Negative electrode for secondary battery and secondary battery

Abstract

This secondary battery is provided with an electrolytic solution together with a positive electrode and a negative electrode, the negative electrode containing a polyrotaxane and an organic fiber compound.

Description

[Technical Field]

[0001] The present technology relates to a negative electrode for a secondary battery and a secondary battery. [Background technology]

[0002] Due to the widespread use of various electronic devices such as mobile phones, secondary batteries have been developed as a power source that is small, lightweight, and capable of obtaining high energy density. These secondary batteries contain a positive electrode, a negative electrode (secondary battery negative electrode), and an electrolyte solution, and various studies have been conducted on the configuration of these secondary batteries.

[0003] Specifically, to obtain excellent cycle characteristics, a polymer compound containing a plurality of cyclic molecules and linear molecules is used as a binder for the negative electrode (see, for example, Patent Document 1). In this polymer compound, the linear polymer penetrates each of the plurality of cyclic molecules. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2018-174038 Summary of the Invention

[0005] Although various studies have been conducted on the configuration of secondary batteries, there is still room for improvement since the low-temperature cycle characteristics and load characteristics are still insufficient.

[0006] Therefore, there is a demand for a negative electrode for a secondary battery and a secondary battery that can achieve excellent low-temperature cycle characteristics and excellent load characteristics.

[0007] A negative electrode for a secondary battery according to an embodiment of the present technology includes a polyrotaxane and an organic fiber compound.

[0008] A secondary battery according to an embodiment of the present technology includes an electrolyte solution together with a positive electrode and a negative electrode, and the negative electrode has a configuration similar to the configuration of the negative electrode for a secondary battery according to the embodiment of the present technology described above.

[0009] Here, "polyrotaxane" refers to a molecular assembly (polymer compound) containing cyclic molecules and linear molecules. The linear molecules penetrate the cyclic molecules and have terminal groups at both ends that sterically hinder the cyclic molecules. Details of the structure and types of polyrotaxanes will be described later.

[0010] According to the negative electrode for a secondary battery or the secondary battery of an embodiment of the present technology, the negative electrode for a secondary battery contains a polyrotaxane and an organic fiber compound, and therefore, excellent low-temperature cycle characteristics and excellent load characteristics can be obtained.

[0011] Note that the effects of the present technology are not necessarily limited to the effects described here, but may be any of a series of effects related to the present technology described below. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a cross-sectional view illustrating a configuration of a negative electrode for a secondary battery according to a first embodiment of the present technology. [Figure 2] 5 is an enlarged cross-sectional view showing the configuration of a negative electrode active material particle in a negative electrode for a secondary battery according to a second embodiment of the present technology. FIG. [Figure 3] 1 is a perspective view illustrating a configuration of a secondary battery according to an embodiment of the present technology. [Figure 4] FIG. 4 is a cross-sectional view illustrating the configuration of the battery element shown in FIG. [Figure 5] FIG. 1 is a block diagram illustrating a configuration of an application example of a secondary battery. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, an embodiment of the present technology will be described in detail with reference to the drawings. The description will be made in the following order. 1. Negative electrode for secondary battery (first embodiment) 1-1.Configuration 1-2. Manufacturing method 1-3. Action and effects 2. Negative electrode for secondary battery (second embodiment) 2-1.Configuration 2-2. Manufacturing method 2-3. Action and effects 3. Secondary battery 3-1.Configuration 3-2.Operation 3-3. Manufacturing method 3-4. Action and effects 4. Variations 5. Uses of secondary batteries

[0014] <1. Negative electrode for secondary battery (first embodiment)> First, a negative electrode for a secondary battery (hereinafter simply referred to as "negative electrode") according to a first embodiment of the present technology will be described.

[0015] This negative electrode is used in a secondary battery, which is an electrochemical device. However, the negative electrode may also be used in other electrochemical devices besides secondary batteries. The type of other electrochemical device is not particularly limited, but specifically includes a capacitor.

[0016] In electrochemical devices such as secondary batteries, the negative electrode absorbs and releases electrode reactants during electrode reactions. The types of electrode reactants are not particularly limited, but are specifically light metals such as alkali metals and alkaline earth metals. Specific examples of alkali metals include lithium, sodium, and potassium, and specific examples of alkaline earth metals include beryllium, magnesium, and calcium.

[0017] In the following, an example will be given in which the electrode reactant is lithium, in other words, lithium is absorbed and released in an ionic state at the negative electrode during the electrode reaction.

[0018] <1-1.Configuration> Fig. 1 shows a cross-sectional configuration of the negative electrode in the first embodiment, although Fig. 1 shows only a part of the negative electrode.

[0019] The negative electrode contains a polyrotaxane and an organic fiber compound. The polyrotaxane may be of one type or two or more types. Similarly, the organic fiber compound may be of one type or two or more types.

[0020] 1, the negative electrode includes a negative electrode current collector 110 and a negative electrode active material layer 120, and the negative electrode active material layer 120 includes the above-mentioned polyrotaxane and organic fiber compound. In this case, the polyrotaxane and the organic fiber compound are each dispersed in the negative electrode active material layer 120.

[0021] The negative electrode active material layer 120 contains a polyrotaxane and an organic fiber compound, and the polyrotaxane and the organic fiber compound are each dispersed in the negative electrode active material layer 120 because the synergistic effect of the polyrotaxane and the organic fiber compound ensures the ionic conductivity of lithium, while suppressing the collapse of the negative electrode active material layer 120 and also suppressing the decomposition reaction of the electrolyte solution, which will be described later.

[0022] In detail, when the negative electrode active material layer 120 contains both polyrotaxane and an organic fiber compound, the following advantages are obtained, unlike when the negative electrode active material layer 120 does not contain either or both of the polyrotaxane and the organic fiber compound.

[0023] First, because polyrotaxane forms a coating with an organic fiber compound as a core on the surface of the negative electrode active material (described later), the surface of the negative electrode active material is reinforced by the coating. This improves the physical strength of the negative electrode active material by utilizing the coating, making the negative electrode active material layer 120 less likely to collapse even when the negative electrode active material expands and contracts during the electrode reaction. In this case, since the negative electrode active material layer 120 is less likely to collapse, the negative electrode active material layer 120 is less likely to slide off the negative electrode current collector 110.

[0024] Second, the surface of the reactive negative electrode active material is protected by the coating, isolating the surface of the negative electrode active material from the electrolyte, making it less likely for the electrolyte to react with the negative electrode active material, and thus suppressing the decomposition reaction of the electrolyte on the surface of the negative electrode active material.

[0025] In this case, the surface of the negative electrode active material is particularly reinforced by the coating, so that the negative electrode active material is less likely to crack even when it expands and contracts during the electrode reaction. This makes it difficult for new reactive surfaces (reactive sites) to be formed on the negative electrode active material, so that the decomposition reaction of the electrolyte is stably suppressed even when the electrode reaction is repeated.

[0026] Third, since the polyrotaxane and the organic fiber compound coexist in the negative electrode active material layer 120, even if part of the coating is decomposed, an additional coating is formed. This allows the coating to exhibit a self-repairing function, so that the collapse of the negative electrode active material layer 120 is continuously suppressed, and the decomposition reaction of the electrolyte solution is also continuously suppressed.

[0027] Fourth, because the organic fiber compound has a porous structure, the coating has a porous structure that reflects the porous structure of the organic fiber compound. As a result, even if a coating is formed on the surface of the negative electrode active material, the porous structure of the coating ensures a migration path for lithium ions. Therefore, ionic conductivity of lithium ions is ensured, making it easier for lithium to be absorbed and released in the negative electrode active material.

[0028] [Negative electrode current collector] The negative electrode current collector 110 has a pair of surfaces on which the negative electrode active material layer 120 is provided. The negative electrode current collector 110 contains one or more types of conductive materials such as metal materials, and specific examples of the conductive materials include copper, aluminum, nickel, and stainless steel.

[0029] The surface of the negative electrode current collector 110 is preferably roughened by electrolysis or the like. This is because the so-called anchor effect is utilized to improve the adhesion of the negative electrode active material layer 120 to the negative electrode current collector 110. However, the negative electrode current collector 110 may be omitted.

[0030] [Negative electrode active material layer] The negative electrode active material layer 120 contains the above-mentioned polyrotaxane and organic fiber compound in addition to the negative electrode active material that absorbs and releases lithium. The negative electrode active material layer 120 may further contain one or more of other materials such as a negative electrode binder and a negative electrode conductive agent.

