JP5656012B2 - Positive electrode active material powder for non-aqueous electrolyte secondary battery, method for producing the same, and non-aqueous electrolyte secondary battery - Google Patents

Description

  Provided is a positive electrode active material particle powder for a non-aqueous electrolyte secondary battery having a large charge / discharge capacity during high-voltage charging and excellent initial charge / discharge efficiency.

  In recent years, electronic devices such as AV devices and personal computers are rapidly becoming portable and cordless, and there is an increasing demand for secondary batteries having a small size, light weight, and high energy density as power sources for driving these devices. In recent years, in consideration of the global environment, electric vehicles and hybrid vehicles have been developed and put into practical use, and the demand for a lithium ion secondary battery having excellent storage characteristics as a large-scale application is increasing. Under such circumstances, a lithium ion secondary battery having an advantage of a large charge / discharge capacity has attracted attention.

Conventionally, as positive electrode active substances useful for high energy-type lithium ion secondary batteries having 4V-grade voltage, LiMn ₂ O ₄ of spinel structure, LiMnO ₂ having a zigzag layer structure, LiCoO ₂ of layered rock-salt structure, LiNiO _{2 and the} like are generally known, and lithium ion secondary batteries using LiNiO ₂ have attracted attention as batteries having a high charge / discharge capacity. However, since this material is inferior in thermal stability during charging and charge / discharge cycle durability, further improvement in characteristics is required.

That is, when LiNiO ₂ pulls out lithium, Ni ³⁺ becomes Ni ⁴⁺ , resulting in a yarn teller strain, and in the region where Li is pulled 0.45, from hexagonal to monoclinic, when further drawn, it changes from monoclinic to hexagonal. The crystal structure changes. Therefore, repeating the charge / discharge reaction makes the crystal structure unstable, the cycle characteristics deteriorate, and the reaction with the electrolyte solution due to oxygen release occurs, resulting in poor battery thermal stability and storage characteristics. there were. In order to solve this problem, research has been conducted on materials in which Co and Al are added to a part of Ni in LiNiO ₂ , but no material that has solved these problems has yet been obtained, and more crystalline properties have been obtained. Li-Ni composite oxide having a high C content is demanded.

Conventionally, various improvements have been made to LiNiO ₂ powder in order to improve various characteristics such as stabilization of crystal structure and charge / discharge cycle characteristics. For example, a Li-Ni-Co-Mn composite oxide is coated on the surface of LiNiAlO ₂ to improve cycle characteristics and thermal stability (Patent Document 1). Li-Ni-Co-Mn composite oxide is mixed to improve the charge / discharge cycle characteristics and thermal stability of Li-Co composite oxide (Patent Document 2), Li-Co composite oxide containing lithium carbonate, Ni Charging / discharging cycle characteristics of Li—Co composite oxide by suspending (OH) ₂ , Co (OH) ₂ , manganese carbonate, or coating Li—Ni—Co—Mn composite oxide by mechanical treatment And a technology for improving high temperature characteristics (Patent Document 3 and Patent Document 4), Li—Co composite oxide, Li—Ni composite oxide, Li—Mn composite oxide comprising composite particles composed of core particles and coated particles Technology that achieves high fillability and high energy density (Patent Document 5), and coating the surface of Li-Co composite oxide with Li-Ni composite oxide suppresses the elution of Co into the electrolyte Technology (Patent Document 6), a technique of covering the surface of Li-Ni-Co composite oxide with Li-Ni-Co-Mn composite oxide and improving thermal stability during charging (Patent Document 7), etc. Are known.

JP 2004-127694 A JP 2005-317499 A JP 2006-319443 A JP 2007-48711 A Japanese Patent Laid-Open No. 9-35715 JP 2000-195517 A JP 2008-251532 A

  A positive electrode active material for a non-aqueous electrolyte secondary battery with excellent charge / discharge capacity and initial charge / discharge efficiency at the time of high-voltage charging is currently the most demanded, but a material that satisfies the necessary and sufficient requirements is still available. Not.

  Accordingly, an object of the present invention is to contain a positive electrode active material particle powder for a non-aqueous electrolyte secondary battery having a large charge / discharge capacity during high-voltage charging and excellent initial charge / discharge efficiency, a production method thereof, and the positive electrode active material particle powder. A nonaqueous electrolyte secondary battery comprising a positive electrode is provided.

The present invention is a compound in which secondary particles serving as nuclei have at least a crystal system belonging to space group R-3m and a crystal system belonging to space group C2 / m, and a powder X-ray diffraction diagram using Cu-Kα rays. The relative intensity ratio (a) / (b) between the intensity (a) of the maximum diffraction peak at 2θ = 20.8 ± 1 ° and the intensity (b) of the maximum diffraction peak at 2θ = 18.6 ± 1 ° is 0. 0.02 to 0.5, and the Mn content is a Li—Mn composite oxide particle having a molar ratio of Mn / (Ni + Co + Mn) of 0.55 or more, on the particle surface of the secondary particle or in the vicinity of the surface. Li _x2 Mn ₂ -y2 Ni _y2 O ₄ (0.95 ≦ x2 ≦ 1.10, 0.45 ≦ y2 ≦ 0.55), or Li _x3 Mn _1-y3 Fe _y3 PO ₄ (0.98) ≦ x3 ≦ 1.10, 0 <y3 ≦ 0.30) A positive electrode active material particle powder for a non-aqueous electrolyte secondary battery in which at least one Li-Mn compound particle is coated or present, and the average of the secondary particles of the positive electrode active material particle powder for a non-aqueous electrolyte secondary battery The particle size is 1.1 times or more of the average particle size of the secondary particles serving as the nucleus, and the weight percentage of the Li—Mn compound particles existing in the vicinity of the coated particles or the surface with respect to the core particles is 0.5% or more. It is a positive electrode active material particle powder for a nonaqueous electrolyte secondary battery, characterized by being 20% or less (Invention 1).

