JP2018152194A - Secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a secondary battery which enables the enhancement of cycle characteristics and the increase in energy density while preventing a short circuit between electrodes.SOLUTION: A secondary battery comprises, as each electrode of positive and negative electrodes, an electrode 110 including a current collector 111 with an edge part, an active material-containing layer 112 supported on at least one face of the current collector 111 and a tab 113 extending from the edge part of the current collector 111, provided that the active material-containing layer 112 includes an end portion supported by the edge part of the current collector 111. The secondary battery further comprises at least one of an organic fiber layer bonded to at least one principal face of the active material layer of the positive or negative electrode, and an inorganic film 3 bonded to at least one principal face of the active material layer of the positive or negative electrode; and a separator 4 covering the organic fiber layer or inorganic film 3, or part of the active material layer 112.SELECTED DRAWING: Figure 1

Description

  Embodiments described herein relate generally to a secondary battery.

In a secondary battery such as a lithium secondary battery, a porous separator is used in order to avoid contact between the positive electrode and the negative electrode. Usually, the separator is prepared as a self-supporting film separate from the positive electrode and the negative electrode. For example, a separator is sandwiched between a positive electrode and a negative electrode to form a unit structure (electrode cell), which is wound or laminated to form a battery group.

A general separator includes a microporous membrane made of polyolefin resin film. Such a separator is manufactured, for example, by extruding a melt containing a polyolefin resin composition into a sheet, extracting and removing substances other than the polyolefin resin, and then stretching the sheet.

Since the separator made of a resin film needs to have mechanical strength so as not to be broken at the time of producing a battery, it is difficult to make it thinner to some extent. Therefore, particularly in a battery of a type in which a large number of electrode cells are stacked or wound, the amount of unit electrode cells that can be stored per unit volume of the battery is limited by the thickness of the separator. This leads to a decrease in battery capacity. In addition, the separator made of a resin film has poor durability, and when used for a secondary battery, there is a disadvantage that the separator deteriorates during repeated charging and discharging and the cycle performance of the battery is lowered.

JP 2010-182922 A

The problem to be solved by the present invention is to provide a secondary battery that can improve energy density while improving cycle characteristics while preventing short circuit between electrodes.

In order to solve the above problems, the secondary battery of the present embodiment includes a current collector having an edge, an active material-containing layer supported on at least one surface of the current collector, and the current collector. A secondary battery comprising a tab extending from an edge, wherein the active material-containing layer includes an electrode including an end carried on the edge of the current collector as a positive electrode and a negative electrode, At least one of an organic fiber layer bonded to at least a main surface of the active material layer of the positive electrode or the negative electrode or an inorganic film bonded to at least a main surface of the active material layer of the positive electrode or the negative electrode; And a separator that covers a part of the layer or the inorganic film or the active material layer.

FIG. 1 is a schematic diagram illustrating electrodes included in the secondary battery according to the embodiment. FIG. 2 is a schematic diagram illustrating electrodes included in the secondary battery according to the embodiment. FIG. 3 is a schematic exploded perspective view of the secondary battery according to the embodiment. FIG. 4 is a schematic diagram illustrating electrodes included in the secondary battery according to the embodiment. FIG. 5 is a schematic diagram illustrating electrodes included in the secondary battery according to the embodiment. FIG. 6 is a schematic diagram illustrating an example method for forming a layer of organic fibers according to an embodiment. FIG. 7 is a table showing the results of the examples.

(First embodiment)
Hereinafter, embodiments will be described with reference to the drawings.

According to the embodiment, a secondary battery is provided. This secondary battery includes an electrode, an inorganic film, and a separator. The electrode includes a current collector, an active material-containing layer, and a tab.
The current collector has an edge. The active material-containing layer is supported on at least one surface of the current collector. The tab extends from the edge of the current collector. The tab has a first surface and a second surface.

In the secondary battery according to the embodiment, the current collector may have a plurality of edges, and a tab may extend from one of them. The current collector can also carry an active material-containing layer on both sides thereof. The electrode can also include an end surface that includes one edge of the current collector that is different from the edge from which the tab extends. The tab is more preferably formed of at least one conductive material selected from the group consisting of aluminum, an aluminum alloy, and copper.

  Hereinafter, the secondary battery according to the embodiment will be described in more detail.

The secondary battery according to the embodiment can be, for example, a nonaqueous electrolyte secondary battery. Alternatively, the secondary battery according to the embodiment may be a secondary battery using an aqueous solution as an electrolyte.

The secondary battery which concerns on embodiment can also comprise the additional electrodes other than the electrode demonstrated previously.

The secondary battery according to the embodiment typically includes one or more negative electrodes and one or more positive electrodes. The electrode described above is preferably a negative electrode.

The negative electrode can include a negative electrode current collector, a negative electrode active material-containing layer carried on at least one surface of the negative electrode current collector, and a negative electrode current collector tab extending from the negative electrode current collector. The negative electrode current collector and the negative electrode current collector tab may be integrated or separate.

As the negative electrode current collector, for example, a metal foil such as aluminum or copper can be used. As the material of the negative electrode current collector tab, the same material as that of the negative electrode current collector can be used.

The negative electrode active material-containing layer can include a negative electrode active material, an optional negative electrode conductive agent, and an optional negative electrode binder.

