JP2008204753A - Lithium secondary battery, and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lithium secondary battery in which a filler layer is formed on the surface of a negative electrode active material layer and influence on battery performance by forming the filler layer is suppressed. <P>SOLUTION: The lithium secondary battery has a positive electrode 30 including a positive electrode active material layer 35, and a negative electrode including the negative electrode active material layer 45, a porous filler layer 48 formed on the surface of the negative electrode active material later and containing insulating fillers and a binder. The lithium secondary battery is constituted so that a ratio (N/P) of the initial capacity (N[mAh/cm<SP>2</SP>]) of a negative electrode 40 having no filler layer 48 to the initial capacity (P[mAh/cm<SP>2</SP>]) of the positive electrode 30 is 1.2-2.0. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a lithium secondary battery having a configuration in which an insulating filler layer is provided on a negative electrode active material layer and a method for manufacturing the same.

Lightweight and high output lithium secondary batteries (typically lithium ion batteries) are expected to increase in demand in the future as power sources for vehicles or power supplies for personal computers and portable terminals. As one form of the lithium secondary battery, a battery including a positive electrode and a negative electrode including an electrode active material capable of occluding and releasing lithium ions and a non-aqueous electrolyte can be given. Patent Document 1 describes a technique of providing a porous protective film on the surface of either the positive electrode active material layer or the negative electrode active material layer in this type of lithium secondary battery. Patent documents 2-5 are mentioned as other conventional technical literature about a lithium secondary battery.
Japanese Patent Laid-Open No. 7-220759 JP 2005-327680 A JP 2004-296098 A Japanese Patent Laid-Open No. 2001-14389 JP 2005-174792 A

  Providing an insulating layer on the surface of the electrode active material layer (for example, a porous protective film as described in Patent Document 1 having an insulating property) This can be an effective technique for improving the prevention of short circuit. As a method for forming such an insulating layer, from the viewpoint of productivity and the like, a filler layer is formed by applying a composition containing an insulating filler and an appropriate binder component to the surface of an electrode (for example, an electrode active material layer). This method can be preferably adopted. However, a lithium secondary battery having such a filler layer tends to have a larger internal resistance (for example, an initial internal resistance) than a lithium secondary battery having a configuration without the filler layer.

  Therefore, the present invention is a lithium secondary battery in which a filler layer is formed on the surface of the negative electrode active material layer, and the influence on the other battery performance (increased initial internal resistance, etc.) due to the formation of the filler layer is suppressed. It is an object of the present invention to provide a lithium secondary battery and a manufacturing method thereof. Moreover, it aims at provision of the vehicle provided with this lithium secondary battery.

  The present inventor has found that the above problem can be solved by intentionally increasing the amount of the negative electrode active material used relative to the positive electrode active material as compared with a normal lithium secondary battery having no filler layer. The present invention has been completed.

The lithium secondary battery provided by the present invention includes a positive electrode having a positive electrode active material layer mainly composed of a positive electrode active material. Moreover, the negative electrode which has the negative electrode active material layer which has a negative electrode active material as a main component, and the filler layer formed in the surface of this negative electrode active material layer is provided. The filler layer is typically porous (that is, a porous structure), and is an insulating filler (a filler mainly composed of an insulating material), and is a filler substantially composed of the insulating material. And a binder. The lithium secondary battery has a ratio between the initial capacity of the positive electrode (P [mAh / cm ² ]) and the initial capacity of the negative electrode (N [mAh / cm ² ]) when the filler layer is not provided. (N / P) is configured to be approximately 1.2 to 2.0.

  Since the lithium secondary battery having such a configuration has the filler layer, the lithium secondary battery is excellent in reliability and can exhibit good battery performance. In other words, the effects of the formation of the filler layer (typically, a decrease in battery performance, typically an increase in the initial internal resistance, a decrease in the initial capacity, etc.) and the effects of the formation of the filler layer ( For example, the effect of improving the reliability of the battery can be realized.

  In the present specification, the “lithium secondary battery” refers to a secondary battery that uses lithium ions as electrolyte ions and is charged / discharged by transfer of electric charges associated with lithium ions between the positive and negative electrodes. A secondary battery generally referred to as a lithium ion battery is a typical example included in the lithium secondary battery in this specification.

  As the insulating filler constituting the filler layer, a filler (inorganic filler) containing an inorganic material (typically a ceramic material) as a main constituent component can be preferably used. In a preferred embodiment of the lithium secondary battery disclosed herein, the insulating filler is an inorganic oxide filler (a filler comprising an inorganic oxide as a main constituent, and a filler substantially composed of an inorganic oxide). It is possible.) A suitable example of such an inorganic oxide filler is alumina particles (typically α-alumina particles).

  The filler layer is preferably formed by applying a slurry containing the insulating filler and the binder to the negative electrode active material layer. A lithium secondary battery having such a filler layer is preferable because of excellent productivity. The slurry may contain, for example, the insulating filler and the binder at a mass ratio of about 80:20 to 99.5: 0.5. A lithium secondary battery including a filler layer formed using a slurry having such a composition can achieve both the durability and battery performance of the filler layer at a high level.

The present invention also provides a method for manufacturing a lithium secondary battery. The manufacturing method includes preparing a positive electrode having a positive electrode active material layer mainly composed of a positive electrode active material and exhibiting a predetermined initial capacity (P [mAh / cm ² ]). Moreover, it has a negative electrode active material layer mainly composed of a negative electrode active material, and exhibits an initial capacity (N [mAh / cm ² ]) of about 1.2 to 2.0 times the initial capacity of the positive electrode ( That is, it includes preparing a negative electrode raw material having an initial capacity ratio (N / P) of about 1.2 to 2.0. In addition, the method includes applying a slurry containing an insulating filler and a binder to the negative electrode active material layer to produce a negative electrode in which a porous filler layer is formed on the surface of the negative electrode active material layer. Then, a lithium secondary battery is constructed using the positive electrode and the negative electrode.

  According to this method, it is possible to efficiently produce a lithium secondary battery that is excellent in reliability because it has a filler layer and that is highly suppressed in deterioration of battery performance due to the formation of the filler layer. This manufacturing method can be preferably employed as a method for manufacturing any of the lithium secondary batteries disclosed herein.

  The negative electrode raw material may be prepared by, for example, preparing the negative electrode raw material as part of the manufacturing method, or by obtaining (for example, purchasing) a negative electrode raw material prepared in advance. Also good. The same applies to the preparation of the positive electrode.

  Further, according to the present invention, there is provided a vehicle including any lithium secondary battery disclosed herein (which may be a lithium secondary battery manufactured by any method disclosed herein). The lithium secondary battery may exhibit performance (for example, high reliability) suitable as a lithium secondary battery mounted on a vehicle. Therefore, such a secondary battery can be suitably used as a power source for a motor (electric motor) mounted on a vehicle such as an automobile.

