JP2013229257A - All-solid lithium secondary battery using sulfur-based cathode material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an all-solid lithium secondary battery which has a long service life with little deterioration in battery performance, has large electric capacity and high performance, and is excellent in safety due to high heat resistance in comparison with a conventional one.SOLUTION: The all-solid lithium secondary battery includes: a cathode containing a sulfur-modified polyacrylonitrile and a sulfide-based solid electrolyte; and an electrolyte layer containing the sulfide-based solid electrolyte. The sulfide-based solid electrolyte contains S, P, and Li as essential components.

Description

  The present invention relates to an all-solid-state lithium secondary battery using a sulfur-based positive electrode material that has high performance, high heat resistance, excellent safety, and long life with little deterioration in battery performance.

Current lithium secondary batteries using non-aqueous organic electrolytes are considered to have problems in safety.
Currently, a separator between a positive electrode and a negative electrode is generally used as a microporous film made of polypropylene or polyethylene, or a structure in which a plurality of these are stacked, and has a thickness of about 15 to 40 μm. The separator penetrates due to foreign matter mixed in the battery or metal dendrite. As a result, the positive and negative electrodes are short-circuited, current flows suddenly, heat is generated, and sometimes ignition occurs. In a high-temperature environment, the separator contracts or melts, so that the positive and negative electrodes are short-circuited and generate heat, sometimes leading to ignition.
Although the organic electrolyte exhibits high ionic conductivity, there is a concern about the risk of leakage and ignition when used as a battery because the electrolyte is liquid and flammable. Moreover, although it depends on the composition, the organic electrolytic solution evaporates at about 100 to 200 ° C., which leads to ignition.

In order to solve these problems, all-solid lithium secondary batteries using solid electrolytes with higher safety instead of liquid electrolytes have been actively developed as electrolytes for next-generation lithium ion batteries. .
There are various types of solid electrolytes, and among them, a sulfide-based solid electrolyte with high conductivity has attracted attention (Patent Document 1).
Since the solid electrolyte also serves as a separator, the use of the solid electrolyte eliminates the need for a separate separator. Moreover, since the solid electrolyte itself has heat resistance, it does not melt or evaporate at a high temperature of several hundred degrees Celsius. Therefore, the use of the solid electrolyte can greatly reduce the risk of the short circuit between the positive and negative electrodes.

  Here, in an all-solid-state secondary battery using a sulfide-based solid electrolyte, a transition metal oxide positive electrode active material is generally used as the positive electrode active material. However, the all-solid battery has a drawback that the sulfide-based solid electrolyte deteriorates the transition metal oxide positive electrode active material.

JP 2005-228570 A

  The present invention has been made in view of the current state of the prior art described above, and its main purpose is that the battery performance is less deteriorated and the life is longer, the electric capacity is larger, and the heat resistance is higher than in the prior art. The object is to provide an all-solid lithium secondary battery excellent in safety.

  An all-solid lithium secondary battery of the present invention includes a positive electrode including sulfur-modified polyacrylonitrile and a sulfide-based solid electrolyte, and an electrolyte layer including a sulfide-based solid electrolyte, and the sulfide-based solid electrolyte includes S And P and Li are all solid lithium secondary batteries.

According to the all solid lithium secondary battery of the present invention, by using an electrolyte layer containing a sulfide solid electrolyte, it is possible to provide a safe and high electric capacity all solid lithium secondary battery.
When sulfur-modified polyacrylonitrile is used as the positive electrode active material, the positive electrode active material in the positive electrode is not deteriorated by the sulfide-based solid electrolyte in the positive electrode, and a long-life all-solid lithium secondary battery can be obtained.
Since both the positive electrode and the electrolyte layer have high heat resistance, a safe and high-performance all-solid lithium secondary battery can be obtained even in a high temperature environment.

In the all solid lithium secondary battery of the present invention, the sulfide solid electrolyte is preferably an all solid lithium secondary battery produced from lithium sulfide and diphosphorus pentasulfide. Moreover, it is preferable that the molar ratio of lithium sulfide and diphosphorus pentasulfide is 68:32 to 73:27.
Thereby, it can be set as an all-solid-state lithium secondary battery with a higher electrical capacity.

The all solid lithium secondary battery of the present invention is preferably an all solid lithium secondary battery in which the sulfide-based solid electrolyte includes a Li ₇ P ₃ S ₁₁ crystal structure.
Thereby, lithium ion conductivity improves and it can be set as a high performance all-solid-state lithium secondary battery.

  According to the present invention, it is possible to provide an all-solid-state lithium secondary battery that has high performance, high heat resistance, excellent safety, and long life with little deterioration in battery performance.

It is a general | schematic expanded sectional view of the all-solid-state lithium secondary battery of this invention. It is the schematic which shows typically the reaction apparatus for manufacturing sulfur modified polyacrylonitrile. It is drawing which shows the Raman spectrum of sulfur-modified polyacrylonitrile. It is drawing which shows typically the sulfur modification polyacrylonitrile obtained by heat-processing in the state which added the conductive support agent. It is drawing which shows the X-ray-diffraction pattern of sulfur modified polyacrylonitrile. 1 is a drawing showing a Raman spectrum of the sulfur-modified polyacrylonitrile of Example 1. 2 is a charge / discharge curve of an all solid lithium secondary battery of Example 1. FIG. 2 is a charge / discharge curve of an all-solid lithium secondary battery of Comparative Example 1.

  Hereinafter, the all solid lithium secondary battery of the present invention will be described.

An all-solid lithium secondary battery of the present invention includes a positive electrode including sulfur-modified polyacrylonitrile and a sulfide-based solid electrolyte, and an electrolyte layer including a sulfide-based solid electrolyte, and the sulfide-based solid electrolyte includes S And P and Li as essential components.
The all solid lithium secondary battery of the present invention is preferably a coin-type lithium secondary battery.