When the electrode described above is a negative electrode, the negative electrode active material-containing layer preferably contains a material that charges and discharges at a potential of 1.0 V vs. Li / Li + or more, and more preferably contains lithium titanate. Is preferred.

Lithium titanate can act as a negative electrode active material. Examples of lithium titanate include Li _{4 + x} Ti ₅ O ₁₂ (0 ≦ x ≦ 3) having a spinel structure and Li _{2 + y} Ti ₃ O ₇ (0 ≦ y ≦ 3) having a ramsteride structure. Can be mentioned.

Such lithium titanate can occlude and release lithium ions at a potential of, for example, 1.55 V (vs. Li / Li +) or higher, so the surface of the negative electrode active material-containing layer containing lithium titanate In principle, lithium dendrite is not deposited even after repeated charge and discharge. Moreover, lithium titanate has almost no volume change accompanying charging / discharging reaction. Thanks to these, the inorganic film and separator to be bonded to the surface of the negative electrode active material-containing layer of the negative electrode can be thinned, and as a result, a higher energy density can be achieved.

Moreover, it is preferable that the lithium titanate has an average primary particle diameter in the range of 0.01 to 3 μm. Such a negative electrode active material-containing layer containing lithium titanate can exhibit high flatness on the surface and high adhesion to the organic fiber layer. Thanks to that,
Peeling of the organic fiber layer from the surface of the negative electrode active material-containing layer can be prevented.

Examples of other active materials that can be included in the negative electrode active material-containing layer include carbonaceous materials such as graphite, tin-silicon alloy materials, and the like.

The particle shape of the negative electrode active material may be any of granular, fibrous, and acicular. In the case of a fiber, the fiber diameter is preferably 0.1 μm or less.

Examples of the negative electrode conductive agent include acetylene black, carbon black, and graphite. Examples of the binder for binding the negative electrode active material and the negative electrode conductive agent include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluorine-based rubber, styrene butadiene rubber, and the like.

The positive electrode can include a positive electrode current collector, a positive electrode active material-containing layer supported on at least one surface of the positive electrode current collector, and a positive electrode current collector tab extending from the positive electrode current collector. The positive electrode current collector and the positive electrode current collector tab may be integrated or separate.

As the positive electrode current collector, for example, a metal foil such as aluminum or copper can be used. As a material for the positive electrode current collector tab, the same material as that for the positive electrode current collector can be used.

The positive electrode active material-containing layer can contain a positive electrode active material, an optional positive electrode conductive agent, and an optional positive electrode binder.

As the positive electrode active material, for example, a general lithium transition metal composite oxide can be used. For _{example, LiCoO 2, LiNi1-xCoxO 2} (0 <x <0.3), LiMnxNiy
CozO ₂ (0 <x <0.5, 0 <y ≦ 0.8, 0 ≦ z <0.5), LiMn ₂ -xMxO ₄ (
M is Li, Mg, Co, Al, Ni, 0 <x <0.2), LiMPO ₄ (M is Fe, Co
, At least one element selected from Ni and Mn).

Examples of the positive electrode conductive agent include carbonaceous materials such as acetylene black, carbon black, and graphite. As the binder, for example, polytetrafluoroethylene (PT
FE), polyvinylidene fluoride (PVdF), and fluorine-based rubber.

The inorganic material included in the inorganic film can include, for example, at least one selected from the group consisting of alumina, titanium, silica, mica, zirconium silicate, barium sulfate, barium oxide, calcium silicate, and zeolite.

The inorganic film is preferably made of an inorganic material having an average particle diameter of 2 μm or less. Moreover, it is preferable that the film thickness of an inorganic film is 20 micrometers or less.

The separator is, for example, polyethylene, polypropylene, polyethylene terephthalate,
At least one selected from the group consisting of cellulose can be included.

The electrode described above can form an electrode group together with the opposite electrode. The structure of the electrode group that the secondary battery according to the embodiment can have is not particularly limited. For example, the electrode group can have a wound structure. The wound structure is a structure in which a laminate obtained by laminating a positive electrode and a negative electrode is wound in a spiral shape so that the positive electrode active material-containing layer and the negative electrode active material-containing layer are spaced apart from each other.
An example of the secondary battery according to the embodiment including the electrode group having the wound structure will be described later.

The secondary battery according to the embodiment may further include an electrolyte. The electrolyte may be impregnated in the electrode group.

In the case of a nonaqueous electrolyte battery, a nonaqueous electrolyte is used as the electrolyte. Examples of the non-aqueous electrolyte include a liquid non-aqueous electrolyte prepared by dissolving an electrolyte in an organic solvent, and a gel non-aqueous electrolyte obtained by combining a liquid electrolyte and a polymer material. The liquid non-aqueous electrolyte can be prepared, for example, by dissolving the electrolyte in an organic solvent at a concentration of 0.5 mol / l or more and 2.5 mol / l or less.
Examples of the electrolyte include lithium perchlorate (LiClO ₄ ), lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), and lithium arsenic hexafluoride (Li
AsF ₆ ), lithium trifluorometasulfonate (LiCF ₃ SO ₃ ), lithium salts such as bistrifluoromethylsulfonylimitolithium [LiN (CF ₃ SO ₂ ) ₂ ], or a mixture thereof can be given. It is preferable that it is difficult to oxidize even at high potential, and LiPF ₆ is most preferable.

