WO2021182614A1 - Positive electrode for secondary cells, method for manufacturing positive electrode for secondary cells, and secondary cell - Google Patents

Abstract

Provided are: a positive electrode for secondary cells, that has high positive electrode capacity density per volume and can increase the energy density of secondary cells; a manufacturing method for said positive electrode for secondary cells; and a secondary cell having high energy density. A positive electrode 10 contains polysulfide 16 indicated by Li₂S_x (x = 4, 6, 8) in a sulfur amount of 0.70 g/cm³ to 2.0 g/cm³, in a self-supporting sponge structure 14 comprising CNT 12 and having a thickness of at least 5 μm and less than 100 μm. The positive electrode 10 is manufactured by: causing the self-supporting sponge structure 14 comprising CNT 12 and having a thickness of at least 5 μm and less than 100 μm to contain polysulfide 16; and forming the CNT 12 and the polysulfide 16 into a complex. The secondary cell has a structure whereby the positive electrode 10, a negative electrode, and a separator are provided inside a container together with an electrolytic solution.

Description

Positive electrode for secondary battery, manufacturing method of positive electrode for secondary battery, secondary battery

The present invention relates to a positive electrode for a secondary battery, a method for manufacturing a positive electrode for a secondary battery, and a secondary battery.

As a positive electrode for realizing a high-capacity secondary battery, a positive electrode using sulfur as a positive electrode active material is attracting attention. Sulfur has a theoretical capacity about 10 times higher than that of the positive electrode active material of the lithium transition metal composite oxide system, but has a problem of poor conductivity. In addition, when sulfur is used as the positive electrode active material, in order to obtain good secondary battery characteristics, it is necessary to use an excess amount of electrolyte solution that is about 10 times or more the sulfur content, and the energy density is high. There is a problem that the next battery cannot be obtained. The present inventors have higher self sponge-like structure of the CNT (carbon nanotube) having conductivity is used as the positive electrode current collector, the sulfur by holding the S _{8 (octasulfur)} to the sponge-like structure A positive electrode that can compensate for the low conductivity and can improve the energy density by not requiring a current collecting foil has been realized. However, even if this positive electrode is used, it is necessary to use an excessive amount of electrolytic solution, and a secondary battery having a high energy density cannot be obtained.

On the other hand, lithium polysulfide (also referred to as lithium polysulfide) represented by _{Li 2} S _{x (x = 4, 6, 8), which is a reaction intermediate between S 8 in} a charged state and Li ₂ S (lithium sulfide) in a discharged state. Research is also underway to use (hereinafter referred to as polysulfide) as a positive electrode material. The _Li 2 _{S x} has a high solubility in the electrolyte solution. A method using a Li ₂ S _x a The dissolved Li ₂ S _x solution in the electrolyte (also referred to as a catholyte solution) have been studied, for also require an excessive amount of the electrolytic solution in this manner, the secondary battery The energy density cannot be increased. Therefore, in order to reduce the amount of electrolyte, Li ₂ S _x was is contained in the positive electrode current collector in the form of a solid positive electrode has been proposed (for example, Non-Patent Documents 1 and 2).

Non-Patent Document 1, using the CNT form CNT is fixed to the carbide of polyacrylonitrile as a positive electrode current collector, it was added dropwise a Li ₂ S ₄ solution CNT form positive electrode produced by drying has been proposed ..

Non-Patent Document 2, using the CNF film made from CNF (carbon nanofibers) as a positive electrode current collector, was added dropwise a Li ₂ S ₈ solution CNF membrane, a positive electrode was prepared by drying has been proposed ..

The positive electrode of Non-Patent Document 1 has a positive electrode current collector having a thickness of 100 μm. The positive electrode of Non-Patent Document 2 has a positive electrode current collector having a thickness of 200 to 250 μm. Since each positive electrode described in Non-Patent Documents 1 and 2 has a thick positive electrode current collector and a small amount of sulfur per volume, it is not possible to increase the positive electrode capacitance density per volume, and the energy density of the secondary battery can be increased. Can't be raised.

Therefore, the present invention provides a method for manufacturing a positive electrode for a secondary battery and a positive electrode for the secondary battery, which has a high positive electrode capacity density per volume and can increase the energy density of the secondary battery, and a secondary battery having a high energy density. The purpose is to provide.

The positive electrode for a secondary battery according to the present invention, the sponge-like structure in which the self-supporting under constructed thickness 5μm or 100μm carbon nanotube _is expressed by _{Li 2 S x (x = 4,6,8} ) It is characterized in that the polysulfide is contained in a sulfur amount of ^{0.70 g / cm 3} or more and 2.0 g / cm ^{3 or less.}

Table positive electrode manufacturing method for a secondary battery according to the present invention, the sponge-like structure in which the self-supporting under constructed thickness 5μm or 100μm carbon nanotube _{Li 2 S x (x = 4,6,8} ) It is characterized in that the carbon nanotube and the polysulfide are compounded by containing the polysulfide.

The secondary battery according to the present invention is characterized in that the above-mentioned positive electrode, negative electrode and separator are provided in a container together with an electrolytic solution.

According to the present invention, the thickness of the sponge-like structure is less than 100μm or 5 [mu] m, when representing the content of Li ₂ S _x spongy structure in sulfur per cathode volume, the amount of sulfur is 0.70 g / cm ³ or more 2.0 g / cm ³ or less, a thin since a sponge-like structure in a large amount of _Li 2 _{S x} are contained, the positive electrode capacity density is high per unit volume, the secondary battery It is possible to provide a method for manufacturing a positive electrode for a secondary battery and a positive electrode for the secondary battery thereof, which can increase the energy density, and a secondary battery having a high energy density.

It is a schematic diagram which shows the structure of the positive electrode for a secondary battery which concerns on 1st Embodiment. It is explanatory drawing explaining the manufacturing method of the positive electrode for a secondary battery which concerns on 1st Embodiment. It is a flowchart explaining the manufacturing method of the positive electrode for a secondary battery which concerns on 1st Embodiment. It is a schematic diagram which shows the structure at the time of charging and the time of discharging of the secondary battery which concerns on 1st Embodiment. It is a schematic diagram which shows the structure of the positive electrode for a secondary battery which concerns on 2nd Embodiment. It is explanatory drawing explaining the 1st method which is an example of the manufacturing method of the positive electrode for a secondary battery which concerns on 2nd Embodiment. It is explanatory drawing explaining the 2nd method which is an example of the manufacturing method of the positive electrode for a secondary battery which concerns on 2nd Embodiment. It is explanatory drawing explaining the 3rd method which is an example of the manufacturing method of the positive electrode for a secondary battery which concerns on 2nd Embodiment.

Hereinafter, the present embodiment will be described in detail with reference to the drawings.

1. 1. First Embodiment 1-1. Overall Configuration In FIG. 1, the positive electrode for a secondary battery (hereinafter referred to as a positive electrode) 10 according to the present embodiment is a self-supporting sponge-like structure 14 composed of CNTs (carbon nanotubes) 12 and having a thickness of 5 μm or more and less than 100 μm. during _polysulfide 16 represented by _{Li 2 S x (x = 4,6,8} ) has a structure which is contained in the 0.70 g / cm ³ or more 2.0 g / cm ³ or less of sulfur content. The amount of sulfur is the mass of sulfur as an element contained in the unit volume of the electrode.

The sponge-like structure 14 is a film having both porosity and independence, and is formed by entwining a plurality of CNTs 12 with each other. The sponge-like structure 14 holds the polysulfide 16 and an electrolytic solution described later. The sponge-like structure 14 functions as a positive electrode current collector for the positive electrode 10.

The sponge-like structure 14 has a thickness of 5 μm or more and less than 100 μm. If the positive electrode current collector is too thick, the positive electrode capacitance density per positive electrode volume (also referred to as volume capacitance density) becomes small. When the positive electrode current collector is too thin, the amount that can hold Li ₂ S _x decreases, the positive electrode capacity density per cathode area (also referred to as the area capacity density) decreases. The thickness of the sponge-like structure 14 is particularly preferably 10 μm or more and 50 μm or less.

The polysulfide 16 is supported on the CNT 12 of the sponge-like structure 14 in a solid state and is composited with the CNT 12. The polysulfide 16 may have a structure that covers the CNT 12 in an island shape, a structure that covers almost the entire surface of the CNT 12, a particle structure, or other predetermined structure. The polysulfide 16 functions as a positive electrode active material of the positive electrode 10.

When the content of the polysulfide 16 in the sponge-like structure 14 is expressed by the amount of sulfur per positive electrode volume, the amount of sulfur is 0.70 g / cm ³ or more and 2.0 g / cm ³ or less. If the content of the polysulfide 16 in the sponge-like structure 14 is too small, the volume volume density is lowered and the electrode performance cannot be improved. If the content of the polysulfide 16 in the sponge-like structure 14 is too large, the voids in the sponge-like structure 14 are filled, so that the electrolytic solution is insufficient and the diffusibility of lithium ions is lowered. From the viewpoint of facilitating the adjustment of voids while increasing the volume volume density, the content of polysulfide 16 in the sponge-like structure 14 shall be 0.95 g / cm ³ or more and 1.6 g / cm ³ or less in terms of sulfur content. Is preferable.

