JP2017050248A - Method for manufacturing sei film-coated negative electrode active material powder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing SEI film-coated negative electrode active material powder, which is less in impurity immixture, and superior in the stability of a charge/discharge performance when a power storage device is arranged by use thereof.SOLUTION: A method for manufacturing SEI film-coated negative electrode active material powder comprises: an electrolytic processing unit preparation step for preparing an electrolytic processing unit having a negative electrode current collector, a negative electrode active material powder layer made of negative electrode active material powder and put in contact with the negative electrode current collector, a porous body, and an alkali-metal ion source which are arranged in this order in a thickness direction, and a nonaqueous electrolyte solution, provided that the negative electrode current collector, the negative electrode active material powder layer, the porous body and the alkali-metal ion source are in contact with the nonaqueous electrolyte solution; a first electrolytic process step for electrically connecting the negative electrode current collector and alkali-metal ion source, which are arranged in the electrolytic processing unit, outside the electrolytic processing unit to predope alkali-metal ions to the negative electrode active material powder, and to form an SEI film on the surface of the negative electrode active material powder; and a powder-collecting step for collecting the negative electrode active material powder having gone through the electrolytic process step.SELECTED DRAWING: Figure 2

Description

The present invention relates to a method for producing an SEI film-coated negative electrode active material powder.

Energy storage systems such as load leveling devices such as photovoltaic power generation and wind power generation, instantaneous voltage drop countermeasure devices for electronic devices such as computers, and energy regeneration devices for electric vehicles and hybrid cars have a large energy capacity. There is a need for an electricity storage device that can be rapidly charged and discharged. As such an electricity storage device capable of rapid charge / discharge and long life, an electricity storage device using an alkali metal ion as a conductive carrier, such as a lithium ion secondary battery and a lithium ion capacitor, has been proposed.

In lithium ion secondary batteries and lithium ion capacitors, during the initial charge, the solvent contained in the non-aqueous electrolyte reacts with the negative electrode active material to form a passive film that is a reaction product on the surface of the negative electrode active material. It is known that Such a passive film is also referred to as a SEI (Solid Electrode Interface) film, and is known to suppress a reaction in which the nonaqueous electrolytic solution decomposes on the surface of the negative electrode active material.

Since the characteristics of the formed SEI film vary depending on the composition of the non-aqueous electrolyte, various non-aqueous electrolytes suitable for forming the SEI film, additives for forming the SEI film, and the like have been developed.
For example, Patent Document 1 discloses a method of adding an additive for forming an SEI film on an electrode, and Patent Document 2 discloses a method of adding a surfactant to a nonaqueous electrolytic solution.

JP 2010-199043 A JP 11-126633 A

However, in any method, since the SEI film is formed inside the electricity storage device during the first charge, the non-aqueous solvent is consumed for the SEI film formation, or lithium ions are taken into the SEI film and the irreversible capacity. There has been a problem that the battery performance is lowered due to a decrease in the battery performance.
Furthermore, a non-aqueous solvent suitable for forming an SEI film is not necessarily the same as a non-aqueous solvent suitable for enhancing the functionality of an electricity storage device, and a non-aqueous electrolyte optimized for forming an SEI film is used. The power storage device has a problem that the battery performance cannot be sufficiently obtained.

As a result of intensive studies by the present inventors in view of the above problems, by arranging and electrically connecting a powdered negative electrode active material and an alkali metal ion supply source in an electrolyte solution via an insulator The present inventors have found that an SEI film is formed on the surface of the negative electrode active material while pre-doping of alkali metal ions to the negative electrode active material proceeds, and the present invention has been achieved.

That is, the manufacturing method of the SEI film-coated negative electrode active material powder of the present invention includes a negative electrode current collector, a negative electrode active material powder layer composed of a negative electrode active material powder in contact with the negative electrode current collector, a porous body, and an alkali metal. Electrolytic treatment in which the ion source is arranged in this order in the thickness direction, and the negative electrode current collector, the negative electrode active material powder layer, the porous body, and the alkali metal ion source are in contact with the nonaqueous electrolytic solution An electrolytic treatment unit preparation step for preparing a unit, and the negative electrode current collector in the electrolytic treatment unit and the alkali metal ion supply source are electrically connected outside the electrolytic treatment unit to obtain the negative electrode active material powder. First, the alkali metal ions are pre-doped, and a first electrolytic treatment step for forming an SEI film on the surface of the negative electrode active material powder, and the negative electrode active material powder that has undergone the electrolytic treatment step are recovered. Characterized by comprising the a that powder recovery step.

The negative electrode active material powder obtained by the method for producing a SEI film-coated negative electrode active material powder of the present invention has an SEI film formed on the surface thereof. Therefore, when the negative electrode active material powder obtained by the method for producing a SEI film-coated negative electrode active material powder of the present invention is used as an electricity storage device, it is not necessary to form a new SEI film by the first charge / discharge. The liquid can be optimized to enhance the functionality of the electricity storage device. Furthermore, since it is not necessary to form the SEI film by the first charge / discharge, it is possible to suppress a decrease in irreversible capacity accompanying the formation of the SEI film.

The SEI film formed on the surface of the negative electrode active material powder by the SEI film-coated negative electrode active material powder manufacturing method of the present invention is a conventionally known SEI film, and the surface of the negative electrode active material powder during the first charge / discharge of the electricity storage device It is a passive film formed in

In the method for producing a SEI film-coated negative electrode active material powder of the present invention, a negative electrode current collector, a negative electrode active material powder layer comprising a negative electrode active material powder in contact with the negative electrode current collector, a porous body, and an alkali metal ion supply The negative electrode current collector, the negative electrode active material powder layer, the porous body, and the alkali metal ion supply source are in contact with the nonaqueous electrolytic solution.
The thickness direction refers to a direction in which the negative electrode current collector, the negative electrode active material powder layer, the porous body, and the alkali metal ion supply source are arranged.

In the manufacturing method of the SEI film-coated negative electrode active material powder of the present invention, when the alkali metal ion supply source and the negative electrode current collector are electrically connected outside the electrolytic treatment unit, the alkali metal ion supply source and the negative electrode active material powder layer Since a potential difference is generated between them, a reaction in which the alkali metal ions in the non-aqueous electrolyte solution are solvated in a non-aqueous solvent proceeds using the potential difference as a driving force, An SEI film is formed by reductive decomposition of the water solvent. Then, on the surface of the alkali metal ion supply source that is the counter electrode, alkali metal ions are supplied into the non-aqueous electrolyte in order to maintain the alkali metal ion concentration in the non-aqueous electrolyte.
By such a reaction, the powdered negative electrode active material (also referred to as negative electrode active material powder) is pre-doped with alkali metal ions, and at the same time, the SEI film-coated negative electrode active material powder in which the SEI film is formed on the surface of the negative electrode active material powder is obtained. can get. Subsequently, by collecting the SEI film-coated negative electrode active material powder, a powdery SEI film-coated negative electrode active material (also referred to as SEI film-coated negative electrode active material powder) having an SEI film formed on the surface can be obtained. .

In the electrolytic treatment process constituting the SEI film-coated negative electrode active material powder production method of the present invention, the method of electrically connecting the alkali metal ion supply source and the negative electrode current collector outside the electrolytic treatment unit is particularly limited. For example, a method of connecting the other end of one wiring extended from the alkali metal ion supply source to the outside of the electrolytic treatment unit to the negative electrode current collector (also referred to as a short circuit method), or an electrolytic treatment from the alkali metal ion supply source There is a method of connecting a first wiring extending outside the unit and a second wiring extending from the negative electrode current collector to the outside of the electrolytic treatment unit via a circuit monitoring control system such as a charge / discharge tester.

