JP7020101B2 - Positive active material for non-aqueous electrolyte secondary battery, manufacturing method of positive positive active material for non-aqueous electrolyte secondary battery, non-aqueous electrolyte secondary battery - Google Patents

Description

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

In recent years, with the spread of portable electronic devices such as mobile phones and notebook personal computers, there is a strong demand for the development of small and lightweight non-aqueous electrolyte secondary batteries having high energy density. As such a secondary battery, there is a lithium ion secondary battery. Lithium metal, lithium alloy, metal oxide, carbon or the like is used as the negative electrode material of the lithium ion secondary battery. These materials are materials capable of desorbing and inserting lithium.

Various studies have also been made on positive electrode materials. The positive electrode materials that have been mainly proposed so far are lithium cobalt composite oxide (LiCoO ₂ ), which is relatively easy to synthesize, lithium nickel composite oxide (LiNiO ₂ ), which uses nickel, which is cheaper than cobalt, and lithium nickel. Examples thereof include a cobalt-manganese composite oxide (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ) and a lithium-manganese composite oxide using manganese (LiMn ₂ O ₄ ).

Of these, the lithium nickel composite oxide and the lithium cobalt composite oxide have excellent cycle characteristics and have low charge transfer resistance (hereinafter referred to as positive electrode resistance), which is the resistance at the interface between the positive electrode active material and the electrolytic solution, so that high output can be obtained. It is attracting attention as a material to be used. On the other hand, in recent years, reduction of positive electrode resistance (lowering resistance) required for high output has been emphasized.

Addition of a foreign element is used as a method for achieving the above-mentioned low resistance, and a transition metal such as W, Mo, Nb, Ta, and Re, which can take an expensive number, is particularly useful.

For example, in Patent Document 1, at least one element selected from Mo, W, Nb, Ta and Re is 0.1 mol% or more and 5 mol with respect to the total molar amount of Mn, Ni and Co. A lithium transition metal-based compound powder for a positive electrode material of a lithium secondary battery, which is characterized by being contained in a proportion of% or less, has been proposed.

In Patent Document 1, a compound containing at least one of Mo, W, Nb, Ta, and Re is finely and uniformly used as a firing precursor of a lithium transition metal compound for a positive electrode material of a lithium secondary battery. By applying heat treatment at a high temperature after the addition as described above, the effect of suppressing grain growth and sintering during firing is exhibited, and the active material is concentrated on the particle surface and is not in the depth direction from the particle surface. It is said that it has been found that having a continuous composition gradient structure distributed with a linear concentration gradient also exerts an effect of significantly improving output characteristics.

According to the lithium transition metal-based compound powder for the positive electrode material of the lithium secondary battery, when used as the positive electrode material of the lithium secondary battery, both cost reduction and high safety, high load characteristics, and improved powder handling are achieved. It is said that it can be planned.

Further, Patent Document 2 describes a positive electrode active material for a non-aqueous electrolyte secondary battery having at least a layered structure of a lithium transition metal composite oxide, wherein the lithium transition metal composite oxide is a primary particle and an aggregate thereof. It exists in the form of particles consisting of one or both of the secondary particles, the aspect ratio of the primary particles is within a predetermined range, and at least the surface of the particles consists of a group consisting of molybdenum, vanadium, tungsten, boron and fluorine. A positive electrode active material for a non-aqueous electrolyte secondary battery having a compound comprising at least one selected is proposed.

According to the positive electrode active material for a non-aqueous electrolyte secondary battery, the conductivity is improved by having a compound having at least one selected from the group consisting of molybdenum, vanadium, tungsten, boron and fluorine on the surface of the particles. It is supposed to be possible. Further, it is said that this improves the initial characteristics without impairing the improvement of the thermal stability, the load characteristics and the output characteristics.

Patent Document 3 relates to a battery composed of a negative electrode, a positive electrode, and a non-aqueous electrolyte containing a lithium salt, which can be reversibly charged and discharged multiple times. Use a metal containing at least one selected from Cu, Si, Ga, W, Zr, B, and Mo, or an intermetal compound obtained by a combination of a plurality of these, or an oxide-coated one. A positive electrode characterized by the above and a battery using the positive electrode have been proposed.

According to the battery, safety can be ensured by absorbing oxygen gas that causes ignition and explosion. Therefore, among the safety tests that have been considered difficult in the past, the temperature is as low as 1.5 to 2.5 ° C. It is said that it can be effective in overcharging that ignites with voltage, overcharging at low temperature, crushing, nailing, and dumping in fire.

In Patent Document 4, a tungstic acid compound is coated on composite oxide particles whose average composition is represented by Li _a Ni _{x Coy} Al _z O ₂ and heat-treated, and the content of carbonic acid ions is high. Positive electrode active materials having a weight of 0.15% by weight or less have been proposed.

According to the positive electrode active material, it is said that gas generation due to decomposition of a non-aqueous electrolytic solution or the like can be suppressed. Alternatively, it is said that gas generation from itself in the positive electrode active material can be suppressed.

Patent Document 5 describes a lithium secondary having a surface layer containing at least one element selected from the group consisting of Mo and W and Li on the surface of a lithium composite oxide powder capable of occluding and releasing Li ions. Positive electrode active materials for batteries have been proposed.

According to the positive electrode active material for a lithium secondary battery, it is possible to obtain a positive electrode active material having improved thermal stability in a charged state as compared with a conventional positive electrode active material while maintaining a high initial discharge capacity. It is said that it is possible to obtain a high energy density lithium secondary battery with improved safety.

Patent Document 6 includes a positive electrode capable of charging and discharging, a negative electrode capable of charging and discharging, and a non-aqueous electrolytic solution, wherein the positive electrode contains active material particles and the active material particles contain a lithium composite oxide. A lithium ion secondary battery in which a molybdenum oxide is present on the surface layer of the active material particles has been proposed.

According to the lithium ion secondary battery, the intermittent cycle characteristics are said to be dramatically improved.

Japanese Unexamined Patent Publication No. 2009-289726 Japanese Unexamined Patent Publication No. 2005-251716 Japanese Unexamined Patent Publication No. 11-16566 Japanese Unexamined Patent Publication No. 2010-40383 Japanese Unexamined Patent Publication No. 2002-73567 Japanese Unexamined Patent Publication No. 2007-188878

By the way, in the positive electrode active material for a non-aqueous electrolyte secondary battery, the reaction with moisture in the atmosphere and the extraction of lithium from the inside of the crystal may cause atmospheric deterioration that causes a decrease in capacity and an increase in positive electrode resistance. be. Then, for example, in the manufacturing process, the positive electrode active material for a non-aqueous electrolyte secondary battery may come into contact with the atmosphere, and even if the positive electrode active material comes into contact with the atmosphere in this way, the battery is sufficiently high when the non-aqueous electrolyte secondary battery is used. It was required to demonstrate its performance. That is, it was required to improve the weather resistance.

However, in the above-mentioned patent documents, such atmospheric deterioration is not recognized, and no consideration is given to enhancing the weather resistance.

Therefore, in view of the problems of the above-mentioned prior art, in one aspect of the present invention, the positive electrode activity for a non-aqueous electrolyte secondary battery, which has a high initial discharge capacity and can maintain a low positive electrode resistance even when exposed to the atmosphere, has excellent weather resistance. The purpose is to provide the substance.

