Negative electrode of a solid-state battery and a solid-state battery

Abstract

To provide a negative electrode of a solid-state battery, in which an inner short circuit or the like due to deposition of a metal lithium hardly occurs even in the case where a charging and a discharging are repeated while having a large filling of an electrode active material, and contribute to an energy efficiency of the further solid-state battery by providing the negative electrode of the solid-state battery.SOLUTION: A negative electrode of a solid-state battery comprises: a negative electrode collector having a metal porous body as a construction material; and a negative electrode active material filled with the negative electrode collector. In the negative electrode collector, a hole part without the metal porous body is provided in a thickness direction from a front surface on the solid-state battery. A hole diameter of the hole part is 100 μm to 180 μm, and a depth in the thickness direction is larger than the hole diameter.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a negative electrode of a solid battery and a solid battery.

Background Art

[0002] In recent years, in order to enable more people to access affordable, reliable, sustainable, and advanced energy, research and development of solid batteries that contribute to energy efficiency have been carried out. Solid batteries have a high energy density and are used in a wide range of applications. In particular, lithium-ion secondary batteries that enable rapid charging and discharging are highly important as a power source for sustainable and advanced energy, such as electric vehicles (EVs) and hybrid electric vehicles (HEVs).

[0003] As a configuration of a solid battery, in order to increase the packing density of an electrode active material, a configuration in which a current collector constituting a negative electrode is a foamed metal is known. Patent Document 1 discloses a semi-solid battery having a foamed metal as a current collector, in which a porous coating layer is disposed on an electrode layer. The porous coating layer in Patent Document 1 can absorb and trap the electrolyte extruded from the electrode layer even when the negative electrode active material expands during charging of the semi-solid battery, and can suppress a decrease in the electrolyte and a decrease in capacity due to repeated charge and discharge.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In order to contribute to further energy efficiency improvement, solid-state batteries are also required to maintain battery life even when charge and discharge are repeated. As required characteristics for this purpose, for example, when the charge and discharge of a solid-state battery are repeated, control of the deposition of lithium ions, sodium ions, etc. on the negative electrode to receive electrons and the deposition of metallic lithium, metallic sodium, etc. on the negative electrode is cited. When metallic lithium or the like is deposited on the negative electrode, the resistance of the solid-state battery may increase due to the formation of gaps between layers, and an internal short circuit may occur where the positive electrode and the negative electrode are in electrical contact. In particular, in a high-capacity negative electrode, the deposition of metallic lithium or the like is likely to occur.

[0006] Under such circumstances, the present invention provides a negative electrode that, when used as a solid-state battery, has a filling density of an electrode active material equal to or higher than a predetermined value and is less likely to be affected by the deposition of metallic lithium or the like such as an internal short circuit. And by providing the negative electrode of such a solid-state battery, it contributes to further energy efficiency improvement of the solid-state battery.

Means for Solving the Problems

[0007] To achieve the above object, the present invention provides the following means. [1] A negative electrode of a solid-state battery, comprising a negative electrode current collector made of a metal porous body and a negative electrode active material filled in the negative electrode current collector, wherein the negative electrode current collector is provided with a hole portion having no metal porous body in the thickness direction from the surface on the solid electrolyte side, and the hole portion has a pore diameter of 100 μm to 180 μm. A negative electrode of a solid-state battery.

[0008] [1] The negative electrode is such that when deposition of metallic lithium or the like occurs on the negative electrode, deposition of metallic lithium or the like is likely to occur intensively inside the hole portion, and it is easy to suppress the deposition of metallic lithium or the like on the negative electrode interface or the like. Therefore, when the negative electrode of [1] is used as a solid-state battery, the amount of the negative electrode active material per unit area of the negative electrode is equal to or higher than a predetermined value, and the battery life is less likely to decrease even when charge and discharge are repeated.

[0009] [2] The ratio of the total volume of the pores to the porosity of the metal porous body (total pore volume / porosity) is 10 vol% or less, the negative electrode of the solid battery according to [1].

[0010] For the negative electrode where the ratio of the total volume of the pores is within the above range, it is easy to maintain a high energy density as a solid battery. If the ratio of the total volume of the pores is too large, it is difficult to maintain a high amount of negative electrode active material, and the energy density tends to decrease. This is because the volume of the pores becomes excessively larger than the volume of the metal lithium or the like deposited during charging and discharging, and it is difficult to maintain the high energy density due to the filling of the negative electrode active material into the metal porous body.