Examples of the organic solvent include cyclic carbonates such as propylene carbonate (PC), ethylene carbonate (EC), and vinylene carbonate, and diethyl carbonate (DE).
C), chain carbonates such as dimethyl carbonate (DMC), methyl ethyl carbonate (MEC), tetrahydrofuran (THF), 2-methyltetrahydrofuran (2Me
THF), dioxolane (DOX) and other cyclic ethers, dimethoxyethane (DME),
Examples include chain ethers such as dietoethane (DEE), γ-butyrolactone (GBL), acetonitrile (AN), and sulfolane (SL). These organic solvents may be used alone or as a mixture of two or more.

Examples of the polymer material include polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyethylene oxide (PEO), and the like.

As the nonaqueous electrolyte, a room temperature molten salt (ionic melt) containing lithium ions, a polymer solid electrolyte, an inorganic solid electrolyte, or the like may be used.

The secondary battery according to the embodiment may further include a battery container that houses the electrode group and the electrolyte.

As a battery container, the metal can formed from aluminum, aluminum alloy, iron, stainless steel etc. can be used, for example. The plate thickness of the battery container is preferably 1.0 mm or less, and more preferably 0.7 mm or less.

Alternatively, as the battery container, a container formed from a laminate film can be used instead of the metal can. As the laminate film, it is preferable to use a multilayer film composed of a metal foil and a resin film covering the metal foil. Polypropylene (PP), polyethylene (PE), nylon, polyethylene terephthalate (PET) as resin
) And the like can be used. The thickness of the laminate film is desirably 0.2 mm or less.

Various shapes such as a square shape, a cylindrical shape, a thin shape, and a coin shape can be adopted as the shape of the battery container depending on the application.

In addition, the secondary battery according to the embodiment may further include a lead electrically connected to the electrode group. For example, the secondary battery according to the embodiment may include two leads. One lead can be electrically connected to the negative electrode current collecting tab. The other lead can be electrically connected to the positive current collecting tab.

The lead material is not particularly limited, and for example, the same material as the positive electrode current collector and the negative electrode current collector can be used.

The secondary battery according to the embodiment may further include a terminal electrically connected to the lead and drawn out from the battery container. For example, the secondary battery according to the embodiment can include two terminals. One terminal can be connected to a lead electrically connected to the negative current collector tab. The other terminal can be connected to a lead electrically connected to the positive current collecting tab.

Although the material of a terminal is not specifically limited, For example, the same material as a positive electrode collector and a negative electrode collector can be used.

Next, an example of the positional relationship among the electrode, the inorganic film 3, and the separator 4 included in the secondary battery according to the embodiment will be described in detail with reference to FIG.

FIG. 1 is a schematic cross-sectional view showing an example of the positional relationship among the electrode, the inorganic film 3 and the separator 4 included in the secondary battery according to the embodiment. These positional relationships shown here indicate a part of the structure of the electrode group 200.

An electrode group 200 shown in FIG. 1 includes an electrode pair 100 and an inorganic film 3 bonded to the surface of the electrode pair 100.
And a separator 4.

The electrode pair 100 includes a first electrode 110 shown in the lower part of FIG. 1 and a second electrode 120 shown in the upper part of FIG.

The first electrode 110 illustrated in FIG. 1 is a negative electrode. The negative electrode 110 includes a negative electrode current collector 111, a negative electrode active material-containing layer 112, and a negative electrode current collector tab 113.

The negative electrode current collecting tab 113 has a first surface 113a and a second surface 113b. The negative electrode current collector 111 and the negative electrode current collector tab 113 are integrated, and a negative electrode active material containing layer 112 is supported on both surfaces of the negative electrode current collector 111.

The second electrode 120 shown in FIG. 1 is a positive electrode. As shown in FIG. 1, the positive electrode 120 includes a positive electrode current collector 121, a positive electrode active material-containing layer 122, and a positive electrode current collector tab 123.

The positive electrode current collecting tab 123 has a first surface 123a and a second surface 123b. The positive electrode current collector 121 and the positive electrode current collector tab 123 are integrated, and a positive electrode active material-containing layer 122 is supported on both surfaces of the positive electrode current collector 121.

In the electrode pair 100 shown in FIG. 1, the negative electrode 110 and the positive electrode 120 have one negative electrode active material-containing layer 1.
12 and one positive electrode active material-containing layer 122 are opposed to each other, and a positive electrode current collecting tab 123 is arranged so as to extend in a direction opposite to the negative electrode current collecting tab 113.

As shown in FIG. 1, the inorganic film 3 is bonded to at least one main surface of the negative electrode-containing layer 122 in the negative electrode active material-containing layer 112 of the negative electrode 110. The inorganic film 3 is bonded to at least one main surface of the positive electrode-containing layer 122 in the positive electrode 120.

As shown in FIG. 1, the separator 4 covers the inorganic film 3 of the negative electrode 110. The separator 4 covers the inorganic film 3 of the positive electrode 120.

  The electrode group 200 has the structure shown in FIG. 2 in addition to the structure shown in FIG.

