Positive electrode for secondary battery, and secondary battery

Abstract

Provided is a secondary battery positive electrode capable of reducing the DC resistance of a secondary battery. The positive electrode for a secondary battery includes a positive electrode current collector and a positive electrode mixture layer disposed on the positive electrode current collector, and the positive electrode mixture layer includes a positive electrode active material and a conductive material. The positive electrode active material contains a lithium transition metal composite oxide and a carbonaceous coating film formed on the surface of the lithium transition metal composite oxide, the carbonaceous coating film contains an alkali metal other than Li and / or an alkaline earth metal, and the conductive material contains a fibrous conductive material.

Description

Technical Field

[0001] This disclosure relates to a positive electrode for a secondary battery and a secondary battery. Background Technology

[0002] In recent years, secondary batteries with high output and high capacity, which have positive electrodes, negative electrodes and electrolytes, and allow Li ions to move between the positive and negative electrodes for charging and discharging, have been widely used.

[0003] For example, Patent Documents 1 and 2 disclose the use of a composite in which a carbonaceous film is formed on the surface of the active material as an active material for secondary batteries.

[0004] Prior art literature

[0005] Patent Document 1: Japanese Patent Application Publication No. 2009-140876

[0006] Patent Document 2: Japanese Patent Application Publication No. 2001-015111 Summary of the Invention

[0007] However, in secondary batteries, the increased demand for rapid charging necessitates a reduction in DC resistance.

[0008] Therefore, the purpose of this disclosure is to provide a positive electrode for a secondary battery that can reduce the DC resistance of the secondary battery.

[0009] A positive electrode for a secondary battery disclosed herein is characterized in that it comprises a positive current collector and a positive electrode additive layer disposed on the positive current collector. The positive electrode additive layer comprises a positive active material and a conductive material. The positive active material comprises a lithium transition metal composite oxide and a carbonaceous film formed on the surface of the lithium transition metal composite oxide. The carbonaceous film contains at least one of an alkali metal and an alkaline earth metal other than Li. The conductive material comprises a fibrous conductive material.

[0010] A secondary battery according to the present disclosure is characterized by comprising a positive electrode, a negative electrode, and an electrolyte for a secondary battery.

[0011] According to a technical solution of this disclosure, the positive electrode for a secondary battery can reduce the DC resistance of the secondary battery. Attached Figure Description

[0012] Figure 1 This is a cross-sectional view of a secondary battery as an example of an implementation method.

[0013] Figure 2 This is a graph showing the TEM-EDX analysis results of the positive electrode active material in the embodiment.

[0014] Figure 3This is a graph showing the XPS analysis results of the positive electrode active material of Examples and Comparative Example 1. Detailed Implementation

[0015] Hereinafter, an example of an embodiment of the non-aqueous electrolyte secondary battery of the present disclosure will be described.

[0016] Figure 1 This is a cross-sectional view of a secondary battery as an example of an implementation method. Figure 1 The secondary battery 10 shown includes: a wound electrode body 14 formed by winding a positive electrode 11 and a negative electrode 12 with a separator 13 in between; an electrolyte; insulating plates 18 and 19 respectively disposed above and below the electrode body 14; and a battery casing 15 housing the above components. The battery casing 15 is composed of a bottomed cylindrical casing body 16 and a sealing body 17 that blocks the opening of the casing body 16. Alternatively, instead of the wound electrode body 14, other forms of electrode bodies, such as a laminated electrode body formed by alternating layers of positive and negative electrodes with a separator in between, can be used. Furthermore, examples of battery casing 15 include cylindrical, square, coin-shaped, button-shaped, and other metal casings, as well as resin casings formed by laminating resin sheets (so-called laminated type).

[0017] Electrolytes, for example, have ionic conductivity (e.g., lithium-ion conductivity). Electrolytes can be liquid electrolytes (electrolytes) or solid electrolytes.

