Non-aqueous secondary battery and method for manufacturing non-aqueous secondary battery

Abstract

To provide: a non-aqueous secondary battery having improved energy density while suppressing generation of gas; and a method for manufacturing the non-aqueous secondary battery.SOLUTION: A non-aqueous secondary battery comprises: a cathode; an anode; and a non-aqueous electrolyte. Therein: the non-aqueous electrolyte contains at least one of calcium ions and magnesium ions at a concentration of 0.1 mol / L or more based on the whole nonaqueous electrolyte; and the cathode contains dehydroascorbic acid. A method for manufacturing the non-aqueous secondary battery includes the steps of: producing the cathode using a cathode composite material in which a cathode active material, a salt containing calcium ions or magnesium ions, and ascorbic acid are mixed; forming the battery including the cathode, the anode, and the non-aqueous electrolyte; and applying a voltage to the battery to decompose the salt. Therein the cathode composite material contains the salt in an amount of 1% by mass or more with respect to the entire cathode composite material.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a non-aqueous secondary battery and a method for manufacturing a non-aqueous secondary battery. [Background technology]

[0002] The positive electrode uses LivT, an olivine-structured active material. a PO4(0≦v≦1、T a A method for forming a battery cell is known in which a non-aqueous secondary battery contains a phosphate represented by a metal phosphate (e.g., Fe, Ni, Co, Mn) and lithium oxalate as a sacrificial salt, and the cell is heated to 30°C to 45°C and then charged at a specific voltage (Patent Document 1). Patent Document 1 describes that lithium ions are released into the electrolyte by the lithium oxalate sacrificial salt, eliminating the need to load an excess amount of positive electrode into the cell for forming a solid electrolyte interphase (SEI), thereby improving the energy density of the battery.

[0003] Also known is an electrolytic solution in which magnesium ions and aluminum ions are dissolved in an ether-based organic solvent, and in which metallic magnesium, a halogenated hydrocarbon, an aluminum halide, and a quaternary ammonium salt are added to the ether-based organic solvent (Patent Document 2). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Special Publication No. 2018-526788 [Patent Document 2] Japanese Patent Application Laid-Open No. 2009-064730 Summary of the Invention [Problem to be solved by the invention]

[0005] In nonaqueous secondary batteries, a relatively high voltage is required to decompose sacrificial salts such as lithium oxalate and Li2C4O6; for example, the battery must be charged to 4.7 to 4.8 V. Such high voltages can cause high potentials and the generation of singlet oxygen, which can lead to the formation of an extraneous film on the active material. These extraneous films can generate gas and may limit the improvement in energy density. Furthermore, the electrolyte in which magnesium ions are dissolved is suitable for magnesium ion batteries.

[0006] An object of the present disclosure is to provide a non-aqueous secondary battery and a method for manufacturing the non-aqueous secondary battery that improves energy density while suppressing gas generation. [Means for solving the problem]

[0007] The means for solving the problems include the following aspects. <1> A non-aqueous secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the non-aqueous electrolyte contains at least one of calcium ions and magnesium ions at a concentration of 0.1 mol / L or more based on the entire non-aqueous electrolyte, and the positive electrode contains dehydroascorbic acid. <2> The non-aqueous electrolyte contains calcium ions, and the negative electrode material has a reaction potential of 0.26V vs. Li / Li. + That's all <1> The nonaqueous secondary battery according to claim 1. <3> The non-aqueous electrolyte contains magnesium ions, and the negative electrode material has a reaction potential of 0.74 V vs. Li / Li. + That's all <1> The nonaqueous secondary battery according to claim 1. <4> The positive electrode contains ascorbic acid and at least one salt selected from the group consisting of magnesium oxide, calcium oxide, and magnesium carbonate, and at least a portion of the calcium ions and magnesium ions are derived from the salt contained in the positive electrode, and the dehydroascorbic acid is derived from the ascorbic acid contained in the positive electrode. <1> ~ <3> 10. The nonaqueous secondary battery according to claim 9, wherein the nonaqueous secondary battery is a battery having a capacitance of 100.degree. <5> A method for manufacturing a non-aqueous secondary battery, the method comprising the steps of: manufacturing a positive electrode from a positive electrode mixture obtained by mixing a positive electrode active material, a salt containing calcium ions or magnesium ions, and ascorbic acid; forming a battery including a positive electrode, a negative electrode, and a non-aqueous electrolyte; and applying a voltage to the battery to decompose the salt, wherein the positive electrode mixture contains 1 mass % or more of the salt based on the total mass of the positive electrode mixture. [Effects of the Invention]

