyte layer 6 in between, includes a conductive path 7 that selectively short-circuits two points in the thickness direction of at least one of the positive electrode and the negative electrode, means 9 for detecting the current flowing through the conductive path, and means 10 for detecting the degree of reaction unevenness in the active material layer in the thickness direction of at least one of the positive electrode and the negative electrode based on the magnitude of the current when the conductive path between two points in the thickness direction of at least one of the positive electrode and the negative electrode is short-circuited.

Description

[Technical Field]

[0001] The present invention relates to a secondary battery, and more particularly to a secondary battery equipped with a configuration for detecting reaction unevenness in the thickness direction of the electrode. [Background technology]

[0002] In simple terms, secondary batteries such as lithium-ion secondary batteries have a laminated structure in which a positive electrode active material layer coated on a current collector foil (positive electrode foil), which may be a metal foil, and a negative electrode active material layer coated on a current collector foil (negative electrode foil), which may be a metal foil, are immersed in an electrolyte, with a separator (in the case of a liquid-based battery) or a solid electrolyte layer (in the case of an all-solid-state battery) in between them. Various configurations have been proposed to address the various problems that may arise in such secondary batteries. For example, Patent Document 1 proposes a configuration in which, in order to grasp the charge state of the secondary battery, a positive electrode plate and a negative electrode plate provided via a separator and the electrolyte are sealed inside an outer casing member, a reference electrode is provided on the negative electrode plate via an insulating member, and a battery state monitoring means monitors the charge state of the secondary battery based on the amount of change per unit time of the measured potential measured at the reference electrode after the secondary battery has stopped charging. Patent Document 2 proposes that, in order to prevent a rapid decline in the performance of a lithium-ion battery, the battery resistance of a lithium-ion battery module is estimated according to the State of Charge (SOC) and temperature of the lithium-ion battery module, and the charging current is appropriately set based on the estimated battery resistance. Patent Document 3 proposes that, in order to suppress capacity reduction and performance changes by mitigating the uneven distribution of active material that occurs during charging and discharging of an all-solid-state secondary battery, and to maintain the energy storage performance of the secondary battery over a long period of time, a unit battery having a positive electrode plate containing a positive electrode active material layer, a negative electrode plate containing a negative electrode active material layer, and a solid layer located between the positive electrode plate and the negative electrode plate is described, Li in the negative electrode active material layer. +To mitigate the concentration difference, a configuration has been proposed in which the charge / discharge device repeatedly performs charge and discharge within a rate range of 0.2C to 0.8C at the timing when the cycle charge / discharge process is performed by multiple charge and discharge cycles. Patent Document 4 proposes a battery comprising a positive electrode plate and a negative electrode plate in which a negative electrode active material layer containing lithium titanate is formed on a negative electrode current collector foil, in order to appropriately restore the battery capacity, by performing a heating mitigation process in which the negative electrode active material layer is heated so that the temperature is higher on the negative electrode current collector foil side than on the surface side of the negative electrode active material layer, thereby mitigating the uneven distribution of lithium ions occurring within the negative electrode active material layer. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2013-118090 [Patent Document 2] Japanese Patent Publication No. 2013-13210 [Patent Document 3] Japanese Patent Publication No. 2015-201994 [Patent Document 4] Japanese Patent Publication No. 2021-51873 [Overview of the project] [Problems that the invention aims to solve]

[0004] In the charging and discharging of secondary batteries as described above, the electrochemical reactions at both the positive and negative electrodes proceed from the surface of the active material layer, respectively. Generally, the rate of reaction in the active material layer increases in the thickness direction from the current collector foil side towards the electrolyte layer side. For example, when charging the negative electrode of a lithium-ion battery, the lithium concentration accumulated in the negative electrode active material layer is higher on the separator side than on the current collector foil side. Such a thickness-direction deviation in the rate of reaction in the active material layer (hereinafter referred to as "reaction unevenness") is gradually mitigated, and the rate of reaction becomes uniform in the thickness direction of the active material layer. However, generally, the rate of mitigation of reaction unevenness is slow, and it takes a considerable amount of time for the reaction unevenness to be eliminated. If such reaction unevenness is not mitigated, the deposition of lithium metal and the resulting degradation may progress, which can stop charging and discharging or cause a decrease in the charging and discharging rate. Furthermore, reaction irregularities affect the potential difference between electrodes, thus reducing the accuracy of charge / discharge control, which is performed based on the voltage between electrodes. For example, if reaction irregularities occur in the active material layer during charging, and there are regions in the thickness direction of the active material layer where the reaction progresses more rapidly, the potential difference between electrodes will become high even if there is still capacity remaining in the battery. This can lead to situations where the system mistakenly determines that charging is complete even though it is not. (The potential difference between electrodes at a given State of Charge (SOC) when reaction irregularities remain in the active material layer is greater than when there are no reaction irregularities in the active material layer. Therefore, if there are reaction irregularities in the active material layer, the voltage between electrodes can be the same as the voltage when the SOC reaches 100% in a state without reaction irregularities in the active material layer, even if the SOC has not reached 100%). Since such reaction irregularities vary depending on various conditions during charging and discharging, it is difficult to estimate their degree from the voltage between electrodes. Thus, it would be convenient if a secondary battery were equipped with a configuration that could detect the degree of such reaction irregularities in the active material layer.

