JP6394020B2 - Composite laminate, lithium battery, and method for producing composite laminate - Google Patents

Description

  The present invention relates to a composite laminate, a lithium battery, and a method for producing a composite laminate.

Conventionally, as a composite laminate, a composite obtained by laminating and sintering a positive electrode active material layer of LiNi _0.8 Co _0.15 Al _0.05 O ₂ and a garnet-type oxide that is a solid electrolyte of Li ₇ La ₃ Zr ₂ O ₁₂ by hot pressing Has been proposed (see, for example, Patent Document 1). In this laminate, the adhesion between the plate-like positive electrode and the plate-like solid electrolyte is improved, and the interface resistance can be further reduced.

JP 2013-243111 A

  However, the above-described composite laminate of Patent Document 1 requires hot press sintering, and there is a restriction of sintering at a high pressure when manufacturing the composite. In addition, when the composite laminate is sintered at normal pressure, a reaction layer having a high interface resistance is generated between the active material layer and the solid electrolyte layer, and may not function as a battery.

  This invention is made | formed in view of such a subject, and it aims at providing the manufacturing method of the composite laminated body which can be laminated | stacked without reducing a function as much as possible, a lithium battery, and a composite laminated body. .

  As a result of diligent research to achieve the above-described object, the present inventors have found that a garnet type containing Sr with respect to a composite oxide containing at least Li and a transition metal (eg, Ni, Co, Mn, etc.). It has been found that when oxides are stacked and sintered at normal pressure, they can be stacked without reducing the function as much as possible, and the present invention has been completed.

  That is, in the composite laminate of the present invention, the first layer containing a garnet-type oxide containing at least La and Sr and the second layer containing a composite oxide containing Li and a transition metal are integrally fired. It is a thing.

  The lithium battery of the present invention includes the composite laminate described above.

  The manufacturing method of the composite laminated body of this invention laminated | stacked the 1st layer containing the garnet-type oxide containing La and Sr at least, and the 2nd layer containing the composite oxide containing Li and a transition metal. It includes a laminating step for forming a laminate, and a firing step for firing the laminate at a firing temperature of 1100 ° C. or lower.

  The method for producing a composite laminate and the composite laminate of the present invention can be laminated without reducing the function as much as possible. The reason why such an effect is obtained is presumed as follows. For example, when a garnet-type oxide containing La and a composite oxide containing Li and a transition metal are stacked and fired, these materials react during firing and a reaction layer is formed between both layers. There are things to do. As a result, the function of the composite laminate decreases, such as an increase in resistance. In the present invention, it is surmised that the inclusion of Sr in the garnet-type oxide further suppresses the reaction between the transition metal in the composite oxide and the garnet-type oxide, and suppresses the above-described functional deterioration. This is because when Sr having a slightly larger ion radius than La is added to the La site, Sr is concentrated on the outside of the crystal grains, while the La concentration is lowered, thereby causing a reaction between the transition metal of the composite oxide and La. It is inferred that this is because of the suppression. As described above, it is considered that the first layer and the second layer can be laminated without reducing the function as much as possible by suppressing the generation of the reaction layer.

An explanatory view showing an example of structure of all solid-state lithium battery. The SEM photograph and elemental analysis result of the garnet-type oxide of Example 4. The XRD measurement result which examined the reactivity of a garnet-type oxide and complex oxide. The relationship figure with the electrical conductivity with respect to content of Sr, and a stability parameter | index. An appearance photograph of a sintered body in which a garnet-type oxide and a composite oxide are mixed. The CV cycle of the all-solid-state battery provided with the composite laminated body of the composition of the comparative example 1. The CV cycle of the all-solid-state battery provided with the composite laminated body of the composition of Example 5. The charging / discharging measurement result of Example 5.

  The composite laminate of the present invention is obtained by integrally firing a first layer containing a garnet-type oxide containing at least La and Sr and a second layer containing a composite oxide containing Li and a transition metal It is. In the composite laminate, the first layer may be a solid electrolyte layer that is an oxide having lithium ion conductivity, and the second layer may be an active material layer that occludes and releases lithium ions. The term “integrated firing” means that the sintered bodies are not bonded to each other, and the powder compact and the sintered compact may be integrally fired, or the powder compact. It is good also as what baked together.

