JP5299710B2 - Positive electrode current collector and manufacturing method thereof - Google Patents

Description

  The present invention relates to a positive electrode current collector used as a battery component and a method for producing the positive electrode current collector.

  A lithium secondary battery (typically a lithium ion battery) that is charged and discharged by interposing lithium ions between the positive electrode and the negative electrode is lightweight and provides high output. The demand for mobile terminals is expected to increase further in the future. In one typical configuration of this type of secondary battery, an electrode having a configuration in which a material (electrode active material) capable of reversibly occluding and releasing lithium ions is held in a conductive member (electrode current collector) is used. Prepare. For example, as a representative example of an electrode active material (positive electrode active material) used for a positive electrode, an oxide containing lithium and one or more transition metal elements as constituent metal elements (hereinafter referred to as “lithium transition metal oxide”). Also called). A typical example of an electrode current collector (positive electrode current collector) used for the positive electrode is a sheet-like or foil-like member mainly composed of aluminum or an aluminum alloy.

  A positive electrode current collector made of aluminum or an aluminum alloy is easily corroded (for example, oxidized). For example, the surface of the positive electrode current collector made of aluminum or an aluminum alloy is immediately oxidized when exposed to the atmosphere, and thus always has an oxide film. When an oxide film is present on the current collector surface, the oxide film is an insulating film, which may increase the electrical resistance between the positive electrode current collector and the positive electrode active material layer.

  Patent Document 1 is disclosed as a technique for suppressing such corrosion (deterioration) of the current collector surface. In Patent Document 1, a natural oxide film on the surface of the current collector is removed using a sputter ion beam etching apparatus, and then a coating layer (carbon film) having good conductivity and corrosion resistance such as carbon on the surface of the current collector. A technique for providing the above is disclosed. Examples of other prior art documents that impart corrosion resistance to the current collector surface include Patent Documents 2, 3, and 4, for example.

Japanese Patent Laid-Open No. 11-250900 Japanese Patent Laid-Open No. 10-106585 JP 2005-259682 A JP 2007-250376 A

However, the natural oxide film of Al ₂ O ₃ is generally low in etching rate, and therefore has a problem that it takes too much time to remove the oxide film. For example, according to a trial calculation by the present inventor, when an oxide film is etched using a standard sputtering apparatus under conditions of a sputtering power of 200 W and a capacity of 13.5 MHz, the etching rate is approximately 1 nm / min. If the thickness of the natural oxide film is about 5 to 10 nm, it takes 5 to 10 minutes to completely remove the oxide film, and the productivity is poor. If the etching time can be further shortened, such an etching process can be realized in a mode suitable for continuous production, for example, in-line, which is useful.

  The present invention has been made in view of the above points, and its main object is a positive electrode current collector having a conductive layer on the surface, and a positive electrode current collector excellent in productivity and the positive electrode current collector. It is to provide a manufacturing method.

The inventor does not significantly increase the electrical resistance value between the positive electrode current collector and the positive electrode active material layer as long as the oxide film has a predetermined thickness or less, and on the contrary, the stability of the positive electrode current collector. It has been found that it contributes to (durability) improvement, and the present invention has been completed.
That is, the positive electrode current collector provided by the present invention is a positive electrode current collector in which a conductive layer having conductivity is formed on a base made of aluminum or an aluminum alloy. The base material has a surface oxide film made of an aluminum oxide having a thickness of 3 nm or less at an interface between the base material body and the conductive layer. Preferably, the contact resistance is adjusted to the thickness of the 0.5mΩ · cm ² or less between the thickness of the surface oxide film is an at 0.5nm or more 3nm or less by etching the substrate and the conductive layer Has been.

According to the positive electrode current collector of the present invention, a surface oxide film (Al ₂ O ₃ layer) that is chemically more stable than Al alone is interposed at the interface between the aluminum substrate and the conductive layer. The durability (stability) of the current collector is improved as compared with the current collector without a film. As a result, the battery life can be extended (that is, stable battery performance can be maintained over a long period of time). In addition, by setting the thickness of the surface oxide film to 3 nm or less, conductivity can be imparted to the oxide film that is an insulating film, and a positive electrode current collector and a positive electrode mixture layer (a layer containing a positive electrode active material) The electrical resistance value between is not significantly increased. That is, according to the configuration of the present invention, it is possible to provide a positive electrode current collector with high output and excellent cycle life.