[First Embodiment]
FIG. 1 is a schematic enlarged cross-sectional view of an all solid lithium secondary battery of the present invention.
In FIG. 1, a coin-type lithium secondary battery 1 includes a battery element 2, a metal case 3, a metal sealing plate 4, a gasket 5, and a spring 6.
The battery element 2 has a positive electrode 21 as a first electrode, a solid electrolyte layer 22 and a negative electrode 23 as a second electrode. The positive electrode 21 has a current collector 211, the negative electrode 23 has a current collector 231 and a metal flat plate. 232. As shown in FIG. 1, the battery element 2 has a positive electrode 21 and a negative electrode 23 laminated so as to sandwich the solid electrolyte layer 22, and a current collector 211 is collected on the lower surface of the positive electrode 21 and an upper surface of the negative electrode 23. An electric body 231 is laminated, and a metal flat plate 232 is laminated on the upper surface of the current collector 231.

(1) Positive first described cathode 21.
The positive electrode 21 has a substantially circular thin plate shape, the lower surface is in contact with the metal case 3 via the current collector 211, and the upper surface is in contact with the solid electrolyte layer 22.
The positive electrode includes sulfur-modified polyacrylonitrile and a sulfide-based solid electrolyte.
As described below, the positive electrode can contain a conductive substance in addition to the sulfur-modified polyacrylonitrile and the sulfide-based solid electrolyte.
Moreover, since the sulfide type solid electrolyte is the same as the sulfide type solid electrolyte contained in the electrolyte layer mentioned below, description here is abbreviate | omitted.
In addition, although it is preferable on battery manufacture that the sulfide type solid electrolyte contained in an electrolyte layer and the sulfide type solid electrolyte contained in a positive electrode are the same, you may differ.
Sulfur-modified polyacrylonitrile is a method in which sulfur powder is mixed with polyacrylonitrile powder and heated in a non-oxidizing atmosphere in a state where sulfur can be prevented from flowing out. This refers to polyacrylonitrile modified with sulfur obtained by reacting with acrylonitrile.
Specifically, it is manufactured by the following method.

Method for producing sulfur-modified polyacrylonitrile
(A) Raw materials In the method of the present invention, sulfur powder and polyacrylonitrile powder are used as raw materials.

  The particle size of the sulfur powder is not particularly limited, but when it is classified using a sieve, it is preferably in the range of about 150 μm to 40 μm, more preferably in the range of about 100 μm to 40 μm. preferable.

  The polyacrylonitrile powder preferably has a weight average molecular weight in the range of about 10,000 to 300,000. Moreover, about the particle size of polyacrylonitrile, when it observes with an electron microscope, what is in the range of about 0.5-50 micrometers is preferable, and what is in the range of about 1-10 micrometers is more preferable.

  The mixing ratio of the sulfur powder and the polyacrylonitrile powder is not particularly limited, but the sulfur powder is preferably about 50 to 1000 parts by weight with respect to 100 parts by weight of the polyacrylonitrile powder, and 50 to 500 parts by weight. More preferably, it is about 150 to 350 parts by weight.

(B) Method for Producing Sulfur-Modified Polyacrylonitrile In the production method of the present invention, the above-described sulfur powder and polyacrylonitrile powder are used as raw materials, and the raw material powder is heated in a non-oxidizing atmosphere while preventing sulfur outflow. To do. Thereby, simultaneously with the ring-closing reaction of polyacrylonitrile, sulfur in the vapor state reacts with polyacrylonitrile, so that polyacrylonitrile modified with sulfur is obtained.

  As an example of a method of heating while preventing the outflow of sulfur, a method of heating in a sealed atmosphere can be employed. In this case, the sealed atmosphere may be maintained in a sealed state to the extent that sulfur vapor generated by heating is not dissipated.

  Further, the non-oxidizing atmosphere may be a reduced pressure state with a low oxygen concentration such that the oxidation reaction does not proceed; an inert gas atmosphere such as nitrogen or argon; a sulfur gas atmosphere or the like.

  There is no particular limitation on the specific method for making the sealed non-oxidizing atmosphere. For example, the raw material is put in a container that maintains the sealing property to the extent that sulfur vapor is not dissipated, and the container is decompressed. Or what is necessary is just to heat as inert gas atmosphere. In addition, a mixture of sulfur powder and polyacrylonitrile powder may be heated in a vacuum packaged state with a material that does not react with sulfur vapor such as an aluminum laminate film. In this case, in order to prevent the packaging material from being damaged by the generated sulfur vapor, for example, the packaged raw material is put in a pressure vessel such as an autoclave containing water and heated, and the generated steam is added from the outside of the packaging material. It is preferable that the pressure is applied. According to this method, since pressure is applied by water vapor from the outside of the packaging material, the packaging material is prevented from being swollen and damaged by sulfur vapor.

  The sulfur powder and the polyacrylonitrile powder may be simply mixed, but for example, the mixture may be formed into a pellet shape.

  The heating temperature is preferably about 250 to 500 ° C, more preferably about 250 to 450 ° C, and further preferably about 250 to 400 ° C.

  Although it does not specifically limit about heating time, Although it changes with actual heating temperature, Usually, what is necessary is just to hold | maintain about 10 minutes-10 hours within the above-mentioned temperature range, and it is preferable to hold | maintain about 30 minutes-6 hours. According to the method of the present invention, it is possible to form sulfur-modified polyacrylonitrile in such a short time.

  In addition, as another example of the method of heating while preventing the outflow of sulfur, sulfur powder and polyacrylonitrile powder are contained in a reaction vessel having an opening for discharging hydrogen sulfide generated by the reaction while sulfur vapor is refluxed. A method of heating the raw material powder can be employed. In this case, the opening for discharging the hydrogen sulfide may be provided at a position where the generated sulfur vapor is liquefied and recirculated almost completely and the outflow of sulfur vapor from the opening can be prevented. For example, by providing an opening in a portion where the temperature in the reaction vessel is about 100 ° C. or less, hydrogen sulfide generated by the reaction is discharged to the outside from the opening, but sulfur vapor is not present in the opening. It can be condensed and returned to the reaction vessel without being discharged outside.

