JP2016110776A - Method for manufacturing lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method arranged so that a whole electrode laminate is uniformly pre-doped with lithium, which allows a lithium ion secondary battery to exhibit a superior capacity appearance rate and a superior capacity-keeping rate.SOLUTION: A method for manufacturing a lithium ion secondary battery 1 including an electrode laminate arranged by laminating a negative electrode 4 having a first porous conductive plate 2 serving as a negative electrode current collector and a negative electrode active material layer 3 formed on the negative electrode current collector, and a positive electrode 7 having a second porous conductive plate 5 serving as a positive electrode current collector and a positive electrode active material layer 6 formed on the positive electrode current collector comprises the steps of: superposing a third porous conductive plate 9 on the surface 3a of the negative electrode active material layer located in the outermost surface of the negative electrode, and further superposing a lithium-supplying plate 10 thereon through the porous conductive plate, thereby preparing an electrode laminate; and performing lithium pre-doping on the electrode laminate with the electrode laminate put in contact with an electrolyte 14.SELECTED DRAWING: Figure 1

Description

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

It has been a problem that the discharge capacity of a lithium ion secondary battery decreases after initial charging. In order to solve this, for example, a lithium pre-doping process in which a negative electrode using silicon oxide (SiO and SiO ₂ ) as a negative electrode active material and lithium metal is reacted before an initial charging process at the time of battery manufacture has been conventionally performed. (See Patent Documents 1 and 2). In the pre-doping step, silicon dioxide (SiO ₂ ) in silicon oxide is changed into lithium silicate (Li ₄ SiO ₄ ) in advance. As a result, it is possible to prevent the occurrence of irreversible capacity such that by-products such as lithium silicate are generated in the subsequent initial charging step or the lithium ion in the electrolyte is lost and the discharge capacity is reduced. it can.

Japanese Patent No. 4928828 International Publication No. 2011/125325

  As described in Patent Document 1, when the lithium metal piece for doping is disposed so as to face the end face (side surface) of the electrode laminate in parallel, the portion close to the lithium metal piece and the portion far from the lithium metal piece of the electrode laminate are arranged. The amount of lithium metal doped and the doping rate are different. For this reason, the whole electrode laminated body cannot be doped uniformly, but there existed a problem that the stress destruction accompanying the non-uniform expansion | swelling of the electrode active material layer and the expansion | swelling arises.

  As described in FIG. 15 of Patent Document 2, lithium metal (7) is indirectly placed on the surface of the negative electrode sheet (10) through a non-conductive separator (3) to perform lithium pre-doping. When it did, the present inventors found the problem that generation | occurrence | production of an irreversible capacity | capacitance cannot fully be suppressed (refer the below-mentioned comparative example 2).

  The present invention has been made in view of the above circumstances, and performs lithium pre-doping uniformly on the entire electrode laminate, and manufacture of a lithium ion secondary battery capable of exhibiting an excellent capacity development rate and capacity maintenance rate. It is an object to provide a method.

[1] A negative electrode in which a negative electrode active material layer is formed on a first porous conductive plate as a negative electrode current collector, and a positive electrode active material on a second porous conductive plate as a positive electrode current collector A method for producing a lithium ion secondary battery comprising an electrode laminate in which a positive electrode formed with a layer is laminated, wherein a third electrode is formed on the surface of the negative electrode active material layer located on the outermost surface of the negative electrode. A process of obtaining an electrode laminate in which a porous conductive plate is stacked and a lithium supply plate is further stacked via the porous conductive plate, and lithium pre-doping is performed in a state where the electrode stack is in contact with an electrolyte. A method for producing a lithium ion secondary battery.
[2] The method for producing a lithium ion secondary battery according to the above [1], wherein an average hole diameter of the through holes of the third porous conductive plate is 0.1 mm or more and 0.4 mm or less.
[3] The lithium ion secondary material according to the above [1] or [2], wherein the area of the negative electrode active material layer located on the outermost surface of the negative electrode is substantially equal to the area of the third porous conductive plate. A method for manufacturing a secondary battery.

  According to the present invention, since the lithium supply plate is arranged via the third porous conductive plate so as to face the electrode active material layer constituting the negative electrode, the surface unevenness of the electrode active material layer and The occurrence of variations in the degree of lithium pre-doping due to the effects of variations in the degree of contact with the lithium supply plate can be reduced. In addition, since the third porous conductive plate is conductive, lithium pre-doping can be rapidly advanced by a potential difference generated between the negative electrode and the lithium supply plate.

It is a cross-sectional schematic diagram which shows an example of the lithium ion secondary battery manufactured in 1st embodiment.