In the first electrolytic treatment process that constitutes the method for producing the SEI film-coated negative electrode active material powder of the present invention, the thickness of the SEI film formed on the surface of the negative electrode active material and the pre-doping are determined according to the current value and the treatment time. The amount of alkali metal changes. Therefore, the current value and the processing time may be set as necessary.
In addition, part or all of the alkali metal inserted into the negative electrode active material powder with the formation of the SEI film is detached (desorbed) from the negative electrode active material powder in the subsequent second electrolytic treatment step. (Also called dope).
The second electrolytic treatment process will be described later. In addition, in the present specification, the term “electrolytic treatment process” includes both the first electrolytic treatment process and the second electrolytic treatment process.

Moreover, in the manufacturing method of the SEI film-coated negative electrode active material powder of the present invention, the electrolytic treatment unit after the first electrolytic treatment step is an alkali metal ion supply source that has lost some or all of the alkali metal ions due to pre-doping, porous Body, SEI film-coated negative electrode active material powder, and negative electrode current collector, but the alkali metal ion source and the SEI film-coated negative electrode active material powder that have lost some or all of the alkali metal ions are disposed through a porous body. Therefore, it can be easily avoided that the alkali metal ion supply source that has lost part or all of the alkali metal ions is mixed into the SEI film-coated negative electrode active material powder.
Therefore, it can be said that the SEI film-covered negative electrode active material powder recovered by the powder recovery process is less contaminated with impurities and has excellent charge / discharge performance stability when used as an electricity storage device.

In the method for producing a SEI film-coated negative electrode active material powder of the present invention, the non-aqueous solvent constituting the non-aqueous electrolyte is at least one selected from the group consisting of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, and propylene carbonate. A mixed solvent of ethylene carbonate and ethylene carbonate is preferred.
When the non-aqueous solvent constituting the non-aqueous electrolyte is a mixed solvent of ethylene carbonate and at least one selected from the group consisting of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, and propylene carbonate, a stable SEI film is formed. It becomes easy to be carried out and it becomes easy to suppress the further decomposition reaction of a nonaqueous solvent.

In the method for producing a SEI film-coated negative electrode active material powder of the present invention, the non-aqueous electrolyte further comprises vinylene carbonate (VC), fluoroethylene carbonate (FEC), lithium bis (oxalate) borate (LiBOB), and sulfonic acid. It is preferable to include at least one additive selected from the group.
When the nonaqueous electrolytic solution contains these additives, the SEI film is easily formed densely, and the further decomposition reaction of the nonaqueous solvent is easily suppressed.

In the method for producing a SEI film-coated negative electrode active material powder of the present invention, the negative electrode active material powder layer is preferably composed of only the negative electrode active material powder.
When the negative electrode active material powder layer is composed only of the negative electrode active material powder, it is not necessary to remove impurities in the powder recovery step, and the production efficiency is improved.
In the negative electrode active material powder layer constituting the electrolytic treatment unit, the negative electrode active material powder is in contact with the non-aqueous electrolyte, but the non-aqueous electrolyte is not treated as a material constituting the negative electrode active material powder layer. .

In the method for producing a SEI film-coated negative electrode active material powder of the present invention, the negative electrode active material powder is preferably at least one selected from the group consisting of C, Si, Sn, SiO and SiO ₂ .
Since the SEI film is easily formed on the surface of the negative electrode active material powder made of these materials by the first electrolytic treatment process, it is suitable for applying the manufacturing method of the present invention.

In the method for producing a SEI film-coated negative electrode active material powder of the present invention, the alkali metal ion is preferably lithium ion.
When the alkali metal ions are lithium ions, the formed SEI film has lithium conductivity by taking in lithium ions, so that it can be particularly preferably used as a negative electrode active material for lithium ion secondary batteries with high energy density. .

In the method for producing a SEI film-coated negative electrode active material powder of the present invention, the alkali metal ion supply source is preferably a carbonaceous material pre-doped with lithium ions.
The carbonaceous material pre-doped with lithium ions is excellent in cycle characteristics, and lithium ions enter between the layers of the carbonaceous material. Therefore, Li as a metal adheres to the surface of the Li metal and accompanies repeated charge and discharge. Since lithium dendrite is unlikely to be generated, the SEI film serving as the Li entrance is uniformly formed by pre-doping, so that Li segregation hardly occurs and the stability in the pre-doping process is excellent.

In the method for producing a SEI film-coated negative electrode active material powder of the present invention, the negative electrode current collector is preferably a copper or stainless steel foil.
When the negative electrode current collector is a copper foil, the electric resistance is small and it is difficult to form an alloy with an alkali metal, so that the electrolytic treatment process can be efficiently advanced.
When the negative electrode current collector is a stainless steel foil, it is difficult to react with the non-aqueous electrolyte in the electrolytic treatment step, and thus it is easy to prevent the negative electrode current collector from being deteriorated.

In the method for producing a SEI film-coated negative electrode active material powder of the present invention, it is preferable that the surface of the foil is subjected to a roughening treatment.
When the surface of the foil is roughened, the contact between the negative electrode current collector and the negative electrode active material powder is improved, so that the formation of the SEI film easily proceeds on the surface of the negative electrode active material powder. Moreover, it becomes easy to suppress that an electric current concentrates on a part of negative electrode collector.

In the method for producing an SEI film-coated negative electrode active material powder of the present invention, in the first electrolytic treatment step, an electric current of 0.05 to 5C based on the total amount of the negative electrode active material powder constituting the electrolytic treatment unit, It is preferable to flow between the negative electrode active material powder layer and the alkali metal ion supply source.
When the current value (also referred to as C rate) in the first electrolytic treatment step is within the above range, it becomes easy to form a sufficiently thick SEI film on the surface of the negative electrode active material powder. The C rate in the first electrolytic treatment step is such that the current value when 1 hour is required to complete the pre-doping for all the negative electrode active material powders constituting the negative electrode active material powder layer is 1C. is there.
However, in the first electrolytic treatment step, it is not necessary to pass a current sufficient to complete the pre-doping for all the negative electrode active material powders constituting the negative electrode active material powder layer, depending on the thickness of the SEI film to be formed. The C rate and processing time may be adjusted.

In the method for producing a SEI film-coated negative electrode active material powder of the present invention, it is preferable to further measure the potential (vs. Li ⁺ / Li) of the negative electrode active material powder layer in the first electrolytic treatment step.
By measuring the potential difference between the negative electrode active material powder layer and the alkali metal ion supply source in the first electrolytic treatment step, the degree of progress of pre-doping can be estimated.
In addition, since the SEI film is easily formed when the potential of the negative electrode active material powder layer becomes 0.6 V or less, the SEI film is formed on the surface of the negative electrode active material powder by measuring the potential of the negative electrode active material powder layer. It can be confirmed whether it is formed.

In the method for producing a SEI film-coated negative electrode active material powder of the present invention, it is preferable to pressurize the electrolytic treatment unit in the thickness direction in the first electrolytic treatment step.
The thickness direction of the electrolytic treatment unit refers to the direction in which the negative electrode current collector, the negative electrode active material powder layer, the porous body, and the alkali metal ion supply source constituting the electrolytic treatment unit are arranged.
By pressurizing the electrolytic treatment unit in the thickness direction in the first electrolytic treatment step, the contact between the negative electrode active material powder and the negative electrode current collector is increased, and the formation of alkali metal ion pre-dope and SEI film is facilitated. .

In the method for producing a SEI film-coated negative electrode active material powder of the present invention, the pressurizing condition is preferably 0.5 to 500 N / cm ² .
By setting the pressurizing condition in the first electrolytic treatment step to 0.5 to 500 N / cm ² , the contact between the negative electrode active material powder and the negative electrode current collector is further enhanced, and the alkali metal ion pre-doping and the SEI film Formation is likely to proceed.
The pressure condition is calculated by dividing the force applied in the thickness direction of the electrolytic treatment unit by the area of the electrolytic treatment unit on the surface to which the force is applied.

In the method for producing a SEI film-coated negative electrode active material powder of the present invention, it is preferable that the negative electrode active material powder in the negative electrode active material powder layer is stirred in the first electrolytic treatment step.
Since the formation of the SEI film on the surface of the negative electrode active material powder proceeds faster as it is closer to the alkali metal ion supply source, the first electrolytic treatment step is performed by stirring the negative electrode active material powder layer in the first electrolytic treatment step. Can be accelerated.