[0011] [3] The ratio of the total volume of the pores to the porosity of the metal porous body (total pore volume / porosity) is 8 vol% or less, the negative electrode of the solid battery according to [1] or [2].

[0012] [3] The solid battery provided with the negative electrode is more likely to maintain a higher energy density. As shown in FIG. 3 described later, according to the present inventors, when the ratio of the total pore volume to the porosity is 8 vol% or less, it is possible to more reliably suppress a decrease in energy density.

[0013] [4] The pores have a depth of 3 μm or more in the thickness direction, the negative electrode of the solid battery according to any one of [1] to [3].

[0014] When the pores have a depth of the above or more, it tends to reliably secure a deposition space when metal lithium or the like is deposited during charging and discharging, and it is likely to become a solid battery with a high energy density.

[0015] [5] The pores have a depth of 5 μm or more in the thickness direction, the negative electrode of the solid battery according to any one of [1] to [4].

[0016] When the pores have a depth of the above or more, it tends to more reliably secure a deposition space of lithium or the like when metal lithium or the like is deposited during charging and discharging, and it is likely to become a solid battery with an even higher energy density.

[0017] [6] The negative electrode of the solid battery according to any one of [1] to [5], wherein the hole portion is a through hole.

[0018] When the hole portion is a through hole, lithium ions and the like tend to be uniformly supplied to the hole portion, and metallic lithium and the like are stably deposited in the hole portion, and the cycle characteristics tend to be more easily maintained.

[0019] [7] The negative electrode of the solid battery according to any one of [1] to [6], wherein the hole portion has a circular or square cross-sectional shape.

[0020] When the cross-sectional shape of the hole portion is circular, metallic lithium and the like tend to be stably deposited in the hole portion. Also, when the cross-section of the hole portion is square, the specific surface area per volume of the hole portion becomes large. Therefore, for example, at the time of rapid charging or the like, it is easy to stably form the deposition of metallic lithium and the like in the hole portion.

[0021] [8] The negative electrode of the solid battery according to any one of [1] to [7], wherein the negative electrode active material is a silicon-based material.

[0022] The above-described negative electrode is preferably used when the negative electrode active material is a silicon-based material.

[0023] [9] A solid battery including the negative electrode according to any one of [1] to [8].

Advantages of the Invention

[0024] According to the solid battery including the above-described negative electrode, it is possible to suppress a decrease in battery life due to the deposition of metallic lithium and the like while setting the packing density of the electrode active material to a predetermined value or more.

Brief Description of the Drawings

[0025]

Figure 1

Figure 2

Figure 3

Embodiments for Carrying out the Invention

[0026] Hereinafter, preferred embodiments of the present invention will be described in detail.

[0027] [Negative Electrode of Solid Battery] The negative electrode of the solid battery of the present embodiment includes a negative electrode current collector made of a metal porous body and a negative electrode active material filled in the negative electrode current collector. The negative electrode current collector is provided with a hole portion having no metal porous body in the thickness direction from the surface on the solid electrolyte side, and the hole portion has a pore diameter of 100 μm to 180 μm.

[0028] The negative electrode of the present embodiment is used in a solid battery having a structure in which a solid electrolyte is filled between the positive electrode and the negative electrode. Solid batteries are known to have advantages such as a low risk of ignition, the ability to perform rapid charging, and being less likely to deteriorate and having a long life. The structure of the solid battery is not particularly limited, and it may have any configuration such as a cylindrical or rectangular wound type, a laminated stacked type, etc.

[0029] Even when the negative electrode of the present embodiment is used in a solid battery, it is less likely to cause a decrease in battery life due to repeated charge and discharge. In this regard, in a solid battery, due to the following reasons, a short-circuit phenomenon when metal lithium or the like is deposited on the negative electrode is more likely to occur than in a secondary battery with a liquid electrolyte. On the other hand, the negative electrode of the present embodiment is likely to suppress the deposition of metal lithium or the like on the negative electrode interface or the like, so that even in a solid battery, the battery life is less likely to decrease.

