JP6202336B2 - Cathode active material for non-aqueous electrolyte secondary battery - Google Patents

Description

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

  Nonaqueous electrolyte secondary batteries such as lithium ion secondary batteries are preferably used for so-called portable power supplies, high-output power supplies for vehicles, and the like because they are lighter and have higher energy density than existing batteries. In such non-aqueous electrolyte secondary batteries, further energy density, higher output density, and higher durability are being studied as part of performance improvement. In this connection, Patent Document 1 discloses that a lithium nickel composite oxide having a carbon content adjusted to a predetermined value or less is used as a positive electrode active material, so that high capacity and high output can be obtained and gas at a high temperature can be obtained. It is described that a non-aqueous electrolyte secondary battery with suppressed generation and excellent thermal stability can be realized.

JP 2013-026199 A

However, a nickel-based positive electrode active material has a thermodynamically unstable crystal structure in a high SOC state, and can be used under severe conditions such as an in-vehicle battery (for example, in a high temperature environment). It is known that the internal resistance increases due to the collapse of the crystal structure when stored for a long period of time. Further, in the non-aqueous electrolyte secondary battery, when a current exceeding the normal level is supplied due to an erroneous operation or the like, overcharge occurs, for example, the positive electrode active material and the non-aqueous electrolyte cause an exothermic reaction, and the battery temperature rises. There is. In recent years, from the viewpoint of improving reliability, it has been required to further suppress the increase in battery temperature.
This invention is made | formed in view of this situation, The objective is to provide the positive electrode active material for non-aqueous-electrolyte secondary batteries which had the outstanding battery characteristic and high overcharge-proof performance. . Another related object is to provide a non-aqueous electrolyte secondary battery including the positive electrode active material.

  According to the present invention, a positive electrode active material for a non-aqueous electrolyte secondary battery is provided. Such a positive electrode active material is composed mainly of a lithium nickel cobalt manganese-based composite oxide containing lithium, nickel, cobalt, and manganese as constituent elements, and constitutes a carbon element and a compound containing the carbon element. And an additive metal element (A). The additive metal element (A) is one or more of sodium (Na), potassium (K), magnesium (Mg), calcium (Ca), strontium (Sr), and barium (Ba). . Further, when the total amount of the positive electrode active material is 100% by mass, the proportion of the carbon element is 0.03% by mass or more and 0.3% by mass or less, and the proportion of the additive metal element (A) is 0%. 0.003 mass% or more and 0.5 mass% or less.

  Lithium nickel cobalt manganese composite oxide (hereinafter sometimes simply referred to as “LNCM oxide”) has a thermodynamically stable crystal structure and a higher theoretical energy density than other oxides. Therefore, excellent battery characteristics (for example, high energy density and high durability) can be realized. Further, the positive electrode active material disclosed herein contains an appropriate amount of carbon-containing compound in the positive electrode active material (typically the surface of the LNCM-based oxide) by including the additive metal element (A). doing. Thereby, the substantial surface area of the LNCM-based oxide is reduced, and the decomposition (polymerization) reaction of the non-aqueous electrolyte during overcharge can be suppressed while the resistance during normal use is kept low. As a result, it is possible to achieve both excellent battery characteristics (for example, high energy density and high durability) and high overcharge resistance.

The content of the additive element (A) can be measured by a general ICP (Inductively Coupled Plasma) emission analysis or atomic absorption analysis technique. The content of carbon element (C) can be measured by a general high-frequency combustion-non-dispersive infrared analysis (NDIR) method. Alternatively, in the analysis of commercially available batteries, a general ion chromatography (IC: Ion Chromatography) method may be employed.
Further, in this specification, “mainly composed of lithium nickel cobalt manganese composite oxide” means that 50% by mass or more of the positive electrode active material is 100% by mass of lithium nickel cobalt manganese composite oxide. (LNCM composite oxide) is typically occupied by 80% by mass or more, preferably 90% by mass or more, more preferably 95% by mass or more, and particularly 98% by mass or more. Means occupying.

It is the chemical composition of a positive electrode active material, and the evaluation result of the nonaqueous electrolyte secondary battery using this positive electrode active material. It is a graph which shows the relationship between the ratio of a carbon element, and the ratio of an addition metal element (A). It is a graph which shows the relationship between the ratio of a carbon element, and the temperature rise at the time of an overcharge test.

  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 (for example, composition and properties of the positive electrode active material) and matters necessary for the implementation of the present invention (for example, constituent elements of the battery that do not characterize the present invention) Or a general manufacturing process) can be understood as a design matter of a person skilled in the art based on the prior art in the field. The present invention can be carried out based on the contents disclosed in this specification and common technical knowledge in the field.

