JP2016181458A - Sheet-like active material particle-containing mold for secondary battery electrode, secondary battery arranged by use thereof, and manufacturing method of secondary battery electrode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sheet-like active material particle-containing mold for a secondary battery electrode, which is arranged by use of an oxide active material of 3 μm or less in volume-average particle diameter D, and which enables the suppression of the worsening in battery performance, such as the decrease in battery energy density or the increase in internal resistance, and enables the exhibition of good moldability even in the case of forming an electrode with an active material layer large in thickness according to compression molding.SOLUTION: A sheet-like active material particle-containing mold for a secondary battery electrode comprises: 65-90 wt% of oxide active material small particles including primary particles of over 1 to 3 μm in volume-average particle diameter (D); 5-30 wt% of oxide large particles having a number-average particle crushing strength of 3 MPa or larger and including primary particles of 8-50 μm in volume-average particle diameter (D); 0.5-10 wt% of a conductive assistant material; and 0.5-5 wt% of an insulative binding material.SELECTED DRAWING: None

Description

  The present invention relates to a sheet-form active material particle-containing molded article for a secondary battery electrode, a secondary battery, and a method for producing a secondary battery electrode.

  Generally, a secondary battery is required to have a high energy density, and it is important that more electrode active materials exist in the battery. Current secondary battery electrodes are manufactured by applying a slurry containing an active material to a metal foil and then drying it. If the slurry is applied thickly to increase the thickness of the active material layer, it will contain an active material during drying. Shrinkage of the layer occurs, cracks are generated in the active material layer, or the active material layer falls from the electrode current collector. In particular, an electrode active material having a primary particle volume average particle diameter of 3 μm or less has a problem that the formability of a sheet-like active material particle-containing molded body applied to an electrode having a thick active material layer is poor. When producing an electrode having high mechanical strength and high reliability and a thick active material layer, it is necessary to improve the moldability of the sheet-like active material particle-containing molded body.

In Patent Document 1, in order to improve the adhesion between the current collector and the active material-containing layer and to improve the cycle performance of the battery, the lithium titanate small particle size active material particles having an average particle size of 1 μm or less, and the average particles An active material-containing layer comprising a lithium titanate large particle size active material particle having a diameter of 2 μm or more and 50 μm or less, wherein the true density of the large particle size active material particles is greater than the true density of the small particle size active material particles The technique which uses the negative electrode provided with a content layer is disclosed. Further, from the viewpoint of mixing particles, in Patent Document 2, the positive electrode active material is a first positive electrode active material and a second positive electrode active material having a volume average particle diameter D ₅₀ smaller than that of the first positive electrode active material. The first positive electrode active material has a D ₅₀ particle size of 10 μm or more and 50 μm or less, and the second positive electrode active material has a D ₅₀ particle size of 1 μm or more and 9 μm or less. A nonaqueous electrolyte secondary battery is disclosed.

Japanese Patent No. 4580949 JP 2007-335318 A

Since the thickness of the active material layer to produce a thick electrode, load characteristics, if the volume average particle diameter D ₅₀ of the primary particles which is excellent in cycle characteristics using the following electrode active material 3 [mu] m, to form an active material layer by compression molding In order to secure moldability due to an increase in specific surface area due to the small particle size, it is necessary to increase the amount of the binder to about 20% by weight of the entire molded body, and in particular, D ₅₀ is 1 μm. In the case of the following, an increase in the necessary amount of binder accompanying the reduction in particle size becomes significant. When the amount of the binder is increased, the energy density of the battery is lowered, the internal resistance is increased, and the battery performance is lowered, which is not preferable.

  The effect of using the large particle size active material particles in the secondary battery described in Patent Document 1 is that voids are formed in the electrode and the impregnation property of the nonaqueous electrolyte is improved. It is supposed that the diffusion area of lithium ions is improved by increasing the contact area of the non-aqueous electrolyte, that is, by increasing the number of ion paths. Further, the effect of using the small particle size active material particles is to effectively improve the lithium ion diffusibility in the electrode by reducing the diffusion distance of lithium ions in the active material particles. Furthermore, the effect of making the true density of the large particle size active material particles larger than the true density of the small particle size active material particles is that when the slurry containing the active material is applied to the current collector, the large particle size active material particles Is likely to settle to the current collector side, so that the adhesion between the current collector and the active material-containing layer is improved, and the electronic conductivity is improved.

  The invention of Patent Document 1 is based on the premise that the active material layer is formed by the slurry casting method, and cannot be applied when the amount of the dispersion solvent is extremely small. Furthermore, in general, the constituent materials in the molded body tend to exhibit better life characteristics when they are uniformly dispersed. In the secondary battery of Patent Document 1, which requires uneven distribution of large particles on the current collector side, performance is improved. May decrease.