[0030] In a solid-state battery, the occurrence of a short-circuit phenomenon when metallic lithium or the like precipitates on the negative electrode interface or the like is considered to be caused by the following reasons or the like. In a solid-state battery, the negative electrode and the solid electrolyte layer form an interface between solids. When metallic lithium precipitates, at the precipitation site, lithium ions become difficult to conduct at the interface between the negative electrode and the solid electrolyte, and the resistance also tends to increase. As a result, cracks are likely to occur in the electrode or the solid electrolyte layer, making it difficult for the cell to function. The precipitated metallic lithium penetrates into the gaps in the solid electrolyte layer, easily causing a short-circuit phenomenon. On the other hand, in a secondary battery in which the electrolyte is liquid, even if cracks occur in the electrode, the liquid electrolyte penetrates into the cracks, and conduction of lithium ions or the like can be maintained. Further, even if metallic lithium or the like precipitates between the electrode and the separator, a short-circuit phenomenon does not occur until the separator is broken, so the time until short-circuit is longer than that of a solid-state battery.

[0031] Further, the solid-state battery including the negative electrode of the present embodiment is suitably used for a lithium-ion secondary battery including a positive electrode, a negative electrode, a solid electrolyte, and other battery elements as required. The lithium-ion secondary battery can be applied to a wide range of uses such as for mobile devices such as mobile phones and notebook personal computers, and for in-vehicle use. The lithium-ion secondary battery only needs to have the configuration of the present embodiment as the negative electrode. As the configuration other than the negative electrode, battery elements of a known lithium-ion secondary battery may be adopted as they are. Examples of the configuration of the lithium-ion secondary battery include a lithium-ion secondary battery in which the negative electrode of the present embodiment, a positive electrode facing the negative electrode, and a solid electrolyte layer located between the positive electrode and the negative electrode are laminated.

[0032] (Negative electrode current collector) The negative electrode current collector is made of a metal porous body as a constituent material. The metal porous body is not particularly limited as long as it is a metal material having a porous space generated by foaming. Examples of the metal constituting the metal porous body may be nickel, nickel-chromium alloy, aluminum, stainless steel, titanium, copper, silver, etc., and copper or stainless steel is preferable.

[0033] The negative electrode current collector made of a metal porous body has a large surface area. The surface area of the negative electrode current collector is not particularly limited, but is preferably 1000 to 6000 m 2 / m 3 . Therefore, by filling the electrode binder containing the negative electrode active material into this negative electrode current collector, the amount of the active material per unit area of the electrode layer can be increased. Thus, the negative electrode of this embodiment has a high energy density when used as a solid battery. Further, when the negative electrode current collector is a metal porous body, it is easy to form a thick film active material layer without thickening the electrode binder. Therefore, the negative electrode of this embodiment easily realizes high capacity when used as a solid battery.

[0034] The negative electrode current collector shall be provided with holes. The holes of the negative electrode current collector will be described with reference to the schematic diagrams of FIGS. 1 and 2. In FIG. 1, the negative electrode current collector 21 of the negative electrode 1 is filled with a negative electrode active material 23. This negative electrode current collector 21 is provided with holes 22 in the thickness direction W from the surface on the solid electrolyte 31 side. The holes 22 do not have the metal porous body constituting the negative electrode current collector, that is, the holes 22 are spaces (voids) without the skeleton of the metal porous body. Note that the holes 22 may have metal lithium precipitates inside when used as a solid battery.

[0035] The reason why the negative electrode provided with the negative electrode current collector having the holes has a high energy density as a solid battery is as follows. When charging and discharging are repeated as a solid battery, lithium ions and electrons existing near the negative electrode easily reach the inside of the holes along the metal skeleton of the negative electrode current collector and the solid electrolyte particles. Such lithium ions easily precipitate stably as metal lithium inside the holes. Such a solid battery can control the precipitation position of lithium compared with a conventional solid battery in which metal lithium precipitates at random positions on the negative electrode. Therefore, internal short circuits and the like caused by the precipitation of metal lithium in the conventional solid battery are suppressed, and a solid battery with high cycle characteristics is obtained.

[0036] The pore diameter R is from 100 μm to 180 μm, preferably from 120 μm to 180 μm. If the pore diameter R is too small, it is necessary to increase the number of holes to maintain the space for the deposition of metallic lithium, and the strength of the negative electrode current collector is likely to decrease. If the pore diameter R is too large, the surface area of the metal porous body becomes small, and it becomes difficult to maintain a high energy density. Further, when the cross-sectional shape (cross-sectional shape) of the hole in the horizontal direction (hereinafter referred to as the "horizontal direction") orthogonal to the thickness direction W is circular, the pore diameter R is the diameter (inner diameter) of the circle, and when the cross-sectional shape is square, it is the diameter of the inscribed circle. The pore diameter R in the present embodiment means the average value calculated from the image of the extracted holes by binarizing the image observed at a magnification of 50 times with an electron microscope from the surface of the negative electrode current collector on the solid electrolyte side.