Further, in the present invention, LiM _p Mn _(1-p) O ₂ (M is Ni and / or Co, 0 <p ≦ 0 ₎ as a compound in which the secondary particle serving as a nucleus has a crystal system belonging to the space group R-3m. 1) including Li ₂ M ′ _(1-q) Mn _q O ₃ (M ′ is Ni and / or Co, 0 <q ≦ 1) as a compound having a crystal system belonging to the space group C2 / m. It is the positive electrode active material particle powder for nonaqueous electrolyte secondary batteries of this invention 1 characterized by the above (this invention 2).

The present invention also relates to a method for producing a positive electrode active material particle powder for a non-aqueous electrolyte secondary battery according to the first or second aspect of the present invention, comprising a precursor particle powder containing Mn, Ni and / or Co, and a lithium compound. Li _x2 Mn _{2 -y2} Ni _y2 O ₄ (secondary particles having an average particle diameter of 3 μm or less) was obtained as secondary particles of the Li—Mn composite oxide obtained by firing the contained mixture in the range of 500 to 1500 ° C. 0.95 ≦ x2 ≦ 1.10, 0.45 ≦ y2 ≦ 0.55), or Li _x3 Mn _1-y3 Fe _y3 PO ₄ (0.98 ≦ x3 ≦ 1.10, 0 <y3 ≦ 0.30) A method for producing a positive electrode active material particle powder for a non-aqueous electrolyte secondary battery, wherein at least one Li—Mn compound particle powder selected from (Invention 3).

  Further, the present invention is a non-aqueous electrolyte secondary battery using the positive electrode containing the positive electrode active material particle powder for non-aqueous electrolyte secondary battery according to the first or second invention (Invention 4). ).

  The positive electrode active material particle powder according to the present invention is suitable as a positive electrode active material particle powder for a non-aqueous electrolyte secondary battery because it can improve the initial charge / discharge efficiency during high-voltage charging.

2 is an X-ray diffraction pattern of Li-Mn composite oxide particle powder that is a nucleus obtained in Reference Example 1. FIG. 4 is a SEM photograph of Li—Mn composite oxide particle powder as a nucleus obtained in Reference Example 1. 4 is a SEM photograph of positive electrode active material particle powder obtained in Reference Example 1. 2 is a SEM photograph of positive electrode active material particle powder obtained in Example 1. 4 is a SEM photograph of positive electrode active material particle powder obtained in Example 3.

  The configuration of the present invention will be described in more detail as follows.

  The positive electrode active material powder according to the present invention has, as a nucleus, secondary particles of a Li—Mn composite oxide composed of a compound having at least a crystal system belonging to the space group R-3m and a crystal system belonging to the space group C2 / m. In addition, one or more of spinel type Li—Mn composite oxide particles or olivine type Li—Mn phosphate compound particles having a specific composition were coated or existed on the particle surface of the secondary particles or in the vicinity of the particle surface. Is. That is, the entire surface of the secondary particles serving as nuclei is coated with one or more of spinel-type Li—Mn composite oxide particles having a specific composition or olivine-type Li—Mn phosphate compound particles, or nuclei In the vicinity of the surface of the secondary particles or a part of the particle surface, one or more of spinel-type Li—Mn composite oxide particles or olivine-type Li—Mn phosphate compound particles having a specific composition are present or coated It has been made.

As a compound having a crystal system belonging to the space group R-3m, LiM _p Mn _(1-p) O ₂ (M is Ni and / or Co, and the range of x is 0 <p ≦ 1) is preferable. _{Specifically, LiCo p Mn 1-p O} 2, LiNi p Mn 1-p O 2, Li (Ni, Co) such as _{p Mn 1-p O 2} is preferred.
The space group R-3m is officially written with a bar on 3 of R3m, but for the sake of convenience, it is described as R-3m.

As a compound having a crystal system belonging to the space group C2 / m, Li ₂ M ′ _(1-q) Mn _q O ₃ (M ′ is Ni and / or Co, and the range of y is 0 <q ≦ 1) is preferable. .

LiM _p Mn ₍₁ ), which is a compound belonging to the crystal system belonging to the space group R-3m, is obtained by performing powder X-ray diffraction on the core Li—Mn composite oxide particles using Cu—Kα rays as a radiation source. _-P) One of the peaks characteristic of O ₂ appears at 2θ = 18.6 ± 1 °, and Li ₂ M ′ _(1-q) Mn _q O, which is a compound belonging to the crystal system belonging to the space group C2 / m One of the peaks characteristic to ₃ appears at 2θ = 20.8 ± 1 °.

  The relative intensity between the intensity (a) of the maximum diffraction peak at 2θ = 20.8 ± 1 ° and the intensity (b) of the maximum diffraction peak at 2θ = 18.6 ± 1 ° of the core Li-Mn composite oxide particles The ratio (a) / (b) is 0.02 to 0.5. When the relative intensity ratio (a) / (b) is less than 0.02, the compound having a crystal system belonging to the space group C2 / m is too small to obtain a sufficient charge / discharge capacity, and the relative intensity ratio ( When a) / (b) exceeds 0.5, there are too many compounds having a crystal system belonging to the space group C2 / m, and smooth lithium ion migration cannot be achieved, and sufficient charge / discharge capacity can be obtained. Absent. The preferred relative strength ratio (a) / (b) is 0.02 to 0.4, the more preferred relative strength ratio (a) / (b) is 0.02 to 0.3, and even more preferred relative strength. The ratio (a) / (b) is 0.02 to 0.2.

  The Li—Mn composite oxide particles serving as the nucleus have a Mn content in a molar ratio of Mn / (Ni + Co + Mn) of 0.55 or more. Below this range, a compound having a crystal system belonging to the space group C2 / m is not sufficiently formed, and the charge / discharge capacity decreases. Preferably it is 0.56 or more, More preferably, it is 0.6 or more, More preferably, it is 0.65 or more. The upper limit is preferably about 0.95.

  It is preferable that the Li—Mn composite oxide particles serving as the nucleus contain 0.001 to 3 wt% of boron. When the boron content is less than 0.001 wt%, the cycle characteristics of the secondary battery using the positive electrode active material particle powder are undesirably lowered. If it exceeds 3 wt%, the charge / discharge capacity decreases, which is not preferable. A preferable boron content is 0.003 to 2 wt%, more preferably 0.005 to 1 wt%, and still more preferably 0.02 to 0.5 wt%.

