JP2015103306A - Positive electrode active material and nonaqueous electrolyte secondary battery including the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a positive electrode active material for nonaqueous electrolyte secondary batteries which allows a current interruption device mechanism to work appropriately while maintaining high battery performance.SOLUTION: A positive electrode active material for nonaqueous electrolyte secondary batteries is one comprising a granular complex oxide including at least cobalt (Co) as a constituent metal element. The complex oxide particle has a higher concentration of Co in the surface part compared to the core part. In a particle size distribution of the complex oxide particles, the ratio (D10/D50) of D10 size representing a cumulative 10%-particle size determined by cumulation from a smaller side of the particle size to D50 size representing a cumulative 50%-particle size satisfies (D10/D50)≤0.75.

Description

  The present invention relates to a positive electrode active material and a non-aqueous electrolyte secondary battery including the positive electrode active material.

  Lithium ion secondary batteries (for example, Patent Document 1) and other non-aqueous electrolyte secondary batteries are becoming increasingly important as power sources for vehicles or as power sources for personal computers and portable terminals. In particular, a lithium ion secondary battery that is lightweight and obtains a high energy density is preferably used as a high-output power source mounted on a vehicle. When such a nonaqueous electrolyte secondary battery is overcharged, excessive charge carriers are released from the positive electrode, and excessive charge carriers are inserted into the negative electrode. For this reason, both the positive electrode and the negative electrode are thermally unstable. When both the positive electrode and the negative electrode become thermally unstable, the organic solvent of the electrolytic solution is eventually decomposed, and an exothermic reaction occurs, thereby impairing the stability of the battery.

  To solve this problem, for example, the battery case is equipped with a current interruption mechanism that interrupts charging when the gas pressure inside the battery exceeds a predetermined pressure, and gas is generated when a predetermined overcharge state is reached in the electrolyte. A non-aqueous electrolyte secondary battery to which a gas generating agent is added is disclosed. As such a gas generating agent, for example, cyclohexylbenzene (CHB) or biphenyl (BP) is used. CHB and BP activate the polymerization reaction during overcharge and generate hydrogen gas. Thereby, the pressure in a battery case becomes high, an electric current interruption mechanism act | operates, and an overcharge electric current is interrupted | blocked.

JP 2003-059489 A

  By the way, as a positive electrode active material of a lithium ion secondary battery, an oxide (lithium transition metal composite oxide) containing lithium (Li) and a transition metal element (M: for example, nickel or cobalt) as constituent metal elements is widely used. It has been. The present inventor is considering increasing the Li / M ratio in the lithium transition metal composite oxide in order to improve output characteristics. However, if the Li / M ratio in the oxide is increased, the battery resistance can be reduced, but the capacity after cycling is reduced, or the amount of gas generated during overcharge is slowed down and the operation of the current interruption mechanism is delayed. There were some events that occurred. Patent Document 1 describes that the cycle characteristics can be improved by increasing the cobalt concentration in the vicinity of the surface of the active material particles from the inside. However, simply increasing the cobalt concentration in the vicinity of the surface of the active material particles leaves room for further improvement in terms of post-cycle capacity and overcharge gas amount. The present invention solves the above problems.

  The positive electrode active material for a non-aqueous electrolyte secondary battery proposed here is a positive electrode active material made of a granular composite oxide containing at least cobalt (Co) as a constituent metal element. In the composite oxide particles, the surface portion of the particles has a higher Co concentration than the center portion. In the particle size distribution of the composite oxide particles, the ratio value (D10 / D50) of D10 diameter corresponding to 10% cumulative from the smaller particle diameter side and D50 diameter corresponding to 50% cumulative (D10 / D50) is ( D10 / D50) ≦ 0.75 is satisfied.

  The positive electrode active material having such a configuration has improved durability because the concentration of Co present in the surface portion of the composite oxide particles is increased as compared with the central portion. In the particle size distribution of the particles, the ratio value (D10 / D50) of D10 diameter corresponding to 10% volume accumulation from the smaller particle diameter side and D50 diameter corresponding to 50% volume accumulation is 0.75. Since it is below, compared with the positive electrode active material in which this (D10 / D50) ratio exceeds 0.75, durability with respect to expansion / contraction stress is high, and it is easy to make contact with a conductive material. Furthermore, since the reaction of the gas generating agent is preferably generated on the surface of the particles, a sufficient amount of gas can be generated during overcharge. For this reason, in the battery constructed using the positive electrode active material, the reliability at the time of overcharging and the high battery performance can be achieved at a high level.

  In the technology disclosed herein, the particle size ratio (D10 / D50) preferably satisfies (D10 / D50) ≦ 0.75, and more preferably satisfies (D10 / D50) ≦ 0.67. Those satisfying (D10 / D50) ≦ 0.6 are particularly preferable. If the particle size ratio (D10 / D50) is too large, the amount of gas generated during overcharging may be insufficient, or the cycle characteristics may be deteriorated. On the other hand, composite oxide particles having an excessively small particle size ratio (D10 / D50) are difficult to manufacture, and the performance improvement effect described above is slowed down, so that there is not much merit. The preferred particle size ratio (D10 / D50) is generally in the range of 0.45 ≦ (D10 / D50), preferably 0.5 ≦ (D10 / D50). For example, a composite oxide particle having a particle size ratio (D10 / D50) of 0.45 or more and 0.75 or less (particularly 0.45 or more and 0.67 or less) is said to achieve both improved cycle characteristics and manufacturability. Appropriate from the viewpoint.

  In a preferred embodiment of the positive electrode active material for a non-aqueous electrolyte two battery disclosed herein, the average Co concentration X (mol%) in the surface portion of the composite oxide particles and the average Co concentration of the entire composite oxide particles The ratio value (X / Y) with Y (mol%) satisfies 1.1 ≦ (X / Y). According to this configuration, since the Co content in the surface portion of the composite oxide particles is moderately high, the above-described effects can be more appropriately exhibited. The upper limit of the concentration ratio (X / Y) is not particularly limited, but is preferably about 1.5 or less. By setting the concentration ratio (X / Y) to (X / Y) ≦ 1.5, required durability of the positive electrode active material particles is ensured, and the performance of the nonaqueous electrolyte secondary battery is stabilized.

Preferably, the composite oxide particles have the following general formula:
_{Li x Ni a Co b Mn c} Me d O 2 (1)
It is a complex oxide shown by.
Here, Me in the formula (1) is not present or is one or two or more elements selected from a transition metal element, a typical metal element, and boron (B). X, a, b, c and d in the above formula are 0.99 ≦ x ≦ 1.12, 0.9 ≦ a + b + c + d ≦ 1.1, 1.05 ≦ x / (a + b + c + d) ≦ 1.2, 0 <A ≦ 0.5, 0 <b ≦ 0.5, 0 <c ≦ 0.5, 0 ≦ d ≦ 0.2. In particular, a real number satisfying 1.08 ≦ x / (a + b + c + d) ≦ 1.1 is preferable. The composite oxide having the composition represented by the general formula (1) is excellent in thermal stability and can realize excellent output characteristics and cycle characteristics. For this reason, the application effect of this invention can be exhibited more.

  The present invention also provides a non-aqueous electrolyte secondary battery comprising the positive electrode active material as described above. That is, the non-aqueous electrolyte secondary battery of the present invention includes any positive electrode active material and a positive electrode including a conductive material disclosed herein, a negative electrode including a negative electrode active material, and an interposition between the positive electrode and the negative electrode. An electrode body including a separator, a battery case that houses the electrode body, an external terminal that is provided in the battery case and connected to the electrode body, and that is housed in the battery case and has a predetermined voltage or higher When the internal pressure of the battery case becomes higher than a predetermined pressure, the non-aqueous electrolyte containing a gas generating agent that reacts at a voltage and generates gas, and the electrode body and the external terminal are electrically connected. A current interrupt mechanism for interrupting the current. In such a non-aqueous electrolyte secondary battery, gas is appropriately generated when the battery is overcharged, and the current interrupting mechanism can be appropriately operated. Moreover, a high capacity can be maintained even after the charge / discharge cycle. Therefore, high battery performance (for example, durability) and reliability at the time of overcharging can be achieved at a higher level.

