JP7159902B2 - Electrode manufacturing method - Google Patents

Description

The present disclosure relates to a method for manufacturing electrodes used in all-solid-state batteries.

An all-solid-state battery is a battery that has a solid electrolyte layer between a positive electrode active material layer and a negative electrode active material layer. It has the advantage of being easy to plot.

An electrode in a normal battery has an active material layer and a current collector that collects current from the active material layer. For example, Patent Document 1 discloses a method for manufacturing electrodes used in liquid-based batteries, and Patent Document 2 discloses a method for manufacturing electrodes used in all-solid-state batteries.

JP 2016-219212 A JP 2015-115103 A

From the viewpoint of improving the performance of all-solid-state batteries, high dispersibility of the electrode material in the active material layer is required. In addition, from the viewpoint of productivity, the electrode manufacturing method is required to have good working efficiency. The present disclosure has been made in view of the above circumstances, and a main object of the present disclosure is to provide a method for manufacturing an electrode with high dispersibility of an electrode material in an active material layer with high work efficiency.

As disclosed in Patent Document 2, the electrode in the all-solid-state battery is made by slurrying (pasting) an active material, a binder, a solid electrolyte, etc. with an appropriate solvent, and applying this electrode slurry on a current collector. It is manufactured by applying, drying, and pressing. On the other hand, in a liquid battery, as disclosed in Patent Document 1, a powder material containing at least an active material and a binder is added with a small amount of solvent to prepare a granule, and the granule is used as a current collector. A method (moisture powder sheeting (MPS)) in which electrodes are formed by press forming on a body is used. Compared with the method described in Patent Document 2, the method described in Patent Document 1 uses a smaller amount of solvent, and thus has the advantage that it does not take much time to dry the electrode. The inventor of the present invention came up with the idea of applying this construction method in order to improve work efficiency in the method of manufacturing electrodes used in all-solid-state batteries. However, it is difficult to uniformly knead the electrode material, and the problem arises that the dispersibility of the electrode material in the active material layer is low. As a result of intensive studies, the inventors have found that the dispersibility is improved by applying a predetermined shearing stress to the granules, and completed the present invention.

That is, in the present disclosure, a method for manufacturing an electrode used in an all-solid-state battery and having a current collector and an active material layer, wherein a powder material containing at least an active material, a binder, and a solid electrolyte is mixed with a solvent. , a granulation step of granulating a wet powder having a solid content of 80% by weight or more and less than 90% by weight; a shearing step of applying a shear stress of 29 kPa or more and 181 kPa or less to the wet powder; a film-forming step of forming the active material layer by passing the wet powder to which the shear stress is applied between adjacent rotating rolls and transferring it onto the current collector. provide a way.

According to the present disclosure, it is possible to efficiently manufacture an electrode in which the electrode material is highly dispersed in the active material layer.

Advantageous Effects of Invention According to the present disclosure, it is possible to efficiently manufacture an electrode in which an electrode material is highly dispersed in an active material layer.

FIG. 3 is a flow chart showing an example of a method for manufacturing an electrode in the present disclosure; 4 is a graph showing the results of Examples and Comparative Examples. 1 is a schematic diagram showing an example of a film forming apparatus having rotating rolls that can be used in the manufacturing method of the present disclosure; FIG. It is a graph which shows the result of an impedance measurement.

FIG. 1 is a flow diagram showing an example of a method for manufacturing an electrode according to the present disclosure. As shown in FIG. 1, in the electrode manufacturing method of the present disclosure, a powder material containing at least an active material, a binder, and a solid electrolyte (SE) is mixed with a solvent, and a wet powder having a solid content within a predetermined range is obtained. Granulate the body (granulation process). Next, a predetermined shearing stress is applied to the wet powder (shearing step). Then, the wet powder to which the shear stress is applied is passed between adjacent rotating rolls and transferred onto a current collector to form an active material layer (film formation step).

According to the present disclosure, an electrode in which the electrode material is highly dispersed in the active material layer can be manufactured with good work efficiency. Specifically, since the solvent is added to the powder material containing the binder in the powder state, there is no need to prepare the binder into a solution, and the drying time of the electrode is reduced due to the high solid content of the wet powder. can be shortened. Thereby, working efficiency can be improved. Furthermore, by applying a predetermined shearing stress to the wet powder, the electrode material in the active material layer can be dispersed. As described above, since the electrode material is well dispersed in the electrode manufactured by the method of the present disclosure, a battery using the electrode has, for example, a suppressed resistance of the electrode.

Hereinafter, each step of the electrode manufacturing method according to the present disclosure will be described in detail.

1. Granulation step In the granulation step of the present disclosure, a powder material containing at least an active material, a binder, and a solid electrolyte is mixed with a solvent to granulate a wet powder having a solid content of 80% by weight or more and less than 90% by weight. It is a process to do.

