Negative electrode composite layer and all-solid-state battery

Abstract

To provide a negative electrode composite layer and an all-solid-state battery capable of enhancing rate performance and cycle performance.SOLUTION: The negative electrode composite layer has a CV value of Cl of 1.30 or less when analyzed by mapping using scanning electron microscopy energy dispersive X-ray spectroscopy (SEM-EDS). The CV value is calculated by dividing the standard deviation (σ) of the count numbers of a specified element counted by elemental mapping by the average (Ave) of the count numbers of the specified element.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a negative electrode mixture layer and an all-solid-state battery. [Background technology]

[0002] With the remarkable development of electronics technology, portable electronic devices are becoming smaller, lighter, thinner, and more multifunctional. There is also a strong demand for batteries, which serve as the power source for electronic devices, to be smaller, lighter, thinner, more reliable, and safer. All-solid-state batteries, which use solid electrolytes, are attracting attention because they are safer than lithium-ion secondary batteries, which use liquid electrolytes.

[0003] Solid electrolytes include oxide-based solid electrolytes, sulfide-based solid electrolytes, complex hydride-based solid electrolytes, and halide-based solid electrolytes. For example, Patent Document 1 discloses a positive electrode composite and an all-solid-state battery containing a sulfide-based solid electrolyte. Patent Document 1 also discloses the preparation of a sulfide solid electrolyte using a mechanochemical milling process. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6531887 Summary of the Invention [Problem to be solved by the invention]

[0005] There is a demand for improvements in the rate characteristics and cycle characteristics of all-solid-state batteries. The rate characteristics are an index of rapid charge / discharge of all-solid-state batteries. The cycle characteristics are an index of deterioration of all-solid-state batteries when they are repeatedly charged and discharged.

[0006] The present disclosure has been made in view of the above problems, and aims to provide a negative electrode mixture layer and an all-solid-state battery that can improve rate characteristics and cycle characteristics. [Means for solving the problem]

[0007] In order to solve the above problems, the following means are provided.

[0008] The negative electrode composite layer according to the first embodiment has a Cl CV value of 1.30 or less when subjected to mapping analysis using scanning electron microscope energy dispersive X-ray spectroscopy (SEM-EDS). The CV value is calculated by dividing the standard deviation (σ) of the counts of a predetermined element counted by element mapping by the average (Ave) of the counts of the predetermined element.

[0009] The negative electrode mixture layer according to the above embodiment may have a CV value of S of 1.80 or less when subjected to mapping analysis using scanning electron microscope energy dispersive X-ray spectroscopy (SEM-EDS).

[0010] The negative electrode mixture layer according to the above embodiment may have a CV value of Zr of 1.50 or less when subjected to mapping analysis using scanning electron microscope energy dispersive X-ray spectroscopy (SEM-EDS).

[0011] An all-solid-state battery according to a second aspect includes the negative electrode mixture layer according to the above aspect. [Effects of the Invention]

[0012] The negative electrode mixture layer and all-solid-state battery according to the above aspect can improve the rate characteristics and cycle characteristics. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a cross-sectional view of an all-solid-state battery according to an embodiment of the present invention; DETAILED DESCRIPTION OF THE INVENTION

[0014] The present embodiment will be described in detail below with reference to the accompanying drawings. The drawings used in the following description may show characteristic portions enlarged for the sake of clarity, and the dimensional ratios of each component may differ from the actual ones. The materials, dimensions, etc. exemplified in the following description are merely examples, and the present disclosure is not limited thereto. Appropriate modifications may be made within the scope of the present disclosure.

[0015] "All-solid-state battery" FIG. 1 is a cross-sectional schematic diagram of an all-solid-state battery 100 according to this embodiment. The all-solid-state battery 100 shown in FIG. 1 includes a power generating element 40 and an exterior body 50. The exterior body 50 covers the periphery of the power generating element 40. The power generating element 40 is connected to the outside via a pair of terminals 60, 62 connected to the power generating element 40. Although a stacked-type battery is shown in FIG. 1, a wound-type battery may also be used. The all-solid-state battery 100 is used, for example, in laminated batteries, prismatic batteries, cylindrical batteries, coin batteries, button batteries, etc.

[0016] <Power generation element> The power generating element 40 includes a solid electrolyte layer 10, a positive electrode 20, and a negative electrode 30. The power generating element 40 is charged or discharged by the exchange of ions between the positive electrode 20 and the negative electrode 30 via the solid electrolyte layer 10 and the exchange of electrons via an external circuit.