In the method for producing the SEI film-coated negative electrode active material powder of the present invention, the direction opposite to the direction of the current flowing in the first electrolytic treatment step is further provided between the first electrolytic treatment step and the powder recovery step. It is preferable to further include a second electrolytic treatment step in which a current is passed in the direction to dedope the alkali metal ions predoped in the negative electrode active material powder.
By performing the second electrolytic treatment step, a part or all of the alkali metal ions predoped in the negative electrode active material powder can be dedoped. Therefore, the negative electrode active material can be designed in accordance with the desired battery performance.
Depending on the types of the negative electrode active material powder and the nonaqueous solvent, a sufficient amount of SEI film may not be formed even if the first electrolytic treatment step is performed until the alkali metal ion pre-doping of the negative electrode active material powder is completed. Sometimes. In such a case, it is conceivable that the alkali metal ions inserted into the negative electrode active material powder are dedoped by performing the second electrolytic treatment step. The negative electrode active material powder that has been dedoped with alkali metal ions in the second electrolytic treatment step can be subjected to the first electrolytic treatment step again. A film can be formed.
Whether or not a sufficient amount of the SEI film has been formed can be confirmed by X-ray photoelectron spectroscopy (XPS) or the like.

In the method for producing an SEI film-coated negative electrode active material powder of the present invention, in the second electrolytic treatment step, a current of 0.05 to 5C is defined based on the total amount of the negative electrode active material powder constituting the electrolytic treatment unit. It is preferable to flow between the negative electrode active material powder layer and the alkali metal ion supply source.
When the C rate in the second electrolytic treatment step is within the above range, the alkali metal ion dedoping from the inside of the negative electrode active material powder is sufficiently facilitated.

In the method for producing the SEI film-coated negative electrode active material powder of the present invention, it is preferable that the potential (vs. Li ⁺ / Li) of the negative electrode active material powder layer is further measured in the second electrolytic treatment step.
By measuring the potential of the negative electrode active material powder layer in the second electrolytic treatment step, it is possible to estimate how much the alkali metal ion dedoping reaction has progressed.

In the method for producing a SEI film-coated negative electrode active material powder of the present invention, it is preferable to pressurize the electrolytic treatment unit in the thickness direction in the second electrolytic treatment step.
By pressurizing the electrolytic treatment unit in the thickness direction in the second electrolytic treatment step, the contact between the negative electrode active material powder and the negative electrode current collector is increased, and the alkali metal ion de-doping easily proceeds.

In the method for producing a SEI film-coated negative electrode active material powder of the present invention, the pressure condition is preferably 0.5 to 500 N / cm ² .
By setting the pressurizing condition in the second electrolytic treatment step to 0.5 to 500 N / cm ² , the contact between the negative electrode active material powder and the negative electrode current collector is further increased, and de-doping of alkali metal ions proceeds. It becomes easy.

In the method for producing a SEI film-coated negative electrode active material powder of the present invention, it is preferable that the negative electrode active material powder in the negative electrode active material powder layer is stirred in the second electrolytic treatment step.
Since the alkali metal ion de-doping proceeds faster as it is closer to the alkali metal ion supply source, the de-doping reaction can be accelerated by stirring the negative electrode active material powder layer in the second electrolytic treatment step.

FIG. 1 is a cross-sectional view schematically showing an example of an electrolytic treatment unit prepared in the method for producing an SEI film-coated negative electrode active material powder of the present invention. FIG. 2 is a conceptual diagram schematically showing an example of a first electrolytic treatment process constituting the method for producing the SEI film-coated negative electrode active material powder of the present invention.

(Detailed description of the invention)
Hereinafter, the method for producing the SEI film-coated negative electrode active material powder of the present invention will be described in detail.

The method for producing an SEI film-coated negative electrode active material powder of the present invention comprises an electrolytic treatment unit preparation step, a first electrolytic treatment step, and a powder recovery step.

First, the electrolytic treatment unit preparation process which comprises the manufacturing method of the SEI film | membrane coating negative electrode active material powder of this invention is demonstrated.

In the electrolytic treatment unit preparation step, the negative electrode current collector, the negative electrode active material powder layer made of the negative electrode active material powder in contact with the negative electrode current collector, the porous body, and the alkali metal ion supply source in this order in the thickness direction. The electrolytic treatment unit is prepared in which the negative electrode current collector, the negative electrode active material powder layer, the porous body, and the alkali metal ion supply source are in contact with the nonaqueous electrolytic solution.

That is, the electrolytic treatment unit prepared in the electrolytic treatment unit preparation step of the present invention includes a negative electrode current collector, a negative electrode active material powder layer made of a negative electrode active material powder in contact with the negative electrode current collector, a porous body, and an alkali. The metal ion supply source is disposed in the thickness direction in this order, and the negative electrode current collector, the negative electrode active material powder layer, the porous body, and the alkali metal ion supply source are in contact with the nonaqueous electrolytic solution.

In addition, the electrolytic treatment unit prepared in the electrolytic treatment unit preparation step that constitutes the method for producing the SEI film-coated negative electrode active material powder of the present invention does not need to be able to retain its shape alone, and can be a container as necessary. Etc. (for example, a resin container). The resin container does not constitute an electrolytic treatment unit.

In the electrolytic treatment unit preparation step that constitutes the method for producing the SEI film-coated negative electrode active material powder of the present invention, the procedure for preparing the electrolytic treatment unit is not particularly limited.
For example, an electrolytic treatment unit can be prepared by the following procedure.
First, a resin container having a bottom surface provided with a current collector that can conduct electricity to the opposite surface is prepared. Subsequently, a negative electrode current collector is disposed so as to cover the bottom surface of the resin container, and a negative electrode active material powder layer is formed by covering the negative electrode current collector so as to cover the powdered negative electrode active material. To do. Thereafter, a porous body having fine pores through which the negative electrode active material powder cannot pass is stacked on the negative electrode active material powder layer so that the negative electrode active material powder constituting the negative electrode active material powder layer cannot move above the porous body. To do. Then, an amount of the non-aqueous electrolyte solution that sufficiently spreads over the porous body and the negative electrode active material powder layer is poured into a resin container. Finally, an alkali metal ion source is brought into contact with the top of the porous body. The entire electrolytic processing unit may be sealed by covering the resin container with a lid or the like. At this time, it is preferable to provide an air vent in either the resin container or the lid.
Note that the negative electrode current collector, the negative electrode active material powder layer, the porous body, and the alkali metal ion supply source are laminated in this order in the thickness direction. Equal to the direction from the bottom to the top of the container.

In the electrolytic treatment unit prepared in the electrolytic treatment unit preparation step that constitutes the method for producing the SEI film-coated negative electrode active material powder of the present invention, the negative electrode active material powder layer does not necessarily need to be composed only of the negative electrode active material powder. At the time of producing the unit, the negative electrode active material powder and the non-aqueous electrolyte are mixed and cooled to a temperature below the melting point of the non-aqueous electrolyte (hereinafter referred to as the negative electrode active material powder solidified with the non-aqueous electrolyte). May be used as the negative electrode active material powder layer.
That is, in the procedure for preparing the electrolytic treatment unit described above, instead of placing the negative electrode active material powder on the negative electrode current collector, the negative electrode active material powder solidified with a non-aqueous electrolyte is used as the negative electrode current collector. It may be arranged on the top. Furthermore, instead of pouring a porous body on the negative electrode active material powder layer and then pouring a sufficient amount of the nonaqueous electrolyte solution into the resin container into the resin container, the porous body and the negative electrode active material powder layer are impregnated with the nonaqueous electrolyte solution. The porous body may be overlaid on the negative electrode active material powder solidified with the non-aqueous electrolyte described above.
In this case, after the electrolytic processing unit is assembled, the first electrolytic processing step is performed after heating to a temperature exceeding the melting point of the nonaqueous electrolytic solution.
Note that the non-aqueous electrolyte used to harden the negative electrode active material powder and the non-aqueous electrolyte impregnated in the porous body may be the same or different.

