JP2012238461A - Secondary battery, and method for manufacturing the same - Google Patents

Abstract

Provided is a secondary battery that reduces resistance by increasing conductivity between a positive electrode current collector and a positive electrode mixture layer and is excellent in durability.
In the secondary battery provided by the present invention, the positive electrode is a positive electrode mixture layer including a positive electrode current collector made of aluminum or an aluminum alloy, and at least a positive electrode active material formed on the positive electrode current collector. And have. The surface of the positive electrode current collector is provided with a compound film containing at least a compound containing fluorine and phosphorus as constituent elements, and the amount of the compound film is 0.02 μmol / cm ² to 0.00 in terms of fluorine atoms. 1 μmol / cm ² .
[Selection] Figure 3

Description

  The present invention relates to a secondary battery. Specifically, the present invention relates to a secondary battery including a positive electrode having a configuration in which a positive electrode material including a positive electrode active material is held by a positive electrode current collector having a film on the surface, and a method for manufacturing the same.

  Lithium-ion secondary batteries, nickel-metal hydride batteries, and other secondary batteries are important as, for example, power sources mounted on vehicles that use electricity as a drive source, or power sources used in personal computers, portable terminals, and other electrical products. It is growing. In particular, a lithium ion secondary battery that is lightweight and has a high energy density is expected to be preferably used as a high-output power source for mounting on a vehicle.

  In a lithium ion secondary battery having a typical configuration, an electrode material mainly composed of a substance (electrode active material) capable of reversibly occluding and releasing lithium ions on a conductive member (electrode current collector) is layered. An electrode having a formed configuration (hereinafter, this layered product is referred to as an “electrode mixture layer”) is provided. An electrode current collector (that is, a positive electrode current collector) used for the positive electrode is made of an aluminum material such as aluminum or an aluminum alloy (an alloy mainly composed of aluminum).

JP 2003-272610 A JP 2007-250376 A JP 2001-250561 A

By the way, in the positive electrode having the above structure, when a compound such as an oxide (typically alumina, aluminum fluoride, etc.) is present on the surface of the positive electrode current collector, the compound is an insulating film. There is a possibility that the resistance at the interface with the positive electrode mixture layer increases, and the internal resistance (for example, initial resistance, reaction resistance, etc.) of the positive electrode increases. Further, when charging / discharging is repeatedly performed, the surface of the positive electrode current collector may be corroded (for example, oxidized), and the internal resistance may increase (that is, the durability may decrease). If the internal resistance in the battery (especially the internal resistance in the positive electrode) can be reduced, a secondary battery with better output performance can be realized. In particular, when a lithium ion secondary battery is used as a drive power source or the like for a vehicle that requires high output, it is important to keep the internal resistance of the battery low.
Therefore, the present invention has been created to solve the above-described conventional problems (requests), and its purpose is to increase resistance between the positive electrode current collector and the positive electrode mixture layer by increasing the resistance. It is to provide a secondary battery that is reduced and excellent in durability. Another object of the present invention is to provide a method for producing a positive electrode for a secondary battery disclosed herein.

In order to achieve the above object, the present invention provides a secondary battery including a positive electrode and a negative electrode. That is, in the secondary battery disclosed herein, the positive electrode includes a positive electrode current collector made of aluminum or an aluminum alloy, and a positive electrode mixture layer including at least a positive electrode active material formed on the positive electrode current collector. Have. On the surface of the positive electrode current collector, a compound film containing at least a compound containing fluorine and phosphorus as constituent elements is provided. The amount of the compound coating is 0.02μmol ^/ cm ² ~0.1μmol ^/ cm 2 with a fluorine atom basis.

In the secondary battery provided by the present invention, the predetermined amount of the compound film is formed on a positive electrode current collector made of aluminum or an aluminum alloy.
According to the secondary battery having such a configuration, the resistance at the interface between the positive electrode current collector and the positive electrode mixture layer is reduced, and corrosion of the positive electrode current collector can be suppressed. Suppression) can be realized. Such a secondary battery is preferable because it can be more excellent in output performance (for example, high output). In addition, although the said patent documents 1-3 are mentioned as a technique which provides the film which consists of a compound containing phosphoric acid on the surface of a positive electrode electrical power collector, all are not disclosed in order to achieve the objective of this invention, and this It is not a technique for solving the problems of the invention.

In one preferred embodiment of the secondary battery disclosed herein, the amount of the compound coating is 0.02μmol ^/ cm ² ~0.06μmol ^/ cm 2 with a fluorine atom basis. According to such a configuration, a secondary battery having a small capacity reduction and excellent durability can be realized. Preferably, the positive electrode active material is a lithium-containing compound capable of inserting and extracting lithium ions. According to this configuration, a secondary battery with higher output performance can be realized.