[0017] (Negative electrode) 1, the negative electrode 30 has a negative electrode current collector 32 and a negative electrode mixture layer 34. The negative electrode mixture layer 34 is in contact with the negative electrode current collector 32. The negative electrode mixture layer 34 is located between the negative electrode current collector 32 and the solid electrolyte layer 10. The negative electrode 30 may be a single layer in which the material constituting the negative electrode current collector 32 and the material constituting the negative electrode mixture layer 34 are mixed.

[0018] The negative electrode current collector 32 is electrically conductive. The negative electrode current collector 32 is made of, for example, a metal such as copper, aluminum, nickel, stainless steel, or iron, or a conductive resin. The negative electrode current collector 32 may be in the form of a powder, a foil, a punched piece, or an expanded piece.

[0019] The negative electrode mixture layer 34 includes a negative electrode active material, a solid electrolyte, and a conductive additive. The negative electrode mixture layer 34 may also include a binder.

[0020] The negative electrode active material may be any compound capable of absorbing and releasing ions, and known active materials used in lithium ion secondary batteries can be used. Examples of the negative electrode active material include carbon materials, metals or alloys capable of reacting with lithium, composite materials of these metals or alloys with carbon materials, oxides, sulfur-modified polyacrylonitrile, metallic lithium, etc. Examples of carbon materials include natural graphite, artificial graphite, mesocarbon microbeads, mesocarbon fiber (MCF), cokes, glassy carbon, and organic compound sintered bodies. Examples of metals or alloys capable of reacting with lithium include Si, SiO x , Sn, and aluminum. The oxides are lithium titanate (Li4Ti5O 12 ), SnO2, etc. The negative electrode active material is natural graphite or lithium titanate (Li4Ti5O 12 ) is particularly preferred.

[0021] The solid electrolyte is, for example, a halide-based solid electrolyte containing Cl. The solid electrolyte does not have to be a halide-based solid electrolyte as long as it contains Cl. The solid electrolyte contained in the negative electrode 30 is a conduction path for lithium ions within the negative electrode 30.

[0022] The solid electrolyte is, for example, Li a E b G c X d ...It may also be expressed as (1).

[0023] In formula (1), a represents the composition ratio of Li in the compound represented by formula (1). In formula (1), a satisfies 0.5 ≤ a < 6.0. When E is Al, Sc, Y, or a lanthanoid, a preferably satisfies 2.0 ≤ a ≤ 4.0, and more preferably satisfies 2.5 ≤ a ≤ 3.5. When E is Zr or Hf, a preferably satisfies 1.0 ≤ a ≤ 3.0, and more preferably satisfies 1.5 ≤ a ≤ 2.5. In the solid electrolyte represented by formula (1), when a satisfies 0.5 ≤ a < 6.0, the content of Li contained in the compound becomes appropriate, and the ionic conductivity of the solid electrolyte increases.

[0024] In formula (1), E is at least one element selected from the group consisting of Al, Sc, Y, Zr, Hf, and lanthanoids. E is an element that forms the skeleton of the halide-based solid electrolyte represented by formula (1). Lanthanoids are La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. The solid electrolyte containing E has a wide potential window and high ionic conductivity. More preferably, E is any one of Al, Sc, Y, Zr, Hf, and La, and even more preferably, E is Al or Zr.

[0025] In formula (1), b is the composition ratio of E in the compound represented by formula (1). b satisfies 0 < b < 2.0, and more preferably satisfies 0.6 ≤ b. Also, b may satisfy b ≤ 1. E is an element with a high density compared to other elements contained in formula (1). A all-solid-state battery containing a solid electrolyte that satisfies b ≤ 1 has a low solid electrolyte density and a high capacity.

