Negative electrode for lithium ion secondary battery and lithium ion secondary battery

Abstract

This lithium ion secondary battery comprises: a positive electrode that intercalates and deintercalates lithium ions; a negative electrode that intercalates and deintercalates the lithium ions and includes a negative electrode active material layer; and an electrolyte solution that contains an aqueous solvent. The negative electrode active material layer contains a plurality of negative electrode active material particles, and has a porous structure in which the plurality of negative electrode active material particles are directly joined together. Each of the plurality of negative electrode active material particles contains anatase-type titanium oxide, and the average particle diameter of the plurality of negative electrode active material particles is 100 nm or less.

Description

[Technical Field]

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

[0002] Due to the widespread use of various electronic devices such as mobile phones, development of lithium-ion secondary batteries has been progressing as a power source that is compact, lightweight, and has high energy density. These lithium-ion secondary batteries include a positive electrode, a negative electrode, and an aqueous electrolyte solution, which contains an aqueous solvent. Various studies have been conducted on technologies related to lithium-ion secondary batteries with aqueous electrolyte solutions.

[0003] Specifically, in a secondary battery having a non-aqueous electrolyte, a negative electrode that is a sintered body of lithium titanate is used, and the average pore size, specific surface area, and relative density of the negative electrode are specified (see, for example, Patent Document 1). In a secondary battery having an electrolyte layer containing a non-aqueous electrolyte, a negative electrode that is a sintered body of an oxide containing lithium and a transition metal element is used, and the relative density of the negative electrode is specified (see, for example, Patent Document 2).

[0004] In secondary batteries with non-aqueous electrolytes, a titanium-titanium oxide composite electrode is used as a negative electrode, and the negative electrode contains anatase-type titanium oxide having a nanotube shape (see, for example, Patent Document 3). In secondary batteries with aqueous electrolytes, a negative electrode containing titanium oxide is used (see, for example, Patent Document 4). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2012 / 086557 Brochure [Patent Document 2] Japanese Patent Application Laid-Open No. 2013-097912 [Patent Document 3] Japanese Patent Application Laid-Open No. 2006-093037 [Patent Document 4] International Publication No. 2020 / 218456 Brochure Summary of the Invention

[0006] Although various studies have been conducted on the technology related to lithium ion secondary batteries with aqueous electrolyte solutions, the operating characteristics of the lithium ion secondary batteries are still insufficient and there is room for improvement.

[0007] Therefore, there is a demand for a negative electrode for a lithium ion secondary battery and a lithium ion secondary battery that can provide excellent operating characteristics.

[0008] According to one embodiment of the present disclosure, a negative electrode for a lithium-ion secondary battery absorbs and releases lithium ions and includes a negative electrode active material layer. The negative electrode active material layer includes a plurality of negative electrode active material particles and has a porous structure in which the plurality of negative electrode active material particles are directly bonded to one another. Each of the plurality of negative electrode active material particles includes anatase titanium oxide, and the average particle size of the plurality of negative electrode active material particles is 100 nm or less.

[0009] Furthermore, a lithium ion secondary battery according to an embodiment of the present technology includes a positive electrode that absorbs and releases lithium ions, a negative electrode, and an electrolyte solution containing an aqueous solvent, and the negative electrode has a configuration similar to that of the negative electrode for the lithium ion secondary battery according to the embodiment of the present technology described above.

[0010] Here, the "average particle size of the plurality of negative electrode active material particles" is calculated based on the observation results (electron microscope photographs) obtained by observing the negative electrode active material layer using an electron microscope. The definition of this "average particle size," i.e., the details of the procedure for calculating the average particle size based on the electron microscope photographs, will be described later.

[0011] According to the negative electrode for a lithium ion secondary battery or the lithium ion secondary battery of one embodiment of the present technology, the negative electrode active material layer has a porous structure in which a plurality of negative electrode active material particles are directly bonded to one another, each of the plurality of negative electrode active material particles contains anatase-type titanium oxide, and the plurality of negative electrode active material particles have an average particle size of 100 nm or less, thereby achieving excellent operating characteristics.

[0012] 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]

[0013] [Figure 1] 1 is a cross-sectional view illustrating a configuration of a lithium-ion secondary battery according to a first embodiment of the present technology. [Figure 2] FIG. 2 is an enlarged cross-sectional view showing the configuration of the negative electrode shown in FIG. [Figure 3] 3 is a schematic diagram showing an electron microscope photograph of a cross section of the negative electrode active material layer shown in FIG. 2. FIG. [Figure 4] FIG. 4 is a cross-sectional view illustrating a configuration of a lithium-ion secondary battery according to a second embodiment of the present technology. [Figure 5] FIG. 1 is a cross-sectional view illustrating the configuration of a lithium ion secondary battery according to a first modification. [Figure 6] FIG. 10 is a cross-sectional view illustrating the configuration of a lithium ion secondary battery according to a third modification. [Figure 7] FIG. 10 is a cross-sectional view illustrating the configuration of a lithium ion secondary battery according to a fourth modification. DETAILED DESCRIPTION OF THE INVENTION

[0014] 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. First embodiment (lithium ion secondary battery) 1-1.Configuration 1-2.Operation 1-3. Manufacturing method 1-4. Action and effects 2. Second embodiment (lithium ion secondary battery) 2-1.Configuration 2-2.Operation 2-3. Manufacturing method 2-4. Action and effects 3. Variations 4. Uses of Lithium-ion Secondary Batteries

[0015] 1. First Embodiment (Lithium-ion Secondary Battery) First, a lithium ion secondary battery according to a first embodiment of the present technology will be described.

[0016] Note that, since the negative electrode for a lithium ion secondary battery according to one embodiment of the present technology (hereinafter simply referred to as the "negative electrode") is a part (one component) of the lithium ion secondary battery, the negative electrode will also be described below.

[0017] The lithium-ion secondary battery described here is a secondary battery in which charge-discharge reactions proceed by utilizing the absorption and release of lithium ions, and includes a positive electrode, a negative electrode, and an aqueous electrolyte solution. This aqueous electrolyte solution is a liquid electrolyte, and more specifically, as described above, is an electrolyte solution containing an aqueous solvent.

[0018] <1-1.Configuration> Fig. 1 shows a cross-sectional structure of the lithium-ion secondary battery of the first embodiment, and Fig. 2 shows an enlarged cross-sectional structure of the negative electrode 30 shown in Fig. 1. Fig. 3 shows a schematic electron microscope photograph 100 of a cross section of the negative electrode active material layer 30B shown in Fig. 2.

[0019] 1 and 2, this lithium ion secondary battery includes an exterior body 10, a positive electrode 20, a negative electrode 30, and an electrolyte solution 40. In Fig. 1, the electrolyte solution 40 is lightly shaded.

[0020] [Exterior body] As shown in FIG. 1, the exterior body 10 is a substantially box-shaped exterior member that houses the positive electrode 20, the negative electrode 30, the electrolyte solution 40, and the like, and has an internal space S.

[0021] This exterior body 10 includes one or more of a metal material, a glass material, a polymer compound, etc. The exterior body 10 may be a rigid metal can, a glass case, a plastic case, etc., or a flexible (or pliable) metal foil, a polymer film, etc.

[0022] [Positive electrode] 1, the positive electrode 20 is disposed in the internal space S and absorbs and releases lithium ions. Here, the positive electrode 20 includes a positive electrode current collector 20A having a pair of surfaces and a positive electrode active material layer 20B provided on both surfaces of the positive electrode current collector 20A. However, the positive electrode active material layer 20B may be provided on only one surface of the positive electrode current collector 20A on the side where the positive electrode 20 faces the negative electrode 30.

[0023] The positive electrode current collector 20A may be omitted. That is, the positive electrode 20 does not include the positive electrode current collector 20A, and may therefore include only the positive electrode active material layer 20B.

[0024] (Positive electrode current collector) The positive electrode current collector 20A is a conductive support member that supports the positive electrode active material layer 20B and contains one or more conductive materials such as metal materials, carbon materials, and conductive ceramic materials. Specific examples of metal materials include titanium, aluminum, and their alloys. Specific examples of conductive ceramic materials include indium tin oxide (ITO).

[0025] In particular, it is preferable that the material forming the positive electrode current collector 20A is insoluble or hardly soluble in the electrolyte 40, and corrosion-resistant, and also has low reactivity with the positive electrode active material described below. For this reason, it is preferable that the positive electrode current collector 20A contains the above-mentioned metal material, because this makes the positive electrode current collector 20A less susceptible to deterioration even when used in a lithium-ion secondary battery.

[0026] The positive electrode current collector 20A may be a conductor whose surface is plated with the above-mentioned conductive material. The material for forming the conductor is not particularly limited and can be selected arbitrarily.

[0027] Here, the positive electrode active material layer 20B is not provided on a part (connection terminal portion 20AT) of the positive electrode current collector 20A, and the connection terminal portion 20AT is led out from the inside (internal space S) of the exterior body 10 to the outside.

[0028] (Cathode active material layer) The positive electrode active material layer 20B contains one or more types of positive electrode active materials that absorb and release lithium ions, but may also contain one or more types of a positive electrode binder, a positive electrode conductive agent, and the like.

