JP2010170716A - Negative electrode for lithium secondary battery and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a negative electrode for a lithium secondary battery, superior in quality stability capable of avoiding a phenomenon in which an negative electrode active material layer is peeled off, and to provide a method of manufacturing the same. <P>SOLUTION: The negative electrode 100 for the lithium secondary battery is structured such that the negative electrode active material layer 30 including a negative electrode active material is retained by a negative electrode collector 10. The negative electrode collector 10 includes a metal base material 20, and a boron carbide film 40 formed on a surface 22 of the base material. The negative electrode 100 is formed with the negative electrode active material layer 30 on the surface 22 of the base material through the boron carbide film 40. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a negative electrode used as a component of a lithium secondary battery, a method for producing the same, and a lithium secondary battery including the negative electrode.

  A lithium secondary battery (typically a lithium ion battery) that is charged and discharged by the movement of 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 lithium secondary battery, a material layer (electrode active material layer) capable of reversibly occluding and releasing lithium ions is held by a conductive member (electrode current collector). Electrode. For example, examples of the electrode active material layer (negative electrode active material layer) used for the negative electrode include carbon-based materials such as graphite carbon and amorphous carbon. A typical example of the electrode current collector (negative electrode current collector) used for the negative electrode is a sheet-like or foil-like member mainly composed of copper or a copper alloy.

  Thus, in the negative electrode having a configuration in which the negative electrode active material layer is held by the negative electrode current collector, if the adhesion between the negative electrode active material layer and the negative electrode current collector is insufficient, the negative electrode active material layer is peeled off from the negative electrode current collector. This can be a factor that causes a drop in battery characteristics such as battery capacity. Therefore, in order to obtain a negative electrode having good battery characteristics, it is important to improve the adhesion between the negative electrode active material layer and the negative electrode current collector. For example, Patent Document 1 discloses a technique for improving the adhesion between the negative electrode active material layer and the negative electrode current collector. Patent Document 2 is disclosed as another conventional technique related to prevention of peeling of the negative electrode active material layer.

JP 2003-217576 A JP 2000-294251 A

Patent Document 1 describes a technique in which an oxide film is formed on the surface of a copper foil by an oxidation process, and then a negative electrode active material layer is formed on the copper foil. However, the oxide film thus formed on the surface of the copper foil has a low reduction resistance and has a property of being easily reduced when exposed to a reducing atmosphere. Therefore, when the negative electrode is exposed to a reduction potential by repeated charge and discharge, a part of the oxide film formed on the surface of the copper foil is reduced and dissolved, and there is no oxide film in close contact with the negative electrode active material layer. In some cases, the negative electrode active material layer may be lifted from the copper foil or easily peeled off.
Further, even when an oxide film is not formed on the surface of the copper foil by oxidation as in Patent Document 1, the copper foil is easily oxidized and is oxidized in a short time when exposed to the atmosphere. There is always a natural oxide film at the interface. FIG. 8A shows an example of the negative electrode 110 in which a natural oxide film 126 is formed at the interface between the copper foil 120 and the negative electrode active material layer 130. Even when the natural oxide film 126 is formed on the surface of the copper foil 120 as described above, as shown in FIG. 8B, when the negative electrode 110 is exposed to a reduction potential by repeated charge and discharge, it is formed on the surface of the copper foil 120. In addition, part of the natural oxide film 126 may be lost. Such disappearance of the natural oxide film 126 is not preferable because the negative electrode active material layer 130 is peeled off from the copper foil 120 as illustrated.

  This invention is made | formed in view of this point, The main objective is to provide the negative electrode for lithium secondary batteries which can avoid the phenomenon that a negative electrode active material layer peels, and was excellent in quality stability. is there. Another object of the present invention is to provide a production method capable of stably (with good quality stability) producing a negative electrode for a lithium secondary battery having such performance.

  The present inventor forms a negative electrode current collector provided with a coating (boron carbide film) made of boron carbide, and forms a negative electrode active material layer containing a negative electrode active material on the boron carbide film of the negative electrode current collector. The present invention has been completed by finding that the above problems can be solved.

  According to the present invention, a negative electrode for a lithium secondary battery having a configuration in which a negative electrode active material layer containing a negative electrode active material is held by a negative electrode current collector (for example, for a non-aqueous electrolyte lithium secondary battery represented by a lithium ion battery). A method of manufacturing a negative electrode) is provided. In the method, a boron carbide film is formed on the surface of a metal substrate that can be used as a negative electrode current collector (for example, it can be preferably formed by sputtering using a target made of boron carbide), and the boron carbide film is formed. Including obtaining a negative electrode current collector. Further, the manufacturing method includes forming a negative electrode active material layer including a negative electrode active material on the boron carbide film of the negative electrode current collector.