[0026] In formula (1), G is substituted for a part of E that forms the skeleton of the solid electrolyte. The compound of formula (1) may not contain G. G is, for example, OH, BO2, BO3, BO4, B3O6, B4O7, CO3, NO3, AlO2, SiO3, SiO4, Si2O7, Si3O9, Si4O 11 , Si6O 18 , PO3, PO4, P2O7, P3O 10, SO3, SO4, SO5, S2O3, S2O4, S2O5, S2O6, S2O7, S2O8, BF4, PF6, BOB, (COO)2, N, AlCl4, CF3SO3, CH3COO, CF3COO, OOC-(CH2)2-COO, OOC-CH2-COO, OOC-CH(OH)-CH(OH)-COO, OOC-CH(OH)-CH2-COO, C6H5SO3, OOC-CH=CH-COO, C(OH)(CH2COOH)2COO, AsO4, BiO4, CrO4, MnO4, PtF6, PtCl6, PtBr6, PtI6, SbO4, SeO4, TeO4, HCOO, and O. G is at least one group selected from the group consisting of PO3, PO4, PO7, PO 10 , SO3, SO4, SO5, S2O3, S2O4, S2O5, S2O6, S2O7, S2O8, and O, and more preferably at least one group selected from the group consisting of SO3, SO4, SO5, S2O3, S2O4, S2O5, S2O6, S2O7, and S2O8. These groups have a strong covalent bond with E. Therefore, when G is contained, E ions are less likely to be reduced, and the solid electrolyte is less likely to be reductively decomposed. A solid electrolyte containing G has a wide potential window on the reduction side and is less likely to be reduced.

[0027] In formula (1), c represents the composition ratio of G in the compound represented by formula (1). c is 0≦c≦6.0, preferably 0.1≦c, and more preferably 0.5≦c. A solid electrolyte containing G in this range has a wide potential window on the reduction side and is less susceptible to reductive decomposition. Furthermore, c is preferably c≦3.0. If the G content is high, the ionic conductivity of the solid electrolyte decreases.

[0028] In formula (1), X is a halide atom. X is an essential atom of the solid electrolyte. X contains Cl. X may consist only of Cl, or may contain at least one element selected from the group consisting of F, Br, and I together with Cl. X has a large ionic radius per valence. The halide-based solid electrolyte represented by formula (1) allows lithium ions to flow easily and has high ionic conductivity by containing X. Further, the halide-based solid electrolyte represented by formula (1) has high ionic conductivity and excellent oxidation resistance and reduction resistance by containing Cl as X.

[0029] In formula (1), d represents the composition ratio of X in the compound represented by formula (1). d satisfies 0 < d ≦ 6.1. Preferably, d satisfies 1.0 ≦ d. When d satisfies 1.0 ≦ d, the strength of the pellet becomes high when the solid electrolyte is pressure-molded into a pellet shape. Also, when d satisfies 1.0 ≦ d, the ionic conductivity of the solid electrolyte becomes high. Further, preferably, d satisfies d ≦ 5.0. This is to avoid a shortage of G and a narrowing of the potential window of the solid electrolyte due to an increase in the content of X.

[0030] The halide-based solid electrolyte represented by formula (1) is, for example, Li2ZrCl6, Li2ZrSO4Cl4, Li2ZrSO3Cl4, Li2ZrPO3Cl4, Li2ZrCO3Cl4, Li2Zr((COO)2) 0.5 Cl5, Li2Zr(CH3COO) 0.2 Cl 5.8 , Li2Zr(CF3COO) 0.2 Cl 5.8 , Li2Zr(HCOO) 0.4 Cl 5.6 , Li2ZrBO2Cl5, Li2ZrBF4Cl5, Li3YSO4Cl4, Li3YCO3Cl4, Li3YBO2Cl5, Li3YBF4Cl5, Li2ZrOCl4.

[0031] The content of the solid electrolyte in the negative electrode composite layer 34 is not particularly limited, but is preferably 1 mass % or more and 50 mass % or less, and more preferably 5 mass % or more and 30 mass % or less, based on the total mass of the negative electrode active material, solid electrolyte, conductive additive, and binder.

[0032] The conductive additive is a carbon material. Examples of the conductive additive include carbon powder, carbon nanotubes, carbon materials, metal fine powder, a mixture of carbon materials and metal fine powder, and conductive oxides. Examples of the carbon powder include carbon black, acetylene black, and ketjen black. Examples of the metal fine powder include powder of copper, nickel, stainless steel, iron, etc. The conductive additive improves the electronic conductivity of the negative electrode mixture layer 34.

[0033] The negative electrode mixture layer 34 may contain a binder. The binder bonds the negative electrode active material, the solid electrolyte, and the conductive additive to one another within the negative electrode mixture layer 34, and also firmly bonds the negative electrode mixture layer 34 to the negative electrode current collector 32. The negative electrode mixture layer 34 preferably contains a binder. The binder preferably has oxidation resistance and good adhesiveness.

