JP2014170655A - Electrode for all-solid-state battery and all-solid-state battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrode for an all-solid-state battery, having an electrode mixture capable of suppressing the change of a composition and reducing an increased amount of a volume due to an addition of a conductive assistant.SOLUTION: Electrodes 1 and 2 for an all-solid-state battery of the present invention are electrodes for an all-solid-state battery including collectors 11 and 21 and electrode mixtures 12 and 22 including an electrode active material, a sulfide-based solid electrolyte and a conductive assistant, respectively. The conductive assistant comprises a metal sulfide.

Description

  The present invention relates to an electrode for an all solid state battery and an all solid state battery using the same.

  As an example of a conventional electrode for an all solid state battery, there is one containing an active material powder, a sulfide-based solid electrolyte powder, and a conductive additive containing at least one of nickel and titanium (Patent Document 1). In addition, as an example of a conventional all-solid battery, a solid electrolyte is interposed between a positive electrode layer and a negative electrode layer, and the positive electrode layer and the negative electrode layer include an electrode active material and a sulfide-based solid electrolyte, acetylene black, carbon fiber, etc. There is a thing containing the conductive support material of this (patent document 2).

JP 2012-133932 A JP 2011-154900 A

  However, in such a conventional all-solid-state battery electrode, when a sulfide-based solid electrolyte powder is used, the composition of the electrolyte may be changed by a chemical reaction between nickel or titanium as a conductive additive and sulfide of the solid electrolyte. is there. Moreover, in such a conventional all solid state battery, when a conductive auxiliary material such as a carbon material having a low density is added, an increase in the volume of the electrode mixture may increase. As a result of these, the discharge energy density may decrease.

  An object of the present invention is to provide an electrode for an all solid state battery having an electrode mixture capable of suppressing a change in composition and reducing an increase in volume due to the addition of a conductive additive, and an all solid state battery using the same. To do.

  An electrode for an all solid state battery according to the present invention is an electrode for an all solid state battery having a current collector, and an electrode mixture containing an electrode active material, a sulfide-based solid electrolyte, and a conductive additive. It is a metal sulfide.

  In this all solid state battery electrode, the metal sulfide is preferably a monosulfide, more preferably a sulfide of a transition metal element, and particularly at least one of NiS, CoS, and FeS. It is more preferable. And it is preferable that the addition amount of a metal sulfide is 1 to 5% by volume ratio with respect to an electrode compound material.

  An all solid state battery according to the present invention is an all solid state battery in which a solid electrolyte is provided between a pair of electrodes, wherein the all solid state battery electrode is used for at least one of the pair of electrodes. It is.

  According to the electrode for an all-solid-state battery of the present invention, the chemical reaction between the sulfide-based solid electrolyte and the conductive additive is suppressed by using a metal sulfide as the conductive additive, thereby suppressing the change in the composition of the electrolyte. be able to. And according to the all solid state battery using the electrode for all solid state battery of the present invention, by using a metal sulfide having a high density for the conductive additive, the increase in the volume of the electrode mixture is reduced. While increasing the volume of the solid battery can be reduced, the electron conductivity can be improved while maintaining the ionic conductivity of the electrode mixture. As a result, the discharge energy density can be improved.

It is sectional drawing which shows the structure of the Example of the all-solid-state battery using the electrode for all-solid-state batteries which concerns on this invention.

An embodiment of an all-solid battery according to the present invention will be described with reference to FIG.
In this embodiment, the case where the all solid state battery is an all solid state lithium ion secondary battery (hereinafter simply referred to as a secondary battery) is shown. As shown in FIG. 1, the secondary battery includes a pair of electrodes that function as a positive electrode 1 and a negative electrode 2, and a lithium ion conductive solid electrolyte that is a solid electrolyte 3 between them. Each of the electrodes 1 and 2 includes electrode composites 12 and 22 and current collectors 11 and 21, respectively. That is, as shown in FIG. 1, the electrode mixture 12 of the positive electrode 1 is disposed adjacent to the surface of the solid electrolyte 3, and the electrode mixture 22 of the negative electrode 2 is adjacent to the back surface facing the surface of the solid electrolyte 3. The current collectors 11 and 21 are disposed on the outermost side.

