JP2020126736A - Secondary battery and manufacturing method thereof - Google Patents

Abstract

To provide a secondary battery which allows a reference electrode layer to be doped with lithium ions in a simple and convenient method.SOLUTION: A secondary battery 100, which is an embodiment disclosed herein comprises: an electrode body 3 having a positive electrode and a negative electrode; a conductive battery case 200 serving to house the electrode body; a reference electrode layer containing a compound of the composition formula, LiTiMO(where M is at least one element selected from Mg, Nb, Cu, Mn, Ni, Fe, Ru, Zr, B, Ca, Co, Cr, V, Sc, Y, La, Zn, Al and Ga, and 0.3≤x≤2.8 (after doping) and 0≤y≤1); and an electrolyte containing lithium ions and arranged in the battery case so that the reference electrode layer is immersed therein. The reference electrode layer is formed on an inner wall of the battery case and faces the positive electrode.SELECTED DRAWING: Figure 1

Description

The present disclosure relates to a secondary battery and a method for manufacturing the secondary battery.

For the purpose of improving the reliability of the secondary battery, it has been studied to provide a reference electrode in the battery to control the potentials of the positive and negative electrodes during charging and discharging. Lithium titanate is an example of the reference electrode, but lithium titanate must be doped with lithium ions in order to stabilize the potential of the reference electrode. In Patent Document 1, a reference electrode containing lithium titanate and a fourth electrode are installed in a battery, and after the battery is hermetically sealed, a voltage is applied between the reference electrode and the fourth electrode to make titanium. A method of doping lithium oxide with lithium ions and a method of separately preparing a reference electrode doped with lithium ions and incorporating the reference electrode in a secondary battery are disclosed.

Special table 2010-539657 gazette

However, the method disclosed in Patent Document 1 has a problem that a space for the fourth electrode must be secured in the battery case. An object of the present disclosure is to provide a secondary battery in which a reference electrode can be doped with lithium ions by a simple method.

Secondary battery which is one embodiment of the present disclosure includes an electrode body having a positive electrode and a negative electrode, a conductive battery case for accommodating the electrode assembly, the composition formula _{Li 4 + x Ti 5 M y} O 12 ( wherein, M is One or more elements selected from Mg, Nb, Cu, Mn, Ni, Fe, Ru, Zr, B, Ca, Co, Cr, V, Sc, Y, La, Zn, Al, and Ga, 0.3≦x≦2.8, satisfying 0≦y≦1), and a lithium ion-containing electrolyte arranged in the battery case so that the reference electrode layer is immersed. And the reference electrode layer is formed on the inner wall of the battery case and faces the positive electrode.

The method of manufacturing a secondary battery which is one embodiment of the present disclosure, on the inner wall of the conductive battery case, in the composition formula _{Li 4 + x Ti 5 M y} O 12 ( wherein, M is Mg, Nb, Cu, Mn, Ni , One or more elements selected from Fe, Ru, Zr, B, Ca, Co, Cr, V, Sc, Y, La, Zn, Al, and Ga, and 0≦x<0.3, 0 ≦y≦1), and a step of forming an electrode body having a positive electrode and a negative electrode with a porous layer adjacent to the outer side of the electrode body so that the positive electrode faces the reference electrode layer. A battery case through a high-quality electrode body holder, a step of injecting an electrolyte containing lithium ions into the battery case so that at least the reference electrode layer is immersed, and the battery case to the negative electrode of the power supply, the positive electrode Is connected to each of the positive electrodes of the power source, and the reference electrode layer is doped with lithium ions.

According to one aspect of the present disclosure, it is possible to provide a secondary battery in which the reference electrode layer can be doped with lithium ions by a simple method.

FIG. 3 is a perspective view of a secondary battery that is an example of an embodiment, showing the internal structure of the battery case and the first reference electrode formation region when the front side of the prismatic outer package is removed. It is a perspective view of an electrode body which is an example of an embodiment. It is the sectional view on the AA line in FIG. It is a perspective view of a secondary battery which is another example of the embodiment, and is a view showing a first reference electrode formation region and a second reference electrode formation region in a state where the front side of the rectangular exterior body is removed. .. It is sectional drawing of the secondary battery which is another example of embodiment. FIG. 2 is a cross-sectional view taken along the line AA in FIG. 1, showing a state in which a reference electrode layer is doped with lithium ions.

When the secondary battery is overcharged, gas may be generated due to oxidative decomposition of the electrolyte on the positive electrode side, or the positive electrode active material may be dissolved, and metallic lithium is deposited on the negative electrode side. there is a possibility. Conventionally, overcharge is suppressed by monitoring the potential difference between the positive electrode and the negative electrode, but the electrode deteriorates due to use.Therefore, if a reference electrode layer that can directly measure the positive electrode and negative electrode potential can be installed in the secondary battery, the secondary battery The reliability of the battery can be further improved. Patent Document 1 discloses a method of installing a reference electrode containing lithium titanate and a fourth electrode for doping lithium ions into the reference electrode. However, since the volume inside the battery case is very limited, it is important to install the fourth electrode, which is used only for doping lithium ions before the actual use of the battery, because of the output characteristics of the battery. There is a problem from a perspective.