[0031] Here, the negative electrode active material layer 120 is provided on both sides of the negative electrode current collector 110. However, the negative electrode active material layer 120 may be provided on only one side of the negative electrode current collector 110.

[0032] The method for forming the negative electrode active material layer 120 is not particularly limited, but specifically includes one or more of a coating method, a vapor phase method, a liquid phase method, a thermal spraying method, and a firing method (sintering method).

[0033] (Negative electrode active material) The type of negative electrode active material is not particularly limited, but specifically, it is one or more of materials such as carbon materials and metal-based materials. That is, the negative electrode active material may be only a carbon material, only a metal-based material, or both a carbon material and a metal-based material. This is because a high energy density can be obtained. However, the type of negative electrode active material may be a material other than either a carbon material or a metal-based material.

[0034] Carbon material is a general term for materials containing carbon as a constituent element. This is because the crystal structure of the carbon material hardly changes during lithium absorption and desorption, allowing a high energy density to be obtained stably. In addition, the carbon material also functions as a negative electrode conductive agent, improving the conductivity of the negative electrode active material layer 120.

[0035] Specific examples of carbon materials include graphitizable carbon, non-graphitizable carbon, and graphite (natural graphite and artificial graphite). The interplanar spacing of the (002) plane of non-graphitizable carbon is not particularly limited, but is specifically 0.37 nm or more. The interplanar spacing of the (002) plane of graphite is not particularly limited, but is specifically 0.34 nm or less.

[0036] Specific examples of carbon materials include pyrolytic carbons, cokes, glassy carbon fibers, organic polymer compound calcined bodies, activated carbon, and carbon blacks. Examples of cokes include pitch coke, needle coke, and petroleum coke. Organic polymer compound calcined bodies are calcined products obtained by calcining (carbonizing) polymer compounds such as phenolic resins and furan resins at an appropriate temperature. Alternatively, the carbon material may be low-crystalline carbon heat-treated at a temperature of approximately 1000°C or less, or amorphous carbon. The shape of the carbon material is not particularly limited, but may be one or more of the following: fibrous, spherical, granular, and flaky.

[0037] Metallic materials are a general term for materials that contain one or more metal elements and semi-metal elements that can form an alloy with lithium, as this allows for a higher energy density to be obtained.

[0038] This metallic material may be a simple substance, an alloy, a compound, a mixture of two or more of these, or a material containing one or more of these phases. The "simple substance" described here refers to a general simple substance, and may contain trace amounts of impurities. In other words, the purity of the simple substance is not necessarily limited to 100%.

[0039] However, the "alloy" described here includes not only materials containing two or more metallic elements as constituent elements, but also materials containing one or more metallic elements and one or more metalloid elements as constituent elements. Furthermore, an "alloy" may also contain one or more non-metallic elements as constituent elements. The structure of the metallic material is not particularly limited, but specifically may be one or more of the following: solid solution, eutectic (eutectic mixture), intermetallic compound, and a mixture of two or more of these.

[0040] Specific examples of metal elements and metalloid elements include magnesium, boron, aluminum, gallium, indium, silicon, germanium, tin, lead, bismuth, cadmium, silver, zinc, hafnium, zirconium, yttrium, palladium, and platinum.

[0041] Among these, silicon is preferable because it has an excellent lithium absorption / desorption ability, and therefore can provide a significantly high energy density.

[0042] Silicon alloys contain, as constituent elements other than silicon, any one or more of metal elements such as tin, nickel, copper, iron, cobalt, manganese, zinc, indium, silver, titanium, germanium, bismuth, antimony, and chromium. Silicon compounds contain, as constituent elements other than silicon, any one or more of non-metal elements such as carbon and oxygen. However, silicon compounds may also contain, as constituent elements other than silicon, any one or more of the metal elements described for silicon alloys.

[0043] Specific examples of silicon alloys include SiB4, SiB6, Mg2Si, Ni2Si, TiSi2, MoSi2, CoSi2, NiSi2, CaSi2, CrSi2, Cu5Si, FeSi2, MnSi2, NbSi2, TaSi2, VSi2, WSi2, ZnSi2, and SiC, etc. However, the composition of the silicon alloy (the mixing ratio of silicon and metal elements) can be changed as desired.

[0044] Specific examples of silicon compounds are Si3N4, Si2N2O, SiO x (0 < x ≤ 2) and LiSiO, etc. However, the range of x may also be 0.2 < x < 1.4.

[0045] In particular, it is preferable that the negative electrode active material contains both a carbon material and a metal-based material for the reasons described below.

[0046] Metal-based materials, particularly materials containing silicon as a constituent element, have the advantage of high theoretical capacity, but on the other hand, have the concern of being prone to intense expansion and contraction during charge and discharge. On the other hand, carbon materials have the concern of low theoretical capacity, but on the other hand, have the advantage of being less prone to expansion and contraction during charge and discharge. Therefore, by using a carbon material and a metal-based material in combination, a high theoretical capacity (i.e., battery capacity) can be obtained while suppressing the expansion and contraction of the negative electrode active material layer 120 during charge and discharge.

[0047] (Polyrotaxane) As described above, polyrotaxane is a molecular aggregate (polymer compound) containing cyclic molecules and linear molecules. This linear molecule penetrates the cyclic molecule and has end groups that cause steric hindrance to the cyclic molecule at both ends. Note that the linear molecule may also be referred to as an axial molecule. Note that polyrotaxane may contain a plurality of cyclic molecules or a plurality of linear molecules.

[0048] The cyclic molecule is a molecule having a cyclic structure provided with a hole for inserting the linear molecule. The type of cyclic molecule is not particularly limited, but specifically, it is any one or two or more of cyclodextrin, crown ether, thiacrown ether, cyclophane, calixarene, thiacalixarene, cucurbituril, pillararene, and cyclic amide, etc. This is because a film derived from polyrotaxane and an organic fiber compound is likely to be stably formed.

[0049] A linear molecule is a molecule with a rod-like structure inserted into a hole (ring) in a cyclic molecule, and as described above, it penetrates the cyclic molecule and has terminal groups at both ends that act as steric hindrance to the cyclic molecule. The terminal groups function as so-called stoppers, and the steric hindrance caused by the presence of the terminal groups makes it difficult for the cyclic molecule to leave the linear molecule.

[0050] The type of linear molecule is not particularly limited, but specifically, it is one or more of polyethylene glycol, polyoxymethylene, polypropylene oxide, polyvinyl alcohol, polyvinylidene fluoride, linear alkane, amide, and ammonium, because this facilitates the stable formation of a coating derived from the polyrotaxane and the organic fiber compound.

[0051] The type of terminal group is not particularly limited, as long as it is one or more bulky groups capable of bonding with the functional group present at the end of the linear molecule. Specific examples of terminal groups include dinitrophenyl, cyclodextrin, adamantyl, trityl, fluoresceinyl, pyrenyl, and anthracenyl groups. Alternatively, the terminal group may be the main chain or side chain of a polymer compound having a number-average molecular weight within the range of 1,000 to 1,000,000. This is because the cyclic molecule is sufficiently unlikely to detach from the linear molecule, thereby facilitating the formation of a more stable coating. The terminal group is introduced at both ends of the linear molecule.

[0052] (organic fiber compounds) The organic fiber compound is a fibrous polymer compound (carbohydrate), and may contain one or more non-carbon elements such as nitrogen as constituent elements.

[0053] The type of organic fiber compound is not particularly limited, but specifically, it is one or more of cellulose, chitin, and chitosan, because this facilitates the stable formation of a coating derived from the polyrotaxane and the organic fiber compound.

[0054] (Negative electrode binder) The negative electrode binder contains one or more of synthetic rubbers and polymeric compounds. Specific examples of synthetic rubbers include styrene-butadiene rubber, fluorine-containing rubber, and ethylene-propylene-diene. Specific examples of polymeric compounds include polyvinylidene fluoride, polyimide, and carboxymethyl cellulose.

[0055] (negative electrode conductive agent) The negative electrode conductive agent contains one or more conductive materials such as carbon materials. The carbon materials may be particulate carbon materials, fibrous carbon materials, or both. Specific examples of particulate carbon materials include graphite, carbon black, acetylene black, and ketjen black. Specific examples of fibrous carbon materials include carbon nanotubes and carbon fibers. However, the conductive material is not limited to carbon materials and may also be a metal material, a polymer compound, or the like.

