JP6460381B2 - Non-aqueous secondary battery and manufacturing method thereof - Google Patents

Description

  The present invention relates to a non-aqueous secondary battery and a method for manufacturing the same.

  A non-aqueous secondary battery such as a lithium ion secondary battery includes a positive electrode having a positive electrode active material, a negative electrode having a negative electrode active material, a separator, and a non-aqueous electrolyte solution. When charging / discharging a non-aqueous secondary battery, a film is formed on the surface of the negative electrode active material and the positive electrode active material due to decomposition of an organic material in the electrolyte solution, and the internal resistance of the battery tends to increase. . As a cause of decomposition of the electrolytic solution, it is known that moisture contained in a minute amount in the electrolytic solution is affected. Therefore, Patent Document 1 discloses that the electrode interface resistance is suppressed by setting the water content in the electrolytic solution to 200 to 500 ppm.

JP 2005-228511 A

  In recent years, higher output is required for non-aqueous secondary batteries. For this reason, it is required to further reduce the internal resistance of the battery.

  This invention is made | formed in view of this situation, and makes it a subject to provide the non-aqueous secondary battery which can suppress internal resistance.

A non-aqueous secondary battery manufacturing method of the present invention includes a positive electrode current collector and a positive electrode active material layer having a positive electrode active material formed on the positive electrode current collector,
A negative electrode current collector, a negative electrode active material layer having a negative electrode active material formed on the negative electrode current collector, a protective layer covering the surface of the negative electrode active material layer and having an inorganic oxide and a binder; A negative electrode having
A method for producing a non-aqueous secondary battery comprising: a separator interposed between the positive electrode and the negative electrode; and an electrolyte having an electrolyte and a non-aqueous solvent,
The water content in the electrolytic solution is adjusted to be 800 ppm or less.

The non-aqueous secondary battery of the present invention is a non-aqueous secondary battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte solution having an electrolyte and a non-aqueous solvent,
The positive electrode has a positive electrode current collector and a positive electrode active material layer having a positive electrode active material formed on the positive electrode current collector,
The negative electrode includes a negative electrode current collector, a negative electrode active material layer having a negative electrode active material formed on the negative electrode current collector, a surface of the negative electrode active material layer, and an inorganic oxide and a binder. Having a protective layer,
The amount of water in the electrolytic solution is 800 ppm or less.

  Since this invention comprises the said structure, the nonaqueous secondary battery which can suppress the internal resistance of a battery, and its manufacturing method can be provided.

It is a figure which shows the relationship between the moisture content in the electrolyte solution of Examples 1-3 and the lithium ion secondary battery of Reference Examples 1 and 2, and discharge resistance.

  A nonaqueous secondary battery and a manufacturing method thereof according to an embodiment of the present invention will be described in detail.

  According to the non-aqueous secondary battery of the present invention, the internal resistance of the battery can be suppressed. The reason is considered as follows.

  The protective layer having an inorganic oxide formed on the surface of the negative electrode active material layer has a function of capturing a decomposition product of the electrolyte generated by a reaction between moisture and the electrolyte. By forming the protective layer having an inorganic oxide on the surface of the negative electrode active material layer, it is possible to suppress the formation of a film by depositing an electrolyte decomposition product on the surface of the negative electrode active material. Therefore, an increase in the internal resistance of the battery can be suppressed with a water content in a wide range of 800 ppm or less compared to the range of the water content in the electrolytic solution described in Patent Document 1. The amount of water in the electrolytic solution refers to the mass ratio of the water in the electrolytic solution in the battery when the mass of the electrolytic solution is 1.

When a fluoride such as LiPF ₆ is used as the electrolyte, HF is generated by the reaction between the fluoride and water if the electrolyte contains moisture. When HF is generated, Li and HF contained in the active material react to generate LiF. LiF is deposited on the negative electrode to form a film, and the internal resistance of the battery is increased.

  By setting the amount of water in the electrolytic solution to 800 ppm or less as in the present invention, the reaction between the electrolyte fluoride salt and water is suppressed, LiF is difficult to deposit on the negative electrode, and the resistance increase is suppressed. .

