Patent Description:
Conventionally widely used is a non-aqueous electrolyte secondary battery comprising a wound electrode assembly in which a band-shaped positive electrode and a band-shaped negative electrode are wound with a separator interposed therebetween and an outer housing can that houses the wound electrode assembly. The electrodes of the electrode assembly (the positive electrode and the negative electrode) in such a wound battery have a mixture layer including an active material and a binder on both surfaces of each metallic current collector, and the positive electrode and the negative electrode are wound with the separator interposed therebetween. Typically, the separator is disposed on the outermost circumference of the electrode assembly, the positive electrode is connected to a sealing assembly, which is to be an external terminal on the positive electrode side, with a positive electrode lead, and the negative electrode is connected to the outer housing can, which is to be an external terminal on the negative electrode side, with a negative electrode lead. In a battery having such a constitution, since current from the band-shaped negative electrode concentrates at the negative electrode lead, an internal resistance is likely to be large.

Patent Literature <NUM> describes that a negative electrode is disposed on the outermost circumference of an electrode assembly, a negative electrode current collector is exposed as a one-surface coated portion eliminating a negative electrode mixture layer on a surface on the outermost circumference side at this position, and the negative electrode current collector is directly contacted with an inner face of an outer housing can to be electrically connected. Patent Literatures <NUM>-<NUM> all disclose batteries comprising wound electrode assemblies in which the outer circumference comprises a bare current collector.

When a clearance between the electrode assembly and the inner face of the outer housing can is narrowed in order to ensure contact of the exposed surface of the negative electrode current collector with the inner face of the outer housing can, insertion during the battery manufacturing is likely to fail, resulting in decreased productivity. Since the negative electrode mixture layer expands during charge, it is also considered to utilize this expansion during charge to strengthen the electrical connection between the negative electrode current collector and the inner face of the outer housing can. In this method, however, the negative electrode mixture layer significantly expands and contracts due to the charge and discharge, and deterioration due to the cycles, such as peeling between the active material and the current collector and isolating the active material which results in no contribution of the active material to the charge and discharge, is likely to be large.

The present disclosure provides a non-aqueous electrolyte secondary battery in which a charge expansion coefficient of the negative electrode mixture layer in a one-surface coated portion, at least a part of which is disposed on the outermost circumference, is set to be large to inhibit the failure during assembly and deterioration with the charge-discharge cycle and to ensure the electrical connection between the exposed surface of the negative electrode current collector on the outermost circumference of the electrode assembly and the inner face of the outer housing can.

A non-aqueous electrolyte secondary battery according to claim <NUM> is provided. According to an aspect of the present disclosure is a non-aqueous electrolyte secondary battery, comprising: a wound electrode assembly in which a band-shaped positive electrode and a band-shaped negative electrode are wound with a separator interposed therebetween; and an outer housing can that houses the electrode assembly, wherein the positive electrode has a positive electrode mixture layer formed on a surface of a sheet-shaped positive electrode current collector, the negative electrode has a negative electrode mixture layer formed on a surface of a sheet-shaped negative electrode current collector, the negative electrode mixture layer includes a chargeable and dischargeable negative electrode active material and a binder, the negative electrode includes: a both-surface coated portion in which the negative electrode mixture layer is formed on both surfaces of the negative electrode current collector; and a one-surface coated portion in which the negative electrode mixture layer is formed on one surface of the negative electrode current collector, at least a part of the one-surface coated portion is disposed on an outermost circumference of the electrode assembly, at least a part of an exposed surface of the negative electrode current collector in the one-surface coated portion is contacted with an inner face of the outer housing can, and a charge expansion coefficient of the negative electrode mixture layer in the one-surface coated portion is larger than a charge expansion coefficient of the negative electrode mixture layer in the both-surface coated portion.

The non-aqueous electrolyte secondary battery according to the present disclosure can achieve a clearance between the electrode assembly and the inner face of the outer housing can during assembly, and can reduce the charge expansion coefficient of the entire negative electrode mixture layer. Thus, the failure during assembly and deterioration due to the charge-discharge cycles can be inhibited, and a good electrical connection can be achieved between the exposed surface of the negative electrode current collector and the inner face of the outer housing can.

Hereinafter, an example of an embodiment of a cylindrical, wound non-aqueous electrolyte secondary battery according to the present disclosure will be described in detail with reference to the drawings. In the following description, specific shapes, materials, values, directions, and the like, which are examples for facilitating understanding of the present invention, may be appropriately modified with specifications of cylindrical secondary batteries. When a plurality of embodiments and modified examples are included in the following description, use in appropriate combination of characteristic portions thereof are anticipated in advance.

