JP2011023146A - Lithium secondary battery, and manufacturing method of the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lithium secondary battery preferable as a high-output power source for vehicle, with thinning of an electrode active material layer achieved while restraining rise of inner resistance. <P>SOLUTION: For the lithium secondary battery provided with a positive electrode having a positive electrode active material layer including a positive electrode collector, a positive electrode active material formed on the surface of the collector and a conductive material, a layer thickness of the positive electrode active material layer is to be 30 μm or less, and the layer contains (A) a polyether based binder made of at least a kind of polyether, and (B) a cellulose based binder made of at least a kind of water-soluble cellulose derivative, with a mass ratio (Aw/Bw) of the mass (Aw) of the polyether based binder (A) in the positive electrode active material layer to the mass (Bw) of the cellulose based binder (B) satisfying Aw/Bw≥1.8. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a lithium secondary battery. More specifically, the present invention relates to a lithium secondary battery for in-vehicle power source that is suitably used as a high-output power source for mounting on a vehicle and a method for manufacturing the battery.

In recent years, secondary batteries such as lithium secondary batteries and nickel metal hydride batteries have become increasingly important as power sources mounted on vehicles using electricity as a drive source, or power sources mounted on personal computers, portable terminals, and other electrical products. . In particular, a lithium secondary battery that is lightweight and has a high energy density is expected to be preferably used as a high-output power source for mounting on a vehicle.
A typical electrode (a positive electrode and a negative electrode) of this type of secondary battery has an electrode active material layer (specifically, an electrode active material layer (specifically, an electrode active material capable of reversibly occluding and releasing chemical species as charge carriers). , A positive electrode active material layer and a negative electrode active material layer) are provided with electrodes having a structure formed respectively on the corresponding positive and negative electrode current collectors. For example, in the case of a positive electrode of a lithium secondary battery, a positive electrode active material such as a lithium transition metal composite oxide is mixed with a highly conductive material powder (conductive material) and a binder in an appropriate solvent. A positive electrode active material layer forming paste-like, slurry-like or ink-like composition (hereinafter, this type of composition is simply referred to as “paste”) is applied to the positive electrode current collector, An active material layer is formed.

  Patent documents 1-3 are mentioned as conventional technology about improvement of battery performance (for example, cycle characteristics) of the above-mentioned lithium secondary battery. In Patent Documents 1 and 2, the binder (binder) contained in the electrode active material layer is at least one selected from the group consisting of a cellulose-based polymer and polyethylene glycol, polyethylene oxide, polypropylene glycol, and polypropylene oxide. A battery using a mixture containing the following is disclosed. Patent Document 3 discloses a battery using a water-soluble polymer and a synthetic rubber latex as the binder.

Japanese Patent Laid-Open No. 11-354127 JP 11-354125 A JP-A-11-339810

  By the way, some uses of the secondary battery are assumed to be used for a long time in a mode in which high-rate charge / discharge is repeated in a short time. For example, a lithium secondary battery used as a power source of a vehicle (typically an automobile, particularly a hybrid automobile or an electric automobile) is a typical example, but the battery used in such a mode is used for a household electric appliance. Compared to a battery, the load on the electrode active material layer accompanying the movement of charge carriers is very large, and the internal resistance increases as the distance from the surface of the current collector increases. In order to suppress such an increase in internal resistance, it is required that the electrode active material layer, which is a movement path of the charge carrier, is excellent in conductivity and has a thin layer thickness. 3, the thickness of the electrode active material layer is as large as 70 to 103 μm, which is not preferable for in-vehicle power supplies.

  The electrode active material layer having a thin layer thickness preferable for in-vehicle power supply is formed by thinly applying the active material layer forming paste on the surface of the current collector. However, the active material layer forming paste having good coatability ( It is difficult to apply a thin coating unless the paste is uniformly dispersed without any lumps such as aggregates and has a good elongation with respect to the current collector. On the other hand, in order to improve the conductivity, it is effective to increase the content of the conductive material (carbon powder or the like) in the paste. However, when the content of the conductive material in the paste is increased in order to improve the conductivity of the electrode active material layer, the conductive materials tend to aggregate with each other, resulting in poor coating properties. As a result, the thin layer thickness It becomes difficult to form the electrode active material layer. Therefore, it can be said that the problem is how to prepare a paste for forming an electrode active material layer without aggregating the conductive material and form an electrode active material layer with a thin layer thickness.

  Therefore, the present invention was created to solve the above-described problems related to the thinning of the electrode active material layer related to the lithium secondary battery, and the object of the present invention is to suppress the increase in internal resistance while suppressing the increase in internal resistance. To provide a lithium secondary battery having excellent battery characteristics (for example, high-rate characteristics or cycle characteristics) as a vehicle-mounted high-output power source that realizes a thin layer (typically, a positive electrode active material layer) . Another object is to provide a vehicle including such a lithium secondary battery.

  In order to achieve the above object, according to the present invention, a positive electrode current collector, a positive electrode having a positive electrode active material layer including a positive electrode active material and a conductive material formed on the surface of the current collector, a negative electrode current collector, and the current collector Provided is a lithium secondary battery comprising a negative electrode having a negative electrode active material layer containing a negative electrode active material formed on the surface of the body. In the lithium secondary battery disclosed herein, the positive electrode active material layer has a layer thickness of 30 μm or less, and includes a polyether binder (A) made of at least one polyether and at least one water-soluble material. A cellulose-based binder (B) composed of a functional cellulose derivative, and the mass (Aw) of the polyether-based binder (A) and the mass (Bw) of the cellulose-based binder (B) in the active material layer And the mass ratio (Aw / Bw) satisfies Aw / Bw ≧ 1.8.

