Battery and method for manufacturing a battery

Abstract

A battery according to an aspect of the present disclosure comprises a positive electrode, a negative electrode, and an electrolyte layer positioned between the positive electrode and the negative electrode. The negative electrode includes a negative electrode current collector and a negative electrode active material layer positioned between the negative electrode current collector and the electrolyte layer. The negative electrode active material layer includes a plurality of columnar bodies containing silicon as a main component, and the Young's modulus of the negative electrode active material layer is 25 GPa or less.

Description

[Technical Field]

[0001] This disclosure relates to batteries and methods for manufacturing batteries. [Background technology]

[0002] Patent Document 1 discloses a battery having a negative electrode that includes a negative electrode active material containing silicon and having a hardness of 10 GPa or more and 20 GPa or less. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] International Publication No. 2017 / 073585 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] In conventional technology, it is desirable to achieve both high capacity and high cycle performance. [Means for solving the problem]

[0005] In one aspect of this disclosure, the battery is Positive electrode and, The negative electrode and, An electrolyte layer located between the positive electrode and the negative electrode, Equipped with, The negative electrode comprises a negative electrode current collector and a negative electrode active material layer located between the negative electrode current collector and the electrolyte layer. The negative electrode active material layer has a plurality of columnar bodies mainly composed of silicon, The Young's modulus of the negative electrode active material layer is 25 GPa or less.

[0006] In one aspect of this disclosure, the battery is Positive electrode and, The negative electrode and, An electrolyte layer located between the positive electrode and the negative electrode, Equipped with, The negative electrode has a negative electrode current collector and a negative electrode active material layer located between the negative electrode current collector and the electrolyte layer, The negative electrode active material layer contains silicon and 1% by mass or less of copper, The Young's modulus of the negative electrode active material layer is 25 GPa or less.

[0007] A method for manufacturing a battery according to an aspect of the present disclosure includes: depositing silicon on a negative electrode current collector by a vapor phase method; and annealing the deposited silicon at a temperature of 300° C. or lower, . Effects of the Invention

[0008] According to the present disclosure, a battery that achieves both capacity and cycle characteristics can be realized. Brief Description of Drawings

[0009] [Figure 1] FIG. 1 is a cross-sectional view showing a schematic configuration of the battery according to Embodiment 1. [Figure 2] FIG. 2 is an example of a cross-sectional SEM image of the negative electrode according to Embodiment 1. [Figure 3] FIG. 3 is a cross-sectional SEM image of the negative electrode in a charged state according to Example 1. [Figure 4] FIG. 4 is a cross-sectional SEM image of the negative electrode in a charged state according to Comparative Example 1. Mode for Carrying Out the Invention

[0010] (Findings underlying the present disclosure) To cope with the rapid proliferation of electric vehicles (EVs), there is an urgent need to develop automotive lithium-ion batteries with features such as high safety, high performance, and long lifespan. In addition, to improve the convenience of EVs, there is a demand for increased driving range per charge and reduced charging time. Because lithium-ion batteries have high energy density and high capacity, the development of high-capacity anode materials is important. Silicon is a promising material for high-capacity anodes. However, silicon anodes that excel in both capacity and cycle characteristics have not yet been obtained.

[0011] Patent Document 1 discloses a lithium secondary battery having a negative electrode containing a negative electrode active material that includes silicon and has a hardness of 10 GPa or more and 20 GPa or less. Patent Document 1 states that silicon and dissimilar metal elements such as aluminum form an intermetallic compound. Furthermore, Patent Document 1 states that the mass ratio of silicon to dissimilar metal elements is between 50:50 and 90:10.

[0012] In Patent Document 1, the negative electrode active material contains a large proportion (10% to 50%) of dissimilar metal elements that do not function as power generation elements in the battery. Furthermore, because silicon and dissimilar metal elements form intermetallic compounds, the capacity of silicon cannot be fully utilized.

[0013] The inventors diligently researched batteries that achieve both high capacity and excellent cycle performance. As a result, they discovered that a battery achieving both high capacity and excellent cycle performance can be realized when the negative electrode active material layer has multiple columnar bodies mainly composed of silicon, and the Young's modulus of the negative electrode active material layer is 25 GPa or less. This is for the following reasons: When the Young's modulus of the negative electrode active material layer is 25 GPa or less, the deformability of the negative electrode active material layer is improved. Therefore, as the negative electrode expands during the initial charging of the battery, the gaps between adjacent columnar bodies decrease, and the surfaces of the columnar bodies are smoothed to conform to the surface of the electrolyte layer facing the negative electrode. As a result, an interface with a large contact area is formed between the negative electrode active material layer and the electrolyte layer. This allows the negative electrode active material layer to maintain its dense columnar structure and a smooth interface with the electrolyte layer even with subsequent expansion and contraction due to charging and discharging. As a result, a battery that achieves both high capacity and excellent cycle performance is realized.

[0014] (Summary of one aspect of this disclosure) The battery relating to the first aspect of this disclosure is Positive electrode and, The negative electrode and, An electrolyte layer located between the positive electrode and the negative electrode, Equipped with, The negative electrode comprises a negative electrode current collector and a negative electrode active material layer located between the negative electrode current collector and the electrolyte layer. The negative electrode active material layer has a plurality of columnar bodies mainly composed of silicon, The Young's modulus of the negative electrode active material layer is 25 GPa or less.