According to one aspect of the present invention in order to solve the above problems.
General formula Li _z Ni _{1-x-y Co} x _My O 2 _{+ α} (0 <x ≦ 0.35, 0 <y ≦ 0.07, 0.85 ≦ z ≦ 1.10, x + y ≦ 0.20, 0 ≦ α ≦ 0.5, the element M is at least one element selected from Mn, V, Mg, Mo, Nb, Ti and Al) , and the primary particles of the lithium nickel composite oxide and the primary particles. Lithium-nickel composite oxide particles with agglomerated secondary particles and
Lithium-molybdenum-containing particles of lithium-molybdenum-containing oxide particles arranged on the surface of the secondary particles of the lithium-nickel composite oxide particles and the surface of the primary particles and containing an oxide containing Li and Mo. With oxide particles,
The total carbon content is less than 0.035% by mass ,
Using the amount of eluted lithium obtained by the Warder method and the specific surface area, the amount of lithium on the particle surface calculated by the following formula (1) is 0.035% by mass · g / m ² or more. Provided is a positive electrode active material for a battery.
Particle surface lithium amount (mass% · g / m ² ) = (eluted lithium amount (mass%)) / (specific surface area (m ² / g)) ・ ・ ・ (1)

According to one aspect of the present invention, it is possible to provide a positive electrode active material for a non-aqueous electrolyte secondary battery having a high initial discharge capacity and excellent weather resistance that can maintain a low positive electrode resistance even when exposed to the atmosphere.

Schematic diagram of the coin-type battery used for battery evaluation in Examples and Comparative Examples. Schematic diagram of the equivalent circuit used for the measurement example and analysis of impedance evaluation. Cross-sectional SEM image of the positive electrode active material produced in the examples.

Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings, but the present invention is not limited to the following embodiments and does not deviate from the scope of the present invention. Can be modified and substituted in various ways.
[Positive electrode active material for non-aqueous electrolyte secondary batteries]
An example of the configuration of the positive electrode active material for a non-aqueous electrolyte secondary battery of the present embodiment will be described.

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”) is lithium having lithium nickel composite oxide primary particles and secondary particles in which the primary particles are aggregated. It can have nickel composite oxide particles and lithium-molybdenum-containing oxide particles.

The lithium nickel composite oxide contained in the lithium nickel composite oxide particles can contain Li (lithium), Ni (nickel), Co (cobalt), and the additive element M. The additive element M is at least one element selected from Mn (manganese), V (vanadium), Mg (magnesium), Mo (molybdenum), Nb (niobium), Ti (titanium) and Al (aluminum). be able to.

The lithium-molybdenum-containing oxide particles can contain oxides containing Li and Mo.

The lithium-molybdenum-containing oxide particles can be arranged on the surface of the secondary particles of the lithium nickel composite oxide particles and on the surface of the primary particles. Further, the positive electrode active material of the present embodiment can contain a total carbon content of less than 0.035% by mass.

As described above, the positive electrode active material of the present embodiment can have the primary particles of the lithium nickel composite oxide and the lithium nickel composite oxide particles having the secondary particles in which the primary particles are aggregated.

The lithium nickel composite oxide contained in the lithium nickel composite oxide particles can contain Li (lithium), Ni (nickel), Co (cobalt), and the additive element M. The composition of the lithium nickel composite oxide is not particularly limited, but is preferably represented by, for example, the general formula _Liz Ni _{1-xy Cox My} O _{2 + α} . In the general formula, x is 0 <x ≦ 0.35, y is 0 <y ≦ 0.07, 0.85 ≦ z ≦ 1.10, x + y ≦ 0.20, 0 ≦ α ≦ 0.5. , Is preferred. Further, the element M is preferably at least one element selected from Mn, V, Mg, Mo, Nb, Ti and Al.

When the lithium nickel composite oxide contained in the lithium nickel composite oxide particles is represented by the above general formula, it is preferable because a particularly high charge / discharge capacity can be obtained.

The lithium-nickel composite oxide particles can also be composed of the lithium-nickel composite oxide represented by the above general formula. However, even in this case, it is not excluded that the unavoidable component mixed in the manufacturing process or the like is contained.

The positive electrode active material of the present embodiment contains lithium nickel composite oxide particles and lithium-molybdenum-containing oxide particles described later. Therefore, when the composition of the positive electrode active material is analyzed, it may be difficult to define the composition of the lithium nickel composite oxide contained in the lithium nickel composite oxide particles. In such a case, the composition of the lithium nickel composite oxide contained in the lithium nickel composite oxide particles used as a raw material used in preparing the positive electrode active material of the present embodiment can be used as the positive electrode active material of the present embodiment. The composition of the lithium nickel composite oxide contained in the lithium nickel composite oxide particles of the above can be used.

The positive electrode active material of the present embodiment can further contain lithium-molybdenum-containing oxide particles containing an oxide containing Li and Mo. The lithium-molybdenum-containing oxide particles can be arranged on the surface of the secondary particles of the lithium nickel composite oxide particles and on the surface of the primary particles existing inside the secondary particles. By arranging the lithium-molybdenum-containing oxide particles on the surface of the secondary particles of the lithium nickel composite oxide particles and on the surface of the primary particles in this way, the positive electrode active material of the present embodiment can be used as a non-aqueous electrolyte secondary. When used in a battery, the positive electrode resistance can be reduced. Therefore, the output characteristics of the non-aqueous electrolyte secondary battery can be improved, and the charge / discharge capacity can be improved.

Generally, when the surface of the positive electrode active material is completely covered with a different compound, the movement (intercalation) of lithium ions is greatly restricted, resulting in the high capacity of the lithium nickel composite oxide. It is believed that the strengths will be erased.

However, in the positive electrode active material of the present embodiment, although the particles containing the lithium-molybdenum-containing oxide are arranged on the surface of the lithium nickel composite oxide particles, lithium is compared with the case where the particles are not arranged. The ionic conductivity is increased, and the movement of lithium ions can be promoted. Therefore, by arranging the lithium-molybdenum-containing oxide particles on the surface of the lithium-nickel composite oxide particles, a conductive path of lithium ions can be formed at the interface with the electrolytic solution, and the positive electrode resistance on the surface of the positive electrode active material is reduced. The output characteristics can be improved.

Further, in the positive electrode active material of the present embodiment, the surface of the secondary particles of the lithium nickel composite oxide particles and the surface of the primary particles existing inside the secondary particles are coated with lithium-molybdenum-containing oxide particles. As described above, by arranging the lithium-molybdenum-containing oxide particles on the surface of the secondary particles of the lithium nickel composite oxide particles and the surface of the primary particles existing inside the secondary particles, the active lithium nickel composite oxide is formed. Can increase the weather resistance of particles. That is, even when the positive electrode active material of the present embodiment is exposed to the atmosphere, the initial discharge capacity can be kept high and the positive electrode resistance can be kept low. In addition, it is possible to suppress deterioration of battery characteristics due to deterioration of the positive electrode active material for a long period of time. That is, the durability of the positive electrode active material can be enhanced.

Here, when the surface of the lithium nickel composite oxide particles is coated only with a layered substance containing no particles, the specific surface area is lowered regardless of the coating thickness. Therefore, even if the coating material has high lithium ion conductivity (lithium ion conductivity), the contact area with the electrolytic solution becomes small, which causes a decrease in charge / discharge capacity and an increase in positive electrode resistance. Is easy to invite. However, in the positive electrode active material of the present embodiment, the lithium-molybdenum-containing oxide particles, which are granular particles, are arranged on the surface of the lithium nickel composite oxide particles, so that the contact area with the electrolytic solution is sufficient. Since the lithium ion conduction can be effectively improved, the charge / discharge capacity can be increased and the positive electrode resistance can be reduced.

In the positive electrode active material of the present embodiment, it is preferable that only particulate lithium-molybdenum-containing oxide particles are arranged on the surface of the lithium nickel composite oxide particles from the viewpoint of increasing the specific surface area. , A part of it may be in the form of a film (sheet).

