JP7718042B2 - Composite solid electrolyte, all-solid-state battery, method for producing composite solid electrolyte, and method for producing all-solid-state battery - Google Patents

Description

The present invention relates to a composite solid electrolyte, an all-solid-state battery, a method for manufacturing a composite solid electrolyte, and a method for manufacturing an all-solid-state battery.

Non-aqueous electrolyte secondary batteries, typified by lithium-ion non-aqueous electrolyte secondary batteries, are widely used in electronic devices such as personal computers and communication terminals, as well as automobiles, due to their high energy density. Non-aqueous electrolyte secondary batteries generally comprise an electrode assembly having a pair of electrically isolated electrodes and a non-aqueous electrolyte sandwiched between the electrodes, and are configured to charge and discharge by transferring ions between the electrodes.

In recent years, with the aim of improving the safety of non-aqueous electrolyte secondary batteries, all-solid-state batteries have been proposed that use sulfide solid electrolytes or the like as non-aqueous electrolytes instead of liquid electrolytes containing organic solvents or the like (see Patent Document 1).

As sulfide solid electrolytes, 70Li ₂ S·30P ₂ S ₅ glass ceramics and 60Li ₂ S·25P ₂ S ₅ ·10Li ₃ N glass ceramics have been reported to exhibit high ionic conductivity of 10 ⁻³ S/cm or more (Solid State Ionics, 177, 2721 (2006), Solid State Ionics, 304, 85 (2016)).

However, when the relationship between applied pressure and cycle performance was evaluated using an all-solid-state Li-Si half cell having a Si:Cu:sulfide solid electrolyte (77.5Li ₂ S · 22.5P ₂ S ₅ ) composition of 1:1:5 (m/m/m), it was reported that the Coulombic efficiency was low even when a high pressure (230 MPa) was applied that did not cause silicon isolation (Journal of the electrochemical society, 160, 1, A77 (2013)). Furthermore, first-principles calculations have revealed that sulfide solid electrolytes inherently have low oxidation resistance and low reduction resistance (ACS Appl. Mater. Interfaces, 7, 23685 (2015)).

Japanese Patent Application Laid-Open No. 2000-340257

In energy storage devices such as nonaqueous electrolyte secondary batteries used in hybrid electric vehicles (hereinafter also referred to as "HEVs") and hybrid industrial machinery (heavy machinery, construction machinery, etc.), there is a need to suppress the decrease in coulombic efficiency during charge/discharge cycles, and further suppression of the decrease in coulombic efficiency is also desired in all-solid-state batteries.

The present invention was made based on the above circumstances, and aims to provide a composite solid electrolyte that can suppress the decrease in coulombic efficiency during the charge-discharge cycle of an all-solid-state battery.

One aspect of the present invention, which has been made to solve the above problems, is a composite solid electrolyte that includes a sulfide solid electrolyte and an additive, wherein the additive is a sulfur-based cyclic compound having an S=O bond, lithium nitrate, or a combination thereof.

Another aspect of the present invention is a method for producing a composite solid electrolyte, comprising mixing a sulfide solid electrolyte with an additive to produce a composite solid electrolyte, wherein the additive is a sulfur-based cyclic compound having an S=O bond, lithium nitrate, or a combination thereof.

A composite solid electrolyte according to one aspect of the present invention can suppress a decrease in coulombic efficiency during charge-discharge cycles of an all-solid-state battery.

FIG. 1 is a schematic cross-sectional view showing an all-solid-state battery according to one embodiment of the present invention. FIG. 2 is a graph showing the relationship between the number of charge/discharge cycles and the coulombic efficiency for the examples and the reference example.

One aspect of the present invention is a composite solid electrolyte comprising a sulfide solid electrolyte and an additive, wherein the additive is a sulfur-based cyclic compound having an S=O bond, lithium nitrate, or a combination thereof.

The inventors believed that improving the reduction resistance of sulfide solid electrolytes was necessary to improve the effect of suppressing the decline in Coulombic efficiency during the charge-discharge cycles of all-solid-state batteries. Upon conducting research, they discovered that the use of specific additives could impart reduction resistance to sulfide solid electrolytes. They then hypothesized that combining specific additives with sulfide solid electrolytes could enhance the reduction resistance of solid electrolytes and suppress the decline in Coulombic efficiency during the charge-discharge cycles of all-solid-state batteries, leading to the present invention.

The composite solid electrolyte includes a sulfide solid electrolyte and an additive, and the additive is a sulfur-based cyclic compound having an S═O bond, lithium nitrate, or a combination thereof, thereby suppressing a decrease in Coulombic efficiency during the charge-discharge cycles of an all-solid-state battery. While the reason for this is unclear, the following reason is presumed. It is known that general sulfide solid electrolytes are susceptible to reductive decomposition and exhibit a large reductive decomposition capacity. The composite solid electrolyte is formed by combining the sulfur-based cyclic compound having an S═O bond with a sulfide solid electrolyte and using it as a solid electrolyte in the negative electrode or in the electrolyte layer interposed between the negative electrode and the positive electrode. It is believed that the sulfur-based cyclic compound having an S═O bond undergoes ring-opening by reduction to form electronically insulating Li ₂ S and Li ₂ O. This results in the formation of an extremely thin, electronically insulating coating on the surface of the negative electrode or the electrolyte layer, thereby suppressing continuous reductive decomposition of the sulfide solid electrolyte and improving the Coulombic efficiency. The reductive decomposition potential of nonaqueous electrolytes used in typical lithium-ion nonaqueous electrolyte secondary batteries is less than 1.0 V (e.g., ethylene carbonate is approximately 0.6 V). Therefore, when 1,3-propene sultone, a sulfur-based cyclic compound having an S═O bond, is used as an additive in a lithium-ion nonaqueous electrolyte secondary battery, it is presumed that the 1,3-propene sultone decomposes before the other components of the nonaqueous electrolyte to form a coating on the surface of the negative electrode, thereby suppressing decomposition of the nonaqueous electrolyte. In contrast, the sulfide solid electrolyte has a higher reductive decomposition potential than 1,3-propene sultone, and therefore, it is believed that the effects of this composite solid electrolyte are achieved through a mechanism different from that of the nonaqueous electrolyte of a lithium-ion nonaqueous electrolyte secondary battery.
On the other hand, in the composite solid electrolyte, lithium nitrate, which has a higher reduction potential than a sulfide solid electrolyte, is combined with the sulfide solid electrolyte and used as the solid electrolyte in the negative electrode or in the electrolyte layer interposed between the negative electrode and the positive electrode, so that the lithium nitrate is reductively decomposed before the sulfide solid electrolyte, and as a result, a thin electronically insulating coating (SEI: Solid Electrolyte Interphase) is formed on the surface of the negative electrode due to the reductive decomposition of lithium nitrate.
Therefore, the composite solid electrolyte can suppress continuous reductive decomposition of the solid electrolyte on the negative electrode side and can suppress a decrease in Coulombic efficiency during charge-discharge cycles. Here, the "SEI" refers to a coating that forms on the negative electrode surface in conjunction with reductive decomposition of the electrolyte during the initial charge. The "SEI" functions as a passive layer that suppresses subsequent reductive decomposition of the electrolyte, and at the same time, provides a site for lithium ion insertion/extraction at the interface between the negative electrode and the electrolyte through lithium ion conduction.