  Hereinafter, preferred embodiments of the present invention will be described. Note that matters other than matters specifically mentioned in the present specification and necessary for the implementation of 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 invention disclosed herein is a lithium secondary battery including a positive electrode having a positive electrode active material and a negative electrode having a negative electrode active material, and is provided on the surface of the negative electrode (typically at least the surface of the negative electrode active material layer). The present invention can be widely applied to a lithium secondary battery having a configuration in which an insulating filler layer is formed, its manufacture, and vehicles equipped with the battery. The external shape of the lithium secondary battery is not particularly limited, and may be, for example, a rectangular parallelepiped shape, a flat shape, a cylindrical shape, or the like.

As the positive electrode active material, a material capable of occluding and releasing lithium ions (typically in particulate form) is used. For example, an oxide-based positive electrode active material having a layer structure used in a general lithium secondary battery, spinel An oxide-based positive electrode active material having a structure can be preferably used. As typical examples of such a positive electrode active material, a lithium nickel composite oxide (typically an oxide having a composition represented by the formula: LiNiO ₂ ;), a lithium cobalt composite oxide (typically LiCoO ₂ ). And a positive electrode active material mainly composed of a lithium transition metal composite oxide such as lithium manganese composite oxide (typically LiMn ₂ O ₄ ). Here, the “lithium nickel composite oxide” means an oxide having lithium and nickel as constituent metal elements, and at least one metal element other than lithium and nickel (that is, a transition metal other than lithium and nickel) Element (and / or typical metal element) in a proportion less than nickel (in terms of the number of atoms. When two or more metal elements other than lithium and nickel are contained, the composite oxide contains less than nickel as the total amount thereof) This also applies to lithium cobalt complex oxides and lithium manganese complex oxides. The technology disclosed herein includes a positive electrode active material (typically, a positive electrode active material having a composition substantially free of manganese) mainly composed of a lithium nickel composite oxide or a lithium cobalt composite oxide. It can be preferably applied to a lithium secondary battery.

  The technology disclosed here is a lithium secondary battery constructed using a positive electrode having such a positive electrode active material and a negative electrode having a negative electrode active material, which will be described later, and the voltage between both electrodes (inter-terminal voltage) is approximately. It can be preferably applied to a lithium secondary battery (typically a lithium ion battery) used in a range of 4.2 V or less (for example, a range of about 3 V to 4.1 V).

  The positive electrode in the technology disclosed herein typically has a configuration in which a layer containing such a positive electrode active material as a main component (positive electrode active material layer) is held by a positive electrode current collector. As the positive electrode current collector, a conductive member made of a metal having good conductivity is preferably used. In particular, it is preferable to use a positive electrode current collector made of aluminum (Al) or an alloy containing aluminum as a main component (aluminum alloy). The shape of the positive electrode current collector is not particularly limited because it may vary depending on the shape of the lithium secondary battery constructed using the obtained positive electrode, such as a rod shape, plate shape, sheet shape, foil shape, mesh shape, etc. It can be in various forms. The current collectors of various shapes may be produced by any conventionally known method in the field of lithium secondary batteries, and do not characterize the present invention. The technology disclosed herein can be preferably applied to a lithium secondary battery including a positive electrode in a form in which a positive electrode active material layer is held on, for example, a sheet-shaped or foil-shaped current collector. As a preferable embodiment of such a lithium secondary battery, a lithium secondary battery including a wound electrode body can be given.

  The positive electrode active material layer is, for example, a liquid composition (typically a paste or slurry composition) in which a positive electrode active material (preferably particulate, for example, lithium nickel composite oxide particles) is dispersed in an appropriate solvent. ) Is applied to the positive electrode current collector, and the composition (positive electrode active material composition) is preferably dried. As the solvent (dispersion medium such as positive electrode active material particles), any of water, organic solvents, and mixed solvents thereof can be used. For example, a positive electrode active material composition in which the solvent is an aqueous solvent (water or a mixed solvent mainly containing water) can be preferably used.

  In addition to the positive electrode active material and the solvent, the positive electrode active material composition requires one or more materials that can be blended in a composition used for forming a positive electrode active material layer in a general lithium secondary battery. Depending on the content. An example of such a material is a conductive material. As the conductive material, various carbon blacks (acetylene black, furnace black, ketjen black, etc.), carbon powder such as graphite powder, or conductive metal powder such as nickel powder can be used.

  Other examples of materials that can be contained in the positive electrode active material composition as needed include a binder and a fluidity modifier. For example, as appropriate from polymers such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), styrene butadiene rubber (SBR), carboxymethyl cellulose (CMC). One or two or more selected polymer materials can be suitably used as the binder and / or fluidity modifier (typically a viscosity modifier such as a thickener).

  Although not particularly limited, the solid content concentration of the positive electrode active material composition (nonvolatile content, that is, the ratio of the positive electrode active material layer forming component) can be, for example, about 40 to 60% by mass. The content ratio of the positive electrode active material in the solid content (positive electrode active material layer forming component) is preferably at least about 50% by mass, and may be, for example, about 75 to 99% by mass. Usually, it is appropriate to set this ratio to about 80 to 95% by mass. In the composition containing the conductive material, for example, the ratio of the positive electrode active material to the positive electrode active material layer forming component can be about 80 to 90% by mass, and the ratio of the conductive material can be about 5 to 15% by mass. In the composition containing the polymer component as described above, the ratio of the polymer component to the positive electrode active material layer forming component can be about 0.5 to 15% by mass. The content of this polymer component may be about 1 to 5% by mass.

  In applying (typically applying) such a positive electrode active material composition to a positive electrode current collector (preferably a foil or sheet), a technique similar to a conventionally known method can be appropriately employed. . For example, a predetermined amount of the above composition may be applied in a layered manner to the surface of the current collector using a suitable coating device (slit coater, die coater, comma coater, etc.).

  On the other hand, as the negative electrode active material, a material capable of occluding and releasing lithium ions is used. For example, an appropriate material can be adopted from various negative electrode active materials used in a general lithium secondary battery. Carbon particles are exemplified as a suitable negative electrode active material in the technology disclosed herein. It is preferable to use a particulate carbon material (carbon particles) containing a graphite structure (layered structure) at least partially. Any carbon material of a so-called graphitic material (graphite), a non-graphitizable carbon material (hard carbon), a graphitizable carbon material (soft carbon), or a combination of these materials is preferably used. obtain. For example, natural graphite, mesocarbon microbeads (MCMB), highly oriented graphite (HOPG), etc. can be used.

