JP2018147697A - Positive electrode active material for nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a positive electrode active material for a nonaqueous electrolyte secondary battery, which can reduce a positive electrode resistance when used for a secondary battery.SOLUTION: A positive electrode active material for a nonaqueous electrolyte secondary battery comprises a spinel type oxide including Li, Mn, Ni and an element M (at least one element selected from Mg, Al, Si, Ti, Cr, Fe, Co, Cu and Zn) in the proportion of Li:Mn:Ni:M=t:2-x-y:x:y (where 0.96≤t≤1.25, 0.40≤x≤0.60 and 0≤y≤0.20). When 30% of Li is drawn out, the positive electrode active material includes one or two cubic crystal phases. In the latter case, the following expression (1) is satisfied: (d1-d2)/d1×100≤0.5 (1), where d1 represents a d value of one phase having a larger d value, and d2 represents a d value of the other phase. When 70% of Li is drawn out, the positive electrode active material includes one or two cubic crystal phases. In the latter case, the following expression (2) is satisfied: (d3-d4)/d3×100≤0.8 (2), where d3 represents a d value of the phase larger in d value, and d4 represents a d value of the other phase.SELECTED DRAWING: Figure 2

Description

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

  In recent years, with the widespread use of portable electronic devices such as mobile phones and notebook computers, there is an increasing demand for small and lightweight secondary batteries having high energy density. In addition, development of a high-power secondary battery is strongly desired as a power source for electric vehicles including hybrid vehicles.

  As a secondary battery satisfying such requirements, there is a lithium ion secondary battery which is a kind of non-aqueous electrolyte secondary battery. This lithium ion secondary battery is composed of a negative electrode, a positive electrode, an electrolytic solution, and the like, and a material capable of desorbing and inserting lithium is used as an active material used as a material for the negative electrode and the positive electrode.

  Currently, research and development of such lithium ion secondary batteries are actively conducted. Among them, a lithium ion secondary battery using a lithium metal composite oxide as a positive electrode material is capable of being used as a battery having a high energy density because a voltage of 4 V class can be obtained.

As a positive electrode material of the lithium ion secondary battery, lithium cobalt composite oxide (LiCoO ₂ ), which is currently relatively easy to synthesize, lithium nickel composite oxide (LiNiO ₂ ) using nickel cheaper than cobalt, lithium Nickel cobalt manganese composite oxide (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ), lithium manganese composite oxide (LiMn ₂ O ₄ ) using manganese, lithium nickel manganese composite oxide (LiNi _0.5 Mn _0.5 O _2), lithium-rich nickel-cobalt-manganese composite oxide _{(Li 2 MnO 3 -LiNi X Mn} y Co z O 2) lithium composite oxide such as have been proposed.

  Among positive electrode materials for lithium ion secondary batteries that are currently under investigation, positive electrode materials having a spinel crystal structure that can realize secondary batteries with particularly excellent thermal stability have attracted particular attention in recent years. Has been made.

  For example, Patent Document 1 discloses a positive electrode active material for a non-aqueous lithium battery characterized by using a lithium manganese composite oxide having an oxygen-deficient spinel structure.

JP-A-8-138675

  However, further improvement in performance is required for lithium ion secondary batteries, and in particular, improvement in output voltage is required. And about the lithium ion secondary battery, in order to raise an output voltage, the positive electrode active material for non-aqueous electrolyte secondary batteries which can suppress positive electrode resistance was calculated | required.

  Accordingly, in view of the problems of the above-described conventional technology, according to one aspect of the present invention, there is provided a positive electrode active material for a non-aqueous electrolyte secondary battery that can suppress positive electrode resistance when a non-aqueous electrolyte secondary battery is used. With the goal.

In order to solve the above problems, according to one aspect of the present invention,
Lithium (Li), manganese (Mn), nickel (Ni), and element M (M) have a mass ratio of Li: Mn: Ni: M = t: 2-xy: x: y (However, it is a spinel type oxide including 0.96 ≦ t ≦ 1.25, 0.40 ≦ x ≦ 0.60, 0 ≦ y ≦ 0.20)
The element M is magnesium (Mg), aluminum (Al), silicon (Si), titanium (Ti), chromium (Cr), iron (Fe), cobalt (Co), copper (Cu), and zinc (Zn). At least one element selected from the group of
Electrochemically, it is composed of one or two cubic phases when 30% of the contained lithium is extracted, and the phase having the larger d value when composed of two-phase cubic crystals When the d value of d1 is d1 and the d value of the other phase is d2, the following equation (1) is satisfied:
(D1-d2) /d1×100≦0.5 (1)
When electrochemically composed of one or two cubic phases when 70% of the contained lithium is extracted, the one having a larger d value when composed of two cubic phases Provided is a positive electrode active material for a non-aqueous electrolyte secondary battery that satisfies the following formula (2) when the d value of the other phase is d3 and the d value of the other phase is d4.

  (D3-d4) /d3×100≦0.8 (2)

  According to one embodiment of the present invention, it is possible to provide a positive electrode active material for a non-aqueous electrolyte secondary battery that can suppress positive electrode resistance when a non-aqueous electrolyte secondary battery is obtained.

Explanatory drawing of the cross-sectional structure of the coin-type battery produced in the Example and the comparative example. Explanatory drawing of the relationship between the amount of drawing of lithium in an Example and a comparative example, and the change of a XRD pattern.

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. However, the present invention is not limited to the following embodiments, and the following embodiments are not departed from the scope of the present invention. Various modifications and substitutions can be made.
[Positive electrode active material for non-aqueous electrolyte secondary battery]
First, a configuration example of the positive electrode active material for a non-aqueous electrolyte secondary battery according to this embodiment will be described.

The positive electrode active material for a non-aqueous electrolyte secondary battery according to the present embodiment is composed of lithium (Li), manganese (Mn), nickel (Ni), and element M (M), with a mass ratio of Li: Mn. : Ni: M = t: 2-xy: x: y (provided that 0.96 ≦ t ≦ 1.25, 0.40 ≦ x ≦ 0.60, 0 ≦ y ≦ 0.20) The spinel oxide contained in
Element M includes magnesium (Mg), aluminum (Al), silicon (Si), titanium (Ti), chromium (Cr), iron (Fe), cobalt (Co), copper (Cu), and zinc (Zn). ) At least one element selected from the group of

  And the positive electrode active material for nonaqueous electrolyte secondary batteries of this embodiment can be comprised by the phase of 1 phase or a cubic phase, when 30% of lithium containing is extracted electrochemically. In the case where the phase is composed of two cubic phases, the following formula (1) is satisfied when the d value of the phase having the larger d value is d1 and the d value of the other phase is d2. be able to.

(D1-d2) /d1×100≦0.5 (1)
Furthermore, the positive electrode active material for a non-aqueous electrolyte secondary battery according to the present embodiment can be electrochemically composed of one or two cubic phases when 70% of the contained lithium is extracted. . And when it is composed of two cubic phases, the following formula (2) is satisfied when the d value of the phase having the larger d value is d3 and the d value of the other phase is d4: Can do.

