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 that has excellent productivity.　The method for manufacturing an all-solid-state secondary battery-mounted circuit board according to the present invention is for manufacturing a circuit board which is formed by mounting thereon an all-solid-state secondary battery that has a power generation element formed by sequentially laminating a positive electrode layer, a solid electrolyte layer, and a negative electrode layer and an exterior body for accommodating the power generation element. The method is characterized: by including a step for mounting the all-solid-state secondary battery on the circuit board by reflow soldering; and in that an open circuit voltage of the all-solid-state secondary battery is adjusted to 0.9 V or less and subjected the battery to the reflow soldering.

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 with excellent productivity.

[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 being developed for use not only as the main power source for electronic devices but also as memory backup power sources. In such applications, lithium secondary batteries are mounted by soldering or the like on circuit boards on which electronic components are mounted. For example, Patent Document 1 proposes a technology for improving the heat resistance of organic electrolyte batteries (lithium secondary batteries) by using a specific organic electrolyte to enable automatic mounting of the battery on a circuit board by reflow soldering.

[0004] However, when a lithium secondary battery is mounted on a circuit board by reflow soldering, the battery is exposed to high temperatures, which can cause a current greater than the current value specified for the battery at room temperature to flow through the circuit, which can degrade battery performance or have adverse effects on electronic components mounted on the circuit board.

[0005] Meanwhile, technologies for solving these problems are also being considered. Patent Document 2 proposes a technology in which the active material of the positive electrode and the active material of the negative electrode in a nonaqueous electrolyte secondary battery (lithium secondary battery) have the same composition, thereby making it possible to reduce the battery voltage to less than 0.1 V when the battery is mounted on a circuit board by reflow soldering, and thereby preventing almost no current from flowing from the battery to the circuit. However, in the case of the nonaqueous electrolyte secondary battery described in Patent Document 2, because the active material of the positive electrode and the active material of the negative electrode have the same composition, there are problems in that it is difficult to increase the battery capacity and the energy density of the battery is low.

[0006] Furthermore, Patent Document 3 proposes a technology for suppressing deterioration of battery performance by setting a lithium ion secondary battery mounted on a circuit board by reflow soldering to a state of charge (SOC) of 0 to 29%.

[0007] JP 2000-48859 A International Publication No. 2007 / 086289 International Publication No. 2023 / 042801

[0008] As described above, various techniques for mounting lithium secondary batteries on circuit boards by reflow soldering have been proposed, but there is still room for improvement in terms of suppressing deterioration of electronic components on the circuit board due to battery mounting and increasing the productivity of circuit boards.

[0009] 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 with excellent productivity.

[0010] 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 having a power generation 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 generation element, and is characterized by comprising a step of mounting the all-solid-state secondary battery on the circuit board by reflow soldering, and adjusting the open circuit voltage of the all-solid-state secondary battery to 0.9 V or less before subjecting it to the reflow soldering.

[0011] According to the present invention, it is possible to provide a method for manufacturing an all-solid-state secondary battery mounted circuit board with excellent productivity.

[0012] 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.

[0013] 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 has a power generating element formed by sequentially stacking a positive electrode layer, a solid electrolyte layer, and a negative electrode layer, 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, the all-solid-state secondary battery is subjected to reflow soldering in a state in which its open circuit voltage is adjusted to 0.9 V or less.

[0014] If the all-solid-state secondary battery satisfies the above-mentioned open circuit voltage, a large current does not flow in the circuit even when it is placed under high temperatures during reflow soldering, and therefore deterioration of electronic components mounted on the circuit board can be suppressed.

[0015] In addition, in order to adjust a secondary battery having an organic electrolyte solution so that the open circuit voltage is 0.9 V or less, for example, the battery may be overdischarged, but doing so will accelerate deterioration of the battery, and will instead increase the defect rate during the manufacture of a circuit board mounting an all-solid-state secondary battery, thereby reducing productivity. Therefore, for example, in Patent Document 3, the battery is mounted on a circuit board in a state as discharged as possible within the charge / discharge range in which the battery is actually used.

[0016] However, in the case of an all-solid-state secondary battery that does not have an organic electrolyte solution and that exchanges ions between the positive electrode layer and the negative electrode layer by a solid electrolyte layer, deterioration to a degree that causes problems in use will not occur even if the battery is overdischarged, for example, to adjust the open circuit voltage to 0.9 V or less. Therefore, according to the manufacturing method of the present invention, when mounting the all-solid-state secondary battery on a circuit board, deterioration of the all-solid-state secondary battery and electronic components mounted on the circuit board can be effectively suppressed, and the occurrence of defective circuit boards can be suppressed, thereby ensuring high productivity.

