A secondary battery that can more quickly mitigate reaction unevenness within electrodes.

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 reaction unevenness in the thickness direction of the active material layer is to be mitigated more quickly. [Solution] A secondary battery 1 has a configuration in which an active material layer 3 coated on the positive electrode current collector foil 2 and an active material layer 5 coated on the negative electrode current collector foil 4 face each other with an electrolyte layer 6 in between. The battery has a conductive path 7 that selectively short-circuits the current collector foil and the electrolyte layer side surface of the active material layer in at least one of the positive electrode and the negative electrode, and is configured so that the reaction unevenness in the active material layer is accelerated by the short-circuiting of the conductive path.

Description

[Technical Field]

[0001] The present invention relates to a secondary battery, and more particularly to a secondary battery equipped with a configuration that more quickly mitigates reaction unevenness in the thickness direction of the electrodes. [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 inter-electrode voltage. 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 inter-electrode voltage 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%). Thus, it would be convenient if a secondary battery had a configuration that could more quickly mitigate 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 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, which can more quickly mitigate reaction unevenness in the thickness direction of the active material layer.

[0006] In this regard, the inventors of the present invention have found that, when reaction unevenness occurs in the thickness direction of the active material layer in the above-mentioned secondary battery, electrically short-circuiting the current collector foil and the separator-side surface of the active material layer at each electrode causes current to flow and mitigates the reaction unevenness in a shorter time. This finding is utilized in the present invention. [Means for solving the problem]

[0007] According to the present invention, the above problems are solved by 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, wherein at least one of the positive electrode and the negative electrode has a conductive path that selectively short-circuits the current collector foil and the surface of the active material layer on the electrolyte layer side, and the short-circuiting of the conductive path is configured to accelerate the mitigation of reaction unevenness in the active material layer of the positive electrode or the negative electrode.

[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, a conductive path is formed in either the positive electrode or the negative electrode, or both, that selectively short-circuits between the current collector foil and the electrolyte layer-side surface of the active material layer. The conductive path may be formed from any conductive material that does not react with lithium. For example, in the negative electrode, copper, nickel, stainless steel, gold, platinum, carbon nanotubes, graphene, etc., can be used, and in the positive electrode, aluminum, nickel, stainless steel, gold, platinum, carbon nanotubes, graphene, etc., can be used. With this configuration, by allowing the direct flow of current between the current collector foil and the electrolyte layer-side surface of the active material layer, it is possible to promote the mitigation of reaction unevenness. More specifically, when there are reaction irregularities within the active material layer of the electrode, the potential difference caused by the concentration difference of the reaction products in the active material layer acts as a driving force, causing the reaction products to move in the direction that alleviates the concentration difference. In the absence of such a conductive path, the driving force is the concentration difference between adjacent regions. However, when a conductive path is created that directly shorts between the current collector foil and the electrolyte layer side surface of the active material layer, the driving force becomes the potential difference caused by the concentration difference between the region adjacent to the current collector foil in the active material layer and the electrolyte layer side surface. This becomes significantly larger than in the case without a conductive path, thus further promoting the alleviation of reaction irregularities. This has been confirmed by experimental examples described later. Short-circuiting by a conductive path may be performed selectively and at appropriate times, for example, after charging and discharging, when it is necessary to alleviate reaction irregularities.

[0010] As described above, when a short circuit is formed between the current collector foil and the electrolyte layer surface of the active material layer using a conductive path, the current flowing through the conductive path increases sharply immediately after the short circuit, then gradually decreases, and when the reaction unevenness is substantially eliminated, the potential difference between the current collector foil and the electrolyte layer surface of the active material layer becomes almost zero, and the current becomes almost zero. Therefore, the short circuit using a conductive path to mitigate the reaction unevenness may be carried out until the current becomes almost zero. When the potential difference between the current collector foil and the electrolyte layer surface of the active material layer becomes almost zero, the electrode voltage reaches equilibrium. For example, when the change in the electrode voltage over one hour during the execution of the short circuit falls below 1 mV, it can be determined that the electrode voltage has reached equilibrium and the mitigation is complete, and the time from the short circuit to the completion of mitigation may be used as the mitigation time.