When the electrolytic treatment unit prepared in the electrolytic treatment unit preparation step constituting the method for producing the SEI film-coated negative electrode active material powder of the present invention is fixed with a resin container, the entire inner surface of the resin container is It is preferable that a through hole or a metal part for taking out an electric current to the outside is provided in a part thereof instead of being made of resin. If a through hole or a metal part for taking out an electric current is provided outside, the current flowing through the negative electrode current collector can be taken out of the container through the through hole or the metal part. Therefore, the negative electrode current collector and the alkali metal ion The supply source can be electrically connected outside the electrolytic treatment unit.

In addition, in the electrolytic treatment unit preparation step that constitutes the method for producing the SEI film-coated negative electrode active material powder of the present invention, the negative electrode current collector and the alkali metal ion supply source constituting the electrolytic treatment unit are used to draw an electric current to the outside. It is preferable to join the wiring (also referred to as electrode tab) by welding or the like. For the alkali metal ion supply source, the electrode tab may be fixed by direct welding or the like, or after the alkali metal ion supply source is fixed to the surface of the current collector for the alkali metal ion supply source, the alkali metal ion supply The source current collector and the electrode tab may be fixed by welding or the like. By fixing the electrode tab to the negative electrode current collector and the alkali metal ion supply source by welding or the like, the electrical contact of the electrolytic processing unit during the first electrolytic processing step is deteriorated and the internal resistance is suppressed from increasing. be able to.

In addition, the electrolytic treatment unit preparatory process in the manufacturing method of the SEI film-coated negative electrode active material powder of the present invention has a dew point of −35 ° C. or less from the viewpoint of preventing stability of each component constituting the electrolytic treatment unit and moisture adsorption. It is preferably performed in an environment, and more preferably in an environment having a dew point of −60 ° C. or lower.
In an environment where the dew point exceeds −35 ° C., the alkali metal salt or alkali metal ion source constituting the non-aqueous electrolyte may react with moisture in the environment and decompose and degrade. Moreover, there is a possibility that moisture in the environment adheres to the surface of the negative electrode active material powder or the porous body and promotes the deterioration of the nonaqueous electrolytic solution in the first electrolytic treatment step.

Next, the negative electrode current collector, the negative electrode active material powder, the porous body, the alkali metal ion supply source, and the non-aqueous electrolyte that constitute the electrolytic treatment unit will be described.

First, the negative electrode current collector will be described.
As the negative electrode current collector constituting the electrolytic treatment unit prepared in the electrolytic treatment unit preparation step constituting the production method of the SEI film-coated negative electrode active material powder of the present invention, a known negative electrode current collector can be used, It is preferable that it does not form an alloy with an alkali metal, such as copper, nickel, stainless steel, etc., and from the viewpoint of manufacturing cost and electrical resistance value, copper is more preferable, manufacturing cost and electrolytic treatment step Stainless steel is more preferable from the viewpoint of reactivity with the non-aqueous electrolyte.

The shape of the negative electrode current collector constituting the electrolytic treatment unit prepared in the electrolytic treatment unit preparation step constituting the method for producing the SEI film-coated negative electrode active material powder of the present invention is not particularly limited. In addition, a foil shape is preferable. When the shape of the negative electrode current collector is foil, the area in contact with the negative electrode active material powder layer is increased.

The negative electrode current collector constituting the electrolytic treatment unit prepared in the electrolytic treatment unit preparation step constituting the method for producing the SEI film-coated negative electrode active material powder of the present invention preferably has a surface subjected to a roughening treatment. .
When the surface of the negative electrode current collector is roughened, the contact between the negative electrode current collector and the negative electrode active material powder is improved, so that alkali metal ion pre-doping and the formation of the SEI film easily proceed. .

The negative electrode current collector constituting the electrolytic treatment unit prepared in the electrolytic treatment unit preparation step constituting the production method of the SEI film-coated negative electrode active material powder of the present invention has a surface roughness in contact with the negative electrode active material powder layer. Ra is preferably 0.25 to 0.35 μm.
When the surface roughness Ra of the surface in contact with the negative electrode active material powder layer of the negative electrode current collector is 0.25 to 0.35 μm, the contact between the negative electrode current collector and the negative electrode active material powder is improved. Metal ion pre-doping and SEI film formation are more likely to proceed.

Subsequently, the negative electrode active material powder layer and the negative electrode active material powder constituting the negative electrode active material powder layer will be described.
The negative electrode active material powder layer that constitutes the electrolytic treatment unit prepared in the electrolytic treatment unit preparation step that constitutes the method for producing the SEI film-coated negative electrode active material powder of the present invention comprises a negative electrode active material powder.
The negative electrode active material powder constituting the negative electrode active material powder layer is preferably at least one selected from the group consisting of C, Si, Sn, SiO and SiO ₂ .
Since the SEI film can be formed on the negative electrode active material powder made of these materials, it is suitable for applying the production method of the present invention.

When the negative electrode active material powder is C, for example, graphite, non-graphitizable carbon, natural graphite, artificial graphite, non-graphitizable carbon, graphitizable carbon, low-temperature calcined carbon, activated carbon and the like are preferable, and graphite, non-graphitizable carbon And artificial graphite is more preferable.

The negative electrode active material powder layer constituting the electrolytic treatment unit prepared in the electrolytic treatment unit preparation step constituting the method for producing the SEI film-coated negative electrode active material powder of the present invention preferably does not contain a conductive additive, More preferably, the negative electrode active material powder alone is used.
If the negative electrode active material powder layer contains a conductive assistant, it is necessary to separate and remove the conductive assistant in the subsequent powder recovery step, which is not preferable from the viewpoint of production efficiency.

Subsequently, the porous body will be described.
The porous body constituting the electrolytic treatment unit prepared in the electrolytic treatment unit preparation step constituting the production method of the SEI film-coated negative electrode active material powder of the present invention is composed of an insulating material, and the nonaqueous electrolyte solution penetrates. In addition, the negative electrode active material powder layer and the alkali metal ion supply source are provided so as not to be short-circuited.

The porous body constituting the electrolytic treatment unit prepared in the method for producing the SEI film-coated negative electrode active material powder of the present invention is an insulating material provided so that the alkali metal ion supply source and the negative electrode active material powder layer are not short-circuited. It is configured.
As an insulating material which comprises a porous body, polyolefin polymers, such as polyethylene, a cellulose compound, etc. are mentioned, for example.

The thickness of the porous body is not particularly limited as long as it can be divided so as not to physically contact the negative electrode active material powder layer and the alkali metal ion supply source, and the size of the negative electrode active material powder layer and the alkali metal ion supply source is not limited. Can be set as appropriate. However, from the viewpoint of diffusion of alkali metal ions, the thickness of the porous body is preferably not too thick, preferably 0.2 mm or less, and more preferably 0.1 mm or less.

Subsequently, the alkali metal ion supply source will be described.
The alkali metal ion supply source constituting the electrolytic treatment unit prepared in the electrolytic treatment unit preparation step constituting the method for producing the SEI film-coated negative electrode active material powder of the present invention is an alkali metal to the negative electrode active material powder through a non-aqueous electrolyte. The composition is not particularly limited as long as ions can be supplied.

Examples of the alkali metal constituting the alkali metal ion supply source include lithium, sodium and potassium. From the viewpoint of energy density, lithium and sodium are preferable, and lithium is more preferable.

Examples of the alkali metal ion source include lithium alloys such as metallic lithium, LiAl, LiZn, Li ₃ Bi, Li ₃ Cd, Li ₃ Sb, Li ₄ Si, and Li ₄ Pb, and carbon that has been pre-doped with lithium ions. Quality materials.
As the carbonaceous material constituting the carbonaceous material pre-doped with lithium ions, the same carbonaceous materials that can be used as the negative electrode active material powder can be suitably used.
Of these, metal lithium is preferable from the viewpoint of production cost, and carbonaceous material pre-doped with lithium ions is preferable from the viewpoint of stability in the pre-doping process.
The carbonaceous material pre-doped with lithium ions already has a space (site) into which alkali metal ions are inserted, so that abnormal precipitation due to poor insertion of alkali metal ions is unlikely to occur in the pre-doping process. Excellent stability in the treatment process.