In the present specification, the “lithium secondary battery” refers to a secondary battery that uses lithium ions as electrolyte ions and is charged and discharged by movement of lithium ions between the positive and negative electrodes. In general, a secondary battery referred to as a lithium ion battery is a typical example included in the lithium secondary battery in this specification.
Further, in this specification, “electrode active material (positive electrode active material and negative electrode active material)” means reversibly occlusion and release of chemical species (that is, lithium ions) serving as charge carriers in a secondary battery (typically A substance that can be inserted and removed).

The positive electrode active material layer of the lithium secondary battery provided by the present invention comprises a polyether binder (A) comprising at least one polyether and a cellulose binder (at least one water-soluble cellulose derivative). B), and the mass ratio (Aw / Bw) of the mass (Aw) of the polyether-based binder (A) and the mass (Bw) of the cellulose-based binder (B) in the active material layer is Aw / Bw ≧ 1.8 is satisfied.
Here, the binder plays a role of bonding the positive electrode active material layer to the current collector by connecting the positive electrode active material, which is the main component of the positive electrode active material layer, with another material (for example, a conductive material). However, when the content (content rate) of the binder in the paste for forming the active material layer is increased, the content of the positive electrode active material or the conductive material is relatively decreased, and thus the conductivity is lowered. On the other hand, if the content (content rate) of the conductive material is increased too much, the conductive material having a small particle diameter (for example, granular carbon particles) is aggregated without being sufficiently dispersed, and thus the paste having poor coating properties for the current collector. As a result, it is difficult to form an electrode active material layer having a thin layer thickness. However, the mass ratio (Aw / Bw) between the polyether-based binder (A) and the cellulose-based binder (B) is Aw / Bw ≧ 1.8 (the upper limit of the mass ratio is not particularly limited. The content (Bw) of the binder (B) is not 0. For example, the upper limit can be set to 3 or less (1.8 ≦ Aw / Bw ≦ 3), and typically 2.8 or less ( If 1.8 ≦ Aw / Bw ≦ 2.8), the conductive material is less likely to be aggregated, and each material constituting the positive electrode active material layer is uniformly dispersed and has good coatability. Is prepared. As a result, a lithium secondary battery including a positive electrode active material layer made of such a paste can be a battery that has excellent conductivity and suppresses an increase in internal resistance.
Further, in the lithium secondary battery disclosed herein, the positive electrode active material layer having a binder mass ratio in the above range has a layer thickness of 30 μm or less (the layer thickness per side of the positive electrode current collector, When the material layer is formed on both sides, it is formed to be 60 μm or less). A lithium secondary battery (typically a battery for in-vehicle power supply) used in a mode in which high-rate charge / discharge is repeated in a short time suppresses an increase in internal resistance by including an electrode active material layer having a layer thickness as thin as possible. be able to. Since the lithium secondary battery disclosed herein includes a positive electrode active material layer formed by applying a paste for forming an active material layer prepared without aggregating a conductive material as described above, the active material layer Can be formed to a thickness of 30 μm or less. In general, the thickness of the electrode active material layer in a battery used in a household electric appliance is often about 60 μm or more, and the thickness of the positive electrode active material layer according to the present invention is 30 μm or less. A lithium secondary battery suitable for use in an in-vehicle power source having excellent battery characteristics (battery capacity, cycle characteristics, or high rate characteristics) in which an increase in internal resistance due to charge / discharge is suppressed can be provided.

  Moreover, in one preferable aspect of the lithium secondary battery provided by the present invention, the positive electrode active material layer contains polyethylene oxide as the polyether-based binder (A), and the cellulose-based binder ( B) contains carboxymethylcellulose. Since the combination of the binders further improves the dispersibility of the conductive material and makes it difficult to generate aggregates, it is possible to provide a lithium secondary battery suitable for use in an in-vehicle power source in which an increase in internal resistance is suppressed. .

In a more preferred embodiment, the positive electrode active material layer includes lithium nickelate (that is, a lithium transition metal composite oxide containing nickel as a transition metal) as the positive electrode active material.
Preferably, the positive electrode active material layer is composed of the polyether binder (A) and the cellulose binder (B), the positive electrode active material, and at least one granular conductive material in an aqueous solvent. The active material layer forming paste mixed in the above is applied to the surface of the positive electrode current collector and is defined as JIS K 5600-2-5 (established in 1999) as the active material layer forming paste. What is used is one having a particle diameter adjusted to 60 μm or less as measured by a dispersion degree evaluation using a grain gauge.
The paste for forming an active material layer prepared to have a particle size of 60 μm or less by the dispersion degree evaluation with a particle gauge defined in JIS K 5600-2-5 (established in 1999) is an aggregate having a predetermined size or more. (Typically, aggregates composed of conductive materials) are not included, and each material is sufficiently dispersed. Therefore, this paste is excellent in the coating property with respect to a positive electrode electrical power collector, and can be apply | coated thinly. As a result, the positive electrode active material layer using the paste has a thin layer thickness and lithium suitable for an in-vehicle power source having battery performance (battery capacity, cycle characteristics or high rate characteristics) in which an increase in internal resistance is suppressed. A secondary battery can be provided.