  In the first embodiment of the present invention, as shown in FIG. 1, a negative electrode active material is formed on a first porous conductive plate 2 (hereinafter also referred to as a negative electrode current collector 2) as a negative electrode current collector. A positive electrode active material layer 6 is formed on a negative electrode 4 formed with the material layer 3 and a second porous conductive plate 5 (hereinafter, also referred to as a positive electrode current collector 5) as a positive electrode current collector. It is a manufacturing method of the lithium ion secondary battery 1 provided with the electrode laminated body by which the positive electrode 7 formed is laminated | stacked.

  In the present embodiment, a third porous conductive plate 9 is placed on the surface of the negative electrode active material layer 3a located on the outermost surface of the first negative electrode 4A (4), and the porous conductive plate 9 is interposed therebetween. In addition, the method further includes a step of obtaining an electrode laminate on which the lithium supply plate 10 is further placed, and performing lithium pre-doping while the electrode laminate is in contact with the electrolytic solution 14.

  In the present specification and claims, the term “conductive plate” means a plate-like conductor, and is not limited to a plate made of a conductive material, but a cloth in which a conductive wire is knitted. It is a term including (net), conductive film, and conductive sheet. Furthermore, the term “metal plate” means a plate-like metal body, and is not limited to a metal plate material, but a plate-like metal cloth (metal net) knitted with a metal wire, and a metal plate. It is a term that includes thinly stretched metal foil, metal film, and metal film.

<About negative electrode>
The material, area, and thickness of the first porous conductive plate 2 constituting the negative electrode 4 are not particularly limited, and the same material, area, and thickness as the negative electrode current collector of a known lithium ion secondary battery can be applied. It is. For example, a perforated metal plate is suitable. Specifically, for example, rolled copper foil or electrolytic copper foil subjected to punching with an area of 40 × 20 cm and a thickness of 5 to 50 μm can be given. The kind of metal which comprises a metal plate is not specifically limited, For example, metals, such as copper, titanium, nickel, stainless steel, are mentioned.

The perforated conductive plate 2 used in the present embodiment is provided with a plurality of through holes that allow the electrolytic solution to pass through the plate. The shape, size, number, and relative arrangement of the plurality of through holes are not particularly limited. The individual holes may be independent from each other or may be connected to each other. If the number of through-holes is too large or arranged unevenly, it may be difficult to hold the negative electrode active material layer 3 on the surface of the porous conductive plate 2. Considering this case, the number and arrangement of the through holes are appropriately adjusted.
From the viewpoint of uniformly diffusing lithium metal to the negative electrode active material layer 3 formed on one side or both sides of the negative electrode current collector 2 when performing lithium pre-doping, the current collector formed with the negative electrode active material layer 3 It is preferable that as many through-holes as possible be arranged over the entire surface of the region.

  The shapes and sizes of the plurality of through holes provided in the negative electrode current collector 2 may be the same as or different from each other. When viewed in the through direction of the through hole (the direction of the central axis), a part of the frame constituting the inner wall of the through hole may be missing. That is, the term “through hole” is a term including a notch provided in the conductive plate.

  The negative electrode active material layer 3 is formed on one side or both sides of the negative electrode current collector 2. The constituent material (negative electrode material) of the negative electrode active material layer 3 is a material containing a negative electrode active material capable of occluding and releasing lithium ions, and causes an irreversible reaction with lithium in the lithium pre-doping step before initial charging. The material is not particularly limited as long as it includes a negative electrode active material, and a known negative electrode material is applicable.

Examples of suitable negative electrode active materials include metal oxides. Examples of the metal oxide include metal oxides that can be alloyed with lithium such as silicon oxide. _{Examples of the} silicon oxide include those represented by the general formula “SiO _z (wherein z is any number from 0.5 to 1.5)”. Here, when the silicon oxide is viewed in “SiO” units, this SiO is amorphous SiO, or around the Si of the nanocluster so that the molar ratio of Si: SiO ₂ is about 1: 1. This is a composite of Si and SiO _{2 in} which SiO ₂ exists. SiO ₂ is presumed to have a buffering action against the expansion and contraction of Si during charging and discharging.

  The silicon oxide is preferably in the form of powder or particles. The average particle diameter of the particulate silicon oxide is not particularly limited, and is preferably 1 to 30 μm, for example.

  The method for forming the negative electrode active material layer 3 is not particularly limited. For example, a negative electrode material containing a negative electrode active material is applied on the negative electrode current collector 2 with a thickness of about 5 to 100 μm, and then the solvent contained in the negative electrode material is dried. By removing, the negative electrode active material layer can be formed on the current collector 2. In addition to the negative electrode active material such as silicon oxide, the negative electrode material preferably contains a binder resin (binder) such as PVDF and SBR, and a conductive aid such as a carbon material and metal particles. The types and combinations of these negative electrode active materials, binder resins, and conductive assistants are not particularly limited, and combinations of materials constituting the negative electrode active material layers of known lithium ion secondary batteries can be applied.