[0015] With the above configuration, as the negative electrode expands during the initial charging of the battery, the gaps between adjacent columnar bodies decrease, and the surfaces of the columnar bodies are smoothed to conform to the surface of the electrolyte layer facing the negative electrode. As a result, an interface with a large contact area is formed between the negative electrode active material layer and the electrolyte layer. This enables the realization of a battery that balances capacity and cycle characteristics.

[0016] In a second aspect of this disclosure, for example, in the battery according to the first aspect, the Young's modulus of the negative electrode active material layer may be 20 GPa or less. With this configuration, the deformability of the negative electrode active material layer is further improved. Therefore, during the initial charging of the battery, an interface with a large contact area is more easily formed between the negative electrode active material layer and the electrolyte layer.

[0017] In a third aspect of this disclosure, for example, in a battery according to the first or second aspect, the thickness of the negative electrode active material layer may be 30 μm or less. With the above configuration, operation of the battery at high input / output speeds becomes possible.

[0018] In a fourth aspect of this disclosure, for example, in a battery according to any one of the first to third aspects, the negative electrode current collector may contain copper as its main component. This configuration is advantageous for suppressing the internal resistance of the battery.

[0019] In a fifth aspect of this disclosure, for example, in a battery according to any one of the first to fourth aspects, the negative electrode active material layer may contain 1% by mass or less of copper. With this configuration, a decrease in battery capacity can be suppressed.

[0020] In a sixth aspect of this disclosure, for example, in a battery according to any one of the first to fifth aspects, the electrolyte layer may include a solid electrolyte having lithium-ion conductivity. With the above configuration, a battery that balances capacity and cycle characteristics can be more reliably realized.

[0021] In the seventh aspect of this disclosure, for example, in the battery according to the sixth aspect, the solid electrolyte may include a sulfide solid electrolyte. With the above configuration, the output characteristics of the battery can be further improved.

[0022] The battery relating to the eighth aspect of this disclosure is Positive electrode and, The negative electrode and, An electrolyte layer located between the positive electrode and the negative electrode, Equipped with, The negative electrode comprises a negative electrode current collector and a negative electrode active material layer located between the negative electrode current collector and the electrolyte layer. The negative electrode active material layer comprises silicon and copper at a concentration of 1% by mass or less. The Young's modulus of the negative electrode active material layer is 25 GPa or less.

[0023] With the above configuration, the deformability of the negative electrode active material layer is improved. As a result, an interface with a large contact area is formed between the negative electrode active material layer and the electrolyte layer. This enables the realization of a battery that balances capacity and cycle characteristics.

[0024] In a ninth aspect of this disclosure, for example, in the battery according to the eighth aspect, the negative electrode active material layer may have a plurality of columnar bodies mainly composed of silicon. With this configuration, as the negative electrode expands during the initial charging of the battery, the gaps between adjacent columnar bodies decrease, and the surfaces of the columnar bodies are smoothed to conform to the surface of the electrolyte layer facing the negative electrode. As a result, an interface with a large contact area is formed between the negative electrode active material layer and the electrolyte layer. This makes it possible to more reliably realize a battery that balances capacity and cycle characteristics.

[0025] In the tenth aspect of this disclosure, for example, in the battery according to the eighth or ninth aspect, the Young's modulus of the negative electrode active material layer may be 20 GPa or less. With this configuration, the deformability of the negative electrode active material layer is further improved. Therefore, during the initial charging of the battery, an interface with a large contact area is more easily formed between the negative electrode active material layer and the electrolyte layer.

[0026] In the eleventh aspect of this disclosure, for example, in a battery according to any one of the eighth to tenth aspects, the thickness of the negative electrode active material layer may be 30 μm or less. With the above configuration, the battery can operate at high input / output speeds.

[0027] In a twelfth aspect of this disclosure, for example, in a battery according to any one of the eighth to eleventh aspects, the negative electrode current collector may contain copper as its main component. This configuration is advantageous for suppressing the internal resistance of the battery.

[0028] In a thirteenth aspect of this disclosure, for example, in a battery according to any one of the eighth to twelfth aspects, the electrolyte layer may include a solid electrolyte having lithium-ion conductivity. With the above configuration, a battery that balances capacity and cycle characteristics can be more reliably realized.

[0029] In a fourteenth aspect of this disclosure, for example, in the battery according to the thirteenth aspect, the solid electrolyte may include a sulfide solid electrolyte. With the above configuration, the output characteristics of the battery can be further improved.

[0030] The battery manufacturing method according to the 15th aspect of this disclosure is: Depositing silicon onto the negative electrode current collector by a vapor phase method, The deposited silicon is annealed at a temperature of 300°C or less. Includes.

[0031] With the above configuration, it is possible to manufacture a battery equipped with a negative electrode in which the negative electrode active material layer has multiple columnar bodies mainly composed of silicon, and the Young's modulus of the negative electrode active material layer is 25 GPa or less. Therefore, it is possible to realize a battery that balances capacity and cycle characteristics.

