JP2021034205A - Solid electrolyte for all-solid lithium ion battery, all-solid lithium ion battery, and method for manufacturing all-solid lithium ion battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solid electrolyte for an all-solid-state lithium-ion battery in which the formation of a reactant is satisfactorily suppressed when fired together with a predetermined positive electrode active material, and an all-solid-state lithium-ion battery using the same. SOLUTION: A solid electrolyte represented by a composition formula: Li7-3x + αLa3Zr2AlxO12 (in the formula, 0 ≦ x <2, 1.1 <(7-3x + α) / (7-3x) ≦ 1.5). Therefore, in 0.15 g of the solid electrolyte, 0.15 g of the composition formula: LiaNibCocMn1-b-cO2 (in the formula, 0.98 ≦ a ≦ 1.05, 0.8 ≦ b ≦ 1.0, 0 ≦ When the positive electrode active material represented by (c ≦ 0.20) is added and pressure is applied at 50 MPa, and discharge plasma sintering is performed at 800 ° C. for 5 minutes, it corresponds to the solid electrolyte as the main component. All solids having a ratio Ib / Ia of 0.036 or less between the integrated intensity Ia of the XRD peak at 2θ = 16.6 ° and the integrated intensity Ib of the XRD peak at 2θ = 23.0 ° corresponding to the reactant LaMnO3. Solid electrolyte for lithium ion batteries. [Selection diagram] None

Description

The present invention relates to a solid electrolyte for an all-solid-state lithium-ion battery, an all-solid-state lithium-ion battery, and a method for producing an all-solid-state lithium-ion battery.

With the rapid spread of information-related devices such as personal computers, video cameras, and mobile phones and communication devices in recent years, the development of batteries used as their power sources has been emphasized. Among the batteries, lithium batteries are attracting attention from the viewpoint of high energy density. Further, high energy density and improvement of battery characteristics are also required for lithium secondary batteries in large-scale applications such as power sources for automobiles and road leveling.

However, in the case of lithium-ion batteries, most of the electrolytic solution is an organic compound, and even if a flame-retardant compound is used, it cannot be said that the risk of fire is completely eliminated. As an alternative candidate for such a liquid-based lithium-ion battery, an all-solid-state lithium-ion battery having a solid electrolyte has been attracting attention in recent years.

Oxide-based Li-ion conductors are attracting attention because of their excellent stability in the atmosphere. In particular, lithium lanthanum zirconium oxide having a cubic garnet-type crystal structure optionally containing Al, Ga, Ta, and Nb has high atmospheric stability and is regarded as a promising solid electrolyte for all-solid-state batteries.

Garnet is generally _{represented by the composition formula of A 3} B ₂ C ₃ O ₁₂ and has a tetragonal and cubic structure. In LLZ (Li ₇ La ₃ Zr ₂ O ₁₂ ), the A site is occupied by ^{La 3+} , the B site ^{is occupied by Zr 4+} , and the C site and the interstitial position ^{are occupied by Li +.} It has been confirmed that the constant ratio LLZ has two phases, a tetragonal phase in which Li is regularly arranged and a high-temperature cubic phase in which Li is irregularly arranged. LLZ showing high ionic conductivity is a cubic crystal, but there is usually a problem that the cubic crystal is unstable. _{To date, there have been reports of Li 7-3 x} La ₃ Zr ₂ Al x O _{12 and the} like, which can stabilize cubic crystals by substituting Li with Al (Non-Patent Documents 1 and 2).

E. Rangasamy, J. Wolfenstine, and J. Sakamoto, Solid State Ionics, 206,28 (2012) M. Matsui, K. Takahashi, K. Sakamoto, A. Hirano, Y. Takeda, O. Yamamoto, and N. Imanishi, Dalton Trans. 43, 1019 (2014)

An all-solid-state lithium-ion battery generally includes a positive electrode active material layer (positive electrode layer), a solid electrolyte, and a negative electrode layer in this order. At this time, if the adjacent positive electrode active material reacts with the solid electrolyte to generate a reactant, the function as a battery may not be fulfilled. However, the oxide-based solid electrolyte represented by the above-mentioned Li ₇ La ₃ Zr ₂ O ₁₂ and Li _{7-3 x} La ₃ Zr ₂ Al x O _{12 is used} as a positive electrode active material during the production of an all-solid-state lithium-ion battery. A step of firing after laminating with the layer is required, but there is a problem that a positive electrode active material and a reactant are easily generated at that time.

