JP2020004663A - Negative electrode for lithium ion battery, lithium ion battery using negative electrode, and manufacturing method of lithium ion battery - Google Patents

Abstract

To obtain a negative electrode for a silicon-containing lithium ion battery having a large capacity and a reduced initial irreversible capacity.SOLUTION: A through hole which penetrates in the negative electrode is formed in a negative electrode in which at least one main surface of a current collector is provided with a negative electrode active material layer in which a negative electrode active material containing silicon is provided, and the negative electrode is pre-doped with lithium ions in advance, and the ratio of the initial discharge capacity to the initial charge capacity in the initial charge and discharge of the negative electrode is 90% or more.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a negative electrode for a lithium ion battery having a through hole penetrating in a thickness direction, and a lithium ion battery including the negative electrode for a lithium ion battery.

Lithium ion secondary batteries are generally a positive electrode in which a positive electrode active material or the like is applied to both surfaces of a positive electrode current collector using a binder, and a negative electrode in which a negative electrode active material or the like is applied to both surfaces of a negative electrode current collector using a binder. Are laminated via an electrolyte layer and housed in a battery case.

2. Description of the Related Art Hitherto, a lithium-ion secondary battery that has reduced manufacturing costs, has no self-discharge failure, has low internal resistance, and has a high capacity has been proposed.
In Patent Literature 1, an active material layer in which a negative electrode active material made of graphite is formed on at least one main surface of a current collector, and a through hole is formed in the negative electrode.
Further, graphite is pre-doped with lithium by an electrochemical method using a metal lithium insertion electrode made of a lithium foil, and then the metal lithium insertion electrode is taken out, thermocompressed again, and sealed.

As described above, carbon, particularly a graphite material, which is advantageous in terms of the life and cost of the charge / discharge cycle, has been used. On the other hand, recently, as a high-capacity negative electrode active material, a material that can be alloyed with lithium has been studied. For example, a Si material absorbs and releases 4.4 mol of lithium ions per mol during charging and discharging, and has a theoretical capacity of about 4200 mAh / g in Li ₂₂ Si ₅ . Such a material that can be alloyed with lithium can increase the energy density of the electrode, and is therefore expected as a negative electrode material for vehicle use.

However, many lithium ion secondary batteries using such a large capacity lithium alloying material as the negative electrode active material have a large irreversible capacity at the time of initial charge and discharge. For this reason, there is a problem that the capacity utilization rate of the filled positive electrode decreases, and the energy density of the battery decreases.
The problem of the initial irreversible capacity has become a major development issue in practical application to a vehicle application requiring a high capacity, and attempts to suppress the initial irreversible capacity have been actively made.

  As a technique for supplementing lithium corresponding to such irreversible capacity, as disclosed in Patent Document 2, a current collector and a negative electrode active material formed on the current collector and pre-doped with lithium ions are disclosed. There is a lithium ion secondary battery including a negative electrode having a negative electrode active material layer containing: a positive electrode, and an electrolyte layer interposed between the positive electrode and the negative electrode. The method for manufacturing a negative electrode active material layer including a negative electrode active material in which lithium ions are pre-doped includes a lithium-based metal film in contact with the surface of the layer including the silicon-containing active material and including lithium and silicon. A step of reacting with an active material is disclosed.

JP 2012-138408 A JP 2011-054324 A

  However, since the lithium pre-doped layer is formed on the surface of the negative electrode active material layer by an amount corresponding to the pre-doping amount, lithium reacts with moisture to change to lithium hydroxide. In order to avoid this, the negative electrode, the separator, the positive electrode, and the separator must be laminated or wound in a dry atmosphere, and the winder must be installed in a dry room or the like.

  The active material containing silicon is doped with lithium by injecting the electrolytic solution. However, merely injecting the electrolytic solution does not necessarily cause the active material to be uniformly doped with lithium ions. It was insufficient to reduce the irreversible capacity.

  An object of the present invention is to obtain a silicon-containing negative electrode having a large capacity and a small initial irreversible capacity.

The lithium ion battery of the present invention has been made in order to solve the above-described problem, and has a thickness on a negative electrode in which a negative electrode active material layer including silicon-containing negative electrode active material is formed on at least one main surface of a current collector. A through hole penetrating in the direction is formed, and the negative electrode is pre-doped with lithium ions.
The ratio of the initial discharge capacity to the initial charge capacity in the initial charge and discharge of the negative electrode is 90% or more.