  According to the present invention, as another aspect for realizing the above object, a positive electrode current collector made of aluminum or an aluminum alloy and a positive electrode mixture layer containing at least a positive electrode active material on the positive electrode current collector are provided. A method for producing a positive electrode for a secondary battery is provided. That is, the secondary battery manufacturing method disclosed herein provides a mixed solution prepared by dissolving a fluorine-containing phosphate compound containing fluorine and phosphorus as constituent elements in a predetermined organic solvent, Forming the compound film containing a compound containing at least fluorine and phosphorus as constituent elements on the surface of the positive electrode current collector by applying the mixed solution to the surface and drying the applied mixed solution; Forming the positive electrode mixture layer on the positive electrode current collector on which the film is formed.

  In the method for producing a positive electrode for a secondary battery according to the present invention, a compound film containing at least a compound having fluorine and phosphorus as constituent elements is formed by applying the above mixed solution to the surface of the positive electrode current collector and drying the mixture. . And since the positive electrode mixture layer is formed on the positive electrode current collector on which the compound film is formed, the resistance at the interface between the positive electrode current collector and the positive electrode mixture layer is reduced, A positive electrode for a secondary battery in which corrosion of the positive electrode current collector is suppressed can be obtained.

In a preferred embodiment of the secondary battery manufacturing method disclosed herein, lithium difluorophosphate (LiPO ₂ F ₂ ) is used as the fluorine-containing phosphate compound dissolved in the organic solvent. According to such a configuration, a compound film containing at least a compound containing fluorine and phosphorus as constituent elements can be easily formed on the surface of the positive electrode current collector.

In a preferred aspect of the method for manufacturing a secondary battery disclosed herein, the content of the lithium difluorophosphate in the mixed solution is 0.02 mol / L to 0.1 mol / L.
According to the positive electrode having such a configuration, a positive electrode having a lower initial resistance and excellent durability can be obtained. Preferably, the content of the lithium difluorophosphate in the mixed solution is 0.02 mol / L to 0.07 mol / L. According to this configuration, a positive electrode having excellent cycle characteristics with little capacity reduction can be obtained.

  In another preferred embodiment of the method for producing a secondary battery disclosed herein, a lithium-containing compound capable of inserting and extracting lithium ions is used as the positive electrode active material. According to this configuration, a positive electrode with better output performance can be obtained.

  According to the present invention, a secondary battery including a positive electrode for a secondary battery manufactured by any of the methods disclosed herein is also provided. Since such a secondary battery is constructed using the positive electrode, it can be a secondary battery with reduced initial resistance and excellent durability.

  As described above, since any of the secondary batteries disclosed herein can be a secondary battery with reduced initial resistance and excellent durability, a plurality of such secondary batteries (for example, 10 or more, preferably Can be used as a driving power source for vehicles (typically automobiles, especially automobiles equipped with electric motors such as hybrid cars, electric cars, and fuel cell cars) in the form of battery packs connected in series. it can.

It is a perspective view which shows typically the external shape of the secondary battery which concerns on one Embodiment of this invention. It is sectional drawing which follows the II-II line | wire in FIG. It is a figure which shows typically the structure of the positive electrode which concerns on one Embodiment of this invention. It is a perspective view which shows typically the external shape of the assembled battery which concerns on one Embodiment of this invention. It is a side view which shows typically the vehicle (automobile) provided with the secondary battery which concerns on this invention.

  Hereinafter, preferred embodiments of the present invention will be described. It should be noted that matters other than matters specifically mentioned in the present specification and necessary for carrying out the present invention can be grasped as design matters of those skilled in the art based on the prior art in this field. The present invention can be carried out based on the contents disclosed in this specification and common technical knowledge in the field.

The secondary battery provided by the present invention is characterized by having a positive electrode in which a predetermined amount of a compound film containing a compound containing at least fluorine and phosphorus as constituent elements is provided on the surface of the positive electrode current collector as described above. Attached.
Hereinafter, as a preferred embodiment of the secondary battery disclosed herein, a lithium ion secondary battery including a positive electrode in which a positive electrode mixture layer is formed on the surface of a positive electrode current collector will be described in detail as an example. However, it is not intended to limit the application target of the present invention to such a battery.

First, the positive electrode for lithium ion secondary batteries provided by the present invention will be described. The positive electrode disclosed here includes a positive electrode current collector and a positive electrode mixture layer containing at least a positive electrode active material on the positive electrode current collector.
The positive electrode current collector used in the positive electrode for a lithium ion secondary battery disclosed herein is mainly composed of aluminum or aluminum, like the positive electrode current collector used in the positive electrode of a conventional lithium ion secondary battery. An aluminum alloy is used. The shape of the positive electrode current collector can vary depending on the shape of the lithium ion secondary battery, and is not particularly limited, and may be various forms such as a foil shape, a rod shape, a plate shape, a sheet shape, and a mesh shape.