[0008] According to the present disclosure, a nonaqueous secondary battery and a method for manufacturing a nonaqueous secondary battery are provided that improve energy density while suppressing gas generation. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 2 is an explanatory diagram illustrating substances contained in the positive electrode and the electrolyte before and after pre-charging. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. When embodiments of the present disclosure are described with reference to the drawings, the configuration of the embodiment is not limited to the configuration shown in the drawings. Components indicated by the same reference numerals in the drawings are the same components. In some drawings, only some components may be designated by reference numerals. The dimensional ratios in the drawings do not necessarily represent the actual dimensional ratios. In the present disclosure, a numerical range indicated using "to" means a range that includes the numerical values before and after "to" as the minimum and maximum values, respectively. In the numerical ranges described in stages in this disclosure, the upper or lower limit value described in a certain numerical range may be replaced with the upper or lower limit value of another numerical range described in stages. In the numerical ranges described in this disclosure, the upper or lower limit value described in a certain numerical range may be replaced with the value shown in the examples. In the present disclosure, the term "process" includes not only an independent process but also a process that cannot be clearly distinguished from other processes, as long as the intended purpose of the process is achieved. In the present disclosure, a combination of two or more preferred embodiments is a more preferred embodiment. In the present disclosure, when there are multiple substances corresponding to each component, the amount of each component means the total amount of the multiple substances unless otherwise specified.

[0011] <Non-aqueous secondary battery> The nonaqueous secondary battery of the present disclosure is a nonaqueous secondary battery (hereinafter also referred to as battery) including a positive electrode, a negative electrode, and a nonaqueous electrolyte solution (hereinafter also referred to as electrolyte solution), in which the electrolyte solution contains at least one of calcium ions and magnesium ions at a concentration of 0.1 mol / L or more based on the entire electrolyte solution, and the positive electrode contains dehydroascorbic acid.

[0012] (positive electrode) The positive electrode is a positive electrode used in a nonaqueous secondary battery, and includes, for example, a current collector and a positive electrode layer disposed on the surface of the current collector. The positive electrode layer may be disposed on one or both surfaces of the current collector. The positive electrode layer can be formed using a positive electrode mixture.

[0013] Examples of materials constituting the current collector of the positive electrode include aluminum, aluminum alloy, nickel, titanium, stainless steel, etc. Examples of the shape of the current collector include foil, mesh, etc.

[0014] The positive electrode mixture contains a positive electrode active material, salt, ascorbic acid, and other materials. The other materials include a conductive material, a binder, an electrolyte, etc. As the positive electrode active material, a conventionally known positive electrode active material can be used depending on the type of battery. For example, in the case of a lithium ion battery, a lithium transition metal oxide (e.g., LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, LiNiO2, LiCoO2, LiFeO2, LiMn2O4, LiNi 0.5 Mn 1.5 O4, etc.), lithium transition metal phosphate compounds (e.g., LiFePO4, etc.), etc. can be used.

[0015] The nonaqueous secondary battery of the present disclosure is applicable not only to lithium ion batteries but also to a wide range of nonaqueous secondary batteries such as sodium ion batteries, potassium ion batteries, etc. In the present disclosure, the case of a lithium ion battery will be described as an example.

[0016] In a nonaqueous secondary battery, when an initial voltage is applied, the salt contained in the positive electrode mixture decomposes, releasing at least one of calcium ions and magnesium ions into the electrolyte. At least a portion of the calcium ions and magnesium ions are derived from the salt contained in the positive electrode. Hereinafter, such salts are also referred to as "sacrificial salts."

