Manufacturing method for all-solid-state secondary battery-mounted circuit board

Abstract

Provided is a manufacturing method for an all-solid-state secondary battery-mounted circuit board capable of satisfactorily maintaining the characteristics of an all-solid-state secondary battery.　The manufacturing method for an all-solid-state secondary battery-mounted circuit board according to the present invention is for manufacturing a circuit board to which is mounted an all-solid-state secondary battery having: a power generation element in which a positive electrode layer including a sulfide-based solid electrolyte and a positive electrode active material having a reaction suppression layer formed on at least portion of a surface thereof, a solid electrolyte layer, and a negative electrode layer are layered in order; and an outer packaging that accommodates the power generation element. The manufacturing method is characterized by: having a step in which the all-solid-state secondary battery is mounted on a circuit board by reflow soldering; and subjecting the all-solid-state secondary battery to the reflow soldering, with the potential of the positive electrode layer being maintained at 2.55 V or lower based on the lithium potential.

Description

Manufacturing method for all-solid-state secondary battery mounted circuit board

[0001] The present invention relates to a method for manufacturing an all-solid-state secondary battery mounted circuit board that can maintain good characteristics of the all-solid-state secondary battery.

[0002] BACKGROUND ART In recent years, with the development of portable electronic devices such as mobile phones and notebook personal computers, and the practical application of electric vehicles, small, lightweight, high-capacity, and high-energy density lithium secondary batteries have come into use.

[0003] Furthermore, lithium secondary batteries are not only used as the main power source for electronic devices, but are also being developed for use as memory backup power sources, etc. In such applications, lithium secondary batteries are mounted by soldering or the like on circuit boards on which electronic components are mounted.

[0004] When mounting a lithium secondary battery on a circuit board, it is desirable to automatically mount the battery on the circuit board by reflow soldering, considering industrial mass production. However, in this case, the battery passes through a reflow furnace set at a very high temperature, and there is a risk that the battery characteristics will deteriorate, especially in the case of a lithium secondary battery using an organic electrolyte, due to evaporation of the organic electrolyte solvent.

[0005] On the other hand, all-solid-state secondary batteries, which do not contain an organic electrolyte solution and in which ions are exchanged between a positive electrode layer and a negative electrode layer by a solid electrolyte layer, have higher heat resistance than batteries with an organic electrolyte solution, and are therefore expected to be able to maintain their characteristics better even when mounted on a circuit board by reflow soldering.

[0006] However, when the sulfide-based solid electrolyte comes into contact with the positive electrode active material, it oxidizes to form a resistive layer, which may cause a decrease in ionic conductivity in the positive electrode. This problem of a decrease in ionic conductivity in the positive electrode due to oxidation of the sulfide-based solid electrolyte is likely to occur particularly when the all-solid-state secondary battery is used at high temperatures.

[0007] Meanwhile, a technology has been developed to suppress the deterioration of the characteristics of all-solid-state secondary batteries, for example, in high-temperature environments (high temperatures within the temperature range in which the battery is used) by coating the surface of the positive electrode active material with a coating layer (reaction-suppressing layer) to suppress the reaction between the sulfide-based solid electrolyte and the positive electrode active material, thereby suppressing oxidative decomposition of the sulfide-based solid electrolyte in the positive electrode (Patent Documents 1 and 2, etc.).

[0008] In addition, Li ６ P.S. ５ Cl and Li ３ P.S. ４ Non-Patent Document 1 reports on the potential window of sulfide-based solid electrolytes such as those mentioned above.

[0009] JP 2016-207567 A JP 2021-141007 A

[0010] ACS Energy Letters, 2019, Vol. 4, pp. 2418-2427

[0011] In the case of the techniques described in Patent Documents 1 and 2, it is possible to effectively suppress deterioration in characteristics even at relatively high temperatures within the temperature range in which all-solid-state secondary batteries are normally used. However, the inventors have made it clear through their studies that if the all-solid-state secondary battery is placed at an extremely high temperature, such as that used in reflow soldering, and then used at a high temperature, deterioration in characteristics of the all-solid-state secondary battery due to oxidative decomposition of the sulfide-based solid electrolyte cannot be effectively suppressed.

[0012] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for manufacturing an all-solid-state secondary battery mounted circuit board that can maintain good characteristics of the all-solid-state secondary battery.

[0013] The method for manufacturing an all-solid-state secondary battery-mounted circuit board of the present invention is a method for manufacturing a circuit board mounted with an all-solid-state secondary battery, the all-solid-state secondary battery having a positive electrode active material having a reaction suppression layer formed on at least a portion of the surface thereof, a power generation element in which a positive electrode layer containing a sulfide-based solid electrolyte, a solid electrolyte layer, and a negative electrode layer are laminated in this order, and an exterior body that houses the power generation element, the method comprising the step of mounting the all-solid-state secondary battery on the circuit board by reflow soldering, and is characterized in that the all-solid-state secondary battery is subjected to the reflow soldering in a state in which the potential of the positive electrode layer is set to 2.55 V or less relative to the lithium potential.

[0014] According to the present invention, it is possible to provide a method for manufacturing an all-solid-state secondary battery mounted circuit board that can maintain good characteristics of the all-solid-state secondary battery.

[0015] FIG. 1 is a cross-sectional view schematically showing an example of an all-solid-state secondary battery that can be used in an all-solid-state secondary-battery-mounted circuit board according to a method of the present invention.

[0016] A method for manufacturing an all-solid-state secondary battery-mounted circuit board of the present invention includes a step of mounting an all-solid-state secondary battery, which includes a power generating element including a cathode active material having a reaction suppression layer formed on at least a portion of its surface, a cathode layer including a sulfide-based solid electrolyte, a solid electrolyte layer, and an anode layer laminated in this order, and an exterior body that houses the power generating element, on a circuit board by reflow soldering. In the manufacturing method of the present invention, in the step, the all-solid-state secondary battery is subjected to reflow soldering while the potential of the cathode layer is set to 2.55 V or less relative to the lithium potential.

[0017] As described above, the reaction suppression layer formed on the surface of the positive electrode active material has the function of suppressing oxidative decomposition of the sulfide-based solid electrolyte due to a reaction between the sulfide-based solid electrolyte and the positive electrode active material, thereby maintaining good characteristics of the all-solid-state secondary battery during use, etc. However, when the all-solid-state secondary battery is subjected to extremely high temperatures such as those used in reflow soldering, the sulfide-based solid electrolyte undergoes oxidative decomposition, particularly in the positive electrode layer, and the product (sulfur) of this oxidative decomposition deteriorates the reaction suppression layer on the surface of the positive electrode active material. Therefore, when the all-solid-state secondary battery (a circuit board on which the all-solid-state secondary battery is mounted) is subsequently used at high temperatures (relatively high temperatures within the temperature range in which the circuit board is normally used), the battery characteristics deteriorate at an accelerated rate.

[0018] As a result of extensive research, the inventors have discovered that the oxidative decomposition of the sulfide-based solid electrolyte in the positive electrode layer at extremely high temperatures, such as those used in reflow soldering, is related to the potential window of the sulfide-based solid electrolyte, and that this oxidative decomposition occurs when the potential of the positive electrode layer relative to the lithium potential exceeds the upper limit of the potential window of the sulfide-based solid electrolyte. The inventors have then completed the present invention, which makes it possible to provide a circuit board in which the oxidative decomposition of the sulfide-based solid electrolyte is suppressed and deterioration of the reaction suppression layer on the surface of the positive electrode active material is suppressed by setting the potential of the positive electrode layer relative to the lithium potential to a predetermined value or less, thereby enabling the provision of a circuit board in which the mounted all-solid-state secondary battery can maintain good characteristics even when used at high temperatures.