[0018] Liquid electrolytes (electrolytes) may include, for example, a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. Non-aqueous solvents may include, for example, esters, ethers, nitriles, amides, and mixtures of two or more of these. Examples of non-aqueous solvents include ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and mixtures thereof. The non-aqueous solvent may contain halogen-substituted derivatives (e.g., fluoroethylene carbonate) in which at least a portion of the hydrogen atoms of these solvents are replaced by halogen atoms such as fluorine. The electrolyte salt may be, for example, a lithium salt such as LiPF6.

[0019] Furthermore, as a solid electrolyte, examples include solid or gel-like polymer electrolytes and inorganic solid electrolytes. Polymer electrolytes may contain, for example, a lithium salt and a matrix polymer, or a non-aqueous solvent, a lithium salt, and a matrix polymer. As a matrix polymer, examples include polymer materials that absorb non-aqueous solvents and gel. Examples of polymer materials include fluoropolymers, acrylic resins, and polyether resins. As an inorganic solid electrolyte, examples include materials known in all-solid-state lithium-ion secondary batteries (e.g., oxide-based solid electrolytes, sulfide-based solid electrolytes, halogen-based solid electrolytes, etc.). While the electrolytes exemplified above are non-aqueous electrolytes, the electrolyte is not limited to non-aqueous electrolytes and may also be an aqueous electrolyte.

[0020] The casing body 16 is, for example, a bottomed cylindrical metal container. A gasket 28 is provided between the casing body 16 and the sealing body 17 to ensure the airtightness of the battery interior. The casing body 16 has, for example, a protrusion 22 extending inward from a portion of its side surface to support the sealing body 17. The protrusion 22 is preferably formed in a ring shape along the circumference of the casing body 16, and supports the sealing body 17 on its upper surface.

[0021] The sealing body 17 has a structure in which a filter 23, a lower valve body 24, an insulating component 25, an upper valve body 26, and a cover 27 are stacked sequentially from the electrode body 14 side. Each component constituting the sealing body 17 has, for example, a circular or annular shape, and all components except the insulating component 25 are electrically connected to each other. The lower valve body 24 and the upper valve body 26 are connected to each other at their respective central portions, and the insulating component 25 is sandwiched between their respective peripheral portions. When the internal pressure of the secondary battery 10 rises due to heat generated by internal short circuits, for example, the lower valve body 24 deforms and ruptures by pushing the upper valve body 26 towards the cover 27, cutting off the current path between the lower valve body 24 and the upper valve body 26. When the internal pressure rises further, the upper valve body 26 ruptures, and gas is discharged from the opening of the cover 27.

[0022] exist Figure 1 In the secondary battery 10 shown, the positive electrode lead 20 mounted on the positive electrode 11 extends to the sealing body 17 side through the through hole of the insulating plate 18, and the negative electrode lead 21 mounted on the negative electrode 12 extends to the bottom side of the housing body 16 through the outer side of the insulating plate 19. The positive electrode lead 20 is connected to the lower surface of the filter 23, which serves as the bottom plate of the sealing body 17, by welding or the like, and the top plate, i.e., the cover 27, of the sealing body 17, which is electrically connected to the filter 23, becomes the positive terminal. The negative electrode lead 21 is connected to the bottom inner surface of the housing body 16 by welding or the like, and the housing body 16 becomes the negative terminal.

[0023] The following is a detailed description of the positive electrode 11, negative electrode 12, and separator 13 that constitute the secondary battery 10.

[0024] [positive electrode]

[0025] The positive electrode 11 has a positive current collector and a positive electrode flux layer disposed on the positive current collector. The positive electrode flux layer can be disposed on one side or both sides of the positive current collector. The positive current collector can be a metal foil stable within the potential range of the positive electrode 11, such as aluminum or aluminum alloy, or a thin film with the metal disposed on its surface. The positive electrode flux layer contains a positive active material and a conductive material. The positive electrode flux layer may contain a binder material. The positive electrode 11 can be manufactured, for example, by coating a positive electrode flux slurry containing a positive active material, a conductive material, and a binder material onto the surface of the positive current collector, allowing the coating to dry, and then calendering the coating using a roller or the like.