[0037] The cross-sectional area of the hole 22 in the horizontal direction is 6.0×10 ―5 cm 2 ~3.0×10 ―4 cm 2 It is preferably so. If the cross-sectional area is too small, the deposition of metallic lithium into the hole 22 hardly occurs appropriately, and if the cross-sectional area is too large, it becomes difficult to maintain a high energy density as a solid battery.

[0038] The depth H of the hole 22 in the thickness direction W is preferably larger than the pore diameter R (see FIG. 2). The depth H is the length from the surface of the negative electrode current collector 21 on the solid electrolyte side to the tip inside the hole 22 (when the hole 22 is a through hole, it is the same as the film thickness of the metal porous body in the thickness direction W). When the depth H of the hole 22 is larger than the pore diameter R, it becomes a negative electrode in which metallic lithium is likely to be stably deposited inside the hole while ensuring a sufficient filling amount of the negative electrode active material 23. Further, from the viewpoint of ensuring a sufficient capacity for depositing metallic lithium inside the hole 22, the depth H of the hole 22 in the thickness direction W is preferably 3 μm or more, and particularly preferably 5 μm or more.

[0039] The number of holes 22 provided in the negative electrode current collector (number of holes) is not particularly limited. From the viewpoint of easily ensuring a sufficient capacity for depositing metallic lithium inside the hole 22, the number of holes is 2 (pieces / cm with respect to the surface area of the negative electrode current collector 212 )Preferably, it is as described above, 5 (pieces / cm 2 )More preferably, it is as described above. Further, from the viewpoint of easily maintaining the strength of the negative electrode current collector, the number of holes is 10 (pieces / cm with respect to the surface area of the negative electrode current collector 21 2 )Preferably, it is 10 or less, and 9 (pieces / cm 2 )More preferably, it is 9 or less.

[0040] As described above, the hole 22 preferably has an internal volume in which metallic lithium can be sufficiently deposited. On the other hand, if the internal volume of the hole 22 is excessive, it will hold a useless space where metallic lithium is not deposited. In this case, it tends to be difficult for the negative electrode to maintain the filling amount of the negative electrode active material and maintain a high energy density as a solid battery. In this regard, when the negative electrode of the present embodiment is used as a solid battery, the amount of metallic lithium deposited on the negative electrode current collector 21 varies depending on the cell configuration, the current value during charging, etc. Considering such variations due to the configuration of the solid battery, the pore diameter R of the hole 22 is preferably 2L or less (R≤2L) with respect to the growth rate L (μm / h) of lithium when charging at 1C. The negative electrode 1 provided on the negative electrode current collector 21 with the pore diameter R within the above range can have a high energy density that can cope with rapid charging and high output as a solid battery. The growth rate L of lithium when charging at 1C is the value obtained by converting the growth amount of lithium deposited when performing constant current charging until reaching a specified capacity of 3 mAh / cm at 1C 2 per hour. The pore diameter R in the present embodiment is preferably determined based on a lithium growth rate L of 50 to 90 μm / h.

[0041] The ratio of the total volume of the pores to the porosity of the metal porous body (total pore volume / porosity) is preferably 10 vol% or less, and particularly preferably 8 vol% or less. The total volume of the pores 22 can be said to be the space provided for the precipitation of metallic lithium. Therefore, when the ratio of the total volume of the pores 22 to the porosity of the metal porous body 21 is within the above range, it is easier to maintain a higher energy density as a solid battery. The lower limit of the above ratio is not limited, but from the viewpoint of easily securing the precipitation space of metallic lithium, 1 vol% or more is preferable, and 5 vol% or more is particularly preferable. The porosity (pore rate) of the negative electrode current collector 21 can be measured by a gas adsorption method or a mercury porosimetry method. The total pore volume is obtained by multiplying the volume per pore by the number of pores. The volume per pore can be calculated from the depth and cross-sectional area measured by observing the pores cut in the horizontal direction by an argon beam or the like with an electron microscope, or from the depth, cross-sectional shape, and pore diameter.