  When a natural oxide film (for example, CuO film) of the metal is formed on the surface of a metal substrate (for example, Cu foil) and an oxide film is interposed at the interface between the substrate and the negative electrode active material layer, the negative electrode active material layer is There is a case where inconveniences such as lifting from the surface of the material and further peeling off may occur. Such an event is considered to be caused by a natural oxide film formed on the surface of the base material being exposed to a reducing atmosphere during charge and discharge to be reduced and dissolved (disappeared). In the negative electrode manufacturing method according to the present invention, a boron carbide film is formed on the substrate surface, and a negative electrode active material layer is formed on the substrate surface via the boron carbide film. By covering the substrate surface with a boron carbide film in this way, the boron carbide film serves as a barrier layer (a layer that protects the copper foil surface so that the copper foil surface is not exposed to an oxidation-reduction atmosphere). It is possible to suppress the formation or disappearance of an oxide film on the substrate surface. This can prevent peeling of the negative electrode active material layer due to generation and disappearance of the natural oxide film. Therefore, according to the present invention, an event in which the negative electrode active material layer peels can be avoided, and a negative electrode for a lithium secondary battery excellent in quality stability can be manufactured.

  In a preferred embodiment of the method disclosed herein, a substrate in which an oxide film (typically a natural oxide film) of the metal is formed on the surface of the substrate is used as the metal substrate. In other words, an oxide film of the metal is formed on the surface of the metal substrate used in the preferred embodiment. In this case, it is preferable to remove the oxide film formed on the surface of the substrate before the boron carbide film forming step. In this way, by removing in advance the oxide film formed on the substrate surface before forming the boron carbide film, the boron carbide film is firmly formed on the solid surface made of the metal of the metal substrate. can do. For this reason, peeling of the negative electrode active material layer can be prevented more reliably.

  In a preferred embodiment of the method disclosed herein, the metal oxide film on the surface of the substrate is removed by at least one of dry etching, wet etching, and reducing agent treatment. By performing dry etching, wet etching, or reducing agent treatment (or some combination of these treatments) in this way, the oxide film on the substrate surface can be removed stably and appropriately.

  In a preferred embodiment of the method disclosed herein, the boron carbide film is formed by sputtering using a target made of boron carbide. Thus, by performing sputtering using a boron carbide target, a boron carbide film containing boron carbide can be efficiently formed on the surface of the substrate.

  Any of the methods disclosed herein can be applied particularly preferably when the metal constituting the substrate is copper or an alloy mainly composed of copper. Copper or a copper alloy has various characteristics preferable as a negative electrode current collector of a lithium secondary battery, but has a property that a natural oxide film (CuO) of copper is easily formed on the surface. Therefore, in the production of a negative electrode in which the base material of the negative electrode current collector is copper or a copper alloy, a boron carbide film is formed on the surface of the base material to prevent metal oxidation on the surface of the base material. The effect of adopting the configuration of the present invention in which the negative electrode active material layer containing the negative electrode active material is formed from above can be exhibited particularly well.

  According to the present invention, there is also provided a lithium secondary battery (for example, a lithium ion battery) constructed using the negative electrode for a lithium secondary battery produced by any of the methods disclosed herein. Since such a lithium ion secondary battery is constructed using the above negative electrode for lithium secondary batteries, it has excellent quality stability and better battery performance (for example, battery capacity even when used for a long period of time). The battery resistance is hardly increased and the durability is high).

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

The cross-sectional schematic diagram for demonstrating the manufacturing process of the negative electrode of the lithium secondary battery which concerns on one Embodiment of this invention. The cross-sectional schematic diagram for demonstrating the manufacturing process of the negative electrode of the lithium secondary battery which concerns on one Embodiment of this invention. The cross-sectional schematic diagram for demonstrating the manufacturing process of the negative electrode of the lithium secondary battery which concerns on one Embodiment of this invention. The cross-sectional schematic diagram for demonstrating the manufacturing process of the negative electrode of the lithium secondary battery which concerns on one Embodiment of this invention. The cross-sectional schematic diagram which shows typically the cross section of the negative electrode with which the lithium secondary battery which concerns on one Embodiment of this invention is provided. The schematic diagram which shows the structure of the lithium secondary battery which concerns on one Embodiment of this invention. The graph which shows the result of the cyclic voltammetry (CV) measurement of an Example. The graph which shows the result of the cyclic voltammetry (CV) measurement of the comparative example 1. The graph which shows the result of the cyclic voltammetry (CV) measurement of the comparative example 2. The cross-sectional schematic diagram which shows typically the cross section of the negative electrode with which the lithium secondary battery which concerns on one Embodiment of this invention is provided. The side view which shows typically the vehicle provided with the lithium secondary battery which concerns on one Embodiment of this invention. The schematic diagram for demonstrating the problem that a negative electrode active material layer peels from copper foil. The schematic diagram for demonstrating the problem that a negative electrode active material layer peels from copper foil.