(D3-d4) /d3×100≦0.8 (2)
Hereinafter, the positive electrode active material for a non-aqueous electrolyte secondary battery of the present embodiment will be specifically described.
(composition)
The positive electrode active material for a non-aqueous electrolyte secondary battery of the present embodiment (hereinafter also simply referred to as “positive electrode active material”) has a spinel structure containing lithium (Li), manganese (Mn), and nickel (Ni). It can be set as the oxide which has. In addition, the positive electrode active material of the present embodiment may be an oxide having a spinel structure that further contains an element M that is an optional additive element.

  The element M includes magnesium (Mg), aluminum (Al), silicon (Si), titanium (Ti), chromium (Cr), iron (Fe), cobalt (Co), copper (Cu), and zinc (Zn). It can contain at least one element selected, that is, one or more elements selected from the above element group.

  The positive electrode active material for a non-aqueous electrolyte secondary battery according to the present embodiment is composed of the above-described lithium (Li), manganese (Mn), nickel (Ni), and element M (M). Ratio) is Li: Mn: Ni: M = t: 2-xy: x: y. Note that t, x, and y satisfy the relational expressions 0.96 ≦ t ≦ 1.25, 0.40 ≦ x ≦ 0.60, and 0 ≦ y ≦ 0.20, respectively.

  In the substance ratio formula, the value of t indicating the lithium content is preferably 0.96 or more and 1.25 or less, more preferably 0.98 or more and 1.20 or less. More preferably, it is 00 or more and 1.20 or less.

  This is also described as a non-aqueous electrolyte secondary battery (hereinafter simply referred to as a “secondary battery”) using the positive electrode active material for the positive electrode by setting t in the above-mentioned range of the substance quantity ratio. This is because the output characteristics and capacity characteristics of (1) can be improved. Specifically, by setting the value of t to 0.96 or more, the positive electrode resistance of the secondary battery can be suppressed and the output characteristics can be improved. Moreover, the initial discharge capacity can be sufficiently increased by setting the value of t to 1.25 or less.

  Nickel (Ni) is an element that contributes to higher potential and higher capacity of the secondary battery.

  The value of x indicating the amount of nickel added is preferably 0.40 or more and 0.60 or less, more preferably 0.40 or more and 0.56 or less, and 0.40 or more and 0.53 or less. More preferably.

  This is because by setting the value of x to 0.40 or more, the secondary battery configured using the positive electrode active material for the positive electrode can sufficiently increase the battery capacity at a voltage of 5 V class. Also, by setting the value of x to 0.60 or less, a positive electrode active material composed of a spinel structure single phase can be obtained more reliably, which is preferable.

  As described above, the positive electrode active material of the present embodiment can contain a predetermined amount of element (addition element) M in addition to the metal elements of lithium, manganese, and nickel.

  As such an element M, as described above, at least one element selected from magnesium, aluminum, silicon, titanium, chromium, iron, cobalt, copper, and zinc can be used.

  The element M can be appropriately selected according to the application of the secondary battery configured using the positive electrode active material and the required performance.

  Since some elements M themselves do not contribute to the oxidation-reduction reaction, the value of y indicating the amount of element M added is preferably 0.20 or less, more preferably 0.15 or less, and More preferably, it is 10 or less. The element M may not be added, and the lower limit value of y indicating the addition amount of the element M can be set to 0 or more, for example.

Therefore, the positive electrode active material of the present embodiment does not include the element M, and may be a material including, for example, lithium (Li), manganese (Mn), and nickel (Ni).
(Crystal phase constituting positive electrode active material when lithium is extracted electrochemically)
The inventors of the present invention have intensively studied a positive electrode active material capable of suppressing positive electrode resistance when a secondary battery is formed.

  When a secondary battery is manufactured using an oxide having a spinel structure having the above-described composition as the positive electrode active material and charged, lithium ions escape from the positive electrode into the electrolyte solution. The lithium can be extracted electrochemically.

  The inventors of the present invention charge the secondary battery, and when the lithium contained in the positive electrode active material is electrochemically extracted, the positive electrode when the predetermined amount of charge, that is, the predetermined amount of extraction is reached. It has been found that the positive electrode resistance can be suppressed when the phase of the crystal structure contained in the active material satisfies a predetermined condition.

  Specifically, the positive electrode active material of the present embodiment preferably satisfies the following conditions for the phase of the crystal structure when lithium contained electrochemically is extracted from the positive electrode active material.

  When 30% of lithium contained is electrochemically extracted from the positive electrode active material, it can be composed of one phase or two-phase cubic phase, and when composed of two-phase cubic phase, When the d value of the phase with the larger d value is d1, and the d value of the other phase is d2, it is preferable to satisfy the following formula (1).

(D1-d2) /d1×100≦0.5 (1)
Furthermore, the positive electrode active material for a non-aqueous electrolyte secondary battery according to the present embodiment has a one-phase or two-phase cubic crystal structure when 70% of lithium contained is electrochemically extracted from the positive electrode active material. In the case of being composed of two cubic phases, when the d value of the phase having the larger d value is d3 and the d value of the other phase is d4, the following formula ( 2) can be satisfied.

(D3-d4) /d3×100≦0.8 (2)
When a secondary battery is manufactured using a positive electrode active material and charged, lithium is in a lithium ion state and is electrochemically extracted from the positive electrode active material contained in the positive electrode as described above.

  According to the study by the inventors of the present invention, from the viewpoint of suppressing the positive electrode resistance, when lithium is electrochemically extracted from the positive electrode active material, the positive electrode active material is a crystalline phase constituting the positive electrode active material. It is preferable that the d value indicating the inter-surface distance is continuously reduced while the phase is one phase. This is because, when electrochemically extracting lithium, the crystal phase constituting the positive electrode active material remains one phase, and the d value indicating the interplanar spacing continuously decreases, the crystal phase constituting the positive electrode active material This is because the lithium sites occupied by lithium are uniformly and close to each other in the crystal structure. For this reason, for example, when discharging is performed in a secondary battery, lithium is again filled in the lithium site, and at this time, lithium is easily diffused in the positive electrode active material.

  However, according to the study of the inventors of the present invention, when lithium is electrochemically extracted from the positive electrode active material, the crystal phase constituting the positive electrode active material may be two or more phases. Specifically, for example, when 30% or 70% of lithium contained in the positive electrode active material is extracted, the crystal phase constituting the positive electrode active material may be two or more phases.