[0005] In view of the above circumstances, the object of the present invention is to provide a configuration for detecting the degree of reaction unevenness in the thickness direction of the active material layer in a secondary battery in which an active material layer coated on the positive electrode current collector foil and an active material layer coated on the negative electrode current collector foil are facing each other with an electrolyte layer (an electrolyte layer with a separator interposed or a solid electrolyte layer) in between.

[0006] In this regard, the inventors of the present invention have found that if there is reaction unevenness in the thickness direction of the active material layer in the above-mentioned secondary battery, a current flows when any two points in the thickness direction of the active material layer are electrically short-circuited, and the greater the degree of reaction unevenness in the thickness direction of the active material layer, the greater the current when any two points in the thickness direction of the active material layer are short-circuited. That is, the degree of reaction unevenness in the thickness direction of the active material layer can be detected by detecting the magnitude of the current when any two points in the thickness direction of the active material layer are short-circuited. This finding is utilized in the present invention. [Means for solving the problem]

[0007] According to the present invention, the above problem is solved by a secondary battery having a configuration in which an active material layer coated on the current collector foil of the positive electrode and an active material layer coated on the current collector foil of the negative electrode face each other with an electrolyte layer in between, the secondary battery comprising: a conductive path that selectively short-circuits two points in the thickness direction of at least one of the positive electrode and the negative electrode; a current detection means for detecting the current flowing through the conductive path; and a reaction unevenness detection means for detecting the degree of reaction unevenness in the active material layer in the thickness direction of at least one of the positive electrode and the negative electrode based on the magnitude of the current when the conductive path between two points in the thickness direction of at least one of the positive electrode and the negative electrode is short-circuited.

[0008] In the above configuration, the secondary battery may typically be a liquid-based secondary battery such as a lithium-ion secondary battery, or it may be an all-solid-state battery. The positive electrode current collector foil (positive foil) and the negative electrode current collector foil (negative foil) may be current collectors made of metal foil in a conventional manner, and the positive electrode active material layer and the negative electrode active material layer may be coated on the positive electrode foil and the negative electrode foil in a conventional manner, respectively. The "electrolyte layer" is, in the case of a liquid-based secondary battery, a layer of separator and the electrolyte solution in which it is immersed, and in the case of an all-solid-state battery, a solid electrolyte layer, and each may be formed from any material in a conventional manner. The positive electrode foil and the negative electrode foil may be held together at their outer edges by a sealing portion.

[0009] Furthermore, in the configuration of the present invention described above, either the positive electrode or the negative electrode, or both, are provided with a conductive path that selectively short-circuits two points in the thickness direction between the current collector foil and the active material layer coated thereon, a current detection means for detecting the current flowing through the conductive path, and a reaction unevenness detection means for detecting the degree of reaction unevenness in the thickness direction of the active material layer based on the magnitude of the current that flows when the current collector foil and the two points in the thickness direction of the active material layer are short-circuited with the conductive path. As already mentioned, when there is reaction unevenness in the thickness direction of the active material layer, it has been found that when any two points in the thickness direction of the active material layer are short-circuited, a current flows, and the magnitude of this current increases as the degree of reaction unevenness increases.Therefore, in the present invention, either the positive electrode or the negative electrode, or both, an attempt is made to short-circuit any two points in the thickness direction of the active material layer with a conductive path, detect the magnitude of the current that flows at that time, and detect the degree of reaction unevenness from the magnitude of the detected current. In other words, the configuration of the present invention makes it possible to detect the degree of reaction unevenness in the thickness direction of the active material layer in a secondary battery. As described in the section on embodiments, when a conductive path is short-circuited between any two points in the thickness direction of an active material layer having reaction unevenness in the thickness direction, the current that flows increases sharply immediately after the short circuit and then gradually decreases. Therefore, the degree of reaction unevenness may be determined by referring to the maximum value of the current immediately after the short circuit. The conductive path may be formed from any conductive material that does not react with lithium. For example, copper, nickel, stainless steel, gold, platinum, carbon nanotubes, graphene, etc. can be used for the negative electrode, and aluminum, nickel, stainless steel, gold, platinum, carbon nanotubes, graphene, etc. can be used for the positive electrode.