In addition, by setting the water content in the electrolytic solution to 800 ppm or less, it is possible to suppress the deposition of electrolyte decomposition products on the surface of the positive electrode active material. This also suppresses an increase in the internal resistance of the battery. For example, when a positive electrode active material containing lithium is used, LiOH in the positive electrode active material reacts with moisture in the electrolytic solution to form LiOH. LiOH and CO ₂ react to produce Li ₂ CO ₃ . CO ₂ is produced during the manufacturing process or produced by decomposition of the electrolytic solution. When Li ₂ CO ₃ is generated, a film having Li ₂ CO ₃ is formed on the surface of the positive electrode active material, and the internal resistance of the battery is increased.

  By making the amount of water in the electrolytic solution 800 ppm or less as in the present invention, the reaction between lithium and water in the positive electrode active material is suppressed, and a film is hardly formed on the surface of the positive electrode active material, thereby suppressing an increase in resistance. it can.

  If the amount of water in the electrolyte exceeds 800 ppm, the internal resistance of the battery may increase. The amount of water in the electrolytic solution is preferably from 50 ppm to 800 ppm, and more preferably from 200 ppm to 800 ppm. If the amount of water in the electrolytic solution is too small, a large amount of energy is required for drying to remove water from the electrolytic solution, which may cause high costs. In particular, the amount of water in the electrolytic solution is most preferably more than 500 ppm and not more than 800 ppm. In this case, the internal resistance of the battery can be effectively suppressed.

  In order to measure the amount of water in the electrolytic solution, for example, the Karl Fischer method may be performed.

  In order to adjust the amount of water in the electrolytic solution, for example, the electrolytic solution may be prepared in an environment in which humidity is controlled. The relative humidity of the environment in which the electrolytic solution is prepared is preferably 35 to 55%. The temperature of the environment in which the electrolytic solution is prepared is preferably 5 to 35 ° C. In order to reduce the amount of water in the electrolytic solution, the prepared electrolytic solution may be dried. The electrolyte solution is preferably dried at a temperature at which the non-aqueous solvent in the electrolyte solution is difficult to evaporate, for example, at 80 to 300 ° C.

  Further, the amount of water in the electrolytic solution after assembling the battery also varies depending on the water contained in the positive electrode, the negative electrode, and the separator. For this reason, the positive electrode, the negative electrode, and the separator may be manufactured in an environment in which humidity is controlled, and may be dried to reduce moisture. Furthermore, when performing the assembly | attachment process which accommodates a positive electrode, a negative electrode, a separator, and electrolyte solution in a battery case, it is good to adjust the humidity of the environment of an assembly | attachment process similarly to the above. Thereby, the moisture content in electrolyte solution can be adjusted to 800 ppm or less reliably.

  Before the assembly process, it is preferable to confirm the amount of water in the electrolytic solution. Assuming that the battery is assembled, the amount of water in the electrolyte also affects the water contained in the electrodes and separator. For this reason, in order to confirm the moisture content in the electrolyte solution in the battery when the battery is assembled, not only the electrolyte solution but also the moisture content (mass) contained in the electrode and the separator is measured. A value obtained by dividing the total amount of moisture measured for the electrolyte solution, the electrode, and the separator by the mass of the electrolyte solution is obtained. This value can be calculated as the amount of water in the electrolyte in the battery.

  Moreover, it is good to confirm the moisture content in electrolyte solution after an assembly | attachment process suitably. To check the amount of water in the electrolyte after assembly, disassemble the battery. The amount of water (mass) contained in the positive electrode, negative electrode, separator and electrolyte after decomposition was measured, and the value obtained by dividing the total amount of water measured by the mass of the electrolyte was used as the amount of water in the electrolyte in the battery. Can be sought.

The electrolytic solution used for the non-aqueous secondary battery of the present invention has an electrolyte and a non-aqueous solvent. The electrolyte may contain lithium ions. As the electrolyte containing lithium ions, for example, a fluoride salt is used. Examples of such fluoride salts include LiAsF ₆ , LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , and LiN (CF ₃ SO ₂ ) ₂ . The concentration of the electrolyte in the electrolytic solution is preferably in the range of 0.5 to 1.7 mol / L.

