Electrochemical device and method for manufacturing electrode for electrochemical device

Abstract

To provide an electrochemical device capable of improving discharge capacity, and to provide a method of manufacturing an electrode for the electrochemical device.SOLUTION: The electrochemical device has a positive electrode containing a positive electrode active material containing crown ether or glyme and a binder containing fluorine, and a negative electrode.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to an electrochemical device and a method for manufacturing an electrode for an electrochemical device. [Background technology]

[0002] Patent Document 1 describes a positive electrode material having a bimodal particle size distribution including large and small particles, and an average particle size (D 50 ) is 3 μm or more. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2019 / 103463 Summary of the Invention [Problem to be solved by the invention]

[0004] Although the technology described in Patent Document 1 can improve electrode density, the elimination of voids reduces the diffusion paths for Li ions, which may result in a decrease in the output characteristics of the battery.

[0005] An object of the present invention is to provide an electrochemical device having improved electrode density and good output characteristics, and a method for manufacturing an electrode for an electrochemical device. [Means for solving the problem]

[0006] An electrochemical device according to one embodiment includes a positive electrode including a positive electrode active material containing a crown ether or a glyme and a binder containing fluorine, and a negative electrode.

[0007] A method for manufacturing an electrode for an electrochemical device according to one embodiment includes the steps of preparing a slurry containing a positive electrode active material and a binder containing fluorine, and adding a crown ether or glyme to the slurry.

[0008] An electrochemical device according to one embodiment has a positive electrode and a negative electrode, in which the MacMullin number Nm (Nm=τ / ε), which is the ratio of tortuosity (tortuosity) τ to porosity ε, is 11.0 or more and 18.0 or less. [Effects of the Invention]

[0009] According to the electrochemical device and the method for producing an electrode for an electrochemical device of the present invention, the electrode density is improved and good output characteristics are obtained. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is an exploded perspective view schematically showing the configuration of a secondary battery according to an embodiment. [Figure 2] FIG. 2 is a cross-sectional view showing the configuration of the electrode body according to the embodiment. [Figure 3] FIG. 3 is a diagram showing the results of SEM-EDX observation of a positive electrode according to a comparative example. [Figure 4] FIG. 4 is a diagram showing the results of SEM-EDX observation of the positive electrode according to the example. [Figure 5] FIG. 5 is a graph showing the results of SEM-EDX observation of a positive electrode according to a comparative example. [Figure 6] FIG. 6 is a graph showing the results of SEM-EDX observation of the positive electrode according to the example. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, embodiments of the present disclosure will be described, but the present disclosure is not limited to these embodiments.

[0012] (Embodiment) Fig. 1 is an exploded perspective view schematically illustrating the configuration of a secondary battery according to an embodiment. The secondary battery 1 shown in Fig. 1 is a laminated lithium-ion secondary battery. As shown in Fig. 1, the secondary battery 1 includes a battery element 20, an exterior member 30, and an adhesive 32.

[0013] The battery element 20 is provided inside an exterior member 30. As shown in FIG. 1, the battery element 20 includes an electrode body 200, a positive electrode lead 21, and a negative electrode lead 22. The positive electrode lead 21 is a terminal drawn from a positive electrode 210 (described later) to the outside of the exterior member 30. That is, the positive electrode lead 21 is a terminal that serves as a positive electrode of the secondary battery 1. In FIG. 1, the positive electrode lead 21 is provided on an end surface of the electrode body 200. The negative electrode lead 22 is a terminal drawn from the inside of a negative electrode 220 (described later) to the outside of the exterior member 30. That is, the negative electrode lead 22 is a terminal that serves as a negative electrode of the secondary battery 1. In FIG. 1, the negative electrode lead 22 is provided on an end surface of the electrode body 200. Details of the electrode body 200 will be described later.

[0014] The exterior member 30 is a case in which the battery element 20 is housed. The exterior member 30 includes two exterior sheets 30a and 30b. The exterior sheets 30a and 30b each include an insulating layer, a metal layer, and an outermost layer. In the example of FIG. 1 , the exterior sheet 30a has a recess 31. As a result, the battery element 20 is housed in the exterior member 30 by housing the battery element 20 in the recess 31 and bonding the peripheral edges of the exterior sheets 30a and 30b.