  Patent Document 2 also discloses that a large and small mixed system is used as the active material particles. The object of the invention is to suppress increase in resistance at the time of charge and discharge. Forming a sheet-shaped active material particle-containing molded article that is applied to an electrode having a thick active material layer, which is a subject of the present invention, and is an object of the present invention, and has excellent moldability There is no problem of providing a body.

When producing an electrode with a thick active material layer, the present inventor mixed a small oxide active material particle having a D ₅₀ of 3 μm or less with a large oxide particle having a D ₅₀ of 8 μm or more, thereby binding the electrode. It has been found that good moldability can be expressed while reducing the material. This is because, in the formation of the active material layer by the compression molding method, unlike the formation by the slurry casting method, the active material particles are uniformly dispersed in the molded body, so that even if the amount of the binder is small, the periphery of the large oxide particles Oxide active material small particles can be effectively bound to each other, and large oxide particles bound to such small oxide active material particles are also sufficient with a small amount of binder and a small contact area. This is a phenomenon caused by effective binding.

As a method for producing a plate-like electrode using the sheet-shaped active material particle-containing molded body of the present invention molded by the compression molding method in this way, for example, two molded sheet-shaped active material particle-containing molded bodies are used. The current collector is sandwiched between and a pressure of 300 kg / cm ² is applied through a 80 ° C. roll press, or the current collector and the active material particle-containing mixture are simultaneously charged into the roll press, and the pressure of 40 kg / cm ² is applied. There is a way to apply.

That is, the present invention is a sheet-shaped active material particle-containing molded article for secondary battery electrodes having a thickness of 0.3 mm or more and 3 mm or less, wherein the primary particles have a volume average particle diameter (D ₅₀ ) of more than 1 μm and 3 μm or less. Small oxide active material particles 65% by weight or more and 90% by weight or less, number average particle compression fracture strength of 3 MPa or more, and primary particles having a volume average particle diameter (D ₅₀ ) of 8 μm or more and 50 μm or less 5% by weight or more and 30% by weight or less, conductive additive 0.5% by weight or more and 10% by weight or less, and binder 0.5% by weight or more and 5% by weight or less, and each constituent material is in the molded body. It is related with the molded object containing the sheet-like active material particle for secondary battery electrodes characterized by existing uniformly disperse | distributing.

  The small oxide active material particles are preferably lithium titanate having a spinel structure.

  The large oxide particles are preferably lithium titanate and / or titanium oxide having a spinel structure.

  The small oxide active material particles are preferably a compound in which a part of ions of lithium manganate and / or lithium manganate are substituted with other metal ions.

According to the present invention, when an electrode having a thick active material layer is produced, it is preferable to mix large oxide particles having a D ₅₀ of 8 μm or more with small oxide active material particles having a D ₅₀ of 3 μm or less. It can be set as the active material particle containing mixture which has a moldability. Moreover, in such a sheet-like active material particle-containing molded article of the present invention, sufficient moldability and mechanical strength can be obtained even with a small amount of binder (5 wt% or less). By obtaining sufficient formability and mechanical strength, the active material mixture is not peeled off from the current collector during electrode molding or transportation, and is excellent in handling. Further, even after the secondary battery is manufactured, since there is no peeling from the current collector, it is possible to suppress an increase in the resistance of the secondary battery. Since a continuous electrode having both mechanical strength and flexibility can be manufactured and wound on a roll, it is excellent in productivity because it can be easily wound and unwound.

  Further, unlike Patent Document 1, since each constituent material is uniformly dispersed in the molded body, the localization of the battery reaction does not occur, thereby suppressing side reactions and expansion / contraction of the secondary battery. And a long-life secondary battery. In addition, the uniform dispersion makes it easy to fill the gaps between the large oxide particles with the small oxide active material particles, which can improve the electrode density, and as a result, improve the energy density of the secondary battery. Is possible.

  Embodiments of the present invention will be described below. The scope of the present invention is defined by the scope of the claims, and is intended to include any modifications within the scope and meaning equivalent to the scope of the claims.

(Sheet-like active material particle-containing molded product for secondary battery electrode)
The sheet-shaped active material particle-containing molded article for secondary battery electrodes of the present invention is an active material particle-containing molded article for sheet-shaped secondary battery electrodes having a thickness of 0.3 mm or more and 3 mm or less. By setting the thickness within this range, a secondary battery having high energy density and high rate characteristics can be obtained.

  The active material particle-containing molded body includes constituent materials of small oxide active material particles, large oxide particles, a conductive additive, and a binder, and the above-described constituent materials are uniformly dispersed in the molded body. Exists. Since each constituent material is uniformly dispersed, a secondary battery having a long life and high energy density can be obtained.

