JP2017188421A - Positive electrode active material particle for nonaqueous electrolyte secondary battery, method for manufacturing the same, and nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a highly stable positive electrode active material particle for a nonaqueous electrolyte secondary battery.SOLUTION: A positive electrode active material particle has a hexagonal layered rock-salt structure, of which the composition formula is given by Li(NiCoMn)O(where 1.00≤x≤1.07, 0.10≤y≤0.40, 0.10≤z≤0.40, and 0.3≤y+z≤0.7). In a case in which such positive electrode active material particles are used for a positive electrode, and Li is used as a negative electrode to assemble a nonaqueous electrolyte secondary battery, and the battery is initially charged at a rate of 0.2 C (a current density of 16 mA/g) to 4.6 V under a 60°C-environment to prepare a graph (a dQ/dV curve) of which the horizontal axis shows a voltage, and the vertical axis shows dQ/dV as a result of differentiation of an initial charge capacity with respect to a voltage, the area in a voltage range of 4.3-4.52 V in the graph is 35 mAh/g or less.SELECTED DRAWING: None

Description

  The present invention relates to a positive electrode active material particle for a nonaqueous electrolyte secondary battery having a hexagonal layered rock salt structure exhibiting high stability, a method for producing the same, and a nonaqueous electrolyte secondary battery.

  In recent years, electronic devices such as AV devices and personal computers are rapidly becoming portable and cordless, and there is an increasing demand for secondary batteries having a small size, light weight, and high energy density as power sources for driving these devices. Under such circumstances, a lithium ion secondary battery having advantages such as a high charge / discharge voltage and a large charge / discharge capacity has attracted attention.

Conventionally, as a positive electrode active material useful for a high energy type lithium ion secondary battery having a voltage of 4 V class, spinel type structure LiMn ₂ O ₄ , hexagonal layered rock salt type structure LiCoO ₂ , LiCo _1-X Ni _X O ₂ , LiNiO _{2 and the} like are generally known. Among them, LiCoO ₂ is excellent in that it has a high voltage and a high capacity, but includes a problem of high manufacturing cost due to a small supply amount of cobalt raw material and a problem of environmental safety of a discarded battery. Therefore, Versatile Ni, ternary had hexagonal layered rock-salt structure is a solid solution of Co and Mn positive electrode active material particles (basic _{composition: Li (Ni x Co y Mn} z) O 2 - or less, the same -) Is actively researched.

  As is well known, the ternary positive electrode active material particles having a hexagonal layered rock salt structure are prepared by mixing Ni compound, Co compound, Mn compound and Li compound at a predetermined ratio, for example, a temperature range of about 700 ° C. to 1000 ° C. Can be obtained by baking.

  In lithium ion secondary batteries using ternary positive electrode active material particles, a material that can suppress deterioration of charge / discharge capacity due to repeated charge / discharge and improve battery stability is currently most demanded. . In particular, it is most required to be stable without deterioration of battery characteristics even when stored in a charged state.

  In order to achieve high stability of the battery, it has been considered important to particularly suppress the destabilization of the crystal structure in the ternary positive electrode active material particles. As the means, a method of controlling the composition balance, crystallite size and particle size distribution of Li, Ni, Co, and Mn compounds used in the ternary positive electrode active material particles, a method of obtaining powder by controlling the firing temperature, a different element A method for strengthening the bonding strength of crystals by adding selenium, a method for achieving the target by surface treatment, and the like are performed.

So far, a material that is LiNi _0.33 Co _0.33 Mn _0.33 O ₂ has been known as positive electrode active material particles for improving battery safety (Patent Document 1). Further, a highly safe material due to a small change in the lattice volume due to the cycle is also known (Patent Document 2). Furthermore, a material that is intended to activate a safety valve of a battery by generating an appropriate gas by adding Ca is also known (Patent Document 3).

JP 2003-059490 A Japanese Patent No. 4900888 JP 2014-143108 A

  As described above, a material that is highly stable as a positive electrode active material for a non-aqueous electrolyte secondary battery and that can improve the stability of the battery is currently most demanded. The manufacturing method has not been obtained.

That is, Patent Document 1 discloses a highly crystalline LiNi _0.33 Co _0.33 Mn _0.33 O ₂ , and although there is an explanation thereof, the stability is still insufficient from a practical point of view. And the stability of the battery cannot be improved sufficiently. Moreover, in the said patent document 2, although the safety | security by small change of the lattice volume by a cycle is called for, stability of a battery is not described in particular, and it is doubtful whether stability of a battery can fully be improved. Moreover, in the said patent document 3, although the method of ensuring the safety | security of a battery by taking out gas intentionally is taken, it lacks stability as positive electrode active material itself, and is still insufficient practically. .