  According to the present invention, the opening diameter of the through hole is 1 μm or more and 50 μm or less, and the opening ratio of the through hole is 0.01% or more and 5% or less.

  Further, according to the present invention, the negative electrode active material containing silicon contains at least one of silicon and silicon oxide.

  Further, according to the present invention, a step of forming a negative electrode plate by forming a negative electrode active material layer by applying a negative electrode active material composition containing silicon to at least one surface of a current collector; Forming a through-hole that penetrates through; forming a laminate in which a negative electrode plate and a positive electrode plate are laminated with a separator interposed therebetween; laminating the laminate with a lithium insertion electrode; And pre-doping the negative electrode plate using the lithium.

  According to the lithium ion battery of the present invention, since the negative electrode on which the negative electrode active material layer containing silicon is provided has a through-hole that penetrates in the thickness direction, lithium ions pass through the through-hole into the inside of the negative electrode. Penetrate up to. Therefore, the distance over which the lithium ions diffuse through the negative electrode is shortened, the distribution of the doped lithium ions in the negative electrode becomes uniform, and the initial irreversible capacity is reduced.

1 is a cross-sectional view of a lithium ion battery according to the present invention.

As shown in FIG. 1, the lithium ion battery of the present invention has an electrode laminate including a negative electrode 1, a positive electrode 2, a separator 3 interposed between the negative electrode and the positive electrode, electrically insulated and conducting lithium ions. And an outer package 4 for packaging the electrode laminate, and an electrolytic solution 5 filled inside the outer package.
In addition, a lithium insertion electrode 6 used for predoping the negative electrode with lithium is disposed outside the outermost negative electrode.

  In the negative electrode of the present invention, a negative electrode active material layer containing silicon is provided on both surfaces of the current collector. The negative electrode active material layer includes a negative electrode active material containing silicon, a conductive additive, and a binder. The negative electrode active material containing silicon is made of silicon metal, silicon alloy, silicon oxide, or a mixture thereof with a carbon material. Silicon metal absorbs and releases 4.4 moles of lithium ions per mole during charge and discharge, and can have a theoretical capacity of about 4200 mAh / g.

The silicon alloy has a composition of an alloy of lithium and a metal that is not alloyed so that the volume expansion and contraction of silicon can be reduced.
The silicon oxide is represented by SiOx, and is silicon oxide that has been subjected to disproportionation treatment to precipitate fine silicon in silicon dioxide.
Further, a mixture of silicon and a carbon material can be obtained by mixing silicon powder and carbonaceous powder, or including silicon powder or silicon alloy powder in a carbonaceous matrix.

  The conductive assistant is not particularly limited as long as it can be used for a lithium ion battery. For example, carbon materials such as carbon black, graphite, and carbon fiber can be used.

  The binder is not limited to the following, and examples thereof include polyamide, polyvinylidene fluoride, and polytetrafluoroethylene.

  The negative electrode is provided with a through hole 7 penetrating in the thickness direction. The through hole has a hole diameter of 1 μm or more and 50 μm or less. It is difficult to perforate so that the hole diameter is less than 1 μm. Even when the laser beam diameter is reduced to submicron, it is difficult to realize a hole diameter of less than 1 μm because a part of the negative electrode active material around the laser beam is separated from the current collector. On the other hand, if it is attempted to maintain the strength of the negative electrode at a predetermined value with a hole diameter exceeding 50 μm, the number of through holes becomes too small. In particular, the pore diameter is desirably from 1 μm to 7 μm. The distance that the lithium ions move in the plane direction of the negative electrode active material is reduced, and the in-plane lithium ion doping becomes more uniform.

  The opening ratio of the through holes is 0.01% or more and 5% or less. If the aperture ratio is less than 0.01%, the effect of making lithium ion doping uniform cannot be exhibited. On the other hand, when the aperture ratio exceeds 5%, the amount of the active material is greatly reduced, and the capacity is reduced.

  The negative electrode is preliminarily doped with lithium. The doping amount of lithium is an amount corresponding to the initial irreversible capacity of the negative electrode active material.