Moreover, this invention provides the manufacturing method of a lithium secondary battery as another side surface. That is, the manufacturing method disclosed herein includes a positive electrode current collector, a positive electrode having a positive electrode active material layer including a positive electrode active material and a conductive material formed on the surface of the current collector, a negative electrode current collector, and the current collector. And a negative electrode having a negative electrode active material layer including a negative electrode active material formed on a surface of the electric body, wherein the positive electrode active material layer is a polymer made of at least one polyether. An ether binder (A), a cellulose binder (B) made of at least one water-soluble cellulose derivative, a positive electrode active material, and at least one granular conductive material are mixed with an aqueous solvent. By applying the active material layer forming paste, the positive electrode active material layer is formed to have a layer thickness of 30 μm or less. Here, the active material layer forming paste is a polyester in the paste. The mass ratio (Aw / Bw) of the mass (Aw) of the cellulose binder (A) and the mass (Bw) of the cellulose binder (B) is adjusted so as to satisfy Aw / Bw ≧ 1.8. It is characterized by being.
Since the positive electrode active material has low conductivity, the content of a highly conductive material (conductive material) such as carbon powder is increased in order to increase the conductivity of the positive electrode active material layer mainly composed of the active material layer. It is realized by. However, if the content of the conductive material in the paste for forming the active material layer is increased while maintaining the content of the active material in a desired range, the content of the binder decreases accordingly, so the particle diameter is small. As a result, it was difficult to form an electrode active material layer with a thin layer thickness. However, the mass ratio (Aw / Bw) between the polyether-based binder (A) and the cellulose-based binder (B) is Aw / Bw ≧ 1.8 (the upper limit of the mass ratio is not particularly limited. The content (Bw) of the binder (B) is not 0. For example, the upper limit can be set to 3 or less (1.8 ≦ Aw / Bw ≦ 3), and typically 2.8 or less ( 1.8 ≦ Aw / Bw ≦ 2.8) By using the paste prepared so as to satisfy the above), a positive electrode active material layer having a layer thickness of 30 μm or less can be formed. Accordingly, it is possible to provide a method for producing a lithium secondary battery suitable for use in an in-vehicle power source having excellent battery characteristics (battery capacity, cycle characteristics, or high rate characteristics) that have excellent conductivity and can suppress an increase in internal resistance. it can.

  In a preferred embodiment of the method disclosed herein, polyethylene oxide is used as the polyether binder (A), and carboxymethyl cellulose is used as the cellulose binder (B). To do. Since the combination of the binders further improves the dispersibility of the conductive material and makes it difficult for aggregates to be generated, a method for manufacturing a lithium secondary battery suitable for use in an in-vehicle power source in which an increase in internal resistance is suppressed is provided. can do.

In a preferred embodiment, the active material layer forming paste has a particle size satisfying 60 μm or less according to dispersity evaluation with a particle gauge defined in JIS K 5600-2-5 (established in 1999). It is characterized by using the prepared one.
By using a paste for forming an active material layer having a particle diameter of 60 μm or less prepared by evaluating the degree of dispersion with a particle gauge defined in JIS K 5600-2-5 (established in 1999), a positive electrode current collector Can be applied thinly. As a result, it is possible to provide a method for manufacturing a lithium secondary battery suitable for use in an in-vehicle power source having excellent battery performance (battery capacity, cycle characteristics or high rate characteristics) in which an increase in internal resistance is suppressed.

  In addition, according to the present invention, a vehicle including the secondary battery disclosed herein (which may be a secondary battery manufactured by any of the methods disclosed herein) is provided. The secondary battery provided by the present invention may exhibit quality and battery performance (battery capacity, cycle characteristics, or high rate characteristics) particularly suitable as a power source for a battery mounted on a vehicle. Therefore, the secondary battery disclosed herein can be suitably used as a power source for a motor (electric motor) mounted on a vehicle such as an automobile including an electric motor such as a hybrid vehicle or an electric vehicle.

It is a perspective view which shows typically the external shape of the lithium secondary battery which concerns on one Embodiment. It is the II-II sectional view taken on the line in FIG. It is a perspective view which shows typically the state which winds and produces an electrode body. It is a graph which shows the relationship between the mass ratio of a binder, and the particle diameter in the paste for active material layer formation. It is a graph which shows the relationship between the mass ratio of a binder, and internal resistance. It is a side view showing typically a vehicle (automobile) provided with a lithium secondary battery concerning one embodiment.

  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.

A preferred embodiment of the lithium secondary battery disclosed herein includes a positive electrode current collector, a positive electrode having a positive electrode active material layer including a positive electrode active material and a conductive material formed on a surface of the current collector, and a negative electrode current collector. A negative electrode having a negative electrode active material layer containing a negative electrode active material formed on the surface of the current collector and the current collector, and a mass ratio (Aw / Bw) of the binder in the positive electrode active material layer; The positive electrode active material layer is characterized by being formed with a layer thickness of 30 μm or less (a layer thickness per one surface of the positive electrode current collector and 60 μm or less when formed on both surfaces). Hereinafter, as a lithium secondary battery disclosed here, a positive electrode and a method for producing the positive electrode will be described in detail by taking a lithium secondary battery (lithium ion battery) including a wound electrode body as an example. It is not intended to be limited to the embodiments. The configuration of the negative electrode, the electrolyte, the battery case, and the like are not particularly limited. For example, the battery case may have a rectangular parallelepiped shape, a flat shape, a cylindrical shape, and the like, and the shape and size of the battery and other configurations may be appropriately changed depending on the application (typically for in-vehicle use). it can.
In addition, in the following drawings, the same code | symbol is attached | subjected to the member and site | part which show | plays the same effect | action, and the overlapping description may be abbreviate | omitted or simplified. In addition, the dimensional relationships (length, width, thickness, etc.) in each drawing do not reflect actual dimensional relationships.

FIG. 1 is a perspective view schematically showing a rectangular lithium secondary battery according to an embodiment, and FIG. 2 is a cross-sectional view taken along line II-II in FIG. FIG. 3 is a perspective view schematically showing a state in which the electrode body is wound and manufactured.
As shown in FIGS. 1 and 2, the lithium secondary battery 100 according to the present embodiment includes a rectangular parallelepiped battery case 10 and a lid body 14 that closes the opening 12 of the case 10. A flat wound electrode body 20 and an electrolyte accommodated from the opening 12 are disposed inside the battery case 10. The lid body 14 is provided with an external positive electrode terminal 38 and an external negative electrode terminal 48 for external connection, and a part of the external terminals 38 and 48 is an internal positive terminal 37 or an internal negative terminal 47 inside the case. Are connected to each.