<FIG> is an axial sectional view of a wound secondary battery <NUM> of an example of an embodiment. Although the secondary battery <NUM> illustrated in <FIG> has a cylindrical shape, the secondary battery <NUM> may have a rectangular cylindrical shape or the like as long as it is the wound battery. In the secondary battery <NUM> illustrated in <FIG>, an electrode assembly <NUM> and a non-aqueous electrolyte (not illustrated) are housed in an outer housing can <NUM>. The electrode assembly <NUM> has a wound structure in which a positive electrode <NUM> and a negative electrode <NUM> are wound with a separator <NUM> interposed therebetween. For a non-aqueous solvent (organic solvent) of the non-aqueous electrolyte, carbonates, lactones, ethers, ketones, esters, and the like may be used, and two or more of these solves may be mixed to be used. When two or more solvents are mixed to be used, a mixed solvent including a cyclic carbonate and a linear carbonate is preferably used. For example, ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), and the like may be used as the cyclic carbonate, and dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and the like may be used as the linear carbonate. For an electrolyte salt of the non-aqueous electrolyte, LiPF<NUM>, LiBF<NUM>, LiCF<NUM>SO<NUM>, and the like, and a mixture thereof may be used. An amount of the electrolyte salt dissolved into the non-aqueous solvent may be set to be, for example, <NUM> to <NUM> mol/L. Hereinafter, for convenience of description, the sealing assembly <NUM> side will be described as "the upper side", and the bottom side of the outer housing can <NUM> will be described as "the lower side".

An opening end part of the outer housing can <NUM> is capped with a sealing assembly <NUM> to seal inside the secondary battery <NUM>. Insulating plates <NUM> and <NUM> are provided on the upper and lower sides of the electrode assembly <NUM>, respectively. A positive electrode lead <NUM> extends upward through a through hole of the insulating plate <NUM>, and welded with the lower face of a filter <NUM>, which is a bottom plate of the sealing assembly <NUM>. In the secondary battery <NUM>, a cap <NUM>, which is a top plate of the sealing assembly <NUM> electrically connected to the filter <NUM>, becomes a positive electrode terminal. Meanwhile, a negative electrode lead <NUM> extends through a through hole of the insulating plate <NUM> toward the bottom side of the outer housing can <NUM>, and welded with a bottom inner face of the outer housing can <NUM>. In the secondary battery <NUM>, the outer housing can <NUM> becomes a negative electrode terminal.

As described later, a negative electrode current collector <NUM> in a one-surface coated portion <NUM> (see <FIG>) is exposed on the outermost circumference of the electrode assembly <NUM>, and the exposed surface of this negative electrode current collector <NUM> is contacted with the inner face of the outer housing can <NUM> to electrically connect the negative electrode <NUM> and the outer housing can <NUM>.

The outer housing can <NUM> is, for example, a bottomed cylindrical metallic outer housing can. A gasket <NUM> is provided between the outer housing can <NUM> and the sealing assembly <NUM> to electrically insulate the outer housing can <NUM> and the sealing assembly <NUM>, and to achieve sealability inside the secondary battery <NUM>. The outer housing can <NUM> has a grooved part <NUM> formed by, for example, pressing the side part thereof from the outside to support the sealing assembly <NUM>. The grooved part <NUM> is preferably formed circularly along the circumferential direction of the outer housing can <NUM>, and supports the sealing assembly <NUM> with the upper face of the grooved part <NUM>.

The sealing assembly <NUM> has the filter <NUM>, a lower vent member <NUM>, an insulating member <NUM>, an upper vent member <NUM>, and the cap <NUM> that are stacked in this order from the electrode assembly <NUM> side. Each member constituting the sealing assembly <NUM> has, for example, a disk shape or a ring shape, and each member except for the insulating member <NUM> is electrically connected each other. The lower vent member <NUM> and the upper vent member <NUM> are connected each other at each of central parts thereof, and the insulating member <NUM> is interposed between each of the circumferential parts thereof. If the internal pressure of the battery increases due to abnormal heat generation, for example, the lower vent member <NUM> breaks and thereby the upper vent member <NUM> expands toward the cap <NUM> side to be separated from the lower vent member <NUM>, resulting in cutting off of an electrical connection between both the members. If the internal pressure further increases, the upper vent member <NUM> breaks, and gas is discharged through an opening 26a of the cap <NUM>.