The method for producing the negative electrode includes the following steps (1) to (3).
(1) A negative electrode active material layer containing a negative electrode active material is formed on a current collector.
(2) A through hole is formed in the thickness direction including the current collector in the negative electrode active material layer formed on the current collector.
(3) The negative electrode tab is joined to an uncoated portion of the current collector on which the active material layer is not applied.
In this step (1), there is no particular limitation as long as it is a manufacturing method used for forming an electrode of a lithium ion battery.
Next, in the step (2), the laser processing apparatus to be used is not limited, but the laser processing apparatus disclosed in Japanese Patent Application No. 2017-168581 is particularly suitable because a through hole having a small diameter can be formed at a high speed. A through hole is formed using the laser processing device.
Next, in the step (3), there is no particular limitation as long as it is a manufacturing method used for forming an electrode of a lithium ion battery.
The negative electrode manufactured as described above is processed into a predetermined shape and used for assembling a lithium ion battery described later.

  In the positive electrode of the lithium ion battery of the present invention, the positive electrode active material layers are provided on both surfaces of the current collector. The positive electrode active material layer includes a positive electrode active material containing a lithium composite oxide, a conductive additive, and a binder. The positive electrode active material containing a lithium composite oxide is not limited as long as it can insert and remove lithium. Examples include lithium cobalt composite oxide, lithium nickel composite oxide, lithium nickel manganese composite oxide, lithium nickel cobalt manganese composite oxide, lithium nickel aluminum composite oxide, lithium manganese oxide, and lithium iron phosphate.

  The conductive assistant is not particularly limited as long as it can be used for a lithium ion battery. For example, carbon materials such as carbon black, graphite, and carbon fiber can be used.

  The binder is not limited to the following, and examples thereof include polyamide, polyvinylidene fluoride, and polytetrafluoroethylene.

  The positive electrode is provided with a through hole penetrating in the thickness direction. The through hole has a hole diameter of 1 μm or more and 50 μm or less. It is difficult to perforate so that the hole diameter is less than 1 μm. On the other hand, if the strength of the positive electrode is to be maintained at a predetermined value with a hole diameter exceeding 50 μm, the number of through holes becomes too small.

  The opening ratio of the through holes is 0.01% or more and 5% or less. If the aperture ratio is less than 0.01%, the effect of making lithium ion doping uniform cannot be exhibited. On the other hand, when the aperture ratio exceeds 5%, the amount of the active material is greatly reduced, and the capacity is reduced.

The method for manufacturing the positive electrode includes the following steps (1) to (3).
(1) A positive electrode active material layer containing a positive electrode active material is formed on a current collector.
(2) A through hole is formed in the thickness direction including the current collector in the positive electrode active material layer formed on the current collector.
(3) The positive electrode tab is joined to an uncoated portion of the current collector on which the active material layer is not applied.
In this step (1), there is no particular limitation as long as it is a manufacturing method used for forming an electrode of a lithium ion battery.
Next, in step (2), through holes are formed using the laser processing apparatus disclosed in Japanese Patent Application No. 2017-168581.
Next, in the step (3), there is no particular limitation as long as it is a manufacturing method used for forming an electrode of a lithium ion battery.
The positive electrode manufactured as described above is processed into a predetermined shape and used for assembling a lithium ion battery described later.

The separator is not particularly limited as long as it can be used for a lithium ion battery.
The electrolyte is not particularly limited as long as it can be used for a lithium ion battery. For example, the non-aqueous electrolyte may be obtained by dissolving at least a part of a lithium salt in an organic solvent. Further, it may be a solid electrolyte.

  The exterior body is not particularly limited as long as it can be used for a lithium ion battery. For example, a metal case or a pouch container may be used.

  A lithium insertion electrode is prepared as a lithium source for predoping lithium into the negative electrode. The lithium supply electrode is obtained by fixing lithium foil or lithium powder on the surface of a lithium foil alone or a current collector. This lithium insertion electrode is joined to a lithium tab made of copper or the like. The lithium amount of the lithium insertion electrode is an amount corresponding to the initial irreversible capacity of silicon contained in the negative electrode active material.

In the lithium ion battery of the present invention, the negative electrode is pre-doped with lithium after assembling the lithium ion battery.
The method for assembling a lithium ion battery includes the following steps (1) to (4).
In step (1), an electrode assembly is assembled. The above-described negative electrode, positive electrode, and separator are processed into a shape having a predetermined size. Next, a predetermined set is laminated with the negative electrode, the separator, the positive electrode, and the separator as one set. In that case, a negative electrode, a separator, a positive electrode, and a separator are stacked in this order. Next, a negative electrode is laminated on the outside of the separator laminated on the outermost layer, and the separator is laminated on the outer sides of the outermost negative electrode on both sides. Next, the lithium insertion electrodes are laminated so that lithium is in contact with the outside of the outermost layer separator on both sides, respectively, to assemble an electrode assembly.

