JP2011181495A - Inorganic electrolyte and lithium secondary battery using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ionic conductive inorganic solid electrolyte high in ionic conductivity, high in thermal-electrochemical stability, and suitable as a material for an electronic device, especially a lithium ion secondary battery; and to provide the lithium ion secondary battery high in reliability, using the electrolyte. <P>SOLUTION: The inorganic solid electrolyte containing lithium sulfide contains 1 mol% or less of aluminum compound to the raw material composition. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an inorganic electrolyte and its use. More specifically, a sulfide-based lithium ion conductive inorganic solid electrolyte that can be suitably used as a composite material with an electrolyte or electrode active material of an all-solid-state lithium ion battery, an electronic device using the same, an electricity storage material, a lithium secondary The present invention also relates to a material for a lithium primary battery.

In recent years, against the backdrop of growing interest in environmental issues, the shift from fossil fuels such as oil and coal to renewable energy such as wind and solar has been promoted. Is attracting attention. Among them, secondary batteries that can be repeatedly charged and discharged are used not only in electronic devices such as mobile phones and laptop computers, but also in various fields such as automobiles and airplanes. Research and development has been conducted with the aim of improving the performance of materials used in secondary batteries. In particular, a lithium-ion battery having a large capacity and a light weight is a secondary battery that is expected to expand further in the future, and is a battery that is most actively researched and developed.
However, most of the lithium secondary batteries currently used use lithium that is chemically or electrochemically highly reactive inside the battery, and in addition, electrolysis of flammable and flammable organic solvents is required. Used for liquid. Therefore, in actual use, there is a problem in reliability at high temperatures or in an overcharge / overdischarge state, and there is a danger of occurrence of a situation such as ignition or burst explosion in severe cases. As a result, at the present time, increasing the safety is a very important issue.
In particular, as a development of applications that make use of the high energy density of lithium secondary batteries, research on in-vehicle power sources such as power sources for hybrid vehicles requires higher energy density, and as a result, the reliability contained in the battery. Inhibitory substances are increased, and it is an even more important issue to secure further safety of the lithium secondary battery.

  In response to these technical demands, lithium ion conductive solid electrolytes using polymer materials or inorganic materials instead of organic electrolytes using flammable and flammable organic solvents used in conventional batteries. Research on materials and research and development of all-solid-state lithium secondary batteries using the materials have been active. In particular, lithium-ion conductive solid electrolytes using inorganic materials are not only flammable and flammable, but are also researched because of their high heat resistance and electrochemical stability. Solid electrolytes with comparable ionic conductivity have also been obtained. In particular, as lithium ion conductive solid electrolytes, researches on sulfide-based lithium ion conductors containing sulfur atoms in their constituent materials and all-solid lithium secondary batteries using the same have been active. It is known that the sulfide-based lithium ion conductor includes an amorphous system, a crystalline system, and a mixture thereof. Furthermore, systems containing atoms such as silicon or germanium and phosphorus are known as these materials.

Among them, when a battery is configured using an electrolyte containing atoms such as silicon and germanium, the potential of the negative electrode is polarized to the vicinity of the reversible deposition potential of lithium during battery charging, and silicon and germanium in the electrolyte are reduced. There is a problem in negative electrode battery performance. Therefore, an electrolyte that does not contain these atoms, for example, a Li ₂ S—P ₂ S ₅ electrolyte, has attracted attention.
However, when synthesizing this electrolyte, the vapor pressure of P ₂ S ₅ (phosphorus sulfide), which is one of the constituent materials, is high, so that the ampule tube filled with the starting material is sealed in a vacuum, and this is sealed at 900 ° C. It was necessary to synthesize lithium ion conductive glass of this system by heating and melting at a close temperature and then rapidly cooling with liquid nitrogen. That is, in the synthesis of this material, it is difficult to synthesize at normal pressure, and the ionic conductivity of the synthesized glassy electrolyte is about 0.1 mS / cm, which is low for application to a practical battery. So much research was not progressing.

  However, in recent years, as a new synthesis method of this material, it has been found that lithium ion conductivity appears by mixing starting materials for synthesis at a high speed for a long time with a planetary ball mill. As a result of the disclosure, research on this material and examination of application to an all-solid lithium secondary battery have been activated rapidly (Patent Document 1). Today, as a result of various studies on the crystal growth state of this material, an ion conductive electrolyte of about 1 to 5 mS / cm can be synthesized (Patent Document 2). However, this material has both amorphous and crystalline materials, and it is impossible to synthesize a material with a constant abundance ratio, so that the battery performance when a battery is configured using this material is made constant. It has the problem that things are difficult.

