Secondary battery electrode, secondary battery, and production method therefor

Abstract

The present disclosure provides a secondary battery electrode that makes it possible to achieve excellent high energy density and high-speed charge / discharge characteristics. The present disclosure relates to a secondary battery electrode containing carbon nanotubes and active material particles that are supported in a dispersed state on the carbon nanotubes and have an average particle size of 2-1000 nm, and in which the mass ratio of the carbon nanotubes with respect to the total mass of the active material particles and the carbon nanotubes is 0.1 wt% or more.

Description

Secondary battery electrode, secondary battery, and manufacturing method thereof

[0001] The present invention relates to an electrode for a secondary battery, a secondary battery, and a method for manufacturing the same. Technology background

[0002] To achieve the SDGs, technological innovation is needed for the storage and utilization of electrical energy converted from various renewable energies. Among these, ion secondary batteries, which have the advantage of high energy density as shown in the Ragone Plot, and supercapacitors, which have the advantage of high output (power) density due to high-speed charging and discharging, are attracting attention.

[0003] The development of ion secondary batteries requires not only further improvements in energy density but also improvements in high-speed charge / discharge characteristics. The development of supercapacitors also requires further improvements in energy density, but the large voltage fluctuations during charge / discharge pose safety challenges.

[0004] Therefore, at present, ion secondary batteries and supercapacitors are used in limited ways depending on the application, and in some cases, the combined use of the two is being considered.

[0005] Li-ion secondary batteries are installed in small mobile devices such as mobile phones and lightweight notebook computers, as well as in electric vehicles that consume large amounts of power. In order to utilize all of their battery capacity, they must be repeatedly charged and discharged at a low rate of approximately 1C or less.

[0006] In contrast to this, Non-Patent Document 1 presents, using an electric vehicle as an example, the goal to be achieved is to build a Li-ion secondary battery that can maintain its original battery capacity at 100C based on the C rate, that is, that can be charged and discharged at an ultra-high speed, and discloses data showing that 54% of the discharge capacity was maintained at 100C.

[0007] Non-Patent Document 2 discloses the performance of a Na-ion secondary battery using a Prussian blue analogue (PBA) consisting of five different metal ions (Mn, Fe, Co, Ni, Cu), i.e., a so-called high-entropy crystal, as the positive electrode. In the case of cubic high-entropy PBA crystals with an average particle diameter of 1 μm, Na ＋The strain caused by the change in lattice size during insertion and removal of the ions is reduced, thereby improving the repetitive durability. Furthermore, it is disclosed that, for example, even when charged and discharged at 8 C, 68% of the discharge capacity at low rates is retained, suppressing the decrease in capacity during high-rate charge and discharge.

[0008] Non-Patent Document 3 describes that Prussian blue (PB) is grown in cubic crystals of 500 nm to 1.5 μm on carbon black, and the aggregation of the PB crystal particles is suppressed. The PB crystal particles are then mixed with an organic binder to form an electrode, which is used to improve the high-rate charge-discharge performance of a Na-ion secondary battery. For example, it discloses that 67% of the discharge capacity at a low rate at 90 C is maintained.

[0009] Non-Patent Document 4 discloses that aggregation of PB crystals is suppressed by precipitating PB crystals with various shapes and particle sizes on mesoporous carbon. In addition to surface-etched PB with a cubic shape of several μm, PB with small particle sizes of 100 to 200 nm is mixed to increase the surface area, improving the high-speed charge / discharge performance of Na-ion secondary batteries. The high conductivity of mesoporous carbon and the numerous pores allow for the formation of Na ＋ It has been shown that the presence of a fast migration path of ions allows the retention of 75% of the low-rate discharge capacity at 28C.

[0010] Non-Patent Document 5 discloses that cubic PBs with particle diameters of 400 to 600 nm are grown in an isolated state on multi-walled carbon nanotube (MWNT) fibers. It has been shown that this improves the high-rate charge / discharge performance of Na-ion secondary batteries in a low-temperature environment, and that 76% of the low-rate discharge capacity is retained at 6 C at room temperature (25°C).

[0011] Non-Patent Document 6 discloses the preparation of an organic binder-free freestanding electrode by precipitating aggregated PB nanoparticles on the surface of bundled single-walled carbon nanotubes (SWNTs). It has been shown that this improves the high-rate charge / discharge performance of Li-ion secondary batteries in a low-temperature environment, and that at room temperature, 48% of the low-rate discharge capacity is retained at 3C.

[0012] Non-Patent Document 7 discloses the preparation of a binder-free freestanding membrane by suspending PBA nanoparticles composed of Mn and Fe with an average particle size of 300 nm, carbon nanotubes (CNTs), and carbon nanofibers (CNFs) in a mixed solvent of ethanol and water using ultrasonic treatment, and filtering the suspension. Scanning electron microscope images of the freestanding membrane show that the CNTs / CNFs and PBA nanoparticles are unevenly entangled, with many areas where only aggregated PBA nanoparticles are densely packed and many areas where only CNTs / CNFs are densely packed, and it has been shown that the membrane retains 79% of its low-rate discharge capacity at 20 C.

[0013] In Non-Patent Document 8, FeOOH nanorods and SWNTs were suspended in water by ultrasonic treatment together with a surfactant, and the resulting filtration membrane was transferred onto a copper foil, which was then heated at 450°C to convert the FeOOH into Fe ３ O ４ In the scanning electron microscope image, agglomerated Fe ３ O ４ The nanorods are entangled with SWNTs and have been shown to retain 60% of their low-rate discharge capacity at 10C in Li-ion secondary batteries.

[0014] Non-Patent Document 9 discloses a positive electrode prepared by a conventional electrode preparation method, in which PBA nanoparticles composed of Zn and Fe with an average particle size of 150 nm are mixed with acetylene black (conductive additive) and polyvinyl fluoride (binder). It is shown that in a Zn-ion secondary battery, 61% of the low-rate discharge capacity is retained at 65C.

[0015] Non-Patent Document 10 discloses a positive electrode prepared by kneading PBA consisting of 20 to 50 nm Cu and Fe with amorphous carbon and graphite (conductive additives) and polyvinyl fluoride (binder) using a conventional electrode preparation method. ＋ The performance of the positive electrode with respect to ion intercalation and deintercalation is shown to be such that 68% of the low-rate discharge capacity is retained at 83C.

[0016] Non-Patent Document 11 discloses a cathode fabricated by a conventional electrode fabrication method, in which 50-200 nm PBA nanoparticles consisting of Mn and Fe are mixed with acetylene black (conductive additive) and polyvinyl fluoride (binder). It is shown that the cathode of a K-ion secondary battery retains 54% of its low-rate discharge capacity at 4C.

[0017] Development of high-speed charge / discharge lithium-ion secondary batteries, FB Technical News No. 64 (2008, 11) Advanced Functional Materials, 32, 2202372 (2022) Advanced Functional Materials, 26, 5315-5321 (2016) ACS Applied Materials & Interfaces, 13, 38202-38212 (2021) Advanced Materials, 28, 7234-7248 (2016) Nanoscale Advances, 4, 510-520 (2022) Small, 15, 1902420 (2019) Advanced Energy Materials, 22, E145-E149 (2010) Energy Storage Materials, 42, 715-722 (2021) Nature Communications, 2, 550 (2011) Nature Communications, 12, 2167 (2021)

[0018] However, in the above-mentioned Non-Patent Documents 1 to 11, the high-rate charge / discharge performance is still not sufficient, and there is a demand for an electrode for a secondary battery that can achieve both high energy density, which is a feature of ion secondary batteries, and excellent high-rate charge / discharge characteristics.

[0019] The gist of the present invention is as follows: (1) An electrode for a secondary battery, comprising: carbon nanotubes; and active material particles having an average particle size of 2 to 1,000 nm dispersed and supported on the carbon nanotubes, wherein the mass ratio of the carbon nanotubes to the total mass of the active material particles and the carbon nanotubes is 0.1 wt % or more. (2) The electrode according to (1) above, wherein the ratio of the number of primary particles to the number of all particles of the active material particles is 70% or more. (3) The electrode according to (1) or (2) above, which does not contain a binder. (4) The electrode according to any of (1) to (3) above, wherein the active material is Prussian blue or an analogue thereof. (5) The electrode according to (4) above, wherein the Prussian blue or an analogue thereof is Fe—Zn Prussian blue or an analogue thereof, Zn—Mn Prussian blue or an analogue thereof, or Fe—Cu Prussian blue or an analogue thereof. (6) A secondary battery comprising the electrode, counter electrode, electrolyte solution, and current collector according to any one of (1) to (5). (7) The secondary battery according to (6), wherein the concentration of the electrolyte solution is 0.8 M or more. (8) The secondary battery according to (6) or (7), wherein the current collector is carbon paper. (9) The secondary battery according to any one of (6) to (8), wherein the secondary battery has an energy density of 60 Wh / kg or more and a power density of 30,000 W / kg or more. (10) The secondary battery according to any one of (6) to (8), wherein the capacity retention rate relative to the capacity at 1 C when an energy density of 60 Wh / kg or more and a power density of 10,000 W / kg or more is obtained. (11) The secondary battery according to any one of (6) to (8), wherein the capacity retention rate relative to the capacity at 1 C when an energy density of more than 100 Wh / kg and a power density of 10,000 W / kg or more is obtained.(12) A method for manufacturing an electrode for a secondary battery, comprising: surface-modifying active material particles having an average particle size of 2 to 1000 nm to prepare a dispersion of active material particles in which the surface-modified active material particles are dispersed; preparing a dispersion of carbon nanotubes; mixing the active material particle dispersion and the carbon nanotube dispersion so that the mass ratio of the carbon nanotubes to the total mass of the active material particles and the carbon nanotubes is 0.1 wt % or more to form a mixture; and applying the mixture to a substrate to obtain an electrode film. (13) The method for manufacturing an electrode for a secondary battery according to (12), wherein applying the mixture to a substrate to obtain an electrode film comprises filtering the mixture with a filter to obtain a filtration membrane. (14) The method according to (12) or (13), wherein the filter is a polytetrafluoroethylene membrane.

[0020] According to the present invention, it is possible to provide an electrode for a secondary battery that can achieve both high energy density and excellent high-rate charge / discharge characteristics.

[0021] FIG. 1 shows the particle size distribution of the active material in the active material dispersion liquid prepared in the Examples and Comparative Examples. FIG. 2 is a schematic diagram of the configuration of the battery used in the charge / discharge evaluation. FIG. 3 is an example of a discharge curve to explain how to determine the numerical value of the Ragone plot. FIG. 4 is a scanning electron microscope image of a binder-free electrode containing different amounts of single-walled carbon nanotubes prepared in the Examples. FIG. 5 is a graph showing the relationship between the C-rate and the capacity of a secondary battery prepared using a binder-free electrode containing different amounts of single-walled carbon nanotubes prepared in the Examples. FIG. 6 is a graph showing the relationship between the C-rate and the battery capacity depending on the concentration of the electrolyte of the secondary battery prepared in the Examples. FIG. 7 is a scanning electron microscope image of an electrode containing different amounts of active material prepared in the Examples. FIG. 8 is a graph showing the charge / discharge characteristics of the secondary battery prepared in the Examples and the C-rate characteristics of secondary batteries containing different amounts of active material. FIG. 9 is a graph showing the capacity change depending on the number of charge / discharge cycles of the secondary battery prepared in the Examples. FIG. 10 is a scanning electron microscope image of a binder-free electrode prepared in an example. FIG. 11 is a graph showing the charge / discharge curves and C-rate characteristics of a secondary battery equipped with a binder-free electrode prepared in an example. FIG. 12 is a graph showing the charge / discharge characteristics of a secondary battery prepared using a binder-free electrode prepared in an example and an aqueous electrolyte solution. FIG. 13 is a graph showing the charge / discharge curves and C-rate characteristics of a secondary battery equipped with a binder-free electrode prepared in an example. FIG. 14 is a scanning electron microscope image of (a) a binder-containing electrode prepared in a comparative example, and (b) a binder-free electrode prepared using an active material suspension in a comparative example. FIG. 15 is an example of a graph illustrating how to determine the slope of the plateau region from the differential curve of the discharge curve. FIG. 16 is a graph showing the C-rate characteristics of (a) a secondary battery prepared using a binder-containing electrode in a comparative example, (b) a secondary battery equipped with a binder-free electrode prepared using an active material suspension in a comparative example, and (c) a secondary battery prepared in an example. Fig. 17 is a Ragone plot showing the relationship between the energy density (capacity) and the power (output) density of the secondary batteries produced in the examples and comparative examples. Fig. 18 is a Ragone plot showing the relationship between the energy density (capacity) and the power (output) density of the secondary batteries produced in the examples and comparative examples, with the horizontal axis representing real numbers.Fig. 19 is a scanning electron microscope image of an electrode prepared in an example, observed from the surface. Fig. 20 is a scanning electron microscope image of an electrode prepared in a comparative example, observed from the surface. Fig. 21 is a scanning electron microscope image of a cross section of electrodes prepared in an example, each having a different loading amount. Fig. 22 is a graph showing the C-rate characteristics of (a) a secondary battery prepared using a binder-containing electrode of a comparative example, (b) a secondary battery including a binder-free electrode prepared using an active material suspension of a comparative example, and (c) a secondary battery prepared in an example.