[0017] Furthermore, in the manufacturing method of the present invention, an all-solid-state secondary battery is used that is not particularly limited in terms of the combination of positive and negative electrode active materials from the viewpoint of mounting on a circuit board, and therefore, it is also possible to use an all-solid-state secondary battery with a high energy density. Thus, according to the manufacturing method of the present invention, it is possible to obtain a circuit board mounted with an all-solid-state secondary battery with a high energy density while increasing productivity.

[0018] The open circuit voltage of the all-solid-state secondary battery to be subjected to reflow soldering for mounting on a circuit board is 0.9 V or less, 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.

[0019] 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.

[0020] 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.

[0021] To put a solid secondary battery into an over-discharge state, 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 ＬBy 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.

[0022] In order to adjust the open circuit voltage to the above-mentioned value by performing a discharge treatment on 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, for example, 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 a single conductive sheet, thereby performing the discharge treatment on the all-solid-state secondary battery. This method is simple and allows the discharge treatment of multiple all-solid-state secondary batteries to be performed simultaneously using a single conductive sheet, thereby further improving the productivity of mounting circuit boards for all-solid-state secondary batteries.

[0023] 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.

[0024] 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.

[0025] The discharge treatment for adjusting the open circuit voltage of the all-solid-state secondary battery is preferably carried out at a temperature of 40° C. or higher and 80° C. or lower. A higher temperature is desirable because the higher the temperature, the more improved the conductivity of the solid electrolyte and the shorter the discharge 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.

[0026] <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.

[0027] 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.

[0028] 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. The external terminal 90 is electrically connected to the negative electrode layer 22 of the power-generating element 20 through a lead 40 and the conductive path 91.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] (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.

[0033] There is no particular limitation on the positive electrode active material 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 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), Li 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), and the like. Among these, only one type may be used, or two or more types may be used in combination.

[0034] 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.

[0035] 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

[0036] When the positive electrode layer contains a solid electrolyte, the positive electrode active material preferably has a reaction suppression layer on its surface to suppress reaction with the solid electrolyte contained in the positive electrode layer.

[0037] If the positive electrode active material and the solid electrolyte come into direct contact in the positive electrode layer, the solid electrolyte may oxidize to form a resistance layer, which may reduce ionic conductivity in the layer. By providing a reaction suppression layer on the surface of the positive electrode active material that suppresses reaction with the solid electrolyte and preventing direct contact between the positive electrode active material and the solid electrolyte, it is possible to suppress the reduction in ionic conductivity in the positive electrode layer due to oxidation of the solid electrolyte.

[0038] 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 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 ４The 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

[0039] The reaction suppression layer 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, which allows for effective suppression of the reaction between the positive electrode active material and the solid electrolyte.

[0040] 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.

[0041] The content of the positive electrode active material in the positive electrode mixture constituting the positive electrode layer is preferably 20 to 95 mass %.

[0042] 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.

[0043] The positive electrode layer may contain a solid electrolyte. The solid electrolyte used in the positive electrode layer is not particularly limited as long as it has Li ion conductivity, and examples thereof include sulfide-based solid electrolytes, hydride-based solid electrolytes, halide-based solid electrolytes, and oxide-based solid electrolytes.

[0044] The sulfide-based solid electrolyte is Li ２ S-P ２ S ５ , Li ２ S-SiS ２ , Li ２S-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－ｅ X 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.

[0045] Examples of hydride-based solid electrolytes include LiBH ４ , LiBH ４ and a solid solution of the following alkali metal compound (e.g., LiBH ４ and 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.

[0046] 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.

[0047] 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 , Li１＋ｐ Al １＋ｐ Ge ２－ｐ (P.O. ４ ) ３ , perovskite-type Li ３ｑ La ２／３－ｑ TiO ３ Examples include:

[0048] Among these solid electrolytes, sulfide-based solid electrolytes are preferred because of their high Li ion conductivity, sulfide-based solid electrolytes containing Li and P are more preferred, and argyrodite-type sulfide-based solid electrolytes are even more preferred because of their particularly high Li ion conductivity and high chemical stability.

[0049] The content of the solid electrolyte in the positive electrode mixture constituting the positive electrode layer is preferably 4 to 80 mass %.

[0050] The positive electrode layer may contain a binder, or may not contain a binder if good moldability can be ensured without using a binder, such as in the case of a positive electrode in which a sulfide-based solid electrolyte is contained and powder of the positive electrode mixture is charged into a molding die and compacted.

[0051] Examples of the binder contained in the positive electrode layer include fluororesins such as polyvinylidene fluoride (PVDF).

[0052] 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).

[0053] 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.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] The thickness of the current collector for the positive electrode layer is preferably 0.01 to 0.1 mm.

[0058] (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.

[0059] 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.

[0060] 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).

[0061] Li [Li １／３－ｃ M １ ｃ Ti ５／３－ｄ M ２ ｄ ]O ４ (1)

[0062] 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.

[0063] 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 Since it is not necessary to substitute with element M １ The ratio c may be 0.