Next, the electrode assembly <NUM> will be described with reference to <FIG> is a perspective view of the electrode assembly <NUM>. As described above, the electrode assembly <NUM> has a wound structure in which the positive electrode <NUM> and the negative electrode <NUM> are spirally wound with the separator <NUM> interposed therebetween. Any of the positive electrode <NUM>, the negative electrode <NUM>, and the separator <NUM> is formed in a band shaped, and spirally wound around a winding core disposed along a winding axis <NUM> to be alternately stacked in the radial direction of the electrode assembly <NUM>. In the radial direction, the winding axis <NUM> side is referred to as the inner peripheral side, and the opposite side thereof is referred to as the outer peripheral side. In the electrode assembly <NUM>, the longitudinal direction of the positive electrode <NUM> and the negative electrode <NUM> becomes a winding direction, and the width direction of the positive electrode <NUM> and the negative electrode <NUM> becomes an axial direction. The positive electrode lead <NUM> extends, on the upper end of the electrode assembly <NUM> toward the axial direction, from a substantial center between the center and the outermost circumference in the radial direction. The negative electrode lead <NUM> extends, on the lower end of the electrode assembly <NUM>, toward the axial direction from proximity of the winding axis <NUM>.

For the separator <NUM>, a porous sheet having an ion permeation property and an insulation property is used. Specific examples of the porous sheet include a fine porous thin film, a woven fabric, and a nonwoven fabric. As a material of the separator <NUM>, olefin resins such as polyethylene and polypropylene are preferable. A thickness of the separator <NUM> is, for example, <NUM> to <NUM>. The separator <NUM> has tended to be thinned as higher capacity and higher output of the battery. The separator <NUM> has a melting point of, for example, approximately <NUM> to <NUM>.

Next, <FIG> is a front view of the positive electrode <NUM> constituting the electrode assembly <NUM> illustrated with an unwound state.

The positive electrode <NUM> has a band-shaped positive electrode current collector <NUM> and a positive electrode mixture layer <NUM> formed on the positive electrode current collector <NUM>. The positive electrode mixture layer <NUM> is formed on at least one of the inner peripheral side and outer peripheral side of the positive electrode current collector <NUM>. For the positive electrode current collector <NUM>, a foil of a metal, such as aluminum, a film in which such a metal is disposed on a surface layer thereof, and the like are used, for example. A preferable positive electrode current collector <NUM> is a foil of metal mainly composed of aluminum or an aluminum alloy. A thickness of the positive electrode current collector <NUM> is, for example, <NUM> to <NUM>.

The positive electrode mixture layer <NUM> is preferably formed on an entire region of both surfaces of the positive electrode current collector <NUM> except for a positive electrode current collector exposed part <NUM>, described later. The positive electrode mixture layer <NUM> preferably includes a positive electrode active material, a conductive agent, and a binder. The positive electrode mixture layer <NUM> is formed by applying a positive electrode mixture slurry including the positive electrode active material, the conductive agent, the binder, and a solvent such as N-methyl-<NUM>-pyrrolidone (NMP) on both the surfaces of the positive electrode current collector <NUM> and drying thereof (positive electrode mixture layer forming step). Then, the positive electrode mixture layer <NUM> is compressed.

Examples of the positive electrode active material may include a lithium-containing transition metal oxide containing a transition metal element such as Co, Mn, and Ni. The lithium-containing transition metal oxide is not particularly limited, and preferably a composite oxide represented by the general formula Li<NUM>+xMO<NUM> (in the formula, -<NUM> < x ≤ <NUM> and M includes at least one of Ni, Co, Mn, and Al).

Examples of the conductive agent included in the positive electrode mixture layer <NUM> may include carbon materials such as carbon black (CB), acetylene black (AB), Ketjenblack, and graphite.

Examples of the binder included in the positive electrode mixture layer <NUM> include fluororesins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), a polyimide (PI), an acrylic resin, and a polyolefinic resin. When the positive electrode mixture slurry is prepared in an aqueous solvent, styrene-butadiene rubber (SBR), nitrile rubber (NBR), CMC or a salt thereof, polyacrylic acid or a salt thereof, polyvinyl alcohol, and the like may be used. The binder is preferably a rubber resin having a repeating molecular structure of double bonds and single bonds, such as SBR and NBR, from a viewpoint of flexibility of the positive electrode <NUM>. These materials may be used singly, or may be used in combination of two or more thereof. A content of the binder in the positive electrode mixture layer <NUM> is <NUM> mass% to <NUM> mass%, and preferably <NUM> mass% to <NUM> mass%.