<Positive electrode active material>
The positive electrode active material disclosed here contains a lithium nickel cobalt manganese composite oxide, a carbon element, and an additive metal element (A).
The lithium nickel cobalt manganese-based composite oxide (LNCM-based oxide) is a main component of the positive electrode active material disclosed herein, and at least lithium (Li), nickel (Ni), and cobalt (Co ) And manganese (Mn).
Here, the LNCM-based oxide is not only an oxide containing only Li, Ni, Co, and Mn but also at least one other metal element M (ie, Li, Ni, Co, and Mn). , Ni, Co, Mn, and / or transition metal elements and / or typical metal elements). Such metal elements M are Na, K, Mg, Ca, Sr, Ba, titanium (Ti), zirconium (Zr), vanadium (V), niobium (Nb), chromium (Cr), molybdenum (Mo), tungsten ( W), iron (Fe), rhodium (Rh), palladium (Pb), platinum (Pt), copper (Cu), zinc (Zn), boron (B), aluminum (Al), gallium (Ga), indium ( It may be one or more elements of In), tin (Sn), lanthanum (La), and cerium (Ce). In other words, the chemical composition of the LNCM oxide may include all or part of the added metal element (A).

  In a preferred embodiment, the LNCM-based oxide includes at least a Zr element and a W element as the metal element M. Thereby, overcharge-proof performance and battery characteristics can be made compatible at an even higher level. The ratio of the substitutional metal element M such as Zr or W is usually 0.01 to 5% by mass when the total of the Ni element, Co element, Mn element and substitutional metal element M is 100% by mass. (For example, 0.05 to 2% by mass). Thereby, the crystal structure of the LNCM oxide is further stabilized, and the effect of the present invention can be exhibited at a higher level.

The proportion of Li element in the whole positive electrode active material is usually about 5 to 10% by mass (for example, 7 to 8% by mass). Moreover, the ratio of Ni element to the whole positive electrode active material is good in it being about normally 15-25 mass% (for example, 19-20 mass%). Moreover, the ratio of the Co element to the whole positive electrode active material is good to be about 15-25 mass% (for example, 19-20 mass%) normally. Moreover, the ratio of the Mn element to the whole positive electrode active material is usually about 15 to 25% by mass (for example, 17 to 18% by mass). When the above-mentioned substituting metal element is included, the ratio of the substituting metal element M to the whole positive electrode active material (when two or more types are included, the total ratio) is usually 0.1 to 5% by mass (typical Is preferably about 0.5 to 1.5% by mass, for example, 1 ± 0.1% by mass.
In a preferred embodiment, the amount of Ni element, the amount of Co element, and the amount of Mn element are substantially the same (for example, the difference in mass ratio in the entire positive electrode active material is 5 mass% or less). By using the LNCM-based oxide having such a composition, it is possible to realize further excellent thermal stability and battery characteristics.

The BET specific surface area of the LNCM-based oxide is not particularly limited, but is preferably 1 m ² / g or more from the viewpoint of securing a reaction field with the charge carrier and productivity (handleability). Further, from the viewpoint of improving durability (for example, high-temperature durability) and suppressing heat generation during overcharge, it is preferably 20 m ² / g or less.
In the present specification, “BET specific surface area” refers to a specific surface area obtained by analyzing a surface area measured by a constant volume adsorption method using nitrogen gas by a BET method (for example, a BET multipoint method).

The LNCM-based oxide disclosed herein typically has a layered crystal structure (for example, a layered rock salt structure belonging to a hexagonal system), and charge carriers (for example, Lithium ions) are thought to move through the LNCM oxide. Each layer of the LNCM-based oxide is laminated along the (003) plane direction. From this viewpoint, the crystallite diameter along the (003) plane direction of the LNCM oxide is preferably 800 to 1600 mm. Thereby, especially with respect to the charge / discharge cycle at a high rate, the resistance can be kept low, and the capacity can be kept high. Accordingly, battery characteristics (particularly, output characteristics and energy density) and overcharge resistance can be achieved at a higher level.
The crystallite diameter can be calculated based on Scherrer's law from the value of a diffraction peak (half width) obtained by X-ray diffraction measurement using CuKα rays.

  Such an LNCM oxide can be produced by a conventionally known production method. Specifically, for example, a hydroxide of the metal element from an aqueous solution containing at least one of the metal elements contained in the LNCM-based oxide (preferably, all of the metal elements other than lithium contained in the oxide). Can be produced by a method in which the metal hydroxide and the lithium compound are mixed and fired.