In the step (2), the electrode assembly is inserted into the outer package, and an electrolyte is injected to produce a battery precursor.
In the step (3), a lithium pre-doping process is performed. As shown in FIG. 1, when the negative electrode tab and the lithium tab are short-circuited and left for a predetermined time, lithium ionized from the lithium insertion electrode is alloyed with silicon and silicon is pre-doped with lithium.
In step (4), the lithium tab is peeled off from the negative electrode tab.
In the step (5), the negative electrode tab and the positive electrode tab are extended to the outside of the package, and the package is sealed to complete the lithium ion battery.

Example 1
The negative electrode includes a negative electrode current collector and a negative electrode active material layer containing silicon provided on both surfaces of the negative electrode current collector. The thickness of the negative electrode active material layer is 6 μm, and the thickness of the negative electrode is 22 μm.
The negative electrode is further provided with a through hole having a diameter of 5 μm penetrating in the thickness direction.
Each through-hole is provided apart from each other so that the opening ratio of the through-hole is 1.0% with respect to the negative electrode surface.

The negative electrode current collector is made of a nickel-plated steel plate having a thickness of 10 μm and a width of 40 mm.
The negative electrode active material layer is composed of silicon particles having an average particle size of 5 μm, a polyimide binder, and acetylene black as a conductive additive in a weight ratio of 80: 15: 5.
The negative electrode active material layer was laid so as to obtain a capacity of 3 mAh per unit area.
Although the method for producing the negative electrode active material layer is not particularly limited, silicon particles and acetylene black are added to N-methyl-2-pyrrolidone containing a solid concentration of 15% by mass of polyamic acid as a precursor of a polyimide-based binder. In addition, the mixture was uniformly dispersed to prepare a negative electrode active material slurry A.
Next, a negative electrode active material slurry was applied to both sides of the nickel-plated steel sheet at a coating thickness of 6 μm so that an uncoated portion having a width of 10 mm was formed on one widthwise edge of the negative electrode current collector. Dried at ° C. Next, heat treatment was performed at 350 ° C. for 1 hour to thermally cure the polyamic acid to imidize it. These were hot-pressed to form a negative electrode plate before through-hole processing.

Next, the negative electrode plate before processing the through hole to be processed is transported from the outside while being obliquely wound on the circumferential surface of the hollow cylindrical body having an opening in the circumferential surface, and is orthogonal to the central axis of the cylindrical body. The reflected laser pulse light was applied to the negative electrode plate to form a through hole.
A negative electrode A having a width of 40 mm and a depth of 35 mm was punched from the negative electrode plate. Then, a nickel tab was welded to the uncoated portion.

The positive electrode includes a positive electrode current collector and a positive electrode active material layer including a nickel-based layered composite oxide provided on both surfaces of the positive electrode current collector. The thickness of the positive electrode active material layer is 80 μm, and the thickness of the positive electrode is 170 μm.
The positive electrode is further provided with a through hole having a diameter of 15 μm penetrating in the thickness direction.
Each through-hole is provided apart such that the opening ratio of the through-hole is 1.0% with respect to the positive electrode surface.

The positive electrode current collector is made of a stainless foil having a thickness of 10 μm and a width of 40 mm.
The positive electrode active material layer includes a nickel-based composite oxide of LiNi _0.8 Co _0.15 Al _0.05 O ₂ having an average particle size of 10 μm as a positive electrode active material, a PVDF-based binder, and acetylene as a conductive additive. Black and 95: 2: 3 by weight.
LiNi _0.8 Co _0.15 Al _0.05 O 2 is 200 mAh / g per unit weight. The weight of the positive electrode active material layer was set so as to obtain a capacity of 3 mAh per unit area.
The method for producing the positive electrode active material layer is not particularly limited, but a nickel-based composite oxide and acetylene black are added to N-methyl-2-pyrrolidone containing a PVDF-based binder at a solid concentration of 15% by mass, and the mixture is uniformly mixed. This was dispersed to prepare a positive electrode active material slurry.
Next, the positive electrode active material slurry was applied to both surfaces of the SUS foil so that the thickness of the coating film on one side was 80 μm, and dried at 120 ° C. These were hot-pressed to prepare a positive electrode plate before processing the through-hole.