[0056] In particular, the negative electrode conductive agent preferably contains a fibrous carbon material, because the electrical conductivity between the negative electrode active materials is improved, thereby reducing the electrical resistance of the negative electrode active material layer 120.

[0057] <1-2. Manufacturing method> When manufacturing a negative electrode, first, a negative electrode active material, a polyrotaxane, and an organic fiber compound are mixed together to form a negative electrode mixture. In this case, a negative electrode binder, a negative electrode conductive agent, and the like may be added to the negative electrode mixture as needed.

[0058] Next, the negative electrode mixture is introduced into a solvent to prepare a paste-like negative electrode mixture slurry. This solvent may be an aqueous solvent or an organic solvent. In this case, the solvent containing the negative electrode mixture may be stirred using a stirring device such as a mixer.

[0059] Finally, the negative electrode mixture slurry is applied to both surfaces of the negative electrode current collector 110 to form the negative electrode active material layer 120. After this, the negative electrode active material layer 120 may be compression molded using a roll press or the like. In this case, the negative electrode active material layer 120 may be heated, or the compression molding may be repeated multiple times.

[0060] As a result, the negative electrode active material layers 120 are formed on both sides of the negative electrode current collector 110, and the negative electrode 100 is completed.

[0061] <1-3. Actions and Effects> According to the negative electrode of the first embodiment, the negative electrode contains a polyrotaxane and an organic fiber compound.

[0062] In this case, as described above, the polyrotaxane forms a coating on the surface of the negative electrode active material with the organic fiber compound as a nucleus, and the synergistic effect of the polyrotaxane and the organic fiber compound ensures the ionic conductivity of lithium, while suppressing the collapse of the negative electrode active material layer 120 and the decomposition reaction of the electrolyte.

[0063] Therefore, in a secondary battery using the negative electrode, excellent low-temperature cycle characteristics and excellent electrical resistance characteristics can be obtained.

[0064] In particular, if the organic fiber compound contains one or more of cellulose, chitin, and chitosan, the ionic conductivity of lithium is sufficiently improved, and the collapse of the negative electrode active material layer 120 and the decomposition reaction of the electrolyte are sufficiently suppressed, thereby achieving even greater effects.

[0065] Furthermore, if the polyrotaxane contains cyclic molecules and linear molecules (terminal groups), the cyclic molecules contain one or more of cyclodextrin, crown ether, thiocrown ether, cyclophane, calixarene, thiocalixarene, cucurbituril, pillararene, and cyclic amide, the linear molecules contain one or more of polyethylene glycol, polyoxymethylene, polypropylene oxide, polyvinyl alcohol, polyvinylidene fluoride, linear alkane, amide, and ammonium, and the terminal groups contain one or more of dinitrophenyl group, cyclodextrin group, adamantyl group, trityl group, fluoresceinyl group, pyrenyl group, and anthracenyl group, the ionic conductivity of lithium is sufficiently improved, and the collapse of the negative electrode active material layer 120 and the decomposition reaction of the electrolyte are sufficiently suppressed, thereby achieving even greater effects.

[0066] Furthermore, if the negative electrode active material layer 120 contains a polyrotaxane and an organic fiber compound together with the negative electrode active material, the polyrotaxane and the organic fiber compound are each dispersed in the negative electrode active material layer 120. Therefore, a coating can be easily formed sufficiently using the polyrotaxane and the organic fiber compound, thereby achieving a greater effect.

[0067] <2. Negative electrode for secondary battery (second embodiment)> Next, a negative electrode for a secondary battery (hereinafter referred to as "negative electrode") according to a second embodiment of the present technology will be described.

[0068] <2-1.Configuration> The negative electrode of the second embodiment has the same configuration as the negative electrode of the first embodiment, except for the configuration of the negative electrode active material layer 120. The configuration of this negative electrode is the same as the configuration of the negative electrode of the first embodiment, except as described below. Note that, hereinafter, reference will be made occasionally to FIG. 1, which has already been described.

[0069] Fig. 2 shows an enlarged cross-sectional configuration of a negative electrode active material particle 121 in the negative electrode of the second embodiment. As shown in Fig. 2, the negative electrode active material layer 120 contains a plurality of particulate negative electrode active materials (negative electrode active material particles 121), and the negative electrode active material particles 121 include a central portion 121X and a coating portion 121Y.

[0070] [Center] The central portion 121X contains one or more of a carbon material, a metal-based material, etc., for absorbing and releasing lithium. Details of the carbon material and the metal-based material are as described above.

[0071] [Coating] The covering portion 121Y covers the surface of the central portion 121X and contains a polyrotaxane and an organic fiber compound. Details regarding the polyrotaxane and the organic fiber compound are as described above. The covering portion 121Y may cover the entire surface of the central portion 121X, or may cover only a portion of the surface of the central portion 121X. In the latter case, a plurality of covering portions 121Y spaced apart from one another may cover the surface of the central portion 121X.

[0072] That is, in the second embodiment, unlike the first embodiment in which the polyrotaxane and the organic fiber compound are each dispersed in the negative electrode active material layer 120, the polyrotaxane and the organic fiber compound are each contained in the coating portion 121Y. As a result, the polyrotaxane and the organic fiber compound are each localized on the surface of the center portion 121X.

[0073] When the coating portion 121Y of the negative electrode active material particle 121 contains polyrotaxane and an organic fiber compound, the same advantages as those of the first embodiment can be obtained. That is, the synergistic effect of the polyrotaxane and the organic fiber compound ensures lithium ion conductivity, while suppressing the collapse of the negative electrode active material layer 120 and the decomposition reaction of the electrolyte.

[0074] In this case, in particular, since the polyrotaxane and the organic fiber compound are each localized on the surface of the center portion 121X, the surface of the negative electrode active material is more likely to be effectively reinforced and protected by the coating, and the self-repair function of the coating is more likely to be effectively exhibited. Therefore, compared to the first embodiment in which the polyrotaxane and the organic fiber compound are not each localized on the surface of the negative electrode active material, the collapse of the negative electrode active material layer 120 is more effectively suppressed, and the decomposition reaction of the electrolyte is also more effectively suppressed.

[0075] [Other materials] Of course, the negative electrode active material layer 120 may further contain one or more of other materials such as a negative electrode binder and a negative electrode conductor. Details regarding the negative electrode binder and the negative electrode conductor are as described above.

[0076] <2-2. Manufacturing method> The method for manufacturing the negative electrode of the second embodiment is the same as the method for manufacturing the negative electrode of the first embodiment, except that the procedure for forming the negative electrode active material layer 120 is different.

[0077] When forming the negative electrode active material layer 120, first, the core portion 121X and the raw materials for forming the coating portion 121Y, that is, polyrotaxane and an organic fiber compound, are mixed together to form a mixture. This core portion 121X is in powder form and contains one or more of the carbon material, metal material, and the like, as described above. Next, the mixture is poured into a solvent to prepare a mixed solution. This solvent may be an aqueous solvent or an organic solvent. In this case, the solvent containing the mixture may be stirred using a stirring device such as a mixer.

[0078] Next, the mixed solution is sprayed using a spraying device such as a spray dryer, whereby coating portion 121Y containing polyrotaxane and an organic fiber compound is formed on the surface of center portion 121X, thereby obtaining a plurality of negative electrode active material particles 121.

[0079] Finally, as described above, a negative electrode mixture slurry is prepared using the plurality of negative electrode active material particles 121, and then the negative electrode mixture slurry is used to form the negative electrode active material layer 120.

[0080] <2-3. Actions and Effects> The negative electrode of the second embodiment contains polyrotaxane and an organic fiber compound. Therefore, for the same reasons as in the first embodiment, the ionic conductivity of lithium is ensured, and the collapse of the negative electrode active material layer 120 and the decomposition reaction of the electrolyte are suppressed. Therefore, a secondary battery using the negative electrode can achieve excellent low-temperature cycle characteristics and excellent electrical resistance characteristics.

[0081] In particular, if the surface of the core 121X that absorbs and releases lithium is covered with the covering portion 121Y and the covering portion 121Y contains a polyrotaxane and an organic fiber compound, the polyrotaxane and the organic fiber compound are each localized on the surface of the core 121X. This further suppresses the collapse of the negative electrode active material layer 120 and the decomposition reaction of the electrolyte solution, thereby achieving a greater effect.

[0082] Other functions and effects of the negative electrode of the second embodiment are similar to those of the negative electrode of the first embodiment.

[0083] <3. Secondary battery> Next, a secondary battery according to an embodiment of the present technology using the above-described negative electrode will be described.

