阅读说明：本技术 电路基板组件 (Circuit substrate assembly ) 是由 由良幸信 前田一树 水上俊介 于 2019-10-29 设计创作，主要内容包括：电路基板组件(8)具备：配线基板(81)；纽扣型二次电池(1),其为利用焊锡回流焊而与配线基板(81)电连接的锂二次电池；以及无线通信器件(82),其与配线基板(81)电连接。纽扣型二次电池1具备：正极,其包含烧结体；负极,其包含烧结体；电解质层,其设置于正极与负极之间；以及外装体,其具有对正极、负极以及电解质层进行收纳的密闭空间。若将正极的容量设为C、将负极的容量设为A,则满足1.03＜C/A＜1.60。(A circuit board assembly (8) is provided with: a wiring board (81); a button-type secondary battery (1) which is a lithium secondary battery electrically connected to a wiring board (81) by solder reflow; and a wireless communication device (82) electrically connected to the wiring board (81). The button-type secondary battery 1 includes: a positive electrode comprising a sintered body; a negative electrode comprising a sintered body; an electrolyte layer disposed between the positive electrode and the negative electrode; and an outer casing having a sealed space for housing the positive electrode, the negative electrode, and the electrolyte layer. When the capacity of the positive electrode is C and the capacity of the negative electrode is A, 1.03 < C/A < 1.60 is satisfied.)

1. A circuit board assembly is provided with:

a wiring substrate;

a button-type secondary battery that is a lithium secondary battery electrically connected to the wiring board by solder reflow; and

a wireless communication device electrically connected to the wiring board,

the button-type secondary battery includes:

a positive electrode including a sintered body;

an anode comprising a sintered body;

an electrolyte layer disposed between the positive electrode and the negative electrode; and

a casing having a sealed space for housing the positive electrode, the negative electrode, and the electrolyte layer,

when the capacity of the positive electrode is C and the capacity of the negative electrode is A,

the condition that C/A is more than 1.03 and less than 1.60 is satisfied.

2. The circuit substrate assembly of claim 1,

the wiring board is free from electronic components mounted after solder reflow soldering.

3. The circuit substrate assembly of claim 1 or 2,

on the wiring board, all electronic components connected to the wiring of the wiring board are electrically connected to the wiring by solder reflow.

4. The circuit substrate assembly of any one of claims 1 to 3,

the thickness of the button-type secondary battery is 0.7-1.6 mm, and the diameter of the button-type secondary battery is 10-20 mm.

5. The circuit substrate assembly of any one of claims 1 to 4,

the positive electrode includes a lithium composite oxide sintered body,

the anode includes a titanium-containing sintered body.

Technical Field

The present invention relates to a circuit substrate assembly including a button-type secondary battery.

[ reference to related application ]

The present application claims the benefit of priority of japanese patent application JP 2018-204399, filed on 30/10/2018, the entire disclosure of which is incorporated herein.

Background

Conventionally, a technology for mounting a button-type secondary battery on a wiring board by solder reflow has been studied. For example, japanese patent No. 4392189 discloses a button-type secondary battery for soldering by reflow soldering, in which a lithium-containing manganese oxide is used as a positive electrode active material. In the button type secondary battery, the concentration of the lithium salt contained in the electrolyte is 1.5-2.5 mol/l, so that the reaction between the electrolyte and the lithium-containing manganese oxide caused by solder reflow is inhibited, and good reflow soldering heat resistance is obtained.

Further, as a coin-type battery using a sintered body, for example, japanese patent No. 5587052 discloses a positive electrode for a lithium secondary battery, in which a lithium composite oxide sintered plate having a thickness of 30 μm or more, a porosity of 3 to 30%, and an open pore ratio of 70% or more is used as a positive electrode active material layer of the positive electrode. Further, International publication No. 2017/146088 discloses a solid electrolyte cell comprising a solid electrolyteA lithium secondary battery, wherein an oriented sintered body plate is used as a positive electrode. The oriented sintered body plate comprises lithium cobaltate (LiCoO)₂) And a plurality of primary particles composed of the lithium composite oxide, wherein the plurality of primary particles are oriented at an average orientation angle of more than 0 DEG and not more than 30 DEG with respect to the plate surface of the positive electrode. Japanese laid-open patent publication No. 2015-185337 discloses that lithium titanate (Li) is used as an electrode₄Ti₅O₁₂) An all-solid-state battery of the sintered body.

However, when the button-type secondary battery is soldered by the reflow method, the manufacturing process of the circuit board assembly is simplified, but when the button-type secondary battery is heated, the battery performance is degraded. As a result, the performance of the circuit substrate assembly including the button-type secondary battery is degraded.

Disclosure of Invention

The invention is suitable for circuit substrate assemblies.

The circuit board assembly according to the present invention includes: a wiring substrate; a button-type secondary battery that is a lithium secondary battery electrically connected to the wiring board by solder reflow; and a wireless communication device electrically connected to the wiring board. The button-type secondary battery includes: a positive electrode including a sintered body; an anode comprising a sintered body; an electrolyte layer disposed between the positive electrode and the negative electrode; and a casing having a sealed space for housing the positive electrode, the negative electrode, and the electrolyte layer. When the capacity of the positive electrode is C and the capacity of the negative electrode is A, 1.03 < C/A < 1.60 is satisfied.

According to the present invention, it is possible to provide a circuit board assembly on which a button-type secondary battery having high battery performance is mounted by reflow soldering.

In a preferred embodiment, no electronic component is mounted on the wiring board after solder reflow. In a more preferred aspect, all electronic components connected to the wiring of the wiring board are electrically connected to the wiring by solder reflow on the wiring board.

Preferably, the thickness of the button-type secondary battery is 0.7-1.6 mm, and the diameter of the button-type secondary battery is 10-20 mm. In a preferred example of the button-type secondary battery, the positive electrode includes a lithium composite oxide sintered body, and the negative electrode includes a titanium-containing sintered body.

The above and other objects, features, aspects and advantages of the present invention will become apparent from the following detailed description of the present invention with reference to the accompanying drawings.

Drawings

Fig. 1 is a diagram showing a structure of a button-type secondary battery.

Fig. 2 is a diagram showing a cross-sectional SEM image of the oriented positive plate.

Fig. 3 is a diagram showing an EBSD image at a cross section of the oriented positive electrode plate.

Fig. 4 is a diagram showing a histogram representing the orientation angle distribution of primary particles in an EBSD image.

Fig. 5 is a side view showing the circuit substrate assembly.

Fig. 6 is a diagram showing an evaluation circuit.

Detailed Description

< button type secondary battery >

Fig. 1 is a diagram showing a structure of a button-type secondary battery 1 according to an embodiment of the present invention. The button-type secondary battery 1 includes: positive electrode 2, negative electrode 3, electrolyte layer 4, outer package 5, positive electrode current collector 62, and negative electrode current collector 63. The electrolyte layer 4 is provided between the positive electrode 2 and the negative electrode 3. The exterior body 5 has a closed space therein. The positive electrode 2, the negative electrode 3, the electrolyte layer 4, the positive electrode current collector 62, and the negative electrode current collector 63 are housed in the sealed space. The exterior body 5 includes: positive electrode can 51, negative electrode can 52, and gasket 53. The positive electrode can 51 includes: a flat plate portion 511, and a peripheral wall portion 512. The flat plate portion 511 has a disc shape. The peripheral wall portion 512 protrudes from the outer peripheral edge of the flat plate portion 511. The positive electrode can 51 is a container for housing the positive electrode 2. The negative electrode can 52 includes: a flat plate portion 521, and a peripheral wall portion 522. The flat plate portion 521 has a disc shape. The peripheral wall portion 522 protrudes from the outer peripheral edge of the flat plate portion 521. The negative electrode can 52 is a container for storing the negative electrode 3.