[0029] The positive electrode active material includes a lithium-containing compound, and the lithium-containing compound is a compound containing lithium as a constituent element. The type of lithium-containing compound is not particularly limited, but specific examples include lithium composite oxides and lithium phosphate compounds. The lithium composite oxide is an oxide containing lithium and one or more transition metal elements as constituent elements, and the lithium phosphate compound is a phosphate compound containing lithium and one or more transition metal elements as constituent elements. The type of transition metal element is not particularly limited, but specific examples include nickel, cobalt, manganese, and iron.

[0030] Specific examples of lithium composite oxides having a layered rock salt crystal structure are LiNiO2, LiCoO2, and 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 Mn0.33 O2, Li 1.2 Mn 0.52 Co 0.175 Ni 0.1 O2 and Li 1.15 (Mn 0.65 Ni 0.22 Co 0.13 )O2, etc. A specific example of a lithium composite oxide having a spinel-type crystal structure is LiMn2O4, etc. Specific examples of lithium phosphate compounds having an olivine-type crystal structure are LiFePO4, LiMnPO4, LiMn 0.5 Fe 0.5 PO4, LiMn 0.7 Fe 0.3 PO4 and LiMn 0.75 Fe 0.25 PO4, etc.

[0031] The positive electrode binder contains one or more of synthetic rubbers and polymer compounds, etc. Specific examples of synthetic rubbers include styrene-butadiene rubbers, and specific examples of polymer compounds include polyvinylidene fluoride and polyimide.

[0032] The positive electrode conductive agent contains one or more conductive materials such as carbon materials, and specific examples of the carbon materials include graphite, carbon black, acetylene black, and ketjen black. However, the conductive material may also be a metal material, a conductive ceramic material, a conductive polymer, or the like.

[0033] [Negative electrode] 1, the negative electrode 30 is disposed in the internal space S and absorbs and releases lithium ions. Here, the negative electrode 30 includes a negative electrode current collector 30A having a pair of surfaces and a negative electrode active material layer 30B provided on both surfaces of the negative electrode current collector 30A. However, the negative electrode active material layer 30B may be provided on only one surface of the negative electrode current collector 30A on the side where the negative electrode 30 faces the positive electrode 20.

[0034] The negative electrode current collector 30A may be omitted. That is, the negative electrode 30 does not include the negative electrode current collector 30A, and may therefore include only the negative electrode active material layer 30B.

[0035] (Negative electrode current collector) The negative electrode current collector 30A is a conductive support member that supports the negative electrode active material layer 30B and includes one or more conductive materials such as metal materials, carbon materials, and conductive ceramic materials. Specific examples of metal materials include stainless steel (SUS), titanium, tin, lead, and alloys thereof. This stainless steel may be highly corrosion-resistant stainless steel to which one or more additive elements such as niobium and molybdenum have been added. Specifically, the stainless steel may be SUS444 or the like to which molybdenum has been added as an additive element. Details regarding the conductive ceramic material are as described above.

[0036] In particular, it is preferable that the material forming the negative electrode current collector 30A is insoluble or hardly soluble in the electrolyte solution 40, and is corrosion-resistant, and also has low reactivity with the negative electrode active material described below. For this reason, it is preferable that the negative electrode current collector 30A contains the above-mentioned metal material, because this makes the negative electrode current collector 30A less susceptible to deterioration even when used in a lithium-ion secondary battery.

[0037] The negative electrode current collector 30A may be a conductor whose surface is plated with the above-mentioned conductive material. The material for forming the conductor is not particularly limited and can be selected arbitrarily.

[0038] Here, the negative electrode active material layer 30B is not formed on a part (connection terminal portion 30AT) of the negative electrode current collector 30A, and the connection terminal portion 30AT is led out from the inside (internal space S) of the exterior body 10 to the outside.

[0039] (Negative electrode active material layer) The negative electrode active material layer 30B contains a negative electrode active material that absorbs and releases lithium ions. However, the negative electrode active material layer 30B may further contain a negative electrode conductive agent, etc. Details regarding the negative electrode conductive agent are the same as those regarding the positive electrode conductive agent.

[0040] Specifically, as shown in FIG. 2, the negative electrode active material layer 30B contains a plurality of particulate negative electrode active materials (hereinafter referred to as "a plurality of negative electrode active material particles 31"), and each of the plurality of negative electrode active material particles 31 is a so-called primary particle.

[0041] The negative electrode active material layer 30B has a porous structure, which is formed by directly bonding a plurality of negative electrode active material particles 31 to one another. That is, in the negative electrode active material layer 30B, the negative electrode active material particles 31 are directly bonded to one another, thereby forming a plurality of voids (pores 32) between the plurality of negative electrode active material particles 31. As a result, the negative electrode active material layer 30B has a porous structure formed by the plurality of negative electrode active material particles 31, as described above.

[0042] More specifically, the negative electrode active material layer 30B is a sintered body of a plurality of negative electrode active material particles 31 formed by a firing method, and therefore the plurality of negative electrode active material particles 31 are directly bonded to one another inside the negative electrode active material layer 30B. Details of the method for forming the negative electrode active material layer 30B using this firing method will be described later.

[0043] As described above, the phrase "directly bonded to each other" means that the negative electrode active material layer 30B is a sintered body of a plurality of negative electrode active material particles 31. That is, the plurality of negative electrode active material particles 31 are not indirectly bonded to each other via a binder, but are directly bonded to each other without the binder. Furthermore, the plurality of negative electrode active material particles 31 are not indirectly bonded to each other via the conductive agent, and therefore are not electrically connected to each other via the conductive agent, but are directly bonded to each other without the conductive agent, and therefore are electrically connected to each other without the conductive agent.

[0044] The reason why the negative electrode active material layer 30B is a sintered body of a plurality of negative electrode active material particles 31 is that the plurality of negative electrode active material particles 31 are physically and electrically connected to one another, thereby increasing the energy density of the negative electrode active material layer 30B and improving the electronic conductivity between the plurality of negative electrode active material particles 31. This reduces the electrical resistance while ensuring the energy density in the negative electrode 30, making it easier to obtain a high discharge capacity in the lithium-ion secondary battery.

[0045] Here, each of the plurality of negative electrode active material particles 31 contains titanium oxide having an anatase crystal structure. This is because anatase titanium oxide is more likely to undergo stable charge / discharge reactions in a strong alkaline electrolyte solution 40 (described later) than titanium oxide having a rutile or brookite crystal structure. This makes it easier to stably obtain a higher discharge capacity in the lithium ion secondary battery.

[0046] Furthermore, the average particle size AS of the plurality of negative electrode active material particles 31 calculated based on the results of observation of a cross section of the negative electrode active material layer 30B using an electron microscope is significantly small, specifically, 100 nm or less. That is, each of the plurality of negative electrode active material particles 31 is what is called a nanoparticle. This is because lithium ions can easily move inside each negative electrode active material particle 31. This is also because the energy density per weight of the negative electrode active material layer 30B is improved, and multiple pores 32 that serve as paths for lithium ions to move inside the negative electrode active material layer 30B are more easily formed. This makes it easier to obtain a higher discharge capacity in the lithium-ion secondary battery.

[0047] In particular, the average particle size AS is preferably 30 nm or less, because this allows lithium ions to move more easily inside the negative electrode active material particles 31. This is also because this further improves the energy density per weight of the negative electrode active material layer 30B, and makes it easier for multiple pores 32 to be formed inside the negative electrode active material layer 30B.

[0048] Although there are no particular restrictions on the lower limit of the average particle size AS, specifically, the average particle size AS is 7 nm or more, because this makes it easier for a plurality of negative electrode active material particles 31 to be formed stably.

[0049] The procedure for calculating the average particle size AS is as follows: To calculate the average particle size AS, an electron microscope photograph 100 shown in FIG.

[0050] Specifically, first, the secondary battery is disassembled to recover the negative electrode 30. Next, the surface of the negative electrode active material layer 30B is observed using an electron microscope to obtain an electron microscope photograph 100. The type of electron microscope is not particularly limited, but specifically, it may be one or more of a scanning electron microscope (SEM) and a transmission electron microscope (TEM). The observation conditions are an acceleration voltage of 5.0 kV and a magnification of 150,000 times.

[0051] In this case, the negative electrode 30 may be cut using an ion milling device or the like to expose a cross section of the negative electrode active material layer 30B, and the cross section of the negative electrode active material layer 30B may then be observed to obtain the electron microscope photograph 100. As the ion milling device, an ion milling device such as the ArBlade (registered trademark) 5000 manufactured by Hitachi High-Tech Corporation may be used.

[0052] In the electron microscope photograph 100, as shown in Fig. 3, a porous structure having a plurality of pores 32 is observed because a plurality of negative electrode active material particles 31 are directly bonded to one another. To simplify the illustration, Fig. 3 shows a case where each of the plurality of negative electrode active material particles 31 has a rectangular planar shape.

[0053] Next, 50 negative electrode active material particles 31 are selected from the plurality of negative electrode active material particles 31 visible in the electron microscope photograph 100, and then the particle size (maximum outer diameter) of each negative electrode active material particle 31 is measured, thereby obtaining the particle sizes S of the 50 particles.

[0054] When selecting 50 negative electrode active material particles 31, the negative electrode active material particle 31 located nearest to the front among the multiple negative electrode active material particles 31 that overlap each other is selected. That is, the negative electrode active material particle 31 (31Y) whose entire outer edge is not visible because it overlaps with one or more other negative electrode active material particles 31 is not selected. In contrast, the negative electrode active material particle 31 (31X) whose entire outer edge is visible because it does not overlap with one or more other negative electrode active material particles 31 is selected. In FIG. 3, some negative electrode active material particles 31X to be selected are shaded.