[0034] Examples of binders that can be used in the negative electrode mixture layer 34 include polyvinylidene fluoride (PVDF) or copolymers thereof, polytetrafluoroethylene (PTFE), polyamide (PA), polyimide (PI), polyamideimide (PAI), polybenzimidazole (PBI), polyethersulfone (PES), polyacrylic acid (PA) and copolymers thereof, metal ion crosslinked polyacrylic acid (PA) and copolymers thereof, maleic anhydride-grafted polypropylene (PP), maleic anhydride-grafted polyethylene (PE), and mixtures thereof. Among these, PVDF is particularly preferable as the binder.

[0035] The binder content in the negative electrode mixture layer 34 is not particularly limited, but is preferably 0.3% by mass to 10% by mass, and more preferably 0.3% by mass to 5% by mass, based on the total mass of the negative electrode active material, solid electrolyte, conductive additive, and binder. If the binder content is too low, it tends to be difficult to form a negative electrode 30 with sufficient adhesive strength. If the binder content is too high, it tends to be difficult to obtain sufficient volume or mass energy density because general binders are electrochemically inactive and do not contribute to discharge capacity.

[0036] Mapping analysis of the negative electrode mixture layer 34 using scanning electron microscope energy dispersive X-ray spectroscopy (SEM-EDS) makes it possible to map the elements contained in the negative electrode mixture layer 34. For example, SEM-EDS can be used to map elements such as chlorine (Cl), sulfur (S), and zirconium (Zr) contained in the negative electrode mixture layer 34. Chlorine (Cl), sulfur (S), and zirconium (Zr) are elements that mainly constitute the solid electrolyte in the negative electrode mixture layer 34.

[0037] The CV value of Cl when the negative electrode mixture layer 34 is subjected to mapping analysis is 1.3 or less. The CV value of Cl when the negative electrode mixture layer 34 is subjected to mapping analysis is preferably 1.19 or less, and more preferably 1.08 or less. The CV value of Cl when the negative electrode mixture layer 34 is subjected to mapping analysis is, for example, 0.1 or more.

[0038] The CV value is calculated by dividing the standard deviation (σ) of the counts of a given element counted by element mapping by the average (Ave) of the counts of that element. The CV value was calculated by first cross-sectioning the solid-state battery using an ion milling machine (Hitachi High-Tech IM-4000). Then, measurements were performed using an energy-dispersive X-ray analyzer (HORIBA_X-MaxN80011) attached to a FE-SEM (Hitachi High-Tech SU8220). The measurement conditions were: magnification: 500x, acceleration voltage: 10 kV, emission current: 10 μA, resolution: 256 × 192, number of layers (number of frames): 100, binning factor: 1, smoothing level: 1, dwell time: 5 ms, and energy range: 10 keV. The CV value indicates the degree (percentage) of measurement variation relative to the average value; a smaller value indicates less variation.

[0039] A small CV value of Cl in the negative electrode mixture layer 34 indicates that the solid electrolyte, which serves as a migration path for Li ions, is uniformly dispersed in the negative electrode mixture layer 34. When the CV value of Cl in the negative electrode mixture layer 34 is 1.3 or less, a migration path for Li ions is secured in the negative electrode mixture layer 34, and the rate characteristics and cycle characteristics of the all-solid-state battery 100 are improved.

[0040] The CV value of S when the negative electrode mixture layer 34 is subjected to mapping analysis is preferably 1.8 or less. The CV value of S when the negative electrode mixture layer 34 is subjected to mapping analysis is more preferably 1.63 or less, and even more preferably 1.47 or less. The CV value of S when the negative electrode mixture layer 34 is subjected to mapping analysis is, for example, 0.1 or more. S is contained in the negative electrode mixture layer 34, for example, as part of G in the halide-based solid electrolyte represented by the above formula (1). When the negative electrode mixture layer 34 does not contain S, the CV value of S cannot be determined. When the CV value of S in the negative electrode mixture layer 34 is 1.8 or less, the rate characteristics and cycle characteristics of the all-solid-state battery 100 are improved. Even when the solid electrolyte is a sulfide-based solid electrolyte, the CV value of S when the negative electrode mixture layer 34 is subjected to mapping analysis is preferably 1.8 or less.