The particles to be coated or present are at least one Li—Mn compound particle selected from spinel type Li—Mn composite oxide particles having a specific composition or olivine type Li—Mn phosphate compound particles.
In the case of a compound other than these, it is difficult to obtain a high discharge capacity and high initial charge / discharge efficiency during high-voltage charging.

When the particles to be coated or present are spinel-type Li—Mn composite oxide particles, the composition is Li _x2 Mn _2-y2 Ni _y2 O ₄ (0.95 ≦ x2 ≦ 1.10, 0.45 ≦ y2 ≦ 0. 55).
When the composition range is out of the above range, it is difficult to obtain a high discharge capacity and high initial charge / discharge efficiency during high-voltage charging.

When the particles to be coated or present are olivine-type Li—Mn phosphate compound particles, the composition is Li _x3 Mn _1-y3 Fe _y3 PO ₄ (0.98 ≦ x3 ≦ 1.10, 0 <y3 ≦ 0.30) It is.
When the composition range is out of the above range, it is difficult to obtain a high discharge capacity and high initial charge / discharge efficiency during high-voltage charging.

In the present invention, the weight percentage of the Li—Mn compound particles to be coated or present on the secondary particles of the Li—Mn composite oxide serving as the nucleus satisfies 0.5% or more and 20% or less.
When the weight percentage is less than 0.5%, it is carried out from a compound having a crystal system belonging to the space group C2 / m such as Li ₂ MnO ₃ contained in particles whose core is the desorption of lithium ions during high voltage charging. As a result, the structure of the core particles changes, and lithium ions are not inserted during discharge, resulting in a decrease in the initial charge / discharge efficiency. On the other hand, when the weight percentage exceeds 20%, it is difficult to obtain a high discharge capacity even by high voltage charging.
When considering both high discharge capacity and high initial charge / discharge efficiency, it is preferable that the amount of Li-Mn compound particles to be coated or present is small. The amount to be coated or present is preferably 10% or less, more preferably 1% to 5%.

  The average particle diameter of the secondary particles of the positive electrode active material particle powder for a non-aqueous electrolyte secondary battery according to the present invention is 1.1 with respect to the average particle diameter of the secondary particles of the Li-Mn composite oxide serving as a nucleus. Control to double or more. When the ratio of the average particle diameter is less than 1.1 times, there is no effect of covering or adhering the Li—Ni compound particles. A preferred particle size ratio is 1.2 or more, more preferably 1.3 to 2.0.

  In addition, as for the average particle diameter of the secondary particle of the positive electrode active material particle powder for nonaqueous electrolyte secondary batteries which concerns on this invention, 1-50 micrometers is preferable. When the average particle size is 1 μm or less, the dispersibility when the Li—Ni composite oxide is used as an electrode slurry is deteriorated. When the thickness exceeds 50 μm, the thickness of the electrode is increased, so that the rate characteristic is deteriorated and the discharge capacity is lowered.

  Next, the manufacturing method of the positive electrode active material particle powder according to the present invention will be described.

  Li-Mn composite oxide particles serving as the core of the positive electrode active material particle powder according to the present invention are prepared by mixing a precursor particle powder containing a transition metal prepared in advance and a lithium compound, and firing in a temperature range of 500 to 1500 ° C. Can be obtained. When boron is contained, the precursor particle powder, the boron compound, and the lithium compound may be mixed and fired.

  The precursor particle powder containing a transition metal in the present invention supplies a mixed solution containing a nickel salt, a cobalt salt, and a manganese salt having a predetermined concentration and an alkaline aqueous solution to a reaction vessel, and has a pH of 7.5 to 13. In this way, the overflowed suspension is seed-circulated to the reaction tank while adjusting the concentration rate in the concentration tank connected to the overflow pipe, and the precursor particle concentration in the reaction tank and the concentration tank is 0.5 to 15 mol. It can be obtained by carrying out the reaction until it reaches / l. After the reaction, washing with water, drying and pulverization may be performed according to a conventional method.

  As the precursor particle powder containing a transition metal in the present invention, various transition metal compounds can be used without any particular limitation. For example, oxides, hydroxides, carbonates or mixtures thereof are preferable, More preferred are transition metal hydroxides.

The precursor particle powder in the present invention preferably has an average particle diameter of 1 to 50 μm and a BET specific surface area of 3 to 120 m ² / g.

  The boron compound that can be used in the present invention is not particularly limited, and various boron compounds can be used. For example, diboron trioxide, boric acid (orthoboric acid), metaboric acid, tetraboric acid, Various borates such as lithium borate are listed, and boric acid is preferred. The mixing ratio of the boron compound is preferably 0.02 to 20 wt% with respect to the precursor particles.

  The lithium compound used in the present invention is not particularly limited, and various lithium salts can be used. For example, lithium hydroxide monohydrate, lithium nitrate, lithium carbonate, lithium acetate, lithium bromide, chloride Examples include lithium, lithium citrate, lithium fluoride, lithium iodide, lithium lactate, lithium oxalate, lithium phosphate, lithium pyruvate, lithium sulfate, and lithium oxide, with lithium carbonate being preferred. The mixing ratio of the lithium compound is preferably 20 to 120 wt% with respect to the precursor particles.

  Moreover, it is preferable that the lithium compound to be used has an average particle diameter of 50 micrometers or less. More preferably, it is 30 μm or less. When the average particle size of the lithium compound exceeds 50 μm, mixing with the precursor particles becomes non-uniform, and it becomes difficult to obtain Li—Mn composite oxide particle powder with good crystallinity.

  The mixing treatment of the precursor particle powder containing the transition metal and the lithium compound may be either dry or wet as long as it can be uniformly mixed.