[0055] Finally, the average value of the particle diameters S of the 50 particles is calculated, and this average value is set as the average particle diameter AS.

[0056] As described above, this negative electrode active material layer 30B is a sintered body of a plurality of negative electrode active material particles 31, and therefore has characteristic structural conditions resulting from the sintered body.

[0057] That is, the volume density of the negative electrode active material layer 30B is sufficiently large, specifically, 1.0 g / cm 3 ~3.5g / cm 3 The specific surface area of the negative electrode active material layer 30B is sufficiently large, specifically, 1 m 2 / g~500m 2 / g, preferably 10m 2 / g~500m 2 / g, because the energy density of the negative electrode 30 is sufficiently increased and the electrical resistance is sufficiently reduced.

[0058] The procedure for measuring the specific surface area of the negative electrode active material layer 30B is as follows. First, the lithium-ion secondary battery is disassembled to recover the negative electrode 30. Next, the negative electrode 30 is washed using a cleaning solvent, and then thoroughly dried using a vacuum heating furnace. In this case, an aqueous solvent such as pure water is used as the solvent, and the heating temperature is set to 60°C to 100°C. Finally, after degassing (200°C x 30 minutes), the specific surface area of the negative electrode active material layer 30B is measured using the BET method (nitrogen gas). As a measuring device, a fully automatic specific surface area measuring device such as Macsorb (registered trademark) manufactured by Mountech Co., Ltd. can be used.

[0059] The porosity of the plurality of pores 32 is not particularly limited, but is specifically 10% to 75%. The porosity is calculated based on the formula: porosity (%)=[1-(volume density of negative electrode active material layer 30B / true density of negative electrode active material layer 30B)]×100.

[0060] The negative electrode active material layer 30B may further contain one or more other negative electrode active materials that absorb and release lithium ions.

[0061] The type of other negative electrode active material is not particularly limited, but specific examples include rutile-type titanium oxide, brookite-type titanium oxide, carbon materials, and metal-based materials, etc. The metal-based materials are materials containing, as constituent elements, one or more of metal elements and semimetal elements that can form an alloy with lithium.

[0062] When the negative electrode active material layer 30B contains other negative electrode active materials, the following measures may be taken to calculate the average particle size AS.

[0063] To determine whether the negative electrode active material layer 30B contains rutile or brookite titanium oxide as another negative electrode active material, X-ray diffraction (XRD) is used to analyze the negative electrode active material layer 30B, which makes it possible to confirm the presence or absence of rutile or brookite titanium oxide based on differences in crystal structure.

[0064] When the negative electrode active material layer 30B contains a carbon material or a metal-based material as another negative electrode active material, the negative electrode active material layer 30B is analyzed using energy dispersive X-ray spectroscopy (EDX). In this case, the presence or location of the carbon material or the metal-based material can be confirmed using element mapping.

[0065] [Electrolyte] The electrolyte 40 is contained in the internal space S, and as described above, is an aqueous electrolyte. That is, the electrolyte 40 is a solution in which an ionic substance that can be ionized in an aqueous solvent is dissolved or dispersed.

[0066] The lithium ion secondary battery of the first embodiment is a so-called single-liquid type lithium ion secondary battery, since it contains one type of aqueous electrolyte (electrolyte 40).

[0067] The electrolyte solution 40 contains an aqueous solvent and one or more ionic substances that can be ionized in the aqueous solvent. More specifically, the electrolyte solution 40 used in the lithium-ion secondary battery contains lithium ions that are absorbed and released in the positive electrode 20 and the negative electrode 30.

[0068] The type of aqueous solvent is not particularly limited, but specifically includes pure water, etc. The type of ionic substance is not particularly limited, but specifically includes one or more of acids, bases, and electrolyte salts, etc. Specific examples of acids include carbonic acid, oxalic acid, nitric acid, sulfuric acid, hydrochloric acid, acetic acid, and citric acid.

[0069] The electrolyte salt is a salt containing a cation and an anion, and more specifically, is one or more lithium salts. Specific examples of lithium salts include lithium carbonate, lithium oxalate, lithium nitrate, lithium sulfate, lithium chloride, lithium acetate, lithium citrate, lithium hydroxide, and imide salts. Examples of imide salts include lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethanesulfonyl)imide.

[0070] In particular, the electrolyte solution 40 used in a single-liquid type lithium-ion secondary battery has a pH of 11 or higher, and therefore, as described above, is preferably strongly alkaline. This is because lithium ions are more likely to move in the electrolyte solution 40, facilitating the progress of charge / discharge reactions.

[0071] For this reason, the electrolyte salt is preferably lithium hydroxide, among others, because the pH of the electrolyte solution 40 is likely to be 11 or higher, and therefore a strongly alkaline electrolyte solution 40 can be easily and stably realized.

[0072] The content of the ionic substance, i.e., the concentration (mol / kg) of the electrolyte solution 40 is not particularly limited and can be set arbitrarily. Specifically, the concentration of the electrolyte solution 40 is preferably 0.2 mol / kg to 4 mol / kg, because this allows a strong alkaline electrolyte solution 40 to be easily and stably obtained.

[0073] The electrolyte salt may contain one or more of the other metal salts in addition to the lithium salt described above. The types of the other metal salts are not particularly limited, but specific examples include alkali metal salts (excluding lithium salts), alkaline earth metal salts, and transition metal salts. Specific examples of alkali metal salts include sodium salts and potassium salts, and specific examples of alkaline earth metal salts include calcium salts and magnesium salts.

[0074] Furthermore, the electrolytic solution 40 is more preferably a saturated solution of an electrolyte salt, because this facilitates stable absorption and desorption of lithium ions during charging and discharging, thereby facilitating stable progress of the charge and discharge reaction.

[0075] To confirm whether the electrolyte solution 40 is a saturated solution of electrolyte salt, the lithium-ion secondary battery is disassembled and the internal space S is visually observed to determine whether electrolyte salt has precipitated. Specifically, the internal space S is observed by observing the liquid electrolyte solution 40, the surface of the positive electrode 20, and the inner wall surface of the exterior body 10. When the electrolyte salt has precipitated and the electrolyte solution 40 (liquid) and a precipitate of the electrolyte salt (solid) coexist, the electrolyte solution 40 is considered to be a saturated solution of the electrolyte salt. To determine the composition of the precipitate, a surface analysis method such as X-ray photoelectron spectroscopy (XPS) or a composition analysis method such as inductively coupled plasma (ICP) optical emission spectroscopy may be used.

[0076] <1-2. Operation> This lithium ion secondary battery operates as described below.

[0077] During charging, when lithium ions are released from the positive electrode 20, the lithium ions move to the negative electrode 30 via the electrolyte 40, and the lithium ions are absorbed in the negative electrode 30.

[0078] During discharge, when lithium ions are released from the negative electrode 30, the lithium ions move to the positive electrode 20 via the electrolyte 40, and the lithium ions are absorbed in the positive electrode 20.

[0079] <1-3. Manufacturing method> When producing this lithium ion secondary battery, the positive electrode 20 and the negative electrode 30 are produced and the electrolyte solution 40 is prepared according to the procedure described below as an example, and then the lithium ion secondary battery is assembled.

[0080] [Preparation of positive electrode] First, a positive electrode active material, a positive electrode binder, and a positive electrode conductive agent are mixed together to obtain a mixture. However, the composition of the mixture can be changed as desired. Next, a paste-like positive electrode mixture slurry is prepared by adding the positive electrode mixture to a solvent. This solvent may be an aqueous solvent or an organic solvent. Finally, the positive electrode mixture slurry is applied to both surfaces of the positive electrode current collector 20A (excluding the connection terminal portion 20AT) to form the positive electrode active material layer 20B. Thereafter, the positive electrode active material layer 20B may be compression-molded using a roll press or the like. In this case, the positive electrode active material layer 20B may be heated, or the compression molding may be repeated multiple times. In this manner, the positive electrode 20 is produced.

[0081] [Preparation of negative electrode] First, a mixture is obtained by mixing the negative electrode active material and the negative electrode binder. However, the composition of the mixture can be changed as desired. In this case, one or more additives may be added to the mixture. The type of additive is not particularly limited, but specific examples include surfactants and sintering aids.

[0082] As described above, the negative electrode active material comprises a plurality of negative electrode active material particles 31 containing anatase titanium oxide and having an average particle size AS of 100 nm or less. The type of negative electrode binder is not particularly limited, as long as it is one or more of the polymer compounds mixed with the negative electrode active material to improve the strength of the powder compact described below. Specific examples of the polymer compound include polyethylene glycol, polyvinyl alcohol, and polyvinyl butyral. Among these, the negative electrode binder is preferably a polymer compound that is decomposed and degreased at a temperature equal to or lower than the temperature at which anatase titanium oxide is fired. Specific examples of surfactants include stearic acid, and specific examples of sintering aids include boron oxide and silicon oxide.

[0083] As a result, a granulated powder containing the negative electrode binder together with the plurality of negative electrode active material particles 31 is obtained.

[0084] Next, the granulated powder is press-molded together with the negative electrode current collector 30A. Conditions such as the pressing pressure can be set as desired. As a result, the granulated powder containing the plurality of negative electrode active material particles 31 is fixed to both sides of the negative electrode current collector 30A, thereby obtaining a powder molded body.