[0041] The CV value of Zr when the negative electrode mixture layer 34 is subjected to mapping analysis is preferably 1.5 or less. The CV value of Zr when the negative electrode mixture layer 34 is subjected to mapping analysis is more preferably 1.37 or less, and even more preferably 1.25 or less. The CV value of Zr when the negative electrode mixture layer 34 is subjected to mapping analysis is, for example, 0.1 or more. Zr is contained in the negative electrode mixture layer 34, for example, as part of E in the halide-based solid electrolyte represented by the above formula (1). When the CV value of S in the negative electrode mixture layer 34 is 1.5 or less, the rate characteristics and cycle characteristics of the all-solid-state battery 100 are improved.

[0042] (positive electrode) 1, positive electrode 20 has a plate-shaped (foil-shaped) positive electrode current collector 22 and a positive electrode mixture layer 24. Positive electrode mixture layer 24 is in contact with at least one surface of positive electrode current collector 22.

[0043] The positive electrode current collector 22 may be made of any conductive material that is resistant to oxidation during charging and corrosion. The positive electrode current collector 22 may be made of, for example, a metal such as aluminum, stainless steel, nickel, or titanium, or a conductive resin. The positive electrode current collector 22 may be in the form of a powder, foil, punched, or expanded.

[0044] Positive electrode mixture layer 24 contains a positive electrode active material, a solid electrolyte, and a conductive additive, and optionally a binder.

[0045] The positive electrode active material is not particularly limited as long as it can reversibly absorb and release, and insert and extract (intercalate and deintercalate) lithium ions, and any positive electrode active material used in known all-solid-state batteries can be used. Examples of the positive electrode active material include lithium-containing metal oxides and lithium-containing metal phosphates.

[0046] Lithium-containing metal oxides include, for example, lithium cobalt oxide (LiCoO), lithium nickel oxide (LiNiO), lithium manganese spinel (LiMnO), and lithium manganese oxides represented by the general formula: LiNi x Co y Mn zO2 (x+y+z=1), lithium vanadium compounds (LiVOPO4, Li3V2(PO4)3), olivine-type LiMPO4 (where M represents at least one element selected from Co, Ni, Mn, and Fe), and lithium titanate (Li4Ti5O 12 ) etc.

[0047] The positive electrode active material may also be lithium-free. Examples of such positive electrode active materials include non-lithium-containing metal oxides (MnO2, V2O5, etc.), non-lithium-containing metal sulfides (MoS2, etc.), and non-lithium-containing fluorides (FeF3, VF3, etc.). When using a lithium-free positive electrode active material, the negative electrode is doped with lithium ions in advance, or a lithium-ion-containing negative electrode is used.

[0048] The solid electrolyte contained in the positive electrode mixture layer 24 is the same as the solid electrolyte contained in the negative electrode mixture layer 34. The CV value of each element when the positive electrode mixture layer 24 is subjected to mapping analysis is not particularly limited. The correlation between the CV value of the positive electrode mixture layer 24 and the rate characteristics and cycle characteristics of the all-solid-state battery 100 does not need to be the same as that of the negative electrode mixture layer 34. For example, the CV value of the positive electrode mixture layer 24 may be correlated with only either the rate characteristics or the cycle characteristics of the all-solid-state battery 100.

[0049] The conductive additive contained in positive electrode mixture layer 24 is the same as the conductive additive contained in negative electrode mixture layer 34, for example.

[0050] The positive electrode mixture layer 24 may contain a binder. The binder bonds the positive electrode active material, the solid electrolyte, and the conductive additive to one another within the positive electrode mixture layer 24, and also firmly bonds the positive electrode mixture layer 24 to the positive electrode current collector 22. The binder contained in the positive electrode mixture layer 24 is the same as the binder contained in the negative electrode 30.

[0051] (solid electrolyte layer) The solid electrolyte layer 10 is sandwiched between the positive electrode 20 and the negative electrode 30. The solid electrolyte layer 10 includes a solid electrolyte that can transfer ions when an external voltage is applied. For example, the solid electrolyte conducts lithium ions and inhibits the transfer of electrons.

[0052] The solid electrolyte layer 10 is, for example, a halide-based solid electrolyte. The solid electrolyte layer 10 includes, for example, the above-mentioned solid electrolyte. The solid electrolyte included in the solid electrolyte layer 10 may be different from the above-mentioned solid electrolyte.

[0053] The solid electrolyte layer 10 may contain a binder in addition to the solid electrolyte. The binder may be the same as that used in the positive electrode 20 or the negative electrode 30.