The length of CNT12 is preferably 1 μm or more. When the length of the CNTs 12 is 1 μm or more, the plurality of CNTs 12 are entangled with each other, and the independence of the sponge-like structure 14 is ensured.

The average diameter of CNT12 is preferably 20 nm or less. The smaller the diameter of the CNT 12, the more flexible, self-supporting and conductive as the sponge-like structure 14. The average diameter of CNT12 is more preferably 15 nm or less, and particularly preferably 10 nm or less.

The specific surface area of CNT12 is ^{preferably 200 m 2} / g or more. When the specific surface area of the CNT 12 is 200 m ² / g or more, the interface with the polysulfide 16 in the sponge-like structure 14 is increased and the electrical connection is improved, and the content of the polysulfide 16 in the sponge-like structure 14 is increased. Since it can be increased, the volume capacity density and the area capacity density are improved. The specific surface area of CNT12 ^{is more preferably 300 m 2} / g or more, and ^{particularly preferably 400 m 2} / g or more. The specific surface area of CNT12 ^{is preferably 1300 m 2} / g or less. If the specific surface area of the CNTs 12 is too large, the CNTs 12 may strongly aggregate with each other, making it difficult to combine with the polysulfide 16. The specific surface area of CNT12 ^{is more preferably 800 m 2} / g or less.

CNT12 preferably has an average number of layers of 1 or more and 10 or less. As the average number of layers of the CNTs 12 is smaller, the CNTs 12 become more flexible and the plurality of CNTs 12 are more likely to be entangled with each other, so that the independence of the sponge-like structure 14 is more reliably ensured. However, if the average number of layers of CNT 12 is too small, the CNT 12 becomes too flexible and entangled with each other, so that it becomes difficult to disperse the raw material powder of CNT 12 and form the sponge-like structure 14. Further, if the average number of layers of the CNT 12 is too small, the specific surface area of the CNT 12 becomes too large. The average number of layers of CNT12 is more preferably 1 or more and 8 or less, and particularly preferably 2 or more and 5 or less.

When the secondary battery is constructed using the positive electrode 10, the positive electrode 10 is provided so as to be in contact with the separator. The thickness of the positive electrode 10 may be reversibly changed by charging and discharging the secondary battery. Specifically, the positive electrode 10 may be one in which the thickness decreases during charging and increases during discharging. At the positive electrode 10, Li ₂ S _x is reduced during discharge to produce Li ₂ S (lithium sulfide), and Li ₂ S _x is oxidized _{during charging to produce S 8} (octasulfur).

Since the positive electrode 10 includes the sponge-like structure 14 as the positive electrode current collector, it is not necessary to include a separate current collector foil. When the positive electrode does not include the current collecting foil, the mass and volume of the positive electrode can be reduced, and the positive electrode capacity density (also referred to as mass capacity density) and volume capacity density per positive electrode mass can be increased. It is more preferable to install a plurality of metal comb-shaped electrodes or thin wires because sufficient conductivity can be secured while reducing the mass of the metal. When the positive electrode 10 does not include the current collecting foil, the thickness of the positive electrode 10 is substantially the same as the thickness of the sponge-like structure 14.

1-2. Manufacturing Method A manufacturing method of the positive electrode 10 according to the present embodiment will be described.

As shown in FIG. 2, positive electrode 10, the self-standing in a sponge-like structure 14 is less than the configured thickness 5μm or 100μm from CNT _12, represented by _{Li 2 S x (x = 4,6,8} ) It is produced by containing polysulfide 16 and combining CNT 12 and polysulfide 16.

CNT12 can be synthesized by a CVD (chemical vapor deposition) method. Examples of the CVD method include Japanese Patent No. 5447365, Japanese Patent No. 5862559, DY Kim, H. Sugime, K. Hasegawa, T. Osawa, and S. Noda, Carbon 49 (6), 1972-1979 (2011). )., Z. Chen, DY Kim, K. Hasegawa, T. Osawa, and S. Noda, Carbon 80, 339-350 (2014). CNT12 may be synthesized by a floating catalyst CVD method or a substrate-supported catalyst CVD method.

The sponge-like structure 14 is prepared by dispersing CNT 12 in a dispersion medium to prepare a dispersion liquid, and removing the dispersion medium from this dispersion liquid. As the dispersion medium, water, an organic solvent, or the like is used. The organic solvent is ethanol, 2-propanol and the like. The dispersion medium is removed from the dispersion, for example by filtering the dispersion using a filter. In the process of removing the dispersion medium from the dispersion liquid, CNT 12 forms a network by van der Waals force and accumulates on the surface of the filter to form a sponge-like structure 14. The sponge-like structure 14 is separated from the filter and collected as a free-standing film. Further, the sponge-like structure 14 is dried using a dryer before or after separation from the filter, if necessary. Instead of filtering the dispersion liquid with a filter and drying it, the dispersion liquid may be applied and dried. The thickness of the sponge-like structure 14 and the mass of CNTs per unit volume of the positive electrode 10 (hereinafter referred to as CNT volume density) can be adjusted by performing a treatment such as pressing.

A specific method for obtaining a positive electrode 10 by combining CNT 12 and polysulfide 16 will be described.

As shown in FIG. 3, the positive electrode 10 _{supplies a solution containing polysulfide 16 (hereinafter referred to as a solution of Li 2} S _x ) to the sponge-like structure 14, and Li ₂ S _{x in the sponge-like structure 14.} It is obtained by sequentially carrying out a supply step S1 for holding the solution of Li ₂ S _x and a drying step S2 for drying the sponge-like structure 14 holding the solution of Li 2 S x and carrying the polysulfide 16 on the CNT 12.

In supplying step S1, first, preparing a solution of _Li 2 _{S x.} The solution of Li ₂ S _{x is prepared by dispersing the powder of S 8 and} the powder of Li ₂ S in a solvent. As the solvent, for example, DME (1,2-dimethoxyethane) is used. Put the powder of the powder and Li ₂ S of S ₈ in a solvent, for example, heated to 45 ° C., by stirring with a stirrer, a solution of _Li 2 _{S x} is dissolved _Li 2 _{S x} is obtained. Then, supplies the solution of the prepared _Li 2 _{S x} spongy structure 14. A solution of Li ₂ S _x as the method for supplying the sponge-like structure 14, a method of dropping a solution of _Li 2 _{S x} spongy structure 14, a sponge-like structure 14 in a solution of _Li 2 _{S x} a method of immersing method or the like of applying a solution of using a spray coating method or the like Li ₂ S _x spongy structure 14.

In the drying step S2, it is preferable to dry by _Li 2 _{S x} solutions sponge-like structure 14 to -58 ° C. or higher 90 ° C. below the temperature was maintained. By setting the drying temperature to −58 ° C. or higher and 90 ° C. or lower, an appropriate amount of solvent molecules remain in the _{sponge-like structure 14, and Li 2} S _x in which the solvent molecules are coordinated is the sponge-like structure 14. Is held in. Solvent molecules coordinated Li ₂ S _x is considered to improve the electrode performance. If the drying temperature is too low, the removal of solvent molecules will be inadequate. The drying temperature is too high, Li ₂ S _x is a state having a stable crystal structure, it is considered to inhibit the reaction between sulfur and lithium, it is difficult to improve the electrode performance. The drying temperature is more preferably 0 ° C. or higher and 90 ° C. or lower, and particularly preferably 20 ° C. or higher and 50 ° C. or lower. The lower limit of the drying temperature (-58 ° C.) is an example on the premise that DME is used as a solvent, and is based on the melting point of DME. The lower limit of the drying temperature may be arbitrarily changed depending on the type of solvent.

The drying time can be set arbitrarily, but is preferably 1 second or more and 24 hours or less, and more preferably 10 seconds or more and 10 hours or less. The drying time is set so that an appropriate amount of solvent molecules remain in the sponge-like structure 14.

The mass ratio of the solvent molecules remaining in the sponge-like structure 14 can be arbitrarily set, but is preferably 5% by mass or more and 80% by mass or less, and more preferably 20% by mass or more and 80% by mass or less. .. The mass ratio of the solvent molecules is a value obtained by dividing the mass of the solvent molecules by the mass of the positive electrode 10. The mass of the positive electrode 10 is the sum of the mass of the sponge-like structure 14, the mass of the polysulfide 16, and the mass of the solvent molecule. If the mass ratio of the solvent molecules is too large, it becomes difficult to reduce the E / S ratio in the secondary battery described later. If the mass ratio of the solvent molecules is too small, it becomes difficult to improve the electrode performance. If the solvent molecule is present even slightly in the sponge-like structure 14, since Li ₂ S _x in a state where the solvent molecule is coordinated is held in a sponge-like structure 14, electrode performance to desired is The mass ratio of the solvent molecules may be reduced as long as it can be obtained. The mass ratio of the solvent molecules can be adjusted by adjusting at least one of the drying temperature and the drying time.

