JP6176489B2 - Method for producing electrode mixture and method for producing electrode - Google Patents

Description

  The present invention relates to a method for producing an electrode mixture and a method for producing an electrode.

Lithium ion secondary batteries are small and have high energy density, and are widely used as power sources for portable electronic devices. As the positive electrode active material of the lithium ion secondary battery, lithium metal composite oxides such as LiCoO ₂ and LiMn ₂ O ₄ are mainly used. In order to produce a positive electrode using a positive electrode active material, a positive electrode active material, a binder, and a solvent are mixed to create a slurry electrode mixture, and the electrode mixture is applied to the surface of the current collector and dried. . As the binder, polyvinylidene fluoride (hereinafter also referred to as “PVdF”) is used.

In order to produce a lithium metal composite oxide as the positive electrode active material, for example, a molten salt method is used. In the molten salt method, a metal compound raw material having a constituent element of a lithium metal composite oxide to be produced is melted together with the molten salt raw material to obtain a lithium metal composite oxide. As the molten salt raw material, for example, alkaline components such as LiOH and Li ₂ CO ₃ are used (Patent Documents 1 and 2). These alkali components may remain on the surface of the positive electrode active material. If an electrode mixture is produced while leaving an alkali component on the surface of the positive electrode active material, the viscosity of the electrode mixture increases with time (Patent Document 3). In the electrode mixture having an increased viscosity, tailing occurs at the coating end when a thin positive electrode layer is formed on the surface of the current collector. Therefore, Patent Document 4 proposes limiting the viscoelasticity of the electrode mixture to a predetermined range.

JP 2011-23121 A JP 2011-1224086 A JP 2007-305574 A JP 2004-281234 A

  The inventor has eagerly sought to reduce the increase in viscosity of the slurry-like electrode mixture over time, using a technique different from the technique described in the above-mentioned patent document.

  This invention is made | formed in view of this situation, and makes it a subject to provide the manufacturing method of the electrode mixture which can reduce the viscosity raise accompanying the time passage of an electrode mixture, and the manufacturing method of an electrode.

  In the method for producing an electrode mixture of the present invention, a lithium metal composite oxide is contacted with a nitrate aqueous solution having a nitrate, and the lithium metal composite oxide subjected to the contact process is mixed with polyvinylidene fluoride and a solvent. And a mixing step.

  The method for producing an electrode of the present invention is characterized in that a positive electrode mixture produced by the method for producing an electrode mixture described above is applied to a current collector.

  According to the present invention, since the lithium metal composite oxide is in contact with the nitrate aqueous solution, it is possible to reduce an increase in viscosity with the passage of time of the electrode mixture.

Lithium metal composite oxides may have alkaline components such as Li ₂ CO ₃ and LiOH remaining on the surface during synthesis. PVdF, which is a binder, tends to deteriorate due to an alkali component and gel. For this reason, the viscosity of an electrode mixture prepared by mixing PVdF and a solvent in a lithium metal composite oxide increases with time.

Therefore, in the present invention, the lithium metal composite oxide is brought into contact with a nitrate aqueous solution having a nitrate such as Mg (NO ₃ ) ₂ . The nitrate reacts with the alkali component to neutralize the alkali component. In the case where the nitrate is magnesium nitrate (Mg (NO ₃ ) ₂ ), the reaction between the nitrate and the alkali component is shown in the following reaction formula (1).
Mg (NO ₃ ) ₂ + 2LiOH → Mg (OH) ₂ + 2LiNO ₃ (1)

  It is considered that the neutralization of the alkali component suppresses the deterioration of PVdF and can suppress the increase in viscosity and gelation of the electrode mixture.

  In addition, when the aqueous solution brought into contact with the lithium metal composite oxide is a nitrate aqueous solution, the oxidizing power is stronger than that of the sulfate aqueous solution, so that there is an effect of neatly dissolving metal or other dust on the active material.

Further, when the nitrate is magnesium nitrate, when the lithium metal composite oxide is brought into contact with the Mg (NO ₃ ) ₂ aqueous solution, Mg (OH) ₂ and MgO remain on the surface of the lithium metal composite oxide, and the lithium metal It is also considered that the stability of the composite oxide is increased. The reason why the stability of the lithium metal composite oxide increases when Mg (OH) ₂ or MgO remains on the surface of the lithium metal composite oxide is that the contact area between the electrolytic solution and the active material decreases.