[0022] The present disclosure relates to an electrode for a secondary battery, the electrode comprising: carbon nanotubes; and active material particles having an average particle size of 2 to 1000 nm dispersed and supported on the carbon nanotubes, wherein the mass ratio of the carbon nanotubes to the total mass of the active material particles and the carbon nanotubes is 0.1 wt % or more. In this application, "secondary battery" refers to an ion secondary battery.

[0023] The electrode disclosed herein can provide a secondary battery electrode that can achieve both high energy density and excellent high-speed charge / discharge characteristics. Specifically, the electrode disclosed herein can achieve both high energy density and excellent high-speed charge / discharge characteristics compared to electrodes produced by conventional processes. The conventional process specifically refers to a suspension process, which refers to a process in which an active material dispersion and a conductive additive dispersion are mechanically mixed, such as by ultrasonic cleaning. The method described in Non-Patent Document 7 is a suspension process in which active material particles are mixed with a carbon nanotube dispersion and stirred while ultrasonically treating to produce an electrode. Furthermore, the electrode disclosed herein can achieve both high energy density and excellent high-speed charge / discharge characteristics compared to conventional binder-containing electrodes. The conventional binder-containing electrode refers to an electrode that contains a binder in addition to the active material and conductive additive to form the electrode.

[0024] The presently disclosed secondary battery electrode (hereinafter also referred to as the present electrode) includes an electrode matrix composed of carbon nanotubes and active material particles, in which active material nanoparticles, which function as a conductive additive, are dispersed among the carbon nanotubes at a high mass ratio (high density) relative to the mass of the carbon nanotubes. Furthermore, the present electrode can maintain an electrode structure including active material nanoparticles dispersed among the carbon nanotubes without requiring an organic binder. The present electrode has well-dispersed active material particles, can have a low content of carbon nanotubes as a conductive additive, and does not require a binder, allowing for a porous electrode matrix. This ensures good contact between the electrolyte and the active material particles, resulting in an unprecedentedly excellent secondary battery electrode that can fully demonstrate its electrode function.

[0025] The electrode can have a configuration in which active material particles are well dispersed and bridged by carbon nanotubes. Because the electrode contains active material nanoparticles at a high mass ratio (high density) dispersed in carbon nanotubes without requiring a binder, the mass ratios of the active material and conductive additive in the electrode, particularly the mass ratio of the active material, can be made higher than in conventional electrodes.

[0026] Furthermore, because this electrode does not require an organic binder, it is possible to prevent the organic binder from adhering to the crystalline surface of the active material nanoparticles, thereby preventing a decrease in the contact area between the active material nanoparticles and the electrolyte solution (hereinafter also referred to as the electrolyte). This allows the electrode to fully utilize the active material nanoparticles more than ever before, and allows electrons to be efficiently transferred from the active material nanoparticles to the carbon nanotubes with low resistance. Furthermore, because this electrode does not require an organic binder, it is also possible to prevent the binder from interfering with the structural distortion (volume change) of the active material that accompanies ion insertion and removal.

[0027] The new electrode structure of this electrode maintains an appropriate amount of space for the electrolyte solution to penetrate, allowing each active material nanoparticle to efficiently contact the electrolyte solution. In addition, the carbon nanotubes, which act as a conductive additive, act to transfer electrons to and from the active material nanoparticles with low resistance.

[0028] Because the present electrode has the above-described structure and function, it is an electrode for a secondary battery that can utilize the inherent high-rate charge / discharge capability of the active material and achieves both high energy density and excellent high-rate charge / discharge characteristics. The present electrode also achieves a capacity of preferably 85% or more, more preferably 90% or more, even more preferably 95% or more, and even more preferably substantially 100% of the theoretical capacity.

[0029] The active material particles contained in the present electrode can have a shape such as spherical, polygonal, wire-like, plate-like, or irregular.

[0030] The active material particles contained in the present electrode have an average particle size of 2 to 1000 nm, preferably 10 to 800 nm, more preferably 20 to 600 nm, and even more preferably 30 to 500 nm.

[0031] The average particle size of the active material particles within the above range is advantageous for high-speed charge / discharge of the battery due to a shorter ion diffusion distance; the large surface area of ​​the active material particles increases the contact area with the electrolyte solution, which is advantageous for high-speed charge / discharge; and the reduction of lattice strain stress in the active material is advantageous for high-speed charge / discharge and improved cycle characteristics. Meanwhile, conventionally, small particle sizes of active material particles have been prone to aggregation and disruption of the electron conduction pathway, necessitating an increased content of conductive additive. However, in this electrode, the active material particles and carbon nanotubes are well dispersed within the electrode, and each active material particle is fixed in a dispersed state within the carbon nanotube network. Therefore, this electrode can achieve both ion migration pathways and electron conduction pathways even with a low carbon nanotube content. The average particle size of the active material particles is the equivalent circle diameter measured based on SEM images. The equivalent circle diameter is the diameter of the smallest circle surrounding the particle.

[0032] The carbon nanotubes contained in this electrode may be single-walled carbon nanotubes (SWNTs) or relatively inexpensive multi-walled carbon nanotubes (MWNTs), but are preferably single-walled carbon nanotubes. Because single-walled carbon nanotubes are thinner than multi-walled carbon nanotubes, they are more likely to be bundled, allowing the overall length of the bundles to be increased, thereby further improving the electronic conductivity of the electrode. The carbon nanotubes may be commercially available, such as TUBALL (registered trademark) manufactured by OCSiAl. Alternatively, commercially available carbon nanotubes with substituents such as carboxylic acid groups or amino groups introduced onto their surfaces may be used, or may be appropriately synthesized and used.

[0033] The method for producing carbon nanotubes is not particularly limited, but may be, for example, single-walled carbon nanotubes produced by the eDIPS (enhanced direct injection pyrolytic synthesis) method. Single-walled carbon nanotubes produced by the eDIPS method are preferable because they have excellent crystallinity and conductivity. The eDIPS method is a type of catalyst / gas contact reaction method that is an advanced version of the gas-phase flow method, which is a type of chemical vapor deposition (CVD) method, and is a method for synthesizing carbon nanotubes by a continuous method without using a substrate.

[0034] The carbon nanotubes contained in the electrode may have a diameter of 1 to 3 nm, a length of about 5 μm to 1 mm, and an aspect ratio of about 1667 to 10,000.

[0035] The carbon nanotubes contained in this electrode are preferably present in the form of bundles of multiple nanotubes. The carbon nanotubes are elongated by bundling, allowing the carbon nanotubes to form continuous paths, further improving the electronic conductivity of the electrode. The number of carbon nanotubes adjacent in the diameter direction that make up a bundle can be approximately 2 to 500. Furthermore, the elongated carbon nanotubes are well entangled with the active material particles, allowing the electrode structure to be maintained without the use of an organic binder.

[0036] (Mass Ratio of Carbon Nanotubes Contained in Electrode) The mass ratio of carbon nanotubes to the total mass of the active material particles and carbon nanotubes in the electrode is 0.1 wt% or more, preferably 0.5 wt% or more, more preferably 1.0 wt% or more, even more preferably 1.5 wt% or more, and even more preferably 2.0 wt% or more. Because the electrode has excellent dispersibility of the active material particles, it can have good electronic and ionic conductivity even with a small mass ratio of carbon nanotubes functioning as a conductive additive. Therefore, the lower limit of the mass ratio of carbon nanotubes can be set to a small range of 0.1 wt% or more, and better C-rate characteristics can be obtained within the above preferred range. Furthermore, in the electrode, the mass ratio of carbon nanotubes functioning as a conductive additive can be reduced to about one-tenth or less compared to conventional electrode fabrication methods in which an active material, a conductive additive, and an organic binder are kneaded. This allows for a relatively large proportion of active material particles in the electrode, resulting in better electrode properties than conventional methods. Furthermore, the proportion of relatively expensive carbon nanotubes can be reduced, thereby reducing the cost of the electrode.

[0037] In this electrode, even if the mass ratio of carbon nanotubes in the electrode is increased, the battery capacity per unit mass of the active material can be maintained at a constant value, so there is no particular upper limit to the mass ratio of carbon nanotubes. However, if the mass ratio of carbon nanotubes to the active material is too high, the effect as a conductive additive saturates and the battery capacity per unit volume of the electrode decreases, so the mass ratio of carbon nanotubes to the mass of the active material particles may be 25 wt% or less, 20 wt% or less, 15 wt% or less, 10 wt% or less, 5 wt% or less, 4 wt% or less, or 3 wt% or less.

[0038] In the present electrode, the ratio of the number of primary particles to the total number of active material particles is preferably 70% or more, more preferably 75% or more, even more preferably 80% or more, and even more preferably 85% or more. When the ratio of the number of primary particles is within the above preferred range, the individual active material particles are better dispersed in the network made of carbon nanotubes, and better battery capacity and high-rate charge / discharge characteristics can be obtained.

[0039] Using a scanning electron microscope (SEM), particles are observed at a magnification that allows the particle shapes to be clearly seen. Particles with clear outlines are judged to be primary particles (isolated particles), while particles with overlapping particles and unclear outlines are judged to be agglomerated particles. Figures 19 and 20 show examples of particles judged to be primary particles and agglomerated particles. Figure 19 is an SEM image of the electrode observed from the surface, and Figure 20 is an SEM image of an electrode produced by a conventional suspension process observed from the surface. Particles surrounded by solid lines are judged to be primary particles, and particles surrounded by dashed lines are judged to be agglomerated particles. Having the ratio of the number of primary particles to the total number of active material particles within the preferred range means that the active material particles are more monodispersed in the electrode, resulting in an electrode with better performance. The proportion of the number of primary particles can be calculated by measuring the number of primary particles and the number of agglomerated particles based on an SEM image and using the following formula (1): proportion of the number of primary particles (%) = (number of primary particles) / (number of primary particles + number of agglomerated particles) × 100 (1).

[0040] The CV value (distribution: (σ1 / D1) × 100) of the interparticle distance of the active material particles contained in this electrode is preferably 40% or less, more preferably 20% or less, even more preferably 10% or less, and even more preferably 5% or less. D1 is the average value of the interparticle distance, and σ1 is its standard deviation. A CV value of the interparticle distance in the above-mentioned preferred range means that the active material particles are better dispersed in the electrode, and an electrode with better performance can be obtained. The interparticle distance can be measured by measuring the distance between the centers of gravity using Voronoi regions.

[0041] The CV value (particle size distribution: (σ2 / D2)×100) of the average particle size of the active material particles contained in this electrode is preferably 40% or less, more preferably 20% or less, even more preferably 10% or less, and even more preferably 5% or less. D2 is the average value of the average particle size, and σ2 is its standard deviation. By having the average particle size within this preferred range, the active material particles can be dispersed more densely and uniformly in the electrode.