The garnet-type oxide contained in the first layer contains Li, La, Sr, and Zr, and is an element different from La, which is at least one element A among alkaline earth metal and lanthanoid elements, and Zr. And a transition element capable of taking 6-coordination with oxygen and at least one element B among typical elements belonging to Group 12 to Group 15. More specifically, the garnet-type oxide has a basic composition Li _{7 + X + YZ} La _{3 -XY} Sr _X A _Y Zr _{2 -Z} B _Z O ₁₂ (wherein the element A includes Ba, Ca, Mg and One or more elements selected from the group consisting of Y, and the element B is one type selected from the group consisting of Sc, Ti, V, Y, Nb, Hf, Ta, Al, Si, Ga and Ge It is more preferable that the above elements are represented by 0 <X ≦ 1, 0 ≦ Y ≦ 1, 0 ≦ Z ≦ 1, and (X + Y) <Z). If this garnet-type oxide contains Sr, it can be laminated with the second layer without reducing the function as much as possible. Moreover, when it contains Sr, melting | fusing point will fall and baking energy can be reduced further, such as reducing a baking temperature. This element A is preferably Ca. When Ca is contained, the lithium ion conductivity can be further improved. The element B is preferably Nb. When Nb is included, lithium ion conductivity can be further increased. In this basic composition formula, the garnet-type oxide more preferably satisfies 0.05 ≦ X ≦ 0.2. Within this range, both the reaction stability with the second layer and the ionic conductivity can be achieved, which is more preferable. If ionic conductivity is given higher priority, 0 <X <0.05 may be satisfied. Alternatively, if priority is given to the reaction stability with the second layer, the range may be 0.2 <X <1.

  Here, the garnet-type oxide is only required to have mainly a garnet-type structure. For example, the garnet-type oxide includes a part of the structure other than the garnet-type structure or the peak position of X-ray diffraction is shifted. It may include a structure that is distorted when viewed from the viewpoint. In addition, as shown by the composition formula, the first layer may partially include other elements and structures. The “basic composition” means that the element A and the element B may each contain a main component element and one or more subcomponent elements.

The garnet-type oxide preferably has an electric conductivity (lithium ion conductivity, 25 ° C.) of 0.4 × 10 ⁻⁴ (S / cm) or more, and 1.0 × 10 ⁻⁴ (S / cm). More preferably, it is 1.4 × 10 ⁻⁴ (S / cm) or more, and most preferably 1.5 × 10 ⁻⁴ (S / cm) or more. This lithium ion conductivity can be appropriately changed by adjusting the addition ratio (X, Y, Z) of Sr, element A, and element B and the firing temperature.

  The garnet-type oxide is preferably baked at 1100 ° C. or lower, more preferably baked at 1050 ° C. or lower, and further preferably baked at 1000 ° C. or lower. In firing at 1100 ° C. or lower, the firing energy can be further reduced. From the viewpoint of forming a garnet structure, the garnet oxide is preferably fired at 800 ° C. or higher. The first layer containing the garnet-type oxide is preferably integrally fired together with the second layer. By doing so, the laminate can be sintered by one firing, so that the firing efficiency is good.

The composite oxide contained in the second layer may contain one or more of Ni, Co, and Mn in addition to Li. For example, the composite oxide may be represented by a basic composition LiNi _a Co _b Mn _c O ₂ (0 ≦ a <1, 0 <b ≦ 1, 0 ≦ c <1, a + b + c = 1). preferable. In this basic composition, 0.2 ≦ a ≦ 0.6, 0.2 ≦ b ≦ 0.6, and 0.2 ≦ c ≦ 0.6 may be satisfied. Further, in this basic composition, 0.3 ≦ a ≦ 0.4, 0.3 ≦ b ≦ 0.4, and 0.3 ≦ c ≦ 0.4 may be satisfied. For example, the composite oxide is a lithium manganese composite oxide having a basic composition formula of Li _(1-n) MnO ₂ (0 <n <1, etc., the same shall apply hereinafter), Li _(1-n) Mn ₂ O _4, etc. Lithium cobalt composite oxide with basic composition formula Li _(1-n) CoO ₂ , lithium nickel composite oxide with basic composition formula Li _(1-n) NiO ₂ , basic composition formula Li _(1-n) Ni _1/3 Co _1/3 Mn _1/3 O ₂ and may be as a lithium-nickel-cobalt-manganese composite oxide.