[0015] The exterior sheets 30a and 30b are constructed by laminating an insulating layer, a metal layer, and an outermost layer in this order from the inside, i.e., the side where the battery element 20 is provided, and then bonding them together by lamination or other processing. The insulating layers of the exterior sheets 30a and 30b are made of resins such as polyethylene, polypropylene, modified polyethylene, modified polypropylene, and polyolefin resins containing ethylene or propylene as monomers. This allows the exterior sheets 30a and 30b to reduce the moisture permeability of the secondary battery 1 and improve its airtightness. The metal layers of the exterior sheets 30a and 30b are metal plate or foil materials such as aluminum, stainless steel, nickel, and iron. The outermost layer may be made of any material, but is preferably made of the same resin as the insulating layer or a material with high resistance to tearing and punctures, such as nylon.

[0016] The adhesive 32 is a member for making the exterior member 30 airtight. The adhesive 32 is provided between the exterior member 30 and the positive electrode lead 21 and the negative electrode lead 22. The material of the adhesive 32 preferably has adhesion to the positive electrode lead 21 and the negative electrode lead 22. For example, when the positive electrode lead 21 and the negative electrode lead 22 are made of a metal material, the adhesive 32 is made of a polyolefin resin such as polyethylene, polypropylene, modified polyethylene, or modified polypropylene. This allows the adhesive 32 to seal the gap between the exterior member 30 and the positive electrode lead 21 and the negative electrode lead 22, thereby making the interior of the exterior member 30 airtight.

[0017] Fig. 2 is a cross-sectional view showing the configuration of an electrode assembly according to an embodiment. More specifically, Fig. 2 is a cross-sectional view showing a portion of one layer of a positive electrode 210 and one layer of a negative electrode 220 in an electrode assembly 200. As shown in Fig. 2, the electrode assembly 200 includes a positive electrode 210, a negative electrode 220, and a separator 230. In the secondary battery 1, the electrode assembly 200 has a structure in which the positive electrode 210 and the negative electrode 220 are stacked with the separator 230 interposed therebetween. The positive electrode 210 and the negative electrode 220 included in the electrode assembly 200 are layered members for the charge / discharge reaction of the secondary battery 1 according to the embodiment.

[0018] The positive electrode 210 includes a positive electrode current collector 211 and a positive electrode active material layer 212. In the positive electrode 210, the positive electrode current collector 211 is laminated between the positive electrode active material layers 212.

[0019] The positive electrode current collector 211 is a conductive layer, and may be made of, for example, aluminum foil, stainless steel foil, etc. In the example of Fig. 1, the positive electrode current collector 211 is shaped as a rectangular sheet having protrusions on the positive electrode lead 21 side. The protrusions of the positive electrode current collector 211 are connected to the positive electrode lead 21.

[0020] The positive electrode active material layer 212 is a layer containing a positive electrode active material. The positive electrode active material includes lithium nickel oxide and further includes carbonate and crown ether. Note that the positive electrode active material may include lithium cobalt oxide instead of lithium nickel oxide.

[0021] Lithium nickel oxide has a composition formula of Li d Ni 1-a-b-c Co a Al b M c O₂. Here, M is at least one element selected from Na, Cu, W, Fe, and Zn. Also, 0 ≦ a ≦ 0.2, 0 ≦ b ≦ 0.2, 0 ≦ c ≦ 0.1, and 0.90 ≦ d ≦ 1.1 are satisfied. That is, the lithium nickel oxide may not contain Co, Al, and M. The values of M and a, b, and c of the lithium nickel oxide can be measured by inductively coupled plasma (ICP) optical emission spectrometry. The lithium nickel oxide preferably contains Co and Al. That is, in the above composition formula, it is preferable to satisfy 0 < a ≦ 0.2 and 0 < b ≦ 0.2, and more preferably to satisfy 0.01 ≦ a ≦ 0.2 and 0.01 ≦ b ≦ 0.2. In this case, the chemical stability of the lithium nickel oxide is improved by the addition of Co and Al.

[0022] The carbonate is a salt of a cation and a carbonate ion (CO₃ 2- ). The cation contains at least one element selected from K, Ca, Ba, Mg, Fe, Co, Na, Mn, Ni, Zn, Rb, Sr, Cs, Cd, and Ag.

[0023] The crown ethers are 12-crown-4 shown in formula (1), 15-crown-5 shown in formula (2), 18-crown-6 shown in formula (3), dibenzo-18-crown-6, diaza-18-crown-6, etc. In formulas (1) to (3), the cases where the crown ether encapsulates a cation are schematically shown, respectively.