[0042] Because the electrode can maintain its shape and characteristics without the need for a binder, it may contain a binder, but preferably does not. By not including a binder, it is possible to prevent the binder from inhibiting ionic and electronic conduction in the active material. Furthermore, for active materials that undergo large volume changes upon ion insertion and extraction, adhesion of a binder to the surface can inhibit the volume change, thereby degrading high-speed charge / discharge performance and lifespan. However, by not including a binder, it is possible to improve high-speed charge / discharge performance and cycle characteristics (lifespan) without inhibiting the volume change. By not including a binder, the volume ratio occupied by the active material and carbon nanotubes in the electrode can be increased, resulting in an electrode with superior performance.

[0043] The active material particles contained in the present electrode are dispersed relatively uniformly in the electrode, thereby improving the battery capacity and high-speed charge / discharge characteristics.

[0044] The active material particles contained in the present electrode may have a positive or negative surface charge (zeta potential). By having the active material particles have a positive or negative surface charge (zeta potential), in the step of preparing a dispersion of active material particles in the method for producing the present electrode described below, the active material particles repel each other, resulting in a good dispersion as primary particles with few agglomerates. Then, by mixing a dispersion in which the active material particles are well dispersed as primary particles with a dispersion of carbon nanotubes, an electrode in which the active material particles are dispersed as primary particles in a carbon nanotube matrix can be obtained. The surface charge can be imparted to the active material particles by a surface charge imparting treatment using a dispersant in the method for producing the present electrode described below. The positive or negative surface charge (zeta potential) of the active material particles can be measured by DLS for the dispersion of the active material particles. The active material particles can be isolated from the electrode and dispersed in an organic solvent such as water or alcohol, and the positive or negative surface charge (zeta potential) of the active material particles can be measured by DLS. The optimum surface charge (zeta potential) for dispersing the active material particles well as primary particles varies depending on the material, shape, and size of the active material particles, but the surface charge (zeta potential) is greater in absolute value than when the above-mentioned surface charge imparting treatment is not performed, and is, for example, −30 to −150 mV.

[0045] Alternatively, the active material particles included in the present electrode may have surface-modifying molecules. The surface-modifying molecules are molecules that have affinity for the solvent of the dispersion liquid used in the affinity treatment method, which may be the solvent used in the electrode fabrication method described below. By having the surface-modifying molecules, the active material particles can be well dispersed in the electrode as primary particles with few agglomerates in the dispersion liquid. Then, by mixing a dispersion in which the active material particles are well dispersed as primary particles with a dispersion of carbon nanotubes, an electrode can be obtained in which the active material particles are dispersed as primary particles in the carbon nanotube matrix. Preferably, the surface-protecting molecules of the active material particles are substances that do not inhibit the intercalation and deintercalation of electrolyte ions. Examples of such surface-protecting molecules include water-soluble polymers such as Nafion, polyvinylpyrrolidone, polyvinyl alcohol, polystyrene sulfonic acid, polyvinyl acetate, polyethylene glycol, and Demol N; sodium bis(2-ethylhexyl) sulfosuccinate; polymethyl methacrylate; and polyoxyethylene nonylphenyl ethers.

[0046] When the active material particles have a negative surface charge (negative zeta potential), the Li in the electrolyte is ＋ , Na ＋ , K. ＋ It is preferable in that it can electrostatically attract cations such as

[0047] The active material particles contained in this electrode can be made of any active material that can be used as an active material for ion secondary batteries. Examples of active material include Prussian blue (PB) or its analogues (PBA), metal-organic frameworks (MOFs) with various transition metal ions as their frameworks, lithium cobalt oxide (LiCoO), lithium nickel oxide (LiNiO), lithium manganese oxide (LiMnO), and LiCo. 1 / 3 Ni 1 / 3 Mn 1 / 3 O2, Li 1+x Mn 2-x-y M y Lithium-Mn spinel substituted with different elements having a composition represented by the formula O4 (where M is one or more metal elements selected from Al, Mg, Co, Fe, Ni, Zn, etc.), lithium titanate (Lix TiO y transition metal oxides such as lithium metal phosphate (LiMPO4, where M is Fe, Mn, Co, or Ni), vanadium oxide (VO) and molybdenum oxide (MoO3), transition metal phosphate compounds, transition metal sulfides such as titanium sulfide (TiS2), carbon materials such as graphite and hard carbon, transition metal carbides, and transition metal nitrides such as lithium cobalt nitride (LiCoN).

[0048] The active material particles contained in this electrode are preferably particles of Prussian blue (PB) or its analog (PBA). Prussian blue or its analog is a porous coordination polymer similar to MOF, characterized by its porosity and rapid ion diffusion rate within the pores. By suppressing structural distortion through the metal composition, stress due to ion intercalation and deintercalation can be reduced. Therefore, an electrode containing Prussian blue or its analog as an active material can achieve a discharge capacity relatively close to the theoretical capacity.

[0049] Prussian blue and its analogues are Li ＋ , Na ＋ , K. ＋ Alkali metal ions and alkaline earth metal ions such as Mg ２＋ , Ca ２＋ In addition to Zn ２＋ and Al ３＋The Prussian blue analogs can insert and extract multivalent ions such as Fe, Mn, Zn, and Cu. Furthermore, Prussian blue analogs can have a wide variety of metal compositions, for example, by combining two or more transition metals or typical metals such as Fe, Mn, Zn, and Cu, allowing them to be synthesized inexpensively. The Prussian blue analogs are preferably Fe-Zn Prussian blue or its analogs (hereinafter also referred to as Fe-ZnPBA or ZnPBA), Fe-Mn Prussian blue or its analogs (hereinafter also referred to as Fe-MnPBA or MnPBA), or Fe-Cu Prussian blue or its analogs (hereinafter also referred to as Fe-CuPBA or CuPBA). By containing a variety of metals, Prussian blue analogs are less susceptible to structural distortion. By using Fe-MnPBA particles as the active material, it is possible to obtain a high-rate charge / discharge secondary battery with a higher capacity than Fe-ZnPBA, exceeding 100 mAh / g. Furthermore, by using metals such as Li, Na, K, Mg, Ca, and Al as the counter electrode in addition to Zn, a metal ion secondary battery with higher voltage and higher energy density can be obtained. Furthermore, as the active material, a redox-active organic substance that is insoluble in the electrolyte solution, such as 3,4,9,10-perylenetetracarboxylic acid diimide, can also be used.

[0050] Fe-ZnPBA has a theoretical capacity of 55 to 75 mAh / g. ｘ [Fe(CN) ６ ] ｙ The Fe-ZnPBA has the basic composition of K contained in the electrolyte solution. ＋ and Na ＋ In Fe-ZnPBA, only iron is a redox site and can store electrical energy, but Zn ｘ By substituting Mn, Fe, or the like, oxidation-reduction of Mn, Fe, or the like is added, making it possible to store even greater electrical energy and increase the capacity.

[0051] Fe-MnPBA has a large theoretical capacity of 150-170 mAh / g. ｘ [Fe(CN) ６ ] ｙThe Fe-MnPBA has the basic composition of K contained in the electrolyte solution. ＋ and Na ＋ For example, when used as a positive electrode of a Zn-ion battery, MnPBA can be used as a Zn-ion positive electrode. ２＋ and 2M K ＋ In a mixed electrolyte solution consisting of ＋ The electrode can be inserted and removed at high speed, and is also capable of high-speed charging and discharging. For example, at 100C, it exhibits an energy density of 60 Wh / kg or more (140 Wh / kg), a power density of 10,000 W / kg or more (23,000 W / kg), and a capacity retention rate of 60% or more. At 150C, it exhibits an energy density of over 100 Wh / kg (126 Wh / kg) and a power density of 10,000 W / kg or more (34,000 W / kg). Even after 80 cycles at 100C, it exhibits an energy density of 120 Wh / kg or more, a power density of 32,000 W / kg or more, and an excellent capacity retention rate of 60% or more. ２＋ and 2M Na ＋ Similar battery characteristics can be obtained with a mixed electrolyte solution consisting of the following: The capacity retention rate is the ratio of the capacity to the capacity at 1 C and 1 cycle.

[0052] Fe-CuPBA has a theoretical capacity of 50-70 mAh / g. ｘ [Fe(CN) ６ ] ｙ The Fe-CuPBA has the basic composition of K contained in the electrolyte solution. ＋ and Na ＋ For example, when used as a positive electrode of a Zn-ion battery, CuPBA can be used as a positive electrode for 1M Zn. ２＋ and 2M K ＋ In a mixed electrolyte solution consisting of K ＋ In a battery using CuPBA as a positive electrode, an energy density of 60 Wh / g or more and a power density of 35,000 W / kg or more can be obtained even after 100 cycles at 500C.

[0053] The thickness of the electrode is not particularly limited, but is, for example, about 0.5 to 100 μm.

[0054] The electrode of the present disclosure can fully function as an electrode when used in a secondary battery, while the oxidation-reduction reaction at the counter electrode can be rate-determining. Therefore, by adjusting the amount of active material carried in the electrode of the present disclosure, the rate characteristics of the secondary battery can be further improved. The amount of active material carried can be adjusted depending on the purpose and is not particularly limited, but is preferably 0.1 to 1.0 mg / cm ２ For example, when the amount of the active material carried is 1.0 mg / cm ２ In this case, the secondary battery can have a capacity retention rate of 90% or more up to 300 C and 80% or more up to 400 C, and the amount of the active material carried is 0.5 mg / cm ２ In the following cases, the secondary battery can have a capacity retention rate of 90% or more up to 1000C.

[0055] In conventional secondary batteries, increasing the C-rate causes the ion transfer rate at the positive electrode to be unable to keep up. However, in secondary batteries using this electrode, increasing the C-rate causes the counter electrode's oxidation-reduction rate to be unable to keep up, limiting the battery performance. Therefore, in secondary batteries using this electrode, if the amount of active material carried in this electrode is reduced according to the oxidation-reduction rate of the counter electrode, the capacity can be maintained even at a high C-rate. If a counter electrode with an improved oxidation-reduction rate, for example by increasing the surface area, can be obtained so that the function of this electrode can be fully utilized, the capacity can be maintained at a high C-rate even if the amount of active material carried in this electrode is increased. In this way, this electrode is the only electrode that can fully utilize the performance of the positive electrode material in secondary batteries.

[0056] Secondary batteries equipped with electrodes according to the present disclosure have excellent high-rate charge / discharge characteristics (C-rate characteristics), and can retain high capacities preferably up to 100 C, more preferably up to 200 C, even more preferably up to 400 C, even more preferably up to 600 C, and even more preferably up to 1000 C. They can retain capacities of preferably 60% or more, more preferably 70% or more, even more preferably 75% or more, even more preferably 80% or more, even more preferably 85% or more, and even more preferably 90% or more of the capacity at 1 C. In this specification, C-rate characteristics are evaluated based on the capacity at 1 C. The reason for using the capacity at 1 C as the reference rather than the theoretical capacity is that there may be some discrepancy between the designed amount of active material supported and the amount of active material actually supported in the electrode, but this discrepancy in the amount of supported material does not affect the evaluation of C-rate characteristics. In secondary batteries using this electrode, the capacity at rates lower than 1 C, for example, 0.1 C, is substantially identical to the capacity at 1 C, and there is substantially no decrease in capacity in the range from above 0 C to 1 C.

[0057] A secondary battery including an electrode of the present disclosure preferably exhibits an energy density of 60 Wh / kg or more and a power density of 30,000 W / kg or more, more preferably an energy density of 70 Wh / kg or more and a power density of 30,000 W / kg or more, even more preferably an energy density of 80 Wh / kg or more and a power density of 30,000 W / kg or more, and even more preferably an energy density of 85 Wh / kg or more and a power density of 30,000 W / kg or more. A secondary battery including an electrode of the present disclosure also preferably exhibits an energy density of 120 Wh / kg or more and a power density of 10,000 W / kg or more, more preferably an energy density of 140 Wh / kg or more and a power density of 10,000 W / kg or more, and even more preferably an energy density of 160 Wh / kg or more and a power density of 10,000 W / kg or more.