[0010] In the configuration of the present invention described above, more specifically, the conductive path may be configured to selectively short-circuit the current collector foil and the electrolyte layer-side surface of the active material layer in at least one of the positive and negative electrodes. This makes it possible to detect the degree of reaction unevenness throughout the thickness direction of the active material layer of the positive or negative electrode.

[0011] Also, in the configuration of the present invention described above, the conductive path may be configured to selectively short-circuit between the current collector foil in at least one of the positive electrode and the negative electrode and a portion closer to the current collector foil than the surface on the electrolyte layer side of the active material layer. As a result, it becomes possible to detect the degree of uneven reaction between the current collector foil in the positive electrode or the negative electrode and any portion in the active material layer. Alternatively, the conductive path may be configured to selectively short-circuit between the surface on the electrolyte layer side of the active material layer in at least one of the positive electrode and the negative electrode and a portion closer to the electrolyte layer than the current collector foil. As a result, it becomes possible to detect the degree of uneven reaction between the surface on the electrolyte layer side of the active material layer in the positive electrode or the negative electrode and any portion in the active material layer. Further, the conductive path may be configured to selectively short-circuit between the current collector foil in at least one of the positive electrode and the negative electrode and an intermediate portion closer to the current collector foil than the surface on the electrolyte layer side of the active material layer and between the intermediate portion and the surface on the electrolyte layer side of the active material layer, and may be configured such that the current flowing through each is detected. As a result, it becomes possible to detect a change in the degree of uneven reaction in the thickness direction of the active material layer of the positive electrode or the negative electrode.

Advantages of the Invention

[0012] Thus, according to the configuration of the present invention, by detecting the current flowing when any two points in the thickness direction of the active material layer are electrically short-circuited, it becomes possible to detect the degree of uneven reaction in the active material layer. The configuration of the present invention may be applied to either one or both of the positive electrode and the negative electrode. Since the degree of uneven reaction in the active material layer changes depending on conditions such as the charge / discharge rate, by examining the degree of uneven reaction generated under various charge / discharge conditions according to the configuration of the present invention, it becomes possible to search for conditions that reduce the uneven reaction.

[0013] Other objects and advantages of the present invention will become apparent from the following description of the preferred embodiments of the present invention.

Brief Description of the Drawings

[0014] [Figure 1] FIG. 1 is a schematic cross-sectional view of a secondary battery to which the present embodiment is applied. [Figure 2] Figs. 2(A) and 2(B) are schematic cross-sectional views with added block diagrams illustrating the configurations in which the electrodes of the secondary battery to which the present embodiment is applied and the conductive paths are connected. (A) represents the first form, and (B) represents the second form. [Figure 3] Fig. 3 is a schematic cross-sectional view of the active material layer illustrating the process in which current flows due to a short circuit caused by the conductive path in the active material layer with reaction unevenness. [Figure 4] Fig. 4 is a schematic diagram of the time change of the current I flowing when the current collector foil and the surface of the active material layer on the electrolyte layer side are short-circuited by the conductive path. T represents time.

Explanation of Reference Numerals

[0015] 1... secondary battery, 2... positive electrode foil, 3... positive electrode active material, 4... negative electrode foil, 5... negative electrode active material layer, 6... separator (electrolyte layer), 7... conductive path, 8... switch, 9, 9a... ammeter, 10... reaction unevenness detector

Best Mode for Carrying Out the Invention

[0016] The present invention will be described in detail with respect to several preferred embodiments while referring to the accompanying drawings below. In the drawings, the same reference numerals indicate the same parts.