In the positive electrode active material of the present embodiment, the particle size of the lithium-molybdenum-containing oxide particles arranged on the surface of the lithium nickel composite oxide particles is not particularly limited. The average particle size of the lithium-molybdenum-containing oxide particles is preferably 1 nm or more and 200 nm or less, for example. This is because when the average particle diameter is 1 nm or more, particularly excellent lithium ion conductivity can be exhibited for lithium-molybdenum-containing oxide particles. Further, by setting the average particle size of the lithium-molybdenum-containing oxide particles to 200 nm or less, the lithium-molybdenum-containing oxide particles can be arranged particularly uniformly on the surface of the lithium-nickel composite oxide particles, and the positive electrode resistance can be increased. This is because it can be particularly reduced and is preferable.

Further, by setting the average particle size of the lithium-molybdenum-containing oxide particles in the above range, the contact area between the positive electrode active material and the electrolytic solution can be sufficiently increased in the case of a non-aqueous electrolyte secondary battery, and lithium ions can be obtained. The conductivity can be particularly increased. Therefore, it is preferable because the charge / discharge capacity can be particularly increased and the positive electrode resistance can be suppressed.

The method for calculating the average particle size of the lithium-molybdenum-containing oxide particles is not particularly limited, but for example, a sample of a positive electrode active material whose cross section has been processed is first prepared. Then, from the field emission scanning electron microscope image of the prepared positive electrode active material sample, the particle diameters of 50 lithium-molybdenum-containing oxide particles are measured using an image processing device, and the average value is calculated. , The average particle size of the lithium-molybdenum-containing oxide particles can be obtained.

As described above, in the positive electrode active material of the present embodiment, the contact with the electrolytic solution occurs on the surface of the primary particles of the lithium nickel composite oxide particles, so that the lithium-molybdenum-containing oxide particles are arranged on the surface of the primary particles. It is important that it is done. Here, the surface of the primary particle is exposed to the voids near and inside the surface of the secondary particle through which the electrolytic solution can permeate through the surface of the primary particle exposed on the outer surface of the secondary particle and the outside of the secondary particle. It includes the surface of primary particles. Further, even the grain boundaries between the primary particles are included if the bonds of the primary particles are incomplete and the electrolytic solution can penetrate.

Contact between the positive electrode active material and the electrolytic solution occurs not only on the outer surface of the secondary particles formed by aggregating the primary particles, but also on the voids near and inside the surface of the secondary particles, and even on the incomplete grain boundaries. .. Therefore, it is preferable to form lithium-molybdenum-containing oxide particles on the surface of the primary particles to promote the movement of lithium ions. Therefore, by arranging the lithium-molybdenum-containing oxide particles on the entire surface of the primary particles, it is possible to further reduce the positive electrode resistance of the lithium nickel composite oxide particles.

However, the lithium-molybdenum-containing oxide particles do not have to be arranged so as to completely cover the entire surface of the primary particles, and may be in a scattered state. Even in the scattered state, if the lithium-molybdenum-containing oxide particles are formed on the surface of the primary particles exposed on the outer surface and the voids inside the lithium nickel composite oxide particles, the positive electrode resistance is sufficiently reduced. be able to.

The surface properties of such lithium-nickel composite oxide particles can be evaluated, for example, by observing with a field emission scanning electron microscope.

In the positive electrode active material of the present embodiment, the lithium-molybdenum-containing oxide particles are arranged on the surface of the lithium nickel composite oxide particles, specifically, the primary particles and the surface of the secondary particles as described above. Is preferable. At this time, the lithium-molybdenum-containing oxide particles may be interspersed as described above, and the degree of uniformity of dispersion is not particularly limited.

However, it is preferable that the lithium-molybdenum-containing oxide particles are uniformly dispersed on the surface of the lithium-nickel composite oxide particles. This is because the lithium-molybdenum-containing oxide particles are uniformly dispersed, so that it is possible to suppress the load on specific particles, so that the cycle characteristics can be improved, and in particular, the positive electrode resistance can be suppressed.

Further, since the lithium-molybdenum-containing oxide particles are uniformly dispersed on the surface of the lithium nickel composite oxide particles, the surface of the exposed active lithium nickel composite oxide particles is reduced, and the deterioration of the positive electrode active material is deteriorated. Since it can be suppressed, it is also preferable from the viewpoint of particularly enhancing the weather resistance.

The lithium-molybdenum-containing oxide particles are particles containing lithium molybdenum represented by the general formula Li _a Mo _b O _c (0 <a ≦ 4, 0 <b ≦ 5, 0 <c ≦ 17). Is preferable.

The lithium-molybdenum-containing oxide particles may be particles made of lithium molybdate represented by the above general formula, but in this case as well, the case of containing unavoidable components mixed in the manufacturing process or the like is excluded. is not it.

In particular, the lithium-molybdenum-containing oxide contained in the lithium-molybdenum-containing oxide particles contained in the positive electrode active material of the present embodiment contains at least one selected from Li ₂ MoO ₄ and Li ₄ MoO ₅ . Is preferred, and more preferably one or more selected from Li ₂ MoO ₄ and Li ₄ MoO ₅ .

The method for evaluating the composition of the lithium-molybdenum-containing oxide contained in the lithium-molybdenum-containing oxide particles is not particularly limited. For example, the positive electrode active material of the present embodiment is evaluated by performing X-ray diffraction and phase identification. can do.

When the lithium-molybdenum-containing oxide contained in the lithium-molybdenum-containing oxide particles contains one or more selected from Li ₂ MoO ₄ and Li ₄ MoO ₅ , the lithium ion conductivity can be particularly enhanced. Therefore, when the positive electrode active material is used in a non-aqueous electrolyte secondary battery, the positive electrode resistance can be particularly suppressed, which is preferable.

The amount of molybdenum contained in the positive electrode active material of the present embodiment derived from the lithium-molybdenum-containing oxide particles is not particularly limited, but with respect to the total number of atoms of Ni, Co, and M contained in the lithium nickel composite oxide particles. And 0.001 at. % Or more 6.0 at. % Or less is preferable. The amount of molybdenum contained in the positive electrode active material of the present embodiment derived from the lithium-molybdenum-containing oxide particles is 0. 02at. % Or more 2.0 at. % Or less, more preferably 0.05 at. % Or more 1.0 at. % Or less is more preferable.

This is because the amount of molybdenum contained in the positive electrode active material of the present embodiment derived from the lithium-molybdenum-containing oxide particles is relative to the total number of atoms of Ni, Co, and M contained in the lithium nickel composite oxide particles. 0.001 at. This is because when it is% or more, a particularly high output characteristic can be exhibited. Further, by setting the molybdenum amount to 6.0 at% or less, it is possible to surely prevent the lithium-molybdenum-containing oxide particles from being excessively arranged, and lithium between the lithium nickel composite oxide particles and the electrolytic solution. This is because the ionic conductivity can be increased and the charge / discharge capacity can be improved.

The weather resistance tends to improve as the number of lithium-molybdenum-containing oxide particles contained in the positive electrode active material increases. Since the output characteristics of the positive electrode active material, the charge / discharge capacity, and the weather resistance are particularly excellent, the amount of molybdenum is 0.05 at. % Or more 1.0 at. % Or less is more preferable.

The total amount of lithium in the positive electrode active material is not particularly limited, but the sum of the atomic numbers of Mo derived from metals other than Li in the positive electrode active material, that is, Ni, Co, additive element M, and lithium-molybdenum-containing oxide particles ( The (Li / Me ratio) between Me) and the number of Li atoms is preferably 0.85 or more and 1.10 or less. This is because when Li / Me is 0.85 or more, the positive electrode resistance in the non-aqueous electrolyte secondary battery using the positive electrode active material can be sufficiently suppressed, so that the output of the battery can be increased, which is preferable. Further, by setting Li / Me to 1.10 or less, the initial discharge capacity of the non-aqueous electrolyte secondary battery using the positive electrode active material can be sufficiently increased, and the positive electrode resistance can be suppressed, which is preferable.