In the drying step S2, performs the normal pressure drying or vacuum drying the sponge-like structure 14 which holds the solution of Li ₂ S _x. Normal pressure drying is performed at a pressure substantially equal to atmospheric pressure. Vacuum drying (also referred to as vacuum drying) is carried out, for example, at a vapor pressure of 28 kPa or less at 50 ° C. of the solvent, preferably a vapor pressure of 6.6 kPa or less at 20 ° C. of the solvent. Vacuum drying enables uniform drying without causing uneven drying. S ₈ is likely to evaporate or sublimate under reduced environment due to the high vapor pressure, Li ₂ S _x has not evaporate in a very small pressure environment vapor pressure. By drying the sponge-like structure 14 holding the solution of _{Li 2} S _{x in a reduced pressure environment, the evaporation of Li 2} S _x is suppressed, and the polysulfide 16 can be reliably supported on the CNT 12. Therefore, in the drying step S2, it is preferable that the sponge-like structure 14 which holds the solution of Li ₂ S _x vacuum dried. The pressure for vacuum drying is an example on the premise that DME is used as a solvent, and is based on the vapor pressure of the solvent. The pressure for vacuum drying may be arbitrarily changed depending on the type of solvent.

The secondary battery according to the present embodiment can be manufactured by installing the positive electrode 10, the negative electrode, the separator, and the electrolytic solution in the container. The secondary battery includes a positive electrode 10, a negative electrode, a separator, an electrolytic solution, and a container, and the positive electrode 10, the negative electrode, and the separator may have a configuration provided in the container together with the electrolytic solution, particularly. Not limited. The secondary battery may be one in which the positive electrode 10 and the negative electrode expand or contract due to charging / discharging, for example. Hereinafter, as an example of the embodiment, a secondary battery in which the positive electrode 10 and the negative electrode expand or contract due to charging / discharging will be described.

As shown in FIG. 4, the secondary battery 20 (20A, 20B) includes a positive electrode 10 (10A, 10B), a negative electrode 22 (22A, 22B), and a separator 24. In FIG. 4, the electrolytic solution and the container are not shown. The secondary battery 20 is provided with a positive electrode 10 on one surface of the separator 24 and a negative electrode 22 on the other surface of the separator 24.

The secondary battery 20A at the time of charging includes a contracted positive electrode 10A provided via the separator 24 and an expanded negative electrode 22A. The secondary battery 20B at the time of discharge includes an expanded positive electrode 10B provided via a separator 24 and a contracted negative electrode 22B.

In the present embodiment, the area of the surface of the positive electrode 10 in contact with the separator 24 does not substantially change, the thickness decreases during charging (10A), and the thickness increases during discharging (10B). Expands or contracts as it changes. The positive electrode active material is polysulfide 16 (not shown) before the first charge / discharge, becomes S ₈ (16 A) in _{the charged state, and becomes Li 2} S (16 B) in the discharged state.

As the negative electrode 22, various negative electrodes used in general secondary batteries can be used. In the present embodiment, a negative electrode in which the thickness changes reversibly by charging / discharging, the thickness increases during charging (22A), and the thickness decreases during discharging (22B) is preferable. This is because the expansion and contraction of the positive electrode 10 and the negative electrode 22 cancel each other out, and the space inside the secondary battery 20 can be effectively utilized. The negative electrode active material 26 of the negative electrode 22 is charged and discharged by inserting and removing ^{lithium ions (Li +} ) into the gaps of the crystal structure of, for example, a carbon material (graphite (C) or the like) or lithium titanate. An active material that charges and discharges by reacting with a substance, lithium such as silicon to form a compound, lithium metal, and the like can be used. During charging and discharging, the expansion and contraction of the negative electrode 22 and the positive electrode 10 cancel each other out, and the change in the thickness of the secondary battery 20 is suppressed. Therefore, as the negative electrode active material 26, it is desirable to use an active material whose volume changes by reacting with lithium such as silicon. In order to enable reversible volume change, it is preferable to include the negative electrode active material 26 inside the self-supporting sponge-like structure 14 of the CNT 12. For example, when silicon is used as the negative electrode active material 26, the negative electrode active material 26 becomes Li ₁₅ Si ₄ (26A) in the charged state and Si (26B) in the discharged state.

The separator 24 can be made of a microporous polymer film. Examples of the microporous polymer film include polyolefin-based, polyester-based, polyacrylonitrile-based, polyphenylene sulfide-based, polyimide-based or fluororesin-based micropore membranes and non-woven fabrics. The separator 24 may be composed of a self-supporting sponge-like structure of insulating fibers. The insulating fiber is a BNNT (boron nitride nanotube) or an organic nanofiber. Examples of the organic nanofibers include cellulose nanofibers and chitin nanofibers.

As the electrolytic solution, a commonly used electrolytic solution such as a non-aqueous electrolytic solution, an ionic liquid, and a gel electrolytic solution can be used. The electrolytic solution is, for example, 1.0 mol / L LiTFSI (lithium bis (trifluoromethanesulfonyl) imide) and 0. It can be prepared by dissolving 2 mol / L of LiNO _{3 (lithium nitrate).} By adjusting the amount of the electrolytic solution, the E / S ratio indicating the ratio of the amount of the electrolytic solution to the amount of sulfur can be adjusted. The smaller the E / S ratio, the smaller the mass of the secondary battery 20, and the higher the energy density of the secondary battery 20 can be. The E / S ratio is preferably 8 or less, more preferably 5 or less.

As the container, a metal can such as iron, stainless steel, or aluminum, which is generally used as a battery can, can be used. Further, a metal and polymer laminated sheet generally used for a laminated battery can also be used.

1-3. Actions and Effects The positive electrode 10 according to the present embodiment includes a positive electrode current collector composed of a self-supporting sponge-like structure 14 of CNT 12 and Li ₂ S _x (x = 4, 6,) contained in the sponge-like structure 14. It includes a positive electrode active material made of polysulfide 16 represented by 8). The thickness of the sponge-like structure 14 is 5 μm or more and less than 100 μm. When the content of the polysulfide 16 in the sponge-like structure 14 is expressed by the amount of sulfur per positive electrode volume, the amount of sulfur is 0.70 g / cm ³ or more and 2.0 g / cm ³ or less. Therefore, since the positive electrode 10 contains a large amount of polysulfide 16 in the thin sponge-like structure 14 and has a large amount of sulfur per volume, the positive electrode capacity density per volume (volume capacity density) is high, and the energy of the secondary battery is high. The density can be increased.

Since the positive electrode 10 includes a sponge-like structure 14 having high conductivity as a positive electrode current collector and does not include a current collector foil, the mass and volume can be reduced, and the mass capacity density and volume capacity density can be increased. can.

Since the positive electrode 10 can reduce the amount of the electrolytic solution used when forming the secondary battery 20, the mass and volume of the secondary battery 20 can be reduced, and the energy density of the secondary battery 20 can be increased. ..

The present invention is not limited to the above embodiment, and can be appropriately modified within the scope of the gist of the present invention.

1-4. Example Table 1 summarizes the positive electrode configurations and electrode performances of Examples 1 to 21 and Comparative Examples 1 to 3.

The configuration of the positive electrode will be explained. Examples 1 to 21 are positive electrodes produced by using the above-mentioned method for producing a positive electrode 10. Comparative Example 1 is a positive electrode described in Non-Patent Document 1. In the positive electrode of Comparative Example 1, a CNT foam in which CNTs are immobilized by thermal decomposition of polyacrylonitrile, that is, carbonization, is used as a positive electrode current collector. The CNT form is described in Document [14] (C. Shen, et al., Electrochimica Acta. 248, 90 (2017).) Cited in Non-Patent Document 1. Comparative Examples 2 and 3 are positive electrodes described in Non-Patent Document 2. In the positive electrodes of Comparative Examples 2 and 3, a CNF film composed of CNF (carbon nanofiber) is used as a positive electrode current collector. The sponge-like structure composed of CNTs, the CNT foam, and the CNF film are carbon matrices formed of a carbon material. The description "CNT" in Table 1 indicates the carbon material constituting the above carbon matrix, and includes not only CNT but also CNF.

The film thickness (a) in Table 1 indicates the thickness of the positive electrode. Actually measured values were used in Examples 1 to 21. In Comparative Example 1, the numerical value of the film thickness (100 μm) of the CNT foam described in Non-Patent Document 1 was used. In Comparative Example 2, the numerical value of the minimum value (200 μm) of the film thickness of the CNF film described in Non-Patent Document 2 was used. In Comparative Example 3, the numerical value of the maximum value (250 μm) of the film thickness of the CNF film described in Non-Patent Document 2 was used.

The type of sulfur (b) indicates the type of polysulfide supported on the CNT. In Examples 1 to 4, 7 to 21, Li ₂ S ₆ was used. In Example 5, Li ₂ S ₄ was used. In Example 6, Li ₂ S ₈ was used. _{In Comparative Example 1, Li 2} S ₄ described in Non-Patent Document 1 is described. _{In Comparative Examples 2 and 3, Li 2} S ₈ described in Non-Patent Document 2 is described.

Diameter (c) indicates the diameter of the positive electrode. Actually measured values were used in Examples 1 to 21. In Comparative Example 1, since it is not described in Non-Patent Document 1, it is displayed as "-". In Comparative Examples 2 and 3, the numerical value of the diameter (10 mm) described in Non-Patent Document 2 was used.

CNT (d) indicates the mass of CNT contained in the positive electrode. In Examples 1 to 21, the numerical values of 0.6 to 4.2 mg, which is the mass of CNTs used in the production of each positive electrode, are described. In Comparative Example 1, since it is not described in Non-Patent Document 1, it is displayed as "-". In Comparative Examples 2 and 3, since it is not described in Non-Patent Document 2, it is displayed as "-".

