JP2015069848A - All-solid-state battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an all-solid-state battery suppressed in deterioration of discharge capacity.SOLUTION: An all-solid-state battery comprises a plurality of stacked cells, each including: a positive electrode having a positive electrode collector and a positive electrode active material layer formed on the positive electrode collector and containing a positive electrode active material; a negative electrode having a negative electrode collector and a negative electrode active material layer formed on the negative electrode collector and containing a negative electrode active material; and a solid electrolyte layer disposed between the positive electrode active material layer and the negative electrode active material layer and containing a solid electrolyte. In the all-solid-state battery, the positive electrode active material, the negative electrode active material, and the solid electrolyte include a sulfide solid electrolyte, and a copper foil is used as the negative electrode collector at a place where battery temperature is relatively low, while a copper foil having a conductive coat or a foil producing no CuS is used at a place where battery temperature is relatively high.

Description

  The present invention relates to an all-solid battery that prevents sulfidation of a negative electrode current collector and suppresses a decrease in discharge capacity.

  With the rapid spread of information-related equipment and communication equipment such as personal computers, video cameras, and mobile phones in recent years, development of batteries that are used as power sources has been regarded as important. Also in the automobile industry and the like, development of high-power and high-capacity batteries for electric vehicles or hybrid vehicles is being promoted. Currently, lithium batteries are attracting attention among various batteries from the viewpoint of high energy density.

  Since lithium batteries currently on the market use an electrolyte containing a flammable organic solvent, it is possible to install safety devices that suppress the temperature rise during short circuits and to improve the structure and materials to prevent short circuits. Necessary. In contrast, a lithium battery in which the electrolyte is changed to a solid electrolyte layer to make the battery completely solid does not use a flammable organic solvent in the battery, so the safety device can be simplified, and manufacturing costs and productivity can be reduced. It is considered excellent. Furthermore, sulfide solid electrolytes are known as solid electrolytes used for such solid electrolyte layers or electrode active material layers. The sulfide solid electrolyte is a material that has high Li ion conductivity and has been attracting attention in order to increase the output of the battery.

  In addition, various metals have been conventionally used as electrode current collectors used in lithium batteries. Of these, copper (Cu), nickel (Ni), and the like are preferably used because of their high conductivity and excellent current collecting characteristics.

  Therefore, in recent years, an attempt has been made to make an all-solid battery with more excellent battery characteristics by combining the above-described sulfide solid electrolyte and the above-described electrode current collector. However, in an all-solid battery using a sulfide solid electrolyte, when a current collector is formed using a conductive material containing Ni or Cu, the current collector and sulfur react, and the solid electrolyte and current collector There has been a problem that the resistance at the interface tends to increase.

  In order to solve such a problem, it has been proposed to provide a reaction suppression layer containing Cr or the like between the negative electrode current collector and the solid electrolyte (Patent Document 1).

JP 2012-49023 A

  In the technique disclosed in Patent Document 1, when a copper foil is used as the negative electrode current collector, the temperature inside the battery is high, and CuS is easily generated when the temperature is high. There was a problem. Also, when using a metal foil other than copper as the negative electrode current collector, electrical conductivity and thermal conductivity are low, and replacing the negative electrode current collector with a metal other than copper has problems of uneven reaction and heat sinking. . Furthermore, when the present inventors used a metal that reacts with sulfur, such as Cu, as a negative electrode current collector in an all-solid battery having a negative electrode layer containing a sulfide solid electrolyte, the metal reacts with the sulfide solid electrolyte. It has been found that the problem that the capacity of the all-solid-state battery decreases due to the sulfur compound produced in this way.

  Therefore, an object of the present invention is to provide an all solid state battery that prevents the negative electrode current collector from being sulfided and suppresses a decrease in discharge capacity.