[0017] The sacrificial salt contained in the positive electrode mixture is preferably a sacrificial salt that generates at least one of calcium ions and magnesium ions upon application of a voltage such as during pre-charging. The calcium ions or magnesium ions are cations generated by decomposition of the sacrificial salt. One or more types of sacrificial salts may be contained. The sacrificial salt may be an alkaline earth metal salt. That is, the sacrificial salt may be a sacrificial salt that releases alkaline earth metal cations upon decomposition. The sacrificial salt is preferably selected based on the cation valence released per unit volume of the sacrificial salt and the theoretical decomposition potential. More preferably, the sacrificial salt is selected based on the effective amount of cations released per unit volume of the sacrificial salt, the theoretical decomposition potential, and the effective amount of cations released from the positive electrode active material. Specific examples of preferred sacrificial salts include magnesium oxide (MgO), calcium oxide (CaO), magnesium carbonate (MgCO), lithium carbonate (LiCO), sodium carbonate (NaCO), lithium peroxide (LiO), and lithium oxalate (LiCO). Among these, at least one salt selected from the group consisting of MgO, CaO, and MgCO is preferred because of its low theoretical decomposition potential and high effective amount of cations released.

[0018] Each of the above-listed sacrificial salts can be made to have a larger amount of effectively released cations per unit volume than the amount of effectively released cations of the positive electrode active material, thereby improving the energy density of the battery. Note that the amount of effectively released cations is not the number of released ions, but the amount of electrons contributing to the reaction when converted to the amount assuming that all monovalent ions are released. Furthermore, the sacrificial salts listed above are known to be decomposed at a relatively low potential based on the theoretical decomposition potential of each sacrificial salt, and therefore can suppress the generation of active oxygen.

[0019] Specifically, the effective amount of released cations per unit volume [mmol / cm ] for each of the sacrificial salts listed above is 3 ] is MgO 178 [mmol / cm 3 ], CaO is 119 [mmol / cm 3 ], MgCO3 is 70 [mmol / cm 3 For example, if the positive electrode active material is LiNi 0.8 Co 0.1 Mn 0.1 In the case of O2, the effective amount of released cations per unit volume is 37 [mmol / cm3 ], each of these sacrificial salts effectively releases cations 1.5 times or more greater than that of the positive electrode active material. Therefore, when each of the sacrificial salts listed above is used, the amount of electrons contributing to the reaction at the electrode is sufficient to increase the energy density of the battery.

[0020] Specifically, the theoretical decomposition potential of each of the sacrificial salts listed above is 2.9 V vs. Li / Li for MgO. + ], CaO is 3.1 [V vs. Li / Li + ], MgCO3 is 3.2 [V vs. Li / Li + Therefore, when each of the sacrificial salts listed above is used, the theoretical decomposition potential is relatively low, and the formation of an excess coating can be suppressed.

[0021] In the nonaqueous secondary battery of the present disclosure, the electrolyte contains at least one of calcium ions and magnesium ions at a concentration of 0.1 mol / L or more based on the entire electrolyte solution. After applying a voltage to the battery by precharging or the like, the electrolyte contains calcium ions or magnesium ions at a concentration of 0.1 mol / L or more based on the entire electrolyte solution. Preferably, the electrolyte contains calcium ions or magnesium ions at a concentration in the range of 0.1 mol / L or more and 0.3 mol / L or less, more preferably 0.1 mol / L or more and 0.2 mol / L or less, based on the entire electrolyte solution. Within the above range, the effect of increasing the energy density of the battery can be more reliably achieved while suppressing the formation of an excess coating. Furthermore, within the above range, there is little risk of the function of the electrolyte being impaired.

[0022] The concentration of calcium ions or magnesium ions in the electrolyte can be adjusted by the amount of sacrificial salt contained in the positive electrode mixture, etc. The concentration of sacrificial ions, including calcium ions and magnesium ions, in the electrolyte after charging is a value measured by inductively coupled plasma mass spectrometry (ICP-MS).

[0023] The electrolyte may contain both calcium ions and magnesium ions. In this case, the electrolyte contains calcium ions or magnesium ions at a total concentration of 0.1 mol / L or more based on the entire electrolyte.