Sulfur (e) indicates the mass of sulfur contained in the positive electrode. In Examples 1 to 21, numerical values of 1.1 to 8.4 mg, which is the mass of sulfur used in the production of each positive electrode, are described. In Comparative Example 1, since it is not described in Non-Patent Document 1, it is displayed as "-". In Comparative Examples 2 and 3, since it is not described in Non-Patent Document 2, it is displayed as "-".

The CNT surface density (f) indicates the mass of CNTs per positive electrode area. In Examples 1 to 21, it was calculated by dividing CNT (d) (mass of CNT) by the area of the positive electrode. ^{In Comparative Example 1, it was calculated by multiplying the density (125 mg / cm 3} ) of the CNT foam described in Non-Patent Document 1 by the film thickness (100 μm). In Comparative Example 2, the numerical value (1.7 mg / cm ² ) described in Non-Patent Document 2 was used. In Comparative Example 3, the numerical value (2.2 mg / cm ² ) described in Non-Patent Document 2 was used.

The sulfur surface density (g) indicates the amount of sulfur per positive electrode area. In Examples 1 to 21, it was calculated by dividing sulfur (e) (mass of sulfur) by the area of the positive electrode. In Comparative Example 1, it was calculated by multiplying the value obtained by dividing the CNT surface density (f) by the mass ratio of CNT by the mass ratio of sulfur. In Comparative Example 1, the mass ratio of sulfur used the numerical value (84%) described in Non-Patent Document 1, and the mass ratio of CNT used the value calculated from the mass ratio of sulfur (16%). In Comparative Examples 2 and 3, the numerical value (6 mg / cm ² ) described in Non-Patent Document 2 was used.

The CNT volume density (h) was calculated by dividing the CNT surface density (f) by the film thickness (a).

The sulfur loading mass (i) indicates the mass of sulfur per unit volume of the positive electrode, and was calculated by dividing the sulfur surface density (g) by the film thickness (a).

The E / S ratio (j) is the volume of the residual solvent molecule obtained by dividing the mass of the solvent molecule remaining in the sponge-like structure 14 by the density of the solvent, and the mass of the additionally charged electrolytic solution as the density of the electrolytic solution. The volume of the additional electrolyte obtained by dividing by is totaled, and the total volume is divided by the amount of sulfur to calculate. In Examples 1 to 21, it was set to 4.0 to 8.0. In Comparative Example 1, the numerical value (4.4 μL / mg) described in Non-Patent Document 1 was used. In Comparative Examples 2 and 3, it was calculated by dividing the ^{amount of electrolytic solution (10 μL / cm 2} ) described in Non-Patent Document 2 by the amount of sulfur (6 mg / cm ^2).

Although not shown in Table 1, in the drying step S2 when manufacturing the positive electrodes of Examples 1 to 8, 11, 14 to 20, the drying conditions are the same, the drying temperature is 45 ° C., the drying time is 60 minutes, and the drying time is normal. Drying under pressure (normal pressure drying) was performed. Other examples will be described with reference to Table 2 described later, but the drying conditions are different.

The electrode performance will be described. The positive electrode of Examples 1 to 21 was housed in a container together with the negative electrode, the separator and the electrolytic solution to prepare a test cell. As the negative electrode, a lithium foil having a thickness of 50 μm was used. The separator used was made of polypropylene. The electrolytic solution was prepared by dissolving _{1.0 mol / L LiTFSI and 0.2 mol / L LiNO 3} in a mixed solution in which DOL and DME were mixed at a volume ratio of 1: 1. Each of the prepared test cells was subjected to a charge / discharge cycle test at a C rate (Capacity rate) of 0.1 C or 0.05 C, and the mass reference capacity (k) was measured. The C rate was defined as 1C = 1.675 mA / mg, assuming that the theoretical volume was expressed relative to the mass of sulfur. Charging and discharging of Examples 1 to 6, 8 to 13, 16 to 20 was carried out at a C rate of 0.1 C, and charging and discharging of Examples 7, 14, 15 and 21 were carried out at a C rate of 0.05 C. The area reference capacity (l) was calculated by multiplying the mass reference capacity (k) by the sum of the CNT surface density (f) and the sulfur surface density (g). The volume reference capacity (m) was calculated by dividing the area reference capacity (l) by the film thickness (a). The mass reference capacitance (k), the area reference capacitance (l), and the volume reference capacitance (m) were defined as the electrode performance. Table 1 shows the maximum value of the mass reference capacity (k) measured in the charge / discharge cycle test, and the area reference capacity (l) and the volume reference capacity (m) calculated based on the mass reference capacity (k). ing. The mass-based capacitance (k) of Comparative Example 1 is the sulfur areal density (g) based on _{the mass-based numerical value (680 mAh / g sulfur} ) of sulfur obtained from the discharge profile (Fig. 5b) described in Non-Patent Document 1. , And the value obtained by dividing by the sum of the CNT areal density (f) and the sulfur areal density (g) was used. The mass reference capacity (k) of Comparative Example 2 is _{obtained by multiplying the mass reference value (900 mAh / g sulfur} ) of sulfur described in Non-Patent Document 2 by the sulfur areal density (g) to obtain the CNT areal density (f). The value obtained by dividing by the sum of the sulfur areal densities (g) was used. The area reference capacity (l) and the volume reference capacity (m) of Comparative Examples 1 to 3 were calculated based on the mass reference capacity (k) as in the examples.

From Table 1, when the positive electrodes of Examples 1 to 21 and the positive electrodes of Comparative Examples 1 to 3 are compared, in Examples 1 to 21 having a film thickness of 5 to 62 μm, Comparative Example 1 having a film thickness of 100 to 250 μm. It was confirmed that the sulfur loading mass (i) and the volume reference capacity (m) were larger than those of 3 to 3. Comparing Examples 1 to 21, it was confirmed that the smaller the film thickness, the larger the volume reference capacity (m), but the smaller the area reference capacity (l).

Table 2 summarizes the relationship between the drying conditions, the DME residual ratio, and the mass reference capacity in the drying step S2 when producing the positive electrodes of Examples 9 to 13.

In Example 13, drying (vacuum drying) was performed at a drying time of 0.17 minutes (10 seconds) and a drying temperature of 20 ° C. (normal temperature) by reducing the pressure so that the pressure difference from the atmospheric pressure was −0.1 MPa. rice field. In Example 9, vacuum drying was performed at a drying time of 10 minutes and a drying temperature of 20 ° C. In Example 12, vacuum drying was performed at a drying time of 60 minutes and a drying temperature of 20 ° C. In Example 11, as described above, drying was performed at normal pressure (normal pressure drying) at a drying time of 60 minutes and a drying temperature of 45 ° C. In Example 10, atmospheric drying was carried out at a drying time of 60 minutes and a drying temperature of 90 ° C. In Table 2, the mass ratio of the solvent molecules remaining in the sponge-like structure is indicated as "DME residual ratio". Table 2 shows the mass reference capacities of the first cycle (1st cycle) and the second cycle (2nd cycle) measured in the charge / discharge cycle test.

From Table 2, it was confirmed that Examples 9, 11 to 13 having a drying temperature of 45 ° C. or lower had a larger DME residual ratio and mass reference capacity than Example 10 having a drying temperature of 90 ° C. Comparing Examples 10 and 11, it was confirmed that in Example 11 having a drying temperature of 45 ° C., the DME residual ratio and the mass reference capacity were larger than those in Example 10 having a drying temperature of 90 ° C. It can be seen that the lower the drying temperature, the higher the DME residual rate and the mass reference capacity tend to be obtained. It was confirmed that the highest DME residual ratio and mass reference capacity were obtained in Example 13 in which vacuum drying was performed at room temperature (20 ° C.) for a short time (10 seconds). Comparing Example 11 having a drying temperature of 45 ° C. and Examples 9, 12 and 13 having a drying temperature of 20 ° C., Example 11 is more than Example 9 and 12 and 13 in terms of mass reference capacity in the first cycle. However, it was confirmed that the mass reference capacity of the second cycle was about the same in Example 11 and Examples 9, 12 and 13. Comparing Examples 9, 12 and 13 in which vacuum drying was performed, in Example 13 having a drying time of 10 seconds, from Example 9 having a drying time of 10 minutes and Example 12 having a drying time of 60 minutes. However, it was confirmed that the DME residual ratio and the mass reference capacity were large. It can be seen that the shorter the drying time, the higher the DME residual rate and the mass reference capacity tend to be obtained.

2. Second Embodiment 2-1. Overall configuration In the first embodiment, the polysulfide 16 is contained in the sponge-like structure 14 composed of CNTs 12, but in the second embodiment, the polysulfides are contained in the sponge-like structure composed of CNTs. In addition, electrolytes and / or additives are further included.

In FIG. 5, the positive electrode for a secondary battery (hereinafter referred to as a positive electrode) 30 according to the second embodiment is a Li ₂ S in a self-supporting sponge-like structure 34 having a thickness of 5 μm or more and less than 100 μm composed of CNT 32. _It contains a polysulfide complex 36 composed of a polysulfide represented by x (x = 4, 6, 8) and an electrolyte and / or an additive. Since the configurations of the CNT 32 and the sponge-like structure 34 have the same configurations as the CNT 12 and the sponge-like structure 14 of the first embodiment, the description thereof will be omitted.

