JP2013089346A - Nonaqueous electrolyte secondary battery and manufacturing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery which exhibits the effect of a dispersant more appropriately and enhances the output characteristics.SOLUTION: In the inventive nonaqueous electrolyte secondary battery, a positive electrode has: a positive electrode collector; and a positive electrode mixture layer formed on the positive electrode collector and containing at least a positive electrode active material, a conductive material and a dispersant. The DBP absorption amount[mL/100 g] of the positive electrode active material is 30 mL/100 g or more. When the DBP absorption amount[mL/100 g] of the positive electrode active material is A, the mass ratio of the positive electrode active material occupying the total solid in the positive electrode mixture layer is x[mass%], the DBP absorption amount[mL/100 g] of the conductive material is B, and the mass ratio of the conductive material occupying the total solid in the positive electrode mixture layer is y[mass%], a calculation value (a) determined according to a following expression a=yB/xA is 0.28-0.47.

Description

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

  Non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries are becoming increasingly important as power sources mounted on vehicles that use electricity as a drive source, or power sources used in personal computers, portable terminals, and other electrical products. ing. In particular, a lithium ion secondary battery that is lightweight and obtains a high energy density is preferable as a high-output power source mounted on a vehicle.

  In a typical example of a non-aqueous electrolyte secondary battery, charge carriers (for example, lithium ions) move back and forth between a positive electrode mixture layer containing a positive electrode active material and a negative electrode mixture layer containing a negative electrode active material. Charging and discharging are performed. Such a positive electrode mixture layer is obtained by, for example, adding a positive electrode active material, a conductive material, and a binder to an appropriate amount of a solvent and kneading the paste-like composition (the paste-like composition includes a slurry-like composition). A composition and an ink-like composition are prepared), and this is applied onto a positive electrode current collector (conductive member) and dried.

JP 2009-193805 A JP 2001-110424 A JP 2005-285606 A

By the way, since a conductive material (for example, carbon material) has a property of easily agglomerating, it re-aggregates when kneading (preparing) the composition (paste), which may increase the viscosity of the composition. . When the viscosity of the composition is too large, there is a possibility that coating unevenness occurs when the composition is applied onto the current collector. It is possible to increase the dispersed state of the conductive material by preventing the aggregation of the conductive material by using a large amount of the solvent during kneading (that is, to reduce the viscosity and improve the conductivity). Since the removal amount increases, the cost for removing the solvent may increase. For this reason, it is conceivable to add a dispersant during kneading to prevent aggregation of the conductive material and lower the viscosity of the composition.
However, if the added amount of the dispersing agent is too large, the added dispersing agent is adsorbed on the positive electrode active material and covers the surface of the positive electrode active material. There is a risk of increase. Thus, in order to prevent the aggregation of the conductive material and suppress the increase in the viscosity of the composition, there is a problem that it is difficult to obtain a desired high output characteristic by simply adding a dispersant.

  Therefore, the present invention has been created to solve the above-described problems, and its object is to provide a nonaqueous electrolyte secondary battery in which the effect of the dispersant is more appropriately exhibited and the output characteristics are improved. And providing a method for suitably producing the non-aqueous electrolyte secondary battery.

The nonaqueous electrolyte secondary battery provided by the present invention is a nonaqueous electrolyte secondary battery including a positive electrode and a negative electrode. That is, in the nonaqueous electrolyte secondary battery disclosed herein, the positive electrode includes a positive electrode current collector, at least a positive electrode active material and a conductive material (typically granular) formed on the positive electrode current collector, and a dispersion. And a positive electrode mixture layer containing an agent. The positive electrode active material has a DBP absorption amount [mL / 100 g] based on JIS K6217-4 of 30 ml / 100 g or more. Here, the DBP absorption amount [mL / 100 g] of the positive electrode active material is A, and the mass ratio of the positive electrode active material to the total solid content in the positive electrode mixture layer is x [mass%] (that is, x [mass]. %] Is expressed as a ratio (p / S) × 100 of the total mass p [g] of the positive electrode active material in the positive electrode mixture layer and the total mass S [g] of the total solid content in the positive electrode mixture layer. And the DBP absorption amount [mL / 100 g] (see JIS K6217-4) of the conductive material is B, and the mass ratio of the conductive material in the total solid content in the positive electrode mixture layer is y [mass%] (that is, y [mass%] is a ratio of the total mass q [g] of the conductive material in the positive electrode mixture layer to the total mass S [g] of the total solid content in the positive electrode mixture layer ( q / S) × 100.) Calculated value a obtained by the following equation (1):
a = yB / xA (1);
Is 0.28 to 0.47.
In the present specification, the “nonaqueous electrolyte secondary battery” refers to a battery provided with a nonaqueous electrolyte (typically, an electrolytic solution containing a supporting salt (supporting electrolyte) in a nonaqueous solvent). The term “secondary battery” refers to a general battery that can be repeatedly charged and discharged, and is a term that includes a so-called chemical battery such as a lithium ion secondary battery and a physical battery such as an electric double layer capacitor.

In the nonaqueous electrolyte secondary battery provided by the present invention, the DBP absorption amount A [mL / 100 g] is 30 mL / 100 g or more (for example, 30 ml / 100 g to 45 ml / 100 g), and the DBP absorption amount is relatively large (that is, the dispersant). A positive electrode active material), and a positive electrode mixture layer having a calculated value a derived from the above formula (1) within the above range. For this reason, the ratio of the dispersing agent adsorb | sucking to the surface of a positive electrode active material can be made small, and the favorable dispersibility of an electrically conductive material can be ensured. As a result, a non-aqueous electrolyte secondary battery with reduced reaction resistance and improved output performance can be obtained.
In addition, the above Patent Documents 1 to 3 disclose techniques that define the DBP absorption amount of the positive electrode active material, the conductive material, or the mixed powder of the positive electrode active material and the conductive material. In the third technique, when the dispersant is added to the positive electrode mixture layer, most of the positive electrode active material is covered with the dispersant, and thus the effects of the invention disclosed herein are not exhibited.

  In a preferred embodiment of the nonaqueous electrolyte secondary battery disclosed herein, the conductive material (typically a granular conductive material) has a DBP absorption amount B [mL / 100 g] of 130 mL / 100 g to 180 mL / 100 g of carbon black (for example, acetylene black, ketjen black, furnace black, etc.). In a nonaqueous electrolyte secondary battery including such carbon black as a conductive material, good conductivity can be obtained. Acetylene black is particularly preferred as the carbon black used.

In another preferred embodiment of the nonaqueous electrolyte secondary battery disclosed herein, the dispersion contained in the positive electrode mixture layer when the conductive material contained in the positive electrode mixture layer is 100% by mass. The mass ratio of the agent is 1% by mass or more and 5% by mass or less.
According to such a configuration, the non-aqueous electrolyte secondary provided with the positive electrode mixture layer in which aggregation of the conductive material is suppressed and the conductive material is well dispersed, and excessive adsorption of the dispersant to the positive electrode active material is suppressed. Since the battery is used, the reaction resistance can be reduced. Preferably, the dispersant is at least one selected from a polymer compound having a hydrophobic group and a hydrophilic group, an anionic compound having a polar functional group, or a cationic compound. Polyvinyl butyral and / or polyvinyl pyrrolidone are preferred as the polymer compound.

According to the present invention, as another aspect for realizing the above object, a positive electrode in which a positive electrode mixture layer including at least a positive electrode active material and a conductive material is formed on a positive electrode current collector, and a negative electrode including at least a negative electrode active material There is provided a method for producing a nonaqueous electrolyte secondary battery, comprising: a negative electrode having a composite material layer formed on a negative electrode current collector. That is, in the method for manufacturing a nonaqueous electrolyte secondary battery disclosed herein, a conductive material dispersion is prepared (prepared) in which the conductive material, the dispersant, and the binder are dispersed in a predetermined solvent. A paste-like positive electrode obtained by mixing the prepared conductive material dispersion and a positive electrode active material having a DBP absorption amount [mL / 100 g] based on JIS K6217-4 of 30 mL / 100 g or more as the positive electrode active material. Preparing (preparing) a composition for forming a mixture layer, and forming the cathode mixture layer by applying the prepared composition for forming a cathode mixture layer on the surface of the cathode current collector and drying it. . Here, the DBP absorption amount [mL / 100 g] of the positive electrode active material is A, and the mass ratio of the positive electrode active material in the total solid content in the positive electrode mixture layer forming composition is x [mass%]. And when DBP absorption amount [mL / 100g] of the said electrically conductive material is set to B, and the mass ratio of this electrically conductive material to the total solid in the said composition for positive electrode mixture layer formation is set to y [mass%]. Calculated value a obtained by the following formula (1):
a = yB / xA (1);
The DBP absorption amount A, the mass ratio x, the DBP absorption amount B, and the mass ratio y are determined so that the value becomes 0.28 to 0.47.