On the other hand, glassy solid electrolytes are attracting attention because they have no anisotropy in their conductivity and can exhibit stable battery characteristics in their bonding properties with electrode active materials. Non-Patent Document 1 discloses a lithium sulfide / phosphorus sulfide / potassium iodide-based solid electrolyte in which ion conductivity is improved by adding potassium iodide. However, since iodide ions are electrochemically unstable and undergo oxidation and reduction in a potential region nobler than about 2.7 V with respect to the redox potential of lithium, the oxidation-reduction reaction is carried out at a potential nobler than this potential. It becomes difficult to use materials such as the electrode active materials shown, such as lithium cobaltate and lithium manganate.
In addition, Patent Documents 3, 4, and 5 and Non-Patent Documents 2 and 3 disclose techniques for improving ion conductivity by selecting an electrolyte composition. However, all of them are electrochemically unstable solid electrolytes whose ion conductivity is as low as about 0.1 mS / cm or reactions at the interface between the positive electrode and the negative electrode occur, and are not yet practically usable. It can be said.

  Thus, as a lithium ion conductive electrolyte for constructing a practical battery, an inorganic solid electrolyte having high ion conductivity and stable characteristics, preferably a glassy electrolyte having no anisotropy in the lithium ion conduction path However, since the bondability with the electrode active material is excellent, development of a material having practical performance is desired.

Japanese Patent Laid-Open No. 11-134937 JP 2002-109955 A JP-A-5-310418 Chinese Patent No. 101013753 JP 2009-064645 A

Solid State Ionics 1984, Vol. 5, P. 663-666 Khimiya v interesakh usutichivogo razvitiya 2007, Vol. 15 No. 2, P.I. 219-223 Journal of Material Science 2004, Vol. 39No. 16-17, P.I. 5125-27

  The present invention has been made in view of the above-described situation, and not only has high ionic conductivity, but also a solid electrolyte having high thermal and electrochemical stability, and a reliable lithium secondary battery using the same. An object is to provide a secondary battery.

To provide higher ion conductivity, a new unit network structure that can form counter ions with lithium ions, which are mobile ions, is constructed, thereby increasing the mobile lithium ions and increasing the ion conductivity. It can be improved. As a material having a possibility of forming a counter ion with a new movable lithium ion, a compound containing an element selected from the group of sulfur, boron, aluminum, gallium, silicon, germanium, phosphorus, arsenic and the like may be used. Can be mentioned. One or more compounds containing these elements are mixed with a matrix-structured compound responsible for lithium ion conduction and thermally reacted to synthesize a network structure of lithium ions and a new counter ion. Thereby, the number of movable lithium ions increases in the synthesized compound, and improvement in lithium ion conductivity is expected.
Among them, the present invention is for the development of solid electrolytes that tend to fall into complicated compositions and manufacturing procedures, particularly for improving lithium ion conductivity, in order to improve electrolyte performance. The inventors have found that addition to a raw material leads to a significant improvement in ionic conductivity, and have led to the present invention.

That is, when forming a new network structure that becomes counter ions with lithium ions, a sulfide ion conductor as a raw material, for example, a well-known amorphous phosphorus sulfide lithium ion conductor, amorphous silicon sulfide Using lithium ion conductor, etc., as a new network forming material, an aluminum compound is added and thermally reacted, so that not only the conventional lithium ion conductor network but also aluminum is newly incorporated into the network As a result, the concentration of lithium ions to be modified as a whole is increased, and the lithium ion conductivity is enhanced.
More specifically, in the lithium ion conductive solid electrolyte raw material comprising lithium sulfide, a lithium ion conductive solid electrolyte is characterized in that it contains 1 mol% or less of an aluminum compound with respect to the raw material composition. .

  In the lithium ion conductive solid electrolyte of the present invention, the aluminum compound to be added is uniformly incorporated into the amorphous network in the base lithium ion conductive solid electrolyte, and is newly formed in addition to the conventional network. Therefore, as the number of mobile lithium ions modified by these networks increases, lithium ion conductivity can be improved, free sulfur atoms are reduced, and sulfur-based lithium ion conductive solid electrolytes generally generate sulfur. This also reduces the redox reaction (about 2.5 V (VS. Li)), and allows the battery reaction of the high-voltage positive electrode active material to proceed advantageously.