  Next, the wound electrode body 20 according to the present embodiment will be described with reference to FIGS. 2 and 3. As shown in FIG. 2, the wound electrode body 20 includes a sheet-like positive electrode sheet 30 having a positive electrode active material layer 34 on the surface of a long positive electrode current collector 32, a long sheet-like separator 50, a long A sheet-like negative electrode sheet 40 having a negative electrode active material layer 44 on the surface of a long negative electrode current collector 42 is formed. As shown in FIG. 3, in the cross-sectional view in the winding axis direction R, the positive electrode sheet 30 and the negative electrode sheet 40 are stacked via two separators 50. 50, the negative electrode sheet 40, and the separator 50 are laminated in this order. The laminate is wound around a shaft core (not shown) in a cylindrical shape, and is formed into a flat shape by squashing the obtained wound electrode body 20 from the side surface direction.

As shown in FIG. 3, the wound electrode body 20 according to the present embodiment includes a positive electrode active material layer 34 formed on the surface of the positive electrode current collector 32 at the center in the winding axis direction R. A portion where the negative electrode active material layer 44 formed on the surface of the negative electrode current collector 42 is overlapped and densely stacked is formed. Further, in a cross-sectional view in the direction along the winding axis direction R, the exposed portion of the positive electrode current collector 32 (positive electrode active material layer) without forming the positive electrode active material layer 34 at one end in the direction R. The non-forming portion 36) is laminated in a state of protruding from the separator 50 and the negative electrode sheet 40 (or a dense laminated portion of the positive electrode active material layer 34 and the negative electrode active material layer 44). That is, a positive electrode current collector laminated portion 35 formed by laminating the positive electrode active material layer non-forming portion 36 in the positive electrode current collector 32 is formed at the end of the electrode body 20. Also, the other end of the electrode body 20 has the same configuration as that of the positive electrode sheet 30, and the negative electrode active material layer non-formation portion 46 in the negative electrode current collector 42 is laminated to form the negative electrode current collector lamination portion 45. ing.
Here, as the separator 50, a separator having a width larger than the width of the laminated portion of the positive electrode active material layer 34 and the negative electrode active material layer 44 and smaller than the width of the electrode body 20 is used, and the positive electrode current collector 32 and the negative electrode The current collectors 42 are disposed so as to be sandwiched between the stacked portions of the positive electrode active material layer 34 and the negative electrode active material layer 44 so as not to contact each other and cause an internal short circuit. However, the width of the separator is not particularly limited, and a separator having a width equal to or larger than that of the electrode body 20 is used, and the positive electrode active material layer non-forming portion 36 and the negative electrode active material non-forming portion 46 are used. The structure by which the separator was arranged in the state which protruded may be sufficient.

First, each component of the positive electrode of the lithium secondary battery 100 according to the present embodiment will be described. The positive electrode disclosed here (typically, the positive electrode sheet 30) includes a positive electrode active material layer 34 formed on the surface of the positive electrode current collector 32.
As the positive electrode current collector 32 serving as the base material of the electrode, a conductive member made of a metal having good conductivity is preferably used. For example, aluminum or an alloy containing aluminum as a main component can be used. The shape of the positive electrode current collector 32 can be different depending on the shape or the like of the lithium secondary battery, and is not particularly limited, and may be various forms such as a rod shape, a plate shape, a sheet shape, a foil shape, and a mesh shape. In the present embodiment, a sheet-like positive electrode current collector 32 having a shape that can be preferably used for the lithium secondary battery 100 including the wound electrode body 20 is used.

Next, materials constituting the positive electrode active material layer 34 formed on the surface of the positive electrode current collector 32 will be described.
On the surface of the positive electrode current collector 32, a polyether binder (A) made of at least one kind of polyether, a cellulose binder (B) made of at least one water-soluble cellulose derivative, and a positive electrode active material A positive electrode active material is applied by applying a paste for forming an active material layer in which a substance and at least one granular conductive material are dispersed in an aqueous solvent (including paste or slurry or ink, the same applies hereinafter). A layer is formed.

As the positive electrode active material which is the main component constituting the positive electrode active material layer 34, a granular active material capable of inserting and extracting lithium is used. A layered oxide positive electrode active material known as a positive electrode active material of this type of lithium secondary battery, an oxide positive electrode active material having a spinel structure, or the like can be preferably used. Examples thereof include lithium transition metal composite oxides such as lithium nickel composite oxides, lithium cobalt composite oxides, and lithium manganese composite oxides.
Here, the lithium nickel-based composite oxide is an oxide having lithium (Li) and nickel (Ni) as constituent metal elements, and at least one other metal element (that is, Li and nickel) in addition to lithium and nickel. A transition metal element other than Ni and / or a typical metal element) is typically less than nickel (in terms of the number of atoms. When two or more metal elements other than Li and Ni are included, the total amount thereof is more than Ni. In a small proportion) includes oxides contained as constituent metal elements. Examples of the metal element other than Li and Ni include, for example, cobalt (Co), aluminum (Al), manganese (Mn), chromium (Cr), iron (Fe), vanadium (V), magnesium (Mg), and titanium (Ti ), Zirconium (Zr), niobium (Nb), molybdenum (Mo), tungsten (W), copper (Cu), zinc (Zn), gallium (Ga), indium (In), tin (Sn), lanthanum (La) And one or more metal elements selected from the group consisting of cerium (Ce). The same meaning is applied to the lithium cobalt complex oxide and the lithium manganese complex oxide. The olivine type lithium phosphate represented by the general formula LiMPO ₄ (M is at least one element of Co, Ni, Mn, Fe; for example, LiFePO ₄ , LiMnPO ₄ ) is used as the positive electrode active material. Also good.