The content of the additive in the composite solid electrolyte is preferably 5% by mass or more and 20% by mass or less. By having the content of the additive be 5% by mass or more and 20% by mass or less, the reduction resistance of the composite solid electrolyte is further improved, and the effect of suppressing the decrease in coulombic efficiency during the charge/discharge cycle of the all-solid-state battery can be further enhanced.

The sulfur-based cyclic compound is preferably a cyclic sulfonate ester. When the sulfur-based cyclic compound is a cyclic sulfonate ester, the reduction resistance of the composite solid electrolyte is further improved, and the effect of suppressing the decrease in coulombic efficiency during the charge-discharge cycle of the all-solid-state battery can be further enhanced.

An all-solid-state battery according to another aspect of the present invention comprises a negative electrode, a positive electrode, and an electrolyte layer interposed between the negative electrode and the positive electrode, wherein the negative electrode, the electrolyte layer, or a combination thereof contains the composite solid electrolyte. In the all-solid-state battery, the negative electrode, the electrolyte layer, or a combination thereof contains the composite solid electrolyte, so the additive is reductively decomposed before the sulfide solid electrolyte. As a result, an electronically insulating coating is formed on the negative electrode side due to the reductive decomposition of the additive, which suppresses the continuous reductive decomposition of the sulfide solid electrolyte on the negative electrode side and is highly effective in suppressing a decrease in coulombic efficiency during charge-discharge cycles.

A method for producing a composite solid electrolyte according to another aspect of the present invention includes mixing a sulfide solid electrolyte with an additive to produce a composite solid electrolyte, wherein the additive is a sulfur-based cyclic compound having an S=O bond, lithium nitrate, or a combination thereof.

The method for producing this composite solid electrolyte involves mixing a sulfide solid electrolyte with an additive to produce a composite solid electrolyte. The additive is a sulfur-based cyclic compound having an S=O bond, lithium nitrate, or a combination thereof, making it possible to produce a composite solid electrolyte that is reduction-resistant and has an excellent effect of suppressing a decrease in coulombic efficiency during the charge-discharge cycle of an all-solid-state battery.

In the method for producing the composite solid electrolyte, the content of the additive in the composite solid electrolyte is preferably 5% by mass or more and 20% by mass or less. By having the content of the additive in the composite solid electrolyte be 5% by mass or more and 20% by mass or less, it is possible to produce a composite solid electrolyte that has improved reduction resistance and is more effective in suppressing a decrease in coulomb efficiency during the charge-discharge cycle of an all-solid-state battery.

A method for manufacturing an all-solid-state battery according to another aspect of the present invention comprises fabricating at least one of an anode and an electrolyte layer using the composite solid electrolyte or a composite solid electrolyte obtained by the method for manufacturing the composite solid electrolyte. Because the method for manufacturing an all-solid-state battery comprises fabricating at least one of an anode and an electrolyte layer using the composite solid electrolyte or a composite solid electrolyte obtained by the method for manufacturing the composite solid electrolyte, it is possible to manufacture an all-solid-state battery that is excellent in suppressing a decrease in coulombic efficiency during charge-discharge cycles.

Embodiments of the composite solid electrolyte, all-solid-state battery, method for manufacturing a composite solid electrolyte, and method for manufacturing an all-solid-state battery according to the present invention are described in detail below.

<Composite solid electrolyte>
The composite solid electrolyte includes a sulfide solid electrolyte and an additive, wherein the additive is a sulfur-based cyclic compound having an S═O bond, lithium nitrate, or a combination thereof. The composite solid electrolyte includes a sulfide solid electrolyte and an additive, wherein the additive is a sulfur-based cyclic compound having an S═O bond, lithium nitrate, or a combination thereof. This composite solid electrolyte has excellent reduction resistance and can suppress a decrease in coulombic efficiency during the charge/discharge cycle of an all-solid-state battery. The composite solid electrolyte can be used in any application requiring ionic conductivity. In particular, the composite solid electrolyte is preferably used in a lithium all-solid-state battery.

The sulfide solid electrolyte preferably has high lithium ion conductivity, and examples thereof include Li ₂ S—P ₂ S ₅ , Li ₂ S—P ₂ S ₅ —LiI, Li ₂ S—P ₂ S ₅ —LiCl, Li ₂ S—P ₂ S ₅ —LiBr, Li ₂ S—P ₂ S ₅ —Li ₂ O, Li ₂ S—P ₂ S ₅ —Li ₂ O—LiI, Li ₂ S—P ₂ S ₅ —Li ₃ N, Li ₂ S—SiS ₂ , Li ₂ S—SiS ₂ —LiI, Li ₂ S—SiS ₂ —LiBr, Li ₂ S—SiS ₂ —LiCl, and Li ₂ S—SiS ₂ —B. _{2S3 -} LiI, _Li2S -SiS2- _{P2S5 - LiI} , _Li2S - _B2S3 , _Li2S - _{P2S5 - ZmS2n} (where _m and n are positive numbers and Z is Ge, Zn or Ga), _Li2S - _GeS2 , _Li2S - _SiS2 - _Li3PO4 , _Li2S - _SiS2 - _LixMOy (where _x and y are positive numbers and _M is P, Si, Ge, B, Al, Ga or In ₎ , _Li10GeP2S12 and _{the like} can be mentioned. Among these, Li ₂ S—P ₂ S ₅ is preferred, and xLi ₂ S·(100−x)P ₂ S ₅ (70≦x≦80) is more preferred from the viewpoint of good lithium ion conductivity.

The additive is a sulfur-based cyclic compound having an S═O bond, lithium nitrate, or a combination thereof. It is believed that by using the sulfur-based cyclic compound having an S═O bond as an additive in the composite solid electrolyte, the sulfur-based cyclic compound undergoes ring-opening by reduction to form electronically insulating Li ₂ S and Li ₂ O. This is believed to result in the formation of an extremely thin electronically insulating coating on the surface of the negative electrode or electrolyte layer. On the other hand, by using lithium nitrate, which has a higher reduction potential than the sulfide solid electrolyte, as an additive in the composite solid electrolyte, the lithium nitrate is reductively decomposed before the sulfide solid electrolyte. As a result, an SEI is formed on the surface of the negative electrode or electrolyte layer. In this way, the composite solid electrolyte can suppress continuous reductive decomposition of the sulfide solid electrolyte on the negative electrode side and suppress a decrease in coulombic efficiency during charge-discharge cycles.