[0032] In the sixteenth aspect of this disclosure, for example, in the battery manufacturing method according to the fifteenth aspect, the annealing time may be 5 hours or more and 30 hours or less. With the above configuration, a battery having a negative electrode in which the negative electrode active material layer has a plurality of columnar bodies mainly composed of silicon, and the Young's modulus of the negative electrode active material layer is 25 GPa or less, can be manufactured more reliably.

[0033] Embodiments of the present disclosure will be described below with reference to the drawings.

[0034] (Embodiment 1) Figure 1 is a cross-sectional view showing the schematic configuration of the battery 1 in Embodiment 1.

[0035] The battery 1 in Embodiment 1 comprises a positive electrode 10, a negative electrode 20, and an electrolyte layer 30 located between the positive electrode 10 and the negative electrode 20. The negative electrode 20 has a negative electrode current collector 21 and a negative electrode active material layer 22 located between the negative electrode current collector 21 and the electrolyte layer 30.

[0036] The negative electrode active material layer 22 has a plurality of columnar bodies mainly composed of silicon. Silicon is the negative electrode active material. The Young's modulus of the negative electrode active material layer 22 is 25 GPa or less. In this disclosure, "main component" means the component that is present in the largest amount by mass ratio.

[0037] Figure 2 is an example of a scanning electron microscope (SEM) image of a cross-section of the negative electrode 20. As shown in Figure 2, the negative electrode active material layer 22 has a plurality of columnar bodies 25 mainly composed of silicon. The negative electrode current collector 21 has a plurality of protrusions 23 and a plurality of recesses 24 on one surface. Each of the columnar bodies 25 is supported by a protrusion 23. The columnar bodies 25 are formed so as to extend outward from one surface of the negative electrode current collector 21 and are spaced apart from each other.

[0038] When the Young's modulus of the negative electrode active material layer 22 is 25 GPa or less, the deformability of the negative electrode active material layer 22 is improved. As a result, as the negative electrode 20 expands during the initial charging of the battery 1, the gaps between adjacent columnar bodies 25 decrease, and the surfaces of the columnar bodies 25 are smoothed to conform to the surface of the electrolyte layer 30 facing the negative electrode 20. Therefore, an interface with a large contact area is formed between the negative electrode active material layer 22 and the electrolyte layer 30. This allows the negative electrode active material layer 22 to maintain its dense columnar structure and maintain its interface with the electrolyte layer 30 even with subsequent expansion and contraction due to charging and discharging. As a result, a battery 1 that balances capacity and cycle characteristics is realized.

[0039] The Young's modulus of the negative electrode active material layer 22 can be measured, for example, using the nanoindentation method. Specifically, the Young's modulus of 12 arbitrarily selected points on the surface of the negative electrode active material layer 22 is measured using a nanoindentation apparatus. From this data, the Young's modulus can be determined by calculating the average value of 10 points, excluding the minimum and maximum values, taking into account measurement errors caused by surface irregularities of the negative electrode active material layer 22.

[0040] Figure 2 shows the uncharged and annealed negative electrode active material layer 22. The Young's modulus is measured on the uncharged and annealed negative electrode active material layer 22. However, even if the battery 1 is charged and discharged, the Young's modulus of the negative electrode active material layer 22 is generally maintained at the value before charging and discharging.

[0041] The Young's modulus of the negative electrode active material layer 22 may be 20 GPa or less. With the above configuration, the deformability of the negative electrode active material layer 22 is further improved. Therefore, during the initial charging of the battery 1, an interface with a large contact area is more easily formed between the negative electrode active material layer 22 and the electrolyte layer 30. The lower limit of the Young's modulus of the negative electrode active material layer 22 is not particularly limited. For example, the lower limit is 10 GPa.

[0042] The negative electrode active material layer 22 mainly contains silicon and also contains copper. With this configuration, the ionic conductivity of the negative electrode active material layer 22 can be improved.

[0043] The electronic conductivity of a negative electrode active material layer containing only silicon is considered to be low. On the other hand, the negative electrode active material layer 22 of this disclosure contains silicon and copper. Generally, copper does not form alloys with lithium. Therefore, copper is not considered to have lithium ion conductivity. However, because the negative electrode active material layer 22 contains silicon and copper, the electronic conductivity of the negative electrode active material layer 22 exceeds that of a negative electrode active material layer containing only silicon.

[0044] The negative electrode active material layer 22 contains less than 1% by mass of copper. Copper does not function as a power generation element in the battery 1. Therefore, if the amount of copper contained in the negative electrode active material layer 22 is less than 1% by mass, the decrease in the capacity of the battery 1 can be suppressed.

[0045] The mass ratio of copper contained in the negative electrode active material layer 22 can be determined, for example, using secondary ion mass spectrometry (SIMS). Specifically, a secondary ion mass spectrometer is used to obtain the concentration distribution in the thickness direction for both copper and silicon elements in the negative electrode 20. The concentration of each element can be calculated by dividing the integral value of each concentration distribution in the negative electrode active material layer 22 by the thickness of the negative electrode active material layer 22. The concentration of copper element calculated in this way is defined as C1, and the concentration of silicon element is defined as C2. C1 / (C1+C2) can be considered as the mass ratio of copper contained in the negative electrode active material layer 22. In the obtained concentration distribution, the interface between the negative electrode active material layer 22 and the negative electrode current collector 21 may be identified as a region with a higher or lower concentration of the element than other areas.