In the positive electrode active material of the present embodiment, the amount of lithium on the particle surface calculated by the following formula (1) using the amount of eluted lithium obtained by the Warder method and the specific surface area is 0.035% by mass · g / m. It is preferably ² or more.

Particle surface lithium amount (mass% · g / m ² ) = (eluted lithium amount (mass%)) / (specific surface area (m ² / g)) ・ ・ ・ (1)
The amount of eluted lithium can be evaluated, for example, by the Warder method, which is one of the neutralization titration methods. Then, the amounts of lithium hydroxide (LiOH) and lithium carbonate (Li ₂ CO ₃ ) can be calculated from the evaluation results, and the sum of these lithium amounts can be used as the eluted lithium amount.

Further, the specific surface area can be obtained by, for example, a nitrogen adsorption method.

From the obtained amount of eluted lithium and the value of the specific surface area, the amount of lithium on the particle surface (mass% · g / m ² ) can be calculated according to the above formula (1).

According to the studies by the inventors of the present invention, when the amount of lithium on the surface of the particles is 0.035% by mass · g / m ² or more, the surface of the lithium nickel composite oxide particles is sufficiently coated with the lithium molybdate particles. The surface activity is suppressed, and the weather resistance is particularly enhanced. Therefore, as described above, the amount of lithium on the particle surface is preferably 0.035 mass% · g / m ² or more.

Although the upper limit of the amount of lithium on the particle surface is not particularly limited, the amount of lithium on the particle surface of the positive electrode active material of the present embodiment is preferably 0.120% by mass · g / m ² or less, for example.

Further, the positive electrode active material of the present embodiment preferably has a total carbon content of less than 0.035% by mass, more preferably 0.030% by mass or less. This is because the total carbon content of the positive electrode active material of the present embodiment is set to less than 0.035% by mass, so that the carbon content is sufficiently suppressed, and the total carbon content is suppressed even when exposed to an atmospheric atmosphere, for example. This is because the degree of performance deterioration due to an increase in carbon content can be suppressed. That is, the weather resistance can be improved.

Although the lower limit of the total carbon content of the positive electrode active material of the present embodiment is not particularly limited, the total carbon content of the positive electrode active material of the present embodiment is, for example, because it is a component that does not have to contain carbon. It can be 0 or more.

Up to this point, the positive electrode active material of the present embodiment has been described. In the positive electrode active material of the present embodiment, the weather resistance can be enhanced by arranging the lithium-molybdenum-containing oxide particles on the surface of the lithium nickel composite oxide particles. That is, even when exposed to the atmosphere, the initial discharge capacity is high and the positive electrode resistance can be maintained low. Further, when the positive electrode active material of the present embodiment is used in a non-aqueous electrolyte secondary battery, the positive electrode resistance can be suppressed and the charge / discharge capacity can be sufficiently increased.
[Manufacturing method of positive electrode active material for non-aqueous electrolyte secondary battery]
Next, a configuration example of a method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to this embodiment will be described. The above-mentioned positive electrode active material for a non-aqueous electrolyte secondary battery can be produced by the method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to the present embodiment. Therefore, some of the matters already described will be omitted.

The method for producing a positive electrode active material of the present embodiment can have the following steps.

Primary of lithium nickel composite oxide containing Li, Ni, Co, and additive element M (where additive element M is at least one element selected from Mn, V, Mg, Mo, Nb, Ti and Al). A water content adjusting step for adjusting the water content of a base material raw material containing water and lithium nickel composite oxide particles having particles and secondary particles in which the primary particles are aggregated.

A mixing step of mixing a base material and lithium-molybdenum-containing oxide particles to prepare a raw material mixture.

A heat treatment step in which a raw material mixture is heat-treated in a non-reducing atmosphere.

Hereinafter, a method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention (hereinafter, also simply referred to as “method for producing a positive electrode active material”) will be described in detail for each step.
(Moisture content adjustment process)
In the water content adjusting step, the water content of the base material raw material containing water and lithium nickel composite oxide particles having primary particles and secondary particles formed by aggregating the primary particles can be adjusted.

At this time, it is preferable to adjust the water content of the base material so that the lithium-molybdenum-containing oxide particles added in the mixing step described later can be dissolved.

When the lithium-molybdenum-containing oxide particles are formed on the surface of the lithium nickel composite oxide particles, the one having an appropriately high water content of the base material raw material containing the lithium nickel composite oxide particles is inside the lithium nickel composite oxide particles. Lithium-molybdenum-containing oxides can easily enter. Therefore, in order to uniformly arrange the lithium-molybdenum-containing oxide particles on the surface of the lithium-nickel composite oxide particles, it is preferable to carry out a moisture content adjusting step to bring the base material raw material into a sufficiently wet state.

In the water content adjusting step, the water content of the base material is not particularly limited, and may be arbitrarily selected depending on, for example, the degree of dispersion of lithium-molybdenum-containing oxide particles required for the obtained positive electrode active material. can.

For example, in the water content adjusting step, it is preferable to adjust the water content of the base material raw material to be 0.1% by mass or more and 20% by mass or less, and to be 0.1% by mass or more and 15% by mass or less. It is more preferable to adjust the amount so as to be 1% by mass or more and 10% by mass or less.

By setting the water content of the base material to 0.1% by mass or more, the lithium-molybdenum-containing oxide particles can be sufficiently dissolved in the mixing step, and lithium can be uniformly dissolved on the surface of the lithium-nickel composite oxide particles. -Molybdenum-containing oxide particles can be dispersed. Therefore, the positive electrode resistance of the obtained positive electrode active material can be sufficiently suppressed, and the weather resistance can be particularly improved.

Further, by setting the water content of the base material to 20% by mass or less, it is possible to particularly suppress Li from coming out of the crystal structure. Therefore, when the obtained positive electrode active material is used in a non-aqueous electrolyte secondary battery, the battery characteristics can be improved, which is preferable.

The method of controlling the water content of the base material is not particularly limited, and examples thereof include a method of immersing lithium nickel composite oxide particles in pure water, stirring the particles appropriately, and then filtering the particles by the filtration time. ..

Further, the moisture content is controlled by a method of dropping pure water onto the lithium nickel composite oxide particles so as to have a desired moisture content, or by drying at an appropriate temperature after the above-mentioned filtration or dropping of pure water. The method etc. can be mentioned.

In the water content adjustment step, purging with a decarbonated atmosphere or an inert gas such as nitrogen so that excess Li in the lithium nickel composite oxide particles does not react with carbon dioxide in the atmosphere to form lithium carbonate. It is preferable to work in the inert gas atmosphere.

This is because when the formation of lithium carbonate occurs, the amount of Li that contributes to charge / discharge decreases, which may lead to a decrease in charge / discharge capacity and an increase in positive electrode resistance.
(Mixing process)
In the mixing step, the base material raw material obtained in the water content adjusting step and the lithium-molybdenum-containing oxide particles can be mixed to prepare a raw material mixture.

The lithium-molybdenum-containing oxide particles are not particularly limited, but for example, lithium molybdenum represented by the general formula _LiaMobOc (0 < _a≤4 , 0 < _b≤5 , 0 <c≤17). Particles can be preferably used. In particular, the lithium-molybdenum-containing oxide particles are Li ₂ MoO as lithium molybdenum from the viewpoint of availability and reactivity, and avoiding contamination of lithium-nickel composite oxides with impurities that cause deterioration of capacity and cycle characteristics. It is more preferred that the particles contain one or more selected from ₄ and Li ₄ MoO ₅ .