[0019] In an all-solid-state secondary battery to be subjected to reflow soldering, the potential of the positive electrode layer is set to 2.55 V or less relative to the lithium potential, which makes it possible to suppress oxidative decomposition of the sulfide-based solid electrolyte in the positive electrode layer during reflow soldering and to suppress deterioration of the reaction suppression layer on the surface of the positive electrode active material.

[0020] In addition, when the potential of the positive electrode layer is set to 2.55 V or less based on the lithium potential, even if a part of the sulfide-based solid electrolyte is oxidized and decomposed in the positive electrode layer during reflow soldering, the resulting product itself may have the function of a sulfide-based solid electrolyte, and therefore, the deterioration of the characteristics of the all-solid-state secondary battery itself can be suppressed. ６ P.S. ５ When using Cl, some Li is removed by reflow soldering after adjusting the potential of the positive electrode layer to 2.55 V or less based on the lithium potential. ６ P.S. ５ Even if Cl is oxidized and decomposed, the decomposition products include Li, which is a type of sulfide-based solid electrolyte. ３ P.S. ４ and Li ３ P.S. ４ Since oxidative decomposition is sufficiently suppressed under the above-mentioned reflow soldering conditions, the characteristics of the all-solid-state secondary battery are maintained favorably.

[0021] In addition, it is preferable that the potential of the positive electrode layer of the all-solid-state secondary battery to be subjected to reflow soldering is adjusted to 2.40 V or less based on the lithium potential. In this case, the oxidative decomposition of the sulfide-based solid electrolyte in the positive electrode layer during reflow soldering can be more effectively suppressed (for example, the all-solid-state secondary battery can be used to more effectively suppress the oxidative decomposition of Li in the sulfide-based solid electrolyte of the positive electrode layer). ６ P.S. ５ If Cl is used, Li will not remain even after reflow soldering. ６ P.S. ５ Since the oxidative decomposition of Cl is suppressed to an extremely high degree, deterioration of the reaction suppression layer on the surface of the positive electrode active material can be further suppressed.

[0022] The lower limit of the potential of the positive electrode layer of the all-solid-state secondary battery to be subjected to reflow soldering is not particularly limited, but is usually 1.3 V based on the lithium potential.

[0023] The potential of the positive electrode layer relative to the lithium potential in an all-solid-state secondary battery to be subjected to reflow soldering is determined as follows (the potential of the positive electrode layer relative to the lithium potential described in the Examples below is a value determined by this method). An all-solid-state secondary battery manufactured with the same specifications is disassembled to remove the power-generating element, and a three-electrode model cell is assembled using lithium metal foil as the reference electrode, and the battery voltage (voltage of the power-generating element) of the all-solid-state secondary battery and the positive electrode potential relative to the lithium potential are measured. By repeating similar measurements for multiple all-solid-state secondary batteries with different battery voltages and creating a data table in which the battery voltage and the positive electrode potential correspond, it becomes possible to estimate the positive electrode potential of an all-solid-state secondary battery by measuring the battery voltage of that all-solid-state secondary battery (a battery used for mounting on a circuit board).

[0024] For an all-solid-state secondary battery having a positive electrode terminal electrically connected to the positive electrode layer and having a portion exposed from the inside of the exterior body to the outside, and a negative electrode terminal electrically connected to the negative electrode layer and having a portion exposed from the inside of the exterior body to the outside, a method can be adopted in which the positive electrode terminal and the negative electrode terminal of the all-solid-state secondary battery are closely attached to each other with a single conductive sheet, thereby discharging the all-solid-state secondary battery. This method is simple and allows multiple all-solid-state secondary batteries to be discharged simultaneously using a single conductive sheet, thereby making it possible to increase the productivity of all-solid-state secondary battery mounting circuit boards.

[0025] A conductive sheet for discharging an all-solid-state secondary battery is preferably a conductive rubber sheet, which is generally more flexible than a resin sheet or a metal sheet, which have high hardness, and therefore can prevent damage when the positive and negative electrode terminals of the all-solid-state secondary battery are brought into close contact with each other, and can also bring the positive and negative electrode terminals into good close contact with each other even when their height positions do not match.

[0026] Conductive rubber sheets include those made by compounding various rubbers with carbon black or metal powder, but conductive silicone rubber sheets made from silicone rubber are preferred because of their excellent heat resistance. For the reasons mentioned above, their hardness (Shore A) is preferably 60 to 65°. Furthermore, if the volume resistivity is in the range of 1 to 10 Ω·cm (for a sheet with a thickness of 1 mm), multiple all-solid-state secondary batteries can be discharged without variability.

[0027] The discharge treatment for adjusting the potential of the positive electrode layer of the all-solid-state secondary battery is preferably carried out at a temperature of 40° C. to 80° C. A higher temperature is desirable because the conductivity of the solid electrolyte improves and discharge can be achieved in a shorter time, but if the temperature rises too high, there is a concern that the battery may deteriorate and there may also be an effect on production equipment such as discharge trays, so it is desirable to carry out the treatment within this range.

[0028] Furthermore, it is more preferable that the all-solid-state secondary battery to be subjected to reflow soldering be adjusted so that the open circuit voltage is 1.0 V or less.

[0029] When an all-solid-state secondary battery is mounted on a circuit board by reflow soldering, if the battery is exposed to an extremely high temperature, a current greater than the current value specified for the battery at room temperature may flow in the circuit, which may adversely affect electronic components mounted on the circuit board. However, if the all-solid-state secondary battery satisfies the above-mentioned open circuit voltage, a large current will not flow in the circuit even if it is exposed to an extremely high temperature during reflow soldering, and therefore deterioration of the electronic components mounted on the circuit board can be suppressed.

[0030] In addition, adjusting a secondary battery having an organic electrolyte solution so that its open circuit voltage is 1.0 V or less can be done, for example, by placing it in an overdischarged state. However, doing so may accelerate battery degradation, which may increase the defect rate during the manufacture of all-solid-state secondary-battery-mounted circuit boards and reduce productivity. However, in the case of an all-solid-state secondary battery that does not have an organic electrolyte solution and uses a solid electrolyte layer to exchange ions between the positive electrode layer and the negative electrode layer, adjusting the open circuit voltage to 1.0 V or less by, for example, placing it in an overdischarged state does not cause degradation to the extent that problems arise in use. Therefore, when mounting an all-solid-state secondary battery on a circuit board, it is possible to effectively suppress degradation of the all-solid-state secondary battery and electronic components mounted on the circuit board, thereby further reducing the occurrence of defective circuit boards manufactured, thereby ensuring higher productivity.

[0031] The open circuit voltage of an all-solid-state secondary battery to be subjected to reflow soldering for mounting on a circuit board is preferably 1.0 V or less, more preferably 0.9 V or less, even more preferably 0.6 V or less, and may be 0 V. An all-solid-state secondary battery that satisfies the above open circuit voltage may be one in an overdischarged state. To bring an all-solid-state secondary battery into an overdischarged state, various discharge treatment methods can be used, as described below, but the open circuit voltage obtained within a practical treatment time is usually 0.05 V or more, and in many cases 0.1 V or more.