Examples of the sulfur-based cyclic compounds having the S=O bond include sultone compounds, cyclic sulfate compounds, cyclic sulfite compounds, sulfolane compounds, cyclic disulfonate compounds, and sulfobenzoic anhydride.

Examples of sultone compounds include 1,3-propane sultone, 1,3-propene sultone, 2,4-butane sultone, and 1,4-butane sultone.

Examples of cyclic sulfite compounds include ethylene sulfite, 1,2-propylene glycol sulfite, trimethylene sulfite, and 1,3-butylene glycol sulfite.

Sulfolane compounds include sulfolane, 3-sulfolene, 1,1-dioxothiophene, 3-methylsulfolane, 3-methyl-2,5-dihydrothiophene-1,1-dioxide, and methyl 3-sulfolene-3-carboxylate.

Examples of cyclic disulfonate compounds include methylene-methane disulfonate ester and ethylene-methane disulfonate ester.

The sulfur-based cyclic compound is preferably a cyclic sulfonate ester. When the sulfur-based cyclic compound is a cyclic sulfonate ester, the reduction resistance of the composite solid electrolyte is further improved, and the effect of suppressing the decrease in coulombic efficiency during the charge-discharge cycle of the all-solid-state battery can be further enhanced.

The lower limit of the additive content in the composite solid electrolyte is preferably 1% by mass, more preferably 3% by mass, and even more preferably 5% by mass. Meanwhile, the upper limit of the additive content is preferably 20% by mass, more preferably 18% by mass, and even more preferably 15% by mass. By ensuring that the additive content is within this range, the reduction resistance of the composite solid electrolyte is further improved, and the effect of suppressing the decrease in coulombic efficiency during the charge-discharge cycle of the all-solid-state battery can be further enhanced. The preferred range of the additive content in the composite solid electrolyte is higher than the additive content in a lithium-ion nonaqueous electrolyte secondary battery. This is because, even if the additive is consumed at the negative electrode-nonaqueous electrolyte interface in a lithium-ion nonaqueous electrolyte secondary battery, the additive is supplied to the negative electrode-nonaqueous electrolyte interface by diffusion from the bulk, allowing the additive to be effective even at a low additive content range. On the other hand, in all-solid-state batteries, particulate additives are present in a dispersed state in the solid electrolyte, making it difficult for the above-mentioned state to occur in non-aqueous lithium-ion electrolyte secondary batteries. As a result, it is thought that the effect is difficult to obtain when the additive content is as low as in non-aqueous lithium-ion electrolyte secondary batteries.

The lower limit of the ionic conductivity of the composite solid electrolyte at 25° C. is preferably 1.0×10 ⁻⁵ S/cm, more preferably 5.0×10 ⁻⁵ S/cm, and even more preferably 1.0×10 ⁻⁴ . When the ionic conductivity of the composite solid electrolyte at 25° C. is within the above range, the high-rate charge/discharge performance of the all-solid-state battery can be improved.

This composite solid electrolyte can be suitably used as a solid electrolyte for the negative electrode and electrolyte layer of all-solid-state batteries.

<All-solid-state battery>
The all-solid-state battery includes a negative electrode, a positive electrode, and an electrolyte layer interposed between the negative electrode and the positive electrode. FIG. 1 is a schematic cross-sectional view showing an all-solid-state battery 10 according to one embodiment of the present invention. The all-solid-state battery 10, which is a secondary battery, includes a negative electrode 1 and a positive electrode 2 arranged with a solid electrolyte layer 3 interposed therebetween. The negative electrode 1 includes a negative electrode substrate 4 and a negative electrode mixture layer 5, with the negative electrode substrate 4 being the outermost layer of the negative electrode 1. The positive electrode 2 includes a positive electrode substrate 7 and a positive electrode mixture layer 6, with the positive electrode substrate 7 being the outermost layer of the positive electrode 2. In the all-solid-state battery 10 shown in FIG. 1 , the positive electrode mixture layer 6, the solid electrolyte layer 3, the negative electrode mixture layer 5, and the negative electrode substrate 4 are stacked in this order on the positive electrode substrate 7.

In this all-solid-state battery, the anode 1, the solid electrolyte layer 3, or a combination thereof contains the composite solid electrolyte. Because the anode 1, the solid electrolyte layer 3, or a combination thereof contains the composite solid electrolyte, this all-solid-state battery is highly effective in suppressing a decrease in coulombic efficiency during charge-discharge cycles.

The all-solid-state battery may also use a solid electrolyte other than the composite solid electrolyte. The other solid electrolyte may be a sulfide solid electrolyte other than the composite solid electrolyte, an oxide-based solid electrolyte, a dry polymer electrolyte, a gel polymer electrolyte, or a quasi-solid electrolyte.

As a sulfide solid electrolyte other than this composite solid electrolyte, the sulfide solid electrolytes described above can be used.

[Negative electrode]
The negative electrode 1 includes a negative electrode substrate 4 and a negative electrode mixture layer 5 laminated on the surface of the negative electrode substrate 4. The negative electrode 1 may have an intermediate layer (not shown) between the negative electrode substrate 4 and the negative electrode mixture layer 5.

(Negative electrode substrate)
The negative electrode substrate 4 is a layer having electrical conductivity. The material of the negative electrode substrate 4 is not limited as long as it is an electrical conductor. For example, the material may be one or more metals selected from the group consisting of copper, aluminum, titanium, nickel, tantalum, niobium, hafnium, zirconium, zinc, tungsten, bismuth, antimony, gold, silver, iron, platinum, chromium, tin, indium, alloys containing one or more of these metals, and stainless steel alloys.

The lower limit of the average thickness of the negative electrode substrate 4 is preferably 3 μm, more preferably 5 μm, and even more preferably 8 μm. The upper limit of the average thickness of the negative electrode substrate 4 is preferably 200 μm, more preferably 100 μm, and even more preferably 50 μm. By setting the average thickness of the negative electrode substrate 4 to be equal to or greater than the above lower limit, the strength of the negative electrode substrate 4 can be sufficiently increased, allowing for a satisfactory formation of the negative electrode 1. By setting the average thickness of the negative electrode substrate 4 to be equal to or less than the above upper limit, sufficient volume for the other components can be ensured.