[0042] The precipitation of metallic lithium on the pores 22 proceeds more stably and the metallic lithium grows more uniformly when it proceeds uniformly on the inner surface of the pores 22 than when the precipitation proceeds non-uniformly depending on the location, and it is easier to maintain the cycle characteristics as a solid battery. From the viewpoint of such uniform precipitation of metallic lithium on the pores 22, the pores 22 are preferably through-holes. When the pores 22 are through-holes, lithium ions can easily penetrate uniformly into the pores 22 from the vertical direction of the pores 22. Therefore, metallic lithium can be more stably and uniformly precipitated than in the case of the pores 22 having a bottom surface.

[0043] In addition, the cross-sectional shape of the hole portion 22 (the shape in the horizontal direction when observing the hole portion 22 from the solid electrolyte side) is not particularly limited, and may be circular, elliptical, square, polygonal, star-shaped, or the like. The cross-sectional shape of the hole portion 22 is preferably circular or square. When the cross-sectional shape is circular, lithium is likely to deposit uniformly on the hole portion 22, and it is easy to maintain the cycle characteristics as a solid battery. When the cross-sectional shape of the hole portion 22 is square, the specific surface area inside the hole portion 22 can be increased. Therefore, when rapid charging or the like is performed as a solid battery, initial lithium deposition is likely to proceed. In the case where the cross-sectional shape is elliptical, the pore diameter is the arithmetic mean of the major axis and the minor axis. In the case of a polygon, it is the diameter of the inscribed circle, and in the case of a star shape, it is the diameter of the circumscribed circle.

[0044] (Negative electrode active material) The negative electrode active material 23 is not particularly limited, and known battery elements of solid batteries can be adopted. Examples of the negative electrode active material 23 include silicon-based materials, carbon-based materials, and metal-based materials. The negative electrode 1 of the present embodiment is preferably used when the negative electrode active material 23 is a high-capacity silicon-based material. Here, when a silicon-based material is used as the negative electrode active material 23, silicon is likely to expand and contract when the solid battery is repeatedly charged and discharged. Therefore, the negative electrode active material 23 tends to slide off from the negative electrode current collector 21, the interface becomes unstable, and the precipitation of metallic lithium is likely to be accelerated. On the other hand, the negative electrode 1 of the present embodiment can also stably deposit metallic lithium on the hole portion 22 even when a silicon-based material negative electrode active material 23 is used. In addition, since the negative electrode current collector 21 is a metal porous body, the negative electrode active material 23 is also less likely to slide off.

[0045] Examples of the silicon-based material of the negative electrode active material 23 include SiOx (0 < x < 2), a composite material of silicon and carbon such as Si-C. Examples of the carbon-based material include graphite, carbon nanotubes, non-graphitizable carbon (hard carbon), graphitizable carbon (soft carbon), and low-temperature fired carbon. Examples of the metal-based material include lithium-based materials, aluminum-based materials, silicon-based materials, and tin-based materials.

[0046] The negative electrode active material 23 is preferably filled at a ratio of 2 mg / cm 2 to 10 mg / cm 2 with respect to the surface area of the negative electrode current collector 21. If the filling amount of the negative electrode active material 23 is too small, it tends to be difficult to maintain a high energy density, and even if the filling amount of the negative electrode active material 23 is excessive, it is difficult to contribute to the improvement of characteristics.

[0047] The negative electrode active material 23 may be filled into the negative electrode aggregate 21 as a negative electrode binder containing a binder. As the binder, known ones may be used, and examples thereof include fluororesin-based materials. Further, the negative electrode binder may contain a conductive auxiliary agent as necessary.

[0048] [Lithium Ion Secondary Battery] The negative electrode of the present embodiment is suitably used for a lithium ion secondary battery including a negative electrode, a positive electrode, a solid electrolyte, and other battery elements as necessary. As the battery elements such as a battery container, known ones may be adopted.

[0049] The solid electrolyte may be any material that can conduct lithium ions and is not particularly limited. As the solid electrolyte, for example, a polymer solid electrolyte such as a polyethylene oxide-based polymer compound, a polymer compound containing at least one of a polyorganosiloxane chain and a polyoxyalkylene chain, a sulfide-based solid electrolyte, an oxide-based solid electrolyte, or the like can be used.