  Here, each constituent material is uniformly dispersed is the presence of small oxide active material particles, large oxide particles, conductive aids and binders at any location in the active material particle-containing molded body. It means that the ratio is within an error range of ± 20% with respect to the average value of the entire active material particle compact. The abundance ratio can be confirmed by SEM observation. For example, the abundance ratio of each constituent material is obtained at any 10 points in the molded body, and the average of the abundance ratio of the 10 points and the abundance ratio of each point. From the difference, it can be determined whether the error range is within ± 20%. When the active material particle-containing molded body is formed by compression molding as in the present invention, each constituent material is uniformly mixed in the molded body. It is within the range and is uniformly dispersed.

  The active material particle-containing molded product has 65% to 90% by weight of small oxide active material particles, 5% to 30% by weight of large oxide particles, and 0.5% by weight of conductive additive. The content is 10% by weight or less and the binder is 0.5% by weight or more and 5% by weight or less. By setting it as such a structure ratio, a shaping | molding characteristic and a battery characteristic can be made favorable.

(Electrode active material, conductive additive, binder)
When the electrode is used for a negative electrode, the oxide active material small particles contained in the sheet-shaped active material particle-containing molded body for secondary battery electrodes of the present invention are composed mainly of titanium as the negative electrode active material contained in the negative electrode. It is preferably an oxide containing molybdenum, molybdenum oxide, niobium oxide, and tungsten oxide, and more preferably, lithium titanate and a group consisting of lithium titanate in which a part of titanium is replaced with other metal ions It is particularly preferable that the other metal ion is niobium because it is effective for good moldability and long life. Moreover, it is particularly preferable that the lithium titanium oxide has a spinel structure from the viewpoint of dimensional stability against charge / discharge.

  The type of large oxide particles is not limited, but lithium titanate and / or titanium oxide having a spinel structure is preferable from the viewpoint of dimensional stability against charge / discharge. In particular, it is preferable that the large oxide particles be the same oxide as the small active material particles because the moldability can be improved without reducing the energy density. When the mixing ratio of the large oxide particles is 5% by weight or more, the effect of improving the moldability is exhibited, and the mixing ratio can be increased until sufficient moldability is exhibited. When an oxide different from the above is used, an energy density of 30% by weight or more tends to decrease, which is not preferable.

The D ₅₀ of the primary particles of the oxide active material small particles is more than 1 μm and 3 μm or less, and the D ₅₀ of the primary particles of the large oxide particles is 8 μm or more and 50 μm or less. It is preferable to obtain The number average particle compression fracture strength of the large oxide particles is preferably 3 MPa or more in order to obtain a high-strength active material layer.

  As the oxide active material small particles used for the positive electrode active material included in the positive electrode combined with the negative electrode containing such a negative electrode active material, lithium manganate and / or a part of lithium manganate ions may be replaced with other metal ions. One or more selected from the group consisting of a substituted compound, lithium iron phosphate, and lithium manganese phosphate is preferable because it is effective for good moldability and long life. More preferably, it is at least one selected from the group consisting of lithium manganate and / or a compound obtained by substituting some of the ions of lithium manganate with other metal ions, wherein the other metal ions are nickel, A metal ion containing at least one selected from aluminum, magnesium, titanium, chromium, cobalt, and iron is particularly preferable because it has an effect of extending the life.

  Also in the positive electrode, the large oxide particles are preferably the same oxide as the small oxide active material particles for the same reason as the negative electrode, and the mixing ratio of the large oxide particles in the compact is 5 wt% or more and 30 wt%. % Or less is preferable.

Also, in the positive electrode, for the same reason as the negative electrode, the D ₅₀ of the primary particles of the small oxide active material particles is more than 1 μm and 3 μm or less, and the D ₅₀ of the primary particles of the large oxide particles is 8 μm or more and 50 μm or less. The number average particle compression fracture strength of the large oxide particles is preferably 3 MPa or more.

  Although it does not specifically limit as a conductive support agent contained in the sheet-like active material particle containing molded object for secondary battery electrodes of this invention, A carbon material and / or a metal microparticle are preferable. Examples of the carbon material include natural graphite, artificial graphite, vapor-grown carbon fiber, carbon nanotube, acetylene black, ketjen black, carbon black, and furnace black. Examples of the metal fine particles include copper, aluminum, nickel, and an alloy containing at least one of these. Further, the fine particles of inorganic material may be plated. These carbon materials and metal fine particles may be used alone or in combination of two or more.

  The mixing ratio of the conductive additive in the molded body is preferably 0.5% by weight or more and 10% by weight or less. By setting it as such a range, the adhesiveness with a binder is maintained, ensuring the electroconductivity of an electrode, and a high-strength active material layer can be obtained.