  Furthermore, the ionic conductivity can be improved by crystal growth of the synthesized amorphous lithium ion conductive solid electrolyte with excellent ionic conductivity. That is, these lithium ion conductive solid electrolytes not only exhibit excellent ion conductivity at room temperature, but also exhibit good ion conductivity even in a low temperature region below room temperature, and also have excellent voltage resistance. It is a battery material that can be suitably used for lithium ion conductive solid electrolytes and electrode-forming composites for batteries such as ion batteries. Naturally, it can be used to configure and provide all-solid lithium secondary batteries And extremely increase industrial value.

Diagram showing the relationship of the additive amount and the ion conductivity of _Al 2 _{S 3} in Li ₂ S / SiS ₂ solid electrolyte Diagram showing the relationship of the additive amount and the ion conductivity of _Al 2 _{S 3} in Li _{2 S /} P ₂ S ₅ solid electrolyte Sectional drawing of the all-solid-state lithium secondary battery using the solid electrolyte obtained by this invention Discharge characteristics of an all-solid lithium secondary battery using the solid electrolyte obtained in the present invention

  The inorganic solid electrolyte of the present invention essentially contains lithium sulfide as a raw material. By including lithium sulfide, an ion conductive solid electrolyte having high ion conductivity and excellent voltage resistance can be obtained. Lithium sulfide contains 10 mol% or more of the entire raw material as 100 mol%. Preferably it is 30 mol% or more, More preferably, it is 45 mol% or more, More preferably, it is 55 mol% or more.

The inorganic solid electrolyte of the present invention is characterized in that the aluminum compound is contained in the range of 1 × 10 ⁻⁶ mol% to 1 mol% with respect to the entire raw material of the sulfide-based lithium ion conductive solid electrolyte. Within this range, a lithium ion conductive solid electrolyte having high ion conductivity and excellent voltage resistance can be obtained. At this time, if an aluminum compound is not included, an inorganic solid electrolyte having high ion conductivity cannot be obtained. Moreover, when the amount exceeding 1 mol% is contained, the ion conductivity is lowered, and the characteristics suitable as a lithium battery material cannot be exhibited.

The addition amount of the aluminum compound to be used may be appropriately adjusted according to the desired characteristics,
The range is preferably 1 × 10 ⁻⁶ mol% to 1 mol%, more preferably 1 × 10 ⁻³ mol% to 0.9 mol%, and still more preferably 1 × 10 ⁻² mol% to 0.8 mol. % Or less.

The aluminum compound used in the present invention is not particularly limited as long as it can react with the sulfide-based lithium ion conductive solid electrolyte raw material. In addition to aluminum oxide and aluminum chalcogenide that are expected to react smoothly, phosphoric acid, sulfuric acid, etc. Mineral oxides and halides, lithium aluminum hydride (LiAlH ₄ ), aluminum alkoxides, and the like, among which aluminum oxide and aluminum chalcogenide are preferable. More preferred are aluminum oxide and aluminum sulfide. Examples of aluminum oxide include α-Al ₂ O ₃ and γ-Al ₂ O ₃ , and examples of aluminum sulfide include Al ₂ S ₃ . Most preferred is Al ₂ S ₃ .

  In the production of the sulfide-based lithium ion conductive solid electrolyte of the present invention, as the sulfide-based lithium ion conductive solid electrolyte raw material used, zinc, boron, gallium, indium, silicon, germanium, tin, phosphorus, arsenic, antimony, etc. A lithium ion conductive solid electrolyte material containing a compound can be used as a raw material. Among these, compounds of zinc, boron, silicon, germanium, tin, and phosphorus are preferable, and compounds of boron, silicon, germanium, and phosphorus are particularly preferable.