[0085] Finally, the powder compact is fired in the atmosphere. The firing conditions, such as the firing temperature and firing time, can be set as desired depending on the composition of the powder compact. In this case, the conditions are adjusted so that the plurality of negative electrode active material particles 31 containing anatase-type titanium oxide are directly bonded to each other while maintaining the primary particle state. For example, the maximum temperature during firing is 500°C to 1200°C. The firing process may also be performed in an oxygen atmosphere.

[0086] In this firing process, the negative electrode binder is degreased during firing, so that the negative electrode active material particles 31 are directly bonded to one another, and pores 32 are formed between the negative electrode active material particles 31. As a result, a bonded body (sintered body) of the negative electrode active material particles 31 is fixed to the surface of the negative electrode current collector 30A, and a negative electrode active material layer 30B having a porous structure is formed. Thus, the negative electrode 30 is produced.

[0087] When producing this negative electrode 30, by appropriately adjusting the conditions such as the pressing pressure, firing temperature, and firing time described above, it is possible to adjust the bonding state of the multiple negative electrode active material particles 31 (multiple primary particles) and also to adjust the volume density and specific surface area of the negative electrode active material layer 30B.

[0088] It should be noted that when producing the negative electrode 30, the above-described method of firing a powder molded body containing a negative electrode binder does not necessarily have to be used. As long as the negative electrode active material layer 30B is formed by directly bonding a plurality of negative electrode active material particles 31 to one another using a firing process, the procedure for producing the negative electrode 30 can be modified as appropriate. Specifically, a powder molded body obtained by press-molding a plurality of negative electrode active material particles 31 without using a negative electrode binder may be fired. Alternatively, a dispersion liquid in which a plurality of negative electrode active material particles 31 are dispersed may be applied to the negative electrode current collector 30A, the dispersion liquid may be dried, and then the negative electrode current collector 30A coated with the dispersion liquid may be fired.

[0089] [Preparation of electrolyte] An ionic substance is added to an aqueous solvent, whereby the ionic substance is dispersed or dissolved in the aqueous solvent, thereby preparing the electrolyte solution 40. In this case, the pH of the electrolyte solution 40 can be adjusted by adjusting conditions such as the type and concentration (mol / kg) of the ionic substance.

[0090] [Assembling lithium-ion secondary batteries] First, the positive electrode 20 and the negative electrode 30 are housed in the internal space S of the exterior body 10. In this case, the connection terminal portions 20AT, 30AT are led out from the inside of the exterior body 10 (internal space S) to the outside.

[0091] Subsequently, the electrolyte solution 40 is supplied into the internal space S through an injection hole (not shown) provided in the exterior body 10, and then the injection hole is sealed.

[0092] Therefore, the electrolyte solution 40 is accommodated in the internal space S in which the positive electrode 20 and the negative electrode 30 are respectively arranged, and a single-liquid type lithium ion secondary battery using one type of aqueous electrolyte solution (electrolyte solution 40) is completed.

[0093] <1-4. Actions and Effects> In the lithium-ion secondary battery of the first embodiment, the negative electrode active material layer 30B of the negative electrode 30 contains a plurality of negative electrode active material particles 31, and the negative electrode active material layer 30B has a porous structure in which the plurality of negative electrode active material particles 31 are directly bonded to one another. Each of the plurality of negative electrode active material particles 31 contains anatase titanium oxide, and the average particle size AS of the plurality of negative electrode active material particles 31 is 100 nm or less.

[0094] In this case, as described above, the negative electrode 30 exhibits a series of functions described below.

[0095] First, because the negative electrode active material layer 30B is a sintered body of a plurality of negative electrode active material particles 31, the plurality of negative electrode active material particles 31 are physically and electrically connected to one another. In this case, the energy density of the negative electrode active material layer 30B increases, and electronic conductivity between the plurality of negative electrode active material particles 31 improves. As a result, the electrical resistance decreases while the energy density is maintained.

[0096] Second, since each of the plurality of negative electrode active material particles 31 contains anatase titanium oxide, the plurality of negative electrode active material particles 31 are stable against the strongly alkaline electrolyte solution 40. This makes it easier for the charge / discharge reaction to proceed stably even when a strongly alkaline electrolyte solution 40 is used.

[0097] Third, because the average particle size AS of the plurality of negative electrode active material particles 31 is 100 nm or less, lithium ions can easily move inside each negative electrode active material particle 31. Furthermore, the energy density per weight of the negative electrode active material layer 30B is improved, and migration paths (plurality of pores 32) for lithium ions are more easily formed inside the negative electrode active material layer 30B.

[0098] For these reasons, in a single-liquid type lithium ion secondary battery using one type of aqueous electrolyte (electrolyte solution 40), a high discharge capacity can be easily and stably obtained, and therefore excellent operating characteristics can be obtained.

[0099] In particular, when the average particle size AS is 30 nm or less, lithium ions can move more easily inside the negative electrode active material particles 31, the energy density per weight of the negative electrode active material layer 30B is improved, and migration paths for lithium ions are more easily formed inside the negative electrode active material layer 30B, thereby achieving a greater effect.

[0100] Furthermore, the volume density of the negative electrode active material layer 30B is 1.0 g / cm 3 ~3.5g / cm 3 and the specific surface area of the negative electrode active material layer 30B is 1 m 2 / g~500m 2 / g, the energy density in the negative electrode 30 increases sufficiently and the electrical resistance decreases sufficiently, so that a greater effect can be obtained.

[0101] Furthermore, if the electrolytic solution 40 has a pH of 11 or higher, lithium ions can easily move in the electrolytic solution 40. This facilitates the progress of charge / discharge reactions, thereby achieving a greater effect.

[0102] Additionally, according to the negative electrode 30, the negative electrode active material layer 30B (plurality of negative electrode active material particles 31) has the above-described configuration. Therefore, for the reasons described above, a lithium ion secondary battery including the negative electrode 30 can obtain excellent operating characteristics.

[0103] 2. Second Embodiment (Lithium-ion Secondary Battery) Next, a lithium ion secondary battery according to a second embodiment of the present technology will be described.

[0104] The lithium ion secondary battery of the second embodiment is a dual-liquid type lithium ion secondary battery that uses two types of aqueous electrolytes (positive electrode electrolyte 61 and negative electrode electrolyte 62), unlike the lithium ion secondary battery of the first embodiment, which is a single-liquid type lithium ion secondary battery that uses one type of aqueous electrolyte (electrolyte 40).

[0105] <2-1.Configuration> Fig. 4 shows a cross-sectional configuration of a lithium-ion secondary battery of the second embodiment, and corresponds to Fig. 1. The lithium-ion secondary battery of the second embodiment described here has the same configuration as the lithium-ion secondary battery of the first embodiment (Fig. 1), except for the points described below.

[0106] As shown in Fig. 4, this lithium ion secondary battery additionally includes a partition wall 50, and also includes a positive electrode electrolyte 61 and a negative electrode electrolyte 62 instead of the electrolyte 40. In Fig. 4, the positive electrode electrolyte 61 is lightly shaded, and the negative electrode electrolyte 62 is darkly shaded.

[0107] The exterior body 10 has two spaces (a positive electrode chamber S1 and a negative electrode chamber S2) separated by a partition wall 50.

[0108] The partition wall 50 is disposed between the positive electrode 20 and the negative electrode 30, and separates the internal space S (see FIG. 1 ) into a positive electrode chamber S1 and a negative electrode chamber S2. As a result, the positive electrode 20 and the negative electrode 30 are separated from each other via the partition wall 50, and also face each other via the partition wall 50.

[0109] The partition wall 50, located between the positive electrode chamber S1 and the negative electrode chamber S2, does not allow anions to pass therethrough, but allows substances (excluding anions) such as lithium ions (cations) that are absorbed and released in the positive electrode 20 and the negative electrode 30 to pass therethrough. This is to prevent the positive electrode electrolyte 61 and the negative electrode electrolyte 62 from mixing with each other. In other words, the partition wall 50 allows lithium ions to pass from the positive electrode chamber S1 to the negative electrode chamber S2, and allows lithium ions to pass from the negative electrode chamber S2 to the positive electrode chamber S1.

[0110] Specifically, the partition wall 50 includes one or both of an ion exchange membrane and a solid electrolyte membrane. The ion exchange membrane is a porous membrane (cation exchange membrane) that is permeable to lithium ions, and the solid electrolyte membrane has lithium ion conductivity. This is because the partition wall 50 improves the permeability of lithium ions.

[0111] In particular, it is preferable that partition wall 50 includes an ion exchange membrane rather than a solid electrolyte membrane. This is because the aqueous solvent in positive electrode electrolyte 61 and the aqueous solvent in negative electrode electrolyte 62 each easily permeate into partition wall 50, thereby improving lithium ion conductivity inside partition wall 50.

[0112] The positive electrode 20 is disposed inside the positive electrode chamber S1 and absorbs and releases lithium ions, and the negative electrode 30 is disposed inside the negative electrode chamber S2 and absorbs and releases lithium ions.

[0113] The positive electrode electrolyte 61 and the negative electrode electrolyte 62 are each an aqueous electrolyte. The positive electrode electrolyte 61 is accommodated inside the positive electrode chamber S1, and the negative electrode electrolyte 62 is accommodated inside the negative electrode chamber S2. Therefore, the positive electrode electrolyte 61 and the negative electrode electrolyte 62 are separated from each other by the partition wall 50 to prevent them from mixing with each other.