The amount of the lithium-molybdenum-containing oxide particles added is not particularly limited, and the lithium-molybdenum-containing oxide particles can be added according to the target composition. For example, in the mixing step, the ratio of the number of atoms of Mo contained in the added lithium-molybdenum-containing oxide particles to the number of atoms of Ni, Co, and M contained in the lithium nickel composite oxide particles is 0.001 at. .. % Or more 6.0 at. It is preferable to add lithium-molybdenum-containing oxide powder so as to be% or less. In particular, the ratio of the number of atoms of Mo contained in the added lithium-molybdenum-containing oxide particles to the number of atoms of Ni, Co, and M contained in the lithium nickel composite oxide particles is 0.02 at. % Or more 2.0 at. It is more preferable to add it so as to be less than%, and 0.05 at. % Or more 1.0 at. It is more preferable to add it so as to be% or less.

The means for mixing the lithium-nickel composite oxide particles and the lithium-molybdenum-containing oxide particles is not particularly limited. Since the reactivity between the wet lithium-nickel composite oxide particles and the lithium-molybdenum-containing oxide particles is good, it is sufficient that the particles can be mixed almost uniformly. As the mixing means, for example, a shaker mixer, a small mixer, or the like can be used.
(Heat treatment process)
In the heat treatment step, the raw material mixture can be heat-treated in a non-reducing atmosphere.

By carrying out the heat treatment step, lithium-molybdenum-containing oxide particles can be formed on the surface of the secondary particles of the lithium nickel composite oxide and the surface of the primary particles existing inside the secondary particles.

The heat treatment temperature is not particularly limited, but is preferably 60 ° C. or higher and 600 ° C. or lower, more preferably 100 ° C. or higher and 600 ° C. or lower, further preferably 100 ° C. or higher and 400 ° C. or lower, and 100 ° C. or higher. It is particularly preferable that the temperature is 200 ° C. or lower.

By setting the heat treatment temperature to 100 ° C. or higher, the water content in the raw material mixture can be evaporated, and a sufficient amount of lithium-molybdenum-containing oxide particles are formed on the surface of the lithium nickel composite oxide particles. This is because it is preferable. Further, by setting the temperature to 100 ° C. or higher, the time for removing water can be shortened, the progress of carbonation of the positive electrode active material can be more reliably suppressed, and the characteristics of the battery using the positive electrode active material can be particularly enhanced. It is possible and preferable.

Further, when the heat treatment temperature is set to 600 ° C. or lower, sintering occurs between the primary particles of the lithium nickel composite oxide, and the added molybdenum component is solidly dissolved on the surface of the lithium nickel composite oxide particles in a layered manner. You can more reliably prevent this from happening. Therefore, the charge / discharge capacity of the battery can be sufficiently increased, which is preferable.

The atmosphere at the time of heat treatment may be a non-reducing atmosphere, but it is preferable to use an oxidizing atmosphere such as an oxygen atmosphere or a vacuum atmosphere in order to avoid a reaction between water and carbon dioxide in the atmosphere and the positive electrode active material.

The heat treatment time is not particularly limited, but is preferably 5 hours or more and 15 hours or less in order to sufficiently evaporate the water content to form lithium-molybdenum-containing oxide particles.
[Non-aqueous 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 the present embodiment may have a configuration including a positive electrode including the positive electrode active material for the non-aqueous electrolyte secondary battery described above.

Hereinafter, a specific description will be given.

The non-aqueous electrolyte secondary battery of the present embodiment (hereinafter, also simply referred to as “secondary battery”) comprises a positive electrode, a negative electrode, a non-aqueous electrolyte solution, and the like, and has the same components as a general non-aqueous electrolyte secondary battery. Consists of. It should be noted that the embodiments described below are merely examples, and the secondary battery of the present embodiment may be modified or improved in various ways based on the embodiments described in the present specification and based on the knowledge of those skilled in the art. It can be carried out in the given form. Further, the secondary battery of the present embodiment is not particularly limited in its use.

Hereinafter, the constituent members included in the secondary battery of the present embodiment will be described.
(A) Positive electrode The secondary battery of the present embodiment may include a positive electrode containing the above-mentioned positive electrode active material.

Specifically, the positive electrode of the secondary battery of the present embodiment can be manufactured by using the above-mentioned positive electrode active material, for example, as follows.

First, a powdery positive electrode active material, a conductive material, and a binder are mixed, and if necessary, activated carbon, a solvent for viscosity adjustment and the like are added, and the mixture is kneaded to prepare a positive electrode mixture paste.

The mixing ratio of each of the positive electrode mixture pastes is also an important factor in determining the performance of the secondary battery. When the total mass of 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 as in the case of the positive electrode of a general non-aqueous electrolyte secondary battery. It is desirable that the content of the conductive material is 1 part by mass or more and 20 parts by mass or less, and the content of the binder is 1 part by mass or more and 20 parts by mass or less.

The obtained positive electrode mixture paste is applied to, for example, the surface of a current collector made of aluminum foil and dried to disperse the solvent. If necessary, pressurization can be performed by a roll press or the like in order to increase the electrode density. In this way, a sheet-shaped positive electrode can be manufactured. The sheet-shaped positive electrode can be cut into an appropriate size according to the target battery and used for manufacturing the battery. However, the method for producing the positive electrode is not limited to the example, and other methods may be used. For example, it can be manufactured by press-molding a positive electrode mixture or a positive electrode mixture paste and then drying it in a vacuum atmosphere.

In the production of the positive electrode, for example, graphite (natural graphite, artificial graphite, expanded graphite, etc.), carbon black material such as acetylene black, ketjen black, etc. can be used as the conductive material.

The binder plays a role of binding the active material particles, for example, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), fluororubber, ethylene propylene diene rubber, styrene butadiene, cellulose resin, and polyacrylic acid. Acids and the like can be used.

If necessary, a solvent that disperses the positive electrode active material, the conductive material, and the activated carbon and dissolves the binder can be added to the positive electrode mixture. As the solvent, for example, an organic solvent such as N-methyl-2-pyrrolidone can be used. In addition, activated carbon can be added to the positive electrode mixture in order to increase the electric double layer capacity.
(B) Negative electrode The negative electrode can be prepared, for example, by the following procedure.

First, a binder is mixed with a negative electrode active material that can occlude and desorb lithium ions, such as metallic lithium or a lithium alloy, and a solvent is added to prepare a negative electrode mixture in the form of a paste. Then, the negative electrode mixture can be applied to the surface of a metal leaf current collector such as copper, dried, and if necessary, compressed to increase the electrode density.

As the negative electrode active material, for example, an organic compound fired body such as natural graphite, artificial graphite, or phenol resin, or a powdery body of a carbon substance such as coke can be used. In this case, as the negative electrode binder, a fluororesin such as PVDF can be used as in the positive electrode, and as the solvent for dispersing these active substances and the binder, N-methyl-2-pyrrolidone or the like can be used. An organic solvent can be used.
(C) Separator A separator is sandwiched between the positive electrode and the negative electrode. The separator separates the positive electrode and the negative electrode and retains an electrolyte, and a thin film such as polyethylene or polypropylene, which has a large number of fine pores, can be used.
(D) Non-aqueous electrolyte solution The non-aqueous electrolyte solution 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, ethylmethyl carbonate and dipropyl carbonate, and moreover, tetrahydrofuran and 2-. One type selected from ether compounds such as methyltetrahydrofuran and dimethoxyethane, sulfur compounds such as ethylmethylsulfone and butaneslton, phosphorus compounds such as triethyl phosphate and trioctyl phosphate, etc. may be used 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 , etc., and a composite salt thereof can be used.

Further, the non-aqueous electrolyte solution may contain a radical scavenger, a surfactant, a flame retardant and the like.
(E) Shape and configuration of the battery The shape of the secondary battery of the present embodiment having the positive electrode, the negative electrode, the separator and the non-aqueous electrolyte solution described above may be various, such as a cylindrical type and a laminated type. be able to.