[0046] The copper contained in the negative electrode active material layer 22 does not exist in elemental form or in the form of an intermetallic compound with silicon. The copper contained in the negative electrode active material layer 22 is diffused into the negative electrode active material layer 22 in ppm units and exists in the form of a solid solution with silicon. With this configuration, it is easy to reduce the Young's modulus of the negative electrode active material layer 22 to 25 GPa or less.

[0047] The presence of copper in the negative electrode active material layer 22 in a solid solution with silicon can be confirmed, for example, by peak profile analysis using X-ray diffraction (XRD) or by structural observation using a transmission electron microscope (TEM).

[0048] The thickness of the negative electrode active material layer 22 may be 30 μm or less. A thickness of 30 μm or less reduces the risk of film cracking during handling in sputtering deposition or subsequent annealing. This enables high input / output operation of the battery 1.

[0049] The thickness of the negative electrode active material layer 22 can be measured by the following method: Observe a cross-section of the negative electrode active material layer 22 using a scanning electron microscope (SEM). The cross-section is parallel to the stacking direction of each layer and includes the centroid of the negative electrode active material layer 22 in a plan view. Select any 20 points from the obtained cross-sectional SEM image. Measure the thickness of the negative electrode active material layer 22 at the 20 arbitrarily selected points. The average of these measurements is considered to be the thickness.

[0050] There is no particular lower limit to the thickness of the negative electrode active material layer 22. The thickness of the negative electrode active material layer 22 may be 5 μm or more. When the thickness of the negative electrode active material layer 22 is 5 μm or more, it is easier to ensure the energy density of the battery 1.

[0051] The negative electrode active material layer 22 may contain amorphous silicon. In this disclosure, "amorphous" is not limited to materials that completely lack a crystalline structure, but also includes materials that have a crystalline region within the range of short-range order. Amorphous materials mean, for example, materials that do not show sharp peaks originating from crystals in X-ray diffraction (XRD), but show broad peaks originating from amorphous materials. In this disclosure, "contains amorphous silicon" means that at least a portion of the negative electrode active material layer 22 contains amorphous silicon. From the viewpoint of lithium ion conductivity, all of the silicon contained in the negative electrode active material layer 22 may be amorphous.

[0052] The negative electrode active material layer 22 does not necessarily have to contain crystalline silicon. The silicon contained in the negative electrode active material layer 22 may consist substantially of amorphous silicon, or may consist solely of amorphous silicon. For example, when the negative electrode active material layer 22 is a thin film, XRD measurements are performed at multiple arbitrary locations on the thin film. In this case, if no sharp peaks are observed at any of the locations, it can be determined that the silicon contained in the negative electrode active material layer 22 is entirely amorphous silicon, consists substantially of amorphous silicon, or contains only amorphous silicon.

[0053] The negative electrode current collector 21 contains copper as its main component. This configuration is advantageous for suppressing the internal resistance of the battery 1.

[0054] The ratio of the mass of copper to the mass of the negative electrode current collector 21 may be 70% by mass or more and 100% by mass or less, or 85% by mass or more and 95% by mass or less.

[0055] The negative electrode current collector 21 may be composed substantially of copper only. In this disclosure, “substantially” means excluding unavoidable impurities that are introduced unintentionally. The above configuration is advantageous in suppressing the internal resistance of the battery 1.

[0056] As the negative electrode current collector 21, for example, electrolytic copper foil whose surface has been roughened by depositing copper by an electrolytic method may be used. As the negative electrode current collector 21, copper alloy foil whose surface has been roughened by depositing copper on the surface of rolled copper alloy foil by an electrolytic method may be used.

[0057] The thickness of the negative electrode current collector 21 may be, for example, 5 μm or more and 50 μm or less, or 8 μm or more and 25 μm or less.

[0058] The electrolyte layer 30 is a layer containing an electrolyte. The electrolyte is, for example, a solid electrolyte. That is, the electrolyte layer 30 may be a solid electrolyte layer.

[0059] The electrolyte layer 30 may also contain a solid electrolyte having lithium-ion conductivity. With the above configuration, a battery 1 that balances capacity and cycle characteristics can be realized more reliably.

[0060] Examples of solid electrolytes included in the electrolyte layer 30 are sulfide solid electrolytes, oxide solid electrolytes, halide solid electrolytes, complex hydride solid electrolytes, and polymer solid electrolytes. With the above configuration, the output characteristics of the battery 1 can be improved.

[0061] The solid electrolyte included in the electrolyte layer 30 may contain a sulfide solid electrolyte. According to the above configuration, the output characteristics of the battery 1 can be further improved.