  As the binder contained in the sheet-shaped active material particle-containing molded article for secondary battery electrodes of the present invention, a binder having a binding property and dispersible in water or an organic solvent is used. For example, although not particularly limited, polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), styrene-butadiene copolymer (SBR), polyacrylic ester , Polyacrylamide, polyvinyl alcohol (PVA), polyimide (PI), carboxymethyl cellulose (CMC), at least one selected from the group consisting of natural polysaccharides such as glucomannan guar gum and derivatives thereof. You may add a dispersing agent and a thickener to these.

  The mixing ratio of the binder in the molded body is preferably 0.5% by weight or more and 5% by weight or less. By setting it within such a range, sufficient binding properties can be imparted without deteriorating battery performance.

(Secondary battery)
The secondary battery using the sheet-shaped active material particle-containing molded body for secondary battery electrode of the present invention generally includes a laminate in which a separator containing an ion conductive electrolyte is sandwiched between a positive electrode and a negative electrode.

  The secondary battery according to the present invention may be one obtained by winding or laminating a separator disposed between a positive electrode and a negative electrode. The positive electrode, the negative electrode, and the separator are impregnated with, for example, a nonaqueous electrolyte that is responsible for ionic conduction. In the case of using a gel-like nonaqueous electrolyte, the electrolyte may be impregnated in the positive electrode and the negative electrode, or may be in a state only between the positive electrode and the negative electrode. If the positive electrode and the negative electrode are not in direct contact with the gel electrolyte, it is not necessary to use a separator.

  The secondary battery according to the present invention may be externally wrapped with a laminate film after being wound or laminated, or may be externally covered with a rectangular, oval, cylindrical, coin-shaped, button-shaped, or sheet-shaped metal can. Also good. The exterior may be provided with a mechanism for releasing generated gas or the like. Further, a mechanism for injecting an additive for recovering the function of the deteriorated nonaqueous electrolyte secondary battery from the outside of the battery may be provided. The number of stacked layers can be appropriately set so as to express a desired battery capacity. In the case of stacking, pressure may be applied in the stacking direction of the electrodes. The pressure may be applied inside the secondary battery or may be applied from the outside of the exterior.

  The secondary battery which concerns on this invention can be made into an assembled battery by connecting two or more in series. The assembled battery comprising the secondary battery of the present invention does not need to control the capacity variation for each secondary battery, so it is also possible to charge and discharge in units of assembled batteries without individually charging and discharging each secondary battery. It is. For the same reason, it is possible to monitor and control the voltage for each assembled battery. Moreover, the assembled batteries connected in series can be connected in parallel. There is no restriction | limiting in particular in the number of parallel, It can design freely by the use to be used.

  Although the use of the assembled battery according to the present invention is not particularly limited, it is preferably used in a grid connection with a commercial power source because of its long life and high safety. When used in a grid connection, charging / discharging may be performed by control other than constant current. For example, charging can be performed by applying a constant voltage equal to or lower than the end voltage, or discharging can be performed by applying a load with a constant wattage or a constant resistance.

  As described above, the secondary battery according to the present invention preferably includes a negative electrode including a titanium-containing oxide as a negative electrode active material. However, the electrolyte solvent decomposes at an abnormally active point of the titanium-containing oxide. Gas may be generated. Therefore, it is preferable to provide a positive electrode including a positive electrode active material mainly composed of lithium cobalt oxide and capable of absorbing the generated gas in a constant charge state. However, since the positive electrode including the positive electrode active material mainly composed of lithium cobalt oxide is vulnerable to overcharge, the secondary battery is provided from the viewpoint of suppressing such gas generation while exhibiting the effects of the present invention. A positive electrode mainly composed of one or more positive electrode active materials selected from the group consisting of lithium manganese oxide and an oxide obtained by substituting a part of the manganese with a different element, and In a preferred embodiment, the second positive electrode different from the first positive electrode is a secondary battery further including a positive electrode including a positive electrode active material mainly composed of the lithium cobalt oxide. By doing in this way, the 2nd positive electrode which apply | coated another active material which operate | moves similarly to a 1st positive electrode separately from the 1st positive electrode in connection with normal charging / discharging can be introduce | transduced. The second positive electrode is electrically separated from the first positive electrode, and after charging the first positive electrode and the second positive electrode to a certain voltage at the same time, the second positive electrode is electrically disconnected to be charged. A second positive electrode in a state can be present in the battery. When the second positive electrode includes a positive electrode active material mainly composed of lithium cobalt oxide, it is possible to absorb the gas generated in the secondary battery.

(Separator)
Examples of the separator used for the secondary battery using the sheet-like active material particle-containing molded body for the secondary battery electrode of the present invention include porous materials and nonwoven fabrics. The material of the separator is preferably one that does not dissolve in the organic solvent that constitutes the electrolytic solution. Specifically, a polyolefin polymer such as polyethylene or polypropylene, a polyester polymer such as polyethylene terephthalate, cellulose, or glass. Inorganic materials.

