JP5809201B2 - Lithium-rich manganese composite oxide cathode active material - Google Patents

Description

  The present invention relates to a lithium-rich manganese composite oxide-based positive electrode active material that can exhibit good battery characteristics.

  Conventionally, a highly conductive substance is used as a positive electrode material or a negative electrode material in order to improve battery performance. In recent years, next-generation batteries such as lithium ion batteries have been increasingly developed, and various kinds of positive electrode materials in such batteries have been developed. For example, lithium-excess manganese composite oxides described in Non-Patent Document 1 are used. Use is also being considered. In order to employ such a lithium-rich manganese composite oxide as a positive electrode material for a next-generation battery, it is necessary to ensure good battery physical properties by making the particles finer because the conductivity itself is low.

J. Li et al, Journal of Power Source 196 (2011), p4821-4825.

  However, simply refining the particles of the lithium-excess manganese composite oxide tends to reduce the tap density, and there is a possibility that desired battery characteristics cannot be sufficiently exhibited.

  Therefore, the subject of this invention is providing the lithium excess manganese complex oxide type positive electrode active material which can express the outstanding battery physical property as a positive electrode material of a lithium ion battery.

Therefore, the present inventors have conducted various studies and found that a lithium-rich manganese composite oxide-based positive electrode active material obtained by performing a specific treatment has a large tap density and can exhibit excellent battery properties. The present invention has been completed.

  That is, the present invention relates to a lithium-excess manganese composite oxide-based positive electrode active material obtained by mixing a lithium-excess manganese composite oxide and conductive carbon and then mixing them while adding compressive force and shearing force. Is to provide.

  The lithium-rich manganese composite oxide-based positive electrode active material of the present invention is a particle in which the lithium-rich manganese composite oxide and conductive carbon are dispersed extremely uniformly and with reduced voids. It is expected to greatly contribute to improving the performance of ion batteries.

2 is an SEM image showing particles of a lithium-rich manganese composite oxide-based positive electrode active material obtained in Example 1.

Hereinafter, the present invention will be described in detail.
The lithium-rich manganese composite oxide-based positive electrode active material of the present invention can be obtained by mixing a lithium-rich manganese composite oxide and conductive carbon and then mixing them while adding compressive force and shearing force. Through this treatment, the lithium-excess manganese composite oxide and conductive carbon are uniformly agglomerated while being uniformly dispersed to form particles (hereinafter also referred to as “composite particles”), thereby reducing voids. Composite particles can be obtained. Alternatively, a conductive carbon layer can be formed by adhering to the surface of particles (hereinafter also referred to as “primary particles”) exhibited by the lithium-rich manganese composite oxide while deforming or extending the conductive carbon. It is preferable to use an airtight container provided with an impeller that rotates at a peripheral speed of 25 to 40 m / s for the process of mixing while applying a compressive force and a shearing force. By introducing the lithium-excess manganese composite oxide and conductive carbon into such a container and operating the container, it is possible to perform a mixing process while applying compressive force and shearing force. In a closed container equipped with such an impeller, the lithium-rich manganese composite oxide and conductive carbon are uniformly mixed by the rotation of the impeller, and a shearing force is also applied while a compressive force is applied between the impeller and the inner wall of the container. The Rukoto. The peripheral speed of the impeller is preferably 25 to 40 m / s, more preferably 27 to 35 m / s, from the viewpoint of increasing the tap density of the resulting composite particles.

  In addition, from the viewpoint of improving the uniformity of the obtained composite particles and shortening the processing time in the sealed container equipped with the impeller, the lithium-excess manganese composite oxide and conductive carbon are introduced into the sealed container. These may be mixed in advance.