  A method of directly forming the negative electrode active material layer 3 on the negative electrode current collector 2 may be adopted, or after forming the negative electrode active material layer 3 on another base material, the negative electrode on the negative electrode current collector 2 is formed. A method in which the active material layer 3 is transferred and further crimped may be employed. Even when the negative electrode active material layer 3 is directly formed on the negative electrode current collector 2, a process of pressure bonding the negative electrode active material layer 3 on the negative electrode current collector 2 may be performed.

<About positive electrode>
The material, area, and thickness of the second porous conductive plate 5 constituting the positive electrode 7 are not particularly limited, and the same material, area, and thickness as those of the positive electrode current collector of a known lithium ion secondary battery can be applied. It is. For example, a perforated metal plate is suitable. Specifically, for example, rolled aluminum foil subjected to punching with an area of 40 × 20 cm and a thickness of 5 to 50 μm can be used. The kind of metal which comprises a metal plate is not specifically limited, For example, metals, such as copper, aluminum, titanium, nickel, stainless steel, are mentioned. Since the areas of the positive electrode 7 and the negative electrode 4 are preferably equal, the area of the second perforated conductive plate 5 is preferably substantially equal to the area of the first perforated conductive plate 2.

  The second porous conductive plate 5 used in the present embodiment is provided with a plurality of through-holes through which the electrolytic solution can pass through the front and back surfaces of the plate. The description of the shape, size, number, and relative arrangement of the plurality of through holes is the same as the description of the through holes provided in the first perforated conductive plate 2 described above.

  The positive electrode active material layer 6 is formed on one side or both sides of the positive electrode current collector. The constituent material (positive electrode material) of the positive electrode active material layer 6 is not particularly limited as long as the material includes a positive electrode active material capable of occluding and releasing lithium ions, and a positive electrode material of a known lithium ion secondary battery can be applied. It is.

Examples of suitable positive electrode active materials include lithium metal acid compounds such as lithium composite cobalt oxide, lithium composite nickel oxide, and lithium composite manganese oxide. As a metal acid lithium compound, a metal acid lithium compound represented by the general formula “LiM _x O _y (wherein M is a metal; x and y are composition ratios of metal M and oxygen O)” Can be illustrated. Specific examples include lithium cobaltate (LiCoO ₂ ), lithium nickelate (LiNiO ₂ ), lithium manganate (LiMn ₂ O ₄ ), and the like. Also include a composition similar olivine-type lithium iron phosphate (LiFePO _4).

In the general formula, M may be a plurality of kinds of metals. As such a metal acid lithium compound, for example, the general formula “LiM ¹ _p M ² _q M ³ _r O _y (wherein M ¹ , M ² and M ³ are different kinds of metals; p, q, r and y are the composition ratios of the metals M ¹ , M ² and M ³ and oxygen O.) ”. Here, p + q + r = x. Examples of the lithium metalate compound represented by the general formula include LiNi _0.33 Mn _0.33 Co _0.33 O _{2 and the} like.

  The method for forming the positive electrode active material layer 6 is not particularly limited. For example, after the positive electrode material containing the positive electrode active material 6 is applied on the positive electrode current collector 5 with a thickness of about 5 to 100 μm, the solvent contained in the positive electrode material is changed. By removing by drying, the positive electrode active material layer 6 can be formed on the positive electrode current collector 5. The positive electrode material preferably contains a binder resin (binder) and a conductive additive in addition to the positive electrode active material such as the lithium metal acid compound. The types and combinations of these positive electrode active materials, binder resins and conductive additives are not particularly limited, and combinations of materials constituting the positive electrode active material layers of known lithium ion secondary batteries can be applied.

  A method of directly forming the positive electrode active material layer 6 on the positive electrode current collector 5 may be adopted, or the positive electrode active material layer 6 may be formed on another substrate and then the positive electrode current collector 5 may be formed on the positive electrode current collector 5. A method of transferring the active material layer 6 and further press-bonding may also be employed. Even when the positive electrode active material layer 6 is directly formed on the positive electrode current collector 5, a process of pressure bonding the positive electrode active material layer 6 on the positive electrode current collector 5 may be performed.

<About electrode laminate>
For the purpose of preventing the short circuit between the two electrodes by placing the negative electrode 4 and the positive electrode 7 facing each other and maintaining the electrolyte, a separator 8 is disposed between the two electrodes, and the first negative electrode 4A (4), separator 8, An electrode laminate in which the positive electrode 7, the separator 8, and the second negative electrode 4B (4) are laminated in this order is obtained. You may press the negative electrode 4 and the positive electrode 7 before or after lamination | stacking, and may adjust the volume density of the electrode active material layer which comprises each electrode.