[0032] The open circuit voltage of an all-solid-state secondary battery as used herein refers to the voltage of the all-solid-state secondary battery measured after charging or discharging the all-solid-state secondary battery, and after 72 hours have passed in an open circuit state in an environment at 23°C after the completion of charging or discharging.

[0033] As used herein, the "overdischarge state" of an all-solid-state secondary battery refers to a state in which the voltage in an open circuit state is lower than the open circuit voltage after rated discharge. Specifically, when the fully charged state of an all-solid-state secondary battery is defined as SOC (state of charge) = 100%, the "overdischarge state" refers to a state in which an all-solid-state secondary battery with an SOC = S% is subjected to rated discharge for (5 x S / 100) hours at a current value of 0.2 C, or a state in which a certain amount of electricity is further discharged from a state in which an equivalent amount of electricity is discharged (SOC = 0%). In other words, the "overdischarge state" refers to a state in which the voltage falls below the lower limit of the normal usage range of an all-solid-state secondary battery (SOC 100 to 0%) and further discharge is performed.

[0034] To over-discharge an all-solid-state secondary battery, a voltage (V Ｌ After the discharge is completed, the polarization inside the all-solid-state secondary battery gradually relaxes and the voltage rises, and the open circuit voltage after 72 hours is V Ｌ It will be higher, but V Ｌ By adjusting the value of the discharge cut-off current and the discharge cut-off current, an all-solid-state secondary battery in an overdischarged state with a desired open-circuit voltage can be obtained. Although various other methods are conceivable, for example, an all-solid-state secondary battery in an overdischarged state with a desired open-circuit voltage can also be obtained by connecting a resistor of 10 to 1000 Ω and maintaining a voltage of 0 V for several minutes to several tens of hours.

[0035] If the all-solid-state secondary battery is in an overdischarged state, the potential of the positive electrode layer is usually equal to or lower than the above-mentioned value based on the lithium potential, and therefore the battery can be subjected to reflow soldering.

[0036] <All-Solid-State Secondary Battery> The all-solid-state secondary battery used in the manufacturing method of the present invention has a power generating element in which a positive electrode layer, a solid electrolyte layer, and a negative electrode layer are laminated in this order, and an exterior body that houses the power generating element.

[0037] A cross-sectional view schematically illustrating an example of an all-solid-state secondary battery is shown in Fig. 1. The all-solid-state secondary battery 10 shown in Fig. 1 has a power generating element 20 having a positive electrode layer 21, a negative electrode layer 22, and a solid electrolyte layer 23 interposed therebetween, and this power generating element 20 is enclosed in an exterior body formed by an exterior container 60 and a lid 70.

[0038] External terminals 80, 90 for electrically connecting the all-solid-state secondary battery 10 to a circuit on a circuit board are provided on the lower surface of the outer casing 60 in the drawing. The external terminal 80 is electrically connected to the positive electrode layer 21 of the power-generating element 20 through a conductive path 81, and serves as a positive electrode terminal. The external terminal 90 is electrically connected to the negative electrode layer 22 of the power-generating element 20 through a lead 40 and a conductive path 91, and serves as a negative electrode terminal.

[0039] The positive electrode layer 21 constituting the power generating element 20 has a positive electrode mixture layer (a compact of a positive electrode mixture) 211 and a current collector 212. The negative electrode layer 22 constituting the power generating element 20 has a negative electrode mixture layer (a compact of a negative electrode mixture) 221 and a current collector 222.

[0040] A conductive sheet (metal foil, foamed metal porous body, etc.) 30 is arranged on the surface of the current collector 212 of the positive electrode layer 21 (the surface opposite to the positive electrode mixture layer 211), and the positive electrode layer 21 is in contact with the current collector 212, thereby establishing electrical conduction with the conductive sheet 30, which in turn is in electrical conduction with the conductive path 81.

[0041] 1 , a spacer 50 is disposed between the lead 40 and the lid 70, and has the effect of pressing the power generating element 20 toward the conductive sheet 30. The effect of this spacer 50 improves the electrical connection between the lead 40 and the negative electrode layer 22 and the conductive path 91, the electrical connection between the positive electrode layer 21 and the conductive sheet 30, and the electrical connection between the conductive sheet 30 and the conductive path 81. A rubber plate, a metal spring (such as a leaf spring), or the like can be used as the spacer 50.

[0042] (Positive Electrode Layer) The positive electrode layer of the all-solid-state secondary battery can be formed, for example, by molding a positive electrode mixture containing a positive electrode active material and the like.

[0043] The positive electrode active material is not particularly limited as long as it is a positive electrode active material used in conventionally known non-aqueous electrolyte secondary batteries, that is, an active material capable of absorbing and releasing Li ions. Specific examples of the positive electrode active material include lithium transition metal composite oxides containing at least one element selected from the group consisting of Mn, Co, and Ni as a transition metal; olivine-type lithium transition metal oxides containing at least one element selected from the group consisting of Fe, Mn, and Co as a transition metal; and the like. More specifically, LiM ｒ Mn ２－ｒ O ４ (wherein M is at least one element selected from the group consisting of Li, Na, K, B, Mg, Ca, Sr, Ba, Ti, V, Cr, Zr, Fe, Co, Ni, Cu, Zn, Al, Sn, Sb, In, Nb, Ta, Mo, W, Y, Ru, and Rh, and 0≦r≦1), a spinel-type lithium manganese composite oxide represented by Li ｒ Mn （１－ｓ－ｒ） Ni ｓ M ｔ O （２－ｕ） F ｖ (wherein M is at least one element selected from the group consisting of Co, Mg, Al, B, Ti, V, Cr, Fe, Cu, Zn, Zr, Mo, Sn, Ca, Sr, and W, and 0.8≦r≦1.2, 0<s<0.5, 0≦t≦0.5, u+v<1, −0.1≦u≦0.2, 0≦v≦0.1), a layered compound represented by １－ｒ M ｒ O ２ (wherein M is at least one element selected from the group consisting of Al, Mg, Ti, V, Cr, Zr, Fe, Ni, Cu, Zn, Ga, Ge, Nb, Mo, Sn, Sb, and Ba, and 0≦r≦0.5), lithium cobalt composite oxide represented by LiNi １－ｒ M ｒ O ２(wherein M is at least one element selected from the group consisting of Al, Mg, Ti, Zr, Fe, Co, Cu, Zn, Ga, Ge, Nb, Mo, Sn, Sb, and Ba, and 0≦r≦0.5), a lithium nickel composite oxide represented by Li １＋ｓ M １－ｒ N ｒ P.O. ４ F ｓ (wherein M is at least one element selected from the group consisting of Fe, Mn, and Co, and N is at least one element selected from the group consisting of Al, Mg, Ti, Zr, Ni, Cu, Zn, Ga, Ge, Nb, Mo, Sn, Sb, V, and Ba, and 0≦r≦0.5, 0≦s≦1) and the like. ２ M １－ｒ N ｒ P ２ O ７ (wherein M is at least one element selected from the group consisting of Fe, Mn, and Co, and N is at least one element selected from the group consisting of Al, Mg, Ti, Zr, Ni, Cu, Zn, Ga, Ge, Nb, Mo, Sn, Sb, V, and Ba, and 0≦r≦0.5) can also be used. As the positive electrode active material, only one of these compounds may be used, or two or more of them may be used in combination.