[0017] Configuration of a secondary battery As schematically depicted in Figure 1, in the secondary battery 1 to which this embodiment is applied, a single cell C is formed by a laminated structure in which a positive electrode active material layer 3 coated on the surface of the positive electrode current collector foil (positive electrode foil) 2 and a negative electrode active material layer 5 coated on the surface of the negative electrode current collector foil (negative electrode foil) 4 face each other with an electrolyte layer 6 in between. The positive electrode foil 2 and the negative electrode foil 4 may be commonly used metal foils such as aluminum foil and copper foil with a thickness of about 10 to several tens of micrometers, respectively. The materials of the positive electrode active material layer 3 and the negative electrode active material layer 5 may be appropriately selected depending on the type of battery (see, for example, the experimental examples described later). Typically, the active material layer is formed by coating a slurry containing appropriately selected active material, conductive additive, binder, etc., onto the current collector foil and drying it to form a layer of about 0.1 mm. When the secondary battery is a liquid-type battery such as a lithium-ion battery, the electrolyte layer 6 becomes a separator 6 immersed in an electrolyte solution filled around it. The separator 6 is formed of a resin film such as polypropylene that allows moving substances such as lithium ions to pass through, and the electrolyte may be appropriately selected depending on the type of battery (see experimental examples described later). The secondary battery may also be an all-solid-state battery, in which case the electrolyte layer 6 will be a solid electrolyte layer formed of appropriately selected materials (see experimental examples described later). Although not shown in the figures, the periphery of each electrode may be surrounded by a seal made of any resin material. The cell C may have a structure in which multiple cells are stacked. In that case, the positive electrode foil 2 of each cell C is bonded to the negative electrode foil 4 of the cell adjacent to the upper side in the figure, and the negative electrode foil 4 of each cell C is bonded to the positive electrode foil 2 of the cell adjacent to the lower side in the figure, thereby forming a state in which multiple cells are connected in series. Thus, the bonded positive electrode foil 2 and negative electrode foil 4 may constitute a "bipolar electrode".

[0018] Configuration for detecting uneven reaction of electrodes As described in the summary of the invention, in this embodiment, in the secondary battery described above, in order to detect the degree of reaction unevenness in the active material layer of each electrode, a conductive path 7 is formed in either the positive electrode or the negative electrode, or both thereof, as shown in Figure 2(A), which electrically selectively short-circuits any two points from the current collector foils 2 and 4 to the surface of the active material layer 3 and 5 on the electrolyte layer 6 side, and a configuration is provided to detect the degree of reaction unevenness by detecting the current flowing when the conductive path 7 is short-circuited. Typically, as shown in the figure, the conductive path 7 is formed to short-circuit between the current collector foils 2 and 4 and the surface of the active material layer 3 and 5 on the electrolyte layer 6 side, and a switch 8 to control the conduction in the conductive path 7 and an ammeter 9 to detect the current may be provided along the way. The conductive path 7 may be formed from any conductive material that does not react with lithium. For example, copper, nickel, stainless steel, gold, platinum, carbon nanotubes, and graphene can be used for the negative electrode, and aluminum, nickel, stainless steel, gold, platinum, carbon nanotubes, and graphene can be used for the positive electrode. The ends of the conductive path 7 may be attached to the surfaces of the current collector foils 2 and 4 and the active material layers 3 and 5 by any method while maintaining electrical conductivity at any point. The ON / OFF control of the switch 8 and the detection of the degree of reaction unevenness from the current value detected by the ammeter may be achieved by the reaction unevenness detector 10. The reaction unevenness detector 10 may be any computer device or circuit device.

[0019] During operation, while the secondary battery is being charged and discharged, switch 8 is in the OFF position, and the conduction of the conductive path 7 is interrupted. When the charging and discharging of the secondary battery stops, switch 8 is turned ON, the conductive path 7 is opened, and the current value flowing through the conductive path 7 is measured by the ammeter 9. The measured value is sent to the reaction unevenness detector 10, which determines the degree of reaction unevenness between the short-circuited parts of the conductive path 7 based on the current value. As described later, the greater the degree of reaction unevenness, the greater the maximum value of the current immediately after the short circuit. Therefore, the reaction unevenness detector 10 may be configured to determine an index value representing the degree of reaction unevenness in accordance with the magnitude of this maximum current.