[0024] [Chemical formula]

[0025] [Chemical formula]

[0026] [ka]

[0027] The positive electrode active material layer 212 is not limited to the above-mentioned materials, and may further contain, for example, a positive electrode binder, a positive electrode conductive additive, and a dispersant.

[0028] The positive electrode binder contains fluorine. The positive electrode binder may be any material, and may include, for example, one or more of synthetic rubber and polymer compounds. Examples of synthetic rubber include styrene butadiene rubber, fluorine-based rubber, and ethylene propylene diene. Examples of polymer compounds include polyvinylidene fluoride (PVdF) and polyimide.

[0029] The positive electrode conductive additive may be any material, including, for example, carbon. Examples of carbon include graphite, carbon black, acetylene black, and ketjen black. However, the positive electrode conductive additive is not limited to these materials, and may be a metal material, a conductive polymer, or the like, as long as it is a conductive material.

[0030] With the above configuration, the positive electrode 210 of this embodiment contains crown ether, which adsorbs carbonate or carbonate ions, resulting in a high concentration of carbonate or carbonate ions. As a result, pH conditions are established that facilitate the fluorine release from the binder, and the fluorine is released from the binder. The released fluorine reacts with Li inside the positive electrode active material and Li2CO3 on the surface to produce LiF. Furthermore, in this embodiment, by adding crown ether to the positive electrode active material, LiF is present at the grain boundaries. In other words, when no crown ether is added, F and C are located close to each other, but when crown ether is added, F is located at a different position from C.

[0031] When Li is released from the positive electrode active material, NiO and NiOOH are generated on the surface of the active material. This changes the state of the positive electrode active material, improving the slipperiness of the active material surface and improving packing (electrode density). In addition, the release of fluorine from the binder causes the binder to decompose or decompose, increasing the diffusion paths for Li ions.

[0032] The type of crown ether is appropriately selected depending on the type (ionic radius) of the cation to be included. As shown in formula (1), 12-crown-4 is, for example, Li + As shown in formula (2), 15-crown-5 is, for example, Na + As shown in formula (3), 18-crown-6 is, for example, K + It encompasses.

[0033] The positive electrode active material may contain a glyme represented by formula (4) instead of the crown ether. When the positive electrode active material contains a glyme, the oxygen site of the glyme and a cation are coordinated to form a stable complex structure, and therefore, the same effect as that of the crown ether described above can be obtained.

[0034] [ka]

[0035] The negative electrode 220 includes a negative electrode current collector 221 and a negative electrode active material layer 222. In the negative electrode 220, the negative electrode current collector 221 is laminated between the negative electrode active material layers 222.

[0036] The negative electrode current collector 221 is a conductor, and for example, copper foil can be used. In the example of Fig. 1, the negative electrode current collector 221 is shaped as a rectangular sheet having protrusions on the negative electrode lead 22 side. The protrusions of the negative electrode current collector 221 are connected to the negative electrode lead 22.

[0037] The negative electrode active material layer 222 is a layer containing a negative electrode active material. The negative electrode active material layer 222 is not limited to being made of only a negative electrode active material, and may also contain, for example, a conductive additive and a binder.

[0038] The negative electrode active material refers to a reducing agent capable of absorbing and desorbing charge carriers of the secondary battery 1 through charge and discharge reactions, such as a carbon material, a metal, a metalloid, a silicon alloy or compound, or a tin (Sn) alloy or compound.

[0039] Examples of the silicon-containing negative electrode active material include elemental silicon, silicon alloys, and silicon compounds. Examples of silicon alloys that can be used as the negative electrode active material include those containing at least one element selected from the group consisting of tin (Sn), nickel (Ni), copper (Cu), iron (Fe), cobalt (Co), manganese (Mn), zinc (Zn), indium (In), silver (Ag), titanium (Ti), germanium (Ge), bismuth (Bi), antimony (Sb), and chromium (Cr) as a second constituent element other than silicon. Examples of silicon compounds that can be used as the first negative electrode active material include silicon oxide (SiO x ) and silicon carbide (SiC), which contain oxygen (O) or carbon (C), and may contain the above-mentioned second constituent element in addition to silicon. The negative electrode active material may also be doped with Li. The negative electrode active material may be SiO x In this case, it is preferable that Li is pre-doped by doping it in the negative electrode production process. x The negative electrode active material may be a composite of Si and other materials such as carbon, or a composite of a Si alloy and other materials such as carbon. In this case, the irreversible capacity can be reduced. In addition, it is preferable that the particle surfaces of the negative electrode active material are partially or entirely coated with carbon. This can improve the electronic conductivity of the particle surfaces of the negative electrode active material.