  Thus, when the positive electrode mixture layer is formed using the positive electrode active material having a DBP absorption amount A [mL / 100 g] of 30 mL / 100 g or more (for example, 30 ml / 100 g to 45 ml / 100 g), the above formula (1) By calculating the DBP absorption amount A, the mass ratio x, the DBP absorption amount B, and the mass ratio y so that the calculated value a falls within the above range. The proportion of the dispersant adsorbed on the positive electrode active material can be reduced, and the conductive material can be dispersed well. Thereby, it is possible to suppress the increase in reaction resistance of the nonaqueous electrolyte secondary battery and improve the output performance.

  In a preferred embodiment of the production method disclosed herein, as the conductive material, carbon black having a DBP absorption amount B [mL / 100 g] of 130 mL / 100 g to 180 mL / 100 g (for example, acetylene black, ketjen black, Furnace black or the like). While carbon black is excellent in conductivity, it has a property of being easily aggregated. Therefore, when manufacturing a non-aqueous electrolyte secondary battery using the above carbon black as a conductive material, a dispersant is used and the balance between the physical properties and mass ratio of the positive electrode active material and the physical properties and mass ratio of the conductive material is specified. In particular, the effect of adopting the configuration of the present invention can be exhibited.

In another preferable aspect of the production method disclosed herein, when the conductive material contained in the conductive material dispersion is 100% by mass, the mass ratio of the dispersant contained in the conductive material dispersion The amount of the dispersing agent is adjusted so that the amount becomes 1 mass% or more and 5 mass% or less.
According to this configuration, it is possible to satisfactorily disperse the conductive material while suppressing an increase in internal resistance due to the addition of the dispersant. In addition, since the solvent can be reduced, the composition for forming a positive electrode mixture layer having a high solid content and a low viscosity can be obtained.

  In another preferred embodiment of the production method disclosed herein, the dispersant is selected from a polymer compound having a hydrophobic group and a hydrophilic group, or an anionic compound or a cationic compound having a polar functional group. Use at least one kind. For example, polyvinyl butyral and / or polyvinyl pyrrolidone is used as the polymer compound. Such a dispersant can favorably disperse the conductive material.

  As described above, any of the nonaqueous electrolyte secondary batteries disclosed herein or the nonaqueous electrolyte secondary battery obtained by any of the manufacturing methods is charged / discharged (particularly at a low temperature (eg, about −30 ° C.)). A non-aqueous electrolyte secondary battery (for example, a lithium ion secondary battery) capable of exhibiting a high output due to a reduced reaction resistance at a high rate (for example, 5C to 50C) can be obtained. For this reason, it can be used as a drive power source for vehicles (typically automobiles, particularly automobiles equipped with electric motors such as hybrid cars, electric cars, and fuel cell cars). As another aspect of the present invention, any of the nonaqueous electrolyte secondary batteries disclosed herein (which may be in the form of an assembled battery in which a plurality of batteries are typically connected in series) is driven. A vehicle provided as a power source is provided.

It is a perspective view which shows typically the external shape of the nonaqueous electrolyte secondary battery which concerns on one Embodiment of this invention. FIG. 2 is a cross-sectional view taken along line II-II in FIG. It is a flowchart for demonstrating the manufacturing method of the nonaqueous electrolyte secondary battery which concerns on one Embodiment of this invention. It is a graph which shows the relationship between the calculated value a of Formula (1), and IV resistance. It is a side view which shows typically the vehicle (automobile) provided with the nonaqueous electrolyte secondary battery which concerns on this invention.

  Hereinafter, preferred embodiments of the present invention will be described. It should be noted that matters other than matters specifically mentioned in the present specification and necessary for carrying out the present invention can be grasped as design matters of those skilled in the art based on the prior art in this field. The present invention can be carried out based on the contents disclosed in this specification and common technical knowledge in the field.

  As a preferred embodiment of the non-aqueous electrolyte secondary battery disclosed herein, a lithium ion secondary battery will be described in detail as an example, but the application target of the present invention is a non-aqueous electrolyte secondary battery of this kind. It is not intended to be limited to batteries. For example, the present invention can also be applied to a non-aqueous electrolyte secondary battery using other metal ions (for example, magnesium ions) as charge carriers.

As shown in FIG. 3, the manufacturing method of the lithium ion secondary battery (nonaqueous electrolyte secondary battery) disclosed herein includes a conductive material dispersion preparation (preparation) step (S10) and a positive electrode mixture layer formation. It includes a composition preparation (preparation) step (S20) and a positive electrode mixture layer formation step (S30).
First, the conductive material dispersion preparation (preparation) step (S10) will be described. The conductive material dispersion preparation (preparation) step includes preparing a conductive material dispersion in which a conductive material, a dispersant, and a binder are dispersed in a predetermined solvent.

As said electrically conductive material, the thing similar to the electrically conductive material used for the positive electrode of a general lithium ion secondary battery can be employ | adopted suitably. For example, various carbon blacks (for example, acetylene black, furnace black, ketjen black, etc.), carbon powders such as graphite powders can be used. Among these, you may use together 1 type, or 2 or more types. Preferably, acetylene black having excellent conductivity is used.
The mass ratio (amount used) of the conductive material is not particularly limited as long as the calculated value a of the formula (1) described later falls within a predetermined range. For example, when the positive electrode active material contained in the positive electrode mixture layer is 100% by mass, 1% by mass to 20% by mass (preferably 5% by mass to 15% by mass, more preferably 7% by mass to 12% by mass). It can be.
The DBP absorption amount B [mL / 100 g] based on JIS K6217-4 “Carbon black for rubber—Basic characteristics—Part 4: Determination of DBP absorption amount” of the conductive material is about 130 mL / 100 g to 180 mL / It is preferably 100 g (for example, approximately 135 mL / 100 g to 175 mL / 100 g).

As the dispersant, for example, a polymer compound having a hydrophobic group (chain) and a hydrophilic group (chain) (for example, polyvinyl butyral, polyvinyl pyrrolidone, etc.) can be preferably used. Other examples of the dispersant include an anionic compound having a predetermined polar functional group (for example, sulfone group, carboxyl group, amino group, etc.) (for example, sulfate, sulfonate, phosphate, etc. of the compound), cation Compound (for example, aliphatic amine). Among these, you may use together 1 type, or 2 or more types. For example, polyvinyl pyrrolidone or polyvinyl butyral can be preferably used. By adsorbing the dispersing agent to the conductive material that easily aggregates during kneading of the composition, the conductive material can be prevented from aggregating to increase the dispersion state of the conductive material and reduce the viscosity of the composition. it can.
Moreover, the mass ratio (use amount) of the dispersant contained in the conductive material dispersion (and the positive electrode mixture layer described later) is the same as that of the conductive material contained in the conductive material dispersion (and the positive electrode mixture layer described later). When it is 100% by mass, it can be 1% by mass to 5% by mass (preferably 2% by mass to 3% by mass). When the usage-amount of a dispersing agent is too less than 1 mass%, there exists a possibility that a electrically conductive material cannot be disperse | distributed favorably. On the other hand, when the amount of the dispersant used is more than 5% by mass, the conductive material itself can be satisfactorily dispersed, but the dispersant itself is excessively contained, which may increase the internal resistance.

  As said binder (binder), the thing similar to the binder used for the positive electrode of a common lithium ion secondary battery can be employ | adopted suitably. For example, when preparing a composition for forming a positive electrode mixture layer using a solvent-based solvent (organic solvent), an organic solvent (nonaqueous solvent) such as polyvinylidene fluoride (PVDF) or polyvinylidene chloride (PVDC). Polymer materials that dissolve in Examples of the organic solvent include N-methyl-2-pyrrolidone (NMP).