[0020] Generation and mitigation of reaction unevenness in the active material layer As explained in the section on the summary of the invention, in the charging and discharging of a secondary battery, the electrochemical reaction at the electrode proceeds from the surface of the active material layer on the electrolyte layer side, so the degree of reaction progresses at the surface of the active material layer is high. For example, in the negative electrode (active material: graphite) during charging of a lithium-ion battery, C6+Li + +e - →LiC6 In this reaction, lithium atoms are bonded to the active material layer. Since lithium ions arrive from the electrolyte layer, as schematically depicted in Figure 3, the lithium concentration is generally determined by the electrolyte layer side Cs Li However, the current collector foil side Cc Li It will be higher than (Cs Li >Cc Li ), resulting in uneven concentration, or reaction unevenness, in the thickness direction of the active material layer. If such uneven reaction occurs and persists, it can lead to premature cessation of charging and discharging or a decrease in the charging and discharging rate. Furthermore, although such uneven reaction (uneven concentration of reaction products) will mitigate even if left undisturbed after charging and discharging stops, the driving force is very small, as it is only a slight difference in concentration between adjacent regions in the thickness direction of the active material layer. Therefore, it will take a considerable amount of time for the uneven reaction to be substantially eliminated.

[0021] Regarding this point, in the research by the inventor of the present embodiment, when any two points in the thickness direction of each electrode after charge and discharge, for example, between the current collector foil and the surface of the active material layer on the electrolyte layer side, are electrically short-circuited, it has been found that current flows. This is because by directly connecting the electrolyte layer side and the current collector foil side of the active material layer, electrons are directly exchanged between the electrolyte layer side and the current collector foil side, and the state that should occur in the electrochemical reaction during charge and discharge spreads more rapidly from the electrolyte layer side to the current collector foil side. For example, in the case of the negative electrode of the lithium-ion battery illustrated in FIG. 3 after charging, in LiC6 and C6, the potential of C6 is higher (Vc>Vs). Therefore, when the region of LiC6 and the region of C6 are directly connected by the conductive path 7, electrons flow from the region of LiC6 on the electrolyte layer side through the conductive path 7 to the region of C6 on the current collector foil side (the current I in the conductive path 7 flows from the current collector foil side to the electrolyte layer side), and at the same time, lithium ions are released from the region of LiC6 on the electrolyte layer side and flow to the region of C6 on the current collector foil side, receive electrons in the region of C6 on the current collector foil side, and become LiC6 and adhere to the active material. In this case, the driving force for relaxing the reaction unevenness is the concentration difference between the electrolyte layer side and the current collector foil side of the active material layer, so it becomes larger than when the electrolyte layer side and the current collector foil side of the active material layer are not connected, and the relaxation of the reaction unevenness proceeds more rapidly (for example, in the case of the negative electrode of a lithium-ion secondary battery, the potential difference between adjacent regions in the thickness direction within the active material layer is several 0.00 V, but the potential difference between the surface of the electrolyte layer side and the surface of the current collector foil side of the active material layer reaches several 0. V).

[0022] Also, regarding the behavior of the current during the short circuit between the current collector foil side and the electrolyte layer side of the active material layer as described above, according to the experiment of the inventor of the present embodiment as described later, as schematically depicted in FIG. 4, it has been confirmed that the current value rapidly increases from the start of the short circuit Sh and then gradually decreases. At that time, it has been found that the maximum value I of the current when the reaction unevenness is large H is larger than the maximum value I of the current when the reaction unevenness is small L . As can be understood from the figure, it has also been observed that the larger the reaction unevenness at any time point after the short circuit, the larger the current value.

[0023] Thus, in this embodiment, after charging and discharging the secondary battery, the current collector foil side and the electrolyte layer side of the active material layer at each electrode are electrically short-circuited at a time, and the current value at that time, for example, the maximum value or the current value at any predetermined time after the short circuit, is detected to detect the degree of reaction unevenness. Since the magnitude of the current value corresponds to the magnitude of the degree of reaction unevenness, the index value of the degree of reaction unevenness may be calculated in accordance with the magnitude of the current value.