  As the negative electrode active material (typically in the form of particles, preferably carbon particles such as graphite particles), for example, those having an average particle diameter of about 5 to 50 μm can be used. Among them, it is preferable to use carbon particles having an average particle diameter of about 5 to 15 μm (for example, about 8 to 12 μm). Thus, carbon particles having a relatively small particle size have a large surface area per unit volume, and thus can be a negative electrode active material suitable for more rapid charge / discharge (for example, high power discharge). Therefore, the lithium secondary battery having such a negative electrode active material can be suitably used, for example, as a lithium secondary battery for vehicle mounting.

  The negative electrode in the technology disclosed herein typically has a configuration in which a layer containing the negative electrode active material as a main component (negative electrode active material layer) is held by a negative electrode current collector. As the negative electrode current collector, a conductive member made of a metal having good conductivity is preferably used. In particular, it is preferable to use a negative electrode current collector made of copper (Cu) or an alloy containing copper as a main component (copper alloy). The shape of the negative electrode current collector is not particularly limited because it can vary depending on the shape of the lithium secondary battery constructed using the obtained negative electrode, as with the positive electrode current collector described above. The technology disclosed herein is, for example, a lithium secondary battery including a negative electrode in a form in which a negative electrode active material layer is held on a sheet-shaped or foil-shaped current collector (for example, a lithium secondary battery including a wound electrode body) ) Can be preferably applied.

  The negative electrode active material layer, for example, applies a liquid composition (typically a paste or slurry composition) in which a negative electrode active material (preferably carbon particles) is dispersed in a suitable solvent to a negative electrode current collector. The composition (negative electrode active material composition) can be preferably prepared by drying. As the solvent (dispersion medium such as carbon particles), any of water, organic solvents, and mixed solvents thereof can be used. For example, a negative electrode active material composition in which the solvent is an aqueous solvent (water or a mixed solvent mainly containing water) can be preferably employed.

  In addition to the negative electrode active material and the solvent, the negative electrode active material composition is one or more materials that can be blended in a composition used for forming a negative electrode active material layer in a general negative electrode for a lithium secondary battery. Can be contained as required. Examples of such materials include binders and fluidity modifiers. For example, the same polymer materials as those exemplified as materials that can be contained in the positive electrode active material composition are suitably used as the binder and / or fluidity modifier (typically, a viscosity modifier, such as a thickener). can do.

  Although not particularly limited, the solid content concentration of the negative electrode active material composition (nonvolatile content, that is, the ratio of the negative electrode active material layer forming component in the composition) is, for example, about 40 to 60% by mass. Is appropriate. The content ratio of the negative electrode active material in the solid content (negative electrode active material layer forming component) can be, for example, about 80% by mass or more (typically about 80 to 99.9% by mass), for example, about 90%. It is preferable to set it to -99%, and it is more preferable to set it as about 95-99 mass%. For example, in the negative electrode active material composition having a composition containing the polymer material as described above, the mass ratio of the negative electrode active material to the polymer material (negative electrode active material: polymer material) included in the composition is about 80:20 to 99.5: 0.5, and the mass ratio may be about 95: 5 to 99: 1.

  In applying (typically coating) such a negative electrode active material composition to a negative electrode current collector (preferably a foil or sheet), a case where the positive electrode active material composition is applied to the positive electrode current collector, Similarly, a technique similar to a conventionally known method can be appropriately employed.

  In the technology disclosed herein, a negative electrode raw material formed by forming a negative electrode active material layer on a negative electrode current collector (that is, a negative electrode in which a filler layer described later is not yet formed on the surface of the negative electrode active material layer). The initial capacity per unit area (N) is about 1.2 to 2.0 times the initial capacity per unit area (P) of the positive electrode (ie, “the negative electrode initial capacity (N) / the initial capacity of the positive electrode ( P) ”so that the initial capacity ratio (N / P) is about 1.2 to 2.0). The amount of the negative electrode active material possessed by the negative electrode raw material (per unit area of the negative electrode current collector) The amount of the negative electrode active material contained in the held negative electrode active material layer, and the negative electrode raw material having a structure in which the negative electrode active material layer is held on both sides of the negative electrode current collector, is included in the negative electrode active material layers on both sides It is preferable to adjust the total amount of the negative electrode active material. The adjustment of the amount of the negative electrode active material can be performed, for example, by appropriately setting the amount of the negative electrode active material composition applied per unit area of the negative electrode current collector (the coating amount in terms of solid content). The initial capacity ratio may be about 1.3 to 1.7, for example. A lithium secondary battery having an initial capacity ratio (N / P) that is too smaller than the above range tends to have an increased initial resistance compared to a lithium secondary battery that does not have a filler layer. On the other hand, a lithium secondary battery having an initial capacity ratio (N / P) that is larger than the above range has a large irreversible capacity value with respect to the initial capacity of the battery, and a small battery capacity (energy density) per fixed volume. Tend to be. By setting the initial capacity ratio (N / P) within the above-mentioned preferable range, a lithium secondary battery exhibiting good battery performance (low initial resistance and / or high energy density) can be realized regardless of the formation of the filler layer. obtain.

The initial capacity (N) of the negative electrode raw material can be measured, for example, by the following method. That is, a measurement cell (half-cell) is constructed by punching the negative electrode raw material into a predetermined size as a measurement electrode and using a metal lithium electrode as a counter electrode. For the measurement cell, lithium was used as the negative electrode active material until the potential of the measurement electrode was 0.01 V (based on metallic lithium; hereinafter, the voltage based on metallic lithium was expressed as “V (vs. Li / Li ⁺ )”). Performing an initial charge / discharge cycle in which ions are inserted and then the lithium ions are released (typically, lithium ions are released until the potential of the measurement electrode reaches 0.5 V (vs. Li / Li ⁺ )). Thus, the initial capacity (N [mAh / cm ² ]) per unit area of the negative electrode raw material is obtained.

The initial capacity (P) of the positive electrode can be measured, for example, by the following method. That is, a measurement cell (half-cell) is constructed by using a positive electrode punched into a predetermined size as a measurement electrode and using a metal lithium electrode as a counter electrode. For the measurement cell, lithium ions were desorbed from the positive electrode active material until the potential of the measurement electrode reached 4.3 V (vs. Li / Li ⁺ ), and then lithium ions were inserted into the positive electrode active material (typically Is the initial capacity per unit area of the positive electrode (P [mAh / Pb] by performing an initial charge / discharge cycle in which lithium ions are inserted until the potential of the measurement electrode reaches 3.0 V (vs. Li / Li ⁺ ). cm ² ]).