(1) Powder material The powder material in the present disclosure contains at least an active material, a binder and a solid electrolyte. The powder material may contain only the active material, the binder, and the solid electrolyte, or may further contain other materials. Other materials include, for example, conductive agents.

The active material is preferably a material that can react with Li ions and that expands and contracts due to charging and discharging. When the electrode is used as a negative electrode, examples of the active material include Si-based active materials. Further, when the electrode is used as a positive electrode, the active material includes, for example, LiCoO ₂ , LiMn ₂ O ₄ , LiNiO ₂ , LiNi _0.5 Mn _1.5 O ₄ , LiNi _1/3 Mn _1/3 Co _{1 /3} O ₂ , LiNi _0.5 Mn _0.5 O ₂ , LiCoPO ₄ , LiFePO ₄ , LiMnPO ₄ and the like.

Examples of the shape of the active material include particulate. The average particle diameter (D ₅₀ ) of the active material is, for example, within the range of 0.1 μm to 50 μm, and may be within the range of 1 μm to 20 μm. The average particle size (D ₅₀ ) of the active material can be determined, for example, from the results of particle size distribution measurement by a laser diffraction scattering method.

From the viewpoint of battery capacity, the proportion of the active material in the powder material is preferably higher, for example, 30% by weight or more, preferably 50% by weight or more, and more preferably 70% by weight or more.

Although the type of binder is not particularly limited, it is preferably a material that dissolves or swells in the solvent described below. Examples of binders include fluorine-based binders such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE).

The proportion of binder in the powder material is, for example, in the range 0.1% to 10% by weight, and may be in the range 0.5% to 5% by weight.

Although the type of solid electrolyte is not particularly limited, for example, a sulfide solid electrolyte can be used. Sulfide solid electrolytes include, for example, Li ₂ SP ₂ S ₅ , Li ₂ SP ₂ S ₅ -LiI, Li ₂ SP ₂ S ₅ -LiCl, Li ₂ SP ₂ S ₅ -LiBr , Li ₂ SP _{2 S 5 —Li 2 O, Li 2 SP 2 S 5 —Li 2 O—LiI, Li 2 S — SiS 2 ,} Li ₂ S—SiS ₂ —LiI, Li ₂ S—SiS ₂ -LiBr, Li2S _{- SiS2 -} LiCl, Li2S _{- SiS2 -} B2S3 _- LiI, Li2S _- SiS2 _- P2S5 _- LiI, Li2S _{- B2S3 ,} Li ₂ SP ₂ S ₅ -Z _m S _n (where m and n are positive numbers; Z is one 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 and y are positive numbers and M is any one of P, Si, Ge, B, Al, Ga and In), Li ₁₀ GeP ₂ S ₁₂ and the like can be mentioned.

The proportion of the solid electrolyte in the powder material is, for example, within the range of 20% to 70% by weight, and may be within the range of 40% to 60% by weight. Powdered materials usually do not contain solvents.

(2) Solvent The type of solvent is not particularly limited as long as it can dissolve the above binder. Examples of the solvent include butyl butyrate and the like. In the present disclosure, the solvent means a solution capable of dispersing the powdery material described above, and is a term that includes a dispersion medium.

The amount of the solvent to be added is such that the solid content of the resulting wet powder is 80% by weight or more and less than 90% by weight, and more preferably 85% by weight or more and 88% by weight or less. If the amount of solvent is too small or too large, there is a risk that the transfer onto the current collector will not be possible. On the other hand, if the amount of solvent is too large, it may take time to dry the electrodes, resulting in deterioration of working efficiency.

(3) Granulation method The method of granulating the wet powder in the present disclosure is not particularly limited, but multistage stirring can be used. For example, as shown in FIG. 1, first stirring for mixing an active material, a binder, a solid electrolyte, and a conductive agent to prepare a powder material, and two-stage stirring after adding a solvent to the powder material (second and the third stirring), the wet powder can be granulated. Examples of the stirring device include a stirrer having rotating blades, and a specific example thereof is a planetary mixer.

The first stirring can be performed, for example, at a speed of 2000 rpm to 5000 rpm for 1 second to 30 seconds.

The second stirring can be performed at a speed of 300-1800 rpm for 1 second to 30 seconds, and the third stirring can be performed at a speed of 2000 rpm to 5000 rpm for 0.5 seconds to 8 seconds. In this way, by performing a plurality of stages of stirring after adding the solvent, it is possible to prevent secondary agglomeration of the powder material to which the solvent has been added.

2. Shearing step The shearing step in the present disclosure is a step of applying a shearing stress of 29 kPa or more and 181 kPa or less to the wet powder described above.