  The above-mentioned conductive material, dispersant and binder can be mixed (kneaded) in a solvent, for example, using an appropriate kneader (planetary mixer, homodisper, clear mix, fill mix, etc.). . In preparing (preparing) the conductive material dispersion, first, the conductive material and the dispersant are kneaded in a solvent, and after the dispersant is adsorbed to the conductive material, the binder is added and kneaded. Also good.

  Next, the composition preparation (preparation) step (S20) for forming the positive electrode mixture layer will be described. In the step of preparing (preparing) a composition for forming a positive electrode mixture layer, a paste-like composition for forming a positive electrode mixture layer formed by mixing the conductive material dispersion prepared in the above step and a positive electrode active material is prepared. It is included.

Examples of the positive electrode active material include lithium-containing compounds (for example, lithium transition metal oxides) that are materials capable of inserting and extracting lithium ions and include a lithium element and one or more transition metal elements. For example, lithium nickel composite oxide (for example, LiNiO ₂ ), lithium cobalt composite oxide (for example, LiCoO ₂ ), lithium manganese composite oxide (for example, LiMn ₂ O ₄ ), or lithium nickel cobalt manganese composite oxide (for example, LiNi _{1). / 3} Co _1/3 Mn _1/3 O ₂ ), a ternary lithium-containing composite oxide.
In addition, a polyanionic compound (for example, LiFePO ₄₎ whose general formula is represented by LiMPO _4, LiMVO _4, or Li ₂ MSiO ₄ (wherein M is at least one element of Co, Ni, Mn, and Fe), etc. ₄ , LiMnPO ₄ , LiFeVO ₄ , LiMnVO ₄ , Li ₂ FeSiO ₄ , Li ₂ MnSiO ₄ , Li ₂ CoSiO ₄ ) may be used as the positive electrode active material.
Moreover, DBP absorption amount A [mL / 100g] based on JISK6217-4 of the said positive electrode active material (typically particulate form) is 30 mL / 100g or more (for example, 30ml / 100g-45ml / 100g). When the DBP absorption amount A [mL / 100 g] is too smaller than 30 mL / 100 g, a high output cannot be obtained in a nonaqueous electrolyte secondary battery (lithium ion secondary battery) provided with such a positive electrode active material.

  In general, the DBP absorption amount of a positive electrode active material (for example, a lithium transition metal oxide powder having a layered structure) composed of dense solid-structure particles is approximately 10 mL / 100 g to 20 mL / 100 g. If other conditions (particle size and the like) are about the same, the DBP absorption amount of the porous or hollow structure particles tends to be larger than the DBP absorption amount of the solid particles. The positive electrode active material in the technology disclosed herein is a particle having such a porous structure or a hollow structure.

  Here, the porous structure refers to a structure (sponge-like structure) in which a substantial part and a void part are mixed over the entire particle. As a typical example of a positive electrode active material having a porous structure, a positive electrode active material obtained by a so-called spray baking method (sometimes referred to as a spray dry method) (typically a secondary in which primary particles are collected). It takes the form of particles.). The hollow structure refers to a structure having a shell portion and a hollow portion (cavity portion) inside thereof. In a preferred embodiment, the shell portion may have a through hole that allows the outside of the particle to communicate with the hollow portion (hereinafter, the hollow structure having the through hole in the shell portion is referred to as a “perforated hollow structure”. The active material particles having such a structure are sometimes referred to as “porous hollow active material particles”. The particles of such a hollow structure (meaning that it includes a perforated hollow structure unless otherwise specified) are such that the substantial part is biased toward the shell part, and a space is secured in the hollow part. In this respect, the particles having a porous structure are clearly distinguished from each other in terms of structure.

  As the material of the active material particles having such a hollow structure, lithium transition metal oxide (typically, lithium transition metal oxide having a layered structure) is preferable. A lithium transition metal oxide (typically lithium nickel oxide) containing at least Ni as a transition metal is particularly preferred.

≪Method for producing perforated hollow active material particles≫
The porous hollow active material particles having the lithium transition metal oxide as a constituent material can be preferably produced, for example, as follows. The production method includes an aqueous solution containing at least one of transition metal elements contained in the lithium transition metal oxide constituting the active material particles (in a preferred embodiment, all of the metal elements other than lithium contained in the oxide). It includes precipitating the transition metal hydroxide from a solution under appropriate conditions (raw material hydroxide generation step). Moreover, the transition metal hydroxide and the lithium compound are mixed (mixing step). Furthermore, it can include firing the mixture (firing step). Hereinafter, a preferred embodiment of such a production method will be described in detail by taking as an example the case of producing a perforated hollow active material particle composed of a LiNiCoMn oxide having a layered structure. It is not intended to be limited to hollow active material particles.

In a preferred embodiment of the method for producing positive electrode active material particles disclosed herein, the raw material hydroxide generation step supplies ammonium ions (NH ₄ ⁺ ) to an aqueous solution of a transition metal compound, and then from the aqueous solution. Depositing particles of transition metal hydroxide. The solvent (aqueous solvent) constituting the aqueous solution is typically water, and may be a mixed solvent containing water as a main component. As the solvent other than water constituting the mixed solvent, an organic solvent (such as a lower alcohol) that can be uniformly mixed with water is preferable. The aqueous solution of the transition metal compound (hereinafter also referred to as “transition metal solution”) constitutes the lithium transition metal oxide in accordance with the composition of the lithium transition metal oxide constituting the active material particles as the production target. It contains at least one (preferably all) transition metal elements (here, Ni, Co and Mn). For example, a transition metal solution containing one or more compounds that can supply Ni ions, Co ions, and Mn ions in an aqueous solvent is used. As the metal ion source compound, sulfates, nitrates, chlorides, and the like of the metals can be appropriately employed. For example, a transition metal solution having a composition in which nickel sulfate, cobalt sulfate and manganese sulfate are dissolved in an aqueous solvent (preferably water) can be preferably used.

The NH ₄ ⁺ may be supplied to the transition metal solution in the form of an aqueous solution (typically an aqueous solution) containing NH ₄ ⁺ , for example, and supplied by directly blowing ammonia gas into the transition metal solution. These supply methods may be used in combination. An aqueous solution containing NH ₄ ⁺ can be prepared, for example, by dissolving a compound (ammonium hydroxide, ammonium nitrate, ammonia gas, or the like) that can be an NH ₄ ⁺ source in an aqueous solvent. In a preferred embodiment, NH ₄ ⁺ is supplied in the form of an aqueous ammonium hydroxide solution (ie, aqueous ammonia).

≪Nucleation stage≫
In a preferred embodiment, the raw material hydroxide generation step comprises a step of depositing transition metal hydroxide nuclei from the transition metal solution (nucleation generation step) and a step of growing the nuclei (particle growth step). Including. In a preferred embodiment, both the nucleation step and the particle growth step are performed in the presence of ammonium ions. At least the particle growth step is preferably performed while controlling the ammonium ion concentration (ammonia concentration) in the solution (for example, controlling it to a predetermined value or less). The particle growth stage is preferably carried out under alkaline conditions at a pH lower than that in the nucleation stage.

  From the viewpoint that it is easy to obtain porous hollow active material particles with little variation (for example, a small number ratio of particles whose particle size or particle structure is greatly deviated from the average), in the nucleation stage, from the transition metal solution, It is preferable to deposit a large number of nuclei within a short time (eg, almost simultaneously). For example, the nuclei may be precipitated from a solution in which the transition metal hydroxide is in a supersaturated state (for example, by allowing the solution to reach a critical degree of supersaturation). In order to suitably realize such a precipitation mode, it is advantageous to perform the nucleation step under a condition of pH 12 or more (typically pH 12 or more and 14 or less, for example, pH 12.2 or more and 13 or less).

The NH ₄ ⁺ concentration (ammonium ion concentration) in the nucleation stage is not particularly limited, but usually it is suitably about 25 g / L or less, for example, about 3 to 25 g / L. The pH and NH ₄ ⁺ concentration can be adjusted by appropriately balancing the usage amount of the ammonia water and the usage amount of an alkaline agent (a compound having an action of tilting the liquidity to alkalinity). The amount used can be grasped as a supply rate to the reaction system, for example. As the alkaline agent, for example, sodium hydroxide, potassium hydroxide and the like can be typically used in the form of an aqueous solution. In a preferred embodiment, an aqueous sodium hydroxide solution is used. In addition, in this specification, the value of pH shall mean pH value on the basis of liquid temperature of 25 degreeC.