Secondary battery which is one embodiment of the present disclosure includes an electrode body having a positive electrode and a negative electrode, a conductive battery case for accommodating the electrode assembly, the composition formula _{Li 4 + x Ti 5 M y} O 12 ( wherein, M is One or more elements selected from Mg, Nb, Cu, Mn, Ni, Fe, Ru, Zr, B, Ca, Co, Cr, V, Sc, Y, La, Zn, Al, and Ga, 0.3≦x≦2.8, satisfying 0≦y≦1), and a lithium ion-containing electrolyte arranged in the battery case so that the reference electrode layer is immersed. And the reference electrode layer is formed on the inner wall of the battery case and faces the positive electrode.

Since the reference electrode layer and the positive electrode face each other via the electrolyte containing lithium ions, when a voltage is applied between the reference electrode layer and the positive electrode, the lithium ions contained in the electrolyte move to the reference electrode layer. Cheap. Therefore, the reference electrode layer can be doped with a sufficient amount of lithium ions, so that the potential of the reference electrode layer is stable and the potentials of the positive electrode and the negative electrode can be measured with high accuracy.

Hereinafter, an example of the embodiment of the present disclosure will be described in detail. In the present embodiment, a prismatic battery including a battery case 200 that is a prismatic metal case is illustrated, but the battery case is not limited to a prismatic shape, and is, for example, a battery case configured by a laminate sheet including a metal layer and a resin layer. May be When a battery case made of a laminate sheet is used, the resin layer is not provided on the portion where the reference electrode layer is formed and the portion where the negative electrode of the power source contacts. Further, although the winding type electrode body 3 is exemplified, a laminated type electrode body may be used. Further, in both the positive electrode and the negative electrode, the case where each active material layer is formed on both surfaces of each core is illustrated, but each active material layer is not limited to the case formed on both surfaces of each core. It may be formed on at least one surface.

As illustrated in FIG. 1, a secondary battery 100 includes a positive electrode and a negative electrode that are wound with a separator interposed therebetween, and has a flat shape and a spirally wound electrode body 3 having a pair of curved portions. An electrolyte and a battery case 200 accommodating the electrode body 3 and the electrolyte are provided. The battery case 200 includes a bottomed tubular prismatic outer casing 1 having an opening, and a sealing plate 2 for sealing the opening of the rectangular outer casing 1. Both the rectangular outer casing 1 and the sealing plate 2 are made of metal, and are preferably made of aluminum or aluminum alloy.

The prismatic outer casing 1 has a bottom portion having a substantially rectangular shape in bottom view, and a side wall portion provided upright on the peripheral edge of the bottom portion. The side wall portion is formed perpendicular to the bottom portion. The dimensions of the rectangular outer package 1 are not particularly limited, but as an example, the lateral length is 60 to 160 mm, the height is 60 to 100 mm, and the thickness is 10 to 40 mm. In this specification, for convenience of description, the direction along the longitudinal direction of the bottom of the rectangular exterior body 1 is the “lateral direction” of the rectangular exterior body 1, the direction perpendicular to the bottom is the “height direction”, the lateral direction, and The direction perpendicular to the height direction is referred to as the “thickness direction”.

The electrolyte is a non-aqueous electrolyte containing a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. As the non-aqueous solvent, for example, carbonates, esters, ethers, nitrites, amides, and a mixed solvent of two or more of these may be used. Examples of the carbonates include cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate and vinylene carbonate; dimethyl carbonate (DMC), ethylmethyl carbonate (EMC), diethyl carbonate (DEC), methylpropyl carbonate. Examples thereof include chain carbonates such as ethyl propyl carbonate and methyl isopropyl carbonate. The non-aqueous solvent may contain a halogen-substituted product obtained by substituting at least part of hydrogen in the above-mentioned solvent with a halogen atom such as fluorine. The electrolyte is not limited to a liquid electrolyte and may be a solid electrolyte using a gel polymer or the like. The electrolyte salt includes a lithium salt. As the lithium salt, LiPF ₆ or the like which is generally used as a supporting salt in the conventional secondary battery 100 can be used. Further, an additive such as vinylene carbonate (VC) can be added as appropriate.

The positive electrode 4 is a long body having a positive electrode core made of metal and a positive electrode active material layer 41 formed on both surfaces of the positive electrode core, and has one end in the lateral direction along the longitudinal direction. A strip-shaped positive electrode core exposed portion 42, from which the positive electrode core is exposed, is formed (see FIG. 2 described later). In this embodiment, the positive electrode active material layers 41 are provided on both surfaces of the positive electrode core from the outer end of the positive electrode 4 to the inner end of the positive electrode 4, that is, both ends in the longitudinal direction of the positive electrode 4. Similarly, the negative electrode 5 is a long body having a negative electrode core body made of metal and a negative electrode active material layer 51 formed on both surfaces of the negative electrode core body. A strip-shaped negative electrode core exposed portion 52 is formed along which the negative electrode core is exposed. In the present embodiment, the negative electrode active material layers 51 are provided on both surfaces of the negative electrode core body from the outer end to the inner end of the negative electrode 5, that is, both ends in the longitudinal direction of the negative electrode 5. In the electrode body 3, the positive electrode core exposed portion 42 is arranged on one end side in the winding axis direction, and the negative electrode core exposed portion 52 is arranged on the other end side in the winding axis, respectively. Has a wound structure.

