Positive electrode for secondary battery, secondary battery, and method for recycling positive electrode for secondary battery

Abstract

Provided is a positive electrode for a secondary battery capable of obtaining excellent battery characteristics and excellent recycling characteristics. The positive electrode for a secondary battery is provided with: a positive electrode active material layer that contains a positive electrode active material and a polymer compound; and a positive electrode current collector that supports the positive electrode active material layer. The positive electrode active material contains a lithium transition metal compound. The thermal weight loss ratio measured when the polymer compound is fired in the atmosphere until the temperature of the polymer compound reaches 400°C is 60% or more.

Description

Positive electrode for secondary battery, secondary battery, and method for recycling positive electrode for secondary battery

[0001] The present technology relates to a positive electrode for a secondary battery, a secondary battery, and a method for recycling a positive electrode for a secondary battery.

[0002] Due to the widespread use of various electronic devices such as mobile phones, secondary batteries have been developed as power sources that are small, lightweight, and have high energy density, and various studies are being conducted on the configuration of these secondary batteries.

[0003] Specifically, to obtain recycled materials, batteries are crushed to obtain crushed material, and then the crushed material is heated in the atmosphere at temperatures of 400°C to 550°C to remove organic matter from the crushed material (see, for example, Patent Document 1). To recover the active material, the positive electrode is heated in an oxygen-containing gas at temperatures of 360°C to 660°C to separate the foil and active material from the positive electrode (see, for example, Patent Document 2). To recover the negative electrode active material, a negative electrode containing an aqueous binder resin such as carboxymethyl cellulose is used, and the negative electrode is heated in an acidic aqueous solution to decompose the aqueous binder resin (see, for example, Patent Document 3).

[0004] In addition, the positive electrode of a lithium ion battery contains a binder such as an acrylic resin or an acetal resin (see, for example, Patent Document 4).

[0005] JP 2012-195073 A JP 2020-191184 A JP 2006-331707 A JP 2018-206675 A

[0006] Although various studies have been conducted on the configuration of secondary batteries, the battery characteristics of the secondary batteries are still insufficient and there is room for improvement. In this case, it is important not only to improve the battery characteristics but also to improve the recyclability of the secondary batteries.

[0007] There is a demand for a positive electrode for a secondary battery, a secondary battery, and a method for recycling a positive electrode for a secondary battery that can provide excellent battery characteristics and excellent recycling characteristics.

[0008] A positive electrode for a secondary battery according to one embodiment of the present disclosure includes a positive electrode active material layer containing a positive electrode active material and a polymer compound, and a positive electrode current collector supporting the positive electrode active material layer. The positive electrode active material contains a lithium transition metal compound. The polymer compound is baked in air until its temperature reaches 400°C, and the measured thermal weight loss of the polymer compound is 60% or more.

[0009] A secondary battery according to an embodiment of the present technology includes a positive electrode for a secondary battery, a negative electrode, and an electrolyte solution, and the positive electrode for a secondary battery has a configuration similar to the configuration of the positive electrode for a secondary battery according to the embodiment of the present technology described above.

[0010] In a method for recycling a positive electrode for a secondary battery according to an embodiment of the present technology, the positive electrode for a secondary battery is baked until the temperature of the positive electrode for a secondary battery reaches 200°C or higher and 500°C or lower, thereby burning off the polymer compound and recovering the positive electrode current collector and the positive electrode active material, and the positive electrode for a secondary battery has a configuration similar to that of the positive electrode for a secondary battery according to the embodiment of the present technology described above.

[0011] Here, "lithium transition metal compound" is a general term for compounds containing lithium and a transition metal element as constituent elements. Furthermore, "polymer compound" is a soluble substance that is contained in the positive electrode active material layer together with the positive electrode active material and can be separated from insoluble substances such as the positive electrode active material by a dissolution treatment using a solvent for dissolution and separation, which will be described later. The lithium transition metal compound and the polymer compound will be described in detail later.

[0012] According to the positive electrode for a secondary battery or the secondary battery of one embodiment of the present technology, the positive electrode for a secondary battery includes a positive electrode active material layer and a positive electrode current collector, the positive electrode active material layer includes a positive electrode active material and a polymer compound, the positive electrode active material includes a lithium transition metal compound, and the polymer compound has a thermal weight loss rate of 60% or more, so that excellent battery characteristics and excellent recyclability can be obtained.

[0013] According to the recycling method for a secondary battery positive electrode in one embodiment of the present technology, the positive electrode for a secondary battery is baked until the temperature of the above-described positive electrode for a secondary battery according to one embodiment of the present technology reaches 200°C to 500°C, thereby burning off the polymer compound and recovering the positive electrode current collector and the positive electrode active material. Therefore, it is possible to obtain excellent battery characteristics and excellent recycling characteristics for a secondary battery using the positive electrode for a secondary battery.

[0014] 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.

[0015] Fig. 1 is a cross-sectional view showing a configuration of a positive electrode for a secondary battery according to an embodiment of the present technology. Fig. 2 is a cross-sectional view showing a configuration of a secondary battery according to a first embodiment of the present technology. Fig. 3 is a cross-sectional view showing a configuration of a secondary battery according to a second embodiment of the present technology. Fig. 4 is a cross-sectional view showing a configuration of a secondary battery according to a first modified example. Fig. 5 is a cross-sectional view showing a configuration of a secondary battery according to a third modified example. Fig. 6 is a cross-sectional view showing a configuration of a secondary battery according to a fourth modified example. Fig. 7 is a cross-sectional view showing a configuration of a secondary battery according to a fifth modified example.

[0016] 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. Positive electrode for secondary battery 1-1. Configuration 1-2. Operation 1-3. Manufacturing method 1-4. Actions and effects 2. Secondary battery (first embodiment) 2-1. Configuration 2-2. Operation 2-3. Manufacturing method 2-4. Actions and effects 3. Secondary battery (second embodiment) 3-1. Configuration 3-2. Operation 3-3. Manufacturing method 3-4. Actions and effects 4. Method for recycling positive electrode for secondary battery 5. Modified example 6. Uses of secondary battery

[0017] 1. Positive Electrode for Secondary Battery First, a positive electrode for a secondary battery (hereinafter simply referred to as "positive electrode") according to an embodiment of the present technology will be described.

[0018] The positive electrode described here is used in a secondary battery, which is an electrochemical device. However, the positive electrode may also be used in an electrochemical device other than a secondary battery. The type of electrochemical device other than a secondary battery is not particularly limited, but specifically includes a capacitor.

[0019] The positive electrode is used in a secondary battery in which charge and discharge reactions proceed by utilizing the absorption and release of an electrode reactant, and the secondary battery includes a positive electrode, a negative electrode, and an aqueous electrolyte solution. The aqueous electrolyte solution is a liquid electrolyte, more specifically, an electrolyte solution containing an aqueous solvent.

[0020] The type of electrode reactant is not particularly limited, but specifically includes light metals such as alkali metals and alkaline earth metals. Specific examples of alkali metals include lithium, sodium, and potassium, and specific examples of alkaline earth metals include beryllium, magnesium, and calcium.

[0021] In the following, an example will be given in which the electrode reactant is lithium. A secondary battery in which charge / discharge reactions proceed by utilizing the absorption and release of lithium ions is known as a lithium secondary battery.

[0022] 1 shows a cross-sectional configuration of a positive electrode 100, which is an example of a positive electrode according to an embodiment of the present technology. As shown in FIG. 1, the positive electrode 100 includes a positive electrode current collector 100A and a positive electrode active material layer 100B.

[0023] [Positive Electrode Current Collector] The positive electrode current collector 100A is a conductive member that supports the positive electrode active material layer 100B, and has a pair of surfaces on which the positive electrode active material layer 100B is provided.

[0024] The positive electrode current collector 100A includes one or more conductive materials such as metals, carbon materials, and conductive ceramic materials. Specific examples of metal materials include titanium, zirconium, chromium, aluminum, and alloys thereof. Specific examples of conductive ceramic materials include indium tin oxide (ITO).

[0025] In particular, it is preferable that the positive electrode current collector 100A is insoluble or hardly soluble in the aqueous electrolyte solution in which the positive electrode 100 is immersed, and is corrosion-resistant, and that it has low reactivity with the positive electrode active material described below. For this reason, it is preferable that the positive electrode current collector 100A contains a metal material, because this suppresses deterioration of the positive electrode current collector 100A during use of a secondary battery including the positive electrode 100.

[0026] In particular, it is preferable that the positive electrode current collector 100A contains one or more of titanium, zirconium, and chromium as a constituent element, because this improves the efficiency of absorbing and releasing lithium ions. In addition, this provides high heat resistance, thereby suppressing side reactions in the positive electrode current collector 100A during firing of the positive electrode 100, which will be described later.

[0027] In this case, the positive electrode current collector 100A may contain titanium as an element, zirconium as an element, chromium as an element, or an alloy. This alloy is an alloy containing one or more of titanium, zirconium, and chromium as constituent elements. However, the purity of the element is not necessarily limited to 100%, and the element may contain any amount of impurities.

[0028] The positive electrode current collector 100A may be a member in which the surface of a base is plated with one or both of the above-mentioned simple substances and alloys. The material for forming the base is not particularly limited and can be selected arbitrarily.

[0029] [Positive Electrode Active Material Layer] The positive electrode active material layer 100B is a layer that absorbs and releases lithium ions, and is provided on both sides of the positive electrode current collector 100A. However, the positive electrode active material layer 100B may be provided on only one side of the positive electrode current collector 100A.

[0030] The positive electrode active material layer 100B contains a positive electrode active material and a polymer compound.

[0031] (Positive Electrode Active Material) The positive electrode active material is a material that absorbs and releases lithium ions, and contains one or more types of lithium transition metal compounds.

[0032] As described above, the lithium transition metal compound is a general term for compounds containing lithium and a transition metal element as constituent elements, and the type of the transition metal element may be one or more. Specific examples of the transition metal element include nickel, cobalt, manganese, and iron.

[0033] However, the lithium transition metal compound may further contain one or more elements other than lithium and transition metal elements as constituent elements. Specific examples of elements other than lithium and transition metal elements are elements belonging to Groups 2 to 15 of the long period periodic table.

[0034] The type of lithium transition metal compound is not particularly limited, but specific examples include lithium composite oxides and lithium phosphate compounds, etc. The lithium composite oxides are oxides containing lithium and transition metal elements as constituent elements, and the lithium phosphate compounds are phosphate compounds containing lithium and transition metal elements as constituent elements.

[0035] A specific example of a lithium composite oxide having a layered rock salt type crystal structure is LiNiO 2　 , LiCoO 2　 , LiCo 0.98 Al 0.01 Mg 0.01 O 2　 , LiNi 0.5　 Co 0.2　 Mn 0.3　 O 2　 , LiNi 0.8　 Co 0.15 Al 0.05 O 2　 , LiNi 0.33 Co 0.33 Mn 0.33 O 2　 , Li 1.2　 Mn 0.52 Co 0.175　 Ni 0.1　 O 2　 and Li 1.15 (Mn 0.65 Ni 0.22 Co 0.13 ) O 2　 And so on.

[0036] Specific examples of lithium composite oxides having a spinel-type crystal structure include LiMn 2　 O 4　 And so on.

[0037] A specific example of a lithium phosphate compound having an olivine-type crystal structure is LiFePO 4　 , LiMnPO 4　 , LiMn 0.5　 Fe 0.5　 P.O. 4　 , LiMn 0.7　 Fe 0.3　 P.O. 4　 and LiMn 0.75 Fe 0.25 P.O. 4　 And so on.

[0038] The average particle diameter (D50) of the positive electrode active material particles is preferably, for example, 1 μm or more and 50 μm or less, and more preferably 10 μm or more and 25 μm or less. When the average particle diameter is greater than 1 μm, deterioration of the positive electrode active material during the firing process is suppressed, making it easier to stably recover the positive electrode active material particles. Meanwhile, when the average particle diameter is smaller than 50 μm, it is easier to form a homogeneous film during the preparation of the positive electrode. The average particle diameter (D50) refers to the median diameter at which the cumulative volume in the volume-based particle size distribution is 50%. The average particle diameter can be measured, for example, using a laser diffraction / scattering particle size distribution analyzer.

[0039] (Polymer Compound) As described above, the polymer compound is contained in the positive electrode active material layer 100B together with the positive electrode active material.

[0040] Specifically, the polymer compound is soluble in a solvent for dissolution and separation, which will be described later, and therefore is a soluble substance that can be separated from insoluble substances such as the positive electrode active material by utilizing a dissolution treatment using the solvent for dissolution and separation, as described above. The soluble substance is a substance that dissolves in the solvent for solvent separation, and the insoluble substance is a substance that does not dissolve in the solvent for solvent separation.