≪Particle growth stage≫
In the particle growth stage, the transition metal hydroxide nuclei (typically particles) precipitated in the nucleation stage are preferably grown under alkaline conditions at a lower pH than in the nucleation stage. For example, the growth may be performed at a pH of less than 12 (typically a pH of 10 or more and less than 12, preferably a pH of 10 or more and 11.8 or less, such as a pH of 11.0 or more and 11.8 or less). The transition metal hydroxide particles (raw material hydroxide particles) obtained through this particle growth stage preferably have a structure in which the density inside the particles is lower than the density of the outer surface portion of the particles. In order to stably obtain transition metal hydroxide particles having such a structure, it is important not to make the NH ₄ ⁺ concentration too high (suppress it low) in the particle growth stage. This increases the deposition rate of the transition metal hydroxide (here, the composite hydroxide containing Ni, Co, and Mn), and the raw material water suitable for the formation of the apertured hollow active material particles disclosed herein. Oxide particles (in other words, raw material hydroxide particles that easily form a fired product having a perforated hollow structure) can be effectively produced. Usually, it is appropriate that the NH ₄ ⁺ concentration in the particle growth stage is 25 g / L or less, preferably 15 g / L or less, more preferably 10 g / L or less (for example, 8 g / L or less). Although NH ₄ ⁺ lower limit of the concentration is not particularly limited, ease control of the manufacturing conditions, quality stability, from the viewpoint of the mechanical strength of the resulting active material particles (such as hardness), generally, the NH ₄ ⁺ concentration It is appropriate to set it to 1 g / L or more (preferably 3 g / L or more). The pH and NH ₄ ⁺ concentration in the particle growth stage can be adjusted in the same manner as in the nucleation stage.

In a preferred embodiment, the NH ₄ ⁺ concentration in the particle growth stage is 7 g / L or less (typically 1 to 7 g / L, for example, 3 to 7 g / L). NH ₄ ⁺ concentration in the particle growth step, for example, may be a substantially the same level as NH ₄ ⁺ concentration in the nucleation stage may be lower than NH ₄ ⁺ concentration in the nucleation stage. In addition, the precipitation rate of the transition metal hydroxide is, for example, the transition metal ions contained in the liquid phase of the reaction liquid with respect to the total number of moles of transition metal ions contained in the transition metal solution supplied to the reaction liquid. It can be grasped by examining the transition of the total number of moles (total ion concentration).

  In each of the nucleation stage and the particle growth stage, the temperature of the reaction solution is preferably controlled so as to be a substantially constant temperature (for example, a predetermined temperature ± 1 ° C.) in a range of about 30 ° C. to 60 ° C. The temperature of the reaction solution may be approximately the same in the nucleation stage and the particle growth stage. Moreover, it is preferable to maintain the reaction liquid and the atmosphere in the reaction tank in a non-oxidizing atmosphere through the nucleation stage and the particle growth stage. Further, the total number of moles (total ion concentration) of Ni ions, Co ions and Mn ions contained in the reaction solution is set to, for example, about 0.5 to 2.5 mol / L through the nucleation stage and the particle growth stage. It is preferably about 1.0 to 2.2 mol / L. The transition metal solution may be replenished (typically continuously supplied) in accordance with the deposition rate of the transition metal hydroxide so that the total ion concentration is maintained. The amounts of Ni ions, Co ions, and Mn ions contained in the reaction solution correspond to the composition of the active material particles as the target product (that is, the molar ratio of Ni, Co, and Mn in the LiNiCoMn oxide constituting the active material particles). It is preferable to set the quantity ratio.

≪Mixing process≫
In a preferred embodiment, the transition metal hydroxide particles thus produced (here, composite hydroxide particles containing Ni, Co and Mn) are separated from the reaction solution, washed and dried. Then, the transition metal hydroxide particles and the lithium compound are mixed at a desired quantitative ratio to prepare an unfired mixture (mixing step). In this mixing step, typically, the quantitative ratio corresponding to the composition of the active material particles as the target (that is, the molar ratio of Li, Ni, Co, Mn in the LiNiCoMn oxide constituting the active material particles) Li compound and transition metal hydroxide particles are mixed. As the lithium compound, lithium compounds that can be converted into oxides upon heating, such as lithium carbonate and lithium hydroxide, can be preferably used.

≪Baking process≫
And the said mixture is baked and the active material particle of a hole hollow structure is obtained (baking process). This firing step is typically performed in an oxidizing atmosphere (for example, in the air). The firing temperature in this firing step can be set to 700 ° C. to 1100 ° C., for example. It is preferable that the maximum baking temperature be 800 ° C or higher (preferably 800 ° C to 1100 ° C, for example, 800 ° C to 1050 ° C). According to the maximum firing temperature within this range, the sintering reaction of the primary particles of the lithium transition metal oxide (preferably Ni-containing Li oxide, here LiNiCoMn oxide) can proceed appropriately. Preferably, the fired product is crushed and sieved after the firing step to adjust the particle size of the active material particles.

  In a preferred embodiment, the mixture is calcined at a temperature T1 of 700 ° C. to 900 ° C. (that is, 700 ° C. ≦ T1 ≦ 900 ° C., for example, 700 ° C. ≦ T1 ≦ 800 ° C., typically 700 ° C. ≦ T1 <800 ° C.). A second firing step, and a result obtained through the first firing step is fired at a temperature T2 of 800 ° C. to 1100 ° C. (ie, 800 ° C. ≦ T2 ≦ 1100 ° C., for example, 800 ° C. ≦ T2 ≦ 1050 ° C.) And a firing step. By this, the active material particle of a perforated hollow structure can be formed more efficiently. T1 and T2 are preferably set so that T1 <T2.

  The first firing stage and the second firing stage are performed continuously (for example, by holding the mixture at the first firing temperature T1, and subsequently raising the temperature to the second firing temperature T2 and maintaining the temperature at T2. Alternatively, after maintaining at the first firing temperature T1, it is once cooled (for example, cooled to room temperature) and, if necessary, crushed and sieved before being subjected to the second firing stage. Good.

In the technique disclosed herein, the first firing stage is a temperature T1 in which the sintering reaction of the target lithium transition metal oxide proceeds and is lower than the melting point and lower than the second firing stage. It can be grasped as a stage for firing. Further, the second firing stage should be understood as a stage in which the sintering reaction of the target lithium transition metal oxide proceeds and the firing is performed at a temperature T2 that is lower than the melting point and higher than the first firing stage. Can do. It is preferable to provide a temperature difference of 50 ° C. or higher (typically 100 ° C. or higher, for example, 150 ° C. or higher) between T1 and T2.
As described above, a preferable example of a positive electrode active material having a DBP absorption amount A [mL / 100 g] of 30 mL / 100 g or more, here, perforated hollow active material particles can be produced.

The operation of preparing the positive electrode mixture layer forming composition by mixing the positive electrode active material having the DBP absorption amount A [mL / 100 g] of 30 mL / 100 g or more and the prepared conductive material dispersion is performed by dispersing the conductive material. It can be carried out in the same manner as when the liquid is prepared.
At this time, in the composition for forming a positive electrode mixture layer, the positive electrode active material occupies the total solid content in the composition for forming a positive electrode mixture layer, where A is the DBP absorption amount [mL / 100 g] of the positive electrode active material. The mass ratio of the conductive material is x [mass%], the DBP absorption amount [mL / 100 g] of the conductive material is B, and the mass of the conductive material in the total solid content in the composition for forming a positive electrode mixture layer Calculated value a obtained by the following formula (1) when the ratio is y [mass%]:
a = yB / xA (1);
The DBP absorption amount A, the mass ratio x, the DBP absorption amount B, and the mass ratio y are determined so that the value becomes 0.28 to 0.47.
When the calculated value a of the above formula (1) is too larger than 0.47, the amount of the positive electrode active material in the positive electrode mixture layer is small (that is, the entire surface area (reaction area) of the positive electrode active material is small). ) Occlusion and release of charge carriers (lithium ions) during charge / discharge are not performed well, and there is a risk that reaction resistance will increase, and a sufficient proportion of the conductive material in the positive electrode mixture layer is sufficient. May not be obtained, and as a result, high output may not be obtained.
On the other hand, when the calculated value a of the above formula (1) is too smaller than 0.28, the amount of the conductive material in the positive electrode mixture layer is small, so that more dispersant is adsorbed on the surface of the positive electrode active material. There is a risk of it. As a result, the surface area (reaction area) of the entire positive electrode active material is reduced, and charge carriers are not occluded and released during charge / discharge, which may increase reaction resistance.

