Negative active material layer

Abstract

To provide a negative electrode active material layer with low resistance.SOLUTION: A negative electrode active material layer used in a solid state battery includes lithium titanate, a sulfide solid electrolyte, and fibrous carbon, and the ratio of the average particle size of the lithium titanate to the average particle size of the sulfide solid electrolyte is 0.75 or more.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present disclosure relates to a negative electrode active material layer. [Background technology]

[0002] A solid-state battery is a battery that has a solid electrolyte layer between a positive electrode active material layer and a negative electrode active material layer, and has the advantage that safety devices can be more easily simplified compared to liquid-type batteries that have an electrolyte solution containing a flammable organic solvent.

[0003] It is also known that lithium titanate is used in solid-state batteries. For example, Patent Document 1 describes Li4Ti5O 12 and a sulfide solid electrolyte. Patent Document 2 discloses a positive electrode for an all-solid-state battery containing a positive electrode active material, a conductive material, lithium titanate, and a sulfide solid electrolyte. Patent Document 3 discloses a negative electrode for a sulfide solid battery containing a sulfide solid electrolyte, a silicon-based active material, and lithium titanate pre-doped with Li. Furthermore, Patent Document 4 discloses Li4Ti5O4 having a volume change rate of 1% or less during charge and discharge and an average powder particle size of 8 μm or less. 12 A sulfide all-solid-state battery using the above as a negative electrode active material has been disclosed. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2021-128885 [Patent Document 2] Patent Publication No. 2021-072259 [Patent Document 3] Japanese Patent Application Publication No. 2019-106352 [Patent Document 4] Patent No. 5376412 Summary of the Invention [Problem to be solved by the invention]

[0005] From the viewpoint of improving battery performance, a solid-state battery with good input / output characteristics is desired. To improve the input / output characteristics of a solid-state battery, for example, it is effective to reduce the resistance of the negative electrode active material layer. The present disclosure has been made in view of the above-described circumstances, and has as its main object to provide a negative electrode active material layer with low resistance. [Means for solving the problem]

[0006] The present disclosure provides an anode active material layer for use in a solid-state battery, the anode active material layer containing lithium titanate, a sulfide solid electrolyte, and fibrous carbon, wherein the ratio of the average particle size of the lithium titanate to the average particle size of the sulfide solid electrolyte is 0.75 or more.

[0007] According to the present disclosure, the negative electrode active material layer contains lithium titanate, a sulfide solid electrolyte, and fibrous carbon, and the ratio of the average particle size of the lithium titanate to the average particle size of the sulfide solid electrolyte is equal to or greater than a predetermined value, resulting in a negative electrode active material layer with low resistance. [Effects of the Invention]

[0008] The present disclosure has an effect of providing a negative electrode active material layer with low resistance. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 2 is a diagram illustrating the ratio of average particle diameters in the present disclosure. [Figure 2] FIG. 1 is a schematic cross-sectional view illustrating a solid-state battery according to the present disclosure. [Figure 3] 1 is a graph showing the relationship between the ratio of average particle diameters and the DC resistance ratio in Examples and Comparative Examples. DETAILED DESCRIPTION OF THE INVENTION

[0010] The negative electrode active material layer in the present disclosure will be described in detail below.

[0011] 1.Negative electrode active material layer The negative electrode active material layer in the present disclosure is used in a solid-state battery and contains lithium titanate, a sulfide solid electrolyte, and fibrous carbon, and the ratio of the average particle size of the lithium titanate to the average particle size of the sulfide solid electrolyte is 0.75 or more. Note that a solid-state battery refers to a battery containing a solid electrolyte, and an all-solid-state battery refers to a solid-state battery that does not contain a liquid-based material.

[0012] According to the present disclosure, the negative electrode active material layer contains lithium titanate, a sulfide solid electrolyte, and fibrous carbon, and the ratio of the average particle size of the lithium titanate to the average particle size of the sulfide solid electrolyte is equal to or greater than a predetermined value, resulting in a negative electrode active material layer with low resistance.