[0054] <Exterior body> The exterior body 50 houses the power generating element 40. The exterior body 50 prevents moisture and other contaminants from entering the interior from the outside. As shown in FIG. 1, the exterior body 50 has a metal foil 52 and a resin layer 54 laminated on each side of the metal foil 52. The exterior body 50 is a metal laminate film in which the metal foil 52 is coated with the resin layer 54 on both sides.

[0055] The metal foil 52 is, for example, aluminum foil or stainless steel foil. The resin layer 54 can be, for example, a resin film such as polypropylene. The materials constituting the inner and outer resin layers 54 may be different. For example, the outer material can be a polymer with a high melting point, such as polyethylene terephthalate (PET) or polyamide (PA), and the inner material can be polyethylene (PE), polypropylene (PP), or the like.

[0056] <Terminal> Terminals 60 and 62 are connected to the negative electrode 30 and the positive electrode 20, respectively. The terminal 62 connected to the positive electrode 20 is a positive electrode terminal, and the terminal 60 connected to the negative electrode 30 is a negative electrode terminal. The terminals 60 and 62 are responsible for electrical connection to the outside. The terminals 60 and 62 are made of a conductive material such as aluminum, nickel, or copper. The connection method may be welding or screw fastening. It is preferable to protect the terminals 60 and 62 with insulating tape to prevent short circuits.

[0057] (Manufacturing method of all-solid-state batteries) First, a negative electrode active material, a solid electrolyte, and a conductive additive are prepared. The negative electrode active material, solid electrolyte, and conductive additive may be commercially available or may be prepared by manufacturing. For example, the solid electrolyte can be manufactured by a mechanochemical method. For example, raw material powders containing predetermined elements in a predetermined molar ratio are mixed and reacted. Alternatively, the solid electrolyte may be manufactured by a solid-phase reaction method.

[0058] Next, a negative electrode composite containing a negative electrode active material, a solid electrolyte, and a conductive additive is mixed using a ball mill. The ball mill is a device that rotates a container containing a sample and balls to grind and mix the sample. Widely used 50cc, 100cc, 250cc, and 500cc pots are used as ball mill components, depending on the amount of the composite. The volume ratio of the balls to the container in the ball mill is 30% to 35%. The volume ratio of the sample to the container in the ball mill is 5% to 20%. The balls used in the ball mill are zirconium balls with a diameter of 1mm to 3mm. The weight ratio of the composite to the ball weight is preferably 0.1 or less. The rotation speed of the ball mill is 37,700 / (pot outer diameter × π) rpm or more. The mixing time using the ball mill is 16 hours or more. By carefully controlling the conditions for producing the negative electrode composite layer 34 in this way, the CV value of Cl in the negative electrode composite layer 34 can be adjusted to a predetermined range.

[0059] The negative electrode composite may be mixed in two stages. In the first stage, the negative electrode active material and the solid electrolyte are mixed using a ball mill. The mixing conditions for the first stage are the same as those described above. Next, in the second stage, the conductive additive is added to the mixture from the first stage and mixed. The mixing conditions for the second stage are gentler than those for the first stage. For example, the second stage may be mixed gently using a mortar, or may be mixed for about an hour using a ball mill at a rotation speed of 50 rpm or less. By dividing the mixing of the negative electrode composite into two stages, it is possible to prevent the conductive additive from being crushed during mixing. For example, if the conductive additive is flaky, it is preferable to mix the negative electrode composite in two stages.

[0060] Next, the mixed negative electrode mixture is made into a paste by adding the negative electrode mixture to a solvent and mixing the mixture. The solvent is, for example, toluene.

[0061] Next, the negative electrode mixture paste is applied onto the negative electrode current collector 32 and dried. The dried paste becomes the negative electrode mixture layer 34.

[0062] Similarly, positive electrode 20 is produced by applying a paste containing a positive electrode active material onto positive electrode current collector 22 and drying it to form positive electrode mixture layer 24 .

[0063] The power generating element 40 can also be produced using, for example, a powder molding method. A guide with a hole is placed on the positive electrode 20, and the guide is filled with a solid electrolyte. The surface of the solid electrolyte is then smoothed, and the negative electrode 30 is placed on top of the solid electrolyte. This sandwiches the solid electrolyte between the positive electrode 20 and the negative electrode 30. Pressure is then applied to the positive electrode 20 and the negative electrode 30 to pressure-molde the solid electrolyte. This pressure molding produces a laminate in which the positive electrode 20, solid electrolyte layer 10, and negative electrode 30 are stacked in this order.