[0064] 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.

[0065] 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.

[0066] The content of the negative electrode active material in the negative electrode mixture constituting the negative electrode layer is preferably 50 to 95 mass %.

[0067] 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.

[0068] The content of the solid electrolyte in the negative electrode mixture constituting the negative electrode layer is preferably 4 to 70 mass %.

[0069] 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 %.

[0070] 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.

[0071] 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).

[0072] 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.

[0073] 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.

[0074] 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.

[0075] 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.

[0076] The thickness of the current collector for the negative electrode layer is preferably 0.01 to 0.1 mm.

[0077] (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.

[0078] 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.

[0079] The solid electrolyte layer may also have a porous body such as a resin nonwoven fabric as a support.

[0080] 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.

[0081] The thickness of the solid electrolyte layer is preferably 10 to 500 μm.

[0082] (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.

[0083] 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.

[0084] (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.

[0085] 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.

[0086] 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.

[0087] Furthermore, when both the outer container and the lid are made of ceramics, they can be sealed by welding with low-melting glass.

[0088] <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.

[0089] <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.

[0090] The present invention will be described in detail below based on examples, but the present invention is not limited to these examples.

[0091] (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.

[0092] 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.

[0093] 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.

[0094] 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.

[0095] 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.

[0096] 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.

[0097] 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%.

[0098] 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%.

[0099] 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.

[0100] 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.

[0101] 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. After 72 hours had elapsed, the open circuit voltage was measured and found to be 0.58 V.

[0102] <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.

[0103] (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

[0104] (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. 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.

[0105] (Example 3) 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 100 hours. The open circuit voltage of this all-solid-state secondary battery 72 hours after discharge was 0.07 V. 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.

[0106] (Example 4) 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 24 hours. The open circuit voltage of this all-solid-state secondary battery 72 hours after discharge was 0.31 V. 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.

[0107] (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. 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.

[0108] (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 0.35 V. The open circuit voltage of this all-solid-state secondary battery 72 hours after discharge was 0.96 V. 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.

[0109] (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 0.5 V. The open circuit voltage of this all-solid-state secondary battery 72 hours after discharge was 1.29 V. 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.

[0110] (Comparative Example 3) An all-solid-state secondary battery was produced in the same manner as in Example 1, except that the final discharge step was not performed. The open circuit voltage of this all-solid-state secondary battery 72 hours after the initial discharge was 2.31 V. 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.

[0111] The following evaluations were performed on the all-solid-state secondary battery-mounted circuit boards of the Examples and Comparative Examples. Twenty all-solid-state secondary battery-mounted circuit boards of each Example and Comparative Example 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 conditions before mounting on the circuit board, and the discharge capacity was measured. Table 1 shows the percentage of electronic components with no defects (i.e., non-defective product rate), the percentage of those that were defective due to bridging, and the discharge capacity of the all-solid-state secondary batteries in a state mounted on a circuit board (referred to as "discharge capacity of all-solid-state secondary battery" in Table 1), along with the open-circuit voltage of the all-solid-state secondary batteries when used to mount the experimental circuit board.

[0112]

[0113] As can be seen from Table 1, no defects occurred in the all-solid-state secondary-battery-mounted circuit boards of Examples 1 to 5, which were manufactured through a process of soldering in a reflow furnace using all-solid-state secondary batteries that had been discharged until the open circuit voltage was 0.9 V or less. On the other hand, defects occurred in the electronic components in the circuit boards of Comparative Examples 1 to 3, which were manufactured through soldering in a reflow furnace using all-solid-state secondary batteries in a state where the open circuit voltage was higher than 0.9 V. Note that, when comparing the circuit boards of the comparative examples, the higher the open circuit voltage of the all-solid-state secondary battery before being placed in the reflow furnace, the lower the yield rate.

[0114] 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.

[0115] 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, similar to conventionally known circuit boards mounted with electronic components.

[0116] 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 mounted with an all-solid-state secondary battery, the all-solid-state secondary battery having 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, the method comprising the step of mounting the all-solid-state secondary battery on the circuit board by reflow soldering, and comprising adjusting the open circuit voltage of the all-solid-state secondary battery to 0.9 V or less before subjecting it to the reflow soldering.

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 placed in an overdischarged state and then subjected to the reflow soldering.

3. 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 negative electrode layer contains lithium titanium oxide as a negative electrode active material, is subjected to the reflow soldering.

4. 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, wherein a conductive sheet is adhered to 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 an open circuit voltage.

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

6. The method for producing an all-solid-state secondary battery mounted circuit board according to claim 4, wherein the conductive sheet is a conductive rubber sheet.

7. The method for manufacturing an all-solid-state secondary battery mounted circuit board according to claim 4, wherein the temperature when the discharge treatment of the all-solid-state secondary battery is performed is 40 to 80° C.

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