  In the composite laminate of the present invention, the first layer may have a thickness of 0.1 μm or more, 1 μm or more, or 10 μm or more. Further, the thickness of the first layer may be 1 mm or less. The same applies to the thickness of the second layer. Since the composite laminate of the present invention does not deteriorate the function of the composite laminate, such as lithium ion conductivity, even if it is sintered in a state where the first layer and the second layer are laminated, the composite laminate is more It can be made thin. In addition, since the unsintered first layer and the second layer can be laminated and fired, the firing process can be simplified and the firing energy can be further reduced.

  The composite laminated body of this invention can be utilized for a lithium battery. This is because the lithium ion conductivity is higher. At this time, the garnet-type oxide may be used as, for example, a solid electrolyte of a lithium battery, or may be used as a separator of a lithium battery. Such a lithium battery includes a composite laminate including a first layer that is a solid electrolyte and a second layer that is a positive electrode active material, and a negative electrode having a negative electrode active material that can occlude and release lithium. Examples of the negative electrode active material used for the negative electrode include inorganic compounds such as lithium metal, lithium alloys, and tin compounds, carbonaceous materials capable of inserting and extracting lithium ions, lithium titanium composite oxides, and conductive polymers. The carbonaceous material is not particularly limited, and examples thereof include cokes, glassy carbons, graphites, non-graphitizable carbons, pyrolytic carbons, and carbon fibers.

  The lithium battery of the present invention includes the composite laminate described above. This lithium battery may be a secondary battery or an all solid-state lithium battery. Although the structure of this lithium battery is not specifically limited, For example, the structure shown in FIG. 1 is mentioned. FIG. 1 is an explanatory diagram showing an example of the structure of the all-solid-state lithium battery 20. The all solid-state lithium battery 20 includes a solid electrolyte layer 10 as a first layer, a positive electrode active material layer 11 as a second layer formed on one side of the solid electrolyte layer 10, and a solid electrolyte layer 10. A negative electrode active material layer formed on one side. A solid electrolyte layer 10 containing a garnet-type oxide and a positive electrode active material layer 11 containing a composite oxide are the composite laminate 12 of the present invention. A current collector 13 is formed on the surface of the positive electrode active material layer 11, and a current collector 15 is formed on the surface of the negative electrode active material layer 14.

  The manufacturing method of the composite laminated body of this invention laminated | stacked the 1st layer containing the garnet-type oxide containing La and Sr at least, and the 2nd layer containing the composite oxide containing Li and a transition metal. A laminating step of forming a laminate, and a firing step of firing the laminate at a firing temperature of 1100 ° C. or lower.

  In the stacking step, the garnet-type oxide or composite oxide described in the composite stack may be used. The garnet-type oxide can be obtained, for example, by mixing raw material components such as Li, La, Sr, Zr, and Nb and firing at a temperature of 1100 ° C. or lower. Since the garnet-type oxide raw material contains Sr, element A, and the like, a garnet-type crystal structure can be obtained at a lower firing temperature. The raw material component is preferably carbonate or hydroxide rather than oxide. At this time, it is preferable to add an excessive amount of Li. In this laminating step, the first layer may be a sintered body and the second layer may be a powder compact, the second layer may be a sintered body and the first layer may be a powder compact, The first layer and the second layer may be formed into a powder compact. It is preferable to sinter the first layer and the second layer as a powder compact in the firing step because the repetition of the firing treatment can be further reduced.

  In the firing step, the laminate is fired at a firing temperature of 1100 ° C. or lower. In this firing step, there is no problem as long as the laminate is fired by applying pressure, but the laminate is preferably fired in an atmospheric pressure atmosphere. If it carries out like this, a composite laminated body can be baked with a simple process. In addition, since the first layer contains Sr, an inert reaction layer having a low electrical conductivity is unlikely to be generated between the first layer and the second layer even if the normal pressure firing is performed. The firing temperature is more preferably 1050 ° C. or less, and still more preferably 1000 ° C. or less. This is because the firing energy can be further reduced. In consideration of the sinterability of the first layer and the second layer, the firing temperature is preferably 800 ° C. or higher, more preferably 900 ° C. or higher, and further preferably 950 ° C. or higher. If the sinterability can be improved, the temperature may be 750 ° C. or higher.