The polysulfide composite 36 is supported on the CNT 32 of the sponge-like structure 34 in a state of being dissolved in a solvent molecule remaining in the solid, semi-solid, or sponge-like structure 34, and is composited with the CNT 32. That is, the polysulfide, electrolyte and / or additive constituting the polysulfide composite 36 is supported on the CNT 32 of the sponge-like structure 34 and is composited with the CNT 32. The polysulfide composite 36 may have a structure that covers the CNT 32 in an island shape, a structure that covers almost the entire surface of the CNT 32, a particle structure, or other predetermined structure. The content of polysulfide in the sponge-like structure 34 is 0.70 g / cm ³ or more and 2.0 g / cm ³ or less, preferably 0.95 g / cm ³ or more 1 in terms of sulfur content, as in the first embodiment. .6 g / cm ³ or less.

Examples of the electrolyte constituting the polysulfide complex 36 include LiTFSI, lithium bis (perfluoroethanesulfonyl) imide (LiBETI), LiClO _{4 , LiBF 4} , LiPF ₆ , lithium trifluoromethanesulfonate (Li triflate), and lithium bis (oxalate) borate. (LiBOB), lithium bis (fluorosulfonyl) imide (LiFSI), LiCF ₃ BO ₃ , Li bromide, Li iodide and the like. _{LiNO 3} described later as an additive can also be used as an electrolyte. The content of the electrolyte in the sponge-like structure 34 can be, for example, a desired electrolytic mass to be contained in the final secondary battery, but is not limited to this, and may be, for example, less than the desired electrolytic mass. ..

Examples of the additive constituting the polysulfide complex 36 include LiNO ₃ , ammonium bis (trifluorosulfonyl) imide (NH ₄ TFSI), fluoroethylene carbonate (FEC) and the like. The electrolyte constituting the above-mentioned polysulfide complex 36 can also be used as an additive. The content of the additive in the sponge-like structure 34 can be, for example, a desired additive amount to be contained in the final secondary battery, but is not limited to this, and is, for example, less than the desired additive amount. May be.

In the positive electrode 30 of the second embodiment, in addition to the polysulfide as the positive electrode active material, the electrolyte and / or the additive constituting the electrolytic solution of the secondary battery is previously supported on the sponge-like structure 34. Therefore, when manufacturing the secondary battery, it is possible to inject only the solvent of the electrolytic solution, or inject the electrolytic solution having a small concentration of the electrolyte and / or the additive. Since the electrolytic solution consisting only of the solvent and the electrolytic solution having a small concentration of the electrolyte and / or the additive have a low viscosity, it easily penetrates into the positive electrode 30, the negative electrode and the separator, and the amount of the electrolytic solution of the secondary battery can be reduced. The E / S ratio can be reduced. The smaller the E / S ratio, the smaller the mass of the secondary battery, and the higher the energy density of the secondary battery can be. Therefore, according to the positive electrode 30 of the second embodiment, it is possible to reduce the E / S ratio and mass of the secondary battery by reducing the amount of the electrolytic solution of the secondary battery, and increase the energy density of the secondary battery. can.

2-2. Manufacturing Method The manufacturing method of the positive electrode 30 according to the second embodiment will be described.

The positive electrode 30, the self-standing in a sponge-like structure 34 is less than the configured thickness 5μm or 100μm from _CNT32, and polysulfides represented by _{Li 2 S x (x = 4,6,8} ), the electrolyte and / or It is produced by containing an additive and combining CNT32, a polysulfide, an electrolyte and / or an additive.

An example of a method for combining CNT32, polysulfide, an electrolyte and / or an additive will be described below.

(First method)
As shown in FIG. 6, referred polysulfides (Li 2 _{S x)} with a solution containing an electrolyte and the additive (hereinafter, polysulfide, a solution containing electrolyte and / or additives and "Li ₂ S _x composite solution" ) was fed to the sponge-like structure 34, a supply step for holding the _Li 2 _{S x} composite solution into a sponge-like structure 34, a sponge-like structure 34 holding the _Li 2 _{S x} composite solution was dried, CNT32 The positive electrode 30 is obtained by sequentially carrying out a drying step of supporting the polysulfide, the electrolyte and the additive in (see FIG. 5). Since the drying step in the first method is the same as the drying step S2 (see FIG. 3) of the first embodiment, the description thereof will be omitted.

In the feeding step of the first method, the Li ₂ S _x composite solution is _{prepared by dispersing the S 8} powder, the Li ₂ S powder, the electrolyte powder, and the additive powder in a solvent. For example, powder of the powder and Li 2 _S of S ₈ to the mixed solution of the additive and a mixed solution of the additive and the electrolyte was prepared, the prepared electrolyte by causing the powder additive and the electrolyte powder is dissolved in a solvent by dissolving with stirring by adding bets can be prepared Li ₂ S _x composite solution. As _{a method of supplying the Li 2} S _x composite solution to the sponge-like structure 34, a method of dropping the solution onto the sponge-like structure 34 or the like can be used as in the supply step S1 in the first embodiment. Li ₂ S _x as the solvent for the complex solution, for example, DME, liquid mixture of the DOL and DME, 1,2-diethoxyethane (DEE), diethylene glycol dimethyl ether (G2), triethylene glycol dimethyl ether (G3), Tetraethylene glycol dimethyl ether (G4), hydrofluoro ether (HFE), N-methyl-2-pyrrolidone (NMP), N, N-dimethylacetamide (DMA), 1,3-dimethyl-2-imidazolidinone (DMI) , 1-Methylimidazole (Melm), ethylmethylsulfone, sulfolane (SL), dimethylsulfoxide (DMSO), acetonitrile (AN), tetrahydrofuran (THF), fluoroethylene carbonate (FEC) and the like can be used.

Supplying step of the first method, in Figure 6, has been supplied Li ₂ S _x composite solution containing a polysulfide electrolyte and additives to the sponge-like structure 34 is not limited to this. It a Li ₂ S _x composite solution containing polysulfide and the electrolyte may be supplied to the sponge-like structure 34, to supply Li ₂ S _x composite solution containing a polysulfide and additives spongy structure 34 You may.

(Second method)
In the first method described above, the Li ₂ S _x composite solution was supplied to the sponge-like structure 34, but in the second method, the solution containing the _{polysulfide (Li 2} S _{x ) (Li 2} S _x solution) was used. , The solution containing the electrolyte (solution of the electrolyte) and the solution containing the additive (solution of the additive) are supplied to the sponge-like structure 34, respectively.

In the second method, as shown in FIG. 7, first, and then feeding the solution of Li ₂ S _x spongy structure 34, provided to hold the solution of Li ₂ S _x in sponge-like structure 34 step , A drying step of drying the sponge-like structure 34 is carried out to prepare a first positive electrode precursor. Next, a supply step of supplying the electrolyte solution to the first positive electrode precursor and holding the electrolyte solution in the first positive electrode precursor, and a drying step of drying the first positive electrode precursor are carried out. 2 Prepare a positive electrode precursor. Next, a supply step of supplying the solution of the additive to the second positive electrode precursor and holding the solution of the additive in the second positive electrode precursor, and a drying step of drying the second positive electrode precursor are carried out. As a result, the positive electrode 30 is manufactured. Since each drying step in the second method is the same as the drying step S2 (see FIG. 3) of the first embodiment, the description thereof will be omitted.

In the feeding step of the second method, the solution of _{Li 2} S _{x is prepared by dispersing the powder of S 8 and} the powder of Li ₂ S in a solvent. The electrolyte solution is prepared by dissolving the electrolyte powder in a solvent. The additive solution is prepared by dissolving the additive powder in a solvent. The _{method of supplying the solution of Li 2} S _x, the solution of the electrolyte, and the solution of the additive to the sponge-like structure 34 is the same as in the supply step S1 in the first embodiment, and the solution is dropped onto the sponge-like structure 34. A method or the like can be used. The solvent used for preparing each solution may be the same solvent or different solvents. In the second method, since the supply and solution of the solution and the electrolyte solution with additives of Li ₂ S _x spongy structure 34 respectively, as a solvent used for preparing each solution, polysulfide, electrolyte, for additives Solvents with high solubility can be selected independently. The solvent of Li ₂ S _x, for example, DME, liquid mixture of the DOL and DME, 1,2-diethoxyethane (DEE), diethylene glycol dimethyl ether (G2), triethylene glycol dimethyl ether (G3), tetraethylene Glycol dimethyl ether (G4), hydrofluoro ether (HFE), N-methyl-2-pyrrolidone (NMP), N, N-dimethylacetamide (DMA), 1,3-dimethyl-2-imidazolidinone (DMI), 1 -Methylimidazole (Melm), ethylmethylsulfone, sulfolane (SL), dimethyl sulfoxide (DMSO), acetonitrile (AN), tetrahydrofuran (THF), fluoroethylene carbonate (FEC) and the like can be used. As the solvent of the electrolyte, for example, in addition to the solvent of the above Li ₂ S _x, it may be an organic solvent such as an alcohol-based or carbonate-based (ethanol, ethylene carbonate, etc.). When the electrolyte is a material that does not react with water, water can be used as the solvent in addition to the above-mentioned organic solvent. As the solvent of the additive, for example, the organic solvent of the above-mentioned electrolyte can be used. When the additive is a material that does not react with water, water can be used as a solvent in addition to the above-mentioned organic solvent.