[0013] Lithium titanate (LTO) exhibits good electronic conductivity through the insertion of Li upon charging. Furthermore, lithium titanate does not expand or contract during charging and discharging. Furthermore, because it is an oxide, lithium titanate has high chemical stability. These factors make it particularly useful as an anode active material in lithium-ion batteries. However, LTO has low ionic conductivity within the particles, so increasing the particle size can lead to a decrease in battery output. Furthermore, reducing the particle size of LTO makes it more susceptible to aggregation. Therefore, when a sulfide solid electrolyte is used in combination with small-particle LTO, the interface between the LTO and the sulfide solid electrolyte becomes insufficient, resulting in increased contact resistance and a decrease in ionic conductivity.

[0014] In contrast, the negative electrode active material layer of the present disclosure contains fibrous carbon in addition to LTO and a sulfide solid electrolyte, thereby reducing the resistance of the negative electrode active material layer. When particulate carbon is used, the electron conduction path between LTO and LTO is a point contact. On the other hand, when fibrous carbon is used, LTO and LTO are bridged to form a point and line electron conduction path. Therefore, the use of fibrous carbon is thought to form a better electron conduction path, thereby reducing resistance. In addition, the specific surface area of ​​particulate carbon is generally larger than that of fibrous carbon (e.g., more than twice as large). Therefore, for example, when forming a negative electrode active material layer using a slurry containing a negative electrode active material, a sulfide solid electrolyte, a conductive material, and a binder, if particulate carbon is used as the conductive material, the particulate carbon is likely to adsorb the binder to its surface, which is thought to increase the resistance component due to the binder and reduce electronic conductivity. From this perspective, it is thought that using fibrous carbon is better able to reduce resistance.

[0015] Furthermore, in the negative electrode active material layer of the present disclosure, the ratio of the average particle size of the LTO to the average particle size of the sulfide solid electrolyte is equal to or greater than a predetermined value, thereby further reducing the resistance of the negative electrode active material layer. This is because, when this ratio is equal to or greater than a predetermined value, favorable interfaces can be formed between the LTO and SE (sulfide solid electrolyte) and between the LTO and LTO particles, improving both ionic conduction (between the SE and LTO) and electronic conduction (between the LTO and LTO), respectively, thereby reducing the overall resistance of the negative electrode active material layer. For example, FIG. 1(a) is a phase diagram illustrating a case in which LTO particles with the largest cross-sectional area are arranged so as to contact the periphery of the maximum cross-sectional surface of the SE particles, and the LTO particles are able to contact each other. The state shown in FIG. 1(a) is achieved when the ratio (r2 / r1) of the LTO particle size (r2) to the SE particle size (r1) is 0.62, i.e., when the average particle size ratio is 0.62, as shown in FIG. 1(b). If the ratio is less than 0.62, LTO particles do not contact each other, and electronic conduction between LTO particles tends to increase, resulting in increased resistance. On the other hand, if the average particle size ratio is 0.62 or greater, LTO particles overlap on a flat surface, enabling the formation of a good interface. However, considering the three-dimensional spread and actual particle shape, it is believed that an average particle size ratio of 0.62 or greater is the minimum required for simultaneous formation of SE-LTO and LTO-LTO interfaces. Based on this value, the inventors conducted extensive research and found that a significant resistance reduction effect is achieved when the average particle size ratio is 0.75 or greater.

[0016] As described above, the negative electrode active material layer according to the present disclosure has low resistance, and therefore a solid state battery using this has good input / output characteristics.