[0011] In the above configuration, a conductive layer may be formed on the electrolyte layer side surface of the active material layer on at least one of the positive and negative electrodes, and the conductive path may be configured to selectively short-circuit between the current collector foil and the conductive layer. The conductive layer is a layer that conducts electricity while simultaneously allowing substances moving between electrodes, such as lithium ions, to pass through. Specifically, it may be a layer made of a conductive material such as carbon material or metal, and having a large number of through holes. For example, the conductive layer may be made of the same material as the active material layer, but with higher electron conductivity than the active material layer by changing the type and amount of conductive additive. For example, the conductive layer may be a gold sputtered layer, or LiNi 0.8 Co 0.1 Mn 0.1 The conductive layer may be a slurry of O2, graphene, conductive carbon black, and polyvinylidene fluoride (=88:4:6:2) (the type of material varies depending on the type of active material. Graphene and conductive carbon black may be conductive materials such as CNT (carbon nanotubes), AB (acetylene black), KB (Ketjen black), or VGCF (vapor-phase carbon fiber)). When a conductive layer is formed as described above and short-circuited with the current collector foil, the reaction unevenness relaxation time is significantly reduced. The conductive layer does not have to cover the entire surface of the electrolyte layer side of the active material layer. Reducing the area of ​​the conductive layer is advantageous in that it saves conductive layer material. Experimental examples have shown that, in order to better promote the relaxation of reaction unevenness, the area of ​​the conductive layer is preferably 50% or more of the surface area of ​​the electrolyte layer side of the active material layer on at least one of the positive and negative electrodes.

[0012] Also, in the above configuration, at least one additional conductive layer may be formed between the conductive layer and the current collector foil in at least one of the positive electrode and the negative electrode, and the conductive path may be configured to selectively short-circuit between the current collector foil, the conductive layer, and the additional conductive layer. As described above, when an additional conductive layer is added, as shown in the experimental examples described later, the relaxation time of the reaction unevenness is further shortened. In that case, preferably, at least one additional conductive layer is preferably arranged at substantially equal intervals between the current collector foil and the conductive layer in at least one of the positive electrode and the negative electrode. Thereby, the relaxation time of the reaction unevenness is shortened compared to when the intervals of the additional conductive layers are not equal.

Advantages of the Invention

[0013] Thus, according to the configuration of the present invention, in a secondary battery having a configuration in which the active material layer coated on the current collector foil of the positive electrode and the active material layer coated on the current collector foil of the negative electrode face each other with the electrolyte layer interposed therebetween, a conductive path is provided to selectively short-circuit between the current collector foil and the surface of the active material layer on the electrolyte layer side, and the short-circuit by such a conductive path accelerates the relaxation of the reaction unevenness in the active material layer. With such a configuration, the reaction unevenness in the active material layer after charge and discharge can be relaxed at an early stage, and it becomes possible to prevent the early stop of charge and discharge and the decrease in the charge and discharge rate.

[0014] 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

[0015] [Figure 1] FIG. 1 is a schematic cross-sectional view of a secondary battery to which the present embodiment is applied. [Figure 2] FIG. 2 is a schematic cross-sectional view of the active material layer for explaining the process in which the reaction unevenness in the active material layer is relaxed by the short-circuit by the conductive path. [Figure 3] FIGS. 3(A) and (B) are schematic diagrams of the time changes of the current I flowing and the voltage V between the electrodes 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 is time. [Figure 4]Figure 4(A) is a schematic cross-sectional view of the electrode of a secondary battery to which this embodiment is applied, with an added block diagram illustrating the configuration of the conductive path connections. Figure 4(B) is a schematic plan view of the surface of the active material layer on the electrolyte layer side. Figures 4(C) and (D) are schematic cross-sectional views of the electrode when a further conductive layer is formed between the current collector foil and the surface of the active material layer on the electrolyte layer side. Figure 4(E) is a schematic cross-sectional view of the electrode when a conductive layer is formed in the electrolyte layer. For simplicity, the switch is omitted in Figures 4(C) to (E). [Explanation of Symbols]

[0016] 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...Conductive layer, 9a...Further conductive layer, 10...Short circuit indicator [Best Mode for Carrying Out the Invention]

[0017] The present invention will be described in detail below with reference to the attached figures, with reference to several preferred embodiments. In the figures, the same reference numerals indicate the same parts.

[0018] 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 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".

[0019] 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 the secondary battery described above, 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 the reaction of , when lithium atoms are bonded to the active material layer, lithium ions arrive from the electrolyte layer. As schematically depicted in FIG. 2, the concentration of lithium is generally higher on the side of the electrolyte layer 6, Cs Li than on the side of the current collector foil 4, Cc Li (Cs Li > Cc Li ), and in the active material layer 5, a concentration gradient, i.e., a reaction gradient, will occur in the thickness direction. And when such a reaction gradient in which the reaction proceeds locally in the thickness direction of the electrode occurs and remains, early termination of charge and discharge and a decrease in the charge and discharge rate will be caused. Also, such a reaction gradient (concentration gradient of reaction products) is relaxed even if left as it is after charge and discharge stops, but its driving force is a slight concentration difference between adjacent regions in the thickness direction of the active material layer, so it is very small, and it will take a considerable amount of time until the reaction gradient is substantially eliminated.