In Figure 7, to a sponge-like structure 34, a solution of Li ₂ S _x, the solution of the electrolyte, but a solution of the additive was fed in this order, the order to supply each solution is not particularly limited. That is, the order of supplying each solution to the sponge-like structure 34 is Li ₂ S _x solution, additive solution, electrolyte solution, electrolyte solution, additive solution, Li ₂ S _x solution. solution sequentially, the solution of the electrolyte, a solution of _Li 2 _{S x,} the order of the solution of the additive, the solution of the additive, the solution of the electrolyte, the order of the solution of _Li 2 _{S x,} solution additives, _Li 2 _{S x} , The solution of the electrolyte may be in this order. The drying step between each supply step may be omitted as appropriate.

In Figure 7, a solution of Li ₂ S _x, the solution of the electrolyte, but the three solutions of a solution of the additive was fed to the sponge-like structure 34, three solutions of electrolyte solutions or additives out of solution Two kinds of solutions except the above may be supplied. The order in which the two solutions are supplied to the sponge-like structure 34 is not particularly limited. That is, the order for supplying the solution to the sponge-like structure 34, a solution of _Li 2 _{S x,} the order of the solution of additive, solution additives, the order of the solution of _Li 2 _{S x,} of _Li 2 _{S x} solution, the order of the solution of the electrolyte solution of the electrolyte, may be the order of the solution of Li ₂ S _x. The drying step between each supply step may be omitted as appropriate.

When the electrolyte and the additive are materials that do not react with water, the electrolyte solution and the additive solution may be supplied to the sponge-like structure 34 in an air environment. By supplying the electrolyte solution and the additive solution to the sponge-like structure 34 in the air environment, the number of processes performed in the argon (Ar) environment can be reduced, and the manufacturing cost and the burden on the environment can be suppressed. For example, sponge and a solution of the solution and the additive of the electrolyte after drying is supplied to the sponge-like structure 34 in an air environment, in feed and drying to sponge-like structure 34 of a solution of Li ₂ S _x By continuously drying the shaped structure 34 in an Ar environment, the manufacturing cost and the burden on the environment can be suppressed, and the positive electrode 30 can be efficiently manufactured.

(Third method)
In the first method, polysulfide, Li ₂ S _x composite solution containing an electrolyte and / or additives fed to the sponge-like structure 34, in the second method, the Li ₂ S _x solution, the electrolyte A solution and a solution of the additive were supplied to the sponge-like structure 34, respectively. In the third method, two kinds of solutions having different combinations of polysulfide, electrolyte and additive are supplied to the sponge-like structure 34, respectively.

In the third method, as shown in FIG. 8, first, _{a solution containing polysulfide (Li 2} S _x ) (a solution of Li ₂ S _x ) is supplied to the sponge-like structure 34, and the sponge-like structure 34 is contained. a supply step for holding the solution of Li ₂ S _x in, carried out and drying step of drying the sponge-like structure 34, to produce a third positive electrode precursor. Next, a supply step of supplying a solution containing the electrolyte and the additive (solution of the electrolyte and the additive) to the third positive electrode precursor and holding the solution of the electrolyte and the additive in the third positive electrode precursor, and the relevant step. The positive electrode 30 is manufactured by carrying out a drying step of drying the third positive electrode precursor. Since each drying step in the third method is the same as the drying step S2 (see FIG. 3) of the first embodiment, the description thereof will be omitted.

In the feeding step of the third method, the solution of _{Li 2} S _{x is prepared by dispersing the powder of S 8 and} the powder of Li ₂ S in a solvent. The electrolyte and additive solutions are prepared by dissolving the electrolyte powder and the additive powder in a solvent. The _{method of supplying the solution of Li 2} S _x, the solution of the electrolyte and the additive to the sponge-like structure 34 is a method of dropping the solution onto the sponge-like structure 34, similarly to the supply step S1 in the first embodiment. Can be used. The solvent used for preparing each solution may be the same solvent or different solvents. In the third method, since the supply and solution of the solution and the electrolyte and additives Li ₂ S _x spongy structure 34 respectively, as a solvent used for preparing each solution, polysulfide electrolyte, the solubility in an additive Higher solvents can be selected respectively. As the solvent for the li ₂ S _x, the as with the second method, for example, DME, liquid mixture of the DOL and DME, 1,2-diethoxyethane (DEE), diethylene glycol dimethyl ether (G2), tri Ethylene glycol dimethyl ether (G3), tetraethylene glycol dimethyl ether (G4), hydrofluoro ether (HFE), N-methyl-2-pyrrolidone (NMP), N, N-dimethylacetamide (DMA), 1,3-dimethyl-2 -Imidazoridinone (DMI), 1-methylimidazole (Melm), ethyl methyl sulfone, sulfolane (SL), dimethyl sulfoxide (DMSO), acetonitrile (AN), tetrahydrofuran (THF), fluoroethylene carbonate (FEC), etc. are used. be able to. As the solvent of the electrolyte and additives, for example, in addition to the solvent of the above Li ₂ S _x, it may be an organic solvent such as an alcohol-based or carbonate-based (ethanol, ethylene carbonate, etc.).

In Figure 8, to a sponge-like structure 34, a solution of Li ₂ S _x, but the solution of the electrolyte and additives were fed in this order, the order to supply each solution is not particularly limited. Order supplies the solution to a sponge-like structure 34, a solution of electrolytes and additives, may be the order of the solution of Li ₂ S _x. When the electrolyte and the additive are materials that do not react with water, water can be used as the solvent in addition to the above-mentioned organic solvent. The drying step between each supply step may be omitted as appropriate.

In FIG. 8, _{two kinds of solutions, a solution of Li 2} S _{x and} a solution of an electrolyte and an additive, were supplied to the sponge-like structure 34, respectively, but the Li ₂ S _x composite solution and the additive containing polysulfide and the electrolyte were supplied. it solutions and the two solutions may be supplied to the sponge-like structure 34, respectively, containing a polysulfide and additives Li ₂ S _x composite solution and the two solutions spongy each of the solution of the electrolyte It may be supplied to the structure 34. The order in which the two solutions are supplied is not particularly limited. That is, the order to supply the two solutions to a sponge-like structure 34 contains a polysulfide and Li ₂ S _x composite solution containing an electrolyte, the order of the solution of additive, solution additives, polysulfide and the electrolyte order Li ₂ S _x composite solution, Li ₂ S _x composite solution containing polysulphide and additives, the order of the solution of the electrolyte solution of the electrolyte, as the order of Li ₂ S _x composite solution containing polysulphide and additives good. The drying step between each supply step may be omitted as appropriate.

When the electrolyte and the additive are materials that do not react with water, a solution of the electrolyte and the additive, a solution of the electrolyte, and a solution of the additive may be supplied to the sponge-like structure 34 in an air environment. By supplying the electrolyte and additive solution, the electrolyte solution, and the additive solution to the sponge-like structure 34 in the air environment, the number of processes performed in the Ar environment can be reduced, and the manufacturing cost and the burden on the environment can be suppressed. Be done. For example, a solution of the electrolyte and additives after drying is supplied to the sponge-like structure 34 in an air environment, sponge-like structure at the feed and drying steps to sponge-like structure 34 of a solution of Li ₂ S _x By continuously drying 34 in an Ar environment, the manufacturing cost and the load on the environment can be suppressed, and the positive electrode 30 can be efficiently manufactured.

In the first to third methods according to the second embodiment, in addition to the polysulfide as the positive electrode active material, the electrolyte and / or the additive constituting the electrolytic solution of the secondary battery is previously supported on the sponge-like structure 34. can do. Therefore, when manufacturing the secondary battery, it is possible to inject only the solvent of the electrolytic solution, or inject the electrolytic solution having a small concentration of the electrolyte and / or the additive. Since the electrolytic solution consisting only of the solvent and the electrolytic solution having a small concentration of the electrolyte and / or the additive have a low viscosity, it easily penetrates into the positive electrode 30, the negative electrode and the separator, and the amount of the electrolytic solution of the secondary battery can be reduced. The E / S ratio can be reduced. Therefore, according to the first to third methods according to the second embodiment, the amount of the electrolytic solution of the secondary battery is reduced to reduce the E / S ratio and mass of the secondary battery, and the secondary battery The energy density can be increased.

In the first to third methods, a predetermined amount of the electrolyte and / or the additive can be previously supported on the sponge-like structure 34, so that the electrolytic mass and / or the addition to be contained in the electrolytic solution of the secondary battery. By adjusting the amount, the final electrolytic mass and / or the amount of the additive can be adjusted. In the production method of the first embodiment, the electrolytic mass and / or the amount of the additive that can be supplied to the secondary battery is limited to the saturated solubility of the electrolyte and / or the additive in the solvent of the electrolytic solution, but the second embodiment. According to the first to third methods described above, a secondary battery containing an electrolyte and / or an additive having a saturation solubility or higher in the solvent of the electrolytic solution can be produced.