  The thickness of the separator is preferably 1 to 500 μm. If it is less than 1 μm, it tends to break due to insufficient mechanical strength of the separator and cause an internal short circuit. On the other hand, when it is thicker than 500 μm, the load characteristics of the battery tend to be reduced due to an increase in the internal resistance of the battery and the distance between the positive and negative electrodes. A more preferable thickness is 10 to 300 μm.

(Electrolytes)
The electrolyte used in the secondary battery using the sheet-shaped active material particle-containing molded article for the secondary battery electrode of the present invention is preferably a non-aqueous electrolyte, and the non-aqueous electrolyte is not particularly limited, but the solute is dissolved in a non-aqueous solvent. Mixed electrolytes, electrolytes in which solutes are dissolved in non-aqueous solvents, gel electrolytes in which polymers are impregnated with ionic liquids, solid electrolytes such as sulfur-based solid electrolytes, ionic liquids and silica fine particles are mixed, and quasi-solid A pseudo-solid electrolyte or the like can be used.

  The non-aqueous solvent preferably includes a cyclic aprotic solvent and / or a chain aprotic solvent, and more preferably a carbonate. Examples of the cyclic aprotic solvent include cyclic carbonates, cyclic esters, cyclic sulfones and cyclic ethers. Examples of the chain aprotic solvent include chain carbonates, chain carboxylic acid esters and chain ethers. In addition to the above, a solvent generally used as a solvent for nonaqueous electrolytes such as acetonitrile may be used. More specifically, dimethyl carbonate, methyl ethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethylene carbonate, propylene carbonate, butylene carbonate, γ-butyrolactone, 1,2-dimethoxyethane, sulfolane, dioxolane, propionic acid Methyl and the like can be used. These solvents may be used singly or in combination of two or more. However, in view of ease of dissolving the solute described later and the high conductivity of ions, a mixed solvent of two or more types is used. It is preferable to use it.

The solute is not particularly limited. For example, in the case of a lithium ion secondary battery, LiClO ₄ , LiBF ₄ , LiPF ₆ , LiAsF ₆ , LiCF ₃ SO ₃ , LiBOB (Lithium Bis (Oxalato) Borate), LiN (SO ₂ ). A compound containing lithium and halogen as constituent elements such as CF ₃ ) ₂ is preferable because it is easily dissolved in a solvent. The concentration of the solute contained in the electrolyte is preferably 0.5 mol / L or more and 2.0 mol / L or less. If it is less than 0.5 mol / L, the desired ionic conductivity may not be exhibited. On the other hand, if it is higher than 2.0 mol / L, the solute may not be dissolved any more. The non-aqueous electrolyte may contain a trace amount of additives such as a flame retardant and a stabilizer.

  When using a non-aqueous electrolyte for the secondary battery, the amount of the non-aqueous electrolyte is not particularly limited, but is preferably 0.1 mL or more per 1 Ah of battery capacity. When the amount is less than 0.1 mL, the conduction of ions accompanying the electrode reaction cannot catch up, and the desired battery performance may not be exhibited. In the case of using a solid electrolyte, it may be pressure-molded as it is, or it may be used after being formed into a sheet using the binder used for the electrode described above.

  A plate-like secondary battery electrode can be obtained by bonding a conductive current collector such as a metal to the molded article containing the sheet-like active material particles for the secondary battery electrode of the present invention. Examples of the conductive material used for the current collector include copper, aluminum, nickel, titanium, an alloy containing at least one of these, and a conductive polymer. Examples of the shape include a foil shape, a mesh shape, a punching shape, an expanded shape, and a foam structure. The conductive material used for such a current collector is only required to be stable at the electrode operating potential, and in a lithium ion battery, copper and its alloys are preferable when the operating potential is 0.7 V or less based on lithium. Above 7 V, aluminum and its alloys are preferred.

  The porosity of the active material layer in the positive electrode and the negative electrode is preferably 15% or more and 60% or less, and more preferably 15% or more and 40% or less. When the porosity is less than 15%, ion diffusion is too limited, and it is difficult to obtain good battery performance. When the porosity is 60% or more, there may be a poor contact between the active materials or between the active material and the conductive additive, and the battery performance may be deteriorated. Further, when the porosity is large, the volume energy density is lowered, and therefore it is preferably within the above range.