As long as the above-described preferred initial capacity ratio can be realized, the coating amount of the negative electrode active material composition (coating amount per unit area of the current collector (in terms of solid content)) is not particularly limited. An appropriate coating amount can be set according to the target performance or the like. For example, when producing a negative electrode used for the construction of a lithium secondary battery having a wound electrode body as described above, a foil-like current collector (for example, a metal foil having a thickness of about 10 to 30 μm ( Copper foil etc.) can be preferably used.) When the above composition is applied to the surface of solid content, the coating amount in terms of solid content (that is, the mass after drying) is about 5 to 20 mg / cm ² (when applied on both sides). Is preferably applied so that the total amount of the both surfaces becomes). Such a coating amount of the negative electrode active material composition may be applied to one side of the current collector, or the negative electrode active material composition may be applied to both sides of the current collector so that the total coating amount falls within the above range. Good. An embodiment in which the negative electrode active material composition is applied to both sides of the current collector (a negative electrode active material layer is provided on both sides of the current collector) can be preferably employed. After coating, the coated material is dried by an appropriate drying means, and pressed as necessary, whereby a negative electrode active material layer can be formed on the surface of the negative electrode current collector.

Although not particularly limited, the density of the negative electrode active material layer may be, for example, about 1.1 to 1.5 g / cm ³ . The density of the negative electrode active material layer may be, for example, about 1.1 to 1.3 g / cm ³ . The press conditions may be set so that a negative electrode active material layer having such a density is formed. In addition, as a press method, conventionally well-known various press methods, such as a roll press method and a flat plate press method, can be employ | adopted suitably.

  The negative electrode disclosed herein has a filler layer containing an insulating filler (for example, alumina particles) and a binder on the surface of the negative electrode active material layer. The filler layer may be formed in almost the entire range of the negative electrode active material layer surface, or may be formed in only a partial range of the negative electrode active material layer surface. Usually, from the viewpoint of the effect of providing the filler layer and the durability of the filler layer, it is preferable to have a configuration in which the filler layer is formed so as to cover at least almost the entire surface of the negative electrode active material layer surface. Note that, in the negative electrode in which the negative electrode active material layer is formed on the negative electrode current collector, a portion where the negative electrode active material layer is not formed (a portion where the negative electrode active material layer is not formed) is left in a part of the current collector. In such a case, a part of the filler layer may extend from the negative electrode active material layer to the portion where the negative electrode active material layer is not formed as long as the effect of the present invention is not significantly impaired.

As the insulating filler constituting the filler layer, fillers mainly composed of various inorganic materials and / or organic materials (resin material, paper, wood, etc.) exhibiting non-conductivity (insulating properties) can be used. . From the viewpoint of durability and reliability, it is preferable to use a filler mainly composed of an inorganic material (inorganic filler). For example, particles (ceramic particles) made of a non-conductive (insulating) inorganic compound can be preferably used as the insulating filler. The inorganic compound may be an oxide, carbide, silicide, nitride or the like of a metal element or a nonmetal element. From the viewpoint of chemical stability, raw material cost, etc., a filler composed of oxide particles such as alumina (Al ₂ O ₃ ), silica (SiO ₂ ), zirconia (ZrO ₂ ), magnesia (MgO) (ie, inorganic oxide filler) ) Can be preferably used. Further, silicide particles such as silicon carbide (SiC) and nitride particles such as aluminum nitride (AlN) can also be used.

  As the insulating filler in the present invention, for example, α-alumina particles similar to the inorganic oxide filler in the technique described in Patent Document 2 can be preferably used. Similar to the technique described in Patent Document 2, the α-alumina particles may be particles (connected particles) having properties in which a plurality of (for example, about 2 to 10) primary particles are connected. Such linked particles can be produced based on the contents described in Patent Document 2 and / or other known documents and the common general technical knowledge in the field, or a corresponding commercial product can be obtained.

The average particle size of the insulating filler used (preferably inorganic oxide filler such as alumina particles) may be about 0.1 to 15 μm, for example. The average particle size referred to here, can be employed common commercial granulometer an average particle size of the measured volume basis using a (laser diffraction particle size distribution measuring apparatus or the like) (D _50). It is preferable to use a filler having an average particle size of about 0.2 to 1.5 μm. According to the filler layer formed using the filler having an average particle size of this degree, the application effect of the present invention can be exhibited better. Moreover, the lithium secondary battery constructed | assembled using the negative electrode of the structure by which such a filler layer was provided on the negative electrode active material may exhibit more favorable battery performance.

  The filler layer can contain a binder (polymer component) for binding the filler in addition to the insulating filler (for example, an inorganic oxide filler). As this binder, the 1 type, or 2 or more types of material suitably selected from the polymer illustrated as a binder which can be mix | blended with a negative electrode active material composition can be used suitably, for example. In addition to the polymers specifically exemplified above, binders that can be preferably used include acrylonitrile-butadiene copolymer rubber (NBR), acrylonitrile-isoprene copolymer rubber (NIR), and acrylonitrile-butadiene-isoprene copolymer rubber. (NBIR) or other rubber containing acrylonitrile as a copolymerization component; acrylic polymer having acrylic acid, methacrylic acid, acrylic acid ester or methacrylic acid ester (eg alkyl ester) as the main copolymerization component; polyvinyl acetate, ethylene -Vinyl acetate resin such as vinyl acetate copolymer (EVA);

  The binder used for forming the negative electrode active material layer and the binder used for forming the filler layer may be the same or different. The invention disclosed herein can be preferably implemented in a mode in which the binders used in both layers are different types of binders. For example, a water-soluble (CMC or the like) binder and / or a water-dispersible binder (SBR or the like) is used for either one of the negative electrode active material layer and the filler layer, and the other is a binder that dissolves in an organic solvent ( PVDF, organic solvent-soluble acrylic polymer, etc.) can be used. This is advantageous in constructing a lithium secondary battery in which the influence on the other battery performance due to the formation of the filler layer is further suppressed.

  The mass ratio between the filler and the binder contained in the filler layer (filler: binder) can be, for example, approximately 80:20 to 99.5: 0.5. The mass ratio may be about 95: 5 to 99: 1. If the ratio of the binder is less than the above mass ratio, the durability of the filler layer tends to be insufficient. On the other hand, when the proportion of the binder is too much than the above mass ratio, the influence on the battery performance (such as a decrease in the initial capacity) due to the provision of the filler layer may become apparent.

  As a method for forming the filler layer on the surface of the negative electrode active material layer, for example, a coating agent (filler layer forming composition) containing a filler (for example, ceramic particles) and a binder is prepared, and the coating agent is used as the negative electrode active material. A method of imparting to the layer can be preferably employed. Usually, a liquid coating agent (typically paste or slurry) in which the filler and binder are dispersed or dissolved in a suitable solvent is applied (typically applied) to the surface of the negative electrode active material layer, and the A method of drying the applied liquid coating agent is simple and preferable. As the solvent (dispersion medium such as filler), any of water (for example, ion-exchanged water), an organic solvent (for example, N-methylpyrrolidone), and a mixed solvent of water and an organic solvent can be used. Although not particularly limited, the solid content concentration of the liquid coating agent (the ratio of the filler layer-forming component in the coating agent) can be, for example, about 30 to 80% by mass. If the solid content concentration is too high, the handling property (coating property, etc.) of the liquid coating agent tends to decrease. On the other hand, if the solid content concentration is too low, the production efficiency of the battery tends to decrease. In addition, depending on the solvent composition of the liquid coating agent, the influence on the battery performance due to the formation of the filler layer (decrease in initial capacity, etc.) may be easily manifested.