The positive electrode collector 6 is connected to the laminated portion of the positive electrode core exposed portion 42, and the negative electrode collector 8 is connected to the laminated portion of the negative electrode core exposed portion 52. A suitable positive electrode current collector 6 is made of aluminum or an aluminum alloy. A suitable negative electrode current collector 8 is made of copper or a copper alloy. The positive electrode terminal 7 is inserted into the positive electrode external conductive portion 13 arranged on the battery outer side of the sealing plate 2, the positive electrode bolt portion 14 connected to the positive electrode external conductive portion 13, and the through hole provided in the sealing plate 2. And a positive electrode insertion portion 15 that is electrically connected to the positive electrode current collector 6. Further, the negative electrode terminal 9 is provided in a negative electrode external conductive portion 16 arranged on the battery outer side of the sealing plate 2, a negative electrode bolt portion 17 connected to the negative electrode external conductive portion 16, and a through hole provided in the sealing plate 2. The negative electrode insertion portion 18 to be inserted is included, and the negative electrode current collector 8 is electrically connected.

The positive electrode terminal 7 and the positive electrode current collector 6 are fixed to the sealing plate 2 via an inner insulating member and an outer insulating member, respectively. The inner insulating member is arranged between the sealing plate 2 and the positive electrode current collector 6, and the outer insulating member is arranged between the sealing plate 2 and the positive electrode terminal 7. Similarly, the negative electrode terminal 9 and the negative electrode current collector 8 are fixed to the sealing plate 2 via the inner insulating member and the outer insulating member, respectively. The inner insulating member is arranged between the sealing plate 2 and the negative electrode current collector 8, and the outer insulating member is arranged between the sealing plate 2 and the negative electrode terminal 9.

The electrode body 3 is housed in the rectangular exterior body 1. The sealing plate 2 is connected to the opening edge portion of the rectangular exterior body 1 by laser welding or the like. The sealing plate 2 has an electrolyte injection hole 10. The electrolyte injection hole 10 is filled with the electrolyte in the battery case 200, and then the electrolyte injection hole 10 is sealed by a sealing plug. The sealing plate 2 is formed with a gas discharge valve 11 for discharging gas when the pressure inside the battery reaches or exceeds a predetermined value.

The secondary battery 100, which is one aspect of the present disclosure, is preferably arranged between the electrode body 3 and the battery case 200, and further includes a porous electrode body holder 12 through which lithium ions can pass (see a later-described diagram). 3). By sandwiching the electrode body holder 12 between the electrode body 3 and the battery case 200, it is possible to prevent the electrode body 3 and the battery case 200 from reliably contacting each other. The electrode body holder 12 is not particularly limited as long as it is porous and permeable to lithium ions. For example, a porous sheet having an insulating property is used. The electrode body holder 12 is a porous material containing at least one selected from the group consisting of polyolefin, polyvinylidene fluoride, polytetrafluoroethylene, polyimide, polyamide, polyamideimide, polyethersulfone, polyetherimide, and aramid, for example. Including a substrate, polyolefins are preferred, and polyethylene and polypropylene are especially preferred. Since the space between the electrode body 3 and the battery case 200 is narrow, it is preferable that the electrode body 3 is housed in the rectangular exterior body 1 while being covered with the electrode body holder 12.

The inner wall surface of the rectangular outer package 1 has a first reference electrode formation region 20. The first reference electrode formation region 20 is a region facing the positive electrode core body exposed portion 42. A reference electrode layer is formed on at least one of the first reference electrode formation region 20 and a second reference electrode formation region 21 described later.

Hereinafter, the electrode body 3 and the reference electrode layer 60 will be described in detail.

[Electrode body]
FIG. 2 is a perspective view of the electrode body 3, and is a developed view of the vicinity of the winding end of the electrode body 3. As illustrated in FIG. 1, in the electrode body 3, the positive electrode 4 and the negative electrode 5 are disposed via the separator 30 so that the positive electrode core exposed portion 42 and the negative electrode core exposed portion 52 are located on the opposite sides in the axial direction. It has a wound structure. In the electrode body 3, the negative electrode 5 has a size slightly larger than that of the positive electrode 4, and is arranged such that the negative electrode active material layer 51 is always present in a region facing the positive electrode active material layer 41. The electrode body 3 has dimensions of, for example, an axial length of 50 to 150 mm, a width of 50 to 90 mm, and a thickness of 8 to 38 mm.

The positive electrode 4 has a positive electrode core body and a positive electrode active material layer 41 provided on the positive electrode core body. As the positive electrode core, a foil of metal such as aluminum or aluminum alloy which is stable in the potential range of the positive electrode 4, a film in which the metal is arranged on the surface layer, and the like can be used. The thickness of the positive electrode core is, for example, 10 to 20 μm. The positive electrode active material layer 41 preferably includes a positive electrode active material, a conductive auxiliary agent such as acetylene black, and a binder such as polyvinylidene fluoride (PVdF), and is provided on both surfaces of the positive electrode core body. The thickness of the positive electrode active material layer 41 is, for example, 50 to 400 μm in total on both sides of the positive electrode core body. The positive electrode 4 is formed by applying a positive electrode active material slurry containing a positive electrode active material, a conductive additive, a binder and the like on a positive electrode core, drying the coating film, and then compressing the positive electrode active material layer 41 to form a positive electrode. It can be produced by forming on both sides of the core.

As the positive electrode active material, for example, a lithium metal composite oxide is used. The metal elements contained in the lithium metal composite oxide include Ni, Co, Mn, Al, B, Mg, Ti, V, Cr, Fe, Cu, Zn, Ga, Sr, Zr, Nb, In, Sn, and Ta, W, etc. are mentioned. One example of a suitable lithium metal composite oxide is a lithium metal composite oxide containing at least one of Ni, Co and Mn. Specific examples include a lithium metal composite oxide containing Ni, Co and Mn, and a lithium metal composite oxide containing Ni, Co and Al. Inorganic compound particles such as tungsten oxide, aluminum oxide, and lanthanoid-containing compound may be fixed to the surface of the lithium metal composite oxide particles.