  The positive electrode and the negative electrode including the sheet-shaped active material particle-containing molded product for the secondary battery electrode of the present invention may be in a form in which a positive electrode active material layer is formed on both sides of a current collector, or a negative electrode active material layer is formed on both sides. Well, a form in which a positive electrode active material layer is formed on one side of the current collector and a negative electrode active material layer is formed on the other side, that is, a bipolar electrode may be used. In order to prevent liquid junction between the negative electrode and the negative electrode, an insulating material is disposed between the positive electrode and the negative electrode. In the case of a bipolar electrode, a separator is disposed between the positive electrode and the negative electrode of the adjacent bipolar electrode, and the layer where the positive electrode and the negative electrode face each other is disposed around the positive electrode and the negative electrode to prevent liquid junction. Insulating material is arranged.

(Molding method)
The method for producing the active material particle-containing mixture that becomes the precursor of the sheet-shaped active material particle-containing molded product for the secondary battery electrode of the present invention is not particularly limited, but small oxide active material particles, large oxide particles, conductive Since an auxiliary material and a binder can be mixed uniformly, it is preferable to use a stirring granulator, a ball mill, a planetary mixer, a jet mill, and a thin-film swirl mixer. The mixing method of the active material mixture is not particularly limited, but it may be prepared by adding a binder dispersed in a solvent after mixing small particles of oxide active material, large particles of oxide, and a conductive additive, or an electrode. Alternatively, the active material, conductive additive, and binder may be mixed and then added with a solvent. Preferably, a method of adding a conductive additive to a mixture of small particles of oxide active material and large particles of oxide and adding a binder dispersed in a solvent, and then mixing them is desirable.

  As described above, a plate-like secondary battery electrode can be obtained by attaching a current collector having conductivity such as metal to the sheet-like active material particle-containing molded article for the secondary battery electrode of the present invention. The method of attaching to the current collector is not particularly limited, the step of sandwiching the current collector between the two sheets of the active material particle-containing sheet for secondary battery electrodes in order to form a current collector sandwich, It is preferable to include a step of pressing the current collector sandwiched article from both sides of the two sheet-shaped active material particle-containing molded bodies for secondary battery electrodes on both sides thereof. Alternatively, it is preferable to include a step of simultaneously pressing the current collector and the active material particle-containing mixture to produce a sheet-shaped active material particle-containing molded body for a secondary battery electrode and simultaneously molding a plate-like secondary battery electrode. The sheet may be dried before or after the electrode is formed.

  The secondary batteries of Examples 1 to 6 and Comparative Examples 1 to 5 were produced by the following method, and the performance was evaluated. Each evaluation condition is as described in Table 1.

(1) Preparation of secondary battery Powders of large and small particles of Li _1.1 Al _0.1 Mn _1.8 O ₄ (LAMO) or Li ₄ Ti ₅ O ₁₂ (LTO) as electrode active materials Each electrode was prepared by mixing 5 parts by weight of conductive auxiliary material (acetylene black) and 5 parts by weight of binder (PTFE) in terms of solid content with respect to 90 parts by weight of powder mixed in the ratio shown in Table 1. An active material-containing mixture corresponding to was prepared, and an electrode was produced using this mixture. A specific method will be described later. Further, instead of the above mixed powder of large particles and small particles, 90 parts by weight of powder of only large particles was used, and an electrode was produced in the same manner, and this was used as a counter electrode in combination with the above electrode to form a secondary battery. Produced.

(Production of electrode active material powder)
Here, each electrode active material was manufactured by the following method.

Li _1.1 Al _0.1 Mn _1.8 O ₄ (LAMO), which is a positive electrode active material, is a method described in literature (Electrochemical and Solid-State Letters, 9 (12), A557 (2006)). Manufactured. That is, an aqueous dispersion of manganese dioxide, lithium carbonate, aluminum hydroxide, and boric acid was prepared, and a mixed powder was obtained by a spray drying method. At this time, the amounts of manganese dioxide, lithium carbonate and aluminum hydroxide were adjusted so that the molar ratio of lithium, aluminum and manganese was 1.1: 0.1: 1.8. Next, the mixed powder was heated at 900 ° C. for 12 hours in an air atmosphere, and then again heated at 650 ° C. for 24 hours. Finally, the powder was washed with 95 ° C. water and dried to obtain a positive electrode active material powder. Volume average particle diameter and number average particle compression fracture strength were adjusted by changing the firing temperature conditions.

The negative electrode active material Li ₄ Ti ₅ O ₁₂ was produced by a method described in the literature (Journal of Electrochemical Society, 142, 1431 (1995)). That is, first, titanium dioxide and lithium hydroxide are mixed so that the molar ratio of titanium and lithium is 5: 4, and then this mixture is heated at 800 ° C. for 12 hours in a nitrogen atmosphere to thereby form a negative electrode active material. A powder was obtained. Similar to LAMO, the volume average particle diameter and the number average particle compression fracture strength were adjusted by using a spray drying method or changing the firing temperature condition.

  The volume average particle diameter was measured by a laser diffraction scattering method particle size distribution analyzer. The number average particle compression fracture strength was measured 10 times using a Shimadzu micro compression tester, and the average strength was calculated.