The secondary battery according to the second embodiment can be manufactured by installing the positive electrode 30, the negative electrode, the separator, and the electrolytic solution in the container. The secondary battery according to the second embodiment includes a positive electrode 30, a negative electrode, a separator, an electrolytic solution, and a container, and has a configuration in which the positive electrode 30, the negative electrode, and the separator are provided in the container together with the electrolytic solution. It suffices if it exists, and is not particularly limited. For example, the secondary battery 20 (see FIG. 4) may be configured by using the positive electrode 30 according to the second embodiment instead of the positive electrode 10 according to the first embodiment.

The electrolytic solution used in the secondary battery according to the second embodiment may be different from the electrolytic solution used in the secondary battery according to the first embodiment. In the first embodiment, for example, an electrolytic solution prepared by dissolving 1.0 mol / L LiTFSI as an electrolyte and 0.2 mol / L LiNO ₃ as an additive in a solvent is used, but in the second embodiment, for example. , Or an electrolyte prepared by dissolving a smaller amount of the electrolyte and / or the additive than in the first embodiment in the solvent and containing a low concentration of the electrolyte and / or the additive. You may. An electrolytic solution consisting only of a solvent or an electrolytic solution containing a low-concentration electrolyte and / or an additive has a low viscosity and easily penetrates into the positive electrode 30, the negative electrode and the separator, and reduces the amount of the electrolytic solution of the secondary battery. The E / S ratio can be reduced. Therefore, according to the secondary battery according to the second embodiment, the E / S ratio and mass of the secondary battery can be reduced and the energy density can be increased by reducing the amount of the electrolytic solution.

In the secondary battery according to the second embodiment, the amount of the electrolytic solution and / or the amount of the additive that can be supplied is not limited to the saturated solubility of the electrolyte and / or the additive in the solvent of the electrolytic solution. The secondary battery according to the second embodiment can be supplied with an electrolyte and / or an additive having a saturation solubility or higher in the solvent of the electrolytic solution.

2-3. _{Actions and Effects The positive electrode 30 according to the second embodiment has Li 2} in a self-standing sponge-like structure 34 having a thickness of 5 μm or more and less than 100 μm composed of CNT 32, similarly to the positive electrode 10 according to the first embodiment. The _{polysulfide represented by S x} (x = 4, 6, 8) is contained in a sulfur amount of ^{0.70 g / cm 3} or more and 2.0 g / cm ^{3 or less.} Therefore, the positive electrode 30 has the same effect as the positive electrode 10 according to the first embodiment. That is, since the positive electrode 30 contains a large amount of polysulfide in the thin sponge-like structure 34 and has a large amount of sulfur per volume, the positive electrode capacity density per volume (volume capacity density) is high, and the energy density of the secondary battery is high. Can be enhanced. Further, since the positive electrode 30 includes a sponge-like structure 34 having high conductivity as a positive electrode current collector and does not include a current collector foil, the mass and volume are reduced, and the mass capacity density and volume capacity density are increased. be able to. Further, since the positive electrode 30 can reduce the amount of the electrolytic solution used when forming the secondary battery, the mass and volume of the secondary battery can be reduced, and the energy density of the secondary battery can be increased.

The positive electrode 30 according to the second embodiment is supported in advance in at least one of the electrolyte and the additive in the sponge-like structure 34 in addition to the polysulfide as the positive electrode active material. Therefore, when manufacturing the secondary battery, it is possible to inject only the solvent of the electrolytic solution, or to inject the electrolytic solution having a small concentration of the electrolyte and / or. Since the solvent of the electrolytic solution and the electrolytic solution having a low concentration of the electrolyte and / or are low in viscosity, they easily permeate into the positive electrode 30, the negative electrode and the separator, and the amount of the electrolytic solution of the secondary battery can be reduced. The ratio can be reduced. In the positive electrode 30 according to the second embodiment, the mass of the secondary battery is reduced and the energy density of the secondary battery is increased by reducing the amount of the electrolytic solution of the secondary battery to reduce the E / S ratio. Can be done.

When producing the positive electrode 30 in the second method and the third method, the solution of Li ₂ S _x, with a solution of an electrolyte and / or additives, as each feeding a sponge-like structure 34, each solution A suitable solvent can be selected. For example, water can be used as a solvent for the electrolyte and / or the additive, and the burden on the environment can be suppressed by not using an organic solvent. Further, Li ₂ with saturated solubility is high solvent of Li ₂ S _x in a solvent S _x, uses a high saturation solubility in the electrolyte solvent in a solvent of the electrolyte, the saturation solubility of the additive in a solvent additive Higher solvents can be used. In producing the positive electrode 30 Li 2 _{S x,} electrolyte, solvents selected from the viewpoint of the respective saturation solubility of the additive, a solvent from the viewpoint of improving the characteristics of the secondary battery when configuring the secondary battery By selecting, good secondary battery characteristics can be obtained.

In the second method and the third method, by supplying the solution of the electrolyte and / or the additive in the atmospheric environment, the process performed in the Ar environment can be reduced, so that the manufacturing cost and the burden on the environment can be suppressed. Be done. The supply of the solution of electrolyte and / or additives after performing in an air environment, the supply and drying of Li ₂ S _x composite solution by performing successively with Ar environment, it can provide a positive electrode 30 efficiently.

2-4. Example Table 3 summarizes the configurations of the positive electrodes and the electrode performance of Examples 22 to 28. (A) to (m) in Table 3 were measured or calculated by the same method as in the first embodiment. The charge / discharge cycle test of the test cell was performed at a C rate of 0.1 C. The C rate was defined as 1C = 1.672 mA / mg. Table 4 summarizes the preparation conditions for the positive electrodes and test cells of Examples 22 to 28.

The method for manufacturing the positive electrodes of Examples 22 to 28 will be described below.

The positive electrode of Example 22 was produced by using the method for producing a positive electrode 10 according to the first embodiment. In Example 22, the _Li 2 _{S 8} solution was added dropwise to a sponge-like structure 14 in Ar environment, and vacuum dried in a drying time of 10 minutes. The Li ₂ S ₈ solution was prepared using DME as a solvent so as to contain 0.1 mg / μL of Li ₂ S ₈ equivalent to sulfur (S) as the positive electrode active material. In the positive electrode of Example 22, 4.76 mg of Li ₂ S ₈ was supported on the sponge-like structure 14, and 2.98 mg of undried solvent remained.

The positive electrode of Example 23 was produced by using the first method, which is an example of the method for producing the positive electrode 30 according to the second embodiment. In Example 23, the _Li 2 _{S 8} complex solution was added dropwise to a sponge-like structure 34 in Ar environment, and dried in the same manner as in Example 22. The Li ₂ S _{8 composite solution uses DME as a solvent, Li 2} S ₈ equivalent to 0.1 mg / μL sulfur (S) as the positive electrode active material, 0.4 M LiTFSI as the electrolyte, and 0.08 M as the additive. It was prepared to contain _{LiNO 3 of the above.} M (molar) is synonymous with mol / L. The positive electrode of Example 23, a sponge-like structure 34, _Li 2 _S 8 of 4.64 mg, LiTFSI in 5.05mg, LiNO ₃ of 0.24mg is supported, undried solvent 5.57mg has remained ..

The positive electrode of Example 24 was produced by using the first method, which is an example of the method for producing the positive electrode 30 according to the second embodiment. The positive electrode of the production conditions of Example 24, Li ₂ S ₈ composite volume ratio and DME and DOL as the solvent of the solution 1: Except for using the mixture was mixed solution in 1, and production conditions of the positive electrode of Example 23 It was the same. The positive electrode of Example 24, a sponge-like structure 34, _Li 2 _S 8 of 4.40Mg, LiTFSI in 4.80 mg, LiNO ₃ of 0.23mg is supported, undried solvent 5.54mg has remained ..

The positive electrode of Example 25 was produced by using the second method, which is an example of the method for producing the positive electrode 30 according to the second embodiment. In Example _25, was fed to the sponge-like structure 34 is divided Li ₂ S 8, LiTFSI, a LiNO _{3. In Example 25, first, a solution of Li 2} S ₈ was added dropwise to the sponge-like structure 34 in an Ar environment, and the mixture was dried under reduced pressure with a drying time of 5 seconds to prepare a first positive electrode precursor. Next, the LiTFSI solution was added dropwise to the first positive electrode precursor to prepare a second positive electrode precursor without drying. Next, the LiNO ₃ solution was added dropwise to the second positive electrode precursor, and the mixture was dried under reduced pressure with a drying time of 10 minutes. The solution of Li ₂ S ₈ was prepared using DME as a solvent so as to contain 0.1 mg / μL of Li ₂ S ₈ equivalent to sulfur (S) as the positive electrode active material. The LiTFSI solution was prepared so as to contain 0.1 g / mL LiTFSI using a mixed solution of DME and DOL mixed at a volume ratio of 1: 1 as a solvent. The LiNO ₃ solution was prepared so as to contain _{0.02 g / mL of LiNO 3} using a mixed solution of DME and DOL mixed at a volume ratio of 1: 1 as a solvent. The positive electrode of Example 25, a sponge-like structure 34, _Li 2 _S 8 of 4.19Mg, LiTFSI in 4.56 mg, LiNO ₃ of 0.22mg is supported, undried solvent 1.24mg has remained ..