[0017] In the negative electrode active material layer, the ratio of the average particle size of the lithium titanate to the average particle size of the sulfide solid electrolyte is usually 0.75 or more, and may be 0.80 or more, 1.00 or more, or 1.20 or more. On the other hand, the ratio of the average particle size of the lithium titanate to the average particle size of the sulfide solid electrolyte is, for example, 2.00 or less, 1.80 or less, or 1.60 or less. Here, the average particle size of the sulfide solid electrolyte and the average particle size of the lithium titanate are respectively represented by D 50 and can be calculated, for example, from measurements using a laser diffraction particle size distribution analyzer or a scanning electron microscope (SEM). The ranges of the average particle size of the sulfide solid electrolyte and the average particle size of lithium titanate will be described later.

[0018] (1) Lithium titanate Lithium titanate functions as a negative electrode active material in the negative electrode active material layer. Lithium titanate is a compound containing at least Li, Ti, and O elements. At least one of the Li and Ti elements may be partially substituted with another element. Examples of lithium titanate include Li2TiO3, Li4Ti5O 12 and Li2Ti2O5. Among these, Li4Ti5O 12 The negative electrode active material layer may contain only one type of lithium titanate, or may contain two or more types of lithium titanate.

[0019] The average particle size of lithium titanate (D 50 ) is, for example, 0.5 μm or more, may be 0.7 μm or more, or may be 1 μm or more. On the other hand, the average particle diameter (D 50) is, for example, 10 μm or less, or may be 5 μm or less, or may be 2 μm or less. As described above, when the average particle size of LTO is increased, the intra-particle ionic conductivity decreases, and when the average particle size of LTO is decreased, the contact resistance at the interface with the sulfide solid electrolyte increases. On the other hand, by setting the average particle size ratio to 0.75 or more, the increase in resistance of the negative electrode active material layer due to the average particle size of LTO can be suppressed. Therefore, in the negative electrode active material layer of the present disclosure, the range of material selection for LTO can be widened.

[0020] The proportion of lithium titanate in the negative electrode active material layer is, for example, 40% by weight or more, or alternatively, 50% by weight or more, or even 60% by weight or more, while the proportion of lithium titanate in the negative electrode active material layer is, for example, 80% by weight or less.

[0021] (2) Sulfide solid electrolyte The sulfide solid electrolyte functions as a solid electrolyte in the negative electrode active material layer. Examples of the sulfide solid electrolyte include solid electrolytes containing Li, X (X is at least one of P, As, Sb, Si, Ge, Sn, B, Al, Ga, and In), and S. The sulfide solid electrolyte may further contain at least one of O and a halogen element. Examples of the halogen element include F, Cl, Br, and I.

[0022] The sulfide solid electrolyte preferably comprises an ionic conductor containing Li, A (A is at least one of P, As, Sb, Si, Ge, Al, and B), and S. Furthermore, the ionic conductor preferably has a high Li content. The ionic conductor preferably has an anionic structure with an ortho-composition (PS4 3- Structure, SiS4 4- Structure, GeS4 4- Structure, AlS3 3- Structure, BS3 3-It is preferable that the anion has an ortho-composition structure as the main anion component, because this has high chemical stability. The proportion of the anion structure with an ortho-composition is preferably 70 mol % or more, and more preferably 90 mol % or more, of the total anion structures in the ionic conductor. The proportion of the anion structure with an ortho-composition can be determined, for example, by Raman spectroscopy, NMR, or XPS.

[0023] The sulfide solid electrolyte may contain, in addition to the ion conductor, a lithium halide, such as LiF, LiCl, LiBr, and LiI, with LiCl, LiBr, and LiI being preferred.

[0024] Specific examples of sulfide solid electrolytes include xLi2S·(100-x)P2S5 (70≦x≦80) and yLiI·zLiBr·(100-yz)Li3PS4 (0≦y≦30, 0≦z≦30).

[0025] The sulfide solid electrolyte may be a glass-based sulfide solid electrolyte or a glass-ceramic-based sulfide solid electrolyte. The glass-based sulfide solid electrolyte can be obtained by vitrifying raw materials. The glass-ceramic-based sulfide solid electrolyte can be obtained, for example, by heat-treating the above-mentioned glass-based sulfide solid electrolyte.