In a preferred embodiment of the positive electrode current collector disclosed herein, the conductive layer is made of a metal or metal carbide that is less susceptible to alkali corrosion (degeneration) than aluminum. In that case, corrosion resistance can be imparted to the conductive layer to protect the aluminum base material that is susceptible to corrosion.

  In a preferred embodiment of the positive electrode current collector disclosed herein, the substrate is a sheet-like aluminum foil. Aluminum is easily processed into a thin film (sheet shape), and therefore has various characteristics preferable as a positive electrode current collector, and is susceptible to corrosion. Therefore, when the substrate is an aluminum foil, the effect of adopting the configuration of the present invention in which an oxide film and a conductive layer are provided on the substrate surface for protection can be exhibited particularly well.

The present invention also provides a method for producing a positive electrode current collector. This positive electrode current collector is a method for producing a positive electrode current collector formed by laminating a conductive layer having conductivity on a base made of aluminum or an aluminum alloy. In this method, a substrate having a surface oxide film made of aluminum oxide at the interface of the substrate body is prepared as the substrate. Then, a thickness adjusting step of adjusting the surface oxide film of the prepared base material to a thickness of 0.5 nm to 3 nm by etching, and forming the conductive layer on the surface oxide film adjusted in thickness And a conductive layer forming step. Preferably, in the thickness adjusting step, the thickness of the surface oxide film is 0.5 nm or more and 3 nm or less, and the contact resistance between the substrate and the conductive layer is 0.5 mΩ · cm ² or less. Adjust to thickness.

  Since the aluminum oxide film has a low etching rate, it takes time for complete removal, but according to the method of the present invention, the surface oxide film is used as a stable layer and intentionally left at a predetermined thickness. The time required for the etching process can be greatly reduced, and the productivity can be improved.

  In a preferred embodiment of the positive electrode current collector manufacturing method disclosed herein, the etching process is performed by sputter etching. Moreover, in one preferable aspect of the positive electrode current collector manufacturing method disclosed herein, the conductive layer is formed by a sputtering method using a metal or a metal carbide as a target.

  According to the present invention, there is also provided a secondary battery (for example, a lithium secondary battery such as a lithium ion battery) constructed using a positive electrode current collector manufactured by any of the methods disclosed herein. Since such a secondary battery is constructed using the positive electrode current collector as a positive electrode, it exhibits better battery performance (for example, low internal resistance, good high output characteristics, durability (stability) Satisfy at least one of high).

  Such a secondary battery is suitable as a secondary battery mounted on a vehicle such as an automobile. Therefore, according to the present invention, there is provided a vehicle including any of the secondary batteries disclosed herein (which may be in the form of an assembled battery in which a plurality of secondary batteries are connected). In particular, since the light weight and high output can be obtained, the battery is a lithium secondary battery (typically a lithium ion battery), and the lithium secondary battery is used as a power source (typically a hybrid vehicle or an electric vehicle). A vehicle (for example, an automobile) provided as a power source of the vehicle is preferable.

Sectional drawing which shows typically the cross section of the positive electrode which concerns on one Embodiment of this invention. The flowchart which shows the manufacturing process of the positive electrode which concerns on one Embodiment of this invention. Process sectional drawing which shows typically the manufacturing process of the positive electrode which concerns on one Embodiment of this invention. Process sectional drawing which shows typically the manufacturing process of the positive electrode which concerns on one Embodiment of this invention. Process sectional drawing which shows typically the manufacturing process of the positive electrode which concerns on one Embodiment of this invention. Process sectional drawing which shows typically the manufacturing process of the positive electrode which concerns on one Embodiment of this invention. The figure which shows typically the manufacturing apparatus of the positive electrode electrical power collector which concerns on one Embodiment of this invention. The graph which shows the relationship between the film thickness of Al oxide film, and contact resistance. The graph which shows the relationship between a contact resistance and the battery capacity in 100C rate. The side view which shows typically the vehicle (automobile) provided with the secondary battery which concerns on one Embodiment of this invention.