[0058] The method for determining the numerical values ​​of the Ragone plot will be described with reference to FIG. 3. FIG. 3 shows an example of a discharge curve. The energy density (Wh / kg) is calculated based on the following formula (2): Energy density (Wh / kg) = V １ ×C １ (2) In the formula, V １(V) is the voltage when the capacitance is half in the graph of FIG. 20, and C １ is the discharge capacity (Ah / kg) in the graph of FIG.

[0059] The power density (W / kg) is calculated based on the following formula (3): Power density (W / kg) = V １ ×C １ / Y (3) In the formula, Y (hours) is a value obtained by converting the unit into hours by dividing the time (seconds) required for measurement by 3600.

[0060] A secondary battery including an electrode according to the present disclosure has a capacity retention rate C at 100 C relative to the capacity at 1 C. １００ / C １ However, it is preferably 60% or more, more preferably 70% or more, even more preferably 80% or more, and even more preferably 90% or more.

[0061] A secondary battery including an electrode according to the present disclosure preferably has a capacity retention rate of 80% or more when obtaining an energy density of 60 Wh / kg or more and a power density of 10,000 W / kg or more.

[0062] A secondary battery including an electrode according to the present disclosure preferably has a capacity retention rate of 60% or more when an energy density of more than 100 Wh / kg and a power density of 10,000 W / kg or more are obtained.

[0063] A secondary battery including an electrode of the present disclosure preferably has a capacity retention rate of 95% or more, more preferably 97% or more, of the theoretical capacity after 200 charge / discharge cycles at 400 C. A secondary battery including an electrode of the present disclosure also has a capacity retention rate of 85% or more, more preferably 90% or more, of the theoretical capacity after 50,000 charge / discharge cycles at 400 C. A secondary battery including an electrode of the present disclosure also has a capacity retention rate of 80% or more, more preferably 85% or more, of the theoretical capacity after 100,000 charge / discharge cycles at 400 C.

[0064] The present disclosure is also directed to a secondary battery comprising the above-described electrode, counter electrode, electrolyte solution, and current collector.

[0065] The solvent of the electrolyte solution contained in this secondary battery can be an organic solvent, water, or a mixture thereof. Organic solvents are preferred because they can easily suppress the formation of dendrites on the negative electrode, while water is preferred from an environmental perspective. Water can dissolve the electrolyte at a high concentration and has high ionic conductivity, so it is preferred for use. On the other hand, if a solvent consisting solely of water is used, the active material may easily dissolve in water, resulting in a decrease in battery performance. Therefore, a solvent in which water and an organic solvent are mixed at an appropriate volume ratio can also be used.

[0066] When water is used as a solvent, the metals that can be used in the negative electrode are limited. However, organic solvents are preferred because they allow various metals to be used in the negative electrode. From a safety perspective, self-extinguishing phosphate esters are preferred as organic solvents. Examples of mixed solvents include a solvent in which water and an organic solvent are mixed at an appropriate volume ratio (e.g., a mixed solvent of water and propylene carbonate). Furthermore, the use of mixed solvents allows for high-concentration dissolution of the electrolyte, increasing its ionic conductivity, while simultaneously preventing dissolution of the active material and suppressing dendrite formation. Furthermore, the inclusion of water and a high-concentration electrolyte can prevent the electrolyte solution from igniting. Organic solvents that dissolve the electrolyte salt can be water-soluble or water-insoluble organic solvents conventionally used as organic solvents for secondary batteries. Examples include phosphate esters such as triethyl phosphate, carbonate esters such as propylene carbonate, amides such as N,N-dimethylformamide, alkyl sulfoxides such as dimethyl sulfoxide, glycol ethers such as diglyme and triglyme, esters such as butyl acetate, and nitriles such as acetonitrile.

[0067] In this secondary battery, the electrolyte may be an aqueous electrolyte, an organic solvent electrolyte, an ionic liquid, a polymer electrolyte, a polymer gel electrolyte, a eutectic electrolyte, or a combination thereof, which exhibits fluidity that easily enters the pores and gaps in the electrode. The electrolyte salt dissolved in water or an organic solvent may be any of the electrolyte salts conventionally used in secondary batteries, such as trifluoromethanesulfonate, trifluoroacetate, di[bis(trifluoromethylsulfonyl)imide] salt, bis(fluorosulfonyl)amide salt, bis(pentafluoroethanesulfonyl)amide salt, hexafluorophosphate, tetrafluoroborate, acetate, chloride salt, perchlorate, sulfate, nitrate, etc. The salt may contain a desired alkali metal ion, alkaline earth metal ion, Al, ３＋ The electrolyte ion may be a salt of a typical metal ion, a transition metal ion, or a combination thereof. ２＋ , Ca ２＋ , Al ３＋ Electrodes in which multivalent cations with small atomic weights such as Li are inserted and removed can increase the capacitance, but the energy change of solvation / desolvation accompanying the insertion and removal into the electrode is large. ＋ , Na ＋ , and K ＋ is preferred in that it can easily realize high-speed charging and discharging. In addition, in order to insert and extract different cations into and from the positive electrode and the negative electrode, a mixed electrolyte solution in which two or more different cations are mixed in any ratio can also be suitably used.

[0068] The electrolyte concentration (electrolyte concentration in the electrolyte) is preferably 0.2 M or more, more preferably 0.3 M or more, even more preferably 0.8 M or more, and even more preferably 1 M or more. The higher the electrolyte concentration, the more the secondary battery can suppress capacity loss even at higher C-rates. For example, in this secondary battery, when the electrolyte concentration is 0.8 M or more, a capacity retention rate of 90% or more can be obtained at 100 C, and a capacity retention rate of 85% or more can be obtained at 200 C.

[0069] In this battery, a plateau region is clearly visible, even at high C. Furthermore, the higher the electrolyte concentration, the higher the voltage in the plateau region. At electrolyte concentrations of 0.8 M or higher, a plateau region is clearly visible even at 200 C. The slope of the plateau region is expressed as the voltage change (ΔV) per unit capacity change (Δbattery capacity (mAh / g)). At 100 C, this battery preferably has a plateau region slope of −0.0060 or less, more preferably −0.0050 or less, and even more preferably −0.0040 or less. In this application, the slope of the plateau region refers to the average slope of the central 60% range between inflection point 1 on the low-capacity side and inflection point 2 on the high-capacity side, as determined from the differential curve of the discharge curve, as shown in FIG. 15.

[0070] The counter electrode can be made of a metal or alloy material, such as an alkali metal such as lithium, sodium, or potassium, an alkaline earth metal such as magnesium or calcium, a Group 13 element such as aluminum, a transition metal such as zinc, iron, nickel, or copper, or an alloy material containing these metals. Preferably, the counter electrode is a metal foil made of zinc or aluminum. Ion secondary batteries using zinc or aluminum as the counter electrode are preferred because they can be used with water or a mixture of water and an organic solvent as the solvent for the electrolyte solution.

[0071] A current collector can be disposed adjacent to this electrode. The current collector to be disposed adjacent to this electrode is not particularly limited as long as it is made of a material that has conventionally been used as a current collector, such as a metal foil, or a porous structure, mesh structure, fiber, or nonwoven fabric, such as carbon paper, graphite paper, carbon cloth, metal mesh, or metal foam (foam). For example, a metal foil, mesh, or foam made of SUS, nickel, aluminum, iron, titanium, or the like can be used.

[0072] The current collector disposed adjacent to the counter electrode can be any material that has conventionally been used as a current collector, such as a porous conductive substrate or a non-porous metal foil, and can be any material that has conventionally been used as a current collector, such as a metal foil made of copper, SUS, nickel, or the like.

[0073] Preferably, the electrode described above is a positive electrode and the counter electrode is a negative electrode.

[0074] The present secondary battery can have the above-described preferable battery characteristics.

[0075] The present disclosure is also directed to a method for manufacturing an electrode for a secondary battery, the method comprising: surface-modifying active material particles having an average particle size of 2 to 1000 nm to prepare a dispersion of active material particles in which the surface-modified active material particles are dispersed; preparing a carbon nanotube dispersion; mixing the active material particle dispersion and the carbon nanotube dispersion so that the mass ratio of the carbon nanotubes to the total mass of the active material particles and the carbon nanotubes is 0.1 wt % or more to form a mixture; and filtering the mixture with a filter to obtain a filtration membrane.

[0076] According to this method, an active material nanoparticle dispersion in which active material nanoparticles have been pre-dispersed in a solvent such as water by chemical surface modification is mixed with a dispersion of carbon nanotubes, which serve as a conductive additive, and the mixture is then filtered to obtain an organic binder-free electrode in which the active material particles are well-dispersed and entangled with the carbon nanotubes. The method for preparing the active material particle dispersion in this method does not involve a physical method such as ultrasonication, but rather involves chemically modifying the surfaces of the active material nanoparticles in advance, allowing the active material nanoparticles to be dispersed in a solvent such as water.

[0077] The aggregated active material particles do not dissolve in water or organic solvents. However, in this method, by bonding protective molecules or ions to elements exposed on the surface of the active material particles, the surfaces of the active material particles are charged within a predetermined range, and the active material particles can be dispersed substantially independently without aggregation due to electrostatic repulsion.

[0078] The active material particles contained in this electrode are composited with carbon nanotubes using a dispersion in which the particles exist as primary particles in a solvent in which aggregation has been suppressed by surface modification in advance. A common method for obtaining a dispersion in which the active material particles are dispersed as primary particles can be used, and is not particularly limited. Preferred methods include the following (A) to (C): (A) a surface charge imparting treatment method in which a dispersant is added to a solvent in which the active material particles are dispersed to impart a positive or negative surface charge (zeta potential) to the active material particles, thereby dispersing them well in the solvent due to electrostatic repulsion; (B) a solvent affinity treatment method in which the particles are surface-modified with molecules that have affinity for the solvent, thereby dispersing them in the solvent; or (C) a method in which (A) and (B) are used together to disperse the active material particles.

[0079] The dispersant (charge-imparting molecule) used in method (A) can bind to available coordination sites exposed on the surface of the active material particles. Active material particles with the dispersant bound to the coordination site surface have a positive or negative surface charge, and can be dispersed as primary particles in a solvent due to electrostatic repulsion between particles. Depending on the material and surface area of ​​the active material particles, an amount of dispersant sufficient to coordinate with most of the available coordination sites on the active material particle surface can be added and thoroughly stirred. In this electrode, a dispersion of active material particles with a positive or negative surface charge prepared by method (A) can be directly mixed with a dispersion of carbon nanotubes and used. The positive or negative surface charge of the active material particles can be measured using DLS for the active material particle dispersion.

[0080] The dispersion prepared by method (B) can be used as is in an electrode as long as the surface-modifying molecules do not inhibit the ionic or electronic conduction of the active material particles. If the surface-modifying molecules inhibit the ionic or electronic conduction of the active material particles, the surface-modifying molecules can be removed by heat treatment within a temperature range that does not decompose the active material particles, or by washing the electrode with a solvent.

[0081] The above method can obtain a dispersion of active material particles well dispersed as primary particles. By using this dispersion, an electrode can be obtained in which the active material particles are well dispersed as primary particles with few particles in a state of agglomeration. The above method or the like can substantially independently disperse the active material particles, thereby obtaining a secondary battery with excellent battery capacity and high-speed charge / discharge characteristics.

[0082] The above methods (A) to (C) will be explained below using an example in which the active material particles are Prussian blue (PB).