  In the composite laminate described in detail above, the first layer and the second layer can be laminated without reducing the function as much as possible. This is because, for example, by containing Sr in the garnet-type oxide, the reaction between the transition metal in the composite oxide and the garnet-type oxide is further suppressed, and an inactive reaction layer having a low electrical conductivity is hardly generated. This is presumed to be due to this. For this reason, it is guessed that the said function fall is suppressed. Further, since the garnet-type oxide contains Sr, elements A and B, etc., it is possible to suppress the decrease in electrical conductivity as much as possible and to further reduce the firing energy. This is because the melting point is lowered by increasing the number of constituent elements, and the atomic coordinates of oxygen ions around the Li ions are changed by substituting elements having different ionic radii at the Zr sites, thereby facilitating the movement of Li ions. This is probably because of this.

  It should be noted that the present invention is not limited to the above-described embodiment, and it goes without saying that the present invention can be implemented in various modes as long as it belongs to the technical scope of the present invention.

  Below, the example which produced the composite laminated body of this invention concretely is demonstrated as an Example.

[Production of garnet-type oxide]
As garnet-type oxides, Li _6.75 La ₃ Zr _1.75 Nb _0.25 O ₁₂ (LLZNb) and Li _{7 + XZ} La _{3 -X} Sr _X Zr ₂ -Z Nb _Z O ₁₂ (Sr-LLZNb) further added with Sr Was synthesized. The starting materials were Li ₂ CO ₃ , La (OH) ₃ , SrCO ₃ , ZrO ₂ and Nb ₂ O ₅ . The starting material was weighed to a stoichiometric ratio. However, in order to make up for the loss of Li in the main sintering, 10 at. Li ₂ CO ₃ was excessively added so as to be a%. Using zirconia balls, mixing and pulverization were performed in ethanol in a planetary ball mill (300 rpm) for 1 hour. After separating the mixed powder of the starting material from the balls and ethanol, LLZNb was calcined in an Al ₂ O ₃ crucible at 950 ° C. for 10 hours and Sr-LLZNb at 900 ° C. for 10 hours in an air atmosphere. Then, this mixed powder was mixed and ground for 1 hour in a planetary ball mill (300 rpm) in ethanol using zirconia balls. The obtained powder was calcined again under the above conditions (950.900 ° C., 10 hours, air atmosphere), and then formed into pellets. The pellet was wrapped in an unmolded calcined product (powder bed) and sintered at 1150 · 1050 ° C. for 36 hours in an air atmosphere to obtain a sample (pellet). In the above basic composition formula, the composition of X = 0 and Z = 0.25 is Comparative Example 1 (LLZNb), the composition of X = 0.05 and Z = 0.40 is Example 1, and X = 0.10 and The composition of Z = 0.30 is Example 2, the composition of X = 0.30 and Z = 0.45 is Example 3, and the composition of X = 0.50 and Z = 0.50 is Example 4. The composition of X = 0.40 and Z = 0.50 was taken as Example 5.

[Composite oxide]
As a LiCoO ₂ (LCO), a cell seed 10N manufactured by Nippon Chemical Co., Ltd. was used. In addition, LiNi _1/3 Co _1/3 Mn _1/3 O ₂ (NCM) manufactured by Toda Kogyo was used.

[LBO synthesis]
Li ₃ BO ₃ (LBO) was obtained by using Li ₂ CO ₃ and B ₂ O ₃ as starting materials, weighing them to a stoichiometric ratio, mixing them with a ball mill, and firing at 600 ° C. for 10 hours.

[Production of composite laminate]
The composite oxide and LBO powder were added to a solvent (alcohol), and ethyl cellulose (EC vehicle manufactured by Nisshin Kasei Co., Ltd.) was added as a binder to obtain a paste. A composite oxide paste was formed on the garnet-type oxide pellets by screen printing and dried to obtain an unsintered laminate. This laminate was baked in the air at 800 ° C. for 1 hour and then at 900 ° C. for 30 minutes to obtain a composite laminate in which garnet-type oxide and composite oxide were integrally sintered.