In the button-type secondary battery 1, the flat plate portion 511 of the positive electrode can 51, the positive electrode current collector 62, the positive electrode 2, the electrolyte layer 4, the negative electrode 3, the negative electrode current collector 63, and the flat plate portion 521 of the negative electrode can 52 are arranged in this order. As described later, the positive electrode current collector 62 and the negative electrode current collector 63 may be omitted.

In the button-type secondary battery 1, the negative electrode can 52 and the positive electrode can 51 are arranged to face each other so that the negative electrode 3 faces the positive electrode 2 with the electrolyte layer 4 interposed therebetween. Spacer 53 is insulating and provided between peripheral wall 512 of positive electrode can 51 and peripheral wall 522 of negative electrode can 52. The plate thickness of each of the positive electrode can 51 and the negative electrode can 52 is, for example, 0.075 to 0.25 mm. As described above, by reducing the plate thicknesses of the positive electrode can 51 and the negative electrode can 52, a certain thickness of the positive electrode 2 and the negative electrode 3 can be secured in the thin button-type secondary battery 1, and the battery capacity can be easily increased. The button-type secondary battery 1 is soldered by a reflow method, and is mounted by being electrically connected to a wiring board by solder reflow.

However, during solder reflow, the button-type secondary battery 1 is heated to a high temperature (for example, 200 to 260 ℃) within a predetermined time, thereby causing various battery performances to deteriorate. However, as shown in the following examples, the inventors of the present invention found that: by adjusting the positive electrode capacity and the negative electrode capacity, the battery performance after heating at the time of solder reflow can be suppressed from being degraded. Thus, a button-type secondary battery suitable for soldering by a reflow method can be provided. Further, by using the button-type secondary battery, it is possible to provide a circuit board assembly on which a button-type secondary battery having high battery performance is mounted by soldering.

In the button-type secondary battery 1, the battery capacity after solder reflow is preferably 65% or more (typically 100% or less) of the battery capacity before solder reflow. Preferably, the battery capacity after solder reflow is 75% or more of the battery capacity before solder reflow.

The positive electrode can 51 and the negative electrode can 52 are made of metal. For example, the positive electrode can 51 and the negative electrode can 52 are formed by press working (drawing) a metal plate of stainless steel, aluminum, or the like. Note that, it is sufficient to form a sealed space in the outer package 5, and the flat plate portions 511 and 521 and the peripheral wall portions 512 and 522 may be formed in the positive electrode can 51 and the negative electrode can 52, respectively, by other methods.

In the button-type secondary battery 1 of fig. 1, the peripheral wall 512 of the positive electrode can 51 is disposed outside the peripheral wall 522 of the negative electrode can 52. Then, positive electrode can 51 is fixed to negative electrode can 52 via gasket 53 by plastically deforming peripheral wall 512 disposed on the outside, that is, by caulking peripheral wall 512. Thereby, the closed space is formed. The area of the flat plate portion 511 of the positive electrode can 51 is larger than the area of the flat plate portion 521 of the negative electrode can 52. The circumference of the peripheral wall 512 of the positive electrode can 51 is larger than the circumference of the peripheral wall 522 of the negative electrode can 52. Since the outer peripheral surface of the peripheral wall 522 of the negative electrode can 52 is covered with the spacer 53, the peripheral wall 522 of the negative electrode can 52 has very few portions that come into contact with the outside atmosphere. The spacer 53 is an annular member disposed between the peripheral wall portions 512 and 522. The spacer 53 is also filled between the peripheral wall 522 and the positive electrode 2 and the like. The spacer 53 is made of an insulating resin such as polypropylene, polytetrafluoroethylene, polyphenylene sulfide, perfluoroalkoxyalkane, polychlorotrifluoroethylene, or the like. Among them, polyphenylene sulfide and perfluoroalkoxyalkane having excellent heat resistance are preferable. The spacer 53 may be a member formed of other insulating materials. In the button-type secondary battery 1, the peripheral wall portion 522 of the negative electrode can 52 may be disposed outside the peripheral wall portion 512 of the positive electrode can 51.

The thickness of the button-type secondary battery 1, i.e., the distance between the outer surface of the flat plate portion 511 of the positive electrode can 51 and the outer surface of the flat plate portion 521 of the negative electrode can 52, is, for example, 0.7 to 1.6 mm. In order to reduce the thickness of a circuit board assembly described later on which the button-type secondary battery 1 is mounted, the upper limit of the thickness of the button-type secondary battery 1 is preferably 1.4mm, and more preferably 1.2 mm. The lower limit of the thickness of the button-type secondary battery 1 is preferably 0.8mm, and more preferably 0.9mm, from the viewpoint of ensuring a certain degree of thickness in the positive electrode 2 and the negative electrode 3 to increase the battery capacity.

The diameter of the button-type secondary battery 1 is, for example, 10 to 20 mm. The button-type secondary battery 1 of fig. 1 has a diameter equal to the diameter of the flat plate portion 511 of the positive electrode can 51. In order to miniaturize the circuit board assembly on which the button-type secondary battery 1 is mounted, the upper limit value of the diameter of the button-type secondary battery 1 is preferably 18mm, and more preferably 16 mm. The lower limit of the diameter of the button-type secondary battery 1 is preferably 10.5mm, and more preferably 11mm, from the viewpoint of ensuring a certain degree of size in the positive electrode 2 and the negative electrode 3 to increase the battery capacity.

As will be described later, in the button-type secondary battery 1, a lithium composite oxide sintered plate is preferably used as the positive electrode 2, and a titanium-containing sintered plate is preferably used as the negative electrode 3. Thus, a button-type lithium secondary battery which has excellent heat resistance, is small and thin, has a high capacity and high output, can be soldered by a reflow soldering method, and can be charged with a Constant Voltage (CV). The energy density of the button-type secondary battery 1 before solder reflow is preferably 35mWh/cm³The above. The lower limit of the energy density is more preferably 40mWh/cm³More preferably 50mWh/cm³. The upper limit of the energy density of the button-type secondary battery 1 is not particularly limited, and is, for example, 200mWh/cm³。

The positive electrode 2 is, for example, a plate-shaped sintered body. The positive electrode 2 being a sintered body means: the positive electrode 2 does not contain a binder or a conductive additive. This is because: even if the green sheet contains a binder, the binder disappears or burns off at the time of firing. Since the positive electrode 2 is a sintered body, the heat resistance of the positive electrode 2 can be ensured against solder reflow. In addition, since the positive electrode 2 does not contain a binder, deterioration of the positive electrode 2 due to the electrolyte 42 described later can be suppressed. The positive electrode 2 is preferably porous, that is, includes pores.

The preferred positive electrode 2 is a lithium composite oxide sintered plate. The lithium composite oxide is particularly preferably lithium cobaltate (typically LiCoO)₂Hereinafter, abbreviated as "LCO". ). Various lithium composite oxide sintered plates and LCO sintered plates are known, and for example, the sintered plates disclosed in japanese patent No. 5587052 and international publication No. 2017/146088 can be used. In the following description, the positive electrode 2 is described as a lithium composite oxide sintered plate, but the positive electrode 2 may be another type of electrode depending on the design of the button-type secondary battery 1. An example of another positive electrode 2 is: comprises a positive electrode active material, a conductive auxiliary agent and a binderAnd the like, and a powder-dispersed positive electrode (so-called coated electrode) produced by coating and drying the positive electrode mixture.