The negative electrode 5 has a negative electrode core body and a negative electrode active material layer 51 provided on the negative electrode core body. As the negative electrode core body, a foil of a metal such as copper or a copper alloy which is stable in the potential range of the negative electrode 5, a film in which the metal is arranged on the surface layer, and the like can be used. The thickness of the negative electrode core body is, for example, 5 to 15 μm. The negative electrode active material layer 51 preferably contains a negative electrode active material and a binder such as styrene-butadiene rubber (SBR) and is provided on both surfaces of the negative electrode core body. The thickness of the negative electrode active material layer 51 is, for example, 50 to 400 μm in total on both sides of the negative electrode core body. The negative electrode 5 is obtained by applying a negative electrode active material slurry containing a negative electrode active material, a binder and the like on a negative electrode core, drying the coating film, and then compressing the negative electrode active material layer 51 on both sides of the negative electrode core. It can be manufactured by forming

As the negative electrode active material, for example, natural graphite such as scaly graphite, lump graphite, and earth graphite, lump artificial graphite, graphite such as graphitized mesophase carbon microbeads, and other graphite are used. As the negative electrode active material, a metal alloying with lithium such as Si or Sn, an alloy containing the metal, a compound containing the metal, or the like may be used, and these may be used in combination with graphite. Specific examples of the compound include silicon compounds represented by SiO _x (0.5≦x≦1.6).

As the separator 30, a porous sheet having ion permeability and insulation is used. The separator 30 is, for example, a porous substrate containing, as a main component, at least one selected from polyolefin, polyvinylidene fluoride, polytetrafluoroethylene, polyimide, polyamide, polyamideimide, polyether sulfone, polyetherimide, and aramid. Polyolefins are preferable, and polyethylene and polypropylene are particularly preferable.

The separator 30 may be composed of only a resin-made porous base material, or may have a multi-layer structure in which a heat-resistant layer containing inorganic particles or the like is formed on at least one surface of the porous base material. .. Further, the resin-made porous base material may have a multilayer structure of polypropylene/polyethylene/polypropylene or the like. The thickness of the separator 30 is, for example, 10 to 30 μm. The separator 30 has, for example, an average pore diameter of 0.02 to 5 μm and a porosity of 30 to 70%. Generally, the wound electrode body 3 includes two separators 30, but the same separators can be used for each separator 30.

The electrode body 3 is manufactured by pressing a wound body of the positive electrode 4 and the negative electrode 5 wound via the separator 30 into a flat shape. In this case, for example, a cylindrical winding body is manufactured using a substantially cylindrical winding core, the winding core is removed, and then the winding body is pressed in the radial direction. Alternatively, the positive electrode 4 and the negative electrode 5 may be wound in a flat shape by using a flat winding core. In this case, the core may be removed and then further pressed to form a flat shape.

In FIG. 2, the outermost periphery of the electrode body 3 is the negative electrode 5. In the present application, the outermost circumference means the positive electrode 4 or the negative electrode 5 arranged on the outermost winding side, and the separator 30 is excluded. For example, when the outermost periphery of the electrode body 3 is the negative electrode 5, it means that the negative electrode 5 covers substantially the entire outer surface of the electrode body 3 excluding the core body exposed portions of both electrodes. The outermost periphery of the electrode body 3 may be either the negative electrode core body or the negative electrode active material layer 51.

[Reference electrode layer]
The reference electrode layer 60 is an electrode serving as a reference when measuring the absolute values of the potentials of the positive electrode 4 and the negative electrode 5. Specifically, the potential between the positive electrode 4 and the reference electrode layer 60 can be measured by measuring the voltage between the positive electrode terminal 7 and the battery case 200 electrically connected to the reference electrode layer 60. The potential of the negative electrode 5 with respect to the reference electrode layer 60 can be calculated by subtracting the previously measured potential of the positive electrode 4 with respect to the reference electrode layer 60 from the separately measured cell voltage. Since the potentials of the positive electrode 4 and the negative electrode 5 are determined based on the potential of the reference electrode, it is preferable that the potential of the reference electrode layer 60 is stable. Reference electrode layer 60, in the composition formula _{Li 4 + x Ti 5 M y} O 12 ( wherein, M is Mg, Nb, Cu, Mn, Ni, Fe, Ru, Zr, B, Ca, Co, Cr, V, Sc, One or more elements selected from Y, La, Zn, Al, and Ga, satisfying 0.3≦x≦2.8 and 0≦y≦1, and hereinafter referred to as “lithium titanate”. Is present). The reference electrode layer 60 can be produced by applying a reference electrode slurry containing at least lithium titanate to a predetermined position on the inner wall of the battery case 200 and drying the coating film. By doping lithium titanate contained in the manufactured reference electrode layer 60 with lithium ions, the potential of the reference electrode layer 60 is stabilized. The lithium titanate having the above composition formula is lithium titanate after being doped with lithium ions.

The reference electrode layer 60 preferably further contains a conductive additive in order to further stabilize the potential of the reference electrode layer 60. Examples of the conductive aid include carbon materials such as carbon black, acetylene black, Ketjen black, and graphite.

The reference electrode layer 60 can include a binder such as styrene-butadiene rubber, polyvinylidene fluoride (PVdF), and a thickener such as carboxymethyl cellulose (CMC), in addition to lithium titanate and a conductive additive.