  The separator 8 is not particularly limited as long as it has insulating properties and can hold or pass the electrolytic solution, and a separator used in a known lithium ion secondary battery is applicable. For example, a porous film or non-woven fabric made of an olefin resin, a porous insulating film made of insulating particles, and the like can be given. A known method in which a composition containing insulating particles is applied to the surface of the negative electrode or positive electrode to form an insulating film as the separator 8 on the surface can also be employed. The thickness of the separator 8 will not be specifically limited if it is the thickness by which insulation is maintained, For example, the thickness of about 5-50 micrometers is mentioned.

  In the present embodiment, the third porous conductive plate 9 and the fourth porous conductive plate 11 are stacked on the surface 3a of each negative electrode active material layer 3 located on the outermost surface of the electrode laminate, Lithium supply plates 10 and 12 are further laminated through these perforated conductive plates 9 and 11. Hereinafter, the third porous conductive plate 9 and the lithium supply plate 10 will be described. However, the description of the fourth porous conductive plate 11 and the lithium supply plate 12 is also the same, and the description thereof will be omitted.

  The lithium supply plate 10 is not brought into contact with the surface 3a of the negative electrode active material layer, and the third porous conductive plate 9 is interposed so that the whole of the negative electrode active material layer 3 is formed during lithium pre-doping performed later. It is possible to dope uniformly throughout. If the lithium supply plate 10 is directly disposed on the surface 3a, the lithium supply plate 10 is in close contact with the surface 3a due to the unevenness of the surface 3a and the effect of wrinkles on the lithium supply plate 10 (for example, lithium metal foil). A floating part is generated. In this case, since the portion to be in close contact is heavily doped, and the floating portion is lightly doped, it is difficult to dope uniformly throughout the negative electrode active material layer 3.

  The third porous conductive plate 9 is provided with a plurality of through holes that allow the electrolyte to pass through the plate. The shape, size, number, and relative arrangement of the plurality of through holes are not particularly limited. The individual holes may be independent from each other or may be connected to each other. From the viewpoint of lithium metal or lithium ions eluted from the lithium supply plate 10 passing through the third porous conductive plate 9 and uniformly diffusing into the negative electrode active material layer 3 when performing lithium pre-doping. In addition, it is preferable that as many through holes as possible be arranged over the entire surface of the region of the porous conductive plate 9 placed on the negative electrode active material layer 3.

The average hole diameter (hole diameter) of the through holes of the third porous conductive plate 9 is, for example, preferably 0.001 mm to 1.0 mm, more preferably 0.01 mm to 0.7 mm, and 0.1 mm to 0. More preferably, 4 mm.
For example, the porosity of the third porous conductive plate 9 is preferably 5 to 50%, more preferably 10 to 35%, and still more preferably 10 to 20%.
The porosity is obtained by a method of calculating from a mass ratio between the conductive plate in which the holes are formed and the conductive plate before the holes are formed. For example, the porosity when the mass ratio is 1/2 is 50%.

  The material constituting the third porous conductive plate 9 is not particularly limited as long as it is a conductive material, and is preferably a material that hardly adsorbs lithium metal and lithium ions. Examples of such a conductive material include metals such as copper, aluminum, and titanium that can also be used as the above-described electrode current collector, alloys, porous resins or conductive cloths containing a conductive polymer, and the like. It is done. More specifically, a metal punching foil (plate), a plate-like mesh, and the like can be exemplified. Among these, it is preferable to use a metal punching foil with less surface irregularities and high flatness.

  The area of the third perforated conductive plate 9 is preferably the same as that of the lithium supply plate 10 or an area that is slightly larger than that. With this area, the lithium supply plate 10 can be prevented from directly contacting the surface 3a of the negative electrode active material layer. Further, from the viewpoint of making the ease of access of the lithium metal or lithium ions eluted from the lithium supply plate 10 to the surface 3a of the negative electrode active material layer substantially uniform over the entire surface 3a, the third porous conductive plate The area 9 is preferably the same as the surface 3a or slightly smaller than the surface 3a (see FIG. 1).

  The thickness of the third porous conductive plate 9 is not particularly limited, and is preferably thinner from the viewpoint that lithium metal or lithium ions eluted from the lithium supply plate 10 can easily pass through and diffuse. For example, a thickness of about 5 μm to 50 μm is suitable.

  The material which comprises the lithium supply board 10 will not be specifically limited if lithium metal or a lithium ion elutes into the electrolyte solution which contacted, The lithium metal containing material used for well-known lithium pre dope is applicable. Examples thereof include a metal foil made of lithium metal or a lithium alloy, a porous resin material containing lithium metal or a lithium alloy, a porous inorganic material containing lithium metal or a lithium alloy, and the like. If the lithium supply plate 10 is a lithium metal foil, the lithium metal foil dissolves and disappears with the progress of lithium pre-doping.