Next, the positive electrode plate to be processed was transported from the outside while being wound obliquely from the outside to the circumferential surface of the hollow cylindrical body having an opening in the circumferential surface, and was reflected so as to be orthogonal to the central axis of the cylindrical body. The positive electrode plate was formed by irradiating the positive electrode plate with laser pulse light to form a through hole.
From this positive electrode plate, a positive electrode A having a width of 35 mm and a depth of 30 mm was punched. Then, an aluminum tab was welded to the uncoated portion.

  Next, a lithium ion secondary battery was prepared. An electrode laminate was prepared by interposing a polyolefin-based microporous film between three negative electrodes A and two positive electrodes A. Further, a lithium foil was laminated with a polyolefin-based microporous film on both sides in the laminating direction of the electrode laminate. A copper tab is welded to the lithium foil. The laminated body was inserted into a resin-metal sealed body so that a part of each tab appeared on the outside, and 1M-LiPF6 EC-DMC electrolyte was injected and sealed. Thus, a lithium ion secondary battery A of No. 1 was prepared.

The lithium ion secondary battery A of Example 1 was subjected to a lithium pre-doping process. The negative electrode tab and the lithium tab were short-circuited for a predetermined time, and lithium was pre-doped into silicon. The open circuit voltage between the negative tab and the lithium tab was 0.003V.
Next, discharge was performed until the voltage between the negative electrode tab and the lithium tab became 1 V.
Next, using the positive electrode tab and the negative electrode tab, the battery was charged at 0.025 C until the battery voltage reached 3.7 V, and then discharged at 0.025 C until the battery voltage reached 2.5 V. The charge capacity was 110 mAh and the discharge capacity was 100 mAh. The irreversible capacity at the first charge / discharge was 9%.

Example 2
The negative electrode includes a negative electrode current collector, and a negative electrode active material layer including silicon oxide and graphite provided on both surfaces of the negative electrode current collector. The thickness of the negative electrode active material layer is 60 μm, and the thickness of the negative electrode is 130 μm.
The negative electrode is further provided with a through hole having a diameter of 5 μm penetrating in the thickness direction.
Each through-hole is provided apart such that the opening ratio of the through-hole is 1.5% with respect to the negative electrode surface.

The negative electrode current collector is made of a nickel-plated steel plate having a thickness of 10 μm and a width of 40 mm.
The negative electrode active material layer is composed of silicon oxide particles having an average particle diameter of 20 μm, graphite having an average particle diameter of 15 μm, and an acrylic binder in a weight ratio of 10: 85: 5.
The anode active material layer was laid so as to obtain a capacity of 3 mAh per unit area.
Although the method for producing the negative electrode active material layer is not particularly limited, silicon oxide particles and graphite are added to deionized water containing an acrylic binder at a solid concentration of 15% by mass, and the mixture is uniformly dispersed. B was created.
Next, the negative electrode active material slurry B was applied to both sides of the nickel-plated steel sheet at a coating thickness of 60 μm so that an uncoated portion having a width of 10 mm was formed at one widthwise edge of the negative electrode current collector. Dried at ° C. These were hot pressed to form a negative electrode plate before through hole processing.

Next, the negative electrode plate before processing the through hole to be processed is transported from the outside while being obliquely wound on the circumferential surface of the hollow cylindrical body having an opening in the circumferential surface, and is orthogonal to the central axis of the cylindrical body. The reflected laser pulse light was applied to the negative electrode plate to form a through hole.
A negative electrode B having a width of 40 mm and a depth of 35 mm was punched from the negative electrode plate. Then, a nickel tab was welded to the uncoated portion.

Next, a lithium ion secondary battery was prepared. An electrode laminate was prepared by interposing a polyolefin-based microporous film between three negative electrodes B and two positive electrodes A. Further, a lithium foil was laminated with a polyolefin-based microporous film on both sides in the laminating direction of the electrode laminate. A copper tab is welded to the lithium foil. This laminated body is inserted into a resin-metal sealing body so that a part of each tab appears outside, and an EC-DMC electrolyte of 1M-LiPF ₆ is injected, sealed, and then performed. A lithium ion secondary battery B of Example 2 was produced.