In view of these problems, in the embodiment of the present invention, a solid electrolyte for an all-solid-state lithium-ion battery in which the formation of a reactant is satisfactorily suppressed when fired together with a predetermined positive electrode active material, and an all-solid-state lithium using the same. It is an object of the present invention to provide an ion battery.

In the embodiment of the present invention, the composition formula: Li _{7-3x + α} La ₃ Zr ₂ Al _x O ₁₂ (in the formula, 0 ≦ x <2, 1.1 <(7-3x + α) / (7-3x) ≦) a solid electrolyte represented by a is) 1.5, to said solid electrolyte 0.15 g, 0.15 g of the composition _{formula: Li a Ni b Co c Mn} 1-bc O 2 ( where 0. 98 ≦ a ≦ 1.05, 0.8 ≦ b ≦ 1.0, 0 ≦ c ≦ 0.20) is added, and the pressure is increased at 50 MPa at 800 ° C. when performing discharge plasma sintering for 5 minutes, 2 [Theta] = 23.0 applicable and integrated intensity I _a of the XRD peaks of 2 [Theta] = 16.6 ° corresponding to the solid electrolyte of the main component, the LaMnO ₃ which is a reaction product A solid electrolyte for an all-solid-state lithium-ion battery in which the ratio I _b / I _a of the XRD peak of ° to the integrated intensity I _{b is controlled to 0.036 or less.}

In another embodiment, the solid electrolyte for an all-solid-state lithium-ion battery of the present invention has 0 ≦ x <1 in the above formula.

An all-solid-state lithium-ion batteries for a solid electrolyte another embodiment of the present invention, the solid electrolyte of 0.15 g, 0.15 g of the composition _{formula: Li a Ni b Co c Mn} 1-bc O 2 ( wherein, The positive electrode active material represented by (0.98 ≦ a ≦ 1.05, 0.8 ≦ b ≦ 1.0, 0 ≦ c ≦ 0.20) was added, and the pressure was increased at 50 MPa to 800. when discharge plasma sintering of 5 minutes was performed at ° C., 2 [Theta] = 23 corresponding with integrated intensity I _a of the XRD peaks of 2 [Theta] = 16.6 ° corresponding to the solid electrolyte of the main component, the LaMnO ₃ which is a reaction product The ratio I _b / I _{a of the} 0.0 ° XRD peak to the integrated intensity I _b is 0.015 or less.

An all-solid-state lithium-ion batteries for a solid electrolyte still another embodiment of the present invention, the solid electrolyte of 0.15 g, 0.15 g of the composition _{formula: Li a Ni b Co c Mn} 1-bc O 2 ( wherein , 0.98 ≦ a ≦ 1.05, 0.8 ≦ b ≦ 1.0, 0 ≦ c ≦ 0.20) was added, and the pressure was increased at 50 MPa. when performing discharge plasma sintering for 5 minutes at 800 ° C., 2 [Theta] corresponding with integrated intensity I _a of the XRD peaks of 2 [Theta] = 16.6 ° corresponding to the solid electrolyte of the main component, the LaMnO ₃ which is a reaction product = The ratio I _b / I _{a of the} 23.0 ° XRD peak to the integrated intensity I _b is 0.011 or less.

In another embodiment, the present invention is an all-solid-state lithium-ion battery including a positive electrode layer, a negative electrode layer, and a solid electrolyte layer, and the solid electrolyte for an all-solid-state lithium-ion battery of the present invention is provided in the solid electrolyte layer.

The present invention in another embodiment, a layer of the all-solid-state lithium-ion batteries for a solid electrolyte according to an embodiment of the present invention, the composition _{formula: Li a Ni b Co c Mn} 1-bc O 2 ( wherein 0.98 The layer of the positive electrode active material represented by (≦ a ≦ 1.05, 0.8 ≦ b ≦ 1.0, 0 ≦ c ≦ 0.20) is laminated and pressurized at 50 MPa, and is 800. This is a method for manufacturing an all-solid-state lithium-ion battery, which comprises a step of performing discharge plasma sintering at ° C. for 5 minutes.