  The carbon element contained in the positive electrode active material disclosed herein is, for example, an unreacted compound used as a raw material in the production of the LNCM-based oxide, an inevitably contained impurity, or a secondary element accompanying the production. It may be a compound produced as a product. The presence form of the carbon element is not particularly limited, but may typically be a metal element carbonate (for example, lithium carbonate), carbonate ion, oxalate ion, or the like. These may be physically attached or chemically (for example, as a functional group) to the surface of the LNCM oxide, or may be mixed in the LNCM oxide alone.

  In the technique disclosed herein, the proportion of the carbon element in the entire positive electrode active material is 0.03 to 0.3% by mass (for example, 0.030 to 0.204% by mass). When the amount of carbon is less than 0.03% by mass, it is difficult to obtain the effects of the present invention, and the reaction of the nonaqueous electrolytic solution may not be sufficiently suppressed during overcharge. On the other hand, when the amount of carbon is more than 0.3% by mass (for example, 0.204% by mass), the resistance increases, and other battery characteristics (for example, output characteristics and cycle characteristics) may tend to decrease. By satisfying the above carbon element ratio, the rise in battery temperature during overcharging can be kept small, and the original characteristics of the battery during normal use and the reliability during overcharging can be combined at a higher level. It becomes.

  Further, the additive metal element (A) contained in the positive electrode active material disclosed herein is a metal element that can constitute a compound containing a carbon element. In the technology disclosed herein, the additive metal element (A) is one or more elements of Na, K, Mg, Ca, Sr, and Ba. The presence form of the additive metal element (A) is not particularly limited. For example, the additive metal element (A) may be included as a substituting metal element of the above-described LNCM oxide, or may constitute a compound with a carbon element. The additive metal element (A) tends to make a carbonic acid compound easily. Therefore, in a typical embodiment, the carbon element and the additive metal element (A) constitute a compound. Specifically, it may be in the form of sodium carbonate, potassium carbonate, magnesium carbonate, calcium carbonate, barium carbonate or the like.

  In the technique disclosed here, the ratio of the additive metal element (A) in the entire positive electrode active material is 0.003 to 0.5 mass% (for example, 0.005 to 0.41 mass%). According to the study by the present inventors, when the amount of the additive metal element is less than 0.003 mass% (typically 0.005 mass%), a sufficient carbon amount is produced in the positive electrode active material in production. It is difficult to contain. On the other hand, when the amount of the additive metal element is more than 0.5% by mass, the resistance increases and other battery characteristics (for example, output characteristics and cycle characteristics) may tend to decrease. By satisfying the ratio of the additive metal element (A), the original characteristics of the battery during normal use and the reliability during overcharge can be combined at a higher level.

<Nonaqueous electrolyte secondary battery>
The present invention also provides a non-aqueous electrolyte secondary battery comprising a positive electrode having a positive electrode active material, a negative electrode having a negative electrode active material, and a non-aqueous electrolyte. Such a non-aqueous electrolyte secondary battery is characterized in that the positive electrode includes the positive electrode active material disclosed herein. Therefore, the other components are not particularly limited, and can be arbitrarily determined according to various uses.

  The positive electrode of the nonaqueous electrolyte secondary battery disclosed herein includes at least the positive electrode active material having the above-described configuration disclosed herein. As such a positive electrode, a positive electrode having a positive electrode active material layer formed by fixing the positive electrode active material on a positive electrode current collector together with a binder, a conductive material and the like is preferable. As the positive electrode current collector, a conductive member made of a highly conductive metal (for example, aluminum, nickel, etc.) is suitable. As the binder, a vinyl halide resin such as polyvinylidene fluoride (PVdF) or a polyalkylene oxide such as polyethylene oxide (PEO) is suitable. As the conductive material, carbon materials such as carbon black (typically acetylene black and ketjen black) and activated carbon are suitable.

  The negative electrode of the nonaqueous electrolyte secondary battery disclosed herein includes at least a negative electrode active material. As such a negative electrode, a negative electrode active material powder (particles) is preferably fixed on a negative electrode current collector together with a binder, a thickener and the like to form a negative electrode active material layer. As the negative electrode current collector, a conductive material made of a metal having good conductivity (for example, copper, nickel, etc.) is suitable. As the negative electrode active material, carbon materials such as graphite (graphite), non-graphitizable carbon (hard carbon), graphitizable carbon (soft carbon) and the like are preferable, and graphite is particularly preferable from the viewpoint of energy density and durability. . As the binder, styrene butadiene rubber (SBR), polytetrafluoroethylene (PTFE) and the like are suitable. As the thickener, a carboxymethyl cellulose (CMC) cellulosic material is suitable. As the negative electrode current collector, a conductive material made of a highly conductive metal (for example, copper) is suitable.