(Electrical conductivity)
The electrical conductivity of the composite laminate was measured. Using an AC impedance analyzer (Agilent 4294A) in a thermostatic chamber, a resistance value was obtained from the arc of the Nyquist plot under the conditions of a frequency of 40 Hz to 110 MHz and an amplitude voltage of 100 mV, and the electrical conductivity was calculated from the resistance value. An Au electrode was used as a blocking electrode when measuring with an AC impedance analyzer. The Au electrode was formed by baking a commercially available Au paste at 850 ° C. for 30 minutes.

(Reactivity evaluation)
The reactivity of the garnet-type oxide and the composite oxide (NCM and LCO) was evaluated. The garnet-type oxide and the composite oxide were mixed at a mass ratio of 2: 1, mixed in a mortar, and heated in a pure gold crucible. Heating was performed in an electric furnace and held at 900 ° C. for 30 minutes. Thereafter, the obtained mixed powder was pulverized in a mortar, and the reactivity was evaluated using an X-ray diffraction measurement device (manufactured by Rigaku, Ultimate IV). The X-ray diffraction measurement was performed under the conditions of 0.01 ° step, 10 ° / min, and measurement range 2θ = 10 to 80 °, with the measurement mode being the fluorescence reduction mode.

(Production and evaluation of all-solid lithium battery)
Au was ion-coated on the surface of the composite laminate produced above (the surface of the composite oxide). Moreover, Li metal was vapor-deposited as a negative electrode active material on the back surface (the surface of the garnet-type oxide in which the composite oxide was not formed) of the produced composite laminated body, and the battery was produced. The battery evaluation is performed by performing a CV cycle in the range of 2.5 V to 4.3 V at 0.1 mV / sec using CC, and CC charging / discharging at 2.5 to 5 V (5 μA / cm ² ). It was.

(Results and discussion)
FIG. 2 shows an SEM photograph and elemental analysis results of the garnet-type oxide of Example 4. As shown in FIG. 2, it was found that when La is replaced with Sr, Sr is concentrated at the grain boundary. FIG. 3 is an XRD measurement result in which the reactivity between the garnet-type oxide and the composite oxide was examined. In the composition of the garnet-type oxide of Comparative Example 1, the peak of LaNiO ₃ as a reaction product was clearly confirmed. Therefore, 2θ = 22.5 to 23.5 ° is selected as the peak range of LaNiO ₃ that does not overlap with the XRD peak of the garnet-type oxide, and the stability index of the garnet-type oxide is obtained using the peak intensity of the XRD. It was. This index was the reciprocal of the value obtained by dividing the peak intensity of the reactant by the total peak intensity of the XRD. FIG. 4 is a relationship diagram of the electrical conductivity and the stability index with respect to the Sr content. As shown in FIG. 4, in the range A where the Sr content X in the basic composition formula is 0.05 ≦ X ≦ 0.2, the reactivity with the composite oxide is low and the electrical conductivity (that is, Li ion conduction). Rate) was a relatively high area. In the range B where 0.2 <X <1, the reactivity with the composite oxide was low, but the electric conductivity was low. In the range C of 0 <X <0.05, the reactivity with the composite oxide was relatively high, but the electric conductivity was high. Therefore, from the relationship between reactivity and Li ion conductivity, the range A of 0.05 ≦ X ≦ 0.2 was considered to be better. FIG. 5 is an appearance photograph of a sintered body in which a garnet-type oxide and a composite oxide (LCO) are mixed. This sintered body is obtained by pressing a powder obtained by mixing garnet-type oxide and composite oxide (LCO) at a volume ratio of 2: 1 by press molding, and firing this molded body at 900 ° C. for 30 minutes. It was. As shown in FIG. 5, when the fired body was visually confirmed, a change in the yellow-green reaction color was observed according to the Sr content, and it was confirmed that the higher the Sr content, the more effective the reaction was suppressed.