[0024] After pre-charging, voids are formed in the positive electrode layer due to the sacrificial salt contained in the positive electrode layer before pre-charging. These voids exist in the positive electrode with an appropriate size, number, distribution, etc., and are thought to improve ion diffusion and contribute to enhanced fast charging performance.

[0025] The positive electrode mixture preferably contains 1.0% by mass or more and 5.0% by mass or less of the sacrificial salt, based on the total amount of the positive electrode mixture, and more preferably 1.5% by mass or more and 4.0% by mass or less. By containing the sacrificial salt in the positive electrode mixture within this range, the effect of adding the sacrificial salt can be more reliably exhibited, the energy density of the battery can be improved, the generation of excess coating can be suppressed, and gas generation can also be suppressed. Specifically, by containing the sacrificial salt in the positive electrode mixture within this range, the total concentration of calcium ions and magnesium ions in the electrolyte can be set to 0.1 mol / L or more based on the total amount of the electrolyte.

[0026] The positive electrode mixture contains ascorbic acid in addition to a sacrificial salt. The sacrificial salt may be oxidized and decomposed by pre-charging, generating active oxygen, typically singlet oxygen. It is believed that singlet oxygen reacts with the electrolyte solvent, forming an excess film. This excess film may consist of organic components, LiF, etc., and may cause gas generation. The ascorbic acid contained in the positive electrode mixture is believed to be preferentially oxidized by singlet oxygen, suppressing the reaction between singlet oxygen and the electrolyte solvent, further suppressing the formation of an excess film.

[0027] After the pre-charge, the ascorbic acid in the positive electrode is oxidized to dehydroascorbic acid. Therefore, in the nonaqueous secondary battery of the present disclosure, the positive electrode contains dehydroascorbic acid. The dehydroascorbic acid is derived from the ascorbic acid contained in the positive electrode.

[0028] The positive electrode mixture preferably contains ascorbic acid in a range of 1% by mass to 8% by mass, and more preferably 2% by mass to 4% by mass, based on the total positive electrode mixture. When the positive electrode mixture contains ascorbic acid within the above range, the effects of adding ascorbic acid are more reliably exhibited, the generation of an excess coating is suppressed, and the generation of gas (particularly gas during battery use) is also suppressed. The gases generated include carbon monoxide, hydrocarbon gases such as ethane, and carbon dioxide.

[0029] The positive electrode mixture may be in the form of a mixture containing components other than the positive electrode active material, the sacrificial salt, and the ascorbic acid, such as a conductive additive, a binder, etc. If necessary, a solvent may be added to the mixture to adjust the viscosity of the mixture.

[0030] Specific examples of the conductive aid include carbon materials such as carbon black (acetylene black, thermal black, furnace black, etc.), carbon nanotubes, and graphite. The conductive additive contained in the positive electrode mixture may be one type alone or two or more types.

[0031] Specific examples of binders include polyvinylidene fluoride (PVDF), polyethylene, polypropylene, polyethylene terephthalate, cellulose, nitrocellulose, carboxymethyl cellulose, polyethylene oxide, polyepichlorohydrin, polyacrylonitrile, styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber (NBR), polyacrylate, and polymethacrylate. The binder contained in the positive electrode mixture may be one type alone or two or more types.

[0032] The positive electrode will be further described with reference to the drawings. As shown in FIG. 1, the positive electrode 10 is configured by disposing a positive electrode layer 12 formed from a positive electrode mixture on the surface of a current collector 11. The positive electrode layer 2 contains a positive electrode active material 13, a sacrificial salt 14, and ascorbic acid 15 dispersed therein. The positive electrode 10 is adjacent to an electrolyte 16. After the battery is precharged, the positive electrode layer 12 in the positive electrode 10 contains the positive electrode active material 13, voids 17 formed by the decomposition of the sacrificial salt 14, and dehydroascorbic acid 18. The sacrificial salt 14 is decomposed to form Mg 2+ or Ca 2+ These alkaline earth metal ions 19 are present in the electrolyte solution 16.