  The shape of the lithium supply plate 10 is not particularly limited as long as it has a flat surface that can be placed on the surface 9a of the third porous conductive plate 9, and is not limited to the “plate material”. It includes shapes such as a thin flat cloth, a thinly stretched foil, and a film formed on the surface 9a of the third porous conductive plate 9. The lithium supply plate 10 may or may not have a plurality of through holes similar to the third porous conductive plate 9.

  The thickness of the lithium supply plate 10 is not particularly limited, and a thickness capable of supplying an amount of lithium metal that compensates for the irreversible capacity of the negative electrode 4 may be set as appropriate. For example, when lithium metal foil is used, a thickness of about 10 μm to 200 μm is suitable.

  In the present embodiment, as shown in FIG. 1, the first negative electrode 4A (4) and the second negative electrode 4B (4) are provided on both sides of the positive electrode 7, and the first negative electrode 4A has a first electrode on the outer surface. The lithium supply plate 10 is laminated via the three porous conductive plates 9, and the lithium supply plate 12 is laminated on the outer surface of the second negative electrode 4B via the fourth porous conductive plate 11. .

  In place of the configuration of the present embodiment, the lithium supply plate may be disposed only on one of the negative electrode 4A and the negative electrode 4B, but from the viewpoint of increasing the processing efficiency of lithium pre-doping, It is preferable to arrange a lithium supply plate.

  As a modification of the present embodiment, there is a lithium ion secondary battery including an electrode stack in which a negative electrode 4 / separator 8 / positive electrode 7 are used as one stacked unit and a plurality of stacked units are stacked with a separator interposed therebetween. It is done. Also in this modification example, as described above, by disposing the lithium supply plates 10 and 12 via the porous conductive plates 9 and 11 respectively on the negative electrodes constituting the uppermost surface and the lowermost surface of the electrode laminate, Similarly, lithium pre-doping can be performed.

  For example, when an electrode laminate in which a large number of positive and negative electrodes of about 20 layers are laminated, a lithium supply plate and a porous conductive plate may be arranged as an intermediate layer of the electrode laminate. In this case, the non-conductive separator and the lithium supply plate are preferably arranged so as not to contact each other, and more preferably, the lithium supply plate is sandwiched between the perforated conductive plates. For example, "Negative electrode -...-Negative electrode-(Perforated conductive plate-Lithium supply plate-Perforated conductive plate)-Separator-Positive electrode-Separator-Negative electrode-" Perforated conductive plate-Lithium supply plate-Perforated Can be laminated like “conductive plate” -separator-positive electrode-separator --- negative electrode.

<Battery assembly>
After the lithium supply plates 10 and 12 are arranged on the negative electrodes 4A and 4B constituting the electrode laminate, the electrode laminate is temporarily sealed with the outer package 13. The kind of the exterior body 13 is not specifically limited, The metal or resin exterior body used for a well-known lithium ion secondary battery is applicable. The form of the battery is not particularly limited, and a known battery form such as a box type, a coin type, a wound type (cylinder type), a sheet type, or the like can be adopted. In the present embodiment, a resin film is used as the exterior body 13 to obtain a sheet-type laminate cell in which the electrode laminate is laminated. When temporarily sealing the cell, lead-out wirings 2z and 5z (tab wiring) electrically connected to the negative electrode current collector 2 and the positive electrode current collector 5 are projected to the outside of the outer package 13. Each lead-out wiring functions as an electrode terminal for connecting to an external circuit.

  The laminated cell is partially unsealed and completely sealed after the electrolyte 14 is injected. The electrolyte 14 is preferably in the form of a gel or liquid, and more preferably a liquid electrolyte. When it is in a gel or liquid state, the diffusion efficiency of lithium metal or lithium ions eluted from the lithium supply body 10 in the electrolyte 14 is increased, and the processing efficiency of lithium pre-doping is improved.

<About electrolyte>
In this embodiment, since lithium metal is contained in the lithium supply body, the electrolyte 14 is preferably a non-aqueous electrolyte solution that does not substantially contain moisture (for example, less than 100 ppm). Examples of the non-aqueous electrolyte include known non-aqueous electrolytes in which a lithium salt is dissolved in a non-aqueous solvent. Specifically, for example, lithium salts such as LiPF ₆ , LiBF ₄ , LiClO ₄ , propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate, dimethoxyethane, γ-butyrolactone, methyl acetate, methyl formate, etc. And an electrolytic solution dissolved in the organic solvent. The lithium salt concentration of the electrolytic solution is not particularly limited, and examples thereof include about 0.5 to 2 mol / L.