  The present invention has been made in view of the above problems, and an object of the present invention is to obtain positive electrode active material particles for a non-aqueous electrolyte secondary battery having high stability, and such a positive electrode active material. The object is to obtain a highly stable non-aqueous electrolyte secondary battery using particles.

  In order to achieve the above object, in the present invention, the positive electrode active material particles are mainly composed of at least Li, Ni, Co and Mn, and the molar ratio of Li / (Ni + Co + Mn) is 1.00 or more and 1.07 or less. The lithium composite oxide was used.

Specifically, the positive electrode active material particles for a non-aqueous electrolyte secondary battery according to the present invention are positive electrode active material particles having a hexagonal layered rock salt structure, and the composition formula is Li _x (Ni _1-yz Co). in _{y Mn z) O 2-δ} (1.00 ≦ x ≦ 1.07,0.10 ≦ y ≦ 0.40,0.10 ≦ z ≦ 0.40,0.3 ≦ y + z ≦ 0.7) Yes, using the positive electrode active material particles as the positive electrode and using Li as the negative electrode, a non-aqueous electrolyte secondary battery was assembled, and initially at a 0.2 C rate (current density 16 mA / g) up to 4.6 V in an environment of 60 ° C. When charging was performed and a graph (dQ / dV curve) showing dQ / dV, which is a value obtained by differentiating the initial charge capacity by voltage on the horizontal axis and voltage on the horizontal axis, the voltage is 4 in the graph. . The size of the area in the range of 3 V or more and 4.52 V or less is 35 mAh / g or less. That.

  The positive electrode active material particles according to the present invention can be used for producing a battery having high stability by having the above-described configuration.

In general, it is considered that the domain of Li ₂ MnO ₃ is important for the stability of the crystal lattice of the ternary composite oxide composed of Ni, Co, and Mn, and the Li content is within the above range (1.00 When less than ≦ x ≦ 1.07), the domain amount of Li ₂ MnO ₃ becomes small and the stability becomes low. On the other hand, when a large amount of Li ₂ MnO ₃ is present in the Li composite oxide, a part of Li ₂ MnO ₃ is activated during high-temperature storage in a charged state, and as a result, the hexagonal layered rock salt structure of the positive electrode active material The total amount of Li in the inside increases, and Li having a low potential is present in the hexagonal layered rock salt structure more than before storage, which may reduce the open circuit voltage.

However, the present inventors have recently assembled a coin cell in which the Li composite oxide having the above-described structure is used as the active material for the positive electrode and the negative electrode is Li, and the 0.2C rate up to 4.6 V in a 60 ° C. environment ( When the initial charge is performed at a current density of 16 mA / g), it corresponds to the amount of active Li ₂ MnO ₃ present in the positive electrode active material in the dQ / dV curve while containing Li in the above molar ratio. Then, it was found that the peak value considered to appear extremely low. That is, according to the positive electrode active material particles according to the present invention, the highly crystalline Li ₂ MnO ₃ domain is not activated even in a charged state, and as a result, an open circuit voltage that may induce various problems. It is possible to obtain a highly stable battery in which a decrease in the resistance is difficult to occur.

  In addition, in the positive electrode active material according to the present invention, since the composition ratio of Ni is 0.30 to 0.70, a positive electrode active material capable of increasing the capacity of the battery while being highly stable is obtained. Can do.

  The positive electrode active material particles according to the present invention preferably have a crystallite size of 200 nm to 900 nm and an average secondary particle diameter (D50) of 3 μm to 20 μm.

  When the crystallite size is smaller than 200 nm, the positive electrode active material particles themselves become unstable. When it is larger than 900 nm, battery characteristics deteriorate when used in a battery. A more preferable range is 200 to 600 nm. Further, when the average secondary particle diameter (D50) is smaller than 3 μm, the density becomes too small when used in a battery, which is not practical. When it is larger than 20 μm, the battery characteristics become unstable. Therefore, it is preferable to be within the above range. Here, the particle size distribution may be bimodal. The average secondary particle diameter (D50) at that time is also 3 to 20 μm. A preferable average secondary particle diameter (D50) is 5 to 18 μm.