[0062] Examples of the sulfide solid electrolyte include Li2S-P2S5, Li2S-SiS2, Li2S-B2S3, Li2S-GeS2, Li 3.25 Ge 0.25 P 0.75 S4, and Li 10 GeP2S 12 . These solid electrolytes may have LiX, Li2O, MO p , or Li q MO r added thereto. X includes at least one selected from the group consisting of F, Cl, Br, and I. M is at least one selected from the group consisting of P, Si, Ge, B, Al, Ga, In, Fe, and Zn. p, q, and r are natural numbers.

[0063] Examples of the oxide solid electrolyte include NASICON-type solid electrolytes represented by LiTi2(PO4)3 and element-substituted derivatives thereof, perovskite-type solid electrolytes containing (LaLi)TiO3, LISICON-type solid electrolytes represented by Li 14 ZnGe4O 16 , Li4SiO4, LiGeO4 and element-substituted derivatives thereof, garnet-type solid electrolytes represented by Li7La3Zr2O 12 and element-substituted derivatives thereof, Li3N and H-substituted derivatives thereof, Li3PO4 and N-substituted derivatives thereof, and glasses and glass ceramics obtained by adding Li2SO4, Li2CO3 and the like to a base of Li-B-O compounds such as LiBO2 and Li3BO3.

[0064] Examples of the halide solid electrolyte have a composition formula of Li α M β X γThe material is represented by the following: α, β, and γ are values ​​greater than 0. M includes at least one element selected from the group consisting of metallic elements and metalloid elements other than Li. X is one or more elements selected from the group consisting of F, Cl, Br, and I. Here, metalloid elements are B, Si, Ge, As, Sb, and Te. Metallic elements are all elements in groups 1 through 12 of the periodic table except hydrogen, and all elements in groups 13 through 16 of the periodic table except B, Si, Ge, As, Sb, Te, C, N, P, O, S, and Se. In other words, metalloid elements or metallic elements are the group of elements that can become cations when forming inorganic compounds with halogen compounds.

[0065] Specific examples of halide solid electrolytes are Li3YX6, Li2MgX4, Li2FeX4, Li(Al,Ga,In)X4, and Li3(Al,Ga,In)X6. In this disclosure, "(Al,Ga,In)" indicates at least one element selected from the group consisting of the elements in parentheses. That is, "(Al,Ga,In)" is synonymous with "at least one selected from the group consisting of Al, Ga, and In." The same applies to other elements.

[0066] Examples of complex hydride solid electrolytes are LiBH4-LiI and LiBH4-P2S5.

[0067] Examples of polymeric solid electrolytes are compounds of polymer compounds and lithium salts. The polymer compound may have an ethylene oxide structure. Having an ethylene oxide structure allows for a higher lithium salt content, thereby increasing ionic conductivity. Examples of lithium salts include LiPF6, LiBF4, LiSbF6, LiAsF6, LiSO3CF3, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiN(SO2CF3)(SO2C4F9), and LiC(SO2CF3)3. At least one lithium salt selected from the group consisting of the above lithium salts may be used alone. Alternatively, a mixture of two or more lithium salts selected from the group consisting of the above lithium salts may be used.

[0068] The electrolyte layer 30 may contain only one solid electrolyte selected from the materials listed as solid electrolytes.

[0069] The electrolyte layer 30 may contain two or more solid electrolytes selected from the materials listed as solid electrolytes. In this case, the multiple solid electrolytes may have different compositions from each other. For example, the electrolyte layer 30 may contain a halide solid electrolyte and a sulfide solid electrolyte.

[0070] The positive electrode 10 comprises a positive electrode current collector 11 and a positive electrode active material layer 12. The positive electrode active material layer 12 is located between the positive electrode current collector 11 and the electrolyte layer 30.

[0071] The material of the positive electrode current collector 11 is not limited to a specific material, and materials commonly used in batteries can be used. Examples of materials for the positive electrode current collector 11 include copper, copper alloys, aluminum, aluminum alloys, stainless steel, nickel, titanium, carbon, lithium, indium, and conductive resins. The shape of the positive electrode current collector 11 is also not limited to a specific shape. Examples of its shape include foil, film, and sheet. The surface of the positive electrode current collector 11 may have irregularities.

[0072] The positive electrode active material layer 12 includes, for example, a positive electrode active material. The positive electrode active material includes, for example, a material having the property of intercalating and releasing metal ions such as lithium ions. Examples of positive electrode active materials include lithium-containing transition metal oxides, transition metal fluorides, polyanionic materials, fluorinated polyanionic materials, transition metal sulfides, transition metal oxysulfides, and transition metal oxynitrides. Examples of lithium-containing transition metal oxides are Li(Ni,Co,Al)O2, Li(Ni,Co,Mn)O2, and LiCoO2. In particular, when a lithium-containing transition metal oxide is used as the positive electrode active material, manufacturing costs can be reduced and the average discharge voltage can be increased. To increase the energy density of the battery, the positive electrode active material may also contain lithium nickel-cobalt manganese oxide. The positive electrode active material may also be, for example, Li(Ni,Co,Mn)O2.