Examples of the apparatus provided with a closed container that can be mixed while applying such compressive force and shearing force include a high-speed shear mill, a blade-type kneader, and the like. (Manufactured by Hosokawa Micron Corporation) can be preferably used. By using such an apparatus, it is possible to easily perform a mixing process while applying a predetermined compressive force and shearing force, and the lithium-rich manganese composite oxide-based positive electrode active material of the present invention can be obtained only by performing such a process. Can be obtained.
As the processing conditions for the mixing, the processing temperature is preferably 5 to 80 ° C., more preferably 10 to 50 ° C., and the processing time is preferably 5 to 90 minutes, more preferably 10 to 60 minutes. The treatment atmosphere is not particularly limited, but is preferably an inert gas atmosphere or a reducing gas atmosphere.

  The mass ratio between the lithium-rich manganese composite oxide and the conductive carbon charged into the sealed container is preferably 97: 3 to 85:15, more preferably 95: 5, from the viewpoint of improving the properties of the obtained battery. It is -88: 12, More preferably, it is 93: 7-90: 10.

  In addition, you may bake the obtained composite particle from a viewpoint of improving battery physical property more. The firing conditions are 400 ° C. or higher, preferably 400 to 800 ° C. for 10 minutes to 3 hours, preferably 0.5 to 1.5 hours under an inert gas atmosphere or reducing conditions.

The lithium-excess manganese composite oxide is a composite oxide containing excess lithium and manganese, and includes one or more selected from Ni, Mn, and Co in addition to Mn as a transition metal element. Especially, the lithium excess manganese complex oxide containing Mn, Co, and Ni as a transition metal element is preferable, and is specifically represented by the following formula.
(1-z) Li ₂ MnO ₃ .zLiMO ₂ (z satisfies 0.25 ≦ z ≦ 0.75, and M represents one or more transition metal elements selected from Ni, Mn and Co) Show.)
Among these, a is preferably 0.25 ≦ a ≦ 0.5 from the viewpoint of further improving battery physical properties. More specifically, examples of the lithium-excess manganese composite oxide include those represented by Li [Li _0.2 Mn _0.56 Ni _0.16 Co _0.08 ] O ₂ .

  The lithium-excess manganese composite oxide is primary particles obtained by mixing, pulverizing, and firing using a transition metal source as a raw material as necessary in addition to a lithium compound and a manganese compound.

  Examples of the lithium compound that can be used include lithium oxide and lithium hydroxide. Specific examples include lithium hydroxide, lithium carbonate, lithium nitrate, lithium oxide, lithium oxalate, and lithium acetate. These may be used alone or in combination of two or more. Among these, lithium hydroxide is preferable from the viewpoint of improving battery physical properties.

  Examples of manganese compounds and other transition metal sources that can be used include sulfates, chlorides, acetates, and oxalates. Among these, sulfate is preferable from the viewpoint of improving battery physical properties. These may be used individually by 1 type, or may be used in combination of 2 or more types, but it is preferable to use 2 or more types including a manganese compound, and it is more preferable to use 3 types in combination.

  In addition to these lithium compound and manganese compound, a transition metal source may be mixed, pulverized, and fired as necessary to obtain primary particles of lithium-rich manganese composite oxide. For example, Journal of Power Source 196 ((2011), p4821-4825) can be used.

Specifically, for example, in addition to a lithium compound and a manganese compound, water is added to a transition metal source as necessary, followed by filtration, followed by washing and drying. Next, a lithium compound and water are further added, mixed, pulverized and fired.
The firing conditions are, for example, a firing temperature of 800 to 1000 ° C. and a firing time of 12 to 48 hours. Further, when firing, an inert gas atmosphere such as nitrogen or argon may be used, or an oxygen atmosphere or an air atmosphere may be used. From this, the lithium excess manganese complex oxide used as a raw material can be obtained.

  The average particle size X of the lithium-excess manganese composite oxide is preferably 20 to 400 nm, more preferably 20 to 350 nm, from the viewpoint of improving battery physical properties obtained by increasing the uniformity as composite particles. And more preferably 20 to 250 nm. The average particle diameter X means a value measured by a dynamic light scattering particle size analyzer (Nanotrack UPA-EX150, manufactured by Nikkiso Co., Ltd.) after uniformly dispersing the sample with a solvent.