  The solvent used for the negative electrode active material composition and the solvent used for the liquid coating agent may be the same or different. In the technique disclosed herein, a solvent different from the solvent of the negative electrode active material composition can be preferably employed as the solvent of the liquid coating agent. For example, when the solvent of the negative electrode active material composition is an aqueous solvent (for example, water), a liquid coating agent containing an organic solvent such as N-methylpyrrolidone (NMP) can be preferably used. Thus, an organic solvent system is formed on the negative electrode active material layer formed using the aqueous negative electrode active material composition (typically containing a water-soluble binder and / or a water-dispersible binder). (Also referred to as a solvent system. Typically, a binder that is soluble in an organic solvent (preferably a binder that hardly dissolves or swells in the aqueous solvent constituting the positive electrode active material composition, typically in the aqueous solvent. Insoluble binder))) is applied to form a filler layer, whereby the applied liquid coating agent affects the state of the negative electrode active material layer (for example, causes swelling). The effect of being able to avoid better is obtained. In addition, this makes it difficult for the binder contained in the liquid coating agent (that is, the binder constituting the filler layer) to penetrate into the negative electrode active material layer. Therefore, even in the configuration in which the filler layer is formed on the negative electrode active material layer, The performance of the negative electrode active material contained in the negative electrode active material layer can be appropriately exhibited. Therefore, a lithium secondary battery with better battery performance can be constructed. Such effects include a solvent-based negative electrode active material composition (typically containing a binder soluble in an organic solvent) and a water-based liquid coating agent (typically water-soluble binder and / or water). It can also be realized in combination with a dispersible binder).

  In the technology disclosed herein, the average pore diameter of pores (voids) contained in the filler layer, the ratio of the total volume of the pores to the volume of the entire filler layer (porosity), the thickness of the filler layer, etc. There is no particular limitation as long as it is set so that the purpose of forming the filler layer (improvement of battery reliability, more specifically, prevention of internal short circuit, etc.) is appropriately achieved and desired battery characteristics are secured. A filler layer having an average pore diameter of about 0.01 to 10 μm (preferably about 0.1 to 4 μm), a filler layer having a porosity of about 20 to 75% by volume (preferably about 35 to 70%), and a thickness of about A filler layer of 1 to 10 μm (preferably about 2 to 6 μm) is a suitable example of the filler layer provided in the lithium secondary battery according to the present invention. The average pore diameter and porosity can be measured using a commercially available mercury porosimeter or the like.

  The lithium secondary battery that can be provided by the present invention is the same as the conventional secondary battery of this type except that the negative electrode (including the negative electrode manufactured by the above-described method) and the positive electrode having the above-described configuration are used. Can be manufactured. The lithium secondary battery typically includes a positive electrode and a negative electrode having a configuration disclosed herein, a separator separating the positive and negative electrodes (for example, a porous resin sheet sandwiched between the positive and negative electrodes), and the positive and negative electrodes. And an electrolyte (typically a non-aqueous electrolyte) disposed between the negative electrodes. There is no particular limitation on the structure (for example, a metal casing or laminate film structure) and size of the battery outer container, or the structure of the electrode body (for example, a wound structure or a laminated structure) having positive and negative electrodes as main components. .

  Hereinafter, an embodiment according to a lithium secondary battery that can be provided by the present invention and a manufacturing method thereof will be described with reference to the drawings.

  As shown in FIGS. 1 to 4, the lithium secondary battery 10 according to the present embodiment includes a metal (resin or laminate film) casing (outer container) 12. The long sheet-like positive electrode 30, separator 50A, negative electrode 40, and separator 50B are stacked in this order in this casing 12, and then wound (in this embodiment, rolled into a flat shape). The wound electrode body 20 is accommodated.

  The positive electrode 30 includes a long positive electrode current collector 32 and a positive electrode active material layer 35 formed on the surface thereof. As the positive electrode current collector 32, a sheet material (typically a metal foil such as an aluminum foil) made of a metal such as aluminum, nickel, or titanium can be used. The positive electrode active material layer 35 may be obtained by applying a suitable positive electrode active material composition as described above to the positive electrode current collector 32. Typically, the composition is applied to the surfaces of both sides of the positive electrode current collector 32. Since the coated material contains moisture, the coated material is then dried in an appropriate temperature range (typically 70 to 200 ° C.) that does not denature the positive electrode active material. Thereby, the positive electrode active material layer 35 can be formed in the desired site | part of the surface of the both sides of the positive electrode collector 32 (FIG. 2). Moreover, the thickness and density of the positive electrode active material layer 35 can be appropriately adjusted by performing an appropriate press process (for example, a roll press process) as necessary.

  On the other hand, the negative electrode 40 includes a long negative electrode current collector 42, a negative electrode active material layer 45 formed on the surface of the negative electrode current collector, and a filler layer 48 formed on the surface of the negative electrode active material layer. (FIGS. 2 and 3). As the negative electrode current collector 42, a sheet material (typically a metal foil such as a copper foil) made of a metal such as copper can be used. As with the positive electrode side, the negative electrode active material layer 45 is coated with a suitable negative electrode active material composition as described above on the surfaces of both sides of the negative electrode current collector 45 and dried at an appropriate temperature. It may be obtained by adjusting the thickness and density of the negative electrode active material layer 45 by performing a pressing process (for example, a roll pressing process). The filler layer 48 is formed by preparing a suitable coating agent (typically a liquid coating agent) as described above, applying the coating agent to the surface of the negative electrode active material layer 45, and drying it at an appropriate temperature. It has been done. In FIG. 2, in order to facilitate understanding of the present invention, a part of the filler layer 48 is removed from a part of the negative electrode 40 (lower left part in the figure) so that the negative electrode active material layer 45 below can be seen. Actually, however, substantially the entire range of the negative electrode active material layer 45 including this portion is covered with the filler layer 48.

  As the separators 50A and 50B that are used while being overlapped with the positive electrode 30 and the negative electrode 40, various porous sheets that are known to be usable for separators for lithium secondary batteries including a non-aqueous electrolyte are used. be able to. For example, a porous resin sheet (film) made of a polyolefin resin such as polyethylene or polypropylene can be preferably used. Although it does not specifically limit, as a property of a preferable porous sheet (typically porous resin sheet), an average pore diameter is about 0.0005-30 micrometers (more preferably 0.001-15 micrometers), and thickness is. The porous resin sheet which is about 5-100 micrometers (more preferably 10-30 micrometers) is illustrated. The porosity of the porous sheet may be, for example, about 20 to 90% by volume (preferably 30 to 80% by volume).