(Production of active material-containing mixture and electrode)
A method for producing an active material-containing mixture and an electrode is described below.

  First, the electrode active material and the conductive additive were mixed using an automatic mortar. The obtained mixed powder is transferred to a mixer, and a binder dispersed in water is added by spraying using a one-fluid nozzle. After preliminary mixing, water is added to adjust the solid content to 90%, and the mixer is again mixed. By mixing, an active material-containing mixture was obtained.

  Next, an active material particle-containing molded body was produced by a compression molding method. That is, the above-mentioned active material-containing mixture was passed through a gap roll and rolled into a sheet having a thickness of 600 μm to obtain an active material particle-containing molded body.

  Observe 10 points in the molded body by SEM, determine the abundance ratio of small oxide active material particles, large oxide particles, conductive additive and binder, and the average value of the abundance ratio of the 10 points When the difference in the abundance ratio of each point was examined, all were within 20%, and each constituent material was uniformly dispersed in the molded body.

  An aluminum expanded metal (aperture 1 mm × 2 mm, thickness 0.1 mm) was sandwiched between the two sheets, formed again by passing through a gap roll, and then vacuum dried at 170 ° C. to produce an electrode. After drying, the thickness of the electrode containing aluminum expanded metal was approximately 1.0 mm. Table 1 shows the moldability of each electrode using a mixture of large particles and small particles. The case where the moldability was good was evaluated as ◯, and the case where cracks occurred in the active material layer or the active material layer was dropped was evaluated as x.

(Production of secondary battery)
LAMO was used as a positive electrode and LTO was used as a negative electrode.

First, an electrode using the mixture of large particles and small particles obtained above and a counter electrode using only large particles were used to laminate a positive electrode / separator / negative electrode in this order to produce a laminate. As the separator, two cellulose non-woven fabrics (thickness 25 μm) were used. Next, an aluminum tab serving as a lead electrode was vibration welded to the positive electrode and the negative electrode, and the laminated body with the tab was put into a bag-shaped aluminum laminate sheet. In the case of using a lithium metal electrode as a negative electrode in order to measure the capacity of the positive electrode and the negative electrode, a nickel tab vibration-welded electrode was used, which was prepared by pressure bonding lithium metal to a stainless steel sheet. After putting a non-aqueous electrolyte (propylene carbonate / ethyl methyl carbonate = 3/7 vol%, LiPF ₆ 1 mol / L) into the bag containing the laminate, the outlet of the bag is drawn out and heat sealed together with the electrode. Thus, a non-aqueous electrolyte secondary battery was produced.

(2) Performance evaluation of secondary battery A secondary battery using LAMO as a positive electrode and LTO as a negative electrode alone or as an assembled battery in which secondary batteries of the same type are connected in series, a metal plate from the outside of the exterior A charge / discharge cycle test was conducted at a current value (1/8 C rate) at which charging or discharging ended in 8 hours. That is, the assembled battery is a current I that flows to an arbitrary point of the series connection, and the current I that flows in common to the included secondary batteries is set to 1/8 C, and all the included secondary batteries are charged and discharged. .

  In this charge / discharge cycle test, the number of cycles is set to 100, and the voltage at both ends of the unit cell or the assembled cell is monitored, and when the voltage per unit cell reaches the end-of-charge voltage of 2.8 V, the control for terminating the charge is performed. Control was performed to end the discharge when the voltage reached 2.0V. Table 1 shows the capacity retention rate of the secondary battery. Here, the capacity retention rate is a percentage value when the discharge capacity after the charge / discharge cycle test is compared with the discharge capacity of the first cycle.

(Examples 1-6)
As in Examples 1 and 2, LTO powder with large oxide particles having a volume average particle diameter of 20 μm and number average particle compression fracture strength of 10 MPa, and small oxide active material particles with volume average particle diameter of 2.5 μm and number average particles When the weight ratio of the large oxide particles to the small oxide active material particles of the LTO powder having a compressive fracture strength of 2 MPa was 5:95 or 30:70, an electrode could be produced. In addition, in Examples 3 and 4 in which the large oxide particles of Examples 1 and 2 were changed to LTO having a number average particle compression fracture strength of 3 MPa, the moldability was good. The battery produced by combining the produced LTO electrode with the counter electrode containing only the large particle LAMO having a volume average particle diameter of 15 μm and a number average particle compressive fracture strength of 10 MPa has a capacity retention rate of 98% or more at 100 cycles and a good value showed that.