  A schematic diagram of an example of a reactor that can be used in this method is shown in FIG. In the apparatus shown in FIG. 2, the reaction vessel containing the raw material powder is put in an electric furnace, and the upper part of the reaction vessel is exposed from the electric furnace. By using such an apparatus, the temperature of the upper part of the reaction vessel is lower than the temperature of the reaction vessel in the electric furnace. At this time, the temperature of the upper part of the reaction vessel may be a temperature at which sulfur vapor is liquefied. In the reaction container shown in FIG. 2, the upper part of the reaction container is provided with a silicone rubber stopper, and an opening for discharging hydrogen sulfide and an opening for introducing an inert gas are provided in the stopper. ing. Furthermore, a thermocouple is installed in the silicone rubber stopper to measure the raw material temperature. The stopper made of silicone rubber has a convex shape downward, and sulfur condensed and liquefied in this portion is dropped into the lower portion of the container. The reaction vessel is preferably made of a material that is resistant to corrosion by heat or sulfur, such as an alumina tamman tube or a heat-resistant glass tube. The silicone rubber stopper is treated with, for example, a fluororesin tape to prevent corrosion.

  In order to create a non-oxidizing atmosphere in the reaction vessel, for example, an inert gas atmosphere such as nitrogen, argon or helium may be introduced from an inert gas inlet at the initial stage of heating. . Since sulfur vapor is gradually generated when the temperature of the raw material rises, when the temperature of the raw material is about 100 ° C. or higher in order to avoid clogging of the inert gas inlet due to precipitated sulfur, the inert gas inlet is Close is preferred. By continuing the heating thereafter, the inert gas is discharged together with the generated hydrogen sulfide, and the inside of the reaction vessel mainly becomes a sulfur vapor atmosphere.

  The heating temperature in this case is preferably about 250 to 500 ° C., more preferably about 250 to 450 ° C., and about 250 to 400 ° C., similarly to the method of heating in a sealed atmosphere. More preferably. The reaction time may be maintained in the temperature range of 250 to 500 ° C. for about 10 minutes to 10 hours in the same manner as described above. Usually, after the inside of the reaction vessel reaches the above temperature range, heating is performed. If stopped, the reaction is exothermic and will be held for the necessary time in the above temperature range. In addition, it is necessary to control the heating conditions so that the maximum temperature reaches the above-described heating temperature including the temperature rise due to the exothermic reaction. In addition, since the reaction is exothermic, a temperature rising rate of 10 ° C. or less per minute is desirable.

  In this method, excess hydrogen sulfide gas generated during the reaction is removed, and the reaction vessel is maintained in a state filled with sulfur liquid and vapor. And polyacrylonitrile can be promoted.

  The hydrogen sulfide discharged from the reaction vessel may be treated by forming a sulfur precipitate by passing a hydrogen peroxide solution, an alkaline aqueous solution or the like.

  After the inside of the reaction vessel reaches a predetermined reaction temperature, the heating is stopped and the mixture is naturally cooled, and the produced mixture of sulfur-modified polyacrylonitrile and sulfur is taken out.

  According to the method of the present invention, sulfur-modified polyacrylonitrile having a high electric capacity can be obtained by such a simple method.

(C) Sulfur-modified polyacrylonitrile According to the method described above, a polyacrylonitrile ring-closing reaction and a reaction between sulfur and polyacrylonitrile occur simultaneously to obtain polyacrylonitrile modified with sulfur.

  The obtained sulfur-modified polyacrylonitrile contains carbon, nitrogen, and sulfur as a result of elemental analysis, and may further contain small amounts of oxygen and hydrogen.

  Among the production methods described above, according to the method of heating in a sealed atmosphere, the obtained sulfur-modified polyacrylonitrile has a carbon content of 40 to 40 as a content in the sulfur-modified polyacrylonitrile, as a result of elemental analysis. 60 mass%, sulfur is 15 to 30 mass%, nitrogen is 10 to 25 mass%, and hydrogen is about 1 to 5 mass%.

  In addition, among the above-described production methods, in the method of heating while discharging hydrogen sulfide gas, the sulfur-modified polyacrylonitrile obtained has a large sulfur content, and the peak area ratio calculation result by elemental analysis and XPS measurement As a content in the sulfur-modified polyacrylonitrile, carbon is 25 to 50% by mass, sulfur is 25 to 55% by mass, nitrogen is 10 to 20% by mass, oxygen is 0 to 5% by mass, and hydrogen is 0 to 5%. The range is about mass%. The sulfur-modified polyacrylonitrile having a high sulfur content obtained by this method has a large electric capacity when used as a positive electrode active material.

  The sulfur-modified polyacrylonitrile obtained by the method of the present invention has a weight loss by thermogravimetric analysis of 10% or less at 400 ° C. when heated from room temperature to 900 ° C. at a heating rate of 20 ° C./min. On the other hand, when a mixture of sulfur powder and polyacrylonitrile powder is heated under the same conditions, a weight decrease is observed from around 120 ° C., and a large weight loss due to the disappearance of sulfur is recognized suddenly at 200 ° C. or higher.

  Furthermore, in the sulfur-modified polyacrylonitrile, as a result of X-ray diffraction by CuKα ray, the sulfur-based peak disappears, and only a broad peak having a diffraction angle (2θ) of around 20 to 30 ° is confirmed.

  From these points, the sulfur-modified polyacrylonitrile obtained by the above-described method is not a simple mixture of sulfur and polyacrylonitrile. And (2) either (1) (2) or (1) (2) in the interlayer or pore of the graphene-like compound formed by the conjugated structure formed by the cyclization reaction of polyacrylonitrile It is considered to exist.