  The manufacturing method of the electrode mixture of this invention performs a contact process and a mixing process to lithium metal complex oxide. Performing the contact step on the lithium metal composite oxide can also be understood as a method for treating the lithium metal composite oxide.

(Lithium metal composite oxide)
Lithium metal composite oxide is a compound used as an electrode active material. Lithium metal composite oxides are often used mainly as a positive electrode active material because of their relatively high redox potential, and in some cases may be used as a negative electrode active material.

Lithium metal composite oxides often have a layered rock salt structure or / and a spinel structure. A lithium metal composite oxide having a layered rock salt structure is also referred to as a layered compound. The lithium metal composite oxide having a layered rock salt structure has a 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, Fe, Cr, Cu, Zn, Ca, Mg, S, Si, Na, K, Al, Zr, Ti, P, Ga, Ge, V, Mo, Nb, W, La, Ni, Co And at least one element, 1.7 ≦ f ≦ 2.1), and Li ₂ MnO ₃ .

  The ratio of b: c: d in the above general formula is 0.5: 0.2: 0.3, 1/3: 1/3: 1/3, 0.5: 0: 0.5, 0 .75: 0.10: 0.15, 0: 0: 1, 1: 0: 0, and 0: 1: 0 are preferable.

That is, specific examples of the lithium metal composite oxide having a layered rock salt structure 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 _0.75 Co _0.1 Mn _0.15 O ₂ , LiMnO ₂ , LiNiO ₂ , and LiCoO ₂ may be at least one kind.

The lithium metal composite oxide having a spinel structure has a general formula: Li _x (A _y Mn _2-y ) O ₄ (A is Ca, Mg, S, Si, Na, K, Al, P, Ga, Ge) It is preferable that at least one element selected and at least one metal element selected from transition metal elements, 0 <x ≦ 2.2, 0 <y ≦ 1). The transition metal element that can constitute A in the general formula is, for example, at least one element selected from Fe, Cr, Cu, Zn, Zr, Ti, V, Mo, Nb, W, La, Ni, and Co. There should be. Specific examples of the lithium metal composite oxide having a spinel structure are preferably at least one selected from LiMn ₂ O ₄ , Li ₂ Mn ₂ O ₄ , and LiNi _0.5 Mn _1.5 O ₄ .

  The lithium metal composite oxide may be based on the above composition formula as a basic composition, and the metal element contained in the basic composition may be replaced with another metal element, and other metal elements such as Mg may be used. In addition to the basic composition, a metal oxide may be used.

  The lithium metal composite oxide is produced, for example, by a molten salt method, a hydrothermal method, a solid phase method, or the like. Among these, in the molten salt method, since an alkali component is used as a molten salt raw material, the alkali component remains on the surface of the lithium metal composite oxide after the synthesis, and there is a fear that the viscosity increases with the passage of time. The lithium metal composite oxide synthesized by the molten salt method is significant in carrying out the method for producing the electrode mixture of the present invention. Even in the hydrothermal method and the solid phase method, alkali components such as lithium hydroxide and lithium carbonate may remain, and in that case, it is meaningful to apply the method for producing an electrode mixture of the present invention.

  In order to produce a lithium metal composite oxide using a molten salt method, a metal compound raw material containing a metal compound containing a metal element, at least a lithium source, and a theoretical composition of lithium contained in the lithium metal composite oxide The molten salt raw material containing a molar ratio of lithium exceeding is reacted in the molten salt.

