JP7109334B2 - Method for manufacturing positive electrode for all-solid-state lithium-ion battery and method for manufacturing all-solid-state lithium-ion battery - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for manufacturing a positive electrode for an all-solid lithium ion battery and a method for manufacturing an all-solid lithium ion battery.

In recent years, as one field of lithium-ion batteries, so-called all-solid-state lithium-ion batteries, in which the electrolyte is a solid electrolyte, are being developed. All-solid-state lithium-ion batteries are attracting attention because they do not use organic solvents, which have been used as electrolytes in lithium-ion batteries until then, and can almost eliminate the risk of explosion or explosion.

However, (1) it is necessary to mix about 20% to 30% of the solid electrolyte in the positive electrode. (3) It is necessary to provide a buffer layer such as lithium niobate on the surface of the positive electrode active material. It turns out. From the viewpoint of manufacturing the positive electrode, the aforementioned (3) is expected to lead to a significant increase in manufacturing man-hours and manufacturing costs. ing.

JP 2010-140725 A JP 2010-140664 A

The current manufacturing process of positive electrode for all-solid-state lithium ion battery is dry mixing of transition metal coprecipitated hydroxide precursor and lithium source, followed by sintering to form lithium transition metal composite oxide. A positive electrode active material precursor is obtained by spraying an organic solution containing lithium alkoxide and niobium alkoxide on the surface of the lithium-transition metal composite oxide, and the positive electrode active material precursor is baked to obtain a positive electrode active material. A positive electrode is formed by mixing a substance and a solid electrolyte. In this case, the firing process is performed twice.

On the other hand, as described above, the mixture of the positive electrode active material and the solid electrolyte is just a mixture of powders, and this mixture is used as a positive electrode as it is, so the degree of contact between particles inevitably affects the conduction of lithium ions. This sometimes hinders improvement in output characteristics. Therefore, as described in Patent Document 1, these all-solid-state lithium ion batteries are produced by the green sheet method as implemented in the laminated component manufacturing process, or as described in Patent Document 2. A process of mixing a positive electrode active material and a solid electrolyte and then firing the mixture is being studied. With such a configuration, the degree of contact between grains can be greatly improved, and therefore an improvement in output can be expected.

However, regarding the utilization of these technologies, since the current positive electrode active material for all-solid-state lithium-ion batteries needs to be coated with lithium niobate or the like as described above, lithium-transition metal composite oxide is used once. , the lithium niobate coating is fired once, and the mixture of the positive electrode active material and the solid electrolyte is fired once. Since the niobium source is put into the manufacturing process and then fired twice, it was expected that the solid solution diffusion of niobium into the entire positive electrode active material could not be prevented and that the buffer layer could not fulfill its role.

Accordingly, an object of an embodiment of the present invention is to provide a simple method for manufacturing a positive electrode containing a Nb-coated positive electrode active material for an all-solid-state lithium ion battery.

The present inventor previously mixed a lithium niobate precursor, a positive electrode active material precursor, and a solid electrolyte, and fired the mixture to form a positive electrode. and a solid electrolyte were mixed in advance and baked to form a positive electrode. As a result, the process produced an object that could not be said to be suitable as a positive electrode for all-solid-state lithium-ion batteries.

In order to solve such a problem, the present inventors prepared a surface coating precursor powder by spraying a niobium oxalate aqueous solution and a lithium ion precursor onto a transition metal hydroxide precursor, respectively. By mixing the precursor powder with the oxide-based solid electrolyte and then firing it, the production of a positive electrode containing a positive electrode active material for an all-solid-state lithium ion battery coated with Nb, which has been conventionally performed three times in the heat treatment process, can be reduced to 1. It has been found that it can be carried out in a single heat treatment step.

In one embodiment of the present invention, a transition metal hydroxide precursor composed of nickel, cobalt and manganese is placed in a rocking mixer, and a niobium oxalate aqueous solution and a lithium ion precursor are sprayed, respectively, to form a surface coating precursor. A method for manufacturing a positive electrode for an all-solid-state lithium ion battery, comprising a step of preparing a solid powder, and a step of mixing and firing the surface-coated precursor powder and the oxide-based solid electrolyte.

A method for producing a positive electrode for an all-solid-state lithium ion battery according to another embodiment of the present invention, wherein the material amount ratio of nickel, cobalt, and manganese in the transition metal hydroxide precursor composed of nickel, cobalt, and manganese is expressed as 85-90:7-9:0-7.5 (excluding 0) when the total amount of nickel, cobalt and manganese is 100.

