JP2020181717A - Manufacturing method of lithium ion secondary battery electrode - Google Patents

Abstract

To make the manufacture of an electrode safe and convenient.SOLUTION: A manufacturing method of a lithium ion secondary battery electrode includes the steps of preparing a resin electrolyte binder by dry-kneading an ionic conductive resin and a lithium salt, dry-kneading an active material, a conductive auxiliary agent, and the resin electrolyte binder to prepare an electrode composite material, and binding the electrode composite material to a current collector by pressing.SELECTED DRAWING: Figure 2

Description

The present invention relates to a method for manufacturing an electrode for a lithium ion secondary battery.

Conventionally, in the electrode of an all-solid-state secondary battery, a resin serving as a binder is dispersed in a solvent, an active material and a conductive auxiliary agent are dispersed therein to form a slurry, and this slurry is applied to the surface of a current collector. , Made by volatilizing the solvent. Such a method includes, for example, those disclosed in Japanese Patent Application Laid-Open No. 2005-051125.

Japanese Unexamined Patent Publication No. 2005-051125

When the solvent is used as the dispersion medium of the binder as described above, a step of volatilizing an unnecessary solvent in the battery is required, which not only complicates the step but also causes problems of safety and environmental load. Further, since the amount of slurry coated is affected by, for example, the viscosity and film thickness of the solvent, complicated parameter management is required, and it is difficult to easily prepare an electrode material with a desired composition. Therefore, a method capable of producing an electrode safely and easily is desired.

One aspect of the present invention is a method of manufacturing an electrode for a lithium ion secondary battery, which comprises a step of dry-kneading an ion conductive resin and a lithium salt to prepare a resin electrolyte binder, and an active material and conductive assistance. It includes a step of dry-kneading the agent and the resin electrolyte binder to prepare an electrode composite material, and a step of binding the electrode composite material to the current collector by pressing.

Depending on the embodiment, the step of dry-kneading the ionic conductive resin and the lithium salt and the step of dry-kneading the active material, the conductive auxiliary agent, and the resin electrolyte binder are one kneading step at a time. Will be done.

Some embodiments include heating at least one of the resin electrolyte binder and the electrode composite material.

In some embodiments, the electrode composite is heated in the pressing process.

Depending on the embodiment, the heating temperature in the heating step is 180 ° C. or higher and 250 ° C. or lower.

In some embodiments, the ionic conductive resin is polyethylene oxide.

In some embodiments, the lithium salt is LiTFSI.

According to the above method, the effect of making the electrode safe and convenient can be obtained.

FIG. 1 is a diagram showing an SEM photograph of the positive electrode composite material before heating and the element distribution in the material. FIG. 2 is a diagram showing an SEM photograph of the positive electrode composite material after heating and the element distribution in the material. FIG. 3 shows the results of measuring the ionic conductivity of PEO, which is an ionic conductive resin, and a resin electrolyte binder in which LiTFSI is added and kneaded in a dry manner.

Hereinafter, various embodiments of the present invention will be described with reference to the drawings.

The electrode may be either a positive electrode or a negative electrode. The electrode includes an active material capable of storing and releasing lithium ions, a conductive auxiliary agent, an ion conductive resin, a lithium salt as an electrolyte, and a current collector.

The active material is not particularly limited, and the active material used for the positive electrode and the negative electrode of the conventional lithium ion secondary battery can be used.

When the electrode is a positive electrode, the active material can be, for example, a sulfide containing a transition metal, an oxide containing lithium and a transition metal, or the like. Examples of such sulfides and oxides include transition metal oxides such as the composite oxide V ₂ O _{5 of} lithium and transition metals, and transition metal sulfides such as TiS ₂ , TiS ₃ , MoS ₃ , and FeS ₂ . and so on. Lithium-transition metal composite oxides include Li-Mn-based composite oxides such as LiMnO ₂ and LiMn ₂ O ₄ , Li-Co-based composite oxides such as LiCoO _2, and Li-Ni-based composite oxides such as LiNiO _2. There are Li-V-based composite oxides such as LiV 2O ₃ . Among these, the active material is preferably a composite oxide of lithium and a transition metal, and particularly preferably LiCoO ₂ (lithium cobalt oxide, LCO). It should be noted that the illustrated chemical formula is not intended to be limited to a stoichiometric composition, and may have partial defects / substitutions or excesses.