The manufacturing method of the positive electrode active material particles for a non-aqueous electrolyte secondary battery according to the present invention is (Ni _1-yz Co _y Mn _z ) (OH) ₂ (0.10 ≦ y ≦ 0.40,. 10 ≦ z ≦ 0.40, 0.3 ≦ y + z ≦ 0.7) as a precursor, and a lithium compound in the precursor has a molar ratio of Li / (Ni + Co + Mn) in the range of 1.00 to 1.07. After being mixed, the composite oxide containing Li, Ni, Co and Mn is obtained by firing at 870 ° C. or higher and 970 ° C. or lower in an oxidizing atmosphere.

  In the method for producing positive electrode active material particles for a non-aqueous electrolyte secondary battery according to the present invention, a Li / (Ni + Co + Mn) ratio and a firing temperature suitable for the area so that the area of the dQ / dV curve is 35 mAh / g or less. Is selected. That is, the molar ratio of Li / (Ni + Co + Mn) is in the range of 1.00 to 1.07, and the firing is performed at 870 ° C. or higher and 970 ° C. or lower in an oxidizing atmosphere. By doing in this way, the positive electrode active material particle which concerns on this invention mentioned above can be obtained. In particular, if the baking is performed at a temperature lower than 870 ° C., the stability is impaired. Moreover, if it is fired at a temperature higher than 970 ° C., the particles grow too much and cracks are generated, resulting in instability. Therefore, according to the method for producing positive electrode active material particles according to the present invention, positive electrode active material particles having high stability as described above can be obtained.

  The non-aqueous electrolyte secondary battery according to the present invention is characterized by using the positive electrode active material particles for the non-aqueous electrolyte secondary battery.

  According to the nonaqueous electrolyte secondary battery according to the present invention, since the positive electrode active material as described above is used, the stability can be improved as described above.

  The positive electrode active material particles for a non-aqueous electrolyte secondary battery according to the present invention are suitable as a positive electrode active material for a non-aqueous electrolyte secondary battery because they exhibit high stability.

In the present invention, when a graph (dQ / dV curve) showing the voltage on the horizontal axis and dQ / dV which is a value obtained by differentiating the initial charge capacity by the voltage on the vertical axis is 4 in the graph. It is a graph for demonstrating the magnitude | size of the area in the range of 0.3V or more and 4.52V or less. It is a graph (dQ / dV curve) in which the horizontal axis represents voltage and the vertical axis represents dQ / dV which is a value obtained by differentiating the initial charge capacity by voltage. 6 is a graph showing changes in open circuit voltage of Example 1 and Comparative Example 1.

  Hereinafter, modes for carrying out the present invention will be described. The following description of the preferred embodiments is merely exemplary in nature and is not intended to limit the invention, its method of application, or its application.

  First, positive electrode active material particles for a nonaqueous electrolyte secondary battery according to an embodiment of the present invention will be described.

  The positive electrode active material particles according to the present embodiment have a hexagonal layered rock salt structure and are composed of a composite oxide containing at least Li, Ni, Co, and Mn.

The range of the Li content of the positive electrode active material particles according to this embodiment is such that the molar ratio represented by Li / (Ni + Co + Mn) is 1.00 to 1.07. In addition, the temperature for firing is 870 to 970 ° C. The positive electrode active material particles of the present invention can be obtained by selecting optimum conditions within the conditions of the molar ratio and the firing temperature. The characteristics of the material are described. Since the presence of the Li ₂ MnO ₃ domain is considered to be important for the stability of the crystal lattice of the Li composite oxide, when the Li content is less than the above range, The amount of Li ₂ MnO ₃ present at random is reduced. As a result, since the stability of the Li composite oxide is lowered, it is considered that the characteristics of the positive electrode active material particles are deteriorated. On the other hand, when the Li content is larger than the above range, the Li ₂ MnO ₃ domain becomes excessive, and there is a concern that the battery capacity and the safety are lowered. As a result, the stability of the battery is reduced. More preferably, the molar ratio represented by Li / (Ni + Co + Mn) is 1.01-1.06.

  In addition, in the positive electrode active material particles according to the present embodiment, the positive electrode active material particles are used as a positive electrode, Li is used as a negative electrode, and a non-aqueous electrolyte secondary battery is assembled. A graph (dQ / dV curve) showing initial charge at a 2C rate (current density 16 mA / g), voltage on the horizontal axis, and dQ / dV which is a value obtained by differentiating the initial charge capacity with voltage on the vertical axis. When prepared, the area in the graph where the voltage is 4.3 V or more and 4.52 V or less is 35 mAh / g or less. Here, the area in the voltage range of 4.3V to 4.52V is as shown in FIG. 1 from the horizontal axis of the graph, the 4.3V point and the 4.52V point on the horizontal axis. It refers to the area of a region surrounded by an extending vertical line and a line (indicated by a broken line in FIG. 1) indicating a dQ / dV value that is a value obtained by differentiating the initial charge capacity with voltage. That is, it refers to the area of the region indicated by hatching in FIG.