A method for producing a positive electrode for an all-solid-state lithium ion battery according to still another embodiment of the present invention, wherein the lithium ion precursor is a lithium nitrate solution, a lithium citrate solution, a lithium hydroxide solution, a lithium acetate solution, and oxalic acid. One or more selected from the group consisting of lithium solutions.

Still another embodiment of the present invention is a method for producing a positive electrode for an all-solid lithium ion battery, wherein the transition metal hydroxide precursor composed of nickel, cobalt and manganese has a specific surface area of 25 m ² /g or more. be.

In another embodiment of the present invention, the positive electrode for an all-solid lithium ion battery manufactured by the method for manufacturing a positive electrode for an all-solid lithium ion battery according to the embodiment of the present invention is used as a positive electrode layer, and the positive electrode layer, the solid electrolyte layer and A method for manufacturing an all-solid lithium ion battery using a negative electrode layer.

According to an embodiment of the present invention, it is possible to provide a simple method for manufacturing a positive electrode containing a Nb-coated positive electrode active material for an all-solid-state lithium ion battery.

(Manufacturing method of positive electrode for all-solid-state lithium-ion battery)
An aqueous transition metal solution prepared so that the molar ratio of nickel source:cobalt source:manganese source is Ni:Co:Mn=85-90:7-9:0-7.5 (excluding Mn=0) prepare. The nickel source, cobalt source, and manganese source may be sulfates, nitrates, hydrochlorides, and the like, respectively.

Next, the transition metal aqueous solution, the sodium hydroxide aqueous solution, and the ammonia water are prepared in separate tanks, and these are put into one reaction tank and reacted by the crystallization method. Subsequently, the reactant was filtered, washed with water and dried to obtain a composition formula: _NiaCobMnc (OH) ₂ [wherein a: _b : _c =85-90:7-9:0-7. 5 (excluding c=0)] is prepared.

At this time, the transition metal hydroxide precursor powder composed of nickel, cobalt and manganese preferably has a specific surface area of 25 m ² /g or more. When the specific surface area of the precursor powder is 25 m ² /g or more, the permissible amount of water adhering to the surface is improved. Therefore, even if the precursor powder has a large amount of moisture, it can be maintained as a powder, so that it is difficult to form "lumps". Since the influence of moisture is reduced in this way, it becomes easier to manufacture the positive electrode even if the firing process is performed only once, as will be described later. As for the specific surface area, a desired specific surface area can be obtained, for example, by appropriately changing the hydroxide production conditions (temperature, pH, atmosphere, etc.).

Next, the hydroxide precursor powder is put into a rocking mixer (dry powder mixer). Subsequently, an aqueous niobium oxalate solution and a lithium ion precursor were sprayed at room temperature for 17 to 300 seconds, smoothed for 900 seconds after spraying, and the precursor powder was placed in a rocking mixer at a rotation speed of 30 Hz and a rocking speed of 30 Hz. An operation of spraying onto the surface is performed to obtain a surface-coated precursor powder coated with niobium oxalate and having lithium ions introduced therein.

The niobium oxalate aqueous solution contains Nb at a concentration of 63 to 189 g/L, and is sprayed so that the substance amount percentage Nb/(Ni+Co+Mn) is 0.27 to 0.55. The lithium ion precursor is one or more selected from the group consisting of lithium nitrate solution, lithium citrate solution, lithium hydroxide solution, lithium acetate solution, and lithium oxalate solution, and Li at a concentration of 50 to 300 g/L, and is sprayed so that the mass percentage Li/(Ni+Co+Mn) is 1.01 to 1.03.

Here, the rocking mixer is a dry powder mixer in which rotation and rocking can be independently changed, and by performing diffusion mixing by rotation and moving mixing by rocking at the same time, uniform mixing in a short time is possible.

Subsequently, the surface-coated precursor powder coated with niobium oxalate and into which lithium ions are introduced, and the oxide-based solid electrolyte are mixed and fired. Specifically, first, a surface-coating precursor powder coated with niobium oxalate and having lithium ions introduced therein is taken out from a rocking mixer, and Li _6.5 La ₃ Zr _1.5 is added to the surface-coating precursor powder. A powder obtained by mixing an oxide-based solid electrolyte such as Ta _0.5 O ₁₂ at a mass percentage of 30 is placed in a Henschel mixer and mixed at 10 to 30 Hz for 5 to 15 minutes.