  In order to solve the above problems, according to the present invention, a positive electrode current collector, a positive electrode formed on the positive electrode current collector and having a positive electrode active material layer containing a positive electrode active material, a negative electrode current collector, and A negative electrode having a negative electrode active material layer formed on the negative electrode current collector and containing a negative electrode active material, and a solid electrolyte layer containing a solid electrolyte disposed between the positive electrode active material layer and the negative electrode active material layer A positive electrode active material, a negative electrode active material and a solid electrolyte containing a sulfide solid electrolyte, and a location where the battery temperature is relatively low as a negative electrode current collector The present invention provides an all solid state battery using a copper foil and a copper foil having a conductive coating or a foil that does not produce CuS in a place where the battery temperature is relatively high.

  According to the present invention, as a negative electrode current collector in a place where the battery temperature is relatively high inside the battery, a copper foil having a conductive coating or a foil that does not generate CuS is used instead of a copper foil. It is possible to suppress generation and prevent variation in capacity, and by using a copper foil as a negative electrode current collector in a place where the battery temperature is relatively high inside the battery, all of the negative electrode current collector is made other than copper. Therefore, the cost increase can be suppressed.

It is sectional drawing of the cell which comprises the all-solid-state battery of this invention. It is sectional drawing of the all-solid-state battery of this invention. It is a graph which shows the position and temperature from the outer periphery in an all-solid-state battery. 1 is a schematic diagram showing the mechanism of an all-solid battery equipped with a heater.

  The present invention will be described below with reference to the drawings. FIG. 1 is a cross-sectional view showing the structure of a cell constituting the all solid state battery of the present invention. As shown in FIG. 1, a cell 10 includes a positive electrode current collector 1, a positive electrode 3 formed on the positive electrode current collector 1, and having a positive electrode active material layer 2 containing a positive electrode active material, and a negative electrode current collector. 4 and a negative electrode 6 having a negative electrode active material layer 5 formed on the negative electrode current collector 4 and containing a negative electrode active material, and disposed between the positive electrode active material layer 2 and the negative electrode active material layer 5. And a solid electrolyte layer 7 containing a solid electrolyte. Hereinafter, each component will be described.

Positive electrode current collector The positive electrode current collector used in the present invention has a function of collecting current in the positive electrode active material layer. Examples of the electrode current collector material used for the positive electrode current collector include vanadium, aluminum, stainless steel, gold, platinum, manganese, iron, and titanium. Among them, aluminum is preferable. About the shape and thickness of a positive electrode electrical power collector, it is preferable to select suitably according to the use etc. of an all-solid-state battery, and they are 1 micrometer-30 micrometers normally.

Next, the positive electrode active material layer used in the present invention will be described. The positive electrode active material layer contains a positive electrode active material and a sulfide solid electrolyte. As the positive electrode active material, a known positive electrode active material can be appropriately used. For example, a layered positive electrode such as LiCoO ₂ , LiNiO ₂ , LiCo _1/3 Ni _1/3 Mn _1/3 O ₂ , LiVO ₂ , LiCrO ₂ or the like. Active materials, spinel type positive electrode active materials such as LiMn ₂ O ₄ , Li (Ni _0.25 Mn _0.75 ) ₂ O ₄ , LiCoMnO ₄ , Li ₂ NiMn ₃ O ₈ , LiCoPO ₄ , LiMnPO ₄ , LiFePO _4, etc. An olivine type positive electrode active material etc. can be mentioned.

  Further, the sulfide solid electrolyte contained in the positive electrode active material layer contains a metal element (M) that becomes conductive ions and sulfur (S). As said M, Li, Na, K, Mg, Ca etc. can be mentioned, for example, Li is especially preferable. In particular, the sulfide solid electrolyte material preferably contains Li, A (A is at least one selected from the group consisting of P, Si, Ge, Al, and B) and S. Furthermore, A is preferably P (phosphorus). Furthermore, the sulfide solid electrolyte material may contain halogens such as Cl, Br, and I. It is because ion conductivity improves by containing a halogen. The sulfide solid electrolyte material may contain O.