  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 the matters specifically mentioned in the present specification and matters necessary for carrying out the present invention (for example, the configuration and manufacturing method of an electrode body including a positive electrode and a negative electrode, the configuration and manufacturing method of a separator and an electrolyte, General techniques relating to the construction of lithium secondary batteries and other batteries, etc.) can be understood as design matters for those skilled in the art based on the prior art in this field.

  Although not intended to be particularly limited, the following is an example in which a negative electrode for a lithium secondary battery (typically a lithium ion battery) is mainly produced using a copper foil-like substrate (copper foil). The present invention will be described in detail with reference to FIGS. 1A to 1D.

  As shown in FIG. 1A, in the method for manufacturing an electrode for a lithium secondary battery disclosed herein, first, a metal substrate 20 that can be used as a negative electrode current collector is prepared (manufactured, purchased, etc.). In this embodiment, foil-like copper (copper foil) having a thickness of about 10 μm to 30 μm, for example, is prepared as the base material 20. The copper foil 20 is oxidized in a short time when exposed to the atmosphere. Therefore, a copper natural oxide film (CuO film) 26 having a thickness of about 10 nm, for example, can be formed on the surface of the prepared copper foil 20 as shown in the figure. Thus, the oxide film 26 formed on the surface of the copper foil 20 has a low reduction resistance, and exhibits a property of being easily reduced when exposed to a reducing atmosphere. When the negative electrode active material layer 30 is formed on the oxide film 26 that is easily reduced, the natural oxide film 26 formed on the surface of the copper foil 20 when the negative electrode 100 is exposed to a reduction potential by repeated charge and discharge. As a result, a part of the oxide film is reduced and dissolved, and the oxide film in close contact with the negative electrode active material layer 30 disappears. Such disappearance of the natural oxide film 26 is not preferable because it causes peeling of the negative electrode active material layer 30 from the copper foil 20.

  In the manufacturing method of the present embodiment, first, as shown in FIG. 1B, a process of removing the natural oxide film 26 of the copper foil 20 to expose the solid surface 22 made of underlying copper is performed. As shown in FIG. 1C, a boron carbide film 40 is formed on the exposed pure surface 22 made of copper, and the negative electrode current collector 10 including the boron carbide film 40 is obtained. Then, as shown in FIG. 1D, a negative electrode active material layer 30 containing a negative electrode active material is formed on the boron carbide film 40 of the obtained negative electrode current collector 10. By covering the copper foil surface 22 with the boron carbide film 40 in this manner, the boron carbide film 40 serves as a barrier layer (a layer that protects the copper foil surface so that the copper foil surface is not exposed to an oxidation-reduction atmosphere). Therefore, it is possible to suppress the generation or disappearance of a new natural oxide film of copper on the copper foil surface 22. This can prevent the negative electrode active material layer 30 from peeling off due to the formation and disappearance of the natural oxide film. Therefore, according to the present invention, it is possible to avoid the phenomenon that the negative electrode active material layer 30 is peeled off, and it is possible to manufacture the negative electrode 100 for a lithium secondary battery excellent in quality stability. According to such a negative electrode, a lithium secondary battery with more stable performance can be constructed. Hereinafter, the manufacturing process of the negative electrode 100 having the negative electrode current collector 10 including the boron carbide film 40 will be described in more detail.

  That is, as shown in FIG. 1B, in the negative electrode manufacturing method according to the present embodiment, following the step of preparing the copper foil 20 on which the copper natural oxide film 26 is formed, the metal oxide film 26 on the surface of the copper foil is formed. Perform the removal process. The process for removing the metal oxide film 26 is not particularly limited. For example, the process is performed by at least one of a dry etching method, a wet etching method, and a reducing agent treatment method (or some combination of these treatments). It can be carried out. When the copper metal oxide film is removed using a dry etching method, a mode in which the metal oxide film is physically removed by Ar etching can be preferably employed. By performing such an Ar etching process on the copper foil surface, the metal oxide film 26 on the copper foil surface can be removed appropriately and stably, and the innocent surface 22 made of underlying copper can be exposed. it can. Note that nitric acid may be used as an etchant when the copper metal oxide film is removed by wet etching.