The metal compound raw material is a raw material for supplying one or more metal elements excluding Li. A metal compound containing a metal element is essential for a metal compound raw material. There is no particular limitation on the valence of the metal element contained in the metal compound. It is preferable to make it below the valence of the metal element contained in the target lithium-containing composite oxide. This is because in the method for producing a lithium metal composite oxide, the valence of the metal element contained in the synthesized lithium-containing composite oxide can be adjusted by adjusting the oxidation state of the molten salt raw material. For example, when the total amount of the molten salt raw material is 100 mol%, if lithium hydroxide is contained in an amount of 50 mol% or more, the reaction proceeds in the molten salt in a highly oxidized state. Even it becomes tetravalent Mn. Therefore, any general metal compound used in the molten salt method can be used. Specifically, if it is a Mn supply source, manganese dioxide (MnO ₂ ), dimanganese trioxide (Mn ₂ O ₃ ), manganese monoxide (MnO), manganese trioxide (Mn ₃ O ₄ ) manganese hydroxide (Mn (OH) ₂ ), manganese oxyhydroxide (MnOOH), and the like. Co sources include cobalt oxide (CoO, Co ₃ O ₄ ), cobalt nitrate (Co (NO ₃ ) ₂ .6H ₂ O), cobalt hydroxide (Co (OH) ₂ ), cobalt chloride (CoCl _2. 6H ₂ O), cobalt sulfate (Co (SO ₄ ) · 7H ₂ O), and the like. If it is Ni supply source, nickel oxide (NiO), nickel nitrate (Ni (NO ₃ ) ₂ .6H ₂ O), nickel sulfate (NiSO ₄ .6H ₂ O), nickel chloride (NiCl ₂ .6H ₂ O), Etc. If Fe source, iron hydroxide (Fe _{(OH) 3),} iron _(FeCl 3 · _6H 2 O) chloride, iron oxide _{(Fe 2 O} 3), iron nitrate _{(Fe (NO 3) 3 ·} 9H 2 O), iron sulfate _{(FeSO 4 · 9H 2 O)} , and the like. Some of the metal elements contained in these oxides, hydroxides or metal salts are metal compounds substituted with other metal elements (for example, Cr, Mn, Fe, Co, Ni, Al, Mg, etc.). May be. Among these, MnO ₂ is preferable for Mn supply sources, Co (OH) ₂ is preferable for Co supply sources, Ni (OH) ₂ is preferable for Ni supply sources, and Fe (OH) ₃ is preferable for Fe supply sources. It is easy to obtain, and it is easy to obtain a relatively high purity.

  Moreover, when a metal compound raw material contains 2 or more types of metal elements, it is good to synthesize | combine beforehand by making the compound containing them into a precursor. That is, before preparing the raw material, it is preferable to perform a precursor synthesis step in which an aqueous solution containing at least two metal elements is made alkaline to obtain a precipitate. As an aqueous solution, a water-soluble inorganic salt, specifically, a nitrate, sulfate, or chloride salt of a metal element is dissolved in water, and the aqueous solution is made alkaline with an alkali metal hydroxide, aqueous ammonia, etc. Is produced as a precipitate. When the lithium-containing composite oxide to be synthesized is a lithium nickel-based composite oxide containing Ni, the production of by-products (NiO) that are difficult to remove is suppressed by adopting a manufacturing method using a precursor. Therefore, it is preferable.

As the molten salt raw material, one or more selected from the group of lithium hydroxide, lithium nitrate, and lithium carbonate may be used. Lithium hydroxide may be anhydrous (LiOH) or hydrated (LiOH.H ₂ O). The mixing ratio of lithium hydroxide is not particularly limited. For example, when the total amount of the molten salt raw material is 100 mol%, 50 mol% or more of lithium hydroxide may be included. Since lithium hydroxide has the highest basicity among lithium salts, it is also used for the purpose of enhancing the oxidizing power of the molten salt. Therefore, for example, in order to produce a lithium-containing composite oxide whose crystal structure belongs to a layered rock salt structure with high quality and efficiency, the proportion of lithium hydroxide in the molten salt raw material is preferably 90 mol% or more, more preferably It is good to set it as 95 mol% or more.

  The blending ratio of the molten salt raw material is defined by the theoretical composition of lithium contained in the target lithium metal composite oxide (Li of the composite oxide / Li of the molten salt raw material) with respect to lithium contained in the molten salt raw material. It is also possible to do. The molten salt raw material plays a role of adjusting not only the lithium supply source but also the oxidation state of the molten salt. Therefore, the molten salt raw material contains lithium exceeding the theoretical composition of lithium contained in the manufactured lithium metal composite oxide. Li in the lithium metal composite oxide / Li in the molten salt raw material may be less than 1 in molar ratio, but is preferably 0.01 to 0.4, and more preferably 0.013 to 0.3, 0.0. 02 to 0.2. If it is less than 0.01, the amount of the lithium metal composite oxide produced with respect to the amount of the molten salt raw material to be used decreases, which is not desirable in terms of production efficiency. On the other hand, if it exceeds 0.4, the amount of the molten salt in which the metal compound raw material is dispersed is insufficient, and the lithium metal composite oxide may aggregate or grow in the molten salt.