On the positive electrode <NUM>, the positive electrode current collector exposed part <NUM> in which a surface of the positive electrode current collector <NUM> is exposed is provided. The positive electrode current collector exposed part <NUM> is a portion to which the positive electrode lead <NUM> is connected and a portion in which a surface of the positive electrode current collector <NUM> is uncovered with the positive electrode mixture layer <NUM>. The positive electrode current collector exposed part <NUM> is formed to be wider in the longitudinal direction than the positive electrode lead <NUM>. The positive electrode current collector exposed part <NUM> is preferably provided on both surfaces of the positive electrode <NUM> to be stacked in the thickness direction of the positive electrode <NUM>. The positive electrode lead <NUM> is joined to the positive electrode current collector exposed part <NUM> with, for example, ultrasonic welding.

In the example illustrated in <FIG>, the positive electrode current collector exposed part <NUM> is provided on the central part in the longitudinal direction of the positive electrode <NUM> and over an entire length in the width direction. The positive electrode current collector exposed part <NUM> may be formed on the initial end part or terminal end part of the positive electrode <NUM>, and is preferably provided at a position of substantially same distance from the initial end part and the terminal end part from a viewpoint of current collectability. The positive electrode lead <NUM> connected to the positive electrode current collector exposed part <NUM> provided at such a position allows the positive electrode lead <NUM> to be disposed to project upward from the end surface in the width direction at a medial position in the radial direction of the electrode assembly <NUM> when wounded as the electrode assembly <NUM>. The positive electrode current collector exposed part <NUM> is provided by, for example, intermittent application in which the positive electrode mixture slurry is not applied on a part of the positive electrode current collector <NUM>.

<FIG> is a front view of the negative electrode <NUM> constituting the electrode assembly <NUM> illustrated with an unwound state. <FIG> is a longitudinal sectional view of the negative electrode <NUM> constituting the electrode assembly <NUM> illustrated with an unwound state.

In the electrode assembly <NUM>, the negative electrode <NUM> is formed to be larger than the positive electrode <NUM> to prevent precipitation of lithium on the negative electrode <NUM>. In specific, a length in the width direction (axial direction) of the negative electrode <NUM> is larger than a length in the width direction of the positive electrode <NUM>. In addition, a length in the longitudinal direction of the negative electrode <NUM> is larger than a length in the longitudinal direction of the positive electrode <NUM>. As a result, at least a portion on which the positive electrode mixture layer <NUM> of the positive electrode <NUM> is formed is disposed opposite to a portion on which a negative electrode mixture layer <NUM> of the negative electrode <NUM> is formed with the separator <NUM> interposed therebetween when wound as the electrode assembly <NUM>.

As illustrated in <FIG>, the negative electrode <NUM> has the band-shaped negative electrode current collector <NUM> and the negative electrode mixture layer <NUM> formed on both surfaces of the negative electrode current collector <NUM>. For the negative electrode current collector <NUM>, a foil of a metal such as copper, a film in which such a metal is disposed on a surface layer thereof, or the like is used, for example. A thickness of the negative electrode current collector <NUM> is, for example, <NUM> to <NUM>.

The negative electrode mixture layer <NUM> is preferably formed on an entire region of both the surfaces of the negative electrode current collector <NUM> except for a negative electrode current collector exposed part <NUM> and a one-surface coated portion <NUM>, described later. The negative electrode mixture layer <NUM> preferably includes a negative electrode active material and a binder. The negative electrode mixture layer <NUM> is formed by applying a negative electrode mixture slurry including the negative electrode active material, the binder, and a solvent such as water on both the surfaces of the negative electrode current collector <NUM> to be dried (negative electrode mixture layer forming step). Then, the negative electrode mixture layer <NUM> is compressed.

In the examples illustrated in <FIG>, the negative electrode current collector exposed part <NUM> is provided on the initial end part in the longitudinal direction of the negative electrode <NUM> and over an entire length in the width direction of the current collector. The negative electrode current collector exposed part <NUM> is a portion to which the negative electrode lead <NUM> is connected and a portion in which a surface of the negative electrode current collector <NUM> is uncovered with the negative electrode mixture layer <NUM>. The negative electrode current collector exposed part <NUM> is formed to be wider in the longitudinal direction than a width of the negative electrode lead <NUM>. The negative electrode current collector exposed part <NUM> is preferably provided on both surfaces of the negative electrode <NUM> to be stacked in the thickness direction of the negative electrode <NUM>.