  The inventor of the present application does not completely remove the natural oxide film on the surface of the positive electrode current collector (aluminum foil), but actively uses it while leaving a part of the positive electrode current collector excellent in durability and productivity. The inventor has obtained knowledge that an electric body can be obtained and has arrived at the present invention.

  Embodiments according to the present invention will be described below with reference to the drawings. In the following drawings, members / parts having the same action are described with the same reference numerals. Note that the dimensional relationship (length, width, thickness, etc.) in each drawing does not reflect the actual dimensional relationship. Further, matters other than matters specifically mentioned in the present specification and matters necessary for carrying out the present invention (for example, a method for producing an electrode active material, a method for preparing an electrode mixture layer forming composition, a separator, The configuration and manufacturing method of the electrolyte, a general technique related to the construction of the lithium secondary battery and other batteries, etc.) can be grasped as design matters of those skilled in the art based on the conventional technology in the field.

  Although not intended to be particularly limited, a positive electrode current collector 10 for a lithium secondary battery (typically a lithium ion battery) having a foil-like base material (aluminum foil) mainly made of aluminum and the The positive electrode current collector according to this embodiment will be described using the positive electrode 30 including the positive electrode current collector as an example.

  As shown in FIG. 1, a positive electrode 30 for a lithium secondary battery disclosed herein includes a positive electrode current collector 10 and a positive electrode mixture layer (a layer containing a positive electrode active material) held by the positive electrode current collector 10. 20.

  The positive electrode current collector 10 is formed by laminating a conductive layer 14 on a base material 12. The substrate 12 is made of aluminum or aluminum alloy, which has excellent conductivity and can be easily processed into a thin film (sheet). In this embodiment, the substrate 12 (that is, the substrate body) is an aluminum foil having a thickness of about 10 μm to 30 μm.

  The conductive layer 14 is made of a conductive material having conductivity, and is formed so as to cover the substrate 12. The conductive layer 14 is interposed between the base material 12 and the positive electrode mixture layer 20 and has a function of reducing resistance at the interface between the base material 12 and the positive electrode mixture layer 20. The conductive layer 14 is preferably made of a material having a low electric resistance, and the resistivity is preferably 500 μΩ · cm or less, more preferably 50 μΩ · cm or less. In this embodiment, the conductive layer 14 is made of tungsten carbide (resistivity: 17 μΩ · cm). The thickness of the conductive layer 14 may be approximately in the range of 5 nm to 100 nm, and in this embodiment is about 20 nm.

Furthermore, a surface oxide film 16 is formed on the surface of the substrate 12 (that is, the interface between the substrate body and the conductive layer 14). The surface oxide film 16 is made of an aluminum oxide such as Al ₂ O _3, and is formed by, for example, natural oxidation of the substrate surface (natural oxide film). Since such an Al ₂ O ₃ film (oxide film) 16 is chemically more stable than Al alone, the durability (stability) of the current collector is higher than that of the current collector without the oxide film. ) Will improve.

  The thickness of the surface oxide film 16 may be approximately 3 nm or less. When the thickness of the surface oxide film 16 is 3 nm or less, the tunnel effect of the oxide film 16 is dramatically improved. Therefore, it is generally possible to impart conductivity to an Al oxide film that is an insulating film, thereby significantly increasing the electrical resistance value between the positive electrode current collector and the positive electrode mixture layer (a layer containing the positive electrode active material). There is no increase.

The lower limit of the film thickness of the surface oxide film 16 should just be a grade which can be coat | covered, without exposing base aluminum (base-material main body). For example, it may be a thickness (monomolecular layer) of one Al ₂ O ₃ molecule. For example, the thickness of the surface oxide film 16 is not less than 0.5 nm and not more than 3 nm, preferably not less than 1 nm and not more than 3 nm. According to such a configuration, the underlying aluminum (base material body) can be uniformly coated with the surface oxide film 16, which can surely contribute to an improvement in the stability (durability) of the positive electrode current collector.