[0041] As long as the polymer compound satisfies the above-described conditions regarding its structure and properties, the function and role of the polymer compound are not particularly limited. For example, the polymer compound may be a positive electrode binder, a positive electrode conductive agent, an additive, or two or more of these.

[0042] The positive electrode binder is a substance that binds particles of the positive electrode active material or the like together. The positive electrode conductive agent is a substance that improves the conductivity of the positive electrode active material layer 100B. The additive is a substance that is contained in the positive electrode active material layer 100B to achieve a desired purpose. This additive may be a substance used to improve the physical properties of the positive electrode active material layer 100B, or may be a substance used to prepare a positive electrode mixture slurry, which will be described later.

[0043] Here, the polymer compound has a predetermined thermal property. Specifically, the polymer compound has a property of being partially or completely burned when baked in the air up to a temperature of 400° C. Thus, the thermal weight loss rate measured when the polymer compound is baked in the air up to a temperature of 400° C. is 60% or more.

[0044] The reason why the positive electrode active material layer 100B contains a polymer compound and the polymer compound has a thermal weight loss rate of 60% or more is as follows.

[0045] First, when the positive electrode 100 is not fired, part or all of the polymer compound functions as a positive electrode binder. This binds particles of the positive electrode active material and the like together, ensuring the physical strength of the positive electrode active material layer 100B. Therefore, when a secondary battery including the positive electrode 100 is used, the positive electrode 100 stably absorbs and releases lithium ions.

[0046] Second, when the positive electrode 100 is baked, part or all of the polymer compound is burned away, and particles of the positive electrode active material and the like that were bound together are separated from each other. As a result, by simply baking the positive electrode 100, the positive electrode current collector 100A and the positive electrode active material can be easily and stably recovered from the positive electrode 100 without the need for complicated processes such as crushing the positive electrode 100 and extracting the residual solution of the positive electrode 100. In this case, the recovery efficiency of the positive electrode active material is particularly improved.

[0047] Third, by baking the positive electrode 100 at a relatively low temperature of 400° C., some or all of the polymer compound is burned away. This allows some or all of the polymer compound to be burned away more easily and stably than when the positive electrode 100 is not baked at a high temperature exceeding 400° C. This allows the positive electrode current collector 100A and the positive electrode active material to be recovered more easily and stably from the positive electrode 100, and also suppresses deterioration of the positive electrode current collector 100A and the positive electrode active material.

[0048] In particular, the thermal weight loss rate of the polymer compound is preferably 70% or more, more preferably 75% or more, or even 80%. The thermal weight loss rate of the polymer compound is further preferably 90%, and particularly preferably 95% or more.

[0049] When measuring the rate of thermal weight loss of a polymer compound, the polymer compound is analyzed using thermogravimetry. The conditions for analyzing a polymer compound using thermogravimetry are as follows. The thermogravimetry device used is a differential thermobalance TG8120 manufactured by Rigaku Corporation. The analysis conditions comply with those specified in JIS K7120-1987 (ISO 11358).

[0050] Specifically, a polymer compound is heated (heating rate = 10°C / min) in the atmosphere (in a dry air stream) while measuring its weight. When the temperature of the polymer compound reaches 400°C, the thermal weight loss rate of the polymer compound is calculated. This thermal weight loss rate is calculated based on the formula: Thermal weight loss rate = [1 - (weight of polymer compound when the temperature reaches 400°C / weight of polymer compound at room temperature (temperature = 23°C))] x 100.

[0051] The procedure for recovering the polymer compound from the positive electrode 100 in order to measure the rate of weight loss due to heat is as follows.

[0052] First, the positive electrode 100 is placed in a solvent for dissolution and separation, and then the solvent for dissolution and separation is stirred. This solvent for dissolution and separation is any one or more of solvents for dissolving the polymer compound contained in the positive electrode active material layer 100B of the positive electrode 100, thereby separating the polymer compound. The type of solvent for dissolution and separation is not particularly limited, and may be an aqueous solvent or a non-aqueous solvent (organic solvent). A specific example of an aqueous solvent is pure water. A specific example of a non-aqueous solvent is an organic solvent such as N-methyl-2-pyrrolidone. As a result, the polymer compound is dissolved in the solvent for dissolution and separation, and the polymer compound is separated from the positive electrode 100.

[0053] The solvent for dissolution and separation is then filtered to recover a filtrate, which does not contain solids (insoluble matters) such as the positive electrode current collector 100A and the positive electrode active material, but contains a dissolved matter (soluble matter) of the polymer compound.

[0054] Finally, the filtrate is dried to obtain a dried product, which is the polymer compound separated from the positive electrode 100. In this way, the polymer compound is recovered from the positive electrode 100.

[0055] The specific structure of the polymer compound is not particularly limited as long as the above-mentioned conditions regarding the rate of weight loss due to heat are satisfied.

[0056] (Burnt-destroying polymer compound) Specifically, the polymer compound contains one or more types of burnt-destroying polymer compounds. Note that the polymer compound may contain substantially only burnt-destroying polymer compounds, since it does not substantially contain non-burnt-destroying polymer compounds, which will be described later.

[0057] The burnable polymer compound has the property of being burned in response to heating (firing), i.e., being burned due to thermal decomposition during firing. In particular, the burnable polymer compound is preferably a polymer compound that generates only a small amount of residual ash upon thermal decomposition.

[0058] Here, the burnable polymer compound has predetermined thermal properties. Specifically, the burnable polymer compound has the property of being mostly burned when baked in the air up to a temperature of 400°C. As a result, the thermal weight loss rate measured when the burnable polymer compound is baked in the air up to a temperature of 400°C is 70% or more. This is because the burnable polymer compound is sufficiently burned during baking, making it easier to recover the positive electrode current collector 100A and the positive electrode active material from the positive electrode 100.

[0059] The thermal weight loss rate of this burnable polymer compound is preferably 75% or more, more preferably 80% or more, even more preferably 90% or more, and particularly preferably 100%, because this makes it easier to recover the positive electrode current collector 100A and the positive electrode active material from the positive electrode 100.

[0060] In particular, when the polymer compound contains a burnable polymer compound, the thermal weight loss rate measured when the polymer compound is baked in air until the temperature of the polymer compound reaches 400°C is preferably 75% or more, more preferably 80% or more, even more preferably 95% or more, and particularly preferably 98% or more, because this further improves the above-mentioned series of advantages. A specific example of a polymer compound described here containing a burnable polymer compound is a polymer compound that does not contain a non-burnable polymer compound, as described below, and contains only a burnable polymer compound.

[0061] The procedure for measuring the thermal weight loss rate of a burnable polymer compound is the same as the procedure for measuring the thermal weight loss rate of a polymer compound. The procedure for recovering the burnable polymer compound from the positive electrode 100 is the same as the procedure for recovering the polymer compound from the positive electrode 100.

[0062] The type of the burnable polymer compound is not particularly limited as long as the burnable polymer compound has the above-mentioned thermal properties.

[0063] Specifically, the burnable polymer compound is a polyacrylic acid ester, a polymethacrylic acid ester, a polyvinyl alcohol, a polyvinyl ether, a polyvinyl ester, a cellulose ester, a cellulose ether, or the like.

[0064] The burnable polymer compound is more preferably an aliphatic polymer compound that does not contain an aromatic ring, and even more preferably a polymer compound that does not contain a sugar chain containing cellulose.

[0065] Specific examples of polyacrylic acid esters include polymethyl acrylate and polyethyl acrylate. Specific examples of polymethacrylic acid esters include polymethyl methacrylate and polyethyl methacrylate. Specific examples of polyvinyl ethers include polyvinyl acetal and polyvinyl butyral. Specific examples of polyvinyl esters include polyvinyl acetate and polyvinyl butyrate. Specific examples of cellulose esters include acetyl cellulose, diacetyl cellulose, and triacetyl cellulose. Specific examples of cellulose ethers include methyl cellulose, ethyl cellulose, carboxymethyl cellulose, and carboxyethyl cellulose.

[0066] The burnable polymer compound may also be a copolymer containing structural units of one or more polymer compounds selected from polyacrylic acid esters, polymethacrylic acid esters, polyvinyl alcohols, polyvinyl ethers, polyvinyl esters, cellulose esters, and cellulose ethers.

[0067] (Non-burnable polymer compound) The polymer compound may further contain one or more of the non-burnable polymer compounds. That is, the polymer compound may contain both the burnable polymer compound and the non-burnable polymer compound. This is because a part or all of the non-burnable polymer compound functions as a positive electrode binder, thereby further improving the binding between particles of the positive electrode active material and the like.

[0068] This non-burnable polymer compound has thermal properties different from those of the burnable polymer compound. Specifically, the non-burnable polymer compound has the property of being hardly burned even when baked in the air up to a temperature of 400° C. As a result, the thermal weight loss rate measured when the non-burnable polymer compound is baked in the air up to a temperature of 400° C. is less than 70%.

[0069] The procedure for measuring the thermal weight loss rate of the non-burnable polymer compound is the same as the procedure for measuring the thermal weight loss rate of the burnable polymer compound. The procedure for recovering the non-burnable polymer compound from the positive electrode 100 is the same as the procedure for recovering the polymer compound from the positive electrode 100.

[0070] Two or more types of solvents for dissolution and separation may be used to recover the polymer compounds (burnable polymer compounds and non-burnable polymer compounds) from the positive electrode 100. Details of the procedure for using two or more types of solvents for dissolution and separation will be described later.

[0071] The type of non-burnable polymer compound is not particularly limited as long as the non-burnable polymer compound has the above-mentioned thermal properties.

[0072] Specific examples of non-burnable polymer compounds include fluorine-containing resins such as polyvinylidene fluoride and polytetrafluoroethylene. Specific examples of non-burnable polymer compounds include non-fluorine-containing resins such as polyether ether ketone, polyphenylene sulfide, and polyimide. A fluorine-containing resin is a polymer compound that contains fluorine as a constituent element, while a non-fluorine-containing resin is a polymer compound that does not contain fluorine as a constituent element.

[0073] However, when the polymer compound contains a non-burnable polymer compound as well as a burnable polymer compound, it is preferable that a predetermined relationship be established regarding the weight of the polymer compound so that the positive electrode current collector 100A and the positive electrode active material can be efficiently recovered from the positive electrode 100 using a firing process.

[0074] (Weight Ratio WR) Specifically, the weight ratio WR expressed by formula (1) is preferably 86% or more, where the value of the weight ratio WR is rounded to one decimal place.

[0075] WR=[W1 / (W1+W2)]×100 (1) (WR is a weight ratio. W1 is the weight of the burnable polymer compound. W2 is the weight of the non-burnable polymer compound.)

[0076] The weight ratio WR is an index representing the amount of burnable polymer compound contained in the positive electrode binder, which can be burned by firing. More specifically, the weight ratio WR is an index representing the proportion of the weight of the burnable polymer compound relative to the sum of the weight of the burnable polymer compound and the weight of the non-burnable polymer compound. The larger the value of the weight ratio WR, the larger the proportion of the burnable polymer compound in the polymer compound, and the smaller the value of the weight ratio WR, the smaller the proportion of the burnable polymer compound in the polymer compound.

[0077] The weight ratio WR is 86% or more because, even if the polymer compound contains both a burnable polymer compound and a non-burnable polymer compound, most of the polymer compound becomes a burnable polymer compound, making the polymer compound more likely to be burned by a baking process. In this case, by baking the positive electrode 100 to burn off the burnable polymer compound, most of the polymer compound becomes more likely to be removed. This makes it easier to separate the positive electrode current collector 100A and the positive electrode active material from the positive electrode 100, and therefore easier to recover the positive electrode current collector 100A and the positive electrode active material.

[0078] In this case, the greater the weight ratio WR, the easier it is to recover the positive electrode current collector 20A and the positive electrode active material, thereby improving the recovery efficiency of the positive electrode current collector 20A and the positive electrode active material. Specifically, the weight ratio WR is preferably 90% or more, more preferably 95% or more, and even more preferably 98%.

[0079] If the weight ratio WR is less than 86%, most of the polymer compound does not become a burnable polymer compound, making the polymer compound less likely to be burned during a firing process. In this case, even if the burnable component (burnable polymer compound) is burned during a firing process of the positive electrode 100, the component that is not burned during the firing process (non-burnable polymer compound) remains. This makes it difficult to separate the positive electrode current collector 100A and the positive electrode active material from the positive electrode 100, making it difficult to recover the positive electrode current collector 100A and the positive electrode active material. In this case, the recovery efficiency of the positive electrode active material is particularly reduced.