  As the non-aqueous solvent, non-aqueous solvents such as cyclic esters, chain esters and ethers can be used. Examples of cyclic esters include ethylene carbonate, propylene carbonate, butylene carbonate, gamma butyrolactone, vinylene carbonate, 2-methyl-gamma butyrolactone, acetyl-gamma butyrolactone, and gamma valerolactone. Examples of chain esters include dimethyl carbonate, diethyl carbonate, dibutyl carbonate, dipropyl carbonate, ethyl methyl carbonate, propionic acid alkyl ester, malonic acid dialkyl ester, and acetic acid alkyl ester. Examples of ethers include tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, 1,2-dimethoxyethane, 1,2-diethoxyethane, and 1,2-dibutoxyethane. A plurality of the above-described solvents may be used in combination as the solvent for the electrolytic solution. In particular, it is preferable to use three types of ethylene carbonate, methyl ethyl carbonate, and dimethyl carbonate in combination.

The protective layer formed on the surface of the negative electrode active material has an inorganic oxide and a binder. Examples of the inorganic oxide used in the protective layer include Al ₂ O ₃ , SiO ₂ , TiO ₂ , ZrO ₂ , MgO, SiC, AlN, BN, CaCO ₃ , MgCO ₃ , BaCO ₃ , talc, mica, and kaolinite. , CaSO ₄ , MgSO ₄ , BaSO ₄ , CaO, ZnO, and zeolite. These inorganic oxides are used alone or in combination. Of these, Al ₂ O ₃ is preferable. Al ₂ O ₃ has a particularly high function of capturing a decomposition product of the electrolytic solution.

  The average particle size of the inorganic oxide is preferably 0.1 to 10 μm, more preferably 0.2 to 5 μm, and particularly preferably 0.3 to 3 μm. If the average particle size of the inorganic oxide is too small, it may be difficult to form a space capable of holding the electrolytic solution in the protective layer. If the average particle size of the inorganic oxide is too large, the thickness of the protective layer increases, and thus the resistance caused by the increase in thickness may adversely affect the battery output. In addition, an average particle diameter means D50 of each component, ie, the median diameter measured on the volume basis. The average particle diameter may be measured with a general particle size distribution measuring device such as a laser diffraction particle size distribution measuring device.

  The negative electrode includes a negative electrode current collector, a negative electrode active material layer having a negative electrode active material formed on the negative electrode current collector, and a protective layer covering the surface of the negative electrode active material layer and having an inorganic oxide and a binder. And have.

  Examples of the binder used in the protective layer include fluorine-containing resins such as polyvinylidene fluoride, polytetrafluoroethylene, and fluororubber, thermoplastic resins such as polypropylene and polyethylene, imide resins such as polyimide and polyamideimide, and carboxymethylcellulose. , Methyl cellulose, styrene butadiene rubber, and alkoxysilyl group-containing resin. These binders may be employed alone or in combination. As the binder used for the protective layer, polyvinylidene fluoride is particularly preferable from the viewpoint of electrochemical stability.

  A preferable mass ratio of the inorganic oxide and the binder in the protective layer is 5: 1 to 200: 1, more preferably 10: 1 to 150: 1, and particularly preferably 15: 1 to 100: 1. is there.

  The thickness of the protective layer is preferably from 0.1 to 12 μm, more preferably from 0.5 to 10 μm, particularly preferably from 1 to 8 μm. When the thickness of the protective layer is too small, the function of capturing the decomposition product of the electrolytic solution of the protective layer may be reduced. When the thickness of the protective layer is excessive, the electrolyte in the electrolytic solution is difficult to pass through the protective layer, and is difficult to reach the negative electrode active material layer, which may increase the battery resistance.

The density of the protective layer, 0.1 g / cm ³ or more 3 g / cm ³ or less are preferred, 0.3 g / cm ³ or more 2.5 g / cm ³ and more preferably less, 0.6 g / cm ³ or more 2 g / cm ³ The following are particularly preferred:

  The protective layer covers the surface of the negative electrode active material layer. The protective layer may have a gap through which the electrolytic solution flows.