<About lithium pre-dope>
By leaving the sealed laminate cell at a predetermined temperature, the lithium pre-dope can be allowed to proceed naturally. At this time, the lithium pre-dope can be further promoted by pressurizing the laminate cell. Lithium metal or lithium ions eluted from the lithium supply bodies 10 and 12 into the electrolyte solution 14 pass through the through holes of the perforated conductive plates 9 and 11 and the through holes of the electrode current collectors 2 and 5, respectively. It diffuses and penetrates into the material layer 3. In the negative electrode active material layer 3, a by-product such as lithium silicate may be generated, and the causative substance of irreversible capacity may be inactivated.

  In this embodiment, since the lithium supply bodies 10 and 12 are not directly attached to the surface 3a of each negative electrode active material layer, and the porous conductive plates 9 and 11 are interposed, lithium metal (lithium ions) is each The anode active material layer 3 can be uniformly diffused and penetrated inside. This mechanism is considered below.

  When a lithium supply body is directly attached to the surface (electrode surface) of each negative electrode active material layer, the electrode surface reacts unevenly. This is because only the portion where the electrode surface and the lithium supplier are in contact with each other easily reacts from a microscopic viewpoint. The portion where the reaction proceeds is physically expanded due to the bonding of lithium. For this reason, the non-uniform reaction causes peeling of the negative electrode active material layer, and generation of wrinkles and waviness due to non-uniform swelling.

  On the other hand, in the case of this embodiment in which perforated conductive plates 9 and 11 such as punching foil are interposed, basically, a plurality of through holes provided at predetermined positions of the perforated conductive plates 9 and 11 are passed through. Lithium metal (lithium ions) is supplied to the electrode surface. That is, since each through-hole becomes a lithium metal supply source, the lithium metal supply source can be uniformly arranged on the electrode surface by controlling the relative arrangement of each through-hole. As a result, each negative electrode active material layer can be uniformly doped with lithium metal. Furthermore, since the porous conductive plates 9 and 11 hold the electrode surface, the active material layer on the electrode surface can be prevented from being peeled off, swollen, or wrinkled.

  Since the perforated conductive plates 9 and 11 used in this embodiment are conductive, a potential difference may be generated between the negative electrode surface and the lithium supply body. It is considered that the presence of this potential difference promotes the elution of lithium metal (lithium ions) from the lithium supplier. The reason is considered as follows. First, lithium ions in the electrolytic solution diffuse and permeate, and are reduced in the negative electrode active material layer to become lithium metal. Thereby, the lithium ion concentration in electrolyte solution falls. Along with this decrease in concentration, it is presumed that the lithium metal of the lithium supplier is ionized and dissolved in the electrolytic solution, and works to suppress the concentration decrease. If lithium pre-doping proceeds by repeating this series of processes, the above-described potential difference may contribute to elution and ionization of lithium metal. In fact, as shown in the experimental results of Comparative Example 2 described later, when a non-conductive porous separator is used instead of the porous conductive plates 9 and 11, the above potential difference does not occur, and lithium pre-doping is accelerated. It was confirmed that it was not done.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the following examples.

(1) Used raw materials The raw materials used in this example are shown below.
-Conductive auxiliary agent acetylene black ("HS-100" manufactured by Denki Kagaku Kogyo Co., Ltd., average particle size (48 nm))
Carbon nanotube ("NT-7" manufactured by Hodogaya Chemical Co., Ltd., average fiber diameter (65nm), average fiber length (6um or more))
Binder Styrene-butadiene resin (hereinafter abbreviated as “SBR”) (manufactured by JSR)
(C) Organic solvent Ethylene carbonate (hereinafter abbreviated as “EC”) (Kishida Chemical Co., Ltd.)
Propylene carbonate (hereinafter abbreviated as “PC”) (manufactured by Kishida Chemical Co., Ltd.)

[Example 1]
(Manufacture of negative electrode materials)
Silicon monoxide (SiO, average particle diameter 1 μm, 69 parts by mass), acetylene black (10 parts by mass), carbon nanotube (6 parts by mass), lithium polyacrylate (30 mol% of all acid groups were converted to lithium salts) In the following, 12 parts by mass, which may be abbreviated as “PAALi”, and SBR (3 parts by mass) are placed in a reagent bottle, and after adding distilled water to adjust the concentration, use a disper. The solution whose concentration was adjusted was mixed at 3000 rpm for 90 minutes. Next, this mixture was subjected to a dispersion treatment for 10 minutes using an ultrasonic homogenizer, and then this dispersion was again mixed for 3 minutes at 2000 rpm using a self-revolving mixer to obtain a negative electrode material. All the operations so far were performed at 25 ° C.