[0080] Here, it has been explained that when a polymer compound contains both a burnable polymer compound and a non-burnable polymer compound, the weight ratio WR is preferably 86% or more. In contrast, when a polymer compound does not contain a non-burnable polymer compound and contains only a burnable polymer compound, the weight ratio WR is calculated to be 100%. Therefore, even when a polymer compound contains only a burnable polymer compound, the condition that the weight ratio WR is 86% or more is necessarily met.

[0081] (Calculation Procedure of Weight Ratio WR) The calculation procedure of the weight ratio WR is as follows.

[0082] First, the positive electrode 100 is placed in a solvent for dissolution and separation, and then the solvent for dissolution and separation is stirred. This solvent for dissolution and separation is a solvent for separating the polymer compounds (burnable polymer compounds and non-burnable polymer compounds) contained in the positive electrode active material layer 100B of the positive electrode 100 by dissolving the polymer compounds. The type of solvent for dissolution and separation is not particularly limited, and may be an aqueous solvent or a non-aqueous solvent. Details regarding the solvent for dissolution and separation are as described above. As a result, the polymer compounds are dissolved in the solvent for dissolution and separation, and the polymer compounds are separated from the positive electrode 100.

[0083] In this case, two types of solvents for solvent separation may be used in combination depending on the solubility of the polymer compound. Specifically, to separate a burnable polymer compound, one or more of the first type of solvent for dissolution and separation is used. Furthermore, to separate a non-burnable polymer compound, one or more of the second type of solvent for dissolution and separation, which is different from the first type of solvent for dissolution and separation, is used. The first type of solvent for dissolution and separation and the second type of solvent for dissolution and separation may both be aqueous solvents or non-aqueous solvents. Of course, one of the first type of solvent for dissolution and separation and the second type of solvent for dissolution and separation may be an aqueous solvent and the other a non-aqueous solvent.

[0084] Subsequently, the solvent for dissolution and separation is filtered to recover the filtrate, which contains the polymer compounds (burnable polymer compounds and non-burnable polymer compounds), and thus the polymer compounds are separated from the positive electrode 100.

[0085] The filtrate is then dried to obtain a dried polymer mixture of the burnable polymer and the non-burnable polymer, and the polymer is then separated using a separation method such as centrifugation, thereby separating the burnable polymer and the non-burnable polymer from each other, and each of the burnable polymer and the non-burnable polymer is then recovered from the positive electrode 100.

[0086] Finally, the weight W1 of the burnable polymer compound and the weight W2 of the non-burnable polymer compound are measured, and then the weight ratio WR is calculated based on the weights W1 and W2.

[0087] (Weight Ratio WRZ) The weight ratio WR described above is a parameter for a burnable polymer compound. In contrast, the weight ratio WRZ, which is a parameter for a non-burnable polymer compound, preferably satisfies a predetermined condition.

[0088] Specifically, the weight ratio WRZ expressed by formula (2) is preferably 0% or more and less than 14% (0%≦WRZ<14%), and more preferably greater than 0% and less than 14% (0%<WRZ<14%). However, the value of the weight ratio WRZ is rounded to one decimal place.

[0089] WRZ = [W2 / (W1+W2)] × 100 (2) (WRZ is the weight ratio. W1 is the weight of the burnable polymer compound. W2 is the weight of the non-burnable polymer compound.)

[0090] The reason why the weight ratio WRZ is 0% or more and less than 14% is that, as described above, even if the polymer compound contains a burnable polymer compound and a non-burnable polymer compound, most of the polymer compound becomes a burnable polymer compound, and therefore the polymer compound is easily burned using a baking treatment. Therefore, for the reasons described above, the positive electrode current collector 100A and the positive electrode active material are easily separated from the positive electrode 100, and the positive electrode current collector 100A and the positive electrode active material are easily recovered.

[0091] In this case, the smaller the weight ratio WRZ, the easier it is to recover the positive electrode current collector 100A and the positive electrode active material, and therefore the recovery efficiency of the positive electrode current collector 100A and the positive electrode active material improves.

[0092] The procedure for calculating the weight ratio WRZ is the same as the procedure for calculating the weight ratio WR described above, except that the weight ratio WRZ is calculated instead of the weight ratio WR.

[0093] (Positive Electrode Conductive Agent) The positive electrode active material layer 100B may further contain a positive electrode conductive agent. This positive electrode conductive agent contains one or more conductive materials such as carbon materials, metal materials, conductive ceramic materials, and conductive polymer compounds. Specific examples of carbon materials include graphite, carbon black, acetylene black, and ketjen black. This graphite may be natural graphite or artificial graphite. Specific examples of metallic materials include titanium, copper, silver, tin, bismuth, lead, and alloys thereof.

[0094] When the positive electrode conductive agent contains a conductive polymer compound, the conductive polymer compound becomes part of the above-mentioned polymer compound. This conductive polymer compound may be a burnable polymer compound or a non-burnable polymer compound.

[0095] In particular, the positive electrode conductive agent preferably contains a carbon material, because the carbon material has high dispersibility in the positive electrode active material layer 100B and the conductivity of the positive electrode active material layer 100B is sufficiently improved.

[0096] <1-2. Operation> In this positive electrode 100, lithium ions are released from the positive electrode active material layer 100B, and lithium ions are absorbed in the positive electrode active material layer 100B.

[0097] <1-3. Manufacturing Method> The positive electrode 100 is manufactured using the following example procedure. The following describes a case where the polymer compound contains a burnable polymer compound and a non-burnable polymer compound, and the positive electrode active material layer 100B contains a positive electrode binder (carbon material).

[0098] First, a positive electrode active material containing a lithium transition metal compound, a positive electrode binder containing polymer compounds (a burnable polymer compound and a non-burnable polymer compound), and a positive electrode conductive agent containing a carbon material are mixed together to form a positive electrode mixture.

[0099] Next, the positive electrode mixture is poured into a solvent to prepare a paste-like positive electrode mixture slurry. This solvent may be an aqueous solvent or a non-aqueous solvent.

[0100] Finally, the positive electrode mixture slurry is applied to both surfaces of the positive electrode current collector 100A to form the positive electrode active material layer 100B. The positive electrode active material layer 100B may then be compression-molded using a compression device such as a roll press. In this case, the positive electrode active material layer 100B may be heated, or the compression molding may be repeated multiple times.

[0101] As a result, the positive electrode active material layers 100B are formed on both sides of the positive electrode current collector 100A, and thus the positive electrode 100 is completed.

[0102] <1-4. Actions and Effects> According to this positive electrode 100, the positive electrode 100 includes a positive electrode current collector 100A and a positive electrode active material layer 100B, the positive electrode active material layer 100B includes a positive electrode active material and a polymer compound, the positive electrode active material includes a lithium transition metal compound, and the polymer compound has a thermal weight loss rate of 60% or more.

[0103] In this case, as described above, a series of actions described below are obtained.

[0104] First, when the positive electrode 100 is not subjected to a firing treatment, particles of the positive electrode active material and the like are bound to each other using part or all of the polymer compound, thereby ensuring the physical strength of the positive electrode active material layer 100B. As a result, when a secondary battery including the positive electrode 100 is used, the positive electrode 100 stably absorbs and releases lithium ions.

[0105] Second, when the positive electrode 100 is subjected to a calcination treatment, part or all of the polymer compound is burned away, and particles of the positive electrode active material and the like that have been bound together are separated from each other. As a result, the positive electrode current collector 100A and the positive electrode active material can be easily and stably recovered from the positive electrode 100 simply by performing the calcination treatment of the positive electrode 100.

[0106] Third, since the positive electrode 100 is baked at a relatively low temperature (= 400°C), some or all of the polymer compound is burned away simply and stably, which allows the positive electrode current collector 100A and the positive electrode active material to be recovered more simply and stably from the positive electrode 100, and also suppresses deterioration of the positive electrode current collector 100A and the positive electrode active material.

[0107] For these reasons, while the absorption and release of lithium ions in the positive electrode active material layer 100B is ensured, the positive electrode current collector 100A and the positive electrode active material can be easily and stably recovered from the positive electrode 100. Therefore, a secondary battery using the positive electrode 100 can achieve excellent battery characteristics and excellent recycling characteristics.

[0108] In particular, if the polymer compound contains a burnable polymer compound and the burnable polymer compound has a thermal weight loss rate of 70% or more, the burnable polymer compound is sufficiently burned away during firing, which makes it easier to recover the positive electrode current collector 100A and the positive electrode active material from the positive electrode 100, thereby achieving a greater effect.

[0109] In this case, if the polymer compound has a thermal weight loss rate of 95% or more, the positive electrode current collector 100A and the positive electrode active material can be more easily recovered from the positive electrode 100, and therefore, an even greater effect can be obtained.

[0110] Furthermore, if the burnable polymer compound contains one or more of polyacrylic acid ester, polymethacrylic acid ester, polyvinyl alcohol, polyvinyl acetal, polyvinyl butyral, polyvinyl acetate, cellulose ester, and cellulose ether, the positive electrode binder is burned away simply and stably during the firing treatment of the positive electrode 100. Therefore, the positive electrode current collector 100A and the positive electrode active material can be recovered from the positive electrode 100 more simply and stably, thereby achieving a greater effect.

[0111] Furthermore, if the polymer compound contains a non-burnable polymer compound together with a burnable polymer compound, and the non-burnable polymer compound has a thermal weight loss rate of less than 70% and a weight ratio WR of 86% or more, the positive electrode current collector 100A and the positive electrode active material can be easily separated from the positive electrode 100 by utilizing a firing treatment of the positive electrode 100. Therefore, even if the polymer compound contains a burnable polymer compound and a non-burnable polymer compound, the positive electrode current collector 100A and the positive electrode active material can be easily recovered, thereby achieving a greater effect.

[0112] Alternatively, if the polymer compound contains a non-burnable polymer compound together with a burnable polymer compound, and the non-burnable polymer compound has a thermal weight loss rate of less than 70% and a weight ratio WRZ of 0% or more and less than 14%, the positive electrode current collector 100A and the positive electrode active material can be easily separated from the positive electrode 100 by utilizing a firing treatment of the positive electrode 100. Therefore, even if the polymer compound contains a burnable polymer compound and a non-burnable polymer compound, the positive electrode current collector 100A and the positive electrode active material can be easily recovered, thereby achieving a greater effect.

[0113] In these cases, if the non-burnable polymer compound contains one or more of polyvinylidene fluoride, polytetrafluoroethylene, polyether ether ketone, polyphenylene sulfide, and polyimide, the adhesion between particles of the positive electrode active material and the like is improved, thereby achieving even greater effects.

[0114] Furthermore, if the positive electrode current collector 100A contains one or more of titanium, zirconium, and chromium as constituent elements, the lithium ion absorption / release efficiency is improved and side reactions of the positive electrode current collector 100A are suppressed during the firing process of the positive electrode 100, thereby achieving even greater effects.

[0115] Furthermore, if the positive electrode active material layer 100B further contains a positive electrode conductive agent, and the positive electrode conductive agent contains a carbon material, the conductivity of the positive electrode active material layer 100B is improved while the positive electrode current collector 100A and the positive electrode active material are easily and stably recovered from the positive electrode 100. Therefore, the battery characteristics are further improved while the recyclability is ensured, and thus a greater effect can be obtained.

[0116] 2. Secondary Battery (First Embodiment) Next, a secondary battery according to a first embodiment of the present technology to which the above-described positive electrode 100 is applied will be described.

[0117] The secondary battery described here is a secondary battery in which charge and discharge reactions proceed using the absorption and release of electrode reactants, and includes a positive electrode, a negative electrode, and an aqueous electrolyte solution. Details regarding the electrode reactants are as described above.

[0118] In the following, as described above, since the electrode reactant is lithium, the secondary battery is a lithium secondary battery (or a lithium ion secondary battery).

[0119] <2-1. Structure> FIG. 2 shows a cross-sectional structure of the secondary battery of the first embodiment.

[0120] As shown in Fig. 2, this 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.

[0121] [Exterior Body] As shown in FIG. 2, the exterior body 10 is a substantially box-shaped exterior member that houses the positive electrode 20, the negative electrode 30, and the electrolyte solution 40, and has an internal space S.

[0122] 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 metal foil, a polymer film, etc.

[0123] 2, the positive electrode 20 is disposed in the internal space S and absorbs and releases lithium ions. The positive electrode 20 has a configuration similar to that of the positive electrode 100, and therefore includes a positive electrode current collector 20A and a positive electrode active material layer 20B.