The thickness and size of the reference electrode layer 60 are not particularly limited as long as the potential of the reference electrode layer 60 is stable. For example, the thickness of the reference electrode layer 60 is preferably 1 to 200 μm, more preferably 1 to 50 μm, and further preferably 1 μm to 10 μm. The thickness of the reference electrode layer 60 is preferably sized is ^{1cm 2 ~400cm 2,} more preferably from 3cm ² ~150cm ^2, and further preferably from 5cm 2 ~25cm. Further, the proportion of lithium titanate contained in the reference electrode layer 60 is preferably 90% by mass or more.

The position where the reference electrode layer 60 is formed will be described with reference to FIG. FIG. 3 is a sectional view taken along the line AA in FIG. The electrode body 3 is installed substantially in the center of the rectangular outer package 1 in the thickness direction so as not to contact the rectangular outer package 1, and is fixed to the sealing plate 2 via a positive electrode current collector 6 (not shown). There is. The reference electrode layer 60 is formed on the inner wall of the battery case 200, more specifically, on the side wall portion or the bottom portion inside the prismatic outer casing 1. By forming the reference electrode layer 60 in a layered manner on the rectangular outer package 1, the reference electrode layer 60 can be electrically connected to the rectangular outer package 1, and the volume of the battery case 200 is not reduced.

The electrode body 3 is a wound type in which a positive electrode 4 and a negative electrode 5 are wound with a separator 30 in between. The electrode body 3 has a positive electrode core exposed portion 42 at one end in the winding axis direction and a negative electrode core exposed portion 52 at the other end in the winding axis direction. The outermost periphery of the electrode body 3 is the negative electrode 5, and the reference electrode layer 60 faces the positive electrode core exposed portion 42.

As shown in FIG. 2, the outermost periphery of the electrode body 3 is the negative electrode 5, and the portion of the electrode body 3 where the positive electrode 4 is located outside the winding is the positive electrode core body exposed portion 42. In this case, the reference electrode layer 60 is formed at a position facing the positive electrode core exposed portion 42, in other words, in the first reference electrode formation region 20 of FIG. 1. Since there is an electrolyte containing lithium ions between the reference electrode layer 60 and the positive electrode 4, when a voltage is applied between the reference electrode layer 60 and the positive electrode 4, the lithium ions contained in the electrolyte are not included in the reference electrode layer 60. Easy to move to. Therefore, the reference electrode layer 60 can be doped with a sufficient amount of lithium ions.

In FIG. 2, the separator 30 is stacked on the outermost negative electrode 5, but the separator 30 may not be stacked on the negative electrode 5. In this case, in FIG. 2, the separator 30 laminated on the negative electrode 5 is laminated under the positive electrode 4, or the length of the separator 30 laminated on the negative electrode 5 is shortened. You can

<Another Example of Embodiment>
FIG. 4 is a perspective view of a secondary battery which is another example of the embodiment, and is a diagram showing a first reference electrode formation region 20 and a second reference electrode formation region 21. The second reference electrode formation region 21 is a part of the inner wall surface of the rectangular exterior body 1 and is a region facing the part of the electrode body 3 excluding the positive electrode core exposed part 42 and the negative electrode core exposed part 52. .. Further, similarly to the example shown in the cross-sectional view of FIG. 3, the reference electrode layer 60 is formed on the inner wall of the battery case 200, more specifically, on the inner side wall portion or bottom portion of the rectangular exterior body 1.

The electrode body 3 is a winding type in which a positive electrode 4 and a negative electrode 5 are wound with a separator 30 in between, and has a positive electrode core exposed portion 42 and a negative electrode core exposed portion 52 at both ends in the winding axis direction. The outermost periphery of the electrode body 3 is the positive electrode 4, and the reference electrode layer 60 faces the portion of the electrode body 3 excluding the negative electrode core exposed portion 52.

When the outermost periphery of the electrode body 3 is the positive electrode 4, the positive electrode 4 exists outside the winding of the electrode body 3 in the portion of the electrode body 3 excluding the negative electrode core exposed portion 52. In this case, the reference electrode layer 60 faces the portion of the electrode body 3 excluding the negative electrode core exposed portion 52, in other words, the first reference electrode formation region 20 or the second reference electrode formation region 21 of FIG. Is formed. Therefore, compared to the case where the outermost periphery is the negative electrode 5, the position where the reference electrode layer 60 is formed can be selected in a wider range. When the outermost periphery of the electrode body 3 is the positive electrode active material layer 41, the negative electrode active material layer 51 does not exist in the region facing the outermost periphery positive electrode active material layer 41, so the outermost periphery of the electrode body 3 is the positive electrode core body. Is preferred.

The separator 30 is preferably laminated on the outermost periphery. In this case, it is possible to prevent the outermost periphery from coming into contact with the rectangular outer package 1. Even when the electrode body holder 12 is between the electrode body 3 and the rectangular outer casing 1, the separator 30 may be laminated on the outermost periphery.

As illustrated in FIG. 5, it is preferable that at least a part of the reference electrode layer 60 is formed on the side surface on the bottom side when the secondary battery 100 is divided in half at the center in the height direction. It is more preferable that at least a part of the battery 100 is formed on the side surface closest to the bottom when the battery 100 is divided into four equal parts in the height direction. Even when there is a portion not filled with the electrolyte in the battery case 200, the reference electrode layer 60 is formed on the bottom side of the prismatic outer casing 1 so that the electrolyte is provided between the reference electrode layer 60 and the positive electrode 4. Can be ensured to exist.