When the dQ / dV curve is created, the way of viewing the graph means that the battery capacity appears in the voltage range where the peak exists. In this experiment, the present inventors have found that a peak exists between 4.3 V and 4.52 V in the dQ / dV curve of the aforementioned coin cell in various experiments. It was found that it is suggested that the activated _Li 2 MnO ₃ is present between the 3V～4.52V. That is, it was found that the amount of Li ₂ MnO ₃ activated by the dQ / dV curve can be quantified.

When a large amount of Li ₂ MnO ₃ is present in the Li composite oxide, a part of Li ₂ MnO ₃ is activated during storage in the charged state, and as a result, the total amount in the hexagonal layered rock salt structure of the positive electrode active material is increased. The amount of Li will increase, and Li, which has a low potential, will be present in the hexagonal layered rock salt structure more than before storage. As a result, the open circuit voltage will decrease, impairing the stability of the battery. End up.

What is important in the present invention is that the peak of dQ / dV in the range of 4.3 V to 4.52 V can be reduced despite the presence of Li ₂ MnO ₃ , that is, the voltage is 4 This means that the area in the range of 3V to 4.52V can be reduced. This is considered to be inactive by increasing the crystallinity of Li ₂ MnO _{3 having} a low crystallinity, which is present in a random state and usually includes stacking faults and crystal distortion. By inactivating the activity of Li ₂ MnO _3, also it is possible to suppress the activation of Li ₂ MnO ₃ when the charging state, the stability and safety of the battery when the battery as a result is improved Conceivable.

Further, in the inventors' view, the cathode active material obtained by the method of the present invention has Li ₂ MnO ₃ deactivated at random in the crystal of the hexagonal layered rock salt structure according to the present invention. It is considered that it becomes a positive electrode active material that brings about a pillar effect and can also exhibit high stability.

  Based on the above, as a result of examination by the present inventors, in the positive electrode active material particles according to the present invention, the area between 4.3 V and 4.52 V in the graph is 35 mAh / g or less in the dQ / dV curve. , Preferably 34.5 mAh / g or less, more preferably 34 mAh / g or less.

  Further, since the positive electrode active material particles in the present embodiment have a Ni composition ratio of 0.30 to 0.70, the battery can be made to have a high capacity while being highly stable when used in the battery. .

  Further, the positive electrode active material particles in the present embodiment include metal elements such as Mg, Al, Ti, V, Fe, Ga, Sr, Y, Zr, Nb, Mo, Ru, In, Sn, Ta, W, and Bi. You may contain. By including these metal elements in the positive electrode active material particles, cycle characteristics, rate characteristics, and stability can be improved when a battery is formed. Here, “containing” includes the fact that the metal element is doped in the positive electrode active material particles and the presence of the metal elements on the surface of the particles.

  In the positive electrode active material particles according to the present embodiment, the crystallite size is 200 to 900 nm, and the average secondary particle diameter is 3 to 20 μm. When the crystallite size is smaller than 200 nm, the crystallite size becomes unstable. When it is larger than 900 nm, battery characteristics are deteriorated. A more preferred range is 200 to 600 nm, and even more preferred is 200 to 400 nm.

  When the average secondary particle diameter (D50) is smaller than 3 μm, the density becomes too small to be practical. When it is larger than 20 μm, it becomes unstable. A more preferable range is 4 to 19 μm.

  Next, a method for producing positive electrode active material particles for a non-aqueous electrolyte secondary battery according to an embodiment of the present invention will be described.

  In order to produce positive electrode active material particles for a non-aqueous electrolyte secondary battery according to this embodiment, first, a precursor, which is a composite compound mainly composed of Ni, Co, and Mn, and a lithium compound are mixed with Li / ( Mix so that the molar ratio represented by (Ni + Co + Mn) is in the range of 1.00 to 1.07. Thereafter, the mixture is fired at 870 ° C. to 970 ° C. in an oxidizing atmosphere, whereby a Li composite oxide containing Li, Ni, Co, and Mn can be obtained.