[0084] The secondary battery described here is a secondary battery that obtains battery capacity by utilizing the absorption and release of electrode reactants, as described above, and includes a positive electrode, a negative electrode, and an electrolyte.

[0085] In this secondary battery, the charge capacity of the negative electrode is larger than the discharge capacity of the positive electrode. That is, the electrochemical capacity per unit area of ​​the negative electrode is set to be larger than the electrochemical capacity per unit area of ​​the positive electrode. This is to prevent deposition of electrode reactants on the surface of the negative electrode during charging.

[0086] Details regarding the type of electrode reactant are as described above. As in the case of the negative electrode, the following will be described as an example in which the electrode reactant is lithium. A secondary battery that obtains battery capacity by utilizing the absorption and desorption of lithium is a so-called lithium ion secondary battery, in which lithium is absorbed and desorbed in an ionic state.

[0087] <3-1. Structure> Fig. 3 shows a perspective view of the secondary battery, and Fig. 4 shows a cross-sectional view of the battery element 20 shown in Fig. 3. However, Fig. 3 shows a state in which the exterior film 10 and the battery element 20 are separated from each other, and the cross section of the battery element 20 along the XZ plane is shown by a broken line. Fig. 4 shows only a portion of the battery element 20.

[0088] 3 and 4, this secondary battery includes an exterior film 10, a battery element 20, a positive electrode lead 31, a negative electrode lead 32, and sealing films 41 and 42. The secondary battery described here is a laminate film type secondary battery that uses a flexible or pliable exterior member (exterior film 10).

[0089] [Exterior film and sealing film] 3, the exterior film 10 is an exterior member that houses the battery element 20 and has a bag-like structure that is sealed when the battery element 20 is housed inside. As a result, the exterior film 10 houses an electrolyte solution together with a positive electrode 21 and a negative electrode 22, which will be described later.

[0090] Here, the exterior film 10 is a single film-like member that is folded in a folding direction F. The exterior film 10 is provided with a recessed portion 10U (so-called deep drawn portion) for accommodating the battery element 20.

[0091] Specifically, the exterior film 10 is a three-layer laminate film in which a fusion layer, a metal layer, and a surface protection layer are laminated in this order from the inside out, and when the exterior film 10 is folded, the outer peripheral edges of the opposing fusion layers are fused to each other. The fusion layer contains a polymer compound such as polypropylene. The metal layer contains a metal material such as aluminum. The surface protection layer contains a polymer compound such as nylon.

[0092] However, the configuration (number of layers) of the exterior film 10 is not particularly limited, and may be one layer, two layers, or four or more layers.

[0093] The sealing film 41 is inserted between the exterior film 10 and the positive electrode lead 31, and the sealing film 42 is inserted between the exterior film 10 and the negative electrode lead 32. However, one or both of the sealing films 41 and 42 may be omitted.

[0094] The sealing film 41 is a sealing member that prevents outside air and the like from entering the inside of the exterior film 10. The sealing film 41 also contains a polymer compound such as polyolefin that has adhesiveness to the positive electrode lead 31, and a specific example of the polyolefin is polypropylene.

[0095] The configuration of the sealing film 42 is the same as the configuration of the sealing film 41, except that the sealing film 42 is a sealing member that has adhesiveness to the negative electrode lead 32. That is, the sealing film 42 contains a polymer compound such as polyolefin that has adhesiveness to the negative electrode lead 32.

[0096] [Battery element] As shown in FIGS. 3 and 4, the battery element 20 is a power generating element including a positive electrode 21, a negative electrode 22, a separator 23, and an electrolyte (not shown), and is housed inside the exterior film 10.

[0097] This battery element 20 is a so-called wound electrode body. That is, the positive electrode 21 and the negative electrode 22 are stacked on top of each other with a separator 23 interposed therebetween, and are wound around a winding axis P while facing each other with the separator 23 interposed therebetween. This winding axis P is an imaginary axis extending in the Y-axis direction.

[0098] The three-dimensional shape of battery element 20 is not particularly limited. Here, battery element 20 is flat, and therefore the shape of a cross section (cross section along the XZ plane) of battery element 20 intersecting winding axis P is a flat shape defined by major axis J1 and minor axis J2. This major axis J1 is an imaginary axis that extends in the X-axis direction and has a length greater than that of minor axis J2, and minor axis J2 is an imaginary axis that extends in the Z-axis direction intersecting with the X-axis direction and has a length smaller than that of major axis J1. Here, the three-dimensional shape of battery element 20 is a flat cylindrical shape, and therefore the shape of the cross section of battery element 20 is a flat, approximately elliptical shape.

[0099] (positive electrode) As shown in FIG. 4, the positive electrode 21 includes a positive electrode current collector 21A and a positive electrode active material layer 21B.

[0100] The positive electrode current collector 21A has a pair of surfaces on which the positive electrode active material layer 21B is provided. The positive electrode current collector 21A contains a conductive material such as a metal material, and a specific example of the conductive material is aluminum.

[0101] Here, the positive electrode active material layer 21B is provided on both sides of the positive electrode current collector 21A and contains one or more types of positive electrode active materials that absorb and release lithium. However, the positive electrode active material layer 21B may be provided on only one side of the positive electrode current collector 21A, on the side where the positive electrode 21 faces the negative electrode 22. The positive electrode active material layer 21B may further contain one or more types of other materials such as a positive electrode binder and a positive electrode conductive agent. The method for forming the positive electrode active material layer 21B is not particularly limited, but specifically may be one or more types of coating methods.

[0102] The type of positive electrode active material is not particularly limited, but specifically includes a lithium-containing compound. This lithium-containing compound is a compound containing lithium and one or more transition metal elements as constituent elements, and may further contain one or more other elements as constituent elements. The type of other element is not particularly limited as long as it is an element other than lithium and transition metal elements, but specifically includes elements belonging to Groups 2 to 15 of the long period periodic table. The type of lithium-containing compound is not particularly limited, but specifically includes oxides, phosphate compounds, silicate compounds, borate compounds, etc.

[0103] Specific examples of oxides are LiNiO2, LiCoO2, LiCo 0.98 Al 0.01 Mg 0.01 O2, LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.8 Co 0.15 Al 0.05 O2, LiNi 0.33 Co 0.33 Mn 0.33 O2, Li 1.2 Mn 0.52 Co 0.175 Ni 0.1 O2, Li 1.15 (Mn 0.65 Ni 0.22 Co 0.13 )O2 and LiMn2O4. Specific examples of phosphate compounds include LiFePO4, LiMnPO4, LiFe 0.5 Mn 0.5 PO4 and LiFe 0.3 Mn 0.7 PO4, etc.

[0104] The details regarding the positive electrode binder and the positive electrode conductive agent are the same as the details regarding the negative electrode binder and the negative electrode conductive agent described above.

[0105] (Negative electrode) The configuration of the negative electrode 22 is the same as that of the negative electrode described above. That is, the negative electrode 22 contains a polyrotaxane and an organic fiber compound. More specifically, as shown in FIG. 4, the negative electrode 22 includes a negative electrode current collector 22A corresponding to the negative electrode current collector 110 and a negative electrode active material layer 22B corresponding to the negative electrode active material layer 120.

[0106] The negative electrode 22 may have a configuration similar to that of the negative electrode of the first embodiment, or may have a configuration similar to that of the negative electrode of the second embodiment.

[0107] (separator) 4, the separator 23 is an insulating porous film interposed between the positive electrode 21 and the negative electrode 22, and allows lithium ions to pass through while preventing contact (short circuit) between the positive electrode 21 and the negative electrode 22. The separator 23 contains a polymer compound such as polyethylene.

[0108] (electrolyte) The electrolyte is a liquid electrolyte that is impregnated into each of the positive electrode 21, the negative electrode 22, and the separator 23, and contains a solvent and an electrolyte salt.

[0109] Here, the solvent contains one or more types of non-aqueous solvents (organic solvents), and the electrolyte solution containing the non-aqueous solvent is a so-called non-aqueous electrolyte solution. The non-aqueous solvent is an ester, an ether, or the like, more specifically, a carbonate ester compound, a carboxylic acid ester compound, a lactone compound, or the like. This is because the dissociation property of the electrolyte salt and the mobility of ions are improved.

[0110] The carbonate ester compounds include cyclic carbonate esters and chain carbonate esters. Specific examples of the cyclic carbonate esters include ethylene carbonate and propylene carbonate, and specific examples of the chain carbonate esters include dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate.