[0020] Regarding this point, in the research by the inventor of the present embodiment, it was found that 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, a 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 after charging of the lithium-ion battery illustrated in FIG. 2, for 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 conduction path 7, electrons flow from the region of LiC6 on the electrolyte layer side through the conduction path 7 to the region of C6 on the current collector foil side (the current I in the conduction path 7 flows from the current collector foil side to the electrolyte layer side), and at the same time, lithium ions Li from the region of LiC6 on the electrolyte layer side +The carbon dioxide is released and flows to the C6 region on the current collector foil side, where it receives electrons and becomes LiC6, which then adheres to the active material. In this case, the driving force for mitigating reaction unevenness is the concentration difference between the electrolyte layer side and the current collector foil side of the active material layer, which is greater than when there is no conductivity between the electrolyte layer side and the current collector foil side of the active material layer, and thus the mitigation of 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 on the electrolyte layer side and the surface on the current collector foil side of the active material layer reaches several 0.0 V).

[0021] In fact, experiments conducted by the inventors of this embodiment revealed that the current during a short circuit between the current collector foil side and the electrolyte layer side of the active material layer, as schematically shown in Figure 3(A), rapidly increases from the start of the short circuit (Sh), then gradually decreases, and reaches virtually zero. The fact that the current becomes virtually zero indicates that the concentration difference of the reaction product between the two short-circuited points has almost disappeared, that is, the unevenness of the reaction has been almost eliminated. Furthermore, when the voltage between the electrodes was measured after charging and discharging, the voltage gradually decreased from immediately after charging and discharging to reach equilibrium, as shown in Figure 3(B). It was observed that the time it took for the voltage to reach virtually equilibrium when there was a short circuit between the current collector foil side and the electrolyte layer side of the active material layer was less than 40% of the time when there was no short circuit between the current collector foil side and the electrolyte layer side of the active material layer (see experimental examples described later). When the voltage between the electrodes reached equilibrium after charging and discharging, it meant that the concentration difference of the reaction product in the thickness direction of the active material layer had almost disappeared. Thus, by short-circuiting the current collector foil side of the active material layer and the electrolyte layer side, the mitigation of reaction unevenness is significantly promoted, and reaction unevenness can be resolved more quickly.

[0022] Configuration to mitigate uneven reaction of electrodes Based on the above findings, in this embodiment, in the secondary battery described above, a conductive path 7 is formed in either the positive electrode or the negative electrode, or both, to electrically selectively short-circuit the current collector foils 2 and 4 and the electrolyte layer 6 side surface of the active material layers 3 and 5, as shown in Figure 4(A). After charging and discharging (while charging and discharging is stopped), a current flows between the current collector foil side and the electrolyte side of the active material layer through the conductive path 7. 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, 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. A switch 8 is provided in the middle of the conductive path 7 to control the conductivity in the conductive path 7, and the ON / OFF control of the switch 8 may be achieved by a short-circuit indicator 10, which may be any type of computer device or circuit device.

[0023] Preferably, a conductive layer 9 is formed on the electrolyte-side surface of the active material layer, and the conductive path 7 is formed to short-circuit the current collector foils 2 and 4 with the conductive layer 9. The conductive layer 9 is a layer that conducts electricity and is also permeable to substances moving between electrodes, such as lithium ions. Specifically, it may be a layer composed of a conductive material such as carbon material or metal, and having a large number of through-holes. By changing the type and amount of conductive additive, it may be a layer with relatively higher electronic conductivity than the active material layer. For example, the conductive layer may be a gold sputtering layer, or a coated layer of a slurry of a mixture of the active material, a conductive carbon material, and a resin such as polyvinylidene fluoride. In the latter case, the type of active material is appropriately selected depending on the type of active material layer to be applied. The conductive carbon material may be graphene, conductive carbon black, CNT (carbon nanotube), AB (acetylene black), KB (Ketjen black), VGCF (vapor-phase carbon fiber), etc. As described above, when the conductive layer 9 is formed and short-circuited with the current collector foil, the reaction unevenness mitigation time (the time until the reaction unevenness is substantially eliminated) is significantly reduced.