FIG. 2 is a schematic cross-sectional view illustrating an example of the positional relationship between the electrode and the inorganic film 3 included in the secondary battery according to the embodiment. These positional relationships shown here indicate a part of the structure of the electrode group 200.

An electrode group 200 shown in FIG. 2 includes an electrode pair 100 and an inorganic film 3 bonded to the surface of the electrode pair 100.
It has.

The electrode pair 100 includes a first electrode 110 shown in the lower part of FIG. 2 and a second electrode 120 shown in the upper part of FIG.

The first electrode 110 illustrated in FIG. 2 is a negative electrode. The negative electrode 110 includes a negative electrode current collector 111, a negative electrode active material-containing layer 112, and a negative electrode current collector tab 113.

The negative electrode current collecting tab 113 has a first surface 113a and a second surface 113b. The negative electrode current collector 111 and the negative electrode current collector tab 113 are integrated, and a negative electrode active material containing layer 112 is supported on both surfaces of the negative electrode current collector 111.

The second electrode 120 shown in FIG. 2 is a positive electrode. As shown in FIG. 2, the positive electrode 120 includes a positive electrode current collector 121, a positive electrode active material-containing layer 122, and a positive electrode current collector tab 123.

The positive electrode current collecting tab 123 has a first surface 123a and a second surface 123b. The positive electrode current collector 121 and the positive electrode current collector tab 123 are integrated, and a positive electrode active material-containing layer 122 is supported on both surfaces of the positive electrode current collector 121.

In the electrode pair 100 shown in FIG. 2, the negative electrode 110 and the positive electrode 120 have one negative electrode active material-containing layer 1.
12 and one positive electrode active material-containing layer 122 are opposed to each other, and a positive electrode current collecting tab 123 is arranged so as to extend in a direction opposite to the negative electrode current collecting tab 113.

As shown in FIG. 2, the inorganic film 3 is bonded to at least one main surface of the negative electrode-containing layer 122 in the negative electrode active material-containing layer 112 of the negative electrode 110. The inorganic film 3 is bonded to at least one main surface of the positive electrode-containing layer 122 in the positive electrode 120.

Here, as shown in FIG. 1, the area where the negative electrode 110 and the positive electrode 120 face each other through the separator is A, and as shown in FIG. 2, the area where the negative electrode 110 and the positive electrode 120 face each other without the separator as B. Then, it is preferable to satisfy the relationship of (Formula 1).
0.1 ≦ A / (A + B) ≦ 0.5 (Formula 1)

The effect of using a thin insulating layer on the electrode is expected more. When the value of Formula 1 is smaller than 0.1, the current during charging / discharging tends to concentrate on the inner peripheral portion, and the deterioration is accelerated. On the other hand, if the ratio is larger than 0.5, the number of secondary member separators in the battery increases, and the energy density decreases. Further, when the basis weight of the electrode active material-containing layer is Wg / m ² , the density is Dg / cc, and the total winding frequency of the separator is R, it is preferable to satisfy the relationship of (Formula 2).
0.015 ≦ RD / W ≦ 1.0 (Expression 2)

The effect of improving the cycle characteristics and the effect of improving the energy density and reducing the resistance are expected by using a thin insulating layer on the electrode.

In addition, the arrangement | positioning relationship of the separator 4 is not limited to a continuous arrangement | positioning, You may arrange | position intermittently.

The electrode group 200 preferably has the configuration as shown in FIG. 1 on the inner side in the wound stacking direction of the wound structure of the electrode group 200.

Next, an example method for forming the inorganic film 3 will be described. The inorganic film 3 described above can be easily formed in a state where it is bonded to the electrode described above, for example, by a coating apparatus such as a die coater or a gravure coater.

The inorganic film 3 can serve as a separator between the active material containing layer of the electrode and the active material containing layer of the opposite electrode.

Such an inorganic film can exhibit higher peel strength than the electrode. Further, such an inorganic film can prevent a short circuit between the electrodes via the end face of the electrode and a portion adjacent thereto.

Further, since the separator 4 is interposed between the electrodes, it can function as a buffer for expansion and contraction of the electrodes. Therefore, for example, distortion of the wound electrode group accompanying charge / discharge can be suppressed, and deterioration in cycle performance can be improved.

  Next, an example of the secondary battery according to the embodiment will be described with reference to the drawings.

  FIG. 3 is a schematic exploded perspective view of the secondary battery of the second example according to the embodiment.

As shown in FIG. 3, the secondary battery 1 of the first example includes an electrode group 200, a container 300, a negative electrode terminal 400, a positive electrode terminal 500, an inorganic film 3 not shown, a separator 4, And a water electrolyte. That is, the secondary battery 1 of the first example is a nonaqueous electrolyte battery.

As shown in FIG. 3, the electrode group 200 includes one negative electrode 110 and one positive electrode 120. The negative electrode 110 and the positive electrode 120 constitute the electrode group 200 described with reference to FIG.

As shown in FIG. 3, one negative electrode 110 and one positive electrode 120 are wound so that the positive electrode 120 has the outermost periphery in a stacked state. That is, the electrode group 200 shown in FIG.
It has a wound structure. In the wound electrode group 200, as shown in FIG. 3, the negative electrode current collecting tab 113 and the positive electrode current collecting tab 123 extend in opposite directions.

