JP6448336B2 - Method for producing lithium ion secondary battery - Google Patents

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

  However, the lithium pre-doping has a problem in that the negative electrode active material layer expands and deforms the outer package of the cell. Furthermore, since the negative electrode active material layer absorbed lithium ions by lithium pre-doping, voids in the negative electrode active material layer were reduced, so that the negative electrode active material layer and the cell that occluded lithium ions during the initial charge were There was a problem that it expanded greatly compared with the case where it did not carry out. This problem not only makes it difficult to compactly store a plurality of cells in a limited container, but also reduces the energy density per volume of the battery. ing.

  This invention is made | formed in view of the said situation, and makes it a subject to provide the manufacturing method of the lithium ion secondary battery which can reduce the expansion | swelling of the cell accompanying a negative electrode active material layer occlusion of lithium ion.

[1] A method for producing a lithium ion secondary battery comprising a cell having a negative electrode active material layer containing silicon oxide and a positive electrode, the volume density of the negative electrode active material layer being 0.8 g / cm ^A method for producing a lithium ion secondary battery, comprising: a pre-doping step of performing lithium pre-doping after adjusting to ^{3 to} 1.5 g / cm ³ and a charging step of performing initial charging while pressurizing the cell.
[2] The method for producing a lithium ion secondary battery according to [1], wherein in the pre-doping step, lithium pre-doping is performed while pressurizing the cell.
[3] the cell is pressurized at 0.3 kg / cm ² or more 6.6 kg / cm ² or less pressure method for producing a lithium ion secondary battery according to [2].
[4] In the charging step, pressurizing the cell at 0.3 kg / cm ² or more 6.6 kg / cm ² or less of pressure, lithium ions according to any one of the above [1] to [3] A method for manufacturing a secondary battery.

  According to the present invention, in order to tighten the negative electrode active material layer to an appropriate volume density by pressurizing the negative electrode active material layer before lithium pre-doping, the expansion of the negative electrode active material layer during lithium pre-doping and the subsequent initial charge Can be reduced. Since the volume density after the pressurization is moderate, the negative electrode active material layer does not prevent lithium from being absorbed during lithium pre-doping and can sufficiently absorb lithium, thereby reducing irreversible capacity and sufficient capacity development rate. Is obtained.

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 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.

(Adjustment of volume density)
In this embodiment, the volume density of the negative electrode active material layer 3 is adjusted to 0.8 g / cm ³ or more and 1.5 g / cm ³ or less before lithium pre-doping. The method for adjusting the volume density is not particularly limited. For example, the negative electrode active material layer 3 having a negative electrode current collector 2 on which the negative electrode active material layer 3 is formed is sandwiched between two flat jigs. A method in which the entire surface is uniformly pressurized in the thickness direction. The negative electrode 4 subjected to the pressure treatment is laminated on the positive electrode 7 via the separator 8 to obtain an electrode laminate.

Volume density of the negative electrode active material layer 3 before the lithium pre-doping is preferably from 0.8 g / cm ³ or more 1.45 g / cm ³ or less, more preferably 0.8 g / cm ³ or more 1.35 g / cm ³ or less, 0.8 g / cm ³ or more 1.25 g / cm ³ more preferably less, 0.8 g / cm ³ or more 1.15 g / cm ³ or less are particularly preferred, 0.8 g / cm ³ or more 1.05 g / cm ³ or less Is most preferred. In the order of the above preferable range, there is a tendency that the increase rate of the cell thickness at the first charge is reduced and the capacity expression rate of the secondary battery is increased.

(Measurement method of volume density)
A plurality of measurement samples are prepared by punching electrodes with a predetermined size (for example, φ16 mm). The mass of each measurement sample is weighed with a precision balance, and the mass of the electrode active material layer is measured. By subtracting the mass of the current collector measured in advance from the measurement result, the mass of the electrode active material layer in the measurement sample can be calculated. Further, the thickness of the electrode active material layer is measured by a known method of observing the measurement sample subjected to cross-section processing with an SEM. Based on the following formula (1), the volume density of the electrode active material layer can be calculated from the average value of the measured values.
Volume density (g / cm ³ ) = Mass (g) of electrode active material layer / [(Thickness of electrode active material (cm) × Punched electrode area (cm ² )] (1)

(Pre-doping process)
After the above pressure treatment, a third porous conductive plate 9 is placed on the surface of the negative electrode active material layer 3 a located on the outermost surface of the negative electrode 4, and lithium is further supplied through the porous conductive plate 9. An electrode laminate on which the plates 10 are stacked is obtained, and lithium pre-doping is performed in a state where the electrode laminate is in contact with the electrolytic solution 14.