  The positive electrode and the negative electrode of the non-aqueous electrolyte secondary battery disclosed herein typically face each other with a separator interposed therebetween. As the separator, a porous resin sheet made of a resin such as polyethylene (PE) or polypropylene (PP) is suitable. In addition, you may equip the single side | surface or both surfaces of the said porous resin sheet with the porous heat-resistant layer.

The non-aqueous electrolyte of the non-aqueous electrolyte secondary battery disclosed herein typically exhibits a liquid state at normal temperature (for example, 25 ° C.), and is preferably always liquid within the operating temperature range (for example, −30 to 60 ° C.). Presents. As the nonaqueous electrolytic solution, a nonaqueous solvent containing a supporting salt (for example, a lithium salt in a lithium ion secondary battery) can be suitably used.
As the non-aqueous solvent, aprotic solvents such as carbonates, esters, ethers, nitriles, sulfones and lactones are suitable. Of these, carbonates such as ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) are preferable from the viewpoint of durability. As the supporting salt, a lithium salt, a sodium salt, a magnesium salt, and the like are preferable, and lithium salts such as LiPF ₆ and LiBF ₄ are particularly preferable.

  In addition, components other than the supporting salt and the non-aqueous solvent described above can be appropriately contained in the non-aqueous electrolyte. Such optional components include, for example, an increase in the amount of gas generated during overcharge, an improvement in battery output performance, an improvement in storage stability (such as suppression of capacity reduction during storage), an improvement in cycle characteristics, and an improvement in initial charge / discharge efficiency. It can be used for such purposes. Examples include gas generating agents such as biphenyl (BP) and cyclohexylbenzene (CHB); film forming agents for lithium bisoxalate borate (LiBOB) and vinylene carbonate (VC); dispersants; thickeners; Is mentioned.

<Applications of non-aqueous electrolyte secondary batteries>
The non-aqueous electrolyte secondary battery disclosed herein can stably achieve higher reliability (overcharge resistance) than conventional products due to the effect of controlling the composition and properties of the positive electrode active material. Is. For example, high energy density, high power density, and high reliability can be combined. Such a non-aqueous electrolyte secondary battery can be used for various applications. Utilizing such characteristics, applications that require high energy density, high input / output density, and high reliability, such as plug-in hybrid vehicles, It can be preferably used as a driving power source mounted on a vehicle such as a hybrid vehicle or an electric vehicle.

  Hereinafter, some examples relating to the present invention will be described. However, the present invention is not intended to be limited to the specific examples.

<Construction of lithium ion secondary battery>
First, a positive electrode active material (Examples 1 to 9) having a chemical composition shown in FIG. 1 was prepared as a positive electrode active material. FIG. 2 shows the relationship between the ratio of the carbon element and the ratio of the added metal element (A). And the non-aqueous electrolyte secondary battery was constructed | assembled using this positive electrode active material, and evaluation was performed.
Specifically, first, the positive electrode active material, acetylene black (AB) as a conductive material, and polyvinylidene fluoride (PVdF) as a binder are mixed, and the viscosity is adjusted with N-methylpyrrolidone (NMP). Thus, a positive electrode active material layer forming slurry was prepared. The slurry was applied to the surface of an aluminum foil (positive electrode current collector) and dried to form a positive electrode active material layer. After rolling this, the sheet-like positive electrode (Examples 1-9) provided with the positive electrode active material layer on the positive electrode current collector was obtained by carrying out slit processing to a predetermined size.

Next, carbon as a negative electrode active material, styrene butadiene rubber (SBR) as a binder, and carboxymethyl cellulose (CMC) as a thickener are mixed, and the viscosity is adjusted with ion-exchanged water, whereby the negative electrode active material is adjusted. A slurry for forming a material layer was prepared. The slurry was applied to the surface of a copper foil (negative electrode current collector) and dried to form a negative electrode active material layer. This was roll-rolled and then slitted to a predetermined size to obtain a sheet-like negative electrode having a negative electrode active material layer on the negative electrode current collector.
The produced sheet-like positive electrode and negative electrode were laminated and wound through a separator sheet to produce electrode bodies (Examples 1 to 9). As the separator, a porous sheet having a three-layer structure made of polypropylene (PP) / polyethylene (PE) / polypropylene (PP) was used.