[0026] The conductive material contained in the positive electrode binder layer includes a fibrous conductive material. Examples of fibrous conductive materials include carbon nanotubes (CNTs), carbon nanofibers (CNFs), vapor-grown carbon fibers, electrospun carbon fibers, polyacrylonitrile (PAN)-based carbon fibers, pitch-based carbon fibers, fibrous metals formed by fiberizing metals such as stainless steel, conductive fibers formed by coating the surface of organic fibers with conductive substances such as metals or carbon materials, and conductive fibers formed by coating the surface of organic fibers with resins containing conductive substances. By including a fibrous conductive material in the positive electrode binder layer, particles of the positive electrode active material are bridged to each other through the fibrous conductive material, thereby improving the electronic conductivity of the positive electrode binder layer and reducing the DC resistance of the secondary battery.

[0027] For example, from the viewpoint of reducing the DC resistance of a secondary battery, the fibrous conductive material preferably contains fibrous carbon, and more preferably contains carbon nanotubes. For example, from the viewpoint of reducing the DC resistance of a secondary battery, the length (fiber length) of the carbon nanotubes is preferably 0.1 μm or more, more preferably 0.1 μm or more and 20 μm or less, more preferably 1 μm or more and 10 μm or less, and even more preferably 1 μm or more and 5 μm or less. For example, from the viewpoint of improving the conductivity of carbon nanotubes, and that the addition of a small amount of carbon fiber resulting from improved conductivity can ensure the conductive path of the positive electrode binder layer, the outermost circumference of the carbon nanotubes is preferably 1 nm or more and 20 nm or less, more preferably 1.5 nm or more and 10 nm or less. The aspect ratio (length of carbon nanotube / outermost circumference) of the carbon nanotubes is preferably 5 or more, more preferably 100 or more. The length and outermost circumference of carbon nanotubes refer to the length and outermost circumference of individual fibers. They can be calculated by measuring the length and outer diameter (outermost circumference) of any 50 carbon nanotubes using an electric field emission scanning microscope (FE-SEM) or a transmission electron microscope (TEM) and then taking the arithmetic mean.

[0028] Carbon nanotubes can be categorized into single-layer carbon nanotubes, double-layer carbon nanotubes, and multilayer carbon nanotubes. A single-layer carbon nanotube (SWCNT) is a cylindrical carbon nanostructure composed of a single layer of graphene sheets. A double-layer carbon nanotube is a cylindrical carbon nanostructure composed of two concentrically stacked graphene sheets. A multilayer carbon nanotube is a cylindrical carbon nanostructure composed of three or more concentrically stacked graphene sheets. Furthermore, a graphene sheet refers to a layer in which the carbon atoms with sp2 hybrid orbitals, which constitute the graphite crystals, are located at the vertices of a regular hexagon.

[0029] For example, from the viewpoint of reducing the DC resistance of the secondary battery, the content of fibrous conductive material is preferably 0.01% to 10% by mass, more preferably 0.1% to 0.5% by mass, relative to the total mass of the positive electrode binder layer.

[0030] Conductive materials can contain conductive materials other than fibrous conductive materials. Examples of conductive materials other than fibrous carbon include particulate conductive materials such as carbon black, acetylene black, Ketjen black, and graphite.

[0031] Examples of binders included in the positive electrode binder layer include fluorinated resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyimide, acrylic resin, and polyolefins. Carboxymethyl cellulose (CMC) or its salts, polyethylene oxide (PEO), etc., can also be used. The binder content relative to the total mass of the positive electrode binder layer is, for example, 0.1% to 10% by mass, preferably 0.5% to 5% by mass.