  The firing temperature is preferably 500 ° C to 1500 ° C. When the temperature is less than 500 ° C., the reaction between Li and Ni, Co, and Mn does not proceed sufficiently and is not sufficiently combined. If the temperature exceeds 1500 ° C., the sintering proceeds excessively, which is not preferable. More preferably, it is a temperature range of 700-1200 degreeC, More preferably, it is a temperature range of 800-1050 degreeC. The atmosphere during firing is preferably an oxidizing gas atmosphere, and more preferably normal air. The firing time is preferably 3 to 30 hours.

  The spinel-type Li—Mn composite oxide particles or the olivine-type Li—Mn phosphate compound particles, which are particles to be coated or exist on the positive electrode active material particle powder according to the present invention, are obtained by a usual method, for example It is obtained by mixing various raw materials and a lithium salt by a solid phase method or a wet method, and firing at 500 ° C. to 1000 ° C. in an air or nitrogen atmosphere.

  The positive electrode active material particle powder according to the present invention comprises spinel-type Li—Mn composite oxide particles or olivine-type Li—Mn phosphorus particles that are coated or exist on or near the particle surface of the core Li—Mn composite oxide particles. The acid compound particles are made to have spinel-type Li—Mn composite oxide particles or olivine-type Li—Mn phosphate compound particles existing on or near the surface of the core secondary particles by mechanical treatment by dry process. . More preferably, the secondary particles of the Li—Mn composite oxide particles and the Li—Mn compound particles are ground and mixed, so that the Li—Mn composite oxide particles serving as the core have Li on the particle surface or in the vicinity of the surface. -Mn compound particles are present.

  The average particle size of the secondary particles of the powder to be coated or present and the average particle size of the secondary secondary particles are the average particle size of the secondary particles of the positive electrode active material particle powder for non-aqueous electrolyte secondary batteries. The average particle diameter of the secondary particles is 1.1 times or more, and the weight percentage of the coated particles or the Li—Mn compound particles existing near the surface with respect to the core particles is 0.5% or more and 20% or less. The average particle size of the secondary secondary particles is usually 1 to 45 μm, preferably 1.5 to 40 μm, and the average particle size of the secondary particles of the powder to be coated or present is Usually, it is 3.0 micrometers or less, Preferably it is 0.8-2.8 micrometers. When producing a positive electrode active material particle powder for a non-aqueous electrolyte secondary battery by grinding and mixing as described above, the average particle diameter of the secondary secondary particles is the average of the secondary particles of the powder to be coated or present. It is preferably larger than the particle diameter, and the average particle diameter of the secondary secondary particles is more preferably 4 to 25 times the average particle diameter of the powder secondary particles to be coated or present. In addition, the secondary particles of the core particles are preferably not broken by grinding and mixing, and the size of the secondary particle diameter is obtained when grinding and mixing is performed only with the core particles under the same conditions as the coating treatment. Is preferably within ± 1.5 μm with respect to the size of the particles before mixing. Under these conditions, the cohesiveness of the coated particles to the core particle surface can be improved by grinding and mixing while applying very strong compaction and shear between the coated particles and the core particles. And particle compositing can be achieved. At this time, in order to release the strong agglomeration of the coated particles between the coated particles, the agglomeration force of the secondary particles of the core particles is important. If this force is weak, the core particles are destroyed by grinding and mixing. As a result, strong agglomeration between the coated particles is not released, and the agglomeration between the coated particles occurs, and Li-Mn compound particles are obtained on or near the particle surface of the Li-Mn composite oxide particles serving as the target nucleus. It becomes difficult.

  If necessary, thermal treatment may be further performed in an oxygen atmosphere at 700 ° C. or higher, preferably 730 ° C. or higher for 2 hours or longer.

  Next, the positive electrode containing the positive electrode active material particle powder for nonaqueous electrolyte secondary batteries according to the present invention will be described.

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

  The secondary battery manufactured using the positive electrode active material particle powder according to the present invention includes the positive electrode, the negative electrode, and an electrolyte.

  As the negative electrode active material, lithium metal, lithium / aluminum alloy, lithium / tin alloy, graphite, graphite, or the like can be used.

  In addition to the combination of ethylene carbonate and diethyl carbonate, an organic solvent containing at least one of carbonates such as propylene carbonate and dimethyl carbonate and ethers such as dimethoxyethane can be used as the solvent for the electrolytic solution.

  Further, as the electrolyte, in addition to lithium hexafluorophosphate, at least one lithium salt such as lithium perchlorate and lithium tetrafluoroborate can be dissolved in the above solvent and used.

The secondary battery manufactured using the positive electrode containing the positive electrode active material particle powder according to the present invention has an initial discharge capacity of 240 mAh / g or more according to an evaluation method to be described later, and it is more preferable that it be higher. Further, the initial charge / discharge efficiency is 90% or more. Further, the irreversible capacity is 40 mAh / g or less, and the DC resistance value in a 4.6 V charged state is 85 Ω · cm ² or less.

<Action>
The cause of the decrease in the initial charge / discharge efficiency of the non-aqueous electrolyte secondary battery that performs high-voltage charging includes a change in crystal structure accompanying the desorption of lithium during charging and decomposition of the electrolytic solution. The cause of this crystal structure change is the non-uniformity of the crystal structure of the core particles. Further, the cause of the decomposition of the electrolytic solution is largely due to the electrolysis of the electrolytic solution itself, but includes the oxidative decomposition of the electrolytic solution by oxygen generated from the material itself.
Although it cannot be said to be a direct method for suppressing the above-mentioned problem, as an example, surface modification of a positive electrode active material for a non-aqueous electrolyte secondary battery is important, and in the prior art (Patent Documents 1 to 4), etc. Although improvement is performed, in Patent Document 1, the composition of the core particles is Li—Ni—Al composite oxide, and the charge / discharge efficiency of the core particles is deteriorated, and the coating state and the coating ratio are described. There is no consideration for improving the initial charge and discharge efficiency during high-voltage charging by coating. Also. In patent document 2, it is thermal stability improvement by mixing Li-Ni-Co-Mn composite oxide to Li-Co composite oxide, and is not considered about the improvement of the first-time charge / discharge efficiency at the time of high voltage charge. . Further, in Patent Document 3, the surface of the Li-Co composite oxide is coated with a Li-Ni-Co-Mn composite oxide, and in Patent Document 4, the surface of the Co composite oxide is made of lithium, nickel, cobalt, manganese metal. Although the capacity is increased and the cycle characteristics and the high-temperature storage characteristics are improved by forming the coating layer, the improvement of the initial charge / discharge efficiency during high-voltage charging is not taken into consideration. In Patent Document 5, Li—Co composite oxide, Li—Ni composite oxide, and Li—Mn composite oxide are formed into composite particles composed of core particles and coated particles to improve the filling property and energy density. However, the description of the composition of the core particles and the covering particles is unclear, and the improvement of the initial charge / discharge efficiency at the time of high-voltage charging is not considered. In Patent Document 6, the surface of the Li—Co composite oxide is coated with the Li—Ni composite oxide to suppress the elution of Co into the electrolyte, but Li—Co which has poor thermal stability during charging. This is a technique for controlling the elution of Co from the composite oxide, and no consideration is given to improving the initial charge / discharge efficiency during high-voltage charging. In Patent Document 7, the Li-Ni-Co-Mn composite oxide is coated on the surface of the Li-Ni-Co composite oxide to improve the thermal stability during charging, but the first time during high-voltage charging. The improvement of charge / discharge efficiency is not considered.