The lithium composite oxide sintered body plate is preferably an oriented positive electrode plate including a plurality of primary particles made of a lithium composite oxide, and the plurality of primary particles are oriented at an average orientation angle of greater than 0 ° and 30 ° or less with respect to a plate surface of the positive electrode.

Fig. 2 is a view showing an example of an SEM image of a cross section perpendicular to the plate surface of the oriented positive electrode plate, and fig. 3 is a view showing an Electron Back Scattering Diffraction (EBSD) image of a cross section perpendicular to the plate surface of the oriented positive electrode plate. Fig. 4 is a diagram showing a histogram representing the orientation angle distribution of the primary particles 21 in the EBSD image of fig. 3 on an area basis. In the EBSD image shown in fig. 3, discontinuity of crystal orientation can be seen. In fig. 3, the orientation angle of each primary particle 21 is indicated by the color shade, and the darker the color, the smaller the orientation angle will be. The orientation angles are: the (003) plane of each primary particle 21 forms an inclination angle with respect to the plate surface direction. In fig. 2 and 3, the black portions inside the oriented positive electrode plate are air holes.

The oriented positive electrode plate is an oriented sintered body composed of a plurality of primary particles 21 bonded to each other. Each primary particle 21 is mainly plate-shaped, but may include primary particles formed in a rectangular parallelepiped shape, a cubic shape, a spherical shape, or the like. The cross-sectional shape of each primary particle 21 is not particularly limited, and may be a rectangle, a polygon other than a rectangle, a circle, an ellipse, or a complex shape other than these.

Each primary particle 21 is made of a lithium composite oxide. The lithium composite oxide is made of Li_xMO₂(0.05 < x < 1.10, M is at least 1 transition metal, and M typically contains 1 or more of Co, Ni, and Mn). The lithium composite oxide has a layered rock salt structure. The layered rock salt structure refers to: a crystal structure in which lithium layers and transition metal layers other than lithium are alternately stacked with oxygen layers interposed therebetween, that is, a crystal structure in which a transition metal ion layer and a lithium single layer are alternately stacked with oxide ions interposed therebetween (typically, α -NaF)eO₂Type structure, i.e. transition metal and lithium in cubic rock salt type structure [111 ]]A structure in which the axes are regularly arranged). Examples of the lithium composite oxide include: li_xCoO₂(lithium cobaltate), Li_xNiO₂(lithium nickelate), Li_xMnO₂(lithium manganate), Li_xNiMnO₂(lithium nickel manganese oxide), Li_xNiCoO₂(lithium nickel cobalt oxide), Li_xCoNiMnO₂(lithium cobalt nickel manganese oxide), Li_xCoMnO₂(lithium cobalt manganese) and the like, and Li is particularly preferable_xCoO₂(lithium cobaltate, typically LiCoO)₂). The lithium composite oxide may contain 1 or more elements selected from Mg, Al, Si, Ca, Ti, V, Cr, Fe, Cu, Zn, Ga, Ge, Sr, Y, Zr, Nb, Mo, Ag, Sn, Sb, Te, Ba, Bi, and W. These elements may be present uniformly in the positive electrode or may be present in a surface-biased manner. When present on the surface, the coating may be uniformly coated or may be present in an island form. When present on the surface, the action of suppressing the reaction with the electrolyte can be expected. In this case, Zr, Mg, Ti, and Al are particularly preferable.

As shown in fig. 3 and 4, the average value of the orientation angles of the primary particles 21, that is, the average orientation angle is greater than 0 ° and 30 ° or less. This brings the following various advantages. First, since each primary particle 21 is in a state of lying down in a direction inclined with respect to the thickness direction, the adhesion between the primary particles can be improved. As a result, lithium ion conductivity between a certain primary particle 21 and other primary particles 21 adjacent to both sides in the longitudinal direction of the primary particle 21 can be improved, and thus, rate characteristics can be improved. Second, the magnification characteristics can be further improved. This is because: when lithium ions are taken in, the oriented positive electrode plate is more dominant in expansion and contraction in the thickness direction than in the plate surface direction, and therefore, the oriented positive electrode plate is smooth in expansion and contraction, and accordingly, the lithium ions are taken in and out.

The average orientation angle of the primary particles 21 is obtained by the following method. First, in an EBSD image obtained by observing a rectangular region of 95 × 125 μm at 1000-fold magnification as shown in fig. 3, 3 horizontal lines obtained by quartering the oriented positive electrode plate in the thickness direction and 3 vertical lines obtained by quartering the oriented positive electrode plate in the plate surface direction are drawn. Next, the orientation angles of all the primary particles 21 intersecting at least 1 line of the 3 horizontal lines and 3 vertical lines are arithmetically averaged, thereby obtaining an average orientation angle of the primary particles 21. From the viewpoint of further improving the magnification characteristics, the average orientation angle of the primary particles 21 is preferably 30 ° or less, and more preferably 25 ° or less. From the viewpoint of further improving the magnification characteristics, the average orientation angle of the primary particles 21 is preferably 2 ° or more, and more preferably 5 ° or more.

As shown in fig. 4, the orientation angle of each primary particle 21 may be widely distributed from 0 ° to 90 °, but it is preferable that most of the orientation angle is distributed in a region larger than 0 ° and 30 ° or less. That is, when the cross section of the oriented sintered body constituting the oriented positive electrode plate is analyzed by EBSD, the total area of the primary particles 21 included in the analyzed cross section, which have an orientation angle greater than 0 ° and equal to or less than 30 ° with respect to the plate surface of the oriented positive electrode plate (hereinafter referred to as "low-angle primary particles"), is preferably 70% or more, and more preferably 80% or more, with respect to the total area of the primary particles 21 included in the cross section (specifically, 30 primary particles 21 for calculating the average orientation angle). This can increase the proportion of the primary particles 21 having high mutual adhesion, and thus can further improve the rate characteristics. In addition, the total area of the primary particles having an orientation angle of 20 ° or less in the low-angle primary particles is more preferably 50% or more of the total area of the 30 primary particles 21 used for calculating the average orientation angle. In addition, the total area of the primary particles having an orientation angle of 10 ° or less in the low-angle primary particles is more preferably 15% or more of the total area of the 30 primary particles 21 used for calculating the average orientation angle.

Since each primary particle 21 is mainly plate-shaped, the cross section of each primary particle 21 extends in a predetermined direction, typically, is substantially rectangular, as shown in fig. 2 and 3. That is, in the case of analyzing the cross section of the oriented sintered body by EBSD, the total area of the primary particles 21 having an aspect ratio of 4 or more in the primary particles 21 included in the analyzed cross section is preferably 70% or more, and more preferably 80% or more, with respect to the total area of the primary particles 21 included in the cross section (specifically, 30 primary particles 21 for calculating the average orientation angle). This can further improve the adhesiveness between the primary particles 21, and as a result, can further improve the rate characteristics. The aspect ratio of the primary particles 21 is: the maximum feret diameter of the primary particles 21 divided by the minimum feret diameter. The maximum feret diameter is: in the EBSD image when the cross section is observed, the maximum distance between the primary particles 21 when the lines are sandwiched by 2 parallel straight lines. The minimum Ferrett diameter is: in the EBSD image, the minimum distance between the parallel 2 straight lines when the primary particles 21 are sandwiched therebetween.

The average particle diameter of the plurality of primary particles constituting the oriented sintered body is preferably 0.5 μm or more. Specifically, the average particle diameter of the 30 primary particles 21 used for calculating the average orientation angle is preferably 0.5 μm or more, more preferably 0.7 μm or more, and still more preferably 1.0 μm or more. This reduces the number of grain boundaries between the primary particles 21 in the lithium ion conduction direction, and improves the overall lithium ion conductivity, thereby further improving the rate characteristics. The average particle diameter of the primary particles 21 is: the equivalent circle diameter of each primary particle 21 is arithmetically averaged. The equivalent circle diameter is: on the EBSD image, the diameter of a circle having the same area as each primary particle 21 is measured.