[0064] Next, external terminals are welded to the positive electrode current collector 22 of the positive electrode 20 and the negative electrode current collector 32 of the negative electrode 30, which form the laminate, by a known method, to electrically connect the positive electrode current collector 22 or the negative electrode current collector 32 to the external terminals. Thereafter, the laminate connected to the external terminals is housed in an exterior body 50, and the opening of the exterior body 50 is hermetically sealed by heat sealing. Through the above steps, the all-solid-state battery 100 according to this embodiment is obtained.

[0065] In the negative electrode mixture layer 34 according to this embodiment, the CV values ​​of predetermined elements are equal to or less than a certain value, and the solid electrolyte is uniformly dispersed. Therefore, in the negative electrode mixture layer 34 according to this embodiment, a conduction path for lithium ions responsible for charge and discharge is ensured. The smooth transfer of lithium ions in each negative electrode active material improves the rate characteristics and cycle characteristics of the all-solid-state battery 100.

[0066] The above describes the embodiments of the present disclosure in detail with reference to the drawings. However, each configuration and combination thereof in each embodiment is an example, and addition, omission, substitution, and other modifications of the configuration are possible within the scope that does not deviate from the spirit of the present disclosure. [Example]

[0067] "Example 1" A negative electrode active material, a solid electrolyte, and a conductive additive were prepared. The negative electrode active material was lithium titanate (Li4Ti5O 12 ) The solid electrolyte was Li2Zr(SO4)Cl4. The conductive additive was graphite. These were placed in a polypropylene container containing 1 mm diameter zirconia balls. The volume ratio of the zirconia balls to the polypropylene container was 31.6%. The weight ratio of the negative electrode mixture to the weight of the zirconia balls was 0.083%. Teflon tape was wrapped around the grooves of the container and the lid was then placed on it.

[0068] The polypropylene container was set on a ball mill stand. A negative electrode mixture consisting of a negative electrode active material, a solid electrolyte, and a conductive additive was mixed using the ball mill. The ball mill rotation speed was 300 rpm. The mixing time was 16 hours. The mass ratio of the negative electrode active material, solid electrolyte, and conductive additive in the negative electrode mixture was negative electrode active material:solid electrolyte:conductive additive = 55 wt %:40 wt %:5 wt %.

[0069] [Charge / discharge evaluation] A full cell for charge and discharge was fabricated, and the charge and discharge efficiency was measured. The full cell of Example 1 was fabricated in the following manner.

[0070] The charge / discharge full cell was fabricated in a glove box with argon gas circulating at a dew point of approximately -70°C. A resin holder, a lower punch (also serving as a negative electrode current collector), and an upper punch (also serving as a positive electrode current collector) were prepared. The lower punch was inserted from the bottom of the resin holder, and 50 mg of solid electrolyte (Li2Zr(SO4)Cl4) was added from the top of the resin holder.

[0071] The pellet making jig has a PEEK (polyether ether ketone) cylinder with an outer diameter of 30 mm, an inner diameter of 10 mm, and a height of 20 mm, and upper and lower punches with a diameter of 9.99 mm. The upper and lower punches are made of die steel (SKD11 material).

[0072] The PEEK cylinder was then vibrated to smooth the surface of the solid electrolyte, after which an upper punch was inserted onto the solid electrolyte and pressed with a press under a load of 373 MPa to form a solid electrolyte layer.

[0073] Next, the upper punch was removed, and 32.9 mg of positive electrode composite was placed on top of the solid electrolyte layer. The positive electrode composite was mixed using a grinder. The PEEK cylinder was vibrated to level the surface of the positive electrode composite. Then, the upper punch was inserted on top of the positive electrode composite, and the mixture was pressed using a press with a load of 373 MPa. Next, the lower punch was removed, and 38.7 mg of negative electrode composite was placed on top of the solid electrolyte layer. The negative electrode composite was mixed using the above method. The PEEK cylinder was vibrated to level the surface of the negative electrode composite. Then, the upper punch was inserted on top of the negative electrode composite, and the mixture was pressed using a press with a load of 373 MPa. The full cell configuration was positive electrode current collector / positive electrode active material layer / solid electrolyte layer / negative electrode active material layer / negative electrode current collector.