Therefore, in the present invention, a powder X using Cu—Kα rays is a compound in which secondary particles serving as nuclei have a crystal system belonging to at least the space group R-3m and a crystal system belonging to the space group C2 / m. Relative intensity ratio (a) / (b) between the intensity (a) of the maximum diffraction peak at 2θ = 20.8 ± 1 ° and the intensity (b) of the maximum diffraction peak at 2θ = 18.6 ± 1 ° in the line diffraction diagram. ) Is 0.02 to 0.5, and the Mn content is Li—Mn composite oxide particles having a molar ratio of Mn / (Ni + Co + Mn) of 0.55 or more, and the particle surface of the secondary particles or Near the surface, the composition is Li _x2 Mn _2-y2 Ni _y2 O ₄ (0.95 ≦ x2 ≦ 1.10, 0.45 ≦ y2 ≦ 0.55), or Li _x3 Mn _1-y3 Fe _y3 PO ₄ ( 0.98 ≦ x3 ≦ 1.10, 0 <y3 ≦ 0.30 A positive electrode active material particle powder for a non-aqueous electrolyte secondary battery coated with or present with at least one Li-Mn compound particle selected from: secondary particles of the positive electrode active material particle powder for a non-aqueous electrolyte secondary battery The average particle size of the secondary particles that are nuclei is 1.1 times or more of the average particle size, and the weight percentage of the Li—Mn compound particles existing in the vicinity of the coated particles or the surface of the nuclei particles is 0.5. By using a positive electrode active material that is not less than 20% and not more than 20% in a non-aqueous electrolyte secondary battery, it is possible to improve the initial charge / discharge efficiency while maintaining a high discharge capacity during high-voltage charging.

  A typical embodiment of the present invention is as follows.

  The composition of the Li—Mn composite oxide particle powder and the Li—Mn compound particle powder was analyzed and confirmed using induction plasma emission spectroscopy ICP-7500 [manufactured by Shimadzu Corporation].

  The average primary particle diameter of the particles was observed and confirmed using a scanning electron microscope SEM-EDX with an energy dispersive X-ray analyzer [manufactured by Hitachi High-Technologies Corporation].

  The average particle diameter is a volume-based average particle diameter measured by a wet laser method using a laser type particle size distribution measuring apparatus LMS-30 [manufactured by Seishin Enterprise Co., Ltd.].

  The presence state of the particles to be coated or present was observed using a scanning electron microscope SEM-EPMA with an energy dispersive X-ray analyzer [manufactured by Hitachi High-Technologies Corporation].

  Identification of the phase of the core particle and measurement of the intensity were performed by X-ray diffraction measurement. The X-ray diffractometer is “X-ray diffractometer RINT-2000 (Rigaku Corporation)” (tube: Cu, tube voltage: 40 kV, tube current: 40 mA, step angle: 0.020 °, counting time: 0.6 s. Divergence slit: 1 °, scattering slit: 1 °, light receiving slit: 0.30 mm).

The initial charge / discharge characteristics were evaluated by a coin cell using the positive electrode active material particle powder according to the present invention.
First, 90% by weight of the positive electrode active material particle powder, 3% by weight of acetylene black as a conductive material, 3% by weight of graphite KS-6, and 4% by weight of polyvinylidene fluoride dissolved in N-methylpyrrolidone as a binder were mixed. Then, it apply | coated to Al metal foil and dried at 150 degreeC. The sheet was punched to 16 mmφ, and then pressure-bonded at 1 t / cm ² to make the electrode thickness 50 μm. A CR2032-type coin cell was manufactured using a lithium mixed with a negative electrode of 16 mmφ and a solution in which EC and DMC in which 1 mol / l LiPF ₆ was dissolved was mixed at a volume ratio of 1: 2.
The initial charge / discharge characteristics are as follows: at room temperature, charge is performed at 20 mA / g up to 4.8 V, and then discharge is performed at 20 mA / g up to 2.0 V. The initial charge capacity, initial discharge capacity and initial irreversible capacity at that time are It was measured.
Further, after the initial discharge is completed, the battery is charged again to 4.6 V, discharged at a current density of 3 C for 18 seconds, and the electrode area is multiplied by the value obtained by dividing the voltage difference of the discharge voltage by the current value of 3 C to obtain a direct current. The resistance value was determined.