Examples of the sulfide solid electrolyte material having Li ion conductivity include Li ₂ S—P ₂ S ₅ , Li ₂ S—P ₂ S ₅ —LiI, Li ₂ S—P ₂ S ₅ —Li ₂ O, Li _{2 S-P 2 S 5 -Li} 2 O-LiI, Li 2 S-SiS 2, Li 2 S-SiS 2 -LiI, Li 2 S-SiS 2 -LiBr, Li 2 S-SiS 2 -LiCl, Li 2 _{S-SiS 2 -B 2 S 3} -LiI, Li 2 S-SiS 2 -P 2 S 5 -LiI, Li 2 S-B 2 S 3, Li 2 S-P 2 S 5 -Z m S n ( provided that , M, and n are positive numbers. Z is any of Ge, Zn, and Ga.), Li ₂ S—GeS ₂ , Li ₂ S—SiS ₂ —Li ₃ PO ₄ , Li ₂ S—SiS ₂ —Li _x MO _y (where, x, y is the number of positive .M is, P, Si, e, B, Al, Ga, either an In.) and the like. The description of “Li ₂ S—P ₂ S ₅ ” means a sulfide solid electrolyte material using a raw material composition containing Li ₂ S and P ₂ S _5, and the same applies to other descriptions. is there.

Also, the sulfide solid electrolyte material, if it is made by using the raw material composition containing Li ₂ S and _P 2 _{S 5,} the proportion of Li ₂ S to the total of Li ₂ S and _P 2 _{S 5} is 50 mol% to 100 mol%, preferably in the range of 70 mol% to 80 mol%, more preferably in the range of 72 mol% to 78 mol%, and further in the range of 74 mol% to 76 mol% preferable. This is because a sulfide solid electrolyte material having an ortho composition or a composition in the vicinity thereof can be obtained, and a sulfide solid electrolyte material having high chemical stability can be obtained. Here, ortho generally refers to one having the highest degree of hydration among oxo acids obtained by hydrating the same oxide. In this embodiment, the crystal composition to which Li ₂ S is added most in the sulfide is referred to as an ortho composition. In the Li ₂ S—P ₂ S ₅ system, Li ₃ PS ₄ corresponds to the ortho composition. In the case of a Li ₂ S—P ₂ S ₅ -based sulfide solid electrolyte material, the ratio of Li ₂ S and P ₂ S ₅ to obtain the ortho composition is Li ₂ S: P ₂ S ₅ = 75: 25 on a molar basis. It is. Instead of _P 2 _{S 5} in the raw material composition, even when using the _Al 2 _{S 3,} or _B 2 _{S 3,} a preferred range is the same. In the Li ₂ S—Al ₂ S ₃ system, Li ₃ AlS ₃ corresponds to the ortho composition, and in the Li ₂ S—B ₂ S ₃ system, Li ₃ BS ₃ corresponds to the ortho composition.

Also, the sulfide solid electrolyte material, if it is made by using the raw material composition containing Li ₂ S and SiS _2, the ratio of Li ₂ S to the total of Li ₂ S and SiS _2, for example 60 mol% ~ It is preferably within the range of 72 mol%, more preferably within the range of 62 mol% to 70 mol%, and even more preferably within the range of 64 mol% to 68 mol%. This is because a sulfide solid electrolyte material having an ortho composition or a composition in the vicinity thereof can be obtained, and a sulfide solid electrolyte material having high chemical stability can be obtained. In the Li ₂ S—SiS ₂ system, Li ₄ SiS ₄ corresponds to the ortho composition. In the case of the Li ₂ S—SiS ₂ -based sulfide solid electrolyte material, the ratio of Li ₂ S and SiS ₂ to obtain the ortho composition is Li ₂ S: SiS ₂ = 66.6: 33.3 on a molar basis. . Instead of SiS ₂ in the raw material composition, even when using a GeS _2, the preferred range is the same. In the Li ₂ S—GeS ₂ system, Li ₄ GeS ₄ corresponds to the ortho composition.