[0114] As a result, the positive electrode electrolyte 61 contained inside the positive electrode chamber S1 is not in contact with the negative electrode 30 but is in contact only with the positive electrode 20. On the other hand, the negative electrode electrolyte 62 contained inside the negative electrode chamber S2 is not in contact with the positive electrode 20 but is in contact only with the negative electrode 30.

[0115] The pH of the positive electrode electrolyte 61 and the pH of the negative electrode electrolyte 62 are different from each other. Specifically, the pH of the negative electrode electrolyte 62 is higher than the pH of the positive electrode electrolyte 61. As long as this pH magnitude relationship is satisfied, the compositions of the positive electrode electrolyte 61 and the negative electrode electrolyte 62 (such as the type of aqueous solvent and the type and concentration of the ionic substance) can be set arbitrarily.

[0116] The pH of the negative electrode electrolyte 62 is higher than that of the positive electrode electrolyte 61 because the difference in pH between the two electrolytes causes a shift in the decomposition potential of the aqueous solvent. This thermodynamically suppresses the decomposition reaction of the aqueous solvent during charge and discharge, while expanding the potential window of the aqueous solvent. This allows for a high voltage to be obtained, and makes it easier for the charge and discharge reaction utilizing the absorption and release of lithium ions to proceed sufficiently and stably.

[0117] In particular, it is preferable that the composition formula (type of electrolyte salt) of positive electrode electrolyte 61 and the composition formula (type of electrolyte salt) of negative electrode electrolyte 62 are different from each other, because this makes it easier to ensure the magnitude relationship regarding the pH described above.

[0118] As long as the above-described magnitude relationship regarding pH is satisfied, the pH values of the positive electrode electrolyte 61 and the negative electrode electrolyte 62 are not particularly limited.

[0119] In particular, the pH of the anode electrolyte 62 in contact with the anode 30 is preferably 11 or higher, more preferably 12 or higher, and even more preferably 13 or higher. This is because the pH of the anode electrolyte 62 becomes sufficiently large, making it easier to maintain the magnitude relationship of the pH described above. Also, the difference between the pH of the cathode electrolyte 61 and the pH of the anode electrolyte 62 becomes sufficiently large, making it easier to maintain the magnitude relationship of the pH between the two.

[0120] Furthermore, the pH of the positive electrode electrolyte 61 in contact with the positive electrode 20 is preferably less than 11. Specifically, the pH of the positive electrode electrolyte 61 is preferably 3 to 8, more preferably 4 to 8, and even more preferably 4 to 6. This is because the pH of the positive electrode electrolyte 61 becomes sufficiently low, making it easier to ensure the above-mentioned pH magnitude relationship and to maintain the pH magnitude relationship. Furthermore, the exterior body 10, the positive electrode current collector 20A, the negative electrode current collector 30A, etc. become less susceptible to corrosion, improving the electrochemical durability (stability) of the lithium-ion secondary battery.

[0121] It is preferable that one or both of the positive electrode electrolyte 61 and the negative electrode electrolyte 62 are saturated solutions of an electrolyte salt (lithium salt), similar to the electrolyte 40 of the first embodiment. This is because the charge / discharge reaction tends to proceed stably during charge / discharge. The method for checking whether each of the positive electrode electrolyte 61 and the negative electrode electrolyte 62 is a saturated solution of a lithium salt is the same as the method for checking whether the electrolyte 40 is a saturated solution of a lithium salt.

[0122] Furthermore, each of the positive electrode electrolyte 61 and the negative electrode electrolyte 62 may be a pH buffer solution. This pH buffer solution may be an aqueous solution in which a weak acid and its conjugate base are mixed, or may be an aqueous solution in which a weak base and its conjugate acid are mixed. This is because the pH of the positive electrode electrolyte and the pH of the negative electrode electrolyte 62 are each easily maintained because the pH fluctuations are sufficiently suppressed.

[0123] In particular, it is preferable that the positive electrode electrolyte 61 contains, as anions, one or more of sulfate ions, hydrogen sulfate ions, carbonate ions, hydrogen carbonate ions, phosphate ions, monohydrogen phosphate ions, dihydrogen phosphate ions, and carboxylate ions. This is because fluctuations in the pH of the positive electrode electrolyte 61 are sufficiently suppressed, making it easier to sufficiently maintain the pH of the positive electrode electrolyte 61. Examples of carboxylate ions include formate ions, acetate ions, propionate ions, tartrate ions, and citrate ions.

[0124] The pH of the positive electrode electrolyte 61 and the negative electrode electrolyte 62 may each contain one or more of trishydroxymethylaminomethane, ethylenediaminetetraacetic acid, and the like as a buffer.

[0125] More specifically, it is preferable that positive electrode electrolyte 61 contains, as an anion, one or more of sulfate ions, hydrogen sulfate ions, carbonate ions, hydrogen carbonate ions, phosphate ions, monohydrogen phosphate ions, and dihydrogen phosphate ions, and that negative electrode electrolyte 62 contains, as anion, hydroxide ions. This is because the pH of positive electrode electrolyte 61 can be easily controlled to be sufficiently high, and the pH of negative electrode electrolyte 62 can be easily controlled to be sufficiently low.

[0126] Here, it is preferable that the positive electrode electrolyte 61 and the negative electrode electrolyte 62 are isotonic solutions that are isotonic with each other. This is because the osmotic pressures of the positive electrode electrolyte 61 and the negative electrode electrolyte 62 are optimized, making it easier to maintain the magnitude relationship between the pH values of the two.

[0127] <2-2. Operation> This lithium ion secondary battery operates as described below.

[0128] During charging, when lithium ions are released from the positive electrode 20, the lithium ions move to the negative electrode 30 through the positive electrode electrolyte 61, the partition wall 50, and the negative electrode electrolyte 62, and the lithium ions are absorbed in the negative electrode 30.

[0129] During discharge, when lithium ions are released from the negative electrode 30, the lithium ions move to the positive electrode 20 through the negative electrode electrolyte 62, the partition wall 50, and the positive electrode electrolyte 61, and the lithium ions are absorbed in the positive electrode 20.

[0130] <2-3. Manufacturing method> The manufacturing procedure for this lithium ion secondary battery is the same as the manufacturing procedure for the lithium ion secondary battery in the first embodiment described above, except for the points described below.

[0131] When preparing each of the positive electrode electrolyte 61 and the negative electrode electrolyte 62, an ionic substance is added to an aqueous solvent. In this case, the pH of the negative electrode electrolyte 62 is made higher than the pH of the positive electrode electrolyte 61 by adjusting conditions such as the type and concentration (mol / kg) of the ionic substance.

[0132] When assembling a lithium-ion secondary battery, first, an exterior housing 10 (positive electrode chamber S1 and negative electrode chamber S2) to which a partition wall 50 has been attached is prepared. Next, a positive electrode 20 is housed inside the positive electrode chamber S1, and a connection terminal portion 20AT is led out from inside the positive electrode chamber S1 to the outside. Furthermore, a negative electrode 30 is housed inside the negative electrode chamber S2, and a connection terminal portion 30AT is led out from inside the negative electrode chamber S2 to the outside. Finally, a positive electrode electrolyte 61 is supplied into the positive electrode chamber S1 through a positive electrode injection hole (not shown) provided in the exterior housing 10, and a negative electrode electrolyte 62 is supplied into the negative electrode chamber S2 through a negative electrode injection hole (not shown) provided in the exterior housing 10. Thereafter, the positive electrode injection hole and the negative electrode injection hole are each sealed.

[0133] As a result, the positive electrode electrolyte 61 is accommodated inside the positive electrode chamber S1 in which the positive electrode 20 is disposed, and the negative electrode electrolyte 62 is accommodated inside the negative electrode chamber S2 in which the negative electrode 30 is disposed. Thus, a dual liquid type lithium ion secondary battery using two types of aqueous electrolytes (positive electrode electrolyte 61 and negative electrode electrolyte 62) is completed.

[0134] <2-4. Actions and Effects> According to the lithium ion secondary battery of the second embodiment, the negative electrode active material layer 30B (plurality of negative electrode active material particles 31) of the negative electrode 30 has the above-described configuration, and the pH of the negative electrode electrolyte 62 is higher than the pH of the positive electrode electrolyte 61. Therefore, for the same reasons as in the lithium ion secondary battery of the first embodiment, excellent operating characteristics can be obtained.

[0135] In this case, in particular, since two types of aqueous electrolytes (positive electrode electrolyte 61 and negative electrode electrolyte 62) with different pH values are used, a high voltage can be obtained, and the charge / discharge reaction utilizing the absorption and release of lithium ions can proceed sufficiently and stably, thereby achieving better operating characteristics.

[0136] Other functions and effects of the lithium ion secondary battery of the second embodiment are similar to those of the lithium ion secondary battery of the first embodiment. Also, functions and effects of the negative electrode 30 of the second embodiment are similar to those of the negative electrode 30 of the first embodiment.

[0137] <3. Modifications> The configuration of the lithium ion secondary battery can be modified as appropriate, as described below. Regarding the series of modifications described below, any two or more of the modifications may be combined with each other.