  However, for example, when lithium is electrochemically extracted from the positive electrode active material, the phases constituting the positive electrode active material are two phases whose crystal structure is cubic, and the difference in d value between the two phases It has been found that when the ratio is not more than a predetermined value, the positive electrode resistance in the secondary battery using the positive electrode active material can be sufficiently suppressed. This is because, when lithium is electrochemically extracted from the positive electrode active material, the positive electrode active material is composed of two cubic phases, and the ratio of the difference in d value between the two phases is less than a predetermined value. This is probably because the lithium sites occupied by lithium are distributed almost uniformly in the crystal structure of the crystal phase constituting the positive electrode active material and are close to each other. For this reason, for example, when discharging is performed in a secondary battery, lithium is charged again into the lithium site. In such a case, lithium is easily diffused in the positive electrode active material, and the positive electrode resistance can be suppressed. .

  For the above reasons, when the positive electrode active material of the present embodiment is electrochemically extracted from the positive electrode active material by 30% of lithium contained therein, the positive electrode active material is a one-phase or two-phase cubic crystal. It can be comprised by the phase of this. When the positive electrode active material when 30% of lithium is extracted is a two-phase cubic crystal, the d value of the phase having the larger d value is d1, and the d value of the other phase is d2. It is preferable to satisfy the formula (1) described above.

  In addition, the positive electrode active material according to the present embodiment has a one-phase or two-phase cubic phase when electrochemically extracting 70% of the lithium contained from the positive electrode active material. Can be configured. When the positive electrode active material when 70% of lithium is extracted is composed of a two-phase cubic phase, the d value of the phase having the larger d value is d3, and the d value of the other phase is d4. In this case, it is preferable to satisfy the above-described formula (2).

  The positive electrode active material in which 30% or 70% of lithium is extracted from the positive electrode active material is, for example, up to 30% when a secondary battery including a positive electrode using the positive electrode active material is prepared and fully charged, for example. Or a positive electrode active material when charged to 70%.

  The following methods can be mentioned as methods for electrochemically evaluating the d value of the positive electrode active material from which 30% or 70% of the lithium contained is extracted.

  For example, a secondary battery having a structure in which a positive electrode active material contained in a positive electrode can be observed in situ using a positive electrode active material to be evaluated is manufactured. Then, the secondary battery is set in a powder X-ray diffractometer so that an XRD (X-Ray Diffraction) pattern of the positive electrode active material contained in the positive electrode of the secondary battery is obtained, or 30% of the full charge, or After charging to 70%, the XRD pattern is measured. Then, the d value can be calculated from the obtained XRD pattern.

  For example, a secondary battery is produced using the positive electrode active material used as evaluation object. Then, after charging the secondary battery to 30% or 70% of full charge, the secondary battery is disassembled, the positive electrode material contained in the positive electrode is taken out, and an XRD pattern is obtained by a powder X-ray diffractometer. taking measurement. Then, the d value can be calculated from the obtained XRD pattern.

  Even in the case of any of the above methods or other methods, the surface used when calculating the d value from the XRD pattern when lithium is extracted by 30% or 70% for the positive electrode active material of the present embodiment, That is, the peak used is not particularly limited. However, since the peak of the (311) plane is easy to discriminate, it is preferable to use the peak attributed (identified) to the (311) plane. That is, it is preferable to calculate the d value by using the (311) plane and the attributed (identified) peak.

When measuring an XRD pattern with a powder X-ray diffractometer, in order to reduce the background, it is preferable to arrange a filter in the radiation source and use X-rays monochromatized only in Kα1 as the light source.
(Specific surface area)
Positive electrode active material of the present embodiment has a specific surface area preferably has the following powder 0.30 m ² / g or more 1.50 m ² / g. In particular, the positive electrode active material of the present embodiment is more preferably a powder having a specific surface area of 0.50 m ² / g or more and 1.50 m ² / g or less.

  The specific surface area of the powder (particles) can be measured and evaluated by the BET method using nitrogen adsorption.

Lithium ion desorption / insertion that occurs in the positive electrode active material during charge / discharge of the secondary battery occurs on the surface of the positive electrode active material. For this reason, about the positive electrode active material of this embodiment, since a positive electrode resistance can be suppressed especially by setting it as a powder whose specific surface area is 0.30 m < ² > / g or more, it is preferable. In addition, by making the positive electrode active material of the present embodiment a powder having a specific surface area of 1.50 m ² / g or less, the electrolytic solution decomposed by a side reaction occurring at the interface between the positive electrode active material and the electrolytic solution is deposited. Even when the charging is performed repeatedly, the increase in the positive electrode resistance can be suppressed.
(Particle structure)
The positive electrode active material of the present embodiment includes secondary particles in which a large number of primary particles are aggregated and single primary particles when observed with an electron microscope such as SEM (scanning electron microscope) or TEM (transmission electron microscope). It is preferable to include at least one selected.

  The secondary particles in which a large number of primary particles are agglomerated are secondary particles having a particle size of 3.0 μm or more and 5.0 μm or less formed by agglomeration of many primary particles of 0.1 μm or more and 2.0 μm or less Particles are preferred. In addition, this secondary particle may have the space enclosed by one or more primary particles, for example, and a space | gap.

Moreover, it is preferable that the primary particle which exists independently has a particle size of 1.0 micrometer or more and 7.0 micrometers or less.
(Volume average particle size)
The positive electrode active material of the present embodiment is preferably a powder having a volume average particle size of 2 μm or more and 8 μm or less when measured with a laser light diffraction / scattering particle size distribution meter. In particular, the positive electrode active material of the present embodiment preferably has a volume average particle size of 3 μm or more and 8 μm or less, and more preferably 3 μm or more and 6 μm or less.

  When the volume average particle size of the positive electrode active material of the present embodiment is in the above range, the secondary battery using the positive electrode active material for the positive electrode can increase the battery capacity per volume, This is because a battery having excellent output characteristics can be obtained.

The positive electrode active material of the present embodiment described above has the above-described composition and satisfies predetermined requirements for the crystal phase when lithium is electrochemically extracted. For this reason, when the positive electrode active material of this embodiment is a secondary battery, the positive electrode resistance can be suppressed and the output voltage can be increased.
[Method for producing positive electrode active material for non-aqueous electrolyte secondary battery]
One structural example of the manufacturing method of the positive electrode active material for nonaqueous electrolyte secondary batteries of this embodiment is demonstrated. In addition, the above-mentioned positive electrode active material can be manufactured with the manufacturing method of the positive electrode active material for non-aqueous electrolyte secondary batteries of this embodiment. For this reason, description of some of the matters already described in relation to the positive electrode active material is omitted.

  The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to the present embodiment (hereinafter also simply referred to as “method for producing a positive electrode active material”) is not particularly limited, and the positive electrode active material described above is produced. Various production methods can be used as long as they are possible.

  The manufacturing method of the positive electrode active material of this embodiment can have the following processes, for example.