On the surface of the positive electrode current collector, a compound film containing at least a compound containing fluorine and phosphorus as constituent elements is provided. The compound in the compound film is not particularly limited as long as it is a compound containing fluorine and phosphorus as constituent elements, and examples thereof include compounds containing PO ₂ F ₂ anion, PO ₃ F anion and the like. Further, the compound film may further contain a compound containing PO ₂ anion, PO ₃ anion, PO ₄ anion and the like. The amount of the compound coating is 0.02μmol ^/ cm ² ~0.1μmol ^/ cm 2 with a fluorine atom basis. If the amount of the compound film is too smaller than 0.02 μmol / cm ^{2 in} terms of fluorine atoms, a sufficient amount of the compound film is not formed on the surface of the positive electrode current collector. The resistance at the interface with the layer cannot be reduced sufficiently. On the other hand, when the amount of the compound film is too larger than 0.1 μmol / cm ^{2 in} terms of fluorine atoms, an excessive amount of the compound film can be formed on the surface of the positive electrode current collector. For this reason, when an excessive compound film moves to the negative electrode side during endurance (during charging / discharging) and undergoes reductive decomposition, the electrolytic solution is consumed, and the capacity retention rate may decrease. Preferably, the amount of the compound coating is 0.02μmol ^/ cm ² ~0.06μmol ^/ cm 2 with a fluorine atom basis. When the amount of the compound coating is within the above range, the resistance can be reduced and the capacity can be prevented from decreasing.
The amount of the compound film (in terms of fluorine atoms) can be measured by a conventionally known method. For example, ion chromatography (ion chromatography mass spectrometry (IC-MS)) using a mass spectrometer as a detector is performed on a solution obtained by adding a compound film to a mixed solvent of water and acetonitrile. A compound having fluorine and phosphorus as constituent elements is quantitatively analyzed in terms of fluorine atoms. For example, when the PO ₂ F ₂ anion is 1 mol, the fluoride ion is 2 mol, and when the PO ₃ F anion is 1 mol, the fluoride ion is 1 mol.

The positive electrode active material used in the positive electrode of the lithium ion secondary battery disclosed herein is a material that can occlude and release lithium ions, and contains lithium and one or more transition metal elements A compound (for example, lithium transition metal complex oxide) is mentioned. For example, lithium nickel composite oxide (for example, LiNiO ₂ ), lithium cobalt composite oxide (for example, LiCoO ₂ ), lithium manganese composite oxide (for example, LiMn ₂ O ₄ ), or lithium nickel cobalt manganese composite oxide (for example, LiNi _{1). / 3} Co _1/3 Mn _1/3 O ₂ ), a ternary lithium-containing composite oxide.
In addition, a polyanionic compound (for example, LiFePO ₄₎ whose general formula is represented by LiMPO _4, LiMVO _4, or Li ₂ MSiO ₄ (wherein M is at least one element of Co, Ni, Mn, and Fe), etc. ₄ , LiMnPO ₄ , LiFeVO ₄ , LiMnVO ₄ , Li ₂ FeSiO ₄ , Li ₂ MnSiO ₄ , Li ₂ CoSiO ₄ ) may be used as the positive electrode active material.

The positive electrode mixture layer of the positive electrode for a lithium ion secondary battery disclosed herein may contain an optional component such as a conductive material and a binder (binder) in addition to the positive electrode active material.
The conductive material is not limited to a specific conductive material as long as it is conventionally used in this type of lithium ion secondary battery. For example, carbon materials such as carbon powder and carbon fiber can be used. As the carbon powder, various carbon blacks (for example, acetylene black, furnace black, ketjen black, etc.), carbon powders such as graphite powder can be used. Among these, you may use together 1 type, or 2 or more types.

  As said binder (binder), the thing similar to the binder used for the positive electrode of a common lithium ion secondary battery can be employ | adopted suitably. For example, when a solvent-based paste-like composition (a paste-like composition includes a slurry-like composition and an ink-like composition) is used as the composition for forming the positive electrode mixture layer, a polyfluoride is used. Polymer materials that dissolve in an organic solvent (non-aqueous solvent) such as vinylidene chloride (PVDF) and polyvinylidene chloride (PVDC) can be used. Alternatively, when an aqueous paste composition is used, a polymer material that can be dissolved or dispersed in water can be preferably used. For example, polytetrafluoroethylene (PTFE), carboxymethyl cellulose (CMC) and the like can be mentioned. In addition, the polymer material illustrated above may be used as a thickener and other additives in the above composition in addition to being used as a binder.

  Here, the “solvent-based paste-like composition” is a concept indicating a composition in which the dispersion medium of the positive electrode active material is mainly an organic solvent. As the organic solvent, for example, N-methylpyrrolidone (NMP) can be used. The “aqueous paste-like composition” is a concept indicating a composition using water or a mixed solvent mainly containing water as a dispersion medium of the positive electrode active material. As a solvent other than water constituting such a mixed solvent, one or more organic solvents (lower alcohol, lower ketone, etc.) that can be uniformly mixed with water can be appropriately selected and used.

Hereinafter, the preferable one aspect | mode of the manufacturing method of the positive electrode for lithium ion secondary batteries disclosed here is demonstrated in detail.
The method for producing a positive electrode for a lithium ion secondary battery disclosed herein includes (1) preparing a mixed solution obtained by dissolving a fluorine-containing phosphate compound containing fluorine and phosphorus as constituent elements in a predetermined organic solvent. (2) applying the mixed solution to the surface of the positive electrode current collector made of aluminum or an aluminum alloy; and (3) drying the applied mixed solution to provide at least fluorine and a surface of the positive electrode current collector. Forming a compound film containing a compound containing phosphorus as a constituent element; and (4) forming the positive electrode mixture layer on the positive electrode current collector on which the compound film is formed.