[0124] The configuration of the positive electrode current collector 20A is the same as the configuration of the positive electrode current collector 100A, except as described below. The configuration of the positive electrode active material layer 20B is the same as the configuration of the positive electrode active material layer 100B, except as described below.

[0125] The positive electrode current collector 20A includes a connection terminal 20AT on which the positive electrode active material layer 20B is not provided, and the connection terminal 20AT is extended to the outside of the exterior body 10. 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.

[0126] 2, the negative electrode 30 is disposed in the internal space S and absorbs and releases lithium ions. The negative electrode 30 includes a negative electrode current collector 30A and a negative electrode active material layer 30B. However, the negative electrode current collector 30A may be omitted.

[0127] (Negative electrode current collector) The negative electrode current collector 30A is a conductive member that supports the negative electrode active material layer 30B, and has a pair of surfaces that support the negative electrode active material layer 30B. The negative electrode current collector 30A contains one or more conductive materials such as a metal material, a carbon material, and a conductive ceramic material.

[0128] Specific examples of metal materials include stainless steel (SUS), titanium, zinc, tin, lead, and alloys thereof. The stainless steel may be a highly corrosion-resistant stainless steel to which one or more of niobium, molybdenum, or other additive elements have been added. Specifically, the stainless steel may be SUS444 to which molybdenum has been added as an additive element. Details regarding the conductive ceramic material are as described above.

[0129] The negative electrode current collector 30A is preferably insoluble or hardly soluble in the electrolyte solution 40 and corrosion-resistant, and also has low reactivity with the negative electrode active material described below. For this reason, the negative electrode current collector 30A preferably contains a metal material, because this suppresses deterioration of the negative electrode current collector 30A during charge and discharge.

[0130] The negative electrode current collector 30A may be a substrate whose surface is plated with the above-mentioned conductive material. The material for forming the substrate is not particularly limited and can be selected arbitrarily.

[0131] Here, the negative electrode current collector 30A includes a connection terminal portion 30AT on which the negative electrode active material layer 30B is not provided, and the connection terminal portion 30AT is led out of the exterior body 10.

[0132] (Negative Electrode Active Material Layer) The negative electrode active material layer 30B is a layer that absorbs and releases lithium ions. Here, the negative electrode active material layer 30B is provided on both sides of the negative electrode current collector 30A. However, the negative electrode active material layer 30B may be provided on only one side of the negative electrode current collector 30A, on the side where the negative electrode 30 faces the positive electrode 20.

[0133] The anode active material layer 30B contains an anode active material, but may further contain one or more of an anode binder, an anode conductive agent, and the like.

[0134] The negative electrode active material is a substance that absorbs and releases lithium ions, and includes one or more of titanium oxide, carbon materials, and metal-based materials. Specific examples of titanium oxide include anatase-type titanium oxide, rutile-type titanium oxide, and brookite-type titanium oxide. Specific examples of carbon materials include graphite. This graphite may be natural graphite or artificial graphite. The metal-based material is a material that includes, as a constituent element, one or more of metal elements and semimetal elements that can form an alloy with lithium.

[0135] [Electrolyte] The electrolyte 40 is contained in the internal space S and is an aqueous electrolyte, as described above. 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.

[0136] The secondary battery of the first embodiment includes one type of aqueous electrolyte (electrolyte 40), and is therefore a so-called single-liquid type secondary battery.

[0137] 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.

[0138] 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.

[0139] The electrolyte salt is a salt containing a cation and an anion. Here, the cation is a lithium ion as described above, and therefore the electrolyte salt contains one or more kinds of lithium salts. The type of the anion is not particularly limited.

[0140] 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 such as lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethanesulfonyl)imide.

[0141] Here, as described above, the type of anion is not particularly limited. Therefore, the anion may contain one or more types of fluorine-containing anions, or may contain one or more types of non-fluorine-containing anions. The fluorine-containing anion is a general term for anions containing fluorine as a constituent element, and specific examples of the fluorine-containing anion include a bis(fluorosulfonyl)imide ion and a bis(trifluoromethanesulfonyl)imide ion. The non-fluorine-containing anion is a general term for anions that do not contain fluorine as a constituent element, and specific examples of the non-fluorine-containing anion are not particularly limited.

[0142] In particular, the anions preferably contain non-fluorine-containing anions rather than fluorine-containing anions, because this suppresses the generation of hydrogen fluoride (HF) during charging and discharging, thereby suppressing corrosion of the components of the secondary battery, such as the exterior body 10, the positive electrode current collector 20A, and the negative electrode current collector 30A.

[0143] When the anion contains a fluorine-containing anion, it is preferable that the content of the fluorine-containing anion in the anion is not too high. Specifically, the content of the fluorine-containing anion in the electrolyte solution is preferably 50 mmol / kg or less. This is because corrosion of the components of the secondary battery is sufficiently suppressed. Note that hydrogen fluoride, which causes corrosion of the components of the secondary battery, is a substance generated due to the decomposition and reaction of the electrolyte salt during charge and discharge, and is also generated during the baking treatment of the positive electrode 100 described below.

[0144] 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.

[0145] The electrolyte salt may further contain one or more of the other metal salts in addition to the lithium salt. The type of the other metal salt is 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.

[0146] 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.

[0147] To confirm whether the electrolyte solution 40 is a saturated solution of electrolyte salt, the secondary battery is disassembled and the internal space S is visually observed to determine whether electrolyte salt has precipitated. To observe the internal space S, specifically, the liquid electrolyte solution 40, the surface of the positive electrode 20, and the inner wall surface of the exterior body 10 are observed. When the electrolyte salt has precipitated and the electrolyte solution 40 (liquid) and the electrolyte salt precipitate (solid) coexist, the electrolyte solution 40 is considered to be a saturated solution of electrolyte salt. To examine 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.

[0148] <2-2. Operation> This secondary battery operates as described below.

[0149] 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 are absorbed in the negative electrode 30. During discharging, when lithium ions are released from the negative electrode 30, the lithium ions move to the positive electrode 20 via the electrolyte 40, and are absorbed in the positive electrode 20.

[0150] <2-3. Manufacturing Method> When producing this secondary battery, the positive electrode 20 and the negative electrode 30 are each produced and the electrolyte solution 40 is prepared using the procedure described below as an example, and then the secondary battery is assembled.

[0151] [Fabrication of Positive Electrode] Positive electrode active material layers 20B are formed on both surfaces of the positive electrode current collector 20A using the same procedure as the fabrication procedure for the positive electrode 100 described above. However, when forming the positive electrode active material layers 20B, the positive electrode mixture slurry is applied to both surfaces of the positive electrode current collector 20A, excluding the connection terminal portion 20AT. In this way, the positive electrode 20 is fabricated.

[0152] [Fabrication of Negative Electrode] First, a negative electrode active material, a negative electrode binder, and a negative electrode conductive agent are mixed together to form a negative electrode mixture. Next, the negative electrode mixture is poured into a solvent to prepare a paste-like negative electrode mixture slurry. This solvent may be an aqueous solvent or an organic solvent. Finally, the negative electrode mixture slurry is applied to both surfaces of the negative electrode current collector 30A, excluding the connection terminal portion 30AT, to form the negative electrode active material layer 30B. The negative electrode active material layer 30B may then be compression-molded using a compression device such as a roll press. In this case, the negative electrode active material layer 30B may be heated, or the compression molding may be repeated multiple times. This completes the fabrication of the negative electrode 30.

[0153] [Preparation of Electrolyte Solution] An ionic substance is added to an aqueous solvent. This disperses or dissolves the ionic substance 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.

[0154] [Assembly of Secondary Battery] First, the positive electrode 20 and the negative electrode 30 are placed in the internal space S of the exterior body 10. In this case, the connection terminal portions 20AT and 30AT are led out to the outside of the exterior body 10.

[0155] 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.

[0156] 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 secondary battery using one type of aqueous electrolyte solution (electrolyte solution 40) is completed.

[0157] <2-4. Actions and Effects> According to the secondary battery of the first embodiment, the positive electrode 20 has a configuration similar to that of the positive electrode 100. Therefore, for the reasons described above, the positive electrode current collector 20A and the positive electrode active material can be easily and stably recovered from the positive electrode 20 while the absorption and release of lithium ions in the positive electrode active material layer 20B is ensured, and therefore excellent battery characteristics and excellent recycling characteristics can be obtained.

[0158] In particular, if the electrolyte solution contains a non-fluorine-containing anion, corrosion of the components of the secondary battery is suppressed, thereby ensuring stable operation of the secondary battery and suppressing deterioration of the positive electrode current collector 20A, thereby achieving a greater effect.

[0159] Furthermore, if the secondary battery is a lithium secondary battery, a sufficient battery capacity can be stably obtained by utilizing the absorption and release of lithium ions, and therefore a greater effect can be obtained.

[0160] Other functions and effects of the secondary battery of the first embodiment are similar to those of the positive electrode 100 .

[0161] 3. Secondary Battery (Second Embodiment) Next, a secondary battery according to a second embodiment of the present technology to which the above-described positive electrode 100 is applied will be described.

[0162] The secondary battery of the second embodiment is a dual-liquid type secondary battery including two types of aqueous electrolytes (a cathode electrolyte 61 and an anode electrolyte 62), unlike the secondary battery of the first embodiment which is a single-liquid type secondary battery including one type of aqueous electrolyte (electrolyte 40).

[0163] <3-1. Configuration> Fig. 3 shows a cross-sectional configuration of a secondary battery of the second embodiment, and corresponds to Fig. 2. The secondary battery of the second embodiment described here has the same configuration as the secondary battery of the first embodiment (Fig. 2), except for the points described below.

[0164] As shown in Fig. 3, this 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. 3, the positive electrode electrolyte 61 is lightly shaded, and the negative electrode electrolyte 62 is darkly shaded.

[0165] The exterior body 10 has two spaces (a positive electrode chamber S1 and a negative electrode chamber S2) separated by a partition wall 50 inside.

[0166] The partition wall 50 is disposed between the positive electrode 20 and the negative electrode 30 and separates the internal space S (see FIG. 2 ) 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.

[0167] The partition wall 50 prevents anions from passing between the positive electrode chamber S1 and the negative electrode chamber S2, 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 through. This is to prevent the positive electrode electrolyte 61 and the negative electrode electrolyte 62 from mixing with each other while ensuring the movement of lithium ions between the positive electrode chamber S1 and the negative electrode chamber S2. 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.

[0168] Specifically, the partition wall 50 includes one or both of a cation exchange membrane and a solid electrolyte membrane. The cation exchange membrane is a porous 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.

[0169] The solid electrolyte membrane may be a so-called inorganic particle membrane. This inorganic particle membrane is a composite membrane containing inorganic particles with lithium ion conductivity, a binder, and a fibrous material. The inorganic particles include one or more inorganic materials such as oxides, sulfides, hydroxides, carbonates, and sulfates. The binder includes one or more polymer compounds such as polyvinyl formal, polyvinyl alcohol, polyvinyl acetal, polyvinyl butyral, polymethyl methacrylate, and polytetrafluoroethylene. The fibrous material includes one or more fibrous materials such as cellulose fibers, polysaccharides, polyvinyl alcohol, polyacrylic acid, anionic derivatives of polystyrene, and cationic derivatives of polystyrene.

[0170] In particular, it is preferable that the partition wall 50 includes a cation exchange membrane rather than a solid electrolyte membrane, because the aqueous solvent contained in the positive electrode electrolyte 61 and the aqueous solvent contained in the negative electrode electrolyte 62 each easily permeate the partition wall 50, thereby improving the conductivity of lithium ions in the partition wall 50.

[0171] The positive electrode 20 is disposed in the positive electrode chamber S1 and absorbs and releases lithium ions, and the negative electrode 30 is disposed in the negative electrode chamber S2 and absorbs and releases lithium ions.

[0172] The positive electrode electrolyte 61 and the negative electrode electrolyte 62 are each an aqueous electrolyte. The positive electrode electrolyte 61 is accommodated in the positive electrode chamber S1, and the negative electrode electrolyte 62 is accommodated in 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 so as not to mix with each other.

[0173] As a result, the positive electrode electrolyte 61 contained in the positive electrode chamber S1 is in contact only with the positive electrode 20, without contacting the negative electrode 30. On the other hand, the negative electrode electrolyte 62 contained in the negative electrode chamber S2 is in contact only with the negative electrode 30, without contacting the positive electrode 20.

[0174] 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.

[0175] The pH of the negative electrode electrolyte 62 is higher than the pH 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. As a result, the decomposition reaction of the aqueous solvent is thermodynamically suppressed during charge and discharge, while the potential window of the aqueous solvent is expanded. Therefore, a high voltage can be obtained, and the charge and discharge reaction utilizing the absorption and release of lithium ions can proceed sufficiently and stably.