FIG. 3 shows an example of a Raman spectrum for sulfur-modified polyacrylonitrile obtained by using 200 parts by weight of a sulfur atom with respect to 100 parts by weight of polyacrylonitrile. Sulfur-modified polyacrylonitrile, in the Raman spectrum, there is a main peak near 1331cm ^-1 of Raman shift, and, 1548cm ^-1 in the range of ^{200cm -1 ~1800cm -1, 939cm -1,} 479cm -1, 381cm ^-1 and 317 cm ^-1 are characterized by having peaks. The above-mentioned Raman shift peak is observed at the same peak position even when the ratio of the sulfur atom to polyacrylonitrile is changed, and characterizes the sulfur-modified polyacrylonitrile obtained by the method of the present invention. . The peaks at 317 cm ⁻¹ , 381 cm ⁻¹ , 479 cm ⁻¹ , and 939 cm ⁻¹ are attributed to vibrations due to the conjugated structure, and are derived from the cyclization reaction of polyacrylonitrile. The peaks at 1331 cm ^-1 and 1548 cm ^-1 correspond to the D band and G band of carbon, respectively, and it is considered that sulfur caused dehydrogenation and promoted graphitization. Since the number of conjugated systems in the molecule increased due to the cyclization reaction, the color of the precursor changed from white to black. The peak at 474 cm ⁻¹ is presumed to be vibrations derived from CS coupling or SS coupling, but identification is difficult because it is in a low wavenumber region. Each of the peaks described above can exist in a range of approximately ± 8 cm ⁻¹ with the above peak position as the center. The Raman shift described above was measured with RMP-320 (excitation wavelength λ = 532 nm, grating: 1800 gr / mm, resolution: 3 cm ⁻¹ ) manufactured by JASCO Corporation. In the Raman spectrum, the number of peaks may change or the position of the peak top may be shifted due to the difference in the wavelength or resolution of incident light.

  The sulfur-modified polyacrylonitrile obtained by the above-described method has a characteristic that the ring-closing reaction that occurs when the polyacrylonitrile, which is the raw material, is heated to form a three-dimensional condensed ring, and is heated by mixing with sulfur. Thus, a sulfur-modified polyacrylonitrile structure in which polyacrylonitrile is three-dimensionally crosslinked is formed.

(D) Heat treatment step The sulfur-modified polyacrylonitrile obtained by the above-described method can be further removed by heating in a non-oxidizing atmosphere when unreacted sulfur is present. Thereby, higher purity sulfur-modified polyacrylonitrile can be obtained. The sulfur-modified polyacrylonitrile after the heat treatment is further improved in charge / discharge cycle characteristics.

  The non-oxidizing atmosphere may be, for example, a reduced pressure state with a low oxygen concentration that does not cause an oxidation reaction; an inert gas atmosphere such as nitrogen or argon.

  The heating temperature is preferably about 150 to 400 ° C, more preferably about 150 to 300 ° C, and still more preferably about 200 to 300 ° C. Note that if the heating time becomes too high, the sulfur-modified polyacrylonitrile may be decomposed.

  The heat treatment time is not particularly limited, but is usually preferably about 1 to 6 hours.

For example, the sulfur-modified polyacrylonitrile obtained by the above-described method is added to a sulfide-based solid electrolyte and conductive materials such as acetylene black (AB), ketjen black (KB), and vapor grown carbon fiber (VGCF). A positive electrode can be manufactured by mixing an auxiliary agent and pressing a current collector on the mixture.
The positive electrode may contain a binder.
As the binder, polyvinylidene difluoride (PVdF), polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), or the like can be used. A method of kneading a mixture of sulfur-modified polyacrylonitrile, a sulfide-based solid electrolyte, a conductive additive, and a binder with a mortar or press to form a film, and then crimping this to a current collector with a press Can also produce a positive electrode.
The amount of the sulfide-based solid electrolyte used is not particularly limited, but can be, for example, about 10 to 100 parts by weight with respect to 100 parts by weight of sulfur-modified polyacrylonitrile. The amount of the conductive aid used is not particularly limited, but can be, for example, about 5 to 30 parts by weight with respect to 100 parts by weight of the sulfur-modified polyacrylonitrile. Further, the amount of the binder used is not particularly limited, but can be, for example, about 10 to 20 parts by weight with respect to 100 parts by weight of the sulfur-modified polyacrylonitrile.

  The current collector is not particularly limited, and materials conventionally used as positive electrodes for lithium secondary batteries, such as stainless steel (SUS), Al, Au, Pt, Ti foils and meshes, and carbon fiber weaves. A cloth, a nonwoven fabric, etc. can be used.

  In addition, among conductive aids, high-crystallinity carbon materials such as vapor grown carbon fiber (VGCF), carbon nanotubes, and graphite inhibit the formation reaction of sulfur-modified polyacrylonitrile accompanying the ring-closing reaction of polyacrylonitrile. Therefore, when producing sulfur-modified polyacrylonitrile, it is preferable to heat-treat in the state added to the sulfur powder and polyacrylonitrile powder as raw materials in order to improve conductivity. In particular, when vapor grown carbon fiber (VGCF) is used, one having a diameter of 100 nm to 500 nm and a length of 5 μm to several 20 μm is preferable. FIG. 4 is a drawing schematically showing the structure of sulfur-modified polyacrylonitrile obtained by heat treatment with the addition of a conductive additive. As shown in FIG. 4, according to this method, it is possible to construct a nano-level conductive network between the surfaces of the sulfur-modified polyacrylonitrile particles having a diameter of about several hundred nanometers, and the positive electrode active material having more excellent conductivity. It can be. The amount of the conductive aid used in this case is not particularly limited, but is about 1 to 50 parts by weight, preferably about 5 to 20 parts by weight with respect to 100 parts by weight of the total amount of the sulfur powder and polyacrylonitrile powder. It can be. The sulfur-modified polyacrylonitrile powder combined with the carbon material obtained by this method has good conductivity, and when applied to a current collector to form a positive electrode, the amount of conductive auxiliary agent and binder is reduced. The electrode capacity density and the electrode output density can be greatly improved.