  Carbon black is preferable as the conductive carbon, and specific examples include acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black. Of these, acetylene black and ketjen black are preferred from the viewpoint of imparting good conductivity. In addition, as the shape of these conductive carbons, from the viewpoint of further improving the physical properties of the battery obtained by coating at least a part of the surface of the primary particles of the lithium-rich manganese composite oxide with a layer made of conductive carbon, a hollow shape is used. It is preferable that it exhibits or a shape including voids.

  Moreover, it is preferable that the conductive carbon used by this invention has the average particle diameter Y below the average particle diameter X which the primary particle of lithium excess manganese complex oxide has. Since the conductive carbon has such an average particle size, the conductive carbon is efficiently arranged in the gap between the particles of the lithium-rich manganese composite oxide, and the highly uniform composite with reduced voids. Body particles can be obtained.

  The ratio (X / Y) of the average particle diameter X of the lithium-excess manganese composite oxide to the average particle diameter Y of the conductive carbon is more efficiently arranged in the gap between the particles of the lithium-excess manganese composite oxide. From the viewpoint of improving the physical properties of the obtained battery and the obtained battery, it is preferably 1 to 20, and more preferably 1.5 to 10. Moreover, the average particle diameter Y which electroconductive carbon has becomes like this. Preferably it is 10-100 nm, More preferably, it is 10-50 nm. In addition, this average particle diameter Y means the value measured by the method similar to the average particle diameter X of the said lithium excess manganese complex oxide.

The tap density of the lithium-rich manganese composite oxide positive electrode active material of the present invention is preferably 0.8 to 2.5 g / cm ³ , more preferably 1.0 to 2.5 g / cm ³ , Preferably it is 1.2-2.5 g / cm < ³ >. Accordingly, the lithium-excess manganese composite oxide-based positive electrode active material of the present invention is a particle in which the voids are extremely reduced and these lithium-excess manganese composite oxide and conductive carbon are very uniformly dispersed. If this is used as the positive electrode material, it is possible to easily improve the physical properties of the obtained battery. Note that the tap density of the lithium-rich manganese composite oxide-based positive electrode active material means that when a measuring container containing a powder sample m (g) with a known weight is mechanically tapped and no volume change is observed. It means a value obtained by reading the powder volume V (cm ³ ) and averaging the values calculated using the formula m / V.

  In addition, the lithium-excess manganese composite oxide and conductive carbon in the lithium-excess manganese composite oxide-based positive electrode active material of the present invention are from the viewpoint of increasing the uniformity and dispersibility thereof, and from the viewpoint of further improving the physical properties of the obtained battery. It is preferable that the surface of at least a part of the primary particles of the lithium-rich manganese composite oxide is covered with a layer made of conductive carbon. The layer made of conductive carbon may cover at least a part of the surface of the primary particles, or may cover almost the entire surface of the primary particles. Thereby, primary particles of lithium-rich manganese composite oxide and conductive carbon can be prevented from aggregating, and lithium-rich manganese composite oxide, which is a composite particle in which conductive carbon is more densely and uniformly dispersed. A physical positive electrode active material is obtained, and the conductivity can be further increased.

  The thickness of the layer made of conductive carbon is preferably 0.1 to 5.0 nm, more preferably 0.5 to 3.0 nm.

  The average particle size Z of the lithium-rich manganese composite oxide-based positive electrode active material of the present invention is 5 to 50 μm from the viewpoint of reducing the weight while maintaining excellent battery properties in the obtained lithium ion battery. The thickness is preferably 5 to 30 μm, more preferably 5 to 20 μm. As described above, the lithium-excess manganese composite oxide-based positive electrode active material of the present invention is a fine composite particle containing uniformly dispersed lithium-excess manganese composite oxide and conductive carbon. By using this to form a positive electrode, a lithium ion battery having excellent battery properties can be obtained. In addition, this average particle diameter Z means the value measured by the method similar to the said average particle diameter X and Y.