  The reaction temperature in the melting reaction corresponds to the temperature of the molten salt and is equal to or higher than the melting point of the molten salt raw material. What is necessary is just to select reaction temperature suitably according to the structure of the lithium containing complex oxide to synthesize | combine. For example, when synthesizing a spinel-structured lithium manganese oxide, not so high reaction activity is required, and therefore, it may be about 300 to 550 ° C. On the other hand, in order to synthesize a lithium-containing composite oxide having a layered rock salt structure, the reaction activity of the molten salt is not sufficient at less than 350 ° C., and a desired lithium metal composite oxide having a layered rock salt structure can be produced with high purity Have difficulty. Further, when the reaction temperature is 350 ° C. or higher, the crystal structure of the obtained composite oxide is stabilized. Therefore, even if it is a mixed molten salt of lithium hydroxide and lithium nitrate and the melting point is less than 350 ° C., the reaction temperature is 350 ° C. or higher. The minimum of preferable reaction temperature is 400 degreeC or more, 450 degreeC or more, 500 degreeC or more, and also 550 degreeC or more. The higher the reaction temperature, the higher the selectivity of the lithium metal composite oxide having a layered rock salt structure and the higher the crystallinity of the lithium metal composite oxide. ) And decomposes violently. Therefore, when using a molten salt raw material containing lithium nitrate, the lithium metal composite oxide can be synthesized under relatively stable conditions as long as it is 500 ° C. or lower. If the reaction temperature is maintained for 30 minutes or more, more desirably 1 to 6 hours, the molten salt and the metal compound are sufficiently reacted. In addition, when the melting reaction is performed in an oxygen-containing atmosphere, for example, in the air, an atmosphere containing oxygen gas and / or ozone gas, a lithium-containing composite oxide having a layered rock salt structure is easily obtained in a single phase. If the atmosphere contains oxygen gas, the oxygen gas concentration is preferably 20 to 100% by volume, more preferably 50 to 100% by volume. Note that the particle diameter of the synthesized lithium metal composite oxide tends to be smaller as the oxygen concentration is higher.

(Contact process)
In the contacting step, the lithium metal composite oxide is brought into contact with an aqueous nitrate solution.

The aqueous nitrate solution is an aqueous solution containing nitrate. Examples of the nitrate include magnesium nitrate (Mg (NO ₃ ) ₂ ) and aluminum nitrate Al (NO ₃ ) ₃ , among which magnesium nitrate is preferable. When the nitrate is magnesium nitrate, when the lithium metal composite oxide is brought into contact with the Mg (NO ₃ ) ₂ aqueous solution, Mg (OH) ₂ and MgO remain on the surface of the lithium metal composite oxide, and the lithium metal composite oxide This is because the stability of things increases.

The molar concentration of nitrate per liter of aqueous nitrate solution is preferably 5 mmol / L or more and 200 mmol / L or less. The lower limit of the molar concentration of nitrate per liter of Mg (NO ₃ ) ₂ aqueous solution is preferably 5 mmol / L, more preferably 50 mmol / L, and the upper limit is ₂₀₀ mmol / L, more preferably 100 mmol / L. It is preferable. When this molar concentration is too low, the electrode mixture may increase in viscosity with time. When this molar concentration is excessive, the initial viscosity of the electrode mixture may increase.

The method for bringing the lithium metal composite oxide into contact with the aqueous nitrate solution will be exemplified below.
・ Immerse the lithium metal composite oxide in an aqueous nitrate solution and stir with a stirrer if necessary. Thereafter, the layered compound is separated from the nitrate aqueous solution by a filtering device such as a filter.
・ Show nitrate solution on lithium metal composite oxide.
・ Place lithium metal composite oxide in running nitrate water.

  In any method, it is preferable to use 3.3 liters or more of an aqueous nitrate solution with respect to 1 kg of the lithium metal composite oxide. Preferably, the lower limit of the amount of the nitrate aqueous solution used with respect to 1 kg of the lithium metal composite oxide is 1 liter or more and 2 liters or more, and the upper limit is preferably 10 liters or less and 5 liters or less.