As shown in FIG. 3, the negative electrode current collector tab 113 is sandwiched between two negative electrode current collector plates 410.
Similarly, the positive electrode current collecting tab 123 is sandwiched between two positive electrode current collecting plates 510.

As shown in FIG. 3, the electrode group 200 is housed in a container 300 having an opening 310. Although the exploded view is shown in FIG. 3, the opening 310 is sealed with a sealing plate 320. The sealing plate 320 includes a negative electrode terminal 400 and a positive electrode terminal 500. Negative terminal 40
0 is electrically connected to the negative electrode current collector plate 410. Similarly, the positive electrode terminal 500 is electrically connected to the positive electrode current collector plate 500.

The secondary battery according to the embodiment may further include an electrolyte. The electrolyte may be impregnated in the electrode group.

The secondary battery according to the embodiment described above preferably has the structure shown in FIG. 1 on the inner side in the winding stacking direction of the winding structure of the electrode group 200, and the structure shown in FIG. Have.

That is, in the wound structure of the electrode group 200, the separator is preferably provided inside the wound stacking direction, so that the distance between the positive electrode and the negative electrode is increased. Thereby, in the wound structure of the electrode group 200, the electrical resistance of the inner part in the wound stacking direction increases, and the current easily flows to the outer part in the wound stacking direction. As a result, more heat is generated in the outer part than in the inner part, but the outer part is more likely to dissipate heat than the inner part.
The generated heat is easily released.

Therefore, deterioration of the battery due to heat generated by charging / discharging can be suppressed.

(Second embodiment)
In the second embodiment, there is a difference in the portion using the organic fiber layer 2 instead of the inorganic film 3. Accordingly, the same portions as those in the first embodiment are denoted by the same reference numerals, and detailed description thereof including the same effects as those in the first embodiment is omitted as appropriate.

According to the embodiment, a secondary battery is provided. The secondary battery includes an electrode, an organic fiber layer, and a separator. The electrode includes a current collector, an active material-containing layer, and a tab. The current collector has an edge. The active material-containing layer is supported on at least one surface of the current collector. The tab extends from the edge of the current collector. The tab has a first surface and a second surface.

FIG. 4 is a schematic cross-sectional view showing an example of a positional relationship among an electrode, an organic fiber layer, and a separator included in the secondary battery according to the second embodiment. These positional relationships shown here indicate that the electrode group 20
Some of the structures of 0 are shown.

As shown in FIG. 4, the organic fiber layer 2 is bonded to at least one main surface of the negative electrode-containing layer 122 in the negative electrode active material-containing layer 112 of the negative electrode 110. The organic fiber layer 2 is bonded to at least one main surface of the positive electrode-containing layer 122 in the positive electrode 120.

As shown in FIG. 4, the separator 4 covers the organic fiber layer 2 of the negative electrode 110. The separator 4 covers the organic fiber layer 2 of the positive electrode 120.

FIG. 5 is a schematic cross-sectional view showing an example of a positional relationship between an electrode and an organic fiber layer included in the secondary battery according to the second embodiment. These positional relationships shown here indicate a part of the structure of the electrode group 200.

As shown in FIG. 5, the organic fiber layer 2 is bonded to at least one main surface of the negative electrode-containing layer 122 in the negative electrode active material-containing layer 112 of the negative electrode 110. The organic fiber layer 2 is bonded to at least one main surface of the positive electrode-containing layer 122 in the positive electrode 120.

Here, as shown in FIG. 4, the area where the negative electrode 110 and the positive electrode 120 face each other through the separator is A, and as shown in FIG. 5, the area where the negative electrode 110 and the positive electrode 120 face each other without the separator as B. Then, it is preferable to satisfy the relationship of (Formula 1).
0.1 ≦ A / (A + B) ≦ 0.5 (Formula 1)

The effect of using a thin insulating layer on the electrode is expected more. Further, when the basis weight of the electrode active material-containing layer is Wg / m ² , the density is Dg / cc, and the total winding frequency of the separator is R, it is preferable to satisfy the relationship of (Formula 2).
0.015 ≦ RD / W ≦ 1.0 (Expression 2)

The effect of improving the cycle characteristics and the effect of improving the energy density and reducing the resistance are expected by using a thin insulating layer on the electrode.

In addition, the arrangement | positioning relationship of the separator 4 is not limited to a continuous arrangement | positioning, You may arrange | position intermittently.

The electrode group 200 preferably has the configuration as shown in FIG. 1 on the inner side in the wound stacking direction of the wound structure of the electrode group 200.

The organic fiber included in the organic fiber layer is, for example, at least selected from the group consisting of polyamide, polyolefin, polyether, polyimide, polyamideimide, polyketone, polysulfone, cellulose, polyvinyl alcohol (PVA), and polyvinylidene fluoride (PVdF). One can be included. Examples of polyolefin include polypropylene (
PP) and polyethylene (PE).

The organic fibers preferably have a thickness of 2 μm or less. An organic fiber layer containing such organic fibers can have sufficient strength, porosity, air permeability, pore diameter, electrolytic solution resistance, oxidation-reduction resistance, and the like, and can function as a good separator. . The thickness of the organic fiber is
Electron microscope (SEM) observation, scanning probe microscope (SPM), transmission electron microscope (TE
M), a scanning transmission electron microscope (STEM) or the like.