  Solid content concentration of positive electrode mixture layer forming composition at this time: solid content concentration [mass%] = (mass of total solid content in composition) / (total mass of total solid content and solvent in composition) Is approximately 50% by mass to 70% by mass (for example, 55% by mass to 60% by mass). The composition according to the present embodiment has a higher solid content concentration than a conventional composition (for example, a solid content concentration of about 45% by mass). Therefore, when the positive electrode mixture layer is formed by drying the composition. The total amount of heat required is small and the time required for drying is shortened. As a result, a drying facility (for example, a drying furnace) smaller than conventional ones can be used, and cost reduction can be realized.

  Next, the positive electrode mixture layer forming step (S30) will be described. In the positive electrode mixture layer forming step, the prepared positive electrode mixture layer forming composition is applied to the surface of the positive electrode current collector, and the composition applied on the positive electrode current collector is dried to obtain the positive electrode mixture material. Forming a layer is included.

As the positive electrode current collector, a conductive member made of a metal having good conductivity is preferably used, like the current collector used in the positive electrode of a conventional lithium ion secondary battery. For example, an aluminum material or an alloy material mainly composed of an aluminum material can be used. The shape of the positive electrode current collector can vary depending on the shape of the lithium ion secondary battery and the like, and thus is not particularly limited, and may be various forms such as a rod shape, a plate shape, a sheet shape, and a foil shape.
As a method of applying the composition for forming a positive electrode mixture layer to the positive electrode current collector, a technique similar to a conventionally known method can be appropriately employed. For example, the composition can be suitably applied to the positive electrode current collector by using an appropriate application device such as a slit coater, a die coater, or a gravure coater.

And the positive mix layer can be formed by drying the said composition apply | coated on the positive electrode electrical power collector.
The drying temperature at the time of drying the composition applied to the positive electrode current collector is, for example, about 100 ° C. to 180 ° C. (for example, 150 ° C.), and the drying time is, for example, about 10 seconds to 120 seconds (for example, 90 ° C.). Second). By removing a solvent (for example, NMP) from the composition, a positive electrode mixture layer is formed on the surface of the positive electrode current collector. In addition, after a positive electrode compound-material layer is formed, you may roll (press) as needed. As a rolling method, conventionally known rolling methods such as a roll press method and a flat plate press method can be employed.

The positive electrode produced as described above contains a positive electrode active material having a DBP absorption amount [mL / 100 g] of 30 mL / 100 g or more, and the DBP absorption amount [mL / 100 g] of the positive electrode active material is A. The mass ratio of the positive electrode active material to the total solid content in the composite material layer is x [mass%], the DBP absorption amount [mL / 100 g] of the conductive material is B, and the total solid content in the positive electrode material layer is Calculated value a obtained by the following formula (1) when the mass ratio of the conductive material in the minute is y [mass%]:
a = yB / xA (1);
Is 0.28 to 0.47, it can be a lithium ion secondary battery (non-aqueous electrolyte secondary battery) with reduced reaction resistance and improved output performance.

Next, the negative electrode provided in the lithium ion secondary battery (nonaqueous electrolyte secondary battery) according to the present embodiment will be described. The negative electrode includes a negative electrode current collector and a negative electrode mixture layer including at least a negative electrode active material formed on the negative electrode current collector.
Examples of the negative electrode active material include a particulate carbon material containing at least a graphite structure (layered structure), a lithium transition metal composite oxide (for example, a lithium titanium composite oxide such as Li ₄ Ti ₅ O ₁₂ ). ), Lithium transition metal composite nitride, etc. Examples of the carbon material include natural graphite, artificial graphite (artificial graphite), non-graphitizable carbon (hard carbon), graphitizable carbon (soft carbon), and the like. Alternatively, the surface of the negative electrode active material may be coated with an amorphous carbon film, for example, at least a part of the negative electrode active material is coated with an amorphous carbon film by mixing and baking the negative electrode active material. A negative electrode active material can be obtained.

The negative electrode mixture layer may contain any component such as a binder (binder) and a thickener as necessary in addition to the negative electrode active material.
As said binder, the thing similar to the binder used for the negative electrode of a general lithium ion secondary battery can be employ | adopted suitably. For example, when an aqueous paste composition is used to form the negative electrode mixture layer, a polymer material that is dissolved or dispersed in water can be preferably used. Polymer materials that disperse in water (water dispersible) include rubbers such as styrene butadiene rubber (SBR) and fluorine rubber; fluorine resins such as polyethylene oxide (PEO) and polytetrafluoroethylene (PTFE); vinyl acetate Examples thereof include copolymers.
Here, the “aqueous paste-like composition” is a concept indicating a composition using water or a mixed solvent mainly composed of water (aqueous solvent) as the predetermined solvent (dispersion medium). As the solvent other than water constituting the mixed solvent, one or more organic solvents (lower alcohol, lower ketone, etc.) that can be uniformly mixed with water can be appropriately selected and used.

  Moreover, as the thickener, a polymer material that is dissolved or dispersed in water or a solvent (organic solvent) can be employed. Examples of water-soluble (water-soluble) polymer materials include cellulose polymers such as carboxymethyl cellulose (CMC), methyl cellulose (MC), cellulose acetate phthalate (CAP), and hydroxypropylmethyl cellulose (HPMC); polyvinyl alcohol ( PVA); and the like.

  The negative electrode mixture layer is formed, for example, as a paste-like negative electrode mixture layer in which the negative electrode active material and other optional components (binder, thickener, etc.) are dispersed in an appropriate solvent (for example, water). By preparing (preparing, purchasing, etc.) the composition, applying (applying) the composition to the surface of the negative electrode current collector, drying the composition, and then pressing (compressing) as necessary. A negative electrode mixture layer is formed. Thereby, a negative electrode provided with a negative electrode current collector and a negative electrode mixture layer can be produced. As the negative electrode current collector, a conductive member made of a metal having good conductivity is preferably used as in the case of the current collector used in the negative electrode of a conventional lithium ion secondary battery. For example, copper, nickel, or an alloy containing these as a main component can be used.

Hereinafter, although one form of the lithium ion secondary battery constructed | assembled using the said positive electrode and negative electrode is demonstrated with reference to drawings, it is not intending to limit this invention to this embodiment. In the following embodiment, a lithium ion secondary battery having a configuration in which a wound electrode body and an electrolyte are housed in a rectangular battery case will be described as an example.
In addition, in the following drawings, the same code | symbol is attached | subjected to the member and site | part which show | plays the same effect | action, and the overlapping description may be abbreviate | omitted. Moreover, the dimensional relationship (length, width, thickness, etc.) in each drawing does not necessarily reflect the actual dimensional relationship.

FIG. 1 is a perspective view schematically showing a lithium ion secondary battery (nonaqueous electrolyte secondary battery) 10 according to the present embodiment. FIG. 2 is a longitudinal sectional view taken along line II-II in FIG.
As shown in FIG. 1, the lithium ion secondary battery 10 according to this embodiment includes a battery case 15 made of metal (a resin or a laminate film is also suitable). The case (outer container) 15 includes a flat cuboid case main body 30 having an open upper end, and a lid body 25 that closes the opening 20. The lid body 25 seals the opening 20 of the case main body 30 by welding or the like. On the upper surface of the case 15 (that is, the lid body 25), a positive electrode terminal 60 electrically connected to the positive electrode sheet (positive electrode) 64 of the wound electrode body 50 and a negative electrode terminal electrically connected to the negative electrode sheet 84 of the electrode body. 80 is provided. In addition, the lid 25 is provided with a safety valve 40 for discharging the gas generated inside the case 15 to the outside of the case 15 when the battery is abnormal, as in the case of the conventional lithium ion secondary battery. . In the case 15, the positive electrode sheet 64 and the negative electrode sheet 84 are laminated together with a total of two separator sheets 95 and wound, and then the obtained wound body is crushed from the side direction and ablated. A flat wound electrode body 50 and an electrolyte (for example, a non-aqueous electrolyte) are accommodated.