(Manufacture of negative electrode)
Using a coating machine equipped with a die head, the above is obtained on both sides of a 10 μm-thick punched copper foil (hole diameter: 0.3 mm, porosity: 16.7%, manufactured by Fukuda Metal Foil Powder Co., Ltd.) A negative electrode material was applied. The conditions at this time were a coating speed of 2 m / min and a drying temperature of 100 ° C. Then, using a roll press machine, by pressing at 25 ° C. under a pressure of 3 tons, a negative electrode active material layer having a thickness of 25 μm is formed on each side of the copper foil as a current collector, A negative electrode was obtained. The obtained negative electrode had dimensions of a negative electrode active material layer portion (104 × 62 mm) and an uncoated portion (tab portion, 2 × 2 cm).

(Manufacture of positive electrode material)
Nickel, cobalt, lithium manganate (Ni: Co: Mn = 1: 1: 1, LiNMC) (93 parts by mass), polyvinylidene fluoride (PVDF) (4 parts by mass), and carbon black ( 3 parts by mass) was mixed to prepare a positive electrode mixed material, which was dispersed in N-methylpyrrolidone (NMP) to obtain a positive electrode material (slurry).

(Manufacture of positive electrode)
Similar to the negative electrode manufacturing process, using a coating machine equipped with a die head, a punching Al foil with a thickness of 15 μm (hole diameter: 0.3 mm, porosity: 16.7%, manufactured by Fukuda Metal Foil Powder Industry Co., Ltd.) The positive electrode material obtained above was applied to both sides of the above. The conditions at this time were a coating speed of 2 m / min and a drying temperature of 140 ° C. Thereafter, by using a roll press machine and pressing at 25 ° C. under a pressure of 5 tons, a positive electrode active material layer having a thickness of 60 μm is formed on both surfaces of the copper foil as a current collector. A positive electrode was obtained. The obtained positive electrode had dimensions of a positive electrode active material layer portion (102 × 60 mm) and an uncoated portion (tab portion, 2 × 2 cm).

(Manufacture of electrolyte)
As an organic solvent, a mixed solvent of EC and PC (EC: PC = 30: 70 (volume ratio)) is weighed into a plastic container, to which a lithium oxalate-boron trifluoride complex is added, and lithium oxalate-3 The concentration of lithium atoms in the boron fluoride complex was adjusted to 1.0 mol / kg and mixed at 23 ° C. to obtain an electrolytic solution.

(Manufacture of lithium ion secondary batteries)
A separator film made of cellulose (manufactured by Nippon Kogyo Paper Industries Co., Ltd., TBL-4620) is placed between the negative electrode and the positive electrode obtained above in the order of first negative electrode-separator-positive electrode-separator-second negative electrode. And the tab for terminals of each electrode was joined by ultrasonic welding, and each tab was made to protrude outward of a negative electrode and a positive electrode, and the electrode laminated body was obtained (refer FIG. 1).

(Lithium doping process)
On each of the negative electrodes constituting the outer surfaces of both of the electrode laminates obtained above, a punched copper foil cut to 106 × 64 mm is overlaid so as to cover the negative electrode active material layer portion, and further on the negative electrode active material layer portion, An amount of lithium metal foil (104 × 62 mm) necessary to compensate for the irreversible capacity was installed.
Next, an aluminum laminate film is arranged so that the terminal tabs protruding from the negative electrode and the positive electrode of the electrode laminate are projected to the outside, and an electrolyte is poured into the electrode laminate, and the outer periphery of the film is laminated. The electrode laminate was processed and vacuum sealed. Thereafter, the obtained cell is set in a pressure jig, the cell is brought into a pressurized state with a force of 2 kN, and is left in a constant temperature bath at 25 ° C. for 48 hours to perform a lithium pre-dope treatment, and a laminate cell. Manufactured. The rated capacity of the manufactured battery is 1000 mAh.

[Example 2]
A laminate cell was produced in the same manner as in Example 1 except that the punching foil used in Example 1 had a hole diameter of 0.35 mm and a porosity of 16%.
[Example 3]
A laminate cell was produced in the same manner as in Example 1 except that the punching foil used in Example 1 had a hole diameter of 0.12 mm and a porosity of 16%.

[Comparative Example 1]
A laminate cell was produced in the same manner as in Example 1 except that the lithium metal foil was directly placed on the negative electrode active material layer constituting both outer surfaces of the electrode laminate without using the punching foil. .
[Comparative Example 2]
Without using a punching foil, a cellulose separator film (manufactured by Nippon Kogyo Paper Industries Co., Ltd., TBL-4620) is layered on the negative electrode active material layer constituting both outer surfaces of the electrode laminate, and further on it. A laminate cell was produced in the same manner as in Example 1 except that a lithium metal foil was installed. In this experiment, when the cell was opened after 48 hours of lithium doping, it was confirmed that the lithium metal foil remained. This cell was sealed again and subjected to performance evaluation.