  As in Examples 5 and 6, similarly in LAMO, large oxide particles have a volume average particle diameter of 15 μm, LAMO powder having a number average particle compression fracture strength of 10 MPa, small oxide active material particles have a volume average particle diameter of 3 μm, When the weight ratio of the large oxide particles to the small oxide active material particles was 5:95 or 30:70 in the LAMO powder having a number average particle compression fracture strength of 2 MPa, an electrode could be produced. A battery produced by combining the produced electrode with a counter electrode containing only a large particle LTO having a volume average particle diameter of 20 μm and a number average particle compressive fracture strength of 10 MPa has a capacity retention rate of 98% or more at 100 cycles and a good value. Indicated.

(Comparative Examples 1-2)
On the other hand, when the ratio of the large oxide particles is 5% by weight or less as in Comparative Example 1 or when the number average particle compression fracture strength of the large oxide particles is 2 MPa as in Comparative Example 2, Electrode production was difficult. When the amount of the large oxide particles is less than 5% by weight, it is considered that the binding force between the particles decreased due to the increase in the specific surface area of the small oxide active material particles. When the compressive fracture strength is less than 3 MPa, the strength of the active material layer itself is low, and it is considered that particle fracture occurs during pressure molding.

(Comparative Example 3)
In the comparative example 3, it shape | molded by the compression molding method using the active material containing mixture hand-mixed using the pestle and the mortar instead of mixing with a mixer. That is, two types of electrode active materials and a conductive aid are mixed using an automatic mortar, the obtained mixed powder is transferred to a stainless steel bowl, a binder dispersed in water is added, and a preliminary material is prepared using an alumina pestle. After mixing, water was added to adjust the solid content concentration to 90%. In this case, there was a tendency for cracks to occur during the production of the electrode or the active material to fall off, making it difficult to produce the electrode.

  Observing 10 points in this active material layer by SEM, obtaining the abundance ratio of each constituent material, and examining the difference between the abundance ratio of each 10 points and the abundance ratio of each point. The difference tended to exceed 20% depending on the location, and it was not uniformly dispersed in the molded body. From the above results, it is considered that it is important to improve the moldability that the constituent materials are uniformly dispersed.

(Comparative Examples 4 and 5)
Comparative Example 4 is a case where the volume average particle diameter of the small oxide active material particles is smaller than 1 μm, and Comparative Example 5 is a case where the volume average particle diameter of the large oxide particles is smaller than 8 μm. There was a trend. It is considered that the use of small oxide active material particles and large oxide particles having a specific volume average particle diameter is necessary in order to obtain the effect of improving moldability.

Claims (7)

A sheet-shaped active material particle-containing molded article for a secondary battery electrode having a thickness of 0.3 mm or more and 3 mm or less,
65% by weight or more and 90% by weight or less of oxide active material small particles whose primary particles have a volume average particle diameter (D ₅₀ ) of more than 1 μm and 3 μm or less,
The number average particle compression fracture strength is 3 MPa or more, and the primary particles have a volume average particle diameter (D ₅₀ ) of 8 μm or more and 50 μm or less of large oxide particles of 5% by weight to 30% by weight,
Including 0.5% by weight or more and 10% by weight or less of a conductive additive, and 0.5% by weight or more and 5% by weight or less of a binder,
Each of the constituent materials is uniformly dispersed in the molded body, and is a molded article containing sheet-like active material particles for a secondary battery electrode.   The sheet-like active material particle-containing molded article for a secondary battery electrode according to claim 1, wherein the small oxide active material particles are lithium titanate having a spinel structure.   The sheet-like active material particle-containing molded article for a secondary battery electrode according to claim 2, wherein the large oxide particles are lithium titanate and / or titanium oxide having a spinel structure.   The sheet-like active material for a secondary battery electrode according to claim 1, wherein the small particles of the oxide active material are a compound obtained by substituting a part of ions of lithium manganate and / or lithium manganate with another metal ion. Particle-containing compact.   The secondary battery using the sheet-like active material particle containing molded object for secondary battery electrodes in any one of Claims 1-4. It is a manufacturing method of the plate-shaped secondary battery electrode using the sheet-like active material particle content forming object for secondary battery electrodes in any one of Claims 1-4, Comprising:
A step of sandwiching a current collector with two sheet-shaped active material particle-containing compacts for a secondary battery electrode to form a current collector sandwich, and the current collector sandwich on both sides, The manufacturing method of a plate-shaped secondary battery electrode including the process of pressing from the both sides of the sheet-like active material particle containing molded object for secondary battery electrodes. It is a manufacturing method of the plate-shaped secondary battery electrode using the sheet-like active material particle containing molded object for secondary battery electrodes in any one of Claims 1-4, Comprising: A collector and an active material particle containing mixture are made. The manufacturing method of a plate-shaped secondary battery electrode including the process of pressing simultaneously and manufacturing the sheet-like active material particle containing molded object for secondary battery electrodes, and shape | molding a plate-shaped secondary battery electrode simultaneously.