  In a preferred embodiment of the non-aqueous electrolyte secondary battery disclosed herein, the conductive material has an average primary particle diameter of approximately 25 nm or less (for example, 10 nm to 25 nm). More preferably, the average primary particle diameter of the conductive material is 20 nm or less, and particularly preferably 18 nm or less. When the positive electrode active material having the particle size ratio (D10 / D50) is used, the proportion of particles having a small particle size in the positive electrode active material is increased. However, if the average primary particle size of the conductive material is controlled as described above. In addition, a conductive path can be satisfactorily formed between the active material particles having a small particle diameter and the conductive path can be maintained. Therefore, the cycle characteristics are improved and the reaction of the gas generating agent is promoted on the surface of the active material particles. Thereby, a decrease in the amount of overcharge gas in the secondary battery having the above-described configuration is suppressed, and high battery performance (for example, high durability) and reliability during overcharge can be achieved at a higher level.

  Any non-aqueous electrolyte secondary battery disclosed herein has a large amount of gas during overcharge as described above, and can maintain a high capacity even after cycling. It is suitable as a battery (typically a battery for driving power supply). Therefore, according to the present invention, there is provided a vehicle including 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 connected). In particular, a vehicle (for example, a plug-in hybrid vehicle (PHV) or an electric vehicle (EV) that can be charged by a household power source) provided with the non-aqueous electrolyte secondary battery as a power source is provided.

It is a schematic diagram of the lithium ion secondary battery which concerns on one Embodiment of this invention. It is a figure for demonstrating the winding electrode body which concerns on one Embodiment of this invention. It is a graph which contrasts IV resistance of each example. It is a graph which contrasts the initial capacity | capacitance of each example, and the capacity | capacitance after a cycle. It is a graph which compares the amount of overcharge gas of each example. It is a graph which shows the relationship between a particle size ratio (D10 / D50) and IV resistance. It is a graph which shows the relationship between a particle size ratio (D10 / D50) and a capacity | capacitance maintenance factor. It is a graph which shows the relationship between a particle size ratio (D10 / D50) and the amount of overcharge gas. It is a graph which shows the relationship between the primary particle size of an electrically-conductive material, and IV resistance. It is a graph which shows the relationship between the primary particle size of an electrically conductive material, and the amount of overcharge gas.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described with reference to the drawings. Each drawing is drawn schematically and does not necessarily reflect the real thing. Note that matters other than matters specifically mentioned in the present specification and necessary for the implementation of 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. Hereinafter, the embodiment of the present invention will be described more specifically with a case where the present invention is applied to a lithium ion secondary battery as a main example, but the application target of the present invention is not intended to be limited.

  In the present specification, “particle size distribution” refers to a volume-based particle size distribution measured by particle size distribution measurement based on a general laser diffraction / light scattering method. Further, in the present specification, the “overcharged state” refers to a state in which a state of charge (SOC) exceeds 100%. Here, the SOC is a state of charge in which the upper limit voltage is obtained in the operating voltage range that can be reversibly charged and discharged (that is, the fully charged state) is 100%, and the lower limit voltage is obtained. This shows the state of charge when (ie, the state where the battery is not charged) is 0%.

  The positive electrode active material used in the lithium ion secondary battery disclosed herein is in the form of particles (typically secondary particles) in which primary particles are collected, and at least cobalt (Co) is a constituent metal element. It consists of a granular complex oxide. In the composite oxide particles (at least one of the secondary particles and the primary particles, preferably both), the surface portion of the particles has a higher Co concentration than the central portion. For example, the value (X / Y) of the ratio between the average Co concentration X (hereinafter referred to as surface Co concentration) in the surface portion of the particle and the average Co concentration Y (hereinafter referred to as total Co concentration) of the entire particle is It is appropriate to satisfy 1.1 ≦ (X / Y) ≦ 1.5, preferably 1.15 ≦ (X / Y) ≦ 1.4, and particularly preferably 1.2 ≦ (X / Y ) ≦ 1.3. Thus, by using the composite oxide particle containing cobalt element for the positive electrode active material, the electronic conductivity of the positive electrode active material can be improved. In addition, since the Co concentration in the surface portion is increased as compared with the central portion as described above, adhesion between the primary particles is strong, and durability is improved.

  In the present specification, “surface Co concentration” refers to composite oxide particles (secondary particles and / or primary particles) measured based on a conventionally known inductively coupled plasma (ICP) emission spectroscopic analysis method. The average ratio (mol%) of Co element in the elements constituting the outermost surface portion of the particles (which varies depending on the measurement conditions, but is about several nm from the surface, for example, about 0.1 nm to about 10 nm from the surface). Or the average ratio (mol%) of Co element with respect to the whole element which comprises the outermost surface of a lithium transition metal complex oxide measured based on a conventionally well-known X-ray photoelectron spectroscopy may be sufficient. Such measurement can be performed, for example, using an analytical instrument based on X-ray photoelectron spectroscopy called XPS (X-ray Photoelectron Spectroscopy), ESCA (Electron Spectroscopy for Chemical Analysis), or the like. Further, in this specification, the “total Co concentration” refers to an average ratio (mol%) of Co element in elements constituting the entire composite oxide particle, which is measured based on a conventionally known inductively coupled plasma emission spectroscopy. ).

  Further, in the particle size distribution of the composite oxide particles, the positive electrode active material disclosed herein is a ratio of the D10 diameter corresponding to 10% cumulative from the smaller particle diameter side to the D50 diameter corresponding to 50% cumulative. (D10 / D50) satisfies the following formula: (D10 / D50) ≦ 0.75.

  Here, the smaller particle size ratio (D10 / D50) means that D10 has a value deviating from D50, that is, the particle size distribution of particles having a particle size smaller than the average particle size is wide, and the average particle size This means that the content of particles having a very small particle diameter with respect to the diameter is large. Therefore, by using the positive electrode active material having the particle size ratio (D10 / D50) as described above, the proportion of particles having a small particle size in the positive electrode active material is increased. Here, particles having a small particle size have higher durability against expansion and contraction than large particles, and are difficult to break. Further, since the specific surface area is relatively large, it is easy to make contact with the conductive material and the conductive path is difficult to break. Therefore, a battery including the positive electrode active material can be excellent in cycle durability.

  Furthermore, according to the knowledge of the present inventor, the reaction of the gas generating agent occurs more favorably on the particle surface having a high Co concentration than on the particle surface having a low Co concentration. Therefore, a particle surface with a high surface Co concentration tends to generate more gas during overcharge than a particle surface with a low Co concentration. In the battery proposed here, the positive electrode active material particles have a higher Co concentration in the surface portion of the particles than in the central portion. Further, by using a positive electrode active material having a particle size ratio (D10 / D50) as described above, the proportion of particles having a small particle size in the positive electrode active material is high. Therefore, the surface Co concentration of small particles occupying most of the specific surface area is increased as compared with the conventional case. Therefore, at the time of overcharge, the reaction of the gas generating agent suitably occurs on the surface of the small particles having a high surface Co concentration, and a desired gas amount can be stably generated. Since the pressure in the battery case increases due to the generation of such gas, the current interruption mechanism can be operated in a shorter time. Therefore, in the lithium ion secondary battery constructed using the positive electrode active material, the reliability during overcharging and the high battery performance can be achieved at a high level.

  According to the study by the present inventor, regarding the improvement in battery performance and the increase in the amount of overcharged gas by defining the particle size ratio (D10 / D50) within the preferred range disclosed herein, the surface Co concentration It was confirmed by the test examples described later that the composite oxide particles having a high particle size were effectively expressed. In other words, by applying the combination of the above-mentioned definition of the particle size ratio (D10 / D50) and the composite oxide particles having a high surface Co concentration, as a synergistic effect by such a combination, the amount of overcharge gas and the battery performance are markedly increased. An improved lithium ion secondary battery can be provided.