[0176] In particular, it is preferable that the composition formula (type of electrolyte salt) of the positive electrode electrolyte 61 and the composition formula (type of electrolyte salt) of the negative electrode electrolyte 62 are different from each other, because this makes it easier to ensure the magnitude relationship regarding the pH described above.

[0177] As long as the above-described magnitude relationship regarding pH is satisfied, the pH of each of the positive electrode electrolyte 61 and the negative electrode electrolyte 62 is not particularly limited.

[0178] 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 ensure the magnitude relationship of the pH described above. Also, this is because 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.

[0179] For this reason, the electrolyte salt contained in the anode electrolyte 62 is preferably lithium hydroxide or the like, among others. This is because the pH of the anode electrolyte 62 is likely to be 11 or higher, and therefore a strongly alkaline anode electrolyte 62 can be easily and stably achieved.

[0180] 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-described pH magnitude relationship and to maintain the pH magnitude relationship. Furthermore, components such as the exterior body 10, the positive electrode current collector 20A, and the negative electrode current collector 30A are less susceptible to corrosion, improving the electrochemical durability of the secondary battery.

[0181] It is preferable that one or both of the positive electrode electrolyte 61 and the negative electrode electrolyte 62 be saturated solutions of an electrolyte salt (lithium salt), similar to the electrolyte 40 of the first embodiment. This is because charge / discharge reactions tend 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.

[0182] 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 61 and the pH of the negative electrode electrolyte 62 are each easily maintained because the pH fluctuations are sufficiently suppressed.

[0183] 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. Specific examples of carboxylate ions include formate ions, acetate ions, propionate ions, tartrate ions, and citrate ions.

[0184] The pH of the positive electrode electrolyte 61 and the negative electrode electrolyte 62 may each contain, as a buffer, one or more of trishydroxymethylaminomethane, ethylenediaminetetraacetic acid, and the like.

[0185] More specifically, it is preferable that the 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 the negative electrode electrolyte 62 contains, as an anion, hydroxide ions. This is because the pH of the positive electrode electrolyte 61 can be easily controlled to be sufficiently high, and the pH of the negative electrode electrolyte 62 can be easily controlled to be sufficiently low.

[0186] In particular, it is preferable that each of the positive electrode electrolyte 61 and the negative electrode electrolyte 62 contains a non-fluorine-containing anion rather than a fluorine-containing anion, because this suppresses corrosion of the components of the secondary battery.

[0187] 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 pH magnitude relationship between the two.

[0188] <3-2. Operation> This secondary battery operates as described below.

[0189] 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 are therefore absorbed in the negative electrode 30. During discharging, 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 are therefore absorbed in the positive electrode 20.

[0190] <3-3. Manufacturing Method> The manufacturing procedure of this secondary battery is the same as the manufacturing procedure of the secondary battery in the first embodiment described above, except for the points described below.

[0191] An ionic substance is added to an aqueous solvent when preparing each of the positive electrode electrolyte 61 and the negative electrode electrolyte 62. 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.

[0192] When assembling a secondary battery, first, the exterior body 10 (cathode chamber S1 and anode chamber S2) with the partition wall 50 already installed therein is prepared. Next, the cathode 20 is placed in the cathode chamber S1, and the connection terminal 20AT is led out to the outside of the cathode chamber S1. Furthermore, the anode 30 is placed in the anode chamber S2, and the connection terminal 30AT is led out to the outside of the anode chamber S2. Finally, the cathode electrolyte 61 is supplied to the cathode chamber S1 through a cathode injection hole (not shown) provided in the exterior body 10, and the anode electrolyte 62 is supplied to the anode chamber S2 through a cathode injection hole (not shown) provided in the exterior body 10. Thereafter, the cathode injection hole and the anode injection hole are each sealed.

[0193] As a result, the positive electrode electrolyte 61 is accommodated in the positive electrode chamber S1 in which the positive electrode 20 is disposed, and the negative electrode electrolyte 62 is accommodated in the negative electrode chamber S2 in which the negative electrode 30 is disposed. Thus, a dual-liquid type secondary battery provided with two types of aqueous electrolytes (positive electrode electrolyte 61 and negative electrode electrolyte 62) is completed.

[0194] <3-4. Actions and Effects> According to the secondary battery of the second embodiment, the positive electrode 20 has a configuration similar to that of the positive electrode 100, and therefore, similar to the secondary battery of the first embodiment, excellent battery characteristics and excellent recyclability can be obtained.

[0195] Other functions and effects of the secondary battery of the second embodiment are similar to those of the secondary battery of the first embodiment.

[0196] 4. Recycling Method of Positive Electrode for Secondary Battery> Next, a method of recycling the positive electrode 100 described above will be described.

[0197] Here, a case will be described in which a secondary battery including the positive electrode 100 is used in order to recycle the positive electrode 100. This secondary battery may be the secondary battery of the first embodiment or the secondary battery of the second embodiment.

[0198] The secondary battery used to recycle the positive electrode 100 may be a normal secondary battery that is still operable because its life has not expired, or a secondary battery that is already inoperable because its life has expired (a so-called secondary battery for disposal).

[0199] In the following, a case will be described in which the secondary battery is the secondary battery of the first embodiment and the polymer compound contains only a burnable polymer compound. In this case, the positive electrode 20 corresponding to the positive electrode 100 is recycled.

[0200] [Recycling Procedure] When recycling the positive electrode 20 corresponding to the positive electrode 100, first, a secondary battery including the positive electrode 20 is prepared. As described above, this secondary battery includes the positive electrode 20, the negative electrode 30, and the electrolyte 40.

[0201] Subsequently, the secondary battery is disassembled to recover the positive electrode 20, and the positive electrode 20 is then washed with a cleaning solvent to wash away the electrolyte solution 40 adhering to the positive electrode 20. The type of cleaning solvent is not particularly limited, but specifically, it is an aqueous solvent such as pure water.

[0202] Finally, the positive electrode 20 is baked until the temperature of the positive electrode 20 reaches 200° C. to 500° C. In this case, a heating device such as an oven is used. The baking time is not particularly limited, but specifically, it is 10 minutes to 12 hours.

[0203] The baking temperature can be set arbitrarily within the range of 200°C to 500°C, as long as the polymer compound (burnable polymer compound) is sufficiently burned away. That is, the baking temperature can be set arbitrarily depending on the type of burnable polymer compound, etc. Among these, the baking temperature is preferably 300°C to 450°C. This is because the burnable polymer compound is more likely to be burned away and deterioration of the positive electrode active material and the positive electrode current collector is more likely to be suppressed.

[0204] In this firing process, the polymer compound is fired, and the burnable polymer compound is burned away. As a result, the burnable polymer compound is removed, and the positive electrode active material layer 20B is decomposed. As a result, the positive electrode current collector 20A and the positive electrode active material are recovered.

[0205] In this case, the particles of the positive electrode active material that have been bound together via the polymer compound are separated from each other, and the particles of the positive electrode conductive agent that have been bound together via the polymer compound are also separated from each other. Furthermore, the particles of the positive electrode active material and the particles of the positive electrode conductive agent that have been bound together via the polymer compound are also separated from each other.

[0206] Therefore, a mixture of the positive electrode current collector 20A and the powder is obtained as a residue after the firing treatment. The powder contains a powdered positive electrode active material and a powdered positive electrode conductive agent.

[0207] The environment in which the calcination treatment is carried out is not particularly limited, but an oxygen-containing atmosphere is preferable. This is because the calcinable polymer compound is more likely to be calcined and therefore more likely to be removed. A specific example of an oxygen-containing atmosphere is air.

[0208] The mixture may then be separated using one or more devices, such as a dry classifier and a vibrating sieve. Conditions such as the air volume are not particularly limited and can be set as desired. In this case, the difference in size between the powders of the positive electrode active material and positive electrode conductive agent and the positive electrode current collector 20A is utilized to separate the powders of the positive electrode active material and positive electrode conductive agent from the positive electrode current collector 20A. This allows the positive electrode current collector 20A to be recovered.

[0209] Finally, the powder from which the positive electrode current collector 20A has been separated is separated into the powdered positive electrode active material and the powdered positive electrode conductor using a separation method such as centrifugation, thereby separating the positive electrode active material from the positive electrode conductor and recovering the positive electrode active material.

[0210] Therefore, the positive electrode current collector 20A and the positive electrode active material are recovered from the positive electrode 20, and the positive electrode current collector 20A and the positive electrode active material can be reused.

[0211] In this case, only a firing process at a relatively low temperature of 200°C to 500°C and a process for separating the mixture are used, so that the positive electrode current collector 20A and the positive electrode active material are easily and stably recovered from the positive electrode 20 without deteriorating either the positive electrode current collector 20A or the positive electrode active material.

[0212] Furthermore, in cases where the positive electrode current collector 20A and the positive electrode active material are each expensive, the high-quality positive electrode current collector 20A and the positive electrode active material can be recovered and then reused, which also provides cost advantages.

[0213] Instead of separating the positive electrode current collector 20A and the positive electrode active material from each other and then reusing them, the positive electrode current collector 20A and the positive electrode active material may be reused in a mixed state without being separated from each other.

[0214] [Recovery Rate] When the weight of the positive electrode active material, which is the raw material used to produce the positive electrode 20, is known, the efficiency of recovering the positive electrode active material using the above-described recycling procedure can be evaluated by calculating the recovery rate E represented by formula (3).

[0215] E = (G2 / G1) × 100 (3) (E is the recovery rate, G1 is the weight of the raw material positive electrode active material, and G2 is the weight of the recovered positive electrode active material.)

[0216] As is clear from formula (3), recovery rate E is an index that indicates how much of the positive electrode active material used as a raw material has been recovered. Therefore, the more the value of recovery rate E is as close to 100% as possible without exceeding 100%, the more efficiently the positive electrode active material can be recovered from positive electrode 20.

[0217] In addition, when the polymer compound contains both a burnable polymer compound and a non-burnable polymer compound, the burnable polymer compound is removed during the baking treatment, but the non-burnable polymer compound is not. In this case, the non-burnable polymer compound remains after the baking treatment, and a portion of the positive electrode active material is not separated from the positive electrode current collector 20A and remains on the surface of the positive electrode current collector 20A. This reduces the amount of recovered positive electrode active material, and the recovery rate E becomes less than 100%.

[0218] Furthermore, if the heat resistance of the positive electrode current collector 20A is insufficient, a portion of the positive electrode current collector 20A may fall off, peel off, or dissolve during the firing process, resulting in a portion of the positive electrode current collector 20A being mixed into the powder after the firing process. In this case, if a portion of the positive electrode current collector 20A is not separated from the positive electrode active material, the portion of the positive electrode current collector 20A will also be recovered together with the positive electrode active material. This results in an excessive increase in the apparent amount of recovered positive electrode active material, resulting in a recovery rate E exceeding 100%.

[0219] [Purity] The cathode active material recovered using the recycling procedures described above can be evaluated for purity, which is the purity of the lithium transition metal compound used as the cathode active material to fabricate cathode 20.

[0220] When evaluating the purity of the positive electrode active material, the positive electrode active material is analyzed using one or more analytical methods such as high-frequency inductively coupled plasma (ICP) emission spectroscopy.

[0221] In this case, the positive electrode active material is first placed in an acid such as nitric acid, and the acid is then heated. This dissolves the positive electrode active material, yielding a solution for analysis. Subsequently, the solution is diluted as necessary. The type of solvent used for dilution is not particularly limited. Finally, the solution is analyzed using the above-described analytical method.

[0222] In this analysis of the positive electrode active material, the purity P (%) represented by formula (4) is calculated based on the concentration of the transition metal element contained as a constituent element in the positive electrode active material.

[0223] P = (C2 / C1) × 100 (4) (P is purity. C1 is the concentration (ppm) of all metal ions (excluding lithium ions) contained in the positive electrode active material. C2 is the concentration (ppm) of transition metal ions contained in the positive electrode active material.)

[0224] As described above, if the heat resistance of the positive electrode current collector 20A is insufficient, the recovery rate E increases due to a portion of the positive electrode current collector 20A being mixed into the powder after the firing treatment, and the recovery rate E may become close to 100%.

[0225] However, since the powder contains not only the positive electrode active material but also a portion of the positive electrode current collector 20A, the proportion of the positive electrode active material in the powder is reduced compared to when the powder does not contain a portion of the positive electrode current collector 20A.

[0226] As a result, if the heat resistance of the positive electrode current collector 20A is insufficient, the purity P will decrease even if the recovery rate E reaches a value close to 100%.