When the secondary battery according to the embodiment is a non-aqueous electrolyte secondary battery in which lithium ions are involved in charging and discharging, it is necessary to ensure ion permeability and electrolyte content, so that an organic fiber layer is formed. It is preferable that 30% or more of the total volume of the fibers is organic fibers having a thickness of 2 μm or less. More preferably, the volume of the organic fibers having a thickness of 2 μm or less occupies 80% or less of the total volume of the fibers forming the organic fiber layer. When the diameter of the organic fiber is 2 μm or less, the influence of hindering the movement of lithium ions can be reduced. These states are
This can be confirmed by SEM observation of the organic fiber layer.

  The organic fiber layer preferably has pores.

The porosity is preferably 50 to 90%, and more preferably 70% to 90%. When the secondary battery according to the embodiment is a battery in which lithium ions are involved in charging and discharging,
The organic fiber layer having such vacancies can reduce the influence of interfering with the movement of lithium ions, so that it can exhibit excellent lithium ion permeability and good electrolyte impregnation. Can show. The porosity of the pores in the organic fiber layer can be confirmed, for example, by mercury porosimetry, calculation from volume and density, SEM observation, and gas desorption method.

The length of the portion of the first surface of the tab where the organic fiber layers are bonded is preferably 1 mm or more and 5 mm or less. The length of the portion of the first surface of the tab where the organic fiber layers are bonded is 1
When the thickness is within the range of 5 mm to 5 mm, peeling of the organic fiber layer from the electrode can be sufficiently suppressed, and when the tab is connected to another member, for example, when the tab is welded, Interference can be ignored. Here, the length is the length in the direction in which the tab extends.

Furthermore, the organic fiber layer is preferably bonded to the surface and end surface of the end portion of the active material-containing layer. Such organic fiber layers can exhibit higher peel strength to the electrode.

Next, an example method for forming the organic fiber layer will be described. The organic fiber layer described above can be easily formed in a state of being bonded to the electrode described above, for example, by an electrospinning method.

In the electrospinning method, a layer of organic fibers can be formed by discharging a raw material solution from the spinning nozzle over the surface of a predetermined electrode while applying a voltage to the spinning nozzle using a high-pressure generator. The applied voltage is appropriately determined according to the solvent / solute species, the boiling point / vapor pressure curve of the solvent, the solution concentration, temperature, nozzle shape, sample-nozzle distance, etc. It can be set to 100 kV. The feed rate of the raw material solution is also appropriately determined according to the solution concentration, solution viscosity, temperature, pressure, applied voltage, nozzle shape, and the like. In the case of a syringe type, for example, it can be about 0.1 to 500 μl / min per nozzle. In the case of multiple nozzles or slits, the supply speed may be determined according to the opening area.

According to the electrospinning method, an organic fiber layer capable of exhibiting a high peel strength with respect to the electrode, specifically, a peel strength of 0.04 N or more can be formed for the following reasons. The peel strength with respect to the electrode is more preferably 0.06 N or more. Peel strength is
For example, the measurement can be performed using a measuring device manufactured by Rheotech Co., Ltd. whose model number is RT-2020D-D-CW or a device having an equivalent function.

In the electrospinning method, the raw material solution is charged by the voltage applied to the spinning nozzle, and the amount of charge per unit volume of the raw material solution increases due to volatilization of the solvent from the raw material solution. Since the volatilization of the solvent and the accompanying increase in the charge amount per unit volume occur continuously, the raw material solution discharged from the spinning nozzle extends in the longitudinal direction and is deposited on the electrode as nano-sized organic fibers. A Coulomb force is generated between the organic fiber and the electrode due to a potential difference between the nozzle and the electrode. Therefore, the contact area with the electrode can be increased by the nano-sized organic fiber, and the organic fiber can be deposited on the electrode by Coulomb force, so that the peel strength of the organic fiber layer to the electrode can be increased. It becomes possible. In addition, as described above, an organic fiber layer that can exhibit higher peel strength can be formed by bonding an organic fiber layer to a tab having a small surface roughness. The peel strength can be controlled, for example, by adjusting the solution concentration, the sample-nozzle distance, and the like.

In the electrospinning method, for example, as shown in FIG.
In the state where the mask M is placed on the portion A ′ where the organic fiber is not desired to be deposited, the spinning nozzle B
As described above, the organic fiber layer C can be formed only at a desired location of the substrate A by discharging the raw material solution.

According to such an electrospinning method, in principle, a single continuous fiber can be formed. Therefore, the organic fiber layer can be given resistance to breakage due to bending and film cracking. The single organic fiber contained in the organic fiber layer has a low probability of fraying or partial loss of the organic fiber layer, which is advantageous in terms of suppressing self-discharge.

Further, according to the electrospinning method, since the organic fiber layer is directly formed on the electrode surface in a dry state, it is substantially avoided that the solvent penetrates into the electrode. The residual amount of the solvent inside the electrode is extremely low at a ppm level or less. The residual solvent inside the electrode causes an oxidation-reduction reaction to cause battery loss, leading to deterioration of battery performance. According to the electrospinning method, the risk of such inconveniences being reduced as much as possible, so that the performance of the battery can be improved.

The raw material solution used in the electrospinning method can be prepared by dissolving an organic material in a solvent at a concentration of, for example, about 5 to 60% by mass.