The alkali metal ion supply source constituting the electrolytic treatment unit prepared in the electrolytic treatment unit preparation step constituting the method for producing the SEI film-coated negative electrode active material powder of the present invention is the negative electrode active material powder constituting the negative electrode active material powder layer. Unlike, it need not be in powder form. However, the speed at which alkali metal ions are supplied from the alkali metal ion source to the non-aqueous electrolyte depends on the contact area between the alkali metal ion source and the non-aqueous electrolyte, that is, the surface area of the alkali metal ion source. The form of the alkali metal ion supply source may be changed accordingly.
The form of the alkali metal ion supply source may be, for example, an integral body such as a lump or a porous body. The alkali metal ion supply source such as powder, granule, or fiber is formed into a predetermined shape with a binder or the like. It may be molded. At this time, in order to increase the conductivity of the alkali metal ion supply source, a conductive aid or the like may be added.

Subsequently, the non-aqueous electrolyte will be described.
If the nonaqueous electrolytic solution constituting the electrolytic treatment unit prepared in the electrolytic treatment unit preparation step constituting the method for producing the SEI film-coated negative electrode active material powder of the present invention has alkali metal ion conductivity, The composition is not particularly limited.

In the electrolytic treatment unit prepared in the electrolytic treatment unit preparation step constituting the SEI film-coated negative electrode active material powder of the present invention, the nonaqueous electrolytic solution constituting the electrolytic treatment unit includes an alkali metal salt and the alkali metal salt. Is made of a non-aqueous solvent capable of dispersing.

In the electrolytic treatment unit prepared in the electrolytic treatment unit preparation step constituting the method for producing the SEI film-coated negative electrode active material powder of the present invention, the alkali metal salt constituting the non-aqueous electrolyte is an alkali metal in a non-aqueous solvent. _is not particularly limited as long as it dissociates into ions and counter _{anions, LiPF 6, LiClO 4, LiBF} 4, LiAsF 6, LiCF 3 SO 3, LiN (CF 3 SO 2) 2, LiC (CF 3 SO 2) 3 , NaPF ₆ , NaClO ₄ , NaBF ₄ , CF ₃ SO ₃ Na, NaAsF _{6 and the} like. Among these, LiPF ₆ or NaPF ₆ is preferable, and LiPF ₆ is more preferable.

In the electrolytic treatment unit prepared in the electrolytic treatment unit preparation step that constitutes the method for producing the SEI film-coated negative electrode active material powder of the present invention, the concentration of the alkali metal salt constituting the nonaqueous electrolytic solution is not particularly limited. It is preferable that it is 5-1.5 mol / L.
When the concentration of the alkali metal salt constituting the non-aqueous electrolyte is less than 0.5 mol / L, the conductivity of the alkali metal ions in the non-aqueous electrolyte is lowered, so that the alkali metal ion pre-doping and the formation of the SEI film are performed. May be difficult to progress.

In the electrolytic treatment unit prepared in the electrolytic treatment unit preparation step constituting the method for producing the SEI film-coated negative electrode active material powder of the present invention, dimethyl carbonate (DMC), ethyl is used as the nonaqueous solvent constituting the nonaqueous electrolytic solution. A mixed solvent of ethylene carbonate (EC) and at least one selected from the group consisting of methyl carbonate (EMC), diethyl carbonate (DEC), and propylene carbonate (PC) is preferable.

In the electrolytic treatment unit prepared in the electrolytic treatment unit preparation step that constitutes the method for producing the SEI film-coated negative electrode active material powder of the present invention, the non-aqueous electrolyte is further vinylene carbonate (VC), fluoroethylene carbonate (FEC), At least one additive selected from the group consisting of lithium bis (oxalate) borate (LiBOB), diphenyl disulfide (DPS), B (4F) S and sulfonic acid, preferably vinylene carbonate (VC), fluoroethylene carbonate ( It is preferable to include at least one additive selected from the group consisting of FEC), lithium bis (oxalate) borate (LiBOB), and sulfonic acid.
When the nonaqueous electrolytic solution contains these additives, the SEI film is easily formed densely, and the further decomposition reaction of the nonaqueous solvent is easily suppressed.

The electrolytic processing unit having the above structure will be further described in detail.
Examples of the electrolytic processing unit having the above structure include the shape shown in FIG.
FIG. 1 is a cross-sectional view schematically showing an example of an electrolytic treatment unit prepared in the method for producing an SEI film-coated negative electrode active material powder of the present invention.

As shown in FIG. 1, the electrolytic treatment unit 1 includes a negative electrode current collector 10, a negative electrode active material powder layer 20 made of a negative electrode active material powder in contact with the negative electrode current collector 10, a porous body 30, and alkali metal ions. The supply source 40 is arranged in this order in the thickness direction (the direction indicated by the double arrow a in FIG. 1), and the negative electrode current collector 10, the negative electrode active material powder layer 20, the porous body 30, and the alkali metal ion supply source 40. Is in contact with a non-aqueous electrolyte (not shown).

Then, the 1st electrolytic treatment process which comprises the manufacturing method of the SEI film | membrane coating negative electrode active material powder of this invention is demonstrated.
The first electrolytic treatment step constituting the SEI film-coated negative electrode active material powder production method of the present invention comprises an alkali metal ion supply source and a negative electrode current collector constituting the electrolytic treatment unit prepared in the electrolytic treatment unit preparation step. This is performed by electrical connection outside the electrolytic treatment unit.
When the alkali metal ion supply source and the negative electrode current collector constituting the electrolytic treatment unit are electrically connected, the alkali metal ion forms the negative electrode active material powder layer from the alkali metal ion supply source via the non-aqueous electrolyte. When supplied to the negative electrode active material powder, pre-doping of alkali metal ions proceeds. At this time, a part of the non-aqueous solvent constituting the non-aqueous electrolyte undergoes a reduction reaction, and an SEI film is formed.

In the first electrolytic treatment step constituting the method for producing the SEI film negative electrode active material powder of the present invention, the alkali metal ions are preferably lithium ions, sodium ions or potassium ions, and are lithium ions or sodium ions. Is more preferable, and lithium ion is still more preferable.
When the alkali metal ions are lithium ions, the formed SEI film has lithium conductivity by taking in lithium ions, so that it can be particularly preferably used as a negative electrode active material for lithium ion secondary batteries with high energy density. .

In the first electrolytic treatment step constituting the method for producing the SEI film-coated negative electrode active material powder of the present invention, the method of electrically connecting the alkali metal ion supply source and the negative electrode current collector outside the electrolytic treatment unit is as follows. , Not particularly limited, for example, a method of connecting the other end of one wiring extending from the alkali metal ion supply source to the outside of the electrolytic treatment unit to the negative electrode current collector (also referred to as a short circuit method), or an alkali metal ion supply source A first wiring extending from the anode to the outside of the electrolytic processing unit and a second wiring extending from the negative electrode current collector to the outside of the electrolytic processing unit via a circuit monitoring control system such as a charge / discharge tester. Can be mentioned.

In the first electrolytic treatment step that constitutes the method for producing the SEI film-coated negative electrode active material powder of the present invention, when an external current is passed between the alkali metal ion supply source and the negative electrode current collector, It is preferable that it is 0.05-5C on the basis of the whole quantity of the negative electrode active material powder which comprises a processing unit, It is more preferable that it is 0.1-3C, It is further more preferable that it is 0.1-1C.
In the first electrolytic treatment step treatment, when the C rate is 0.05 to 5C, the alkali metal ion pre-doping and the SEI film formation on the negative electrode active material powder can be sufficiently advanced. If the C rate in the first electrolytic treatment step is less than 0.05C, the time required for the first electrolytic treatment step is too long, which is not preferable from the viewpoint of production efficiency. On the other hand, when the C rate in the first electrolytic treatment step exceeds 10 C, the crystal structure of the negative electrode active material powder to be subjected to the electrolytic treatment may be destroyed, or abnormal precipitation of alkali metal ions may occur.
The C rate in the first electrolytic treatment step is 1 C when the current value when 1 hour is required to complete the pre-doping for all the negative electrode active material powders constituting the negative electrode active material powder layer. . That is, in the case where the first electrolytic treatment step is performed until the pre-doping is completed for all negative electrode active material powders constituting the negative electrode active material powder layer with a C rate of 0.05 to 5C, the first electrolytic treatment step is completed. 6 minutes to 20 hours are required.