The lithium ion secondary battery B of Example 2 was subjected to lithium pre-doping. The negative electrode tab and the copper tab were short-circuited for a predetermined time, and lithium was pre-doped into silicon. The open circuit voltage between the negative tab and the copper tab was 0.003V.
Next, discharging was performed until the voltage between the negative electrode tab and the copper tab became 1 V.
Next, using the positive electrode tab and the negative electrode tab, the battery was charged at 0.025 C until the battery voltage became 4.0 V, and then discharged at 0.025 C until the battery voltage became 2.7 V. The charge capacity was 110 mAh and the discharge capacity was 100 mAh. The irreversible capacity at the first charge / discharge was 9%.

Example 3
The negative electrode includes a negative electrode current collector and a negative electrode active material layer containing silicon oxide provided on both surfaces of the negative electrode current collector. The thickness of the negative electrode active material layer is 60 μm, and the thickness of the negative electrode is 130 μm.
The negative electrode is further provided with a through hole having a diameter of 5 μm penetrating in the thickness direction.
Each through-hole is provided apart such that the opening ratio of the through-hole becomes 2.0% with respect to the negative electrode surface.

The negative electrode current collector is made of a SUS foil having a thickness of 10 μm and a width of 40 mm.
The negative electrode active material layer is composed of silicon oxide particles having an average particle diameter of 20 μm, a polyimide binder, and acetylene black as a conductive additive in a weight ratio of 82: 15: 3.
The negative electrode active material layer was laid so as to obtain a capacity of 3 mAh per unit area.
Although the method for producing the negative electrode active material layer is not particularly limited, silicon oxide particles and acetylene black are added to N-methyl-2-pyrrolidone containing 15% by mass of a solid content of polyamic acid as a precursor of a polyimide-based binder. Was added and uniformly dispersed to prepare a negative electrode active material slurry C.
Next, a negative electrode active material slurry was applied to both sides of the SUS foil at a coating thickness of 60 μm so that an uncoated portion having a width of 10 mm was formed on one widthwise edge of the negative electrode current collector. Dried. Next, heat treatment was performed at 350 ° C. for 1 hour to thermally cure the polyamic acid to imidize it. These were hot-pressed to form a negative electrode plate before through-hole processing.

Next, the negative electrode plate before processing the through hole to be processed is transported from the outside while being obliquely wound on the circumferential surface of the hollow cylindrical body having an opening in the circumferential surface, and is orthogonal to the central axis of the cylindrical body. The reflected laser pulse light was applied to the negative electrode plate to form a through hole.
A negative electrode C having a width of 40 mm and a depth of 35 mm was punched from the negative electrode plate. Then, a nickel tab was welded to the uncoated portion.

  Next, a lithium ion secondary battery C of Example 3 was produced. An electrode laminate was prepared by interposing a polyolefin-based microporous film between three negative electrodes B and two positive electrodes A. Further, a lithium foil was laminated with a polyolefin-based microporous film on both sides in the laminating direction of the electrode laminate. A copper tab is welded to the lithium foil. The laminated body was inserted into a resin-metal sealed body so that a part of each tab appeared on the outside, and 1M-LiPF6 EC-DMC electrolyte was injected and sealed. A lithium ion secondary battery C of No. 3 was produced.

The lithium ion secondary battery C of Example 3 was subjected to lithium pre-doping. The negative electrode tab and the copper tab were short-circuited for a predetermined time, and lithium was pre-doped into silicon. The open circuit voltage between the negative tab and the copper tab was 0.003V.
Next, discharging was performed until the voltage between the negative electrode tab and the copper tab became 1 V.
Next, using the positive electrode tab and the negative electrode tab, the battery was charged at 0.025 C until the battery voltage became 4.0 V, and then discharged at 0.025 C until the battery voltage became 2.7 V. The charge capacity was 110 mAh and the discharge capacity was 100 mAh. The irreversible capacity at the first charge / discharge was 9%.

Comparative Example 1
The negative electrode D of Comparative Example 1 was the same as Example 1 except that no through-hole was formed in the negative electrode plate.
The positive electrode B of Comparative Example 1 was the same as Example 1 except that no through hole was formed in the positive electrode plate.