  The composite oxide particles disclosed herein preferably have a particle size ratio (D10 / D50) that satisfies (D10 / D50) ≦ 0.75, and satisfies (D10 / D50) ≦ 0.67. Are more preferable, and those satisfying (D10 / D50) ≦ 0.6 are particularly preferable. If the particle size ratio (D10 / D50) is too large, the amount of gas during overcharge may be insufficient or the cycle characteristics may be deteriorated. On the other hand, composite oxide particles having an excessively small particle size ratio (D10 / D50) are difficult to manufacture, and the performance improvement effect described above is slowed down, so that there is not much merit. The preferred particle size ratio (D10 / D50) is generally in the range of 0.45 ≦ (D10 / D50), preferably 0.5 ≦ (D10 / D50). For example, a composite oxide particle having a particle size ratio (D10 / D50) of 0.45 or more and 0.75 or less (particularly 0.45 or more and 0.67 or less) is said to achieve both improved cycle characteristics and manufacturability. Appropriate from the viewpoint.

  As a positive electrode active material, as long as the above-described conditions are satisfied, one or more kinds of materials conventionally used in lithium ion secondary batteries can be used without particular limitation. For example, a layered lithium transition metal composite oxide (which may be a rock salt structure or a spinel structure), that is, an oxide containing a lithium element and two or more transition metal elements including cobalt as constituent metal elements is given. It is done. The layered lithium transition metal composite oxide can be preferably used because it can be a battery having a high capacity and a high energy density when used as a positive electrode active material.

Examples of the lithium transition metal composite oxide of a layered, for example, the general formula _{(1): Li x Ni a} Co b Mn c Me d O 2 ( where Me is either missing or transition metal elements, typical metal elements and boron One or two or more elements selected from (B), where x, a, b, c and d are 0.99 ≦ x ≦ 1.12, 0.9 ≦ a + b + c + d ≦ 1.1, 05 ≦ x / (a + b + c + d) ≦ 1.2, 0 <a ≦ 0.5, 0 <b ≦ 0.5, 0 <c ≦ 0.5, 0 ≦ d ≦ 0.2 Lithium transition metal composite oxide represented by.). Note that in the chemical formulas showing the lithium transition metal oxide in this specification, the composition ratio of O (oxygen) is shown as 2 for convenience, but it is not strict, and some compositional variation (typically 1.95). Included in the range of 2.05 or less).

  As shown in the above formula (1), the lithium transition metal composite oxide used here contains lithium (Li), nickel (Ni), cobalt (Co) and manganese (Mn) as essential constituent elements. . Such a lithium transition metal composite oxide may contain at least one other metal element Me in addition to Li, Ni, Co, and Mn (that is, d <0), or may not contain (that is, d <0). d = 0.) Typically, the metal element Me may be one or more selected from transition metal elements other than Li, Ni, Co, and Mn, typical metal elements, and the like. More specifically, tungsten (W), magnesium (Mg), calcium (Ca), strontium (Sr), titanium (Ti), zirconium (Zr), vanadium (V), niobium (Nb), chromium (Cr) , Molybdenum (Mo), iron (Fe), rhodium (Rh), palladium (Pb), platinum (Pt), copper (Cu), zinc (Zn), boron (B), aluminum (Al), gallium (Ga) , Indium (In), tin (Sn), lanthanum (La), cerium (Ce), and the like. For example, W, Zr, Mg, and Ca can be preferably used. The amount of Me element (that is, the value of d in the above formula (I)) is not particularly limited, but can be, for example, 0 ≦ d ≦ 0.2 (for example, 0 ≦ d ≦ 0.02).

  Moreover, a, b, c in the above formula (1) are 0.9 ≦ a + b + c + d ≦ 1.1, 1.05 ≦ x / (a + b + c + d) ≦ 1.2, 0 <a ≦ 0.5, 0 < There is no particular limitation as long as b ≦ 0.5 and 0 <c ≦ 0.5 are satisfied, and any number of a, b, and c may be the largest. In other words, the first element of Ni, Co, and Mn (the element that is contained most on the basis of the number of atoms) may be any of Ni, Co, and Mn. For example, a can be 0.1 or more (typically 0.3 or more) and less than 0.5 (typically 0.45 or less, such as 0.4 or less). b can be 0.1 or more (typically 0.3 or more) and 0.5 or less (typically 0.45 or less, for example 0.4 or less). c can be 0.1 or more (typically 0.3 or more) and 0.5 or less (typically 0.45 or less, for example 0.4 or less). In a preferred embodiment, a, b, and c (that is, amounts of Ni, Co, and Mn) are approximately the same.

Further, x in the above formula (1) is a value determined so as to satisfy the charge neutrality condition. For example, 0.99 ≦ x ≦ 1.12, 1.05 ≦ x / (a + b + c + d) ≦ 1.2 is there. Here, x / (a + b + c + d) is a value indicating a molar ratio (Li / M _all ) between Li and the sum of all other constituent metal elements M _all (Ni, Co, Mn, Me). Preferably 1.05 ≦ (Li / M _all ) ≦ 1.2, more preferably 1.08 ≦ (Li / M _all ) ≦ 1.15, and particularly preferably 1.08 ≦ (Li / M _all ) ≦ 1.12. Such a Li-rich lithium transition metal composite oxide has low electronic conductivity and can achieve excellent output characteristics. On the other hand, the Li-rich lithium transition metal composite oxide tends to reduce the amount of gas generated during overcharge, but according to this configuration, the above-mentioned definition of the particle size ratio (D10 / D50), By applying in combination with composite oxide particles having a high surface Co concentration, a sufficient amount of overcharge gas can be ensured even when the above Li-rich lithium transition metal composite oxide is used.

  Such a lithium transition metal complex oxide is typically in the form of particles (secondary particles) in which primary particles are gathered. The Co concentration of such particles is not particularly limited as long as the ratio value (X / Y) between the surface Co concentration X and the overall Co concentration Y satisfies (X / Y)> 1, but for example, the overall Co concentration Y May be 5 mol% or more (preferably 10 mol% or more) and 40 mol% or less (preferably 30 mol% or less). Further, the surface Co concentration X only needs to be larger than the overall Co concentration Y, and can be, for example, 6 mol% or more (typically 12 mol% or more) and 48 mol% or less (typically 36 mol% or less). When the Co concentration (surface Co concentration X or total Co concentration Y, preferably both) is within the above range, high battery performance and reliability during overcharge can be achieved at a higher level.

  Although the properties of such particles are not particularly limited, for example, the average particle diameter (D50 diameter) is 0.5 μm or more (typically 1 μm or more, such as 2 μm or more, preferably 3 μm or more), and 20 μm or less (typically May be 15 μm or less, for example, 10 μm or less). The D10 diameter may be any diameter as long as it satisfies (D10 / D50) ≦ 0.75, for example, 0.3 μm or more (typically 0.7 μm or more, for example, 1.5 μm or more, preferably 4.5 μm or more. ) And 15 μm or less (typically 12 μm or less, for example, 8 μm or less). When the properties of the positive electrode active material particles are in the above range, the positive electrode active material layer produced using such particles can be dense and highly conductive. Moreover, since an appropriate space | gap can be hold | maintained in a positive electrode active material layer, electrolyte solution can penetrate | invade easily into this active material layer, and the reaction field with a gas generating agent can be ensured widely at the time of overcharge. Therefore, high battery performance (for example, high durability) and reliability during overcharging can be achieved at a higher level.

The method for producing such a particulate lithium transition metal composite oxide is not particularly limited. For example, a metal element hydroxide (precursor) is obtained by a wet method (precursor generation step). It can be produced by mixing the precursor and a suitable lithium source (mixing step) and firing the mixture at a predetermined temperature (firing step). The average composition above general formula in the following _(1): as an example a positive electrode active material represented by _{Li x Ni a Co b Mn c} Me d O 2, there is a case for explaining a manufacturing method of the positive electrode active material The present invention is not intended to be limited to such specific embodiments.