It is preferable that the 1st electrolytic treatment process which comprises the manufacturing method of the SEI film | membrane coating negative electrode active material powder of this invention is performed at 0-50 degreeC.
When the temperature at which the first electrolytic treatment step is performed is less than 0 ° C., the alkali metal ion diffusion coefficient of the nonaqueous electrolytic solution constituting the electrolytic treatment unit becomes too small, so that the pre-doping is difficult to proceed, and the SEI film is formed. It may take too long. Moreover, when the temperature which performs a 1st electrolytic treatment process exceeds 50 degreeC, the decomposition reaction of the alkali metal salt which comprises a non-aqueous electrolyte solution may occur easily.

In the first electrolytic treatment step constituting the SEI film-coated negative electrode active material powder production method of the present invention, it is preferable to measure the potential (vs. Li ⁺ / Li) of the negative electrode active material powder layer.
Since the potential of the negative electrode active material powder layer decreases as the pre-doping of alkali metal ions proceeds, the progress of pre-doping of the negative electrode active material powder layer can be grasped by measuring the potential.

The method for measuring the potential (vs. Li ⁺ / Li) of the negative electrode active material powder layer in the first electrolytic treatment step constituting the method for producing the SEI film-coated negative electrode active material powder of the present invention is not particularly limited, A method of subtracting a voltage drop (also referred to as IR drop) due to the internal resistance of the electrolytic processing unit by measuring the potential between the alkali metal ion supply source and the negative electrode current collector, or using a reference electrode (also referred to as a reference electrode) Methods and the like.
In order to calculate the IR drop of the electrolytic treatment unit, it is necessary to consider various factors, and measurement becomes difficult. Therefore, it is preferable to use a reference electrode for ease of measurement.
By using the reference electrode, the potential of the alkali metal ion supply source and the negative electrode active material powder layer constituting the electrolytic treatment unit can be accurately measured, so that the progress of alkali metal ion pre-doping can be controlled more precisely. It becomes easy.

In the first electrolytic treatment step that constitutes the method for producing the SEI film-coated negative electrode active material powder of the present invention, the first step is performed until the potential of the negative electrode active material powder layer becomes 0.6 V (vs. Li ⁺ / Li) or less. It is preferable to perform the electrolytic treatment step.
The formation of the SEI film on the negative electrode active material powder easily proceeds efficiently when the potential of the negative electrode active material powder layer is 0.6 V (vs. Li ⁺ / Li) or less.

In addition, even after the completion of the first electrolytic treatment step (that is, after the pre-doping for the negative electrode active material powder is completed), when a sufficient amount of the SEI film is not formed on the surface of the negative electrode active material powder, A step of dedoping a part of the alkali metal ions pre-doped in the negative electrode active material powder by flowing a current in a direction opposite to the direction of the current flowing in the first electrolytic treatment step (second electrolytic treatment step) May be performed.

In the first electrolytic treatment step constituting the method for producing the SEI film-coated negative electrode active material powder of the present invention, it is preferable to pressurize the electrolytic treatment unit in the thickness direction.
The thickness direction of the electrolytic treatment unit is a direction in which the negative electrode current collector, the negative electrode active material powder layer, the porous body, and the alkali metal ion supply source are arranged, and the electrolytic treatment unit is added to the thickness direction. By pressing, the contact property between the negative electrode current collector and the negative electrode active material powder layer can be enhanced. When the contact property between the negative electrode current collector and the negative electrode active material powder layer increases, pre-doping of the negative electrode active material powder easily proceeds.

In the first electrolytic treatment step constituting the method for producing the SEI film-coated negative electrode active material powder of the present invention, when the electrolytic treatment unit is pressurized in the thickness direction, the pressure condition is 0.5 to 500 N / cm ² . It is preferably 0.5 to 100 N / cm ² , more preferably 1 to 50 N / cm ² .
On the other hand, by setting the pressure condition to 0.5 to 500 N / cm ² , the contact property between the negative electrode active material powder and the negative electrode current collector is further increased, and the formation of the pre-dope and the SEI film is facilitated.
When the pressurization condition is less than 0.5 N / cm ² , the contact between the negative electrode active material powder and the negative electrode current collector due to pressurization may not be sufficiently improved, so the formation of pre-dope and SEI film is efficient. May not progress. Further, when the pressurization condition exceeds 500 N / cm ² , the pressure applied to the negative electrode active material powder is too large, and the crystal structure of the negative electrode active material powder may be destroyed or the SEI film once formed may be peeled off. . Further, when the pressurization condition exceeds 500 N / cm ² , the pressure applied to the negative electrode active material powder layer is too large, so that the nonaqueous electrolyte solution becomes poor and the first electrolytic treatment step is efficient. May not progress.
The pressure condition is calculated by dividing the force applied in the thickness direction of the electrolytic treatment unit by the area of the electrolytic treatment unit on the surface to which the force is applied.

In the first electrolytic treatment step constituting the method for producing the SEI film-coated negative electrode active material powder of the present invention, the negative electrode active material powder in the negative electrode active material powder layer is preferably stirred.
It is considered that the pre-doping of the negative electrode active material powder of alkali metal ions proceeds faster as it is closer to the alkali metal ion supply source. Therefore, by stirring the negative electrode active material powder layer in the first electrolytic treatment step, the negative electrode active material powder that has already been pre-doped with alkali metal ions and the negative electrode active material that has not yet been pre-doped with alkali metal ions By changing the position of the powder, the progress of pre-doping and the formation of the SEI film can be accelerated.

In the first electrolytic treatment step constituting the SEI film-coated negative electrode active material powder production method of the present invention, the nonaqueous electrolytic solution constituting the electrolytic treatment unit is distributed from the alkali metal ion side toward the negative electrode active material powder layer. You may let them.
Since the non-aqueous electrolyte solution closer to the alkali metal ion source side has a higher alkali metal ion concentration in the non-aqueous electrolyte solution, the non-aqueous electrolyte solution should be circulated from the alkali metal ion source side toward the negative electrode active material powder layer. Thus, since the diffusion rate of alkali metal ions in the non-aqueous electrolyte can be apparently increased, the progress of pre-doping and the formation of the SEI film can be accelerated.

The first electrolytic treatment process described above will be further described in detail.
The first electrolytic treatment process described above can be described with reference to the schematic diagram shown in FIG. 2, for example.
FIG. 2 is a conceptual diagram schematically showing an example of a first electrolytic treatment process constituting the method for producing the SEI film-coated negative electrode active material powder of the present invention.

As shown in FIG. 2, in the first electrolytic treatment step, the alkali metal ion supply source 40 and the negative electrode current collector 10 constituting the electrolytic treatment unit 1 prepared in the electrolytic treatment unit preparation step are electrically connected. Is done.

The electrolytic treatment unit need not be capable of holding its shape alone, and the electrolytic treatment unit 1 may be housed in a resin container 60 as shown in FIG. Moreover, since the metal part 61 for taking out an electric current from the negative electrode collector 10 outside is provided in the bottom face 60a of the resin container 60, the metal part 61 and the alkali metal ion supply source 40 are electrolyzed. By electrically connecting outside the unit 1, the alkali metal ion supply source 40 and the negative electrode current collector 10 can be electrically connected. Note that the entire inner wall surface of the resin container 60 should not be made of metal. If the entire inner wall surface of the resin container 60 is made of metal, the alkali metal ion supply source 40 and the negative electrode current collector 10 are electrically connected inside the electrolytic treatment unit, so that the current is controlled from the outside. It becomes impossible to do. Therefore, it becomes impossible to control the progress of the pre-doping of the negative electrode active material powder layer in the first electrolytic treatment step.