First, a process of preparing a mixed solution obtained by dissolving a fluorine-containing phosphate compound containing fluorine and phosphorus as constituent elements in a predetermined organic solvent will be described.
The fluorine-containing phosphoric acid compound having fluorine and phosphorus as constituent elements disclosed herein is not particularly limited as long as it contains fluorine and phosphorus as constituent elements. For example, monofluorophosphate, difluorophosphate, etc. Is mentioned. Examples of the monofluorophosphate include lithium monofluorophosphate (Li ₂ PO ₃ F), sodium monofluorophosphate, potassium monofluorophosphate, and the like. Examples of the difluorophosphate include lithium difluorophosphate (LiPO ₂ F ₂ ), sodium difluorophosphate, and potassium difluorophosphate. Preferably, lithium difluorophosphate is used. Since lithium difluorophosphate has a relatively high solubility in an organic solvent, the amount of the compound coating can be adjusted relatively easily.
Examples of the organic solvent (nonaqueous solvent) include cyclic carbonates such as ethylene carbonate (EC) and propylene carbonate (PC), chains such as dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC). -Containing carbonates, cyclic esters such as γ-butyrolactone and γ-valerolactone, chain esters such as methyl acetate and methyl propionate, cyclic ethers such as tetrahydrofuran and dioxane, chain ethers such as dimethoxyethane, and sulfur-containing substances such as dimethyl sulfoxide Non-aqueous organic solvent etc. are mentioned.
In this step, a mixed solution prepared by dissolving the fluorine-containing phosphate compound (for example, lithium difluorophosphate) in the organic solvent (for example, EMC) is prepared. Here, the content of the fluorine-containing phosphate compound in the mixed solution (that is, the amount of the fluorine-containing phosphate compound dissolved in the organic solvent) is preferably 0.015 mol / L or more (for example, 0.02 mol). / L to 0.1 mol / L, preferably 0.02 mol / L to 0.07 mol / L). If the content of the fluorine-containing phosphate compound is less than 0.02 mol / L, a sufficient amount of the compound film may not be formed on the surface of the positive electrode current collector.

  Next, a process of applying the above mixed solution to the surface of a positive electrode current collector made of aluminum or an aluminum alloy will be described. As a method for applying (coating) the prepared mixed solution to the surface of the positive electrode current collector, a conventionally known technique can be applied and there is no particular limitation. For example, a method using a coating device such as a slit coater, a method of immersing the positive electrode current collector in a mixed solution, a method of spraying the mixed solution on the surface of the positive electrode current collector, and the like can be mentioned.

  Next, a process of forming a compound film containing at least fluorine and phosphorus as constituent elements on the surface of the positive electrode current collector by drying the applied mixed solution will be described. As a method of drying the mixed solution, a technique similar to a conventionally known method can be appropriately employed. For example, the compound film containing at least a compound containing fluorine and phosphorus as constituent elements can be formed on the surface of the positive electrode current collector by drying the mixed solution satisfactorily by natural drying, hot air, low-humidity air, or the like. In addition, before drying the said mixed solution, you may wash | clean the surface of a positive electrode electrical power collector with the said organic solvent (The organic solvent contained in a mixed solution may be sufficient) as needed.

Next, a process of forming a positive electrode mixture layer on the positive electrode current collector on which the compound film is formed will be described.
A paste-like composition for forming a positive electrode mixture layer in which the positive electrode active material, a conductive material, and a binder (binder) are dispersed in a predetermined solvent (the paste-like composition includes a slurry-like composition and an ink) Hereinafter, a paste-like composition is simply referred to as “paste”). Then, after the prepared paste for forming the positive electrode mixture layer is applied to the surface of the positive electrode current collector on which the compound film is formed (typically applied) and dried to form the positive electrode mixture layer, Compress (press) as necessary. Thereby, the positive electrode provided with the positive electrode electrical power collector in which the compound film was formed, and a positive electrode compound material layer is producible.
In addition, as a method of apply | coating the said paste, the technique similar to a conventionally well-known method can be employ | adopted suitably. For example, the paste can be suitably applied to the positive electrode current collector by using an appropriate application device such as a slit coater, a die coater, or a gravure coater. Moreover, when drying a solvent, it can dry favorably by using natural drying, a hot air, low-humidity air, a vacuum, infrared rays, far-infrared rays, and an electron beam individually or in combination. Furthermore, as a compression method, a conventionally known compression method such as a roll press method or a flat plate press method can be employed.

  As shown in FIG. 3, the positive electrode 64 manufactured through the above steps includes a positive electrode current collector 62 and a positive electrode mixture layer 66 formed on the positive electrode current collector 62. The surface of the body 62 is provided with a compound film 68 containing a compound containing at least fluorine and phosphorus as constituent elements. For this reason, resistance at the interface between the positive electrode current collector 62 and the positive electrode mixture layer 66 is reduced, and corrosion of the positive electrode current collector 62 can be suppressed, so that high durability (for example, suppression of increase in resistance) is achieved. Can be realized.