In the present embodiment, the negative electrode lead <NUM> is joined to a surface on the inner peripheral side of the negative electrode current collector <NUM> with, for example, ultrasonic welding. One end part of the negative electrode lead <NUM> is disposed on the negative electrode current collector exposed part <NUM>, and the other end part extends downward from the lower end of the negative electrode current collector exposed part <NUM>. The negative electrode current collector exposed part <NUM> is provided by, for example, intermittent application in which the negative electrode mixture slurry is not applied on a part of the negative electrode current collector <NUM>.

On a terminal end part of the negative electrode <NUM> disposed on the outermost circumference side of the electrode assembly <NUM>, a one-surface coated portion <NUM> in which the negative electrode mixture layer <NUM> is formed only on one surface of the inner circumference side of the negative electrode current collector <NUM> is provided, and the negative electrode current collector <NUM> is exposed on a surface of the outer circumference side of the one-surface coated portion <NUM>. In the negative electrode mixture layer <NUM> (42B) in the one-surface coated portion <NUM>, a charge expansion coefficient is set to be larger than that in the negative electrode mixture layer <NUM> (42A) in the both-surface coated portion.

The negative electrode current collector <NUM> exposed in the one-surface coated portion <NUM> is contacted with the inner face of the outer housing can <NUM> (see <FIG>), and separately to the negative electrode lead <NUM>, the negative electrode <NUM> and the outer housing can <NUM> are electrically connected. The negative electrode current collector exposed part <NUM> and the one-surface coated portion <NUM> are preferably provided by, for example, intermittent application in which the negative electrode mixture slurry is not applied on a part of the negative electrode current collector <NUM>.

The negative electrode active material is not particularly limited as long as it may reversibly occlude and release lithium (Li) ions, and for example, carbon materials such as natural graphite and artificial graphite, metals that form an alloy with lithium such as silicon (Si) and tin (Sn), or an alloy or oxide including them may be used.

Examples of the binder included in the negative electrode mixture layer <NUM> include fluororesins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), a polyimide (PI), an acrylic resin, and a polyolefinic resin. When the negative electrode mixture slurry is prepared in an aqueous solvent, styrene-butadiene rubber (SBR), nitrile rubber (NBR), CMC or a salt thereof, polyacrylic acid or a salt thereof, polyvinyl alcohol, and the like may be used. The binder is preferably a rubber resin having a repeating molecular structure of double bonds and single bonds, such as SBR and NBR, from a viewpoint of flexibility of the negative electrode <NUM>. These materials may be used singly, or may be used in combination of two or more thereof. A content of the binder in the negative electrode mixture layer <NUM> is <NUM> mass% to <NUM> mass%, and preferably <NUM> mass% to <NUM> mass%.

<FIG> is a radial sectional view (a cross section viewed from the axial direction) of proximity of the outermost circumference of the negative electrode <NUM> (the positive electrode <NUM> and the separator <NUM> are omitted). As illustrated in <FIG>, the negative electrode mixture layer <NUM> is absent on the outer circumference side of the negative electrode <NUM>, which is of the outermost circumference, and the negative electrode current collector <NUM> is exposed.

<FIG> is a radial sectional view (a cross section viewed from the axial direction) of a part of proximity of the outermost circumference of the electrode assembly <NUM>. As illustrated, the negative electrode <NUM> is positioned inside the outer housing can <NUM>, the negative electrode current collector <NUM> is exposed on the outer circumference side of the negative electrode <NUM>, and this exposed surface of the negative electrode current collector <NUM> is contacted with the inner face of the outer housing can <NUM>. On the inner circumference side of the negative electrode <NUM>, the positive electrode <NUM> in which the positive electrode mixture layer <NUM> is formed on both the side of the positive electrode current collector <NUM> is positioned with the separator <NUM> interposed therebetween. On the inner circumference side of the positive electrode <NUM>, the negative electrode <NUM> is positioned with the separator <NUM> interposed therebetween.