When the electrode is a negative electrode, the active material is, for example, a carbonaceous material such as graphite or hard carbon, a silicon-based material, a germanium, a tin-based material, or a composite oxide containing lithium and a transition metal (eg, Li ₄ Ti ₅ O _12). ) And so on.

Examples of the ionic conductive resin include polyethylene oxide, polypropylene oxide, polyvinyl alcohol, polyvinylidene fluoride, polyphosphazene, polyethylene sulfide, polyhexafluoropropylene and the like, and derivatives thereof. Of these, polyethylene oxide (PEO) is particularly preferable.

Examples of the lithium salt include lithium hexafluorophosphate (LiPF ₆ ), lithium trifluoromethanesulfonate (LiCF ₃ SO ₃ , LiTFS), lithium bis (trifluoromethanesulfonyl) imide (LiN (CF ₃ SO ₂ ) ₂ , LiTFSI). ), Lithium bis (fluorosulfonyl) imide (LiN (FSO ₂ ) ₂ , LiFSI), Lithium bis (trifluoromethanesulfonyl) imide (LiN (CF ₃ SO ₂ ) ₂ , LiTFSI), Lithium bis (pentafluoroethanesulfonyl) imide (LiN (CF ₂ CF ₃ SO ₂ ) ₂ , LiBETI), lithium bis (oxalate) bolate (LiB (C ₂ O4) ₂ , LiBOB) and the like. Of these, LiTFSI is particularly preferable. One type of lithium salt may be used, or two or more types may be used in combination. The melting point of the lithium salt is preferably higher than the softening temperature of the ionic conductive resin.

The conductive auxiliary agent is not particularly limited, and for example, carbon materials such as carbon black and graphite, metal powders such as copper, nickel, stainless steel, and iron, and powders such as conductive oxides such as indium tin oxide (ITO). , These can be a mixture.

The material of the current collector is not particularly limited, and examples thereof include aluminum, titanium, stainless steel, nickel, iron, calcined carbon, conductive polymer, and conductive glass. The form of the current collector is also not particularly limited, and may be a foil, a film, a sheet, a perforated material thereof, a net-like body, an expanded metal, a porous body, a foam, a fibrous body, or the like. For example, aluminum foil can be used.

The method for manufacturing the electrodes of the lithium ion secondary battery will be described below. First, the active material, the conductive auxiliary agent, the ionic conductive resin, and the lithium salt as described above are prepared. The form of the ionic conductive resin is not limited and may be granular or powdery. The ionic conductive resin and the lithium salt are dry-kneaded without using a solvent to form a resin electrolyte binder. Next, the resin electrolyte binder, the active material, and the conductive auxiliary agent are dry-kneaded without using a solvent to form an electrode composite material. These two kneading steps may be performed at the same time. That is, the active material, the conductive auxiliary agent, the ionic conductive resin, and the lithium salt can be kneaded in one step to form an electrode composite material. When the resistance to kneading is relatively small, such as when a powdered ionic conductive resin is used, it is convenient to knead in one step in this way. For kneading, any suitable instrument capable of mechanically stirring, such as a mortar, can be used. At the time of any kneading, the material may be heated at a temperature equal to or higher than the softening temperature of the ion conductive resin to soften the ion conductive resin, if necessary, in order to facilitate the kneading. The heating temperature is preferably a temperature at which decomposition of the active material, the lithium salt, and the conductive auxiliary agent does not occur. For example, when PEO is used as the ionic conductive resin, the temperature is preferably 180 ° C. or higher and 250 ° C. or lower, and particularly preferably about 200 ° C. Even if the step of actively heating is not included, the ionic conductive resin can be softened to some extent by the heat generated by stirring. The volume ratio of the resin electrolyte binder in the electrode composite material is preferably 5 wt% or more and 50 wt% or less.