Next, as shown in FIG. 1C, a boron carbide film 40 is formed on the solid copper foil surface 22 made of copper exposed by removing the metal oxide film 26. The boron carbide film 40 may be a film containing at least boron carbide (carbon boride), and a boron carbide film consisting essentially of boron carbide (carbon boride) is particularly preferable. Such boron carbide may be a two-component system of carbon and boron. For example, boron carbide having a composition such as B ₄ C, B ₁₃ C ₂ , or B ₁₁ C ₄ can be preferably used.

  Such boron carbide is excellent in reduction resistance. Therefore, even if the negative electrode is exposed to a strong reduction potential (negative electrode use potential), the boron carbide is not reduced and dissolved. Boron carbide is also inert to the oxidation reaction, and therefore a surface oxide film is not formed even when exposed to the atmosphere. Further, boron carbide has poor reactivity with lithium and therefore does not alloy with lithium by charge / discharge. Thus, since boron carbide exhibits preferable properties such as excellent resistance to reduction, no formation of a surface oxide film, and no lithium alloying, a barrier layer suitable for the purpose of the present invention (the copper foil surface is in an oxidation-reduction atmosphere). Can be preferably used as a layer for protecting the surface of the copper foil so as not to be exposed to the surface. Boron carbide has high strength and has appropriate adhesion to the copper foil 20 and the negative electrode active material layer 30. Therefore, by interposing the boron carbide film 40 at the interface between the copper foil 20 and the negative electrode active material layer 30, the adhesion between the copper foil 20 and the negative electrode active material layer 30 can be improved.

As a method for forming such a boron carbide film 40 on the copper foil surface 22, a known film forming method, for example, a physical vapor deposition method (PVD method, for example, sputtering method), a chemical vapor deposition method (CVD method, for example, plasma CVD method). Etc. can be preferably employed. The formation of the boron carbide film 40 by such a vapor deposition method is typically performed under reduced pressure conditions (for example, in an inert gas atmosphere having a pressure of about 0.01 Pa to 100 Pa). In the technique disclosed herein, as a method of manufacturing the boron carbide film 40 on the copper foil surface 22, for example, a sputtering method using a target made of boron carbide (for example, B ₄ C) can be preferably employed. Thus, by performing sputtering using boron carbide, the boron carbide film 40 containing boron carbide can be efficiently formed on the copper foil surface 22.

  The thickness of the boron carbide film 40 is not particularly limited as long as it can cover the base material uniformly. For example, the thickness of the boron carbide film 40 can be set to about 3 nm to 100 nm, and it is usually preferable to set the thickness to about 5 nm to 20 nm. If the thickness of the boron carbide film 40 is too large, the energy density of the battery constructed using this negative electrode may tend to decrease, and if the thickness of the boron carbide film 40 is too small, the boron carbide The strength of the film 40 may be insufficient. Note that the thickness of the boron carbide film 40 can be arbitrarily controlled by adjusting the formation conditions (for example, sputtering film formation conditions) of the boron carbide film.

  Moreover, it is preferable to arrange | position so that the range (area | region) which forms the said boron carbide film 40 among the surfaces of the base material 20 may include the range in which the negative electrode active material layer 30 is formed at least. For example, when the negative electrode active material layer 30 is formed only on one side of the foil-shaped substrate 20 (may be a part of the single side or may be the entire range), the entire range of the single side is formed. It is preferable to adopt a mode in which the boron carbide film 40 is formed. Moreover, when the said negative electrode active material layer 30 is formed in both surfaces of this base material 20, it is good to employ | adopt the aspect which forms the said boron carbide film | membrane 40 over the whole range of this both surfaces.

  Thus, by forming the boron carbide film 40 on the copper foil surface 22, the negative electrode current collector 10 including the boron carbide film 40 can be obtained. Therefore, the above steps can be grasped as a method for producing a negative electrode current collector or a process for preparing (manufacturing) a negative electrode current collector.

  Next, a process for manufacturing the negative electrode 100 using the negative electrode current collector 10 having the surface provided with the boron carbide film 40 will be described.

  That is, a negative electrode active material layer forming paste containing a negative electrode active material and an appropriate dispersion medium is applied to the negative electrode current collector 10 obtained as described above from above the boron carbide film 40 (typically Apply). The negative electrode active material (typically in particulate form) is not particularly limited as long as it is the same as that used for a typical lithium ion secondary battery. Representative examples of the negative electrode active material layer used for the negative electrode include carbon-based materials such as graphite carbon and amorphous carbon, lithium transition metal composite oxide (lithium titanium composite oxide, etc.), lithium transition metal composite nitride, and the like. The

  The negative electrode active material layer forming paste comprises the above-described negative electrode active material (typically active material particles) and other negative electrode active material layer forming components used as necessary in a suitable dispersion medium. It can be prepared by mixing. Thereby, the negative electrode active material layer forming paste in which the negative electrode active material powder is dispersed in the dispersion medium containing other positive electrode mixture layer forming components used as necessary is obtained. Examples of the dispersion medium include water or a mixed solvent mainly composed of water (aqueous solvent). As the 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. It is not limited to an aqueous solvent, and may be a non-aqueous solvent. As the non-aqueous solvent, an organic solvent such as N-methylpyrrolidone (NMP) can be used.