The negative electrode mixture layer <NUM> (42B) in the one-surface coated portion <NUM> positioned on the outermost circumference of the electrode assembly <NUM> has a property different from the negative electrode mixture layer <NUM> (42A) in the both-surface coated portion on the inner circumference side. That is, in the negative electrode <NUM> of the non-aqueous electrolyte secondary battery of the present embodiment, the negative electrode mixture layer 42B in the one-surface coated portion <NUM> has a larger charge expansion coefficient than the negative electrode mixture layer 42A in the both-surface coated portion.

In the present embodiment, the charge expansion coefficient of the negative electrode mixture layer <NUM> (42B) in the one-surface coated portion <NUM> is set to be larger, and examples of the techniques therefor are as follows.

Examples of the negative electrode active material having a large charge expansion coefficient include a silicon material including Si and a tin material including Sn. The silicon material and the tin material are not essential, but the negative electrode mixture layer <NUM> (42B) preferably includes the silicon material in the present embodiment. Examples of the silicon material include Si, an oxide of Si, and lithium silicate. As the oxide of Si, a composite in which Si particles are dispersed in a SiO<NUM> phase may be used, for example. The silicon material is preferably used with the carbon material.

Increasing the charge expansion coefficient of the negative electrode mixture layer <NUM> (42B) in the one-surface coated portion <NUM> may allow the exposed surface of the negative electrode current collector <NUM> on the outermost circumference and the inner face of the outer housing can <NUM> to be certainly contacted with each other during charge to achieve good current collectability without excessively narrowing the clearance between the electrode assembly <NUM> and the inner face of the outer housing can <NUM> during the insertion into outer housing can <NUM>. Although the negative electrode mixture layer <NUM> contracts with discharge, initial expansion is large compared with contract thereafter. Therefore, an initial charge after the insertion of the electrode assembly <NUM> may allow the negative electrode current collector <NUM> on the outermost circumference to be contacted with the inner face of the outer housing can, and may maintain the good electrical contact with charge and discharge also thereafter.

In the present embodiment, the entire one-surface coated portion <NUM> is disposed on the outermost circumference of the electrode assembly <NUM>, but the range where the one-surface coated portion <NUM> is disposed does not necessarily coincide with the outermost circumference of the electrode assembly <NUM>. As long as at least a part of the one-surface coated portion <NUM> is disposed on the outermost circumference of the electrode assembly <NUM>, at least a part of the exposed surface of the negative electrode current collector <NUM> may be sufficiently contacted with the inner face of the outer housing can. For example, the one-surface coated portion <NUM> is preferably disposed within a range of <NUM>% or more of a circumference length of the outermost circumference of the electrode assembly <NUM>. A part of the one-surface coated portion <NUM> may be disposed so as to extend toward the initial winding side from the outermost circumference of the electrode assembly <NUM>. In this case, as illustrated in <FIG>, the inner circumference side of the positive electrode mixture layer <NUM> is required to be opposite to the outer circumference side of the negative electrode mixture layer <NUM> with the separator <NUM> interposed therebetween, and thereby the one-surface coated portion <NUM> is formed from the terminal end part of the negative electrode <NUM> within a range not to exceed a position opposite to the terminal end of the inner face side of the positive electrode mixture layer <NUM>. Accordingly, the range where the negative electrode mixture layer <NUM> (42B) in the one-surface coated portion <NUM> is opposed to the positive electrode mixture layer <NUM> is limited to one round or less, and thereby deterioration due to peeling between the active material and the current collector and due to isolation of the active material may be inhibited even with the increased charge expansion coefficient of the negative electrode mixture layer <NUM> (42B) in the one-surface coated portion <NUM>.

This configuration may inhibit the failure during the insertion of the electrode assembly <NUM> into the outer housing can <NUM> and deterioration due to the charge-discharge cycles, and may allow the exposed surface of the negative electrode current collector <NUM> and the inner face of the outer housing can <NUM> to be certainly contacted with each other to achieve the good current collectability.

Hereinafter, the present disclosure will be further described with Examples, but the present disclosure is not limited to these Examples.

Graphite and an oxide of Si were used as negative electrode active materials. Mixing of <NUM> parts by mass of graphite, <NUM> parts by mass of the oxide of Si having an average particle diameter of <NUM>, <NUM> part by mass of carboxymethylcellulose (CMC), and <NUM> part by mass of styrene-butadiene rubber (SBR), with water was performed to produce a negative electrode slurry <NUM>. That is, a content of the binder (CMC and SBR) to the negative electrode active material in the negative electrode slurry <NUM> was <NUM> mass%. The Si proportion and Si particle diameter in the present disclosure mean a proportion and an average particle diameter in the negative electrode active material of the oxide of Si, respectively, and the average particle diameter is a median diameter (D50) on a volumetric basis.