Reference example 1
First, core particles were produced according to the following production method. 14 L (liter) of water was put in a closed reaction tank, and kept at 50 ° C. while nitrogen gas was circulated. Further, 1.5M Ni, Co, Mn mixed sulfate aqueous solution, 0.8M sodium carbonate aqueous solution and 2M ammonia aqueous solution were continuously added with stirring so that pH = 8.2 (± 0.2). . During the reaction, only the filtrate was discharged out of the system with a concentrating device, and the solid content was retained in the reaction tank. After the reaction for 20 hours, a slurry of the coprecipitation product was collected. The collected slurry was filtered, washed with water, and dried at 105 ° C. overnight to obtain a coprecipitation precursor powder.
The obtained coprecipitation precursor, lithium carbonate powder and boric acid were weighed and mixed well. Using an electric furnace, this was fired at 800 ° C. for 5 hours under air flow to obtain Li—Mn composite oxide particle powder.
As a result of the X-ray diffraction measurement shown in FIG. 1, the obtained Li—Mn composite oxide particle powder includes a crystal system belonging to the space group R-3m and a crystal system belonging to the space group C2 / m. The peak intensity ratio (a) / (b) was 0.11.
As a result of ICP composition analysis, the molar ratios were Li / (Ni + Co + Mn) = 1.33 and Ni: Co: Mn = 21.6: 12.4: 66, respectively. Moreover, as a result of observing the particles of the Li—Mn composite oxide particles with a scanning electron microscope (SEM), primary particles having an average primary particle diameter of 0.07 μm aggregated to form secondary particles. Moreover, the average particle diameter of Li-Mn complex oxide particle powder was 12.1 micrometers. In the coin cell using this Li—Mn composite oxide particle powder as the positive electrode active material, the charge capacity was 306.8 mAh / g, the discharge capacity was 270 mAh / g, and the initial irreversible capacity was 36.8 mAh / g. It was. Moreover, the DC resistance value in a 4.6V charge state was 86.4 ohm * cm < ² >.

Further, particles to be coated were produced according to the following production method. An aqueous solution prepared by mixing 2 mol / l nickel sulfate, cobalt sulfate, and manganese sulfate so that Ni: Co: Mn = 40: 20: 40 and a 5.0 mol / l aqueous ammonia solution were simultaneously supplied into the reaction vessel.
The reaction tank was always stirred with a blade-type stirrer, and at the same time, a 2 mol / l sodium hydroxide aqueous solution was automatically supplied so that the pH was 11.5 ± 0.5. The produced Ni—Co—Mn hydroxide is overflowed, concentrated in a concentration tank connected to the overflow pipe, circulated to the reaction tank, and the Ni—Co—Mn hydroxide concentration in the reaction tank and the concentration tank is increased. The reaction was continued for 40 hours until reaching 4 mol / l.
After the reaction, the taken-out suspension was washed with water 10 times the weight of the Ni—Co—Mn hydroxide using a filter press, then dried, and Ni: Co: Mn = 33. : Ni: Co-Mn hydroxide particles having an average particle diameter of 9.5 μm were obtained. Ni—Co—Mn hydroxide particles and lithium carbonate were mixed at a molar ratio of Li / (Ni + Co + Mn) = 1.05.
This mixture was calcined at 925 ° C. for 4 hours in an oxygen atmosphere and crushed. As a result of ICP analysis, the chemical composition of the obtained fired product was Li _1.05 Ni _0.40 Co _0.20 Mn _0.40 O ₂ . The particles were pulverized by an airflow pulverizer to obtain a Li—Ni—Co—Mn composite oxide having an average secondary particle size of 2 μm.

After mixing these core particles and the particles to be coated in a weight ratio of the ratio of particles to be coated: particles to be coated = 99: 1, Li ₁ is applied to the surface of the core particles using a mechanical attritor _{. Positive} electrode active material particle powder coated with 1% of ₀₅ Ni _0.40 Co _0.20 Mn _0.40 O ₂ was obtained. The average particle diameter of the secondary particles of this positive electrode active material particle powder was 13.4 μm. Moreover, in the coin cell using this positive electrode active material particle powder, the charge capacity was 284.4 mAh / g, the discharge capacity was 256 mAh / g, and the initial irreversible capacity was 28.4 mAh / g. Moreover, the DC resistance value in a 4.6V charge state was 85.0 Ω · cm ² .

Reference example 2
A positive electrode in which 15% of Li _1.05 Ni _0.40 Co _0.20 Mn _0.40 O ₂ was coated on the surface of the core particles in the same manner as in Reference Example 1 except that the weight ratio of the particles to be coated was 15%. Active material particle powder was obtained. The average particle diameter of the secondary particles of this positive electrode active material particle powder was 14.5 μm. Moreover, in the coin cell using this positive electrode active material particle powder, the charge capacity was 275.3 mAh / g, the discharge capacity was 245 mAh / g, and the initial irreversible capacity was 30.3 mAh / g. Moreover, the DC resistance value in a 4.6V charge state was 82.2 Ω · cm ² .

Reference example 3
The composition of the coating to the particles and _{Li 1.05 Ni 0.60 Co 0.20 Mn 0.20} O 2, except that the weight ratio 15%, Li ₁ on the surface of the core particles in the same manner as in Reference Example 1 _.05 Ni _0.60 Co _0.20 Mn _0.20 O ₂ A positive electrode active material particle powder coated with 15% was obtained. The average particle diameter of the secondary particles of this positive electrode active material particle powder was 14.2 μm. Moreover, in the coin cell using this positive electrode active material particle powder, the charge capacity was 286.5 mAh / g, the discharge capacity was 255 mAh / g, and the initial irreversible capacity was 31.5 mAh / g. Moreover, the DC resistance value in a 4.6V charge state was 83.6 ohm * cm < ² >.

Example 1
Core particles were obtained in the same manner as in Reference Example 1.
The particles to be coated were produced according to the following production method. Under nitrogen aeration, 0.5 mol of manganese sulfate was added to 3.5 mol of sodium hydroxide to make the total amount 1 L, and the obtained manganese hydroxide was aged at 90 ° C. for 1 hour. After aging, air was passed through, oxidized at 90 ° C., washed with water and dried to obtain manganese oxide particles. The manganese oxide particles were soaked so that the concentration of the manganese oxide particles was 10 wt%. A 0.2 mol / l nickel sulfate aqueous solution was continuously supplied into the reaction tank so that Mn: Ni = 75: 25. Suspension containing manganese oxide particles coated with nickel hydroxide, while the reaction vessel is constantly stirred with a stirrer and at the same time, 0.2 mol / l sodium hydroxide aqueous solution is automatically supplied so that pH = 10 or more. Got.
The suspension was washed with water 10 times the weight of the manganese oxide particles using a filter press and then dried, and the average particle diameter of Mn: Ni = 75: 25 was 4.8 μm. Manganese oxide particles coated with nickel hydroxide were obtained.
The obtained Mn ₃ O ₄ particle powder coated with nickel hydroxide and lithium carbonate were mixed and baked in an air atmosphere at 960 ° C. for 3 hours to obtain lithium manganate particle powder. As a result of ICP analysis composition analysis of the powder particles, it was Li _1.01 Mn _1.51 Ni _0.49 O ₄ . The particles were pulverized using an airflow pulverizer to obtain Li—Mn composite oxide particles having an average secondary particle size of 1.5 μm.