  As shown in FIG. 2, the positive electrode active material composition is not applied to one end portion along the longitudinal direction of the positive electrode sheet 30, and thus a portion where the positive electrode active material layer 35 is not formed (active material layer unformed portion). ) Is provided. In addition, at one end portion along the longitudinal direction of the negative electrode sheet 40, a portion where the negative electrode active material composition and the coating agent are not applied and thus the negative electrode active material layer 45 and the filler layer 48 are not formed is provided. . When the positive and negative electrode sheets 30 and 40 are overlapped with the two separators 50A and 50B, the active material layers 35 and 45 are overlapped and the active material layer non-formed portion of the positive electrode sheet and the active material layer of the negative electrode sheet are not formed. The positive and negative electrode sheets 30 and 40 are slightly shifted and overlapped so that the portions are separately arranged at one end and the other end along the longitudinal direction. In this state, a total of four sheets 30, 40, 50 </ b> A, 50 </ b> B are wound, and then the obtained wound body is crushed from the lateral direction to be ablated, thereby obtaining a flat wound electrode body 20.

  Next, the obtained wound electrode body 20 is accommodated in the housing 12 (FIG. 4), and the positive electrode active material layer unformed portion and the negative electrode active material layer unformed portion are partly outside the housing 12. The external connection positive terminal 14 and the external connection negative terminal 16 are electrically connected to each other.

Then, an appropriate non-aqueous electrolyte (for example, a non-aqueous electrolyte such as a mixed solvent of diethyl carbonate and ethylene carbonate containing an appropriate amount of a lithium salt such as LiPF ₆ ) is placed (injected) in the casing 12, The opening of the housing 12 is sealed by welding the housing and the lid member 13 corresponding to the housing, and the construction (assembly) of the lithium secondary battery 10 according to the present embodiment is completed. In addition, the sealing process of the housing | casing 12 and an electrolyte solution arrangement | positioning (injection) process may be the same as the method currently performed by manufacture of the conventional lithium secondary battery, and do not characterize this invention.

  Since the lithium secondary battery according to the present invention has the filler layer as described above, the lithium secondary battery has high reliability and excellent battery performance. For example, a lithium secondary battery that exhibits substantially the same battery performance as a lithium secondary battery having no filler layer (typically, an initial resistance and / or initial capacity with a lithium secondary battery that does not have the filler layer) Difference of ± 10%, more preferably ± 5% or less lithium secondary battery). Due to such characteristics, the lithium secondary battery according to the present invention can be suitably used as a power source for a motor (electric motor) mounted on a vehicle such as an automobile. Accordingly, as schematically shown in FIG. 6, the present invention provides a power source for such a lithium secondary battery 10 (which may be in the form of an assembled battery formed by connecting a plurality of lithium secondary batteries 10 in series). A vehicle (typically a vehicle, in particular a vehicle including a motor such as a hybrid vehicle, an electric vehicle, and a fuel cell vehicle) 1 is provided.

  In carrying out the present invention, it is not necessary to clarify the reason why good battery performance is realized regardless of the formation of the filler layer by setting the initial capacity ratio between the positive electrode and the negative electrode within a predetermined range. The following can be considered. That is, when the filler layer is formed on the negative electrode active material layer by a technique such as application of the coating agent, a part of the coating agent may penetrate into the negative electrode active material layer. The soaked filler layer forming component (particularly the binder) can be a factor that hinders lithium ions from entering and leaving the negative electrode active material. For example, when the binder adheres around the negative electrode active material, the lithium ions can be prevented from entering and exiting. According to the invention disclosed herein, the initial capacity ratio (N / P) between the positive electrode and the negative electrode is set to the above-described preferred range (typically more suitable than the suitable initial capacity ratio when the filler layer is not provided). In the negative electrode active material layer in which the filler layer is formed, the ratio of the amount of the soaked component to the amount of the negative electrode active material contained in the negative electrode active material layer can be relatively reduced. This is considered to suppress the influence on the battery performance. Also, rather than increasing both the initial capacity of the positive electrode and the initial capacity of the negative electrode, the ratio of the initial capacity of the negative electrode to the positive electrode is increased (typically, the use of the negative electrode active material is unchanged without changing the amount of positive electrode active material used). By increasing the amount), it is considered that the effect of preventing the influence on the battery performance is efficiently realized while suppressing a decrease in battery capacity per unit volume (decrease in energy density).

  Hereinafter, although the test example regarding this invention is demonstrated, it is not intending to limit this invention to what is shown to this specific example.

<Example 1: Production of a battery having a filler layer and an initial capacity ratio of 1.1>
A positive electrode was produced as follows. That is, lithium nickelate (LiNiO ₂ ) powder, acetylene black, carboxymethylcellulose (CMC), and polytetrafluoroethylene as a positive electrode active material have a mass ratio of 87: 11: 1: 1 and a solid content. A paste-like positive electrode active material composition was prepared by mixing with ion-exchanged water so that the concentration was 45% by mass. Applying such a composition to both sides of a long aluminum foil having a thickness of about 15 μm as a positive electrode current collector so that the total coating amount (in terms of solid content) of both surfaces is 13 mg / cm ² and drying. Thus, a positive electrode active material layer having a thickness of 120 μm was formed on both surfaces of the positive electrode current collector, and then pressed so that the total thickness of the positive electrode was 85 μm, to obtain a positive electrode sheet.

Moreover, the negative electrode raw material was produced as follows. That is, natural graphite (negative electrode active material) having an average particle diameter of 10 μm, styrene butadiene rubber and carboxymethyl cellulose are ionized so that the mass ratio of these materials is 98: 1: 1 and the solid content concentration is 45 mass%. A slurry-like negative electrode active material composition was prepared by mixing with exchange water. The above composition is applied to both sides of a long copper foil having a thickness of about 15 μm as a negative electrode current collector so that the total coating amount (in terms of solid content) on both sides is 8.6 mg / cm ² and dried. Then, the negative electrode active material layer was pressed so that the density was 1.3 g / cm ³ . Thus, a negative electrode raw material having a negative electrode active material layer on the surface of the negative electrode current collector was obtained.

  The initial capacities of the positive electrode sheet and negative electrode raw material prepared above were measured, respectively.