[0074] The full cell of Example 1 was charged and discharged under the following conditions to measure the rate characteristics. The voltage range when measuring the rate characteristics was 1.3 V to 2.8 V. Charging was performed at a constant current of 0.1 C, and after the constant voltage, charging was terminated when the current reached a value equivalent to 0.05 C. Discharging was performed at 0.1 C (the current value at which charging or discharging is completed in 10 hours when constant current charging or discharging is performed at 25°C) and 1.0 C. The discharge capacity when discharging at 0.1 C was set as 100%, and the ratio of the discharge capacity when discharging at 1.0 C (rate characteristics (unit: %)) was calculated. The charge capacity and discharge capacity in the charge and discharge tests were measured using a secondary battery charge and discharge tester (manufactured by Meiden Hokuto Co., Ltd.).

[0075] The cycle characteristics were measured using a secondary battery charge / discharge tester (manufactured by Meiden Hokuto Co., Ltd.). The cycle characteristics were measured using a CC-CV charge / CC discharge format. Specifically, the battery was first charged at a constant current of 0.5C up to a maximum charge voltage of 2.8V, and then charged at a constant voltage of 2.8V in constant voltage mode (2.8V). The battery was then discharged at a constant current of 0.5C until the battery voltage reached 1.3V. The discharge capacity after the end of charge / discharge was measured, and the battery capacity Q1 at the first cycle was calculated. This battery capacity Q1 was the initial discharge capacity.

[0076] Next, the battery was charged at a constant current of 0.5C up to a maximum charging voltage of 2.8V, and then charged at a constant voltage of 2.8V in constant voltage mode (2.8V). The battery was then discharged at a constant current of 0.5C until the battery voltage reached 1.3V. This charge / discharge cycle was counted as one cycle, and 200 charge / discharge cycles were performed. The discharge capacity after the end of the charge / discharge cycle was measured, and the battery capacity Q2 after the 200-cycle test was calculated.

[0077] The cycle characteristic is a ratio calculated by dividing the battery capacity Q2 after 200 cycles by the initial battery capacity Q1. The cycle characteristic of Example 1 was 85.2%.

[0078] A cross section of the negative electrode composite layer of a full cell fabricated under the same conditions was cut out and subjected to elemental mapping, which determined the CV values ​​of Cl, S, and Zr in the negative electrode composite layer.

[0079] "Examples 2 to 4, Comparative Examples 1 to 4" Examples 2 to 4 and Comparative Examples 1 to 4 differ from Example 1 in that the mixing conditions for producing the negative electrode composite were changed. Otherwise, the samples of Examples 2 to 4 and Comparative Examples 1 to 4 were evaluated in the same manner as Example 1.

[0080] The evaluation results of Examples 2 to 4 and Comparative Examples 1 to 4 are summarized in Table 1 below. In Examples 3 and 4, the negative electrode mixture was mixed in two stages. In the first stage, the negative electrode active material and the solid electrolyte of the negative electrode mixture were mixed, and in the second stage, the mixture was mixed with the conductive additive.

[0081] [Table 1]

[0082] Examples 1 to 4 had smaller CV values ​​for Cl, S, and Zr than Comparative Examples 1 to 4. Examples 1 to 4 had higher rate characteristics and cycle characteristics than Comparative Examples 1 to 4. [Explanation of symbols]

[0083] 10 Solid electrolyte layer 20 positive electrode 22 Positive electrode current collector 24 Positive electrode mixture layer 30 negative electrode 32 Negative electrode current collector 34 Negative electrode composite layer 40 Power generating element 50 Exterior body 52 Metal foil 54 Resin layer 60,62 terminals

Claims

1. the CV value of Cl when subjected to mapping analysis using scanning electron microscope energy dispersive X-ray spectroscopy (SEM-EDS) is 1.30 or less; The CV value is calculated by dividing the standard deviation (σ) of the count number of a predetermined element counted by element mapping by the average (Ave) of the count number of the predetermined element.

2. 2. The negative electrode mixture layer according to claim 1, wherein the CV value of S in mapping analysis using scanning electron microscope energy dispersive X-ray spectroscopy (SEM-EDS) is 1.80 or less.

3. 2. The negative electrode mixture layer according to claim 1, wherein the CV value of Zr when subjected to mapping analysis using scanning electron microscope energy dispersive X-ray spectroscopy (SEM-EDS) is 1.50 or less.

4. An all-solid-state battery comprising the negative electrode mixture layer according to claim 1 .

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