  Although there is no restriction | limiting in particular in the porosity of a protective layer, 5-95% is preferable, 20-90% is more preferable, 35-85% is further more preferable, 40-80% is especially preferable.

  In order to form a protective layer on the surface of the negative electrode active material layer, for example, a step of preparing a protective layer forming composition by dispersing the constituent components of the protective layer in a solvent, and the protective layer forming composition as the negative electrode What is necessary is just to implement a drying process, after implementing the process apply | coated on an active material layer or a separator. The blending amount of the constituent components of the protective layer in the protective layer forming composition is preferably within the range of 10 to 50% by mass. By changing the blending amount, the density and porosity of the protective layer to be formed can be changed. As the solvent used for the preparation of the protective layer-forming composition, those in which particles composed of an inorganic compound or a resin compound are not dissolved are preferable, for example, from N-methyl-2-pyrrolidone, methanol, ethanol, methyl isobutyl ketone, and water. What is necessary is just to select suitably. In the coating process, a conventionally known method such as a roll coating method, a dip coating method, a doctor blade method, a spray coating method, or a curtain coating method may be used. The drying step may be performed under normal pressure conditions or under reduced pressure conditions using a vacuum dryer. The drying temperature may be appropriately set within a range where the binder does not decompose, and is preferably a temperature equal to or higher than the boiling point of the solvent, for example, 80 to 300 ° C. What is necessary is just to set drying time suitably according to an application quantity and drying temperature.

  The negative electrode active material layer has a negative electrode active material. As the negative electrode active material, a known material employed in each battery may be used. For example, as a negative electrode active material of a lithium ion secondary battery, a carbon-based material that can occlude and release lithium, an element that can be alloyed with lithium, a compound that has an element that can be alloyed with lithium, or a polymer material is exemplified. can do. When a carbon-based material is used, the solvent used for forming the negative electrode active material layer is often water. In this case, the negative electrode active material layer is likely to contain a large amount of water, and when the battery is assembled using this, the water in the negative electrode active material layer is also contained in the electrolyte, resulting in electrolysis. The amount of water in the liquid tends to increase. In this case, in particular, it is preferable to adjust the water content of the electrolytic solution after assembling the battery to 800 ppm or less by managing the water content in the negative electrode active material layer.

  Examples of the carbon-based material include non-graphitizable carbon, artificial graphite, natural graphite, cokes, graphites, glassy carbons, organic polymer compound fired bodies, carbon fibers, activated carbon, and carbon blacks. Here, the organic polymer compound fired body refers to a material obtained by firing and carbonizing a polymer material such as phenols and furans at an appropriate temperature.

Specifically, elements that can be alloyed with lithium include Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra, Ti, Ag, Zn, Cd, Al, Ga, In, Si. , Ge, Sn, Pb, Sb, Bi can be exemplified, and Si or Sn is particularly preferable. Specific examples of compounds having elements that can be alloyed with lithium include ZnLiAl, AlSb, SiB ₄ , SiB ₆ , Mg ₂ Si, Mg ₂ Sn, Ni ₂ Si, TiSi ₂ , MoSi ₂ , CoSi ₂ , NiSi ₂ , _{CaSi 2, CrSi 2, Cu 5} Si, FeSi 2, MnSi 2, NbSi 2, TaSi 2, VSi 2, WSi 2, ZnSi 2, SiC, Si 3 N 4, Si 2 N 2 O, SiO v (0 <v ≦ 2), SnO _w (0 <w ≦ 2), SnSiO ₃ , LiSiO 2 or LiSnO, and SiO _x (0.5 ≦ x ≦ 1.5) is particularly preferable. Moreover, tin compounds (Cu-Sn alloy, Co-Sn alloy, etc.) can be illustrated as a compound which has an element which can be alloyed with lithium. Specific examples of the polymer material include polyacetylene and polypyrrole.