[0044] From the viewpoint of reducing side reactions that cause battery capacity degradation and increasing the density of the positive electrode, the average particle diameter of the positive electrode active material is preferably 0.1 μm or more, more preferably 0.5 μm or more, and is preferably 25 μm or less, more preferably 10 μm or less. The positive electrode active material may be primary particles or secondary particles formed by aggregation of primary particles. When the positive electrode layer contains a solid electrolyte, using a positive electrode active material with an average particle diameter in the above range can ensure a large interface with the solid electrolyte, thereby further improving the load characteristics of the battery.

[0045] The average particle diameter of the positive electrode active material and the average particle diameter of other particles (such as solid electrolytes) referred to in this specification are determined by a particle size distribution measuring device (such as a Microtrac particle size distribution measuring device "HRA9320" manufactured by Nikkiso Co., Ltd.) and are the 50% diameter value (D) in the volume-based integrated fraction when determining the integrated volume from particles with small particle sizes. ５０ ) means

[0046] The positive electrode active material has a reaction suppression layer on at least a portion of its surface for suppressing reaction with the sulfide-based solid electrolyte contained in the positive electrode layer.

[0047] The reaction suppression layer may be made of a material that has ion conductivity and can suppress the reaction between the positive electrode active material and the sulfide-based solid electrolyte. Examples of materials that can form the reaction suppression layer include oxides containing Li and at least one element selected from the group consisting of Nb, P, B, Si, Ge, Ti, Zr, Ta, and W, more specifically, LiNbO ３ Nb-containing oxides such as Li ３ P.O. ４ , Li ３ BO ３ , Li ４ SiO ４ , Li ４ GeO ４ , LiTiO ３ , LiZrO ３ , Li ２ WO ４ The reaction suppression layer may contain only one of these oxides, or may contain two or more of them, or may contain a composite compound of two or more of these oxides. Among these oxides, it is preferable to use an Nb-containing oxide, such as LiNbO ３ It is more preferable to use

[0048] The reaction suppression layer is present on at least a portion of the surface of the positive electrode active material, and more specifically, it is preferably present on the surface in an amount of 0.1 to 2.0 parts by mass per 100 parts by mass of the positive electrode active material. This range allows for effective suppression of the reaction between the positive electrode active material and the solid electrolyte.

[0049] Examples of methods for forming a reaction suppression layer on the surface of a positive electrode active material include the sol-gel method, mechanofusion method, CVD method, PVD method, and ALD method.

[0050] The content of the positive electrode active material in the positive electrode mixture constituting the positive electrode layer is preferably 20 to 95 mass %.

[0051] Examples of the conductive additive for the positive electrode layer include carbon materials such as carbon black (thermal black, furnace black, channel black, ketjen black, acetylene black, etc.), graphite (natural graphite, artificial graphite), graphene, vapor-grown carbon fiber, carbon nanofiber, and carbon nanotube; powders of Cu, Ni, Al, Au, and Pd alone or alloys thereof, or porous bodies thereof; and the like. These may be used alone or in combination of two or more. The content of the conductive additive in the positive electrode layer is preferably 0.1 to 15% by mass.

[0052] The positive electrode layer contains a sulfide-based solid electrolyte. ２ S-P ２ S ５ , Li ２ S-SiS ２ , Li ２ S-P ２ S ５ -GeS ２ , Li ２ S-B ２ S ３ In addition to particles of glass, thio-LISICON type particles [Li １０ GeP ２ S １２ , Li ９．５４ Si １．７４ P １．４４ S １１．７ Cl ０．３ Li12-12a-b+c+6d-eM, etc. １ ３＋ａ－ｂ－ｃ－ｄ M ２ ｂ M ３ ｃ M ４ ｄ M ５ １２－ｅX ｅ (However, M １ is Si, Ge or Sn, M ２ is P or V, M ３ is Al, Ga, Y or Sb, M ４ is Zn, Ca, or Ba, M ５ is either S or S and O, and X is F, Cl, Br or I, 0≦a<3, 0≦b+c+d≦3, 0≦e≦3], or argyrodite type [Li ６ P.S. ５ Li, such as Cl ７－ｋ P.S. ６－ｋ X ｋ (wherein X represents one or more halogen elements, and 0.2<k<2.0), Li ７－ｘ＋ｙ P.S. ６－ｘ Cl ｘ＋ｙ (where 0.05≦y≦0.9, −3.0x+1.8≦y≦−3.0x+5.7), Li ７－ｈ P.S. ６－ｈ Cl ｉ Br ｊ (where h=i+j, 0<h≦1.8, 0.1≦i / j≦10.0) can also be used.

[0053] Among these sulfide-based solid electrolytes, sulfide-based solid electrolytes containing Li and P are more preferred, and argyrodite-type sulfide-based solid electrolytes, which have particularly high Li ion conductivity and high chemical stability, are even more preferred.

[0054] The positive electrode layer may contain another solid electrolyte together with the sulfide-based solid electrolyte. The other solid electrolyte that can be used together with the sulfide-based solid electrolyte is not particularly limited as long as it has Li ion conductivity, and examples of the other solid electrolyte that can be used include hydride-based solid electrolytes, halide-based solid electrolytes, and oxide-based solid electrolytes.

[0055] Examples of hydride-based solid electrolytes include LiBH ４ , LiBH ４ and a solid solution of the following alkali metal compound (e.g., LiBH ４and the alkali metal compound in a molar ratio of 1:1 to 20:1. The alkali metal compound in the solid solution may be at least one selected from the group consisting of lithium halides (LiI, LiBr, LiF, LiCl, etc.), rubidium halides (RbI, RbBr, RbF, RbCl, etc.), cesium halides (CsI, CsBr, CsF, CsCl, etc.), lithium amide, rubidium amide, and cesium amide.

[0056] Examples of halide-based solid electrolytes include monoclinic LiAlCl ４ , defect spinel type or layer structure LiInBr ４ , monoclinic Li ６－３ｍ Y ｍ X ６ (wherein 0 < m < 2 and X = Cl or Br), and other known compounds described in, for example, WO 2020 / 070958 and WO 2020 / 070955 can also be used.

[0057] Examples of oxide-based solid electrolytes include Li ２ O-Al ２ O ３ -SiO ２ -P ２ O ５ -TiO ２ Li-based glass ceramics ２ O-Al ２ O ３ -SiO ２ -P ２ O ５ -GeO ２ Lithium-ion-based glass ceramics, garnet-type ７ La ３ Zr ２ O １２ , NASICON type Li １＋Ｏ Al １＋Ｏ Ti ２－Ｏ (P.O. ４ ) ３ , Li １＋ｐ Al １＋ｐ Ge ２－ｐ (P.O. ４ ) ３ , perovskite-type Li ３ｑ La２／３－ｑ TiO ３ Examples include:

[0058] When a sulfide-based solid electrolyte is used in combination with another solid electrolyte, the proportion of the sulfide-based solid electrolyte is preferably 20% by mass or more when the total amount of solid electrolytes in the positive electrode mixture constituting the positive electrode layer is taken as 100% by mass. Note that, since the solid electrolyte contained in the positive electrode layer may entirely be a sulfide-based solid electrolyte, the upper limit of the proportion of the sulfide-based solid electrolyte when the total amount of solid electrolytes in the positive electrode mixture constituting the positive electrode layer is taken as 100% by mass is 100% by mass.

[0059] The content of the solid electrolyte in the positive electrode mixture constituting the positive electrode layer is preferably 4 to 80 mass %.

[0060] The positive electrode layer may contain a binder. However, since the positive electrode layer contains a sulfide-based solid electrolyte that has the effect of enhancing its formability, the binder need not be contained if good formability can be ensured without using a binder.