  As the current collectors 11 and 21, copper (Cu), magnesium (Mg), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn), aluminum (Al ), Germanium (Ge), indium (In), lithium (Li), tin (Sn), or a plate-like body, foil-like body or powder made of an alloy thereof. In this embodiment, Sn is used as the current collector 11 of the positive electrode 1 (hereinafter simply referred to as the positive current collector 11), and Sn is used as the current collector 21 of the negative electrode 2 (hereinafter simply referred to as the negative current collector 21). Adopts Cu respectively.

  The electrode composites 12 and 22 are a mixture in which an electrode active material that secures an electron conduction path between particles, a sulfide-based solid electrolyte, and a conductive additive are mixed at a predetermined ratio in order to perform an oxidation-reduction reaction for sending and receiving electrons. It is a material. In this embodiment, a lithium ion conductive solid electrolyte is used as the sulfide-based solid electrolyte. Thus, by mixing a lithium ion conductive solid electrolyte with the electrode active material, ion conductivity can be imparted in addition to electron conductivity, and an ion conduction path can be secured between the particles.

The electrode active material suitable for the electrode mixture 12 of the positive electrode 1 (hereinafter simply referred to as the positive electrode mixture 12) is not particularly limited as long as it can insert and desorb lithium ions. For example, lithium-nickel composite oxide (LiNi _x M _1-x O ₂ , where M is at least one of Co, Al, Mn, V, Cr, Mg, Ca, Ti, Zr, Nb, Mo and W Elements), layered oxides such as lithium cobaltate (LiCoO ₂ ), lithium nickelate (LiNiO ₂ ), lithium manganate (LiMn ₂ O ₄ ), lithium iron phosphate (LiFePO ₄ ) having an olipine structure, spinel structure A solid solution such as lithium manganate (LiMn ₂ O ₄ , Li ₂ MnO ₃ , LiMO ₂ ) or a mixture thereof, or a sulfide such as sulfur (S) or lithium sulfide (Li ₂ S) can also be used. In this embodiment, as the positive electrode active material 12a, specifically, a lithium / nickel / cobalt / aluminum composite oxide (LiNi _0.8 Co _0.15 Al _0.05 O ₂ , hereinafter abbreviated as NCA). Is adopted.

On the other hand, examples of the electrode active material suitable for the electrode mixture 22 of the negative electrode 2 (hereinafter simply referred to as the negative electrode mixture 22) include carbon materials such as natural graphite, artificial graphite, graphite carbon fiber, and resin-fired carbon. It will not be limited if it is compounded with a sulfide type solid electrolyte. For example, a metal oxide such as lithium titanate (Li ₄ Ti ₅ O ₁₂ ) can also be used. In this embodiment, natural or artificial graphite is employed.

The electrode active materials usable for both electrodes 1 and 2 include zirconia (ZrO ₂ ), alumina on the surface of the electrode active material 12 a used for the positive electrode mixture 12 and the electrode active material used for the negative electrode mixture 22. (Al ₂ O ₃ ), lithium titanate (Li ₄ Ti ₅ O ₁₂ ), lithium niobate (LiNbO ₃ ), carbon (C) and the like may be used.

As the lithium ion conductive solid electrolyte, a material composed of an organic compound or an inorganic compound, or a mixture of an organic and an inorganic compound can be used, and those known in the field of lithium ion batteries can be used. In the present embodiment, since the sulfide solid electrolyte is known to have higher ionic conductivity than other inorganic compounds, a sulfide inorganic solid electrolyte is employed. Specifically, Li ₂ S—P ₂ S ₅ system, Li ₂ S—GeS ₂ system, Li ₂ S—Ge ₂ S ₂ system, Li ₂ S—GeS ₂ —P ₂ S ₅ system, Li ₂ S— Examples thereof include glass ceramics such as GeS ₂ —ZnS and Li ₂ S—SiS ₂ . In the present _embodiment employs a Li 2 _S-P 2 _{S 5} -based glass ceramic.