As the organic material, those mentioned above as the organic fiber material that can be included in the organic fiber layer can be used. In particular, polyimide and polyvinylidene fluoride (PVdF) have been considered to be materials that are generally difficult to be fibrous. However, it has been found that fibers containing these materials can be formed as a layer according to the electrospinning method.

The solvent for dissolving the organic material is not particularly limited. Any solvent such as dimethylacetamide (DMAc), dimethylsulfoxide (DMSO), N, N′dimethylformamide (DMF), N-methylpyrrolidone (NMP), water, alcohols, etc. A solvent can be used. Also,
For an organic material having low solubility, electrospinning is performed while melting the sheet-like organic material with a laser or the like. In addition, mixing of a high boiling point organic solvent and a low melting point solvent is allowed.

Or the layer of an organic fiber can be formed in the state couple | bonded with the electrode by the inkjet method, the jet dispenser method, or the spray coating method.

In the organic fiber layer, the porosity can be increased if the organic fiber contained in the organic fiber layer is in a sparse state. For example, it is not difficult to obtain a layer having a porosity of about 90%. For example, when the secondary battery according to the embodiment is a non-aqueous electrolyte secondary battery in which lithium ions are involved in charge and discharge, by increasing the porosity, the lithium ion has excellent permeability and good non-aqueous electrolyte impregnation Can be achieved.

The secondary battery according to the embodiment described above preferably has the structure shown in FIG. 4 on the inner side in the winding stacking direction of the winding structure of the electrode group 200, and the structure shown in FIG. Have.

That is, in the wound structure of the electrode group 200, since the separator is preferably provided on the inner side in the wound stacking direction, the distance between the positive electrode and the negative electrode is increased. Thereby, in the wound structure of the electrode group 200, the electrical resistance of the inner part in the wound stacking direction increases, and the current easily flows to the outer part in the wound stacking direction. As a result, more heat is generated in the outer part than in the inner part, but the outer part is more likely to dissipate heat than the inner part.
The generated heat is easily released.

Therefore, deterioration of the battery due to heat generated by charging / discharging can be suppressed.

(Example)
Examples will be described below.

Example 1
[Preparation of positive electrode]
Lithium nickel cobalt manganese composite oxide LiNi _1/3 Co _1/3 M as positive electrode active material
n _1/3 O ₂ and lithium cobalt composite oxide LiCoO ₂ were prepared. These are LiNi _{1
/ 3} Co _1/3 Mn _1/3 O ₂ and LiCoO ₂ were mixed at a ratio of 2: 1 to obtain an active material mixture. This active material mixture, acetylene black as a conductive agent, graphite as a further conductive agent, and polyvinylidene fluoride as a binder are in a mass ratio of 100: 2: 3: 3.
The ratio was mixed. The mixture thus obtained was charged into N-methyl-2-pyrrolidone as a solvent, and this was kneaded and stirred with a planetary mixer to prepare a positive electrode slurry. This positive electrode slurry was applied and dried so that a partially uncoated part was formed on the front and back of an aluminum foil having a thickness of 12 μm. A slit was formed so that the coated width was 90 mm and the uncoated width was 25 mm, and then compressed by a roll press to produce a positive electrode.

[Preparation of negative electrode]
Lithium titanate Li ₄ Ti ₅ O ₁₂ was prepared as a negative electrode active material. This active material, graphite as a conductive agent, and polyvinylidene fluoride as a binder are in a mass ratio of 100: 1.
Mixing at a ratio of 0: 5. The mixture thus obtained was charged into N-methyl-2-pyrrolidone as a solvent, and this was kneaded and stirred with a planetary mixer to prepare a negative electrode slurry.
This negative electrode slurry was applied and dried so that a partially uncoated part was formed on the front and back of an aluminum foil having a thickness of 12 μm. A slit was formed so that the coating width was 95 mm and the uncoated width was 20 mm, and then compression was performed by a roll press to produce a negative electrode.

[Formation of insulating layer on positive electrode]
A slurry was prepared by mixing 95% by weight of Al ₂ O ₃ , 1% by weight of carboxymethyl cellulose as a dispersant and 4% by weight of a styrene butadiene rubber binder as a binder, and adding pure water. This slurry was coated on the positive electrode coating portion on the front and back surfaces by a gravure method and dried to prepare a positive electrode in which inorganic particle layers were integrally formed.

[Formation of insulating layer on negative electrode]
A slurry was prepared by mixing 95% by weight of Al ₂ O ₃ , 1% by weight of carboxymethyl cellulose as a dispersant and 4% by weight of a styrene butadiene rubber binder as a binder, and adding pure water. This slurry was coated on the negative electrode coating part on the front and back surfaces by a gravure method and dried to prepare a negative electrode in which inorganic particle layers were integrally formed.

[Production of wound electrode group]
The negative electrode produced as described above and the positive electrode produced as described above were laminated, and a cellulose separator was interposed between the positive electrode and the negative electrode to obtain a laminate. Then, this laminated body was moved to the winding apparatus, the whole laminated body was bent, and it wound in the shape of a spiral. The used amount of the intervening cellulose separator was adjusted so that RD / W = 1.0. The wound electrode group thus obtained was pressed to obtain a flat wound electrode group.