[0061] Examples of the binder contained in the positive electrode layer include fluororesins such as polyvinylidene fluoride (PVDF).

[0062] When a binder is required in the positive electrode mixture constituting the positive electrode layer, the content thereof is preferably 15% by mass or less, and more preferably 0.5% by mass or more. On the other hand, when a binder is not required in the positive electrode mixture constituting the positive electrode layer from the viewpoint of formability, the content thereof is preferably 0.5% by mass or less, more preferably 0.3% by mass or less, and even more preferably 0% by mass (i.e., no binder is contained).

[0063] The positive electrode layer may have a current collector. Examples of the current collector for the positive electrode layer include metal foils such as aluminum and stainless steel; sheet-like conductive porous substrates such as punched metal, mesh, expanded metal, and foamed metal; and carbon sheets. As the sheet-like conductive porous substrate, it is preferable to use a foamed metal porous body. A specific example of a foamed metal porous body is "Celmet (registered trademark)" from Sumitomo Electric Industries, Ltd.

[0064] The positive electrode layer can be formed, for example, by compressing a positive electrode mixture prepared by mixing a positive electrode active material, a conductive additive, a solid electrolyte, and, if necessary, a binder, by pressure molding or the like.

[0065] In the case of a positive electrode layer having a current collector, it can be formed by, for example, pressing the current collector onto a pressed molded body of the positive electrode mixture obtained as described above.

[0066] The thickness of the positive electrode layer is usually 50 μm or more, but from the viewpoint of increasing the capacity of the battery, it is preferably 200 μm or more, and is usually 2000 μm or less.

[0067] The thickness of the current collector for the positive electrode layer is preferably 0.01 to 0.1 mm.

[0068] (Negative Electrode Layer) The negative electrode layer of the all-solid-state secondary battery can be formed, for example, by molding a negative electrode mixture containing a negative electrode active material and the like.

[0069] As the negative electrode active material, for example, one or a mixture of two or more carbonaceous materials capable of absorbing and releasing lithium, such as graphite, pyrolytic carbons, cokes, glassy carbons, fired organic polymer compounds, mesocarbon microbeads (MCMB), and carbon fibers, can be used. Also usable as the negative electrode active material are simple substances, compounds, and alloys thereof containing elements such as Si, Sn, Ge, Bi, Sb, and In; compounds capable of charging and discharging at low voltages close to those of lithium metal, such as lithium-containing nitrides or lithium-containing oxides; lithium metal; and lithium / aluminum alloys. For example, Li ４ Ti ５ O １２Lithium titanium oxides such as TiO ２ , NbO ２．５－δ (0≦δ≦0.5), MoO ３－δ (0≦δ≦1), WO ３－δ (0≦δ≦1), TiNb ２ O ７ Metal oxides such as WS ２ , MoS ２ or a mixture of two or more of these metal sulfides can also be used as the negative electrode active material.

[0070] Among these, it is preferable to use lithium titanium oxide. Examples of the lithium titanium oxide include those represented by the following general formula (1).

[0071] Li [Li １／３－ｃ M １ ｃ Ti ５／３－ｄ M ２ ｄ ]O ４ (1)

[0072] In the general formula (1), M １ is at least one element selected from the group consisting of Na, Mg, K, Ca, Sr and Ba, and M ２ is at least one element selected from the group consisting of Al, V, Cr, Fe, Co, Ni, Zn, Ym, Zr, Nb, Mo, Ta, and W, and 0≦c<1 / 3 and 0≦d<5 / 3.

[0073] That is, in the lithium titanium oxide represented by the general formula (1), a part of the Li site is an element M １ However, in the general formula (1), the element M １ In the lithium titanium oxide represented by the general formula (1), Li is an element M １ Therefore, the element M １ The ratio c may be 0.

[0074] In addition, in the lithium titanium oxide represented by the general formula (1), the element M ２is a component for increasing the electronic conductivity of lithium titanium oxide, and element M ２ When d, which represents the ratio of M to M, is in the range of 0<d<5 / 3, the effect of improving the electronic conductivity can be satisfactorily secured. ２ Since it is not necessary to contain element M ２ The value d representing the ratio may be 0.

[0075] Only lithium titanium oxide may be used as the negative electrode active material. However, when lithium titanium oxide and other negative electrode active materials are used, the proportion of the negative electrode active materials other than lithium titanium oxide in the total amount of the negative electrode active materials is preferably 30 mass% or less.

[0076] The content of the negative electrode active material in the negative electrode mixture constituting the negative electrode layer is preferably 50 to 95 mass %.

[0077] The negative electrode layer can contain a solid electrolyte. The solid electrolyte contained in the negative electrode layer can be one or more of the sulfide-based solid electrolytes, hydride-based solid electrolytes, halide-based solid electrolytes, and oxide-based solid electrolytes previously exemplified as solid electrolytes that can be contained in the positive electrode layer. Among the solid electrolytes exemplified above, sulfide-based solid electrolytes are more preferably used because they have high Li ion conductivity and also have the function of enhancing the negative electrode layer, and argyrodite-type sulfide-based solid electrolytes are even more preferably used.

[0078] The content of the solid electrolyte in the negative electrode mixture constituting the negative electrode layer is preferably 4 to 70 mass %.

[0079] The negative electrode layer may contain a conductive additive. Specific examples include carbon materials such as graphite (natural graphite, artificial graphite), graphene, carbon black, vapor-grown carbon fiber, carbon nanofiber, and carbon nanotube. The content of the conductive additive in the negative electrode layer is preferably 1 to 10 mass %.

[0080] The negative electrode layer may or may not contain a binder. Specific examples thereof include the same binders as those exemplified above as binders that can be contained in the positive electrode layer. For example, when the negative electrode layer contains a sulfide-based solid electrolyte, if good formability can be ensured in forming the negative electrode layer without using a binder, the negative electrode layer may not contain a binder.

[0081] When a binder is required in the negative electrode mixture constituting the negative electrode layer, the content thereof is preferably 15% by mass or less, and preferably 0.5% by mass or more. On the other hand, when good formability can be obtained without the binder being contained in the negative electrode mixture constituting the negative electrode layer, the content thereof is preferably 0.5% by mass or less, more preferably 0.3% by mass or less, and even more preferably 0% by mass (i.e., no binder is contained).

[0082] The negative electrode layer may have a current collector. Examples of the current collector for the negative electrode layer include sheet-like conductive porous substrates such as copper or nickel foil, punched metal, mesh, expanded metal, and foamed metal; carbon sheets; and the like. As the sheet-like conductive porous substrate, it is preferable to use a foamed metal porous body. A specific example of a foamed metal porous body is "Celmet (registered trademark)" by Sumitomo Electric Industries, Ltd.

[0083] The negative electrode layer can be formed, for example, by compressing a negative electrode mixture prepared by mixing a negative electrode active material, a conductive additive, a solid electrolyte, and, if necessary, a binder, by pressure molding or the like.

[0084] In the case of a negative electrode layer having a current collector, it can be formed by, for example, pressing a current collector onto a pressed molded product of the negative electrode mixture obtained as described above.

[0085] The thickness of the negative electrode layer is usually 100 μm or more, but is preferably 200 μm or more from the viewpoint of increasing the capacity of the battery, and is usually 3000 μm or less.

[0086] The thickness of the current collector for the negative electrode layer is preferably 0.01 to 0.1 mm.