  In the present invention, the positive electrode contains a sulfide-based solid electrolyte in addition to the sulfur-modified polyacrylonitrile. The sulfide-based solid electrolyte can be the same as the sulfide-based solid electrolyte contained in the electrolyte layer to be described later. However, the composition may be appropriately adjusted with respect to that of the solid electrolyte layer, and the crystallinity It may be a solid electrolyte or a glassy solid electrolyte. It is preferable to use the same electrolyte layer as the battery.

(2) Electrolyte layer Next, the electrolyte layer will be described.
The solid electrolyte layer 22 includes a lithium ion conductive solid electrolyte, and the lithium ion conductive solid electrolyte is a sulfide-based solid electrolyte. The sulfide-based solid electrolyte contains S, P and Li as essential components.
The sulfide-based solid electrolyte may contain at least one element selected from the group consisting of B, Si, Ge, and Al.
The solid electrolyte layer 22 has a circular thin plate shape that is substantially the same as the positive electrode.

The sulfide-based solid electrolyte includes, for example, lithium sulfide (Li ₂ S) and diphosphorus pentasulfide (P ₂ S ₅ ); lithium sulfide, simple phosphorus and simple sulfur; or lithium sulfide, diphosphorus pentasulfide, simple phosphorus and / or Or simple substance sulfur can be manufactured as a raw material.

When the sulfide-based solid electrolyte is produced from lithium sulfide and diphosphorus pentasulfide, the mixing molar ratio is usually 50:50 to 80:20, preferably 60:40 to 75:25. Particularly preferably, it is about Li ₂ S: P ₂ S ₅ = 68: 32 to 73:27 (molar ratio).

  A glassy solid electrolyte can be obtained by subjecting the mixture of the above materials to a melt reaction, followed by rapid cooling or treatment by a mechanical milling method (hereinafter sometimes referred to as MM method). When the obtained glassy solid electrolyte is further heat-treated, a sulfide-based solid electrolyte that is a crystalline solid electrolyte is obtained.

The sulfide-based solid electrolyte preferably has a crystal structure of a Li ₇ P ₃ S ₁₁ structure.
When a sulfide-based solid electrolyte having a crystal structure of Li ₇ P ₃ S ₁₁ structure is used for an all-solid lithium secondary battery, a higher-performance all-solid lithium secondary battery can be manufactured.
Here, the crystal structure of the Li ₇ P ₃ S ₁₁ structure is 2θ = 17.8, 18.2, 19.8, 21.8, 23.8, 25.9, 29. A peak is observed at 5, 30.0 deg.

The particle size of the sulfide-based solid electrolyte particles is preferably 0.01 μm or more and 100 μm or less, and more preferably 0.01 μm or more and 50 μm or less. The particle size can be determined by a laser diffraction particle size distribution measuring method.
If it is less than 0.01 μm, handling may be difficult. If it is larger than 50 μm, the contact area with the active material may be reduced, and ion conductivity may be lowered. More preferably, the particle size of the sulfide-based solid electrolyte particles is 0.05 μm or more and 20 μm or less.

The laser diffraction particle size distribution measurement method can measure the particle size distribution without drying the composition. Specifically, the particle size in the composition is irradiated with a laser and the scattered light is analyzed to determine the particle size. Measure the distribution.
In the present invention, the solid electrolyte is measured in a dry state.
The specific measurement method is as follows. As a measuring device, for example, Mastersizer 2000 manufactured by Malvern Instruments Ltd. can be used.
First, 110 ml of dehydrated toluene (Wako Pure Chemicals, product name: special grade) was placed in the dispersion tank of the apparatus, and 6% of dehydrated tertiary butyl alcohol (Wako Pure Chemicals, special grade) was added as a dispersant. Added. After sufficiently mixing the above mixture, a solid electrolyte is added and the particle size is measured.
Here, the addition amount of the solid electrolyte is adjusted so that the laser scattering intensity corresponding to the particle concentration falls within the specified range (10 to 20%) on the operation screen specified by the above apparatus. If this range is exceeded, multiple scattering may occur, making it impossible to obtain an accurate particle size distribution. On the other hand, if the amount is less than this range, the S / N ratio is deteriorated and there is a possibility that accurate measurement cannot be performed.

  In the above apparatus, since the laser scattering intensity is displayed based on the addition amount of the solid electrolyte, the addition amount that falls within the laser scattering intensity range is found.

(3) The negative electrode negative electrode 23 contains a negative electrode active material.
A sulfide-based solid electrolyte and / or a conductive aid may be included.

In the all solid lithium secondary battery of the present invention, Li is not contained in sulfur-modified polyacrylonitrile, which is a positive electrode active material.
Therefore, it is necessary to use a material containing Li and capable of inserting and extracting lithium ions as the negative electrode active material. As the negative electrode active material, those known as a negative electrode active material in this battery field can be used. For example, a Li-metal alloy can be used, and among these, a Li-In alloy is stably used.
The sulfide-based solid electrolyte is the same as that contained in the solid electrolyte layer.

  Examples of the conductive assistant include substances selected from carbon materials, metal powders and metal compounds, and mixtures thereof.

The negative electrode may contain a binder.
Binders include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), fluorine-containing resins such as fluorine rubber, thermoplastic resins such as polypropylene and polyethylene, ethylene-propylene-dienemer (EPDM), and sulfonation. EPDM, natural butyl rubber (NBR) or the like can be used alone or as a mixture of two or more.