[0111] The carboxylic acid ester compound is a chain carboxylic acid ester, etc. Specific examples of the chain carboxylic acid ester include ethyl acetate, ethyl propionate, propyl propionate, and ethyl trimethylacetate.

[0112] The lactone compound is a lactone, etc. Specific examples of lactones include γ-butyrolactone and γ-valerolactone.

[0113] The ethers may be lactone compounds, as well as 1,2-dimethoxyethane, tetrahydrofuran, 1,3-dioxolane, 1,4-dioxane, and the like.

[0114] The electrolyte salt contains one or more light metal salts such as lithium salts. Specific examples of lithium salts include lithium hexafluorophosphate (LiPF), lithium tetrafluoroborate (LiBF), lithium trifluoromethanesulfonate (LiCFSO), lithium bis(fluorosulfonyl)imide (LiN(FSO)), lithium bis(trifluoromethanesulfonyl)imide (LiN(CFSO)), lithium tris(trifluoromethanesulfonyl)methide (LiC(CFSO)), lithium bis(oxalato)borate (LiB(CO)), lithium monofluorophosphate (LiPFO), and lithium difluorophosphate (LiPFO). This is because high battery capacity can be obtained.

[0115] The content of the electrolyte salt is not particularly limited, but specifically, it is 0.3 mol / kg to 3.0 mol / kg relative to the solvent, because high ionic conductivity can be obtained.

[0116] The electrolytic solution may further contain one or more additives, including, but not limited to, unsaturated cyclic carbonates, halogenated cyclic carbonates, sulfonates, phosphates, acid anhydrides, nitrile compounds, and isocyanate compounds.

[0117] Specific examples of unsaturated cyclic carbonates include vinylene carbonate, vinylethylene carbonate, and methyleneethylene carbonate. Specific examples of halogenated cyclic carbonates include monofluoroethylene carbonate and difluoroethylene carbonate. Specific examples of sulfonic acid esters include propane sultone and propene sultone. Specific examples of phosphate esters include trimethyl phosphate and triethyl phosphate. Specific examples of acid anhydrides include succinic anhydride, 1,2-ethanedisulfonic anhydride, and 2-sulfobenzoic anhydride. Specific examples of nitrile compounds include succinonitrile. Specific examples of isocyanate compounds include hexamethylene diisocyanate.

[0118] [Positive and negative leads] 3 and 4, the positive electrode lead 31 is a positive electrode terminal connected to the positive electrode current collector 21A of the positive electrode 21, and is led from the inside to the outside of the exterior film 10. The positive electrode lead 31 contains a conductive material such as a metal material, and a specific example of the conductive material is aluminum. The shape of the positive electrode lead 31 is not particularly limited, but specifically may be either a thin plate shape or a mesh shape.

[0119] 3 and 4, the negative electrode lead 32 is a negative electrode terminal connected to the negative electrode current collector 22A of the negative electrode 22, and is led from the inside to the outside of the exterior film 10. The negative electrode lead 32 contains a conductive material such as a metal material, and a specific example of the conductive material is copper. Here, the details regarding the lead-out direction and shape of the negative electrode lead 32 are the same as those of the lead-out direction and shape of the positive electrode lead 31.

[0120] <3-2. Operation> When the secondary battery is charged, lithium is released from the positive electrode 21 in the battery element 20 and is absorbed into the negative electrode 22 via the electrolyte. On the other hand, when the secondary battery is discharged, lithium is released from the negative electrode 22 in the battery element 20 and is absorbed into the positive electrode 21 via the electrolyte. During these charge and discharge cycles, lithium is absorbed and released in an ionic state.

[0121] <3-3. Manufacturing method> When manufacturing a secondary battery, the positive electrode 21 and the negative electrode 22 are each fabricated and an electrolyte solution is prepared according to the procedure described below as an example. Then, the positive electrode 21, the negative electrode 22, and the electrolyte solution are used to assemble a secondary battery, and the assembled secondary battery is subjected to a stabilization treatment.

[0122] [Preparation of positive electrode] First, a paste-like cathode mixture slurry is prepared by adding a mixture (cathode mixture) of a cathode active material, a cathode binder, and a cathode conductive agent to a solvent. This solvent may be an aqueous solvent or an organic solvent. Next, the cathode mixture slurry is applied to both sides of the cathode current collector 21A to form the cathode active material layer 21B. Finally, the cathode active material layer 21B may be compression-molded using a roll press or the like. In this case, the cathode active material layer 21B may be heated, or the compression molding may be repeated multiple times. As a result, the cathode active material layer 21B is formed on both sides of the cathode current collector 21A, thereby producing the cathode 21.

[0123] [Preparation of negative electrode] The negative electrode 22 is fabricated by forming the negative electrode active material layers 22B on both surfaces of the negative electrode current collector 22A using a procedure similar to the procedure for fabricating the negative electrode described above. In this case, the same procedure as the procedure for fabricating the negative electrode of the first embodiment may be used, or the same procedure as the procedure for fabricating the negative electrode of the second embodiment may be used.

[0124] [Preparation of electrolyte] An electrolyte salt is added to a solvent, whereby the electrolyte salt is dispersed or dissolved in the solvent, thereby preparing an electrolytic solution.

[0125] [Secondary battery assembly] First, a positive electrode lead 31 is connected to the positive electrode current collector 21A of the positive electrode 21 using a joining method such as welding, and a negative electrode lead 32 is connected to the negative electrode current collector 22A of the negative electrode 22 using a joining method such as welding.

[0126] Next, the positive electrode 21 and the negative electrode 22 are stacked together with the separator 23 interposed therebetween, and then the positive electrode 21, the negative electrode 22, and the separator 23 are wound together to produce a wound body (not shown). This wound body has a configuration similar to that of the battery element 20, except that the positive electrode 21, the negative electrode 22, and the separator 23 are not impregnated with an electrolyte solution. Next, the wound body is pressed using a press or the like to form the wound body into a flat shape.

[0127] Next, after the roll is housed inside the recess 10U, the exterior film 10 (adhesive layer / metal layer / surface protection layer) is folded to make the exterior films 10 face each other. Next, the outer peripheral edges of two sides of the opposing adhesive layers are joined together using an adhesive method such as heat fusion, thereby housing the roll inside the bag-shaped exterior film 10.

[0128] Finally, an electrolyte solution is poured into the bag-shaped exterior film 10, and then the outer peripheral edges of the remaining side of the fusion layer are joined together using an adhesive method such as heat fusion. In this case, a sealing film 41 is inserted between the exterior film 10 and the positive electrode lead 31, and a sealing film 42 is inserted between the exterior film 10 and the negative electrode lead 32.

[0129] As a result, the wound body is impregnated with the electrolyte, producing the battery element 20 which is a wound electrode body, and the battery element 20 is sealed inside the bag-shaped exterior film 10, thereby assembling a secondary battery.

[0130] [Secondary battery stabilization] The assembled secondary battery is charged and discharged. Various conditions, such as the ambient temperature, the number of charge / discharge cycles (number of cycles), and the charge / discharge conditions, can be set as desired. This forms a coating on the surface of each of the positive electrode 21 and the negative electrode 22, electrochemically stabilizing the state of the secondary battery. This completes the secondary battery.

[0131] <3-4. Actions and Effects> In this secondary battery, the negative electrode 22 has the same configuration as the negative electrode described above. Therefore, while ensuring lithium ion conductivity, the collapse of the negative electrode active material layer 120 and the decomposition reaction of the electrolyte are suppressed, resulting in excellent low-temperature cycle characteristics and excellent electrical resistance characteristics.

[0132] In particular, if the secondary battery is a lithium ion secondary battery, a sufficient battery capacity can be stably obtained by utilizing the absorption and release of lithium, and therefore a greater effect can be obtained.

[0133] Other functions and effects of this secondary battery are similar to those of the negative electrode described above.

[0134] <4. Modifications> Next, modifications of the negative electrode and secondary battery will be described.

[0135] The configurations of the negative electrode and the secondary battery can be modified as appropriate, as described below, although any two or more of the series of modifications described below may be combined with each other.

[0136] [Variation 1] In the first embodiment, the negative electrode does not include a coating portion 121Y, and therefore the polyrotaxane and the organic fiber compound are each dispersed in the negative electrode active material layer 120. In the second embodiment, the negative electrode active material particles 121 of the negative electrode include a coating portion 121Y, and the coating portion 121Y contains the polyrotaxane and the organic fiber compound, and therefore the polyrotaxane and the organic fiber compound are each localized on the surface of the center portion 121X in the negative electrode active material layer 120.