[0138] [Variation 1] In the first embodiment, the positive electrode 20 and the negative electrode 30 are separated from each other via the electrolyte solution 40. However, as shown in FIG. 5 corresponding to FIG. 1, the lithium ion secondary battery further includes a separator 70, so the positive electrode 20 and the negative electrode 30 may be separated from each other via the separator 70. The configuration of the lithium ion secondary battery shown in FIG. 5 is the same as the configuration of the lithium ion secondary battery shown in FIG. 1, except as described below.

[0139] The separator 70 is disposed between the positive electrode 20 and the negative electrode 30 and is adjacent to each of the positive electrode 20 and the negative electrode 30. The separator 70 is an insulating porous membrane that separates the positive electrode 20 and the negative electrode 30 from each other and allows lithium ions to pass through, and the separator 70 is impregnated with the electrolyte solution 40. There are no particular limitations on the material from which the separator 70 is formed, as long as it is a porous insulating material.

[0140] Specifically, separator 70 is a polymer compound film. Separator 70 contains one or more polymer compounds such as polyolefin, and specific examples of the polymer compounds include polyethylene and polypropylene.

[0141] Alternatively, the separator 70 is a solid electrolyte membrane. This solid electrolyte membrane is a so-called inorganic particle membrane, and the inorganic particle membrane contains inorganic particles, a binder, and a fibrous material.

[0142] The inorganic particles are in the form of multiple particles and contain one or more inorganic materials. The inorganic materials are compounds containing one or more metal elements (cations) such as Mg, Al, Si, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Sr, Y, Zr, Nb, Mo, Ru, Rh, Pd, Ag, In, Ba, Hf, Ta, W, Re, Ir, Pt, and Au as constituent elements. The inorganic materials include one or more oxides, sulfides, hydroxides, carbonates, sulfates, etc.

[0143] In particular, the inorganic material is preferably an inorganic solid electrolyte having excellent alkali metal ion conductivity and high water resistance. This is because hydrolysis is less likely to occur inside the lithium ion secondary battery. Specifically, inorganic solid electrolytes having excellent alkali metal ion conductivity have a NASICON structure, and more specifically, lithium phosphate solid electrolytes represented by the general formula LiM2(PO4)3. Here, M is any one or more of metal elements such as Ti, Ge, Sr, Zr, Sn, and Al. In particular, M preferably contains any one or more of metal elements selected from Ge, Zr, and Ti, and Al.

[0144] A specific example of a lithium phosphate solid electrolyte having a NASICON structure is LATP (Li 1+x Al x Ti 2-x (PO4)3), Li 1+x Al x Ge 2-x (PO4)3 and Li 1+x Al x Zr 2-xIt is (PO4)3 or the like. However, x satisfies 0 < x ≦ 5, and preferably satisfies 0.1 ≦ x ≦ 0.5. Among them, the lithium phosphate solid electrolyte is preferably LATP. This is because excellent water resistance can be obtained, making hydrolysis less likely to occur inside the lithium-ion secondary battery.

[0145] Alternatively, the inorganic material is preferably an oxide-based solid electrolyte. Specifically, the oxide-based solid electrolyte is amorphous LIPON (Li 2.9 PO 3.3 N 0.46 ), LLZ (Li7La3Zr2O 12 ) having a garnet structure, and the like.

[0146] Alternatively, the inorganic material is oxide-based ceramics, carbonates, sulfates, nitride-based ceramics, and the like. Specific examples of oxide-based ceramics are alumina, silica, zirconia, yttria, magnesium oxide, calcium oxide, barium oxide, strontium oxide, and vanadium oxide. Specific examples of carbonates are sodium carbonate, potassium carbonate, magnesium carbonate, calcium carbonate, barium carbonate, lanthanum carbonate, and cerium carbonate. Specific examples of sulfates are calcium sulfate, magnesium sulfate, aluminum sulfate, gypsum, and barium sulfate. Specific examples of phosphates are hydroxyapatite, zirconium phosphate, and titanium phosphate. Specific examples of nitride-based ceramics are silicon nitride, titanium nitride, boron nitride, and the like. Among them, alumina, silica, calcium oxide, and the like are preferably in the state of glass ceramics.

[0147] Note that the shape of the inorganic particles, the average particle size of the inorganic particles, the content of the inorganic particles in the inorganic particle film, etc. are not particularly limited and can be arbitrarily set. However, since the inorganic particles are the main component in the inorganic particle film, the content of the inorganic particles in the inorganic particle film is preferably sufficiently large. This is because the separator 70 becomes denser and the hydrophobicity of the separator 70 is improved.

[0148] The binder contains one or more polymeric compounds. These polymeric compounds are polymerized compounds of hydrocarbon monomers having specific functional groups, and the functional groups contain one or more of elements such as O, S, N, and F as constituent elements. Specific examples of polymeric compounds include polyvinyl formal, polyvinyl alcohol, polyvinyl acetal, polyvinyl butyral, polymethyl methacrylate, and polytetrafluoroethylene.

[0149] The molecular weight of the binder and the content of the binder in the inorganic particle film are not particularly limited and can be set arbitrarily.

[0150] The fibrous substance is a plurality of fibrous forms and includes one or more of the fibrous materials. The fibrous material preferably includes one or more of the hydrophilic functional groups, such as hydroxyl, sulfonic, and carboxyl groups. Specific examples of the hydrophilic functional groups include cellulose fibers, polysaccharides, polyvinyl alcohol, polyacrylic acid, anionic derivatives of polystyrene, and cationic derivatives of polystyrene. An example of an anionic derivative of polystyrene is polystyrene sulfonate, and an example of a cationic derivative of polystyrene is polystyrene trialkylbenzylammonium. Among these, cellulose fibers are preferred. However, specific examples of the fibrous material may also be derivatives of the above-mentioned series of specific examples, or copolymers of two or more of the series of specific examples.

[0151] As described above, the fibrous material contains a hydrophilic functional group, which makes it easier for the electrolyte solution 40 to be trapped between two or more fibrous materials. This makes it easier for the separator 70 to swell when the separator 70 is impregnated with the electrolyte solution 40.

[0152] The average fiber diameter of the fibrous material and the content of the fibrous material in the inorganic particle film are not particularly limited and can be set as desired.

[0153] Here, the separator 70 may be a laminate in which a polymer compound film and an inorganic particle film are stacked on top of each other. In this case, the number of layers of the polymer compound film and the inorganic particle film is not particularly limited and can be set arbitrarily.

[0154] When producing this inorganic particle film, first, a slurry is prepared by adding an inorganic particle film, a binder, and a fibrous material to a solvent such as an organic solvent. The slurry is then poured into a mold. Finally, the slurry is dried to volatilize the solvent, and the mold is then removed. This completes an inorganic particle film containing inorganic particles, a binder, and a fibrous material.

[0155] In this case as well, lithium ions can move between the positive electrode 20 and the negative electrode 30 via the separator 70, and therefore the same effect as in the case shown in FIG. 1 can be obtained.

[0156] [Variation 2] In the second embodiment, the partition walls 50 may be the solid electrolyte membrane (inorganic particle membrane) described in Modification 1. Details regarding this inorganic particle membrane are as described above.

[0157] In this case as well, lithium ions can move between the positive electrode 20 and the negative electrode 30 via the partition wall 50, and therefore the same effect as in the case shown in FIG. 1 can be obtained.

[0158] [Variation 3] In the first embodiment, as shown in Fig. 1, electrolytic solution 40, which is a liquid electrolyte, is used. However, as shown in Fig. 6, which corresponds to Fig. 1, electrolyte layers 81 and 82, which are gel electrolytes, may be used instead of electrolytic solution 40. The configuration of the lithium ion secondary battery shown in Fig. 6 is the same as the configuration of the lithium ion secondary battery shown in Fig. 1, except for the points described below.

[0159] Here, the lithium ion secondary battery additionally includes a separator 70 and electrolyte layers 81 and 82. As described above, the separator 70 is disposed between the positive electrode 20 and the negative electrode 30. The electrolyte layer 81 is disposed between the positive electrode 20 and the separator 70, and the electrolyte layer 82 is disposed between the negative electrode 30 and the separator 70. As a result, the electrolyte layer 81 is adjacent to both the positive electrode 20 and the separator 70, and the electrolyte layer 82 is adjacent to both the negative electrode 30 and the separator 70.

[0160] Each of the electrolyte layers 81 and 82 contains a polymer compound together with the electrolytic solution 40, and the electrolytic solution 40 is held by the polymer compound. The type of polymer compound is not particularly limited, but specifically, it may be one or more of polyvinylidene fluoride, polyethylene oxide, etc. In FIG. 6, each of the electrolyte layers 81 and 82 is lightly shaded.

[0161] Details regarding separator 70 are as described above, except that it is an insulating porous membrane that separates electrolyte layers 81, 82 from each other and allows lithium ions to pass through. Specifically, separator 70 contains one or more types of polymer compounds such as polyolefins, and specific examples of polyolefins include polyethylene and polypropylene. Alternatively, separator 70 may be the solid electrolyte membrane (inorganic particle membrane) described in Modification 1. Details regarding this inorganic particle membrane are as described above.

[0162] When forming electrolyte layer 81, a sol-like precursor solution is prepared by mixing electrolytic solution 40, a polymer compound, and a dilution solvent together, and then the precursor solution is applied to the surface of positive electrode 20. The procedure for forming electrolyte layer 82 is the same as the procedure for forming electrolyte layer 81, except that the precursor solution is applied to the surface of negative electrode 30.