  The negative electrode active material layer includes a binder and / or a conductive aid as necessary. As a binder, the thing similar to what is used for a protective layer can be used. Although there is no restriction | limiting in particular about the usage-amount of a binder, The range of 1-50 mass parts of binders with respect to 100 mass parts of active materials is preferable. This is because when the amount of the binder is too small, the moldability of the electrode is lowered, and when the amount of the binder is too large, the energy density of the electrode is lowered.

  A conductive additive is added to increase conductivity. Examples of the conductive assistant include carbon black, graphite, acetylene black, ketjen black (registered trademark), and vapor grown carbon fiber (Vapor Grown Carbon Fiber) which are carbonaceous fine particles. These conductive assistants can be added to the active material layer alone or in combination of two or more. Although there is no restriction | limiting in particular about the usage-amount of a conductive support agent, For example, it can be set as 1-30 mass parts of conductive support agents with respect to 100 mass parts of active materials.

  In order to form the negative electrode active material layer on the surface of the negative electrode current collector, a conventionally known method such as a roll coating method, a dip coating method, a doctor blade method, a spray coating method, or a curtain coating method is used. What is necessary is just to apply | coat an anode active material directly on the surface of a body. Specifically, a composition for forming a negative electrode active material layer containing a negative electrode active material and, if necessary, a negative electrode binder and / or a conductive aid is prepared, and an appropriate solvent is added to the composition to add a paste and To do. A solution in which a binder is dissolved in a solvent in advance or a dispersed suspension may be used. Examples of the solvent include N-methyl-2-pyrrolidone, methanol, ethanol, methyl isobutyl ketone, and water. The paste is applied to the surface of the negative electrode current collector and then dried. Drying may be performed under normal pressure conditions or under reduced pressure conditions using a vacuum dryer. What is necessary is just to set drying temperature suitably, and the temperature beyond the boiling point of the said solvent is preferable, for example, 80-300 degreeC is good. What is necessary is just to set drying time suitably according to an application quantity and drying temperature. In order to increase the density of the negative electrode active material layer, a compression step may be added to the dried current collector on which the negative electrode active material layer is formed.

  The positive electrode includes a positive electrode current collector and a positive electrode active material layer having a positive electrode active material formed on the positive electrode current collector. As the positive electrode current collector, the same one as the negative electrode current collector can be used.

  The positive electrode active material is a material that can occlude and release metal ions. The positive electrode active material may be a material that can occlude and release lithium ions. Such a positive electrode active material is preferably made of a lithium composite metal oxide having lithium and a transition metal.

Examples of the lithium composite metal oxide include, for example, the general formula: Li _a Ni _b Co _c Mn _{d De} O _f (0.2 ≦ a ≦ 1.2, b + c + d + e = 1, 0 ≦ e <1, D is Li, At least one element selected from Fe, Cr, Cu, Zn, Ca, Mg, S, Si, Na, K, Al, Zr, Ti, P, Ga, Ge, V, Mo, Nb, W, and La; .7 ≦ f ≦ 2.1) and Li ₂ MnO ₃ can be mentioned. The lithium composite metal oxide has a general formula: Li _x A _y Mn _{2 -y} O ₄ (A is a transition metal element, Ca, Mg, S, Si, Na, K, Al, P, Ga, and Ge. At least one element selected from the group consisting of: a spinel compound represented by 0 <x <2, 0 ≦ y ≦ 1), and a solid solution composed of a mixture of a spinel compound and a layered compound, LiMPO ₄ , LiMVO ₄ or A polyanionic compound represented by Li ₂ MSiO ₄ (wherein M is selected from at least one of Co, Ni, Mn, and Fe) may be used.

Examples of the layer compound include LiNi _0.5 Co _0.2 Mn _0.3 O ₂ , LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , LiNi _0.5 Mn _0.5 O ₂ , LiNi _{0. And} at least one selected from _.75 Co _0.1 Mn _0.15 O ₂ , LiMnO ₂ , LiNiO ₂ , and LiCoO ₂ . Examples of the spinel compound include LiNi _0.5 Mn _1.5 O ₄ and LiMn ₂ O ₄ . Examples of the polyanion compound include LiFePO ₄ , LiCoPO ₄ , Li ₂ CoPO ₄ F, Li ₂ MnSiO ₄ , and Li ₂ FeSiO ₄ .