When these compounds are used, they are not particularly limited as long as they can react with the sulfide-based lithium ion conductive solid electrolyte raw material, as in the case of aluminum compounds, but oxides, chalcogenides, mineral salts, hydrogens that are expected to have a smooth reaction are used. Compound, halide, alkoxide compound and the like. Of these, oxides and chalcogenides are preferable. More preferred are oxides and sulfides. Specifically, B ₂ O ₃ , B ₂ S ₃ , SiO ₂ , SiS ₂ , GeO ₂ , GeS ₂ , P ₂ O ₅ , P ₄ O ₆ , P ₄ O ₈ , P ₄ O ₁₀ , P ₂ S ₅ , P ₄ S ₃ , P ₄ S ₅ , P ₄ S ₇ , and P ₄ S ₁₀ .

  In the present invention, sulfide is most preferably used, and preferably contains at least one compound selected from the group consisting of phosphorus sulfide, silicon sulfide, germanium sulfide, and boron sulfide. More preferred are silicon sulfide and phosphorus sulfide.

  The said compound contains 5-90 mol% by making the whole raw material used when manufacturing a sulfide type lithium ion conductive solid electrolyte into 100 mol%. Preferably, it is 10-70 mol%, More preferably, it is 15-50 mol%. Within the above range, a sulfide-based lithium ion conductive solid electrolyte having high ion conductivity and excellent voltage resistance can be obtained. The above compounds may be used alone or in combination. When mixing two or more, it is made for the sum total of the addition amount of the said compound to enter into said range. Moreover, the sum total of the said compound, lithium sulfide, and an aluminum compound does not exceed 100 mol%.

  The crystalline state of the sulfide-based lithium ion conductive solid electrolyte of the present invention is not particularly limited, but in the case of a sulfide-based lithium ion conductive solid electrolyte having the same level of lithium ion conductivity, it may be in a glass state. preferable. This is because if the crystal phase remains, the crystal grain boundary becomes resistance to ion conduction, and the characteristics are difficult to stabilize due to the influence of the crystallization rate and the crystal diameter, so vitrification (amorphization) occurs. Thus, stable characteristics can be exhibited. On the other hand, in order to improve lithium ion conductivity, it is an effective method to crystallize a synthesized glassy compound, and if a crystal phase exhibiting good ion conductivity can be more selectively grown. Thus, it is possible to exhibit excellent lithium ion conductivity, and as a result, the performance of the all-solid lithium secondary battery can be improved.

In producing the sulfide-based lithium ion conductive solid electrolyte of the present invention, since lithium sulfide is reactive with oxygen and water, the reaction is preferably performed in an inert dry gas atmosphere such as nitrogen or argon or in a vacuum. . As the reaction method, a known method for synthesizing a sulfide-based lithium ion conductive solid electrolyte can be adopted, but the following method is preferable.
(1) Method of rapidly cooling the melt (2) Method of performing a mechanochemical reaction (3) Method of firing at 500 ° C. or less in an inert gas or vacuum (4) Method of repeating pulverization / pelletization / firing of the raw material mixture Etc.
When the solid phase reaction described in (2) to (4) is performed, the raw material is pulverized to reduce the particle size to 50 μm or less, preferably 30 μm, more preferably 10 μm or less and uniformly mixed before the reaction, This is preferable because the reaction time is shortened and fluctuations in characteristics of the obtained sulfide-based lithium ion conductive solid electrolyte are reduced.

  For the production of an amorphous glassy inorganic solid electrolyte, the methods (1) and (2) are preferred. (1) includes a method of easily obtaining a glassy inorganic solid electrolyte by flowing a raw material mixture melted at around 1000 ° C. into liquid nitrogen or twin cooling rolls. Regarding (2), there is a method of obtaining a glassy inorganic solid electrolyte without applying a high temperature by using a high shear pulverizing and mixing apparatus such as a ball mill.

  The all solid primary and secondary batteries of the present invention are mainly composed of a positive electrode, an electrolyte, and a negative electrode. As the positive electrode in the secondary battery, a positive electrode active material, a sulfide-based lithium ion conductive solid electrolyte, and as required It consists of a positive electrode mixture composition containing additives, such as a conductive support agent and a binder. The negative electrode comprises a negative electrode active material, and, if necessary, a negative electrode mixture composition containing additives such as a sulfide-based lithium ion conductive solid electrolyte, a conductive additive, and a binder.

  Examples of the positive electrode active material include sulfur, lithium manganate, lithium cobaltate, lithium nickelate, manganese-cobalt composite oxide positive electrode active material, nickel-manganese-cobalt composite oxide positive electrode active material, vanadium pentoxide, and vanadium. Lithium acid, lithium salt of olivine-type iron phosphate, polyacetylene, polypyrene, polyaniline, polyphenylene, polyphenylene sulfide, polyphenylene oxide, polypyrrole, polyfuran, polyazulene, and the like can be used.