[0032] The positive electrode active material contained in the positive electrode compound layer includes a lithium transition metal composite oxide and a carbonaceous film formed on the surface of the lithium transition metal composite oxide. The carbonaceous film contains at least one of an alkali metal and an alkaline earth metal other than Li. This improves the electronic conductivity of the positive electrode active material. Furthermore, combined with the effect of adding the aforementioned fibrous conductive material, the electronic conductivity of the positive electrode compound layer is further improved, thereby reducing the DC resistance of the secondary battery.

[0033] Lithium transition metal composite oxides, for example, contain secondary particles formed by the aggregation of primary particles. Here, the surface of the lithium transition metal composite oxide refers to the surface of the secondary particles of the lithium transition metal composite oxide. That is, a carbonaceous film is present at least on the surface of the secondary particles of the lithium transition metal composite oxide. The carbonaceous film may exist in a dotted manner, covering at least a portion of the surface of the secondary particles of the lithium transition metal composite oxide, or it may exist covering the entire surface of the secondary particles. Furthermore, the carbonaceous film may exist at the interface where the primary particles of the lithium transition metal composite oxide are in contact with each other.

[0034] The particle size of the primary particles constituting the secondary particles of lithium transition metal composite oxides is, for example, 0.02 μm to 2 μm. The particle size of the primary particles is determined as the diameter of the circumcircle in a particle image observed by scanning electron microscopy (SEM). The average particle size of the secondary particles of lithium transition metal composite oxides is, for example, 2 μm to 30 μm. Here, the average particle size refers to the median particle size (D50) on a volumetric basis. D50 refers to the particle size at which the cumulative frequency in the volumetric particle size distribution reaches 50% from the smallest particle size, and is also known as the median diameter. The particle size distribution of the secondary particles of lithium transition metal composite oxides can be measured using a laser diffraction particle size distribution measuring device (e.g., Microtrack Bell, MT3000II) with water as the dispersion medium.

[0035] Lithium transition metal composite oxides, for example, possess layered rock salt structures belonging to space group R-3m or space group C2 / m. From the perspectives of high capacity and crystal structure stability, lithium transition metal composite oxides preferably have a layered rock salt structure belonging to space group R-3m. The layered rock salt structure of lithium transition metal composite oxides can include a transition metal layer, a Li layer, and an oxygen layer. Li ions present in the Li layer can reversibly enter and exit, thereby facilitating the charge and discharge reactions of the battery.

[0036] The content of Co in the lithium transition metal composite oxide, relative to the total moles of metal elements other than Li, is preferably 5 mol% or less, more preferably 2 mol% or less, further preferably 1 mol% or less, and particularly preferably 0.1 mol%. Co is a rare metal and expensive, so it is preferable to reduce its usage.

[0037] Lithium transition metal composite oxides can be made from the general formula Li a Ni 1-x-y Mn x M y O 2+b The formula is expressed as follows: 0.9 ≤ a ≤ 1.1, 0 ≤ x ≤ 0.5, 0 ≤ y ≤ 0.1, 0.5 ≤ 1 - xy ≤ 0.95, and -0.05 ≤ b ≤ 0.05. Element M is an element other than Li, Ni, Mn, and oxygen. Furthermore, the value of 'a', representing the molar ratio of lithium, increases or decreases depending on the charge-discharge cycle. From the viewpoint of stabilizing the crystal structure of lithium transition metal composite oxides, element M is preferably selected from at least one of Co, Nb, Al, Zr, B, Fe, Cu, Zn, Sn, W, Mo, Si, Ti, Fe, and Cr.

[0038] The content of elements constituting lithium transition metal complex oxides can be determined by inductively coupled plasma optical emission spectrometry (ICP-AES), electron probe microanalysis (EPMA), etc.