Next, the negative electrode provided in the lithium ion secondary battery disclosed here will be described. The negative electrode includes a negative electrode current collector and a negative electrode mixture layer formed on the negative electrode current collector.
As the negative electrode active material, one or more materials conventionally used for negative electrodes of lithium ion secondary batteries can be used without particular limitation. For example, carbon materials such as graphite (graphite), oxide materials such as lithium titanium oxide (Li ₄ Ti ₅ O ₁₂ ), metals such as tin, aluminum (Al), zinc (Zn), silicon (Si), or Examples thereof include metal materials composed of metal alloys mainly composed of these metal elements. Graphite materials such as natural graphite and artificial graphite can be suitably used. Further, a coated graphite material in which the surface of the graphite material is coated with an amorphous carbon film is preferably used. Here, the above amorphous carbon film, a low crystallinity carbon, bond formation other than very small crystallites, sp ² hybrid orbital composed of carbon atoms laminated irregular, sp ² hybrid orbital of the carbon surface It is carbon comprising carbon having etc.

The negative electrode mixture layer may contain any component such as a binder (binder) and a thickener as necessary in addition to the negative electrode active material.
As said binder, the thing similar to the binder used for the negative electrode of a general lithium ion secondary battery can be employ | adopted suitably. For example, when an aqueous paste composition is used to form the negative electrode mixture layer, a polymer material that is dissolved or dispersed in water can be preferably used. Polymer materials that disperse in water (water dispersible) include rubbers such as styrene butadiene rubber (SBR) and fluorine rubber; fluorine resins such as polyethylene oxide (PEO) and polytetrafluoroethylene (PTFE); vinyl acetate Examples thereof include copolymers.

  Moreover, as the thickener, a polymer material that is dissolved or dispersed in water or a solvent (organic solvent) can be employed. Examples of water-soluble (water-soluble) polymer materials include cellulose polymers such as carboxymethyl cellulose (CMC), methyl cellulose (MC), cellulose acetate phthalate (CAP), and hydroxypropylmethyl cellulose (HPMC); polyvinyl alcohol ( PVA); and the like.

  The negative electrode mixture layer is, for example, for forming a paste-like negative electrode mixture layer in which the negative electrode active material and other optional components (binder, thickener, etc.) are dispersed in an appropriate solvent (for example, water). Prepare the composition (preparation, purchase, etc.), apply (apply) the composition to the surface of the negative electrode current collector, dry the composition, and then press (compress) the negative electrode as necessary. A composite layer is formed. Thereby, a negative electrode provided with a negative electrode current collector and a negative electrode mixture layer can be produced.

Hereinafter, although one form of the lithium ion secondary battery constructed | assembled using the said positive electrode and the said negative electrode is demonstrated referring drawings, it is not intending limiting this invention to this embodiment. That is, as long as the positive electrode and the negative electrode are employed, the shape (outer shape and size) of the lithium ion secondary battery to be constructed is not particularly limited. In the following embodiment, a lithium ion secondary battery having a configuration in which a wound electrode body and an electrolytic solution are housed in a rectangular battery case will be described as an example.
In addition, in the following drawings, the same code | symbol is attached | subjected to the member and site | part which show | plays the same effect | action, and the overlapping description may be abbreviate | omitted. Moreover, the dimensional relationship (length, width, thickness, etc.) in each drawing does not necessarily reflect the actual dimensional relationship.

FIG. 1 is a perspective view schematically showing a lithium ion secondary battery (secondary battery) 10 according to the present embodiment. FIG. 2 is a longitudinal sectional view taken along line II-II in FIG.
As shown in FIG. 1, the lithium ion secondary battery 10 according to this embodiment includes a battery case 15 made of metal (a resin or a laminate film is also suitable). The case (outer container) 15 includes a flat cuboid case main body 30 having an open upper end, and a lid body 25 that closes the opening 20. The lid body 25 seals the opening 20 of the case main body 30 by welding or the like. On the upper surface of the case 15 (that is, the lid body 25), a positive electrode terminal 60 electrically connected to the positive electrode sheet (positive electrode) 64 of the wound electrode body 50 and a negative electrode terminal electrically connected to the negative electrode sheet 84 of the electrode body. 80 is provided. In addition, the lid 25 is provided with a safety valve 40 for discharging the gas generated inside the case 15 to the outside of the case 15 when the battery is abnormal, as in the case of the conventional lithium ion secondary battery. . In the case 15, the positive electrode sheet 64 and the negative electrode sheet 84 are laminated together with a total of two separator sheets 95 and wound, and then the obtained wound body is crushed from the side direction and ablated. A flat wound electrode body 50 and an electrolyte (for example, a non-aqueous electrolyte) are accommodated.