Manganese, nickel, and in some cases using water-soluble raw materials so that the substance amount ratio (molar ratio) of each element is “Mn: Ni: M = (2-xy): x: y”. Is a precursor crystallization step in which a mixed aqueous solution further containing element M is prepared and reacted in a reaction vessel with an initial aqueous solution containing an alkali metal aqueous solution or the like to obtain a positive electrode active material precursor (manganese nickel composite hydroxide).
Lithium manganese nickel obtained by mixing a positive electrode active material precursor obtained in the precursor crystallization step and a lithium compound and firing at a temperature of 800 ° C. or higher and 1000 ° C. or lower in an oxidizing atmosphere to obtain a lithium manganese nickel composite oxide Complex oxide production process.

Below, each process is demonstrated.
(Precursor crystallization process)
First, a plurality of metal compounds such as a metal compound containing manganese are dissolved in water at a predetermined ratio to prepare a mixed aqueous solution. Specifically, for example, a metal compound containing manganese, a metal compound containing nickel, and optionally a metal compound further containing element M can be dissolved in water to prepare a mixed aqueous solution. It is preferable to prepare the mixed aqueous solution so that the composition ratio of each metal at this time is the same as the composition ratio of each metal excluding lithium in the finally obtained positive electrode active material. Therefore, the ratio of the metal compound dissolved in water is adjusted so that the composition ratio of each metal in the mixed aqueous solution is the same as the composition ratio of each metal excluding lithium in the positive electrode active material of the present embodiment. It is preferable to prepare a mixed aqueous solution. Specifically, it can be produced such that the substance amount ratio of each element is Mn: Ni: M = (2-xy): x: y. In addition, it is preferable that x and y are the same range as the case of the positive electrode active material as stated above, for example, it is preferable to satisfy | fill 0.40 <= x <= 0.60 and 0 <= y <= 0.20.

  The metal compound used is not particularly limited as long as it is water-soluble, but sulfate is preferable from the viewpoint of cost. In addition, when the water-soluble suitable raw material is not found by element M etc., it is not necessary to add to mixed aqueous solution.

  Next, water is put into the reaction vessel, and an initial aqueous solution is prepared by adding an appropriate amount of an aqueous alkali metal solution such as an aqueous sodium hydroxide solution and an ammonia supplier such as aqueous ammonia to the water.

  At this time, the initial aqueous solution is preferably prepared so that the pH value is 11.2 to 12.2 and the ammonia concentration is 2 g / L to 15 g / L on the basis of the liquid temperature of 25 ° C.

  This is because, by setting the pH value of the initial aqueous solution to 11.2 or more, it is possible to suppress contamination of impurities due to anions constituting the raw metal compound into the obtained positive electrode active material precursor. And the pH value of initial stage aqueous solution shall be 12.2 or less, and it can prevent reliably that the positive electrode active material precursor obtained becomes microparticles | fine-particles.

  In addition, it is preferable that the ammonia concentration of the initial aqueous solution be 2 g / L or more because the sphericity of the obtained positive electrode active material precursor can be particularly improved. On the other hand, by setting the ammonia concentration of the initial aqueous solution to 15 g / L or less, it is possible to suppress an excessive increase in the solubility of nickel forming the ammonia complex and obtain a positive electrode active material precursor having a desired composition. ,preferable.

  The atmosphere in the reaction vessel is preferably a non-oxidizing atmosphere (oxygen concentration: 1 vol% or less). By setting the atmosphere in the reaction vessel to a non-oxidizing atmosphere, particularly an oxygen concentration of 1% by volume or less, it is possible to suppress oxidation of manganese, for example, it is possible to suppress precipitation of manganese oxide as fine particles, which is preferable. Specifically, for example, an inert atmosphere such as a nitrogen atmosphere is preferable.

  The temperature of the reaction vessel is preferably 40 ° C. or higher and 60 ° C. or lower, and more preferably 40 ° C. or higher and 55 ° C. or lower.

  Since the temperature of the reaction vessel naturally rises due to reaction heat and stirring energy, it is preferable to set the set temperature to 40 ° C. or higher because excessive energy is not consumed for cooling. However, if the temperature exceeds 60 ° C., the amount of ammonia evaporated increases and it becomes difficult to maintain the target ammonia concentration. Therefore, it is preferable to set the temperature to 60 ° C. or lower as described above.

  In addition, it is preferable that the temperature in a reaction tank exists in the said range during a precursor crystallization process. Moreover, it is preferable to maintain the initial aqueous solution and the following reaction aqueous solution within the same temperature range.

  After preparing the initial aqueous solution and setting the conditions in the reaction vessel, the mixed aqueous solution can be dropped into the reaction vessel at a constant rate to obtain a reaction aqueous solution.

  At this time, in accordance with the dropping of the mixed aqueous solution, an ammonia supplier, for example, aqueous ammonia, and an aqueous alkali metal solution, such as an aqueous sodium hydroxide solution, are also dropped at a constant rate, and the pH value of the aqueous reaction solution is 11. It is preferable to control so that the ammonia concentration of the reaction aqueous solution is maintained at 2 g / L or more and 15 g / L or less at 2 or more and 12.2 or less.

  As described above, the positive electrode active material precursor (manganese nickel composite hydroxide particles) can be crystallized.

Thereafter, the slurry containing the positive electrode active material precursor particles recovered from the overflow provided in the reaction vessel is filtered and dried, whereby powdered positive electrode active material precursor particles, that is, manganese nickel composite hydroxide particles are obtained. can get.
(Lithium manganese nickel composite oxide production process)
In the lithium manganese nickel composite oxide production step, the following lithium mixture preparation step and firing step can be performed.

  First, the positive electrode active material precursor obtained in the precursor crystallization step has a lithium content of 46 atom% or more and 62.5 atoms with respect to the total number of metal atoms contained in the positive electrode active material precursor. The lithium mixture preparation step of preparing the lithium mixture can be carried out by adding and mixing the lithium compound so that the amount is less than or equal to%.

  In this case, the lithium compound to be added is not particularly limited, but for example, one or more selected from lithium hydroxide, lithium nitrate, and lithium carbonate can be used. In addition, the lithium compound can also use 2 or more types of mixtures selected from the said lithium compound group. In particular, as the lithium compound, it is preferable to use lithium carbonate that is stable in an air atmosphere.

  When preparing a lithium mixture, for example, in the precursor crystallization process, if a suitable water-soluble raw material for the element M or the like cannot be found, the compound containing the element M has the same composition ratio as that of interest. In addition to the positive electrode active material precursor and the lithium compound, they may be mixed. It does not specifically limit as a compound containing the element M to add, For example, an oxide, a hydroxide, a carbonate, or its mixture etc. can be used.

  Next, a baking step of baking the obtained lithium mixture in an oxygen-containing atmosphere can be performed.

  The firing conditions at this time are not particularly limited, but for example, firing is preferably performed at a temperature of 800 ° C. to 1000 ° C. for 5 hours to 36 hours. And after completion | finish of baking by baking temperature, it is preferable to cool to room temperature with the cooling rate of 5 to 10 degree-C / min.

  This is because the specific surface area of the positive electrode active material to be obtained can be made particularly suitable by setting the firing temperature to 800 ° C. or higher and 1000 ° C. or lower.