  Among these, lithium manganate, lithium cobaltate, lithium nickelate, manganese-cobalt composite oxide-based positive electrode active materials, nickel-manganese-cobalt composite oxide-based positive electrode actives currently used as positive electrodes for lithium secondary batteries In addition to substances and the like, sulfur and lithium salts of olivine-type iron phosphate are preferable from the viewpoints of safety, stability against overcharge, and production cost. From the viewpoint of the storage capacity, sulfur is more preferable.

  As the conductive aid, conductive carbon is mainly used. Examples of the conductive carbon include carbon black such as ketjen black and acetylene black, fiber-like carbon, graphite, and graphite. Among these, ketjen black, acetylene black, graphite and the like are preferable.

  The positive electrode mixture composition can form a positive electrode mixture without using a new additive due to the binder ability of the sulfide-based lithium ion conductive solid electrolyte, but further uses additives such as a binder and a dispersant. It is also possible to do. The additive is not particularly limited, and various dispersants such as anionic, nonionic or cationic surfactants, polymer dispersants, and rubber components having binding properties, poly (meth) acrylic acid Etc. can be used. A more stable conductivity of the positive electrode film can be achieved by promoting the formation of fine particles of the positive electrode active material and the conductive auxiliary agent and improving the dispersibility.

  When using additives other than sulfide type lithium ion conductive solid electrolyte for a positive mix composition, it is preferable that the content is 5-20 mass% with respect to 100 mass% of conductive support agents. When the content of the dispersant is in such a range, the positive electrode active material and the conductive additive can be sufficiently uniformly dispersed. More preferably, it is 6 to 15% by mass with respect to 100% by mass of the conductive additive.

  As the negative electrode active material, those generally used as the negative electrode active material can be used. Carbon, natural graphite, lithium metal, and Al, Si, Ge, obtained by firing a polymer, organic matter, pitch, and the like. At least one selected from Sn, Pb, In, Zn and Ti, or a lithium alloy containing each element, an oxide containing each element, a material capable of reversibly occluding and releasing lithium such as lithium titanate, etc. Can be used.

  When a binder is used in the negative electrode mixture composition, the negative electrode mixture can be formed without using a new additive due to the binder ability of the sulfide-based lithium ion conductive solid electrolyte. It is also possible to use additives such as The additive is not particularly limited, and various dispersants such as anionic, nonionic or cationic surfactants, polymer dispersants, and rubber components having binding properties, poly (meth) acrylic acid Etc. can be used. A more stable conductivity of the negative electrode can be achieved by promoting the atomization of the negative electrode and the conductive additive and improving the dispersibility by the dispersant.

  The present invention will be described in more detail with reference to the following examples. However, the present invention is not limited to these examples. Unless otherwise specified, “part” means “part by weight” and “%” means “mass%”.

In order to prevent the influence of oxygen and moisture, operations such as weighing and mixing of raw materials were performed in a glove box in which the atmosphere was controlled with an inert dry gas and the dew point was controlled to −50 ° C. or lower. In addition, when taking out from the glove box during production or measurement, it was taken out in a sealed state.
The measurement was performed under the following conditions.

[Pellet making]
140 mg of an inorganic solid electrolyte that was sufficiently ground in a mortar was weighed into a mold having an inner diameter of 10 mm, uniformly filled, and then subjected to a press machine to press-mold at 5 t / cm ² .
[Ionic conductivity]
The prepared pellet was inserted into an insulating alumina jig, sandwiched between SUS electrodes, and measured by the complex impedance method under compression at 5 t / cm 2 as a whole. As a measuring device, an impedance analyzer SI1260 (manufactured by Solartron) was used.