The shear stress is 29 kPa or more and 181 kPa or less, may be 40 kPa or more and 100 kPa or less, or may be 50 kPa or more and 80 kPa or less. Moreover, the shear stress can be calculated by multiplying the viscosity at the shear rate by the shear rate. The shear rate can be calculated by π×rotor outer diameter×rotor speed/clearance. Therefore, the shear stress can be adjusted by, for example, the viscosity of wet powder and the rotor speed.

The treatment time of this step is not particularly limited, but may be, for example, 30 seconds or longer, 1 minute or longer, 5 minutes or longer, or 10 minutes or longer. On the other hand, the processing time is, for example, 30 minutes or less, and may be 20 minutes or less.

In the shearing step in the present disclosure, any device that can apply the above shear stress can be used without particular limitation, and for example, a mincer or the like can be used.

3. Film-forming process The film-forming process in the present disclosure is a process of forming an active material layer by passing the above-described wet powder to which shear stress is applied between adjacent rotating rolls and transferring it onto a current collector. is.

A device for transferring the wet powder to the current collector is not particularly limited as long as it has a rotating roll and can be used. For example, a film forming apparatus 10 as shown in FIG. 3 can be exemplified.

Examples of current collectors include current collectors commonly used in all-solid-state batteries. Examples of materials for the current collector include nickel, SUS, copper, and carbon.

An electrode having a current collector and an active material layer can be manufactured by usually performing a drying treatment after transferring the wet powder onto the current collector.

4. Electrode An electrode manufactured by the method of the present disclosure has a current collector and an active material layer formed on the current collector.

The electrodes in the present disclosure are used in all-solid-state batteries, and preferably used in all-solid-state lithium-ion batteries. The electrode in the present disclosure may be used as a positive electrode or a negative electrode in an all-solid-state battery.

Further, the all-solid-state battery may be a primary battery or a secondary battery, and is preferably a secondary battery. This is because they can be repeatedly charged and discharged, and are useful, for example, as batteries for vehicles. Examples of the shape of the battery include coin type, laminate type, cylindrical type, rectangular type, and the like.

Note that the present disclosure is not limited to the above embodiments. The above embodiment is an example, and any device that has substantially the same configuration as the technical idea described in the claims of the present disclosure and achieves the same effect is the present invention. It is included in the technical scope of the disclosure.

[Example 1]
An active material (Si particles), a binder (PVDF powder), a conductive agent (VGCF), and a sulfide solid electrolyte (Li ₂ SP ₂ S ₅ system) were mixed into a negative electrode active material: binder: conductive agent: sulfide solid. The electrolytes were weighed in a weight ratio of 53.3:1.1:4.3:41.4. These were stirred at 4500 rpm for 15 seconds in a stirrer with rotating blades to obtain a mixture of powdered materials. To the resulting mixture, butyl butyrate was added so that the solid content was 89% by weight, and the mixture was stirred at 800 rpm for 30 seconds, and then stirred at 4500 rpm for 2 seconds. This granulated the wet powder. A shear stress of 167 kPa was applied to the resulting wet powder for 720 seconds. After that, the wet powder was transferred to a current collector (Cu foil) through a three-roll film-forming machine, and dried by heating. As a result, an electrode having an active material layer formed on the current collector was obtained.

[Examples 2 to 8]
An electrode was produced in the same manner as in Example 1, except that the solid fraction and shear stress of the wet powder were changed as shown in Table 1.

[Comparative Example 1]
Conventionally, electrode fabrication was performed by applying a slurry as follows. First, PVDF was dissolved in butyl butyrate to prepare a binder solution. This binder solution, the same active material, conductive agent, and sulfide solid electrolyte as in Example 1 were dissolved in butyl butyrate to prepare a slurry. This slurry was applied onto a current collector (Cu foil) using a paper applicator so as to have a uniform thickness. Then, it was dried to obtain an electrode. The solid content of the prepared slurry was 43% by weight.

[Comparative Example 2]
An electrode was obtained in the same manner as in Example 1, except that a solution of PVDF in butyl butyrate was used as the binder and the shearing process was not performed.

[Comparative Examples 3 to 8]
As shown in Table 1, electrodes were obtained in the same manner as in Example 1, except that the solid content and shear stress were changed.