(Negative electrode mixture layer)
The negative electrode mixture layer 5 can be formed from a so-called negative electrode mixture containing a negative electrode active material. The negative electrode mixture may contain a mixture or composite containing a negative electrode active material and a solid electrolyte. The solid electrolyte may be the composite solid electrolyte. The negative electrode mixture may also contain the composite solid electrolyte that does not form a mixture or composite with the negative electrode active material. The negative electrode mixture may contain optional components such as a solid electrolyte other than the composite solid electrolyte, a conductive agent, a binder, a filler, etc., as necessary.

<Negative electrode active material>
The negative electrode active material can be appropriately selected from known negative electrode active materials. A material capable of absorbing and releasing lithium ions is typically used as the negative electrode active material for lithium ion secondary batteries. Examples of negative electrode active materials include metal Li; metals or semimetals such as Si and Sn; metal oxides or semimetal oxides such as Si oxide, Ti oxide, and Sn oxide; titanium-containing oxides such as Li ₄ Ti ₅ O ₁₂ , LiTiO _{2 , and} TiNb ₂ O ₇ ; polyphosphate compounds; silicon carbide; carbon materials such as graphite and non-graphitic carbon (easily graphitizable carbon or non-graphitizable carbon). Among these materials, graphite and non-graphitic carbon are preferred. In the negative electrode active material layer, one of these materials may be used alone, or two or more may be mixed and used.

"Graphite" refers to a carbon material in which the average lattice spacing (d ₀₀₂ ) of the (002) plane, as determined by X-ray diffraction before charge/discharge or in a discharged state, is 0.33 nm or more and less than 0.34 nm. Examples of graphite include natural graphite and artificial graphite. Artificial graphite is preferred from the viewpoint of being able to obtain a material with stable physical properties.

"Non-graphitic carbon" refers to a carbon material in which the average lattice spacing (d ₀₀₂ ) of the (002) plane, as determined by X-ray diffraction before charge/discharge or in a discharged state, is 0.34 nm or more and 0.42 nm or less. Examples of non-graphitic carbon include non-graphitizable carbon and graphitizable carbon. Examples of non-graphitic carbon include resin-derived materials, petroleum pitch or petroleum pitch-derived materials, petroleum coke or petroleum coke-derived materials, plant-derived materials, and alcohol-derived materials.

Here, "discharged state" refers to a state in which the open circuit voltage of a single-electrode battery using a negative electrode containing a carbon material as the negative electrode active material as the working electrode and metallic Li as the counter electrode is 0.7 V or higher. Because the potential of the metallic Li counter electrode in the open circuit state is approximately equal to the redox potential of Li, the open circuit voltage of the single-electrode battery is approximately equal to the potential of the negative electrode containing the carbon material relative to the redox potential of Li. In other words, an open circuit voltage of 0.7 V or higher in the single-electrode battery means that sufficient lithium ions capable of being absorbed and released during charging and discharging have been released from the carbon material, which is the negative electrode active material.

The term "non-graphitizable carbon" refers to a carbon material having the above d ₀₀₂ of 0.36 nm or more and 0.42 nm or less.

The term "easily graphitizable carbon" refers to a carbon material having the above d ₀₀₂ of 0.34 nm or more and less than 0.36 nm.

The lower limit of the content of the negative electrode active material in the negative electrode mixture is preferably 10% by mass, and more preferably 15% by mass. The upper limit of the content of the negative electrode active material is preferably 60% by mass, more preferably 70% by mass, even more preferably 80% by mass, even more preferably 90% by mass, and particularly preferably 95% by mass. By keeping the content of the negative electrode active material within the above range, the electrical capacity of the all-solid-state battery can be increased.

<Mixture or Complex>
The mixture is a mixture prepared by mixing the negative electrode active material and the composite solid electrolyte by mechanical milling, etc. For example, the mixture of the negative electrode active material and the composite solid electrolyte can be obtained by mixing particulate negative electrode active material and particulate composite solid electrolyte.
Examples of the composite include a composite in which the negative electrode active material and the composite solid electrolyte are chemically or physically bonded, a composite in which the negative electrode active material and the composite solid electrolyte are mechanically combined, etc. The composite is one in which the negative electrode active material and the composite solid electrolyte exist within a single particle, and examples of the composite include one in which the negative electrode active material and the composite solid electrolyte form an aggregated state, and one in which the composite solid electrolyte-containing coating is formed on at least a portion of the surface of the negative electrode active material.
The mixture or composite may contain a solid electrolyte other than the composite solid electrolyte.
When the negative electrode active material contained in the negative electrode mixture and the composite solid electrolyte form a mixture or a composite, the reduction resistance of the composite solid electrolyte can be improved while maintaining high ionic conductivity, and therefore, the effect of suppressing a decrease in coulombic efficiency during charge-discharge cycles is excellent.

When the negative electrode mixture contains the composite solid electrolyte, the lower limit of the content of the composite solid electrolyte in the negative electrode mixture may be 5% by mass, and preferably 10% by mass. The upper limit of the content of the composite solid electrolyte in the negative electrode mixture is preferably 90% by mass, more preferably 85% by mass, even more preferably 80% by mass, and particularly preferably 75% by mass. By setting the content of the composite solid electrolyte in the negative electrode mixture within this range, the effect of suppressing the decrease in coulombic efficiency during the charge-discharge cycle of an all-solid-state battery can be further improved when the negative electrode contains the composite solid electrolyte.

The negative electrode mixture may contain a solid electrolyte other than the composite solid electrolyte. When the negative electrode mixture contains a solid electrolyte other than the composite solid electrolyte, the lower limit of the total content of solid electrolytes in the negative electrode mixture may be 5% by mass, and preferably 10% by mass. The upper limit of the total content of solid electrolytes in the negative electrode mixture is preferably 90% by mass, more preferably 85% by mass, even more preferably 80% by mass, and particularly preferably 75% by mass. By keeping the total content of solid electrolytes within the above range, the electrical capacity of the all-solid-state battery can be increased.

<Other optional ingredients>
The conductive agent is not particularly limited. Examples of such conductive agents include natural or artificial graphite, carbon black such as furnace black, acetylene black, and ketjen black, metals, and conductive ceramics. The conductive agent may be in the form of powder or fiber. The content of the conductive agent in the negative electrode mixture may be, for example, 0.5% by mass or more and 30% by mass or less. The negative electrode mixture may not contain a conductive agent.

The binder is not particularly limited. Examples of binders include thermoplastic resins such as fluororesins (polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), etc.), polyethylene, polypropylene, polyacrylic, and polyimide; elastomers such as ethylene-propylene-diene rubber (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), and fluororubber; and polysaccharide polymers.