According to an embodiment of the present invention, there is provided a solid electrolyte for an all-solid-state lithium-ion battery in which the formation of a reactant is satisfactorily suppressed when fired together with a predetermined positive electrode active material, and an all-solid-state lithium-ion battery using the same. be able to.

(Solid electrolyte for all-solid-state lithium-ion batteries)
The solid electrolyte for an all-solid-state lithium-ion battery according to the embodiment of the present invention has a composition formula: Li _{7-3x + α} La ₃ Zr ₂ Al _x O ₁₂ (in the formula, 0 ≦ x <2, 1.1 <(7). -3x + α) / (7-3x) ≦ 1.5). The solid electrolyte for an all-solid-state lithium-ion battery according to the embodiment of the present invention has a composition formula: Li _{7-3x + α} La ₃ Zr ₂ Al _x O ₁₂ , which is higher than the _{constant ratio of Li “Li 7-3x”.} It has an excess of Li by "α", which is an excess of Li. Then, in the _{solid electrolyte for all-solid-state lithium-ion batteries represented by the composition formula: Li 7-3x + α} La ₃ Zr ₂ Al _x O ₁₂ , the degree of Li excess is set to 1.1 <(7-3x + α) /. By controlling (7-3x) ≦ 1.5, the formation of a reactant is satisfactorily suppressed when fired together with the positive electrode active material. Further, in the above formula, 0 ≦ x <1 may be satisfied.

All-solid-state lithium-ion batteries for a solid electrolyte according to an embodiment of the present invention, in the solid electrolyte of 0.15 g, 0.15 g of the composition _{formula: Li a Ni b Co c Mn} 1-bc O 2 ( wherein 0 The positive electrode active material represented by (.98 ≦ a ≦ 1.05, 0.8 ≦ b ≦ 1.0, 0 ≦ c ≦ 0.20) was added and pressurized at 50 MPa, and the temperature was 800 ° C. in when performing discharge plasma sintering for 5 minutes, 2 [Theta] = 23 corresponding with integrated intensity I _a of the XRD peaks of 2 [Theta] = 16.6 ° corresponding to the solid electrolyte of the main component, the LaMnO ₃ which is a reaction product. The ratio I _b / I _{a of the} 0 ° XRD peak to the integrated intensity I _b is controlled to 0.036 or less. Here, discharge plasma sintering (SPS: Spark Plasma Sintering) shows a processing method in which sintering is performed by mechanical pressurization and pulse energization heating. In addition to the thermal and mechanical energy used for general sintering, the driving force for sintering is a combination of electromagnetic energy due to pulse energization, self-heating of the object to be fired, and discharge plasma energy generated between particles. It is supposed to be.

The solid electrolyte for an all-solid-state lithium-ion battery according to the embodiment of the present invention has a positive electrode active material having a predetermined composition added at a predetermined ratio as described above, and then pressurized at 50 MPa for 5 minutes at 800 ° C. when performing discharge plasma sintering, and integrated intensity I _a of the XRD peaks of 2 [Theta] = 16.6 ° corresponding to the solid electrolyte of the main component, XRD of 2 [Theta] = 23.0 ° corresponding to LaMnO ₃ which is a reaction product The ratio I _b / I _{a of the} peak to the integrated intensity I _b is controlled to 0.036 or less. Therefore, the solid electrolyte for an all-solid-state lithium-ion battery according to the embodiment of the present invention requires a step of laminating with a layer of a positive electrode active material and then firing at the time of manufacturing the all-solid-state lithium-ion battery. It becomes difficult to generate a positive electrode active material and a reactant, and good operation as an all-solid-state lithium-ion battery becomes possible.

All-solid-state lithium-ion batteries for a solid electrolyte according to an embodiment of the present invention, in the solid electrolyte of 0.15 g, 0.15 g of the composition _{formula: Li a Ni b Co c Mn} 1-bc O 2 ( wherein 0 The positive electrode active material represented by (.98 ≦ a ≦ 1.05, 0.8 ≦ b ≦ 1.0, 0 ≦ c ≦ 0.20) was added and pressurized at 50 MPa, and the temperature was 800 ° C. in when performing discharge plasma sintering for 5 minutes, 2 [Theta] = 23 corresponding with integrated intensity I _a of the XRD peaks of 2 [Theta] = 16.6 ° corresponding to the solid electrolyte of the main component, the LaMnO ₃ which is a reaction product. The ratio I _b / I _{a of the} 0 ° XRD peak to the integrated intensity I _b is preferably controlled to 0.015 or less, more preferably to 0.011 or less, and 0. More preferably, it is controlled to be .010 or less.