The porosity of the positive electrode 2 (for example, a lithium composite oxide sintered plate) is preferably 20 to 60%, more preferably 25 to 55%, still more preferably 30 to 50%, and particularly preferably 30 to 45%. The stress relaxation effect and the high capacity due to the pores can be expected, and in the case of the oriented sintered body, the adhesiveness between the primary particles 21 can be further improved, and therefore, the rate characteristics can be further improved. The porosity of the sintered body was calculated by polishing the cross section of the positive electrode plate by CP (cross section polisher) polishing, observing the cross section with SEM at 1000 magnifications, and converting the obtained SEM image into 2 values. The average equivalent circle diameter of each pore formed in the oriented sintered body is not particularly limited, but is preferably 8 μm or less. As the average equivalent circle diameter of each pore is smaller, the adhesiveness between the primary particles 21 can be further improved, and as a result, the magnification characteristics can be further improved. The average equivalent circle diameter of the pores is: the arithmetic mean of the equivalent circle diameters of 10 pores on the EBSD image was obtained. The equivalent circle diameter is: on the EBSD image, the diameter of a circle having the same area as each air hole. The pores formed in the oriented sintered body may be open pores connected to the outside of the positive electrode 2, and preferably do not penetrate through the positive electrode 2. The air holes may be closed air holes.

In the positive electrode 2 (for example, a lithium composite oxide sintered plate), the average pore diameter is preferably 0.1 to 10.0. mu.m, more preferably 0.2 to 5.0. mu.m, and still more preferably 0.3 to 3.0. mu.m. When the content is within the above range, stress concentration is suppressed from occurring locally in the large pores, and stress in the sintered body is easily and uniformly released.

The thickness of the positive electrode 2 is preferably 60 to 450 μm, more preferably 70 to 350 μm, and further preferably 90 to 300 μm. Within this range, the active material capacity per unit area can be increased to increase the energy density of the button-type secondary battery 1, and the deterioration of the battery characteristics (particularly, the increase in the resistance value) due to the repetition of charge and discharge can be suppressed.

The negative electrode 3 is, for example, a plate-shaped sintered body. The anode 3 being a sintered body means: the negative electrode 3 does not contain a binder or a conductive additive. This is because: even if the green sheet contains a binder, the binder disappears or burns off at the time of firing. Since negative electrode 3 is a sintered body, heat resistance of negative electrode 3 can be ensured against solder reflow. The negative electrode 3 contains no binder, and a negative electrode active material (LTO or Nb described later)₂TiO₇Etc.), thereby enabling to obtain a high capacity and a good charge-discharge efficiency. The negative electrode 3 is preferably porous, that is, includes pores.

The negative electrode 3 is preferably a titanium-containing sintered body plate. The titanium-containing sintered body plate preferably contains lithium titanate Li₄Ti₅O₁₂(hereinafter referred to as "LTO") or Nb-Ti composite oxide Nb₂TiO₇More preferably, LTO is contained. It should be noted that LTO typically has a spinel structure, but may have other structures during charge and discharge. For example, LTO is charged and discharged with Li₄Ti₅O₁₂(spinel structure) and Li₇Ti₅O₁₂The reaction proceeds with coexistence of two phases (rock salt structure). Therefore, LTO is not limited to the spinel structure. For example, an LTO sintered body sheet can be produced by the method described in Japanese patent laid-open publication No. 2015-185337. In the following description, the negative electrode 3 is described as a titanium-containing sintered body plate, but the negative electrode 3 may be another type of electrode depending on the design of the button-type secondary battery 1. An example of other negative electrodes 3 is: a powder dispersion type negative electrode (so-called coated electrode) is produced by coating and drying a negative electrode mixture containing a negative electrode active material, a conductive assistant, a binder and the like.

The titanium-containing sintered body plate has a structure in which a plurality of (i.e., a large number of) primary particles are bonded. Therefore, these primary particles are preferably made of LTO or Nb₂TiO₇And (4) forming.

The thickness of the negative electrode 3 is preferably 70 to 500. mu.m, more preferably 85 to 400. mu.m, and still more preferably 95 to 350. mu.m. The thicker the LTO sintered plate, the easier it is to realize a battery with high capacity and high energy density. For example, the thickness of the negative electrode 3 is obtained by measuring the distance between the plate surfaces observed substantially in parallel when the cross section of the negative electrode 3 is observed by SEM (scanning electron microscope).

The average particle diameter of the plurality of primary particles constituting the negative electrode 3, that is, the primary particle diameter, is preferably 1.2 μm or less, more preferably 0.02 to 1.2 μm, and still more preferably 0.05 to 0.7. mu.m. When the amount is within this range, both lithium ion conductivity and electron conductivity are easily achieved, which contributes to an improvement in rate performance.

The negative electrode 3 preferably contains pores. When negative electrode 3 contains pores, particularly open pores, the electrolyte can penetrate into negative electrode 3 when assembled in a battery, and as a result, lithium ion conductivity can be improved. This is because: the lithium ion conduction in the negative electrode 3 includes 2 types of conduction via the constituent particles of the negative electrode 3 and conduction via the electrolyte in the pores, and in this case, the conduction via the electrolyte in the pores has an overwhelming rate.

The porosity of the negative electrode 3 is preferably 20 to 60%, more preferably 30 to 55%, and still more preferably 35 to 50%. When the amount is within this range, both lithium ion conductivity and electron conductivity are easily achieved, which contributes to an improvement in rate performance.

The average pore diameter of the negative electrode 3 is, for example, 0.08 to 5.0. mu.m, preferably 0.1 to 3.0. mu.m, and more preferably 0.12 to 1.5. mu.m. When the amount is within this range, both lithium ion conductivity and electron conductivity are easily achieved, which contributes to an improvement in rate performance.

In the button-type secondary battery 1 of fig. 1, the electrolyte layer 4 includes a separator 41 and an electrolyte 42. The separator 41 is provided between the positive electrode 2 and the negative electrode 3. The separator 41 is porous, and the separator 41 is mainly impregnated with the electrolyte 42. When the positive electrode 2 and the negative electrode 3 are porous, the positive electrode 2 and the negative electrode 3 are also impregnated with the electrolyte 42. The electrolyte 42 may be present in the gap between the positive electrode 2, the negative electrode 3, the separator 41, and the outer package 5.

The separator 41 is preferably a cellulose or ceramic separator. A cellulose separator is advantageous in that it is inexpensive and has excellent heat resistance. In addition, unlike the widely used polyolefin separator having poor heat resistance, the cellulose separator has not only excellent heat resistance itself but also excellent wettability with respect to γ -butyrolactone (GBL), which is an electrolyte component having excellent heat resistance. Therefore, when the electrolyte containing GBL is used, the electrolyte can sufficiently penetrate (without bouncing) into the separator. On the other hand, the ceramic separator has an advantage that it is excellent in heat resistance and can be integrally produced as 1 integral sintered body together with the positive electrode 2 and the negative electrode 3. In the case of a ceramic separator, the ceramic constituting the separator is preferably selected from MgO and Al₂O₃、ZrO₂、SiC、Si₃N₄At least 1 of AlN and cordierite, more preferably MgO and Al₂O₃And ZrO₂At least 1 kind of (1).