  Since a sulfide-based solid electrolyte is used for the positive electrode mixture 12 and the negative electrode mixture 22 as described above, a metal sulfide is used as the conductive additive for the purpose of suppressing changes in the composition of the electrolyte. The metal sulfide is preferably a monosulfide formed by combining a divalent sulfide ion and a divalent metal ion. This is because monosulfide has a high density and can improve the discharge energy density. Furthermore, the metal sulfide is more preferably a transition metal element sulfide having high electrical conductivity. In this embodiment, nickel sulfide (NiS), cobalt sulfide (CoS), and iron sulfide (FeS) are employed as the metal sulfide.

Here, as Experimental Examples 1 to 7, secondary batteries using a positive electrode mixture 12 containing a metal sulfide as a conductive additive were produced. Moreover, the comparative example 1 containing the carbon fiber (VGCF: trademark) synthesize | combined by the gaseous-phase method as a conductive support material was produced. Furthermore, as a reference example, a secondary battery was fabricated using a positive electrode mixture 12 that did not contain a conductive additive. For Experimental Examples 1 to 7, Comparative Example 1 and Reference Example 1, evaluation experiments for measuring the discharge energy density were performed.
[Experimental Example 1]
50 mg of Li ₂ S—P ₂ S ₅ glass ceramic powder was weighed and placed in a cylindrical mold made of an alloy tool steel (SKD: cold die steel) with an inner diameter of 10 mm, and pressure was 188 MPa using a single-acting press. Was pressed once to form a solid electrolyte 3. Next, graphite powder and Li ₂ S (70 mol%)-P ₂ S ₅ (30 mol%) powder were mixed at a ratio of 60:40, and 15 mg of the obtained mixture was weighed and put into a cylindrical mold. Then, using a single-acting press, it was pressure-molded three times at a pressure of 188 MPa. The graphite powder used here is coated with low crystalline carbon. In preparation of the positive electrode mixture 12, after mixing 70 mg of NCA and 2 mg of NiS having a true density of 5.3 g / cm ³ (volume percent concentration 1.2 vol%, volume ratio 1.2%), Li ₂ S (70 mol%) was mixed. ) -P ₂ S ₅ (30 mol%) glass ceramic powder 30 mg was added and mixed, and 20 mg of the resulting mixture was weighed and charged from the side opposite to the side where the negative electrode mixture 22 of the cylindrical mold was charged. Using a dynamic press machine, it was press-molded three times successively at 376 MPa, 752 MPa, and 1050 MPa, and taken out from the cylindrical mold. Finally, the negative electrode mixture 22 side is inserted into a hole of 11 mm in diameter opened in the insulating film 4 (illustrated in FIG. 1) covering Cu of the negative electrode current collector 21, and the positive electrode current collector 11 is placed on the positive electrode mixture 12. Is placed in a bag-like container having a positive electrode lead and a negative electrode lead in a vacuum state, and the secondary battery is connected by connecting the positive electrode current collector 11 to the positive electrode lead and the negative electrode current collector 21 to the negative electrode lead. Produced. Here, the bag-like container is sucked (evacuated) and kept at a certain degree of vacuum (hereinafter referred to as a vacuum state) so that it is not affected by moisture.