[Method of manufacturing secondary battery]
The secondary battery 100 having the above configuration is manufactured, for example, through the following steps.
(1) on a conductive inner wall of the battery case 200, in the composition formula _{Li 4 + x Ti 5 M y} O 12 ( wherein, M is Mg, Nb, Cu, Mn, Ni, Fe, Ru, Zr, B, Ca, A compound consisting of one or more elements selected from Co, Cr, V, Sc, Y, La, Zn, Al, and Ga and satisfying 0≦x<0.3, 0≦y≦1) A step of forming the reference electrode layer 60 including.
(2) The electrode case 3 having the positive electrode 4 and the negative electrode 5 is inserted into the battery case 200 via the porous electrode body holder 12 adjacent to the outside of the electrode body 3 so that the positive electrode 4 faces the reference electrode layer 60. Step of housing.
(3) A step of injecting an electrolyte containing lithium ions into the battery case 200 so that at least the reference electrode layer 60 is immersed.
(4) A step of connecting the battery case 200 to the negative electrode of the power source and the positive electrode 4 to the positive electrode of the power source, and doping the reference electrode layer 60 with lithium ions (see FIG. 6 ).

Of the method for manufacturing the secondary battery 100, the step of doping the reference electrode layer 60 with lithium ions will be described with reference to FIG. Through the steps (1) to (3) described above, in the battery case 200 having the rectangular outer package 1 and the sealing plate 2, the reference electrode layer 60 formed on the side wall or the bottom surface of the rectangular outer package 1 is formed. The electrode body 3 fixed to the sealing plate 2 via the positive electrode current collector 6 and the negative electrode current collector 8 is arranged so as not to contact the battery case 200. The positive electrode 4 and the reference electrode layer 60 on the outer side of the winding of the electrode body 3 face each other, and an electrolyte containing lithium ions exists between the reference electrode layer 60 and the positive electrode 4.

Next, in the step (4) described above, the battery case 200 is connected to the negative pole of the power source, and the positive electrode 4 is connected to the positive pole of the power source. Specifically, the negative pole of the power source is connected to either the rectangular outer casing 1 or the sealing plate 2 included in the battery case 200, while the positive pole of the power source is connected to the positive electrode terminal 7. Since a potential difference is generated between the reference electrode layer 60 on the battery case 200 and the positive electrode 4 connected to the positive electrode terminal 7, lithium ions in the electrolyte are attracted to the reference electrode layer 60 on the negative electrode side. Lithium titanate contained in the electrode layer 60 is doped with lithium ions. Since the potential of lithium titanate doped with lithium ions is stabilized, the reference electrode layer 60 can be used as a reference electrode for measuring the potential of the positive electrode 4 or the negative electrode 5.

The step of sealing the battery case 200 can be performed before the step (4). Note that the step of sealing the battery case 200 may be performed after the step (4). For example, the electrolyte injection hole 10 of the battery case 200 may be sealed after the reference electrode layer 60 is doped with lithium ions in a state where the electrolyte injection hole 10 of the battery case 200 is not sealed. In this case, it is preferable to dope the reference electrode layer 60 with lithium ions in a dry environment. However, by performing the step of sealing the battery case 200 before the step (4), the reference electrode layer 60 doped with lithium does not come into contact with moisture in the atmosphere, and the potential of the reference electrode layer 60 is reduced. It will be more stable. Therefore, it is more preferable to perform the step of sealing the battery case 200 before the step (4).

Hereinafter, the present disclosure will be further described with reference to examples, but the present disclosure is not limited to these examples. Further, the secondary batteries according to each example and each comparative example were manufactured in a non-dry environment without using a dry room, and the secondary battery according to the reference example was manufactured in a controlled dry environment in a dry room. ..

<Example 1>
[Preparation of positive electrode]
As the positive electrode active material, lithium metal composite oxide particles represented by LiNi _0.35 Co _0.35 Mn _0.30 O ₂ were used. The positive electrode active material, polyvinylidene fluoride dispersed in N-methyl-2-pyrrolidone (NMP), and acetylene black were mixed at a solid content mass ratio of 91:2:7 to prepare a positive electrode active material slurry. Prepared. Next, the positive electrode active material slurry was applied on both surfaces of a positive electrode core body made of an aluminum alloy having a thickness of 15 μm, and the coating film was vacuum dried to volatilize and remove NMP. However, the positive electrode core was exposed without providing the positive electrode active material slurry on both surfaces at one end along the longitudinal direction of the positive electrode core to provide a positive electrode core exposed portion. The dried coating film was compressed using a rolling roll, and then cut into a predetermined electrode plate size to prepare a positive electrode plate having positive electrode active material layers formed on both surfaces of the positive electrode current collector.

[Preparation of negative electrode]
Natural graphite, styrene butadiene rubber (SBR), and carboxymethyl cellulose (CMC) were mixed at a solid content mass ratio of 98:1:1, and water was added in an appropriate amount to prepare a negative electrode active material slurry. Next, the negative electrode active material slurry was applied to both surfaces of a negative electrode core body made of a copper foil having a thickness of 8 μm, and the coating film was vacuum dried to volatilize and remove water. However, the negative electrode core was exposed without providing the negative electrode active material slurry on both surfaces at one end along the longitudinal direction of the negative electrode core to provide a negative electrode core exposed portion. The dried coating film was compressed using a rolling roll, and then cut into a predetermined electrode size to prepare a negative electrode having a negative electrode active material layer formed on both surfaces of a rectangular negative electrode core.