Mixing of <NUM> parts by mass of graphite, <NUM> parts by mass of an oxide of Si having an average particle diameter of <NUM>, <NUM> part by mass of carboxymethylcellulose (CMC), and <NUM> part by mass of styrene-butadiene rubber (SBR), with water was performed to produce a negative electrode slurry <NUM>.

The oxide of Si in the negative electrode slurry <NUM> was replaced with one having an average particle diameter of <NUM>.

The amount of styrene-butadiene rubber (SBR) added in the negative electrode slurry <NUM> was changed to <NUM> parts by mass. That is, a content of the binder (CMC and SBR) to the negative electrode active material in the negative electrode slurry <NUM> was <NUM> mass%.

On a copper foil, two types of the negative electrode slurry for a both-surface coated portion and for a one-surface coated portion were applied by using a multilayer die coater with changing the negative electrode slurry depending on a portion to be coated. That is, the negative electrode slurry for the both-surface coated portion was applied on a part to be for the both-surface coated portion, and the negative electrode slurry for the one-surface coated portion was applied on a part to be for one-surface coated portion. Thereafter, the applied film was dried, the dried applied film was rolled, and then cut to a predetermined electrode plate size to produce a negative electrode.

In an N-methylpyrrolidone (NMP) solvent, LiNi<NUM>Co<NUM>Al<NUM>O<NUM> as a positive electrode active material, acetylene black, which is a carbon conductive agent, and polyvinylidene fluoride (PVDF) having an average molecular weight of <NUM> million were mixed at a mass ratio of <NUM>:<NUM>:<NUM> by using a mixer to prepare a positive electrode mixture slurry with a solid content of <NUM>%. The prepared slurry was applied on both surfaces of an aluminum foil, dried, rolled, and then cut to a predetermined electrode plate size to produce a positive electrode plate.

Into <NUM> parts by mass of a mixed solvent of ethylene carbonate (EC) and dimethyl carbonate (DMC) (EC:DMC = <NUM>:<NUM> at a volume ratio), <NUM> parts by mass of vinylene carbonate (VC) was added, and LiPF<NUM> as a lithium salt was dissolved at <NUM> mole/litter to prepare an electrolyte liquid as a non-aqueous electrolyte.

Lead terminals were attached to each of the above positive electrode and the above negative electrode, and the electrodes were wound with a separator interposed therebetween to produce an electrode assembly. In this time, the one-surface coated portion of the negative electrode was disposed on the outermost circumference of the electrode assembly. The wound product was inserted into an outer housing can, which is a battery container, and the negative electrode lead was welded with a bottom of the container. Then, the positive electrode lead was ultrasonic-welded with a sealing assembly, the above electrolyte liquid was injected, and the sealing assembly was calked to seal the battery. A rated capacity of the produced battery is <NUM> mAh.

The battery was charged at a constant current of <NUM> It until <NUM> V. The battery was further charged at a constant voltage of <NUM> V until a current reached <NUM> It. Then, the battery was discharged at a constant current of <NUM> It until a voltage reached <NUM> V to measure a discharge capacity.

A charging depth of the battery (State of Charge: SOC) was adjusted to <NUM>% from the above result of the discharge capacity, and then the battery was discharged at a current of <NUM> It for <NUM> seconds to measure a change in voltage ΔV at a time after the <NUM> seconds. From the change in voltage ΔV and the current value in the discharge, a direct-current resistance (DCR) was determined with the following formula. It is to be noted that It (A) = Rated Capacity (Ah) / <NUM> (h).

Charge and discharge under the same condition as in the above measurement method of the discharge capacity were performed with <NUM> cycles to calculate a capacity maintenance rate with the following formula.

The slurry <NUM> was used as the slurry for the both-surface coated portion, and the slurry <NUM> was used as the slurry for the one-surface coated portion.

The slurry <NUM> was used as the slurry for the both-surface coated portion and as the slurry for the one-surface coated portion.

Table <NUM> shows the DCR and capacity maintenance rate with changing the content proportions of the silicon material (Si proportions) in the negative electrode mixture layer 42A in the both-surface coated portion disposed on the inner circumference side of the outermost circumference and in the negative electrode mixture layer 42B in the one-surface coated portion <NUM> disposed on the outermost circumference.