[0087] (Solid electrolyte layer) For the solid electrolyte layer in the all-solid-state secondary battery, one or more of the sulfide-based solid electrolytes, hydride-based solid electrolytes, halide-based solid electrolytes, and oxide-based solid electrolytes exemplified above as solid electrolytes that can be contained in the positive electrode layer can be used. Among the above-exemplified solid electrolytes, it is more preferable to use a sulfide-based solid electrolyte, and it is even more preferable to use an argyrodite-type sulfide-based solid electrolyte, in order to improve the battery characteristics.

[0088] The solid electrolyte layer can be formed by a method of compressing a solid electrolyte by pressure molding or the like; a method of applying a solid electrolyte layer-forming composition prepared by dispersing a solid electrolyte in a solvent onto a substrate, a positive electrode layer, or an negative electrode layer, drying the composition, and, if necessary, performing pressure molding such as pressing.

[0089] The solid electrolyte layer may also have a porous body such as a resin nonwoven fabric as a support.

[0090] It is preferable to select a solvent for the solid electrolyte layer-forming composition that is less likely to deteriorate the solid electrolyte. In particular, sulfide-based solid electrolytes and hydride-based solid electrolytes undergo chemical reactions with trace amounts of water, so it is preferable to use a nonpolar aprotic solvent, such as hydrocarbon solvents such as hexane, heptane, octane, nonane, decane, decalin, toluene, and xylene. It is particularly preferable to use an ultra-dehydrated solvent with a water content of 0.001% by mass (10 ppm) or less. Fluorine-based solvents such as "Vertrel (registered trademark)" manufactured by DuPont-Mitsui Fluorochemicals, "Zeorolla (registered trademark)" manufactured by Nippon Zeon Co., Ltd., and "Novec (registered trademark)" manufactured by Sumitomo 3M Co., Ltd., as well as nonaqueous organic solvents such as dichloromethane and diethyl ether can also be used.

[0091] The thickness of the solid electrolyte layer is preferably 10 to 500 μm.

[0092] (Power-generating element) The power-generating element is formed by sequentially stacking a positive electrode layer, a solid electrolyte layer, and a negative electrode layer. To obtain the power-generating element, for example, a positive electrode layer (or a negative electrode layer) may be formed in advance by pressure molding, and the solid electrolyte layer and the negative electrode layer (or a positive electrode layer) may be sequentially pressure molded using this as a base material, or a positive electrode layer may be formed by pressure molding on one side of a solid electrolyte layer previously formed by pressure molding, and the negative electrode layer may be formed by pressure molding on the other side of the solid electrolyte layer.

[0093] The shape of the power generating element in plan view is not particularly limited, and may be a circle, an ellipse, a polygon such as a square, or the like.

[0094] (Exterior Body) As the exterior body of the all-solid-state secondary battery, a battery container having an exterior container and a lid as shown in Fig. 1, a flat battery container (such as a coin shape or button shape) having a metal exterior can and a metal sealing can, etc. can be used. As an exterior body compatible with surface mounting by reflow soldering, a container in which external terminals are provided on the same surface of the exterior body as shown in Fig. 1 can be preferably used.

[0095] In the case of a battery container having an outer container and a lid as shown in Fig. 1, the outer container can be made of ceramics or resin. The lid can be made of ceramics, resin, or metal (such as an iron-nickel alloy or an iron-nickel-cobalt alloy, or an iron-based alloy). Furthermore, in the outer container, the external terminals and the conductive paths connecting the electrodes of the electrode stack to the external terminals can be made of metals such as manganese, cobalt, nickel, copper, molybdenum, silver, palladium, tungsten, platinum, and gold, or alloys containing these metals.

[0096] The outer container and the lid can be sealed by bonding them together with an adhesive. In addition, when a metal lid is used, the lid side of the side wall of the recess in the outer container can be made of metal (an iron-based alloy such as an iron-nickel alloy or an iron-nickel-cobalt alloy), and the lid can be welded to this or brazed with an alloy such as gold-tin (Au-Sn) to achieve sealing.

[0097] Furthermore, when both the outer container and the lid are made of ceramics, they can be sealed by welding with low-melting glass.

[0098] <Circuit Board> The circuit board on which the all-solid-state secondary battery is mounted is not particularly limited, and a known substrate on which various components can be mounted by reflow soldering, on which wiring and solder paste are printed by a known method, and on which necessary electronic components are mounted can be used.

[0099] <Manufacturing of All-Solid-State Secondary Battery-Mounted Circuit Board> The all-solid-state secondary battery is mounted on the circuit board by reflow soldering. Specifically, the circuit board on which the all-solid-state secondary battery is mounted is heated in a reflow furnace to solder the all-solid-state secondary battery to the circuit board, thereby manufacturing the all-solid-state secondary battery-mounted circuit board.

[0100] The present invention will be described in detail below based on examples, but the present invention is not limited to these examples.

[0101] (Example 1) <Fabrication of all-solid-state secondary battery> Lithium titanate (Li ４ Ti ５ O １２ , negative electrode active material) and a sulfide-based solid electrolyte (Li ６ P.S. ５ Cl) and graphene (conductive additive) were mixed in a mass ratio of 50:41:9 to prepare a negative electrode mixture.

[0102] In addition, LiNbO ３ LiCoO having an average particle size of 5 μm on which a coating layer of ２ (positive electrode active material) and a sulfide-based solid electrolyte (Li ６ P.S. ５ Cl) and graphene were mixed in a mass ratio of 65:30.7:4.3 to prepare a positive electrode mixture.

[0103] Next, a sulfide-based solid electrolyte (Li ６ P.S. ５A powder of HCl) was placed in a powder molding die and subjected to pressure molding at a surface pressure of 70 MPa using a press to form a provisionally molded layer of a solid electrolyte layer. Furthermore, the negative electrode mixture was placed on the upper surface of the provisionally molded layer of the solid electrolyte layer and pressure molding was performed at a surface pressure of 50 MPa to form a provisionally molded layer of a negative electrode on the provisionally molded layer of the solid electrolyte layer.

[0104] Next, a nickel foamed metal porous body (nickel "Celmet" (registered trademark)) manufactured by Sumitomo Electric Industries, Ltd., cut to a diameter of 7.25 mm (thickness: 1.2 mm, porosity: 98%) was placed on the provisionally molded layer of the negative electrode formed on the provisionally molded layer of the solid electrolyte layer, and pressure molding was performed at a surface pressure of 300 MPa to form an integrated product of the solid electrolyte layer and the negative electrode layer.

[0105] Furthermore, after the mold was turned upside down, the positive electrode mixture was placed on the upper surface of the solid electrolyte layer in the mold (the surface opposite to the surface having the negative electrode), and pressure molding was performed at a surface pressure of 50 MPa, thereby forming a provisionally molded layer of the positive electrode on the solid electrolyte layer.

[0106] Next, a cut piece of the same nickel foamed metal porous body used for the negative electrode was placed on the provisionally molded layer of the positive electrode formed on the solid electrolyte layer, and pressure molding was performed at a surface pressure of 1400 MPa to obtain an electrode laminate.

[0107] In the obtained electrode laminate, the thickness of the negative electrode mixture layer of the negative electrode layer, the thickness of the porous metal substrate, and the thickness of the portion of the porous metal substrate embedded in the negative electrode mixture layer were 1250 μm, 50 μm (4% of the thickness of the porous metal substrate before use in the negative electrode), and 10 μm (20% of the total thickness of the porous metal substrate), respectively. In addition, the area ratio of the portion of the negative electrode mixture exposed on the surface of the negative electrode layer was 7%.