  The lithium metal composite oxide subjected to the contact step may be subjected to a drying step as necessary. In the drying step, the lithium metal composite oxide subjected to the contact step is dried. In order to dry the lithium metal composite oxide, the lithium metal composite oxide may be placed at a temperature of 120 ° C. or higher and 300 ° C. or lower. In addition, hot air drying and cold air drying may be used. In the case of hot air drying, hot air of approximately 40 to 100 ° C. may be used. In the case of cold air drying, cold air of approximately −5 to 5 ° C. may be used.

(Mixing process)
In the mixing step, PVdF as a binder is mixed with the lithium metal composite oxide that has been subjected to the contact step and the drying step as necessary to form an electrode mixture. The electrode mixture is in the form of a slurry having fluidity.

Lithium metal composite oxide is one type of electrode active material. Lithium metal composite oxide is often used as a positive electrode active material. The lithium metal composite oxide may be mixed with another positive electrode active material in the mixing step. For example, the positive electrode active material may include a solid solution composed of a mixture of a lithium metal composite oxide and a spinel such as LiMn ₂ O ₄ or Li ₂ Mn ₂ O ₄ .

  The electrode mixture includes a lithium metal composite oxide as an electrode active material, PVdF as a binder, a solvent, and a conductive aid as necessary.

  Polyvinylidene fluoride (PVdF) is a component having a function as a binder. The electrode mixture may contain other binders together with PVdF. In addition to PVdF, the binder includes fluorine-containing resins such as polytetrafluoroethylene and fluororubber, thermoplastic resins such as polypropylene and polyethylene, imide resins such as polyimide and polyamideimide, and alkoxysilyl group-containing resins. You may go out.

  In the electrode mixture, the mass ratio of PVdF to 100 parts by mass of the lithium metal composite oxide is preferably 2 parts by mass or more and 5 parts by mass or less, and more preferably 3 parts by mass or more and 4 parts by mass or less. When the mass ratio of PVdF to the lithium metal composite oxide is excessive, the energy density of the electrode may be lowered. When the mass ratio of PVdF to the lithium metal composite oxide is too small, the moldability of the electrode may be reduced.

  The blending ratio of PVdF to lithium metal composite oxide in the electrode mixture is preferably a mass ratio of lithium metal composite oxide: PVdF = 1: 0.005 to 1: 0.5. This is because when the PVdF is too small, the moldability of the electrode is lowered, and when the PVdF is too much, the energy density of the electrode is lowered.

  The electrode mixture may further contain a conductive additive. The conductive assistant is added to increase the conductivity of the electrode. Therefore, the conductive auxiliary agent may be added arbitrarily when the electrode conductivity is insufficient, and may not be added when the electrode conductivity is sufficiently excellent. The conductive auxiliary agent may be any chemically inert electronic high conductor, such as carbon black, graphite, acetylene black, ketjen black (registered trademark), vapor grown carbon fiber (Vapor Grown Carbon). Fiber: VGCF) and various metal particles are exemplified. These conductive assistants can be added to the active material layer alone or in combination of two or more.

  The mixing ratio of the conductive additive to the lithium metal composite oxide in the electrode mixture is preferably a mass ratio of electrode active material: conductive auxiliary = 1: 0.05 to 1: 0.3.

  Examples of the solvent contained in the electrode mixture include N-methyl-2-pyrrolidone (NMP), methanol, methyl isobutyl ketone, and water. When the entire electrode mixture containing a solvent is 100% by volume, the content of the solvent is preferably 50% by volume or more and 85% by volume or less.

  An electrode mixture is obtained by adding a lithium metal composite oxide, PVdF and a solvent subjected to the contact step, and a solvent, and if necessary, mixing them to form a slurry.

  The viscosity of the electrode mixture is preferably 25000 mPA · s or less, more preferably 15000 mPA · s or less and 10000 mPA · s or less. If the viscosity of the electrode mixture is excessively high, tailing may occur at the end of application during application to the current collector, and the handleability during application may be reduced.

(electrode)
An electrode is formed by apply | coating the electrode mixture manufactured above to the surface of an electrical power collector. Examples of methods for applying the electrode mixture to the surface of the current collector include conventionally known methods such as a roll coating method, a die coating method, a dip coating method, a doctor blade method, a spray coating method, and a curtain coating method. The electrode mixture is applied to the surface of the current collector and then dried. The solvent may be compressed after drying to increase the electrode density.