According to the positive electrode current collector 10 of this embodiment, a surface oxide film (Al ₂ O ₃ layer) 16 that is chemically more stable than Al alone is interposed at the interface between the aluminum base 12 and the conductive layer 14. Therefore, the durability (stability) of the current collector is improved as compared with the current collector without the oxide film 16. As a result, the battery life can be extended (that is, stable battery performance can be maintained over a long period of time). In addition, by setting the thickness of the surface oxide film 16 to 3 nm or less, conductivity can be imparted to the oxide film which is an insulating film, and the positive electrode current collector 10 and the positive electrode mixture layer (including the positive electrode active material) The electrical resistance value between the two layers is not significantly increased. That is, according to the configuration of the present embodiment, it is possible to provide the positive electrode current collector 10 having high output and excellent cycle life.

The conductive layer 14 is preferably made of a metal or metal carbide that is less susceptible to corrosion than aluminum in addition to conductivity. In that case, corrosion resistance can be imparted to the conductive layer 14 to protect the aluminum substrate 12 that is susceptible to corrosion. Examples of such metal materials include steel materials such as stainless steel (SUS), hafnium (Hf), tantalum (Ta), zirconium (Zr), vanadium (V), chromium (Cr), molybdenum (Mo), and niobium (Nb). ), Tungsten (W) or the like, or an alloy thereof (for example, nickel chromium alloy (Ni-Cr)). Examples of the carbon-based material include carbon (C) and metal carbides such as WC, TaC, HfC, NbC, Mo ₂ C, VC, Cr ₃ C ₂ , TiC, and ZrC. Of these, tungsten (W) or tungsten carbide (WC) is particularly preferable.
In addition, what is necessary is just to perform the corrosion-resistant material evaluation suitably by the corrosion test according to the corrosive environment which can be assumed.

About the positive mix layer 20, what is necessary is just a layer containing the positive electrode active material for lithium secondary batteries. In this embodiment, the positive electrode mixture layer 20 is composed of a positive electrode active material and other positive electrode mixture layer forming components (for example, a conductive additive and a binder) used as necessary. As the positive electrode active material, for example, a material mainly composed of a lithium transition metal composite oxide containing lithium and one or more transition metal elements as constituent metal elements is preferably used. Preferable examples include LiMn ₂ O ₄ , LiCoO ₂ , LiNiO ₂ , LiFePO ₄ , LiMnPO ₄ , LiNiMnCoO _{2 and the} like.

  Subsequently, a method of manufacturing the positive electrode 30 including the positive electrode current collector 10 will be described with reference to FIGS. 2 and 3A to 3D. In this embodiment, a natural oxide film generated on the base material 12 is used as a stable layer (surface oxide film) 16 interposed at the interface between the base material 12 and the conductive layer 14.

  That is, as shown in the flow of FIG. 2, first, a base material (aluminum foil) having an oxide film formed on the surface is prepared (S10), and then the surface oxide film of the base material 12 is etched to a thickness of 3 nm or less. It adjusts to (S20). Then, the conductive layer 14 is formed on the surface oxide film 16 whose thickness is adjusted (S30), and the positive electrode current collector 10 is manufactured (S40). Thereafter, the positive electrode mixture layer 20 is applied on the conductive layer 14 of the positive electrode current collector 10 (S50), thereby obtaining the positive electrode 30 according to the present embodiment (S60).

  The aluminum oxide film (natural oxide film) requires a long time for complete removal because of its low etching rate. However, according to the method of the present embodiment, the natural oxide film 16 is used as a stable layer and left intentionally. Therefore, the time required for the etching process can be greatly shortened. For example, according to a trial calculation by the present inventor, when an oxide film is etched using a standard sputtering apparatus under conditions of a sputtering power of 200 W and a capacity of 13.5 MHz, the etching rate is approximately 1 nm / min. If the thickness of the natural oxide film formed on the aluminum foil (current collector) is about 5 nm, it takes 5 minutes to completely remove the natural oxide film. On the other hand, in this embodiment, it is sufficient to remove at least 2 nm. That is, in the method of this embodiment, the etching time can be reduced to half or less, and the productivity of the current collector is greatly improved.

  Furthermore, it demonstrates concretely, adding FIG. 3A-FIG. 3D. 3A to 3D are process cross-sectional views schematically showing the manufacturing process of the positive electrode current collector.