Subsequently, the mixed powder is filled into an alumina sagger. Next, the firing furnace was filled with oxygen, and the alumina sagger was placed in the firing furnace to create an oxygen atmosphere of 0.1 MPa and fired at 750° C. for 7 hours. After cooling to room temperature, the alumina sagger is taken out from the firing furnace into dry air to obtain a positive electrode body.

According to the above method, since only one firing step is required, the heat treatment cost is reduced and the production lead time is also reduced. As described above, according to the manufacturing method according to the embodiment of the present invention, a positive electrode containing a Nb-coated positive electrode active material for an all-solid-state lithium ion battery can be manufactured by a very simple method. In addition, the positive electrode active material contained in the positive electrode is a lithium-nickel-cobalt-manganese composite oxide whose surface is uniformly coated with Nb.

(Method for manufacturing all-solid-state lithium-ion battery)
A positive electrode layer is formed using a positive electrode for an all-solid lithium ion battery manufactured by the method for manufacturing a positive electrode for an all-solid lithium ion battery according to an embodiment of the present invention, and a solid electrolyte layer, the positive electrode layer and the negative electrode layer are provided. All-solid-state lithium-ion batteries can be made.

The following examples are provided for a better understanding of the invention and its advantages, but the invention is not limited to these examples.

(Example 1)
An aqueous transition metal solution, an aqueous sodium hydroxide solution, and an aqueous ammonia prepared so that the molar ratio of nickel sulfate:cobalt sulfate:manganese sulfate was Ni:Co:Mn=90:7:3 were prepared in separate tanks. The mixture was put into one reaction tank, reacted by crystallization, filtered, washed with water and dried to obtain a precursor powder represented by the composition formula: Ni _0.90 Co _0.07 Mn _0.03 (OH) ₂ . This precursor powder had an average particle diameter D50 of 10 μm and a specific surface area (BET) of 45 m ² /g.

Next, the precursor powder was put into a rocking mixer. Subsequently, a niobium oxalate aqueous solution containing 63 to 189 g/L of Nb is sprayed onto the precursor powder so that Nb/(Ni+Co+Mn) becomes 0.55 mol%, and Li is contained at 50 to 300 g/L. A lithium citrate solution was sprayed so that Li/(Ni+Co+Mn) was 1.01% by mass to obtain a surface coating precursor powder. In the spraying step, the surface of the precursor powder in the rocking mixer was sprayed at room temperature at a spraying time of 200 seconds, a smoothing time of 900 seconds after spraying, a rotation frequency of 30 Hz, and a rocking frequency of 30 Hz.

Subsequently, the surface-coating precursor powder was taken out from the rocking mixer, and 30% by mass of an oxide-based solid electrolyte having a composition formula: Li _6.5 La ₃ Zr _1.5 Ta _0.5 O ₁₂ was added to the surface-coating precursor powder. The powder obtained by mixing so as to obtain a mixture was placed in a Henschel mixer and mixed at 10 to 30 Hz for 5 to 15 minutes.

Subsequently, the mixed powder is filled into an alumina sagger. Next, the firing furnace was filled with oxygen, and the alumina sagger was placed in the firing furnace to create an oxygen atmosphere of 0.1 MPa and fired at 750° C. for 7 hours. After cooling this to room temperature, the positive electrode body of Example 1 was obtained by taking out the alumina sagger from the firing furnace into dry air.

(Comparative example 1)
An aqueous transition metal solution, an aqueous sodium hydroxide solution, and an aqueous ammonia prepared so that the molar ratio of nickel sulfate:cobalt sulfate:manganese sulfate was Ni:Co:Mn=90:7:3 were prepared in separate tanks. The mixture was put into one reaction tank, reacted by crystallization, filtered, washed with water and dried to obtain a precursor powder represented by the composition formula: Ni _0.90 Co _0.07 Mn _0.03 (OH) ₂ . This precursor powder had an average particle diameter D50 of 10 μm and a specific surface area (BET) of 45 m ² /g.