(Manufacturing method of solid electrolyte for all-solid-state lithium-ion battery)
Next, a method for producing a solid electrolyte for an all-solid-state lithium-ion battery according to an embodiment of the present invention will be described in detail. First, the raw materials Li salt, La salt, Zr salt and aluminum oxide are weighed so that the stoichiometric ratio of Li: La: Zr: Al is 7.1 or more: 3: 2: 0.25, and Li Is charged so as to be 20 mol% or more of the constant ratio composition. By adding the Li raw material in excess in this way, the ratio of La, which is a component of the reactant, is relatively reduced, and the _{reaction for producing impurities (LaMnO 3} ) is suppressed.
Next, the Li salt, La salt, Zr salt and aluminum oxide are wet-mixed with a ball mill under an ethanol solvent for 20 hours and dried to obtain a raw material mixed powder.
Next, the obtained powder is calcined at 800 ° C. to 1000 ° C. for 1 hour to 40 hours to obtain a solid electrolyte for an all-solid-state lithium-ion battery according to the embodiment of the present invention.

(All-solid-state lithium-ion battery)
An all-solid-state lithium-ion battery can be produced by forming a solid electrolyte layer using the solid electrolyte for an all-solid-state lithium-ion battery according to the embodiment of the present invention, and having the solid electrolyte layer, a positive electrode layer, and a negative electrode layer. Specifically, first, the composition formula: Li _a Ni _b Co _c Mn _1-bc O ₂ (in the formula, 0.98 ≦ a ≦ 1.05, 0.8 ≦ b ≦ 1.0, 0 ≦ c ≦ The positive electrode active material layer represented by (0.20), the solid electrolyte layer for an all-solid-state lithium-ion battery according to the embodiment of the present invention, and the negative electrode layer are laminated in this order and pressurized at 50 MPa. In this state, discharge plasma sintering is performed at 800 ° C. for 5 minutes. As a result, the solid electrolyte for an all-solid-state lithium-ion battery is less likely to generate a positive electrode active material and a reactant, and good operation as an all-solid-state lithium-ion battery becomes possible.

Hereinafter, examples for better understanding the present invention and its advantages will be provided, but the present invention is not limited to these examples.

(Example 1)
Li ₂ CO ₃ , La (OH) ₃ , La ₂ Zr ₂ O ₇ and Al ₂ O _{3 so} that Li: La: Zr: Al has a stoichiometric ratio of 7.7: 3: 2: 0.25. Weighed in.
Next, Li ₂ CO ₃ , La (OH) ₃ , La ₂ Zr ₂ O ₇ and Al ₂ O ₃ are wet-mixed in a ball mill under an ethanol solvent for 20 hours and dried at 50 ° C. for 12 hours to obtain a white color. Raw material mixed powder was obtained.
Next, the obtained powder was calcined at 1000 ° C. for 1 h to obtain a solid electrolyte sample having _{a composition formula: Li 7.7} La ₃ Zr ₂ Al _0.25 O _12.

(Example 2)
Li ₂ CO ₃ , La (OH) ₃ , La ₂ Zr ₂ O ₇ and Al ₂ O _{3 so} that Li: La: Zr: Al has a stoichiometric ratio of 9.38: 3: 2: 0.25. Weighed in.
Next, Li ₂ CO ₃ , La (OH) ₃ , La ₂ Zr ₂ O ₇ and Al ₂ O ₃ are wet-mixed in a ball mill under an ethanol solvent for 20 hours and dried at 50 ° C. for 12 hours to obtain a white color. Raw material mixed powder was obtained.
Next, the obtained powder was calcined at 1000 ° C. for 1 h to obtain a solid electrolyte sample having _{a composition formula: Li 9.38} La ₃ Zr ₂ Al _0.25 O _12.