[0137] However, the negative electrode configuration in the first embodiment and the negative electrode configuration in the second embodiment may be combined with each other. Specifically, the negative electrode active material layer 120 may contain a plurality of negative electrode active material particles 121 (central portions 121X and coating portions 121Y) as well as a polyrotaxane and an organic fiber compound. That is, in the negative electrode active material layer 120, the polyrotaxane and the organic fiber compound may each be localized on the surface of the central portions 121X, and the polyrotaxane and the organic fiber compound may each be dispersed around the negative electrode active material particles 121.

[0138] In this case, too, the synergistic effect of the polyrotaxane and the organic fiber compound ensures the ionic conductivity of lithium, while suppressing the collapse of the negative electrode active material layer 120 and the decomposition reaction of the electrolyte, thereby achieving the same effect.

[0139] [Variation 2] A porous film separator 23 was used. However, although not specifically shown here, a laminated separator including a polymer compound layer may also be used.

[0140] Specifically, the laminated separator includes a porous membrane having a pair of surfaces and a polymer compound layer disposed on one or both surfaces of the porous membrane. This is because the separator's adhesion to each of the positive electrode 21 and the negative electrode 22 is improved, thereby suppressing miswinding of the battery element 20. This makes it less likely for the secondary battery to swell even if a decomposition reaction of the electrolyte occurs. The polymer compound layer includes a polymer compound such as polyvinylidene fluoride. This is because polyvinylidene fluoride and the like have excellent physical strength and are electrochemically stable.

[0141] One or both of the porous film and the polymer compound layer may contain one or more types of insulating particles. This is because the insulating particles promote heat dissipation when the secondary battery generates heat, thereby improving the safety (heat resistance) of the secondary battery. The insulating particles contain one or more types of inorganic materials and resin materials. Specific examples of inorganic materials include aluminum oxide, aluminum nitride, boehmite, silicon oxide, titanium oxide, magnesium oxide, and zirconium oxide. Specific examples of resin materials include acrylic resin and styrene resin.

[0142] When fabricating a laminated separator, a precursor solution containing a polymer compound and a solvent is prepared, and then the precursor solution is applied to one or both sides of a porous membrane. In this case, instead of applying the precursor solution to the porous membrane, the porous membrane may be immersed in the precursor solution. In addition, multiple insulating particles may be added to the precursor solution.

[0143] Even when this laminated separator is used, the same effect can be obtained because lithium ions are able to move between the positive electrode 21 and the negative electrode 22. In this case, as described above, the safety of the secondary battery is particularly improved, and therefore, a greater effect can be obtained.

[0144] [Variation 3] An electrolyte solution, which is a liquid electrolyte, was used, but although not specifically shown here, an electrolyte layer, which is a gel electrolyte, may also be used.

[0145] In a battery element 20 using an electrolyte layer, a positive electrode 21 and a negative electrode 22 are stacked one on top of the other with a separator 23 and an electrolyte layer interposed therebetween, and the positive electrode 21, the negative electrode 22, the separator 23, and the electrolyte layer are wound together. The electrolyte layer is interposed between the positive electrode 21 and the separator 23, and also between the negative electrode 22 and the separator 23. However, the electrolyte layer may be interposed only between the positive electrode 21 and the separator 23, or may be interposed only between the negative electrode 22 and the separator 23.

[0146] This electrolyte layer contains a polymer compound together with an electrolytic solution, and the electrolytic solution is held by the polymer compound. This is because leakage of the electrolytic solution is prevented. The composition of the electrolytic solution is as described above. The polymer compound contains polyvinylidene fluoride, etc. When forming the electrolyte layer, a precursor solution containing the electrolytic solution, the polymer compound, a solvent, etc. is prepared, and then the precursor solution is applied to one or both surfaces of each of the positive electrode 21 and the negative electrode 22.

[0147] Even when this electrolyte layer is used, the same effect can be obtained because lithium ions can move between the positive electrode 21 and the negative electrode 22 via the electrolyte layer. In this case, leakage of the electrolyte solution is prevented as described above, and therefore a greater effect can be obtained.

[0148] <5. Uses of secondary batteries> Finally, the uses (application examples) of the secondary battery will be described.

[0149] The use of the secondary battery is not particularly limited. The secondary battery used as a power source may be a main power source for electronic devices, electric vehicles, etc., or an auxiliary power source. A main power source is a power source that is used preferentially regardless of the presence or absence of other power sources. An auxiliary power source may be a power source used in place of the main power source, or a power source that can be switched from the main power source.

[0150] Specific examples of uses for secondary batteries are as follows: Electronic devices such as video cameras, digital still cameras, mobile phones, laptop computers, headphone stereos, portable radios, and portable information terminals. Storage devices such as backup power supplies and memory cards. Power tools such as power drills and power saws. Battery packs installed in electronic devices. Medical electronic devices such as pacemakers and hearing aids. Electric vehicles such as electric cars (including hybrid cars). Power storage systems such as home or industrial battery systems that store power in preparation for emergencies. In these uses, one secondary battery may be used, or multiple secondary batteries may be used.

[0151] The battery pack may include a single cell or a battery pack. The electric vehicle is a vehicle that operates (travels) using a secondary battery as a driving power source, and may be a hybrid vehicle that also includes a driving source other than the secondary battery. In a home power storage system, the power stored in the secondary battery, which is a power storage source, can be used to power home electrical appliances, etc.

[0152] Here, an example of the use of the secondary battery will be specifically described. The configuration described below is merely an example and can be modified as appropriate.

[0153] Figure 5 shows the block diagram of a battery pack, which is an application example of a secondary battery. The battery pack described here is a battery pack (a so-called soft pack) that uses one secondary battery, and is installed in electronic devices such as smartphones.

[0154] 5, the battery pack includes a power supply 51 and a circuit board 52. The circuit board 52 is connected to the power supply 51 and includes a positive terminal 53, a negative terminal 54, and a temperature detection terminal 55.

[0155] Power source 51 includes one secondary battery. In this secondary battery, a positive electrode lead is connected to positive electrode terminal 53, and a negative electrode lead is connected to negative electrode terminal 54. Power source 51 is connected to an external power source via positive electrode terminal 53 and negative electrode terminal 54, and is therefore capable of charging and discharging. Circuit board 52 includes control unit 56, switch 57, thermosensitive resistor element (so-called PTC element) 58, and temperature detection unit 59. However, PTC element 58 may be omitted.

[0156] The control unit 56 includes a central processing unit (CPU) and memory, and controls the operation of the entire battery pack. The control unit 56 detects and controls the usage state of the power source 51 as necessary.

[0157] When the voltage of power supply 51 (secondary battery) reaches the overcharge detection voltage or the overdischarge detection voltage, control unit 56 turns off switch 57 to prevent charging current from flowing through the current path of power supply 51. The overcharge detection voltage is not particularly limited, but specifically is 4.20V±0.05V, and the overdischarge detection voltage is not particularly limited, but specifically is 2.40V±0.10V.

[0158] Switch 57 includes a charge control switch, a discharge control switch, a charge diode, a discharge diode, etc., and switches between the presence and absence of a connection between power supply 51 and an external device in response to an instruction from control unit 56. Switch 57 includes a field effect transistor (MOSFET) using a metal oxide semiconductor, etc., and the charge / discharge current is detected based on the ON resistance of switch 57.

[0159] Temperature detection unit 59 includes a temperature detection element such as a thermistor, measures the temperature of power supply 51 using temperature detection terminal 55, and outputs the temperature measurement result to control unit 56. The temperature measurement result measured by temperature detection unit 59 is used when control unit 56 controls charging and discharging in the event of abnormal heat generation, and when control unit 56 performs correction processing when calculating the remaining capacity. [Example]

[0160] An embodiment of the present technology will be described.

[0161] <Experimental Examples 1 to 4 and Comparative Examples 1 to 5> As will be described below, after the secondary battery was fabricated, the characteristics of the secondary battery were evaluated.

[0162] [Secondary battery production] The secondary battery (laminate film type lithium ion secondary battery) shown in FIGS. 3 and 4 was fabricated by the following procedure.

[0163] (Preparation of positive electrode) First, 95 parts by mass of a positive electrode active material (lithium cobalt oxide (LiCoO) which is a lithium-containing compound (oxide)), 3 parts by mass of a positive electrode binder (polyvinylidene fluoride), and 2 parts by mass of a positive electrode conductive agent (Ketjen black which is an amorphous carbon material) were mixed together to prepare a positive electrode mixture. Next, the positive electrode mixture was added to a solvent (N-methyl-2-pyrrolidone which is an organic solvent), and the solvent was stirred to prepare a paste-like positive electrode mixture slurry.