[0033] After pre-charging, the positive electrode layer 12 contains voids 17 formed by the sacrificial salt 14. These voids 17 exist in an appropriate amount within the positive electrode 10, and are thought to improve the diffusibility of various ions and contribute to enhanced rapid charging performance.

[0034] (Negative electrode) The negative electrode includes, for example, a current collector and a negative electrode layer disposed on the current collector and containing a negative electrode active material. Examples of the negative electrode active material include carbon materials such as graphite, hard carbon, soft carbon, and activated carbon, silicon, metallic lithium, lithium alloys, and lithium titanate (LTO). Examples of materials constituting the negative electrode current collector include copper, copper alloys, nickel, titanium, and stainless steel. Examples of the shape of the negative electrode current collector include foil and mesh.

[0035] For example, magnesium metal is known to be less likely to form dendrites, and even if metal deposition occurs, there are few safety concerns. Therefore, it is not necessarily necessary to suppress metal deposition. However, if metal deposition on the negative electrode is to be prevented, it is preferable to use a negative electrode material in which the charge / discharge reaction proceeds at a potential higher than the deposition / dissolution reaction potential. An example of a negative electrode material that suppresses metal deposition is Li4Ti5O. 12 , TiNb2O7, SiO, etc.

[0036] The deposition-dissolution reaction potential of calcium metal is 0.21V vs. Li / Li +Therefore, when the non-aqueous electrolyte contains calcium ions, the negative electrode material provided in the negative electrode has a reaction potential of 0.26 V vs. Li / Li. + It is preferable that the deposition-dissolution reaction potential of magnesium metal is 0.69 V vs. Li / Li or more. + Therefore, when the non-aqueous electrolyte contains magnesium ions, the negative electrode material provided in the negative electrode has a reaction potential of 0.74V vs. Li / Li + It is preferable that this is equal to or greater than this.

[0037] (electrolyte) The electrolyte may be either liquid or solid. As a liquid electrolyte (electrolytic solution), a known electrolyte such as LiPF6 dissolved in an organic solvent can be used without any particular limitation. Specific examples of the organic solvent include cyclic or chain carbonates such as ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), etc. The solvent may be a mixture of two or more solvents, or may be a mixture containing a cyclic carbonate and a chain carbonate. The solvent may contain an additive such as vinylene carbonate (VC). As the solid electrolyte, known solid electrolytes such as sulfide solid electrolytes, oxide solid electrolytes, and halide solid electrolytes can be used without any particular limitation.

[0038] (separator) The lithium ion secondary battery may include a separator disposed between the positive electrode and the negative electrode. Examples of the separator include nonwoven fabric, cloth, and microporous film mainly composed of polyolefin such as polyethylene or polypropylene.

[0039] <Method of manufacturing non-aqueous secondary battery> The method for manufacturing a nonaqueous secondary battery of the present disclosure includes the steps of: manufacturing a positive electrode from a positive electrode mixture obtained by mixing a positive electrode active material, a salt containing at least one of calcium ions and magnesium ions, and ascorbic acid; forming a battery including a positive electrode, a negative electrode, and a nonaqueous electrolyte; and applying a voltage to the battery to decompose the salt, wherein the positive electrode mixture contains 1 mass % or more of the salt based on the total mass of the positive electrode mixture.

[0040] (Process for manufacturing positive electrode) The method for manufacturing a nonaqueous secondary battery according to the present disclosure includes the step of manufacturing a positive electrode using a positive electrode mixture comprising a positive electrode active material, a salt containing at least one of calcium ions and magnesium ions, and ascorbic acid. The salt used in the positive electrode mixture is the sacrificial salt described above, which decomposes upon application of voltage to release at least one of calcium ions and magnesium ions. The proportions of salt and ascorbic acid contained in the positive electrode mixture are as described above in the section on "Nonaqueous Secondary Battery."