The electrolyte 42 is not particularly limited, and the button-type secondary battery 1 isIn the case of a lithium secondary battery, a commercially available electrolyte solution for a lithium battery such as a liquid obtained by dissolving a lithium salt in a nonaqueous solvent such as an organic solvent may be used. Particularly preferred is an electrolyte solution having excellent heat resistance, and such an electrolyte solution preferably contains lithium tetrafluoroborate (LiBF) in a nonaqueous solvent₄). In this case, the nonaqueous solvent is preferably at least 1 selected from the group consisting of γ -butyrolactone (GBL), Ethylene Carbonate (EC), and Propylene Carbonate (PC), more preferably a mixed solvent of EC and GBL, a single solvent of PC, a mixed solvent of PC and GBL, or a single solvent of GBL, and particularly preferably a mixed solvent of EC and GBL or a single solvent of GBL. The nonaqueous solvent contains gamma-butyrolactone (GBL), and thus has a high boiling point, resulting in a significant increase in heat resistance. From this viewpoint, the EC in the nonaqueous solvent containing EC and/or GBL: the volume ratio of GBL is preferably 0: 1-1: 1(GBL ratio 50 to 100 vol%), more preferably 0: 1-1: 1.5(GBL ratio 60 to 100 vol%), preferably 0: 1-1: 2(GBL ratio of 66.6 to 100 vol%), preferably 0: 1-1: 3(GBL ratio 75 to 100 vol%). Lithium tetrafluoroborate (LiBF) dissolved in non-aqueous solvent₄) This also greatly improves heat resistance of the electrolyte having a high decomposition temperature. LiBF in the electrolyte 42₄The concentration is preferably 0.5 to 2mol/L, more preferably 0.6 to 1.9mol/L, still more preferably 0.7 to 1.7mol/L, and particularly preferably 0.8 to 1.5 mol/L.

The electrolyte 42 may further include Vinylene Carbonate (VC) and/or fluoroethylene carbonate (FEC) and/or vinylethylene carbonate (VEC) as additives. Both VC and FEC are excellent in heat resistance. Therefore, when the electrolyte 42 contains these additives, an SEI film having excellent heat resistance can be formed on the surface of the negative electrode 3.

When the button-type secondary battery 1 is provided with the positive electrode current collector 62 and/or the negative electrode current collector 63, the material and shape thereof are not particularly limited, and the current collector is preferably a metal foil such as a copper foil or an aluminum foil. In addition, from the viewpoint of reducing the contact resistance, a positive electrode-side carbon layer 621 is preferably provided between the positive electrode 2 and the positive electrode current collector 62. Similarly, from the viewpoint of reducing the contact resistance, it is preferable to provide a negative electrode side carbon layer 631 between the negative electrode 3 and the negative electrode current collector 63. The positive electrode-side carbon layer 621 and the negative electrode-side carbon layer 631 are both preferably made of conductive carbon, and each carbon layer may be formed by applying a conductive carbon paste by screen printing or the like, for example. As another method, metal or carbon may be formed on the electrode current collecting surface by sputtering. Examples of the metal species include Au, Pt, and Al.

< method for producing positive electrode >

The lithium composite oxide sintered plate, which is a preferable positive electrode 2, can be produced by any method, and in one example, is produced through the steps of (a) producing a green sheet containing a lithium composite oxide, (b) producing a green sheet containing an excessive lithium source as desired, and (c) laminating and firing the green sheet.

(a) Production of Green sheet containing lithium Complex oxide

First, a raw material powder composed of a lithium composite oxide is prepared. The powder preferably comprises a composition of LiMO₂(M as described above.) synthesized plate-like particles (e.g., LiCoO)₂Plate-like particles). The volume-based D50 particle size of the raw material powder is preferably 0.3 to 30 μm. For example, LiCoO can be implemented as follows₂A method for producing plate-like particles. First, Co is mixed₃O₄Raw material powder and Li₂CO₃Raw material powders are mixed and fired (at 500 to 900 ℃ C. for 1 to 20 hours), thereby synthesizing LiCoO₂And (3) powder. The obtained LiCoO₂The powder was pulverized by a jar mill to a particle size of 0.2 to 10 μm based on the volume D50 to obtain a plate-like LiCoO capable of conducting lithium ions parallel to the plate surface₂Particles. The LiCoO₂The particles can be obtained by using LiCoO₂A method of crushing after growth of green sheets of powder slurry, a flux method, hydrothermal synthesis, single crystal growth using a melt, a sol-gel method, and the like. The resulting LiCoO₂The particles are easily cleaved along the cleavage plane. LiCoO by Using fragmentation₂The particles are cleaved to prepare LiCoO₂Plate-like particles.

The plate shape can be changedThe particles are used alone as a raw material powder, and the plate-like powder may be mixed with another raw material powder (e.g., Co)₃O₄Particles) was used as the raw material powder. In the latter case, it is preferable to cause the plate-like powder to function as template particles for imparting orientation, and to cause another raw material powder (e.g., Co)₃O₄Particles) function as matrix particles that can grow along the template particles. In this case, the template particles and the matrix particles are preferably arranged in a ratio of 100: 0-3: 97 as a raw material powder. Mixing Co₃O₄In the case where the raw material powder is used as the matrix particles, Co₃O₄The volume-based D50 particle size of the raw material powder is not particularly limited, and may be, for example, 0.1 to 1.0. mu.m, but is preferably smaller than LiCoO₂The volume basis D50 particle size of the template particles. Can also be prepared by mixing Co (OH)₂The raw material is heat-treated at 500 to 800 ℃ for 1 to 10 hours to obtain the matrix particles. In addition, the matrix particles may be made of Co in addition to₃O₄In addition, Co (OH) may be used₂Particles, LiCoO may also be used₂Particles.

The raw material powder is made of LiCoO₂When the template particles are 100% in structure, or LiCoO is used as the matrix particles₂In the case of particles, flat LiCoO having a relatively large sheet (for example, 90 mm. times.90 mm square) can be obtained by firing₂A sintered body plate. The mechanism is uncertain, and the conjecture is as follows: because LiCoO is not carried out in the sintering process₂The composition (2) is less likely to cause a volume change or local unevenness in firing.

The raw material powder is mixed with a dispersion medium and various additives (binder, plasticizer, dispersant, etc.) to form a slurry. For the purpose of promoting grain growth and compensating for volatile components in the firing step described later, LiMO may be added to the slurry in an excess amount of about 0.5 to 30 mol%₂Other lithium compounds (e.g., lithium carbonate). The slurry preferably does not contain a pore-forming material. The slurry is preferably stirred and defoamed under reduced pressure to adjust the viscosity to 4000 to 10000 cP. The obtained slurry was formed into a sheet to obtain a green sheet containing a lithium composite oxide. Thus obtainingThe obtained green sheet was an independent sheet-like molded body. The independent sheets (also sometimes referred to as "free-standing films") refer to: a sheet (including a sheet having an aspect ratio of 5 or more) which can be handled as a single body independently from another support. That is, the independent sheet does not include a sheet that is fixed to another support (such as a substrate) and integrated with the support (cannot be separated or is difficult to separate). The sheet molding is preferably performed by a molding method capable of applying a shearing force to plate-like particles (for example, template particles) in the raw material powder. This makes it possible to set the average tilt angle of the primary particles to be greater than 0 ° and 30 ° or less with respect to the plate surface. The doctor blade method is preferable as a molding method capable of applying a shearing force to the plate-like particles. The thickness of the green sheet containing a lithium composite oxide may be appropriately set so as to have a desired thickness after firing as described above.