[0108] In the obtained electrode laminate, the thickness of the positive electrode mixture layer of the positive electrode layer, the thickness of the porous metal substrate, and the thickness of the portion of the porous metal substrate embedded in the positive electrode mixture layer were 900 μm, 50 μm (4% of the thickness of the porous metal substrate before use in the positive electrode), and 10 μm (20% of the total thickness of the porous metal substrate), respectively. The area ratio of the portion of the positive electrode mixture exposed on the surface of the positive electrode layer was 7%.

[0109] A recessed container (ceramic depth 2.5 mm) having a cross-sectional structure similar to that shown in FIG. 1 and made of ceramics, with a seal ring made of an iron-nickel-cobalt alloy placed on the upper sidewall, was fitted with a 7.25 mm diameter nickel-based porous metal foam, the same material used for the positive and negative electrode layers, cut to a diameter of 7.25 mm, and placed on the inner bottom surface. The electrode laminate was then placed on top of it, with the positive electrode layer facing downwards. A lead (Ni foil) was placed on the negative electrode layer of the electrode laminate, and a 400 μm thick rubber sheet (spacer) was then placed on top of that. A lid made of an iron-nickel-cobalt alloy was then placed on the sidewall of the recess in the outer container, and the rubber sheet was compressed in the thickness direction while the lid and outer container were welded together to seal the outer container and lid, resulting in an all-solid-state secondary battery. In the resulting all-solid-state secondary battery, the rubber sheet serving as a spacer was compressed in the thickness direction, causing the electrode laminate to press against the porous metal layer made of the foamed porous metal. The thickness of the porous metal layer in the all-solid-state secondary battery was 200 μm.

[0110] This all-solid-state secondary battery was charged at a constant current of 1.6 mA until the voltage reached 2.6 V, then charged at a constant voltage of 2.6 V until the current reached 0.05 mA, and then discharged at a constant current of 1.6 mA until the voltage reached 1.0 V. The discharge capacity at this time was approximately 8 mAh.

[0111] Next, this all-solid-state secondary battery was subjected to constant current discharge at a current value of 0.8 mA until the voltage reached 0.0 V, and subsequently to constant voltage discharge at a voltage of 0.0 V until the current reached 0.01 mA, and the open circuit voltage was measured after 72 hours, and was found to be 0.58 V. The potential of the positive electrode layer at this time was 2.13 V relative to the lithium potential.

[0112] <Mounting of All-Solid-State Secondary Battery to Experimental Circuit Board> Next, solder paste was applied to an experimental circuit board with a bridging (terminal short circuit due to solder) incidence rate of 20±5%, and electronic components (components with a temperature resistance of 260°C) and the above-mentioned all-solid-state secondary battery were placed in the reflow furnace. The electronic components and the all-solid-state secondary battery were soldered to the circuit board under the temperature profile conditions such that the surface temperature at the top center of the all-solid-state secondary battery was as follows, thereby producing an all-solid-state secondary battery-mounted circuit board. Note that lead-free solder (Sn-3.0Ag-0.5Cu) was used as the solder.

[0113] (Temperature profile conditions for soldering in a reflow oven) Preheating: 165°C x 90 seconds Main heating: 230°C or higher (peak temperature 250°C) x 30 seconds

[0114] (Example 2) An all-solid-state secondary battery was produced in the same manner as in Example 1, except that the voltage in the final discharge step was changed to 0.2 V. The open circuit voltage of this all-solid-state secondary battery 72 hours after discharge was 0.82 V, and the potential of the positive electrode layer was 2.37 V relative to the lithium potential. Then, an all-solid-state secondary battery-mounted circuit board was produced in the same manner as in Example 1, except that this all-solid-state secondary battery was used.

[0115] (Example 3) An all-solid-state secondary battery was produced in the same manner as in Example 1, except that the voltage in the final discharge step was changed to 0.35 V. The open circuit voltage of this all-solid-state secondary battery 72 hours after discharge was 0.96 V, and the potential of the positive electrode layer was 2.51 V relative to the lithium potential. Then, an all-solid-state secondary battery-mounted circuit board was produced in the same manner as in Example 1, except that this all-solid-state secondary battery was used.

[0116] Example 4 An all-solid-state secondary battery was produced in the same manner as in Example 1, except that the final discharge step was changed so that a conductive rubber sheet (conductive silicone rubber sheet manufactured by Kyowa Kogyo Co., Ltd., model number: KSR60069, hardness Shore A: 62°, volume resistivity: 5 Ω cm, thickness: 1 mm) was adhered to the positive electrode terminal and the negative electrode terminal, and discharge was maintained at 60° C. for 2 hours. The open circuit voltage of this all-solid-state secondary battery 72 hours after discharge was 0.30 V, and the potential of the positive electrode layer was 1.85 V relative to the lithium potential. Then, an all-solid-state secondary battery-mounted circuit board was produced in the same manner as in Example 1, except that this all-solid-state secondary battery was used.

[0117] Example 5 An all-solid-state secondary battery was produced in the same manner as in Example 1, except that the discharge cut-off current value in the final discharge step was changed to 0.00 mA and the cut-off time was changed to 48 hours. The open circuit voltage of this all-solid-state secondary battery 72 hours after discharge was 0.13 V, and the potential of the positive electrode layer was 1.68 V relative to the lithium potential. Then, an all-solid-state secondary battery-mounted circuit board was produced in the same manner as in Example 1, except that this all-solid-state secondary battery was used.

[0118] (Comparative Example 1) An all-solid-state secondary battery was produced in the same manner as in Example 1, except that the voltage in the final discharge step was changed to 0.45 V. The open circuit voltage of this all-solid-state secondary battery 72 hours after discharge was 1.14 V, and the potential of the positive electrode layer was 2.69 V relative to the lithium potential. Then, an all-solid-state secondary battery-mounted circuit board was produced in the same manner as in Example 1, except that this all-solid-state secondary battery was used.

[0119] (Comparative Example 2) An all-solid-state secondary battery was produced in the same manner as in Example 1, except that the voltage in the final discharge step was changed to 0.6 V. The open circuit voltage of this all-solid-state secondary battery 72 hours after discharge was 1.29 V, and the potential of the positive electrode layer was 2.84 V relative to the lithium potential. Then, an all-solid-state secondary battery-mounted circuit board was produced in the same manner as in Example 1, except that this all-solid-state secondary battery was used.

[0120] (Comparative Example 3) An all-solid-state secondary battery was produced in the same manner as in Example 1, except that the voltage in the final discharge step was changed to 0.75 V. The open circuit voltage of this all-solid-state secondary battery 72 hours after discharge was 1.73 V, and the potential of the positive electrode layer was 3.28 V relative to the lithium potential. Then, an all-solid-state secondary-battery-mounted circuit board was produced in the same manner as in Example 1, except that this all-solid-state secondary battery was used.

[0121] (Comparative Example 4) An all-solid-state secondary battery was produced in the same manner as in Example 1, except that the voltage in the final discharge step was changed to 1.0 V. The open circuit voltage of this all-solid-state secondary battery 72 hours after discharge was 2.22 V, and the potential of the positive electrode layer was 3.77 V relative to the lithium potential. Then, an all-solid-state secondary battery-mounted circuit board was produced in the same manner as in Example 1, except that this all-solid-state secondary battery was used.