[0227] [Function and Effect] According to the recycling method for the positive electrode 20 corresponding to this positive electrode 100, the positive electrode 20 is baked until the temperature of the positive electrode 20 reaches 200°C to 500°C, thereby burning off the polymer compound and recovering the positive electrode current collector 20A and the positive electrode active material.

[0228] As a result, as described above, by simply using simple processes such as the firing process and the separation process, the positive electrode current collector 20A and the positive electrode active material can be easily and stably recovered from the positive electrode 20. Therefore, it is possible to obtain excellent battery characteristics and excellent recycling characteristics for a secondary battery using the positive electrode 20.

[0229] In particular, if the positive electrode 20 is fired in an oxygen-containing atmosphere, the polymer compound is likely to be burned away during the firing treatment of the positive electrode 20. Therefore, the positive electrode active material is easily recovered from the positive electrode 20, and the recovery rate E and purity P are also improved, resulting in a greater effect.

[0230] Furthermore, if the positive electrode current collector 20A and the positive electrode active material are separated from each other, the positive electrode current collector 20A and the positive electrode active material can be used separately from each other, thereby achieving a greater effect.

[0231] 5. Modifications The configuration of the secondary battery can be modified as appropriate, as described below. The series of modifications described below may be combined with each other.

[0232] [Variation 1] In the first embodiment, as shown in Fig. 2, the positive electrode 20 and the negative electrode 30 are separated from each other via the electrolyte solution 40. However, as shown in Fig. 4 which corresponds to Fig. 2, the secondary battery further includes a separator 70, so that the positive electrode 20 and the negative electrode 30 may be separated from each other via the separator 70. The configuration of the secondary battery shown in Fig. 4 is the same as the configuration of the secondary battery shown in Fig. 2, except as described below.

[0233] 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.

[0234] Specifically, the separator 70 is a polymer film containing one or more polymer compounds such as polyolefins, and specific examples of the polymer compounds include polyethylene and polypropylene.

[0235] 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 a plurality of inorganic particles, a binder, and a plurality of fibrous materials.

[0236] Each of the inorganic particles contains 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 contain one or more oxides, sulfides, hydroxides, carbonates, sulfates, and the like.

[0237] In particular, the inorganic material is preferably an inorganic solid electrolyte having excellent alkali metal ion conductivity and high water resistance, because hydrolysis is less likely to occur inside the secondary battery. Specifically, the inorganic solid electrolyte having excellent alkali metal ion conductivity has a NASICON structure, and more specifically, LiM 2　 (P.O. 4　 ) 3　 The lithium phosphate solid electrolyte may be represented by the general formula: where M is one or more of metal elements such as Ti, Ge, Sr, Zr, Sn, and Al. In particular, M preferably contains one or more of metal elements selected from Ge, Zr, and Ti, and Al.

[0238] A specific example of a lithium phosphate solid electrolyte having a NASICON structure is LATP (Li 1+x　 Al x　 Ti 2-x　 (P.O. 4　 ) 3　 ), Li 1+x　 Al x　 Ge 2-x　 (P.O. 4　 ) 3　 and Li 1+x　 Al x　 Zr 2-x　 (P.O. 4　 ) 3　etc. However, x satisfies 0<x≦5, and preferably 0.1≦x≦0.5. Among them, the lithium phosphate solid electrolyte is preferably LATP, because it provides excellent water resistance and makes hydrolysis less likely to occur inside the secondary battery.

[0239] Alternatively, the inorganic material is preferably an oxide-based solid electrolyte. Specifically, the oxide-based solid electrolyte is amorphous LIPON (Li 2.9　 P.O. 3.3　 N 0.46 ) and LLZ (Li 7　 La 3　 Zr 2　 O 12 ) etc.

[0240] Alternatively, the inorganic material may be an oxide ceramic, a carbonate, a sulfate, or a nitride ceramic. Specific examples of oxide ceramics include alumina, silica, zirconia, yttria, magnesium oxide, calcium oxide, barium oxide, strontium oxide, and vanadium oxide. Specific examples of carbonates include sodium carbonate, potassium carbonate, magnesium carbonate, calcium carbonate, barium carbonate, lanthanum carbonate, and cerium carbonate. Specific examples of sulfates include calcium sulfate, magnesium sulfate, aluminum sulfate, gypsum, and barium sulfate. Specific examples of phosphates include hydroxyapatite, zirconium phosphate, and titanium phosphate. Specific examples of nitride ceramics include silicon nitride, titanium nitride, and boron nitride. Among these, alumina, silica, and calcium oxide are preferably in the form of glass ceramics.

[0241] The shape of the inorganic particles, the average particle size of the inorganic particles, and the content of the inorganic particles in the inorganic particle film are not particularly limited and can be set as desired. However, because the inorganic particles are the main component of the inorganic particle film, it is preferable that the content of the inorganic particles in the inorganic particle film is sufficiently large. This is because the separator 70 becomes denser and the hydrophobicity of the separator 70 is improved.

[0242] The binder contains one or more polymeric compounds. These polymeric compounds are compounds formed by polymerizing 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.

[0243] 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.

[0244] Each of the multiple fibrous substances contains one or more of the fibrous materials. The fibrous materials preferably contain one or more of the hydrophilic functional groups, with specific examples of the hydrophilic functional groups being hydroxyl groups, sulfonic groups, and carboxyl groups. Specific examples of the fibrous materials 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 materials may also be derivatives of the above-mentioned series of specific examples, or copolymers of two or more of the series of specific examples.

[0245] As described above, the fibrous material contains a hydrophilic functional group, and therefore the electrolytic solution 40 is easily trapped between two or more fibrous materials, which makes it easier for the separator 70 to swell when the separator 70 is impregnated with the electrolytic solution 40.

[0246] 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.

[0247] 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. The number of layers of the polymer compound film and the inorganic particle film is not particularly limited and can be set arbitrarily.

[0248] When producing an inorganic particle film, first, an inorganic particle film, a binder, and a fibrous material are introduced into a solvent such as an organic solvent to prepare a slurry. Then, the slurry is poured into a mold. Finally, the slurry is dried to volatilize the solvent, and the mold is removed. This completes an inorganic particle film containing inorganic particles, a binder, and a fibrous material.

[0249] In this case, lithium ions can also move between the positive electrode 20 and the negative electrode 30 via the separator 70, and the same effect can be obtained.

[0250] [Modification 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.

[0251] In this case, lithium ions can also move between the positive electrode 20 and the negative electrode 30 via the partition wall 50, and the same effect can be obtained.

[0252] [Modification 3] In the first embodiment, as shown in Fig. 2, electrolytic solution 40, which is a liquid electrolyte, is used. However, as shown in Fig. 5, which corresponds to Fig. 2, electrolyte layers 81, 82, which are gel electrolytes, may be used instead of electrolytic solution 40. The configuration of the secondary battery shown in Fig. 5 is the same as the configuration of the secondary battery shown in Fig. 2, except for the points described below.

[0253] Here, the secondary battery additionally includes a separator 70 and electrolyte layers 81, 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.

[0254] Each of the electrolyte layers 81, 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. 5, the electrolyte layers 81, 82 are each lightly shaded.

[0255] The details of 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 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. The details of the inorganic particle membrane are as described above.

[0256] When forming the electrolyte layer 81, a sol-like precursor solution is prepared by mixing the electrolytic solution 40, the polymer compound, and a dilution solvent together, and then the precursor solution is applied to the surface of the positive electrode 20. The procedure for forming the electrolyte layer 82 is the same as the procedure for forming the electrolyte layer 81, except that the precursor solution is applied to the surface of the negative electrode 30.

[0257] In this case, the same effect can be obtained because lithium ions can move between the positive electrode 20 and the negative electrode 30 via the electrolyte layers 81 and 82. In this case, leakage of the electrolyte solution 40 can be particularly prevented.

[0258] [Modification 4] In the second embodiment, as shown in Fig. 3, positive electrode electrolyte 61 and negative electrode electrolyte 62, which are liquid electrolytes, are used. However, as shown in Fig. 6 corresponding to Fig. 3, electrolyte layers 91, 92, which are gel electrolytes, may be used instead of positive electrode electrolyte 61 and negative electrode electrolyte 62. The configuration of the secondary battery shown in Fig. 6 is the same as the configuration of the secondary battery shown in Fig. 3, except for the points described below.

[0259] Here, the 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.

[0260] The electrolyte layer 91 contains a polymer compound together with the cathode electrolyte 61, and the cathode electrolyte 61 is held by the polymer compound. The electrolyte layer 92 contains a polymer compound together with the anode electrolyte 62, and the anode electrolyte 62 is held by the polymer compound. Details regarding the types of polymer compounds are as described above. In FIG. 6 , the electrolyte layer 91 containing the cathode electrolyte 61 is lightly shaded, and the electrolyte layer 92 containing the anode electrolyte 62 is darkly shaded.

[0261] When forming the electrolyte layer 91, a sol-like precursor solution is prepared by mixing the positive electrode electrolyte 61, the polymer compound, and a dilution solvent together, and the precursor solution is then applied to the surface of the positive electrode 20. When forming the electrolyte layer 92, a sol-like precursor solution is prepared by mixing the negative electrode electrolyte 62, the polymer compound, and a dilution solvent together, and the precursor solution is then applied to the surface of the negative electrode 30.

[0262] 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.

[0263] In this case, the same effect can be obtained because lithium ions can move between the positive electrode 20 and the negative electrode 30 via the electrolyte layers 91, 92. In this case, leakage of the positive electrode electrolyte 61 and the negative electrode electrolyte 62 can be particularly prevented.

[0264] [Modification 5] In each of the first and second embodiments, a secondary battery using an aqueous electrolyte solution containing an aqueous solvent has been described. However, instead of the aqueous electrolyte solution, a nonaqueous electrolyte solution containing a nonaqueous solvent (organic solvent) may be used.

[0265] 7 shows a cross-sectional structure of a secondary battery using a non-aqueous electrolyte, which is a so-called coin-type secondary battery. Specifically, as shown in FIG. 7, the secondary battery includes a positive electrode 101, a negative electrode 102, a separator 103, a positive electrode can 104, a negative electrode can 105, a gasket 106, and an electrolyte (not shown).

[0266] The positive electrode 101 is housed in a positive electrode can 104, and the negative electrode 102 is housed in a negative electrode can 105. The positive electrode 101 and the negative electrode 102 are stacked together with a separator 103 interposed therebetween, and the positive electrode 101, the negative electrode 102, and the separator 103 are each impregnated with an electrolyte. The positive electrode can 104 and the negative electrode can 105 are crimped together with a gasket 106, so that the positive electrode 101, the negative electrode 102, and the separator 103 are sealed within the positive electrode can 104 and the negative electrode can 105.

[0267] The configuration of the positive electrode 101 is similar to that of the positive electrode 20, except that a positive electrode active material layer 20B is provided on one side of the positive electrode current collector 20A. The configuration of the negative electrode 102 is similar to that of the negative electrode 30, except that a negative electrode active material layer 30B is provided on one side of the negative electrode current collector 30A. It is preferable that each of the positive electrode current collector and the negative electrode current collector is stable against a non-aqueous electrolyte solution. The separator 103 is a porous film containing one or more types of polymer compounds such as polyethylene.

[0268] The nonaqueous electrolyte solution contains a nonaqueous solvent and an electrolyte salt. The nonaqueous solvent may be of one type or two or more types. The electrolyte salt may be of one type or two or more types.

[0269] The non-aqueous solvent includes a carbonate ester compound, a carboxylic acid ester compound, a lactone compound, etc. Specific examples of the carbonate ester compound include ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. Specific examples of the carboxylic acid ester compound include ethyl acetate, ethyl propionate, propyl propionate, and ethyl trimethylacetate. Specific examples of the lactone compound include γ-butyrolactone and γ-valerolactone.

[0270] The electrolyte salt is a lithium salt or the like. A specific example of the lithium salt is lithium hexafluorophosphate (LiPF 6　 ), lithium tetrafluoroborate (LiBF 4　 ), lithium perchlorate (LiClO 4　 ), lithium trifluoromethanesulfonate (LiCF 3　 SO 3　 ), lithium bis(fluorosulfonyl)imide (LiN(FSO 2　 ) 2　 ), lithium bis(trifluoromethanesulfonyl)imide (LiN(CF 3　 SO 2　 ) 2　 ), lithium tris(trifluoromethanesulfonyl)methide (LiC(CF 3　 SO 2　 ) 3　 ), lithium bis(oxalato)borate (LiB(C 2　 O 4　 ) 2　 ), lithium monofluorophosphate (Li 2　 PFO 3　 ) and lithium difluorophosphate (LiPF 2　 O 2　 ) etc.