[0083] The preparation of a dispersion of active material particles in which surface-modified active material particles are dispersed includes, for example, (a) mixing an aqueous solution containing an anionic metal cyano complex having a metal atom M1 as a central metal with an aqueous solution containing a metal cation of a metal atom M2 to precipitate crystals of a Prussian blue-type metal complex having a metal atom M1 and a metal atom M2, and then (b) mixing a solution in which a ligand L is dissolved in a solvent with the crystals of the Prussian blue-type metal complex to obtain a dispersion of Prussian blue-type metal complex ultrafine particles.

[0084] An example of method (B) is to use water (OH) coordinated with metal on the surface of PB particles. ２ When the alkyl chain-containing organic compound is substituted with an alkyl chain-containing organic compound, the hydrophobic interaction on the PB surface improves the affinity with the hydrophobic organic solvent, resulting in independent dispersion (dissolving in an ink-like state). In other words, the alkyl chain-containing organic compound is used as a dispersant. The alkyl chain-containing organic compound is preferably an alkylamine having an amino group.

[0085] An example of method (A) is a method in which ferrocyanide ions or ferricyanide ions are coordinated to metals on the surface of PB particles via cyanide ligands (OH ２ When the PB is substituted and bonded with PB, the surface charge of the PB becomes negative (it has a negative zeta potential), and the electrostatic repulsion between the particles allows the particles to be dispersed independently particularly well in water.

[0086] As an example of method (C), an organic compound having an alkyl chain can be appropriately mixed with ferrocyanide ions or ferricyanide ions to modify the surface, thereby enabling good dispersion in a hydrophilic organic solvent.

[0087] After electrode fabrication, surface-bound alkylamines and the like can be removed from the PB surface by heating at normal or reduced pressure at a temperature at which the PB does not thermally decompose if they are organic molecules with low vapor pressure. Alternatively, even organic molecules with high vapor pressure can be removed by thoroughly washing with a solvent that has weak coordination power for the surface metal, such as alcohols, nitriles, amides, sulfoxides, or fatty acids, which can facilitate the desorption and insertion of electrolyte ions into the PB nanoparticles. The washing solvent also needs to be removed after the removal of alkylamines and the like, so a low boiling point is desirable, but the solvent can also be washed and replaced with another low-boiling point solvent.

[0088] When the active material particles are Prussian blue or its analogs (PBA), the coordination sites exposed on the crystal surface that can bind to the dispersant vary depending on the particle size. A 10 nm cubic crystal has coordination sites equivalent to approximately 15 mol% of the total metal amount, and a 100 nm cubic crystal has coordination sites equivalent to approximately 1.5 mol% of the total metal amount. Simply add a sufficient amount of dispersant to cover the coordination sites on the crystal surface and stir.

[0089] Even when the active material particles are other than Prussian blue (PB), for example, when they are metal oxides, a dispersion of active material particles in which surface-modified active material particles are dispersed using the above-mentioned method can be prepared. For example, the nanoparticle powder can be dispersed in water by adding an aqueous solution of a surfactant such as sodium dodecyl sulfate (SDS) or sodium dodecylbenzenesulfonate (SDBS) to the metal oxide nanoparticle powder and stirring or ultrasonic treatment. Alternatively, an aqueous dispersion of the nanoparticle powder can be obtained by mixing and stirring the metal oxide nanoparticle powder with an aqueous solution of a polymer having a water-soluble functional group such as a carboxylic acid, such as polymethacrylic acid.

[0090] (Carbon Nanotube Dispersion) The carbon nanotube dispersion may be commercially available, such as TB004M manufactured by KJ Specialty Paper Co., Ltd., EC1.5 manufactured by Meijo Nano Carbon Co., Ltd., or 9487SW manufactured by Tokushiki Co., Ltd. The concentration of the carbon nanotube dispersion is preferably 0.005 to 5 wt %, more preferably 0.015 to 3 wt %. If desired, the carbon nanotube dispersion having the preferred concentration may be diluted and used. The carbon nanotube dispersion may be prepared by dispersing carbon nanotubes in water, an organic solvent, or a mixture thereof using a surfactant and, if desired, ultrasonic treatment.

[0091] (Method for Producing Electrode Film) The method for producing an electrode film from a mixture of a dispersion of active material particles and a dispersion of carbon nanotubes is not particularly limited. Preferably, the electrode film can be produced using a filtration method in which the mixture of the dispersion of active material particles and the dispersion of carbon nanotubes is filtered. The filtration method utilizes the filtration pressure when filtering the mixture to form a binder-free electrode that maintains its structure. Furthermore, the filtration and washing process can remove excess surfactant contained in commercially available carbon nanotube dispersions as well as excess dispersant used when producing the dispersion of active material particles. The filter used in the filtration method is preferably a chemically stable polytetrafluoroethylene (PTFE) membrane. The PTFE membrane on which the electrode film is formed by the filtration method can function as a separator when constructing a battery.

[0092] Alternatively, a mixture of a dispersion of active material particles and a dispersion of carbon nanotubes may be spray-coated onto a heated filter, followed by washing with water to remove the surfactant. Alternatively, if the mixture of the dispersion of active material particles and the dispersion of carbon nanotubes is in a high-concentration paste form, it may be directly applied to a current collector such as carbon paper. Prior to forming the electrode film, a high-concentration dispersion of active material particles and a high-concentration dispersion of carbon nanotubes may be mixed and stirred to entangle the active material particles with the carbon nanotubes, followed by centrifuging to remove excess surfactant contained in the carbon nanotube dispersion and excess dispersant used in preparing the dispersion of active material particles. The centrifuged mixture may then be mixed with various solvents and applied to a current collector such as carbon paper.

[0093] The present invention will be specifically explained below with reference to examples, but the present invention is not limited to these examples.

[0094] (Example 1) <Preparation of binder-free electrode of ZnPBA and its battery characteristics> (Synthesis of ZnPBA powder) 0.961 g (2.28 × 10 ―３ mol, Kanto Chemical Co., Inc., purity 99.0% or higher) was dissolved in 10 ml of distilled water, and 1.36 g (4.56 × 10 ―３ mol, Kanto Chemical Co., Inc., purity 99.5% or more) was dissolved in 10 ml of distilled water, and the two were mixed and stirred for 1 hour. Then, after centrifuging (4000 rpm, 2600 × g, 15 minutes), the mixture was washed 10 times with distilled water and dried under reduced pressure to obtain ZnPBA powder. The composition of the obtained ZnPBA powder was K ０．６５ Zn １．７４ [Fe(CN) ６ ]・3.81H ２ The theoretical capacity was 63.9 Ah / g.

[0095] (Preparation of ZnPBA Dispersion) 0.29 g of the obtained ZnPBA powder was added with 5 ml of an aqueous solution of sodium hexacyanoferrate (II) decahydrate as a dispersant, which was 5.1 mol% of the total metal amount of ZnPBA, and the mixture was stirred for 2 weeks to obtain a dispersion of sodium-containing ZnPBA. The composition of the obtained sodium-containing ZnPBA was ０．１６ K ０．６５ Zn １．７４ [Fe(CN) ６ ] １．０４ ・3.81H ２ The theoretical capacity was 64.5 mAh / g. The sodium-containing ZnPBA has a structure in which ferrocyanide ions are coordinated to metals located on the surface of the ZnPBA.

[0096] (Analysis of ZnPBA Dispersion) The obtained 5.1 mol % coated ZnPBA dispersion was subjected to dynamic light scattering measurement and zeta potential measurement (Otsuka Electronics Co., Ltd., ELSZ-2000).

[0097] The particle size (diameter) distribution of ZnPBA measured by dynamic light scattering is shown by the solid line in Figure 1. The particle size (diameter) in the dispersion was about 150 to 200 nm, and since the size of the single crystal of ZnPBA was about 150 to 200 nm, it can be seen that a substantially monodisperse ZnPBA dispersion was obtained.

[0098] Zeta potential measurement revealed that the ZnPBA particles had a negative charge of −46.7 mV. It was found that the large surface charge of the ZnPBA particles caused them to repel each other, suppressing aggregation and achieving high dispersion.

[0099] (Preparation of ZnPBA binder-free electrode) The obtained ZnPBA dispersion and a single-walled carbon nanotube (SWNT) dispersion (0.4 wt%, KJ Specialty Paper Co., Ltd., TB004M) were mixed to prepare a binder-free electrode having a SWNT content of 3.0 wt% and a ZnPBA loading of 1.0 mg / cm. ２ The amount of SWNT is the ratio of the mass of SWNT to the total mass of SWNT and ZnPBA.

[0100] 19 shows an SEM image of the electrode surface. The particles surrounded by the solid line were determined as primary particles, and the particles surrounded by the dashed line were determined as aggregated particles. The ratio of the number of primary particles to the total number of active material particles was calculated based on the above formula (1). The ratio of the number of primary particles was 87%.

[0101] The resulting mixture was suction filtered onto a PTFE membrane filter (pore size 0.1 μm, Sumitomo Electric Industries, Ltd., HPW-010-30) and heated at 120° C. to obtain a ZnPBA binder-free electrode.

[0102] (Preparation of Negative Electrode) A counter electrode (negative electrode) was prepared by polishing Zn foil (0.1 mm thick, Takeuchi Metal Foil & Powder Co., Ltd., 99.99%) with waterproof abrasive paper (Sankyo Rikagaku, #1500).

[0103] (Preparation of Electrolyte) 4 M sodium trifluoromethanesulfonate (NaOTf) (Tokyo Chemical Industry Co., Ltd.) and 1 M zinc trifluoromethanesulfonate (Zn(OTf)) were added to a mixed solvent of propylene carbonate (Kanto Chemical Co., Ltd.) and distilled water (propylene carbonate:distilled water = 7:3). ２ ) (Tokyo Chemical Industry Co., Ltd.) were mixed to prepare an electrolyte solution.

[0104] (Preparation of Secondary Battery) The prepared ZnPBA binder-free electrode was used as the positive electrode, the prepared negative electrode, the prepared electrolyte, the PTFE membrane filter used for filtration of the electrode as a separator, and carbon paper (Mitsubishi Chemical Corporation, MFO) as a current collector. ＋ The deintercalation of Zn occurs at the negative electrode. ２＋ We fabricated an ion secondary battery driven by the dissolution / precipitation of . Figure 2 shows a schematic diagram of the secondary battery configuration.

[0105] Examples 2 to 7 Secondary batteries were fabricated in the same manner as in Example 1, except that the amount of SWNT was changed to 0.1 wt %, 0.5 wt %, 1.0 wt %, 1.5 wt %, 5.0 wt %, and 10.0 wt %.

[0106] Figure 4 shows scanning electron microscope (SEM) images (JEOL Ltd., JSM-7600F) of ZnPBA binder-free electrodes containing different SWNT amounts. Figure 4 shows scanning electron microscope images of ZnPBA binder-free electrodes containing 0.1 wt%, 3.0 wt%, and 10.0 wt% SWNTs, prepared in Examples 1, 2, and 7. It is clear from Figure 4 that when the SWNT amount is 0.1 to 3 wt%, most of the ZnPBA active material particles exist as primary particles, with linear SWNTs woven throughout the ZnPBA primary particles. Even when the SWNT amount is 10 wt%, most of the ZnPBA active material particles exist as primary particles, but the area ratio occupied by the SWNTs is high, and the ZnPBA primary particles appear to be embedded within the SWNTs.

[0107] (Exclusive Area Ratio of Primary Particles) The exclusive area ratio of ZnPBA primary particles in electrodes with different SWNT amounts was determined using the SEM image in Figure 4 and the following formula (4). Table 1 shows the exclusive area ratio of ZnPBA primary particles in ZnPBA binder-free electrodes containing 0.1 to 20 wt% SWNTs produced in Examples 1, 2, 6, and 7. Primary particles are non-aggregated particles whose outlines can be clearly recognized in SEM photographs. Exclusive area ratio (%) = [(existing area of ​​primary particles) / (observed area)] x 100 (4)

[0108]

[0109] When the SWNT amount was 0.1 to 3 wt%, individual ZnPBA particles were clearly visible, and the ZnPBA primary particles showed an area ratio of approximately 90%. When the SWNT amount was 10 wt%, ZnPBA primary particles were also clearly visible, but the area ratio occupied by SWNTs was large, and the area ratio of the ZnPBA primary particles was 34%.