  As such a lithium transition metal oxide, for example, a lithium transition metal oxide powder prepared and provided by a conventionally known method can be used as it is. For example, the oxide can be prepared by mixing several raw material compounds appropriately selected according to the atomic composition at a predetermined molar ratio and firing by an appropriate means. In addition, a granular lithium transition metal oxide powder substantially composed of secondary particles having a desired average particle size and / or particle size distribution by pulverizing, granulating and classifying the fired product by appropriate means Can be obtained. In the present embodiment, the particle diameter of the lithium transition metal oxide powder is not particularly limited, but the positive electrode active material layer 34 is formed using each of the lithium transition metal oxide powders having different particle diameters. Also good.

  Moreover, as said electrically conductive material, electroconductive powder materials, such as carbon powder and carbon fiber, are used preferably. As the carbon powder, various carbon blacks such as acetylene black, furnace black, ketjen black, and graphite powder are preferable. In addition, even if only 1 type is used among these, 2 or more types may be used together. In addition, conductive fibers such as carbon fibers and metal fibers, metal powders such as copper and nickel, and organic conductive materials such as polyphenylene derivatives can be contained alone or as a mixture thereof.

  Next, the binder will be described. The binder used for forming the positive electrode active material layer 34 includes a polyether binder (A) made of at least one polyether and a cellulose binder made of at least one water-soluble cellulose derivative. (B) is used. Since both the polyether binder (A) and the cellulose binder (B) are soluble (or dispersed) in an aqueous solvent and exhibit viscosity, the positive electrode active material and the conductive material are bound together. Take a role.

  Examples of the polyether binder (A) include polyethylene oxide (PEO), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), polyoxyethylene alkyl ether (AE), and polyoxyethylene alkyl. Examples thereof include phenyl ether (APE), polypropylene oxide (PPO), polyethylene glycol (PEG), and polypropylene glycol (PPG). The polyether binder (A) that is particularly preferably used is PEO.

Examples of the cellulose binder (B) include carboxymethylcellulose (CMC), hydroxyethylcellulose (HEC), hydroxypropylcellulose (HPC), methylcellulose (MC), cellulose acetate phthalate (CAP), hydroxypropylmethylcellulose ( HPMC), hydroxypropyl methylcellulose phthalate (HPMCP) and the like. Of these, CMC can be particularly preferably used.
In addition, the said polyether type | system | group binder (A) and the said cellulose type binder (B) may each be used individually by 1 type, and may be used in combination of 2 or more types. In addition to the polyether binder (A) and the cellulose binder (B), vinyl acetate copolymer, styrene butadiene block copolymer (SBR), acrylic acid modified SBR resin (SBR type) Latex), rubber such as gum arabic, polytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), ethylene -A small amount of fluorine-based resin such as tetrafluoroethylene copolymer (ETFE) may be added.

  The aqueous solvent is typically water, but any water-based solvent may be used as long as it exhibits aqueous properties as a whole. For example, an aqueous solution containing a lower alcohol (methanol, ethanol, etc.) may be used. That is, as the solvent for dissolving (or dispersing) the binder contained in the active material layer forming paste, water or a mixed solvent mainly composed of water can be preferably used. As the solvent other than water constituting the 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. For example, it is preferable to use a solvent in which about 80% by mass or more (more preferably about 90% by mass or more, more preferably about 95% by mass or more) of the aqueous solvent is water. A particularly preferred example is a solvent consisting essentially of water.

  The positive electrode active material layer 34 of the lithium secondary battery 100 according to the present embodiment is coated with an active material layer forming paste formed by mixing the positive electrode active material, the conductive material, and the binder with an aqueous solvent. The layer thickness of the positive electrode active material layer 34 is 30 μm or less per one side of the positive electrode current collector 32 (in the case where the positive electrode active material layer 34 is formed on both surfaces of the positive electrode current collector 32, the layer is formed). The thickness is 60 μm or less), typically 10 to 30 μm (for example, 20 to 30 μm), preferably 25 μm or less (for example, 10 to 25 μm). In a lithium secondary battery (typically a battery for an in-vehicle power supply) that is used in such a manner that high-rate charge / discharge is repeated in a short time, the load on the electrode active material layer due to the movement of charge carriers is close to the surface of the current collector Therefore, the increase in internal resistance can be suppressed by providing an electrode active material layer having the thinnest possible layer thickness. The thickness of the positive electrode active material layer 34 according to the lithium secondary battery 100 disclosed herein is as follows. Since it is formed to be 30 μm or less, it can be a battery in which an increase in internal resistance due to high rate charge / discharge is suppressed.

Moreover, the positive electrode active material layer 34 of the lithium secondary battery 100 according to the present embodiment includes the mass (Aw) of the polyether-based binder (A) and the mass of the cellulose-based binder (B) in the active material layer. The mass ratio (Aw / Bw) to (Bw) is Aw / Bw ≧ 1.8 (the upper limit of the mass ratio is not particularly limited, but the content (Bw) of the cellulosic binder (B) is not 0. For example, the upper limit can be set to 3 or less (1.8 ≦ Aw / Bw ≦ 3), and typically 2.8 or less (1.8 ≦ Aw / Bw ≦ 2.8). Meet. A preferable range is 2 ≦ Aw / Bw ≦ 2.8 (particularly 2 ≦ Aw / Bw ≦ 2.5).
Here, since the conductive material is a material having a small particle size and insoluble in an aqueous solvent, increasing the content of the conductive material causes the conductive materials to aggregate and uniformly disperse the constituent materials. It was difficult. However, when the mass ratio (Aw / Bw) of the polyether-based binder (A) and the cellulose-based binder (B) satisfies Aw / Bw ≧ 1.8, the conductive material is less likely to be aggregated, A paste with good coatability in which each material constituting the positive electrode active material layer is uniformly dispersed is prepared. Therefore, a lithium secondary battery including a positive electrode active material layer made of such paste is excellent in conductivity and can suppress an increase in internal resistance. In addition, when the said mass ratio (Aw / Bw) is larger than 3, adjustment of a paste with favorable dispersibility becomes difficult and is not preferable.