The filler is not particularly limited. Examples of fillers include polyolefins such as polypropylene and polyethylene; inorganic oxides such as silicon dioxide, alumina, titanium dioxide, calcium oxide, strontium oxide, barium oxide, magnesium oxide, and aluminosilicates; hydroxides such as magnesium hydroxide, calcium hydroxide, and aluminum hydroxide; carbonates such as calcium carbonate; sparingly soluble ionic crystals such as calcium fluoride, barium fluoride, and barium sulfate; nitrides such as aluminum nitride and silicon nitride; mineral-derived substances such as talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, and mica; and synthetic versions of these.

The lower limit of the average thickness of the negative electrode mixture layer 5 is preferably 30 μm, more preferably 60 μm. The upper limit of the average thickness of the negative electrode mixture layer 5 is preferably 1000 μm, more preferably 500 μm, and even more preferably 200 μm. By setting the average thickness of the negative electrode mixture layer 5 to the above lower limit or more, an all-solid-state battery with a high energy density can be obtained. By setting the average thickness of the negative electrode mixture layer 5 to the above upper limit or less, an all-solid-state battery with excellent high-rate discharge performance and a negative electrode with a high active material utilization rate can be obtained.

(middle class)
The intermediate layer is a coating layer on the surface of the negative electrode substrate 4, and contains conductive particles such as carbon particles to reduce the contact resistance between the negative electrode substrate 4 and the negative electrode mixture layer 5. The configuration of the intermediate layer is not particularly limited, and the intermediate layer can be formed, for example, from a composition containing a resin binder and conductive particles.

[Solid electrolyte layer]
The solid electrolyte layer 3 contains an electrolyte for the solid electrolyte layer. In addition to the above-mentioned composite solid electrolyte, examples of the electrolyte for the solid electrolyte layer include oxide-based solid electrolytes, other sulfide solid electrolytes, dry polymer electrolytes, gel polymer electrolytes, and pseudo-solid electrolytes. Among these, sulfide solid electrolytes are preferred, and the composite solid electrolyte is more preferred, from the viewpoints of good ionic conductivity and ease of interface formation. By including the composite solid electrolyte in the solid electrolyte layer 3, the reduction resistance of the composite solid electrolyte can be improved while maintaining high ionic conductivity, resulting in an excellent effect of suppressing a decrease in Coulomb efficiency during charge-discharge cycles.

The electrolyte for the solid electrolyte layer may have a crystalline structure or may be amorphous without a crystalline structure. An oxide such as _Li3PO4 , a halogen, a halogen compound, or _the like may be added to the electrolyte for the solid electrolyte layer.

The lower limit of the average thickness of the solid electrolyte layer 3 is preferably 1 μm, more preferably 3 μm. The upper limit of the average thickness of the solid electrolyte layer 3 is preferably 50 μm, more preferably 20 μm. By making the average thickness of the solid electrolyte layer 3 equal to or greater than the above lower limit, it is possible to reliably insulate the positive electrode and negative electrode. By making the average thickness of the solid electrolyte layer 3 equal to or less than the above upper limit, it is possible to increase the energy density of the all-solid-state battery.

[Positive electrode]
The positive electrode 2 includes a positive electrode substrate 7 and a positive electrode mixture layer 6 laminated on the surface of the positive electrode substrate 7. Similar to the negative electrode 1, the positive electrode 2 may have an intermediate layer between the positive electrode substrate 7 and the positive electrode mixture layer 6. This intermediate layer may have the same configuration as the intermediate layer of the negative electrode 1.

(Positive electrode substrate)
The positive electrode substrate 7 can have the same configuration as the negative electrode substrate 4. The material of the positive electrode substrate 7 is not limited as long as it is a conductor. For example, it can be one or more metals selected from the group consisting of copper, aluminum, titanium, nickel, tantalum, niobium, hafnium, zirconium, zinc, tungsten, bismuth, antimony, gold, silver, iron, platinum, chromium, tin, indium, alloys containing one or more of these metals, and stainless steel alloys.

The lower limit of the average thickness of the positive electrode substrate 7 is preferably 3 μm, and more preferably 5 μm. The upper limit of the average thickness of the positive electrode substrate 7 is preferably 200 μm, more preferably 100 μm, and even more preferably 50 μm. By making the average thickness of the positive electrode substrate 7 equal to or greater than the above lower limit, the strength of the positive electrode substrate 7 can be sufficiently increased, allowing for a satisfactory formation of the positive electrode 2. By making the average thickness of the positive electrode substrate 7 equal to or less than the above upper limit, sufficient volume can be secured for the other components.

(Positive electrode mixture layer)
The positive electrode mixture layer 6 can be formed from a so-called positive electrode mixture containing a positive electrode active material. The positive electrode mixture may contain a mixture or composite containing a positive electrode active material and the sulfide solid electrolyte. The positive electrode mixture may contain the sulfide solid electrolyte that does not form a mixture or composite with the positive electrode active material. The sulfide solid electrolyte may be the composite solid electrolyte. Like the negative electrode mixture, the positive electrode mixture that forms the positive electrode mixture layer 6 may contain optional components such as a solid electrolyte other than the sulfide solid electrolyte, a conductive agent, a binder, a filler, etc., as necessary.

<Cathode active material>
The positive electrode active material contained in the positive electrode mixture layer 6 can be a known material commonly used in all-solid-state batteries. As the positive electrode active material, a material capable of absorbing and releasing lithium ions is typically used. Examples of the positive electrode active material include lithium transition metal composite oxides having an α-NaFeO ₂ crystal structure, lithium transition metal composite oxides having a spinel crystal structure, polyanion compounds, chalcogen compounds, and sulfur. Examples of lithium transition metal composite oxides having α-NaFeO type ₂ crystal structure include Li[Li _x Ni _1-x ]O ₂ (0≦x<0.5), Li[Li _x Ni _γ Co _(1-x-γ) ]O ₂ (0≦x<0.5, 0<γ<1), Li[Li _x Co _(1-x) ]O ₂ (0≦x<0.5), Li[Li _x Ni _γ Mn _(1-x-γ) ]O ₂ (0≦x<0.5, 0<γ<1), Li[Li _x Ni _γ Mn _β Co _(1-x-γ-β) ]O ₂ (0≦x<0.5, 0<γ, 0<β, 0.5<γ+β<1), Li[Li _x Ni _γ Co _β Al _{(1-x-γ-β) )} ]O ₂ (0≦x<0.5, 0<γ, 0<β, 0.5<γ+β<1), etc. Examples of lithium transition metal composite oxides having a spinel crystal structure include Li _x Mn ₂ O ₄ and Li _x Ni _γ Mn _(2-γ) O ₄ , etc. Examples of polyanion compounds include LiFePO ₄ , LiMnPO ₄ , LiNiPO ₄ , LiCoPO ₄ , Li ₃ V ₂ (PO ₄ ) ₃ , Li ₂ MnSiO ₄ , and Li ₂ CoPO ₄ F, etc. Examples of chalcogen compounds include titanium disulfide, molybdenum disulfide, and molybdenum dioxide. Atoms or polyanions in these materials may be partially substituted with atoms or anion species of other elements. The surfaces of these materials may be coated with other materials. In the positive electrode active material layer, one of these materials may be used alone, or two or more may be mixed and used. In the positive electrode mixture layer 6, one of these compounds may be used alone, or two or more may be mixed and used.