  The current collector is not particularly limited as long as it is a metal that can withstand a voltage suitable for the active material to be used. The current collector refers to a chemically inert electronic high conductor that keeps a current flowing through an electrode during discharging or charging of a non-aqueous secondary battery. As the current collector, at least one selected from silver, copper, gold, aluminum, tungsten, cobalt, zinc, nickel, iron, platinum, tin, indium, titanium, ruthenium, tantalum, chromium, molybdenum, and stainless steel, etc. Metal materials can be exemplified. The current collector may be covered with a known protective layer. What collected the surface of the electrical power collector by the well-known method may be used as an electrical power collector.

  The current collector can take the form of a foil, a sheet, a film, a linear shape, a rod shape, a mesh, or the like. Therefore, for example, a metal foil such as a copper foil, a nickel foil, an aluminum foil, and a stainless steel foil can be suitably used as the current collector. When the current collector is in the form of foil, sheet or film, the thickness is preferably in the range of 1 μm to 100 μm.

(battery)
As described above, the electrode manufactured by the manufacturing method of the present invention constitutes a battery together with the other electrode and the electrolyte. As described above, the electrode manufactured by the manufacturing method of the present invention is often used as a positive electrode, and can constitute a battery together with a negative electrode and an electrolyte. In particular, a secondary battery can be configured, and when a non-aqueous electrolyte is used as the electrolyte, a non-aqueous secondary battery can be configured.

  When the electrode manufactured by the manufacturing method of the present invention is a positive electrode as described above, the negative electrode used in the non-aqueous secondary battery includes a current collector and a negative electrode mixture bound to the surface of the current collector. Have.

As the negative electrode active material, a material that can occlude and release metal ions such as lithium ions can be used. Therefore, there is no particular limitation as long as it is a simple substance, alloy, or compound that can occlude and release metal ions such as lithium ions. For example, as a negative electrode active material, Li, group 14 elements such as carbon, silicon, germanium and tin, group 13 elements such as aluminum and indium, group 12 elements such as zinc and cadmium, group 15 elements such as antimony and bismuth, magnesium , Alkaline earth metals such as calcium, and group 11 elements such as silver and gold may be employed alone. When silicon or the like is used for the negative electrode active material, a silicon atom reacts with a plurality of lithiums, so that it becomes a high-capacity active material. However, there is a problem that volume expansion and contraction due to insertion and extraction of lithium becomes significant. In order to reduce the fear, it is also preferable to employ an alloy or compound in which another element such as a transition metal is combined with a simple substance such as silicon as the negative electrode active material. Specific examples of the alloy or compound include tin-based materials such as Ag-Sn alloy, Cu-Sn alloy, Co-Sn alloy, carbon-based materials such as various graphites, SiO _x (disproportionated to silicon simple substance and silicon dioxide). Examples thereof include silicon-based materials such as 0.3 ≦ x ≦ 1.6), silicon alone, or composites obtained by combining silicon-based materials and carbon-based materials. In addition, as the negative electrode active material, oxides such as Nb ₂ O ₅ , TiO ₂ , Li ₄ Ti ₅ O ₁₂ , WO ₂ , MoO ₂ , Fe ₂ O ₃ , or Li _3-x M _x N (M = A nitride represented by (Co, Ni, Cu) may be employed. One or more of these materials can be used as the negative electrode active material.

  The negative electrode has a current collector and a negative electrode mixture bound to the surface of the current collector. As the negative electrode current collector, for example, the one described for the positive electrode current collector can be adopted.

  The negative electrode mixture contains a negative electrode active material and, if necessary, a binder and / or a conductive aid.

  The negative electrode current collector is not particularly limited as long as it is a metal that can withstand a voltage suitable for the active material to be used, and for example, the one described for the positive electrode current collector can be adopted. As the negative electrode binder and the conductive additive, those described for the positive electrode can be adopted.

  A separator is used in the non-aqueous secondary battery as necessary. The separator separates the positive electrode and the negative electrode and allows metal ions such as lithium ions to pass while preventing a short circuit of current due to contact between the two electrodes. As separators, natural resins such as polytetrafluoroethylene, polypropylene, polyethylene, polyimide, polyamide, polyaramide (Aromatic polyamide), polyester, polyacrylonitrile, etc., polysaccharides such as cellulose, amylose, fibroin, keratin, lignin, suberin, etc. Examples thereof include porous bodies, nonwoven fabrics, and woven fabrics using one or more electrically insulating materials such as polymers and ceramics. The separator may have a multilayer structure. Since the electrolytic solution has a slightly high viscosity and a high polarity, a membrane in which a polar solvent such as water can easily penetrate is preferable. Specifically, a film in which a polar solvent such as water soaks into 90% or more of the existing voids is more preferable.