  In the precursor generation step, typically, an aqueous solution (typically an acidic solution) containing a nickel (Ni) source, a cobalt (Co) source, a manganese (Mn) source, and a Me element source as starting materials. Hereinafter, an “aqueous solution A”) and an aqueous solution containing a cobalt (Co) source (hereinafter referred to as “aqueous solution B”) are prepared as separate solutions, and these are prepared under alkaline conditions (pH>). 7), the metal element hydroxide is precipitated (crystallized). Here, the amount of the metal source (Ni source, Mn source, Me source) excluding the Co source in the aqueous solution A may be appropriately determined so as to be the molar ratio of a, c, d in the general formula (1). The amount of Co source in the aqueous solution B is such that the sum of the amount of Co source in the aqueous solution B and the amount of Co source in the aqueous solution A is the molar ratio of b in the general formula (1). It is advisable to determine as appropriate.

  The aqueous solution A can be prepared by dissolving a predetermined amount of a transition metal element source (Ni source, Co source, Mn source, Me source, typically a water-soluble ionic compound) in an aqueous solvent. . The order in which these transition metal element sources are added to the aqueous solvent is not particularly limited. Moreover, you may prepare by preparing the aqueous solution containing each transition metal element source separately, and mixing this aqueous solution. The anion of the metal element source can be appropriately selected so that the metal element source is water-soluble, and may be, for example, sulfate ion, nitrate ion, carbonate ion, hydroxide ion, chloride ion, or the like. All or a part of these metal element source anions may be the same or different from each other. Each of these metal element sources can be in a solvated state such as a hydrate. Similarly, the aqueous solution B can be prepared by dissolving a predetermined amount of Co source in an aqueous solvent. The preparation method of the aqueous solution can be the same as that of the aqueous solution A. As the Co source, the same one as used in the aqueous solution A can be used.

  The aqueous solvent used in preparing the aqueous solution (aqueous solution A and aqueous solution B) is typically water, but a mixed solvent mainly composed of water can also be used. As the solvent other than water constituting the mixed solvent, one or more organic solvents (for example, lower alcohol, lower ketone, etc.) that can be uniformly mixed with water can be appropriately selected and used. Moreover, when the water solubility of the raw material compound to be used is low, a compound (acid, base, etc.) that can improve the solubility can be appropriately added to the aqueous solvent.

As the compound capable of making the aqueous solution alkaline, a compound containing a strong base (alkali metal hydroxide, etc.) and / or a weak base (ammonia, etc.) and not inhibiting the formation (precipitation) of the hydroxide is preferably used. Can do. For example, sodium hydroxide (NaOH), potassium hydroxide (KOH), ammonium hydroxide _(NH 4 OH), lithium hydroxide (LiOH), sodium carbonate (NaCO _3), potassium carbonate _(KCO 3), lithium carbonate (LiCO ₃ ), ammonium carbonate ((NH ₄ ) ₂ CO ₃ ), ammonium nitrate (NH ₄ NO ₃ ), ammonia gas (NH ₃ ) or the like can be used. Of these, the use of sodium hydroxide is preferred. Such a compound is preferably added so that the pH immediately after the preparation of the aqueous solution (initial stage) is approximately 12 ≦ pH ≦ 13 (for example, 12 ≦ pH <13). By setting it within the above range, a large number of nuclei slowly precipitate from the reaction solution, so that a hydroxide having a wider particle size distribution (for example, a large content of small particles whose particle diameter is greatly deviated from the average) is suitably generated. can do. In addition, in this specification, the value of pH points out the value measured at room temperature (liquid temperature of 25 degreeC) using the commercially available pH meter.

  In the precursor generation step, first, a compound capable of making the aqueous solution A alkaline (for example, sodium hydroxide) is added to the aqueous solution A, and mixed and stirred at an appropriate speed to thereby form a metal element (here, Ni, Co, Mn and Me) are precipitated (crystallized). In this step, a positive electrode active material having desired properties (particle size distribution and specific surface area) can be obtained by appropriately adjusting the deposition conditions (for example, reaction temperature, reaction time, alkali concentration of aqueous solution, pH). . As a tendency, in order to obtain a positive electrode active material having a wider particle size distribution, it is preferable to increase the reaction time. For example, 10 hours to 30 hours, preferably 14 hours to 24 hours. The temperature of the aqueous solution may be set to a temperature not higher than the boiling point of the aqueous solvent (typically 20 ° C. to 80 ° C., for example, 40 ° C. to 60 ° C.).

Then, the obtained hydroxide particles are added to the aqueous solution B, a compound capable of making the aqueous solution B alkaline (for example, sodium hydroxide) is added, and the hydroxide is mixed and stirred at an appropriate speed. Cobalt (Co) hydroxide is deposited on the surface of the particles. Thereby, a precursor in which the Co concentration (surface Co concentration and total Co concentration) is adjusted to a suitable range can be obtained. The average composition of the entire such precursors have the general formula _{(2): Ni a Co b} Mn c Me d (OH) 2 ( where, a, b, c, d may be similar to the general formula (1) .); By using the hydroxide obtained by the above-described wet method as a precursor, positive electrode active material particles in which the Co concentration (surface Co concentration and total Co concentration) is maintained in a suitable range can be produced.

In the mixing step, the obtained precursor and the lithium source are mixed. The mixing method is not particularly limited, and a conventionally known dry mixing method or wet mixing method can be employed. As the lithium source, a general lithium compound used for forming a lithium oxide can be used without particular limitation. Examples thereof include lithium salts such as lithium carbonate (LiCO ₃ ), lithium hydroxide (LiOH), lithium nitrate (LiNO ₃ ), lithium sulfate (Li ₂ SO ₄ ), and lithium chloride (LiCl). These Li sources can be used alone or in combination of two or more. For the mixing ratio of the precursor and the Li source, the number of moles of Li source relative to the total number of moles of all the metal elements contained in the precursor is selected so that x in the formula (1) has a desired value. Then, it may be determined appropriately based on that.

  In the firing step, the positive electrode active material particles disclosed herein can be produced by firing the mixture of the precursor and the Li source. Although a calcination temperature is not specifically limited, For example, it is 650 degreeC or more (typically 700 degreeC or more, for example, 750 degreeC or more), and can be 1050 degreeC or less (typically 1000 degreeC or less). In order to obtain a higher output, it is preferable that the maximum firing temperature is in the range of 850 ° C. to 980 ° C. (more preferably, 850 ° C. to 950 ° C.). Such firing conditions can be preferably employed in the production of a positive electrode active material used in a lithium secondary battery for applications where emphasis is placed on enhancing output performance, such as a hybrid vehicle.

  The obtained fired product is typically pulverized and then sieved to a desired particle size as necessary to be used as a positive electrode active material. In this way, it is possible to produce a positive electrode active material in which the Co concentration ratio (X / Y) and the particle size distribution (D10 / D50 ratio) satisfy the preferred ranges.

  Hereinafter, the configuration of the lithium ion secondary battery in which the positive electrode active material is used will be described in order. Here, an example of a lithium ion secondary battery in which a wound type electrode body (hereinafter referred to as a “wound electrode body”) and a nonaqueous electrolyte solution are accommodated in a rectangular (here, rectangular box shape) case is shown as an example. To The battery structure is not limited to the illustrated example, and is not particularly limited to a prismatic battery.

  FIG. 1 is a cross-sectional view of a lithium ion secondary battery 100 according to an embodiment of the present invention. FIG. 2 is a view showing a wound electrode body 200 housed in the lithium ion secondary battery 100.

  A lithium ion secondary battery 100 according to an embodiment of the present invention is configured in a flat rectangular battery case (that is, an exterior container) 300 as shown in FIG. As shown in FIG. 2, in the lithium ion secondary battery 100, a flat wound electrode body 200 is housed in a battery case 300 together with a liquid electrolyte (electrolytic solution) (not shown).

<Battery case 300>
The battery case 300 has a box-shaped (that is, bottomed rectangular parallelepiped) case main body 320 having an opening at one end (corresponding to the upper end in a normal use state of the battery 100), and is attached to the opening. It is comprised from the sealing board (lid body) 340 which consists of a rectangular-shaped plate member which block | closes an opening part.