[Preparation of battery for evaluation]
A negative electrode was produced in the same manner as in Example 1, except that the shear stress was changed to 45 kPa. A positive electrode active material (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ) and a sulfide solid electrolyte (LiI—Li ₂ O—Li ₂ SP ₂ S ₅ ) are combined into a positive electrode active material: a sulfide solid electrolyte = 75:25 weight ratio. After that, 1.5 parts by weight of the PVDF binder and 3.0 parts by weight of the conductive agent (VGCF) were weighed with respect to 100 parts by weight of the positive electrode active material. These materials were mixed and butyl butyrate was added. After that, the mixture was kneaded for 1 minute using an ultrasonic homogenizer to obtain a positive electrode slurry. The resulting positive electrode slurry was applied to the surface of a current collector (Al foil) using an applicator (350 μm), and dried by heating. Then, it was roll-pressed at 25° C. and a linear pressure of 1 ton/cm. Thus, a positive electrode having a positive electrode active material layer on the current collector was obtained. In an inert gas atmosphere, the positive electrode active material layer of the positive electrode and the negative electrode active material layer of the negative electrode were arranged and pressed so as to face each other with the solid electrolyte layer interposed therebetween. After that, it was sealed with an Al laminate to obtain a battery 1 for evaluation.
Evaluation battery 2 was obtained in the same manner as described above, except that the negative electrode was produced in the same manner as in Comparative Example 1. Furthermore, evaluation battery 3 was obtained in the same manner as above, except that the shearing process was not performed in the preparation of the negative electrode.

[evaluation]
(Possibility of film formation)
When the wet powders obtained in Examples 1 to 8 and Comparative Examples 2 to 8 were transferred onto the current collector, the transfer state to the current collector and the residual wet powder on the rotating roll were visually observed. The condition was observed and evaluated. Table 1 shows the results. In Table 1, ◯ means that the film was formed, △ means that the wet powder was partially stuck to the rotating roll and could not be transferred to the current collector, and △ means that the transfer was not possible on the current collector at all. was written as x.

(work efficiency)
In Comparative Example 1 in which an electrode was produced by a conventional method, the time required to prepare the binder and the time required to dry the electrode were used as the reference, and the time required to prepare the binder and The time required to dry the electrodes was compared. Table 1 shows the results. In Table 1, the case where the time was shorter than that of Comparative Example 1 was indicated by ◯, and the case where the same time as Comparative Example 1 was required was indicated by x.

(dispersion degree)
Using a scanner (GT-F740, manufactured by Epson Corporation), each film-formed electrode was scanned in grayscale, the number of brightnesses in the range of 0 to 255 was obtained, and the standard deviation was calculated and compared. . Table 1 shows the results. In Table 1, when the standard deviation is less than 3, it is indicated by ◯, and when the standard deviation is 3 or more, it is indicated by x.

In the above evaluation items, when all of the evaluation items were ◯, the overall evaluation was judged to be ◯, and when even one of the evaluation items was x, the overall evaluation was judged to be ×. The results of Examples 1-8 and Comparative Examples 2-8 are also plotted in FIG.

(impedance measurement)
Impedance measurement was performed on the obtained three batteries for evaluation under conditions of 25° C. and SOC (State-Of-Charge) of 60%. The results are shown in FIG.

As shown in Table 1, in Comparative Example 2 in which the binder was added in the form of a solution, the dispersion of the electrode was good, but the working efficiency was poor because the binder was prepared in the form of a solution. In addition, in Comparative Examples 3 to 8 in which the binder was added in powder form, although the drying time of the electrode was shortened, the solid content (NV) and shear stress were outside the predetermined ranges, so film formation was not possible. , the degree of dispersion was poor. On the other hand, in Examples 1 to 8, work efficiency was also good, and an electrode in which the powder material in the electrode was well dispersed could be manufactured.

FIG. 4 shows the results of impedance measurement, with the right plot for evaluation battery 3 and the left plot for evaluation batteries 1 and 2. In FIG. As can be seen from FIG. 4 , the evaluation battery 1 whose negative electrode was produced by the method of the present disclosure showed the same resistance value as the plot of the evaluation battery 2 whose negative electrode was produced by the slurrying method. The evaluation battery 3, in which the negative electrode was manufactured without performing the process, had a higher electrode resistance than the evaluation batteries 1 and 2. This is presumably because evaluation battery 3 did not undergo the shearing process, and thus there were places in the negative electrode where the solid electrolyte was densely packed, and the ionic conduction path was broken.

DESCRIPTION OF SYMBOLS 1... Wet powder 2... Current collector 3... Rotating roll 10... Film-forming apparatus

Claims (1)

A method for manufacturing an electrode used in an all-solid-state battery and having a current collector and an active material layer,
A solvent is mixed with a powder material containing at least an active material, a binder, and a sulfide solid electrolyte , and the ratio of the sulfide solid electrolyte is 20% by weight or more and 70% by weight or less, and the solid content is 80% by weight. A granulation step of granulating wet powder of 90% by weight or more,
A shearing step of applying a shearing stress of 29 kPa or more and 181 kPa or less to the wet powder;
a film forming step of forming the active material layer by passing the wet powder to which the shear stress is applied between adjacent rotating rolls and transferring it onto the current collector;
A method for manufacturing an electrode having

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