  Among them, what is important in the present invention is to appropriately select the molar ratio and the firing temperature within the conditions of the molar ratio and the firing temperature set as described above so that the value of dQ / dV is in the above-described range. There is something that can be done.

  The composite compound as a precursor containing at least Ni, Co, and Mn in the present invention can be obtained by coprecipitation of a wet reaction or the like. Specifically, Ni sulfate, Co sulfate, and Mn sulfate are 1.5 mol%. The solution was dissolved so as to become 0.3 mol% of caustic soda, and 0.1 mol of ammonia solution was added dropwise at the same time to cause coprecipitation reaction, and the reaction product was obtained by overflowing, and then washed with water and dried. Obtained.

  In the drying step after the wet reaction, drying is preferably performed so that a hydroxide, oxyhydroxide or spinel phase of Ni, Co or Mn exists in the precursor by XRD diffraction.

  Also, other metal elements can be added in the course of the wet reaction. The added metal element may be present in the hydroxide particles or may be present at the outer edge of the hydroxide particles. Examples of the metal element that can be added include Mg, Al, Ti, V, Fe, Ga, Sr, Y, Zr, Nb, Mo, Ru, In, Sn, Ta, W, and Bi.

The precursor obtained by the wet process preferably has an average secondary particle diameter (D50) in the range of 3 μm to 20 μm. When the average secondary particle diameter is in the above range, a high crystal domain of Li ₂ MnO ₃ can be present at random in the firing step with the Li compound.

  The lithium compound used in the present invention is not particularly limited, and various lithium salts can be used. For example, lithium hydroxide monohydrate, lithium nitrate, lithium carbonate, lithium acetate, lithium bromide, chloride Examples include lithium, lithium citrate, lithium fluoride, lithium iodide, lithium lactate, lithium oxalate, lithium phosphate, lithium pyruvate, lithium sulfate, and lithium oxide. Among them, lithium carbonate or lithium hydroxide / monohydric acid Japanese products are preferred.

  Next, a positive electrode using a positive electrode active material composed of positive electrode active material particles for a non-aqueous electrolyte secondary battery according to an embodiment of the present invention will be described.

  The secondary battery manufactured using the positive electrode containing the positive electrode active material particle which concerns on this embodiment is comprised from the said positive electrode, a negative electrode, and electrolyte.

  When manufacturing the positive electrode containing the positive electrode active material particles according to the present embodiment, a conductive agent and a binder are added to and mixed with the positive electrode active material particles according to a conventional method. As the conductive agent, acetylene black, carbon black, graphite, and the like are preferable, and as the binder, polytetrafluoroethylene, polyvinylidene fluoride, and the like are preferable.

  In the present invention, as the negative electrode active material, lithium metal, lithium / aluminum alloy, lithium / tin alloy, graphite, graphite or the like can be used.

  In addition to the combination of ethylene carbonate (EC) and diethyl carbonate (DEC), the solvent of the electrolytic solution includes at least carbonates such as propylene carbonate (PC) and dimethyl carbonate (DMC), and ethers such as dimethoxyethane. One kind of organic solvent can be used.

Further, as the electrolyte, in addition to lithium hexafluorophosphate (LiPF ₆ ), at least one lithium salt such as lithium perchlorate (LiClO) or lithium tetrafluoroborate (LiBF ₄ ) is dissolved in the above solvent. Can be used.

  When the non-aqueous electrolyte secondary battery manufactured using the positive electrode containing the positive electrode active material particles according to the present embodiment and using Li as the negative electrode is subjected to an overcharge test by an evaluation method described later, dQ / dV The area in the range where the voltage in the curve graph is 4.3 V or more and 4.52 V or less is 35 mAh / g or less.

When the positive electrode active material particles according to the present invention are used, the high crystal domains of Li ₂ MnO ₃ are randomly present in the crystal lattice of the positive electrode active material due to being in the above area, and a hexagonal layered rock salt structure In addition, it is possible to solve the problem that the open circuit voltage decreases after charging by inactivation of Li ₂ MnO ₃ .

  Representative examples of the present invention are as follows.

  The composition of the positive electrode active material particles was prepared by dissolving 1.0 g of a sample in 25 ml of a 20% hydrochloric acid solution by heating, transferring to a 100 ml volumetric flask after cooling, preparing pure water by adding pure water, and measuring the ICAP [Optima 8300. Each element was quantified and determined using Perkin Elmer Co., Ltd.].

  Identification of the phase of the compound of the positive electrode active material particles is performed using an X-ray diffractometer [SmartLab Co., Ltd., Rigaku] in the range of 2θ / θ of 10 ° to 90 ° in 1.2 ° increments of 0.02 °. / min step scan.