[0122] Except for not performing the final discharge step, an all-solid-state secondary battery was fabricated in the same manner as in Example 1. When the same charge and discharge as those performed on the battery of Example 1 were performed under the same conditions as those used for the initial charge and discharge before mounting on the circuit board, the open circuit voltage of this all-solid-state secondary battery was 2.31 V, and the potential of the positive electrode layer was 3.81 V relative to the lithium potential.

[0123] The following evaluations were performed on the all-solid-state secondary battery-mounted circuit boards of the Examples and Comparative Examples. The all-solid-state secondary battery-mounted circuit boards of the Examples and Comparative Examples were removed from the reflow furnace and cooled to 23°C. Thereafter, the all-solid-state secondary batteries on each circuit board were charged and discharged under the same conditions as the initial charge and discharge before mounting on the circuit board, and the discharge capacity (capacity after passing through the reflow furnace) was measured. In addition, the batteries of the Reference Example were charged and discharged under the same conditions as the batteries on the circuit boards of the Examples and Comparative Examples, and the discharge capacity (Reference Example capacity) was measured. The capacity after passing through the reflow furnace for the batteries on each circuit board of the Examples and Comparative Examples was divided by the Reference Example capacity, and the value was expressed as a percentage to evaluate the capacity after passing through the reflow furnace for the batteries on each circuit board.

[0124] In addition, for the batteries on each circuit board after measuring the capacity after passing through the reflow oven, charging was performed under the same conditions as the initial charge / discharge before mounting on the circuit board, and then each circuit board was stored in a thermostatic chamber at 115 ° C. for 50 days. Next, each circuit board removed from the thermostatic chamber was cooled to 23 ° C., and the batteries on each circuit board were charged under the same conditions as the initial charge / discharge before mounting on the circuit board. The impedance of each battery (impedance after storage / recharge) was measured, and then discharged under the same conditions as the initial charge / discharge before mounting on the circuit board, and the discharge capacity of each battery (recovery capacity after storage / recharge) was measured. Note that the impedance after storage / recharge for the batteries on each circuit board in the Examples and Comparative Examples was evaluated by dividing the value by the impedance measured after charging under the same conditions as the batteries on the circuit board in the Examples and Comparative Examples, and expressed as a percentage. In addition, the recovery capacity after storage / recharge for the batteries on each circuit board in the Examples and Comparative Examples after storage / recharge was evaluated by dividing the value by the capacity of the Reference Example, and expressed as a percentage. The impedance of each battery was determined by measuring the AC impedance at 1 kHz with an applied voltage of 10 mV.

[0125] These results, together with the state of the all-solid-state secondary battery at the stage of mounting on each circuit board, are shown in Table 1. Note that the "potential of the positive electrode layer" of the all-solid-state secondary battery shown in Table 1 is based on the lithium potential.

[0126]

[0127] As shown in Table 1, the all-solid-state batteries according to Examples 1 to 5, which were manufactured using all-solid-state secondary batteries in which the potential of the positive electrode layer relative to the lithium potential was adjusted to a suitable value, exhibited a relatively large discharge capacity (recovery capacity) even after storage at a high temperature of 115°C, compared to the batteries according to Comparative Examples 1 to 4, which were manufactured using batteries with an inappropriate potential. Furthermore, the increase in impedance was relatively suppressed, and the battery characteristics after high-temperature storage were well maintained, even after the battery was mounted on the circuit board by reflow soldering. This result is thought to be due to the fact that, as described above, in the batteries on the circuit boards of Examples 1 to 5, deterioration of the reaction suppression layer on the surface of the positive electrode active material was suppressed, and oxidative decomposition of the sulfide-based solid electrolyte due to reaction with the positive electrode active material in the positive electrode layer was well suppressed, even during subsequent high-temperature storage.

[0128] The present invention can be implemented in other forms without departing from the spirit of the present invention. The embodiments disclosed in this application are merely examples, and the present invention is not limited to these embodiments. The scope of the present invention shall be interpreted in accordance with the appended claims rather than the description in the above specification, and all modifications within the scope of the claims are included in the scope of the claims.

[0129] An all-solid-state secondary battery-mounted circuit board obtained by the manufacturing method of the present invention can be used as a component of various electronic devices, etc., similar to conventionally known circuit boards mounted with electronic components.

[0130] REFERENCE SIGNS LIST 10 All-solid-state secondary battery 20 Power generating element 21 Positive electrode layer 211 Positive electrode mixture layer (molded body of positive electrode mixture) 212 Current collector 22 Negative electrode layer 221 Negative electrode mixture layer (molded body of negative electrode mixture) 222 Current collector 23 Solid electrolyte layer 30 Conductive sheet 40 Lead 50 Spacer 80, 90 External terminals 81, 91 Conduction path

Claims

1. A method for producing a circuit board on which an all-solid-state secondary battery is mounted, the all-solid-state secondary battery having a power generating element in which a positive electrode layer containing a positive electrode active material having a reaction suppression layer formed on at least a portion of the surface thereof, a solid electrolyte layer and a negative electrode layer are laminated in that order, the power generating element being housed in an exterior body, the method comprising the steps of: mounting the all-solid-state secondary battery on a circuit board by reflow soldering; and subjecting the all-solid-state secondary battery to the reflow soldering in a state in which the potential of the positive electrode layer is 2.55 V or less based on the lithium potential.

2. The method for manufacturing an all-solid-state secondary battery-mounted circuit board according to claim 1, wherein the all-solid-state secondary battery is subjected to the reflow soldering in a state in which the potential of the positive electrode layer is 2.40 V or less based on a lithium potential.

3. The all-solid-state secondary battery has a positive electrode terminal electrically connected to the positive electrode layer and having a portion exposed from the inside of the exterior body to the outside, and a negative electrode terminal electrically connected to the negative electrode layer and having a portion exposed from the inside of the exterior body to the outside, and a method for manufacturing an all-solid-state secondary battery-mounted circuit board according to claim 1, comprising the steps of: bringing a conductive sheet into close contact with the positive electrode terminal and the negative electrode terminal of the all-solid-state secondary battery before being subjected to the reflow soldering, thereby performing a discharge treatment of the all-solid-state secondary battery and adjusting the potential of the positive electrode layer.

4. The method for manufacturing an all-solid-state secondary battery mounted circuit board according to claim 3, wherein the discharge treatment of a plurality of the all-solid-state secondary batteries is carried out simultaneously using a single conductive sheet.

5. The method for producing an all-solid-state secondary battery mounted circuit board according to claim 3, wherein the conductive sheet is a conductive rubber sheet.

6. The method for manufacturing an all-solid-state secondary battery mounted circuit board according to claim 3, wherein the temperature when the discharge treatment of the all-solid-state secondary battery is performed is 40 to 80° C.

7. The method for producing an all-solid-state secondary battery-mounted circuit board according to claim 1, wherein the all-solid-state secondary battery, in which the positive electrode layer contains, as the positive electrode active material, a lithium transition metal composite oxide containing, as a transition metal, at least one element selected from the group consisting of Mn, Co, and Ni, is subjected to the reflow soldering.

8. The method for producing an all-solid-state secondary battery-mounted circuit board according to claim 1, wherein the all-solid-state secondary battery, in which the positive electrode layer contains an olivine-type lithium transition metal oxide containing at least one element selected from the group consisting of Fe, Mn, and Co as a transition metal, as the positive electrode active material, is subjected to the reflow soldering.

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