The secondary battery is placed in a thermostat, the temperature is 30 ° C., the pressure applied to the secondary battery is 78.4 MPa, the charge end voltage is 4.0 V, the charge current is 0.1 mA / cm ² , and the discharge end voltage is 2.0 V. Under the conditions of a discharge current of 0.1 mA / cm ² , charging and discharging with a constant current were performed, and an evaluation experiment for determining the discharge energy density Wh / kg-NCA was performed. The values are shown in Table 1. Here, in this specification, the unit [Wh / kg-NCA] refers to the discharge energy density per weight of NCA. The calculation is based on a known method, and is obtained by dividing the energy [Wh] obtained from the voltage and capacity by the weight [kg] of the NCA.
[Experiment 2]
In the production of the positive electrode mixture 12, a positive electrode mixture 12 to which FeS having a true density of 4.8 g / cm ³ was added so as to have a concentration of 1.2 vol% (volume ratio 1.2%) was used as a conductive additive. Other than that, a secondary battery was fabricated in the same manner as in Example 1, and an evaluation experiment was performed. The discharge energy density in Experimental Example 2 is shown in Table 1.
[Experiment 3]
In the production of the positive electrode mixture 12, CoS having a true density of 5.5 g / cm ³ was added as a conductive auxiliary so as to have a concentration of 1.2 vol% (volume ratio: 1.2%). Similarly, a secondary battery was produced and an evaluation experiment was performed. The discharge energy density in Experimental Example 3 is shown in Table 1.
[Experimental Example 4]
In the production of the positive electrode mixture 12, the same NiS as in Example 1 was added as a conductive auxiliary so as to have a concentration of 0.6 vol% (volume ratio 0.6%). A secondary battery was fabricated and an evaluation experiment was performed. The discharge energy density in Experimental Example 4 is shown in Table 1.
[Experimental Example 5]
In the production of the positive electrode mixture 12, the same NiS as that of Example 1 was added so as to have a concentration of 2.4 vol% (volume ratio 2.4%) as the conductive auxiliary material, and the others were the same as in Example 1. A secondary battery was fabricated and an evaluation experiment was performed. The discharge energy density in Experimental Example 5 is shown in Table 1.
[Experimental Example 6]
In the production of the positive electrode mixture 12, the same NiS as that of Example 1 was added so as to have a concentration of 4.8 vol% (volume ratio of 4.8%) as the conductive auxiliary material. A secondary battery was fabricated and an evaluation experiment was performed. The discharge energy density in Experimental Example 6 is shown in Table 1.
[Experimental Example 7]
In the production of the positive electrode mixture 12, the same NiS as in Example 1 was added as a conductive additive so as to have a concentration of 6.0 vol% (volume ratio 6.0%). A secondary battery was fabricated and an evaluation experiment was performed. The discharge energy density in Experimental Example 7 is shown in Table 1.
[Comparative Example 1]
A positive electrode to which carbon fiber (VGCF: registered trademark) synthesized by a vapor phase method having a true density of 2.0 g / cm ³ is added as a conductive additive so as to have a concentration of 4.8 vol% (volume ratio 4.8%). A composite material 12 was prepared, and the others were fabricated in the same manner as in Example 1, and the same evaluation experiment as in Experimental Example 1 was performed. The discharge energy density in Comparative Example 1 is shown in Table 1.
[Reference Example 1]
As Reference Example 1, a secondary battery was prepared in the same manner as in Example 1 without adding a conductive additive to the positive electrode mixture 12, and the same evaluation experiment as in Experimental Example 1 was performed. The discharge energy density in Reference Example 1 is shown in Table 1.

  As shown in Table 1, the discharge energy density of Comparative Example 1 is 493 Wh / kg-NCA, which is almost the same value as the discharge energy density 496 Wh / kg-NCA of Reference Example 1 in which no conductive additive is added, and VGCF ( (Registered trademark) does not have an appropriate effect as a conductive additive.