[0024] In the above configuration, any two points that are short-circuited between the current collector foil side and the electrolyte layer side of the active material layer at each electrode are typically the current collector foil and the electrolyte layer side surface of the active material layer, as described above, but they may be any two different points in the thickness direction of the active material layer, thereby allowing for the detection of differences in the rate of reaction between any two points. Alternatively, as shown in Figure 2(B), three or more points along the thickness direction of the electrode, for example, the intermediate portion between the current collector foil and the active material layer and the electrolyte layer side surface, may be short-circuited, and the current flowing through each of these sections may be detected, allowing for the detection of differences in the rate of reaction between each section. This makes it possible to understand the distribution of reaction unevenness in the thickness direction within the active material layer.

[0025] Experimental example The effectiveness of this embodiment was confirmed by the following experimental examples. It should be understood that these experimental examples are illustrative of the effectiveness of this embodiment and do not limit the scope of the present invention.

[0026] In the experiment, after charging liquid-based batteries and all-solid-state batteries prepared by the method described below at various charge rates, the maximum value of the current that flowed when the current collector foil of each electrode and the electrolyte layer surface of the active material layer were short-circuited was measured, and it was confirmed that reaction irregularities could be detected from these maximum current values.

[0027] Liquid-based batteries and all-solid-state batteries were prepared as follows: (1) Liquid-type battery - For the positive electrode, the positive electrode active material (LiNi 0.8 Co 0.1 Mn0.1 O2, a conductive additive (acetylene black), and a binder (polyvinylidene fluoride) are mixed in a mass ratio of 96:2:2, and N-methyl-2-pyrrolidone (NMP) is added to prepare a slurry. This slurry is then applied to aluminum foil that will serve as the current collector, and after drying, the basis weight is 80 mg / cm². 2 A positive electrode active material layer was formed by coating with a doctor blade in such a manner, and this was used as the positive electrode. For the negative electrode, graphite as the negative electrode active material, styrene-butadiene rubber (SBR) as a binder, and carboxymethylcellulose (CMC) as a dispersant were mixed in a mass ratio of 95:2.5:2.5, and pure water was added to prepare a slurry. This slurry was then applied to the copper foil that would become the current collector foil, and after drying, the basis weight was 60 mg / cm². 2 The negative electrode active material layer was formed by coating with a doctor blade in this manner, and this was used as the negative electrode. Then, the prepared positive electrode active material layer and the negative electrode active material layer were placed facing each other with a polypropylene separator in between, and an electrolyte of 1.1 M LiPF6 / EC (ethyl carbonate):DMC (dimethyl carbonate):EMC (ethyl methyl carbonate) (3:4:3 v / v) was filled between the electrodes to form a small single-pair laminate cell of a liquid-type battery. The area of ​​the opposing part of the electrodes was 21 cm². 2 That's what I decided.

[0028] (2) All-solid-state battery - For the positive electrode, the positive electrode active material (LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 A positive electrode slurry was prepared by mixing O2, a solid electrolyte (10LiI·90Li3PS4), a conductive material (carbon nanotubes), a binder (styrene-butadiene rubber), and a dispersion medium (tetralin) (the mixing ratio of the positive electrode active material to the sulfide solid electrolyte was 7:3 by volume, and the mixing ratio of the positive electrode active material, conductive material, and binder was 100:3:0.7 by mass). The slurry was then coated onto aluminum foil, which would serve as the current collector foil, dried at 100°C for 30 minutes, and then a 1cm diameter layer was formed from it. 2A circular component was punched out to form the positive electrode. For the negative electrode, a negative electrode slurry was prepared by mixing a negative electrode active material (Si), a solid electrolyte (10LiI·90Li3PS4), a conductive material (carbon nanotube), a binder (styrene-butadiene rubber), and a dispersion medium (diisobutyl ketone) (the mixing ratio of the negative electrode active material to the sulfide solid electrolyte was 4:6 by volume, and the mixing ratio of the negative electrode active material, conductive material, and binder was 100:1:2 by mass). This slurry was then coated onto copper foil that would serve as the current collector foil, dried at 100°C for 30 minutes, and then a diameter of 1 cm was formed. 2 A circular component was punched out to form the negative electrode. The solid electrolyte layer was 1 cm in diameter. 2 A solid electrolyte (10LiI·90Li3PS4) is filled into a cylindrical jig, at a rate of 1 ton / cm³. 2 It was prepared by pressing with a pressure of 6 tons / cm². Thereafter, the positive electrode, solid electrolyte layer, and negative electrode were stacked in this order inside a cylindrical jig, and pressed at 6 tons / cm². 2 By pressing with pressure, a small single-pair cell of an all-solid-state battery was formed.