[0039] The carbonaceous coating only needs to contain at least one alkali metal and alkaline earth metal other than Li. From the viewpoint of improving the electronic conductivity of the positive electrode active material, it is preferable to contain at least one of Na and K. Furthermore, from the viewpoint of improving the electronic conductivity of the positive electrode active material, the carbonaceous coating preferably also contains S. Additionally, the carbonaceous coating may contain Li. The presence of S in the carbonaceous coating can be confirmed by energy dispersive X-ray spectrophotometry (TEM-EDX). The presence of alkali metals such as Na and K and alkaline earth metals in the carbonaceous coating can be confirmed by X-ray photoelectron spectrophotometry (XPS).

[0040] The thickness of the carbonaceous coating is, for example, less than 30 nm. The lower limit of the thickness of the carbonaceous coating is, for example, 1 nm. The thickness of the carbonaceous coating is determined by observing an image of the cross-section of the positive electrode active material using a transmission electron microscope (TEM).

[0041] In addition to containing a lithium transition metal composite oxide with a carbonaceous film formed on its surface, the positive electrode additive layer may also contain other positive electrode active materials. Examples of other positive electrode active materials include lithium transition metal composite oxides without a carbonaceous film on their surface. The content of lithium transition metal composite oxides with a carbonaceous film formed on their surface is preferably 90% by mass or more, and more preferably 99% by mass or more, relative to the total mass of the positive electrode active materials.

[0042] The following describes an example of a method for forming a carbonaceous film on the surface of a lithium transition metal composite oxide.

[0043] (1) Dissolve anionic surfactants in water to prepare an aqueous solution.

[0044] (2) Add lithium transition metal composite oxide powder to the above aqueous solution and stir to prepare a suspension of lithium transition metal composite oxide dispersed in aqueous solution.

[0045] (3) The residue obtained by filtering the above suspension is calcined, thereby forming a carbonaceous film on the surface of the lithium transition metal composite oxide.

[0046] Anionic surfactants adsorb onto the surface of lithium transition metal complex oxides in water, forming a substantially uniform carbonaceous film. The surfactant is not particularly limited as long as it contains carbon (C) and at least one of an alkali metal or alkaline earth metal other than lithium. Preferably, the surfactant contains at least one of sodium (Na) and potassium (K). Additionally, the surfactant may contain sulfur (S). Examples of surfactants include sodium dodecyl sulfate and potassium dodecyl sulfate. The concentration of the surfactant in the aqueous solution is, for example, 0.1% to 10% by mass, preferably 1% to 10% by mass.

[0047] [negative electrode]

[0048] The negative electrode 12, for example, has a negative electrode current collector and a negative electrode binder layer disposed on the negative electrode current collector. The negative electrode binder layer may be disposed on one or both surfaces of the negative electrode current collector. The negative electrode current collector may be a metal foil, such as copper or a copper alloy, that is stable within the potential range of the negative electrode 12, or a thin film with the metal disposed on its surface. The negative electrode binder layer, for example, contains a negative electrode active material and a binder. The negative electrode 12 may be manufactured, for example, by coating the surface of the negative electrode current collector with a negative electrode binder slurry containing a negative electrode active material and a binder, drying the coating, and then calendering the coating using a roller or the like.

[0049] As the negative electrode active material contained in the negative electrode compound layer, there are no particular limitations as long as it can reversibly absorb and release lithium ions; generally, carbon materials such as graphite are used. Graphite can be any of the following: natural graphite such as flake graphite, block graphite, and amorphous graphite; artificial graphite such as block graphite; and artificial graphite such as graphitized mesophase carbon microspheres. In addition, as the negative electrode active material, metals alloyed with Li such as Si and Sn, metal compounds containing Si and Sn, and lithium-titanium composite oxides can be used. For example, SiO₂... x (0.5≤x≤1.6) represents Si-containing compounds, or compounds composed of Li 2y SiO (2+y) (0<y<2) indicates that Si-containing compounds with Si particles dispersed in the lithium silicate phase can be used in conjunction with graphite.