[0050] As the positive electrode, for example, one in which a layer containing a positive electrode active material is formed on a positive electrode current collector may be adopted. The positive electrode active material is not particularly limited, and known materials may be applied. Examples of the positive electrode active material include layered positive electrode active material particles, spinel-type positive electrode active materials, olivine-type positive electrode active materials, and the like. The layer containing the positive electrode active material may contain a binder, a conductive auxiliary agent, a solid electrolyte, and the like. The binder and the conductive auxiliary agent are not particularly limited, and known ones as materials for solid batteries may be applied.

[0051] [Method for Manufacturing Negative Electrode] The negative electrode of this embodiment can be manufactured by a manufacturing method including a step of filling a negative electrode current collector made of a metal porous body with a negative electrode active material, and a step of forming pore portions in the negative electrode precursor. Other manufacturing steps are not particularly limited, and known methods used as manufacturing methods for solid-state batteries may be applied.

[0052] (Step of filling negative electrode active material) The method of filling the negative electrode current collector with the negative electrode active material is not particularly limited, and known methods may be applied. This filling step may be, for example, a method of coating a negative electrode mixture containing the negative electrode active material inside the voids of the negative electrode current collector using a die coater or the like. Instead of die coating, the coating of the negative electrode mixture may be dipping coat, plunger type die coat, comma coat, blade coat, or the like. From the viewpoint of easily maintaining a high energy density, the coating amount of the negative electrode active material on the negative electrode current collector is preferably 2 mg / cm 2 ~10 mg / cm 2 . The method of this embodiment may further have a drying step of drying the negative electrode current collector after the step of filling the negative electrode active material. The drying step preferably has conditions in the range of a pressure of 100 to 800 MPa and a drying temperature of 25°C to 120°C.

[0053] (Step of forming pore portions) The step of forming pore portions may apply a known method as long as it can form pore portions having the above-described pore diameter and depth in the negative electrode current collector. The step of forming pore portions may be, for example, a method using a roll press that presses a roll having predetermined irregularities on the surface with a predetermined pressure. By adjusting the shape and depth of the irregularities provided on the roll and the pressing pressure, pore portions having the pore diameter and depth of this embodiment can be formed.

Examples

[0054] Hereinafter, examples of the present invention will be described, but the present invention is not limited to the following examples.

[0055] [Example 1] As the negative electrode current collector, having a thickness of 1 mm, a porosity of 98%, and a specific surface area of 5800 m 2 / m 3 The foamed copper of 3 was prepared.

[0056] A negative electrode mixture containing silicon (average particle size 5 μm) as a negative electrode active material, acetylene black as a conductive assistant, and styrene-butadiene rubber (SBR) as a binder was prepared. The prepared negative electrode mixture was filled onto a negative electrode current collector using a die coater so that the coating amount was 10 mg / cm 2 After filling, the negative electrode current collector was dried in a vacuum at 120°C for 12 hours.

[0057] Next, the negative electrode current collector was roll-pressed at a pressure of 500 MPa using a normal roll press machine. Next, using a roll in which circular protrusions with a diameter of 180 μm were arranged at intervals of 5.1 per cm 2 the negative electrode current collector was roll-pressed at a pressure of 500 MPa. Regarding the holes formed in the negative electrode current collector after roll pressing, the average value of the hole diameters and the number of holes within a range 100 times the observation field of the electron microscope were counted. Also, the average value of the cross-sectional area of the holes in the horizontal direction was calculated. The measurement results are shown in Table 1 together with the measurement results of the following Examples and Comparative Examples.

[0058] [Examples 2 to 4] The interval between the circular protrusions arranged on the roll was 4.6 per cm 2 (Example 2), 4.1 per cm 2 (Example 3), 2.6 per cm 2 (Example 4) A negative electrode with holes formed was produced in the same manner as in Example 1, except that a roll was used.

[0059] [Example 5] The same cell design as in Example 1 was implemented, except that the hole diameter in the negative electrode was set to 100 μm and the number of holes was set to 9.2 per cm 2 A roll in which the circular protrusions arranged on the roll had a diameter of 100 μm was used.

[0060] [Comparative Example 1] For the negative electrode current collector coated with the negative electrode active material and dried, a negative electrode current collector was produced in the same manner as in Example 1, except that the second roll press was not performed. In the negative electrode current collector of Comparative Example 1, when observed within a range of 100 times the field of view of the electron microscope, pores of 500 nm or more that were visible could not be observed.