[0040] Examples of carbon materials that can be used as the negative electrode active material include MCMB (MesoCarbon MicroBeads), artificial graphite, natural graphite, non-graphitizable carbon, and graphitizable carbon. More specifically, examples of materials that can be used as the negative electrode active material include pyrolytic carbons, cokes, glassy carbon fiber, fired organic polymer compounds, activated carbon, and carbon blacks. Examples of cokes include pitch coke, needle coke, and petroleum coke. Here, fired organic polymer compounds are produced by firing polymer compounds such as phenolic resins and furan resins at an appropriate temperature and carbonizing them.

[0041] The negative electrode active material is not limited to the above-mentioned materials and may include other materials capable of absorbing and releasing lithium, such as metals, semimetal alloys or compounds, and tin (Sn) alloys or compounds. Examples of metals and semimetals that can be used as the negative electrode active material include tin (Sn), lead (Pb), aluminum (Al), indium (In), zinc (Zn), antimony (Sb), bismuth (Bi), cadmium (Cd), magnesium (Mg), boron (B), gallium (Ga), germanium (Ge), arsenic (As), silver (Ag), zirconium (Zr), yttrium (Y), and hafnium (Hf). Among these, germanium, tin, and lead are preferred. Tin is more preferred because of its high ability to absorb and release lithium and its ability to achieve high energy density.

[0042] Examples of tin alloys that can be used as the negative electrode active material include those containing at least one of nickel, copper, iron, cobalt, manganese, zinc, indium, silver, titanium, germanium, bismuth, antimony, and chromium as a second constituent element other than tin. Examples of tin compounds that can be used as the negative electrode active material include those containing oxygen or carbon, and may contain the above-mentioned second constituent element in addition to tin.

[0043] The separator 230 is a film that insulates the positive electrode 210 from the negative electrode 220. The separator 230 is provided between the positive electrode 210 and the negative electrode 220 so that the positive electrode 210 and the negative electrode 220 do not come into direct contact with each other. In the example of Fig. 1, the shape of the separator 230 is a rectangular sheet when viewed in a plan view in the thickness direction.

[0044] The separator 230 is preferably made of a material that is electrically stable, chemically stable against the positive electrode active material, the negative electrode active material, and the electrolyte, and is insulating. For example, the separator 230 can be made of a polymer nonwoven fabric, a porous film, or a layer of glass or ceramic fibers. The separator 230 is more preferably made of a porous polyolefin film. This improves battery safety by preventing short circuits and providing a shutdown function.

[0045] The electrolyte solution is impregnated into the separator 230. In the example of Fig. 1, the electrolyte solution fills the space inside the exterior member 30. The electrolyte solution is a non-aqueous electrolyte solution containing an electrolyte salt and a solvent that dissolves the electrolyte salt.

[0046] Examples of electrolyte salts include lithium salts such as lithium perchlorate (LiClO), lithium hexafluorophosphate (LiPF), lithium tetrafluoroborate (LiBF), lithium bis(trifluoromethanesulfonyl)imide (LiN(SOCF)), lithium bis(pentafluoroethanesulfonyl)imide (LiN(SOCF)), and lithium hexafluoroarsenate (LiAsF).

[0047] Examples of the solvent include lactone-based solvents such as γ-butyrolactone, γ-valerolactone, δ-valerolactone, and ε-caprolactone; carbonate-based solvents such as ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate; ether-based solvents such as 1,2-dimethoxyethane, 1-ethoxy-2-methoxyethane, 1,2-diethoxyethane, tetrahydrofuran, and 2-methyltetrahydrofuran; nitrile-based solvents such as acetonitrile; sulfolane-based solvents; phosphoric acids; phosphate ester solvents; and pyrrolidones.

[0048] The electrolytic solution may further contain an additive such as a fluorinated carboxylic acid ester, a sulfonic acid ester, a sulfonic acid anhydride, or a carboxylic acid anhydride.

[0049] Next, a method for manufacturing the positive electrode 210 of the secondary battery 1 will be described.