Regardless of which shape is adopted, the positive electrode and the negative electrode are laminated via a separator to form an electrode body, and the obtained electrode body is impregnated with a non-aqueous electrolytic solution and communicates with the positive electrode current collector and the outside. A secondary battery can be obtained by connecting between the positive electrode terminal and the negative electrode current collector and the negative electrode terminal leading to the outside by using a current collecting lead or the like and sealing the battery case.
(F) Characteristics The above-mentioned positive electrode active material has excellent weather resistance. Therefore, the secondary battery of the present embodiment using the above-mentioned positive electrode active material can be a battery having a stable high initial discharge capacity and suppressed positive electrode resistance. That is, it is possible to obtain a secondary battery having a high capacity and a high output.

The secondary battery of the present embodiment provided with the positive electrode using the positive electrode active material described above preferably has an initial discharge capacity of 150 mAh / g or more, and is preferably 165 mAh / g, for example, in the case of a 2032 type coin type battery. It is more preferably g or more.

Further, since the above-mentioned positive electrode active material is excellent in weather resistance, it can be said that it exhibits stable characteristics, has high thermal stability, and is also excellent in safety.

The use of the secondary battery of the present embodiment is not particularly limited, but since it exhibits stable characteristics as described above, a small portable electronic device such as a notebook personal computer or a mobile phone terminal, which is always required to have a high capacity. It can be suitably used as a power source for equipment. Further, it can be suitably used for an electric vehicle battery that requires high output.

Further, since the secondary battery of the present embodiment has excellent safety and can be miniaturized and high in output, it can be suitably used as a battery for an electric vehicle whose mounting space is restricted. The secondary battery of the present embodiment can be used not only as a power source for an electric vehicle driven by purely electric energy but also as 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.

Hereinafter, the present invention will be specifically described with reference to examples of the present invention, but the present invention is not limited to these examples.
(Evaluation methods)
(1) Initial discharge capacity, positive electrode resistance ratio Using the positive electrode active materials manufactured in each Example and Comparative Example, a 2032 type coin type battery 11 (hereinafter referred to as a coin type battery) shown in FIG. 1 is manufactured, and the same is manufactured. Battery characteristics were evaluated.

As shown in FIG. 1, the coin-type battery 11 is composed of a case 12 and an electrode 13 housed in the case 12.

The case 12 has a positive electrode can 12a that is hollow and has one end open, and a negative electrode can 12b that is arranged in the opening of the positive electrode can 12a. When the negative electrode can 12b is arranged in the opening of the positive electrode can 12a, a space for accommodating the electrode 13 is formed between the negative electrode can 12b and the positive electrode can 12a.

The electrode 13 is composed of a positive electrode 13a, a separator 13c, and a negative electrode 13b, and is laminated so as to be arranged in this order. The positive electrode 13a contacts the inner surface of the positive electrode can 12a via the current collector 14, and the negative electrode 13b is the negative electrode. It is housed in the case 12 so as to come into contact with the inner surface of the can 12b via the current collector 14. A current collector 14 is also arranged between the positive electrode 13a and the separator 13c.

The case 12 is provided with a gasket 12c, and the gasket 12c fixes the relative movement between the positive electrode can 12a and the negative electrode can 12b so as to maintain a non-contact state. Further, the gasket 12c also has a function of sealing the gap between the positive electrode can 12a and the negative electrode can 12b and airtightly blocking the space between the inside and the outside of the case 12.

The coin-type battery 11 was manufactured as follows.

First, 52.5 mg of the positive electrode active material, 15 mg of acetylene black, and 7.5 mg of polytetrafluoroethylene resin (PTFE) prepared in each Example and Comparative Example were mixed and pressed to a diameter of 11 mm and a thickness of 100 μm at a pressure of 100 MPa. Molding was performed to prepare a positive electrode 13a. The prepared positive electrode 13a was dried in a vacuum dryer at 120 ° C. for 12 hours.

Using the positive electrode 13a, the negative electrode 13b, the separator 13c, and the electrolytic solution, the above-mentioned coin-type battery 11 was produced in a glove box having an Ar atmosphere in which the dew point was controlled to −80 ° C.

For the negative electrode 13b, a graphite powder having an average particle diameter of about 20 μm punched into a disk shape having a diameter of 14 mm and a negative electrode sheet coated with polyvinylidene fluoride on a copper foil were used. Further, a polyethylene porous membrane having a film thickness of 25 μm was used for the separator 13c. As the electrolytic solution, an equal amount mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) using 1M LiClO ₄ as a supporting electrolyte (manufactured by Tomiyama Pure Chemical Industries, Ltd.) was used.

The initial discharge capacity and the positive electrode resistivity, which indicate the performance of the manufactured coin-type battery 11, were evaluated as follows.

The initial discharge capacity is set to the cutoff voltage 4 with the current density for the positive electrode set to 0.1 mA / cm ² after the open circuit voltage OCV (Open Circuit Voltage) is stabilized by leaving it for about 24 hours after manufacturing the coin-type battery 11. The initial discharge capacity was defined as the capacity when the battery was charged to 3 V, paused for 1 hour, and then discharged to a cutoff voltage of 3.0 V.

The positive electrode resistance was evaluated as follows.

When the coin-type battery 11 is charged with a charging potential of 4.1 V and the frequency dependence of the battery reaction is measured by the AC impedance method using a frequency response analyzer and a potential galvanostat (manufactured by Solartron, 1255B), FIG. The Nyquist plot shown in A) is obtained. Since this Nyquist plot is represented as the sum of the solution resistance, the negative electrode resistance and its capacitance, and the characteristic curve showing the positive electrode resistance and its capacitance, the equivalent circuit shown in FIG. 2B is used based on this Nyquist plot. The fitting calculation was performed, and the value of the positive electrode resistance was calculated.

The positive electrode resistance of the positive electrode active material immediately after the production in Example 1 is set to 100, and the positive electrode resistance after the weather resistance test of Example 1 and the positive electrode resistances of other Examples and Comparative Examples are the production of Example 1. It is shown as the ratio of the positive electrode active material immediately after to the positive electrode resistance, that is, the positive electrode resistance ratio.
(2) Moisture content 1 g of the base material raw material containing the water after the water content adjustment step and the lithium nickel composite oxide particles is weighed and heated at 120 ° C. until the weight does not decrease, and the base material raw material before and after heating is heated. The moisture content was calculated from the change in weight.
(3) Amount of Lithium on Particle Surface The amount of lithium eluted from the positive electrode active material prepared in each Example and Comparative Example was evaluated by the Warder method, which is one of the neutralization titration methods. From the evaluation results, the amounts of lithium hydroxide (LiOH) and lithium carbonate (Li ₂ CO ₃ ) were calculated, and the sum of these lithium amounts was taken as the eluted lithium amount. The specific surface area of the positive electrode active material was determined by the nitrogen adsorption method. From the obtained amount of eluted lithium and the value of the specific surface area, the amount of lithium on the particle surface (mass% · g / m ² ) = (amount of eluted lithium (mass%)) / (specific surface area (m ² / g)) was calculated. ..
(4) Total carbon content The carbon content of the positive electrode active material prepared in each Example and Comparative Example, or the positive electrode active material after the weather resistance test was analyzed by the high frequency combustion-infrared absorption method. Specifically, the measurement was performed using a carbon-sulfur simultaneous analyzer (LECO model: CS600 type).
(5) Composition The composition of the positive electrode active material produced in each Example and Comparative Example was analyzed by an ICP emission spectrometry method using an ICP emission spectrometer (725ES manufactured by VARIAN).

Specific conditions of Examples and Comparative Examples will be described below. In the following examples and comparative examples, each sample of special grade reagent manufactured by Wako Pure Chemical Industries, Ltd. was used for producing the positive electrode active material and the secondary battery.
(Example 1)
First, it is represented by Li _1.030 Ni _0.91 Co _0.06 Al _0.03 O ₂ obtained by a known technique in which an oxide powder containing Ni as a raw material and lithium hydroxide are mixed and fired. Lithium-nickel composite oxide particles to be prepared were prepared. It was prepared as a lithium-nickel composite oxide powder, which is an aggregate of a plurality of lithium-nickel composite oxide particles.