  The material of the battery case 300 may be the same as that used in the conventional sealed battery, and there is no particular limitation. A battery case 300 mainly composed of a lightweight and highly heat conductive metal material is preferable, and aluminum or the like is exemplified as such a metal material.

  As shown in FIG. 1, a positive electrode terminal 420 and a negative electrode terminal 440 for external connection are formed on the sealing plate 340. Between the two terminals 420 and 440 of the sealing plate 340, a thin-walled safety valve 360 configured to release the internal pressure of the battery case 300 when the internal pressure of the battery case 300 rises to a predetermined level or more, and a liquid injection port 350 are formed. Has been. In FIG. 1, the liquid injection port 350 is sealed with a sealing material 352 after liquid injection.

<< Wound electrode body 200 (electrode body) >>
As shown in FIG. 2, the wound electrode body 200 includes a long sheet-like positive electrode (positive electrode sheet 220) and a long sheet-like negative electrode (negative electrode sheet 240) similar to the positive electrode sheet 220 in total of two sheets. Long sheet separators (separators 262 and 264).

<< Positive electrode sheet 220 >>
The positive electrode sheet 220 includes a strip-shaped positive electrode current collector 221 and a positive electrode active material layer 223. For the positive electrode current collector 221, for example, a metal foil suitable for the positive electrode can be suitably used. In this embodiment, an aluminum foil is used as the positive electrode current collector 221. An uncoated portion 222 is set along the edge on one side in the width direction of the positive electrode current collector 221. In the illustrated example, the positive electrode active material layer 223 is held on both surfaces of the positive electrode current collector 221 except for the uncoated portion 222 set on the positive electrode current collector 221. The positive electrode active material layer 223 includes the positive electrode active material particles, the conductive material, and the binder described above.

≪Conductive material≫
Examples of the conductive material include carbon materials such as carbon powder and carbon fiber. As the conductive material, one kind selected from such conductive materials may be used alone, or two or more kinds may be used in combination. As the carbon powder, various carbon blacks (for example, acetylene black, oil furnace black, graphitized carbon black, carbon black, graphite, ketjen black), graphite powder, and the like can be used. Here, the average primary particle size based on SEM observation and image analysis of the conductive material is suitably about 25 nm or less (for example, 10 nm to 25 nm), preferably 20 nm or less, and particularly preferably 18 nm or less. It is. When a positive electrode active material having the particle size distribution (particle size ratio D10 / D50 is 0.75 or less) is used, the proportion of particles having a small particle size in the positive electrode active material is increased. By controlling the average primary particle size, it is possible to satisfactorily form a conductive path between the small particle size and the active material particles, and to maintain the conductive path. Therefore, the cycle characteristics are improved and the reaction of the gas generating agent is promoted on the surface of the active material particles. Thereby, the reduction in the amount of gas generated at the time of overcharging in the secondary battery having the above configuration is suppressed, and high battery performance (for example, high durability) and reliability at the time of overcharging can be achieved at a higher level. .

≪Binder≫
Further, the binder binds the positive electrode active material particles and the conductive material particles included in the positive electrode active material layer, or binds these particles to the positive electrode current collector 221. As such a binder, a polymer that can be dissolved or dispersed in a solvent to be used can be used. For example, in a positive electrode mixture composition using an aqueous solvent, cellulosic polymers (carboxymethylcellulose (CMC), hydroxypropylmethylcellulose (HPMC), etc.), rubbers (vinyl acetate copolymer, styrene butadiene copolymer (SBR)) ), Water-soluble or water-dispersible polymers such as acrylic acid-modified SBR resin (SBR latex) and the like can be preferably used. In the positive electrode mixture composition using a non-aqueous solvent, a polymer (polyvinylidene fluoride (PVDF), polyvinylidene chloride (PVDC), polyacrylonitrile (PAN), etc.) can be preferably employed.

≪Thickener, solvent≫
The positive electrode active material layer 223 is prepared by, for example, preparing a positive electrode mixture in which the above-described positive electrode active material particles, a conductive material, and a binder are mixed in a paste (slurry) with a solvent, applied to the positive electrode current collector 221, and dried And is formed by rolling. At this time, as the solvent for the positive electrode mixture, either an aqueous solvent or a non-aqueous solvent can be used. A suitable example of the non-aqueous solvent is N-methyl-2-pyrrolidone (NMP). The polymer material exemplified as the binder may be used for the purpose of exhibiting a function as a thickener or other additive of the positive electrode mixture in addition to the function as a binder.

<< Negative Electrode Sheet 240 >>
As shown in FIG. 2, the negative electrode sheet 240 includes a strip-shaped negative electrode current collector 241 and a negative electrode active material layer 243. For the negative electrode current collector 241, for example, a metal foil suitable for the negative electrode can be suitably used. In this embodiment, a strip-shaped copper foil having a thickness of about 10 μm is used for the negative electrode current collector 241. On one side in the width direction of the negative electrode current collector 241, an uncoated part 242 is set along the edge. The negative electrode active material layer 243 is held on both surfaces of the negative electrode current collector 241 except for the uncoated portion 242 set on the negative electrode current collector 241. The negative electrode active material layer 243 includes negative electrode active material particles. Here, the negative electrode active material layer 243 is formed by applying a negative electrode mixture containing negative electrode active material particles to the negative electrode current collector 241, drying, and pressing to a predetermined thickness.

<Negative electrode active material particles>
As the negative electrode active material particles contained in the negative electrode active material layer 243, one kind or two or more kinds of substances conventionally used in lithium ion secondary batteries can be used without particular limitation. Preferable examples include carbon-based materials such as graphite carbon and amorphous carbon, lithium transition metal oxides, and lithium transition metal nitrides. Moreover, as a suitable example of the said separator sheet, what was comprised with porous polyolefin resin is mentioned.

<< Separators 262, 264 >>
As shown in FIG. 2, the separators 262 and 264 are members that separate the positive electrode sheet 220 and the negative electrode sheet 240. In this example, the separators 262 and 264 are made of a strip-shaped sheet material having a predetermined width and having a plurality of minute holes. As the separators 262 and 264, for example, a single layer structure separator or a multilayer structure separator made of a porous polyolefin resin can be used. In this example, as shown in FIG. 2, the width b1 of the negative electrode active material layer 243 is slightly wider than the width a1 of the positive electrode active material layer 223. Furthermore, the widths c1 and c2 of the separators 262 and 264 are slightly wider than the width b1 of the negative electrode active material layer 243 (c1, c2>b1> a1).

  In the example illustrated in FIG. 2, the separators 262 and 264 are configured by sheet-like members. The separators 262 and 264 may be members that insulate the positive electrode active material layer 223 and the negative electrode active material layer 243 and allow the electrolyte to move. Therefore, it is not limited to a sheet-like member. The separators 262 and 264 may be formed of a layer of insulating particles formed on the surface of the positive electrode active material layer 223 or the negative electrode active material layer 243, for example, instead of the sheet-like member. Here, as the particles having insulating properties, inorganic fillers having insulating properties (for example, fillers such as metal oxides and metal hydroxides) or resin particles having insulating properties (for example, particles such as polyethylene and polypropylene). ).

<< Electrolyte (nonaqueous electrolyte) >>
As the electrolytic solution (non-aqueous electrolytic solution), the same non-aqueous electrolytic solution conventionally used for lithium ion secondary batteries can be used without any particular limitation. Such a nonaqueous electrolytic solution typically has a composition in which a supporting salt is contained in a suitable nonaqueous solvent. Examples of the non-aqueous solvent include ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, 1,3-dioxolane, and the like. One kind or two or more kinds selected from the group can be used. Examples of the supporting salt include LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) _{3 and the} like. Lithium salts can be used. As an example, a nonaqueous electrolytic solution in which LiPF ₆ is contained in a mixed solvent of ethylene carbonate and diethyl carbonate (for example, a mass ratio of 1: 1) at a concentration of about 1 mol / L can be given.