[0050] First, a positive electrode active material, a fluorine-containing positive electrode binder, and a positive electrode conductive agent are mixed together to form a positive electrode mixture. The positive electrode mixture is then added to a solvent to prepare a paste-like positive electrode mixture slurry. This solvent may be an aqueous solvent or an organic solvent. A carbonate and a crown ether are added to the positive electrode mixture slurry and mixed. Alternatively, a carbonate and a glyme may be added to the positive electrode mixture slurry instead of the crown ether and mixed.

[0051] Thereafter, the positive electrode mixture slurry is applied to both surfaces of the positive electrode current collector 211 and dried. This forms the positive electrode active material layer 212. The positive electrode active material layer 212 may then be compression-molded using a compression device such as a roll press. In this case, the positive electrode active material layer 212 may be heated, or the compression molding may be repeated multiple times. During this heat treatment, fluorine released from the binder reacts with Li in the positive electrode active material to produce LiF. In the positive electrode active material from which Li has been released, NiO and NiOOH are produced on the active material surface. This changes the state of the positive electrode active material, improving the slipperiness of the active material surface and improving packing properties (electrode density).

[0052] Carbonates generally have large particle sizes, but dissolve in the slurry to allow them to be uniformly present. This allows the reactions that occur in the slurry to occur uniformly throughout the slurry. As a result, in this embodiment, the carbonates are uniformly dispersed, making it possible to suppress the progression of localized deterioration.

[0053] (Example) The secondary battery 1 according to the embodiment uses the following materials. Cathode active material: NCA Binder: PVDF Conductive agent: carbon black Crown Ether: 18-Crown-6-Ether Carbonate: K2CO3 Electrolyte: 1M LiPF6EC:EMC=1:1

[0054] Table 1 shows the amount of crown ether contained in the positive electrode active material, packing property, MacMullin number Nm, and 5 C / 0.2 C discharge capacity expression rate of the secondary batteries according to the examples and comparative examples. Note that the packing property (%) in Table 1 indicates the value of electrode density normalized by setting the electrode density of the positive electrode active material layer 212 of Example 5 as 100%.

[0055] [Table 1]

[0056] In the secondary batteries 1 according to the examples and comparative examples shown in Table 1, the crystal structure of the positive electrode active material is a layered rock salt type. The composition of the positive electrode active material is mainly Ni with additions of Co, Mn, and Al. The Ni ratio in the positive electrode 210 is 80% or more and 98% or less. For example, in one example of the positive electrode 210, the Ni ratio of the positive electrode active material is 94.83%, the Co ratio is 3.32%, and the Al ratio is 1.85%. Alternatively, in another example of the positive electrode 210, the Ni ratio of the positive electrode active material is 98.17% and the Al ratio is 1.83%.

[0057] Examples 1 to 9 shown in Table 1 differ in the amount of crown ether contained in the positive electrode active material of the positive electrode 210. Comparative Example 1 shows the characteristics of a secondary battery 1 in which 1 wt % of crown ether is added to the electrolyte solution rather than the positive electrode 210. That is, in Comparative Example 1, the positive electrode 210 does not contain any crown ether. In Comparative Example 2, no crown ether is added to either the positive electrode 210 or the electrolyte solution.

[0058] Here, the quantitative determination method of crown ether in the examples and comparative examples will be explained. First, 5 g of the composite layer was peeled off from the electrode body 200, immersed in 100 ml of NMP (N-methyl-2-pyrrolidone) solvent, and centrifuged for 30 minutes to extract the liquid phase. "18-crown-6 ether" was used as a standard solution. The standard solution was diluted with NMP to 250, 500, 1000, and 1500 ppm to prepare samples for the calibration curve.

[0059] The extracted solution is measured using GC / MS (gas chromatography mass spectrometry) and quantified from the peak area. When the analysis is performed under the same analytical conditions, the peak area (peak height) of the target component is thought to be proportional to the amount of the component. This property is utilized in the absolute calibration curve method. The operating procedure for the absolute calibration curve method is as follows:

[0060] (1) Prepare a standard mixed solution of the components to be analyzed in 3-5 concentrations. (2) A fixed amount of each sample is injected into a GC / MS for analysis, and the peak area is calculated from the recorded chromatogram. This is done for each concentration sample. (3) Create a calibration curve by plotting the concentration of the standard sample on the horizontal axis and its peak area on the vertical axis. (4) Analyze a sample of unknown concentration under the same conditions as the analysis used to create the calibration curve, and measure the peak area. (5) The peak area of ​​the unknown sample is fitted to the calibration curve to calculate the concentration of the target component.