[0061] [Comparative Example 2] A cell design similar to that of Example 1 was implemented, except that the pore diameter in the negative electrode was 200 μm. The diameter of the circular protrusions arranged on the roll was 200 μm, and the interval between the protrusions was 4.7 per cm 2 A negative electrode with pores formed was produced in the same manner as in Example 1, except that a roll with the above specifications was used.

[0062] [Comparative Example 3] A cell design similar to that of Example 1 was implemented, except that the pore diameter in the negative electrode was 80 μm. The diameter of the circular protrusions arranged on the roll was 80 μm, and the interval between the protrusions was 10.8 per cm 2 A negative electrode with pores formed was produced in the same manner as in Example 1, except that a roll with the above specifications was used.

[0063] For the negative electrodes of each of the above-prepared Examples and Comparative Examples, the processing accuracy and electrode strength were confirmed by the following measurement methods.

[0064] [Processing Accuracy] The fabricated negative electrode was cut into 1 cm squares using an insulating ceramic blade, and then horizontally cut with an argon beam (intensity: 4 kV, irradiation time: 12 hr, temperature: -60 °C) using a cross-section preparation device (JEOL, model number: IB-19530CP) in a vacuum to confirm workability. Also, the cut cross-section was observed with an electron microscope to confirm the horizontal cross-sectional shape of the holes and the depth of the holes. In Examples 1 to 5 and Comparative Example 2, a circular cross-sectional shape was observed. In Comparative Example 3, the metal porous body collapsed during cutting, and the cross-sectional shape after processing could not be confirmed. The holes in Examples 1 to 5 were all through-holes. The results of workability and the cross-sectional shape, cross-sectional area, and depth of the holes are shown in Table 1. Also, the ratio of the total volume of the holes to the porosity of the negative electrode current collector (total hole volume / porosity) is shown in Table 1. The total volume of the holes was calculated by multiplying the volume per hole, which was calculated from the average value of the cross-sectional area and depth, by the number of holes. Workability was evaluated according to the following criteria. <Evaluation of Workability> 〇: It could be cut well, and the cross-section and shape of the holes after processing could be confirmed. △: The holes were distorted by the argon beam during processing, the shape of the holes was slightly deformed, and it could not be clearly confirmed. ×: The metal porous body collapsed during cutting, the cutting could not be performed well, and the shape of the cross-section after processing could not be confirmed.

[0065] [Electrode Strength] Regarding the negative electrode fabricated above, using a bending test device (manufactured by MTI, model number EQ-MBT-12-LD), it was bent under the condition of a mandrel diameter of 32 mm to confirm the presence or absence of peeling of the negative electrode active material, etc. The results of the electrode strength evaluated according to the following criteria are shown in Table 1. <Evaluation of Electrode Strength> 〇: No peeling of the negative electrode active material was observed. △: Partial peeling of the active material was confirmed. ×: In addition to the peeling of the active material, the structure of the electrode collapsed.

[0066] [Fabrication of Lithium-Ion Secondary Battery] The positive electrode active material Li(Ni 0.6 Co 0.2 Mn0.2 ) O2, thio-LISICON (Li 3.25 Ge 0.25 P 0.75S4 ), acetylene black as a conductive aid, styrene-butadiene rubber (SBR) as a binder, and butyl butyrate as a solvent were charged into a planetary mixer and stirred at 2000 rpm for 3 minutes, followed by defoaming for 1 minute to prepare a positive electrode mixture. The mass ratio of the positive electrode active material, solid electrolyte, conductive aid, and binder was 75:22:3:3. The positive electrode mixture was applied onto an aluminum foil as a positive electrode current collector and heated at 60°C. After heating, roll pressing was performed to obtain a positive electrode having a positive electrode mixture layer with a density of 3.1 g / cc and a basis weight of 26 mg / cm 2 .

[0067] Next, thio-LISICON (Li 3.25 Ge 0.25 P 0.75 S4) was powder molded at a molding pressure of 150 MPa using a zirconium tube with a diameter of 10 mm to obtain a solid electrolyte layer with a diameter of 10 mm. The positive electrode with a diameter of 10 mm and the solid electrolyte layer were pressure molded at a molding pressure of 1000 MPa to obtain a laminate of the positive electrode and the solid electrolyte layer (positive electrode-solid electrolyte layer laminate).