  In this embodiment, the cell 1 in which the electrode laminate and the electrolyte solution 14 are enclosed in the outer package 13 is obtained, and lithium pre-doping is performed while the cell 1 is pressurized. The method for pressurizing the cell 1 is not particularly limited, and examples thereof include a method in which the cell 1 is sandwiched between two flat jigs and the entire surface of the cell 1 is uniformly pressed in the thickness direction. By leaving the cell 1 at a predetermined temperature, the lithium pre-doping can be allowed to proceed naturally. Although pressurization of the cell 1 during lithium pre-doping is not essential, the negative electrode active material layer 3 tends to swell as the pre-doping progresses, and therefore it is preferable to suppress this swell by pressurization. In addition, holding the cell 1 in a fixed volume by holding the cell 1 between the jigs during lithium pre-doping pressurizes the cell 1 by antagonizing the holding and the increase in the internal pressure of the negative electrode active material layer 3 and the cell 1. . Therefore, as a method of pressurization during lithium pre-doping, a method of positively applying pressure from the outside, and a method of converting the increase in the internal pressure of cell 1 to pressurization of cell 1 while keeping the volume of cell 1 constant, At least one of the above can be adopted.

The extent of pressurizing the cell 1 in the pre-doping process, depending on the kind of the negative electrode material constituting the negative electrode 4, the thickness direction of the negative electrode 4, 0.3 kg / cm ² or more 6.6 kg / cm ² or less of It is preferable to pressurize with pressure. If it is less than 0.3 kg / cm ² , the effect of preventing the cell 1 from swelling may not be obtained. If it exceeds 6.6 kg / cm ² , swelling of the cell 1 can be prevented, but the negative electrode active material layer 3 and the positive electrode active material layer 6 may be physically crushed.

(Charging process)
After the pre-doping process, the terminal 2z connected to the negative electrode current collector 2 of the cell 1 and the terminal 5z connected to the positive electrode current collector 5 are respectively connected to an external power source to charge the cell 1. In order to suppress the swelling of the cell 1 at the time of the initial charge when the cell 1 is charged for the first time, the initial charge is performed while pressurizing the cell 1. The method of pressurization is not particularly limited, and for example, the same method as the pressurization method of the cell 1 and the negative electrode active material layer 3 in the pre-doping step can be adopted.

The extent of pressurizing the cell 1 in the charging step, depending on the kind of the negative electrode material constituting the negative electrode 4, the cell 1 to the thickness direction, 0.3 kg / cm ² or more 6.6 kg / cm ² or less of It is preferable to pressurize with pressure. If it is less than 0.3 kg / cm ² , the effect of preventing the cell 1 from swelling may not be obtained. If it exceeds 6.6 kg / cm ² , swelling of the cell 1 can be prevented, but the negative electrode active material layer 3 and the positive electrode active material layer 6 may be physically crushed.

  Hereafter, each structure of the lithium ion secondary battery which concerns on this embodiment is demonstrated in detail. In particular, preferred embodiments are exemplified from the viewpoint of enhancing the effect of lithium pre-doping.

<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 auxiliary agent in addition to a positive electrode active material such as a metal acid lithium 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, a third porous conductive plate 9 and a 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, and these The lithium supply plates 10 and 12 are further laminated through the 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.

  Here, by pressurizing the laminate cell with the porous conductive plates 9 and 11 at the time of lithium pre-doping, the electrode laminate is suppressed from expanding and the increase in the electrode thickness is more effectively suppressed. can do. Furthermore, since the lithium dope reaction proceeds uniformly over the entire electrode stack due to the presence of the perforated conductive plates 9, 11, electrode distortion that occurs when the dope reaction proceeds non-uniformly. Can be prevented. As a result, it is possible to prevent peeling of the negative electrode active material layer 3 that occurs when distortion occurs, and to further improve the adhesion of the negative electrode active material layer 3 to the negative electrode current collector 2.

  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, a non-uniform reaction causes peeling of each negative active material layer, and causes wrinkles and undulations 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 7 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 nanotubes (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 distilled water is added thereto to adjust the concentration. 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 on the pressurization conditions which become "the volume density of the negative electrode active material layer before a pre dope process" of Table 1, it is thick on both surfaces on the copper foil which is a collector. Each negative active material layer having a thickness of 25 μm was formed to obtain a negative electrode. 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).
The volume density of the negative electrode active material layer determined by the above-described method was 1.0 g / cm ³ .

(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. Then, using a roll press machine, by pressing on the pressurization conditions which become "the volume density of the negative electrode active material layer before a pre dope process" of Table 1, it is thick on both surfaces on the copper foil which is a collector. A positive electrode active material layer having a thickness of 60 μm was formed to obtain a positive electrode. 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 pre-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 was set in a pressure jig, the cell was brought into a pressurized state with a force of 3.3 kg / cm ² , and left in a constant temperature bath at 25 ° C. for 48 hours to perform lithium pre-doping treatment. The laminate cell was manufactured. The rated capacity of the manufactured battery is 1000 mAh.
Thereafter, when the manufactured laminate cell was charged for the first time, the cell was put into a pressurized state with a force of 3.3 kg / cm ² .

[Examples 2 to 17]
The laminate cell assembled in the same manner as in Example 1 was put into a pressurized state as shown in Table 1, and a pre-doping step and a subsequent charging step were performed to manufacture laminate cells of Examples 2 to 17. However, when the volume density of the negative electrode active material layer before lithium pre-doping was adjusted in the same manner as in Example 1, the pressure state at the time of preparing the negative electrode was appropriately changed. Moreover, Examples 11-13 performed lithium pre dope in the state which does not pressurize a cell.