<Gas generating agent>
In this embodiment, the non-aqueous electrolyte contains, for example, a gas generating agent that reacts and generates gas when the battery voltage becomes equal to or higher than a predetermined voltage. As such a gas generating agent, for example, cyclohexylbenzene (CHB) or biphenyl (BP) can be used. Cyclohexylbenzene (CHB) and biphenyl (BP), for example, contact with the surface of the positive electrode (typically the surface of the positive electrode active material) during overcharge of about 4.35 V to 4.6 V, and oxidative decomposition, Hydrogen ions are generated by polymerization. The hydrogen ions diffuse into the negative electrode and receive electrons on the negative electrode to generate hydrogen as a reducing gas. Typically, the following polymerization reaction is activated, and gas (here, hydrogen gas) is generated.

・ Cyclohexylbenzene (CHB)
_{n [C 12 H 16] →} (C 12 H 14) n + nH 2
・ Biphenyl (BP)
_{n [C 12 H 10] →} (C 12 H 8) n + nH 2

For example, the amount of the gas generating agent added to the non-aqueous electrolyte is preferably about 0.05 wt% or more and 4.0 wt% or less. In addition, the addition amount of a gas generating agent is not limited to this, It is good to adjust so that a predetermined amount of gas may be generated on predetermined conditions. Further, the gas generating agent is not limited to cyclohexylbenzene (CHB) and biphenyl (BP). Here, (C ₁₂ H ₁₄ ) _n or (C ₁₂ H ₈ ) _n can be generated as a polymerized film in a polymerization reaction in which gas is generated.

<< Attachment of wound electrode body 200 >>
In this embodiment, the wound electrode body 200 is flatly bent in one direction orthogonal to the winding axis WL, as shown in FIG. In the example shown in FIG. 2, the uncoated portion 222 of the positive electrode current collector 221 and the uncoated portion 242 of the negative electrode current collector 241 are spirally exposed on both sides of the separators 262 and 264, respectively. In this embodiment, as shown in FIG. 1, the middle part of the uncoated part 222 (242) is gathered and collected by the electrode terminals 420 and 440 (internal terminals) arranged inside the battery case 300. Welded to tabs 420a, 440a. In such a wound electrode body 200, the electrolyte enters the wound electrode body 200 from the axial direction of the wound axis WL.

<< Current interrupting mechanism 460 >>
Further, as described above, in the lithium ion secondary battery 100, a gas generating agent is added to the electrolytic solution. For example, when the battery is overcharged at about 4.35V to 4.6V, gas is generated. The pressure inside becomes high. The current interrupt mechanism 460 is a mechanism that interrupts the current path when the pressure in the battery case becomes abnormally high. In this embodiment, as shown in FIG. 1, the current interruption mechanism 460 is constructed inside the positive electrode terminal 420 so that the conduction path of the battery current in the positive electrode is interrupted. In addition, the specific structure of the electric current interruption mechanism 460 is disclosed by patent document 1, for example. The current interruption mechanism disclosed here can be appropriately employed as the current interruption mechanism 460 of the lithium ion secondary battery 100. For this reason, the specific structure of the current interrupt mechanism 460 is not particularly mentioned here. In addition, the specific structure of the electric current interruption mechanism 460 is not limited to the structure disclosed by the patent document mentioned above, A various mechanism can be employ | adopted.

<< Test Example 1 >>
Several 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.

Example 1
Nickel sulfate (NiSO ₄ ) as a nickel source, cobalt sulfate (CoSO ₄ ) as a cobalt source, and manganese sulfate (MnSO ₄ ) as a manganese source, the molar ratio of Ni: Co: Mn is 0.4: An aqueous NiCoMn solution (aqueous solution A) was prepared by dissolving in an aqueous solution so that the ratio was 0.2: 0.4. Further, cobalt sulfate (CoSO ₄ ) as a cobalt source was dissolved in an aqueous solution to prepare an aqueous Co solution (aqueous solution B).

An appropriate amount of NaOH was added to the aqueous solution A and stirred to precipitate (crystallize) a hydroxide having a basic composition represented by Ni _0.4 Co _0.2 Mn _0.4 (OH) ₂ from the reaction solution. . The precipitate was added to the aqueous solution B, NaOH was added, and the mixture was stirred and mixed at an appropriate rate to precipitate cobalt (Co) hydroxide on the surface of the hydroxide particles. The precipitate was taken out from the reaction vessel, washed with water, and dried to obtain a precursor composed of a hydroxide having an overall composition represented by Ni _0.334 Co _0.333 Mn _0.333 (OH) ₂ . Lithium carbonate (Li ₂ CO ₃ ) as a lithium source was mixed with this precursor so that the molar ratio of (Ni + Co + Mn): Li was 1: 1.09, and the mixture was mixed at 800 ° C. to By firing at 950 ° C. for 5 to 15 hours, a particulate positive electrode active material having an overall composition represented by Li _1.09 (Ni _0.334 Co _0.333 Mn _0.333 ) O ₂ was obtained.

  The Co concentration of the positive electrode active material particles obtained above was measured by ICP emission spectroscopic analysis (model “ICPE-9000” manufactured by Shimadzu Corporation was used). Specifically, the surface part of the positive electrode active material particles (region from the particle surface to approximately 1000 nm) is dissolved in acid to prepare a sample solution, and the Co concentration in the sample solution is measured. The surface Co concentration X (mol%) was determined. Moreover, the whole positive electrode active material particle was melt | dissolved in the acid, the sample solution was prepared, and the Co density | concentration Y (mol%) of positive electrode active material particle was grasped | ascertained by measuring Co concentration in this sample solution. As a result, the surface Co concentration (X) is about 40 mol%, the total Co concentration (Y) is 33.3 mol%, and the value obtained by dividing the surface Co concentration (X) by the total Co concentration (Y) (X / Y) was about 1.2.

Further, when the properties of the positive electrode active material particles were measured, the average particle diameter (D50 diameter) was 6.50 μm, the D10 diameter was 4.36 μm, and the value obtained by dividing the D10 diameter by the D50 diameter (D10 / D50). ) Was 0.67. The specific surface area was 1.18 m ² / g.

The above-obtained positive electrode active material powder, acetylene black (AB) as a conductive material, and polyvinylidene fluoride (PVDF) as a binder are N− such that the mass ratio of these materials is 93: 4: 3. A paste composition (positive electrode paste) for forming a positive electrode active material layer was prepared by kneading with methyl pyrrolidone (NMP). The total weight of this positive electrode paste on both sides of a long aluminum foil (positive electrode current collector) having a thickness of about 15 μm is 30 mg in total weight (coating amount in terms of solid content, that is, dry mass of the positive electrode active material layer) on both surfaces. The positive electrode active material layer was formed by coating at a rate of / cm ² and drying with 120 ° C. hot air. Subsequently, it pressed so that the density of this positive electrode active material layer might be 2.8 g / cm < ³ >, and the positive electrode sheet was produced. In this example, Denka Black HS-100 having an average primary particle size of 35 nm was used as AB.

Graphite (powder), styrene butadiene rubber (SBR), and carboxymethyl cellulose (CMC) as a negative electrode active material are mixed with ion-exchanged water so that the mass ratio of these materials is 98: 1: 1. A paste-like composition (negative electrode paste) for forming an active material layer was prepared. This negative electrode paste was applied to both sides of a long copper foil (negative electrode current collector) having a thickness of about 10 μm so that the opposing capacity ratio with respect to the positive electrode was 1.4 and dried to form a negative electrode active material layer. . Subsequently, it pressed so that the density of this negative electrode active material layer might be 1.3 g / cm < ³ >, and the negative electrode sheet was produced.

The prepared positive electrode sheet and negative electrode sheet were overlapped and wound via two separators to prepare an electrode body. This electrode body was accommodated in a battery case together with a non-aqueous electrolyte. As a non-aqueous electrolyte, LiPF ₆ was dissolved at a concentration of about 1 mol / L in a mixed solvent containing ethylene carbonate (EC) and diethyl carbonate (DEC) at a volume ratio of 3: 7 at a concentration of about 1 mol / L. The solution was used. Further, cyclohexylbenzene (CHB) as a gas generating agent was added to the nonaqueous electrolytic solution. The amount of the gas generating agent added was 1% by mass with respect to the electrolytic solution. Next, a lithium ion secondary battery for evaluation was constructed by performing a conditioning treatment.