  First, as shown in FIG. 3A, a base 12 made of aluminum or aluminum alloy is prepared. In this embodiment, it is an aluminum foil. Since the aluminum foil is immediately oxidized when exposed to the atmosphere, it has a surface oxide film (natural oxide film) 16 on the surface of the base body. The thickness of the surface oxide film 16 is not particularly limited because it varies depending on environmental conditions and the like, but is generally formed with a thickness of about 5 nm or more.

  Next, as shown in FIG. 3B, the surface oxide film 16 of the substrate 12 is adjusted to a thickness of 3 nm or less by etching (thickness adjusting step). The etching process can be performed by dry etching, for example. In this embodiment, a part of the oxide film 16 is removed by performing sputter etching with inert gas ions such as Ar gas. The sputtering method is not particularly limited as long as it uses ion bombardment by discharge plasma. Since the aluminum oxide film has a low etching rate by Ar sputtering, it takes time to completely remove the aluminum oxide film. However, in this embodiment, the aluminum oxide film 16 remains at a predetermined thickness or less, so that the etching time can be shortened. . Note that the etching method is not limited to sputtering, and other etching methods can also reduce the time.

  After adjusting the thickness of the surface oxide film 16 to 3 nm or less, next, as shown in FIG. 3C, the conductive layer 14 is formed on the natural oxide film 16 having a thickness of 3 nm or less. The method for forming the conductive layer 14 is not particularly limited. For example, physical vapor deposition (PVD) such as sputtering, ion plating (IP), arc ion plating (AIP), or chemical vapor deposition such as plasma CVD. (CVD) may be used. In this embodiment, the conductive layer is formed by a sputtering method using a conductive material (for example, WC) as a target. By forming the conductive layer 14 on the surface oxide film 16, further progress of oxidation on the substrate surface can be suppressed.

  In this way, the positive electrode current collector 10 in which the conductive layer 14 is laminated on the base material 12, and has the surface oxide film 16 having a thickness of 3 nm or less at the interface between the base material 12 and the conductive layer 14. The body 10 can be produced.

  After the positive electrode current collector 10 is manufactured, the positive electrode mixture layer 20 is then formed on the conductive layer 14 as shown in FIG. 3D. The formation of the positive electrode mixture layer 20 may be performed, for example, by applying a paste-like positive electrode mixture from above the conductive layer 14 and drying it. The paste-like electrode mixture is prepared by dispersing the positive electrode active material powder and other positive electrode mixture layer forming components (such as a conductive material and a binder) used as necessary in a suitable dispersion medium. You can do it. Such a dispersion medium may be water or a mixed solvent mainly composed of water, or may be a non-aqueous medium organic medium (for example, N-methylpyrrolidone).

  In the case of using water or a mixed solvent mainly composed of water, the lithium ions constituting the lithium transition metal composite oxide can exhibit alkalinity by leaching into the aqueous medium. When the layer 14 plays a role as a protective film, the reaction between the aqueous composition and the substrate 12 (typically, corrosion reaction due to alkali) can be prevented.

  Thus, the positive electrode 30 provided with the positive electrode current collector 10 according to the present embodiment can be obtained. In addition, you may adjust the thickness and the density of the positive mix layer 20 suitably after performing drying by performing an appropriate press process (for example, roll press process) as needed.

  In FIG. 4, an example of the manufacturing apparatus 90 of the positive electrode collector 10 which concerns on this embodiment is shown. The manufacturing apparatus 90 includes a chamber 91 configured to be able to depressurize the inside, a gas introduction unit 92 that introduces gas into the chamber 91, and a base material holding unit 93 that holds the base material 12 in the chamber 91. Further, an etching processing unit 95 and a conductive layer film forming unit 96 are provided inside the chamber 91.

  The gas introduction unit 92 introduces a gas into the chamber 91 and forms a gas atmosphere in the chamber 91. The introduced gas is, for example, an inert gas (Ar gas in the present embodiment). You may add an active gas as needed.