  Further, it is preferable to set the firing time to 5 hours or longer, because the temperature in the firing container can be made particularly uniform, and a positive electrode active material having uniform characteristics can be obtained. However, the firing time is preferably 36 hours or less from the viewpoint of energy efficiency because there is no significant change from the case where the firing time exceeds 36 hours and it is 36 hours or less.

  And by making a cooling rate into 5 degrees C / min or more, when charging / discharging about the obtained secondary battery using the positive electrode active material, phase separation arises about a positive electrode active material, and the extent is suppressed. it can. For this reason, about the obtained positive electrode active material, since positive electrode resistance can be suppressed and cycling characteristics can be improved, it is preferable.

  Although the cooling rate may be faster than 10 ° C / min, it is often industrially difficult to perform cooling faster than 10 ° C / min, so the cooling rate should be 10 ° C / min or less. Is preferred.

The oxygen-containing atmosphere may be an atmosphere containing oxygen, and may be, for example, an air atmosphere or under air flow.
After cooling, the obtained lithium manganese nickel composite oxide can be used as a positive electrode active material as it is.

  When mild sintering is seen in the obtained positive electrode active material, a crushing treatment may be added after the lithium nickel manganese composite oxide production step.

When the crystal structure of the positive electrode active material obtained as described above is measured by XRD, it can be confirmed that it is a spinel crystal structure.
[Nonaqueous electrolyte secondary battery]
Next, a configuration example of the non-aqueous electrolyte secondary battery of the present embodiment will be described.

  The non-aqueous electrolyte secondary battery of this embodiment can have a positive electrode using the above-described positive electrode active material as a positive electrode material.

  First, the structural example of the structure of the non-aqueous electrolyte secondary battery of this embodiment is demonstrated.

  The non-aqueous electrolyte secondary battery of this embodiment can have a structure substantially similar to that of a general non-aqueous electrolyte secondary battery except that the positive electrode active material described above is used as the positive electrode material.

  Specifically, the nonaqueous electrolyte secondary battery of the present embodiment can have a structure including a case and a positive electrode, a negative electrode, a nonaqueous electrolyte, and a separator housed in the case.

  More specifically, a positive electrode and a negative electrode can be laminated through a separator to form an electrode body, and the obtained electrode body can be impregnated with a non-aqueous electrolyte. Then, between the positive electrode current collector of the positive electrode and the positive electrode terminal that communicates with the outside, and between the negative electrode current collector of the negative electrode and the negative electrode terminal that communicates with the outside using a current collecting lead, etc., respectively, It can have a sealed structure.

  The structure of the nonaqueous electrolyte secondary battery of the present embodiment is not limited to the above example, and various shapes such as a cylindrical shape and a stacked shape can be adopted as the outer shape.

A configuration example of each member will be described below.
(Positive electrode)
First, the positive electrode will be described.

  The positive electrode is a sheet-like member, and can be formed, for example, by applying and drying a positive electrode mixture paste containing the above-described positive electrode active material on the surface of a current collector made of, for example, aluminum foil. In addition, a positive electrode is suitably processed according to the battery to be used. For example, a cutting process for forming an appropriate size according to a target battery, a pressure compression process using a roll press or the like for increasing the electrode density, and the like can be performed.

  The above-mentioned positive electrode mixture paste can be formed by adding a solvent to the positive electrode mixture and kneading. The positive electrode mixture can be formed by mixing the positive electrode active material described above in a powder form, a conductive material, and a binder.

  The conductive material is added to give an appropriate conductivity to the electrode. The material of the conductive material is not particularly limited. For example, graphite such as natural graphite, artificial graphite and expanded graphite, and carbon black materials such as acetylene black and ketjen black can be used.

  The binder plays a role of holding the positive electrode active material. The binder used for such a positive electrode mixture is not particularly limited. For example, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), fluororubber, ethylene propylene diene rubber, styrene butadiene, cellulose resin, polyacrylic. One or more selected from acids and the like can be used.

  In addition, activated carbon etc. can also be added to a positive electrode compound material. By adding activated carbon or the like to the positive electrode mixture, the electric double layer capacity of the positive electrode can be increased.

  The solvent has a function of dissolving the binder and dispersing the positive electrode active material, the conductive material, activated carbon, and the like in the binder. Although the solvent is not particularly limited, for example, an organic solvent such as N-methyl-2-pyrrolidone can be used.

In addition, the mixing ratio of each substance in the positive electrode mixture paste is not particularly limited, and can be the same as that of the positive electrode of a general nonaqueous electrolyte secondary battery, for example. For example, when the solid content of the positive electrode mixture excluding the solvent is 100 parts by mass, the content of the positive electrode active material is 60 parts by mass or more and 95 parts by mass or less, and the content of the conductive material is 1 part by mass or more and 20 parts by mass or less. The binder content can be 1 part by mass or more and 20 parts by mass or less.
(Negative electrode)
The negative electrode is a sheet-like member formed by applying a negative electrode mixture paste to the surface of a metal foil current collector such as copper and drying it.

  The negative electrode is formed by substantially the same method as the positive electrode described above, although the components constituting the negative electrode mixture paste, the composition thereof, and the current collector material are different. Done.

  The negative electrode mixture paste can be made into a paste by adding an appropriate solvent to the negative electrode mixture obtained by mixing the negative electrode active material and the binder.

  As the negative electrode active material, for example, a material containing lithium, such as metallic lithium or a lithium alloy, or an occlusion material that can occlude and desorb lithium ions can be employed.

  The occlusion material is not particularly limited, and for example, one or more selected from natural graphite, artificial graphite, a fired organic compound such as phenol resin, and a powdery carbon material such as coke can be used.

When such an occlusion material is employed as the negative electrode active material, a fluorine-containing resin such as PVDF can be used as the binder, as with the positive electrode, and as a solvent for dispersing the negative electrode active material in the binder, An organic solvent such as N-methyl-2-pyrrolidone can be used.
(Separator)
The separator is disposed so as to be sandwiched between the positive electrode and the negative electrode, and has a function of separating the positive electrode and the negative electrode and holding the electrolyte.

As a material for the separator, for example, a thin film such as polyethylene or polypropylene and a film having a large number of fine holes can be used. However, the separator is not particularly limited as long as it has the above function.
(Non-aqueous electrolyte)
The non-aqueous electrolyte is obtained by dissolving a lithium salt as a supporting salt in an organic solvent.

  Examples of the organic solvent include cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, and trifluoropropylene carbonate; chain carbonates such as diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, and dipropyl carbonate; Ether compounds such as methyltetrahydrofuran and dimethoxyethane; sulfur compounds such as ethyl methyl sulfone and butane sultone; phosphorus compounds such as triethyl phosphate and trioctyl phosphate alone or in combination of two or more. be able to.

As the supporting salt, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiN (CF ₃ SO ₂ ) ₂ , and complex salts thereof can be used.