[0026] Average particle size of sulfide solid electrolyte (D 50 ) is, for example, 0.5 μm or more, may be 0.7 μm or more, or may be 1 μm or more. On the other hand, the average particle diameter (D 50 ) is, for example, 10 μm or less, may be 5 μm or less, may be 3 μm or less, or may be 2.5 μm or less.

[0027] The proportion of the sulfide solid electrolyte in the negative electrode active material layer is, for example, 10% by weight or more, or alternatively, 20% by weight or more, or even 30% by weight or more, while the proportion of lithium titanate in the negative electrode active material layer is, for example, 50% by weight or less.

[0028] The total ratio of the sulfide solid electrolyte and lithium titanate in the negative electrode active material layer is, for example, 80% by weight or more, or may be 90% by weight or more, or may be 95% by weight or more. In the negative electrode active material layer, the weight ratio of lithium titanate to the sulfide solid electrolyte is, for example, 1.5% by weight or more, or may be 2.0% by weight or more, or may be 2.5% by weight or more. Meanwhile, the weight ratio of lithium titanate to the sulfide solid electrolyte is, for example, 10% by weight or less, or may be 5.0% by weight or less.

[0029] (3) Fibrous carbon The fibrous carbon functions as a conductive material in the negative electrode active material layer. The aspect ratio (fiber length / fiber diameter) of the fibrous carbon is, for example, 2 or more, and may be 5 or more. The aspect ratio (fiber length / fiber diameter) of the fibrous carbon is, for example, 500 or less. Examples of the fibrous carbon include vapor grown carbon fiber (VGCF), carbon nanotube (CNT), and carbon nanofiber (CNF).

[0030] The proportion of fibrous carbon in the negative electrode active material layer is, for example, 0.3 wt % or more, and may be 0.5 wt % or more, while the proportion of fibrous carbon in the negative electrode active material layer is, for example, 3 wt % or less, and may be 2 wt % or less.

[0031] (4) Negative electrode active material layer The negative electrode active material layer may contain a binder as needed. Examples of the binder include fluoride-based binders such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinylidene fluoride-polyhexafluoropropylene copolymer (PVDF-HFP), and fluorine-containing rubber; and rubber-based binders such as butadiene rubber, hydrogenated butadiene rubber, styrene-butadiene rubber (SBR), hydrogenated styrene-butadiene rubber, nitrile butadiene rubber, hydrogenated nitrile butadiene rubber, and ethylene-propylene rubber.

[0032] The proportion of the binder in the negative electrode active material layer is, for example, 0.3 wt % or more, and may be 0.5 wt % or more. On the other hand, the proportion of the binder in the negative electrode active material layer is, for example, 5 wt % or less, and may be 3 wt % or less. The thickness of the negative electrode active material layer is, for example, 0.1 μm or more and 1000 μm or less. The negative electrode active material layer in the present disclosure is used in the all-solid-state battery described below and other solid-state batteries.

[0033] 2. Solid state battery A solid-state battery including the negative electrode active material layer of the present disclosure will be described in detail below, taking an "all-solid-state battery" as an example. FIG. 2 is a schematic cross-sectional view illustrating an example of an all-solid-state battery of the present disclosure. The all-solid-state battery 10 shown in FIG. 2 has a positive electrode active material layer 1, a negative electrode active material layer 2, a solid electrolyte layer 3 disposed between the positive electrode active material layer 1 and the negative electrode active material layer 2, a positive electrode current collector 4 that collects current from the positive electrode active material layer 1, and a negative electrode current collector 5 that collects current from the negative electrode active material layer 2. The negative electrode active material layer 2 is the layer described above in "1. Negative electrode active material layer."

[0034] According to the present disclosure, the presence of the above-described negative electrode active material layer provides a solid-state battery with good input / output characteristics.