[0110] Examples 8 to 14: NaOTf and Zn(OTf) electrolytes ２ Secondary batteries were fabricated in the same manner as in Example 1, except that the concentrations of the aqueous solutions of 1, 2, 3, 4, 5, 6, 7, and 8 M were set to 0.1 M, 0.2 M, 0.3 M, 0.5 M, 0.6 M, 0.7 M, and 0.8 M, respectively.

[0111] Example 15: NaOTf and Zn(OTf) in electrolyte２ A secondary battery was fabricated in the same manner as in Example 1, except that the concentrations of each of the above were set to 1 M, and a mixed solvent of propylene carbonate (hereinafter also referred to as PC) and distilled water (hereinafter also referred to as water) (propylene carbonate:distilled water=9:1) was used.

[0112] (Example 16) The concentration of NaOTf in the electrolyte was set to 2 M, and Zn(OTf) ２ A secondary battery was fabricated in the same manner as in Example 1, except that the concentration of the electrolyte was set to 1 M and a mixed solvent of propylene carbonate and distilled water (propylene carbonate:distilled water=9:1) was used.

[0113] (Examples 17 to 19) The amount of active material carried was 0.75 mg / cm ２ , 0.5 mg / cm ２ , and 0.25 mg / cm ２ Except for this, secondary batteries were fabricated in the same manner as in Example 5. The amounts of the active materials supported were obtained by reducing the mixed amounts of the same ZnPBA dispersion and SWNT dispersion used in Example 5 to 75%, 50%, and 25%, respectively, while maintaining the mixing ratio.

[0114] 7 shows scanning electron microscope (SEM) images of the surfaces of the electrodes prepared in Examples 5 and 17 to 19, each having a different amount of ZnPBA active material carried thereon. ２ , (b) 0.5mg / cm ２ , (c) 0.75mg / cm ２ , and (d) 1.0 mg / cm ２ 21 shows SEM images of ZnPBA binder-free electrodes with active material loadings of 1000 to 10 ...

[0115] (Example 20) The concentration of NaOTf in the electrolyte was set to 2 M, and Zn(OTf) ２A secondary battery was fabricated in the same manner as in Example 19, except that the concentration of the propylene carbonate solution was set to 1 M and a mixed solvent of propylene carbonate and distilled water (propylene carbonate:distilled water=9:1) was used.

[0116] Example 21 A secondary battery was fabricated in the same manner as in Example 15, except that the amount of the dispersant was set to 13.7 mol %.

[0117] Comparative Example 1 A secondary battery was fabricated in the same manner as in Example 1, except that the amount of SWNT was set to 0.05 wt %.

[0118] (Comparative Example 2) <Production of ZnPBA binder-free electrode using suspension and battery characteristics> (Preparation of ZnPBA suspension) 20 ml of distilled water was added to 0.29 g of ZnPBA powder obtained by the same method as in Example 1, and the mixture was treated for 1 hour using an ultrasonicator (ASONE, MCD-2P) to obtain a ZnPBA suspension.

[0119] (Analysis of ZnPBA Suspension) The obtained ZnPBA suspension was subjected to dynamic light scattering measurement and zeta potential measurement (Otsuka Electronics Co., Ltd., ELSZ-2000).

[0120] The particle size (diameter) distribution of ZnPBA measured by dynamic light scattering is shown by the dashed line in Figure 1. The ZnPBA particles had a negative charge of -23.1 mV, but the repulsive force between them was small, and the particle sizes ranged from 400 to over 10,000 nm, with the presence of aggregates.

[0121] (Preparation of ZnPBA binder-free electrode) The obtained ZnPBA suspension and a single-walled carbon nanotube (SWNT) dispersion (0.4 wt%, KJ Specialty Paper Co., Ltd., TB004M) were mixed to prepare a binder-free electrode having a SWNT content of 3.0 wt% and a ZnPBA loading of 1.0 mg / cm. ２ The mixture was mixed in the amounts shown below to obtain a mixed solution.

[0122] 20 shows an SEM image of the electrode surface. The particles surrounded by the solid line were determined as primary particles, and the particles surrounded by the dashed line were determined as aggregated particles. The ratio of the number of primary particles to the total number of active material particles was calculated based on the above formula (1). The ratio of the number of primary particles was 22%.

[0123] The resulting mixture was suction filtered through a PTFE membrane filter (pore size 0.1 μm, Sumitomo Electric Industries, Ltd., HPW-010-30) and heated at 120° C. to obtain a ZnPBA binder-free electrode. A secondary battery was produced using the resulting electrode in the same manner as in Example 15.

[0124] (Comparative Example 3) <Preparation of ZnPBA binder-containing electrode and battery characteristics> (Isolation of surface-coated ZnPBA) The ZnPBA (coating amount 5.1 mol%) dispersion prepared in Example 1 was centrifuged (15,000 rpm, 22,400 × g, 10 minutes) to isolate ZnPBA powder.

[0125] (Preparation of Binder-Containing Electrode) 21 mg of the isolated ZnPBA powder, 3.0 mg of polyvinylvinylidene fluoride (PVDF, Sigma-Aldrich, weight-average molecular weight Mw ∼ 523,000), 6.3 mg of SuperP (MTI Corporation), which is a particulate conductive carbon particle, and 200 μL of 1-methyl-2-pyrrolidone (Sigma-Aldrich) were mixed and mixed for 4 hours using an automatic mortar (AMM-140D, Nitto Kagaku Co., Ltd.) to obtain a paste. The mass ratio of ZnPBA:SuperP:PVDF was 7:2:1. The obtained paste was applied to carbon paper and dried by heating (120 °C, 1 hour) to prepare a binder-containing ZnPBA electrode. A secondary battery was prepared using the obtained electrode in the same manner as in Example 15. The amount of ZnPBA supported was 1.0 mg / cm ２ It was.

[0126] 14 shows (a) an SEM image of the binder-containing ZnPBA electrode prepared in Comparative Example 3, and (b) an SEM image of the ZnPBA binder-free electrode prepared using the ZnPBA suspension prepared in Comparative Example 2. In the binder-containing ZnPBA electrode of Comparative Example 3, the particulate conductive carbon particles and the ZnPBA particles segregated and were separated from each other. In the ZnPBA binder-free electrode prepared using the ZnPBA suspension of Comparative Example 2, ZnPBA aggregates were observed, and this result agrees with the results of dynamic light scattering measurement (dashed line in FIG. 1 ).

[0127] The occupied area ratio of the primary particles in the electrodes prepared in Comparative Examples 2 and 3 was calculated using the above formula (4). Table 2 shows the occupied area ratio of the primary particles of ZnPBA in the electrodes prepared in Comparative Examples 2 and 3.

[0128] The binder-containing electrode of Comparative Example 3, which included a dispersion step and a kneading step by surface treatment, had relatively good dispersibility, and the area ratio of primary particles was 37.5%. On the other hand, the binder-free electrode of Comparative Example 2, which was produced using a ZnPBA suspension that did not include a dispersion step and a kneading step, exhibited significant aggregation of ZnPBA particles, and the area ratio of primary particles was 8.4%.

[0129]

[0130] The battery characteristics of the secondary batteries prepared in each example were evaluated using a potentio / galvanostat analyzer ECstat-302 manufactured by EC Frontier as a charge / discharge device and an SB9 manufactured by EC Frontier as a charge / discharge evaluation cell.

[0131] <Battery Capacity Due to Dispersant> The secondary battery fabricated in Comparative Example 2, to which no dispersant was added, achieved a capacity of 63% of the theoretical capacity at 100 C, whereas the secondary batteries fabricated in Examples 15 and 21, to which a dispersant was added, achieved capacities of 86% and 87%, respectively, of the theoretical capacity at 100 C. Battery capacity (hereinafter also referred to as capacity) is the capacity per unit mass of the positive electrode active material.

[0132] <Battery Characteristics Depending on SWNT Amount> The charge / discharge characteristics (C-rate characteristics) of the ZnPBA binder-free electrode were measured depending on the SWNT amount. Fig. 5 shows a graph showing the relationship between the capacity retention and the C-rate for secondary batteries fabricated using the ZnPBA binder-free electrodes containing 0.05 wt%, 0.1 wt%, 0.5 wt%, 1.5 wt%, 3.0 wt%, and 10.0 wt% SWNTs fabricated in Comparative Example 1 and Examples 1 to 3, 5, and 7. The capacity retention is the ratio of the capacity when the C-rate is changed to the capacity at 1 C as the reference.

[0133] Good C rate characteristics were obtained when the SWNT amount was 0.1 wt% or more, even better C rate characteristics were obtained when it was 0.5 wt% or more, and even better C rate characteristics were obtained when it was 1.5 to 3.0 wt%. It was shown that when the SWNT amount was within the above range, a good balance between electronic conductivity and ionic conductivity was achieved.

[0134] The battery with the smallest capacity at 1 C was the battery prepared in Comparative Example 1 with a SWNT content of 0.05 wt%, which exhibited a capacity of 56.6 mAh / g (87.7% of the theoretical capacity). The battery with the largest capacity was the battery prepared in Example 7 with a SWNT content of 10 wt%, which exhibited a capacity of 69.6 mAh / g (108.2% of the theoretical capacity) at 1 C. The reason why the theoretical capacity exceeds 100% is that, as mentioned above, there is a discrepancy between the design value of the active material loading amount and the active material loading amount when the electrode is actually prepared (the same applies below).

[0135] <Change in Battery Capacity Depending on Electrolyte Concentration> The battery capacity of the secondary batteries fabricated by changing the electrolyte concentration in Examples 1 and 8 to 16 was evaluated. In the concentration range of 0.1 to 0.8 M, the solvent was propylene carbonate alone, and NaOTf and Zn(OTf) ２ The concentration of 1M is 1M Na(OTf) and 1M Zn(OTf) in a mixed solvent of propylene carbonate and distilled water (propylene carbonate:distilled water = 9:1). ２ The 2M concentration is obtained by dissolving 2M Na(OTf) and 1M Zn(OTf) in a mixed solvent of propylene carbonate and distilled water (propylene carbonate:distilled water = 9:1). ２ The 4M concentration was obtained by dissolving 4M Na(OTf) and 1M Zn(OTf) in a mixed solvent of propylene carbonate and distilled water (propylene carbonate:distilled water = 7:3). ２ The above is dissolved.

[0136] Figure 6 shows a graph illustrating the relationship between C-rate and capacity retention as a function of electrolyte concentration. The graph in Figure 6 shows the relative capacity, with 1 C being 100%. As the electrolyte concentration increased, the C-rate characteristics improved. It is believed that the higher the electrolyte concentration, the higher the ion concentration near the active material particles, which shortens the ion diffusion distance and allows for smooth ion exchange.

[0137] The battery with the largest capacity at 1C was the battery prepared in Example 1 with an electrolyte concentration of 4 M, which exhibited a capacity of 75.7 mAh / g (117.3% of the theoretical capacity), and the battery with the smallest capacity was the battery prepared in Example 8 with an electrolyte concentration of 0.1 M, which exhibited a capacity of 70.0 mAh / g (108.5% of the theoretical capacity).

[0138] <Effect of Active Material Loading Amount on Battery Characteristics> The secondary batteries fabricated in Examples 5 and 17 to 19 had capacities at 1 C of 97.6%, 95.6%, 96.2%, and 93.8% of the theoretical capacity, respectively, showing essentially the same capacity. They also showed essentially the same capacity at 100 C. Figure 8 shows the charge / discharge curves of the secondary battery fabricated in Example 18 and the C-rate characteristics of the secondary batteries fabricated in Examples 5 and 17 to 19. The secondary battery fabricated in Example 18 exhibited a capacity of 61.5 mAh / g at 1 C, which was 95.3% of the theoretical capacity (64.5 mAh / g). Even with an increased C-rate, the battery capacity showed a gradual decrease, and even at 1000 C, it showed a high capacity of 60.6 mAh / g and a clear plateau region with a slope of -0.0032. When the active material loading amount was 0.5 mg / cm ２ and 0.25 mg / cm ２ The secondary battery maintained a capacity retention rate of over 90% up to 1000 C. The smaller the amount of the active material carried, the better the C rate characteristics. This is due to the Zn content of the metal zinc plate, which is the counter electrode. ２＋ This is because the response speed of dissolution / precipitation is rate-determining.