Similarly to the positive electrode, a mixture of a conductive additive and a binder is kneaded using a mortar or a press to form a film, and the negative electrode is also bonded by a method of pressing this to a current collector with a press. Can be manufactured.
As the current collector, a current collector similar to the positive electrode can be used.

(4) Metal flat plate The metal flat plate 232 is provided as a current collector, and a known current collector can be used.
For example, a SUS flat plate or a layer coated with Au or the like that reacts with a sulfide-based solid electrolyte such as Au, Pt, Al, Ti, graphite, Cu, or Ni can be used.

(5) Metal Case The metal case 3 is a case for sealing the battery element 2 and the like, and includes a substantially circular bottom plate on which the positive electrode 21 is placed, and a cylinder press-molded integrally with the bottom plate. It consists of a side plate. The metal case 3 is typically a stainless steel case and houses the battery element 2, the gasket 5, the spring 6, and the side plate of the metal sealing plate 4. The metal case 3 that houses the battery element 2, the gasket 5, the spring 6, and the side plate of the metal sealing plate 4 seals the battery element 2 and the spring 6 by caulking the upper part of the side plate.
Further, the metal case 3 is in contact with the above-mentioned bottom plate facing the positive electrode 21, so that it is electrically connected to the positive electrode 21 and becomes the first electrode terminal (positive electrode terminal).

(6) Metal Sealing Plate The metal sealing plate 4 is usually a stainless steel sealing plate, a substantially circular upper plate that contacts the spring 6, and a cylindrical shape that is press-molded integrally with the upper plate. It consists of side plates. The side plate has a double-cylindrical structure composed of an outer side plate and an inner side plate. The upper part of the side plate of the metal case 3 that is caulked on the inside engages with the tip of the outer side plate of the double cylindrical structure via the gasket 5. Thereby, the metal sealing plate 4 is firmly attached to the metal case 3, and the metal case 3 and the metal sealing plate 4 seal the battery element 2 and the spring 6.
The metal sealing plate 4 is in contact with the spring 6 in a state where the upper plate faces the negative electrode 23, and is further insulated from the metal case 3 by the gasket 5. Therefore, the metal sealing plate 4 is electrically connected to the negative electrode 23 and becomes the second electrode terminal (negative electrode terminal).

(7) The gasket gasket 5 is made of an insulating resin and insulates the metal case 3 and the metal sealing plate 4.
The gasket 5 has a substantially cylindrical shape, and is formed with an annular groove into which the outer side plate and the inner side plate of the metal sealing plate 4 are inserted. In the gasket 5, the battery element 2 is fitted into the inner surface of the cylinder, the outer side plate and the inner side plate of the metal sealing plate 4 are fitted into the annular groove, and further, the gasket 5 is fitted into the side plate of the metal case 3. Thereby, the gasket 5 seals the battery element 2 and the spring 6 inside the metal case 3 and the metal sealing plate 4. Further, the positive electrode 21, the solid electrolyte layer 22, the negative electrode 23 and the side plate of the metal sealing plate 4 are insulated, and further, the metal case 3 and the metal sealing plate 4 are insulated.

(8) Spring The spring 6 of the present embodiment is a kind of wave washer, and has a structure in which an annular metal plate is pressed into a shape having a plurality of waves. The material of the spring 6 is a conductive metal, and usually spring steel or the like is used.
The spring 6 is housed between the current collector 231 of the negative electrode 23 and the metal sealing plate 4, and the formed wave-shaped convex portion is in contact with the metal sealing plate 4 to form the formed wave. The concave portion of the mold is in contact with the current collector 231. Thereby, the current collector 231 and the metal sealing plate 4 are electrically connected, and the electrical connection between the positive electrode 21 and the metal case 3 can be maintained. Further, the spring 6 increases the contact surface pressure between the current collector 231 and the negative electrode 23, the contact surface pressure between the negative electrode 23 and the solid electrolyte layer 22, and the contact surface pressure between the solid electrolyte layer 22 and the positive electrode 21. it can. Thus, since the battery element 2 is pressurized by the spring 6, the coin-type lithium secondary battery 1 can suppress a decrease in current density due to poor contact.

Here, the pressure applied to the battery element 2 by the spring 6 is preferably about 0.1 MPa or more. In this way, the coin-type lithium secondary battery 1 can effectively suppress a decrease in current density.
The pressure applied to the battery element by the spring 6 is more preferably 3 MPa or more. More preferably, it is 10 MPa or more.
Moreover, although the spring 6 of this embodiment is set as the structure mentioned above, it is not limited to this structure. That is, it is an example of a conductive elastic body. Therefore, springs of various shapes (for example, spring washers made of a conductive material) can be used. Further, instead of the spring 6, another conductive elastic body (for example, a resin plate having elasticity applied with a conductive paint or a spacer made of a resin having conductivity and elasticity) may be used.

Moreover, as for the spring 6 of this embodiment, the some recessed part has pressed the electrical power collector 231 below.
Here, preferably, the spring 6 of the present embodiment is capable of pressing the current collector 231 more uniformly. For example, although not shown, it is preferable to have a structure in which substantially hemispherical convex portions and concave portions are arranged on a disc. In this way, the spring 6 has a contact surface pressure between the current collector 231 and the negative electrode 23, a contact surface pressure between the negative electrode 23 and the solid electrolyte layer 22, and a contact surface pressure between the solid electrolyte layer 22 and the positive electrode 21. And at the same time, the contact surfaces can be made substantially uniform. By doing so, it is possible to avoid problems such as insufficient contact being obtained due to variations in contact surface pressure and a decrease in current density, and the reliability of the coin-type lithium secondary battery 1 can be improved.

  The present invention may be a laminated cell or the like, and is not limited to the above embodiment.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples.