Next, a method for manufacturing the positive electrode (typically, the positive electrode sheet 30) of the lithium ion battery 100 disclosed herein will be described.
As shown in FIG. 3, the positive electrode can be produced by forming a positive electrode active material layer 34 on the surface of the positive electrode current collector 32. In forming the positive electrode active material layer 34, first, a paste for forming an active material layer is prepared. The active material layer forming paste comprises a mass ratio (Aw) of a polyether binder (A) composed of at least one polyether and a cellulose binder (B) composed of at least one water-soluble cellulose derivative. / Bw) is Aw / Bw ≧ 1.8 (the upper limit of the mass ratio is not particularly limited, but the content (Bw) of the cellulosic binder (B) is not 0. For example, the upper limit is 3 or less (1 A polyether binder (A) and a cellulose binder (B) weighed so as to satisfy .8 ≦ Aw / Bw ≦ 3) are prepared, and a positive electrode active material and at least one granular material are prepared. It can prepare by mixing with an aqueous solvent with the electrically conductive material.

  After preparing the active material layer forming paste, the particle size is measured for the paste by evaluating the degree of dispersion with a grain gauge defined in JIS K 5600-2-5 (established in 1999). A paste prepared so that the measured particle diameter is 60 μm or less (preferably 55 μm or less, for example, 50 μm) is used. The active material layer forming paste prepared to have a particle size of 60 μm or less does not contain agglomerates of a predetermined size or larger (typically agglomerates of a conductive material), and each material is sufficiently dispersed. is there. Therefore, the coating property with respect to the positive electrode current collector 32 is excellent, and the paste can be applied thinly. Therefore, in this embodiment, it is preferable to apply to the surface of the positive electrode current collector 32 using a paste having a particle size of 60 μm or less. As a method of applying, a technique similar to a conventionally known method can be appropriately employed. For example, the paste can be suitably applied to the positive electrode current collector 32 by using an appropriate application device such as a gravure coater, a slit coater, a die coater, or a comma coater. In addition, the compatible paste having a particle size of 60 μm or less can be irradiated with a distance close to (for example, 65 μm or less) between the paste irradiation port of the coating apparatus and the positive electrode current collector 32 serving as a coating surface. The positive electrode active material layer 34 having a small thickness can be formed.

  And after apply | coating the said paste for active material layer formation, the positive electrode active material layer 34 is formed by drying and compressing (pressing) the solvent (typically water) contained in this paste. As the compression method, a conventionally known compression method such as a roll press method or a flat plate press method can be employed. In adjusting the thickness, the thickness may be measured with a film thickness measuring instrument, and the press pressure may be adjusted to compress a plurality of times until a desired thickness is obtained. In the present embodiment, the positive electrode active material layer 34 has a layer thickness of 30 μm or less per one side of the positive electrode current collector 32 (in the case where the positive electrode active material layer 34 is formed on both surfaces of the positive electrode current collector 32, the layer thickness). Is 60 μm or less), typically 10 to 30 μm (for example, 20 to 30 μm), preferably 25 μm or less (for example, 10 to 25 μm). Thereby, the positive electrode of the lithium secondary battery 100 provided with the positive electrode active material layer 34 with thin layer thickness can be produced.

  The lithium secondary battery 100 that can be provided by the present invention may be the same as that provided in a conventional secondary battery of this type, except for the positive electrode including the positive electrode active material layer 34 described above, and is not particularly limited. Hereinafter, other components will be described, but the present invention is not intended to be limited to such embodiments.

  For example, the negative electrode (typically, the negative electrode sheet 40) may have a configuration in which a negative electrode active material layer 44 is formed on a long negative electrode current collector 42 (for example, copper foil). As the negative electrode active material capable of inserting and extracting lithium constituting the negative electrode active material layer 44, one or more of materials conventionally used in lithium secondary batteries can be used without particular limitation. For example, a carbon particle is mentioned as a suitable negative electrode active material. A particulate carbon material (carbon particles) containing a graphite structure (layer structure) at least partially is preferably used. Any carbon material of a so-called graphitic material (graphite), a non-graphitizable carbonaceous material (hard carbon), a graphitizable carbonaceous material (soft carbon), or a combination of these materials is preferably used. obtain. In particular, the graphite particles can be a negative electrode active material more suitable for rapid charge / discharge (for example, high-power discharge) because the particle size is small and the surface area per unit volume is large.

In addition to the negative electrode active material, the negative electrode active material layer 44 can contain one or two or more materials that can be blended in a general lithium secondary battery as required. As such a material, various polymer materials that can function as a binder as listed as a constituent material of the positive electrode active material layer 34 can be similarly used.
The negative electrode active material layer 44 is a paste or slurry composition prepared by adding a negative electrode active material and a binder to an appropriate solvent (water, an organic solvent and a mixed solvent thereof) and dispersing or dissolving them. Is preferably applied to the negative electrode current collector 42, and the solvent is dried and compressed.