[0073] The main surface area of ​​battery 1 is, for example, 1 cm². 2 More than 100cm 2 The following applies. In this case, battery 1 can be used in portable electronic devices such as smartphones and digital cameras. Alternatively, the main surface area of ​​battery 1 is 100 cm². 2 More than 1000cm 2 The following is also possible. In this case, battery 1 can be used as a power source for large mobile devices such as electric vehicles. "Main surface" means the surface of battery 1 that has the largest surface area.

[0074] <Battery manufacturing method> The battery 1 according to this embodiment can be manufactured, for example, by the following method.

[0075] As the negative electrode current collector 21, for example, electrolytic copper foil whose surface has been roughened by depositing copper using an electrolytic method is used.

[0076] Electrolytic copper foil can be obtained as follows: First, a metal drum is immersed in an electrolyte solution in which copper ions are dissolved. By passing an electric current through the drum while it is rotated, copper is deposited on the surface of the drum. Electrolytic copper foil can be obtained by peeling off the copper deposited on the surface of the drum. One or both sides of the electrolytic copper foil may be subjected to a roughening treatment or other surface treatment.

[0077] Next, silicon is deposited on the negative electrode current collector 21 to form a silicon thin film. This forms multiple columnar bodies 25, mainly composed of silicon, on the negative electrode current collector 21.

[0078] Methods for forming multiple columnar bodies 25, mainly composed of silicon, include, for example, chemical vapor deposition (CVD), sputtering, vapor deposition, thermal spraying, and plating. Among these, vapor-phase methods such as CVD, sputtering, and vapor deposition can be used from the viewpoint of adhesion with the negative electrode current collector 21 and suppression of surface oxidation. Copper is an element that diffuses easily into silicon. Therefore, when copper is used as the negative electrode current collector 21 in particular, the adhesion between copper and silicon is improved, and the expansion of the silicon-copper interface during charging is suppressed.

[0079] Finally, the formed silicon thin film is annealed at a temperature of 300°C or less. This creates the negative electrode 20.

[0080] Silicon forms intermetallic compounds with copper at high temperatures. Annealing a silicon thin film at low temperatures below 300°C can suppress the formation of intermetallic compounds between silicon and dissimilar metal elements. This allows the full capacity of silicon to be utilized.

[0081] Furthermore, by annealing the silicon thin film at a low temperature of 300°C or less, the diffusion of copper into the negative electrode active material layer 22 can be suppressed. As a result, the amount of copper contained in the negative electrode active material layer 22 can be kept to 1 mass% or less, thereby suppressing a decrease in the capacity of the battery 1.

[0082] The annealing temperature of the silicon thin film may be 250°C or lower, or 200°C or lower. There is no particular lower limit to the annealing temperature of the silicon thin film. For example, the annealing temperature of the silicon thin film may be 100°C or higher.

[0083] The annealing time for a silicon thin film is, for example, between 5 hours and 30 hours. Alternatively, the annealing time for a silicon thin film may be between 10 hours and 20 hours.

[0084] Examples of the shape of the battery 1 in Embodiment 1 include coin-shaped, cylindrical, rectangular, sheet-shaped, button-shaped, flat, and stacked types. [Examples]

[0085] The details of this disclosure will be explained below using examples and comparative examples. The following examples are illustrative and the disclosure is not limited to these examples.

[0086] Example 1 [Fabrication of the negative electrode] As the negative electrode current collector, electrolytic copper foil with a surface roughened by electrolytic copper deposition was used. The thickness of the electrolytic copper foil before roughening was 18 μm. The thickness of the electrolytic copper foil after roughening was 28 μm. The arithmetic mean roughness Ra of the surface of the electrolytic copper foil was measured using a laser microscope. Ra was 0.6 μm. A silicon thin film was formed by depositing silicon on the electrolytic copper foil using a sputtering apparatus. Argon gas was used for sputtering. The pressure of the argon gas was 0.1 Pa. Finally, the silicon thin film was annealed at 200°C for 20 hours. This obtained the negative electrode of Example 1. The thickness of the negative electrode active material layer made of silicon was 10 μm. In this embodiment, a rolled foil with a roughened surface was used as the negative electrode current collector in order to increase the contact area between the negative electrode active material layer and the negative electrode current collector, thereby maintaining good adhesion between the negative electrode active material layer and the negative electrode current collector during the charge-discharge cycle.

[0087] [Preparation of solid electrolytes] In an argon glove box with a dew point of -60°C or lower, the raw material powders, Li2S and P2S5, were weighed in a molar ratio of Li2S:P2S5 = 75:25. The raw material powders were ground and mixed in a mortar to obtain a mixture. The mixture was then milled using a planetary ball mill (Fritsch, P-7 type) at 510 rpm for 10 hours. This yielded a glassy solid electrolyte. The obtained solid electrolyte was heat-treated in an inert atmosphere at 270°C for 2 hours. This yielded a glass-ceramic Li2S-P2S5 sulfide solid electrolyte.