This electrode composite material is bound to the current collector by a press to form an electrode. At this time, a solid electrolyte may be used as a base material, on which the electrode composite material may be molded. Further, in this electrode forming step, the electrode composite material may be heated if necessary. Also in this case, the heating temperature is preferably a temperature equal to or higher than the softening temperature of the ionic conductive resin. The heating temperature is preferably a temperature at which decomposition of the active material, the lithium salt, the conductive additive, and the solid electrolyte does not occur. For example, when PEO is used as the ionic conductive resin, the temperature is preferably 180 ° C. or higher and 250 ° C. or lower, and particularly preferably about 200 ° C. This heating step is performed for the purpose of improving the diffusibility of the resin electrolyte binder in the gaps between the active materials, improving the moldability of the electrode, and improving the binding property of the electrode composite material to the current collector or the solid electrolyte. Can be done.

The positive electrode or the negative electrode produced by the above method can form a lithium ion secondary battery by combining a pair of electrodes and an electrolyte layer. The specific shape and structure of the battery are not particularly limited. This battery can be an all-solid-state lithium ion secondary battery using a solid electrolyte in the electrolyte layer. The solid electrolyte may be an inorganic solid electrolyte or an organic solid electrolyte. As the inorganic solid electrolyte, various oxide-based and sulfide-based electrolytes are known. Examples of oxide-based electrolytes include Li _0.34 La _0.51 TiO _2.94 , Li ₇ La ₃ Zr ₂ O ₁₂ , Li ₇ La ₃ Zr _2-x Ta _x O ₁₂ , Li ₄ SiO ₄ , Li ₃ PO ₄ -Li ₄ There is a SiO ₄ system. Examples of sulfide-based electrolytes include Li ₃ PS ₄ , Li ₇ P ₃ S ₁₁ , Li ₁₀ GeP2S ₁₂ , Li ₂ SP ₂ S ₅ series, Li ₂ S-SiS ₂ series, and Li ₂ S-SiS ₂ -Li. There are ₃ PO ₄ series.

Since the electrode manufacturing method described above does not require a step of volatilizing the solvent without using a solvent, there is an advantage that the electrode can be manufactured safely and easily.

Although the present invention has been described above with specific embodiments, the present invention is not limited to these embodiments, and those skilled in the art can perform various substitutions, improvements, and the like without deviating from the object of the present invention. It is possible to make changes.

[Production example]
In the following, examples of producing electrodes and some experimental results will be described. In an agate mortar, 1.00 g of PEO (gum-like) as an ionic conductive resin and 0.36 g of LiTFSI (powder manufactured by Kanto Chemical Co., Inc.) as a lithium salt were dry-kneaded for 30 minutes to form a resin electrolyte binder. 0.3 g of this resin electrolyte binder, 0.7 g of LCO (manufactured by Nippon Kagaku Kogyo Co., Ltd., Celseed C10) separately Nb-coated as an active material, and carbon black powder (manufactured by Denka, manufactured by Denka) as a conductive auxiliary agent. Li-400) was dry-kneaded with 0.05 g for 30 minutes to prepare a positive electrode composite material. A plate-shaped sintered body of Li ₇ La ₃ Zr _2-x Ta _x O ₁₂ (manufactured by Toshima Manufacturing Co., Ltd.) was prepared, and the surface was sanded with # 2000 sandpaper. 10 mg of the obtained positive electrode composite material was sandwiched between the plate-shaped sintered body of this Li ₇ La ₃ Zr _2-x Ta _x O ₁₂ and an aluminum foil (perforated with a diameter of 8 to 9.5 mm), and a glass plate was used. By pressing from the aluminum foil side, the positive electrode composite material was stretched and spread, and was bound to the solid electrolyte and the aluminum foil to form a positive electrode.

[Experiment 1]
The thermal stability of each material used in the above production example was examined by thermal analysis. Specifically, the presence or absence of decomposition was investigated by measuring the change in weight while performing the program temperature rise for each material. The temperature at which decomposition occurred in each material is as follows.
Positive electrode composite material: 300 ° C
PEO: 300 ° C
PEO + LiTFSI: 290 ° C
LCO: 800 ° C or higher Carbon black: 800 ° C or higher From this result, it was confirmed that PEO and other materials did not change in weight even when heated to 200 ° C or 250 ° C, and decomposition did not occur. ..