  Moreover, when the sulfide solid electrolyte material is formed using a raw material composition containing LiX (X = Cl, Br, I), the ratio of LiX is, for example, in the range of 1 mol% to 60 mol%. It is preferably within a range of 5 mol% to 50 mol%, more preferably within a range of 10 mol% to 40 mol%.

The sulfide solid electrolyte material may be sulfide glass, crystallized sulfide glass, or a crystalline material obtained by a solid phase method. The sulfide glass can be obtained, for example, by performing mechanical milling (ball mill or the like) on the raw material composition. Crystallized sulfide glass can be obtained, for example, by subjecting sulfide glass to a heat treatment at a temperature equal to or higher than the crystallization temperature. When the sulfide solid electrolyte material is a Li ion conductor, the Li ion conductivity at room temperature is preferably, for example, 1 × 10 ⁻⁵ S / cm or more, and preferably 1 × 10 ⁻⁴ S / cm or more. More preferably.

  In addition to the sulfide solid electrolyte and the positive electrode active material described above, the positive electrode active material layer used in the present invention may contain, for example, a conductive material or a binder as necessary. Examples of the conductive material include acetylene black, ketjen black, and carbon fiber. Examples of the binder used for the positive electrode active material layer include fluorine-containing binders such as PTFE and PVDF.

  The content of the positive electrode active material in the positive electrode active material layer is preferably larger from the viewpoint of capacity, for example, in the range of 40% by mass to 99% by mass, particularly in the range of 45% by mass to 70% by mass. Is preferred. Further, the content of the conductive material is preferably smaller as long as desired electronic conductivity can be ensured, and is preferably in the range of 0.1% by mass to 30% by mass, for example. Further, the content of the binder is preferably smaller as long as the negative electrode active material and the like can be stably fixed, and is preferably in the range of 0.5% by mass to 30% by mass, for example. Further, the content of the sulfide solid electrolyte is preferably smaller as long as desired ion conductivity can be ensured, for example, preferably in the range of 1% by mass to 60% by mass.

  The thickness of the positive electrode active material layer is, for example, preferably in the range of 0.1 μm to 1000 μm, and more preferably in the range of 1 μm to 100 μm.

  The method for forming the positive electrode active material layer in the present invention is not particularly limited as long as it is a method capable of forming a uniform positive electrode active material layer with a desired thickness. For example, a method may be used in which a material for the positive electrode active material layer is pressed to form a pellet. A slurry containing the material for the positive electrode active material layer and a solvent is prepared, and this is formed on the positive electrode current collector with a predetermined thickness The method of forming by apply | coating to may be sufficient. Especially, it is preferable that it is the formation method using a slurry.

Next, the negative electrode active material layer used in the present invention will be described. The negative electrode active material layer includes a negative electrode active material and a sulfide solid electrolyte. Examples of the negative electrode active material include a metal active material and a carbon active material. Examples of the metal active material include In, Al, Si, and Sn. On the other hand, examples of the carbon active material include mesocarbon microbeads (MCMB), highly oriented graphite (HOPG), hard carbon, and soft carbon.

  The sulfide solid electrolyte material used for the negative electrode active material layer can be the same as that described in the above-mentioned section of the positive electrode active material layer, and thus description thereof is omitted here. In addition, about the sulfide solid electrolyte used for a negative electrode active material layer, it may be the same as that used for a positive electrode active material layer, and may differ.

  In addition to the sulfide solid electrolyte and the negative electrode active material, the negative electrode active material layer used in the present invention may contain, for example, a conductive material or a binder as necessary. The conductive material and the binder can be the same as those described in the above-described section of the positive electrode active material layer, and thus description thereof is omitted here. Moreover, about content of each structural material of a negative electrode active material layer, since it can be made to be the same as that of what was demonstrated by the term of the positive electrode active material layer, description here is abbreviate | omitted. The thickness and the formation method of the negative electrode active material layer can be the same as the thickness and the formation method of the positive electrode active material layer, and thus description thereof is omitted here.