The separator 50 is a sheet interposed between the positive electrode sheet 30 and the negative electrode sheet 40, and is disposed so as to be in contact with the positive electrode active material layer 34 of the positive electrode sheet 30 and the negative electrode active material layer 44 of the negative electrode sheet 40. The Then, short-circuit prevention due to the contact between the active material layers 34 and 44 in the positive electrode sheet 30 and the negative electrode sheet 40 and the conduction path between the electrodes by impregnating the electrolyte (non-aqueous electrolyte) in the pores of the separator 50. It plays a role of forming (conductive path).
As a constituent material of the separator 50, a porous sheet (microporous resin sheet) made of a resin can be preferably used. Particularly preferred are porous polyolefin resins such as polypropylene, polyethylene, and polystyrene.

Moreover, the electrolyte can use the thing similar to the nonaqueous electrolyte conventionally used for a lithium secondary battery without limitation. Such a nonaqueous electrolytic solution typically has a composition in which a supporting salt is contained in a suitable nonaqueous solvent. Examples of the non-aqueous solvent include one or two selected from the group consisting of propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and the like. More than seeds can be used. Examples of the supporting salt include LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ). ₃ , 1 type, or 2 or more types of lithium compounds (lithium salt) selected from LiI etc. can be used.

The produced positive electrode sheet 30 and negative electrode sheet 40 are stacked and wound together with two separators 50, and the obtained wound electrode body 20 is formed into a flat shape by crushing and ablating from the side surface direction. The lithium secondary battery 100 of the present embodiment can be constructed by containing the electrolyte and sealing the opening 12 by injecting the electrolyte.
In particular, the structure, size, material (for example, can be made of metal or laminate film) of the battery case 10, and the structure of the electrode body (for example, a wound structure or a laminated structure) having the positive and negative electrodes as main components, etc. There is no limit.

  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.

<Construction of lithium secondary battery according to sample A>
A lithium secondary battery according to Sample A was constructed as follows.
First, the positive electrode of the lithium secondary battery according to Sample A was produced. That is, a positive electrode active material layer forming paste was prepared for forming the positive electrode active material layer in the positive electrode. The paste is based on 87 parts by mass of a positive electrode active material (here, lithium nickelate), 10 parts by mass of acetylene black as a conductive material, and 1 part by mass of polyethylene oxide (PEO) as a polyether binder, Polytetrafluoroethylene (PTFE) / water suspension having a solid content of 80% is mixed with 1 part by weight of carboxymethylcellulose (CMC) as a cellulose-based binder by adding 85 parts by weight of ion-exchanged water. It was prepared by adding 1.3 parts by mass. And about the prepared paste, the particle diameter by the dispersity evaluation by the grain gauge prescribed | regulated by JISK5600-2-5 (1999 establishment) was measured.
Next, the positive electrode active material layer forming paste is applied to both surfaces of the positive electrode current collector so that the coating amount of the positive electrode active material per unit area is 86 mg / cm ² on the aluminum foil (thickness 15 μm) as the positive electrode current collector. And dried. Next, the sheet was stretched into a sheet shape with a roller press to form a thickness of 58 μm (the layer thickness per side was about 20 μm), and the positive electrode active material layer was slit so as to have a predetermined width to prepare a positive electrode sheet. .

Next, the negative electrode of the lithium secondary battery according to Sample A was produced. That is, when forming the negative electrode active material layer in the negative electrode, a negative electrode active material layer forming paste was prepared. The paste is prepared by adding 98 parts by mass of graphite as a negative electrode active material, 1 part by mass of a styrene butadiene block copolymer (SBR) as a binder, and 1 part by mass of carboxymethyl cellulose (CMC) to ion-exchanged water. And mixing.
Then, the negative electrode paste was applied to both sides of the negative electrode current collector so that the coating amount of the negative electrode active material per unit area was 6.4 mg / cm ² on the copper foil (thickness 10 μm) as the negative electrode current collector. Dried. Next, the sheet was stretched into a sheet shape with a roller press to form a thickness of 57 μm, and a negative electrode sheet was formed by slitting so that the negative electrode active material layer had a predetermined width.

A lithium secondary battery 100 was constructed using the prepared positive electrode sheet and negative electrode sheet. That is, a positive electrode sheet and a negative electrode sheet were laminated together with two separators, and this laminated sheet was wound to produce a wound electrode body. And this electrode body was accommodated in a container with electrolyte, and the cylindrical lithium secondary battery of diameter 18mm and height 65mm (18650 type | mold) was constructed | assembled. As the electrolyte, a nonaqueous electrolytic solution having a composition in which 1 mol / L LiPF ₆ was dissolved in a 1: 1 (volume ratio) mixed solvent of propylene carbonate (PC) and diethyl carbonate (DEC) was used.

<Construction of lithium secondary batteries according to samples B to J>
Lithium secondary batteries according to Samples B to J were constructed. That is, in the lithium secondary batteries according to Samples B to J, the composition ratio of the positive electrode active material layer forming paste (specifically, the respective mass parts of the positive electrode active material, PEO, and CMC) is changed as shown in Table 1. Except for the above, the lithium secondary battery according to Sample A was constructed in the same manner.
Moreover, about each positive electrode active material layer forming paste, the particle diameter by the dispersion degree evaluation by the grain gauge prescribed | regulated by JISK5600-2-5 (1999 establishment) was measured. FIG. 4 shows a graph in which the particle diameter of the paste used for the construction of the lithium secondary batteries according to Samples A to J is plotted. The horizontal axis of FIG. 4 shows the mass ratio (PEO / CMC) of the binder, and the vertical axis shows the particle diameter (μm).

[Measurement of internal resistance]
The internal resistance value at 25 ° C. of each lithium secondary battery according to the constructed samples A to J was measured. That is, under a temperature condition of 25 ° C., the battery capacity was measured by charging at a constant current to 4.1 V at 5 A and then discharging at a constant current to 2.5 V at 5 A. Further, the battery was charged to 3.537 V at 5 A, and the current was attenuated while keeping the voltage constant, and constant voltage charging was performed until the current became 100 mA. After a 30-minute pause, a constant current was discharged at 20 A, the voltage after 4 seconds was measured, and the internal resistance value was calculated. A graph plotting the calculated internal resistance is shown in FIG. The horizontal axis of FIG. 5 shows the mass ratio (PEO / CMC) of the binder, and the vertical axis shows the internal resistance value (mΩ).