In Example <NUM>, the DCR is largely reduced compared with Comparative Example <NUM>. As above, increasing the Si proportion of the one-surface coated portion <NUM> disposed on the outermost circumference reduces the DCR. Example <NUM> exhibits the capacity maintenance rate similar to that in Comparative Example <NUM>, but in Comparative Example <NUM>, the capacity maintenance rate is lowered compared with Comparative Example <NUM>, although the DCR is largely reduced. That is, setting the Si proportion of the one-surface coated portion <NUM> to be larger than that of the both-surface coated portion can inhibit lowering of the capacity maintenance rate and can reduce the DCR.

Table <NUM> shows the DCR and capacity maintenance rate with changing the average particle diameters of the silicon material (Si particle diameters) in the negative electrode mixture layer 42A in the both-surface coated portion disposed on the inner circumference side of the outermost circumference and in the negative electrode mixture layer 42B in the one-surface coated portion <NUM> disposed on the outermost circumference.

In Example <NUM>, the DCR is largely reduced compared with Comparative Example <NUM>. As above, increasing the Si particle diameter of the one-surface coated portion <NUM> disposed on the outermost circumference reduces the DCR. Example <NUM> exhibits the capacity maintenance rate similar to that in Comparative Example <NUM>, but in Comparative Example <NUM>, the capacity maintenance rate is lowered compared with Comparative Example <NUM>, although the DCR is largely reduced. That is, setting the Si particle diameter of the one-surface coated portion <NUM> to be larger than that of the both-surface coated portion can inhibit lowering of the capacity maintenance rate and can reduce the DCR.

Table <NUM> shows the DCR and capacity maintenance rate with changing the contents of the binder in the negative electrode mixture layer 42A in the both-surface coated portion disposed on the inner circumference side of the outermost circumference and in the negative electrode mixture layer 42B disposed on the outermost circumference.

In Example <NUM>, the DCR is largely reduced compared with Comparative Example <NUM>. As above, increasing the content of the binder in the one-surface coated portion <NUM> disposed on the outermost circumference reduces the DCR. Example <NUM> exhibits the capacity maintenance rate similar to that in Comparative Example <NUM>, but in Comparative Example <NUM>, the capacity maintenance rate is largely lowered compared with Comparative Example <NUM>, although the DCR is largely reduced. That is, setting the content of the binder in the one-surface coated portion <NUM> to be larger than that of the both-surface coated portion can inhibit lowering of the capacity maintenance rate and can reduce the DCR.

From the above, it is found that lowering of the capacity maintenance rate can be inhibited and the DCR can be reduced when the charge expansion coefficient of the negative electrode mixture layer <NUM> (42B) in the one-surface coated portion <NUM> disposed on the outermost circumference is set to be larger than that in the both-surface coated portion disposed on the inner circumference side of the outermost circumference.

Claim 1:
A non-aqueous electrolyte secondary battery (<NUM>), comprising:
a wound electrode assembly (<NUM>) in which a band-shaped positive electrode (<NUM>) and a band-shaped negative electrode (<NUM>) are wound with a separator (<NUM>) interposed therebetween; and
an outer housing can (<NUM>) that houses the electrode assembly (<NUM>), wherein
the positive electrode (<NUM>) has a positive electrode mixture layer (<NUM>) formed on a surface of a sheet-shaped positive electrode current collector (<NUM>),
the negative electrode (<NUM>) has a negative electrode mixture layer (<NUM>) formed on a surface of a sheet-shaped negative electrode current collector (<NUM>),
the negative electrode mixture layer (<NUM>) includes a chargeable and dischargeable negative electrode active material and a binder,
the negative electrode (<NUM>) includes a both-surface coated portion in which the negative electrode mixture layer (<NUM>, 42A) is formed on both surfaces of the negative electrode current collector (<NUM>) and a one-surface coated portion (<NUM>) in which the negative electrode mixture layer (<NUM>, 42B) is formed on one surface of the negative electrode current collector (<NUM>),
at least a part of the one-surface coated portion (<NUM>) is disposed on an outermost circumference of the electrode assembly (<NUM>),
at least a part of an exposed surface of the negative electrode current collector (<NUM>) in the one-surface coated portion is contacted (<NUM>) with an inner face of the outer housing can (<NUM>), and
a charge expansion coefficient of the negative electrode mixture layer (<NUM>, 42B) in the one-surface coated portion (<NUM>) is larger than a charge expansion coefficient of the negative electrode mixture layer (<NUM>, 42A) in the both-surface coated portion.