(Evaluation of electrode appearance)
In each of the above examples and comparative examples, four laminate cells were produced. Some of the produced laminate cells were opened, and the appearance of the negative electrode was visually inspected. Establishing 10-step evaluation criteria, determining that a non-defective product with no change in appearance compared to before lithium doping is “10”, and that a defective product in which the negative electrode active material layer is severely peeled and swollen after lithium doping is “0” Judged. In this evaluation, the closer the evaluation is to 10, the better the appearance is, and the closer the evaluation is to 0, the more damaged the appearance is.

(Evaluation of charge / discharge characteristics of lithium ion secondary battery)
About the lithium ion secondary battery obtained by each said Example and comparative example, constant current constant voltage charge of 0.1C was performed at 25 degreeC until the electric current value converged to 0.05C with the upper limit voltage of 4.2V. Thereafter, a constant current discharge of 0.1 C was performed up to 2.5V. Subsequently, the charge / discharge current was set to 0.5 C, and the charge / discharge cycle was repeated three times in the same manner to stabilize the state of the lithium ion secondary battery. Next, charging / discharging was performed in the same manner with a charging / discharging current of 0.2 C, and a capacity expression rate ({[discharge capacity (mAh) of the first cycle) / [rated capacity (mAh)]} × 100) (% ), The charge / discharge current is set to 1 C in the same manner, the charge / discharge cycle is repeated, and the capacity retention rate at 100 cycles ({[discharge capacity at the 100th cycle (mAh)] / [discharge capacity at the first cycle (mAh) )]} × 100) (%).

From the above results, according to the lithium pre-doping methods of Examples 1 to 3, an electrode having an excellent appearance (that is, excellent structural strength) can be obtained with almost no damage to the negative electrode active material layer, and the capacity It is clear that a lithium ion secondary battery having an excellent expression rate and capacity retention rate can be manufactured.
On the other hand, in Comparative Example 1, it was found that the negative electrode active material layer was damaged by the lithium pre-doping because the evaluation of the electrode appearance was poor. When the lithium ion secondary battery of Comparative Example 1 using the damaged negative electrode was used and the charge / discharge cycle exceeding 100 cycles was further continued, the negative electrode was further damaged, and the capacity development rate and the capacity maintenance rate were reduced. The decline is thought to progress. Further, in Comparative Example 2, the negative electrode active material layer was not damaged by the lithium pre-doping because the evaluation of the electrode appearance was good, but the target lithium pre-doping was sufficiently achieved because the capacity expression rate was poor. You can see that it was not done. The reason why lithium pre-doping was not sufficiently performed was that the separator used in Comparative Example 2 was a non-conductive cellulose separator, and therefore no potential difference occurred between the lithium metal foil and the negative electrode active material layer. This is probably because the efficiency of pre-doping has decreased.

  The present invention can be widely used in the field of lithium ion secondary batteries.

DESCRIPTION OF SYMBOLS 1 ... Lithium ion secondary battery, 2 ... 1st porous electroconductive board (negative electrode collector), 3 ... Negative electrode active material layer, 3a ... Surface of negative electrode active material layer, 4A, 4B, 4 ... Negative electrode, 5 2nd porous conductive plate (positive electrode current collector), 6 ... positive electrode active material layer, 6a ... surface of positive electrode active material layer, 7 ... positive electrode, 8 ... separator, 9 ... 3rd porous conductive plate DESCRIPTION OF SYMBOLS 10 ... Lithium supply board, 11 ... 4th perforated electroconductive board, 12 ... Lithium supply board, 13 ... Exterior body, 14 ... Electrolyte

Claims (3)

A negative electrode in which a negative electrode active material layer is formed on a first porous conductive plate as a negative electrode current collector;
A positive electrode in which a positive electrode active material layer is formed on a second porous conductive plate as a positive electrode current collector;
A method for producing a lithium ion secondary battery comprising an electrode laminate in which is laminated,
A third porous conductive plate is placed on the surface of the negative electrode active material layer located on the outermost surface of the negative electrode, and an electrode laminate in which a lithium supply plate is further placed over the porous conductive plate is obtained. A method for producing a lithium ion secondary battery, comprising a step of performing lithium pre-doping while the electrode laminate is in contact with an electrolyte.   The method for producing a lithium ion secondary battery according to claim 1, wherein an average hole diameter of the through holes of the third porous conductive plate is 0.1 mm or more and 0.4 mm or less.   3. The method of manufacturing a lithium ion secondary battery according to claim 1, wherein an area of the negative electrode active material layer located on the outermost surface of the negative electrode is substantially equal to an area of the third porous conductive plate.

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