[0163] In this case, too, lithium ions can move between the positive electrode 20 and the negative electrode 30 via the electrolyte layers 81 and 82, so that the same effect as in the case shown in Fig. 1 can be obtained. In this case, leakage of the electrolyte solution can be particularly prevented.

[0164] [Variation 4] In the second embodiment, as shown in Fig. 4, positive electrode electrolyte 61 and negative electrode electrolyte 62, which are liquid electrolytes, are used. However, as shown in Fig. 7, which corresponds to Fig. 4, electrolyte layers 91 and 92, which are gel electrolytes, may be used instead of positive electrode electrolyte 61 and negative electrode electrolyte 62. The configuration of the lithium ion secondary battery shown in Fig. 7 is the same as the configuration of the lithium ion secondary battery shown in Fig. 4, except for the points described below.

[0165] Here, the lithium ion secondary battery additionally includes electrolyte layers 91 and 92. The electrolyte layer 91 is disposed between the positive electrode 20 and the partition wall 50, and the electrolyte layer 92 is disposed between the negative electrode 30 and the partition wall 50. As a result, the electrolyte layer 91 is adjacent to both the positive electrode 20 and the partition wall 50, and the electrolyte layer 92 is adjacent to both the negative electrode 30 and the partition wall 50.

[0166] The electrolyte layer 91 contains a polymer compound together with the positive electrode electrolyte 61, and the positive electrode electrolyte 61 is held by the polymer compound. The electrolyte layer 92 contains a polymer compound together with the negative electrode electrolyte 62, and the negative electrode electrolyte 62 is held by the polymer compound. Details regarding the types of polymer compounds are as described above. In FIG. 7, the electrolyte layer 91 containing the positive electrode electrolyte 61 is lightly shaded, and the electrolyte layer 92 containing the negative electrode electrolyte 62 is darkly shaded.

[0167] When forming electrolyte layer 91, a sol-like precursor solution is prepared by mixing positive electrode electrolyte 61, a polymer compound, and a dilution solvent together, and then the precursor solution is applied to the surface of positive electrode 20. When forming electrolyte layer 92, a sol-like precursor solution is prepared by mixing negative electrode electrolyte 62, a polymer compound, and a dilution solvent together, and then the precursor solution is applied to the surface of negative electrode 30.

[0168] The details of the configuration of the partition walls 50 are as described above. However, the partition walls 50 may be the solid electrolyte membrane (inorganic particle membrane) described in Modification 1. The details of this inorganic particle membrane are as described above.

[0169] In this case, too, lithium ions can move between the positive electrode 20 and the negative electrode 30 via the electrolyte layers 91, 92, so that the same effect as in the case shown in Fig. 4 can be obtained. In this case, leakage of the electrolyte can be particularly prevented.

[0170] <4. Uses of lithium-ion secondary batteries> The uses (application examples) of lithium ion secondary batteries are not particularly limited. Lithium ion secondary batteries used as power sources may be the main power source for electronic devices, electric vehicles, etc., or may be 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 is a power source that is used in place of the main power source, or a power source that can be switched from the main power source.

[0171] Specific examples of uses for lithium ion 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, etc. 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, etc. In these uses, one lithium ion secondary battery may be used, or multiple lithium ion secondary batteries may be used.

[0172] The battery pack may use a single cell or a battery pack. The electric vehicle is a vehicle that operates (travels) using a lithium-ion secondary battery as its driving power source, and may be a hybrid vehicle that also has a driving source other than the lithium-ion secondary battery. In a home power storage system, it is possible to use household electrical appliances and the like by using the power stored in the lithium-ion secondary battery, which is the power storage source.

[0173] Of course, the lithium ion secondary battery may be used for purposes other than the series of applications exemplified here. [Example]

[0174] An embodiment of the present technology will be described.

[0175] <Examples 1 to 11 and Comparative Examples 1 to 4> An electrochemical measurement cell was fabricated using the negative electrode 30, and the characteristics of the negative electrode 30 were then evaluated.

[0176] [Preparation of electrochemical measurement cell] A cell for electrochemical measurements having a configuration similar to that of the single-liquid type lithium ion secondary battery (FIG. 1) described in the first embodiment was fabricated by the procedure described below.

[0177] (Preparation of negative electrode) First, 100 parts by mass of a negative electrode active material (a plurality of negative electrode active material particles 31 containing anatase-type titanium oxide (TiO2)), 10 parts by mass of a negative electrode binder (polyethylene glycol), and 1 part by mass of an additive (Triton X (registered trademark) surfactant manufactured by Nacalai Tesque, Inc.) were mixed together to obtain a granulated powder. The average particle size AS (nm) of the plurality of negative electrode active material particles 31 is as shown in Table 1.

[0178] Subsequently, a negative electrode current collector 30A (mesh-like titanium foil, thickness=200 μm) and the granulated powder were press-molded together using a press machine to obtain a powder compact.

[0179] Finally, the powder compact was fired in air (firing temperature = 750°C). As a result, the plurality of negative electrode active material particles 31 were directly bonded to one another, and negative electrode active material layers 30B, which were sintered bodies of the plurality of negative electrode active material particles 31, were formed on both sides of the negative electrode current collector 30A. In this way, the negative electrode 30 was produced.

[0180] The volume density (g / cm 3 ) and specific surface area (m 2 / g) are as shown in Table 1. However, the specific surface area shown is only for some of the negative electrode active material layers 30B (Examples 1, 2, 5 to 7 and Comparative Example 1) among the series of negative electrode active material layers 30B (Examples 1 to 11 and Comparative Examples 1 to 4). When producing the negative electrode 30, the volume density of the negative electrode active material layer 30B was adjusted by changing the pressing pressure described above.

[0181] For comparison, a negative electrode 30 was fabricated in the same manner except that rutile-type titanium oxide was used instead of anatase-type titanium oxide.

[0182] For comparison, lithium titanium composite oxide (Li4Ti5O 12 A negative electrode 30 was fabricated by the same procedure except that Lithium-Oxide-Tetrasilane (LTO) was used.

[0183] (Preparation of Electrolyte) An ionic substance (electrolyte salt) was added to a solvent (water, which is an aqueous solvent), and the solvent was then stirred to prepare an aqueous electrolyte solution 40. The type of electrolyte salt, the concentration (mol / kg) of electrolyte solution 40, and the pH of electrolyte solution 40 are as shown in Table 1. The electrolyte salts used were lithium hydroxide (LiOH), lithium carbonate (Li2CO3), and a mixture of lithium hydroxide and potassium hydroxide (KOH).

[0184] For comparison, a non-aqueous electrolyte solution was also prepared by adding an ionic substance (lithium hexafluorophosphate (LiPF6) as an electrolyte salt) to a solvent (ethylene carbonate (EC) and dimethyl carbonate (DMC) as non-aqueous organic solvents) and then stirring the solvent. In this case, the mixing ratio (weight ratio) of the solvents was ethylene carbonate:dimethyl carbonate = 50:50.

[0185] (Assembly of electrochemical measurement cell) First, the positive electrode 20 and the negative electrode 30 were each housed in the internal space S of a glass exterior body 10 (glass beaker). In this case, nickel metal foil was used as the positive electrode 20. Furthermore, the connection terminals 20AT and 30AT were each led out from the inside of the exterior body 10 to the outside. Next, a reference electrode (a silver / silver chloride electrode, not shown) was placed in the internal space S. Finally, the electrolyte 40 was supplied to the internal space S. As a result, the electrolyte 40 was housed in the internal space S, completing the electrochemical measurement cell.

[0186] [Anode characteristic evaluation] When the operating characteristics (discharge characteristics) of the negative electrode 30 were evaluated, the results shown in Table 1 were obtained.

[0187] When evaluating the discharge characteristics, the electrochemical measurement cell was charged and discharged in a room temperature environment (temperature = 23°C) to calculate the discharge capacity (mAh / g), which is an index for evaluating the discharge characteristics. This discharge capacity is the discharge capacity (mAh) per weight (g) of the negative electrode active material (plurality of negative electrode active material particles 31).

[0188] During charging, the battery was charged at a constant current of 1 C until the voltage reached -1.45 V versus the reference electrode (silver-silver chloride), and then charged at a constant voltage of -1.45 V until the current reached 0.5 C. During discharging, the battery was discharged at a constant current of 1 C until the voltage reached -1.00 V versus the reference electrode. 1 C is the current value at which the battery capacity (theoretical capacity) is fully discharged in 1 hour, and 0.5 C is the current value at which the battery capacity is fully discharged in 2 hours.

[0189] [Table 1]

[0190] [Consideration] As shown in Table 1, in an electrochemical measurement cell equipped with a negative electrode 30 in which the negative electrode active material layer 30B was a sintered body of a plurality of negative electrode active material particles 31, the discharge capacity varied depending on the configuration of the negative electrode 30 and other factors.

[0191] Specifically, in an electrochemical measurement cell using an aqueous electrolyte (electrolyte 40), no discharge capacity was obtained when rutile-type titanium oxide was used as the material for forming the plurality of negative electrode active material particles 31 (Comparative Example 2), and the discharge capacity decreased when lithium titanium composite oxide (LTO) was used as the material for forming the plurality of negative electrode active material particles 31 (Comparative Example 3).

[0192] In addition, in the lithium ion secondary battery using a non-aqueous electrolyte (Comparative Example 4), the discharge capacity could not be calculated because the above-mentioned charge termination condition was reached too quickly and discharge could not be performed.