[0061] The apparatus and measurement conditions used for quantifying crown ethers in the Examples and Comparative Examples are as follows:

[0062] Device: Gas chromatograph mass spectrometer (GC / MS): 7980B, 5977B GC / MSD (Agilent Technologies) Headspace sampler: 7697A Headspace Sampler (Agilent Technologies) Column: DB-624 UI (30 m, φ0.25 mm, 1.4 μm, Agilent Technologies)

[0063] Measurement conditions Column temperature: 40°C (5 min hold) → 40°C / min → 240°C (3 min hold) Inlet temperature: 200℃ Carrier gas: Helium Carrier gas flow rate: 1 mL / min Split ratio: 30:1, Split flow rate: 30 mL / min Total flow: 34mL / min Septum purge flow: 3mL / min Column flow rate: 1 mL / min Ion source: EI Ion source temperature: 230℃ Quadrupole temperature: 150°C, electron energy: 70.0 eV Measurement type: TIC and SIM Scan range (m / z): 40-400

[0064] Another method for quantifying crown ethers other than GC / MS is XPS (X-ray photoelectron spectroscopy). In this case, an electrode is analyzed using XPS to detect the COC bond of the crown ether. The crown ether is quantified based on data for which the amount added is known.

[0065] The McMullin number Nm shown in Table 1 is the ratio (Nm = τ / ε) of the tortuosity (tortuosity) τ to the porosity ε of the positive electrode 210. Here, the Li ion diffusion path in the positive electrode 210 refers to the path that the Li ions take when diffusing. The Li migration path considered from an atomic-level model is thought to involve Li ions passing through interstitial spaces, empty spaces, lattice defects, etc. in the atomic structure, and proposed Li diffusion paths include paths within the crystal where they can move, boundaries within the crystal, and the outer walls of the crystal.

[0066] Factors that change the structure of the electrode are the arrangement of the active material and the distribution of conductive additives and binders. In order to form a sufficient void network with the minimum amount of voids required, the positive electrode is optimized to minimize the MacMullin number Nm (=τ / ε). The larger the MacMullin number Nm, the more the target battery system becomes rate-limited by ion diffusion in the electrolyte. In other words, structural optimization is required to create the minimum amount of voids required.

[0067] In the measurement of the McMullin number Nm shown in Table 1, the positive electrode diameter was φ16.5 mm and φ15.0 mm. The electrolyte was 10 × 10 -3 mol / dm 3 TBAClO4 EC:DEC = 1:1 wt% (0.42 mS / cm) was used. Nonwoven fabric was used for the separator 230, and the excess rate of the electrolyte was 130% relative to the voids in the cell components. To calculate the McMullin number Nm, a VMP-3 (Bio-logic) was used for impedance measurement, and the measurement conditions were 10 mV, 1 MHz-0.05 Hz, and 6 pts / decade.

[0068] The McMullin number Nm was calculated by fitting the plot obtained from the impedance measurement. Data fitting was performed using the transmission line model (TLM-Q), which is one of the models used in fields such as electronics and electrochemistry. The transmission line model (TLM-Q) is a model used to describe the flow of current in contact areas such as horizontal contacts.

[0069] The "5C / 0.2C discharge capacity expression rate" shown in Table 1 was calculated by measuring the discharge load characteristics of the fabricated batteries at 0.2C and 5C. The discharge load characteristics were measured in a thermostatic chamber at 25°C.

[0070] (0.2C discharge load characteristics) For the 0.2C discharge load characteristics, the fabricated battery was allowed to rest for 3 hours beforehand, then charged at a constant current and constant voltage of 1.0C to an upper limit voltage of 4.25V and a lower limit current of 0.01C, and then allowed to rest for 1 minute. After that, the battery was discharged at a current of 0.2C to a lower limit voltage of 2.5V, and then allowed to rest for 5 minutes.

[0071] (5C discharge load characteristics) The fabricated battery was allowed to rest for 3 hours beforehand, then charged at a constant current and constant voltage at 1.0 C up to an upper voltage of 4.25 V and a lower current of 0.01 C, and after resting for 1 minute, discharged at 0.5 C down to a lower voltage of 2.5 V, and then rested for 5 minutes.