The core particles and the particles to be coated are mixed at a weight ratio of a ratio of particles to be core: particles to be coated = 99: 1, and then Li _1.01 is applied to the surface of the core particles using a mechanical _attritor. A positive electrode active material particle powder coated with 1% of Mn _1.51 Ni _0.49 O ₄ was obtained. The average particle diameter of the secondary particles of this positive electrode active material particle powder was 14.8 μm. Moreover, in the coin cell using this positive electrode active material particle powder, the charge capacity was 276.9 mAh / g, the discharge capacity was 252 mAh / g, and the initial irreversible capacity was 24.9 mAh / g. Moreover, the DC resistance value in a 4.6V charge state was 46.8 ohm * cm < ² >.

Example 2
_Positive electrode active material particle powder in which 15% of Li _1.01 Mn _1.51 Ni _0.49 O ₄ is coated on the surface of the core particles in the same manner as in Example 1 except that the weight ratio of the particles to be coated is 15%. Got. The average particle diameter of secondary particles of the positive electrode active material particle powder was 15.8 μm. Moreover, in the coin cell using this positive electrode active material particle powder, the charge capacity was 264.1 mAh / g, the discharge capacity was 243 mAh / g, and the initial irreversible capacity was 21.1 mAh / g. Moreover, the DC resistance value in a 4.6V charge state was 50.1 Ω · cm ² .

Example 3
The core particles were obtained in the same manner as in Reference Example 1.
The particles to be coated were produced according to the following production method. Mix 1.5M Mn and Fe mixed sulfate aqueous solution and LiOH, then mix 2mol% ascorbic acid and 1.5M phosphoric acid aqueous solution with respect to the number of moles of metal, and in autoclave at 180 ° C for 3 hours. Processed. Then, after washing with twice the water, drying, mixing 5% sucrose, firing in nitrogen at 650 ° C. for 5 hours, pulverizing using an airflow pulverizer, An olivine-type Li—Mn phosphate compound having an average particle diameter of 2 μm was obtained. As a result of composition analysis of this material, it was Li _1.02 Mn _0.8 Fe _0.2 PO ₄ . It was.

These core particles and particles to be coated are mixed in a weight ratio of the ratio of particles to be coated: particles to be coated = 99: 1, and then Li _1.02 is applied to the surface of the core particles using a mechanical _attritor. Positive electrode active material particle powder coated with 1% of Mn _0.8 Fe _0.2 PO ₄ was obtained. The average particle diameter of the secondary particles of this positive electrode active material particle powder was 13.5 μm. Moreover, in the coin cell using this positive electrode active material particle powder, the charge capacity was 283.0 mAh / g, the discharge capacity was 266 mAh / g, and the initial irreversible capacity was 17.0 mAh / g. Moreover, the DC resistance value in a 4.6V charge state was 43.4 ohm * cm < ² >.

Example 4
_Positive electrode active material particle powder in which 15% of Li _1.02 Mn _0.8 Fe _0.2 PO ₄ is coated on the surface of the core particles in the same manner as in Example 3 except that the weight ratio of the particles to be coated is 15% Got. The average particle diameter of the secondary particles of this positive electrode active material particle powder was 13.8 μm. Moreover, in the coin cell using this positive electrode active material particle powder, the charge capacity was 266.0 mAh / g, the discharge capacity was 250 mAh / g, and the initial irreversible capacity was 16.0 mAh / g. Moreover, the DC resistance value in a 4.6V charge state was 47.4 ohm * cm < ² >.

Reference example 4
A positive electrode in which 30% of Li _1.05 Ni _0.40 Co _0.20 Mn _0.40 O ₂ was coated on the surface of the core particles in the same manner as in Reference Example 1 except that the weight ratio of the particles to be coated was 30%. Active material particle powder was obtained. The average particle diameter of the secondary particles of this positive electrode active material particle powder was 16 μm. Moreover, in the coin cell using this positive electrode active material particle powder, the charge capacity was 293.0 mAh / g, the discharge capacity was 208 mAh / g, and the initial irreversible capacity was 85.0 mAh / g. Moreover, the DC resistance value in a 4.6V charge state was 88.6 ohm * cm < ² >.

Reference Example 5
Positive electrode in which 30% of Li _1.05 Ni _0.60 Co _0.20 Mn _0.20 O ₂ was coated on the surface of the core particles in the same manner as in Reference Example 3 except that the weight ratio of the particles to be coated was 30%. Active material particle powder was obtained. The average particle diameter of the secondary particles of this positive electrode active material particle powder was 16.5 μm. Moreover, in the coin cell using this positive electrode active material particle powder, the charge capacity was 269.2 mAh / g, the discharge capacity was 210 mAh / g, and the initial irreversible capacity was 59.2 mAh / g. Moreover, the DC resistance value in a 4.6V charge state was 87.5 Ω · cm ² .

Reference Example 6
_Cathode active material particle powder in which 30% of Li _1.01 Mn _1.51 Ni _0.49 O ₄ is coated on the surface of the core particles in the same manner as in Example 1 except that the weight ratio of the particles to be coated is 30%. Got. The average particle diameter of the secondary particles of this positive electrode active material particle powder was 16.6 μm. Moreover, in the coin cell using this positive electrode active material particle powder, the charge capacity was 237.5 mAh / g, the discharge capacity was 190 mAh / g, and the initial irreversible capacity was 47.5 mAh / g. Moreover, the DC resistance value in a 4.6V charge state was 85.4 ohm * cm < ² >.