  The negative electrode active material layer forming paste may contain, in addition to the negative electrode active material and the dispersion medium, materials used for the negative electrode active material layer forming paste in the production of a general negative electrode, if necessary. Typical examples of such materials include conductive materials and binders. As the conductive material, carbon powder such as carbon black (acetylene black or the like), conductive metal powder such as nickel powder, or the like can be used. As the binder, a water-soluble or water-dispersible polymer such as polyvinylidene fluoride (PVDF) can be used.

  The operation of applying (typically coating) such a negative electrode active material layer forming paste to the negative electrode current collector is performed by using the negative electrode current collector provided with the boron carbide film 40 on the surface as described above. Except for the point of use, a conventional general negative electrode for a lithium secondary battery can be produced in the same manner. For example, it is manufactured by applying a predetermined amount of the paste for forming a negative electrode active material layer on the negative electrode current collector 10 from above the boron carbide film 40 using a suitable coating apparatus (die coater or the like). Can be done. After coating, the coated material is dried (typically 70 to 200 ° C.) by an appropriate drying means, whereby the negative electrode 100 in which the negative electrode active material layer 30 is formed on the surface of the negative electrode current collector 10 can be obtained. .

  FIG. 2 schematically shows a cross-sectional structure of a negative electrode 100 for a lithium secondary battery that is preferably manufactured by applying the negative electrode manufacturing method disclosed herein. The negative electrode 100 includes a negative electrode current collector 10 having a boron carbide film 40 on the surface of a base material 20 made of copper foil, and a negative electrode active material layer 30 formed on the surface of the negative electrode current collector 10. This negative electrode active material layer 30 is laminated on the copper foil 20 via the boron carbide film 40 as described above. The negative electrode active material layer 30 is a negative electrode active material layer forming paste containing a negative electrode active material (typically active material particles), a dispersion medium, and other negative electrode active material layer forming components used as necessary. It is formed by applying on the surface of the negative electrode current collector 10 from above the boron carbide film 40 and drying it.

  Here, a boron carbide film 40 is provided on the surface of the copper foil 20 to which the negative electrode active material layer forming paste is applied. Therefore, it is possible to prevent the copper foil surface 22 from being oxidized when the negative electrode active material layer forming paste is dried by a suitable drying means (typically 70 to 200 ° C.). That is, the copper foil 20 is easily oxidized, and the copper foil surface 22 may be oxidized by heat when drying the negative electrode active material layer forming paste. However, according to the manufacturing method of this embodiment, the boron carbide film 40 serves as an anti-oxidation layer for copper foil (a layer for protecting the copper foil surface so that the copper foil surface is not oxidized), so that the copper foil surface 22 is prevented from being oxidized by heat during drying. Can do. Thereby, a new oxide film can be prevented from being formed on the copper foil surface 22 in the negative electrode manufacturing process, and the negative electrode 100 excellent in quality stability can be provided stably. According to the manufacturing method described above, the oxide film 26 formed on the copper foil surface 22 is removed in advance before the boron carbide film 40 is formed, so that the copper foil on the pure surface 22 made of copper is formed. The boron carbide film 40 can be firmly formed. For this reason, peeling of the negative electrode active material layer 30 can be prevented more reliably.

  The negative electrode for a lithium secondary battery provided by the method of the present embodiment can form the negative electrode active material layer 30 having good adhesion to the negative electrode current collector 10 as described above, and is excellent in quality stability. Therefore, it can be preferably used as a constituent element of a lithium secondary battery of various forms or a constituent element (for example, positive electrode) of an electrode body incorporated in the lithium secondary battery. For example, any of the negative electrodes disclosed herein, a positive electrode having a positive electrode current collector, 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.

  Hereinafter, an embodiment of a lithium secondary battery constructed using a negative electrode (negative electrode sheet) 100 manufactured by applying the method of the present invention will be described with reference to a schematic diagram shown in FIG. In the lithium secondary battery 1000, the negative electrode current collector 10 having the boron carbide film 40 on the surface of the base material 20 made of copper foil is used as the negative electrode current collector 10.