Solid electrolyte layer The solid electrolyte layer used in the present invention contains a solid electrolyte. The solid electrolyte is not particularly limited as long as it has ion conductivity. The above-described sulfide solid electrolyte, Li ₂ O—B ₂ O ₃ —P ₂ O ₅ , Li ₂ O—SiO ₂ , oxide amorphous solid electrolytes such as Li ₂ O—B ₂ O ₃ and Li ₂ O—B ₂ O ₃ —ZnO, LiI, LiI—Al ₂ O ₃ , Li ₃ N, Li ₃ N—LiI— LiOH, Li _{1 + x} Al _x Ti _2-x (PO ₄ ) ₃ (0 ≦ x ≦ 2), Li _{1 + x + y} A _x Ti _2-x Si _y P _3-y O ₁₂ (A = Al or Ga, 0 ≦ x ≦ 0.4, 0 <y ≦ 0.6), [(A _1/2 Li _1/2 ) _1−x B _x ] TiO ₃ (A = La, Pr, Nd, Sm, B = Sr or Ba, 0 _{≦ x ≦ 0.5), Li 5} La 3 Ta 2 O 12, Li 7 La 3 Zr _{O 12, Li 6 BaLa 2 Ta} 2 O 12, Li 3 PO (4-3 / 2x) N x (x <1), Li 3.6 Si 0.6 P 0.4 O crystalline oxide such as ₄ -An oxynitride etc. can be mentioned. Among these, a sulfide solid electrolyte is preferable.

  The thickness of the solid electrolyte layer is, for example, preferably in the range of 0.1 μm to 1000 μm, and more preferably in the range of 0.1 μm to 300 μm.

  The method for forming the solid electrolyte layer is not particularly limited as long as a uniform solid electrolyte layer can be formed with a desired thickness, and can be the same as the method for forming the positive electrode active material layer described above. The description here is omitted.

Joining Method The joining method of the constituent layers in the all-solid-state battery used in the present invention is not particularly limited as long as the constituent layers can be stacked and brought into contact with each other in the order described above. For example, an electrode active material layer is formed on each electrode current collector, a solid electrolyte layer is formed on either the positive electrode active material layer or the negative electrode active material layer, and then the solid electrolyte By placing the layer and the other electrode active material layer in contact with each other, a method of joining the constituent layers can be exemplified. Also, for example, after a laminate having a positive electrode active material layer, a solid electrolyte layer, and a negative electrode active material layer is formed by pressing or the like, each electrode active material layer of the laminate is brought into contact with each electrode current collector. By arranging the layers, a method of joining the constituent layers can be exemplified.

  Moreover, it is preferable to perform the press-press process which press-presses the all-solid-state battery which laminated | stacked each structural layer. The press pressure in the pressure press treatment is not particularly limited as long as it is a pressure that can improve the density of the solid electrolyte layer, the electrode active material layer, and the like and improve the adhesion of each layer, and is sulfide type. It can be appropriately selected depending on the shape and material of the solid battery.

  The pressure pressing method is not particularly limited as long as it is a method capable of increasing the density of the solid electrolyte layer and the active material layer of the all-solid-state battery and improving the adhesion of each constituent layer. It can be the same as the pressure press method used for the manufacturing method of an all-solid-state battery. Specific examples include a roll press method and a flat press method.

  As shown in FIG. 2, an all solid state battery can be obtained by stacking a plurality of cells thus manufactured and sealing them in a case 8. In such an all-solid battery, when the temperature distribution during use is measured, the inside of the battery is relatively higher than the outer periphery as shown in FIG. When copper foil is used as the negative electrode current collector, sulfur in the sulfide solid electrolyte reacts with copper to form copper sulfide CuS, but CuS is more easily generated at higher temperatures, and therefore the inside of the battery is more than the outer periphery. A large amount of CuS is generated. As a result, capacity variation occurs in the battery, and the capacity decreases.