  The non-aqueous electrolyte may contain a radical scavenger, a surfactant, a flame retardant, etc. for improving battery characteristics.

  The non-aqueous electrolyte secondary battery of this embodiment includes a positive electrode using the above-described positive electrode active material as a positive electrode material. For this reason, it can be set as the non-aqueous electrolyte secondary battery which has the outstanding battery characteristic.

  The nonaqueous electrolyte secondary battery of the present embodiment using the above-described positive electrode active material can suppress the positive electrode resistance and increase the output voltage as described above. For this reason, while having a high operating potential, it has a high capacity and excellent output characteristics.

Specifically, the positive electrode active material of the present embodiment is used as a positive electrode to form a 2032 type coin-type battery, the current density is 0.1 mA / cm ² , and the battery is charged to a cutoff voltage of 5.0 V for 1 hour. When the battery is discharged to a cut-off voltage of 3.0 V after the suspension, the initial discharge capacity is preferably 125 mAh / g or more, and more preferably 130 mAh / g or more. Further, the positive electrode resistance of the 2032 type coin-type battery is preferably 28Ω or less, and more preferably 25Ω or less.

  Furthermore, when the positive electrode active material of the present embodiment is used as a positive electrode material and a secondary battery is configured using a sheet in which graphite powder and polyvinylidene fluoride are applied to a copper foil as a negative electrode, the cycle is repeated at 60 ° C. for 200 cycles. The capacity retention ratio, which is the ratio of the discharge capacity obtained in the first cycle divided by the discharge capacity after 200 cycles after conditioning, is preferably 65% or more, and more preferably 70% or more. The capacity retention rate is more preferably 75% or more.

  The application of the non-aqueous electrolyte secondary battery of the present embodiment is not particularly limited, and can be used for applications requiring various power sources. However, since it has the above characteristics, it can be particularly preferably used as a power source for small portable electronic devices (such as notebook personal computers and mobile phone terminals) that always require a high capacity. In addition, since the nonaqueous electrolyte secondary battery of the present embodiment can be reduced in size and increased in output, it can be suitably used as a power source for an electric vehicle that is restricted by a mounting space.

  The non-aqueous electrolyte secondary battery of this embodiment is not only a power source for an electric vehicle driven purely by electric energy but also a power source for a so-called hybrid vehicle used in combination with a combustion engine such as a gasoline engine or a diesel engine. Can also be used.

Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples.
[Example 1]
A positive electrode active material was prepared and evaluated according to the following procedure.
(Method for producing positive electrode active material)
First, a method and conditions for producing a lithium manganese nickel composite oxide that is a positive electrode active material will be described.
(A) Precursor crystallization step First, the temperature in the tank was set to 40 ° C. while stirring the water in a reaction tank (5 L) up to a half amount. Moreover, the inside of the reaction tank was made into nitrogen atmosphere (oxygen concentration: 1 volume% or less). Until the precursor crystallization step is completed, the temperature in the reaction vessel is kept at 40 ° C., and the atmosphere in the vessel is kept to be a nitrogen atmosphere having an oxygen concentration of 1% by volume or less. The reaction aqueous solution is also kept at 40 ° C.

  A 25% by mass sodium hydroxide aqueous solution and 25% by mass ammonia water were added to the water in the reaction vessel to prepare an initial aqueous solution. The initial aqueous solution was prepared by adding the above sodium hydroxide aqueous solution and aqueous ammonia so that the pH value was 11.5 based on the liquid temperature of 25 ° C. and the ammonia concentration was 5 g / L.

  Further, manganese sulfate and nickel sulfate were dissolved in pure water so that the molar ratio of manganese to nickel was Mn: Ni = 1.50: 0.50 to prepare a 2.0 mol / L mixed aqueous solution. .

  While stirring the initial aqueous solution prepared in the reaction vessel, the above-mentioned mixed aqueous solution was dropped into the initial aqueous solution at a constant rate to obtain a reaction aqueous solution.

  When dropping the mixed aqueous solution, 25% by mass ammonia water and 25% by mass sodium hydroxide aqueous solution were also added dropwise at a constant rate, and the pH value of the reaction aqueous solution was adjusted to 11.5 based on the liquid temperature of 25 ° C. Was maintained at 5 g / L.

  As described above, the mixed aqueous solution was dropped into the initial aqueous solution to crystallize manganese nickel composite hydroxide particles (hereinafter referred to as “composite hydroxide particles”) serving as a precursor of the positive electrode active material.

Thereafter, the slurry containing the composite hydroxide particles recovered from the overflow provided in the reaction vessel was filtered, and the resulting crystallized product was washed with ion-exchanged water to remove water-soluble impurities. The crystallized product after washing was dried to obtain powdered composite hydroxide particles.
(B) Lithium Manganese Nickel Composite Oxide Generation Step The composite hydroxide particles obtained in the precursor crystallization step are mixed with the total number of manganese and nickel atoms contained in the composite hydroxide particles. Lithium carbonate weighed so that the content was 50 atomic% was added and mixed to obtain a lithium mixture (lithium mixture preparation step). When mixing, a tumbler shaker mixer (Dalton Co., Ltd., T2F) was used.

  The obtained lithium mixture was baked at 900 ° C. for 12 hours in an air flow using an atmosphere baking furnace (manufactured by Siliconit Co., Ltd., BM-50100M). After firing, the mixture was cooled to room temperature at 10 ° C./min to obtain a lithium manganese nickel composite oxide (firing step).

Since the obtained lithium manganese nickel composite oxide was slightly sintered, it was crushed using a hammer mill (MF10, manufactured by IKA Japan Co., Ltd.) to obtain a positive electrode active material.
(Method for evaluating positive electrode active material)
The positive electrode active material powder obtained by the above-described procedure was evaluated. The evaluation method will be described below.
(A) Evaluation of composition About the obtained positive electrode active material, the composition was evaluated using the ICP emission-spectral-analysis apparatus (Varian company make, 725ES). As a result, it was confirmed that the obtained positive electrode active material had a molar ratio of Li, Mn, and Ni represented by Li: Mn: Ni = 1.00: 1.50: 0.50.
(B) Crystal structure A positive electrode is produced using the obtained positive electrode active material as a positive electrode material, a laminate cell type battery using the positive electrode and a lithium foil as a negative electrode is produced, and the crystal structure changes during charge / discharge operation. In order to evaluate, in-situ XRD (X-ray diffraction) measurement was performed. In in-situ XRD measurement, an X-ray diffractometer (manufactured by BRUKER, D8 DISCOVER) is used, and a monochromatic CuKα1 is used as an X-ray source. Measurements were taken at a scan rate of 0.01 degrees / second. The charge / discharge of the laminate cell type battery was performed at a charge / discharge rate of 0.03C. From the obtained XRD pattern, using the peak attributed to the (311) plane in the crystal structure of the lithium manganese nickel composite oxide, the d value was determined by Bragg's law represented by the formula (A). Regarding the d value of the peak attributed to this (311) plane, when the crystal structure at a charge depth (SOC) of 30% obtained by electrochemically extracting 30% of lithium contained is two phases, The change rate of the d value when the d value of one phase having a large d value is d1 and the d value of the other phase having a small d value is d2 was obtained from the equation (1). Further, when the crystal structure in SOC 70% obtained by electrochemically extracting 70% of the lithium contained is two phases, the d value of the phase having the larger d value out of the two phases is d3, and the d value is smaller. The rate of change of the d value when the d value of the phase was d4 was determined from the equation (2).