[0029] For the conductive paths that short-circuit the current collector foil and the electrolyte-side surface of the active material layer of each electrode, a 0.1 mm diameter aluminum wire was used for the positive electrode and a 0.1 mm diameter copper wire was used for the negative electrode, with their ends connected to the current collector foil and the electrolyte-side surface of the active material layer.

[0030] To detect reaction unevenness in the electrodes of each prepared battery, first, each battery with a State of Charge (SOC) of 0% was subjected to constant current charging for 1 minute at the respective charging rates shown below. Here, the charging rate is an index value of the current supply rate, and at a charging rate of N[C], the current is supplied at a rate that achieves charging from 0% to 100% SOC in 1 / N time. It should be noted that prior analysis had shown that the degree of reaction unevenness occurring in the thickness direction of the electrode increases as the charging rate increases. Then, immediately after charging stopped, the conductive path and the current collector foil were short-circuited, and the current flowing through the conductive path was measured for 0.1 seconds to determine the maximum current value.

[0031] In the results, first, the current at each electrode after short-circuiting increased rapidly from the initial Sh at the start of the short circuit, as shown in Figure 4, and then gradually decreased. The charge rate and the maximum current after short-circuiting at each electrode of each battery were as follows. In Table 1, the No. column is the experimental example number, the L / S column is the type of battery, where L is liquid and S is all-solid. The + / - column is the polarity of the measured electrode, where + is the positive electrode and - is the negative electrode. The N column is the charge rate. The Imax column is the maximum current value after short-circuiting.

[0032] [Table 1]

[0033] Based on the results above, in all cases—the positive electrode (Experimental Examples 1-3) and negative electrode (Experimental Examples 4-6) of liquid-based batteries, and the positive electrode (Experimental Examples 7-9) and negative electrode (Experimental Examples 10-12) of all-solid-state batteries—increasing the charging rate significantly increased the maximum current value after a short circuit. As already mentioned, the degree of reaction unevenness increases with increasing charging rate, so from the above results, it was confirmed that the degree of reaction unevenness can be detected from the maximum current value after a short circuit.

[0034] Thus, according to this embodiment, the degree of reaction unevenness in the thickness direction within the active material layer generated by charging and discharging of a secondary battery can be detected from the current value that flows when two points in the thickness direction of the active material layer are short-circuited. The degree of reaction unevenness may be expressed by an index value appropriately determined from this current value.

[0035] While the above description has been made in relation to embodiments of the present invention, it will be clear to those skilled in the art that many modifications and changes are readily possible, and that the present invention is not limited to the embodiments illustrated above, but can be applied to various devices without departing from the concept of the present invention.

Claims

1. A secondary battery having a configuration in which an active material layer coated on a positive electrode current collector foil and an active material layer coated on a negative electrode current collector foil face each other with an electrolyte layer in between, the secondary battery comprising: a conductive path that selectively short-circuits two points in the thickness direction of at least one of the positive electrode and the negative electrode; a current detection means for detecting the current flowing through the conductive path; and a reaction unevenness detection means for detecting the degree of reaction unevenness in the active material layer in the thickness direction of at least one of the positive electrode and the negative electrode based on the magnitude of the current when the conductive path between two points in the thickness direction of at least one of the positive electrode and the negative electrode is short-circuited.

2. A secondary battery according to claim 1, wherein the conductive path is configured to selectively short-circuit the current collector foil and the surface of the active material layer on the electrolyte layer side in at least one of the positive electrode and the negative electrode.

3. A secondary battery according to claim 1, wherein the conductive path is configured to selectively short-circuit the current collector foil in at least one of the positive electrode and the negative electrode, and the portion of the active material layer closer to the current collector foil than the surface of the active material layer on the electrolyte layer side.

4. A secondary battery according to claim 1, wherein the conductive path is configured to selectively short-circuit the surface of the active material layer on the electrolyte layer side of at least one of the positive electrode and the negative electrode and the portion closer to the electrolyte layer than the current collector foil.

5. A secondary battery according to claim 1, wherein the conductive path is configured to selectively short-circuit the space between the current collector foil and an intermediate portion of the active material layer that is closer to the current collector foil than the surface of the active material layer on the electrolyte layer side, and the space between the intermediate portion and the surface of the active material layer on the electrolyte layer side, and the current flowing through each of these is detected.

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