[0050] Examples of binders included in the negative electrode binder layer include styrene-butadiene rubber (SBR), nitrile rubber (NBR), carboxymethyl cellulose (CMC) or its salts (CMC-Na, CMC-K, CMC-NH4, etc., and also partially neutralized salts), polyacrylic acid (PAA) or its salts (PAA-Na, PAA-K, etc., and also partially neutralized salts), and polyvinyl alcohol (PVA). These can be used individually or in combination of two or more. The binder content is, for example, 0.1 to 10 parts by weight, preferably 0.5 to 5 parts by weight, relative to 100 parts by weight of the negative electrode active material. Furthermore, the negative electrode binder layer may contain conductive materials similar to those in the positive electrode.

[0051] [Diaphragm]

[0052] The diaphragm 13 may be made of a porous sheet material, for example, that has ion permeability and insulation properties. Specific examples of porous sheets include microporous films, woven fabrics, and nonwoven fabrics. Preferred materials for the diaphragm include polyolefins such as polyethylene and polypropylene, and cellulose. The diaphragm 13 may be a laminate containing a cellulose fiber layer and a thermoplastic resin fiber layer such as an olefin resin. Alternatively, it may be a multilayer diaphragm containing a polyethylene layer and a polypropylene layer, or a diaphragm coated with a material such as an aramid resin or ceramic.

[0053] Example

[0054] The present disclosure will be further described below through embodiments and comparative examples, but the present disclosure is not limited to the following embodiments.

[0055] [Preparation of positive electrode active material]

[0056] <Example>

[0057] Sodium dodecyl sulfate, used as a surfactant, was dissolved in water to prepare a 10% (w / w) aqueous solution. LiNi was then added to this aqueous solution. 0.8 Mn 0.2 A lithium transition metal composite oxide containing O2 was stirred to prepare a suspension with a concentration of 1000 g / L. The suspension was filtered, and the resulting residue was vacuum calcined. This yielded a lithium transition metal composite oxide with a carbonaceous film formed on its surface. This was used as the positive electrode active material in this example. Transmission electron microscopy (TEM) observation showed that the thickness of the carbonaceous film was 10 nm. Furthermore, as... Figure 2 As shown, observations using energy-dispersive X-ray spectroscopy (TEM-EDX) revealed a peak originating from S near 2.2 keV, confirming the presence of S in the carbonaceous coating. Furthermore, as... Figure 3 As shown, XPS analysis of the positive electrode active material in the examples confirmed the presence of Na in the carbonaceous coating.

[0058] [The production of the positive electrode]

[0059] A positive electrode active material, acetylene black, carbon nanotubes (length: 2.5 μm, aspect ratio: 300), and polyvinylidene fluoride were mixed in a solid component mass ratio of 100:1:0.5:1. This mixture was then combined with N-methyl-2-pyrrolidone (NMP) to prepare a positive electrode slurry. Next, this positive electrode slurry was coated onto one side of a positive electrode current collector made of 15 μm thick aluminum foil. After the coating dried, it was calendered using calendering rollers and cut into specified electrode sizes to produce an evaluation positive electrode. A 20 mm × 20 mm region for the positive electrode function and a 5 mm × 5 mm connection region for the lead wire were formed on the positive electrode. Then, the positive electrode slurry layer formed on the connection region was further removed to expose the positive electrode current collector. The exposed portion of the positive electrode current collector was then connected to the positive electrode lead wire, and a specified area around the outer periphery of the positive electrode lead wire was covered with an insulating film.

[0060] [Making the negative electrode]

[0061] A lithium metal foil (300 μm thick) was cut into 25 mm × 25 mm pieces to obtain the negative electrode for evaluation. The lithium metal foil was connected to the negative electrode lead via a 5 mm × 5 mm Ni mesh, and a specified area around the negative electrode lead was covered with an insulating film.

[0062] [Modulation of non-aqueous electrolytes]

[0063] Ethyl carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) were mixed in a volume ratio of 20:5:75. Lithium hexafluorophosphate (LiPF6) was dissolved at a concentration of 1.3 mol / L relative to this mixed solvent to prepare a non-aqueous electrolyte (non-aqueous electrolyte solution).