  FIG. 2A shows XRD patterns of the positive electrode active material obtained in this example before charging (SOC 0%), at a charging depth of 30% (SOC 30%), and at a charging depth of 70% (SOC 70%). .

  In the XRD pattern before charging, there is one peak 211 corresponding to the (311) plane, and it can be confirmed that it is composed of a single cubic phase.

  In addition, even at a charge depth of 30% (SOC 30%), there is one peak 221 corresponding to the (311) plane, and it can be confirmed that it is composed of a single cubic phase. In addition, since it comprised by the single phase, calculation of the ratio of the difference of d value between two phases in SOC30% was not performed.

  Then, at a charging depth of 70% (SOC 70%), the peak corresponding to the (311) plane is broken into two, generating peaks 231A and 231B, and the positive electrode active material is composed of two-phase cubic crystals. Was confirmed.

  The ratio of the difference in d value between the two phases at a charging depth of 70% was calculated according to the above-described calculation formula.

（ｃ）比表面積、体積平均粒径
得られた正極活物質の粉末の比表面積を、全自動ＢＥＴ比表面積測定装置（株式会社マウンテック製、マックソーブ）を用いて測定した。その結果、正極活物質の粉末の比表面積が０．９６ｍ^２／ｇであることを確認した。

(C) Specific surface area, volume average particle diameter The specific surface area of the obtained positive electrode active material powder was measured using a fully automatic BET specific surface area measuring device (manufactured by Mountec Co., Ltd., Macsorb). As a result, it was confirmed that the specific surface area of the positive electrode active material powder was 0.96 m ² / g.

  Further, when the volume-based average particle diameter of the positive electrode active material powder was determined using a laser diffraction / scattering particle size distribution analyzer (manufactured by Nikkiso Co., Ltd., Microtrac HRA), it was confirmed to be 6.4 μm. In Table 1, the volume average particle diameter (volume reference average particle diameter) is simply shown as the average particle diameter.

As one of evaluations of the obtained positive electrode active material, a 2032 type coin-type battery 10 shown in FIG. 1, which is a nonaqueous electrolyte secondary battery, was prepared and evaluated using the prepared positive electrode active material. A method for producing a non-aqueous electrolyte secondary battery will be described below.
(Production method of secondary battery)
The coin battery 10 includes a case 11 and an electrode 12 accommodated in the case 11.

  The case 11 has a positive electrode can 111 that is hollow and open at one end, and a negative electrode can 112 that is disposed in the opening of the positive electrode can 111, and the negative electrode can 112 is disposed in the opening of the positive electrode can 111. A space for accommodating the electrode 12 is formed between the negative electrode can 112 and the positive electrode can 111.

  The electrode 12 includes a positive electrode 121, a separator 122, and a negative electrode 123, which are stacked in this order, so that the positive electrode 121 is in contact with the inner surface of the positive electrode can 111 and the negative electrode 123 is in contact with the inner surface of the negative electrode can 112. In the case 11.

  The case 11 includes a gasket 113, and the gasket 113 allows relative movement so that the positive electrode can 111 and the negative electrode can 112 are not in contact with each other, that is, electrically maintained. Regulated and fixed. In addition, the gasket 113 has a function of sealing the gap between the positive electrode can 111 and the negative electrode can 112 and blocking the inside and outside of the case 11 in an airtight and liquidtight manner.

  This coin-type battery 10 was produced as follows. First, 52.5 mg of the obtained positive electrode active material, 15 mg of acetylene black, and 7.5 mg of polytetrafluoroethylene resin (PTFE) were mixed and thinned to a weight of about 10 mg with a diameter of 10 mm to produce the positive electrode 121. This was dried in a vacuum dryer at 120 ° C. for 12 hours.

  Using the positive electrode 121, the negative electrode 123, the separator 122, and the electrolytic solution, the coin-type battery 10 was produced in a glove box in an Ar atmosphere in which the dew point was controlled at −80 ° C.

  As the negative electrode 123, a lithium foil punched into a disk shape having a diameter of 14 mm, or a negative electrode sheet in which graphite powder having an average particle diameter of about 20 μm and polyvinylidene fluoride were applied to a copper foil was used. The initial discharge capacity and the positive electrode resistance described later were evaluated by a battery using the above-described lithium foil for the negative electrode. In addition, the cycle characteristics, specifically the capacity retention rate, were evaluated by a battery using the above-described graphite powder and a negative electrode sheet in which polyvinylidene fluoride was applied to a copper foil on the negative electrode.

As the separator 122, a polyethylene porous film having a film thickness of 25 μm was used. As the electrolytic solution, a 3: 7 mixed solution (manufactured by Toyama Pharmaceutical Co., Ltd.) based on a volume ratio of ethylene carbonate (EC) and diethyl carbonate (DEC) using 1M LiPF ₆ as a supporting electrolyte was used.

[Battery evaluation]
A method for evaluating the performance of the obtained coin-type battery 10 will be described.

The initial discharge capacity is about 24 hours after the coin-type battery 10 using the lithium foil as the negative electrode is manufactured. After the open circuit voltage OCV (open circuit voltage) is stabilized, the current density with respect to the positive electrode is 0.1 mA / The capacity when the battery was charged to a cutoff voltage of 5.0 V as cm ² and discharged to a cutoff voltage of 3.0 V after a pause of 1 hour was defined as the initial discharge capacity.

  When a battery evaluation was performed on a coin-type battery having a positive electrode formed using the positive electrode active material, the initial discharge capacity was 140 mAh / g.

  Positive electrode resistance was evaluated by measuring DC-IR resistance.

Specifically, after charging the coin-type battery 10 using lithium foil as the negative electrode to 60% of the initial discharge capacity, sandwiching a pause for 1 minute, discharging at a current density of 0.4 mA / cm ² for 10 seconds, The battery was charged for 10 seconds with a current density of 0.4 mA / cm ² again after a 1-minute pause. This operation was repeated under the conditions of 1.3 mA / cm ² , 4.0 mA / cm ² and 6.6 mA / cm ² to measure the difference between the voltage at the start of discharge and the voltage until the end of discharge at each current density. .

  Next, the current density was plotted on the vertical axis and the voltage difference was plotted on the horizontal axis, and the obtained linear relationship was found to have a slope by first-order linear approximation, and this slope was taken as the positive electrode resistance (DC-IR resistance).