[0193] In contrast, in an electrochemical measurement cell using an aqueous electrolyte (electrolyte 40), when anatase-type titanium oxide was used as the material for forming multiple negative electrode active material particles 31 (Examples 1 to 11 and Comparative Example 1), the discharge capacity varied significantly depending on the average particle size AS.

[0194] That is, when the average particle size AS was larger than 100 nm (Comparative Example 1), the discharge capacity decreased, but when the average particle size AS was 100 nm or less (Examples 1 to 11), the discharge capacity increased.

[0195] In particular, when the average particle size AS was 100 nm or less, the following trends were observed. When the average particle size AS was 30 nm or less, the discharge capacity increased. When the volume density of the negative electrode active material layer 30B was 1.0 g / cm 3 ~3.5g / cm 3 In this case, a sufficient discharge capacity was obtained.

[0196] <Examples 12 and 13 and Comparative Example 5> Furthermore, a lithium ion secondary battery was fabricated using the negative electrode 30, and the characteristics of the lithium ion secondary battery were evaluated.

[0197] [Fabrication of lithium-ion secondary batteries] The two-liquid type lithium ion secondary battery (FIG. 4) described in the second embodiment was fabricated according to the procedure described below.

[0198] (Preparation of positive electrode) First, 91 parts by mass of a positive electrode active material (LiFePO4, a lithium phosphate compound), 3 parts by mass of a positive electrode binder (polyvinylidene fluoride), and 6 parts by mass of a positive electrode conductive agent (graphite) were mixed together to prepare a positive electrode mixture. Next, the positive electrode mixture was added to a solvent (N-methyl-2-pyrrolidone, an organic solvent), and the solvent was stirred to prepare a paste-like positive electrode mixture slurry. Finally, the positive electrode mixture slurry was applied to both sides (excluding the connection terminal portion 20AT) of a positive electrode current collector 20A (titanium foil, thickness = 10 μm) using a coating device, and the positive electrode mixture slurry was then dried to form a positive electrode active material layer 20B. This produced the positive electrode 20.

[0199] (Preparation of negative electrode) The negative electrodes 30 were fabricated by the above-described procedure. Here, as shown in Table 2, two types of negative electrodes 30 (Examples 7 and 10) were fabricated using anatase-type titanium oxide as the material for forming the plurality of negative electrode active material particles 31, and a negative electrode 30 (Comparative Example 3) was fabricated using a lithium-titanium composite oxide as the material for forming the plurality of negative electrode active material particles 31.

[0200] (Preparation of positive electrode electrolyte) An ionic substance (lithium sulfate (LiSO) as an electrolyte salt) was added to a solvent (pure water as an aqueous solvent), and the solvent was then stirred to prepare an aqueous electrolyte solution, positive electrode electrolyte 61. The concentration (mol / kg) and pH of positive electrode electrolyte 61 are as shown in Table 2.

[0201] (Preparation of negative electrode electrolyte) The above-described electrolyte 40 was used as the negative electrode electrolyte 62. The concentration (mol / kg) and pH of the negative electrode electrolyte 62 are as shown in Table 2.

[0202] (Lithium-ion secondary battery assembly) First, a glass container with a partition wall 50 (a cation exchange membrane, Nafion115 (registered trademark), manufactured by Sigma-Aldrich Japan G.K.) attached thereto was prepared as the exterior body 10. Inside this exterior body 10, a positive electrode chamber S1 and a negative electrode chamber S2 were separated from each other in advance via the partition wall 50. Next, a positive electrode 20 was housed inside the positive electrode chamber S1, and then a negative electrode 30 was housed inside the negative electrode chamber S2. In this case, the connection terminals 20AT and 30AT were each led out from the inside of the exterior body 10 to the outside. Next, a positive electrode electrolyte 61 was supplied inside the positive electrode chamber S1, and a negative electrode electrolyte 62 was supplied inside the negative electrode chamber S2. As a result, the positive electrode electrolyte 61 was housed inside the positive electrode chamber S1, and the negative electrode electrolyte 62 was housed inside the negative electrode chamber S2, completing a dual-liquid type lithium-ion secondary battery.

[0203] [Characteristics evaluation of lithium-ion secondary batteries] The operating characteristics (initial charge / discharge characteristics and cycle characteristics) of the lithium ion secondary battery were evaluated according to the procedure described below, and the results shown in Table 2 were obtained.

[0204] (Initial charge / discharge characteristics) First, the charge capacity was measured by charging the lithium ion secondary battery in a room temperature environment (temperature = 23°C). When anatase titanium oxide was used as the material forming the plurality of negative electrode active material particles 31, constant current charging was performed at a current of 2C until the voltage reached 1.7V. When lithium titanium composite oxide was used as the material forming the plurality of negative electrode active material particles 31, constant current charging was performed at a current of 2C until the voltage reached 2.0V. 2C is the current value at which the battery capacity is fully discharged in 0.5 hours.

[0205] Subsequently, the lithium ion secondary battery was discharged in the same environment to measure the discharge capacity. During discharge, regardless of the type of material forming the plurality of negative electrode active material particles 31, constant current discharge was performed at a current of 2 C until the voltage reached 1.2 V.

[0206] Finally, the initial charge-discharge efficiency, which is an index for evaluating the initial charge-discharge characteristics, was calculated based on the formula: initial charge-discharge efficiency (%)=(discharge capacity / charge capacity)×100.

[0207] (Cycle characteristics) First, the discharge capacity (discharge capacity at the first cycle) was measured by charging and discharging the lithium-ion secondary battery in a room temperature environment (temperature = 23°C). Next, the discharge capacity (discharge capacity at the 15th cycle) was measured by repeatedly charging and discharging the lithium-ion secondary battery in the same environment until the number of cycles reached 15. The charge and discharge conditions were the same as those used to examine the initial charge and discharge characteristics. Finally, the capacity retention rate, an index for evaluating cycle characteristics, was calculated based on the formula: capacity retention rate (%) = (discharge capacity at the 15th cycle / discharge capacity at the 1st cycle) × 100.

[0208] [Table 2]

[0209] [Consideration] As shown in Table 2, in a lithium ion secondary battery equipped with two types of aqueous electrolytes (positive electrode electrolyte 61 and negative electrode electrolyte 62) and a negative electrode 30 including a negative electrode active material layer 30B (a sintered body of a plurality of negative electrode active material particles 31), the charge / discharge efficiency and the capacity retention rate each varied depending on the configuration of the negative electrode 30.

[0210] Specifically, when a lithium-titanium composite oxide was used as the material for forming the plurality of negative electrode active material particles 31 (Comparative Example 5), the charge / discharge efficiency decreased. In this case, the lithium ion secondary battery could not be repeatedly charged and discharged, and therefore the capacity retention rate could not be calculated.

[0211] In contrast, when anatase-type titanium oxide was used as the material for forming the plurality of negative electrode active material particles 31 (Examples 12 and 13), the charge / discharge efficiency was significantly increased. In this case, unlike when a lithium-titanium composite oxide was used, not only was it possible to repeatedly charge and discharge the lithium ion secondary battery, but a sufficient capacity retention rate was also obtained.

[0212] [summary] The results shown in Tables 1 and 2 indicate that when the negative electrode active material layer 30B of the negative electrode 30 contains a plurality of negative electrode active material particles 31, the negative electrode active material layer 30B has a porous structure in which the plurality of negative electrode active material particles 31 are directly bonded to one another, each of the plurality of negative electrode active material particles 31 contains anatase-type titanium oxide, and the plurality of negative electrode active material particles 31 have an average particle size AS of 100 nm or less, the discharge characteristics, initial charge / discharge characteristics, and cycle characteristics of a lithium-ion secondary battery containing an aqueous electrolyte solution are all improved, thereby achieving excellent operating characteristics.

[0213] The configuration of the lithium ion secondary battery according to the present technology has been described above with reference to an embodiment and examples. However, the configuration of the lithium ion secondary battery according to the present technology is not limited to the configuration described in the embodiment and examples, and various modifications are possible.

[0214] 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 that absorbs and releases lithium ions; a negative electrode that absorbs and releases lithium ions and includes a negative electrode active material layer; an electrolyte solution including an aqueous solvent; Equipped with the negative electrode active material layer includes a plurality of negative electrode active material particles and has a porous structure in which the plurality of negative electrode active material particles are directly bonded to one another; each of the plurality of negative electrode active material particles contains anatase titanium oxide; the average particle size of the plurality of negative electrode active material particles is 15 nm or more and 100 nm or less; the negative electrode active material layer has a volume density of 1.1 g / cm 3 or more and 2.8 g / cm 3 or less; the specific surface area of the negative electrode active material layer is 10 m 2 / g or more and 50 m 2 / g or less; Lithium-ion secondary battery.

2. The average particle size is 30 nm or less. The lithium ion secondary battery according to claim 1 .

3. The electrolyte has a pH of 11 or greater. The lithium ion secondary battery according to claim 1 or 2.

4. moreover, a positive electrode chamber in which the positive electrode is disposed; a negative electrode chamber in which the negative electrode is disposed; a partition wall that is disposed between the positive electrode chamber and the negative electrode chamber and allows the lithium ions to pass through; Equipped with The electrolyte solution is a positive electrode electrolyte accommodated inside the positive electrode chamber; an anode electrolyte contained in the anode chamber and having a pH greater than the pH of the cathode electrolyte; Including, The lithium ion secondary battery according to claim 1 or 2.

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