<< Example 2 >>
A lithium ion secondary battery was constructed in the same procedure as in Example 1 except that the average primary particle size of AB (conductive material) contained in the positive electrode active material layer was changed to 16 nm.

≪Comparative example 1≫
Nickel sulfate (NiSO ₄ ) as a nickel source, cobalt sulfate (CoSO ₄ ) as a cobalt source, and manganese sulfate (MnSO ₄ ) as a manganese source, the molar ratio of these elements Ni: Co: Mn is 1: A NiCoMn aqueous solution was prepared by dissolving in an aqueous solution to a ratio of 1: 1. An appropriate amount of NaOH was added to the NiCoMn aqueous solution and stirred to precipitate (crystallize) hydroxide from the reaction solution. The precipitate was taken out from the reaction vessel, washed with water, and dried to obtain a precursor composed of a hydroxide having a basic composition represented by Ni _0.334 Co _0.333 Mn _0.333 (OH) ₂ . Lithium carbonate (Li ₂ CO ₃ ) as a lithium source was mixed with this precursor so that the molar ratio of (Ni + Co + Mn): Li was 1: 1.09, and the mixture was mixed at 800 ° C. to By firing at 950 ° C. for 5 to 15 hours, a particulate positive electrode active material represented by Li _1.09 (Ni _0.334 Co _0.333 Mn _0.333 ) O ₂ was obtained. The value (D10 / D50) obtained by dividing the D10 diameter of the obtained positive electrode active material particles by the D50 diameter was 0.84. Using this positive electrode active material, a lithium ion secondary battery was constructed in the same procedure as in Example 1.

«Comparative example 2»
In the positive electrode active material manufacturing process of Comparative Example 1 described above, the molar ratio of Ni: Co: Mn was changed to 1: 1.2: 1 to change Li _1.09 (Ni _0.313 Co _0.375 Mn _0.312). ) A particulate positive electrode active material represented by O ₂ was prepared. Using this positive electrode active material, a lithium ion secondary battery was constructed in the same procedure as in Example 1.

«Comparative Example 3»
In the positive electrode active material manufacturing process of Comparative Example 1 described above, the molar ratio of Ni: Co: Mn was changed to 1: 1.4: 1 to change Li _1.09 (Ni _0.94 Co _0.412 Mn _0.294). ) A particulate positive electrode active material represented by O ₂ was prepared. Using this positive electrode active material, a lithium ion secondary battery was constructed in the same procedure as in Example 1.

<< Comparative Example 4 >>
In the positive electrode active material manufacturing process of Example 1 described above, the positive electrode active material was prepared by changing the precursor manufacturing conditions (for example, hydroxide precipitation conditions (for example, reaction temperature, reaction time, pH of aqueous solution)). did. The value (D10 / D50) obtained by dividing the D10 diameter of the obtained positive electrode active material particles by the D50 diameter was 0.84. Using this positive electrode active material, a lithium ion secondary battery was constructed in the same procedure as in Example 1.

<< Comparative Example 5 >>
In the positive electrode active material manufacturing process of Example 1 described above, the molar ratio of Ni: Co: Mn in the aqueous solution A was changed to 0.45: 0.1: 0.45, and the overall composition was Li _1.09. A particulate positive electrode active material represented by (Ni _0.334 Co _0.333 Mn _0.333 ) O ₂ was produced. The obtained positive electrode active material particles have a surface Co concentration (X) of about 46.6 mol%, an overall Co concentration (Y) of 33.3 mol%, and a surface Co concentration (X) of the total Co concentration (Y). The value (X / Y) divided by was about 1.4. Moreover, the value (D10 / D50) which remove | divided D10 diameter of positive electrode active material particle | grains by D50 diameter was 0.84. Using this positive electrode active material, a lithium ion secondary battery was constructed in the same procedure as in Example 1.

<Evaluation of lithium ion secondary battery for evaluation test>
About the lithium ion secondary battery of each said example, initial stage capacity | capacitance after a cycle, capacity retention, IV resistance, and the amount of overcharge gas were evaluated.

≪Measurement of initial capacity≫
About the lithium ion secondary battery for evaluation of each example, the initial stage capacity | capacitance was measured by the following procedures 1-3.
Procedure 1: After reaching 3.0V by constant current discharge of 1C, discharge by constant voltage discharge for 2 hours, and then rest for 10 seconds.
Procedure 2: After reaching 4.1 V by constant current charging at 1 C, charge for 2.5 hours by constant voltage charging, and then rest for 10 seconds.
Procedure 3: After reaching 3.0 V by constant current discharge of 0.5 C, discharge at constant voltage discharge for 2 hours, and then stop for 10 seconds.
Here, the discharge capacity (CCCV discharge capacity) in the discharge from the constant current discharge to the constant voltage discharge in the procedure 3 was defined as “initial capacity”.

<Capacity after cycle>
After the initial charge, a charge / discharge pattern for repeating CC charge / discharge at 10 C was applied to each of the test batteries, and a cycle test was performed. Specifically, a charge / discharge cycle in which a test battery is charged to 4.1 V at a constant current of 10 C at 25 ° C. and then discharged to 3.0 V at a constant current of 10 C is continuously performed 500 times. It was. Then, the discharge capacity after the cycle was measured under the same conditions as the initial capacity.

<IV resistance>
The IV resistance was measured according to the following procedure.
Procedure 1: After discharging at a constant current of 1 C to 3.0 V under a temperature condition of 25 ° C., charge at a constant current and a constant voltage at 1 C to obtain a charged state of SOC 20%.
Procedure 2: After Procedure 1, discharge treatment is performed at 10A (corresponding to 10C) for 10 seconds.
Here, the measured current value measured in the procedure 2 is divided by the voltage drop value that is a value obtained by subtracting the voltage value at the time of 10 seconds from the initial voltage value in the procedure 2. The value was obtained as an IV resistance value.

《Overcharge gas amount》
The amount of overcharge gas is the same as the electrode plate group used in the lithium ion secondary battery (a laminate of a positive electrode sheet, a negative electrode sheet, and a separator), and a laminate bag together with an electrolyte containing a gas generating agent. And vacuum-sealing to produce a laminate cell. The lamination cell is subjected to a conditioning process. Before the overcharge test, the weight of the laminate cell in water was measured in advance, and then the laminate cell was charged in a 25 ° C. test tank at a constant current of 0.5 C to obtain an SOC 145% overcharge state. Thereafter, the discharge treatment is performed up to 3 V, taken out from the test tank, the weight in water is measured again, the volume change of the laminate cell is measured based on the Archimedes method, and this is gradually calculated by 1 C capacity. This value was calculated as the amount of overcharged gas.

That is, the volume change ΔV of the laminate cell is obtained by the following equation.
ΔV = ρw × (W−W1)
Here, ρw is the density of water, W is the underwater weight of the laminate cell before overcharging, and W1 is the underwater weight of the laminate cell after overcharging.

  The results of the above test for each example are shown in Table 1 and FIGS. Table 1 summarizes the configuration for each example. FIG. 3 is a graph comparing the IV resistance of each example. FIG. 4 is a graph comparing the initial capacity and post-cycle capacity of each example. In FIG. 4, the initial capacity and post-cycle capacity of each example are shown as relative values when the initial capacity of Comparative Example 1 is 100. FIG. 5 is a graph comparing the amount of overcharge gas in each example.