[0088] [Battery construction] The following steps were performed using the obtained negative electrode and solid electrolyte. 80 mg of solid electrolyte was weighed, and the cross-sectional area of ​​the inner diameter was 0.7 cm². 2 The material was placed inside an electrically insulating cylinder and pressure-molded at 50 MPa. This created an electrolyte layer. Next, a negative electrode, punched out to the same size as the inner diameter of the cylinder, was placed on one side of the electrolyte layer with the negative electrode active material layer in contact with the electrolyte layer, and pressure-molded at 600 MPa. This created a laminate consisting of the negative electrode and the electrolyte layer. Subsequently, a 200 μm thick layer of metallic indium, a 300 μm thick layer of metallic lithium, and a 200 μm thick layer of metallic indium were placed on top of the electrolyte layer of the laminate in this order. This created a three-layer laminate consisting of a negative electrode, an electrolyte layer, and an indium-lithium-indium layer. Next, both ends of the three-layer laminate were clamped with stainless steel pins, and a pressure of 150 MPa was applied to the three-layer laminate with bolts. This resulted in a battery having a negative electrode as the working electrode and an indium-lithium-indium layer as the counter electrode. Finally, the battery of Example 1 was fabricated by using an electrically insulating ferrule to isolate and seal the inside of the electrically insulating outer cylinder from the outside atmosphere.

[0089] ≪Comparative Example 1≫ [Fabrication of the negative electrode] In Comparative Example 1, annealing was not performed on the silicon thin film formed by sputtering. Otherwise, the negative electrode for Comparative Example 1 was fabricated using the same method as in Example 1.

[0090] Using the obtained negative electrode, a battery of Comparative Example 1 was fabricated in the same manner as in Example 1.

[0091] (Mass ratio of copper contained in the negative electrode active material layer) The mass ratio of copper contained in the negative electrode active material layer of Example 1 was determined using secondary ion mass spectrometry (SIMS). Specifically, the concentration distribution in the thickness direction for copper and silicon elements in the negative electrode was obtained using a secondary ion mass spectrometer (ULVAC-PHI, TRIFT2). Using the method described above, the concentration of copper element C1 and the concentration of silicon element C2 were calculated from each concentration distribution. From the value of C1 / (C1+C2), it was confirmed that the amount of copper contained in the negative electrode active material layer of Example 1 was 1% by mass or less.

[0092] (Young's modulus of the negative electrode active material layer) The Young's modulus of the negative electrode active material layers in Example 1 and Comparative Example 1 was measured using the nanoindentation method. Specifically, the Young's modulus of 12 arbitrarily selected points on the surface of the negative electrode active material layer was measured using a nanoindentation device (iNano, KLA). The indentation depth of the indenter was 10 μm. From the obtained measurements, the Young's modulus (GPa) was determined by calculating the average value of 10 points, excluding the minimum and maximum values, taking into account measurement errors due to surface irregularities of the negative electrode active material layer. The results are shown in Table 1.

[0093] (Charge / Discharge Test) Next, charge-discharge tests were conducted using the batteries of Example 1 and Comparative Example 1 under the following conditions.

[0094] At room temperature, the battery was charged with a constant current of 0.2 mA, corresponding to a 0.05C rate (20-hour rate) relative to its theoretical capacity. Charging was terminated when the potential of the working electrode, relative to the counter electrode, reached -0.62 V. Next, the battery was discharged at a current of 0.2 mA, and discharge was terminated when the potential of the working electrode, relative to the counter electrode, reached 1.40 V. This allowed us to obtain the initial discharge capacity (mAh / g) of the battery at a 0.05C rate. The results are shown in Table 1.

[0095] (Measurement of battery resistance) The electrical resistance was measured using the batteries from Example 1 and Comparative Example 1 under the following conditions.

[0096] The battery was charged with a constant current at a current value equivalent to a 0.05C rate. Charging was terminated when the potential of the working electrode, relative to the counter electrode, reached -0.62V. Subsequently, the interfacial resistance was measured at 25°C using the AC impedance method at frequencies from 10mHz to 1MHz. This determined the interfacial resistance (Ωcm) of the fully charged battery. 2 ) was obtained. The results are shown in Table 1.

[0097] (Evaluation of input characteristics) The input characteristics were evaluated using the batteries from Example 1 and Comparative Example 1 under the following conditions.

[0098] The battery was charged with a constant current at 60°C at a current value equivalent to the 6C rate, with a capacity of 3000mAh / g, which is approximately 70% of the theoretical capacity (4200mAh / g) of the negative electrode active material (silicon). Charging was terminated when the potential of the working electrode, relative to the counter electrode, reached -0.62V, and the charge capacity at the 6C rate was measured. The ratio of the charge capacity at the 6C rate to the charge capacity at the 0.05C rate was calculated. This obtained the input characteristics (%) of the battery at the 6C rate relative to the 0.05C rate. The results are shown in Table 1.

[0099] (Electrification endurance test) An electrical endurance test was conducted using the batteries of Example 1 and Comparative Example 1 under the following conditions.

[0100] Constant current charging was performed at a current value equivalent to a 0.3C rate until the potential of the working electrode, relative to the counter electrode, reached -0.62V. Subsequently, constant voltage charging was performed at a constant voltage of -0.62V until the current value decayed to a 0.05C rate. After that, the battery was discharged to 1.4V at a current value equivalent to a 0.3C rate. These operations constituted one cycle, and the cycle was repeated. The discharge capacity after the first cycle and the discharge capacity after 300 cycles were measured. The ratio of the discharge capacity after 300 cycles to the discharge capacity after the first cycle was calculated. This gave the battery's discharge capacity retention rate (%) after 300 cycles. The results are shown in Table 1.