[0164] Next, the cathode mixture slurry was applied to both sides of the cathode current collector 21A (aluminum foil with a thickness of 10 μm) using a coating device, and then the cathode mixture slurry was dried to form the cathode active material layer 21B. Finally, the cathode active material layer 21B was compression-molded using a roll press, and the cathode current collector 21A on which the cathode active material layer 21B was formed was cut into a strip shape (width = 70 mm × length = 800 mm). In this way, the cathode 21 was produced.

[0165] (Preparation of negative electrode) Here, negative electrodes 22 having two types of structures (dispersion type and coating type) were fabricated.

[0166] When producing the dispersion-type negative electrode 22, first, 65.4 parts by mass of a negative electrode active material (mesocarbon microbeads (MCMB) which is a carbon material), 30 parts by mass of another negative electrode active material (silicon oxide (SiO) which is a metal-based material), 3 parts by mass of a negative electrode binder (polyvinylidene fluoride), 1 part by mass of a negative electrode conductive agent (carbon nanotubes), 0.3 parts by mass of polyrotaxane, and 0.3 parts by mass of an organic fiber compound were mixed together to form a negative electrode mixture.

[0167] The polyrotaxane used was ASM's Selm Super Polymer SH2400P (CD / PEG). This polyrotaxane contains cyclodextrin as a cyclic molecule and polyethylene glycol with adamantyl groups at both ends as a linear molecule. The molecular weight of the linear molecule is 20,000, and the overall molecular weight of the polyrotaxane is 400,000.

[0168] The organic fiber compounds used were cellulose (CEL), chitin (CHN), and chitosan (CHT).

[0169] Next, the negative electrode mixture was added to a solvent (N-methyl-2-pyrrolidone, an organic solvent), and the solvent containing the negative electrode mixture was stirred using a planetary mixer to prepare a paste-like negative electrode mixture slurry. Next, the negative electrode mixture slurry was applied to both sides of the negative electrode current collector 22A (copper foil with a thickness of 8 μm) using a coating device, and the negative electrode mixture slurry was then dried with hot air to form the negative electrode active material layer 22B.

[0170] Finally, the negative electrode active material layer 22B was compression-molded using a roll press, and then the negative electrode current collector 22A on which the negative electrode active material layer 22B was formed was cut into a strip shape (width = 72 mm × length = 810 mm), thereby producing a dispersed negative electrode 22.

[0171] When preparing the coated negative electrode 22, first, 98 parts by mass of a powdered metal-based material (silicon oxide (SiO)), 1 part by mass of polyrotaxane (CD / PEG), and 1 part by mass of an organic fiber compound (CEL) were mixed together to prepare a mixture.

[0172] Next, the mixture was poured into a solvent (pure water, which is an aqueous solvent), and the solvent containing the mixture was stirred to prepare a mixed solution. Next, the mixed solution was sprayed using a spray dryer, and the spray was dried. As a result, a coating portion 121Y containing a polyrotaxane and an organic fiber compound was formed on the surface of the core portion 121X containing a metal-based material, and thus a plurality of negative electrode active material particles 121 was obtained.

[0173] Next, 65.4 parts by mass of the negative electrode active material (MCMB), 30.6 parts by mass of other negative electrode active material (plural negative electrode active material particles 121), 3 parts by mass of a negative electrode binder (polyvinylidene fluoride), and 1 part by mass of a negative electrode conductive agent (carbon nanotubes) were mixed together to prepare a negative electrode mixture. Next, the negative electrode mixture was added to a solvent (N-methyl-2-pyrrolidone, an organic solvent), and the solvent containing the negative electrode mixture was stirred using a planetary mixer to prepare a paste-like negative electrode mixture slurry.

[0174] Next, the anode active material layer 22B was formed using the anode mixture slurry in the same manner as in the case of fabricating the dispersed-type anode 22, and the anode active material layer 22B was compression-molded. Then, the anode current collector 22A on which the anode active material layer 22B was formed was cut into strips. In this way, the coated anode 22 was fabricated.

[0175] For comparison, a negative electrode 22 was fabricated in the same manner except that one or both of the polyrotaxane and the organic fiber compound were not used. In this case, the amount of the negative electrode active material (carbon material) was adjusted depending on the presence or absence of the polyrotaxane and the organic fiber compound.

[0176] (Preparation of Electrolyte) After adding an electrolyte salt (lithium salt, lithium hexafluorophosphate (LiPF6)) to a solvent (cyclic ethylene carbonate and chain ethylene carbonate), the solvent containing the electrolyte salt was stirred. In this case, the mixing ratio (mass ratio) of the solvents was 50:50, and the content of the electrolyte salt was 1 mol / L (=1 mol / dm 3 ) Thus, the electrolyte solution was prepared.

[0177] (Secondary battery assembly) First, a positive electrode lead 31 (aluminum foil) was welded to the positive electrode current collector 21A of the positive electrode 21, and a negative electrode lead 32 (copper foil) was welded to the negative electrode current collector 22A of the negative electrode 22.

[0178] Next, the positive electrode 21 and the negative electrode 22 were stacked together with a separator 23 (a microporous polyethylene film having a thickness of 25 μm) interposed therebetween, and then the positive electrode 21, the negative electrode 22, and the separator 23 were wound to prepare a wound body. Next, the wound body was pressed using a press machine to form the wound body into a flat shape.

[0179] Next, the exterior film 10 was folded so as to sandwich the wound body accommodated in the recess 10U. An aluminum laminate film was used as this exterior film 10, in which a fusion layer (a polypropylene film having a thickness of 30 μm), a metal layer (aluminum foil having a thickness of 40 μm), and a surface protection layer (a nylon film having a thickness of 25 μm) were laminated in this order from the inside. Next, the outer peripheral edges of two sides of the fusion layer were heat-sealed to each other, thereby accommodating the wound body inside the bag-shaped exterior film 10.

[0180] Finally, an electrolyte solution was poured into the bag-shaped exterior film 10, and then the outer peripheral edges of the remaining side of the fusion layer were heat-sealed to each other in a reduced pressure environment. In this case, a sealing film 41 (a polypropylene film having a thickness of 5 μm) was inserted between the exterior film 10 and the positive electrode lead 31, and a sealing film 42 (a polypropylene film having a thickness of 5 μm) was inserted between the exterior film 10 and the negative electrode lead 32.

[0181] As a result, the wound body was impregnated with the electrolyte, thereby producing the battery element 20. Thus, the battery element 20 was sealed inside the exterior film 10, and a secondary battery was assembled.

[0182] (Stabilization of secondary batteries) The secondary battery was charged and discharged for one cycle in a room temperature environment (temperature = 23°C). During charging, it was charged at a constant current of 0.2 C until the voltage reached 4.4 V, and then it was charged at a constant voltage of 0.025 C at that voltage of 4.4 V. During discharging, it was discharged at a constant current of 0.2 C until the voltage reached 3.0 V. 0.2 C is the current value that fully discharges the battery capacity (theoretical capacity) in 5 hours, and 0.025 C is the current value that fully discharges the battery capacity in 40 hours.

[0183] As a result, a coating was formed on the surface of each of the positive electrode 21 and the negative electrode 22, and the secondary battery was electrochemically stabilized. Thus, the secondary battery was completed.

[0184] (Secondary battery design) When producing this secondary battery (a laminate film type lithium ion secondary battery), the capacity ratio was designed according to the procedure described below.

[0185] First, a positive electrode 21 was fabricated using the same procedure except that a positive electrode active material layer 21B was formed on only one surface of a positive electrode current collector 21A. Also, a negative electrode 22 was fabricated using the same procedure except that a negative electrode active material layer 22B was formed on only one surface of a negative electrode current collector 22A.

[0186] Next, a test secondary battery (a coin-type secondary battery, not shown) was fabricated using the positive electrode 21 as the test electrode and a lithium metal plate as the counter electrode. Also, a test secondary battery (a coin-type secondary battery, not shown) was fabricated using the negative electrode 22 as the test electrode and a lithium metal plate as the counter electrode.