The precursor together with LiOH·H ₂ O was weighed into one bag so that the material amount ratio Li/(Ni + Co + Mn + Nb) was 1.01 in an air atmosphere with a humidity of 60%, and the opening was measured while the bag was inflated. was gripped with one hand to prevent the powder from leaking out, and the other hand that was not gripped was placed on the bottom of the bag, and the bag was shaken with both hands for rough mixing. All of the loosely mixed powders were placed in a Henschel mixer from the bag and mixed at 1500 rpm for 5 minutes, and the mixed powders were filled in an alumina sagger. Oxygen is filled in the firing furnace, the alumina sagger is placed in the firing furnace to create an oxygen atmosphere of 0.1 MPa, held at 350 ° C. for 2 hours, held at 490 ° C. for 8 hours, and further heated. It was held at 750° C. for 4 hours. This was cooled to room temperature at 5°C/min. After cooling, the alumina sagger was taken out from the kiln into dry air and pulverized with a roll crusher and an ACM pulverizer. The pulverized powder was added together with lithium ethoxide and niobium pentaethoxide so that the material amount ratio of (Ni+Co+Mn):LiOC ₂ H ₅ :Nb(OC ₂ H ₅ ) ₅ =1:0.0033:0.0033. Then, both alkoxides are dispersed in ethanol to form a dispersion, and the crushed powder and the dispersion are coated with lithium niobium oxide in a conventional manner using a tumbling flow apparatus to form a positive electrode. An active material was obtained. An oxide-based solid electrolyte having a composition formula: Li _6.5 La ₃ Zr _1.5 Ta _0.5 O ₁₂ was mixed with the positive electrode material active material so as to be 30% by mass, and further baked at 750 ° C. for 7 hours. A cathode body of Example 1 was obtained.

(Evaluation of battery performance)
-Evaluation of battery characteristics (all-solid-state lithium-ion battery)-
A mold having an inner diameter of 10 mm was filled with a Li--In alloy, Li _6.5 La ₃ Zr _1.5 Ta _0.5 O ₁₂ , a positive electrode body and Al foil in this order, and pressed at 500 MPa. An all-solid lithium ion battery was produced by constraining the compact after pressing at 100 MPa using a metal jig. For this battery, the initial capacity obtained at a charge/discharge rate of 0.05C (25°C, upper limit charge voltage: 3.7V, lower limit discharge voltage: 2.5V) was measured. Next, charging and discharging were repeated 10 times at a charging and discharging rate of 1 C (25° C., upper limit charging voltage: 3.7 V, lower limiting discharging voltage: 2.5 V). The capacity obtained in the first discharge at a charge/discharge rate of 1C is defined as discharge capacity 1, the capacity obtained in the tenth discharge at a charge/discharge rate of 1C is defined as discharge capacity 2, and (discharge capacity 2) / (discharge The ratio of capacity 1) was defined as a percentage and cycle characteristics (%) were obtained.
Table 1 shows test conditions and evaluation results.

In Example 1, the battery characteristics were comparable to or superior to those in Comparative Example 1, although only one firing step was required.

Claims (5)

a step of putting a transition metal hydroxide precursor composed of nickel, cobalt and manganese into a rocking mixer, and spraying an aqueous niobium oxalate solution and a lithium ion precursor, respectively, to prepare a surface coating precursor powder; ,
a step of mixing and sintering the surface-coating precursor powder and an oxide-based solid electrolyte;
A method for producing a positive electrode for an all-solid-state lithium ion battery comprising: The amount ratio of nickel, cobalt, and manganese in the transition metal hydroxide precursor composed of nickel, cobalt, and manganese is 85 to 90 when the total amount of nickel, cobalt, and manganese is 100: 7 to 9: The method for producing a positive electrode for an all-solid lithium ion battery according to claim 1, which is represented by 0 to 7.5 (excluding 0). 3. The lithium ion precursor according to claim 2, wherein the lithium ion precursor is one or more selected from the group consisting of lithium nitrate solution, lithium citrate solution, lithium hydroxide solution, lithium acetate solution, and lithium oxalate solution. A method for manufacturing a positive electrode for an all-solid-state lithium-ion battery. The positive electrode for an all-solid lithium ion battery according to any one of claims 1 to 3, wherein the transition metal hydroxide precursor composed of nickel, cobalt and manganese has a specific surface area of 25 m ² /g or more. Production method. The positive electrode for an all-solid lithium ion battery manufactured by the method for manufacturing a positive electrode for an all-solid lithium ion battery according to any one of claims 1 to 4 is used as a positive electrode layer, and the positive electrode layer, the solid electrolyte layer and the negative electrode layer are A method for manufacturing an all-solid-state lithium-ion battery, which uses the method to manufacture an all-solid-state lithium-ion battery.