  A separator is sandwiched between the positive electrode and the negative electrode as necessary 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 connected to the outside using a current collecting lead or the like, an electrolyte is added to the electrode body to add a non-aqueous secondary battery It is good to do. Moreover, the non-aqueous secondary battery of this invention should just be charged / discharged in the voltage range suitable for the kind of active material contained in an electrode.

  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 the non-aqueous secondary battery include various home electric appliances, office equipment, industrial equipment, and the like driven by batteries, such as personal computers and mobile communication devices, in addition to vehicles. Further, the non-aqueous secondary battery of the present invention includes a wind power generation, solar power generation, hydroelectric power generation and other power system power storage device and power smoothing device, power for ships and / or auxiliary power supply sources, 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.

(Comparative Example 1)
First, a lithium metal composite oxide LiNi _0.5 Co _0.2 Mn _0.3 O ₂ (NCM) synthesized by a molten salt method was prepared. LiNi _0.5 Co _0.2 Mn _0.3 O ₂ has a layered rock salt structure. LiNi _0.5 Co _0.2 Mn _0.3 O ₂ (NCM), acetylene black (AB) as a conductive additive, polyvinylidene fluoride (PVdF) as a binder, N-methyl-2-pyrrolidone (NMP) ) At a mass ratio of NCM: AB: PVdF: NMP = 54.2: 1.8: 3: 41 to prepare a positive electrode slurry (electrode mixture) (mixing step). The obtained positive electrode slurry was Comparative Example 1.

Example 1
LiNi _0.5 Co _0.2 Mn _0.3 O ₂ was subjected to a contact process and a drying process. In the contact step, LiNi _0.5 Co _0.2 Mn _0.3 O ₂ was washed with an Mg (NO ₃ ) ₂ aqueous solution. The Mg (NO ₃ ) ₂ aqueous solution has Mg (NO ₃ ) ₂ dissolved in water. Mg _{(NO 3) 2} aqueous Mg _{(NO 3) 2} concentration was 5mM (5mmol / L). 0.2 liter of Mg (NO ₃ ) ₂ aqueous solution (normal temperature) was put in a beaker. 60 g of LiNi _0.5 Co _0.2 Mn _0.3 O ₂ was added per liter of Mg (NO ₃ ) ₂ aqueous solution and stirred for 10 minutes with a stirrer.

Next, the Mg (NO ₃ ) ₂ aqueous solution was passed through a filter, and LiNi _0.5 Co _0.2 Mn _0.3 O ₂ contained in the Mg (NO ₃ ) ₂ aqueous solution was separated by filtration.

In the drying step, LiNi _0.5 Co _0.2 Mn _0.3 O ₂ was dried at 150 ° C. for 1 hour.

The dried LiNi _0.5 Co _0.2 Mn _0.3 O ₂ was subjected to the same mixing step as in Comparative Example 1 to obtain a positive electrode slurry. The obtained positive electrode slurry was designated as Example 1.

(Example 2)
In Example 2, a positive electrode slurry was prepared in the same manner as in Example 1 except that the Mg (NO ₃ ) ₂ concentration of the Mg (NO ₃ ) ₂ aqueous solution was 50 mM.

(Example 3)
In Example 2, a positive electrode slurry was prepared in the same manner as in Example 1 except that the Mg (NO ₃ ) ₂ concentration of the Mg (NO ₃ ) ₂ aqueous solution was 100 mM.

Example 4
In Example 2, a positive electrode slurry was prepared in the same manner as in Example 1 except that the Mg (NO ₃ ) ₂ concentration of the Mg (NO ₃ ) ₂ aqueous solution was 200 mM.

(Example 5)
In Example 2, a positive electrode slurry was prepared in the same manner as in Example 1 except that the Mg (NO ₃ ) ₂ concentration of the Mg (NO ₃ ) ₂ aqueous solution was 500 mM.