The average particle size of the lithium nickel composite oxide particles was 12.0 μm, and the specific surface area was 0.3 m ² / g. The average particle size was evaluated using the volume integrated average value in the laser diffraction / scattering method, and the specific surface area was evaluated using the BET method by adsorbing nitrogen gas.

Further, when the cross section of the lithium nickel composite oxide particles was observed with a scanning electron microscope, it was confirmed that the lithium nickel composite oxide particles had primary particles and secondary particles in which the primary particles were aggregated.
(1) Moisture content adjustment step In the water content adjustment step, the water content of the base material was controlled as follows.

Specifically, first, 75 g of lithium nickel composite oxide particles (Li _1.030 Ni _0.91 Co _0.06 Al _0.03 O ₂ ) were added to 100 mL of pure water, and the mixture was washed with water for 15 minutes. .. Then, suction filtration was performed for 3 minutes in a decarboxylated air atmosphere to prepare a base material with a controlled moisture content.

1 g of the base material raw material after suction filtration was weighed and heated at 120 ° C. until the weight did not decrease, and the water content was calculated from the weight before and after heating. The water content at this time was 3% by mass.
(2) Mixing step As lithium-molybdenum-containing oxide particles so that Mo is 0.2 at.% With respect to Ni, Co, and Al in the lithium nickel composite oxide particles of the base material whose water content is adjusted. Commercially available lithium molybate particles (powder) were added and mixed for 5 minutes under a nitrogen atmosphere to prepare a raw material mixture. As the lithium molybdate particles, particles made of Li ₂ MoO ₄ are used, and lithium molybdate powder, which is an aggregate of the particles, is used as a raw material.
(3) Heat Treatment Step As a heat treatment step, the raw material mixture obtained in the mixing step was vacuum dried at 190 ° C. for 12 hours.

After the heat treatment step is completed, the particles are sieved with an opening of 38 μm and crushed to contain Mo and Li on the surface of the secondary particles of the lithium metal oxide and the surface of the primary particles existing inside the secondary particles, that is, molybdenum acid. A positive electrode active material represented by Li _0.98 Ni _0.908 Co _0.06 Al _0.03 Mo _0.002 O ₂ having lithium particles was obtained.

When the molybdenum content and Li / Me of the obtained positive electrode active material were analyzed in the same manner as above, it was confirmed that the molybdenum content was 0.2 at.% And the Li / Me was 0.980. Furthermore, the total amount of carbon immediately after the production of the positive electrode active material and the amount of lithium on the particle surface were calculated. In addition, as a weather resistance test, the total carbon content after standing in an air atmosphere (humidity 40%, temperature 25 ° C.) for 3 days was analyzed. The total carbon content of the obtained positive electrode active material immediately after production was 0.021% by mass, and the total carbon content after the weather resistance test was 0.060% by mass.

The amount of lithium on the particle surface immediately after the production of the obtained positive electrode active material was 0.049% by mass · g / m ² .

In addition, the battery characteristics of the coin-type battery 11 shown in FIG. 1 having a positive electrode immediately after production and a positive electrode produced using the positive electrode active material after the weather resistance test were evaluated. The evaluation results are shown in Table 1.
(Example 2)
A positive electrode active material was prepared and evaluated in the same manner as in Example 1 except that the water content of the base material was adjusted to 8% by mass in the water content adjusting step. Table 1 shows the conditions of the manufacturing process and the evaluation results.
(Example 3)
A positive electrode active material was prepared and evaluated in the same manner as in Example 1 except that the heat treatment in the heat treatment step was carried out in the same manner as in Example 1 except that the temperature was set to 300 ° C. in an oxygen atmosphere. Table 1 shows the conditions of the manufacturing process and the evaluation results.
(Example 4)
In the mixing step, a positive electrode active material was prepared and evaluated in the same manner as in Example 1 except that lithium molybdate particles were added so that Mo was 1.0 at.% With respect to Ni, Co, and Al. Was done. Table 1 shows the conditions of the manufacturing process and the evaluation results.
(Example 5)
In the mixing step, Mo was 0.05 at. With respect to Ni, Co and Al. A positive electrode active material was prepared and evaluated in the same manner as in Example 1 except that lithium molybdate particles were added so as to be%. Table 1 shows the conditions of the manufacturing process and the evaluation results.
(Example 6)
In the heat treatment step, a positive electrode active material was prepared and evaluated in the same manner as in Example 1 except that the heat treatment was carried out in an oxygen atmosphere and the temperature was set to 700 ° C. Table 1 shows the conditions of the manufacturing process and the evaluation results.
(Example 7)
In the heat treatment step, a positive electrode active material was prepared and evaluated in the same manner as in Example 1 except that the heat treatment temperature was set to 60 ° C. Table 1 shows the conditions of the manufacturing process and the evaluation results.
(Example 8)
In the water content adjusting step, a positive electrode active material was prepared and evaluated in the same manner as in Example 1 except that the water content of the base material was adjusted to be 20% by mass. Table 1 shows the conditions of the manufacturing process and the evaluation results.
(Example 9)
In the mixing step, Mo was 0.01 at. With respect to Ni, Co and Al. A positive electrode active material was prepared and evaluated in the same manner as in Example 1 except that lithium molybdate particles were added so as to be%. Table 1 shows the conditions of the manufacturing process and the evaluation results.
(Example 10)
In the mixing step, Mo was 5.0 at. With respect to Ni, Co and Al. A positive electrode active material was prepared and evaluated in the same manner as in Example 1 except that lithium molybdate particles were added so as to be%. Table 1 shows the conditions of the manufacturing process and the evaluation results.
(Comparative Example 1)
The lithium-nickel composite oxide particles used as the base material in Example 1 were used as they were as the positive electrode active material and evaluated. That is, the lithium molybdate particles were not formed on the surface of the lithium nickel composite oxide particles.

Table 1 shows the conditions of the manufacturing process and the evaluation results.
(Comparative Example 2)
The lithium nickel composite oxide particles used as the base material in Example 1 and commercially available Li ₂ MoO ₄ and powder were mixed so that the Mo content was 0.2 at.%. At this time, the water content of the obtained mixture becomes 0. Then, it was heat-treated at 720 ° C. for 1 hour in an oxygen atmosphere. Table 1 shows the evaluation results of the obtained positive electrode active material.
(Comparative Example 3)
The lithium-nickel composite oxide used as the base material in Example 1 was dispersed in a solution in which disodium disodium dihydrate dihydrate was dissolved, and the mixture was stirred at 25 ° C. for 3 hours. Then, it filtered and dried at 100 degreeC for 2 hours. At this time, the dissolved amount of disodium molybdate dihydrate in the solution was set to 0.2 mol% with respect to the lithium nickel composite oxide. Lithium hydroxide was added to the obtained Mo-supported lithium composite oxide so that the molar ratio was Mo / Li = 2/1, and the mixture was calcined at a temperature of 750 ° C. for 10 hours in an oxygen atmosphere. Table 1 shows the evaluation results of the obtained positive electrode active material.

ここで、図３に実施例１で得られた正極活物質の断面ＳＥＭ観察結果の一例を示す。図３（Ａ）はモリブデンの分布をマッピングしたものであり、図３（Ｂ）は、断面ＳＥＭ観察画像に、図３（Ａ）に示したモリブデンの分布のマッピング結果を重ね合せたものである。

Here, FIG. 3 shows an example of the cross-sectional SEM observation result of the positive electrode active material obtained in Example 1. FIG. 3 (A) is a mapping of the distribution of molybdenum, and FIG. 3 (B) is a superimposition of the mapping result of the distribution of molybdenum shown in FIG. 3 (A) on the cross-sectional SEM observation image. ..