Any lithium metal oxide used as the positive electrode active material may have the above composition formula as a basic composition, and a metal element included in the basic composition may be substituted with another metal element. Moreover, you may use as a positive electrode active material the thing which does not contain a charge carrier (for example, lithium ion which contributes to charging / discharging). For example, sulfur alone (S), a compound in which sulfur and carbon are compounded, a metal sulfide such as TiS ₂ , an oxide such as V ₂ O ₅ and MnO ₂ , a compound containing polyaniline and anthraquinone, and these aromatics in the chemical structure In addition, conjugated materials such as conjugated diacetate-based organic substances and other known materials can also be used. Further, a compound having a stable radical such as nitroxide, nitronyl nitroxide, galvinoxyl, phenoxyl, etc. may be adopted as the positive electrode active material. When using a positive electrode active material that does not contain a charge carrier such as lithium, it is necessary to add a charge carrier to the positive electrode and / or the negative electrode in advance by a known method. The charge carrier may be added in an ionic state or in a non-ionic state such as a metal. For example, when the charge carrier is lithium, a lithium foil may be coated on the surface of the positive electrode current collector.

  The positive electrode active material layer includes a positive electrode active material and, if necessary, a binder and / or a conductive aid. As the binder and the conductive additive included in the positive electrode active material layer as necessary, the same binder and conductive additive as necessary included in the negative electrode active material can be used. Forming the positive electrode active material layer on the surface of the positive electrode current collector can be performed in the same manner as the method of forming the negative electrode active material layer.

  The separator is interposed between the positive electrode and the negative electrode. The separator is preferably made of resin. Examples of the resin separator include a porous film using one or more synthetic resins such as polytetrafluoroethylene, polypropylene, polyethylene, polyester, and polyamide. The resin separator may have a single-layer structure using a single synthetic resin or a laminated structure in which a plurality of synthetic resin layers are stacked. The thickness of the resin separator is not particularly limited, but is preferably in the range of 5 μm to 100 μm, more preferably in the range of 10 μm to 50 μm, and particularly preferably in the range of 20 μm to 30 μm.

  A separator is sandwiched between the positive electrode and the negative electrode to form an electrode body. The electrode body may be either a stacked type in which the positive electrode, the separator and the negative electrode are stacked, or a wound type in which the positive electrode, the separator and the negative electrode are sandwiched. After connecting between the positive electrode current collector and the negative electrode current collector to the positive electrode terminal and the negative electrode terminal leading to the outside using a current collecting lead or the like, an electrolyte is added to the electrode body to form a non-aqueous secondary battery. Good.

  The shape of the nonaqueous secondary battery of the present invention is not particularly limited, and various shapes such as a cylindrical shape, a square shape, a coin shape, and a laminate shape can be adopted.

  The non-aqueous secondary battery of the present invention may be mounted on a vehicle. The vehicle may be a vehicle that uses electric energy from a non-aqueous secondary battery for all or a part of its power source. For example, the vehicle may be an electric vehicle or a hybrid vehicle. When a non-aqueous secondary battery is mounted on a vehicle, a plurality of non-aqueous secondary batteries may be connected in series to form an assembled battery. Examples of devices equipped with non-aqueous secondary batteries include various home appliances driven by batteries such as personal computers and portable communication devices, office equipment, and industrial equipment, in addition to vehicles. Further, the non-aqueous secondary battery of the present invention includes wind power generation, solar power generation, hydroelectric power generation and other power system power storage devices and power smoothing devices, power of ships and / or power supply sources of auxiliary machinery, aircraft, Power supply for spacecraft and / or auxiliary equipment, auxiliary power supply for vehicles that do not use electricity as a power source, power supply for mobile home robots, power supply for system backup, power supply for uninterruptible power supply, You may use for the electrical storage apparatus which stores temporarily the electric power required for charge in the charging station for electric vehicles.