In addition, as the positive electrode active material, lithium alloys such as Li-Al, Li-In, Li-Sn, Li-Pb, Li-Bi, Li-Ga, Li-Sr, Li-Si, Li-Zn, Li-Cd, Li-Ca, and Li-Ba, and materials other than the compounds represented by the above general formula, such as MnO ₂ , FeO ₂ , TiO ₂ , V ₂ O ₅ , V ₆ O ₁₃ , and TiS ₂ , which have a reaction potential more noble than that of the negative electrode material, can be used.

The lower limit of the content of the positive electrode active material in the positive electrode mixture is preferably 10% by mass, and more preferably 15% by mass. The upper limit of the content of the positive electrode active material is preferably 60% by mass, more preferably 70% by mass, even more preferably 80% by mass, even more preferably 90% by mass, and particularly preferably 95% by mass. By keeping the content of the positive electrode active material within the above range, the electrical capacity of the all-solid-state battery can be increased.

<Mixture or Complex>
The mixture is a mixture prepared by mixing the positive electrode active material and the sulfide solid electrolyte, etc., by mechanical milling, etc. For example, the mixture of the positive electrode active material and the sulfide solid electrolyte, etc., can be obtained by mixing a particulate positive electrode active material and a particulate sulfide solid electrolyte, etc.
Examples of the composite include a composite having a chemical or physical bond between the positive electrode active material and the sulfide solid electrolyte, etc., and a composite obtained by mechanically combining the positive electrode active material and the sulfide solid electrolyte, etc. The composite is one in which the positive electrode active material and the sulfide solid electrolyte, etc. are present within a single particle, and examples include one in which the positive electrode active material and the sulfide solid electrolyte, etc. form an aggregated state, and one in which a coating containing the sulfide solid electrolyte, etc. is formed on at least a portion of the surface of the positive electrode active material.

When the positive electrode mixture contains a solid electrolyte, the lower limit of the solid electrolyte content may be 5% by mass, and preferably 10% by mass. The upper limit of the solid electrolyte content in the positive electrode mixture is preferably 90% by mass, more preferably 85% by mass, even more preferably 80% by mass, and particularly preferably 75% by mass. By keeping the solid electrolyte content within the above range, the electrical capacity of the all-solid-state battery can be increased.

The lower limit of the average thickness of the positive electrode mixture layer 6 is preferably 30 μm, more preferably 60 μm. The upper limit of the average thickness of the positive electrode mixture layer 6 is preferably 1000 μm, more preferably 500 μm, and even more preferably 200 μm. By setting the average thickness of the positive electrode mixture layer 6 to the above lower limit or more, an all-solid-state battery with a high energy density can be obtained. By setting the average thickness of the positive electrode mixture layer 6 to the above upper limit or less, an all-solid-state battery with excellent high-rate discharge performance and a positive electrode with a high active material utilization rate can be obtained.

<Method of manufacturing composite solid electrolyte>
The method for producing the composite solid electrolyte includes mixing a sulfide solid electrolyte with an additive, which is the sulfur-based cyclic compound having an S═O bond, lithium nitrate, or a combination thereof.

Examples of methods for producing the above-mentioned composite solid electrolyte include (1) a method in which a sulfide solid electrolyte is first synthesized, and then an additive is mixed therein to synthesize the composite solid electrolyte; and (2) a method in which the starting material for the sulfide solid electrolyte is mixed with an additive to produce a composite solid electrolyte precursor containing the additive, and then the composite solid electrolyte is synthesized from the composite solid electrolyte precursor.

(1) Method of synthesizing a composite solid electrolyte containing an additive after synthesizing a sulfide solid electrolyte In this method, a composite solid electrolyte synthesis step is carried out after a sulfide solid electrolyte synthesis step.

(Sulfide solid electrolyte synthesis process)
In this step, for example, the sulfide solid electrolyte is produced by the following procedure.
Starting materials for the sulfide solid electrolyte ( _Li2S , _P2S5 , _etc. ) are mixed in a predetermined molar ratio in a mortar or the like, and then the sulfide solid electrolyte is produced. Methods for producing the sulfide solid electrolyte include, for example, mechanical milling and melt quenching.
In the case of producing a sulfide solid electrolyte glass ceramic, a sulfide solid electrolyte is produced and then heat-treated at a temperature equal to or higher than the crystallization temperature, whereby the sulfide solid electrolyte glass ceramic can be produced. The crystallization temperature can be determined by measurement using a differential scanning calorimeter (DSC).

(Composite solid electrolyte synthesis process)
In this step, the sulfide solid electrolyte is mixed with an additive by, for example, mechanical milling, etc., to synthesize a composite solid electrolyte. The preferred range of the content of the additive in the composite solid electrolyte is as described above.

(2) Method of synthesizing a composite solid electrolyte after mixing a starting material of a sulfide solid electrolyte with an additive: In this method, a starting material of a sulfide solid electrolyte (such as _Li2S or _{P2S5 )} is mixed with an additive to prepare a composite solid electrolyte precursor containing the additive. The composite solid electrolyte can then be prepared by, for example, mechanical milling, melt quenching, or heat treatment.

This method for producing a composite solid electrolyte involves mixing a sulfide solid electrolyte with the additive to produce a composite solid electrolyte. This makes it possible to produce a composite solid electrolyte that is reduction-resistant and has an excellent effect of suppressing a decrease in coulombic efficiency during the charge-discharge cycle of an all-solid-state battery.

<Method of manufacturing all-solid-state battery>
The method for producing an all-solid-state battery includes fabricating at least one of an anode and an electrolyte layer using the composite solid electrolyte or a composite solid electrolyte obtained by the method for producing the composite solid electrolyte. The method for producing an all-solid-state battery may also include other steps, such as a step of preparing an anode mixture, a step of preparing an electrolyte for the solid electrolyte layer, a step of preparing a cathode mixture, and a step of stacking the anode, the solid electrolyte layer, and the positive electrode. Details of the composite solid electrolyte and the composite solid electrolyte obtained by the method for producing the composite solid electrolyte are as described above.