  As shown in Table 1, in Example 1, the discharge energy density is 514 Wh / kg-NCA, and by adding NiS to the positive electrode mixture 12 as a conductive additive, electrons are added between the positive electrode active material and the conductive additive. It can be confirmed that the conduction path is formed, the conductivity is improved, and the discharge energy density is improved as compared with Comparative Example 1. Also in Examples 2 and 3, FeS and CoS each had the same effect as NiS addition in Example 1, and the discharge energy densities were 513 Wh / kg-NCA and 509 Wh / kg-NCA, respectively, from Comparative Example 1 Also improved. In Examples 4 to 7, by adding 0.6 to 6.0% of the conductive auxiliary material NiS by volume ratio, the discharge energy density is 505 Wh / kg-NCA, 524 Wh / kg-NCA, 516 Wh / kg-NCA in order, It was 507 Wh / kg-NCA, and it can be confirmed that it was improved over Comparative Example 1. And when Experimental Example 6 and Comparative Example 1 are compared, the addition amount as the conductive additive is the same concentration of 4.8 vol%, and the additive amount of the conductive additive in Experimental Examples 1 to 5 is the concentration of 4.8 vol. % Or less. From these facts, by using a metal sulfide having a higher true density than that of the carbon material, a discharge energy density higher than that when the carbon material is used (Comparative Example 1) can be obtained even if the amount of addition is reduced. Is shown. As a result, it shows that the performance of the all-solid-state battery is improved as compared with the case where the carbon material is used as the conductive additive.

  According to the electrode for an all-solid-state battery of the present invention, the use of metal sulfide as a conductive additive suppresses the chemical reaction between the sulfide-based solid electrolyte and the conductive additive, thereby suppressing changes in the electrolyte. it can. And according to the all-solid-state battery using the electrode for all-solid-state batteries of this invention, the increase amount of the volume of the electrode compound materials 12 and 22 is reduced by using a metal sulfide with a high density for a conductive support material. Therefore, the increase in the volume of the all-solid-state battery can be reduced, and the electron conductivity can be improved while maintaining the ionic conductivity of the electrode composites 12 and 22. As a result, the discharge energy density can be improved.

実験例１〜７の結果から、金属硫化物の添加量は、正極合材１２に対して体積比１〜５％であることがより好ましいことがわかる。また、実験例１〜７の結果から、本実施例に係る電極合材は正極１にのみ用いたが、適切な効果が得られることがわかった。したがって、一対の電極のうち少なくとも一方に、全固体電池用電極を用いられればよいことがわかる。

From the results of Experimental Examples 1 to 7, it can be seen that the addition amount of the metal sulfide is more preferably 1 to 5% by volume with respect to the positive electrode mixture 12. Moreover, although the electrode compound material which concerns on a present Example was used only for the positive electrode 1 from the result of Experimental example 1-7, it turned out that a suitable effect is acquired. Therefore, it is understood that an all solid state battery electrode may be used for at least one of the pair of electrodes.

  In the present embodiment, no binder is used for the pressure molding of the electrode mixtures 12 and 22, but the electrode mixture may naturally be pressure molded using a binder.

1 Positive electrode (electrode)
11 Positive current collector (current collector)
12 Positive electrode mixture (electrode mixture)
2 Negative electrode (electrode)
21 Negative electrode current collector (current collector)
22 Negative electrode composite (electrode composite)
3 Solid electrolyte 4 Insulating film

Claims (6)

An electrode for an all-solid battery having a current collector and an electrode mixture containing an electrode active material, a sulfide-based solid electrolyte, and a conductive additive,
An electrode for an all-solid battery, wherein the conductive additive is a metal sulfide.   The electrode for an all-solid-state battery according to claim 1, wherein the metal sulfide is a monosulfide.   3. The electrode for an all solid state battery according to claim 1, wherein the metal sulfide is a sulfide of a transition metal element.   The electrode for an all solid state battery according to any one of claims 1 to 3, wherein the metal sulfide is at least one of NiS, CoS, and FeS.   The electrode for an all-solid-state battery according to any one of claims 1 to 4, wherein the addition amount of the metal sulfide is 1 to 5% by volume with respect to the electrode mixture. An all-solid battery in which a solid electrolyte is provided between a pair of electrodes,
An all solid state battery using the all solid state battery electrode according to any one of claims 1 to 5 as at least one of the pair of electrodes.

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