As shown in FIG. 5, the lithium secondary battery according to Samples F to J in which the mass ratio of the binder (the mass ratio of PEO / CMC) is 1.75 or more has an internal resistance of 2.8 mΩ or less. From the internal resistance of the lithium secondary batteries according to Samples A to E (all of 3 mΩ or more), it was shown that the increase in internal resistance was suppressed.
Moreover, according to FIG. 4, it was confirmed that the particle diameter of the lithium secondary battery which concerns on the said samples FJ is all 60 micrometers or less. As is clear from these results, a paste prepared with a binder mass ratio (PEO / CMC mass ratio) of 1.75 or more or a paste prepared with a particle size of the paste of 60 μm or less was used. The lithium secondary battery constructed in this way was shown to suppress the increase in internal resistance.

  As mentioned above, although this invention was demonstrated by suitable embodiment, such description is not a limitation matter and of course various modifications are possible. For example, the present invention is not limited to the above-described wound type battery, and can be applied to lithium secondary batteries having various shapes. Further, the size and other configurations of the battery can be appropriately changed depending on the application (typically for in-vehicle use).

  The lithium secondary battery according to the present invention includes an electrode active material layer having a thin layer thickness in which an increase in internal resistance is suppressed. Due to such characteristics, the lithium secondary battery according to the present invention can be suitably used as a power source (especially high output power source) for a motor (electric motor) mounted on a vehicle such as an automobile. Therefore, according to the present invention, as shown in FIG. 6, a vehicle including such a lithium secondary battery 100 (which may be in the form of an assembled battery formed by connecting a plurality of such batteries 100 in series) as a power source. 1 (typically automobiles, in particular automobiles equipped with electric motors such as hybrid cars and electric cars) can be provided.

DESCRIPTION OF SYMBOLS 1 Vehicle 10 Battery case 12 Opening part 14 Cover body 20 Winding electrode body 30 Positive electrode sheet 32 Positive electrode collector 34 Positive electrode active material layer 35 Positive electrode collector lamination | stacking part 36 Positive electrode active material layer non-formation part 37 Positive electrode current collection terminal 38 External positive electrode current collector terminal 40 Negative electrode sheet 42 Negative electrode current collector 44 Negative electrode active material layer 45 Negative electrode current collector laminated portion 46 Negative electrode active material layer non-formation portion 47 Negative electrode current collector terminal 48 External negative electrode current collector terminal 50 Separator 100 Lithium secondary Battery R Winding axis direction

Claims (8)

Positive electrode having positive electrode active material layer including positive electrode current collector and positive electrode active material and conductive material formed on surface of current collector, negative electrode current collector, and negative electrode active material formed on surface of current collector A lithium secondary battery comprising a negative electrode having a negative electrode active material layer containing
The positive electrode active material layer has a layer thickness of 30 μm or less, and is made of a polyether binder (A) made of at least one polyether and a cellulose binder made of at least one water-soluble cellulose derivative. (B) and
Here, the mass ratio (Aw / Bw) of the mass (Aw) of the polyether-based binder (A) and the mass (Bw) of the cellulose-based binder (B) in the positive electrode active material layer is Aw / A lithium secondary battery characterized by satisfying Bw ≧ 1.8.   The positive electrode active material layer includes polyethylene oxide as the polyether-based binder (A) and carboxymethyl cellulose as the cellulose-based binder (B). 2. The lithium secondary battery according to 1.   The lithium secondary battery according to claim 1, wherein the positive electrode active material layer includes lithium nickelate as the positive electrode active material. The positive electrode active material layer is formed by mixing the polyether-based binder (A) and the cellulose-based binder (B), the positive electrode active material, and at least one granular conductive material with an aqueous solvent. The active material layer forming paste is formed by applying to the surface of the positive electrode current collector,
As the paste for forming the active material layer, a paste having a particle diameter adjusted to 60 μm or less by a dispersion degree evaluation with a grain gauge specified in JIS K 5600-2-5 (established in 1999) is used. The lithium secondary battery according to claim 1, wherein: Positive electrode having positive electrode active material layer including positive electrode current collector and positive electrode active material and conductive material formed on surface of current collector, negative electrode current collector, and negative electrode active material formed on surface of current collector And a negative electrode having a negative electrode active material layer containing a lithium secondary battery comprising:
The positive electrode active material layer includes a polyether binder (A) made of at least one kind of polyether, a cellulose binder (B) made of at least one water-soluble cellulose derivative, a positive electrode active material, and at least By applying an active material layer forming paste formed by mixing a kind of granular conductive material with an aqueous solvent, the layer thickness is formed to be 30 μm or less,
Here, the active material layer forming paste has a mass ratio (Aw / mass) of the mass (Aw) of the polyether binder (A) and the mass (Bw) of the cellulose binder (B) in the paste. Bw) is prepared so as to satisfy Aw / Bw ≧ 1.8.   The production method according to claim 5, wherein polyethylene oxide is used as the polyether binder (A), and carboxymethyl cellulose is used as the cellulose binder (B).   As the active material layer forming paste, a paste prepared so as to satisfy a particle size of 60 μm or less based on a dispersion degree evaluation with a particle gauge defined in JIS K 5600-2-5 (established in 1999) is used. The manufacturing method of Claim 6 characterized by the above-mentioned.   A vehicle comprising the lithium secondary battery according to any one of claims 1 to 4 or the lithium secondary battery produced by the production method according to any one of claims 5 to 7.

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