  The measurement result was 23.4Ω.

The cycle characteristics were evaluated by measuring the capacity retention rate when 200 cycles of charge / discharge were performed. Specifically, a coin-type battery 10 produced by using a sheet in which graphite powder and polyvinylidene fluoride are coated on a copper foil on a negative electrode, a current density of 0.3 mA / cm in a thermostat kept at 25 ° C. ² after charging to a cut-off voltage of 4.9 V, conditioning after repeating a cycle of discharging to a cut-off voltage of 3.5 V after a pause of 1 hour, and then in a thermostatic chamber maintained at 60 ° C., Charging to a cut-off voltage of 4.9 V at a current density of 2.0 mA / cm ² , repeating a cycle of discharging to a cut-off voltage of 3.5 V after a pause of 1 hour, and measuring the discharge capacity of each cycle It was evaluated by.

As a result, the capacity retention rate, which is a ratio of the discharge capacity obtained in the first cycle after conditioning of the coin-type battery of Example 1 divided by the discharge capacity obtained in the 200th cycle after conditioning, is 75. %Met.
[Example 2]
In the lithium manganese nickel composite oxide production step, after baking at 900 ° C. for 12 hours, the positive electrode active material was prepared in the same procedure as in Example 1 except that the cooling rate when cooling to room temperature was 5 ° C./min. Prepared and evaluated.

  FIG. 2B shows XRD patterns of the positive electrode active material obtained in this example before charging (SOC 0%), at a charging depth of 30% (SOC 30%), and at a charging depth of 70% (SOC 70%). .

  In the XRD pattern before charging (SOC 0%), there is one peak 212 corresponding to the (311) plane, and it can be confirmed that it is composed of a single phase.

  At a charge depth of 30% (SOC 30%), the peak corresponding to the (311) plane is broken into two, generating a peak 222A and a peak 222B, confirming that the positive electrode active material is composed of two-phase cubic crystals. did it.

  Even at a charging depth of 70% (SOC 70%), the peak corresponding to the (311) plane is broken into two, generating peaks 232A and 232B, and the positive electrode active material is composed of two-phase cubic crystals. It could be confirmed.

  The ratio of the difference in d value between the two phases at a charging depth of 30% and a charging depth of 70% was calculated according to the above-described calculation formula.

In the same manner as in Example 1, a secondary battery was produced using the obtained positive electrode active material and evaluated. The evaluation results are shown in Table 1.
[Examples 3 to 5]
In preparing the mixed aqueous solution in the precursor crystallization step, manganese sulfate, nickel sulfate, and sulfate of element M are mixed with a molar ratio of manganese, nickel, and element M of Mn: Ni: M = 1.50. : 0.45: 0.05 was dissolved in pure water to prepare a 2.0 mol / L mixed aqueous solution. A positive electrode active material was prepared and evaluated in the same manner as in Example 2 except that the mixed aqueous solution was used. Further, in the same manner as in Example 1, a secondary battery was produced using the obtained positive electrode active material and evaluated. The evaluation results are shown in Table 1.
As element M, cobalt (Co) was used in Example 3, iron (Fe) was used in Example 4, and titanium (Ti) was used in Example 5.
[Comparative Example 1]
In the lithium manganese nickel composite oxide production step, after baking at 900 ° C. for 12 hours, the positive electrode active material was prepared in the same procedure as in Example 1 except that the cooling rate when cooling to room temperature was 2 ° C./min. Prepared and evaluated.

  FIG. 2C shows XRD patterns of the positive electrode active material obtained in Comparative Example 1 before charging (SOC 0%), at a charging depth of 30% (SOC 30%), and at a charging depth of 70% (SOC 70%). .

  In the XRD pattern before charging (SOC 0%), there is one peak 213 corresponding to the (311) plane, and it can be confirmed that it is composed of a single phase.

  At a charge depth of 30% (SOC 30%), the peak corresponding to the (311) plane is broken into two, generating peaks 223A and 223B, confirming that the positive electrode active material is composed of two-phase cubic crystals. did it.

  Even at a charge depth of 70% (SOC 70%), the peak corresponding to the (311) plane is broken into two, generating peaks 233A and 233B, and the positive electrode active material is composed of two-phase cubic crystals. It could be confirmed.

  The ratio of the difference in d value between the two phases at a charging depth of 30% and a charging depth of 70% was calculated according to the above-described calculation formula.

  Further, in the same manner as in Example 1, a secondary battery was produced using the obtained positive electrode active material and evaluated. The evaluation results are shown in Table 1.

表１に示した結果によると、実施例１〜５については、電気化学的に、含有するリチウムの３０％または７０％を引き抜いた際に１相、または２相の立方晶の相で構成され、２相の立方晶の相で構成される場合に、２相間でのｄ値の差の割合が所定の範囲内にあることを確認できた。

According to the results shown in Table 1, Examples 1 to 5 are electrochemically composed of one or two cubic phases when 30% or 70% of the contained lithium is extracted. In the case of being composed of two-phase cubic phases, it was confirmed that the ratio of the difference in d value between the two phases was within a predetermined range.

  On the other hand, in Comparative Example 1, the ratio of the difference in d value between two phases at SOC 30% was 0.90%, and the ratio of the difference in d value between two phases at SOC 70% was 1.01%. It was confirmed that it was larger than ˜5.

  And about Examples 1-5, compared with the comparative example 1, it has confirmed that positive electrode resistance could be suppressed significantly.

Claims (3)

Lithium (Li), manganese (Mn), nickel (Ni), and element M (M) have a mass ratio of Li: Mn: Ni: M = t: 2-xy: x: y (However, it is a spinel type oxide including 0.96 ≦ t ≦ 1.25, 0.40 ≦ x ≦ 0.60, 0 ≦ y ≦ 0.20)
The element M is magnesium (Mg), aluminum (Al), silicon (Si), titanium (Ti), chromium (Cr), iron (Fe), cobalt (Co), copper (Cu), and zinc (Zn). At least one element selected from the group of
Electrochemically, it is composed of one or two cubic phases when 30% of the contained lithium is extracted, and the phase having the larger d value when composed of two-phase cubic crystals When the d value of d1 is d1 and the d value of the other phase is d2, the following equation (1) is satisfied:
(D1-d2) /d1×100≦0.5 (1)
When electrochemically composed of one or two cubic phases when 70% of the contained lithium is extracted, the one having a larger d value when composed of two cubic phases A positive electrode active material for a non-aqueous electrolyte secondary battery that satisfies the following formula (2) when the d value of the first phase is d3 and the d value of the other phase is d4.
(D3-d4) /d3×100≦0.8 (2)   The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the positive electrode active material is a powder having a volume average particle diameter of 2 μm or more and 8 μm or less. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1 or 2 having a specific surface area of less powder 0.30 m ² / g or more 1.50 m ² / g.

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