[Comparative Examples 1-6]
The laminate cell assembled in the same manner as in Example 1 was put into a pressurized state shown in Table 1, and a pre-doping step and a subsequent charging step were performed to produce laminate cells of Comparative Examples 1 to 6. However, when the volume density of the negative electrode active material layer before lithium pre-doping was adjusted in the same manner as in Example 1, the pressure state at the time of preparing the negative electrode was appropriately changed. Moreover, the comparative example 1 performed lithium pre dope in the state which does not pressurize a cell. Moreover, Comparative Examples 1-2 and 4 performed the first charge in the state which does not pressurize a cell.

(Evaluation of cell thickness)
About the thickness of each produced laminate cell, it measured before lithium pre dope and after the first charge. The increase rate of the thickness after the first charge when the thickness before lithium pre-doping was set to 1 was calculated. The results are shown in Table 2.

(Evaluation of charge / discharge characteristics of lithium ion secondary battery)
About each produced lithium ion secondary battery, after performing constant-current constant-voltage charge of 0.1C at 25 degreeC until the electric current value converges to 0.05C as upper limit voltage 4.2V, 0.1C constant-current Discharging 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) (% ), Charge / discharge current is set to 1C, charge / discharge cycle is repeated in the same manner, and capacity retention rate at 100 cycles ({[discharge capacity at 100th cycle (mAh)] / [discharge capacity at 1st cycle (mAh)] ]} × 100) (%) was calculated. The results are shown in Table 2.

From the above results, in Examples 1 to 9, the density of the negative electrode active material layer before lithium pre-doping is moderate, and the cell is sufficiently pressurized in both the lithium pre-doping step and the initial charging step. It can be seen that the swelling of the cell after charging is small and the capacity retention rate is also good. In Examples 11-13, since the cell was not pressurized at the time of lithium pre dope, it turns out that the swelling of the cell after charge is larger than Examples 1-9.
In Examples 14 to 17, good results were obtained as in Examples 1 to 9. From the results of Examples 14 to 17, it can be seen that as the density of the negative electrode active material layer before lithium pre-doping increases, the increase rate of the cell thickness increases and the capacity retention rate decreases. This indicates that the density of the negative electrode active material layer affects the degree or effect of lithium pre-doping.
On the other hand, in Comparative Examples 1, 2, and 4, since the cell was not pressurized during the initial charge, it can be seen that the swelling of the cell after charging is large. Further, in Comparative Example 3 (reference example), it can be seen that since the degree of pressurization of the cell at the first charge is small, the swelling of the cell after charging is large. In Comparative Examples 5 and 6, it can be seen that the volume density of the negative electrode active material layer before lithium pre-doping is excessively high, so that the capacity retention rate is lowered and the increase rate of cell swelling is high.

[Comparative Example 7]
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 Comparative 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. Further, the capacity expression rate was inferior to that of Comparative Example 1. From this result, it can be seen that the lithium pre-doping efficiency is improved when the lithium metal foil is disposed on the negative electrode active material layer via the conductive porous conductive plate rather than the non-conductive separator.

  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 (6)

A method for producing a lithium ion secondary battery comprising a negative electrode having a negative electrode active material layer containing silicon oxide and a cell having a positive electrode,
After adjusting the volume density of the negative electrode active material layer to 0.8 g / cm ³ or more and 1.5 g / cm ³ or less, a pre-doping step of performing lithium pre-doping, and a charging step of performing initial charging while pressurizing the cell; A method for producing a lithium ion secondary battery.   The method for producing a lithium ion secondary battery according to claim 1, wherein in the pre-doping step, lithium pre-doping is performed while pressurizing the cell. Pressurizing the cell at 0.3 kg / cm ² or more 6.6 kg / cm ² or less pressure method for manufacturing a lithium ion secondary battery according to claim 2. In the charging step, pressurizing the cell at 0.3 kg / cm ² or more 6.6 kg / cm ² or less pressure method for producing a lithium ion secondary battery according to any one of claims 1 to 3 . In the pre-doping step,
A porous conductive plate is placed on the surface of the negative electrode active material layer,
Obtaining an electrode laminate in which a lithium supply plate is placed on the porous conductive plate,
4. The lithium ion secondary according to claim 2, wherein the electrode laminate is sandwiched between two flat jigs in a state where the electrode laminate is in contact with the electrolytic solution, and lithium pre-doping is performed under pressure. Battery manufacturing method. Prior to the pre-doping step, the negative electrode is sandwiched between two flat jigs, and the entire surface of the negative electrode active material layer is uniformly pressed in the thickness direction, whereby the volume density of the negative electrode active material layer is reduced to 0. 0. 8g / cm ³ 1.5 g / cm or more ³ The manufacturing method of the lithium ion secondary battery as described in any one of Claims 1-5 adjusted to the following.

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