<Charge / discharge test>
A cross-sectional view of the all-solid lithium secondary battery used in this embodiment is shown in FIG.
[Creation of electrode mixture]
Positive electrode mixture: 11.7 g of lithium cobaltate and 5 g of sulfide lithium ion conductive solid electrolyte were mixed well in a mortar, then filled in a mold together with a titanium conductive metal wire mesh, and a diameter of 13 mmφ with a press machine was adjusted to a thickness of 0.1 mm. Press-molded into a 6 mm disk.
Negative electrode composite; 12 g of artificial graphite and 5 g of sulfide lithium ion conductive solid electrolyte were pressure-molded by the same method as the positive electrode composite to obtain a disk having a diameter of 13 mm and a thickness of 0.6 mm.
[Create battery element]
After the positive electrode mixture prepared above, the sulfide lithium ion conductive solid electrolyte was smoothly filled in the mold used to create the electrode mixture, and then the other electrode mixture was stacked, By applying pressure at 5 t / cm ² , a battery element in which a solid electrolyte was interposed between positive and negative electrodes was obtained.
[Creation of all-solid lithium secondary battery]
Insulating ceramics provided on the aluminum battery lid (4) after connecting the electrode lead plates (9, 13) and the lead wires (5, 6) shown in FIG. It was connected to the positive and negative electrode terminals (1, 2) via (3).
Subsequently, the battery element connected to the battery lid is inserted into an aluminum battery container (8) filled with an epoxy resin (7) that is electrically insulative and inert to the battery constituent material, and the resin is cured. Thereafter, aluminum solder was used for the battery lid and the battery container, and the battery element was completely sealed to obtain an all-solid lithium secondary battery.
[Charging / discharging conditions]
Charging / discharging was performed under the following conditions to determine the discharge capacity.
Charging current: 127 μA / cm ² (constant current), cutoff voltage: 4.2 V
・ Discharge current: 67 μA / cm ²

Example 1
1.28 parts of lithium sulfide, 1.71 parts of silicon sulfide and 0.01 part of aluminum sulfide were weighed in a glove box, ground and mixed in an agate mortar, filled in a carbon crucible, After inserting into an electric furnace with atmosphere control and heating and melting at 950 ° C. for 3 hours, the molten sample was inserted into liquid nitrogen to obtain an amorphous sulfide-based lithium ion conductive solid electrolyte. The ionic conductivity measured at 25 ° C. was 2.86 mS / cm.

(Examples 2 to 5)
An amorphous solid electrolyte was obtained in the same manner as in Example 1 except that the composition of the raw materials used for the synthesis was as shown in Table 1. The ionic conductivity of the obtained electrolyte is shown together in Table 1.

(Comparative Example 1)
In Example 1, an amorphous solid electrolyte was obtained in the same manner as in Example 1 except that aluminum sulfide was not used. The ionic conductivity measured at 25 ° C. was 0.10 mS / cm.

(Example 6)
The same amount of raw material weighed in the glove box as in Example 1 was filled and sealed in an alumina pot for planetary ball mill together with alumina balls for grinding, taken out from the glove box, and ground for 45 hours at 350 rpm using a planetary ball mill grinder. By mixing, a sulfide-based lithium ion conductive solid electrolyte was obtained. The ionic conductivity measured at 25 ° C. was 0.27 mS / cm.

(Example 7)
After 0.98 parts of lithium sulfide, 2.01 parts of phosphorus sulfide, and 0.014 part of aluminum sulfide are weighed in a glove box and ground and mixed in an agate mortar, the inner wall is filled into a quartz tube coated with carbon, and then the quartz tube Was vacuum sealed.
This is heated and melted at a temperature of 950 ° C. for 3 hours in an electric furnace, and then inserted into liquid nitrogen, whereby the molten sample is quenched to obtain an amorphous sulfide-based lithium ion conductive solid electrolyte. Synthesized. The ionic conductivity measured at 25 ° C. was 0.32 mS / cm.

(Examples 8 to 10)
An amorphous solid electrolyte was obtained in the same manner as in Example 7, except that the raw material composition used in the synthesis was the composition described in Table 2. Table 2 shows the ionic conductivity of the obtained electrolyte.

(Comparative Example 2)
In Example 7, a solid electrolyte was obtained by the same method as Example 7 except that aluminum sulfide was not used. The resulting amorphous solid electrolyte had an ionic conductivity at 25 ° C. of 0.19 mS / cm.