[0072] (Calculation of discharge capacity development rate) The discharge capacity development rate was calculated as the ratio of the discharge capacity at 0.2C to that at 5C based on the following formula (5). Discharge capacity development rate (%) = (discharge capacity at 5 C) / (discharge capacity at 0.2 C) × 100 (5)

[0073] As shown in Table 1, in Examples 3 to 7, the content of crown ether in the positive electrode active material was 0.11 wt % or more and 1.80 wt % or less.

[0074] Within the range of crown ether amounts shown in Examples 3 to 7, the packing property (electrode density) of the positive electrode 210 of the secondary battery 1 is 97.7% or more. Within the range of crown ether amounts shown in Examples 3 to 7, the MacMullin number Nm is 11.0 or more and 18.0 or less. Within the range of crown ether amounts shown in Examples 3 to 7, the discharge capacity expression rate is 65% or more and 75% or less.

[0075] More preferably, in Examples 4 to 6, the content of crown ether in the positive electrode active material is 0.26 wt % or more and 0.53 wt % or less.

[0076] Within the range of crown ether amounts shown in Examples 4 to 6, the packing property (electrode density) of the positive electrode 210 of the secondary battery 1 is 99% or more. Within the range of crown ether amounts shown in Examples 4 to 6, the MacMullin number Nm is 11.0 or more and 13.0 or less. Within the range of crown ether amounts shown in Examples 4 to 6, the discharge capacity expression rate is 70% or more and 75% or less.

[0077] In Examples 1 and 2, the crown ether content in the positive electrode active material was 0.05 wt% or less, and in Examples 8 and 9, the crown ether content in the positive electrode active material was 2.04 wt% or more. In Examples 1, 2, 8, and 9, the packing degree (electrode density) was smaller than that in Examples 3 to 7 described above. Specifically, in Examples 1, 2, 8, and 9, the packing degree (electrode density) was 94.2% or more. Furthermore, in Examples 1, 2, 8, and 9, the MacMullin number Nm was 20.0 or more and 25.0 or less. Furthermore, in Examples 1, 2, 8, and 9, the discharge capacity expression rate was 30% or more and 45% or less.

[0078] In Comparative Examples 1 and 2, no crown ether was added to the positive electrode active material. In this case, in Comparative Examples 1 and 2, the packing degree (electrode density) and discharge capacity expression rate were smaller and the MacMullin number Nm was larger than at least in Examples 3 to 7. Specifically, in Comparative Examples 1 and 2, the packing degree (electrode density) was 94.4%, the MacMullin number Nm was 25.0, and the discharge capacity expression rate was 35%.

[0079] As described above, it was shown that packing (electrode density) can be improved and the discharge capacity expression rate can be increased by adjusting the crown ether content in the positive electrode active material to 0.11 wt% to 1.8 wt%, more preferably 0.26 wt% to 0.53 wt%. It was also shown that the MacMullin number Nm can be adjusted to 11.0 to 18.0, more preferably 11.0 to 13.0, by adjusting the crown ether content.

[0080] FIG. 3 shows the results of SEM-EDX observation of a positive electrode according to a comparative example. FIG. 3(a) is a cross-sectional SEM photograph of a positive electrode according to a comparative example, FIG. 3(b) is a diagram showing the carbon distribution in FIG. 3(a), and FIG. 3(c) is a diagram showing the fluorine distribution in FIG. 3(a). FIG. 4 shows the results of SEM-EDX observation of a positive electrode according to an example. FIG. 4(a) is a cross-sectional SEM photograph of a positive electrode according to an example, FIG. 4(b) is a diagram showing the carbon distribution in FIG. 4(a), and FIG. 4(c) is a diagram showing the fluorine distribution in FIG. 4(a). FIG. 5 is a graph showing the results of SEM-EDX observation of a positive electrode according to a comparative example. FIG. 6 is a graph showing the results of SEM-EDX observation of a positive electrode according to an example.

[0081] The measurement conditions for the SEM-EDX (Energy Dispersive X-ray Spectroscopy) shown in Figures 3 to 6 were as follows: The acceleration voltage during measurement was set to 2 kV, and the aperture opening was set to 60 μm. The magnification was set to 3000x, and the resolution during observation and analysis was set to 512 pixels. The process time and dwell time indicate the processing time and set waiting time during measurement, which were set to 6 seconds and 10 μs, respectively. The target count value was set to 1 million times.