  The etching processing unit 95 etches the surface oxide film 16 generated on the surface of the substrate 12. The etching processing unit 95 may be an apparatus capable of performing dry etching, and is a sputtering apparatus here. The etching processing unit 95 etches the surface oxide film of the substrate 12 and adjusts the thickness to 3 nm or less. The etching amount may be controlled by appropriately adjusting, for example, the sputtering conditions and the substrate conveyance speed.

  The conductive layer deposition unit 96 forms the conductive layer 14 on the surface oxide film 16 whose thickness has been adjusted. In this embodiment, the conductive layer deposition unit 96 is a sputtering apparatus, and deposits a conductive material on the surface oxide film 16 by sputtering using a conductive material (here, WC) as a target. It has become.

  The substrate holding unit 93 holds the substrate 12 in the chamber 91 and conveys the substrate 12 continuously or intermittently. In this embodiment, the base material 12 is a sheet-like aluminum foil. The aluminum foil 12 is drawn out from the roll state 97 and is conveyed in the chamber 91 as the base material holding part 93 rotates. Then, after undergoing thickness adjustment processing in the etching processing unit 95 and then subjected to film formation processing in the conductive layer film forming unit 96, the positive electrode current collector 10 is again wound into the roll state 98. The wound positive electrode current collector 10 may then be sent to the positive electrode mixture layer 20 forming step.

  According to the manufacturing apparatus 90 according to this embodiment, the etching process of the surface oxide film 16 and the film formation process of the conductive layer 14 are continuously performed while the sheet-like substrate 12 is conveyed continuously or intermittently. Therefore, the productivity of the positive electrode current collector 10 is improved. In addition, since the surface oxide film 16 is not completely removed in the etching process, the productivity is further improved.

  Since the positive electrode current collector according to this embodiment is excellent in current collecting performance as described above, it is preferably used as a component of various types of batteries or a component of an electrode body (for example, a positive electrode) incorporated in the battery. Can be done. For example, a positive electrode including any positive electrode current collector disclosed herein, a negative electrode, an electrolyte disposed between the positive and negative electrodes, and a separator (solid or gel) that typically separates the positive and negative electrodes And can be omitted in a battery using an electrolyte in the form of a lithium secondary battery. Structure (for example, metal casing or laminate film structure) and size of an outer container constituting such a battery, or structure of an electrode body (for example, a wound structure or a laminated structure) having a positive / negative electrode current collector as a main component There is no particular restriction on the etc.

  In the battery constructed in this way, the positive electrode current collector having a current collecting performance superior to the positive electrode mixture layer 20 while the surface of the base material is firmly protected by the aluminum oxide film 16 and the conductive layer 14. 10 is an excellent battery performance. For example, by constructing a battery using the positive electrode current collector, a battery having excellent output characteristics can be provided.

  Next, in order to confirm that the battery characteristics can be improved by constructing a battery using the positive electrode current collector according to the present invention, the film thickness of the Al oxide film and the contact resistance at the substrate / conductive layer interface I investigated the relationship.

That is, when the film thickness of the Al ₂ O ₃ film interposed between the base material and the conductive layer is changed, how the contact resistance between the base material and the conductive layer changes accordingly. Examined. Specifically, first, an aluminum foil as a substrate was prepared, and the natural oxide film formed on the surface of the aluminum foil was completely removed by sputter etching. Then, to form a predetermined thickness of the Al ₂ O ₃ film on the aluminum foil surface that completely removing the oxide film. The Al ₂ O ₃ film was formed using a general sputtering apparatus. As conditions for forming the Al ₂ O ₃ film, Al ₂ O ₃ was used as a target, and Ar gas and O ₂ gas were introduced into the sputtering apparatus (Ar flow rate: 17 sccm, O ₂ flow rate: 0.34 sccm). The sputtering power was set to 200 W, the sputtering pressure was 6.7 × 10 ⁻¹ Pa, the ultimate pressure was 3.0 × 10 ⁻³ Pa, and the substrate was not heated.