[0041] A conventionally known method can be used to form the positive electrode mixture. For example, materials for forming the positive electrode mixture are mixed to form the positive electrode mixture. A method for forming the positive electrode, for example, involves applying the positive electrode mixture to the surface of a current collector and then disposing a positive electrode layer on the surface of the current collector. The disposition is performed, for example, by applying a slurry of the positive electrode mixture to one or both sides of the current collector. If necessary, a pressure treatment may be performed to adjust the density of the positive electrode layer. The thickness of the positive electrode layer is not particularly limited and can be selected, for example, from the range of 10 μm to 100 μm.

[0042] (Battery formation process) The method for manufacturing a non-aqueous secondary battery according to the present disclosure includes the step of forming a battery including a positive electrode, a negative electrode, and a non-aqueous electrolyte. The step of forming a battery is a step of assembling a structure constituting a secondary battery. A conventionally known method can be used as the method. The positive electrode, negative electrode, and non-aqueous electrolyte are as described above in the section on non-aqueous secondary batteries. For example, the positive electrode manufactured in the step of manufacturing a positive electrode is placed in a battery case (external container) so as to face the negative electrode with a separator interposed therebetween, and the non-aqueous electrolyte is injected and sealed to form the secondary battery structure.

[0043] (Salt decomposition process) The method for manufacturing a nonaqueous secondary battery according to the present disclosure includes a step of forming a battery including a positive electrode, a negative electrode, and a nonaqueous electrolyte, and then applying a voltage to the battery to decompose the salt (sacrificial salt). Pre-charging can be used as a method for applying a voltage to the battery. In pre-charging, a voltage capable of decomposing the sacrificial salt may be applied depending on the type of sacrificial salt used. For example, as described above, when the sacrificial salt is magnesium oxide, the theoretical decomposition potential of magnesium oxide is 2.9 V vs. Li / Li. + Therefore, it is preferable to perform pre-charging by applying a voltage exceeding this theoretical decomposition potential.

[0044] As described above, the nonaqueous secondary battery and the method for manufacturing a nonaqueous secondary battery according to the present disclosure can improve energy density while suppressing the formation of an excess film by using the sacrificial salt and ascorbic acid contained in the positive electrode to preferentially oxidize the calcium ions or magnesium ions and ascorbic acid released by decomposition of the sacrificial salt to form dehydroascorbic acid. In this case, calcium ions or magnesium ions remain in the electrolyte at a relatively high concentration, thereby improving energy density. Furthermore, in the positive electrode, the sacrificial salt is decomposed to form appropriate voids, which improves ion diffusibility and improves rapid charging performance. [Example]

[0045] The present disclosure will be described in more detail below with reference to examples, but the present disclosure is not limited to these examples.

[0046] [Examples 1 to 3, Comparative Examples 1 to 3] <Battery manufacturing> A battery cell for charge / discharge testing was fabricated with the following configuration. Cell type: Small single-opposed laminate cell ·Opposing area (positive electrode): 21cm 2 ·Cathode active material: NCM (LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2) Positive electrode current collector: Aluminum foil ·Negative electrode active material: Metal Li ·Negative electrode current collector: copper foil Non-aqueous electrolyte: 1.1M, LiPF6 / EC:DMC:EMC (volume ratio of EC / DMC / EMC is 3 / 4 / 3) Separator: Polypropylene separator

[0047] The positive electrode was manufactured as follows. The positive electrode active material (88 parts by mass), acetylene black (10 parts by mass) as a conductive material, polyvinylidene fluoride (2 parts by mass) as a binder, sacrificial salt (1.8 to 4.7% by mass) shown in Table 1, and ascorbic acid (4% by mass) shown in Table 1 were mixed, and the viscosity was adjusted with a solvent to obtain a positive electrode mixture. The positive electrode mixture was applied to aluminum foil and dried at 80°C for 5 minutes to obtain a positive electrode. The addition ratios of the sacrificial salt and ascorbic acid shown in Table 1 are based on the total positive electrode mixture.

[0048] <Battery evaluation> The obtained positive electrode, separator, and negative electrode containing metallic Li as the active material were laminated in this order to prepare a battery cell, and the prepared battery cell was housed in a laminate film and filled with an electrolyte to prepare small one-face laminate cell type evaluation batteries for Examples 1 to 3 and Comparative Examples 1 to 3. The evaluation battery for Comparative Example 1 is an evaluation battery in which neither a sacrificial salt nor ascorbic acid is added to the positive electrode mixture, and the evaluation batteries for Comparative Examples 2 to 3 are evaluation batteries in which no ascorbic acid is added to the positive electrode mixture.