That is, the positive electrode sheet was punched into a predetermined size (circular shape with an area of 2 cm ² ) to prepare a measurement electrode. This measurement electrode and a metal lithium foil (counter electrode) of the same size are placed opposite to each other with a separator (using a porous polyethylene sheet having a thickness of 0.02 mm) interposed between the measurement electrode and a stainless steel container together with the electrolyte. A coin-type cell (measuring cell) having a diameter of 2 mm and a diameter of 32 mm (2032 type) was constructed. As the electrolytic solution, non-aqueous electrolysis having a composition in which a supporting salt (here, LiPF ₆ ) is dissolved in a 3: 7 (volume ratio) mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) at a concentration of 1 mol / L. The liquid was used. In the measurement cell, lithium ions are desorbed from the positive electrode active material at a current density of 0.1 mA / cm ² until the potential of the measurement electrode becomes 4.3 V (vs. Li / Li ⁺ ). By inserting lithium ions at a current density of 1 mA / cm ² until the potential of the measurement electrode becomes 3.0 V (vs. Li / Li ⁺ ), the initial capacity per unit area of the positive electrode sheet (the initial capacity P [ mAh / cm ² ]).

The negative electrode raw material was punched into a predetermined size (circular shape with an area of 2 cm ² ) to prepare a measurement electrode. This measurement electrode and a metallic lithium foil (counter electrode) of the same size are placed opposite to each other with a separator (using a porous polyethylene sheet having a thickness of 0.02 mm) interposed in the stainless steel container together with the non-aqueous electrolyte. A coin type cell (measuring cell) having a thickness of 2 mm and a diameter of 32 mm (2032 type) was constructed. Then, for the measurement cell, inserting lithium ions into the negative electrode active material until the potential of the measuring electrode at a current density of 0.1mA / cm ² is 0.01 V (vs. Li / Li ^+), then 0.1mA The initial capacity per unit area of the negative electrode raw material (the initial capacity of the negative electrode raw material) is obtained by releasing lithium ions until the potential of the measurement electrode becomes 0.5 V (vs. Li / Li ⁺ ) at a current density of / cm ^2. N [mAh / cm ² ]).

  The initial capacity ratio (N / P) between the positive electrode sheet (positive electrode) and the negative electrode raw material calculated from these measurement results was 1.1.

  A filler layer was formed on the surface of the negative electrode active material layer constituting the negative electrode raw material. That is, α-alumina particles (linked particles) having an average particle diameter of 0.6 μm and acrylic polymer as a binder are such that the mass ratio of these materials is 96: 4 and the solid content concentration is 40% by mass. Was mixed with N-methylpyrrolidone (NMP) to prepare a slurry coating agent (liquid coating agent). This liquid coating agent was applied and dried so as to cover the entire surface of the negative electrode active material layer. The coating amount of the coating agent was such that the thickness of the filler layer obtained after drying was 4 μm.

  Using the negative electrode thus obtained and the positive electrode (positive electrode sheet), a general cylindrical lithium ion battery 100 having a diameter of 18 mm and a height of 65 mm (that is, 18650 type) (FIG. 5) in the following procedure. Reference) was made.

As a non-aqueous electrolyte (electrolytic solution), a supporting salt (here, LiPF ₆ ) was dissolved at a concentration of 1 mol / L in a 3: 7 (volume ratio) mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC). A non-aqueous electrolyte (electrolytic solution) having a composition was used.

  And the negative electrode and positive electrode which were produced above were laminated | stacked with two separators (here the porous polyethylene sheet was used), this laminated sheet was wound, and the wound electrode body was produced. This electrode body was housed in a container together with a nonaqueous electrolyte, and the container opening was sealed to construct a lithium ion battery. Thereafter, an appropriate conditioning process (for example, a constant current charging for 3 hours at a charging rate of 1/10 C, and then charging at a constant current constant voltage up to 4.1 V at a charging rate of 1/3 C; The initial charge / discharge treatment was repeated 2 to 3 times with a constant current discharge to 3.0 V at a discharge rate of 2 to 3 times. Thus, the ratio (N / P) of the initial capacity (P) of the positive electrode to the initial capacity of the negative electrode without the filler layer (ie, the initial capacity of the negative electrode raw material) (N) is 1.1. Thus, a 18650 type cylindrical lithium ion battery configured as described above was obtained.

<Example 2: Production of battery having filler layer and initial capacity ratio of 1.2>
As in the preparation of the negative electrode raw material according to Example 1, except that the coating amount of the negative electrode active material composition on the negative electrode current collector (total coating amount in terms of solid content [mg / cm ² ]) is the coating amount of Example 1 The negative electrode raw material which concerns on Example 2 was produced by changing application | coating conditions so that it might be 1.2 / 1.1 times with respect to this. The negative electrode active material layer was pressed so that the density of the negative electrode active material layer after the press was the same density (1.3 g / cm ³ ) as in Example 1 (the same applies to the following examples). A filler layer was formed on the surface of this negative electrode raw material in the same manner as in Example 1 to obtain a negative electrode according to Example 2. Then, in the same manner as in Example 1 except that the negative electrode according to this example was used instead of the negative electrode according to Example 1, the initial capacity (P) of the positive electrode and the initial capacity (N of the negative electrode without the filler layer) ) To obtain a lithium ion battery having a ratio (N / P) of 1.2.

<Example 3: Production of battery having filler layer and initial capacity ratio of 1.4>
As in the preparation of the negative electrode raw material according to Example 1, except that the coating amount of the negative electrode active material composition on the negative electrode current collector (total coating amount in terms of solid content [mg / cm ² ]) is the coating amount of Example 1 The negative electrode raw material which concerns on Example 3 was produced by changing application | coating conditions so that it might become 1.4 / 1.1 times with respect to this. A filler layer was formed on the surface of this negative electrode raw material in the same manner as in Example 1 to obtain a negative electrode according to Example 3. Then, in the same manner as in Example 1 except that the negative electrode according to this example was used instead of the negative electrode according to Example 1, the initial capacity (P) of the positive electrode and the initial capacity (N of the negative electrode without the filler layer) ) To obtain a lithium ion battery having a ratio (N / P) of 1.4.

<Example 4: Production of battery having filler layer and initial capacity ratio of 2.0>
As in the preparation of the negative electrode raw material according to Example 1, except that the coating amount of the negative electrode active material composition on the negative electrode current collector (total coating amount in terms of solid content [mg / cm ² ]) is the coating amount of Example 1 The negative electrode raw material which concerns on Example 4 was produced by changing coating conditions so that it might be 2.0 / 1.1 times with respect to this. A filler layer was formed on the surface of this negative electrode raw material in the same manner as in Example 1 to obtain a negative electrode according to Example 4. Then, in the same manner as in Example 1 except that the negative electrode according to this example was used instead of the negative electrode according to Example 1, the initial capacity (P) of the positive electrode and the initial capacity (N of the negative electrode without the filler layer) ) To obtain a lithium ion battery having a ratio (N / P) of 2.0.