[0035] (1) Negative electrode active material layer The negative electrode active material layer in the present disclosure is the same as that described above in "1. Negative electrode active material layer," and therefore will not be described here.

[0036] (2) Positive electrode active material layer The positive electrode active material layer in the present disclosure is a layer containing at least a positive electrode active material, and may also contain at least one of a conductive material, a solid electrolyte, and a binder, as necessary.

[0037] Examples of the positive electrode active material include oxide active materials, such as LiCoO2, LiMnO2, LiNiO2, LiVO2, and LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, etc., rock salt layered active materials, LiMn2O4, Li4Ti5O12 , Li(Ni 0.5 Mn 1.5 )O4, and olivine type active materials such as LiFePO4, LiMnPO4, LiNiPO4, and LiCoPO4.

[0038] A protective layer containing a Li-ion conductive oxide may be formed on the surface of the oxide active material. This is because it can suppress the reaction between the oxide active material and the solid electrolyte. An example of the Li-ion conductive oxide is LiNbO3. The thickness of the protective layer is, for example, 1 nm or more and 30 nm or less.

[0039] The positive electrode active material may be in the form of particles, for example. 50 ) is not particularly limited, but may be, for example, 10 nm or more, or may be 100 nm or more. On the other hand, the average particle diameter (D 50 ) is, for example, 50 μm or less, and may be 20 μm or less.

[0040] The conductive material, solid electrolyte, and binder are the same as those described above in "1. Negative electrode active material layer," and therefore will not be described here. The thickness of the positive electrode active material layer is, for example, 0.1 μm or more and 1000 μm or less.

[0041] (3) Solid electrolyte layer The solid electrolyte layer in the present disclosure is a layer disposed between the positive electrode active material layer and the negative electrode active material layer and containing at least a solid electrolyte. The solid electrolyte layer preferably contains a sulfide solid electrolyte as the solid electrolyte. The solid electrolyte layer may also contain a binder. The solid electrolyte and binder are the same as those described above in "1. Negative electrode active material layer," and therefore will not be described here. The thickness of the solid electrolyte layer is, for example, 0.1 μm or more and 1000 μm or less.

[0042] (4) Other configurations The solid-state battery of the present disclosure typically includes a positive electrode current collector that collects current from the positive electrode active material layer and a negative electrode current collector that collects current from the negative electrode active material layer. The positive electrode current collector and the negative electrode current collector may be, for example, foil-shaped. Examples of materials for the positive electrode current collector include SUS, aluminum, nickel, and carbon. Examples of materials for the negative electrode current collector include SUS, copper, nickel, and carbon.

[0043] The solid-state battery according to the present disclosure may also include an exterior housing that houses the positive electrode current collector, the positive electrode material layer, the solid electrolyte layer, the negative electrode active material layer, and the negative electrode current collector. The type of the exterior housing is not particularly limited, but examples thereof include a laminate exterior housing.

[0044] The solid-state battery according to the present disclosure may also include a constraining jig that applies a constraining pressure to the positive electrode active material layer, the solid electrolyte layer, and the negative electrode active material layer in the thickness direction. The constraining pressure is, for example, 0.1 MPa or more and 100 MPa or less.

[0045] (5) Solid state battery The solid-state battery in the present disclosure is typically a lithium-ion secondary battery. The lithium-ion secondary battery may be a solid-state battery that does not contain a liquid material (an all-solid-state lithium-ion secondary battery). The use of the solid-state battery is not particularly limited, and examples thereof include power sources for vehicles such as hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), electric vehicles (BEVs), gasoline-powered vehicles, and diesel-powered vehicles. The solid-state battery in the present disclosure may also be used as a power source for mobile objects other than vehicles (e.g., railways, ships, and aircraft), and may also be used as a power source for electrical appliances such as information processing devices.