(Example 3)
Li ₂ CO ₃ , La (OH) ₃ , La ₂ Zr ₂ O ₇ and Al ₂ O _{3 so} that Li: La: Zr: Al has a stoichiometric ratio of 7.19: 3: 2: 0.25. Weighed in.
Next, Li ₂ CO ₃ , La (OH) ₃ , La ₂ Zr ₂ O ₇ and Al ₂ O ₃ are wet-mixed in a ball mill under an ethanol solvent for 20 hours and dried at 50 ° C. for 12 hours to obtain a white color. Raw material mixed powder was obtained.
Next, the obtained powder was calcined at 1000 ° C. for 1 h to obtain a solid electrolyte sample having _{a composition formula: Li 7.19} La ₃ Zr ₂ Al _0.25 O _12.

(Comparative Example 1)
Li ₂ CO ₃ , La (OH) ₃ , La ₂ Zr ₂ O ₇ and Al ₂ O _{3 so} that Li: La: Zr: Al has a stoichiometric ratio of 6.25: 3: 2: 0.25. Weighed in.
Next, Li ₂ CO ₃ , La (OH) ₃ , La ₂ Zr ₂ O ₇ and Al ₂ O ₃ are wet-mixed in a ball mill under an ethanol solvent for 20 hours and dried at 50 ° C. for 12 hours to obtain a white color. Raw material mixed powder was obtained.
Next, the obtained powder was calcined at 1000 ° C. for 1 h to obtain a solid electrolyte sample having _{a composition formula: Li 6.25} La ₃ Zr ₂ Al _0.25 O _12.

(Comparative Example 2)
Li ₂ CO ₃ , La (OH) ₃ , La ₂ Zr ₂ O ₇ and Al ₂ O _{3 so} that Li: La: Zr: Al has a stoichiometric ratio of 6.88: 3: 2: 0.25. Weighed in.
Next, Li ₂ CO ₃ , La (OH) ₃ , La ₂ Zr ₂ O ₇ and Al ₂ O ₃ are wet-mixed in a ball mill under an ethanol solvent for 20 hours and dried at 50 ° C. for 12 hours to obtain a white color. Raw material mixed powder was obtained.
Next, the obtained powder was calcined at 1000 ° C. for 1 h to obtain a solid electrolyte sample having _{a composition formula: Li 6.88} La ₃ Zr ₂ Al _0.25 O _12.

(Evaluation)
Each evaluation was carried out under the following conditions using the solid electrolyte samples of each Example and Comparative Example thus prepared.
-Evaluation of the formation peak of the reactant of the XRD pattern-
0.15 g of each of the solid electrolyte samples of each Example and Comparative Example was collected, and 0.15 g of the composition formula: LiNi _0.8 Co _0.1 Mn _0.1 O ₂ (in the formula, 0.98 ≤ a ≤ 1.05, 0.8). The positive electrode active material represented by (≦ b ≦ 1.0, 0 ≦ c ≦ 0.20) was added, and the mixture mixed using a milk stick and a milk pot was pressurized at 50 MPa, and 5 at 800 ° C. Discharge plasma sintering was performed for 1 minute. As the discharge plasma sintering apparatus, SPS-515S manufactured by Sumitomo Coal Mining Co., Ltd. was used.
Next, the XRD pattern was evaluated for each of the solid electrolyte samples of Examples and Comparative Examples after discharge plasma sintering.

In the XRD pattern, _{the peak of the reactant LaMnO 3} appears at the position of 2θ = 23.0 °. _{Therefore, when examined, a strong peak of LaMnO 3} was confirmed at the position of 2θ = 23.0 ° in the XRD patterns of Comparative Examples 1 and 2. On the other hand, in the XRD pattern of Example 1, a very weak peak _{of LaMnO 3 was confirmed at the position of 2θ = 23.0 °.}
From the peak intensity of the XRD pattern, in the solid electrolyte sample of Example 1, the ratio _{of the integrated intensity I a of 2θ = 16.6 ° corresponding to the solid electrolyte to the integrated intensity I b} of the XRD peak of the reaction product LaMnO _3. I _b / I _{a is 0.015, I b} / I _a is 0.240 in the solid electrolyte sample of Comparative Example 1 _{, and I b} / I _a is 0.079 in the solid electrolyte sample of Comparative Example 2. It was confirmed that there was.
Further, in the solid electrolyte sample of Example 2, the ratio I _b / I _{a of the integrated intensity I a of 2θ = 16.6 ° corresponding to the solid electrolyte and the integrated intensity I b} of the XRD peak of the reaction product LaMnO ₃ Was 0.011.
Further, in the solid electrolyte sample of Example 3, the ratio I _b / I _{a of the integrated intensity I a of 2θ = 16.6 ° corresponding to the solid electrolyte and the integrated intensity I b} of the XRD peak of the reaction product LaMnO ₃ Was 0.036.
Table 1 shows the numerical values of (7-3x + α) / (7-3x) relating to the compositions of Examples 1 to 3 and Comparative Examples 1 and 2, and the integrated intensity ratio I _b / I _a .