(Negative electrode mixture preparation process)
In this step, an anode mixture for forming an anode is prepared. When the anode mixture contains a mixture or composite including an anode active material and the composite solid electrolyte, this step includes, for example, mixing the anode active material and the composite solid electrolyte using a mechanical milling method or the like to prepare a mixture or composite of the anode active material and the composite solid electrolyte. Alternatively, the anode mixture may be prepared without using the mechanical milling method. In this case, for example, the method may include preparing an anode mixture paste containing an anode active material, a solid electrolyte, a conductive agent, etc., and applying the paste to an anode substrate. When the anode mixture contains the composite solid electrolyte, the composite solid electrolyte or a composite solid electrolyte obtained by the method for producing the composite solid electrolyte is used.

(Solid electrolyte layer production process)
In this process, a solid electrolyte layer is produced. In this process, the solid electrolyte layer can be obtained by processing a predetermined material for the solid electrolyte layer electrolyte using a mechanical milling method. The solid electrolyte layer electrolyte may also be produced by heating the predetermined material for the solid electrolyte layer electrolyte above its melting temperature using a melt quenching method, melting and mixing the two at a predetermined ratio, and then quenching. Other methods for synthesizing the solid electrolyte layer electrolyte include, for example, a solid-phase method in which the solid electrolyte is sealed under reduced pressure and fired, a liquid-phase method such as solution deposition, a gas-phase method (PLD), and a method in which the solid electrolyte is fired in an argon atmosphere after mechanical milling. When the solid electrolyte layer electrolyte is the composite solid electrolyte, the composite solid electrolyte or a composite solid electrolyte obtained by the method for producing the composite solid electrolyte is used as the solid electrolyte layer electrolyte.

(Positive electrode mixture preparation process)
In this process, a cathode mixture for forming a cathode is prepared. The method for preparing the cathode mixture is not particularly limited and can be appropriately selected depending on the purpose. Examples include compression molding of a cathode active material, mechanical milling of a predetermined material for the cathode mixture, and sputtering using a target material for the cathode active material. When the cathode mixture contains a mixture or composite containing a cathode active material and a sulfide solid electrolyte, this process includes, for example, mixing the cathode active material and the sulfide solid electrolyte using a mechanical milling method or the like to prepare a mixture or composite of the cathode active material and the sulfide solid electrolyte. Similarly to the negative electrode mixture preparation process, the cathode mixture may also be prepared without using the mechanical milling method. In this case, for example, the process may include preparing a cathode mixture paste containing a cathode active material, a solid electrolyte, a conductive agent, etc., and applying the paste to a cathode substrate.

(Lamination process)
In this step, a negative electrode having a negative electrode substrate and a negative electrode mixture layer, a solid electrolyte layer, and a positive electrode having a positive electrode substrate and a positive electrode mixture layer are laminated. In this step, the negative electrode, the solid electrolyte layer, and the positive electrode may be laminated in this order or vice versa, and the order of lamination of the layers is not particularly important. The negative electrode is formed, for example, by pressure molding the negative electrode substrate and the negative electrode mixture, the solid electrolyte layer is formed, for example, by pressure molding an electrolyte for the solid electrolyte layer, and the positive electrode is formed, for example, by pressure molding the positive electrode substrate and the positive electrode mixture.

The negative electrode, solid electrolyte layer, and positive electrode may be laminated by pressure molding the negative electrode substrate, negative electrode mixture, electrolyte for the solid electrolyte layer, positive electrode substrate, and positive electrode mixture all at once. The positive electrode, negative electrode, or a layer thereof may be molded in advance, and then pressure molded together with the solid electrolyte layer to laminate them.

The method for manufacturing this all-solid-state battery involves fabricating at least one of the negative electrode and the electrolyte layer using the composite solid electrolyte or the composite solid electrolyte obtained by the method for manufacturing the composite solid electrolyte, thereby enabling the manufacture of an all-solid-state battery that is excellent at suppressing the decline in coulombic efficiency during charge-discharge cycles.

[Other embodiments]
The present invention is not limited to the above-described embodiment, and can be practiced in various forms with various modifications and improvements in addition to the above-described embodiment.

The all-solid-state battery according to the present invention may also include layers other than the negative electrode, positive electrode, and solid electrolyte layer, such as an intermediate layer or adhesive layer.

<Example>
The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

[Preparation of composite solid electrolyte]
Example 1
In a glove box with an argon atmosphere having a dew point of -50°C or less, Li ₂ S (99.98% by mass, manufactured by Aldrich) and P ₂ S ₅ (99% by mass, manufactured by Aldrich) were weighed to a molar ratio of 75:25, and then mixed in a mortar. This mixed sample was placed in a sealed zirconia pot. Milling was performed for 45 hours at an orbital rotation speed of 510 rpm using a planetary ball mill (manufactured by FRITSCH, model number Premium line P-7) to obtain 75Li ₂ S·25P ₂ S ₅ .

Next, _75Li2S · _25P2S5 and _lithium nitrate as an additive were weighed and mixed in a mass ratio of 90:10, and then mechanically milled using a planetary ball mill at an orbital rotation speed of 370 rpm for 2 hours to synthesize the composite solid electrolyte of Example 1.

Example 2
A composite solid electrolyte of Example 2 was synthesized in the same manner as in Example 1, except that the additive was changed to 1,3-propene sultone (PRS), which is a cyclic sulfonic acid ester.

(Comparative Example 1)
The 75Li ₂ S·25P ₂ S ₅ in Example 1 before mixing with the additive was used as Comparative Example 1.

(Comparative Example 2)
A composite solid electrolyte of Comparative Example 2 was synthesized in the same manner as in Example 1, except that the additive was changed to lithium iodide.

[Fabrication of Reduction Resistance Evaluation Cell]
120 mg of each of the solid electrolytes of Example 1, Example 2, Comparative Example 1, and Comparative Example 2 was inserted into a polycarbonate tube with an inner diameter of 10 mm, and then pressure-molded at 360 MPa. After releasing the pressure, a metal Li foil was attached to the counter electrode side, and a metal In foil was attached to the working electrode side, and then pressure-molded at 120 MPa to obtain pellets. These were inserted into a Hohsen HS cell to prepare a cell for evaluating reduction resistance. The pellets in each reduction resistance evaluation cell were pressurized to about 5 MPa by a spring in the HS cell.

[evaluation]
(Charge-discharge cycle test: Coulomb efficiency)
(1) Charge-Discharge Cycle Test Each reduction resistance evaluation cell was stored in a constant temperature bath at 50°C for 30 minutes, and then subjected to constant current and constant voltage charge-discharge at a current density of 0.1 mAhcm ^-1 for a charge-discharge time of 10 hours. The charge cut-off voltage for charge was 0.2 V. The discharge cut-off voltage for discharge was 1.1 V. A 30-minute pause was provided after each charge and discharge step. These charge and discharge steps constitute one cycle, and three cycles were repeated for Example 1, Example 2, and Comparative Example 1, and four cycles were repeated for Comparative Example 2. The charge, discharge, and pause were all performed in a constant temperature bath at 50°C.
(2) Coulombic efficiency For each reduction resistance evaluation cell in the charge-discharge cycle test, the percentage of the discharge capacity (Ah) in the first to fifth cycles relative to the amount of electricity (Ah) charged in the first to fifth cycles was calculated as the "Coulombic efficiency (%)" in the first to fifth cycles. The results are shown in Figure 2.