[0271] However, as described above, the electrolyte salt preferably contains a non-fluorine-containing anion, and therefore, the electrolyte salt preferably contains a lithium salt such as lithium perchlorate rather than a lithium salt such as lithium hexafluorophosphate.

[0272] When the positive electrode 101 is recovered from a secondary battery in order to recycle the positive electrode 101, the positive electrode 101 is washed using a non-aqueous solvent such as dimethyl carbonate as a washing solvent.

[0273] In this case, too, lithium ions can move between the positive electrode 101 and the negative electrode 102 via the separator 103, so the same effect can be obtained.

[0274] 6. Uses of Secondary Batteries There are no particular limitations on the uses (application examples) of secondary batteries. A secondary battery used as a power source may be a main power source for electronic devices, electric vehicles, and the like, 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 a main power source, or a power source that can be switched from a main power source.

[0275] Specific examples of uses for secondary batteries are as follows: Electronic devices such as video cameras, digital still cameras, mobile phones, laptop computers, headphone stereos, portable radios, and portable information terminals. Storage devices such as backup power supplies and memory cards. Power tools such as power drills and power saws. Battery packs installed in electronic devices. Medical electronic devices such as pacemakers and hearing aids. Electric vehicles such as electric cars (including hybrid cars). Power storage systems such as home or industrial battery systems that store power in preparation for emergencies. In these uses, one secondary battery may be used, or multiple secondary batteries may be used.

[0276] The battery pack may use a single cell or a battery pack. The electric vehicle is a vehicle that operates (travels) using a secondary battery as a driving power source, and may be a hybrid vehicle that also has a driving source other than the secondary battery. In a home power storage system, it is possible to use household electrical appliances by using the power stored in the secondary battery, which is a power storage source.

[0277] Of course, the secondary battery may be used for purposes other than the series of purposes exemplified here.

[0278] An embodiment of the present technology will be described.

[0279] Experimental Examples 1 to 14 and Comparative Examples 1 and 2 As described below, secondary batteries were manufactured and then evaluated.

[0280] [Fabrication of Test Secondary Battery] Here, a three-electrode cell was fabricated as a test secondary battery for simple evaluation of the secondary battery. When fabricating this test secondary battery, a test electrode corresponding to the positive electrode was fabricated.

[0281] (Preparation of Test Electrode) First, a positive electrode active material (lithium manganese oxide (LiMn 2　 O 4　 A positive electrode mixture was prepared by mixing 93 parts by mass of a positive electrode composite powder (aluminum oxide, average particle diameter: approximately 20 μm), 5 parts by mass of a polymer compound (burnable polymer compound) functioning as a positive electrode binder, and 2 parts by mass of a positive electrode conductive agent (carbon material or metal material).

[0282] The burnable polymer compounds used were polyethyl acrylate (PEA, average molecular weight = 10,000, Tg = 45°C), a polyacrylic acid ester; polymethyl methacrylate (PMMA, average molecular weight = 800,000), a polymethacrylic acid ester; polyvinyl butyral (PVB, average molecular weight = 52,000, Tg = 71°C), a polyvinyl ether; polyvinyl acetate (PVAC, average degree of polymerization = 1,500) and polyvinyl alcohol (PVA, average degree of polymerization = 1,500), both of which are polyvinyl esters; and carboxymethyl cellulose (CMC, average molecular weight = 350,000), a cellulose ester.

[0283] Powdered artificial graphite (Gr) was used as the carbon material, and powdered titanium (Ti) was used as the metal material.

[0284] When preparing this positive electrode mixture, another polymer compound (non-burnable polymer compound) functioning as a positive electrode binder was also used as needed. As the non-burnable polymer compound, polyvinylidene fluoride (PVDF) was used.

[0285] The types, compositions, and contents (wt %) of the polymer compounds (burnable polymer compounds and non-burnable polymer compounds) were as shown in Tables 1 to 3. In the "Polymer Compound (Positive Electrode Binder)" columns shown in Tables 1 to 3, the "burnable" column shows the type of burnable polymer compound, and the "non-burnable" column shows the type of non-burnable polymer compound.

[0286] Next, the positive electrode mixture was poured into a solvent (N-methyl-2-pyrrolidone, an organic solvent), and the solvent was stirred to prepare a paste-like positive electrode mixture slurry.

[0287] Subsequently, the positive electrode mixture slurry was applied to both sides of a positive electrode current collector (thickness=20 μm) using a coating device, and then the positive electrode mixture slurry was dried to form a positive electrode active material layer.

[0288] The materials used for the positive electrode current collector were metallic titanium (metallic Ti), which is a simple substance of titanium, SUS304 (Cr alloy), which is a stainless steel (chromium alloy), metallic copper (metallic Cu), which is a simple substance of copper, and metallic aluminum (metallic Al), which is a simple substance of aluminum.

[0289] Finally, the positive electrode active material layer was compression molded using a roll press, thereby producing test electrodes (Examples 1 to 13).

[0290] After the test electrode was completed, the thermal weight loss rate (%) and weight ratio WR (%) of the polymer compound were examined. The results are shown in Table 1.

[0291] For comparison, other test electrodes were also prepared as shown in Table 3. Specifically, a test electrode was prepared using the same procedure except that only a non-burnable polymer compound (polyvinylidene fluoride) was used as the polymer compound functioning as the positive electrode binder (Comparative Example 1). Furthermore, a test electrode was prepared using the same procedure except that the weight ratio WR was changed by decreasing the mixing ratio of the burnable polymer compound and increasing the mixing ratio of the non-burnable polymer compound (Comparative Example 2).

[0292] Although not specified in Tables 1 to 3, the weight ratio WRZ was 0% when the weight ratio WR was 100%, 2% when the weight ratio WR was 98%, and 50% when the weight ratio WR was 50%.

[0293] (Preparation of Electrolyte Solutions) Here, one type of aqueous electrolyte solution and two types of non-aqueous electrolyte solutions were prepared as the electrolyte solutions.

[0294] Specifically, an ionic substance (lithium sulfate) was added to an aqueous solvent (pure water), and the aqueous solvent was then stirred to prepare an aqueous electrolyte solution (Examples 1 to 9, 12 to 14, and Comparative Examples 1 and 2). In this case, the concentration of the ionic substance was 2 mol / L (=2 mol / dm 3　 )

[0295] In addition, an ionic substance (lithium perchlorate) was added to a non-aqueous solvent (ethylene carbonate, a cyclic carbonate ester, and dimethyl carbonate, a chain carbonate ester), and the non-aqueous solvent was stirred to prepare a non-aqueous electrolyte solution (Example 10). This lithium perchlorate contains perchlorate ions (ClO), a non-fluorine-containing anion. - In this case, the mixing ratio of the non-aqueous solvent was set to cyclic carbonate ester:chain carbonate ester = 30:70. The concentration of the ionic substance was set to 1 mol / L (= 1 mol / dm 3　 )

[0296] Furthermore, a non-aqueous electrolyte solution (Example 11) was prepared by the same procedure except that lithium hexafluorophosphate was used instead of lithium perchlorate as the ionic substance. This lithium hexafluorophosphate contains a fluorine-containing anion, hexafluorophosphate ion (PF6 - )

[0297] (Assembly of test secondary battery) After placing the electrolyte in a beaker, a three-electrode cell, which is a test secondary battery, was assembled by immersing a part of each of the test electrode, counter electrode (metallic nickel), and reference electrode (silver-silver chloride) in the electrolyte.

[0298] [Evaluation of Secondary Battery] When the battery characteristics (capacity characteristics) and recycling characteristics of the test secondary battery were evaluated, the results shown in Tables 1 to 3 were obtained.

[0299] (Capacity Characteristics) When evaluating the capacity characteristics, the discharge capacity (mAh) was measured by charging and discharging the test secondary battery in a room temperature environment (temperature = 23° C.) After that, the test capacity (mAh / g), which is an index for evaluating the capacity characteristics, was calculated by dividing the discharge capacity by the weight (g) of the positive electrode active material.

[0300] During charging, the test secondary battery was charged at a current of 1 C until the potential of the test electrode (vs. the reference electrode) reached 1.2 V, and during discharging, the test secondary battery was discharged at a current of 1 C until the potential of the test electrode (vs. the reference electrode) reached 0.6 V. Note that 1 C is a current value at which the battery capacity (theoretical capacity) is fully discharged in 1 hour.

[0301] (Recycling Characteristics) When evaluating the recycling characteristics, the capacity characteristics were evaluated using a test secondary battery, and then the recovery rate E (%) and purity P (%), which are indices for evaluating the recycling characteristics, were calculated using a procedure similar to the recycling procedure for the positive electrode 20 described above.

[0302] The calculation procedure for the recovery rate E was as described above. In this case, an aqueous solvent (pure water) was used as the cleaning solvent. The test electrodes were fired in the air under the firing conditions of a firing temperature of 400°C and a firing time of 1 hour. (Examples 1 to 13, Comparative Examples 1 and 2)

[0303] The same procedure was used except that the firing conditions were changed to a firing temperature of 800° C. (Example 14).

[0304] The calculation procedure for the purity P was as described above. In this case, nitric acid was used as the acid, and ICP atomic emission spectroscopy was used as the analytical method. In addition, when calculating the purity P, attention was focused on manganese ions contained as a constituent element in the positive electrode active material (lithium transition metal compound).

[0305] As described above, in Tables 1 to 3, the positive electrode active materials (lithium transition metal compounds) of Examples 1 to 14 and Comparative Examples 1 and 2 were lithium manganese oxide (LiMn 2　 O 4　 The electrolytes of Examples 1 to 9, 12 to 14 and Comparative Examples 1 and 2 are aqueous electrolytes. The electrolyte of Example 10 contains perchlorate ions (ClO4 - The electrolyte of Example 11 is a non-aqueous electrolyte containing hexafluorophosphate ions (PF6 - ) is a non-aqueous electrolyte solution containing the above-mentioned cations. The positive electrode current collectors of Examples 1 to 14 and Comparative Examples 1 to 2 are made of the materials shown in Tables 1 to 3. The positive electrode conductive materials of Examples 1 to 14 and Comparative Examples 1 to 2 are made of the materials and have the contents shown in Tables 1 to 3. The polymer compounds of Examples 1 to 14 and Comparative Examples 1 to 2 are divided into burnable polymer compounds and non-burnable polymer compounds, and are made of the materials and have the contents shown in Tables 1 to 3. The firing conditions for Examples 1 to 13 and Comparative Examples 1 to 2 when calculating the recovery rate are a firing temperature of 400°C and a firing time of 1 hour. The firing conditions for Example 14 when calculating the recovery rate are a firing temperature of 800°C and a firing time of 1 hour.

[0306] The thermal weight loss percentage (%) of the polymer compounds shown in Tables 1 to 3 when the temperature reaches 400°C is the combined thermal weight loss percentage (%) of the burnable polymer compounds and the non-burnable polymer compounds. The thermal weight loss percentages (%) of the burnable polymer compounds and the non-burnable polymer compounds are as follows: The thermal weight loss percentage (%) of polyethyl acrylate (PEA) is 100%. The thermal weight loss percentage (%) of polymethyl methacrylate (PMMA) is 100%. The thermal weight loss percentage (%) of polyvinyl butyral (PVB) is 95%. The thermal weight loss percentage (%) of polyvinyl alcohol (PVA) is 100%. The thermal weight loss percentage (%) of polyvinyl acetate (PVAC) is 75%. The thermal weight loss percentage (%) of carboxymethyl cellulose (CMC) is 98%. The thermal weight loss rate (%) of polyvinylidene fluoride (PVDF) is 1%.

[0307]

[0308]

[0309]

[0310] [Discussion] As shown in Tables 1 to 3, the test capacity, recovery rate E, and purity P varied depending on the configuration of the test electrode.

[0311] Specifically, when the thermal weight loss rate of the polymer compound was less than 60% (Comparative Examples 1 and 2), a high test capacity was obtained in some cases, but the recovery rate E was 0%. In such cases, the purity P could not be calculated.

[0312] In contrast, when the rate of thermal weight loss of the polymer compound was 60% or more (Examples 1 to 11), a high test capacity was obtained, as well as a high recovery rate E and a high purity P.

[0313] In particular, when the thermal weight loss rate of the polymer compound is 60% or more, a series of trends described below were observed.

[0314] First, when a burnable polymer compound was used as the polymer compound, a sufficient test volume was obtained, and a sufficient recovery rate E and a sufficient purity P were also obtained, regardless of the type of the burnable polymer compound.