  On the other hand, copper has the highest electrical conductivity and thermal conductivity among the metal foils that can be used as a current collector foil, so if a metal foil other than copper is used instead of copper as the negative electrode current collector, the electrical conductivity, etc. The characteristics will be degraded. It is also conceivable to provide a copper foil with a coating that suppresses the reaction with sulfur. However, such a coating generally leads to a cost increase of 2 to 3 times that of the copper foil, which is not realistic.

  Therefore, in the present invention, a copper foil is used as a negative electrode current collector in a place where the reaction with sulfur is unlikely to occur and the battery temperature is relatively low such as the outer periphery of the battery, and the battery temperature as in the battery is low. In a relatively high place, a copper foil having a conductive coat that hardly reacts with sulfur as a negative electrode current collector or a foil that does not generate CuS is used.

  The conductive coat can be formed from a layer containing one or more conductive elements such as C, Ni, Cr, W, Ti, Mn and the like. This conductive coat is formed by coating the surface of the copper foil with a conductive element by sputtering. The thickness of this conductive layer is preferably 1 nm to 5000 nm.

  As the foil that does not generate CuS, it is preferable to use a foil formed of a conductive element such as Fe, SUS, Ni, Ti, or Cr. The thickness is a general thickness used for a negative electrode current collector, usually 1 μm to 30 μm.

  Moreover, in order to improve the input / output in a low-temperature environment in an all-solid-state battery, as shown in FIG. 4, heating the all-solid-state battery using the heater 9 is proposed. In such a mechanism, since the temperature of the cell close to the heater is higher than that of the other cells, there is the same problem as described above that the capacity is reduced due to the formation of CuS. Therefore, by using the all solid state battery of the present invention in such a mechanism and using a copper foil having a conductive coat or a foil that does not generate CuS as a negative electrode current collector of a cell adjacent to a heater, Generation can be suppressed.

  Examples of the all solid state battery of the present invention include a sulfide type all solid lithium battery, a sulfide type all solid sodium battery, a sulfide type all solid potassium battery, a sulfide type all solid magnesium battery, and a sulfide type all solid calcium battery. Among them, a sulfide-based all solid lithium battery is preferable. The all solid state battery may be a primary battery or a secondary battery, but is preferably a secondary battery. This is because it can be repeatedly charged and discharged and is useful, for example, as an in-vehicle battery. Examples of the shape of the all solid state battery include a coin type, a laminate type, a cylindrical type, and a square type.

DESCRIPTION OF SYMBOLS 1 Positive electrode collector 2 Positive electrode active material layer 3 Positive electrode 4 Negative electrode collector 5 Negative electrode active material layer 6 Negative electrode 7 Solid electrolyte 8 Case 9 Heater 10 All-solid-state battery

Claims (3)

A positive electrode current collector, and a positive electrode having a positive electrode active material layer formed on the positive electrode current collector and containing a positive electrode active material;
A negative electrode current collector, and a negative electrode having a negative electrode active material layer formed on the negative electrode current collector and containing a negative electrode active material;
An all-solid battery comprising a plurality of stacked cells each having a solid electrolyte layer containing a solid electrolyte disposed between the positive electrode active material layer and the negative electrode active material layer,
The positive electrode active material, the negative electrode active material, and the solid electrolyte include a sulfide solid electrolyte,
As the negative electrode current collector, a copper foil is used in a place where the battery temperature is relatively low, and a copper foil having a conductive coating or a foil that does not generate CuS is used in a place where the battery temperature is relatively high. All solid battery.   The all-solid-state battery according to claim 1, wherein the place where the battery temperature is relatively high is anywhere other than the outermost periphery of the all-solid-state battery.   The all-solid-state battery according to claim 1, wherein the place where the battery temperature is relatively high is an electrode adjacent to a heater.

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