  At the time of the above lamination, as shown in FIG. 2, the positive electrode mixture layer non-formed portion of the positive electrode sheet 64 (that is, the portion where the positive electrode current collector 62 is exposed without forming the positive electrode mixture layer 66) and the negative electrode sheet The negative electrode composite material layer non-formed portion 84 (that is, the portion where the negative electrode current collector 82 is exposed without forming the negative electrode composite material layer 90) protrudes from both sides in the width direction of the separator sheet 95. And the negative electrode sheet 84 are overlapped with a slight shift in the width direction. As a result, in the lateral direction with respect to the winding direction of the wound electrode body 50, the electrode mixture layer non-forming portions of the positive electrode sheet 64 and the negative electrode sheet 84 are respectively wound core portions (that is, the positive electrode mixture layer forming portion of the positive electrode sheet 64. And a portion where the negative electrode mixture layer forming portion of the negative electrode sheet 84 and the two separator sheets 95 are wound tightly) protrude outward. The positive electrode terminal 60 is joined to the protruding portion on the positive electrode side, and the positive electrode sheet 64 and the positive electrode terminal 60 of the wound electrode body 50 formed in the flat shape are electrically connected. Similarly, the negative electrode terminal 80 is joined to the negative electrode side protruding portion, and the negative electrode sheet 84 and the negative electrode terminal 80 are electrically connected. The positive and negative electrode terminals 60 and 80 and the positive and negative electrode current collectors 62 and 82 can be joined by, for example, ultrasonic welding, resistance welding, or the like.

As said electrolyte, the thing similar to the non-aqueous electrolyte conventionally used for a lithium ion secondary battery can be used without limitation. Such a nonaqueous electrolytic solution typically has a composition in which a supporting salt is contained in a suitable nonaqueous solvent (organic solvent). As said non-aqueous solvent, 1 type, or 2 or more types selected from EC, PC, DMC, DEC, EMC etc. can be used, for example. Further, as the supporting salt (supporting electrolyte), for _example, it can be used lithium salts such as LiPF 6, LiBF _4. Further, difluorophosphate (LiPO ₂ F ₂ ) or lithium bisoxalate borate (LiBOB) may be dissolved in the non-aqueous electrolyte.
Moreover, as said separator sheet, a conventionally well-known thing can be especially used without a restriction | limiting. For example, a porous sheet made of resin (a microporous resin sheet) can be preferably used. Porous polyolefin resin sheets such as polyethylene (PE), polypropylene (PP), and polystyrene (PS) are preferred.

Next, an example of an assembled battery (typically an assembled battery in which a plurality of single cells are connected in series) including the lithium ion secondary battery 10 as a single battery and a plurality of the single batteries will be described.
As shown in FIG. 4, the assembled battery 200 includes a plurality of (typically 10 or more, preferably about 10 to 30, for example, 20) lithium ion secondary batteries (unit cells) 10 respectively. The wide surfaces of the battery case 15 are arranged in the facing direction (stacking direction) while being inverted one by one so that the positive electrode terminals 60 and the negative electrode terminals 80 are alternately arranged. A cooling plate 110 having a predetermined shape is sandwiched between the arranged cells 10. The cooling plate 110 functions as a heat dissipating member for efficiently dissipating the heat generated in each unit cell 10 during use, and preferably a cooling fluid (typically air) between the unit cells 10. ) (For example, a shape in which a plurality of parallel grooves extending vertically from one side of the rectangular cooling plate to the opposite side are provided on the surface). A cooling plate made of metal having good thermal conductivity or lightweight and hard polypropylene or other synthetic resin is suitable.

A pair of end plates (restraint plates) 120 and 120 are disposed at both ends of the unit cell 10 and the cooling plate 110 arranged as described above. One or a plurality of sheet-like spacer members 150 as length adjusting means may be sandwiched between the cooling plate 110 and the end plate 120. The cell 10, the cooling plate 110 and the spacer member 150 arranged in the above manner are applied with a predetermined restraining pressure in the stacking direction by a fastening restraint band 130 attached so as to bridge between both end plates. It is restrained. More specifically, by tightening and fixing the end portion of the restraining band 130 to the end plate 120 with screws 155, the unit cells and the like are restrained so that a predetermined restraining pressure is applied in the arrangement direction. Thereby, restraint pressure is also applied to the wound electrode body 50 housed in the battery case 15 of each unit cell 10.
In addition, between the adjacent unit cells 10, one positive electrode terminal 60 and the other negative electrode terminal 80 are electrically connected by a connecting member (bus bar) 140. Thus, the assembled battery 200 of the desired voltage is constructed | assembled by connecting each cell 10 in series.

  EXAMPLES Examples relating to the present invention will be described below, but the present invention is not intended to be limited to those shown in the examples.