[0046] The present disclosure is not limited to the above-described embodiments. The above-described embodiments are merely examples, and any configuration that is substantially identical to the technical idea described in the claims of the present disclosure and that provides similar effects is included within the technical scope of the present disclosure. [Example]

[0047] [Comparative Example 1] (Preparation of negative electrode) Negative electrode active material (Li4Ti5O 12 3.0 g of particles (density: 3.5 g / cc), 0.033 g of conductive material (acetylene black, AB), 0.039 g of binder (butadiene rubber binder, density: 0.9 g / cc), and 3.71 g of dispersion medium (tetralin) were weighed and mixed for 30 minutes using an ultrasonic homogenizer (UH-50, manufactured by SMT). After mixing, 1.0 g of sulfide solid electrolyte (LiI-LiBr-Li2S-P2S5-based glass ceramic, composition: 10LiI 15LiBr 75 (0.75Li2S 0.25P2S5), density: 2 g / cc) was added and mixed again for 30 minutes using an ultrasonic homogenizer (UH-50, manufactured by SMT). This produced a negative electrode mixture paste. The average particle size (D 50 ) were 0.7 μm and 0.9 μm, respectively.

[0048] The negative electrode mixture paste was applied to a negative electrode current collector (Ni foil, 22 μm thick) by the blade method using an applicator and dried on a hot plate at 100 °C for 30 minutes. This resulted in a negative electrode having a negative electrode current collector and a negative electrode active material layer. The negative electrode weight was adjusted so that the negative electrode charge specific capacity was 1.1 times that of the positive electrode charge specific capacity of 185 mAh / g.

[0049] (Fabrication of all-solid-state batteries) Cathode active material (LiNi 0.8 Co 0.15 Al 0.05A LiNbO protective layer was formed on the surface of a LiNbO2 (LiNbO2, density: 4.65 g / cc, average particle size: 5 μm) using a rolling fluidized bed granulation coating device. This resulted in a composite positive electrode active material. 4.0 g of the composite positive electrode active material, 0.094 g of conductive material (VGCF), 1.024 g of the sulfide solid electrolyte, 0.017 g of binder (butadiene rubber binder), and 2.77 g of dispersion medium (tetralin) were weighed and mixed using an ultrasonic homogenizer (UH-50, manufactured by SMT Corporation). This resulted in a positive electrode mixture paste. The positive electrode mixture paste was applied to a positive electrode current collector (Al foil, 15 μm thick) using an applicator by the blade method and dried on a hot plate at 100 °C for 30 minutes. This resulted in a positive electrode having a positive electrode current collector and a positive electrode active material layer.

[0050] Heptane, a heptane solution containing 5% by mass of a butadiene rubber binder, and a sulfide solid electrolyte (LiI-LiBr-Li2S-P2S5-based glass ceramic, average particle size 2.5 μm) were added to a polypropylene container and mixed for 30 seconds using an ultrasonic homogenizer (UH-50 manufactured by SMT Co., Ltd.). Next, the container was shaken for 3 minutes to obtain a paste for the solid electrolyte layer.

[0051] The positive electrode was pre-pressed. After pressing, a paste for a solid electrolyte layer was applied to the surface of the positive electrode active material layer using a die coater, and the positive electrode was dried on a hot plate at 100°C for 30 minutes. 2 This resulted in a positive electrode side laminate having a solid electrolyte layer on the surface of the positive electrode active material layer.

[0052] The negative electrode was pre-pressed. After pressing, a paste for a solid electrolyte layer was applied to the surface of the negative electrode active material layer using a die coater, and the negative electrode was dried on a hot plate at 100°C for 30 minutes. 2 This resulted in a negative electrode laminate having a solid electrolyte layer on the surface of the negative electrode active material layer.