[Experiment 2]
In order to investigate the molten state of PEO, the appearance was observed while raising the temperature of the positive electrode composite material of the above-mentioned production example. The results are shown in the table below.

As shown in the table, no melting was observed from room temperature to 150 ° C, but melting was observed from 180 ° C to 250 ° C. Melting was observed at 300 ° C, but discoloration was also observed at the same time. In addition, it was confirmed that there was no significant change such as discoloration even when the mixture was held at 200 ° C for 30 minutes.

[Experiment 3]
In order to investigate the dispersed state of the resin electrolyte binder, the element distribution before and after heating was investigated for the positive electrode composite material of the above-mentioned production example. FIG. 1 shows the results of the positive electrode composite material before heating, and FIG. 2 shows the results of heating the composite material at 200 ° C. for 30 minutes. The upper left of FIGS. 1 and 2 is a scanning electron micrograph of the positive electrode composite material. The other four images represent the element distribution measured by the energy dispersive X-ray analyzer in light and dark (the higher the concentration, the brighter). The upper center is carbon (C), the upper right is oxygen (O), and the lower is lower. The left is for sulfur (S) and the lower right is for cobalt (Co). As can be seen from the comparison between FIGS. 1 and 2, carbon and sulfur derived from the resin electrolyte binder are unevenly distributed before heating, and there is a portion that does not exist around the cobalt derived from the active material. This can cause high resistance for lithium ions. On the other hand, after heating, it was confirmed that carbon and sulfur were distributed over the entire surface so as to fill the gaps between cobalt derived from the active material. Therefore, it was confirmed that the molten resin electrolyte binder was effectively diffused into the electrode when heated in the temperature range during kneading or pressing. As a result, it is considered that the binding property to the current collector foil and the solid electrolyte becomes better. In addition, since the resin electrolyte binder is considered to diffuse efficiently between particles due to the capillary phenomenon, the amount of the resin electrolyte binder that does not contribute to the battery capacity should be reduced and the energy density of the battery should be increased as compared with the case where heating is not performed. Can be done.

[Experiment 4]
The ionic conductivity of each of the PEO used in the above production example and the resin electrolyte binder containing LiTFSI dry-kneaded in the above production example was measured. As shown in the results shown in FIG. 3, it was found that the ionic conductivity of the resin electrolyte binder can be increased by kneading with LiTFSI.

[Experiment 5]
An all-solid-state lithium-ion secondary battery was produced by combining the positive electrode produced on the plate-shaped sintered body of Li ₇ La ₃ Zr _2-x Ta _x O _{12 in} the above production example with the negative electrode. The negative electrode was manufactured by pressing graphite as a negative electrode active material and Li ₃ PS ₄ , which is a sulfide-based solid electrolyte, by a conventional method. When a charging test was conducted on the obtained lithium ion secondary battery, it was confirmed that the battery had a certain charging performance.

Claims (7)

A method of manufacturing electrodes for lithium-ion secondary batteries.
The process of preparing a resin electrolyte binder by dry-kneading an ionic conductive resin and a lithium salt,
A step of dry-kneading the active material, the conductive auxiliary agent, and the resin electrolyte binder to prepare an electrode composite material, and
A method comprising the step of binding an electrode composite material to a current collector by a press. The method according to claim 1, wherein the step of dry-kneading the ionic conductive resin and the lithium salt and the step of dry-kneading the active material, the conductive auxiliary agent, and the resin electrolyte binder are one kneading. A method performed at once as a process. The method according to claim 1 or 2, which comprises a step of heating at least one of the resin electrolyte binder and the electrode composite material. The method according to claim 3, wherein the electrode composite material is heated in the pressing step. The method according to claim 3, wherein the heating temperature in the heating step is 180 ° C. or higher and 250 ° C. or lower. The method according to any one of claims 1 to 5, wherein the ionic conductive resin is polyethylene oxide. The method according to any one of claims 1 to 6, wherein the lithium salt is LiTFSI.