  As mentioned above, although embodiment of the non-aqueous secondary battery of this invention was described, this invention is not limited to the said embodiment. The present invention can be implemented in various forms without departing from the gist of the present invention, with modifications and improvements that can be made by those skilled in the art.

Example 1
The battery of the present invention was manufactured as follows.

  All the steps for producing the following lithium ion secondary battery were performed at a relative humidity of 25% and a temperature of 50 ° C.

98 parts by mass of natural graphite having an average particle size of 20 μm as a negative electrode active material, and 1 part by mass of styrene butadiene rubber as a binder and 1 part by mass of carboxymethyl cellulose were mixed. This mixture was dispersed in an appropriate amount of ion-exchanged water to prepare a slurry. A copper foil having a thickness of 20 μm was prepared as a negative electrode current collector. The slurry was applied in a film form on the surface of the copper foil using a doctor blade. The copper foil coated with the slurry was dried to remove water, and then the copper foil was pressed to obtain a bonded product. The obtained joined product was heat-dried at 120 ° C. for 6 hours with a vacuum dryer to obtain a copper foil on which a negative electrode active material layer was formed. The mass of the negative electrode active material layer per 1 cm ^{2 of the} copper foil was 11.1 mg, and the density of the negative electrode active material layer was 1.4 g / cm ³ .

In order to prepare the composition for forming a protective layer, 96 parts by mass of Al ₂ O ₃ having an average particle diameter of 0.5 μm and 4 parts by mass of polyvinylidene fluoride were mixed to prepare a mixture. N-methyl-2-pyrrolidone was added to the mixture to obtain a protective layer forming composition containing 32% by mass of the mixture.

The said protective layer formation composition was apply | coated to the film form on the negative electrode active material layer of copper foil using the doctor blade. This was dried at 120 ° C. for 6 hours to form a protective layer having a thickness of 6 μm on the negative electrode active material layer. The mass of the protective layer per 1 cm ^{2 of the} negative electrode active material layer was 11.1 mg, the density of the protective layer was 1.2 g / cm ³ , and the porosity of the protective layer was 70%. This was used as a negative electrode.

94 parts by mass of lithium-containing metal oxide having a layered rock salt structure with an average particle diameter of 10 μm represented by LiNi _5/10 Co _2/10 Mn _3/10 O _{2 as} a positive electrode active material, and 3 masses of acetylene black as a conductive auxiliary Part and 3 parts by mass of polyvinylidene fluoride as a binder were mixed. This mixture was dispersed in an appropriate amount of N-methyl-2-pyrrolidone to prepare a slurry. An aluminum foil having a thickness of 20 μm was prepared as a positive electrode current collector. The slurry was applied to the surface of the aluminum foil using a doctor blade so as to form a film. The aluminum foil coated with the slurry was dried at 80 ° C. for 20 minutes to remove N-methyl-2-pyrrolidone by volatilization to form a positive electrode active material layer. The mass of the positive electrode active material layer per 1 cm ^{2 of} aluminum foil was 18.4 mg, and the density of the positive electrode active material layer was 3.1 g / cm ³ . The aluminum foil on which this positive electrode active material layer was formed was used as the positive electrode.

  A rectangular sheet (112 × 136 mm, thickness 25 μm) made of a polyethylene resin film was prepared as a resin separator.

In order to prepare an electrolytic solution, 30 volume parts of ethylene carbonate, 30 volume parts of ethyl methyl carbonate, and 40 volume parts of dimethyl carbonate were mixed to prepare a mixed solvent. LiPF ₆ was dissolved to 1 mol / L in the mixed solvent. The obtained solution was used as an electrolytic solution.

  Next, the moisture content (g) of the positive electrode, negative electrode, separator, and electrolyte contained in one battery was measured using a Karl Fischer device. The mass (g) of the electrolyte contained in one battery was measured. A value obtained by dividing the total of the measured values of the water content of the positive electrode, the negative electrode, the separator, and the electrolytic solution by the mass of the electrolytic solution was calculated as the amount of water contained in the electrolytic solution in the battery. The amount of water contained in the electrolyte solution in the battery of Example 1 was 323 ppm in terms of mass ratio.