  At the time of the above lamination, as shown in FIG. 2, the positive electrode mixture layer non-formed portion of the positive electrode sheet 64 (that is, the portion where the positive electrode current collector 62 is exposed without forming the positive electrode mixture layer 66) and the negative electrode sheet The negative electrode composite material layer non-formed portion 84 (that is, the portion where the negative electrode current collector 82 is exposed without forming the negative electrode composite material layer 90) protrudes from both sides in the width direction of the separator sheet 95. And the negative electrode sheet 84 are overlapped with a slight shift in the width direction. As a result, in the lateral direction with respect to the winding direction of the wound electrode body 50, the electrode mixture layer non-forming portions of the positive electrode sheet 64 and the negative electrode sheet 84 are respectively wound core portions (that is, the positive electrode mixture layer forming portion of the positive electrode sheet 64. And a portion where the negative electrode mixture layer forming portion of the negative electrode sheet 84 and the two separator sheets 95 are wound tightly) protrude outward. The positive electrode terminal 60 is joined to the protruding portion on the positive electrode side, and the positive electrode sheet 64 and the positive electrode terminal 60 of the wound electrode body 50 formed in the flat shape are electrically connected. Similarly, the negative electrode terminal 80 is joined to the negative electrode side protruding portion, and the negative electrode sheet 84 and the negative electrode terminal 80 are electrically connected. The positive and negative electrode terminals 60 and 80 and the positive and negative electrode current collectors 62 and 82 can be joined by, for example, ultrasonic welding, resistance welding, or the like.

As said electrolyte, the thing similar to the non-aqueous electrolyte conventionally used for a lithium ion secondary battery can be used without limitation. Such a nonaqueous electrolytic solution typically has a composition in which a supporting salt is contained in a suitable nonaqueous solvent (organic solvent). Examples of the non-aqueous solvent include one or more selected from ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), and the like. Can be used. Further, as the supporting salt (supporting electrolyte), for _example, it can be used lithium salts such as LiPF 6, LiBF _4. Further, difluorophosphate (LiPO ₂ F ₂ ) or lithium bisoxalate borate (LiBOB) may be dissolved in the non-aqueous electrolyte.
Moreover, as said separator sheet, a conventionally well-known thing can be especially used without a restriction | limiting. For example, a porous sheet made of resin (a microporous resin sheet) can be preferably used. A porous polyolefin resin sheet such as polyethylene (PE) or polypropylene (PP) is preferred. For example, a PE sheet, a PP sheet, a sheet having a three-layer structure (PP / PE / PP structure) in which PP layers are laminated on both sides of the PE layer, and the like can be suitably used.

  EXAMPLES Examples relating to the present invention will be described below, but the present invention is not intended to be limited to those shown in the examples.

[Preparation of positive electrode active material]
As the positive electrode active material in the following experiments, active material particles having a perforated hollow structure produced as follows were used.
Ion exchange water is put into a reaction tank set at a temperature of 40 ° C., and nitrogen gas is circulated while stirring to replace the ion exchange water with nitrogen, and oxygen gas (O ₂ ) concentration in the reaction tank is 2 Adjusted to 0.0% non-oxidizing atmosphere. Next, a 25% aqueous sodium hydroxide solution and 25% aqueous ammonia were added so that the pH measured on the basis of the liquid temperature of 25 ° C. was 12.5 and the NH ₄ ⁺ concentration in the liquid was 5 g / L.

  In nickel sulfate, cobalt sulfate, and manganese sulfate, the molar ratio of Ni: Co: Mn is 0.33: 0.33: 0.33, and the total molar concentration of these metal elements is 1.8 mol / L. A mixed aqueous solution was prepared by dissolving in water. By supplying this mixed aqueous solution, 25% NaOH aqueous solution and 25% aqueous ammonia into the reaction vessel at a constant rate, the reaction solution was controlled to pH 12.5 and ammonia concentration 5 g / L, while the NiCoMn was removed from the reaction solution. The composite hydroxide was crystallized (nucleation stage).

When 2 minutes and 30 seconds had elapsed from the start of the supply of the mixed aqueous solution, the supply of the 25% NaOH aqueous solution was stopped. The mixed aqueous solution and 25% aqueous ammonia were continuously supplied at a constant rate. After the pH of the reaction solution dropped to 11.6, the supply of 25% aqueous NaOH solution was resumed. Then, while controlling the reaction solution to pH 11.6 and the ammonia concentration described later, the operation of supplying the above mixed aqueous solution, 25% NaOH aqueous solution and 25% ammonia water was continued for 4 hours to grow NiCoMn composite hydroxide particles. (Particle growth stage). The product was then removed from the reaction vessel, washed with water and dried. In this manner, composite hydroxide particles having a composition represented by Ni _0.33 Co _0.33 Mn _0.33 (OH) _{2 + α} (where α is 0 ≦ α ≦ 0.5) were obtained. .

The composite hydroxide particles were heat-treated at 150 ° C. for 12 hours in an air atmosphere. Next, Li ₂ CO ₃ as the lithium source and the composite hydroxide particles are combined into the number of moles of lithium (M _Li ) and the total number of moles of Ni, Co and Mn constituting the composite hydroxide (M _Me ). And the mixture (M _Li : M _Me ) was 1.15: 1. This mixture was fired at 760 ° C. for 4 hours (first firing stage), and then fired at 950 ° C. for 10 hours (second firing stage). Thereafter, the fired product was crushed and sieved. In this manner, an active material particle sample having a composition represented by Li _1.15 Ni _0.33 Co _0.33 Mn _0.33 O ₂ was obtained.

  In the above active material particle sample preparation process, by adjusting the conditions of the reaction liquid used when preparing the composite hydroxide particles, more specifically, the ammonia concentration of the reaction liquid is adjusted to 1 to 15 g in the particle growth stage. By maintaining (controlling) each at a different concentration between / mL, the DBP absorption amount x by the above-described method is 43 mL / 100 g (sample S1), 39 mL / 100 g (sample S2), and 38 mL / 100 g (sample S3), respectively. , 37 mL / 100 g (sample S4), 36 mL / 100 g (sample S5), 34 mL / 100 g (sample S6), and 32 mL / 100 g (sample S7) were produced.

[Production of lithium ion secondary battery]
<Example 1>
Active material particles (DBP absorption A: 43 mL / 100 g) of the sample S1 as the positive electrode active material, acetylene black (DBP absorption B: 140 mL / 100 g) as the conductive material, PVDF as the binder, Weigh so that the mass ratio of polyvinyl butyral as a dispersant is 90: 8: 2: 0.2, and use the above materials excluding the positive electrode active material (ie, conductive material, binder, and dispersant) in the solvent NMP. A conductive material dispersion was prepared by dispersing. The conductive material dispersion and the weighed positive electrode active material were mixed and kneaded to prepare a paste-like composition for forming a positive electrode mixture layer. The composition was applied onto a positive electrode current collector (aluminum foil) having a thickness of 15 μm at an application amount of 10 mg / cm ² to volatilize NMP, whereby a positive electrode mixture layer was formed on the positive electrode current collector. A positive electrode sheet was produced. At this time, the calculated value a of the above formula (1) was 0.29.
On the other hand, natural graphite as a negative electrode active material, SBR as a binder, and CMC as a thickener are weighed so that the mass ratio is 98: 1: 1, and these materials are dispersed in ion-exchanged water. Thus, a paste-like composition for forming a negative electrode mixture layer was prepared. A negative electrode sheet in which a negative electrode mixture layer is formed on the negative electrode current collector is prepared by coating the composition on a negative electrode current collector (copper foil) having a thickness of 10 μm and volatilizing ion-exchanged water. did.
Then, the prepared positive electrode sheet and negative electrode sheet are placed opposite to each other with a separator sheet (polypropylene / polyethylene composite porous membrane) interposed therebetween (laminated), and this is accommodated in a laminate type case (laminate film) together with the electrolyte. As a result, a lithium ion secondary battery (rated capacity 150 mAh) according to Example 1 was produced. As the electrolytic solution, a solution obtained by dissolving 1 mol / L LiPF ₆ in a mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 3: 7 was used.