[0024] The conductive layer 9 may be formed over the entire surface of the electrolyte-side surface of the active material layer, but it does not have to cover the entire surface of the active material layer. For example, the conductive layer 9 may have a comb-like shape, as shown in Figure 4(B). This allows for material savings for the conductive layer 9. According to experiments described later, preferably, the area of ​​the conductive layer 9 may be 50% or more of the surface area of ​​the electrolyte-side surface of the active material layer on at least one of the positive and negative electrodes. Furthermore, the conductive layer 9 does not necessarily have to be formed on the electrolyte-side surface of the active material layer, but may be provided slightly inward from such a surface towards the current collector foil (up to about 10% of the thickness of the active material layer). This is because if the distance from the active material layer to the conductive layer 9 is relatively short, electron exchange with the conductive layer 9 can be achieved quickly. Moreover, the conductive layer 9 may be formed on the surface of the electrolyte layer 6 facing the active material layer, as shown in Figure 4(E).

[0025] Furthermore, as shown in Figures 4(C) and (D), at least one additional conductive layer 9a may be interposed within the active material layer between the current collector foils 2 and 4 and the conductive layer 9. This further reduces the reaction unevenness relaxation time. Experiments described later have shown that the reaction unevenness relaxation time can be further reduced by positioning the additional conductive layer 9a between the current collector foils 2 and 4 and the conductive layer 9 at substantially equal intervals (the intervals may be shifted by up to about 5%).

[0026] During operation, when reaction irregularities need to be mitigated, for example, after charging and discharging, the switch 8 is turned ON and the conductive path 7 is opened. The elimination of reaction irregularities can be confirmed when the voltage between the electrodes becomes substantially balanced (although not shown in the diagram, a voltmeter for detecting the voltage between the electrodes may be provided).

[0027] 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.

[0028] In the experiment, liquid-based batteries and all-solid-state batteries prepared by the method described below were charged at a predetermined charge rate. Then, the current collector foil of each electrode and the electrolyte layer surface of the active material layer were short-circuited, and the time (relaxation time) until the reaction unevenness was resolved was measured.

[0029] 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 Mn 0.1 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.

[0030] (2) All-solid-state battery - For the positive electrode, the positive electrode active material (LiNi 1 / 3 Co 1 / 3 Mn 1 / 3A 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. 2 A circular component was punched out to form the positive electrode. For the negative electrode, the negative electrode active material (Li4Ti5O 12 A negative electrode slurry was prepared by mixing a solid electrolyte (10LiI·90Li3PS4), a conductive material (carbon nanotubes), 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). The slurry was then coated onto copper foil which would serve as the current collector foil, dried at 100°C for 30 minutes, and then a diameter of 1 cm was formed from it. 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.

[0031] Furthermore, the following procedure was performed on each sample of the electrodes of each battery. Experimental Example 1 - LiNi 0.8 Co 0.1 Mn 0.1 A slurry of O2, graphene, conductive carbon black, and PVdF (=88:4:6:2) was applied to form a conductive layer. Experimental Example 2- Gold was sputtered onto the entire surface of the electrolyte layer side of the active material layer of the positive electrode of the liquid-type battery to create a conductive layer. Even when gold sputtering is applied to the entire surface, electron microscopy reveals areas not covered by gold, indicating the presence of microscopic through-pores, allowing lithium ions to pass through (the same applies below). Experimental Example 3 - Gold was sputtered onto 50% of the surface of the electrolyte layer side of the positive electrode of the liquid-type battery to create a conductive layer. Experimental Example 4 -In forming the active material layer of the positive electrode of the liquid-type battery, slurry coating and drying, followed by gold sputtering over the entire surface, were repeated three times to form a positive electrode active material layer having one conductive layer and two further conductive layers. The spacing of the conductive layers was set to conductive layer-further conductive layer 1:further conductive layer 1-further conductive layer 2:further conductive layer 2-current collector foil = 33:34:33. Experimental Example 5 - Gold was sputtered onto the entire surface of the electrolyte layer side of the active material layer of the negative electrode of the liquid-type battery to create a conductive layer. Experimental Example 6 - Gold was sputtered onto the entire surface of the electrolyte layer side of the positive electrode of the all-solid-state battery to create a conductive layer. Comparative Example 1 -A battery without a conductive layer was used as the positive electrode of the liquid-based battery. Comparative Example 2 -A battery without a conductive layer was used as the negative electrode for the liquid-based battery. Comparative Example 3 -The preparation was the same as in Experimental Example 4, except that the spacing of the conductive layers was set to 10:45:45. Comparative Example 4 - Gold was sputtered onto 30% of the surface of the active material layer on the electrolyte layer side of the positive electrode of the liquid-type battery to create a conductive layer. Comparative Example 5 -A battery without a conductive layer was used as the positive electrode of the all-solid-state battery.