Claims (6)

Composition formula: Li _{7-3x + α} La ₃ Zr ₂ Al _x O ₁₂
(In the formula, 0 ≦ x <2, 1.1 <(7-3x + α) / (7-3x) ≦ 1.5)
It is a solid electrolyte represented by
In the solid electrolyte of 0.15 g, 0.15 g of the composition _{formula: Li a Ni b Co c Mn} 1-bc O 2 ( wherein, 0.98 ≦ a ≦ 1.05,0.8 ≦ b ≦ 1. When the positive electrode active material represented by (0, 0 ≦ c ≦ 0.20) is added and pressure is applied at 50 MPa, discharge plasma sintering is performed at 800 ° C. for 5 minutes, the solid component of the main component is solid. Ratio I _b / I _{of the integrated intensity I a} of the XRD peak of 2θ = 16.6 ° corresponding to the electrolyte _{and the integrated intensity I b} of the XRD peak of 2θ = 23.0 ° corresponding to the reactant LaMnO _{3. A} solid electrolyte for an all-solid lithium-ion battery in which a is 0.036 or less. The solid electrolyte for an all-solid-state lithium-ion battery according to claim 1, wherein in the above formula, 0 ≦ x <1. In the solid electrolyte of 0.15 g, 0.15 g of the composition _{formula: Li a Ni b Co c Mn} 1-bc O 2 ( wherein, 0.98 ≦ a ≦ 1.05,0.8 ≦ b ≦ 1. When the positive electrode active material represented by (0, 0 ≦ c ≦ 0.20) is added and pressure is applied at 50 MPa, discharge plasma sintering is performed at 800 ° C. for 5 minutes, the solid component of the main component is solid. Ratio I _b / I _{of the integrated intensity I a} of the XRD peak of 2θ = 16.6 ° corresponding to the electrolyte _{and the integrated intensity I b} of the XRD peak of 2θ = 23.0 ° corresponding to the reactant LaMnO _{3. The} solid electrolyte for an all-solid lithium-ion battery according to claim 1 or 2, wherein a is 0.015 or less. In the solid electrolyte of 0.15 g, 0.15 g of the composition _{formula: Li a Ni b Co c Mn} 1-bc O 2 ( wherein, 0.98 ≦ a ≦ 1.05,0.8 ≦ b ≦ 1. When the positive electrode active material represented by (0, 0 ≦ c ≦ 0.20) is added and pressure is applied at 50 MPa, discharge plasma sintering is performed at 800 ° C. for 5 minutes, the solid component of the main component is solid. Ratio I _b / I _{of the integrated intensity I a} of the XRD peak of 2θ = 16.6 ° corresponding to the electrolyte _{and the integrated intensity I b} of the XRD peak of 2θ = 23.0 ° corresponding to the reactant LaMnO _{3. The} solid electrolyte for an all-solid lithium-ion battery according to claim 3, wherein a is 0.011 or less. An all-solid-state lithium-ion battery comprising a positive electrode layer, a negative electrode layer, and a solid electrolyte layer, and the solid electrolyte layer for an all-solid-state lithium-ion battery according to any one of claims 1 to 4. A layer of the all-solid-state lithium-ion batteries for a solid electrolyte according to claim 1, the composition formula: _{Li a Ni b Co c Mn 1} -bc O 2 ( wherein, 0.98 ≦ a ≦ The layers of the positive electrode active material represented by (1.05, 0.8 ≦ b ≦ 1.0, 0 ≦ c ≦ 0.20) are laminated, and in a state of being pressurized at 50 MPa, 5 at 800 ° C. A method for manufacturing an all-solid-state lithium-ion battery, which comprises a step of performing discharge plasma sintering for one minute.