<Example 1>
After immersing an aluminum foil (thickness: 15 μm) as a positive electrode current collector in a solution of 0.01 mol / L lithium difluorophosphate (LiPO ₂ F ₂ ) dissolved in ethyl methyl carbonate (EMC), Remove the aluminum foil from the solution and clean the surface with EMC. By drying the cleaned aluminum foil current collector, an aluminum foil provided with a compound film containing at least a compound containing fluorine and phosphorus as constituent elements was obtained. The amount of the compound film at this time was 0.014 μmol / cm ² in terms of fluorine atoms.
Next, the mass ratio of LiNi _1/3 Mn _1/3 Co _1/3 O ₂ as the positive electrode active material, acetylene black (AB) as the conductive material, and PVDF as the binder is 90: 8: 2 was weighed and these materials were dispersed in NMP to prepare a paste-like composition for forming a positive electrode mixture layer. The composition is applied onto an aluminum foil (positive electrode current collector) coated with the phosphoric acid compound coating, dried at a coating amount of 6 mg / cm ² per side, and subjected to a roll press treatment to form a positive electrode composite on the aluminum foil. A sheet-like positive electrode formed by forming a material layer was produced.
Further, these materials were weighed so that the mass ratio of natural graphite whose surface was coated with an amorphous carbon film, SBR as a binder, and CMC as a thickener was 98: 1: 1. A paste-like composition for forming a negative electrode mixture layer was prepared by dispersing in ion-exchanged water. The composition is applied on a copper foil (negative electrode current collector) with a coating amount of 4 mg / cm ² per side, dried, and subjected to a roll press to form a negative electrode mixture layer on the copper foil. A sheet-like negative electrode was produced.
Then, the sheet-like positive electrode and the sheet-like negative electrode prepared above are arranged opposite to each other with a separator sheet (polypropylene / polyethylene composite porous membrane) interposed therebetween (laminated), and this is laminated with an electrolyte solution in a laminate type case (laminate) The lithium ion secondary battery according to Example 1 (hereinafter, sometimes simply referred to as “secondary battery”) was constructed by housing in a film. As the electrolytic solution, a solution obtained by dissolving 1 mol / L LiPF ₆ in a mixed solvent of ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) in a volume ratio of 1: 1: 1 was used. .

<Example 2>
The lithium foil according to Example 2 was the same as Example 1 except that an aluminum foil (thickness 15 μm) as a positive electrode current collector was immersed in a solution of 0.02 mol / L LiPO ₂ F ₂ in EMC. An ion secondary battery was constructed. The amount of the compound film at this time was 0.02 μmol / cm ² in terms of fluorine atoms.

<Example 3>
The lithium according to Example 3 was the same as Example 1 except that an aluminum foil (thickness 15 μm) as a positive electrode current collector was immersed in a solution of 0.05 mol / L LiPO ₂ F ₂ in EMC. An ion secondary battery was constructed. The amount of the compound film at this time was 0.032 μmol / cm ² in terms of fluorine atoms.

<Example 4>
The lithium foil according to Example 4 was the same as Example 1 except that an aluminum foil (thickness 15 μm) as a positive electrode current collector was immersed in a solution of 0.07 mol / L LiPO ₂ F ₂ in EMC. An ion secondary battery was constructed. The amount of the compound film at this time was 0.06 μmol / cm ² in terms of fluorine atoms.

<Example 5>
The lithium according to Example 5 was the same as Example 1 except that an aluminum foil (thickness 15 μm) as a positive electrode current collector was immersed in a solution of 0.1 mol / L LiPO ₂ F ₂ in EMC. An ion secondary battery was constructed. The amount of the compound film at this time was 0.1 μmol / cm ² in terms of fluorine atoms.

<Example 6>
A lithium ion secondary battery according to Example 6 was constructed in the same manner as in Example 1 except that an aluminum foil (thickness: 15 μm) having no compound coating on the surface thereof was used as the positive electrode current collector.

<Initial resistance measurement>
First, an appropriate conditioning process (for example, a constant current (CC) charge for 3 hours at a charge rate of 1/10 C of the theoretical capacity of the positive electrode, and a charge rate of 1/3 C is applied to each lithium ion secondary battery constructed above. An initial charging / discharging process in which an operation of charging at a constant current up to 4.1 V and an operation of discharging at a constant current of up to 3.0 V at a discharge rate of 1/3 C are performed 2-3 times. Here, 1C means the amount of current that can charge the battery capacity (Ah) predicted from the theoretical capacity of the positive electrode in one hour.
Each secondary battery after the conditioning treatment was adjusted to a SOC 60% charge state at a charge rate of 1 / 3C. Thereafter, a constant current discharge is performed for 10 seconds at a discharge rate of 3 C under a temperature condition of −15 ° C., and the initial resistance [Ω] is determined from the slope of the first-order approximation line of the current (I) -voltage (V) plot value. Asked. Table 1 shows the initial resistance of the secondary battery of each example.

<Measurement of capacity retention>
About each secondary battery after the said initial resistance measurement, the capacity | capacitance maintenance factor after storing for 30 days on 60 degreeC temperature conditions was measured. That is, after each secondary battery is charged to 4.1V at 1C by the constant current constant voltage (CCCV) method, it is discharged to 3V by 1 / 3C by the CC method, and further discharged to 3V by 1/3 by the CCCV method. did. The capacity obtained at this time was defined as the initial battery capacity. Each secondary battery whose initial battery capacity was measured was adjusted to a SOC 80% charge state by the CCCV method. Next, after each of these secondary batteries was stored in a constant temperature bath at 60 ° C. for 30 days, the battery capacity after storage of each secondary battery (battery capacity after storage) was measured in the same manner as the method for measuring the initial battery capacity. ) Was measured. Here, the following formula: {(battery capacity after storage) / (initial battery capacity)} × 100 was defined as the capacity retention rate [%] after 30 days storage. Table 1 shows the capacity retention ratio of each secondary battery.