<Example 2>
The mass ratio of the sample S2 (DBP absorption A: 39 mL / 100 g), acetylene black (DBP absorption B: 142 mL / 100 g), PVDF, and polyvinyl butyral is 90.5: 7.5: 2: 0. The conductive material dispersion liquid according to Example 2 was prepared by weighing the mixture so as to be .2 and dispersing the above materials excluding the positive electrode active material in the solvent NMP. The composition for forming a positive electrode mixture layer according to Example 2 was prepared by mixing and kneading the conductive material dispersion according to Example 2 and the weighed positive electrode active material. A lithium ion secondary battery according to Example 2 was produced in the same manner as in Example 1 except that the composition for forming a positive electrode mixture layer according to Example 2 was used. At this time, the calculated value a of the above formula (1) was 0.3.
<Example 3>
The mass ratio of the sample S3 (DBP absorption amount A: 38 mL / 100 g), acetylene black (DBP absorption amount B: 175 mL / 100 g), PVDF, and polyvinyl butyral is 93: 5: 2: 0.2. Thus, the above-mentioned materials excluding the positive electrode active material were dispersed in a solvent NMP to prepare a conductive material dispersion according to Example 3. The composition for forming a positive electrode mixture layer according to Example 3 was prepared by mixing and kneading the conductive material dispersion according to Example 3 and the weighed positive electrode active material. A lithium ion secondary battery according to Example 3 was produced in the same manner as in Example 1 except that the composition for forming a positive electrode mixture layer according to Example 3 was used. At this time, the calculated value a of the above formula (1) was 0.25.
<Example 4>
The mass ratio of the sample S3 (DBP absorption amount A: 38 mL / 100 g), acetylene black (DBP absorption amount B: 175 mL / 100 g), PVDF, and polyvinyl butyral is 90: 8: 2: 0.2. Thus, the above-mentioned materials excluding the positive electrode active material were dispersed in a solvent NMP to prepare a conductive material dispersion according to Example 4. The composition for forming a positive electrode mixture layer according to Example 4 was prepared by mixing and kneading the conductive material dispersion according to Example 4 and the weighed positive electrode active material. A lithium ion secondary battery according to Example 4 was produced in the same manner as in Example 1 except that the composition for forming a positive electrode mixture layer according to Example 4 was used. At this time, the calculated value a of the above formula (1) was 0.41.
<Example 5>
The mass ratio of the sample S3 (DBP absorption A: 38 mL / 100 g), acetylene black (DBP absorption B: 175 mL / 100 g), PVDF, and polyvinyl butyral is 88: 10: 2: 0.2. Thus, the above material excluding the positive electrode active material was dispersed in the solvent NMP to prepare a conductive material dispersion according to Example 5. The composition for forming a positive electrode mixture layer according to Example 5 was prepared by mixing and kneading the conductive material dispersion according to Example 5 and the weighed positive electrode active material. A lithium ion secondary battery according to Example 5 was produced in the same manner as in Example 1 except that the composition for forming a positive electrode mixture layer according to Example 5 was used. At this time, the calculated value a of the above formula (1) was 0.52.

<Example 6>
The mass ratio of the sample S3 (DBP absorption amount A: 38 mL / 100 g), acetylene black (DBP absorption amount B: 175 mL / 100 g), PVDF, and polyvinyl butyral is 85: 13: 2: 0.2. Thus, the above material excluding the positive electrode active material was dispersed in the solvent NMP to prepare a conductive material dispersion according to Example 6. The composition for forming a positive electrode mixture layer according to Example 6 was prepared by mixing and kneading the conductive material dispersion according to Example 6 and the weighed positive electrode active material. A lithium ion secondary battery according to Example 6 was produced in the same manner as in Example 1 except that the composition for forming a positive electrode mixture layer according to Example 6 was used. At this time, the calculated value a of the above formula (1) was 0.7.
<Example 7>
The mass ratio of sample S4 (DBP absorption A: 37 mL / 100 g), acetylene black (DBP absorption B: 135 mL / 100 g), PVDF, and polyvinyl butyral is 91: 7: 2: 0.2. Thus, the above material excluding the positive electrode active material was dispersed in the solvent NMP to prepare a conductive material dispersion according to Example 7. The composition for forming a positive electrode mixture layer according to Example 7 was prepared by mixing and kneading the conductive material dispersion according to Example 7 and the weighed positive electrode active material. A lithium ion secondary battery according to Example 7 was produced in the same manner as in Example 1 except that the composition for forming a positive electrode mixture layer according to Example 7 was used. At this time, the calculated value a of the above formula (1) was 0.28.
<Example 8>
The mass ratio of the sample S4 (DBP absorption amount A: 37 mL / 100 g), acetylene black (DBP absorption amount B: 135 mL / 100 g), PVDF, and polyvinyl butyral is 90.5: 7.5: 2: 0. The conductive material dispersion according to Example 8 was prepared by weighing the mixture so as to be .2 and dispersing the above-described materials excluding the positive electrode active material in the solvent NMP. The composition for forming a positive electrode mixture layer according to Example 8 was prepared by mixing and kneading the conductive material dispersion according to Example 8 and the weighed positive electrode active material. A lithium ion secondary battery according to Example 8 was produced in the same manner as in Example 1 except that the composition for forming a positive electrode mixture layer according to Example 8 was used. At this time, the calculated value a of the above formula (1) was 0.3.
<Example 9>
The mass ratio of the sample S5 (DBP absorption amount A: 36 mL / 100 g), acetylene black (DBP absorption amount B: 140 mL / 100 g), PVDF, and polyvinyl butyral is 90: 8: 2: 0.2. Thus, the above material excluding the positive electrode active material was dispersed in a solvent NMP to prepare a conductive material dispersion according to Example 9. The composition for forming a positive electrode mixture layer according to Example 9 was prepared by mixing and kneading the conductive material dispersion according to Example 9 and the weighed positive electrode active material. A lithium ion secondary battery according to Example 9 was produced in the same manner as in Example 1 except that the composition for forming a positive electrode mixture layer according to Example 9 was used. At this time, the calculated value a of the above formula (1) was 0.35.

<Example 10>
The mass ratio of the sample S6 (DBP absorption A: 34 mL / 100 g), acetylene black (DBP absorption B: 140 mL / 100 g), PVDF, and polyvinyl butyral is 88: 10: 2: 0.2. Thus, the above material excluding the positive electrode active material was dispersed in a solvent NMP to prepare a conductive material dispersion according to Example 10. The composition for forming a positive electrode mixture layer according to Example 10 was prepared by mixing and kneading the conductive material dispersion according to Example 10 and the weighed positive electrode active material. A lithium ion secondary battery according to Example 10 was produced in the same manner as in Example 1 except that the composition for forming a positive electrode mixture layer according to Example 10 was used. At this time, the calculated value a of the above formula (1) was 0.47.
<Example 11>
The mass ratio of the sample S7 (DBP absorption amount A: 32 mL / 100 g), acetylene black (DBP absorption amount B: 140 mL / 100 g), PVDF, and polyvinyl butyral is 90: 8: 2: 0.2. Thus, the above-mentioned materials excluding the positive electrode active material were dispersed in a solvent NMP to prepare a conductive material dispersion according to Example 11. The composition for forming a positive electrode mixture layer according to Example 11 was prepared by mixing and kneading the conductive material dispersion according to Example 11 and the weighed positive electrode active material. A lithium ion secondary battery according to Example 11 was produced in the same manner as in Example 1 except that the composition for forming a positive electrode mixture layer according to Example 11 was used. At this time, the calculated value a of the above formula (1) was 0.39.
<Example 12>
Mass ratio of Li _1.15 Ni _0.33 Co _0.33 Mn _0.33 O ₂ (DBP absorption A: 28 mL / 100 g), acetylene black (DBP absorption B: 175 mL / 100 g), PVDF, and polyvinyl butyral as a positive electrode active material Was measured to be 90.5: 7.5: 2: 0.2, and the above-mentioned materials excluding the positive electrode active material were dispersed in the solvent NMP to prepare a conductive material dispersion according to Example 12. The composition for forming a positive electrode mixture layer according to Example 12 was prepared by mixing and kneading the conductive material dispersion according to Example 12 and the weighed positive electrode active material. A lithium ion secondary battery according to Example 12 was produced in the same manner as in Example 1 except that the composition for forming a positive electrode mixture layer according to Example 12 was used. At this time, the calculated value a of the above formula (1) was 0.52.
<Example 13>
The mass ratio of Li _1.15 Ni _0.33 Co _0.33 Mn _0.33 O ₂ (DBP absorption A: 28 mL / 100 g), acetylene black (DBP absorption B: 175 mL / 100 g), PVDF, and polyvinyl butyral is 93: 5: 2: Weighed to 0.2, and dispersed the above materials excluding the positive electrode active material in the solvent NMP to prepare a conductive material dispersion according to Example 13. The composition for forming a positive electrode mixture layer according to Example 13 was prepared by mixing and kneading the conductive material dispersion according to Example 13 and the weighed positive electrode active material. A lithium ion secondary battery according to Example 13 was produced in the same manner as in Example 1 except that the composition for forming a positive electrode mixture layer according to Example 13 was used. At this time, the calculated value a of the above formula (1) was 0.34. Table 1 shows the configurations of the lithium ion secondary batteries according to Examples 1 to 13. In Table 1, the dispersant is an addition amount (% by mass) with respect to the total amount of the positive electrode active material, the conductive material, and the binder.