(b) Production of Green sheet containing excess lithium Source (optional Process)

If desired, a green sheet containing an excessive amount of a lithium source is prepared separately from the green sheet containing the lithium composite oxide. The excess lithium source is preferably LiMO in which components other than Li disappear by firing₂Other lithium compounds. A preferable example of such a lithium compound (excess lithium source) is lithium carbonate. The excess lithium source is preferably in a powder form, and the volume-based D50 particle size of the excess lithium source powder is preferably 0.1 to 20 μm, and more preferably 0.3 to 10 μm. Then, the lithium source powder is mixed with a dispersion medium and various additives (a binder, a plasticizer, a dispersant, etc.) to form a slurry. The slurry obtained is preferably stirred and defoamed under reduced pressure to adjust the viscosity to 1000 to 20000 cP. The resulting slurry was formed into a sheet to obtain a green sheet containing an excessive lithium source. The green sheet thus obtained is also a separately independent sheet-like molded body. The sheet molding can be carried out by various known methods, but is preferably carried out by a blade method. The thickness of the green sheet containing an excess lithium source is preferably set to: the molar ratio (Li/Co ratio) of the Li content in the green sheet containing the excess lithium source to the Co content in the green sheet containing the lithium composite oxide can be made to be preferably 0.1 or more, and more preferably 0.1 to 1.1.

(c) Lamination and firing of green sheets

A green sheet containing a lithium composite oxide (e.g., LiCoO)₂Green sheet) and green sheet containing an excess of lithium source (e.g., Li) used as desired₂CO₃Green sheets) are sequentially placed on the lower setter plate, and the upper setter plate is placed thereon. The upper and lower load bearing plates are made of ceramic, preferably zirconia or magnesia. If the setter plate is made of magnesium oxide, the pores tend to be small. The upper setter plate may have a porous structure, a honeycomb structure, or a dense structure. When the upper setter plate is dense, the sintered body plate tends to have a small number of pores and a large number of pores. If necessary, the green sheet containing an excess lithium source is preferably cut into a size such that the molar ratio of the Li content in the green sheet containing an excess lithium source to the Co content in the green sheet containing a lithium composite oxide (Li/Co ratio) is preferably 0.1 or more, more preferably 0.1 to 1.1.

In a green sheet containing a lithium composite oxide (for example, LiCoO)₂Green sheet) is placed on a lower baking plate, and the green sheet may be degreased as desired and then baked at 600 to 850 ℃ for 1 to 10 hours. In this case, a green sheet containing an excessive amount of a lithium source (e.g., Li)₂CO₃Green sheet) and an upper burn-in board are sequentially placed on the obtained burn-in board.

Then, the green sheet and/or the calcined plate are degreased as desired while being sandwiched between baking plates, and then heat-treated (baked) at a baking temperature in an intermediate temperature range (for example, 700 to 1000 ℃) to obtain a lithium composite oxide sintered plate. The firing step may be performed 2 times or 1 time. When firing is performed 2 times, the firing temperature at the 1 st time is preferably lower than the firing temperature at the 2 nd time. The sintered body plate thus obtained is also in the form of a separate sheet.

< method for producing negative electrode >

The negative electrode 3, i.e., the titanium-containing sintered body plate, can be preferably produced by any method. For example, the LTO sintered plate is preferably produced through the steps of (a) producing a green sheet containing LTO and (b) firing the green sheet containing LTO.

(a) Production of Green sheet containing LTO

First, lithium titanate Li is prepared₄Ti₅O₁₂The constituted raw material powder (LTO powder). The starting powder may be commercially available LTO powder or may be synthesized anew. For example, a powder obtained by hydrolyzing a mixture of titanium tetraisopropoxide and lithium isopropoxide may be used, or a mixture containing lithium carbonate, titanium dioxide, or the like may be fired. The volume-based D50 particle size of the raw material powder is preferably 0.05 to 5.0 μm, and more preferably 0.1 to 2.0. mu.m. If the particle diameter of the raw material powder is large, pores tend to become large. When the particle size of the raw material is large, a pulverization treatment (for example, jar mill pulverization, bead mill pulverization, jet mill pulverization, or the like) may be performed to obtain a desired particle size. Then, the raw material powder is mixed with a dispersion medium and various additives (a binder, a plasticizer, a dispersant, etc.) to form a slurry. For the purpose of promoting grain growth and compensating for volatile components in the firing step described later, a lithium compound other than LTO (for example, lithium carbonate) may be added to the slurry in an excess amount of about 0.5 to 30 mol%. The slurry is preferably stirred and defoamed under reduced pressure to adjust the viscosity to 4000 to 10000 cP. The obtained slurry was formed into a sheet to obtain a green sheet containing LTO. The green sheet thus obtained was an independent sheet-like molded body. The independent sheets (also sometimes referred to as "free-standing films") refer to: a sheet (including a sheet having an aspect ratio of 5 or more) which can be handled as a single body independently from another support. That is, the independent sheet does not include a sheet that is fixed to another support (such as a substrate) and integrated with the support (cannot be separated or is difficult to separate). The sheet molding can be carried out by various known methods, but is preferably carried out by a blade method. The thickness of the LTO-containing green sheet may be appropriately set so as to have a desired thickness as described above after firing.

(b) Firing of LTO-containing Green sheet

The green sheet containing LTO was placed on a setter plate. The setter plates are made of ceramic, preferably zirconia or magnesia. Preferably, a coining process is applied to the setter plate. The green sheet thus placed on the setter was placed in a sagger. The sagger is also made of ceramic, preferably alumina. Then, in this state, the sintered LTO plate is obtained by degreasing as desired and then firing the degreased substrate. The firing is preferably carried out at 600 to 900 ℃ for 0.1 to 50 hours, more preferably at 700 to 800 ℃ for 0.3 to 20 hours. The sintered body plate thus obtained is also in the form of a separate sheet. The temperature rise rate during firing is preferably 100 to 1000 ℃/h, more preferably 100 to 600 ℃/h. In particular, the rate of temperature rise is preferably employed in the temperature rise process of 300 to 800 ℃ and more preferably 400 to 800 ℃.

(c) Summary of the invention

The LTO sintered body plate can be preferably manufactured as described above. In this preferred production method, it is effective to 1) adjust the particle size distribution of the LTO powder and/or 2) change the temperature increase rate during firing, and these operations are considered to contribute to the various properties of the LTO sintered body plate.

< Circuit Board Assembly >

Fig. 5 is a side view showing a circuit substrate assembly 8 including the above-described button-type secondary battery 1. The circuit substrate assembly 8 further includes: a wiring board 81, a wireless communication device 82, and other electronic components 83. The wiring board 81 is a so-called printed wiring board and has conductive wiring on the upper surface. The wiring may be provided inside or on the lower surface of the wiring substrate 81. In fig. 5, 1 wiring board 81 is shown, but the wiring board 81 may have a structure in which a plurality of portions of wiring boards are assembled.

The button-type secondary battery 1 is fixed to the wiring board 81 in a posture in which the negative electrode can 52 faces the wiring board 81. In the button-type secondary battery 1, a lead 191 is electrically connected to the positive electrode can 51 and a lead 192 is electrically connected to the negative electrode can 52. The ends of the leads 191 and 192 farthest from the button-type secondary battery 1 are connected to the wiring of the wiring board 81 by solder 811. The leads 191 and 192 are connected to the wiring by soldering using a reflow method. In other words, the button-type secondary battery 1 is electrically connected to the wiring board 81 by solder reflow. The button-type secondary battery 1 may be fixed to the wiring board 81 in a posture in which the positive electrode can 51 faces the wiring board 81.

The wireless communication device 82 is an electrical loop module including an antenna and a communication loop. The terminals of the wireless communication device 82 are connected to the wires of the wiring board 81 by solder. The terminals of the wireless communication device 82 and the wiring are connected by soldering by a reflow method. In other words, the wireless communication device 82 is electrically connected to the wiring board 81 by solder reflow. The wireless communication device 82 is a device that communicates using an electric wave. The wireless communication device 82 may be a device dedicated to transmission, or may be a device capable of transmission and reception.