[0082] As shown in Figures 3 and 5, in the comparative example where no crown ether was added, fluorine was dispersed and present in the same location as carbon. In contrast, as shown in Figures 4 and 6, in the example where crown ether was added, fluorine was present at a position separate from carbon and also in areas where no carbon was present (see, for example, the areas indicated by the arrows in Figures 4(a) and 4(c)). This indicates that in the example, the state of the positive electrode active material changed, improving the slipperiness of the active material surface and improving packing (electrode density).

[0083] In the embodiment, the configuration of a secondary battery 1 is shown as an electrochemical device, but this is merely an example and is not intended to be limiting. The present disclosure can also be applied to electrochemical devices such as capacitors and fuel cells. Furthermore, the configuration of a laminate film-type battery is shown as the secondary battery 1, but is not limited to this. The secondary battery 1 of the present disclosure may also be, for example, a cylindrical, coin, or button battery.

[0084] The above-described embodiments are provided to facilitate understanding of the present invention and are not intended to limit the present invention. The present invention may be modified or improved without departing from the spirit and scope of the present invention, and equivalents thereof are also included in the present invention.

[0085] The present disclosure may also have the following configurations.

[0086] (1) a positive electrode including a positive electrode active material including a crown ether or a glyme and a binder including fluorine; a negative electrode; Electrochemical devices. (2) The content of the crown ether in the positive electrode active material is 0.11 wt% or more and 1.80 wt% or less. The electrochemical device according to (1). (3) The content of the crown ether in the positive electrode active material is 0.26 wt % or more and 0.53 wt % or less. The electrochemical device according to (1). (4) The MacMullin number Nm (Nm=τ / ε), which is the ratio of torsion (tortuosity) τ to porosity ε, of the positive electrode is 11.0 or more and 18.0 or less. An electrochemical device according to any one of (1) to (3). (5) LiF is generated at the grain boundaries of the positive electrode active material. An electrochemical device according to any one of (1) to (4). (6) preparing a slurry containing a positive electrode active material and a binder containing fluorine; adding a crown ether or glyme to the slurry. A method for manufacturing electrodes for electrochemical devices. (7) After the step of adding crown ether or glyme to the slurry, the step of drying the slurry is included. (6) A method for producing an electrode for an electrochemical device according to (6). (8) A positive electrode having a MacMullin number Nm (Nm = τ / ε), which is the ratio of tortuosity (tortuosity) τ to porosity ε, of 11.0 to 18.0, a negative electrode; Electrochemical devices. [Explanation of symbols]

[0087] 1 Secondary battery 20 Battery element 21 Positive lead 22 Negative lead 30 Exterior materials 30a, 30b Exterior sheet 31 Depression 32 Adhesive 200 Electrode body 210 Positive electrode 211 Positive electrode current collector 212 Cathode active material layer 220 negative electrode 221 Negative electrode current collector 222 Negative electrode active material layer 230 Separator

Claims

1. a positive electrode including a positive electrode active material including a crown ether or a glyme and a binder including fluorine; a negative electrode; Electrochemical devices.

2. The content of the crown ether in the positive electrode active material is 0.11 wt % or more and 1.80 wt % or less. The electrochemical device of claim 1 .

3. The content of the crown ether in the positive electrode active material is 0.26 wt % or more and 0.53 wt % or less. The electrochemical device of claim 1 .

4. The positive electrode has a MacMullin number Nm (Nm=τ / ε), which is the ratio of torsion (degree of tortuosity) τ to porosity ε, of 11.0 or more and 18.0 or less. The electrochemical device of claim 1 .

5. LiF is generated at the grain boundaries of the positive electrode active material. The electrochemical device of claim 1 .

6. A slurry containing a positive electrode active material and a binder containing fluorine is prepared; adding a crown ether or glyme to the slurry. A method for manufacturing electrodes for electrochemical devices.

7. After the step of adding a crown ether or glyme to the slurry, the step of drying the slurry is included. The method for producing an electrode for an electrochemical device according to claim 6 .

8. a positive electrode having a MacMullin number Nm (Nm = τ / ε), which is the ratio of tortuosity (degree of tortuosity) τ to porosity ε, of 11.0 or more and 18.0 or less; a negative electrode; Electrochemical devices.

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