In the first electrolytic treatment step, the alkali metal ion supply source 40 and the negative electrode current collector 10 may be simply electrically connected, but if necessary, a circuit monitoring control system 70 such as a charge / discharge tester. May be provided between the alkali metal ion supply source 40 and the negative electrode current collector 10.
Further, unlike the electrolytic treatment unit process shown in FIG. 2, the entire electrolytic treatment unit may be sealed by covering a resin container with a lid or the like. At this time, it is preferable to provide an air vent on the lid or the like in the resin container.

Hereinafter, the second electrolytic treatment process will be described.
In the method for producing a SEI film-coated negative electrode active material powder according to the present invention, a current in a direction opposite to the direction of the current flowing in the first electrolytic treatment step is further provided between the first electrolytic treatment step and the powder recovery step. It is preferable to further include a second electrolytic treatment step in which the negative electrode active material powder is dedoped with alkali metal ions pre-doped in the negative electrode active material powder.
By performing the second electrolytic treatment step, a part or all of the alkali metal ions predoped in the negative electrode active material powder can be dedoped. Therefore, the negative electrode active material can be designed in accordance with the desired battery performance.
In addition, since the negative electrode active material powder that has been dedoped with alkali metal ions in the second electrolytic treatment step can be subjected to the first electrolytic treatment step again, the first electrolytic treatment step is subsequently performed. As a result, an SEI film can be further formed.

When the production method of the SEI film-coated negative electrode active material powder of the present invention includes the second electrolytic treatment step, the C rate in the second electrolytic treatment step is based on the total amount of the negative electrode active material powder constituting the electrolytic treatment unit. It is preferably 0.05 to 5C, more preferably 0.1 to 3C, and still more preferably 0.1 to 1C.
In the second electrolytic treatment step treatment, when the C rate is 0.05 to 5C, the alkali metal ion dedoping to the negative electrode active material powder can sufficiently proceed.

When the method for producing the SEI film-coated negative electrode active material powder of the present invention includes the second electrolytic treatment step, the potential of the negative electrode active material powder layer (vs. Li ⁺ / Li) is measured in the second electrolytic treatment step. It is preferable.
By measuring the potential of the negative electrode active material powder layer in the second electrolytic treatment step, it is possible to estimate how much the alkali metal ion dedoping reaction has progressed.

When the method for producing the SEI film-coated negative electrode active material powder of the present invention includes the second electrolytic treatment step, it is preferable to pressurize the electrolytic treatment unit in the thickness direction in the second electrolytic treatment step.
By pressurizing the electrolytic treatment unit in the thickness direction in the second electrolytic treatment step, the contact between the negative electrode active material powder and the negative electrode current collector is increased, and the alkali metal ion de-doping easily proceeds.

When the manufacturing method of the SEI film-coated negative electrode active material powder of the present invention includes the second electrolytic treatment step, and the electrolytic treatment unit is pressurized in the thickness direction in the second electrolytic treatment step, the pressure condition is 0.5. It is preferable that it is -500N / cm < ² >.
By setting the pressurizing condition to 0.5 to 500 N / cm ² , the contact property between the negative electrode active material powder and the negative electrode current collector is further increased, and the de-doping of alkali metal ions easily proceeds.
When the pressurization condition is less than 0.5 N / cm ² , the contact between the negative electrode active material powder and the negative electrode current collector due to pressurization may not be sufficiently improved, so that the dedoping and the formation of the SEI film are efficient. May not progress. Further, when the pressurization condition exceeds 500 N / cm ² , the pressure applied to the negative electrode active material powder is too large, and the crystal structure of the negative electrode active material powder may be destroyed or the SEI film once formed may be peeled off. . Furthermore, when the pressurization condition exceeds 500 N / cm ² , the pressure applied to the negative electrode active material powder layer is too large, so that the non-aqueous electrolyte solution becomes poor and the second electrolytic treatment step is efficient. May not progress.

In the second electrolytic treatment step constituting the SEI film-coated negative electrode active material powder production method of the present invention, the non-aqueous electrolyte constituting the electrolytic treatment unit is directed from the negative electrode active material powder layer side to the alkali metal ion supply source. May be distributed.
During the second electrolytic treatment step, the non-aqueous electrolyte solution closer to the alkali metal ion supply source side has a lower alkali metal ion concentration in the non-aqueous electrolyte solution, so the non-aqueous electrolyte solution is alkaline from the negative electrode active material powder layer side. By flowing toward the metal ion supply source, the diffusion rate of alkali metal ions in the non-aqueous electrolyte can be apparently increased, so that the progress of dedoping can be accelerated.

In the method for producing an SEI film-coated negative electrode active material powder of the present invention, a sufficient amount on the surface of the negative electrode active material powder even after each of the first electrolytic treatment step and the second electrolytic treatment step is performed once When the SEI film is not formed, the first electrolytic treatment process and the second electrolytic treatment process may be repeated until a sufficient amount of the SEI film is formed.

Below, it enumerates about the effect of the manufacturing method of the SEI film | membrane coating negative electrode active material powder of this invention.
(1) The negative electrode active material powder obtained by the method for producing a SEI film-coated negative electrode active material powder of the present invention has a SEI film formed on the surface thereof. Therefore, when the negative electrode active material powder obtained by the method for producing a SEI film-coated negative electrode active material powder of the present invention is used as an electricity storage device, it is not necessary to form a new SEI film by the first charge / discharge. The liquid can be optimized to enhance the functionality of the electricity storage device.

(2) When the negative electrode active material powder obtained by the production method of the SEI film-coated negative electrode active material powder of the present invention is used, it is not necessary to form the SEI film at the first charge / discharge, and therefore irreversible with the formation of the SEI film. It can suppress that a capacity | capacitance falls.

(3) In the method for producing an SEI film-coated negative electrode active material powder of the present invention, it is possible to easily avoid mixing in an alkali metal ion supply source that has lost some or all of the alkali metal ions. There are few, and it is excellent in stability of the charge / discharge performance at the time of setting it as an electrical storage device.

(Example)
Examples in which the present invention is disclosed more specifically are shown below. In addition, this invention is not limited only to these Examples.

Example 1
In Example 1, a stainless steel 2032 type coin cell was used as a member for holding the electrolytic treatment unit. Of the following operations, (a) and (c) were performed in a dry room having a dew point of −60 ° C. or lower.
(A) Electrolytic treatment unit preparation step First, a copper foil having a thickness of 60 μm was punched into a circle having a diameter of 15 mm.
The punched copper foil was placed in the center of the bottom surface of the 2032 type coin cell case, and a polypropylene gasket was arranged so as to cover the periphery of the copper foil. Subsequently, 1 g of graphite powder [crushed graphite material (ET-10) manufactured by IBIDEN Co., Ltd. (D50 = 1.5 μm)] as a negative electrode active material powder was left on the copper foil, and the negative electrode active material powder layer was left standing. Two polypropylene separators (thickness: 100 μm) were stacked on the negative electrode active material powder layer and allowed to stand.
After adding 2 mL of non-aqueous electrolyte [LiPF ₆ 1 mol / L solution (DMC: EC = 1: 1)] inside the coin cell case, metal lithium foil (thickness 200 μm) punched out to 15 mm on the separator ) And a spacer (made of stainless steel) and a wave washer (made of stainless steel) were placed, and a coin cell cap was put on. Then, the electrolytic processing unit accommodated in the coin cell was produced by producing a coin cell by caulking with a caulking machine.

(B) First Electrolytic Treatment Step The coin cell produced was placed in a constant temperature bath at 25 ° C. and charged at 0.1 C using a charge / discharge tester. The potential of the negative electrode active material powder layer at the end of charging was 0.2 V (vs. Li ⁺ / Li). The time required was 10 hours.