[0187] Next, a test secondary battery using the positive electrode 21 as the test electrode was charged to measure its electrical capacity, and then the charge capacity of the positive electrode 21 per thickness of the positive electrode active material layer 21B was calculated based on the electrical capacity and the thickness of the positive electrode active material layer 21B. During charging, the battery was charged at a constant current of 0.1 C until the voltage reached 4.45 V, and then at a constant voltage of 4.45 V until the current was reduced to 1 / 10. 0.1 C is the current value at which the battery capacity is fully discharged in 10 hours.

[0188] Next, a test secondary battery using the negative electrode 22 as the test electrode was charged to measure the electric capacity, and then the charge capacity of the negative electrode 22 per thickness of the negative electrode active material layer 22 B was calculated based on the electric capacity and the thickness of the negative electrode active material layer 22 B. During charging, constant current charging was performed at a current of 0.1 C until the voltage reached 0 V, and then constant voltage charging was performed at the voltage of 0 V until the current was reduced to 1 / 10.

[0189] Finally, the capacity ratio was calculated based on the charge capacity of the positive electrode 21 and the charge capacity of the negative electrode 22. This capacity ratio is calculated based on the formula: capacity ratio = charge capacity of the positive electrode 21 / charge capacity of the negative electrode 22.

[0190] When producing the above secondary battery (a laminate film type lithium ion secondary battery), the concentrations and application speeds of the positive electrode mixture slurry and the negative electrode mixture slurry were adjusted so that the capacity ratio was 0.9.

[0191] [Characteristic evaluation of secondary batteries] The low-temperature cycle characteristics and load characteristics were evaluated according to the procedures described below, and the results shown in Table 1 were obtained.

[0192] (Low temperature cycle characteristics) First, the discharge capacity (discharge capacity at the first cycle) was measured by charging and discharging the secondary battery in a low-temperature environment (temperature = 5°C). Next, the discharge capacity (discharge capacity at the 100th cycle) was measured by repeatedly charging and discharging the secondary battery in the same environment until the number of cycles reached 100. Finally, the cycle retention rate, which is an index for evaluating low-temperature cycle characteristics, was calculated based on the formula: cycle retention rate (%) = (discharge capacity at the 100th cycle / discharge capacity at the 1st cycle) × 100. The charge and discharge conditions were the same as those used for stabilizing the secondary battery.

[0193] The cycle retention values ​​shown in Table 1 are normalized by setting the cycle retention value in Comparative Example 1, in which neither polyrotaxane nor an organic fiber compound was used, at 100.00. In this case, the cycle retention value is rounded to two decimal places.

[0194] (Load characteristics) First, the discharge capacity (discharge capacity at the first cycle) was measured by charging and discharging the secondary battery in a room temperature environment (temperature = 23 °C). The charge and discharge conditions were the same as those used when the secondary battery was stabilized.

[0195] Next, the secondary battery was charged and discharged in the same environment to measure the discharge capacity (discharge capacity at the second cycle). The charge and discharge conditions were the same as those at the first cycle, except that the discharge current was changed to 2C. 2C is the current value at which the battery capacity is fully discharged in 0.5 hours.

[0196] Finally, the load retention rate, which is an index for evaluating load characteristics, was calculated based on the formula: load retention rate (%)=(discharge capacity at second cycle / discharge capacity at first cycle)×100.

[0197] The values ​​of the load retention ratios shown in Table 1 are, like the values ​​of the cycle retention ratios described above, normalized by setting the value of the load retention ratio in Comparative Example 1 to 100.00, and are rounded to two decimal places.

[0198] [Table 1]

[0199] [Consideration] As shown in Table 1, the cycle retention rate and the load retention rate each varied greatly depending on the configuration of the negative electrode 22. In the following, the cycle retention rate and the load retention rate in Comparative Example 1, in which neither the polyrotaxane nor the organic fiber compound was used, are used as the comparison standard.

[0200] When only polyrotaxane was used (Comparative Examples 2 and 3), the cycle retention rate decreased significantly, and the load retention rate also decreased. When only the organic fiber compound was used (Comparative Examples 4 and 5), the cycle retention rate increased slightly, but the load retention rate remained the same.

[0201] According to these results, it is expected that when both polyrotaxane and an organic fiber compound are used, the cycle retention rate and the load retention rate will decrease.

[0202] However, in practice, when both the polyrotaxane and the organic fiber compound were used (Examples 1 to 4), the synergistic effect of the polyrotaxane and the organic fiber compound resulted in results contrary to the above-mentioned expectations. Specifically, the cycle retention rate was significantly increased and the load retention rate was also increased, regardless of the structure of the negative electrode 22 (dispersed type or coated type).

[0203] [summary] As can be seen from the results shown in Table 1, when the negative electrode 22 contained polyrotaxane and an organic fiber compound, a high cycle retention rate and a high load retention rate were obtained. Therefore, the secondary battery was able to achieve excellent low-temperature cycle characteristics and excellent load characteristics.

[0204] The present technology has been described above with reference to an embodiment and examples. However, the configuration of the present technology is not limited to the configuration described in the embodiment and examples, and can be modified in various ways.

[0205] Specifically, the secondary battery has been described as having a laminate film structure, but the structure of the secondary battery is not particularly limited, and may be cylindrical, prismatic, coin-shaped, button-shaped, or the like.

[0206] The battery element has been described as having a wound structure. However, the structure of the battery element is not particularly limited, and may be a stacked structure or a zigzag structure. In the stacked structure, the positive and negative electrodes are stacked on top of each other, and in the zigzag structure, the positive and negative electrodes are folded in a zigzag pattern.

[0207] Furthermore, although the electrode reactant is lithium in the above description, the electrode reactant is not particularly limited. Specifically, as described above, the electrode reactant may be other alkali metals such as sodium and potassium, or alkaline earth metals such as beryllium, magnesium, and calcium. In addition, the electrode reactant may be other light metals such as aluminum.

[0208] The effects described in this specification are merely examples, and the effects of the present technology are not limited to the effects described in this specification. Therefore, other effects may be obtained with respect to the present technology.

Claims

1. a positive electrode, a negative electrode, and an electrolyte; the negative electrode includes a polyrotaxane, an organic fiber compound, and a negative electrode active material that occludes and releases an electrode reactive substance, the negative electrode active material includes a center portion that occludes and releases the electrode reactant, and a coating portion that coats a surface of the center portion, the coating portion includes the polyrotaxane and the organic fiber compound; Secondary battery.

2. The organic fiber compound includes at least one of cellulose, chitin, and chitosan. The secondary battery according to claim 1 .

3. the polyrotaxane includes a cyclic molecule and a linear molecule passing through the cyclic molecule, the linear molecule has terminal groups at both ends that are sterically hindrances to the cyclic molecule; the cyclic molecule comprises at least one of cyclodextrin, crown ether, thiocrown ether, cyclophane, calixarene, thiocalixarene, cucurbituril, pillararene, and cyclic amide; the linear molecule includes at least one of polyethylene glycol, polyoxymethylene, polypropylene oxide, polyvinyl alcohol, polyvinylidene fluoride, a linear alkane, an amide, and an ammonium; the terminal group includes at least one of a dinitrophenyl group, a cyclodextrin group, an adamantyl group, a trityl group, a fluoresceinyl group, a pyrenyl group, and an anthracenyl group; The secondary battery according to claim 1 .

4. It is a lithium-ion secondary battery. The secondary battery according to any one of claims 1 to 3.

5. The negative electrode active material includes polyrotaxane, an organic fiber compound, and an electrode reactive substance. the negative electrode active material includes a center portion that occludes and releases the electrode reactant, and a coating portion that coats a surface of the center portion, the coating portion includes the polyrotaxane and the organic fiber compound; Negative electrode for secondary batteries.

6. The organic fiber compound includes at least one of cellulose, chitin, and chitosan. The negative electrode for a secondary battery according to claim 5 .

7. The polyrotaxane includes a cyclic molecule and a linear molecule that penetrates the cyclic molecule, the linear molecule has terminal groups at both ends that are sterically hindrances to the cyclic molecule; the cyclic molecule comprises at least one of cyclodextrin, crown ether, thiocrown ether, cyclophane, calixarene, thiocalixarene, cucurbituril, pillararene, and cyclic amide; the linear molecule includes at least one of polyethylene glycol, polyoxymethylene, polypropylene oxide, polyvinyl alcohol, polyvinylidene fluoride, a linear alkane, an amide, and an ammonium; the terminal group includes at least one of a dinitrophenyl group, a cyclodextrin group, an adamantyl group, a trityl group, a fluoresceinyl group, a pyrenyl group, and an anthracenyl group; The negative electrode for a secondary battery according to claim 5 or 6.

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