As shown in Figure 2, the composite solid electrolytes of Examples 1 and 2, which contained a sulfur-based cyclic compound having an S=O bond or lithium nitrate as an additive, were more effective in suppressing the decrease in coulombic efficiency during charge-discharge cycles than Comparative Example 1, which contained no additive, and Comparative Example 2, which contained lithium iodide as an additive.

These results demonstrate that the composite solid electrolyte according to one aspect of the present invention can suppress the decrease in coulombic efficiency during the charge-discharge cycle of an all-solid-state battery.

The composite solid electrolyte and all-solid-state battery according to the present invention are highly effective in suppressing the decline in coulombic efficiency during charge-discharge cycles, and are therefore suitable for use, for example, as all-solid-state batteries for HEVs and the solid electrolytes used therein.

1 Negative electrode 2 Positive electrode 3 Solid electrolyte layer 4 Negative electrode substrate 5 Negative electrode mixture layer 6 Positive electrode mixture layer 7 Positive electrode substrate 10 All-solid-state battery

Claims (13)

A sulfide solid electrolyte and an additive are included,
the additive is a sulfur-based cyclic compound having an S═O bond,
The composite solid electrolyte wherein the sulfur-based cyclic compound is 1,3-propene sultone
(However, this does not include the case where the sulfide solid electrolyte comprises (Li ₂ S) _l -(P ₂ S ₅ ) _m -(YX ₂ ) _n (Y is at least one selected from the group consisting of Ge, Si and Sn, X is at least one selected from the group consisting of S, Se and Te, l, m and n are each 0 or greater, and at least two of l, m and n are greater than 0), and is contained in an electrolyte solution containing a solvent and a lithium salt as a solvent-soluble precursor.) A sulfide solid electrolyte and an additive are included,
the additive is a sulfur-based cyclic compound having an S═O bond,
A composite solid electrolyte in which the content of the additive exceeds 5 mass %.
(However, this does not include the case where the sulfide solid electrolyte comprises (Li ₂ S) _l -(P ₂ S ₅ ) _m -(YX ₂ ) _n (Y is at least one selected from the group consisting of Ge, Si and Sn, X is at least one selected from the group consisting of S, Se and Te, l, m and n are each 0 or greater, and at least two of l, m and n are greater than 0), and is contained in an electrolyte solution containing a solvent and a lithium salt as a solvent-soluble precursor.) A sulfide solid electrolyte and an additive are included,
the additive is lithium nitrate,
A composite solid electrolyte having a content of the additive of more than 5 mass %. A sulfide solid electrolyte and an additive are included,
the additive is lithium nitrate,
Composite solid electrolyte for the negative electrode
(However, this does not include the case where the sulfide solid electrolyte comprises (Li ₂ S) _l -(P ₂ S ₅ ) _m -(YX ₂ ) _n (Y is at least one selected from the group consisting of Ge, Si and Sn, X is at least one selected from the group consisting of S, Se and Te, l, m and n are each 0 or greater, and at least two of l, m and n are greater than 0), and is contained in an electrolyte solution containing a solvent and a lithium salt as a solvent-soluble precursor.) The composite solid electrolyte according to any one of claims 1 to 4, wherein the content of the additive in the composite solid electrolyte is 20 mass% or less. The composite solid electrolyte according to claim 2, wherein the sulfur-based cyclic compound is a cyclic sulfonate ester. a negative electrode, a positive electrode, and an electrolyte layer interposed between the negative electrode and the positive electrode;
7. An all-solid-state battery, wherein the negative electrode, the electrolyte layer, or a combination thereof contains the composite solid electrolyte according to claim 1. mixing a sulfide solid electrolyte with an additive to prepare a composite solid electrolyte;
the additive is a sulfur-based cyclic compound having an S═O bond,
Method for producing a composite solid electrolyte in which the sulfur-based cyclic compound is 1,3-propene sultone
(However, this does not include the case where the sulfide solid electrolyte comprises (Li ₂ S) _l -(P ₂ S ₅ ) _m -(YX ₂ ) _n (Y is at least one selected from the group consisting of Ge, Si and Sn, X is at least one selected from the group consisting of S, Se and Te, l, m and n are each 0 or greater, and at least two of l, m and n are greater than 0), and is contained in an electrolyte solution containing a solvent and a lithium salt as a solvent-soluble precursor.) mixing a sulfide solid electrolyte with an additive to prepare a composite solid electrolyte;
the additive is a sulfur-based cyclic compound having an S═O bond,
A method for producing a composite solid electrolyte in which the content of the additive exceeds 5 mass %
(However, this does not include the case where the sulfide solid electrolyte comprises (Li ₂ S) _l -(P ₂ S ₅ ) _m -(YX ₂ ) _n (Y is at least one selected from the group consisting of Ge, Si and Sn, X is at least one selected from the group consisting of S, Se and Te, l, m and n are each 0 or greater, and at least two of l, m and n are greater than 0), and is contained in an electrolyte solution containing a solvent and a lithium salt as a solvent-soluble precursor.) mixing a sulfide solid electrolyte with an additive to prepare a composite solid electrolyte;
the additive is lithium nitrate,
A method for producing a composite solid electrolyte, wherein the content of the additive exceeds 5 mass %. mixing a sulfide solid electrolyte with an additive to prepare a composite solid electrolyte;
the additive is lithium nitrate,
A method for manufacturing a composite solid electrolyte for use as an anode
(However, this does not include the case where the sulfide solid electrolyte comprises (Li ₂ S) _l -(P ₂ S ₅ ) _m -(YX ₂ ) _n (Y is at least one selected from the group consisting of Ge, Si and Sn, X is at least one selected from the group consisting of S, Se and Te, l, m and n are each 0 or greater, and at least two of l, m and n are greater than 0), and is contained in an electrolyte solution containing a solvent and a lithium salt as a solvent-soluble precursor.) The method for producing a composite solid electrolyte according to any one of claims 8 to 11, wherein the content of the additive in the composite solid electrolyte is 20 mass% or less. 13. A method for producing an all-solid-state battery, comprising: producing at least one of a negative electrode and an electrolyte layer using the composite solid electrolyte according to any one of claims 1 to 6 or the composite solid electrolyte obtained by the method for producing a composite solid electrolyte according to any one of claims 8 to 12.