[0032] Except for Comparative Examples 1, 2, and 5, a conductive path that can be selectively short-circuited was installed between the conductive layer (including further conductive foil) and the current collector foil. For the conductive path, an aluminum wire with a diameter of 0.1 mm was used for the positive electrode and a copper wire with a diameter of 0.1 mm was used for the negative electrode, with the ends of each wire connected to the current collector foil and the electrolyte-side surface of the active material layer.

[0033] In measuring the relaxation time for reaction unevenness in the electrode samples of each prepared battery, first, each battery with a State of Charge (SOC) of 0% was subjected to constant current charging at a charge rate of 2[C] for 1 minute. Here, the charge rate is an index value of the current supply rate, and at a charge rate of N[C], the current is supplied at a rate that achieves charging from 0% to 100% SOC in 1 / N time. Then, while monitoring the inter-electrode voltage, immediately after charging stopped, the conductive path and the current collector foil were short-circuited, and the point in time when the inter-electrode voltage reached substantially equilibrium was detected. Since the inter-electrode voltage gradually decreases to reach equilibrium as depicted in Figure 3(B), the point in time when the change in the inter-electrode voltage V over 1 hour ΔV fell below 1mV was determined to be the point in time when substantially equilibrium was reached, and this point was defined as the completion of reaction unevenness relaxation. The relaxation time was defined as the length from the point of charging stop to the point of relaxation completion.

[0034] The relaxation time results for each electrode of each battery were as follows. In Table 1, the No. column is the sample number (Ei: Experimental Example i, Ci: Comparative Example i). 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 / C column is the number of conductive layers. The P% column is the ratio of the distance of the conductive layer from the electrolyte layer to the thickness of the active material layer. The A% column is the ratio of the area of ​​the conductive layer to the surface area of ​​the active material layer. The T / E column is the relaxation time [seconds]. [Table 1]

[0035] Refer to the results in the table above, (a) From Experimental Examples 1 and 2 and Comparative Example 1, and Experimental Example 5 and Comparative Example 2, it was shown that forming a conductive layer on both the positive and negative electrodes and short-circuiting the conductive layer with the current collector foil shortens the relaxation time. (b) From Experimental Examples 2 and 3 and Comparative Example 4, it was shown that when the area ratio A% of the conductive layer was 50%, the relaxation time was reduced to less than one-third, while when the area ratio A% was 30%, it remained at less than half. This indicates that by setting the area ratio of the conductive layer to 50% or more, an effective reduction in relaxation time can be achieved. (c) Experimental examples 2 and 4 showed that the relaxation time could be further shortened by increasing the number of conductive layers. (d) From Experimental Example 4 and Comparative Example 3, it was shown that when multiple conductive layers are formed within the active material layer, the relaxation time can be further reduced by arranging them at equal intervals. (e) From Experimental Example 6 and Comparative Example 5, it was shown that even in all-solid-state batteries, forming a conductive layer and short-circuiting the conductive layer with the current collector foil shortens the relaxation time.

[0036] Thus, according to this embodiment, the uneven reaction in the thickness direction within the active material layer that occurs due to the charging and discharging of the secondary battery can be mitigated more quickly by short-circuiting the current collector foil and the surface of the active material layer on the electrolyte layer side.

[0037] 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, wherein at least one of the positive electrode and the negative electrode has a conductive path that selectively short-circuits the current collector foil and the surface of the active material layer on the electrolyte layer side, and the short-circuiting of the conductive path is configured to accelerate the mitigation of reaction unevenness in the active material layer of the positive electrode or the negative electrode.

2. A secondary battery according to claim 1, wherein a conductive layer is formed on 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 conductive path is configured to selectively short-circuit the current collector foil and the conductive layer.

3. A secondary battery according to claim 2, wherein at least one further conductive layer is formed between the conductive layer and the current collector foil in at least one of the positive electrode and the negative electrode, and the conductive path is configured to selectively short-circuit the current collector foil, the conductive layer and the further conductive layer.

4. A secondary battery according to claim 3, wherein the at least one further conductive layer is arranged at substantially equal intervals between the current collector foil and the conductive layer in at least one of the positive electrode and the negative electrode.

5. A secondary battery according to claim 2, wherein the area of ​​the conductive layer is 50% or more of the surface area of ​​the active material layer on the electrolyte layer side of at least one of the positive electrode and the negative electrode.

Images