  The value of the average secondary particle diameter (D50) is a volume-based average particle diameter measured by a wet laser method using a laser type particle size distribution measuring apparatus Microtrac HRA [manufactured by Nikkiso Co., Ltd.].

  For calculating the crystallite size of the positive electrode active material particles, an X-ray diffractometer [manufactured by SmartLab Co., Ltd., Rigaku] uses a slit of 2/3 degrees, and 2θ / θ ranges from 10 ° to 90 °, Performed at a step of 1.2 ° / min in increments of .02 °. Thereafter, the crystallite size was calculated by performing Rietveld analysis using text data.

  In the Rietveld analysis, a value when Rwp is 13 to 20 and the S value is 1.3 or less is used. For the analysis method, for example, “RA. Young, ed.,“ The Rietveld Method ” , Oxford University Press (1992) ”.

  Below, the positive electrode active material particle which concerns on this invention and the method and result which performed battery evaluation using a 2032 type coin cell are demonstrated.

About the coin cell concerning battery evaluation, it produced as follows. First, 90% by weight of a composite oxide as a positive electrode active material particle powder according to each Example and Comparative Example described later, 3% by weight of acetylene black as a conductive material, 3% by weight of graphite, and N-methylpyrrolidone as a binder After being mixed with 4% by weight of polyvinylidene fluoride dissolved in, it was applied to an Al metal foil and dried at 120 ° C. This sheet was punched out to 14 mmΦ, and then pressure-bonded at 1.5 t / cm ² was used as the positive electrode. A 2032 type coin cell was manufactured using a solution in which EC and DMC mixed with 1 mol / L LiPF ₆ dissolved in a volume ratio of 1: 2 were used as the negative electrode made of metallic lithium having a thickness of 500 μm punched to 16 mmΦ.

  A graph (dQ / dV curve) showing the dQ / dV which is a value obtained by differentiating the voltage on the horizontal axis and the initial charge capacity on the vertical axis is 4. Initial charge is performed at a charge density of 0.2 C rate (current density 16 mA / g) up to 6 V, and the voltage at that time is plotted on the horizontal axis and dQ / dV which is a value obtained by differentiating the initial charge capacity by voltage is used on the vertical axis Thus, a graph with a voltage in the range of 4.2 V to 4.6 V was created.

  As for the measurement of the open circuit voltage, after assembling the 2032 type coin cell as described above, CC-CV charge to 4.3 V at 0.1 C rate at 25 ° C., CC discharge to 3.0 V, and then 4.3 V CC-CV charge was performed until then, the coin cell was placed in an environment of 60 ° C., and the voltage transition was measured in an open circuit state.

  Next, the manufacturing method of the positive electrode active material particle which concerns on each Example and a comparative example is demonstrated.

Example 1
Ni sulfate, Co sulfate, and Mn sulfate were weighed so that each element had a molar ratio of Ni: Co: Mn = 5: 2: 3 and co-precipitated by the wet reaction described above. The composite hydroxide (precursor) was obtained by washing with water and drying (Ni _0.5 Co _0.2 Mn _0.3 ).

The precursor and lithium carbonate were mixed in a mortar for 1 hour so that the molar ratio of Li / (Ni + Co + Mn) was 1.035 to obtain a uniform mixture. Positive electrode active material particles in which 50 g of the obtained mixture is put in an alumina crucible and kept at 930 ° C. for 5 hours in an oxidizing atmosphere to become Li _1.035 (Ni _0.5 Co _0.2 Mn _0.3 ) O _2. Got.

Example 2
Using the precursor of the composite compound synthesized in Example 1 above, the precursor and lithium carbonate were mixed for 1 hour in a mortar so that the Li / (Ni + Co + Mn) molar ratio was 1.065. A mixture was obtained. 50 g of the obtained mixture was put in an alumina crucible and held at 960 ° C. in an air atmosphere for 5 hours to obtain positive electrode active material particles that became Li _1.065 (Ni _0.5 Co _0.2 Mn _0.3 ) O _2. Obtained.

Example 3
Using the composite compound precursor synthesized in Example 1 above, the precursor and lithium carbonate were mixed for 1 hour in a mortar so that the Li / (Ni + Co + Mn) molar ratio was 1.020. A mixture was obtained. 50 g of the obtained mixture was put in an alumina crucible, and positive electrode active material particles that became Li _1.020 (Ni _0.5 Co _0.2 Mn _0.3 ) O ₂ by holding at 910 ° C. for 5 hours in an air atmosphere were obtained. Obtained.