Example 1
(Production Example 1-Electrolyte layer)
(1) Production of lithium sulfide (Li ₂ S) Lithium sulfide was produced according to the method of the first aspect (two-step method) of JP-A-7-330312. Specifically, N-methyl-2-pyrrolidone (NMP) 3326.4 g (33.6 mol) and lithium hydroxide 287.4 g (12 mol) were charged into a 10 liter autoclave equipped with a stirring blade, and 300 rpm, 130 The temperature was raised to ° C. After the temperature rise, hydrogen sulfide was blown into the liquid at a supply rate of 3 liters / minute for 2 hours.
Subsequently, this reaction solution was heated in a nitrogen stream (200 cc / min) to dehydrosulfide a part of the reacted hydrogen sulfide. As the temperature increased, water produced as a by-product due to the reaction between hydrogen sulfide and lithium hydroxide started to evaporate, but this water was condensed by the condenser and extracted out of the system. While water was distilled out of the system, the temperature of the reaction solution rose, but when the temperature reached 180 ° C., the temperature increase was stopped and the temperature was kept constant. After the dehydrosulfurization reaction was completed (about 80 minutes), the reaction was completed to obtain lithium sulfide.

(2) Purification of lithium sulfide After decanting NMP in the 500 mL slurry reaction solution (NMP-lithium sulfide slurry) obtained in (1) above, 100 mL of dehydrated NMP was added and stirred at 105 ° C. for about 1 hour. . NMP was decanted at that temperature. Further, 100 mL of NMP was added, stirred at 105 ° C. for about 1 hour, NMP was decanted at that temperature, and the same operation was repeated a total of 4 times. After completion of the decantation, lithium sulfide was dried at 230 ° C. (temperature higher than the boiling point of NMP) under a nitrogen stream for 3 hours under normal pressure. The impurity content in the obtained lithium sulfide was measured.
Incidentally, lithium sulfite _(Li 2 _SO 3), the content of each sulfur oxide lithium sulfate _(Li 2 SO ₄₎ and lithium thiosulfate _{(Li 2 S 2 O 3)} , and N- methylamino acid lithium (LMAB) Was quantified by ion chromatography. As a result, the total content of sulfur oxides was 0.13% by mass, and LMAB was 0.07% by mass.

(3) Manufacture of a sulfide-based solid electrolyte Using the lithium sulfide and diphosphorus pentasulfide (manufactured by Aldrich) manufactured in (2) above, the solid electrolyte was produced in the same manner as in Example 1 of International Publication WO07 / 066539. Was prepared and crystallized.
Specifically, it was performed as follows.
0.6492 g (0.01417 mol) of lithium sulfide produced in the above (2) and 1.3492 g (0.00607 mol) of diphosphorus pentasulfide (manufactured by Aldrich) were mixed well. Then, the mixed powder, 10 zirconia balls having a diameter of 10 mm, and a planetary ball mill (manufactured by Fritsch Co., Ltd .: Model No. P-7) are put into an alumina pot and completely sealed, and the alumina pot is filled with nitrogen, The atmosphere was nitrogen.
Then, for the first few minutes, the planetary ball mill was rotated at a low speed (85 rpm) to sufficiently mix lithium sulfide and diphosphorus pentasulfide. Thereafter, the rotational speed of the planetary ball mill was gradually increased to 370 rpm. Mechanical milling was performed for 20 hours at a rotational speed of the planetary ball mill at 370 rpm. As a result of evaluating the mechanically milled white yellow powder by X-ray measurement, it was confirmed that the powder was vitrified (sulfide glass). It was 220 degreeC when the glass transition temperature of this sulfide glass was measured by DSC (differential scanning calorimetry).
This sulfide glass was heated at 300 ° C. for 2 hours in a nitrogen atmosphere.
The obtained sulfide glass ceramic was measured by X-ray diffraction. As a result, 2θ = 17.8, 18.2, 19.8, 21.8, 23.8, 25.9, 29.5, 30.0 deg. A peak was observed.

The obtained sulfide-based solid electrolyte was shaped to a diameter of 13 mm (1.327 cm ² ) and 100 mg.

(Production Example 2-Positive Electrode)
Polyacrylonitrile powder and sulfur powder were added at a weight ratio of 1: 5 and mixed in a mortar to obtain a starting material. This raw material was placed in an alumina tamman tube (outer diameter 60 mm, inner diameter 50 mm, length 180 mm, alumina SSA-S, manufactured by Nikkato) used as a reaction vessel.

  The opening of the alumina tamman tube is covered with a silicone rubber plug (No. 15) fixed to a rubber adapter, and the silicone rubber plug is exposed to the internal atmosphere of the alumina tamman tube with a fluororesin tape wrapped around the silicone. The rubber stopper was kept out of direct contact with the internal atmosphere.

  Silicone rubber plugs are drilled in three locations, with an alumina protective tube (outer diameter 4 mm, inner diameter 2 mm, length 250 mm, alumina SSA-S, manufactured by Nikkato) and two alumina tubes (outer diameter 6 mm). , Inner diameter 4 mm, length 150 mm, alumina SSA-S, manufactured by Nikkato). The tip of the thermocouple placed in the alumina protective tube was brought into contact with the sample and used for measuring the sample temperature. The two alumina tubes were used as an inert gas introduction tube and an internal gas exhaust tube, respectively, and were arranged so as to protrude 3 mm from the bottom surface of the lid. An argon gas pipe was connected to the gas introduction pipe, and a pipe for passing hydrogen peroxide solution was connected to the gas exhaust pipe to form a hydrogen sulfide gas trap.

  2 is put into an electric furnace (crucible furnace, opening 80 mm, heating portion 100 mm of the Tamman tube), and argon is introduced into the alumina Tamman tube at 100 cc / min. For 10 minutes. The sample inside the alumina tanman tube was heated at a temperature rising rate of 5 ° C. per minute, and the argon gas was stopped at 100 ° C. Gas was generated inside from around 200 ° C., and heating was stopped at 360 ° C. The temperature of the sample increased to 400 ° C. and then decreased. The product was taken out after cooling to near room temperature.