[0049] (Measurement method) The following measurements were carried out, and the measurement results are shown in the respective columns of Table 1. In the "Type of sacrificial salt" and "Addition of ascorbic acid" columns of Table 1, "None" indicates that the respective salts were not added. In Table 1, the "sacrificial ion concentration in the electrolyte after charging" value was measured using the method described above. The "effective volumetric energy density of the positive electrode" is a theoretical value of the volumetric energy density calculated taking into account the types of positive and negative electrode active materials, the voids after decomposition of the sacrificial salt, and the volume of the positive electrode active material added to the positive electrode mixture for SEI formation. The "gas generation amount during storage at 60°C for one week" is the value measured by placing the test battery in a sealed bag and storing it in an incubator controlled to maintain a temperature of 60°C for one week, after which the amount of gas generated from the test battery was measured using the Archimedes method. The "1C capacity / 0.1C capacity ratio" was calculated by charging the battery to 4.25 V at a current of 0.1 C using a constant current-constant voltage method, followed by discharging to 3.0 V at a current of 1 C using a constant current-constant voltage method. The ratio of the 1C capacity to the 0.1C capacity was calculated.

[0050] [Table 1]

[0051] (Evaluation results) As is clear from Table 1, the addition of ascorbic acid and a sacrificial salt as in Examples 1 to 3 improved the energy efficiency and rapid charging performance of the positive electrode while suppressing gas generation, compared to the addition of neither a sacrificial salt nor ascorbic acid as in Comparative Example 1. On the other hand, the addition of a sacrificial salt but no ascorbic acid as in Comparative Examples 2 and 3 resulted in increased gas generation. As described above, the electrolyte solution contains calcium ions or magnesium ions at a concentration of 0.1 mol / L or more based on the entire non-aqueous electrolyte solution, and the positive electrode mixture contains ascorbic acid, thereby improving the energy density of the positive electrode and suppressing gas generation. [Explanation of symbols]

[0052] 10 positive electrode 11 Current collector 12 Positive electrode layer 13 Cathode active material 14 Sacrificial Salt 15. Ascorbic Acid 16 Electrolyte 17 void 18 Dehydroascorbic acid 19 Alkaline earth metal ions

Claims

1. A non-aqueous secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte solution, the non-aqueous electrolyte contains at least one of calcium ions and magnesium ions at a concentration of 0.1 mol / L or more based on the entire non-aqueous electrolyte; The positive electrode of the nonaqueous secondary battery contains dehydroascorbic acid.

2. the non-aqueous electrolyte contains calcium ions, The negative electrode material provided in the negative electrode has a reaction potential of 0.26 V vs. Li / Li ＋ 2. The nonaqueous secondary battery according to claim 1, wherein the nonaqueous secondary battery is a battery having the above structure.

3. the non-aqueous electrolyte contains magnesium ions, The negative electrode material provided in the negative electrode has a reaction potential of 0.74 V vs. Li / Li ＋ 2. The nonaqueous secondary battery according to claim 1, wherein the nonaqueous secondary battery is a battery having the above structure.

4. the positive electrode contains ascorbic acid and at least one salt selected from the group consisting of magnesium oxide, calcium oxide, and magnesium carbonate, at least a portion of the calcium ions and the magnesium ions are derived from a salt contained in the positive electrode; 2. The nonaqueous secondary battery according to claim 1, wherein the dehydroascorbic acid is derived from ascorbic acid contained in the positive electrode.

5. a step of producing a positive electrode using a positive electrode mixture obtained by mixing a positive electrode active material, a salt containing calcium ions or magnesium ions, and ascorbic acid; forming a battery comprising the positive electrode, the negative electrode, and a non-aqueous electrolyte; applying a voltage to the battery to decompose the salt; The positive electrode mixture contains the salt in an amount of 1 mass % or more based on the total mass of the positive electrode mixture.

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