[Production of electrode body]
The positive electrode and the negative electrode were wound with a strip-shaped polyethylene/polypropylene microporous membrane separator interposed between them so that the exposed cores of the positive electrode and the negative electrode were located on the axially opposite sides of the wound body. After that, the wound body was pressed in the radial direction and formed into a flat shape, to prepare a wound electrode body. The wound body was formed by stacking a separator, a positive electrode, a separator, and a negative electrode in this order from the inside of the winding, and winding the wound body around a cylindrical winding core (the same two separators were used). The outermost periphery of the electrode body was the negative electrode.

[Preparation of reference electrode]
Lithium titanate having a composition formula Li ₄ Ti ₅ O ₁₂ , carboxymethyl cellulose (CMC), and styrene butadiene rubber (SBR) were mixed at a solid content mass ratio of 98.9:0.7:0.4, A reference electrode slurry was prepared by adding an appropriate amount of water. Next, the reference electrode slurry was applied to the inner wall of the side surface of the battery case so as to face the exposed portion of the positive electrode core so that the application amount was 1 mg/cm ² . After that, the battery case was dried to remove water used as a dispersion medium at the time of preparing the reference electrode slurry to form a reference electrode layer. The formation area of the reference electrode layer was 8 cm ² .

[Preparation of electrolyte]
Ethylene carbonate (EC), ethylmethyl carbonate (EMC), and diethyl carbonate (DEC) were mixed at a volume ratio of 3:3:4 (25° C., 1 atm). LiPF ₆ was dissolved in the mixed solvent at a concentration of 1 mol/L, and 0.3% by mass of vinylene carbonate (VC) was added to the total mass of the electrolyte to prepare an electrolyte.

[Preparation of secondary battery]
A secondary battery (square battery) was produced using the electrode body, the electrolyte, and a prismatic battery case made of aluminum. The electrode body is covered with a porous electrode body holder to form a prismatic bottomed cylindrical outer can that constitutes the battery case (lateral length 148.0 mm (inner dimension 146.8 mm), thickness 17.5 mm (inner dimension 16. 5 mm) and a height of 65.0 mm (inner dimension 64.0 mm)). The positive electrode terminal was attached to the sealing plate constituting the battery case, and the positive electrode current collector was connected to the positive electrode terminal. Further, the negative electrode terminal was attached to the sealing plate, and the negative electrode current collector was connected to the negative electrode terminal. Then, the positive electrode current collector was welded to the positive electrode core exposed portion and the negative electrode current collector was welded to the negative electrode core exposed portion. The electrolyte was poured into an outer can and the opening of the battery case was closed with a sealing plate.

[Doping the reference electrode layer with lithium ions]
By connecting the battery case of the fabricated secondary battery to the negative electrode of the power source and the positive electrode terminal to the positive electrode of the power source, and charging the battery at 0.0015 It (7.5 mA) for 60 seconds, lithium was added to the reference electrode layer. Doped with ions. The potential of the reference electrode layer after doping with lithium ions is considered to be 1.55V.

<Example 2>
The solid content mass ratio of the reference electrode slurry was 96.9:2 with lithium titanate having a composition formula Li ₄ Ti ₅ O ₁₂ , acetylene black, carboxymethyl cellulose (CMC), and styrene butadiene rubber (SBR). A secondary battery was made in the same manner as in Example 1 except that the ratio was changed to 0:0.7:0.4.

<Comparative Examples 1 to 3>
In Comparative Examples 1 to 3, secondary batteries were produced in the same manner as in Example 1 except that the following was changed.
(1) Comparative Example 1: No reference electrode layer was prepared.
(2) Comparative Example 2: The reference electrode layer was formed at a position not facing the exposed portion of the positive electrode core body.
(3) Comparative Example 3: The reference electrode layer was formed at a position not facing the exposed portion of the positive electrode core body, and the reference electrode layer was not doped with lithium ions.

<Reference example>
After preparation of the reference electrode layer and before preparation of the secondary battery, the electrolyte was injected into the outer can, and the separately prepared lithium electrode was inserted so as to face the reference electrode layer through the porous electrode body holder. The outer can was connected to the negative electrode of the power source and the lithium electrode was connected to the positive electrode of the power source, and the reference electrode layer was doped with lithium ions by charging at 0.0015 It (7.5 mA) for 60 seconds. After that, a lithium battery was extracted and then a secondary battery was manufactured.

Each of the secondary batteries of Examples 1 and 2, Comparative Examples 1 to 3, and Reference Example was produced by 10 cells, and the stability of the reference electrode layer was evaluated by the following method. The evaluation results are shown in Table 1. It was

[Evaluation of stability of reference electrode layer]
Each secondary battery was charged with a constant current of 1 It (5 A) in a temperature environment of 25° C., and then with a constant voltage of 3.52 V for 2.5 hours, and the depth of charge (SOC) was 20%. After standing at room temperature for 2.5 hours, the voltage of the positive electrode with respect to the battery case (positive electrode/battery case) was measured. The voltage of the negative electrode with respect to the battery case (negative electrode/battery case) was calculated by subtracting the voltage of the positive electrode with respect to the battery case from the separately measured cell voltage. From the measurement results of 10 cells, the average value of the positive electrode/battery case and the negative electrode/battery case and the standard deviation of the positive electrode/battery case were calculated. Further, the SOC of the secondary battery was set to 50% and the measurement was performed in the same manner as in the case where the SOC was 20% except that the voltage during constant voltage charging was set to 3.69V. Further, the SOC of the secondary battery was set to 80% in the same manner as in the case where the SOC was 20% except that the voltage during constant voltage charging was set to 3.91 V, and the same measurement was performed.