The other electronic components 83 mounted on the wiring board 81 suitably include: a circuit that generates a signal to be transmitted, a circuit that processes a received signal, a sensor, various measurement devices, a terminal to which a signal from the outside is input, and the like.

The circuit substrate assembly 8 is preferably utilized as part of an IoT device. "IoT" is short for Internet of Things (Internet of Things), "IoT device" refers to: all devices connected to a network to exhibit a specific function.

Conventionally, a step of mounting a button-type secondary battery on a socket is performed after the socket is mounted on a wiring board by solder reflow. In the circuit board assembly 8, the button-type secondary battery 1 is mounted on the wiring board 81 by solder reflow, and therefore the mounting process can be simplified. Preferably, the wiring board 81 does not have an electronic component mounted thereon after solder reflow. This simplifies the handling of the circuit board assembly 8 after solder reflow. Here, "post-solder reflow mounting" does not include connection of external wiring to the circuit board. More preferably, on the wiring board 81, all the electronic components connected to the wiring of the wiring board 81 are electrically connected to the wiring by solder reflow. Such a process can be realized by mounting the button-type secondary battery 1 on the wiring board 81 by solder reflow.

< example >

Next, examples will be explained. Herein, the preparation ofThe button-type secondary batteries of examples 1 to 5 and comparative examples 1 and 2 shown in table 1 were prepared and evaluated. In the following description, LiCoO will be used₂Abbreviated as "LCO", by reaction of Li₄Ti₅O₁₂Abbreviated as "LTO".

[ Table 1]

< example 1 >

(1) Production of positive electrode

First, Co weighed so that the Li/Co molar ratio was 1.01 was added₃O₄Powder (manufactured by orthodox chemical industries Co., Ltd.) and Li₂CO₃The powders (manufactured by Kyowa Kagaku Co., Ltd.) were mixed, and the mixture was held at 780 ℃ for 5 hours, and the obtained powder was pulverized and crushed by a jar mill to a volume D50 of 0.4 μm to obtain a powder composed of LCO plate-like particles. 100 parts by weight of the obtained LCO powder, 100 parts by weight of a dispersion medium (toluene: isopropanol: 1), 10 parts by weight of a binder (polyvinyl butyral: model BM-2, manufactured by hydrochemical industries, Ltd.), 4 parts by weight of a plasticizer (DOP: di (2-ethylhexyl) phthalate, manufactured by Fumigu chemical Co., Ltd.), and 2 parts by weight of a dispersant (product name RHEODOL SP-O30, manufactured by Kao corporation) were mixed. The resulting mixture was stirred under reduced pressure to be defoamed, and the viscosity was adjusted to 4000cP, thereby preparing an LCO slurry. The viscosity was measured by using a LVT viscometer manufactured by Brookfield corporation. The slurry thus prepared was molded into a sheet shape on a PET film by a doctor blade method, thereby forming an LCO green sheet. The thickness of the dried LCO green sheet was 240. mu.m.

The LCO green sheet peeled from the PET film was cut into a 50mm square by a cutter, and placed at the center of a magnesia setter plate (90 mm square in size and 1mm in height) as a lower setter plate. A porous magnesia setter plate as an upper setter plate was placed on the LCO sheet. The LCO sheet was placed in an alumina sagger (Nikkato, Inc.) of 120mm square in a state of being sandwiched between setter plates. At this time, the alumina sagger was not sealed, and a gap of 0.5mm was opened, and the lid was closed. The obtained laminate was heated to 600 ℃ at a heating rate of 200 ℃/h, degreased for 3 hours, and then heated to 800 ℃ at a heating rate of 200 ℃/h, and held for 5 hours to be fired. After firing, the temperature was lowered to room temperature, and the fired body was taken out from the alumina sagger. This gave an LCO sintered body plate having a thickness of about 200. mu.m. The LCO sintered plate was cut into a circular shape having a diameter of 10mm by a laser beam machine to obtain a positive electrode plate.

(2) Production of negative electrode

First, 100 parts by weight of LTO powder (product of Shiyu Kagaku Co., Ltd.), 100 parts by weight of a dispersion medium (toluene: isopropanol: 1), 20 parts by weight of a binder (polyvinyl butyral: model BM-2, product of hydrochemical Co., Ltd.), 4 parts by weight of a plasticizer (DOP: di (2-ethylhexyl) phthalate, product of Heiji Kagaku K Co., Ltd.), and 2 parts by weight of a dispersant (product of RHDOL SP-O30, product of Kao Co., Ltd.) were mixed. The obtained negative electrode raw material mixture was stirred and defoamed under reduced pressure, and the viscosity was adjusted to 4000cP, thereby preparing LTO slurry. The viscosity was measured by using a LVT viscometer manufactured by Brookfield corporation. The slurry thus prepared was molded into a sheet shape on a PET film by a doctor blade method, thereby forming an LTO green sheet.

The obtained green sheet was cut into a 25mm square by a cutter, and placed on a zirconia setter plate which had been press-molded. The green sheet on the setter plate was placed in an alumina sagger, held at 500 ℃ for 5 hours, heated at a heating rate of 200 ℃/h, and fired at 765 ℃ for 1 hour. The obtained LTO sintered plate was cut into a circular shape having a diameter of 10.2mm by a laser beam machine to obtain a negative electrode plate. The thickness of the negative plate was about 230 μm.

(3) Manufacture of button type secondary battery

A button-type secondary battery 1 schematically shown in fig. 1 was produced as follows.

(3a) Bonding the negative electrode plate and the negative electrode collector with the conductive carbon paste

Mixing acetylene black and polyimide amide according to a mass ratio of 3: 1, and NMP (N-methyl-2-pyrrolidone) as a solvent in an appropriate amount were mixed together to prepare a conductive carbon paste. A conductive carbon paste was screen-printed on an aluminum foil as a negative electrode current collector. The negative electrode plate produced in the above (2) was placed in an undried print pattern (i.e., a region coated with a conductive carbon paste), and vacuum-dried at 60 ℃ for 30 minutes to produce a negative electrode structure in which the negative electrode plate and the negative electrode collector were joined via a carbon layer. The thickness of the carbon layer was 10 μm.

(3b) Preparing a positive electrode collector with a carbon layer

Mixing acetylene black and polyimide amide according to a mass ratio of 3: 1, and NMP (N-methyl-2-pyrrolidone) as a solvent in an appropriate amount were mixed together to prepare a conductive carbon paste. A conductive carbon paste was screen-printed on an aluminum foil as a positive electrode current collector, and then vacuum-dried at 60 ℃ for 30 minutes, thereby producing a positive electrode current collector having a carbon layer formed on the surface thereof. The thickness of the carbon layer was 5 μm.

(3c) Assembly of button type secondary battery

The positive electrode collector, the carbon layer, the LCO positive electrode plate, the cellulose separator, the LTO negative electrode plate, the carbon layer, and the negative electrode collector are housed between the positive electrode can and the negative electrode can so as to be stacked in order from the positive electrode can toward the negative electrode can, and after filling with the electrolyte, the positive electrode can and the negative electrode can are caulked with a gasket to seal them. Thus, a button cell type lithium secondary battery (button type secondary battery 1) having a diameter of 12mm and a thickness of 1.0mm was produced. In this case, LiBF is used as the electrolyte₄A liquid obtained by dissolving Ethylene Carbonate (EC) and γ -butyrolactone (GBL) in an organic solvent having a concentration of 1.5mol/L, in which: 3 by volume ratio.