[0064] [Evaluation of battery manufacturing]

[0065] An evaluation battery was fabricated using evaluation-grade positive and negative electrodes. First, the positive and negative electrodes were placed face-to-face with the positive electrode binder layer overlapping the negative lithium metal layer, separated by a separator, to obtain an electrode assembly. Next, a rectangular Al laminate film (100 μm thick) cut into 60 × 90 mm sections was folded in half, and the 60 mm long side was heat-sealed at 230°C to form a 60 × 45 mm cylinder. Then, the fabricated electrode assembly was placed inside the cylinder, aligning the end face of the Al laminate film with the insulating film of each lead, and heat-sealed at 230°C. Finally, 0.3 cm³ of [unsealed] [electrolyte] was injected from the unsealed short side of the Al laminate film. 3 The non-aqueous electrolyte was injected, and then allowed to stand for 3 minutes under reduced pressure of 0.06 MPa to allow the electrolyte to permeate each compound layer. Finally, the end face of the Al laminate film on the injected side was heat-sealed at 230°C to fabricate an evaluation battery. The evaluation battery was fabricated in a dry environment with a dew point below -50°C.

[0066] [Evaluation of DC resistance (DCIR)]

[0067] At 25°C, the battery was charged at a constant current of 0.2C to 4.5V, then charged at a constant voltage of 4.5V to 0.05C. Next, it was discharged at a constant current of 0.2C until the cell voltage reached 2.5V. Then, it was charged at a constant current of 0.2C until the state of charge (SOC) reached 50%. After a 2-hour pause, the resistance value was calculated by observing the voltage drop before and after 30 seconds of discharge at a current of 0.3C, and this value was used as the DCIR.

[0068] <Comparative Example 1>

[0069] Sodium dodecyl sulfate was not added in the preparation of the positive electrode active material, carbon nanotubes were not added in the preparation of the positive electrode, and acetylene black was changed from 1 part by weight to 1.5 parts by weight. Otherwise, the evaluation battery was prepared in the same manner as in the examples. Additionally, as... Figure 3 As shown, the presence of Na could not be confirmed in the XPS analysis of the positive electrode active material of Comparative Example 1.

[0070] <Comparative Example 2>

[0071] In the fabrication of the positive electrode, carbon nanotubes were not added, and the amount of acetylene black was changed from 1 part by weight to 1.5 parts by weight. Otherwise, the evaluation battery was fabricated in the same manner as in the example.

[0072] <Comparative Example 3>

[0073] Sodium dodecyl sulfate was not added in the preparation of the positive electrode active material, and the evaluation battery was prepared in the same manner as in the examples.

[0074] The evaluation results of the DCIR of the batteries of the examples and comparative examples are shown in Table 1. In Table 1, the DCIR value of Comparative Example 1 is set to 100, and the DCIR values ​​of the examples and other comparative examples are expressed as relative values.

[0075] Table 1

[0076]

[0077] As shown in Table 1, the DCIR of the battery in the embodiment is lower than that of the batteries in Comparative Examples 1 to 3. This result shows that by using a lithium transition metal composite oxide with a carbonaceous film containing at least one of alkali metals and alkaline earth metals other than Li as the positive electrode active material, and by using a fibrous conductive material as the conductive material contained in the positive electrode binder layer, it is possible to reduce the DC resistance of the battery.

[0078] This disclosure is further illustrated by the following embodiments.

[0079] Technical Component 1:

[0080] A positive electrode for a secondary battery includes a positive current collector and a positive electrode flux layer disposed on the positive current collector.

[0081] The positive electrode mixture layer contains a positive electrode active material and a conductive material.

[0082] The positive electrode active material comprises a lithium transition metal composite oxide and a carbonaceous film formed on the surface of the lithium transition metal composite oxide, wherein the carbonaceous film contains at least one of an alkali metal other than Li and an alkaline earth metal.