Next, a WC layer (thickness: 100 nm) as a conductive layer was formed on the formed Al ₂ O ₃ film to produce a positive electrode current collector. The WC layer was formed using a general sputtering apparatus. As conditions for forming the WC layer, tungsten carbide (WC) was used as a target, and Ar gas was introduced into the sputtering apparatus (Ar flow rate: 11.5 sccm). The sputtering power was 200 W, the sputtering pressure was 6.7 × 10 ⁻¹ Pa, the ultimate pressure was 3.0 × 10 ⁻³ Pa, the film formation time was 30 minutes, and the substrate was not heated.

Thereafter, by changing the film thickness of the Al ₂ O ₃ film interposed between the substrate and the WC layer, positive electrode current collectors having different Al ₂ O ₃ film thicknesses were produced. Specifically, positive electrode current collectors were prepared in which the thickness of the Al ₂ O ₃ film was 0 nm (no Al ₂ O ₃ film), 1 nm, 3 nm, 5 nm, and 10 nm, respectively. And constant current was supplied with respect to each produced positive electrode electrical power collector, and contact resistance was computed by the change of the voltage characteristic at that time. The result is shown in FIG. The horizontal axis in FIG. 5 represents the film thickness (nm) of the Al ₂ O ₃ film, and the vertical axis represents the contact resistance (mΩ · cm ² ).

As is clear from FIG. 5, it was found that when the film thickness of the Al ₂ O ₃ film interposed between the base material and the WC layer is 3 nm or less, the contact resistance is reduced to 0.5 mΩ · cm ² or less. . From this, if the Al oxide film on the substrate surface is adjusted to 3 nm or less, the positive electrode current collector and the positive electrode active material layer are not increased without increasing the electrical resistance value between the positive electrode current collector and the positive electrode active material layer. It was confirmed that an Al oxide film can be interposed between the two and the battery characteristics can be preferably improved.

As a reference example, FIG. 6 shows the relationship between contact resistance and battery characteristics. FIG. 6 shows a case where a test coin cell is constructed using a positive electrode current collector having a conductive layer on the substrate surface, and when the contact resistance of the positive electrode current collector is variously changed, the discharge rate is 100C accordingly. It is the test result which investigated how the battery capacity of a coin cell changes. The horizontal axis in FIG. 6 represents the contact resistance (mΩ · cm ² ) of the positive electrode current collector, and the vertical axis represents the 100 C capacity (mΩ · cm ² ) of the coin cell.

As is apparent from FIG. 6, it can be seen that the 100 C capacity of the coin cell significantly increases when the contact resistance is 1 mΩ · cm ² or less. This is considered to be due to the fact that the high-rate characteristics of the coin cell greatly depend on the contact resistance of the positive electrode current collector. Therefore, by adjusting the surface oxide film thickness of the base material to 3 nm or less and making the contact resistance at the base material / conductive layer interface 1 mΩ · cm ² or less, battery characteristics (particularly battery characteristics at high rate) can be obtained. I found that it can be improved.

Note that the test coin cell manufactured as the reference example described above is manufactured as follows. First, an aluminum foil as a substrate was prepared, and the natural oxide film formed on the surface of the aluminum foil was completely removed by sputter etching. And the electroconductive layer (thickness 20nm) was formed in the aluminum foil surface from which the oxide film was removed completely, and the positive electrode collector used for the coin cell for a test was produced. Thereafter, positive electrode current collectors having different contact resistances were obtained by changing the constituent materials of the base material and the conductive layer. Specifically, as shown in Table 1, positive electrode current collectors having different contact resistances at the substrate / conductive layer interface were prepared by variously changing the constituent materials of the substrate and the conductive layer. In Test Example 1, an untreated Al foil in which a natural oxide film remained was used as it was as a positive electrode current collector, and in Test Example 2, a pure gold base material was used as a positive electrode current collector.

  Next, a test coin cell was constructed using each positive electrode current collector, and the battery capacity of the coin cell at each discharge rate was evaluated. The results are shown in Table 1. As can be seen from Table 1, when the contact resistance of the positive electrode current collector is reduced, the battery capacity at a high rate (particularly at a rate of 50 C or higher) is improved. Also from this result, it was confirmed that the high rate characteristic of the coin cell greatly depends on the contact resistance of the positive electrode current collector. In addition, regarding various battery constituent materials other than the positive electrode current collector (for example, a positive electrode active material, a negative electrode, an electrolyte disposed between the positive and negative electrodes, a separator separating the positive and negative electrodes, etc.), the manufacturing field of lithium secondary batteries In the same manner as in the production of conventionally known battery constituent materials.