  Unreacted sulfur remaining in the product was removed by grinding the product in a mortar and placing 2 g of the product in a glass tube oven and heating at 250 ° C. for 3 hours while evacuating. By this operation, unreacted sulfur was evaporated, and sulfur-modified polyacrylonitrile was obtained.

  The obtained product was subjected to X-ray diffraction measurement. CuKα was used as the X-ray source. The obtained X-ray diffraction pattern is shown in FIG. When the diffraction angle (2θ) was in the range of 20 ° to 30 °, only a broad diffraction peak having a peak position near 25 ° was observed.

Further, the product was subjected to Raman analysis using RMP-320 (excitation wavelength λ = 532 nm, grating: 1800 gr / mm, resolution: 3 cm ⁻¹ ) manufactured by JASCO Corporation. The obtained Raman spectrum is shown in FIG. In FIG. 6, the horizontal axis is the Raman shift (cm ⁻¹ ), and the vertical axis is the relative intensity. As can be seen from FIG. 6, according to the Raman analysis results of the product, there are a main peak in the vicinity of 1328cm ^-1, and, 1558cm ^-1 in the range of ^{200cm -1 ~1800cm -1, 946cm -1,} 479cm - ^{1, 379cm -1,} the peak was present around 317cm ^-1.

  Using the obtained sulfur-modified polyacrylonitrile as an active material, the solid electrolyte obtained in Production Example 1, acetylene black (AB) and vapor grown carbon fiber (VGCF) as a conductive additive, Sulfur-modified polyacrylonitrile: solid electrolyte: AB: VGCF = 50: 50: 3: 2 was mixed in a mortar to obtain a positive electrode mixture.

(Production Example 3-Negative electrode)
A negative electrode was obtained by punching a Li-In alloy foil having a thickness of 0.5 mm into a circular shape having a diameter of 12 mm and press-bonding a SUS mesh having a diameter of 12 mm.

(Production Example 4-Battery)
90 mg of the above solid electrolyte was put into a cylindrical mold made of die steel SKD11 having a diameter of 13.0 mm, pressurized with 1 MPa, 6.096 mg of the above positive electrode mixture was added, and pressurized with 1 MPa, and further to a diameter of 12 mm. The punched SUS mesh was put in and pressurized at 50 MPa. Subsequently, the negative electrode was introduced from the side opposite to the positive electrode to form a three-layer structure, and then pressurized with 10 MPa to obtain a battery pellet.
The battery pellet was made into a 2032 type coin cell with the configuration shown in FIG. 1 to produce a coin type battery of Example 1. That is, PP was used for the gasket, and 0.5 mm SUS plates were used for the positive and negative spacers. A disc spring was applied as the spring. When this disc spring and two 0.5 mm spacers were applied, the pressure inside the coin battery was 10 MPa.
Note that the pressure inside the coin cell was measured at a substantially central portion of the solid electrolyte by using pressure sensitive paper.

Comparative Example 1
LiNi _0.8 Co _0.15 Al _0.05 O ₂ was used as the positive electrode active material, and a positive electrode mixture was produced at an active material: solid electrolyte = 70: 30 weight ratio. A positive electrode was produced using 9.153 mg of the positive electrode mixture. Using this positive electrode and In as the negative electrode, a coin-type battery of Comparative Example 1 was produced in the same manner as in Production Example 3 above. In addition, since Li was contained in the positive electrode, In which does not contain Li was used for the negative electrode.

  7 is a charge / discharge curve of the coin-type battery of Example 1, and FIG. 8 is a charge / discharge curve of the coin-type battery of Comparative Example 1. The vertical axis represents voltage, and the horizontal axis represents the electric capacity per gram of active material.

The test of Example 1 was performed under the following conditions.
Voltage range: 3.0-1.0V vs Li ⁺ / Li
Current: 0.02C
Test temperature: 60 ° C

The test of Comparative Example 1 was performed under the following conditions.
Voltage range: 3.7-1.8V vs In
Current: 0.03C
Test temperature: 60 ° C

As shown in FIG. 8, it can be seen that the all-solid lithium secondary battery of Comparative Example 1 has a greatly reduced electric capacity as the number of cycles progresses.
On the other hand, as shown in FIG. 7, the all-solid lithium secondary battery of Example 1 shows that the decrease in electric capacity is significantly smaller than that of the comparative example even when the number of cycles proceeds.
From this result, it can be seen that the all solid lithium secondary battery of the present invention is a high performance all solid lithium secondary battery having a long battery life with little deterioration in battery performance and a large electric capacity.

  The present invention is suitably used as a main power source for mobile communication devices, portable electronic devices, electric bicycles, electric motorcycles, electric vehicles and the like.

DESCRIPTION OF SYMBOLS 1 Coin type lithium secondary battery 2 Battery element 3 Metal case 4 Metal sealing board 5 Gasket 6 Spring 21 Positive electrode 211 Current collector 22 Solid electrolyte layer 23 Negative electrode 231 Current collector 232 Metal flat plate

Claims (4)

A positive electrode comprising sulfur-modified polyacrylonitrile and a sulfide-based solid electrolyte;
An electrolyte layer containing a sulfide-based solid electrolyte, and
The all-solid-state lithium secondary battery, wherein the sulfide-based solid electrolyte contains S, P, and Li as essential components.   The all-solid-state lithium secondary battery according to claim 1, wherein the sulfide-based solid electrolyte is manufactured from lithium sulfide and diphosphorus pentasulfide.   The all-solid-state lithium secondary battery according to claim 2, wherein a molar ratio of the lithium sulfide to the phosphorous pentasulfide is 68:32 to 73:27. The all-solid-state lithium secondary battery according to any one of claims 1 to ₃ , wherein the sulfide-based solid electrolyte includes a Li ₇ P ₃ S ₁₁ crystal.