（実施例１１）
実施例１で合成した非晶質硫化物系リチウムイオン伝導性固体電解質を粉砕し、実施例７で使用した石英菅内に充填、真空封入したものを、グローブボックス中から取り出し、３５０℃の温度で２時間加熱し、非晶質状態から結晶成長をさせ、Ｘ線回折を試みると共に、そのイオン伝導度の測定を行った。
その結果、結晶化したことを示す幾つかの結晶ピークの存在が認められると共に、２５℃でのイオン伝導度は、３．５ｍＳ／ｃｍを示し、イオン伝導度の向上が認められた。

(Example 11)
The amorphous sulfide type lithium ion conductive solid electrolyte synthesized in Example 1 was pulverized, filled in the quartz cage used in Example 7, and vacuum-sealed, taken out from the glove box, and heated at 350 ° C. Heating was performed for 2 hours, crystal growth was started from an amorphous state, X-ray diffraction was attempted, and the ionic conductivity was measured.
As a result, the presence of several crystal peaks indicating crystallization was observed, and the ionic conductivity at 25 ° C. was 3.5 mS / cm, indicating an improvement in ionic conductivity.

(Example 12)
By subjecting the amorphous sulfide-based lithium ion conductive solid electrolyte synthesized in Example 7 to the same treatment as in Example 11 and crystal growth from an amorphous state, the ionic conductivity at 25 ° C. is 2.5 mS / cm was exhibited, and a marked improvement in ionic conductivity was observed.

(Example 13)
Using the amorphous sulfide type lithium ion conductive solid electrolyte synthesized in Example 7, an all-solid lithium secondary battery was prepared, and a charge / discharge test of the prepared battery was performed. The discharge capacity was about 65 mAh / g.

(Example 14)
Using the sulfide-based lithium ion conductive solid electrolyte synthesized in Example 12, an all-solid lithium secondary battery was prepared, and the prepared battery was subjected to a charge / discharge test. The discharge capacity was about 115 mAh / g.

(Comparative Example 3)
Using the sulfide-based lithium ion conductive solid electrolyte prepared in Comparative Example 2, an all-solid lithium secondary battery was prepared, and the prepared battery was subjected to a charge / discharge test. The discharge capacity was about 60 mAh / g.

The results of Examples 13 and 14 and Comparative Example 3 are shown in FIG. As can be seen from Example 13 and Comparative Example 3, the ionic conductivity of the electrolyte used in these all solid lithium secondary batteries was practically low, 0.32 mS / cm and 0.19 mS / cm. In the solid electrolyte according to the embodiment of the present invention containing aluminum sulfide, the discharge capacity is improved as compared with the comparative battery.
When a sulfide-based solid electrolyte is used, the free sulfur component present in the electrolyte {the oxidation-reduction reaction proceeds near the potential of about 2.5 V (vs. Li)} is oxidized at the contact interface with the positive electrode active material. It is said that the formation of a thin resistance layer at the interface and the charge / discharge performance is hindered by receiving, but the presence of aluminum reduces the free sulfur component in the electrolyte, and as a result, the junction interface with the positive electrode. The inventors speculate that the growth of the resistance layer formed by the above can be inhibited, and as a result, the voltage drop immediately after the start of discharge is reduced and the discharge capacity is improved.
Further, in the battery of Example 14, a battery whose ionic conductivity was improved to the order of 10 ⁻³ S / cm by crystallizing an amorphous electrolyte was used. Looking at the discharge performance of these batteries, it is clear that the discharge performance of the all-solid-state lithium battery of the present invention is excellent and that the theoretical capacity of lithium cobaltate is discharged. At the same time, the charge / discharge overvoltage of this battery is drastically reduced, and it is difficult to explain simply by improving the ionic conductivity. By using the electrolyte of the present invention, the formation of a resistance layer that is supposed to occur at the positive electrode interface is suppressed. It is judged that it leads to the effect to do.

Claims (7)

An inorganic solid electrolyte comprising lithium sulfide, comprising 1 mol% or less of an aluminum compound relative to a raw material composition The inorganic solid electrolyte according to claim 1, comprising at least one compound selected from the group consisting of phosphorus sulfide, silicon sulfide, germanium sulfide, and boron sulfide. 3. The inorganic solid electrolyte according to claim 1, wherein the aluminum compound is chalcogenide or an oxide. The inorganic solid electrolyte according to claim 1 or 2, wherein the aluminum compound is a sulfide. The inorganic solid electrolyte according to claim 1, wherein the inorganic solid electrolyte is in a glass state. A lithium secondary battery using the inorganic solid electrolyte according to claim 1. The all-solid-state lithium secondary battery of Claim 6 which used sulfur as a positive electrode active material.

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