  As mentioned above, although this invention was demonstrated by suitable embodiment, such description is not a limitation matter and of course various modifications are possible. For example, the type of battery is not limited to the above-described lithium ion secondary battery, but may be batteries having various contents with different electrode body constituent materials and electrolytes, such as nickel metal hydride batteries, nickel cadmium batteries, lithium ion capacitors, and metal-air batteries. May be.

  Since the battery according to the present embodiment is excellent in durability and high rate capacity as described above, it can be suitably used as a power source for a motor (electric motor) mounted on a vehicle such as an automobile. That is, as shown in FIG. 7, the secondary battery according to the present embodiment is arranged as a single battery in a predetermined direction, and the single battery is constrained in the arrangement direction to construct the assembled battery 100, and the assembled battery A vehicle 1 including 100 as a power source (typically, an automobile including an electric motor such as an automobile, particularly a hybrid automobile, an electric automobile, or a fuel cell automobile) can be provided.

DESCRIPTION OF SYMBOLS 1 Vehicle 10 Positive electrode collector 12 Base material 14 Conductive layer 16 Surface oxide film 20 Positive electrode mixture layer 30 Positive electrode 90 Manufacturing apparatus 91 Chamber 92 Gas introduction part 93 Base material holding part 95 Etching process part 96 Conductive layer film-forming part 97 Roll State 98 roll state 100 assembled battery

Claims (14)

A positive electrode current collector formed by laminating a conductive layer having conductivity on a substrate made of aluminum or an aluminum alloy,
The substrate has a surface oxide film made of aluminum oxide at the interface between the substrate body and the conductive layer, and the thickness of the surface oxide film is 0.5 nm or more and 3 nm or less by etching, A positive electrode current collector, wherein the contact resistance between the substrate and the conductive layer is adjusted to a thickness of 0.5 mΩ · cm ² or less.   The positive electrode current collector according to claim 1, wherein the conductive layer is made of a metal or metal carbide that is less susceptible to corrosion by alkali than aluminum.   The positive electrode current collector according to claim 1, wherein the conductive layer is made of tungsten or tungsten carbide.   The positive electrode current collector according to any one of claims 1 to 3, wherein the base material is a sheet-like aluminum foil. A method for producing a positive electrode current collector obtained by laminating a conductive layer having conductivity on a substrate made of aluminum or an aluminum alloy,
As the substrate, a substrate having a surface oxide film made of aluminum oxide on the surface of the substrate body is prepared,
The contact resistance between the base material and the conductive layer in the positive electrode current collector obtained by etching the surface oxide film of the base material with a thickness of 0.5 nm to 3 nm by etching is 0.5 mΩ · a thickness adjusting step for adjusting to a thickness of cm ² or less;
And a conductive layer forming step of forming the conductive layer on the thickness-adjusted surface oxide film. The manufacturing method of Claim 5 which prepares the base material which has a surface oxide film which consists of a natural oxide film of aluminum whose thickness is 5 nm or more on the surface of this base-material main body as said base material. The manufacturing method according to claim 5, wherein the conductive layer is made of tungsten or tungsten carbide. The manufacturing method according to claim 5, wherein the etching process is performed by sputter etching. The formation of the conductive layer, a metal or metal carbide is performed by a sputtering method using a target, the production method according to any one of claims 5 to 8. It said substrate is an aluminum foil sheet, a manufacturing method according to any one of claims 5 9. 11. The manufacturing according to claim 5, wherein the thickness adjusting step and the conductive layer forming step are continuously performed on the transported base material on a manufacturing line. Method. A method for manufacturing a lithium secondary battery, comprising:
As positive electrode current collector, characterized by the use of positive electrode current collector manufactured by the method according to any one of claims 5 11, the lithium secondary battery production method. A secondary battery comprising the positive electrode current collector according to any one of claims 1 to 4 or the positive electrode current collector produced by the production method according to any one of claims 5 to 11 . A vehicle equipped with the secondary battery according to claim 13 .

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