Reference Example 7
_Cathode active material particle powder in which Li _1.02 Mn _0.8 Fe _0.2 PO ₄ is coated on the surface of the core particles in the same manner as in Example 3 except that the weight ratio of the particles to be coated is 30% Got. The average particle diameter of the secondary particles of this positive electrode active material particle powder was 14.3 μm. Moreover, in the coin cell using this positive electrode active material particle powder, the charge capacity was 234.9 mAh / g, the discharge capacity was 195 mAh / g, and the initial irreversible capacity was 39.9 mAh / g. Moreover, the DC resistance value in a 4.6V charge state was 84.3 ohm * cm < ² >.

  Table 1 shows various characteristics of the positive electrode active material particle powders obtained in Examples 1 to 4 and Reference Examples 1 to 7.

The positive electrode active material particles obtained in Examples 1 to 4 each have an initial discharge capacity of 240 mAh / g or more and an initial charge / discharge efficiency of 90% or more. Further, the irreversible capacity was 40 mAh / g or less, and the DC resistance value in a 4.6 V charged state was 85 Ω · cm ² or less.

  The SEM photograph of the Li-Mn composite oxide particle powder used as the nucleus obtained in Reference Example 1 is shown in FIG. 2, and the SEM photograph of the positive electrode active material particle powder obtained in Reference Example 1, Examples 1 and 3 is shown in FIG. Shown in FIGS.

  2 and 3, the positive electrode active material particles obtained in Reference Example 1 have a surface state that changes with respect to the particle surfaces of the secondary particles of the Li—Mn composite oxide serving as the nucleus, and the particles It can be seen that Li—Mn compound particles are coated on the surface of the secondary particles of the Li—Mn composite oxide serving as the nucleus.

  Similarly, from FIG. 4, the positive electrode active material particles obtained in Example 1 have the surface state changed with respect to the surface of the secondary particles of the Li—Mn composite oxide particles serving as the nucleus, and the particles It can be seen that the Li—Mn compound particles are coated on the surface of the secondary particles of the Li—Mn composite oxide serving as the nucleus.

  Similarly, from FIG. 5, the positive electrode active material particles obtained in Example 3 have the surface state changed with respect to the surface of the secondary particles of the Li—Mn composite oxide particles serving as the nucleus, and the particles are It can be seen that the Li—Mn compound particles are coated on the surface of the secondary particles of the Li—Mn composite oxide serving as the nucleus.

  From the above results, it was confirmed that the positive electrode active material particle powder for non-aqueous electrolyte secondary battery according to the present invention is effective as an active material for high-capacity non-aqueous electrolyte battery excellent in initial charge / discharge efficiency during high-voltage charging. It was done.

The positive electrode active material particle powder according to the present invention is suitable as a positive electrode active material particle powder for a non-aqueous electrolyte secondary battery because the initial charge / discharge efficiency during high voltage charging is improved.

Claims (4)

A secondary particle serving as a nucleus is a compound having at least a crystal system belonging to the space group R-3m and a crystal system belonging to the space group C2 / m, and 2θ = 20 in a powder X-ray diffraction diagram using Cu—Kα rays. The relative intensity ratio (a) / (b) between the intensity (a) of the maximum diffraction peak at 8 ± 1 ° and the intensity (b) of the maximum diffraction peak at 2θ = 18.6 ± 1 ° is 0.02 to 0. a .5, Mn content is a Li-Mn composite oxide particles is Mn / (Ni + Co + Mn ) is 0.55 or more in molar ratio, the particle table surface of the secondary particles, the composition is _Li x2 Mn _2-y2 Ni _y2 O ₄ (0.95 ≦ x2 ≦ 1.10, 0.45 ≦ y2 ≦ 0.55), or Li _x3 Mn _1-y3 Fe _y3 PO ₄ (0.98 ≦ x3 ≦ 1.10) , 0 <y3 ≦ 0.30), at least one Li—Mn conversion A cathode active material particle powder for a non-aqueous electrolyte secondary battery in which a product particle is coated or present, and a secondary particle whose average particle diameter is the nucleus of the cathode active material particle powder for the non-aqueous electrolyte secondary battery not less than 1.1 times the average particle diameter of the particles, and the weight percentage of L i-Mn compound particles is coated particle element for the core particle is equal to or less than 20% or more 0.5% Positive electrode active material particle powder for non-aqueous electrolyte secondary battery. LiM _p Mn _(1-p) O ₂ (M is Ni and / or Co, 0 <p ≦ 1) as a compound having a crystal system in which the core secondary particle belongs to the space group R-3m, the space group The compound having a crystal system belonging to C2 / m includes Li ₂ M ′ _(1-q) Mn _q O ₃ (M ′ is Ni and / or Co, 0 <q ≦ 1). The positive electrode active material particle powder for nonaqueous electrolyte secondary batteries as described in 2. It is a manufacturing method of the positive electrode active material particle powder for nonaqueous electrolyte secondary batteries of Claim 1 or 2, Comprising: The mixture containing the precursor particle powder containing Mn, Ni, and / or Co, and a lithium compound is 500- Li _x Mn _{2 -y 2} Ni _{y 2} O ₄ (0.95 _{≦≦ 5} μm) with secondary particles having an average particle diameter of 3 μm or less is obtained as the secondary particles of Li—Mn composite oxide particles obtained by firing at a temperature of 1500 ° C. x2 ≦ 1.10, 0.45 ≦ y2 ≦ 0.55), or Li _x3 Mn _1-y3 Fe _y3 PO ₄ (0.98 ≦ x3 ≦ 1.10, 0 <y3 ≦ 0.30) by mixing grinding at least one Li-Mn compound particles, non characterized in that is coated or present a Li-Mn compound particles in the particle table surface of the Li-Mn composite oxide particles as a core Cathode active material for water electrolyte secondary battery Method for producing particles. A nonaqueous electrolyte secondary battery comprising a positive electrode containing the positive electrode active material particle powder for a nonaqueous electrolyte secondary battery according to claim 1.