Example 4
Ni sulfate, Co sulfate, and Mn sulfate were weighed so that each element had a molar ratio of Ni: Co: Mn = 1: 1: 1 and coprecipitated by the wet reaction described above. The composite oxide particles (precursor) were obtained by washing with water and drying (Ni _0.33 Co _0.33 Mn _0.33 ).

The precursor and lithium carbonate were mixed in a mortar for 1 hour so that the molar ratio of Li / (Ni + Co + Mn) was 1.040 to obtain a uniform mixture. Positive electrode active material particles which are put into Li _1.040 (Ni _0.33 Co _0.33 Mn _0.33 ) O ₂ by putting 50 g of the obtained mixture in an alumina crucible and holding at 940 ° C. for 5 hours in an oxidizing atmosphere. Got.

Example 5
Ni sulfate, Co sulfate, and Mn sulfate were weighed so that each element had a molar ratio of Ni: Co: Mn = 6: 2: 2 and coprecipitated by the wet reaction described above. Washing with water and drying were performed to obtain (Ni _0.6 Co _0.2 Mn _0.2 ) composite oxide particles (precursor).

The precursor and lithium hydroxide monohydrate were mixed in a mortar for 1 hour so that the molar ratio of Li / (Ni + Co + Mn) was 1.015 to obtain a uniform mixture. Positive electrode active material particles in which 50 g of the obtained mixture is put in an alumina crucible and kept at 880 ° C. for 5 hours in an oxidizing atmosphere to become Li _1.015 (Ni _0.6 Co _0.2 Mn _0.2 ) O _2. Got.

Comparative Example 1
Using the precursor of the composite compound synthesized in Example 1 above, the precursor and lithium carbonate were mixed for 1 hour in a mortar so that the Li / (Ni + Co + Mn) molar ratio was 1.080. A mixture was obtained. 50 g of the obtained mixture was put in an alumina crucible, and positive electrode active material particles that became Li _1.080 (Ni _0.5 Co _0.2 Mn _0.3 ) O ₂ by holding in an air atmosphere at 890 ° C. for 5 hours were obtained. Obtained.

Comparative Example 2
Using the precursor of the composite compound synthesized in Example 1 above, the precursor and lithium carbonate were mixed for 1 hour in a mortar so that the Li / (Ni + Co + Mn) molar ratio was 0.980. A mixture was obtained. 50 g of the obtained mixture was put in an alumina crucible, and positive electrode active material particles that became Li _0.980 (Ni _0.5 Co _0.2 Mn _0.3 ) O ₂ by holding in an air atmosphere at 880 ° C. for 5 hours were obtained. Obtained.

Comparative Example 3
Using the precursor of the composite compound synthesized in Example 4 above, the precursor and lithium carbonate were mixed for 1 hour in a mortar so that the Li / (Ni + Co + Mn) molar ratio was 1.080. A mixture was obtained. 50 g of the obtained mixture was put in an alumina crucible and kept at 920 ° C. for 5 hours in an air atmosphere to obtain positive electrode active material particles that became Li _1.080 (Ni _0.33 Co _0.33 Mn _0.33 ) O _2. Obtained.

Comparative Example 4
Using the precursor of the composite compound synthesized in Example 1 above, the precursor and lithium carbonate were mixed for 1 hour in a mortar so that the Li / (Ni + Co + Mn) molar ratio was 1.030. A mixture was obtained. 50 g of the obtained mixture was put in an alumina crucible and held at 850 ° C. in an air atmosphere for 5 hours to obtain positive electrode active material particles that became Li _1.030 (Ni _0.5 Co _0.2 Mn _0.3 ) O _2. Obtained.

Comparative Example 5
Using the precursor of the composite compound synthesized in Example 4 above, the precursor and lithium carbonate were mixed for 1 hour in a mortar so that the Li / (Ni + Co + Mn) molar ratio was 1.100. A mixture was obtained. 50 g of the obtained mixture was put in an alumina crucible and held at 960 ° C. in an air atmosphere for 5 hours to obtain positive electrode active material particles that became Li _1.080 (Ni _0.33 Co _0.33 Mn _0.33 ) O _2. Obtained.