  Next, an assembly process for accommodating the positive electrode, the negative electrode, the separator, and the electrolytic solution in the battery case was performed. The assembly process was performed in a dry room environment. The details of the assembly process are as follows. A resin separator was installed on the protective layer of the negative electrode, and then a positive electrode was installed to form an electrode plate group. The electrode plate laminate obtained by laminating a plurality of electrode plate groups is inserted into a metal can (123 mm × 141 mm × 26.5 mm) made of aluminum and having a plate thickness of 3 mm. A secondary battery was obtained. The positive electrode and the negative electrode have a tab that can be electrically connected to the outside, and a part of the tab extends to the outside of the lithium ion secondary battery.

(Example 2)
The lithium ion secondary battery of Example 2 is the same as the lithium ion secondary battery of Example 1 except that it was left for 7 hours in an environment of 50% relative humidity and 25 ° C. before sealing the metal can. is there.

  The water content of the electrolyte contained in the lithium ion secondary battery of Example 2 was 623 ppm.

(Example 3)
The lithium ion secondary battery of Example 3 is the same as the lithium ion secondary battery of Example 1 except that it was left to stand for 12 hours in an environment of 50% relative humidity and 25 ° C. before sealing the metal can. is there.

  The water content of the electrolyte contained in the lithium ion secondary battery of Example 3 was 800 ppm.

(Reference Example 1)
The lithium ion secondary battery of Reference Example 1 is the same as the lithium ion secondary battery of Example 1 except that it was left to stand in an environment of 50% relative humidity and 25 ° C. for 20 hours before sealing the metal can. is there.

  The water content of the electrolyte contained in the lithium ion secondary battery of Reference Example 1 was 1131 ppm.

(Reference Example 2)
The lithium ion secondary battery of Reference Example 2 is the same as the lithium ion secondary battery of Example 1 except that it was left to stand for 35 hours in an environment of 50% relative humidity and 25 ° C. before sealing the metal can. is there.

  The water content of the electrolyte contained in the lithium ion secondary battery of Reference Example 2 was 1696 ppm.

<Resistance measurement>
The discharge resistance of the lithium ion secondary batteries of Examples 1 to 3 and Reference Examples 1 and 2 was measured. The discharge resistance (Ω) is a value obtained by dividing a voltage change amount when a current corresponding to 1 C is discharged for 10 seconds at a voltage of 20% SOC (State of charge) by the current value. The measurement results are shown in FIG.

  The lithium ion secondary batteries of Examples 1 to 3 maintained low resistance. The reference examples 1 and 2 had higher discharge resistance than Examples 1-3. It was found that when the water content in the electrolytic solution was 800 ppm or less, the discharge resistance of the lithium ion secondary battery was kept low, but increased when it exceeded 800 ppm.

Claims (6)

A non-aqueous secondary battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte solution having an electrolyte and a non-aqueous solvent,
The positive electrode has a positive electrode current collector and a positive electrode active material layer having a positive electrode active material formed on the positive electrode current collector,
The negative electrode includes a negative electrode current collector, a negative electrode active material layer having a negative electrode active material formed on the negative electrode current collector, a surface of the negative electrode active material layer, and Al ₂ O ₃ and a fluorine-containing resin . With a protective layer having
The non-aqueous secondary battery, wherein the amount of water in the electrolytic solution is more than 500 ppm and not more than 800 ppm. The thickness of the protective layer is 0.1 to 12 µm, the density of the protective layer is 0.1 to ³ g / cm ³ , or the porosity of the protective layer is 5 to 95%. non-aqueous secondary battery according to 1. The non-aqueous secondary battery according to claim 1 , wherein the negative electrode active material includes a carbon-based material. The non-aqueous secondary battery according to claim 1 , wherein the separator is made of resin. A method for manufacturing the non-aqueous secondary battery according to claim 1,
A method for producing a non-aqueous secondary battery, characterized in that the amount of water in the electrolytic solution is adjusted to be more than 500 ppm and not more than 800 ppm. The method for producing a non-aqueous secondary battery according to claim 5, wherein the adjustment is performed in an environment with a relative humidity of 35 to 55% .

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