[0101] [Table 1]

[0102] ≪Consideration≫ As shown in Table 1, immediately after the formation of the silicon thin film, the Young's modulus of the negative electrode active material layer in Comparative Example 1 was 30 GPa. In contrast, in Example 1, where the silicon thin film was formed and then annealed at 200°C for 20 hours, the Young's modulus of the negative electrode active material layer decreased to 20 GPa. This is thought to be because, after the formation of the silicon thin film, annealing at a temperature of 300°C or lower caused copper diffusion in the ppm range in the negative electrode active material layer, resulting in the formation of a silicon-copper solid solution.

[0103] Furthermore, as shown in Table 1, the battery of Example 1, which has a negative electrode containing the negative electrode active material layer described above, showed an increase in initial discharge capacity, a reduction in interfacial resistance, an improvement in input characteristics, and an improvement in the retention rate of discharge capacity.

[0104] (Cross-sectional observation of the negative electrode) Figure 3 is a cross-sectional SEM image of the negative electrode in the charged state in Example 1. The cross-sectional SEM image in Figure 3 was obtained from the negative electrode removed after disassembling the battery in the charged state following an electrical endurance test. In this disclosure, "charged state" means a state in which the depth of charge is 50% or more. The negative electrode of Example 1 comprised a negative electrode current collector mainly composed of copper and a negative electrode active material layer having multiple columnar bodies mainly composed of silicon. The Young's modulus of the negative electrode active material layer was 20 GPa. The mass ratio of copper contained in the negative electrode active material layer was 1 mass% or less. As shown in Figure 3, in the negative electrode of Example 1, it was observed that in the charged state, the negative electrode active material layer maintained a dense columnar structure while continuing to maintain a smooth interface with the electrolyte layer.

[0105] Figure 4 shows an SEM image of the negative electrode in the charged state in Comparative Example 1. The cross-sectional SEM image in Figure 4 was obtained from the negative electrode removed after disassembling the battery in the charged state following the current endurance test. As shown in Figure 4, the negative electrode of Comparative Example 1 had many voids in the negative electrode active material layer. The density of the negative electrode active material layer of Comparative Example 1 was lower than that of Example 1. The surface smoothness of the negative electrode active material layer of Comparative Example 1 was impaired compared to that of Example 1. The reason why the initial discharge capacity, interfacial resistance, input characteristics, and discharge capacity retention rate of the battery in Comparative Example 1 were all inferior to that of the battery in Example 1 is thought to be due to a decrease in the contact area between the negative electrode active material layer and the electrolyte layer.

[0106] From the above results, in the battery of Example 1, which used a negative electrode containing a negative electrode active material layer with a Young's modulus reduced to 25 GPa or less, the columnar bodies easily deformed into a dense columnar structure during the expansion process of the negative electrode during the initial charge. Specifically, the gaps between adjacent columnar bodies decreased, and the surface of the columnar bodies was smoothed to conform to the surface of the electrolyte layer facing the negative electrode. As a result, an interface with a large contact area was formed between the negative electrode active material layer and the electrolyte layer. This allowed the negative electrode active material layer to maintain its dense columnar structure and a smooth interface with the electrolyte layer even during subsequent expansion and contraction associated with charging and discharging. Furthermore, in the battery of Example 1, the amount of copper contained in the negative electrode active material layer was small (less than 1 mass%), so the capacity of the silicon active material was fully utilized. As a result, a battery that balances capacity and cycle characteristics was realized. [Industrial applicability]

[0107] The battery described herein can be used, for example, as a lithium-ion secondary battery for use in automobiles. [Explanation of Symbols]

[0108] 1 battery 10 positive electrode 20 negative electrode 30 Electrolyte layer 11 Positive electrode current collector 12 Cathode active material layer 21 Negative electrode current collector 22 Negative electrode active material layer 23 Convex part 24 recesses 25 Column

Claims

1. Positive electrode and, The negative electrode and, An electrolyte layer containing a sulfide solid electrolyte located between the positive electrode and the negative electrode, Equipped with, The negative electrode comprises a negative electrode current collector mainly composed of copper, and a negative electrode active material layer made of copper and silicon, located between the negative electrode current collector and the electrolyte layer. The negative electrode active material layer comprises a plurality of columnar bodies containing silicon, and 1% by mass or less of copper present in the silicon in a solid solution state. The Young's modulus of the negative electrode active material layer is 25 GPa or less. battery.

2. The Young's modulus of the negative electrode active material layer is 20 GPa or less. The battery according to claim 1.

3. The thickness of the negative electrode active material layer is 30 μm or less. The battery according to claim 1 or 2.

4. A method for manufacturing a battery according to claim 1, Depositing silicon onto the negative electrode current collector by a vapor phase method, The deposited silicon is annealed at a temperature of 300°C or less. including, Battery manufacturing method.

5. The annealing time is between 5 hours and 30 hours. A method for manufacturing a battery according to claim 4.

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