Next, a lithium ion secondary battery D of Comparative Example 1 was prepared. An electrode laminate was prepared by interposing a polyolefin-based microporous film between three negative electrodes D and two positive electrodes B. Further, a lithium foil was laminated with a polyolefin-based microporous film on both sides in the laminating direction of the electrode laminate. A copper tab is welded to the lithium foil. This laminated body was inserted into a resin-metal sealed body so that a part of each tab appeared outside, and a 1M-LiPF ₆ EC-DMC electrolyte was injected and sealed, and sealed. Thus, a lithium ion secondary battery D was manufactured.

The lithium ion secondary battery D of Comparative Example 1 was subjected to a lithium pre-doping treatment. The negative electrode tab and the copper tab were short-circuited for a predetermined time, and lithium was pre-doped into silicon. The open circuit voltage between the negative tab and the copper tab was 0.010V.
Next, discharging was performed until the voltage between the negative electrode tab and the copper tab became 1 V.
Next, using the positive electrode tab and the negative electrode tab, the battery was charged at 0.025 C until the battery voltage became 4.0 V, and then discharged at 0.025 C until the battery voltage became 2.7 V. The charge capacity was 110 mAh and the discharge capacity was 90 mAh. The irreversible capacity at the first charge / discharge was 18%.

  The lithium ion secondary batteries of Examples 1 to 3 of the present invention have an initial irreversible capacity of 10% or less, which is smaller than 18% of Comparative Example 1. The following can be considered as the reason. Since there is a through hole penetrating the active material layer, lithium ions ionized from the lithium foil can uniformly reach the negative electrode. Therefore, it is necessary to conduct ions from the outer edge of the negative electrode to the center as in Comparative Example 1. Therefore, it is considered that they can be pre-doped uniformly.

The distribution of the pre-doped concentration of lithium in the negative electrodes of the lithium ion secondary batteries of Example 1 of the present invention and Comparative Example 1 was examined. From the negative electrode, a ribbon having a width of 5 mm and a length of 40 mm was cut out in the width direction, and the ribbon was divided into eight equal parts to prepare a sample for lithium concentration measurement.
The lithium concentration was measured using ICP-MS (inductively coupled plasma mass spectrometer).
The standard deviation of the lithium concentration of Example 1 was 15%, while the standard deviation of the lithium concentration of Comparative Example 1 was 43%.
In the battery of Comparative Example 1, the diffusion direction of lithium ions is parallel to the electrode surface, whereas in the battery of Example 1, the diffusion of lithium ions in the vertical direction is considered to have an effect.

DESCRIPTION OF SYMBOLS 1 Negative electrode 2 Positive electrode 3 Separator 4 Outer body 5 Electrolyte solution 6 Lithium insertion electrode 7 Through-hole

Claims (6)

In a negative electrode for a lithium ion battery, which is provided with a negative electrode active material layer containing silicon on at least one surface of the current collector,
A through-hole penetrating the negative electrode in the thickness direction is provided,
The negative electrode active material layer is pre-doped with lithium,
A negative electrode for a lithium ion battery, wherein the ratio of the initial discharge capacity to the initial charge capacity in the initial charge and discharge of the negative electrode is 90% or more. The opening diameter of the through hole is 1 μm or more and 50 μm or less,
The negative electrode for a lithium ion battery according to claim 1, wherein an opening ratio of the through hole is 0.01% or more and 5% or less.   The negative electrode for a lithium ion battery according to claim 1, wherein the negative electrode active material containing silicon includes at least one of silicon and silicon oxide.   A lithium ion battery comprising the negative electrode for a lithium ion battery according to claim 1. In a method for producing a lithium ion battery, wherein the ratio of the initial discharge capacity to the initial charge capacity in the initial charge and discharge of the negative electrode is 90% or more,
A step of forming a negative electrode plate by applying a negative electrode active material composition containing silicon on at least one surface of the current collector to form a negative electrode active material layer,
Forming a through hole penetrating in the thickness direction of the negative electrode plate;
A step of forming a laminate in which the negative electrode plate and the positive electrode plate are laminated via a separator,
A method for producing a lithium ion battery, comprising: laminating the laminate and a lithium insertion electrode, and pre-doping the negative electrode plate using lithium derived from the lithium insertion electrode. In the step of forming the through hole,
The opening diameter of the through hole is 1 μm or more and 50 μm or less,
The method for manufacturing a lithium ion battery according to claim 4, wherein a through hole having an opening ratio of 0.01% or more and 5% or less is formed.

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