  As shown in the figure, a lithium ion battery 1000 according to the present embodiment includes a case 210 made of metal (a resin or a laminate film is also suitable). The case (outer container) 210 includes a flat rectangular parallelepiped case main body 220 whose upper end is opened, and a lid body 230 that closes the opening. On the upper surface of the case 210 (that is, the lid body 230), a positive electrode terminal 270 that is electrically connected to the positive electrode of the wound electrode body 80 and a negative electrode terminal 280 that is electrically connected to the negative electrode of the electrode body are provided. In the case 210, for example, a long sheet-like positive electrode (positive electrode sheet) 50 and a long sheet-like negative electrode (negative electrode sheet) 100 are laminated together with a total of two long sheet-like separators (separator sheets) 60. A flat wound electrode body 80 produced by winding and then crushing the resulting wound body from the side direction and kidnapping is housed.

  Each of the negative electrode sheet 100 and the positive electrode sheet 50 has a configuration in which an electrode mixture layer mainly composed of an electrode active material is provided on both surfaces of a long sheet-like electrode current collector. At one end in the width direction of the electrode sheets 100 and 50, an electrode mixture layer non-formed portion where the electrode mixture layer is not provided on any surface is formed. In the lamination, the positive electrode sheet 50 and the negative electrode active material layer non-formed portion of the negative electrode sheet 100 and the negative electrode active material layer non-formed portion of the negative electrode sheet 100 protrude from both sides of the separator sheet 60 in the width direction. The negative electrode sheet 100 is overlaid with a slight shift in the width direction. As a result, in the horizontal direction with respect to the winding direction of the wound electrode body 80, the electrode mixture layer non-formed portions of the positive electrode sheet 50 and the negative electrode sheet 100 are respectively wound core portions (that is, the positive electrode mixture layer forming portion of the positive electrode sheet 50). And a portion where the negative electrode active material layer forming portion of the negative electrode sheet 100 and the two separator sheets 60 are wound tightly) 82. A positive electrode lead terminal 272 and a negative electrode lead terminal 282 are attached to the positive electrode side protruding portion (ie, the non-forming portion of the positive electrode mixture layer) 50A and the negative electrode side protruding portion (ie, the non-forming portion of the negative electrode active material layer) 100A, respectively. Are electrically connected to the positive terminal 270 and the negative terminal 280, respectively.

In addition, components other than the negative electrode sheet 100 which comprise this winding electrode body 80 may be the same as that of the electrode body of the conventional lithium ion battery, and there is no restriction | limiting in particular. For example, the positive electrode sheet 50 can be formed by providing a positive electrode mixture layer mainly composed of a positive electrode active material for a lithium ion battery on a long positive electrode current collector. As the positive electrode current collector, an aluminum foil or other metal foil suitable for the positive electrode is preferably used. As the positive electrode active material, one or more of materials conventionally used in lithium ion batteries can be used without any particular limitation. Preferable examples include LiMn ₂ O ₄ , LiCoO ₂ , LiNiO _{2 and the} like.

  On the other hand, in the negative electrode sheet 100, as shown in FIG. 2, the boron carbide film 40 is formed on the surface of the elongated base material 10, and the negative electrode active material layer 30 is formed on the boron carbide film 40. . For the substrate 10, a copper foil (this embodiment) or other metal foil suitable for the negative electrode is preferably used. As the negative electrode active material, one or more of materials conventionally used in lithium ion batteries can be used without any particular limitation. Preferable examples include carbon-based materials such as graphite carbon and amorphous carbon, lithium transition metal composite oxides (lithium titanium composite oxides, etc.), lithium transition metal composite nitrides, and the like.

  Moreover, as a suitable example of the separator sheet 60 used between the positive and negative electrode sheets 100 and 50, a sheet composed of a porous polyolefin-based resin can be cited. For example, a porous separator sheet made of synthetic resin (for example, made of polyolefin such as polyethylene) having a thickness of about 5 to 30 μm (for example, 25 μm) can be suitably used. When a solid electrolyte or a gel electrolyte is used as the electrolyte, a separator may not be necessary (that is, in this case, the electrolyte itself can function as a separator).

Then, the wound electrode body 80 is accommodated in the main body 220 from the upper end opening of the case main body 220 and an electrolytic solution containing an appropriate electrolyte is disposed (injected) in the case main body 220. The electrolyte is lithium salt such as LiPF _6, for example. For example, an appropriate amount (for example, concentration 1M) of a lithium salt such as LiPF ₆ is dissolved in a nonaqueous electrolytic solution such as a mixed solvent of diethyl carbonate and ethylene carbonate (for example, a mass ratio of 1: 1) and used as the electrolytic solution. be able to.