  With respect to the positive electrode active material particles of each Example and Comparative Example obtained as described above, the crystallite size and the average secondary particle diameter (D50) were measured according to the above methods, and each Example according to the above methods. And the coin cell was produced using the positive electrode active material particle of a comparative example, the dQ / dV curve was created similarly to the above, and the area of the range of 4.3V-4.52V in the graph was determined. The results are shown in Table 1 below, and the dQ / dV curves of Example 1 and Comparative Example 1 are shown in FIG. Further, FIG. 3 shows the results of the time dependence of the open circuit voltage when the batteries prepared with the positive electrode active material in Example 1 and Comparative Example 1 measured by the above method are stored at 60 ° C.

  As shown in Table 1 and FIG. 2, the coin-type battery using the positive electrode active material particles of Example 1 is the dQ / dV curve described above, and the area is 35 mAh / g in the range of 4.3 V to 4.52 V in the graph. It was in the range of and showed a low value. On the other hand, in Comparative Example 1, it can be seen that the area exceeds 35 mAh / g in the range of 4.3 V to 4.52 V in the dQ / dV curve.

  Further, as shown in Table 1, in addition to Example 1, the molar ratio of Li / (Ni + Co + Mn) is 1.01 or more and 1.07 or less, and the firing temperature is 870 ° C. to 970 ° C. -5 is 35 mAh / g or less in the range of 4.3V or more and 4.52V or less in a dQ / dV curve. That is, a battery with high safety can be obtained by using the positive electrode active material particles of Examples 1 to 5.

  In addition, as shown in FIG. 3, it can be seen that the open circuit voltage shown in Example 1 is slower to decrease than the open circuit voltage shown in Comparative Example 1.

  From the above, it can be seen that a battery having high stability can be obtained by using the positive electrode active material according to the present invention.

  Since the positive electrode active material particles for a non-aqueous electrolyte secondary battery according to the present invention can be made highly stable when used as a battery, they are suitable as a positive electrode active material for a non-aqueous electrolyte secondary battery.

Reference example 1
Ni sulfate, Co sulfate, and Mn sulfate were weighed so that each element had a molar ratio of Ni: Co: Mn = 6: 2: 2 and coprecipitated by the wet reaction described above. Washing with water and drying were performed to obtain (Ni _0.6 Co _0.2 Mn _0.2 ) composite oxide particles (precursor).

Further, as shown in Table 1, in Example 2 other than Example 1, the molar ratio of Li / (Ni + Co + Mn) is 1.02 or more and 1.07 or less, and the firing temperature is 910 ° C. to 970 ° C. 1-4, in the dQ / dV curve, the area at 4.52V below the range of 4.3V or less 35 mAh / g. That is, a battery with high safety can be obtained by using the positive electrode active material particles of Examples 1 to 4 .

Claims (4)

Cathode active material particles having a hexagonal layered rock salt structure, the composition formula is
Li _x (Ni _1-yz Co _y Mn _z ) O _2-δ
(1.00 ≦ x ≦ 1.07, 0.10 ≦ y ≦ 0.40, 0.10 ≦ z ≦ 0.40, 0.3 ≦ y + z ≦ 0.7)
And
Using the positive electrode active material particles as a positive electrode and using Li as a negative electrode, a non-aqueous electrolyte secondary battery is assembled, and an initial charge is performed at a 0.2 C rate (16 mA / g) up to 4.6 V in a 60 ° C. environment. When a graph (dQ / dV curve) showing the voltage on the horizontal axis and dQ / dV which is a value obtained by differentiating the initial charge capacity by the voltage on the vertical axis is 4.3 V or more in the graph. Positive electrode active material particles for a non-aqueous electrolyte secondary battery, wherein the size of the area in a range of 0.5 V or less is 35 mAh / g or less.   The positive electrode active material particle according to claim 1, wherein the crystallite size is 200 nm or more and 900 nm or less, and the average secondary particle diameter (D50) is 3 μm or more and 20 μm or less. A method for producing positive electrode active material particles according to claim 1 or 2,
Using a precursor represented by the following composition formula,
(Ni _1-yz Co _y Mn _z ) OH ₂
(0.10 ≦ y ≦ 0.40, 0.10 ≦ z ≦ 0.40, 0.3 ≦ y + z ≦ 0.7)
The lithium compound was mixed with the precursor so that the molar ratio of Li / (Ni + Co + Mn) was in the range of 1.00 to 1.07, and then fired at 870 ° C. to 970 ° C. in an oxidizing atmosphere. A method for producing positive electrode active material particles, comprising obtaining a composite oxide containing Ni, Co and Mn.   A nonaqueous electrolyte secondary battery using the positive electrode active material particles according to claim 1.