  6 is a CV cycle of an all-solid battery provided with a composite laminate having the composition of Comparative Example 1. FIG. FIG. 7 is a CV cycle of an all-solid-state battery including the composite laminate of the composition of Example 5. FIG. 6 shows the measurement results of a battery using the composite layered body fired at 750 ° C. for 1 hour with the composition of Comparative Example 1 and 900 ° C. for 30 minutes. FIG. 7 shows the measurement results of the battery using the composite laminate obtained by firing at 800 ° C. for 1 hour with the composition of Example 5 and 900 ° C. for 30 minutes. As shown in FIG. 6, it was found that the composition of Comparative Example 1 did not charge and discharge when fired at 900 ° C. For example, when the garnet-type oxide and the composite oxide are co-fired at the time of producing the composite, the firing temperature may be relatively high (for example, 850 ° C. or higher), which is not preferable in the composition of Comparative Example 1. . On the other hand, in the composition of Example 5, since it was charged and discharged even when baked at 900 ° C., it was considered that the effect of Sr appeared. FIG. 8 shows the charge / discharge measurement results of Example 5. As shown in FIG. 8, in the all-solid-state lithium battery provided with the composite laminated body of Example 5, it was confirmed that CC charging / discharging can be performed in the range of 2.5V-5.0V without a problem.

  DESCRIPTION OF SYMBOLS 10 Solid electrolyte layer, 11 Positive electrode active material layer, 12 Composite laminated body, 13 Current collector, 14 Negative electrode active material layer, 15 Current collector, 20 All solid-state lithium battery.

Claims (10)

A first layer containing a garnet-type oxide containing at least La and Sr and a second layer containing a composite oxide containing Li and a transition metal are integrally fired ,
The garnet-type oxide has a basic composition Li _{7 + X + YZ} La _{3 -XY} Sr _X A _Y Zr _{2 -Z} B _Z O ₁₂ (wherein the element A is from the group consisting of Ba, Ca, Mg and Y) One or more selected elements, and the element B is one or more elements selected from the group consisting of Sc, Ti, V, Y, Nb, Hf, Ta, Al, Si, Ga, and Ge. 0.05 ≦ X ≦ 0.2, 0 ≦ Y ≦ 1, 0 ≦ Z ≦ 1, and (X + Y) <Z are satisfied).
Composite laminate. The composite laminate according to claim 1 , wherein the garnet-type oxide satisfies 0.05 ≦ X ≦ 0.1. Said composite oxide is represented by the basic composition _{LiNi a Co b Mn c O 2} (0 ≦ a <1,0 <b ≦ 1,0 ≦ c <1, a + b + c = 1), in claim 1 or 2 The composite laminate described. The composite laminate according to claim 3 , wherein the composite oxide satisfies 0.2 ≦ a ≦ 0.6, 0.2 ≦ b ≦ 0.6, and 0.2 ≦ c ≦ 0.6. The lithium battery provided with the composite laminated body of any one of Claims 1-4 . A laminating step of forming a laminate in which a first layer containing a garnet-type oxide containing at least La and Sr and a second layer containing a composite oxide containing Li and a transition metal are laminated;
Anda firing step of firing the laminate at a sintering temperature of 1100 ° C. or less,
The garnet-type oxide has a basic composition Li _{7 + X + YZ} La _{3 -XY} Sr _X A _Y Zr _{2 -Z} B _Z O ₁₂ (wherein the element A is from the group consisting of Ba, Ca, Mg and Y) One or more selected elements, and the element B is one or more elements selected from the group consisting of Sc, Ti, V, Y, Nb, Hf, Ta, Al, Si, Ga, and Ge. 0.05 ≦ X ≦ 0.2, 0 ≦ Y ≦ 1, 0 ≦ Z ≦ 1, and (X + Y) <Z are satisfied).
A method for producing a composite laminate. The method for producing a composite laminate according to claim 6 , wherein the garnet-type oxide satisfies 0.05 ≦ X ≦ 0.1. Said composite oxide is represented by the basic composition _{LiNi a Co b Mn c O 2} (0 ≦ a <1,0 <b ≦ 1,0 ≦ c <1, a + b + c = 1), in claim 6 or 7 The manufacturing method of the composite laminated body of description. In the laminating step, a laminated body is formed by laminating the first layer containing the garnet-type oxide powder and the second layer containing the composite oxide powder;
Wherein In the baking step, baking the laminate including the powder, method for producing a composite laminate according to any one of claims 6-8. The method for producing a composite laminate according to any one of claims 6 to 9 , wherein in the firing step, the laminate is fired at a firing temperature of 800 ° C or higher and 1000 ° C or lower.