The secondary batteries of Comparative Examples 1 to 3 all showed potentials of the positive electrode/battery case and the negative electrode/battery case different from those of the secondary battery of the reference example produced in a dry environment, and the standard deviation was also large and unstable.

On the other hand, in the secondary battery of Example 1, substantially the same potentials and standard deviations of the positive electrode/battery case and the negative electrode/battery case as the secondary battery of the reference example produced in a dry environment were obtained. In the secondary battery of Example 1, the electrode body having a positive electrode and a negative electrode, a conductive battery case for accommodating the electrode assembly, in the composition formula _{Li 4 + x Ti 5 M y} O 12 ( wherein, M is Mg, Nb , Cu, Mn, Ni, Fe, Ru, Zr, B, Ca, Co, Cr, V, Sc, Y, La, Zn, Al, and Ga, and one or more elements selected from 0.3 ≦x≦2.8, satisfying 0≦y≦1), and an electrolyte containing lithium ions, which is arranged in the battery case so that the reference electrode layer is immersed. Since the reference electrode layer is formed on the inner wall of the battery case and faces the positive electrode, it is possible to provide a secondary battery in which the reference electrode layer can be doped with lithium ions by a simple method. Further, the standard deviation of the secondary battery of Example 2 was smaller than that of Example 1 and became stable. In order to make the potential more stable, the reference electrode layer preferably further contains a conductive auxiliary agent.

DESCRIPTION OF SYMBOLS 1 prismatic exterior body, 2 sealing plate, 3 electrode body, 4 positive electrode, 5 negative electrode, 6 positive electrode current collector, 7 positive electrode terminal, 8 negative electrode current collector, 9 negative electrode terminal, 10 electrolyte injection hole, 11 gas discharge valve, 12 electrode body holder, 13 positive electrode external conductive part, 14 positive electrode bolt part, 15 positive electrode insertion part, 16 negative electrode external conductive part, 17 negative electrode bolt part, 18 negative electrode insertion part, 20 first reference electrode formation region, 21 second Reference electrode formation region, 30 Separator, 41 Positive electrode active material layer, 42 Positive electrode core exposed part, 51 Negative electrode active material layer, 52 Negative electrode core exposed part, 60 Reference electrode layer, 100 Secondary battery, 200 Battery case

Claims (9)

An electrode body having a positive electrode and a negative electrode,
A conductive battery case that accommodates the electrode body,
In the composition formula _{Li 4 + x Ti 5 M y} O 12 ( wherein, M is Mg, Nb, Cu, Mn, Ni, Fe, Ru, Zr, B, Ca, Co, Cr, V, Sc, Y, La, Zn, A reference electrode layer containing a compound of one or more elements selected from Al and Ga, which satisfies 0.3≦x≦2.8 and 0≦y≦1),
An electrolyte containing lithium ions, which is disposed in the battery case so that the reference electrode layer is immersed,
The secondary battery, wherein the reference electrode layer is formed on an inner wall of the battery case and faces the positive electrode. The secondary battery according to claim 1, further comprising a porous electrode body holder that is disposed between the electrode body and the battery case and through which lithium ions can pass. The electrode body is a winding type in which the positive electrode and the negative electrode are wound via a separator, and has a positive electrode core body exposed portion at one end in the winding axis direction and the other end in the winding axis direction. Has a negative electrode core exposed part,
The outermost periphery of the electrode body is the negative electrode,
The secondary battery according to claim 1, wherein the reference electrode layer faces the exposed portion of the positive electrode core body. The electrode body is a winding type in which the positive electrode and the negative electrode are wound via a separator, and has a positive electrode core body exposed portion at one end in the winding axis direction and the other end in the winding axis direction. Has a negative electrode core exposed part,
The outermost periphery of the electrode body is the positive electrode,
The secondary battery according to claim 1, wherein the reference electrode layer faces a portion of the electrode body excluding a negative electrode core body exposed portion. The secondary battery according to claim 3, wherein the separator is laminated on the outermost periphery. The secondary battery according to claim 1, wherein the reference electrode layer further contains a conductive auxiliary agent. 7. The reference electrode layer according to claim 1, wherein at least a part of the reference electrode layer is formed on a side surface on the bottom side when the reference electrode layer is divided in half at the center in the height direction of the secondary battery. Next battery. On the inner wall of the conductive battery case, in the composition formula _{Li 4 + x Ti 5 M y} O 12 ( wherein, M is Mg, Nb, Cu, Mn, Ni, Fe, Ru, Zr, B, Ca, Co, Cr, Reference electrode layer containing a compound of one or more elements selected from V, Sc, Y, La, Zn, Al, and Ga, and satisfying 0≦x<0.3 and 0≦y≦1. A step of forming
A step of accommodating an electrode body having a positive electrode and a negative electrode in the battery case via a porous electrode body holder adjacent to the outside of the electrode body so that the positive electrode faces the reference electrode layer;
Injecting an electrolyte containing lithium ions into the battery case so that at least the reference electrode layer is immersed,
Connecting the battery case to a negative pole of a power source and the positive electrode to a positive pole of the power source, and doping the reference electrode layer with lithium ions. The method for manufacturing a secondary battery according to claim 8, further comprising a step of sealing the battery case before the step of doping the reference electrode layer with lithium ions.

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