[0083] The conductive material contains fibrous conductive material.

[0084] Technical Component 2:

[0085] According to the technical configuration 1, the positive electrode for a secondary battery comprises carbon nanotubes with a length of 0.1 μm or more and an aspect ratio of 5 or more.

[0086] Technical Component 3:

[0087] According to technical configuration 1 or 2, the positive electrode for a secondary battery further contains S.

[0088] Technical Component 4:

[0089] According to any one of the technical configurations 1 to 3, the carbonaceous coating contains at least one of Na and K.

[0090] Technical Component 5:

[0091] According to any one of the technical configurations of the positive electrode for a secondary battery, the content of Co in the lithium transition metal composite oxide is 5 mol% or less relative to the total molar number of metal elements other than Li.

[0092] Technical Component 6:

[0093] According to any one of the technical configurations 1 to 5, the positive electrode for a secondary battery, wherein the lithium transition metal composite oxide is composed of the general formula Li a Ni 1-x-y Mn x M y O 2+b (Where, 0.9≤a≤1.1, 0≤x≤0.5, 0≤y≤0.1, 0.5≤1-xy≤0.95 and -0.05≤b≤0.05 are satisfied, and element M is an element other than Li, Ni, Mn and oxygen.)

[0094] Technical Component 7:

[0095] According to any one of the technical configurations 1 to 6, the thickness of the carbonaceous film for a secondary battery is 30 nm or less.

[0096] Technical components 8:

[0097] A secondary battery comprising a positive electrode, a negative electrode, and an electrolyte as described in any one of technical configurations 1 to 7.

[0098] Explanation of reference numerals in the attached figures

[0099] 10 Secondary battery, 11 Positive electrode, 12 Negative electrode, 13 Separator, 14 Electrode body, 15 Battery casing, 16 Casing body, 17 Sealing body, 18, 19 Insulating plate, 20 Positive lead, 21 Negative lead, 22 Protrusion, 23 Filter, 24 Lower valve body, 25 Insulating component, 26 Upper valve body, 27 Cover, 28 Gasket.

Claims

1. A positive electrode for a secondary battery, comprising a positive electrode current collector and a positive electrode mixture layer disposed on the positive electrode current collector, the positive electrode mixture layer comprising a positive electrode active material and a conductive material, the positive electrode active material comprising a lithium transition metal complex oxide and a carbonaceous coating film formed on a surface of the lithium transition metal complex oxide, the carbonaceous coating film containing at least one of an alkali metal and an alkaline earth metal other than Li, the conductive material containing a fibrous conductive material.

2. The positive electrode for a secondary battery according to claim 1, the fibrous conductive material comprising a carbon nanotube having a length of 0.1 μm or more and an aspect ratio of 5 or more.

3. The positive electrode for a secondary battery according to claim 1 or 2, the carbonaceous coating film further containing S.

4. The positive electrode for a secondary battery according to claim 1 or 2, the carbonaceous coating film containing at least one of Na and K.

5. The positive electrode for a secondary battery according to claim 1 or 2, a content of Co in the lithium transition metal complex oxide is 5 mol% or less relative to a total number of moles of metal elements other than Li.

6. The positive electrode for a secondary battery according to claim 1 or 2, The lithium transition metal composite oxide is represented by the general formula Li a Ni 1-x-y Mn x M y O 2+b wherein the following are satisfied 0.9≤a≤1.1, 0≤x≤0.5, 0≤y≤0.1, 0.5≤1-x-y≤0.95, and -0.05≤b≤0.05, and the element M is an element other than Li, Ni, Mn, and oxygen.

7. The positive electrode for a secondary battery according to claim 1 or 2, a thickness of the carbonaceous coating film is 30 nm or less.

8. A secondary battery comprising the positive electrode for a secondary battery according to claim 1 or 2, a negative electrode, and an electrolyte.

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