(C) Second Electrolytic Treatment Step Following the first electrolytic treatment step, a current is passed using a charge / discharge tester in a direction opposite to the direction of the current flowing in the first electrolytic treatment step, and 0.1 C Was discharged. The potential of the negative electrode active material powder layer at the end of the second electrolytic treatment step was 1.5 V (vs. Li ⁺ / Li). The time required was 10 hours.

(D) Powder recovery process The coin cell which finished the 1st electrolytic treatment process and the 2nd electrolytic treatment process was decomposed | disassembled, and the negative electrode active material powder layer was collect | recovered.
The collected negative electrode active material powder layer was washed with an organic solvent and dried to obtain a SEI film-coated negative electrode active material powder.

(Comparative Example 1)
A negative electrode active material powder according to Comparative Example 1 was obtained in the same procedure as Example 1 except that the electrolytic treatment process was not performed and the sample was left in a constant temperature bath at 25 ° C. for 10 hours without being connected to a charge / discharge tester. It was.

(Comparative Example 2)
A negative electrode active material powder according to Comparative Example 2 was obtained in the same procedure as in Example 1 except that the negative electrode current collector and the negative electrode active material powder layer were formed by the following method.
By making the graphite powder used in Example 1 a negative electrode active material powder, and thoroughly mixing with acetylene black as a conductive additive, PVdF copolymer binder as a binder, N-methyl-2-pyrrolidone (MNP), A negative electrode active material slurry was obtained.
The negative electrode active material slurry was applied on only one side of a copper foil having a thickness of 60 μm by using a baker type applicator so that the thickness of the negative electrode active material layer after drying was 50 μm.
The copper foil coated with the negative electrode active material slurry was dried at 60 ° C. for 10 minutes, and then heated under reduced pressure at 120 ° C. for 10 hours and at 200 ° C. for 17 hours to dry under reduced pressure. After drying, the negative electrode active material layer was punched into a circle so that the area where the negative electrode active material layer was formed was 15 mm.

(Measurement of XRD pattern)
When the powder X-ray diffraction (XRD) patterns of the negative electrode active material powders according to Example 1 and Comparative Examples 1 and 2 were measured, no peaks derived from impurities were observed in the XRD patterns of Example 1 and Comparative Example 1. However, in the XRD pattern of the negative electrode active material powder according to Comparative Example 2, an impurity peak considered to be a conductive additive could be confirmed.

(Measurement of XPS)
When XPS spectra were measured for the negative electrode active material powders according to Example 1 and Comparative Examples 1 and 2, lithium carbonate which is the main component of the SEI film was formed on the surface layer of the negative electrode active material powders according to Example 1 and Comparative Example 2. It was confirmed that was formed.
On the other hand, on the surface of the negative electrode active material powder according to Comparative Example 1, almost no elements constituting lithium carbonate or the like as the main component of the SEI film were detected.

From the measurement results of the XRD and XPS, it is considered that the SEI film is sufficiently formed in the negative electrode active material powder according to Example 1 and further does not contain impurities.

From the above results, it was found that the SEI film can be formed on the surface of the negative electrode active material powder by using the method for producing the SEI film coated negative electrode active material powder of the present invention.

DESCRIPTION OF SYMBOLS 1 Electrolytic processing unit 10 Negative electrode collector 20 Negative electrode active material powder layer 30 Porous body 40 Alkali metal ion supply source

Claims (20)

A negative electrode current collector, a negative electrode active material powder layer made of a negative electrode active material powder in contact with the negative electrode current collector, a porous body, and an alkali metal ion supply source are arranged in this order in the thickness direction, and the negative electrode An electrolytic treatment unit preparation step of preparing an electrolytic treatment unit in which a current collector, the negative electrode active material powder layer, the porous body, and the alkali metal ion supply source are in contact with a nonaqueous electrolytic solution;
The negative electrode current collector in the electrolytic treatment unit and the alkali metal ion supply source are electrically connected outside the electrolytic treatment unit, and the negative electrode active material powder is pre-doped with the alkali metal ions. A first electrolytic treatment step of forming an SEI film on the surface of the negative electrode active material powder;
A method for producing a negative electrode active material powder coated with an SEI film, comprising: a powder recovery step of recovering a negative electrode active material powder that has undergone an electrolytic treatment step. The non-aqueous solvent constituting the non-aqueous electrolyte is a mixed solvent of at least one selected from the group consisting of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, and propylene carbonate and ethylene carbonate. Manufacturing method of SEI film-coated negative electrode active material powder. The SEI film coating according to claim 1 or 2, wherein the non-aqueous electrolyte further includes at least one additive selected from the group consisting of vinylene carbonate, fluoroethylene carbonate, lithium bis (oxalate) borate, and sulfonic acid. Manufacturing method of negative electrode active material powder. The said negative electrode active material powder layer consists of only the said negative electrode active material powder, The manufacturing method of the SEI film | membrane covering negative electrode active material powder in any one of Claims 1-3. The negative active material powder, C, Si, Sn, SiO and at least one method of producing SEI film-coated anode active material powder according to any one of claims 1 to 4 which is selected from the group consisting of SiO ₂ . The said alkali metal ion is a lithium ion, The manufacturing method of the SEI film | membrane coating | cover negative electrode active material powder in any one of Claims 1-5. The method for producing an SEI film-coated negative electrode active material powder according to claim 1, wherein the alkali metal ion supply source is a carbonaceous material pre-doped with lithium ions. The method for producing a SEI film-coated negative electrode active material powder according to claim 1, wherein the negative electrode current collector is a copper or stainless steel foil. The method for producing an SEI film-coated negative electrode active material powder according to claim 8, wherein the surface of the foil is subjected to a roughening treatment. In the first electrolytic treatment step, a current of 0.05 to 5 C is applied between the negative electrode active material powder layer and the alkali metal ion supply source based on the total amount of the negative electrode active material powder constituting the electrolytic treatment unit. The manufacturing method of the SEI film | membrane coating negative electrode active material powder in any one of Claims 1-9 sent between. The production of the SEI film-coated negative electrode active material powder according to any one of claims 1 to 10, wherein in the first electrolytic treatment step, the potential (vs. Li ⁺ / Li) of the negative electrode active material powder layer is further measured. Method. The method for producing an SEI film-coated negative electrode active material powder according to any one of claims 1 to 11, wherein in the first electrolytic treatment step, the electrolytic treatment unit is pressurized in the thickness direction. The method for producing an SEI film-coated negative electrode active material powder according to claim 12, wherein the pressurizing condition is 0.5 to 500 N / cm ² . The method for producing an SEI film-coated negative electrode active material powder according to claim 1, wherein the negative electrode active material powder in the negative electrode active material powder layer is stirred in the first electrolytic treatment step. The negative electrode active material powder is pre-doped between the first electrolytic treatment step and the powder recovery step by passing a current in a direction opposite to the direction of the current flowing in the first electrolytic treatment step. The method for producing an SEI film-coated negative electrode active material powder according to claim 1, further comprising a second electrolytic treatment step of dedoping the alkali metal ions. In the second electrolytic treatment step, a current of 0.05 to 5 C is applied between the negative electrode active material powder layer and the alkali metal ion supply source based on the total amount of the negative electrode active material powder constituting the electrolytic treatment unit. The method for producing a SEI film-coated negative electrode active material powder according to claim 15, wherein the SEI film-coated negative electrode active material powder is passed in between. The method for producing an SEI film-coated negative electrode active material powder according to claim 15 or 16, further comprising measuring a potential (vs. Li ⁺ / Li) of the negative electrode active material powder layer in the second electrolytic treatment step. The method for producing an SEI film-coated negative electrode active material powder according to any one of claims 15 to 17, wherein in the second electrolytic treatment step, the electrolytic treatment unit is pressurized in the thickness direction. The method for producing a SEI film-coated negative electrode active material powder according to claim 18, wherein the pressurizing condition is 0.5 to 500 N / cm ² . The method for producing a SEI film-coated negative electrode active material powder according to any one of claims 15 to 19, wherein in the second electrolytic treatment step, the negative electrode active material powder in the negative electrode active material powder layer is agitated.

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