Next, this electrode body was accommodated in a rectangular battery case made of aluminum, and a non-aqueous electrolyte was injected. As the non-aqueous electrolyte, a mixed solvent containing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) at a volume ratio of 3: 4: 3, and LiPF ₆ as a supporting salt is used. A solution dissolved at a concentration of about 1.1 mol / L was used. The lithium ion secondary battery of Examples 1-9 (theoretical capacity 3.6 Ah) in which only the positive electrode active material is different by sealing the opening of the battery case and attaching a thermocouple to the outer surface (abdomen) of the battery case. Built.

<Resistance measurement>
The battery thus constructed was subjected to a conditioning treatment, and then the initial capacity was confirmed in a voltage range of 3.0 to 4.2 V to confirm that there was no abnormality. Next, the battery resistance was measured under a temperature environment of 25 ° C. Specifically, the battery is first adjusted to a state of SOC 60%, and then discharged for 10 seconds at a constant current of 130 A. The following formula: (battery voltage at start of discharge−battery voltage after 10 seconds) / current; Was used to measure the DC-IR resistance (mΩ). The results are shown in FIG.

  As shown in FIG. 1, macroscopically, an increase in resistance was observed with an increase in the proportion of carbon element and / or the proportion of added metal element (A). For example, in a battery that requires a high energy density and a high output density, such as those used for vehicle driving power supplies, it is desirable that the resistance is 3 mΩ or less (for example, 2.6 mΩ or less). That is, from the results of this study, when the battery characteristics during normal use are taken into consideration, the carbon element ratio is 0.3% by mass (for example, 0.204% by mass) or less when the entire positive electrode active material is 100% by mass. In addition, it was found that the ratio of the additive metal element is 0.5% by mass or less (eg, 0.41% by mass or less).

<Overcharge test>
Next, under a temperature environment of 25 ° C., the battery was adjusted to a SOC of 30%, and then charged with a constant current of 10 C to an overcharged state with an upper limit voltage of 10 V. And battery rise temperature (DELTA) T (degreeC) from 1 minute after shutdown was confirmed. The results are shown in FIG. Moreover, the relationship between the ratio of a carbon element and the temperature rise at the time of an overcharge test is shown in FIG.

As shown in FIGS. 1 and 3, when the total amount of the positive electrode active material is 100% by mass, if the carbon element ratio is 0.03% by mass or more, the temperature change during overcharge is 30 ° C. or less (for example, It was found that the calorific value can be suppressed to a minimum. Further, from FIG. 2, a correlation is generally recognized between the ratio of the carbon element and the ratio of the added metal element (A). In order to realize the ratio of the carbon element, the ratio of the added metal element (A) is 0. It was found necessary to be 0.003 mass% (typically 0.005 mass%) or more.
As described above, according to the technology disclosed herein, the original characteristics of the battery during normal use and the reliability during overcharge can be combined at a high level. Such a result represents the effect of the present invention.

  As mentioned above, although this invention was demonstrated in detail, the said embodiment is only an illustration and what changed and modified the above-mentioned specific example is included in the invention disclosed here.

Claims (2)

A positive electrode active material used for construction of a non-aqueous electrolyte secondary battery,
Mainly lithium nickel cobalt manganese based composite oxide containing lithium element , nickel element , cobalt element , manganese element , and zirconia element as constituent elements,
A carbon element and an additive metal element (A),
Here, the additive metal element (A) is one or more elements selected from the group consisting of Na, K, Mg, Ca, Sr and Ba,
At least a part of the carbon element and at least a part of the additive metal element (A) constitute a carbonate,
When the whole positive electrode active material is 100% by mass,
The proportion of the lithium element is 5% by mass or more and 10% by mass or less,
The proportion of the nickel element is 15% by mass or more and 25% by mass or less,
The proportion of the cobalt element is 15% by mass or more and 25% by mass or less,
The proportion of the manganese element is 15% by mass or more and 25% by mass or less,
The proportion of the zirconia element is 0.1% by mass or more and 5% by mass,
The proportion of the carbon element is 0.03% by mass or more and 0.204% by mass or less,
The positive electrode active material for nonaqueous electrolyte secondary batteries whose ratio which the said addition metal element (A) accounts is 0.005 mass% or more and 0.41 mass% or less. A non-aqueous electrolyte secondary battery comprising the positive electrode active material according to claim 1.

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