[Conditioning process]
The lithium ion secondary batteries according to Examples 1 to 13 were charged with a constant current (CC) for 3 hours at a rate of 1/3 C (1 C is a current value that can be fully charged and discharged in 1 hour). Then, the operation of charging to 4.1 V at a rate of 1/3 C and the operation of discharging to 3 V at a rate of 1/3 C were repeated three times.

[IV resistance measurement test]
About the secondary battery concerning each example after the said conditioning process, IV resistance (reaction resistance) was measured. The IV resistance was measured as follows. That is, the secondary battery according to each example is charged with a constant current of 3 V to 1 C, adjusted to a SOC (State of Charge) 60%, and then at a temperature of −30 ° C. and 10 C (high rate discharge). A constant current (CC) discharge was performed for 2 seconds, and IV resistance [mΩ] was determined from the slope of the first-order approximation line of the current (I) -voltage (V) plot value. The measurement results of the IV resistance of the secondary batteries according to the above examples are shown in Table 1 and FIG.

As shown in Table 1 and FIG. 4, in the secondary batteries according to Example 3, Example 5, Example 6, and Example 12, the IV resistance (reaction resistance) is increased as compared with the secondary batteries according to other examples. It was confirmed. That is, it was confirmed that when the value of the calculated value a of the above formula (1) is 0.28 to 0.47, the IV resistance is reduced and good performance (that is, high output) is exhibited.
In the secondary battery according to Example 13, the value of the calculated value a of the above formula (1) is 0.34, but the DBP absorption A is as low as 28 mL / 100 g, and the surface area (reaction area) of the positive electrode active material is small. It is presumed that IV resistance has increased because it is not sufficiently secured.
From the above results, the DBP absorption amount A [mL / 100 g] is 30 mL / 100 g or more (for example, 32 mL / 100 g or more), and the calculated value a obtained by the above formula (1) is 0.28 to 0.47. It was confirmed that a certain secondary battery exhibited good battery performance with reduced IV resistance (reaction resistance).

  As mentioned above, although the specific example of this invention was demonstrated in detail, the said embodiment and Example are only illustrations and do not limit a claim. The technology described in the claims includes various modifications and changes of the specific examples illustrated above.

  The non-aqueous electrolyte secondary battery according to the present invention is suppressed in an increase in internal resistance during charge / discharge (particularly during low-temperature (for example, −30 ° C.) high-rate charge / discharge) and has excellent output performance. It can be used as a non-aqueous electrolyte secondary battery. For example, as shown in FIG. 5, it can be suitably used as a power source (drive power source) for a vehicle driving motor mounted on a vehicle 100 such as an automobile. The non-aqueous electrolyte secondary battery (lithium ion secondary battery) 10 used in the vehicle 100 may be used alone, or may be used in the form of an assembled battery that is connected in series and / or in parallel. Good.

10 Lithium ion secondary battery (non-aqueous electrolyte secondary battery)
15 Battery Case 20 Opening 25 Lid 30 Case Body 40 Safety Valve 50 Winding Electrode Body 60 Positive Terminal 62 Positive Electrode Current Collector 64 Positive Electrode Sheet (Positive Electrode)
66 Positive electrode mixture layer 80 Negative electrode terminal 82 Negative electrode current collector 84 Negative electrode sheet (negative electrode)
90 Negative electrode composite material layer 95 Separator sheet 100 Vehicle (automobile)

Claims (13)

A non-aqueous electrolyte secondary battery comprising a positive electrode and a negative electrode,
The positive electrode includes a positive electrode current collector, and a positive electrode mixture layer including at least a positive electrode active material, a conductive material, and a dispersant formed on the positive electrode current collector,
The positive electrode active material has a DBP absorption amount [mL / 100 g] based on JIS K6217-4 of 30 mL / 100 g or more,
Here, the DBP absorption amount [mL / 100 g] of the positive electrode active material is A, the mass ratio of the positive electrode active material in the total solid content in the positive electrode mixture layer is x [mass%], and
When the DBP absorption amount [mL / 100 g] of the conductive material is B and the mass ratio of the conductive material to the total solid content in the positive electrode mixture layer is y [mass%], the following formula (1) Calculated value a obtained by:
a = yB / xA (1);
Is a nonaqueous electrolyte secondary battery.   2. The nonaqueous electrolyte secondary battery according to claim 1, wherein the conductive material is carbon black having a DBP absorption amount [mL / 100 g] B of 130 mL / 100 g to 180 mL / 100 g.   The non-aqueous electrolyte secondary battery according to claim 2, wherein the conductive material is acetylene black.   When the conductive material contained in the positive electrode mixture layer is 100% by mass, the mass ratio of the dispersant contained in the positive electrode mixture layer is 1% by mass or more and 5% by mass or less. The nonaqueous electrolyte secondary battery according to any one of claims 1 to 3.   The dispersant is at least one selected from a polymer compound having a hydrophobic group and a hydrophilic group, an anionic compound having a polar functional group, or a cationic compound. The nonaqueous electrolyte secondary battery according to any one of 4.   The non-aqueous electrolyte secondary battery according to claim 5, wherein the polymer compound is polyvinyl butyral and / or polyvinyl pyrrolidone. A positive electrode in which a positive electrode mixture layer containing at least a positive electrode active material and a conductive material is formed on the positive electrode current collector; and a negative electrode in which a negative electrode mixture layer containing at least a negative electrode active material is formed on the negative electrode current collector. A non-aqueous electrolyte secondary battery manufacturing method comprising:
Preparing a conductive material dispersion obtained by dispersing the conductive material, a dispersant, and a binder in a predetermined solvent;
Paste positive electrode mixture formed by mixing the prepared conductive material dispersion and a positive electrode active material having a DBP absorption amount [mL / 100 g] based on JIS K6217-4 of 30 mL / 100 g or more as the positive electrode active material. Preparing a composition for layer formation;
Forming the positive electrode mixture layer by applying the prepared composition for forming a positive electrode mixture layer on the surface of the positive electrode current collector and drying the composition;
Including
Here, the DBP absorption amount [mL / 100 g] of the positive electrode active material is A, and the mass ratio of the positive electrode active material in the total solid content in the composition for forming a positive electrode mixture layer is x [mass%]. ,and,
When the DBP absorption amount [mL / 100 g] of the conductive material is B, and the mass ratio of the conductive material to the total solid content in the composition for forming a positive electrode mixture layer is y [mass%] Calculated value a obtained by equation (1):
a = yB / xA (1);
The nonaqueous electrolyte secondary battery is characterized in that the DBP absorption amount A, the mass ratio x, the DBP absorption amount B, and the mass ratio y are determined so as to be 0.28 to 0.47. Manufacturing method.   The manufacturing method according to claim 7, wherein carbon black having a DBP absorption amount B [mL / 100 g] of 130 mL / 100 g to 180 mL / 100 g is used as the conductive material.   The manufacturing method according to claim 8, wherein acetylene black is used as the conductive material.   When the conductive material contained in the conductive material dispersion is 100% by mass, the dispersant is such that the mass ratio of the dispersant contained in the conductive material dispersion is 1% by mass to 5% by mass. The manufacturing method according to any one of claims 7 to 9, wherein the amount of the is adjusted.   11. The method according to claim 7, wherein at least one selected from a polymer compound having a hydrophobic group and a hydrophilic group, an anionic compound having a polar functional group, or a cationic compound is used as the dispersant. The production method according to item.   The production method according to claim 11, wherein polyvinyl butyral and / or polyvinyl pyrrolidone is used as the polymer compound.   The non-aqueous electrolyte secondary battery according to any one of claims 1 to 6 or the production method according to any one of claims 7 to 12, wherein the non-aqueous electrolyte secondary battery is used as a drive power source for a vehicle. Non-aqueous electrolyte secondary battery.

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