[Battery assembly]
A sealing body having a positive electrode lead connected to the positive electrode terminal and a negative electrode lead connected to the negative electrode terminal was prepared. The positive electrode uncoated portion arranged at one end of the wound electrode group and the positive electrode lead were ultrasonically bonded. Moreover, the negative electrode uncoated part arrange | positioned at the other end of the winding type electrode group, and the negative electrode lead were ultrasonically bonded. The battery unit was obtained by inserting and fitting this into an outer can and welding the sealing body and the outer can.

[Injection of non-aqueous electrolyte and completion of non-aqueous electrolyte secondary battery]
Ethylene carbonate and dimethyl carbonate were mixed at a ratio of 1: 1 to prepare a non-aqueous solvent. In this non-aqueous solvent, 1 mol / liter of lithium hexafluorophosphate LiPF ₆ as an electrolyte was added.
It was dissolved so as to have a concentration of L. Thus, a non-aqueous electrolyte was obtained. This non-aqueous electrolyte was poured into the battery unit from a liquid inlet provided in the sealing body. After the injection, an aluminum sealing member was fitted into the injection port, and the periphery of the sealing member was welded to the sealing body. Thus, the nonaqueous electrolyte battery of Example 1 was completed.

(Example 2)
The amount of separator used was adjusted to be RD / W = 0.015, and the rest was the same as in (Example 1).

(Example 3)
The amount of the separator used was adjusted so as to be A / (A + B) = 0.5, and the others were the same as in (Example 1).

(Example 4)
The amount of separator used was adjusted so as to be A / (A + B) = 0.1, and other than that was the same as (Example 1).

(Comparative Example 1)
Adjust the amount of separator used so that A / (A + B) = 1.0 without forming an insulating layer on the positive and negative electrodes, otherwise

Same as (Example 1).

(Comparative Example 2)
The amount of separator used was adjusted so as to be A / (A + B) = 1.0, and the rest was the same as in (Example 1).

(Comparative Example 3)
The separator was not used, and the others were the same as (Example 1).

[result]
Each result is shown in FIG.

In FIG. 7, the insulating layer is not formed on the electrode surface, and Comparative Example 1 in which an independent separator is interposed between all the opposing positive and negative electrodes, or an insulating layer is formed on the electrode surface and further between the opposing positive and negative electrodes Compared to Comparative Example 3 in which all independent separators are interposed, it is shown that the Example is superior both in terms of low initial resistance and in terms of volume energy density after cycling. Also,
Compared to Comparative Example 3 in which an insulating layer is formed on the electrode surface and no independent separator is used, the example is markedly superior in terms of volume energy density after cycling.

Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions can be made without departing from the spirit of the invention.
Can be replaced or changed. For example, the same effect can be obtained even if the positive electrode and the negative electrode are replaced. These embodiments and their modifications are included in the scope and gist of the invention, and are also included in the invention described in the claims and the equivalents thereof.

DESCRIPTION OF SYMBOLS 1 ... Secondary battery, 2 ... Organic fiber layer, 3 ... Inorganic membrane, 4 ... Separator

Claims (9)

A current collector having an edge; an active material-containing layer supported on at least one surface of the current collector; and a tab extending from the edge of the current collector, wherein the active material-containing layer includes the current collector. A secondary battery including an electrode including an end carried on the edge of an electric body as a positive electrode and a negative electrode,
At least one of an organic fiber layer bonded to at least a main surface of the positive electrode or negative electrode active material layer or an inorganic film bonded to at least a main surface of the positive electrode or negative electrode active material layer;
A separator covering a part of the organic fiber layer or the inorganic film or the active material layer;
A secondary battery comprising: The formula (1) is satisfied, where the positive electrode and the negative electrode have an area A where the positive electrode and the negative electrode face each other through the separator, and the positive electrode and the negative electrode face each other without an intervening separator. The secondary battery as described.
0.1 ≦ A / (A + B) ≦ 0.5 (1) The formula (2) is satisfied, where the basis weight of the active material-containing layer is W g / m2, the density is D g / cc, and the total winding frequency of the separator is R. The secondary battery according to claim 2.
0.015 ≦ RD / W ≦ 1.0 (2) The secondary battery according to claim 1, wherein the organic fiber layer has a thickness of less than 20 μm. The organic fiber layer has a porosity of 50% or more and 90% or less.
The secondary battery as described in any one of Claims 4 thru | or 4. The organic fiber layer has a porosity of 70% or more and 90% or less.
The secondary battery as described in any one of Claims 4 thru | or 4. The material of the organic fiber layer is polyimide, polyamide, polyamideimide, polyvinylidene fluoride, cellulose, polyolefin, polyether, polyetherimide, polyketone, polysulfone, polyethersulfone, polyvinyl alcohol, polyvinyl acetal, isobutylene and anhydrous maleic The secondary battery according to any one of claims 1 to 6, wherein the secondary battery is selected from the group consisting of an acid copolymer. The material of the inorganic film is alumina, titanium, silica, mica, zirconium silicate,
The secondary battery according to any one of claims 1 to 7, wherein the secondary battery is selected from the group consisting of barium sulfate, barium oxide, and calcium silicate. The secondary battery according to any one of claims 1 to 8, wherein the active material-containing layer includes lithium titanate.

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