  Thereafter, the opening is sealed by welding or the like with the lid 230, and the assembly of the lithium ion battery 1000 according to the present embodiment is completed. The sealing process of the case 210 and the process of placing (injecting) the electrolyte may be the same as those used in the production of a conventional lithium ion battery, and do not characterize the present invention. In this way, the construction of the lithium ion battery 1000 according to this embodiment is completed.

  Since the lithium secondary battery constructed in this way is constructed using the negative electrode for a lithium secondary battery, the lithium secondary battery is excellent in quality stability and shows better battery performance (for example, for long-term use). In other words, the battery capacity is less deteriorated, the battery resistance is hardly increased, and the durability is high.

  In order to confirm that a lithium secondary battery excellent in quality stability can be constructed by constructing a lithium secondary battery using the negative electrode for lithium secondary battery, the following experiment was conducted as an example.

That is, sputtering is performed on both surfaces of a 10 μm-thick copper foil as a base material using boron carbide as a target under conditions of an atmospheric pressure of 6.7 × 10 ⁻¹ Pa and a sputtering power of 200 W using a general sputtering apparatus. As a result, a boron carbide film (boron carbide sputtered film having a film thickness of about 10 nm) was formed on the surface of the substrate to obtain a negative electrode current collector. Next, the obtained negative electrode current collector was housed in a cell container as a working electrode, and an appropriate electrolyte was injected to prepare a test cell of the example. A lithium metal plate was used as the reference electrode and the counter electrode. Moreover, as Comparative Example 1 and Comparative Example 2, test cells of Comparative Example 1 and Comparative Example 2 were prepared using an Al plate and an Au plate as working electrodes, respectively. A test cell was produced in the same manner as in the example except that an Al plate and an Au plate were used as the working electrode.

And after repeating charge / discharge of 3000 cycles with respect to each test cell of the produced Example, Comparative Example 1, and Comparative Example 2 at a test temperature of 60 ° C., cyclic voltammetry (CV) measurement was performed. Under the CV measurement conditions, the potential scan range of the working electrode with respect to the lithium metal plate was set to ⁰ V to 5 V (vs. Li ⁺ / Li) including the negative electrode working potential range in a typical lithium secondary battery. The results are shown in FIG. 4 (Example), FIG. 5A (Comparative Example 1), and FIG. 5B (Comparative Example 2). In each figure, the horizontal axis represents the scanning potential (V), and the vertical axis represents the current density (A / cm ² ).

  As is clear from FIG. 5A, when the Al plate of Comparative Example 1 was used, a large reduction peak was observed in the potential range of 0V to 5V. This is considered to be a reduction current when a part of the Al plate is alloyed with lithium. Further, as apparent from FIG. 5B, when the Au plate of Comparative Example 2 was used, a large reduction peak was observed in the potential range of 0V to 4V. This is considered to be a reduction current when a part of the Au plate is alloyed with lithium.

  On the other hand, as is clear from FIG. 4, when using the copper foil with the carbon boron film of the example formed on the surface, neither the oxidation peak nor the reduction peak was observed in the potential range of 0 V to 5 V, It was confirmed that the carbon boron film was not oxidized / reduced in this potential range (0 V to 5 V). This confirms that the boron carbide film is not reduced and dissolved at the negative electrode working potential and does not alloy with lithium, and the barrier layer suitable for the purpose of the present invention (the copper foil surface is not exposed to the oxidation-reduction atmosphere). Thus, it was confirmed that it can be preferably used as a layer for protecting the copper foil surface.

  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, in the example illustrated in FIG. 2, the configuration in which the negative electrode active material layer 30 is formed on one surface (upper surface in the drawing) of the negative electrode current collector 10 is illustrated. Then, the negative electrode active material layer 30 may be formed on the upper surface and the lower surface. In that case, the boron carbide film 40 may be formed on both surfaces (upper surface and lower surface in the drawing) of the negative electrode current collector 10 on which the negative electrode active material layer 30 is formed.