(4) Measurement of

(4a) Measurement of C/A of electrode

Before assembling the button-type secondary battery of (3c) above, the average thickness of the positive electrode and the negative electrode was measured by a 3D shape measuring machine (VR 3200, manufactured by Keyence corporation) as a reference value. In example 1, the thickness of the positive electrode (i.e., positive electrode plate) was 183 μm, and the thickness of the negative electrode (i.e., negative electrode plate) was 240 μm.

Next, the capacity C of the positive electrode was determined for each 1cm²Actual capacity (mAh) of the positive plate at 25 ℃ of area. The actual capacitance is set as: after constant current-constant voltage charging at a potential of 4.25V for lithium metal with a current of 0.2C was performed for 10 hours, constant current discharge was performed at a current of 0.2C until the electric capacity reached 3.0V for lithium metal.

On the other hand, as the capacity A of the negative electrode plate, the capacity per 1cm of the negative electrode plate was determined²Actual capacity (mAh) of the negative plate at 25 ℃ of area. The actual capacitance is set as: after constant current-constant voltage charging at 0.8V for 0.2C current and lithium metal was performed for 10 hours, constant current discharge at 0.2C current was performed until the electric capacity at 2.0V was reached. Finally, the ratio of the capacity C of the positive electrode plate to the capacity a of the negative electrode plate was calculated and set as C/a. In example 1, the C/A of the electrode was 1.05.

The capacities of the positive electrode and the negative electrode may be calculated from their weights.

(4b) Solder reflow test

In the assembly of the button-type secondary battery of (3C) above, 2 button-type secondary batteries were assembled using the same electrode as the electrode subjected to the C/a measurement of the electrode of (4 a). One for the solder reflow test and the other for the reference without the solder reflow test.

The button-type secondary battery for solder reflow test and a DC-DC converter (XCL 101a331 ER-G, manufactured by TOREX SEMICONDUCTOR corporation) as a booster IC were heated at 260 ℃ for 30 seconds by using a reflow apparatus (UNI-5016F, manufactured by Antom corporation), and were connected to a circuit board. On the other hand, the button-type secondary battery for reference and the DC-DC converter were connected to the wiring board by soldering by a manual operation.

(4c) Evaluation circuit

The circuit of fig. 6 is configured as a circuit for evaluating a button-type secondary battery (hereinafter referred to as an "evaluation circuit"). In the evaluation circuit, a resistor 92 (manufactured by BECKMAN, AR500L25) set to 220 Ω and a relay switch 93 (manufactured by Omron, G2R-1-SN DC24) were connected to the constant voltage output side of 3.3V of the DC-DC converter 91. A stabilization power supply 94 (PMX 500-0.1A, manufactured by Chrysanthemum, Water and gas industries, Ltd.) and an electronic load device 95 (PLZ-30F, manufactured by Chrysanthemum, Water and gas industries, Ltd.) were connected to the input side of the relay switch 93.

A voltmeter 96 (MR 8870, manufactured by japan electric company) is connected to an input side of the DC-DC converter 91 so as to monitor an output of the button-type secondary battery 1, and an ammeter 97 (CT 6700, manufactured by japan electric company) is connected to an output side of the DC-DC converter 91 so as to check an output current of the DC-DC converter 91.

(4d) Determination of output Performance ratio

In the evaluation circuit, a current of 15mA as an output from the DC-DC converter 91 was passed for 1s, and the amount of pressure drop of the button-type secondary battery 1 at that time was measured for each of the button-type secondary battery 1 subjected to the solder reflow test and the button-type secondary battery 1 for reference that was not subjected to the solder reflow test. As the output performance ratio, a value obtained by dividing a measurement value in the case where the solder reflow test is performed by a measurement value in the case where the solder reflow test is not performed is used. When the output performance ratio is 0.65 or more, that is, 65% or more, the evaluation is passed. In example 1, the output performance ratio was 90%. The exact cause of the decrease in output performance by the solder reflow test is not clear, but it is presumed that an increase in battery resistance is one of the main causes.

(4e) Drive time test

The test of (4d) was performed, and a driving time test of 3000 cycles was performed with 1 cycle of an operation of applying a current of 15mA for 1s and then stopping the operation for 5 s. When the voltage of the button-type secondary battery 1 was 2.0V or more after 3000 cycles, the driving time test was evaluated as passed. Example 1 was passed.

< examples 2 to 5 >

In example 2, the thickness of the positive electrode was 200. mu.m, the thickness of the negative electrode was 240. mu.m, and the C/A ratio of the electrode was 1.15. The output performance ratio is 92%, the output performance is still sufficient after the soldering tin reflow soldering test, and the driving time test is also qualified.

In example 3, the thickness of the positive electrode was 210 μm, the thickness of the negative electrode was 230 μm, and the C/A ratio of the electrode was 1.25. The output performance ratio was 93%, and the solder reflow test still had sufficient output performance and passed the drive time test.

In example 4, the thickness of the positive electrode was 230. mu.m, the thickness of the negative electrode was 210. mu.m, and the C/A ratio of the electrode was 1.50. The output performance ratio was 93%, and the solder reflow test still had sufficient output performance and passed the drive time test.

< comparative examples 1 and 2 >

In comparative example 1, the thickness of the positive electrode was 175 μm, the thickness of the negative electrode was 240 μm, and the C/A ratio of the electrode was 1.02. The output performance ratio was 60%, and the output performance after the solder reflow test was insufficient. The drive time test was also not acceptable.

In comparative example 2, the thickness of the positive electrode was 245 μm, the thickness of the negative electrode was 200 μm, and the C/A ratio of the electrode was 1.70. The output performance ratio was 90%, and the output performance after the solder reflow test was sufficient, but the drive time test was not satisfactory.

< evaluation >

Judged from the results of table 1: the influence of solder reflow on the battery performance increases whether the C/a of the electrode is too large or too small. The cause of this phenomenon is not clear, but it is considered that the main cause is: by adjusting the C/a of the electrode, the influence of the reaction between the electrolyte and lithium in the active material due to heating is reduced, or the potential rise of the active material due to the influence of heating is reduced.

If the required value for the output performance ratio is specified to be 65% or more, the 60% of comparative example 1 is only slightly lower than the required output performance ratio, and in example 1, C/a is 1.05, and therefore, it is determined that the C/a of the battery needs to be at least 1.03. On the other hand, in example 4, C/A is 1.50, and in comparative example 6, C/A is 1.70, and therefore, it is judged that C/A is preferably less than 1.60.

In summary, the C/A of the cell preferably satisfies 1.03 < C/A < 1.60. When the button-type secondary battery satisfies this condition, a circuit board assembly on which the button-type secondary battery having high battery performance is mounted by reflow soldering can be provided. In particular, even in a thin button-type secondary battery, the influence of solder reflow on the battery performance can be reduced.

The button-type secondary battery 1 described above can be variously modified.

The button-type secondary battery 1 for soldering by the reflow method is particularly suitable for use in an IoT device, but may be used for other applications.

The sintered bodies of the positive electrode 2 and the negative electrode 3 may contain other layers. That is, the positive electrode 2 and the negative electrode 3 may include a sintered body, and are substantially sintered bodies. The sintered bodies of the positive electrode 2 and the negative electrode 3 are not limited to those described above. The structure of the package 5 is not limited to the above example.

The configurations in the above embodiments and the modifications may be appropriately combined as long as they are not contradictory to each other.

Although the present invention has been described and illustrated in detail, the foregoing description is illustrative and not restrictive. Thus, it can be said that: numerous variations or modifications may be employed without departing from the scope of the invention.

Description of the symbols

1 button type secondary battery

2 positive electrode

3 negative electrode

4 electrolyte layer

5 outer package

8 circuit substrate assembly

81 wiring board

82 radio communication device