The positive electrode of Example 26 was produced by using the second method, which is an example of the method for producing the positive electrode 30 according to the second embodiment. In Example 26, first, a LiTFSI solution was dropped onto the sponge-like structure 34 in an air environment to prepare a first positive electrode precursor without drying. _{Next, the LiNO 3} solution was added dropwise to the first positive electrode precursor in the air environment, and the mixture was dried under reduced pressure with a drying time of 10 minutes to prepare a second positive electrode precursor. _{Next, a solution of Li 2} S ₈ was added dropwise to the second positive electrode precursor in an Ar environment, and the mixture was dried under reduced pressure with a drying time of 10 minutes. The Li ₂ S ₈ solution, the LiTFSI solution, and the LiNO ₃ solution were prepared under the same conditions as the respective solutions of Example 25. The positive electrode of Example 26, a sponge-like structure 34, _Li 2 _S 8 of 4.38Mg, LiTFSI in 4.77mg, LiNO ₃ of 0.23mg is supported, undried solvent 4.11mg has remained ..

The positive electrode of Example 27 was produced by using the first method, which is an example of the method for producing the positive electrode 30 according to the second embodiment. _{The conditions for producing the positive electrode of Example 27 include Li 2} S ₈ equivalent to 0.1 mg / μL of sulfur (S) as the positive electrode active material and 0.2 M LiNO _{3 as the additive, using DME as the solvent.} except prepared Li ₂ S ₈ complex solution that was used as were the same as the production conditions of the positive electrode of example 23. That is, in an Ar environment, the Li ₂ S ₈ composite solution was added dropwise to the sponge-like structure 34 and dried. The positive electrode of Example 27, a sponge-like structure 34, _Li 2 _S 8 of 4.43mg, LiNO ₃ of 0.58mg is supported, undried solvent 4.65mg remained.

The positive electrode of Example 28 was produced by using the second method, which is an example of the method for producing the positive electrode 30 according to the second embodiment. In Example 28, LiNO ₃ and Li ₂ S ₈ were divided and supplied to the sponge-like structure 34. In Example 28, first, a LiNO ₃ solution was added dropwise to the sponge-like structure 34 in an air environment, and the mixture was dried under reduced pressure with a drying time of 10 minutes to prepare a first positive electrode precursor. _{Next, a solution of Li 2} S ₈ was added dropwise to the first positive electrode precursor in an Ar environment, and the mixture was dried under reduced pressure with a drying time of 10 minutes. The Li ₂ S ₈ solution and the LiNO ₃ solution were prepared under the same conditions as _{the Li 2} S ₈ solution and the LiNO _{3 solution of Example 26.} The positive electrode of Example 28, a sponge-like structure 34, _Li 2 _S 8 of 4.33mg, LiNO ₃ of 0.68mg is supported, undried solvent 4.03mg remained.

The test cells using the positive electrodes of Examples 22 to 28 will be described below.

The positive electrode of Examples 22 to 28 was housed in a container together with the negative electrode, the separator and the electrolytic solution to prepare a test cell. As the negative electrode, a lithium foil having a thickness of 50 μm was used. The separator used was made of polypropylene. As the solvent of the electrolytic solution, a mixed solution in which DME and DOL were mixed at a volume ratio of 1: 1 was used.

A test cell using the positive electrode of Example 22 in which Li ₂ S ₈ was carried was prepared by dissolving 1 mol / L LiTFSI as an electrolyte and 0.20 mol / L LiNO ₃ as an additive in the above solvent. The electrolyte was injected (see Table 4). From Tables 3 and 4, it was confirmed that Example 22 had a large volume reference capacity and mass reference capacity.

For the test cell using the positive electrodes of Examples 23 to 26 in which LiTFSI and LiNO _{3 are supported in addition to Li 2} S _{8 , the LiTFSI concentration and the LiNO 3} concentration in the test cell are the positive electrodes of Example 22. Only the above solvent was injected as the electrolytic solution so as to be equivalent to _{the LiTFSI concentration and the LiNO 3} concentration of the electrolytic solution in the test cell. From Tables 3 and 4, it was confirmed that Examples 23 to 26 had a large volume reference capacity and mass reference capacity.

_{By using the positive electrode of Example 27, LiNO 3} (additive) having a saturation solubility or higher in the solvent of the electrolytic solution in the secondary battery can be supplied. In addition to _{Li 2} S _{8 , Li NO 3} is supported on the positive electrode of Example 27. In the test cell using the positive electrode of Example 27, the LiTFSI concentration was equivalent to the LiTFSI concentration (1 mol / L) _{of the electrolytic solution of Example 22, and the LiNO 3 concentration was the LiNO 3} concentration (0) of the electrolytic solution of Example 22. An electrolytic solution prepared to have a concentration of 0.80 mol / L, which is higher than .20 mol / L), was injected. As a result, in the test cell using the positive electrode of Example 27, the _{concentration of LiNO 3} in the test cell was 1.04 mol / L _{due to the LiNO 3 supported on the positive electrode and the LiNO 3} contained in the electrolytic solution. rice field. Here, the _{saturated solubility of LiNO 3} in DME is estimated to be about 1 mol / L (C. Burke et al., Proceedings of the National Academy of Sciences of the United States of America, 112, (2015) 9293. Etc. reference). Therefore, the test cell using the positive electrode of Example 27 is supplied with _{an additive (LiNO 3) having a saturation solubility or higher in the solvent of the electrolytic solution.} From Tables 3 and 4, it was confirmed that Example 27 had a large volume reference capacity and mass reference capacity.

The test cell using the positive electrode of Example 28 does not contain the electrolyte LiTFSI contained in the test cell using the positive electrode of Examples 22 to 27, and LiNO ₃ supported on the positive electrode is made to function as an electrolyte. ing. In addition to _{Li 2} S _{8 , Li NO 3} is supported on the positive electrode of Example 28. The test cell using the positive electrode of Example 28, LiNO ₃ concentration in the test cell so that 0.53 mol / L, was injected only the solvent as an electrolyte. From Tables 3 and 4, it was confirmed that Example 28 had a large volume reference capacity and mass reference capacity.

10,30 positive electrode (positive electrode for secondary battery)
12,32 Carbon nanotubes (CNT)
14,34 Sponge-like structure 16 Polysulfide (Li ₂ S _x (x = 4, 6, 8))
20 Rechargeable battery 22 Negative electrode 24 Separator 36 Polysulfide composite

Claims (14)

1. A sponge-like structure in which the self-supporting under constructed thickness 5μm or 100μm from carbon _nanotubes, polysulfides represented by _{Li 2 S x (x = 4,6,8} ) is, 0.70 g / cm ³ or more 2 A positive electrode for a secondary battery containing a sulfur content of 0.0 g / cm ^{3 or less.}
2. Contain a polysulfide represented spongy structure in which autonomous below configured thickness 5μm or 100μm from carbon nanotubes _{Li 2 S x (x = 4,6,8} ), the carbon nanotube and said polysulfide A method for manufacturing a positive electrode for a secondary battery.
3. A supply step of supplying the solution containing the polysulfide to the sponge-like structure and holding the solution in the sponge-like structure.
   The method for producing a positive electrode for a secondary battery according to claim 2, further comprising a drying step of drying the sponge-like structure holding the solution and supporting the polysulfide on the carbon nanotubes.
4. The method for manufacturing a positive electrode for a secondary battery according to claim 3, wherein in the drying step, the sponge-like structure holding the solution is dried at a temperature of −58 ° C. or higher and 90 ° C. or lower.
5. The method for manufacturing a positive electrode for a secondary battery according to claim 3 or 4, wherein in the drying step, the sponge-like structure holding the solution is vacuum-dried.
6. The method for producing a positive electrode for a secondary battery according to any one of claims 2 to 5, wherein the amount of sulfur in the polysulfide in the sponge-like structure is 0.70 g / cm ³ or more and 2.0 g / cm ^{3 or less.} ..
7. The positive electrode for a secondary battery according to claim 1, wherein the sponge-like structure further contains an electrolyte and / or an additive in addition to the polysulfide.
8. The secondary according to claim 2, wherein the sponge-like structure contains an electrolyte and / or an additive in addition to the polysulfide, and the carbon nanotube, the polysulfide, the electrolyte and / or the additive are combined. A method for manufacturing a positive electrode for a battery.
9. The method for producing a positive electrode for a secondary battery according to claim 8, wherein a solution containing the polysulfide, the electrolyte and / or the additive is supplied to the sponge-like structure.
10. The method for producing a positive electrode for a secondary battery according to claim 8, wherein the solution containing the polysulfide, the solution containing the electrolyte, and / or the solution containing the additive are supplied to the sponge-like structure, respectively.
11. The method for producing a positive electrode for a secondary battery according to claim 10, wherein the solution containing the electrolyte and / or the solution containing the additive is supplied to the sponge-like structure in an atmospheric environment.
12. A secondary battery in which the positive electrode, the negative electrode, and the separator according to claim 1 are provided in a container together with an electrolytic solution.
13. A secondary battery in which the positive electrode, the negative electrode, and the separator according to claim 7 are provided in a container together with an electrolytic solution.
14. The secondary battery according to claim 13, which contains the electrolyte and / or the additive having a saturation solubility or higher of the solvent of the electrolytic solution.

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