As shown in FIGS. 3 (A) and 3 (B), it was confirmed that the lithium nickel composite oxide particles 32 contained primary particles and secondary particles in which the primary particles were aggregated. Further, it was confirmed that the lithium-molybdenum-containing oxide particles 31 were arranged on the surface of the secondary particles of the lithium nickel composite oxide particles 32 and the surface of the primary particles.

It was confirmed from the results of X-ray diffraction analysis that the obtained positive electrode active material contained lithium nickel composite oxide particles and lithium-molybdenum-containing oxide particles. It was also confirmed from the results of the above X-ray diffraction that Li ₂ MoO ₄ was contained as the lithium-molybdenum-containing oxide.

Similarly, when cross-sectional SEM observation was performed in Examples 2 to 10, it was confirmed that the lithium nickel composite oxide particles contained primary particles and secondary particles in which the primary particles were aggregated. Further, it was confirmed that the lithium-molybdenum-containing oxide particles were arranged on the surface of the secondary particles of the lithium nickel composite oxide particles and the surface of the primary particles. Furthermore, in Examples 2 to 10, it was also confirmed from the results of X-ray diffraction that Li ₂ MoO ₄ was contained as the lithium-molybdenum-containing oxide.

Then, as shown in Table 1, it was also confirmed that the positive electrode active materials of Examples 1 to 10 were positive electrode active materials having a lower total carbon content than those of Comparative Examples 1 to 3. The total carbon amount is an index depending on the amount of lithium carbonate possessed by the positive electrode active material, and when the total carbon amount is low, that is, when the amount of lithium carbonate is small, the decrease in the amount of Li that contributes to charging and discharging can be suppressed. It can be said that it has excellent battery characteristics.

Then, in Examples 1 to 10, it was confirmed that the initial discharge capacity was high and the positive electrode resistivity was small even after the weather resistance test. That is, it was confirmed that the weather resistance was excellent.

This reduces the surface of the exposed active lithium nickel composite oxide particles by arranging the lithium-molybdenum-containing oxide particles on the surface of the secondary particles of the lithium nickel composite oxide particles and the surface of the primary particles. It is probable that the deterioration of the positive electrode active material when exposed to the air could be suppressed.

Further, since the positive electrode active materials of Examples 1 to 10 have a low total carbon content as described above, the total carbon content can be maintained low even when exposed to the atmosphere, and the total carbon content increases. This is probably because the degree of performance degradation could be suppressed.

On the other hand, in Comparative Example 1, lithium-molybdenum-containing oxide particles were not formed on the surface of the lithium-nickel composite oxide particles. Therefore, it can be confirmed that the positive electrode resistivity is significantly higher immediately after production as compared with Examples 1 to 10, and the initial discharge capacity is low and the positive electrode resistivity is also high after the weather resistance test. rice field. Therefore, it was confirmed that the weather resistance was not sufficient.

In Comparative Example 2, a mixture of lithium-nickel composite oxide particles containing no water and lithium-molybdenum-containing oxide particles is fired to obtain a positive electrode active material.

As described above, the cation mixing is proceeding by firing the raw material mixture containing no water. Further, when the cross-sectional SEM observation of the positive electrode active material produced in Comparative Example 2 was carried out, it was confirmed that the lithium-molybdenum-containing oxide particles were hardly present on the surface of the lithium-nickel composite oxide particles. It is considered that this is because the added lithium-molybdenum-containing oxide particles diffused during the heat treatment and did not remain as particles.

Therefore, as compared with Examples 1 to 10, the initial discharge capacity after the weather resistance test was low, the positive electrode resistance ratio was high, and it was confirmed that the weather resistance was inferior.

In Comparative Example 3, lithium nickel composite oxide particles are dispersed in a solution in which disodium molybdate dihydrate is dissolved, and then a lithium raw material is further added and then fired to prepare a positive electrode active material. ..

Therefore, the drying time becomes long, and the total carbon content is as high as 0.035% by mass. As a result, it was confirmed that the positive electrode resistivity after the weather resistance test was high and the weather resistance was inferior.

The amount of lithium on the particle surface of Comparative Example 1 in which the lithium-molybdenum-containing oxide particles were not arranged on the surface of the lithium-nickel composite oxide particles and the amount of lithium on the particle surface when the treatment was performed. The difference is considered to be an index of the amount of lithium-molybdenum-containing oxide particles located on the surface of the lithium-nickel composite oxide particles.

In Comparative Examples 2 and 3, the amount of lithium on the particle surface was almost the same as that in Comparative Example 1, and most of the added molybdenum was solid-solved inside the lithium nickel composite oxide particles. It is inferred.

From the above results, the positive electrode active materials of Examples 1 to 10 have excellent weather resistance, and the battery using the positive electrode active material as the positive electrode is stable and has a high initial discharge capacity and a low positive electrode resistance. I was able to confirm that. Therefore, it was confirmed that the batteries produced by using the positive electrode active materials of Examples 1 to 10 are batteries having excellent characteristics.

11 Coin-type battery 13a Positive electrode

Claims (7)

General formula Li _z Ni _{1-x-y Co} x _My O 2 _{+ α} (0 <x ≦ 0.35, 0 <y ≦ 0.07, 0.85 ≦ z ≦ 1.10, x + y ≦ 0.20, 0 ≦ α ≦ 0.5, the element M is at least one element selected from Mn, V, Mg, Mo, Nb, Ti and Al) , and the primary particles of the lithium nickel composite oxide and the primary particles. Lithium-nickel composite oxide particles with agglomerated secondary particles and
Lithium-molybdenum-containing particles of lithium-molybdenum-containing oxide particles arranged on the surface of the secondary particles of the lithium-nickel composite oxide particles and the surface of the primary particles and containing an oxide containing Li and Mo. With oxide particles,
The total carbon content is less than 0.035% by mass ,
Using the amount of eluted lithium obtained by the Warder method and the specific surface area, the amount of particle surface lithium calculated by the following formula (1) is 0.035% by mass · g / m ² or more. Positive electrode active material for batteries.
Particle surface lithium amount (mass% · g / m ² ) = (eluted lithium amount (mass%)) / (specific surface area (m ² / g)) ・ ・ ・ (1) The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the lithium-molybdenum-containing oxide contains one or more selected from Li ₂ MoO ₄ and Li ₄ MoO ₅ . Primary of lithium nickel composite oxide containing Li, Ni, Co, and additive element M (where additive element M is at least one element selected from Mn, V, Mg, Mo, Nb, Ti and Al). A moisture content adjusting step for adjusting the moisture content of the base material raw material containing the particles and the lithium nickel composite oxide particles having the secondary particles in which the primary particles are aggregated, and water.
A mixing step of mixing the base material and lithium-molybdenum-containing oxide particles to prepare a raw material mixture.
It has a heat treatment step of heat-treating the raw material mixture in a non-reducing atmosphere.
A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery in which the water content of the base material is made 0.1% by mass or more and 20% by mass or less in the water content adjusting step . The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 3 , wherein the water content of the base material is made 0.1% by mass or more and 15% by mass or less in the water content adjusting step. In the mixing step, the ratio of the number of atoms of Mo contained in the added lithium-molybdenum-containing oxide particles to the number of atoms of Ni, Co, and the additive element M contained in the lithium nickel composite oxide particles is 0. .02 at. % Or more 2.0 at. The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 3 or 4 , wherein the lithium-molybdenum-containing oxide particles are added so as to be% or less. The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of claims 3 to 5 , wherein the heat treatment temperature in the heat treatment step is 100 ° C. or higher and 600 ° C. or lower. A non-aqueous electrolyte secondary battery comprising a positive electrode containing the positive electrode active material for the non-aqueous electrolyte secondary battery according to claim 1 or 2 .

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