  As shown in Table 1 and FIGS. 3 to 5, in the batteries according to Examples 1 and 2, IV resistance can be kept relatively low, and high output characteristics can be exhibited at a high level. In contrast, the battery according to Comparative Example 1 has a relatively high IV resistance and low output characteristics. In addition, the batteries according to Examples 1 and 2 have a high initial capacity, and a high capacity is maintained even after cycling. On the other hand, the batteries according to Comparative Examples 2 and 3 have a low initial capacity and a low post-cycle capacity retention rate. Although the batteries according to Comparative Examples 4 and 5 have a relatively high initial capacity, the post-cycle capacity retention rate tends to be lower than that of Examples 1 and 2. Furthermore, the batteries according to Examples 1 and 2 have a large amount of overcharged gas and are at a level at which the current interrupt mechanism can operate appropriately (relatively early). On the other hand, in the batteries according to Comparative Examples 1 to 5, the gas generation amount is slowed down, and the operation of the flow blocking mechanism tends to be delayed as compared with Examples 1 and 2. When using a positive electrode active material in which the Co concentration in the surface portion is higher than that in the central portion and the particle size ratio (D10 / D50) is 0.75 or less as in this test, the output characteristics, initial capacity, and The amount of overcharge gas can be increased while keeping the post-cycle capacity high, and the current interrupt mechanism can be operated appropriately.

<< Test Example 2 >>
In this example, in the positive electrode active material manufacturing process of Example 1 described above, the precursor manufacturing conditions (for example, hydroxide precipitation conditions (for example, reaction temperature, reaction time, alkali concentration of aqueous solution, pH)) are changed. Thus, positive electrode active materials were prepared with various particle size ratios (D10 / D50). Using such a positive electrode active material, a lithium ion secondary battery was constructed in the same procedure as in Example 1, and the IV resistance, capacity retention rate, and overcharge gas amount were evaluated. Here, the capacity retention rate was calculated by (initial capacity / capacity after cycle). The results are shown in FIGS. 6 is a graph showing the relationship between the particle size ratio (D10 / D50) and the IV resistance, FIG. 7 is a graph showing the relationship between the particle size ratio (D10 / D50) and the capacity retention ratio, and FIG. It is a graph which shows the relationship between a particle size ratio (D10 / D50) and the amount of overcharge gas.

As is clear from FIG. 6, the IV resistance tended to decrease as the particle size ratio (D10 / D50) decreased. In the case of the battery used here, by setting the particle size ratio (D10 / D50) to 0.75 or less, an extremely low IV resistance of 39.2 mΩ or less could be realized. From the viewpoint of improving the output characteristics, the particle size ratio (D10 / D50) is preferably 0.75 or less, and more preferably 0.67 or less. Further, as apparent from FIG. 7, the capacity retention rate showed an increasing tendency as the particle size ratio (D10 / D50) decreased. In the case of the battery used here, by setting the particle size ratio (D10 / D50) to 0.75 or less, an extremely high capacity retention rate of 0.91 or more was realized. From the viewpoint of improving durability, the particle size ratio (D10 / D50) is preferably 0.75 or less, and more preferably 0.6 or less. Further, as apparent from FIG. 8, the amount of overcharged gas tended to increase as the particle size ratio (D10 / D50) decreased. In the case of the battery used here, by setting the particle size ratio (D10 / D50) to 0.75 or less, an extremely high overcharge gas amount of 55 cm ³ or more was realized. From the viewpoint of reliability during overcharge, the particle size ratio (D10 / D50) is preferably 0.75 or less, more preferably 0.67 or less, and 0.5 or more and 0.6 or less. It is particularly preferable to do this.

<< Test Example 3 >>
In this example, in the lithium ion secondary battery manufacturing process of Example 1 described above, the lithium ion secondary battery is constructed by varying the primary particle size of the conductive material (AB), and the IV resistance and the amount of overcharge gas are set. evaluated. The results are shown in FIGS. FIG. 9 is a graph showing the relationship between the primary particle size of the conductive material and the IV resistance, and FIG. 10 is a graph showing the relationship between the primary particle size of the conductive material and the amount of overcharge gas.

As is clear from FIG. 9, the IV resistance tended to decrease as the primary particle size of the conductive material decreased. In the case of the battery used here, an extremely low IV resistance of 37.3 mΩ or less was realized by setting the primary particle size of the conductive material to 25 nm or less. From the viewpoint of improving output characteristics, the primary particle size of the conductive material is preferably 25 nm or less, and more preferably 20 nm or less. Further, as apparent from FIG. 10, the amount of overcharged gas tended to increase as the primary particle size of the conductive material decreased. In the case of the battery used here, an extremely high overcharge gas amount of 74 cm ³ or more was realized by setting the primary particle size of the conductive material to 25 nm or less. From the viewpoint of reliability during overcharge, the primary particle size of the conductive material is preferably 25 nm or less, and more preferably 20 nm or less.

  As mentioned above, although this invention was demonstrated in detail, the said embodiment and Example are only illustrations and what changed and changed the above-mentioned specific example is contained in the invention disclosed here.

  Since the lithium ion secondary battery proposed here exhibits excellent performance as described above, it can be used as a lithium ion secondary battery for various applications. For example, it can be suitably used as a power source for a motor (electric motor) mounted on a vehicle such as an automobile. Such lithium ion secondary batteries may be used in the form of an assembled battery formed by connecting a plurality of them in series and / or in parallel. Therefore, according to the technology disclosed herein, a vehicle (typically an automobile, particularly a hybrid automobile, an electric automobile, or a fuel cell automobile) provided with such a lithium ion secondary battery (which may be in the form of an assembled battery) as a power source. An automobile equipped with such an electric motor) can be provided.

  In addition, here, a lithium ion secondary battery has been exemplified, but the secondary battery proposed here is also employed in the structure of a secondary battery other than a lithium ion secondary battery unless specifically limited. sell.

100 lithium ion secondary battery 200 wound electrode body 220 positive electrode sheet 221 positive electrode current collector 223 positive electrode active material layer 240 negative electrode sheet 241 negative electrode current collector 243 negative electrode active material layer 262, 264 separator 300 battery case

Claims (7)

A positive electrode active material for a non-aqueous electrolyte secondary battery comprising a granular composite oxide containing at least cobalt (Co) as a constituent metal element,
In the composite oxide particles, the surface portion of the particles has a higher Co concentration than the center portion,
In the particle size distribution of the composite oxide particles, a ratio value (D10 / D50) of D10 diameter corresponding to 10% cumulative from the smaller particle diameter side and D50 diameter corresponding to 50% cumulative is (D10 / D50). D50) A positive electrode active material for a non-aqueous electrolyte secondary battery that satisfies ≦ 0.75.   The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the ratio value (D10 / D50) satisfies (D10 / D50) ≦ 0.67.   The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the ratio value (D10 / D50) satisfies 0.45 ≦ (D10 / D50).   The ratio value (X / Y) of the average Co concentration X (mol%) in the surface portion of the composite oxide particles and the average Co concentration Y (mol%) of the entire composite oxide particles is 1.1 ≦ The positive electrode active material for a nonaqueous electrolyte secondary battery according to claim 1, wherein (X / Y) ≦ 1.5 is satisfied. The composite oxide particles have the following general formula:
_{Li x Ni a Co b Mn c} Me d O 2 (1)
(X, a, b, c and d in the formula (1) are
0.99 ≦ x ≦ 1.12,
0.9 ≦ a + b + c + d ≦ 1.1,
1.05 ≦ x / (a + b + c + d) ≦ 1.2,
0 <a ≦ 0.5, 0 <b ≦ 0.5, 0 <c ≦ 0.5, 0 ≦ d ≦ 0.2, Me is not present or is a transition metal element, One or more elements selected from a typical metal element and boron (B). )
The positive electrode active material for nonaqueous electrolyte secondary batteries as described in any one of Claims 1-4 which is complex oxide shown by these. An electrode body comprising: a positive electrode including the positive electrode active material according to any one of claims 1 to 5; a conductive material; a negative electrode including a negative electrode active material; and a separator interposed between the positive electrode and the negative electrode. ,
A battery case that houses the electrode body;
An external terminal provided in the battery case and connected to the electrode body;
A non-aqueous electrolyte containing a gas generating agent that is contained in the battery case, reacts at a voltage equal to or higher than a predetermined voltage, and generates a gas;
A nonaqueous electrolyte secondary battery comprising: a current interruption mechanism that interrupts electrical connection between the electrode body and the external terminal when an internal pressure of the battery case becomes higher than a predetermined pressure. The non-aqueous electrolyte secondary battery according to claim 6, wherein an average primary particle diameter of the conductive material is 25 nm or less.

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