[0139] <Cycle Characteristics (Durability)> The secondary battery prepared in Example 20 was evaluated for cycle characteristics up to 100,000 cycles at 400 C. FIG. 9 shows the capacity retention as a function of the number of cycles (number of charge / discharge cycles). The prepared secondary battery exhibited a capacity of 62.9 mAh / g at 200 cycles, which was 97.5% of the theoretical capacity (64.5 mAh / g). Even after 50,000 or more charge / discharge cycles, the battery still maintained 90% or more of its initial capacity, and even after 100,000 charge / discharge cycles, it still maintained 85% or more of its initial capacity, demonstrating excellent cycle characteristics.

[0140] (Evaluation of Battery Characteristics Influenced by the Presence or Absence of Binder and Dispersibility of Active Material) FIG. 16 shows the C-rate characteristics (capacity retention) of (a) a secondary battery equipped with a binder-containing electrode of Comparative Example 3, (b) a secondary battery equipped with a binder-free electrode prepared using the active material suspension of Comparative Example 2, and (c) a secondary battery prepared in Example 15. The secondary battery (a) equipped with the binder-containing electrode of Comparative Example 3 exhibited a low battery capacity of about 50% of the capacity at 1 C during 100 C charge / discharge, and the battery capacity significantly decreased as the C-rate increased. The secondary battery (b) equipped with the binder-free electrode prepared using the active material suspension of Comparative Example 2 also exhibited a low battery capacity of about 63% of the capacity at 1 C during 100 C charge / discharge, and the battery capacity decreased as the C-rate increased. The secondary battery (c) equipped with the binder-free electrode prepared in Example 15 exhibited a high battery capacity of about 86% of the capacity at 1 C during 100 C charge / discharge and excellent C-rate characteristics.

[0141] Tables 3-1 and 3-2 show the secondary battery manufacturing conditions for Examples 1 to 21 and Comparative Examples 1 to 3, including the amount of dispersant, the amount of SWNT, the amount of active material carried, and the electrolyte concentration, as well as the ratio of the number of primary particles, the energy density (Wh / kg) when the power density was 10,000 (W / kg), and the capacity retention (%) when an energy density of 60 Wh / kg or more and a power density of 10,000 W / kg were obtained. In the column for energy density (Wh / kg) when the power density was 30,000 W / kg, a "-" was displayed if the power density did not reach 30,000 W / kg. In the column for capacity retention (%) when an energy density of 60 Wh / kg or more and a power density of 10,000 W / kg or more were obtained, a "-" was displayed if the capacity retention was less than 60%.

[0142]

[0143] (Example 22) <Preparation of MnPBA binder-free electrode and its battery characteristics> (Synthesis of MnPBA) Zinc acetate tetrahydrate 1.47 g (6.00 × 10 －３ mol, Kanto Chemical Co., Inc., purity 99.0% or higher) was dissolved in 10 ml of distilled water, and 1.27 g (3.00 × 10 －３mol, Kanto Chemical Co., Inc., purity 99.5% or more) was dissolved in 50 ml of distilled water, and the two were mixed and stirred for 1 hour. Next, after centrifuging (4000 rpm, 2600 × g, 15 minutes), the mixture was washed 10 times with distilled water and dried under reduced pressure to obtain MnPBA powder. The composition of the obtained MnPBA powder was K １．６５ Mn １．２２ [Fe(CN) ６ ]・1.35H ２ The theoretical capacity was 153.43 mAh / g.

[0144] (Preparation of MnPBA Dispersion) 0.10 g of the obtained MnPBA powder was mixed with 0.054 g (2.75 × 10) of potassium hexacyanoferrate (II) trihydrate (21 mol % of the total metal amount of MnPBA) as a dispersant. －４ 5 ml of an aqueous solution of 100% potassium iodide (mol) was added to the solution and stirred for 2 weeks to obtain a potassium-containing MnPBA dispersion. １．８４ Mn １．１２ [Fe(CN) ６ ]・1.24H ２ The potassium-containing MnPBA has a structure in which ferrocyanide ions are coordinated to metals located on the surface of the MnPBA.

[0145] (Preparation of MnPBA binder-free electrode) The obtained MnPBA dispersion liquid was mixed with a single-walled carbon nanotube (SWNT) dispersion liquid (0.4 wt %, KJ Specialty Paper Co., Ltd., TB004M) to obtain a mixed liquid. The SWNT content was 2.6 wt %.

[0146] The resulting mixture was suction filtered through a PTFE membrane filter (pore size 0.1 μm, Sumitomo Electric Industries, Ltd., HPW-010-30) and heated at 120° C. to obtain a MnPBA binder-free electrode. The amount of MnPBA supported on the resulting MnPBA electrode was 0.5 mg / cm. ２ It was.

[0147] (Preparation of Negative Electrode) Zn foil (0.1 mm thick, Takeuchi Metal Foil & Powder Co., Ltd., 99.99%) was polished with waterproof abrasive paper (Sankyo Rikagaku, #1500) and used as a negative electrode.

[0148] (Preparation of Electrolyte) A mixed solution (volume ratio 9:1) of propylene carbonate (Kanto Chemical Co., Ltd.) and distilled water was used as a solvent, and 2 M potassium trifluoromethanesulfonate (K(OTf)) (Tokyo Chemical Industry Co., Ltd.) and 1 M Zn(OTf) were used as an electrolyte. ２ (Tokyo Chemical Industry Co., Ltd.) was dissolved in the solution to prepare an electrolyte solution.

[0149] (Preparation of Secondary Battery) The prepared MnPBA binder-free electrode was used as the positive electrode, the prepared negative electrode, the prepared electrolyte, the PTFE membrane filter used for filtration of the electrode as a separator, and carbon paper (Mitsubishi Chemical Corporation, MFO) as a current collector. ＋ The deintercalation of Zn occurs at the negative electrode. ２＋ We fabricated an ion secondary battery driven by the dissolution / precipitation of . Figure 2 shows a schematic diagram of the secondary battery configuration.

[0150] An SEM image of the prepared MnPBA binder-free electrode is shown in Figure 10. The MnPBA particles had an average particle size of about 30 nm, and SWNTs were uniformly present throughout the entire field of view.

[0151] (Example 23) <Battery Combining MnPBA and Aqueous Electrolyte> (Preparation of Aqueous Electrolyte) Aqueous electrolyte solution containing 2M K(OTf) and 1M Zn(OTf) was added to distilled water as a solvent. ２ A secondary battery was fabricated in the same manner as in Example 22, except that a mixed ion aqueous solution prepared by dissolving the above was used as the electrolyte.

[0152] (Comparative Example 4) <Production of MnPBA binder-free electrode using suspension and battery characteristics> (Preparation of MnPBA suspension) 5.0 ml of distilled water was added to 0.105 g of MnPBA powder obtained by the same method as in Example 22, and the mixture was treated for 1 hour using an ultrasonicator (ASONE, MCD-2P) to obtain a MnPBA suspension.

[0153] (Preparation of MnPBA binder-free electrode) The obtained MnPBA suspension was mixed with a single-walled carbon nanotube (SWNT) dispersion (0.4 wt%, KJ Specialty Paper Co., Ltd., TB004M) to obtain a mixed solution. The SWNT content was 2.6 wt%.

[0154] The resulting mixture was suction filtered through a PTFE membrane filter (pore size 0.1 μm, Sumitomo Electric Industries, Ltd., HPW-010-30) and heated at 120° C. to obtain a MnPBA binder-free electrode. The amount of MnPBA supported on the resulting MnPBA electrode was 1.00 mg / cm. ２ Using the obtained electrode, a secondary battery was fabricated in the same manner as in Example 22.

[0155] (Comparative Example 5) <Preparation of MnPBA binder-containing electrode and battery characteristics> (Preparation of binder-containing electrode) 21.0 mg of MnPBA powder obtained by the same method as in Example 22, 3.0 mg of polyvinylvinylidene fluoride (PVDF, Sigma-Aldrich, weight average molecular weight Mw ~ 523,000), 6.0 mg of SuperP (particulate conductive carbon particles) (MTI Corporation), and 200 μL of 1-methyl-2-pyrrolidone (Sigma-Aldrich) were mixed and mixed for 4 hours using an automatic mortar (AMM-140D, Nitto Kagaku Co., Ltd.) to obtain a paste. The mass ratio of MnPBA:SuperP:PVDF was 7:2:1. The obtained paste was applied to carbon paper and dried by heating (120 ° C, 1 hour) to prepare a binder-containing MnPBA electrode. The amount of MnPBA supported was 1.0 mg / cm ２ Using the obtained electrode, a secondary battery was fabricated in the same manner as in Example 22.

[0156] The battery characteristics of the secondary batteries prepared in Examples 22 and 23 and Comparative Example 4 were evaluated using a potentio / galvanostat analyzer ECstat-302 manufactured by EC Frontier as a charge / discharge device and an SB9 manufactured by EC Frontier as a charge / discharge evaluation cell.

[0157] Figure 11 shows the charge-discharge curves and C-rate characteristics of the secondary battery equipped with the MnPBA binder-free electrode prepared in Example 22. The prepared secondary battery exhibited a capacity of 153.00 mAh / g at 1 C, which was 99.1% of the theoretical capacity (154.32 mAh / g). As the C-rate increased, the battery capacity decreased relatively significantly up to 50 C. From 50 to 150 C, the capacity decreased gradually as the C-rate increased. However, even at 100 C, the battery exhibited a capacity of 100 mAh / g or more, and even at 150 C, the battery exhibited a high capacity of 85 mAh / g, and also showed a clear plateau region with a slope (average) of -0.0040.

[0158] Figure 12 shows the charge / discharge characteristics of a secondary battery prepared using the MnPBA binder-free electrode and aqueous electrolyte prepared in Example 23. The prepared secondary battery exhibited a capacity of 125.3 mAh / g at 1 C, which was 81.7% of the theoretical capacity (153.43 mAh / g). The prepared secondary battery did not show much capacity reduction even when the C rate was increased, exhibited a capacity of 100 mAh / g or more at 100 C and a capacity retention rate of 70%, and showed a flat plateau region with a slope (average value) of -0.0028 from 1 C to 100 C. In other words, it was demonstrated that the secondary battery prepared using the aqueous electrolyte prepared in this example is capable of high-speed charge / discharge.

[0159] FIG. 22 shows the C-rate characteristics (high-rate charge / discharge characteristics) of (a) a secondary battery equipped with the binder-containing electrode of Comparative Example 5, (b) a secondary battery equipped with the binder-free electrode prepared using the active material suspension of Comparative Example 4, and (c) a secondary battery prepared in Example 22. The secondary battery (a) equipped with the binder-containing electrode of Comparative Example 5 showed a significant decrease in battery capacity as the C-rate increased. The secondary battery (b) equipped with the binder-free electrode prepared using the active material suspension of Comparative Example 4 also showed a decrease in battery capacity as the C-rate increased. The secondary battery (c) equipped with the binder-free electrode prepared in Example 22 showed excellent C-rate characteristics.

[0160] Table 4 shows the secondary battery manufacturing conditions, such as the amount of dispersant, the amount of SWNT, the amount of supported active material, and the concentration of the electrolyte, in Examples 22 and 23 and Comparative Examples 4 and 5, as well as the ratio of the number of primary particles, the energy density (Wh / kg) when the power density was 10,000 (W / kg), and the capacity retention rate (%) when an energy density of 60 Wh / kg or more and a power density of 10,000 W / kg were obtained.