<Example 5: Production of battery having filler layer and initial capacity ratio of 2.1>
As in the preparation of the negative electrode raw material according to Example 1, except that the coating amount of the negative electrode active material composition on the negative electrode current collector (total coating amount in terms of solid content [mg / cm ² ]) is the coating amount of Example 1 The negative electrode raw material which concerns on Example 5 was produced by changing coating conditions so that it might become 2.1 / 1.1 times with respect to this. A filler layer was formed on the surface of this negative electrode raw material in the same manner as in Example 1 to obtain a negative electrode according to Example 5. Then, in the same manner as in Example 1 except that the negative electrode according to this example was used instead of the negative electrode according to Example 1, the initial capacity (P) of the positive electrode and the initial capacity (N of the negative electrode without the filler layer) ) To obtain a lithium ion battery having a ratio (N / P) of 2.1.

<Example 6: Production of battery having initial capacity ratio of 1.1 and no filler layer>
In this example, the negative electrode raw material produced in Example 1 was used for the negative electrode as it was (that is, without forming a filler layer on the surface of the negative electrode active material layer). In other respects, the negative electrode active material was configured in the same manner as in Example 1 so that the ratio (N / P) of the initial capacity (P) of the positive electrode to the initial capacity (N) of the negative electrode was 1.1. A lithium ion battery having no filler layer on the surface was obtained.

[Measurement of initial resistance]
For the lithium ion batteries obtained in Examples 1 to 6, the initial resistance value (IV resistance value) at 25 ° C. of each battery was measured.

  That is, each battery was adjusted to a 60% charge state (SOC; State of Charge) by constant current constant voltage (CC-CV) charging under a temperature condition of 25 ° C. Thereafter, discharging and charging for 10 seconds were alternately performed at 25 ° C. under the conditions of 0.2C, 0.5C, and 1C, and voltage values 10 seconds after the start of discharge were plotted to create an IV characteristic graph. . From the slope of the IV characteristic graph, the initial IV resistance value (mΩ) at 25 ° C. was calculated.

[Measurement of initial battery capacity]
For the lithium ion batteries obtained in Examples 1 to 6, the initial discharge capacity (initial capacity) at 25 ° C. of each battery was measured.

  That is, by charging each battery to an upper limit voltage of 4.1 V with a constant current of 1 C under a temperature condition of 25 ° C., and then discharging to 3.0 V with a constant current of 1 C, 4.1 V of each battery. The -3.0V discharge capacity was measured.

  The initial resistance value and the initial capacity value of each battery obtained by the above measurement were measured for the initial resistance measured for the lithium ion battery according to Example 6 (battery having an initial capacity ratio of 1.1 and no filler layer). The value and the initial capacity value are set to 100, and the measured values of other batteries are shown in Table 1 as ratios to the measured values of the lithium ion battery according to Example 6.

  As is apparent from the results shown in Table 1, by setting the initial capacity ratio (N / P) to 1.2 or more in a lithium ion battery having a structure in which a filler layer is formed on the surface of the negative electrode active material layer (Example 2) To 5), despite the formation of the filler layer, the initial capacity ratio (N / P) is 1.1, and the good initial stage is substantially the same as that of the lithium ion battery (Example 6) having no filler layer. Resistance value was realized. Furthermore, according to the lithium ion battery (Examples 2 to 4) having the filler layer and the initial capacity ratio (N / P) in the range of 1.2 to 2.0, the filler layer is A good initial capacity substantially equal to that of the lithium ion battery (Example 6) not having was realized. The initial resistance and initial capacity of the lithium ion batteries according to Examples 2 to 4 were different from each other by ± 5% or less from the initial resistance and initial capacity of the lithium ion battery according to Example 6. Particularly good results were obtained with a lithium ion battery (Example 3) having a filler layer and an initial capacity ratio (N / P) in the range of 1.3 to 1.7. Thus, the compatibility of the conflicting effects of the formation of the filler layer (and hence the improvement in reliability) and the maintenance of good battery performance (for example, the initial resistance and the initial capacity), as well shown in Table 1, This is an effect that appears specifically when (N / P) is within a predetermined range.

  As mentioned above, although this invention was demonstrated in detail, the said embodiment and Example are only illustrations and what changed and changed the above-mentioned specific example is contained in the invention disclosed here. For example, the present invention is not limited to the above-described wound type battery, and can be applied to various shapes of lithium secondary batteries.

It is a perspective view which shows typically the external shape of the lithium secondary battery which concerns on one Embodiment. It is a partially broken top view which shows the positive / negative electrode and separator which comprise the wound electrode body which concerns on one Embodiment. It is the III-III sectional view taken on the line in FIG. It is the IV-IV sectional view taken on the line in FIG. It is a perspective view which shows typically the shape of the 18650 type lithium ion battery produced as an Example. It is a side view which shows typically the vehicle (automobile) provided with the lithium secondary battery of this invention.

Explanation of symbols

1 Vehicle (Automobile)
DESCRIPTION OF SYMBOLS 10,100 Lithium secondary battery 12 Case 20 Winding electrode body 30 Positive electrode 32 Positive electrode current collector 35 Positive electrode active material layer 40 Negative electrode 42 Negative electrode current collector 45 Negative electrode active material layer 48 Filler layer 50A, 50B Separator

Claims (7)

A positive electrode having a positive electrode active material layer mainly composed of a positive electrode active material;
A negative electrode having a negative electrode active material layer mainly composed of a negative electrode active material, and a porous filler layer formed on the surface of the negative electrode active material layer and containing an insulating filler and a binder;
A lithium secondary battery comprising:
The ratio (N / P) of the initial capacity (P [mAh / cm ² ]) of the positive electrode to the initial capacity (N [mAh / cm ² ]) of the negative electrode without the filler layer is 1.2. A lithium secondary battery configured to be -2.0.   The lithium secondary battery according to claim 1, wherein the insulating filler is an inorganic oxide filler.   The lithium secondary battery according to claim 2, wherein the inorganic oxide filler is alumina particles.   4. The lithium secondary battery according to claim 1, wherein the filler layer is formed by applying a slurry containing the insulating filler and the binder to the negative electrode active material layer. 5.   The lithium secondary battery according to claim 4, wherein the slurry contains the insulating filler and the binder in a mass ratio of 80:20 to 99.5: 0.5. Providing a positive electrode having a positive electrode active material layer mainly composed of a positive electrode active material and exhibiting a predetermined initial capacity (P [mAh / cm ² ]);
A negative electrode raw material having a negative electrode active material layer mainly composed of a negative electrode active material and having an initial capacity (N [mAh / cm ² ]) of 1.2 to 2.0 times the initial capacity of the positive electrode. To prepare;
Producing a negative electrode in which a porous filler layer is formed on the surface of the negative electrode active material layer by applying a slurry containing an insulating filler and a binder to the negative electrode active material layer; and
Constructing a lithium secondary battery using the positive electrode and the negative electrode;
A method for manufacturing a lithium secondary battery.   A vehicle comprising the lithium secondary battery according to any one of claims 1 to 5 or the lithium secondary battery manufactured by the method according to claim 6.

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