[0315] In this case, when the polymer compound contained only burnable polymer compounds and its thermal weight loss rate was 95% or more, a high test capacity was obtained, as well as a high recovery rate E and a high purity P.

[0316] Second, when the burnable polymer compound included any one of polyacrylic acid ester, polyvinyl butyral, polyvinyl alcohol, and cellulose ether, a sufficient test volume was obtained, and a sufficient recovery rate E and a sufficient purity P were also obtained.

[0317] The trends described here were similarly obtained when the burnable polymer compound included any one of polymethacrylate ester, polyvinyl acetal, polyvinyl acetate, and cellulose ester.

[0318] Third, when a non-burnable polymer compound was used together with a burnable polymer compound as the polymer compound and the weight ratio WR was 86% or more, a high test capacity was obtained, as well as a high recovery rate E and a high purity P.

[0319] Fourth, when a non-burnable polymer compound was used together with a burnable polymer compound as the polymer compound and the weight ratio WRZ was 0% or more and less than 14%, a high test capacity was obtained, as well as a high recovery rate E and a high purity P.

[0320] In these cases, when the non-burnable polymer compound contained polyvinylidene fluoride, a sufficient test volume was obtained, as well as a sufficient recovery rate E and a sufficient purity P.

[0321] The trends described here were similarly obtained when the non-burnable polymer compound included any of polytetrafluoroethylene, polyetheretherketone, polyphenylene sulfide, and polyimide.

[0322] Fifth, regardless of the material of the positive electrode current collector, a high test capacity was obtained, and a high recovery rate E and a high purity P were also obtained.

[0323] In this case, when the positive electrode current collector contained either titanium or chromium as a constituent element, the test capacity and purity P both increased, and a high recovery rate E was obtained within a range not exceeding 100%.

[0324] The tendency described here was similarly obtained even when the positive electrode current collector contained zirconium as a constituent element.

[0325] Sixth, when the test electrode contained a positive electrode conductive agent, the test capacity increased more, and the recovery rate E and purity P also increased more.

[0326] In this case, when a carbon material was used as the positive electrode conductive agent rather than a metal material, the recovery rate E was ensured, while the test capacity and purity P were increased.

[0327] Seventh, when a non-aqueous electrolyte was used, the purity P increased more when a non-fluorine-containing anion was used as the anion than when a fluorine-containing anion was used.

[0328] Here, when the test electrode was baked until the temperature of the test electrode reached 200° C. to 500° C. (Example 1), a high recovery rate E and a high purity P were obtained while the test capacity was ensured.

[0329] In contrast, when the test electrode was fired until the temperature of the test electrode became higher than 500°C (Example 14), a high test capacity and a high purity P were obtained, but the recovery rate E decreased due to deterioration of the positive electrode active material.

[0330] [Summary] From the results shown in Tables 1 to 3, when the positive electrode active material layer contained a positive electrode active material and a polymer compound, the positive electrode active material contained a lithium transition metal compound, and the polymer compound had a thermal weight loss rate of 60% or more, a high test capacity was obtained, as well as a high recovery rate E and a high purity P. Therefore, the test secondary battery exhibited excellent battery characteristics and excellent recyclability.

[0331] Furthermore, by baking the test electrode until the temperature of the test electrode reached 200°C to 500°C, the positive electrode current collector was recovered from the test electrode together with the positive electrode active material. In this case, a high test capacity was obtained, as well as a high recovery rate E and a high purity P. Therefore, the test secondary battery exhibited excellent battery characteristics and excellent recyclability.

[0332] The configuration of the secondary battery according to the present technology has been described above with reference to several embodiments and examples. However, the configuration of the secondary battery according to the present technology is not limited to the configurations described in the above embodiments and examples, and various modifications are possible.

[0333] 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.

[0334] The present technology can also be configured as follows. <1> A positive electrode for a secondary battery, comprising: a positive electrode active material layer containing a positive electrode active material and a polymer compound; and a positive electrode current collector supporting the positive electrode active material layer, wherein the positive electrode active material contains a lithium transition metal compound, and wherein a thermal weight loss rate measured when the polymer compound is baked in the air until its temperature reaches 400°C is 60% or more. <2> The positive electrode for a secondary battery according to <1>, wherein the polymer compound contains a burnable polymer compound, and wherein a thermal weight loss rate measured when the burnable polymer compound is baked in the air until its temperature reaches 400°C is 70% or more. <3> The positive electrode for a secondary battery according to <1>, wherein a thermal weight loss rate measured when the polymer compound is baked in the air until its temperature reaches 400°C is 95% or more. <4> The positive electrode for a secondary battery according to <2>, wherein the burnable polymer compound contains a structural unit of at least one polymer compound selected from polyacrylic acid esters, polymethacrylic acid esters, polyvinyl alcohol, polyvinyl ethers, polyvinyl esters, cellulose esters, and cellulose ethers. <5> The positive electrode for a secondary battery according to <2>, wherein the burnable polymer compound contains at least one of polyacrylic acid esters, polymethacrylic acid esters, polyvinyl alcohol, polyvinyl acetal, polyvinyl butyral, polyvinyl acetate, cellulose esters, and cellulose ethers. <6> The positive electrode for a secondary battery according to <2>, wherein the burnable polymer compound is a copolymer containing structural units of at least two polymer compounds selected from polyacrylic acid esters, polymethacrylic acid esters, polyvinyl alcohol, polyvinyl ethers, polyvinyl esters, cellulose esters, and cellulose ethers. <7> The positive electrode for a secondary battery according to any one of <2> to <6>, wherein the polymer compound further comprises a non-burnable polymer compound, wherein a thermal weight loss rate measured when the non-burnable polymer compound is baked in the atmosphere until the temperature of the non-burnable polymer compound reaches 400°C is less than 70%, and wherein the weight ratio represented by formula (1) is 98% or more.WR=[W1 / (W1+W2)]×100 (1) (WR is a weight ratio, W1 is the weight of the burnable polymer compound, and W2 is the weight of the non-burnable polymer compound.) <8> The positive electrode for a secondary battery according to any one of <2> to <6>, wherein the polymer compound further contains a non-burnable polymer compound, wherein a thermal weight loss rate measured when the non-burnable polymer compound is baked in air until the temperature of the non-burnable polymer compound reaches 400°C is less than 70%, and wherein the weight ratio represented by formula (2) is 0% or more and less than 14%. WRZ=[W2 / (W1+W2)]×100 (2) (WRZ is a weight ratio. W1 is the weight of the burnable polymer compound. W2 is the weight of the non-burnable polymer compound.) <9> The positive electrode for a secondary battery according to <7> or <8>, wherein the non-burnable polymer compound includes at least one of polyvinylidene fluoride, polytetrafluoroethylene, polyether ether ketone, polyphenylene sulfide, and polyimide. <10> The positive electrode for a secondary battery according to any one of <1> to <9>, wherein the positive electrode current collector includes at least one of titanium, zirconium, and chromium as a constituent element. <11> The positive electrode for a secondary battery according to any one of <1> to <10>, wherein the positive electrode active material layer further includes a positive electrode conductive agent, and the positive electrode conductive agent includes a carbon material. <12> A secondary battery comprising the positive electrode for secondary batteries according to any one of <1> to <11>, a negative electrode, and an electrolyte. <13> The secondary battery according to <12>, wherein the electrolyte contains an anion, and the anion does not contain fluorine as a constituent element. <14> The secondary battery according to <12> or <13>, which is a lithium secondary battery. <15> A method for recycling a positive electrode for secondary batteries according to any one of <1> to <11>, comprising firing the positive electrode for secondary batteries until the temperature of the positive electrode for secondary batteries reaches 200°C or higher and 500°C or lower, thereby burning off the polymer compound and recovering a positive electrode current collector and a positive electrode active material. <16> The method for recycling a positive electrode for secondary batteries according to <15>, comprising firing the positive electrode for secondary batteries in an oxygen-containing atmosphere.<17> The method for recycling a positive electrode for a secondary battery according to <15> or <16>, wherein the positive electrode current collector and the positive electrode active material are separated from each other.

[0335] 20,100... Positive electrode, 20A, 100A... Positive electrode current collector, 20B, 100B... Positive electrode active material layer, 30... Negative electrode

Claims

1. A positive electrode for a secondary battery comprising: a positive electrode active material layer containing a positive electrode active material and a polymer compound; and a positive electrode current collector supporting the positive electrode active material layer, wherein the positive electrode active material contains a lithium transition metal compound, and the polymer compound is baked in the atmosphere until the temperature of the polymer compound reaches 400°C, and the thermal weight loss rate measured when the thermal weight loss rate is 60% or more.

2. The positive electrode for a secondary battery according to claim 1, wherein the polymer compound includes a burnable polymer compound, and the thermal weight loss rate measured when the burnable polymer compound is baked in air until the temperature of the burnable polymer compound reaches 400°C is 70% or more.

3. The positive electrode for a secondary battery according to claim 1, wherein the polymer compound has a thermal weight loss rate of 95% or more when calcined in air until the temperature of the polymer compound reaches 400°C.

4. The positive electrode for a secondary battery according to claim 2, wherein the burnable polymer compound contains a structural unit of at least one type of polymer compound selected from the group consisting of polyacrylic acid esters, polymethacrylic acid esters, polyvinyl alcohols, polyvinyl ethers, polyvinyl esters, cellulose esters and cellulose ethers.

5. The positive electrode for a secondary battery according to claim 2, wherein the burnable polymer compound includes at least one of polyacrylic acid ester, polymethacrylic acid ester, polyvinyl alcohol, polyvinyl acetal, polyvinyl butyral, polyvinyl acetate, cellulose ester and cellulose ether.

6. The positive electrode for a secondary battery according to claim 2, wherein the burnable polymer compound is a copolymer containing structural units of at least two types of polymer compounds selected from the group consisting of polyacrylic acid esters, polymethacrylic acid esters, polyvinyl alcohols, polyvinyl ethers, polyvinyl esters, cellulose esters and cellulose ethers.

7. The positive electrode for a secondary battery according to any one of claims 2 to 6, wherein the polymer further comprises a non-burnable polymer, the thermal weight loss rate measured when the non-burnable polymer is burned in air until the temperature of the non-burnable polymer reaches 400°C is less than 70%, and the weight ratio represented by formula (1) is 86% or more. WR = [W1 / (W1+W2)] x 100 ... (1) (WR is the weight ratio. W1 is the weight of the burnable polymer. W2 is the weight of the non-burnable polymer.) 8. The positive electrode for a secondary battery according to any one of claims 2 to 6, wherein the polymer further comprises a non-burnable polymer, the non-burnable polymer is burned in air until the temperature of the non-burnable polymer reaches 400°C, and the thermal weight loss rate measured when the non-burnable polymer is burned in air until the temperature of the non-burnable polymer reaches 400°C is less than 70%, and the weight ratio represented by formula (2) is 0% or more and less than 14%. WRZ = [W2 / (W1+W2)] x 100 ... (2) (WRZ is the weight ratio. W1 is the weight of the burnable polymer. W2 is the weight of the non-burnable polymer.) 9. The positive electrode for a secondary battery according to claim 7 or 8, wherein the non-burnable polymer compound includes at least one of polyvinylidene fluoride, polytetrafluoroethylene, polyether ether ketone, polyphenylene sulfide and polyimide.

10. The positive electrode for a secondary battery according to any one of claims 1 to 9, wherein the positive electrode current collector contains at least one of titanium, zirconium and chromium as a constituent element.

11. The positive electrode for a secondary battery according to any one of claims 1 to 10, wherein the positive electrode active material layer further contains a positive electrode conductive agent, and the positive electrode conductive agent contains a carbon material.

12. A secondary battery comprising: the positive electrode for a secondary battery according to any one of claims 1 to 11; a negative electrode; and an electrolyte.

13. The secondary battery according to claim 12, wherein the electrolyte contains anions, and the anions do not contain fluorine as a constituent element.

14. The secondary battery according to claim 12 or 13, which is a lithium secondary battery.

15. A method for recycling a positive electrode for a secondary battery according to any one of claims 1 to 11, comprising baking the positive electrode for a secondary battery until the temperature of the positive electrode for a secondary battery is 200°C or higher and 500°C or lower, thereby burning off the polymer compound and recovering the positive electrode current collector and the positive electrode active material.

16. The method for recycling a positive electrode for a secondary battery according to claim 15, further comprising firing the positive electrode for a secondary battery in an oxygen-containing atmosphere.

17. The method for recycling a positive electrode for a secondary battery according to claim 15 or 16, further comprising separating the positive electrode current collector and the positive electrode active material from each other.

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