[0053] The positive electrode side laminate and the negative electrode side laminate were each punched and then laminated together so that their solid electrolyte layers were bonded together. Here, the laminate was laminated in a state in which an unpressed solid electrolyte layer (solid electrolyte layer paste) was transferred between the solid electrolyte layer of the positive electrode side laminate and the solid electrolyte layer of the negative electrode side laminate. Thereafter, the laminate was subjected to a pressure of 2 ton / cm at 160°C. 2 The resulting power generating element was laminated and constrained at 5 MPa to obtain an all-solid-state lithium ion secondary battery for evaluation.

[0054] [Comparative Examples 2 to 5] Negative electrode active material (Li4Ti5O 12 All-solid-state lithium ion secondary batteries were fabricated in the same manner as in Comparative Example 1, except that the average particle diameter of the sulfide solid electrolyte (LiI-LiBr-LiS-P2S5-based glass ceramic) was changed as shown in Table 1.

[0055] [Examples 1 to 7] An all-solid-state lithium ion secondary battery was fabricated in the same manner as in Comparative Example 1, except that the conductive material in the negative electrode active material layer was changed from particulate carbon (acetylene black) to fibrous carbon (vapor grown carbon fiber: VGCF), and the average particle size of the negative electrode active material and the average particle size of the sulfide solid electrolyte were changed as shown in Table 1.

[0056] [Comparative Examples 6 to 9] All-solid-state lithium-ion secondary batteries were fabricated in the same manner as in Comparative Example 1, except that the average particle size of the negative electrode active material and the average particle size of the sulfide solid electrolyte were changed as shown in Table 1.

[0057] [evaluation] (2 seconds DC resistance measurement) First, the all-solid-state lithium ion secondary batteries produced in Comparative Examples 1 to 9 and Examples 1 to 7 were repeatedly charged and discharged twice under the following conditions. The second discharge capacity was measured, and the batteries were charged at a constant current equivalent to 1 C to half the second discharge capacity. This adjusted the SOC of each battery to 50%. Charging: Constant current charging was performed at a current equivalent to 1C, and after the cell voltage reached 2.7V, constant voltage charging was performed, and was terminated when the charging current reached the equivalent of 0.01C. Discharge: Constant current discharge was performed at a current equivalent to 1C, and was stopped when the voltage reached 1.5V.

[0058] Each battery adjusted to a 50% SOC state was subjected to constant current discharge at a current equivalent to 63 C, and the DC resistance value (Ω) was calculated by dividing the difference between the voltage before charge and the voltage after 2 seconds of charge by the current equivalent to 63 C. In addition, the resistance ratio (DCIR ratio) of each comparative example and example was calculated when the resistance value of comparative example 1 was set to 1. The results are shown in Table 1. In addition, the relationship between the average particle size ratio (LTO / SE) and the DCIR ratio in each comparative example and example is shown in Figure 3.

[0059] [Table 1]

[0060] As shown in Table 1 and Figure 3, Examples 2 to 4 and 7 had lower resistance than Comparative Examples 1 to 4, respectively, confirming that changing the conductive material from particulate carbon (AB) to fibrous carbon (VGCF) could reduce resistance. Furthermore, Examples 1 to 7 and Comparative Examples 6 to 9 confirmed that setting the average particle size ratio (LTO / SE) to 0.75 or more could reduce resistance. These results confirmed that using fibrous carbon as the conductive material and setting the average particle size ratio (LTO / SE) to 0.75 or more could synergistically reduce resistance. [Explanation of symbols]

[0061] 1...Cathode active material layer 2...Negative electrode active material layer 3...Solid electrolyte layer 4...Positive electrode current collector 5...Negative electrode current collector 10...All-solid-state battery

Claims

[Claim 1] A negative electrode active material layer used in a solid-state battery, The battery contains lithium titanate, a sulfide solid electrolyte, and fibrous carbon, a ratio of an average particle size of the lithium titanate to an average particle size of the sulfide solid electrolyte is 0.75 or more; The sulfide solid electrolyte has an average particle size of 0.9 μm or more and 1.2 μm or less, The negative electrode active material layer contains tetralin.

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