[0068] The positive electrode-solid electrolyte layer laminate obtained above was joined to the negative electrode of Example 1 at 60 MPa to fabricate a lithium-ion secondary battery. Lithium-ion secondary batteries were also fabricated for the negative electrodes of Examples 2 to 5 and Comparative Examples 1 to 3 by the same manufacturing method.

[0069] [Charge and Discharge Test] For the fabricated lithium-ion secondary battery, under a temperature condition of 60°C, CC charging was performed at a 0.05C rate up to 4.3V, and after a rest time of 10 minutes, a charge and discharge test was conducted at 0.05C with a cut-off potential of 2.5V. The charge and discharge test started from charging. Table 1 shows the evaluation of the state of Li precipitation and the energy density as the charge and discharge test results of the lithium-ion secondary batteries of each example and comparative example. The state of Li precipitation was evaluated based on the charge and discharge curve according to the following criteria. <Evaluation of Li Precipitation> 〇: No specific variations were observed in the charging curve. △: In the charging curve, a voltage drop due to a micro short circuit was observed, but charging could be carried out. ×: During charging, a short circuit occurred due to abnormal Li deposition, and sufficient charging could not be achieved.

[0070] [Li growth rate when charging at 1C] For the lithium-ion secondary batteries of each example and comparative example, the growth rate was measured when constant current charging was performed until the specified capacity of 3 mAh / cm 2 was reached at 1C. The growth of lithium was measured by microscopic observation to confirm that lithium was deposited in the pores. As a result of the above measurement, in all examples and comparative examples, the growth thickness of lithium per hour, that is, the Li growth rate, was 90 μm / h.

[0071] Fig. 3 shows a graph of the results of the energy density against the porosity for the lithium-ion secondary battery of Example 1. Here, the porosity is the ratio of the total volume of the pores to the porosity of the negative electrode current collector.

[0072]

Table 1

[0073] From Table 1, it was shown that the lithium-ion secondary batteries of Examples 1 to 5 all had high energy density values exceeding 800 Wh / L. The lithium-ion secondary battery of Comparative Example 1 had a high energy density value, but due to unstable Li deposition, abnormal charging occurred during charging and a micro short circuit occurred, and stable charge and discharge could not be performed. Therefore, the secondary battery of Comparative Example 1 may cause internal short circuits, etc. The lithium-ion secondary battery of Comparative Example 2 had a lower energy density than Examples 1 to 5. The lithium-ion secondary battery of Comparative Example 3 had its electrode rupture during the charge and discharge test (the energy density could not be measured).

[0074] Also, as shown in FIG. 3, when the ratio of the total volume of the holes to the porosity exceeds 8%, the energy density tends to decrease, and when the ratio exceeds 10%, it tends to decrease significantly. From this, it is considered that when the ratio of the total volume of the holes to the porosity is 8% or less, it is easy to stably maintain a high energy density.

Explanation of Symbols

[0075] 1 Negative electrode 21 Negative electrode current collector 22 Hole 23 Negative electrode active material 31 Solid electrolyte W Thickness direction R (Hole) pore diameter H (Hole) depth

Claims

1. A negative electrode of a solid-state battery, comprising: a current collector for the negative electrode made of a metal porous body, and a negative electrode active material filled in the current collector for the negative electrode. The current collector for the negative electrode is provided with holes that do not have a metal porous body in the thickness direction from the surface on the solid electrolyte side. The holes have a pore diameter of 100 μm to 180 μm. A negative electrode of a solid-state battery.

2. The negative electrode of the solid-state battery according to Claim 1, wherein the ratio of the total volume of the holes to the porosity of the metal porous body (total hole volume / porosity) is 10 vol% or less.

3. The negative electrode of the solid-state battery according to Claim 1, wherein the ratio of the total volume of the holes to the porosity of the metal porous body (total hole volume / porosity) is 8 vol% or less.

4. The negative electrode of the solid-state battery according to Claim 1, wherein the depth of the holes in the thickness direction is 3 μm or more.

5. The negative electrode of the solid-state battery according to Claim 1, wherein the depth of the holes in the thickness direction is 5 μm or more.

6. The negative electrode of the solid-state battery according to Claim 1, wherein the holes are through holes.

7. The negative electrode of the solid-state battery according to Claim 1, wherein the cross-sectional shape of the holes is circular or square.

8. The negative electrode of the solid-state battery according to Claim 1, wherein the negative electrode active material is a silicon-based material.

9. A solid-state battery comprising the negative electrode according to any one of Claims 1 to 8.

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