<Measurement of resistance increase rate>
About each secondary battery after the said capacity maintenance factor measurement, the resistance (resistance after a preservation | save) of each secondary battery was measured by the method similar to the method of measuring the said initial stage resistance. Here, the following formula: {(resistance after storage−initial resistance) / (initial resistance)} × 100 was defined as a resistance increase rate [%] after storage for 30 days. Table 1 shows the capacity retention ratio of each secondary battery.

As shown in Table 1, in the secondary batteries according to Examples 2 to 5, since a sufficient amount of the compound film is formed on the surface of the positive electrode current collector, the amount of the compound film is related to Example 1 that is not sufficient. It was confirmed that the initial resistance was reduced and the rate of increase in resistance was small (that is, excellent in durability) as compared with the secondary battery and the secondary battery according to Example 6 in which no compound film was formed. Further, it was confirmed that the secondary batteries according to Examples 2 to 4 were superior in capacity retention rate compared with the secondary battery according to Example 5. From this result, the amount of the compound coating, it is reasonable with fluorine atoms terms are within the scope of ^{0.02μmol / cm 2 ~0.1μmol / cm 2} , more 0.02μmol ^/ cm 2 ~0.06μmol It was confirmed that it was preferably within the range of / cm ² .

  As mentioned above, although the specific example of this invention was demonstrated in detail, these are only illustrations and do not limit a claim. The technology described in the claims includes various modifications and changes of the specific examples illustrated above.

  Since the secondary battery according to the present invention has reduced resistance and excellent durability, it can be used as a lithium ion secondary battery for various applications. For example, as shown in FIG. 5, it can be suitably used as a power source (drive power source) for a vehicle driving motor mounted on a vehicle 100 such as an automobile. The lithium ion secondary battery 10 used for the vehicle 100 may be used alone, or may be used in the form of an assembled battery 200 that is connected in series and / or in parallel.

DESCRIPTION OF SYMBOLS 10 Lithium ion secondary battery 15 Battery case 20 Opening part 25 Cover body 30 Case main body 40 Safety valve 50 Winding electrode body 60 Positive electrode terminal 62 Positive electrode current collector 64 Positive electrode sheet (positive electrode)
66 Positive electrode mixture layer 68 Compound coating 80 Negative electrode terminal 82 Negative electrode current collector 84 Negative electrode sheet (negative electrode)
90 Negative electrode composite material layer 95 Separator sheet 100 Vehicle (automobile)
110 Cooling plate 120 End plate 130 Restraint band 140 Connection member 150 Spacer member 155 Screw 200 Battery assembly

Claims (10)

A secondary battery comprising a positive electrode and a negative electrode,
The positive electrode has a positive electrode current collector made of aluminum or an aluminum alloy, and a positive electrode mixture layer containing at least a positive electrode active material formed on the positive electrode current collector,
The surface of the positive electrode current collector is provided with a compound film containing a compound containing at least fluorine and phosphorus as constituent elements,
The amount of the compound coating is 0.02μmol ^/ cm ² ~0.1μmol ^/ cm 2 with a fluorine atom in terms, the secondary battery. Wherein the amount of the compound coating is 0.02μmol ^/ cm ² ~0.06μmol ^/ cm 2 with a fluorine atom in terms secondary battery according to claim 1.   The secondary battery according to claim 1, wherein the positive electrode active material is a lithium-containing compound capable of inserting and extracting lithium ions. A method for producing a positive electrode for a secondary battery comprising: a positive electrode current collector made of aluminum or an aluminum alloy; and a positive electrode mixture layer containing at least a positive electrode active material on the positive electrode current collector,
Preparing a mixed solution obtained by dissolving a fluorine-containing phosphoric acid compound having fluorine and phosphorus as constituent elements in a predetermined organic solvent;
Applying the mixed solution to the surface of the positive electrode current collector;
Forming a compound film containing a compound containing at least fluorine and phosphorus as constituent elements on the surface of the positive electrode current collector by drying the applied mixed solution;
Forming the positive electrode mixture layer on the positive electrode current collector on which the compound film is formed;
The manufacturing method of the positive electrode for secondary batteries including this.   The production method according to claim 4, wherein lithium difluorophosphate is used as the fluorine-containing phosphate compound to be dissolved in the organic solvent.   The production method according to claim 5, wherein a content of the lithium difluorophosphate in the mixed solution is 0.02 mol / L to 0.1 mol / L.   The production method according to claim 5, wherein a content of the lithium difluorophosphate in the mixed solution is 0.02 mol / L to 0.07 mol / L.   The manufacturing method according to any one of claims 4 to 7, wherein a lithium-containing compound capable of inserting and extracting lithium ions is used as the positive electrode active material.   A secondary battery provided with the positive electrode for secondary batteries obtained by the manufacturing method as described in any one of Claims 4-8.   An assembled battery constructed as a driving power source for a vehicle, wherein a plurality of the secondary batteries according to claim 1, 2, 3 or 9 are connected in series.

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