(Viscosity measurement)
The initial viscosity and the viscosity after 2 days (48 hours) of the positive electrode slurries of Examples 1 to 5 and Comparative Example 1 were measured. The viscosity was measured with a B-type viscometer. The results are shown in Table 1. In Table 1, “Mg (NO ₃ ) ₂ concentration in aqueous solution” indicates the molar concentration of Mg (NO ₃ ) ₂ dissolved per liter of Mg (NO ₃ ) ₂ aqueous solution. “Initial viscosity” indicates the viscosity of the positive electrode slurry immediately after the lithium metal composite oxide is mixed with AB, PVdF, and NMP to produce the positive electrode slurry. “Viscosity after 2 days” indicates the viscosity of the positive electrode slurry when two days have elapsed since the positive electrode slurry was prepared by mixing AB, PVdF, and NMP. “Viscosity increase rate (%)” is calculated from 100 × (viscosity after 2 days−initial viscosity) / initial viscosity.

As shown in Table 1, Examples 1-5 which performed the contact process had a low viscosity increase rate compared with the comparative example 1 which did not perform the contact process. In Examples 1 to 3, the viscosity after 2 days was lower than that of Comparative Example 1. In Examples 1 and 2, the initial viscosity was lower than that in Comparative Example 1. As the Mg (NO ₃ ) ₂ concentration in the aqueous solution increased, the initial viscosity and the viscosity after 2 days also increased. Therefore, lithium metal composite oxide by washing with Mg _{(NO 3) 2} solution, it is possible to suppress the viscosity increase, Mg _{(NO 3)} Mg in ₂ aqueous solution _{(NO 3) 2} concentration 5mM or 100mM or less It was found that the increase in viscosity can be effectively suppressed.

The lithium metal composite oxide LiNi _0.5 Co _0.2 Mn _0.3 O ₂ used in Comparative Example 1 and each example was purchased from a commercial product prepared by the molten salt method. The same measurement was performed with the salt synthesized. When synthesizing by the molten salt method, lithium is used as the molten salt raw material, and together with lithium contained in the metal compound raw material, the total amount of lithium exceeds the theoretical molar ratio of the composite lithium metal composite oxide. Used. In the synthesized lithium metal composite oxide, the molten salt raw material and the metal compound raw material are combined, and the molar ratio is Li: Ni: Co: Mn = 1.0: 0.5: 0.2: 0.3. A melt reaction was carried out using the raw materials. The reaction temperature was 500 to 700 ° C., and the reaction time was 1 to 6 hours. After the melting reaction, the mixture was cooled to obtain a lithium metal composite oxide LiNi _0.5 Co _0.2 Mn _0.3 O ₂ . Using this synthesized lithium metal composite oxide, it was washed with an aqueous Mg (NO ₃ ) ₂ solution having the same concentration as in Examples 1 to 5, dried, mixed with PVdF, AB, and NMP, and used for the positive electrode A slurry was obtained. A positive electrode slurry was similarly prepared for a lithium metal composite oxide that was not washed with an aqueous Mg (NO ₃ ) ₂ solution. Was carried out similar to the above viscosity measurement for these positive electrode slurry, as compared with the case where those who were washed with Mg (NO _{3) 2} aqueous solution was not carried out washing with Mg (NO _{3) 2} aqueous solution There was a tendency for the viscosity increase to be suppressed.

Claims (5)

Contacting the lithium metal composite oxide with a nitrate aqueous solution having a nitrate;
The lithium-metal composite oxide subjected to the contacting step includes a mixing step of mixing a polyvinylidene fluoride and a solvent, and
The nitrate has Mg (NO ₃ ) ₂ ,
The method for producing an electrode mixture , wherein a concentration of Mg (NO ₃ ) _{2 in} 1 liter of the aqueous nitrate solution is 5 mmol / L or more and ₂₀₀ mmol / L or less . After the contacting step, the manufacturing method of the electrode mixture according to claim 1 to perform the drying step of drying the lithium-metal composite oxide. The solvent method of producing an electrode mixture according to claim 1 or 2 having a N- methyl-2-pyrrolidone. The method for producing an electrode mixture according to any one of claims 1 to 3 , wherein the lithium metal composite oxide has a layered rock salt structure. The manufacturing method of the electrode characterized by apply | coating the positive mix manufactured by the manufacturing method of the electrode mixture of any one of Claims 1-4 to a collector.