[0161]

[0162] (Example 24) <Preparation of CuPBA binder-free electrode and its battery characteristics> (Synthesis of CuPBA) 1.45 g (6.00 × 10 －３ mol, Kanto Chemical Co., Inc., purity 99.2% or higher) was dissolved in 10 ml of distilled water, and 1.27 g (3.00 × 10 －３ mol, Kanto Chemical Co., Inc., purity 99.5% or higher) was dissolved in 50 ml of distilled water, and the two were mixed and stirred for 1 hour. Then, after centrifugation (4000 rpm, 2600 × g, 15 minutes), the mixture was washed 10 times with distilled water and dried under reduced pressure to obtain CuPBA powder. The composition of the obtained CuPBA powder was as follows: K ０．２８ Cu １．８４ [Fe(CN) ６ ]・7.05H ２ The theoretical capacity was 57.4 mAh / g.

[0163] (Preparation of CuPBA Dispersion) 0.10 g of the obtained CuPBA powder was mixed with 0.052 g (1.23 × 10) of potassium hexacyanoferrate (II) trihydrate (20.1 mol % of the total metal amount of CuPBA) as a dispersant. －４ mol) aqueous solution was added and stirred for 2 weeks to obtain a potassium-containing CuPBA dispersion. ０．５８ Cu １．６９ [Fe(CN) ６ ]・6.47H ２ The theoretical capacity was 58.4 mAh / g. The obtained potassium-containing CuPBA has a structure in which ferrocyanide ions are coordinated to metals located on the surface of the CuPBA.

[0164] (Preparation of CuPBA binder-free electrode) The obtained CuPBA dispersion and a single-walled carbon nanotube (SWNT) dispersion (0.4 wt%, KJ Specialty Paper Co., Ltd., TB004M) were mixed to prepare a binder-free electrode having a SWNT content of 2.7 wt% and a CuPBA loading of 0.5 mg / cm. ２ The mixture was mixed in the amounts shown below to obtain a mixed solution.

[0165] The resulting mixture was suction filtered onto a PTFE membrane filter (pore size 0.1 μm, Sumitomo Electric Industries, Ltd., HPW-010-30) and heated at 120° C. to obtain a CuPBA binder-free electrode.

[0166] (Preparation of Negative Electrode) Zn foil (0.1 mm thick, Takeuchi Metal Foil & Powder Co., Ltd., 99.99%) was polished with waterproof abrasive paper (Sankyo Rikagaku, #1500) and used as a negative electrode.

[0167] (Preparation of Electrolyte) A mixed solution of propylene carbonate and distilled water (volume ratio 9:1) was used as a solvent, and 2M K(OTf) and 1M Zn(OTf) were used as electrolytes. ２ was dissolved to prepare an electrolyte solution.

[0168] (Preparation of Secondary Battery) The prepared CuPBA binder-free electrode was used as the positive electrode, the prepared negative electrode, the prepared electrolyte, the PTFE membrane filter used for filtration of the electrode as a separator, and carbon paper (Mitsubishi Chemical Corporation, MFO) as a current collector. ＋ The deintercalation of Zn occurs at the negative electrode. ２＋ We fabricated an ion secondary battery driven by the dissolution / precipitation of . Figure 2 shows a schematic diagram of the secondary battery configuration.

[0169] Comparative Example 6 Preparation of CuPBA Suspension 5.0 ml of distilled water was added to 0.100 g of CuPBA powder obtained in the same manner as in Example 24, and the mixture was treated for 1 hour using an ultrasonicator (ASONE, MCD-2P) to obtain a CuPBA suspension.

[0170] (Preparation of CuPBA binder-free electrode) The obtained CuPBA suspension and a single-walled carbon nanotube (SWNT) dispersion (0.4 wt%, KJ Specialty Paper Co., Ltd., TB004M) were mixed to prepare a binder-free electrode with a SWNT content of 2.7 wt% and a CuPBA loading of 0.5 mg / cm. ２ The mixture was mixed in the amounts shown below to obtain a mixed solution.

[0171] The resulting mixture was suction filtered through a PTFE membrane filter (pore size 0.1 μm, Sumitomo Electric Industries, Ltd., HPW-010-30) and heated at 120° C. to obtain a CuPBA binder-free electrode. A secondary battery was produced using the resulting electrode in the same manner as in Example 24.

[0172] (Comparative Example 7) <Preparation of CuPBA binder-containing electrode and battery characteristics> (Preparation of binder-containing electrode) 21.1 mg of CuPBA powder obtained by the same method as in Example 24, 3.0 mg of polyvinylvinylidene fluoride (PVDF, Sigma-Aldrich, weight average molecular weight Mw ~ 523,000), 6.0 mg of SuperP (MTI Corporation), which is a particulate conductive carbon particle, and 200 μL of 1-methyl-2-pyrrolidone (Sigma-Aldrich) were mixed and mixed for 4 hours using an automatic mortar (AMM-140D, Nitto Kagaku Co., Ltd.) to obtain a paste. The mass ratio of CuPBA:SuperP:PVDF was 7:2:1. The obtained paste was applied to carbon paper and dried by heating (120 ° C, 1 hour) to prepare a binder-containing CuPBA electrode. The amount of CuPBA supported was 0.5 mg / cm ２ Using the obtained electrode, a secondary battery was fabricated in the same manner as in Example 24.

[0173] The battery characteristics of the secondary batteries prepared in Example 24 and Comparative Examples 6 and 7 were evaluated using a potentio / galvanostat analyzer ECstat-302 manufactured by EC Frontier as a charge / discharge device and an SB9 manufactured by EC Frontier as a charge / discharge evaluation cell.

[0174] Figure 13 shows the charge-discharge curves and C-rate characteristics of a secondary battery equipped with a CuPBA binder-free electrode. The C-rate characteristics were calculated based on the 1C durability capacity. The fabricated battery exhibited a capacity of 51.7 mAh / g at 0.5C, which was 88.5% of the theoretical capacity (58.4 mAh / g). While the capacity gradually decreased with increasing C-rate, even at 1000C it still exhibited more than 85% of the capacity at 0.5C. The fabricated battery also clearly exhibited a plateau region with a slope of -0.0051 at 100C.

[0175] Table 5 shows the secondary battery manufacturing conditions of Example 24 and Comparative Examples 6 and 7, including the amount of dispersant, the amount of SWNT, the amount of active material carried, and the electrolyte concentration, as well as the ratio of the number of primary particles, the energy density (Wh / kg) when the power density was 10,000 (W / kg), and the capacity retention (%) when an energy density of 60 Wh / kg or more and a power density of 10,000 W / kg were obtained. In the column for energy density (Wh / kg) when the power density was 30,000 W / kg, a "-" was displayed if the power density did not reach 30,000 W / kg. In the column for capacity retention (%) when an energy density of 60 Wh / kg or more and a power density of 10,000 W / kg or more were obtained, a "-" was displayed if the capacity retention was less than 60%.

[0176]

[0177] <Comparison by Ragone Plot> Fig. 17 shows a Ragone plot showing the relationship between the energy density (capacity) and the power (output) density of the secondary batteries fabricated in Examples 5, 18, 19, 22, and 24, and Comparative Examples 2 to 7. In addition to the above comparative examples, the Ragone plot also shows the half-cell described in Non-Patent Document 9, which uses ZnPBA as the active material, as a conventional technology. The half-cell described in Non-Patent Document 11, which uses MnPBA as the active material, and the half-cell described in Non-Patent Document 10, which uses CuPBA as the active material, show the Zn / Zn ２＋The Ragone plot is shown using voltages converted from a reference. For reference, the energy density (capacity) and power (output) density regions of conventional capacitors, supercapacitors, ion secondary batteries, and fuel cells are also shown.

[0178] Generally, the capacitance and voltage decrease as the C rate increases, so the Ragone plot tilts upward to the left. If the capacitance and voltage are not the same even when the C rate is increased, the plot will be straight up.

[0179] In conventional ion secondary batteries, １ The energy density decreases at 100 C (10 C), which is due to a decrease in capacity and voltage caused by the influence of internal ion diffusion, etc. In contrast, the secondary batteries fabricated in Examples 18, 22, and 24 exhibited a decrease in energy density at 100 C (10 ２ C), and the capacitance is one order of magnitude higher at 1000C (10 ３ C), it was possible to suppress the capacity decrease, and it was possible to achieve both a higher energy density and excellent high-speed charge / discharge characteristics than before.

[0180] 18 shows a Ragone plot, with the horizontal axis representing real numbers, illustrating the relationship between energy density (capacity) and power (output) density for the secondary batteries fabricated in Examples 5, 18, 19, 22, and 24 and Comparative Examples 2 to 7. The energy density of the secondary batteries fabricated in the comparative examples dropped significantly before the power density reached 10,000 W / kg, but the secondary batteries fabricated in the examples had a power density of 30,000 W / kg or more and an energy density of 60 Wh / kg or more.

[0181] The secondary batteries fabricated in Examples 5, 18, 19, and 24 had a capacity retention rate of 80% or more relative to the capacity at 1 C when obtaining an energy density of 60 Wh / kg or more and a power density of 10,000 W / kg or more.

[0182] The secondary battery produced in Example 22 had a capacity retention rate of 60% or more relative to the capacity at 1 C when obtaining an energy density of more than 100 Wh / kg and a power density of 10,000 W / kg or more.

Claims

1. Carbon nanotubes, and The active material particles having an average particle size of 2 to 1000 nm are supported in a dispersed state on the carbon nanotubes. Including, a mass ratio of the carbon nanotubes to a total mass of the active material particles and the carbon nanotubes is 0.1 wt % or more; The active material particles have a positive or negative surface charge or are surface-modified with an organic compound having an alkyl chain. Electrodes for secondary batteries.

2. The electrode according to claim 1 , wherein a ratio of the number of primary particles to the number of all particles of the active material particles is 70% or more.

3. 10. The electrode of claim 1 which is binder-free.

4. 2. The electrode of claim 1, wherein the active material is Prussian blue or an analog thereof.

5. 5. The electrode of claim 4, wherein the Prussian blue or analogue thereof is Fe-Zn Prussian blue or analogue thereof, Fe-Mn Prussian blue or analogue thereof, or Fe-Cu Prussian blue or analogue thereof.

6. A secondary battery comprising the electrode according to any one of claims 1 to 5, a counter electrode, an electrolyte solution, and a current collector.

7. The secondary battery according to claim 6 , wherein the concentration of the electrolyte solution is 0.8 M or more.

8. 7. The secondary battery according to claim 6, wherein the current collector is carbon paper.

9. The secondary battery according to claim 6, having an energy density of 60 Wh / kg or more and a power density of 30,000 W / kg or more.

10. 7. The secondary battery according to claim 6, wherein the capacity retention rate relative to the capacity at 1 C when obtaining an energy density of 60 Wh / kg or more and a power density of 10,000 W / kg or more is 80% or more.

11. The secondary battery according to claim 6, wherein the capacity retention rate relative to the capacity at 1 C when obtaining an energy density of more than 100 Wh / kg and a power density of 10,000 W / kg or more is 60% or more.

12. surface-modifying active material particles having an average particle size of 2 to 1000 nm, and preparing a dispersion of active material particles in which the surface-modified active material particles are dispersed; Preparing a carbon nanotube dispersion; mixing the active material particle dispersion liquid and the carbon nanotube dispersion liquid so that a mass ratio of the carbon nanotubes to a total mass of the active material particles and the carbon nanotubes is 0.1 wt % or more to form a mixed liquid; and Applying the mixture onto a substrate to obtain an electrode film. A method for producing an electrode for a secondary battery, comprising the steps of:

13. The method for producing an electrode for a secondary battery according to claim 12 , wherein applying the mixed solution onto a substrate to obtain an electrode film comprises filtering the mixed solution through a filter to obtain a filtered film.

14. The method according to claim 12 or 13, wherein the filter is a polytetrafluoroethylene membrane.