In the example described above, as shown in FIGS. 1A to 1D, the metal oxide film (CuO) 26 on the surface of the copper foil is completely removed to expose the solid surface 22 made of underlying copper, Thereafter, the case where the boron carbide film 40 is formed on the innocent surface 22 made of exposed copper is exemplified, but the present invention is not limited thereto. For example, a part (residue) of the metal oxide film 26 is left on the copper foil surface 22 without completely removing the metal oxide film 26 on the copper foil surface, and the copper foil surface 22 including the residue of the metal oxide film 26 is left on the copper foil surface 22. A boron carbide film 40 may be formed. Thus, even when the boron carbide film 40 is formed on the copper foil surface 22 including the residue of the metal oxide film 26, the copper foil surface 22 is not exposed to the oxidation-reduction atmosphere by the barrier layer 40 made of boron carbide. Since the surface 22 can be protected, the disappearance of the residue of the metal oxide film 26 on the copper foil surface 22 can be suppressed, and the peeling of the negative electrode active material layer 30 due to the disappearance of the residue of the metal oxide film 26 can be prevented. Can be prevented.
Furthermore, as shown in FIG. 6, the natural oxide film 26 on the copper foil surface is not removed at all, and the natural oxide film 26 is left as it is on the copper foil surface 22, and the copper foil surface 22 including the natural oxide film 26 is left. A boron carbide film 40 may be formed. Thus, even when the boron carbide film 40 is formed on the copper foil surface 22 including the natural oxide film 26, the copper foil surface 22 is prevented from being exposed to the redox atmosphere by the barrier layer 40 made of boron carbide. Therefore, the disappearance of the natural oxide film 26 on the copper foil surface 22 can be suppressed, and the peeling of the negative electrode active material layer 30 due to the disappearance of the metal oxide film 26 can be prevented.

  In addition, since the lithium secondary battery (for example, lithium ion secondary battery) according to the present invention is excellent in quality stability and exhibits better battery performance as described above, a motor (in particular, a motor mounted on a vehicle such as an automobile ( It can be suitably used as a power source for an electric motor. Therefore, as schematically shown in FIG. 7, the present invention provides a vehicle (typically an automobile, particularly a hybrid automobile) provided with such a lithium secondary battery (typically, a battery pack formed by connecting a plurality of series batteries) 1000 as a power source. , An automobile equipped with an electric motor such as an electric vehicle and a fuel cell vehicle.

10 Negative electrode current collector 20 Base material (copper foil)
22 Base material (copper foil) surface 26 Oxide film 30 Negative electrode active material layer 40 Boron carbide film 50 Positive electrode 60 Separator 80 Winding electrode body 100 Negative electrode 210 for lithium secondary battery Case 220 Case body 230 Lid body 270 Positive electrode terminal 272 Positive electrode lead Terminal 280 Negative electrode terminal 282 Negative electrode lead terminal 1000 Lithium secondary battery

Claims (14)

A method for producing a negative electrode for a lithium secondary battery having a configuration in which a negative electrode active material layer containing a negative electrode active material is held by a negative electrode current collector,
Forming a boron carbide film on the surface of the metal substrate, obtaining a negative electrode current collector provided with the boron carbide film;
Forming a negative electrode active material layer containing a negative electrode active material on the boron carbide film of the negative electrode current collector. An oxide film of the metal is formed on the surface of the metal substrate,
The manufacturing method of Claim 1 which has the process of removing the said metal oxide film formed in the surface of this base material before the said boron carbide film formation process.   The manufacturing method according to claim 2, wherein the metal oxide film on the surface of the substrate is removed by at least one of dry etching, wet etching, and reducing agent treatment.   The said boron carbide film is a manufacturing method as described in any one of Claim 1 to 3 formed by sputtering using the target which consists of boron carbide.   The manufacturing method according to claim 1, wherein the metal is copper or an alloy mainly composed of copper. A negative electrode for a lithium secondary battery having a configuration in which a negative electrode active material layer containing a negative electrode active material is held by a negative electrode current collector,
The negative electrode current collector comprises a metal substrate and a boron carbide film formed on the surface of the substrate,
A negative electrode for a lithium secondary battery, wherein the negative electrode active material layer is formed on the surface of the base material via the boron carbide film.   The negative electrode for a lithium secondary battery according to claim 6, wherein the metal is copper or an alloy mainly composed of copper. A method for producing a negative electrode current collector for a lithium secondary battery, comprising:
A method for producing a negative electrode current collector for a lithium secondary battery, comprising a step of forming a boron carbide film containing boron carbide on a surface of a metal substrate for the negative electrode current collector. An oxide film of the metal is formed on the surface of the metal substrate,
The manufacturing method of Claim 8 which has the process of removing the said metal oxide film formed in the surface of this base material before the said boron carbide film formation process.   The manufacturing method according to claim 9, wherein the metal oxide film on the surface of the base material is removed by at least one of dry etching, wet etching, and reducing agent treatment.   The manufacturing method according to claim 8, wherein the boron carbide film is formed by sputtering using a target made of boron carbide.   The manufacturing method according to claim 8, wherein the metal is copper or an alloy mainly composed of copper.   The lithium secondary battery constructed | assembled using the negative electrode for lithium secondary batteries of Claim 6 or 7.   A vehicle comprising the lithium secondary battery according to claim 13.

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