  The method for producing a lithium ion battery using the lithium-rich manganese composite oxide-based positive electrode active material of the present invention thus obtained is not particularly limited, and any known method can be used. For example, the lithium-rich manganese composite oxide-based positive electrode active material is mixed with additives such as a binder and a solvent to obtain a coating solution. At this time, if necessary, a conductive additive may be further added and mixed. The binder is not particularly limited, and any known agent can be used. Specific examples include polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl chloride, and ethylene propylene diene polymer. Moreover, it does not specifically limit as this conductive support agent, Any well-known agent can be used. Specific examples include acetylene black, ketjen black, natural graphite, artificial graphite, and fibrous carbon. Next, such a coating solution is applied onto a positive electrode current collector such as an aluminum foil and dried to obtain a positive electrode.

  The lithium-rich manganese composite oxide positive electrode active material of the present invention is useful in that it exhibits a very excellent discharge capacity as a positive electrode of a lithium ion battery. A lithium battery to which such a positive electrode can be applied is not particularly limited as long as it has a positive electrode, a negative electrode, an electrolytic solution, and a separator as essential components.

  Here, as long as lithium ions can be occluded at the time of charging and released at the time of discharging, the material structure is not particularly limited, and a known material structure can be used. For example, a carbon material such as lithium metal, graphite, or amorphous carbon. It is preferable to use an electrode formed of an intercalating material capable of electrochemically inserting and extracting lithium, particularly a carbon material.

  The electrolytic solution is obtained by dissolving a supporting salt in an organic solvent. The organic solvent is not particularly limited as long as it is an organic solvent that is usually used for an electrolyte solution of a lithium ion secondary battery. For example, carbonates, halogenated hydrocarbons, ethers, ketones, nitriles, lactones An oxolane compound or the like can be used.

The type of the supporting salt is not particularly limited, but an inorganic salt selected from LiPF ₆ , LiBF ₄ , LiClO ₄ and LiAsF ₆ , a derivative of the inorganic salt, LiSO ₃ CF ₃ , LiC (SO ₃ CF ₃ ) ₂ and LiN (SO ₃ CF ₃ ) ₂ , LiN (SO ₂ C ₂ F ₅ ) ₂ and LiN (SO ₂ CF ₃ ) (SO ₂ C ₄ F ₉ ), and organic salt derivatives It is preferable that it is at least 1 sort of.

  The separator plays a role of electrically insulating the positive electrode and the negative electrode and holding the electrolytic solution. For example, a porous synthetic resin film, particularly a polyolefin polymer (polyethylene, polypropylene) porous film may be used.

  EXAMPLES Hereinafter, although this invention is demonstrated concretely based on an Example, this invention is not limited to these Examples.

[Production Example 1]
Lithium hydroxide, manganese sulfate, nickel sulfate and cobalt sulfate were used, mixed and pulverized, and calcination (calcination temperature 900 ° C., calcination time) according to the method described in Journal of Power Source 221 ((2013), p122-127). 24 hours) to obtain primary particles (average particle size 200 nm) of the lithium-excess manganese composite oxide.

[Example 1]
93 g of primary particles of the lithium-rich manganese composite oxide obtained in Production Example 1 and 7 g of Ketjen Black (manufactured by Lion Corporation, average particle size 30 nm) were mixed in advance to obtain a mixture, and the resulting mixture was fine-particle composite Chemical device Nobilta (manufactured by Hosokawa Micron) was mixed at 25 to 35 ° C. for 30 minutes to obtain composite particles A. The obtained composite particles A had an average particle diameter of 20 μm and a tap density of 1.49 g / cm ³ .
The SEM image of the obtained composite particle A is shown in FIG.

[Comparative Example 1]
2.63 g primary particles of the lithium-rich manganese composite oxide obtained in Production Example 1, 0.09 g of Ketjen Black (Lion Corporation, average particle size 30 nm) and a dispersion stabilizer (Carboxymethylcellulose, Daicel Finechem Co.) 30 g of water added with zirconia is put together with zirconia balls in a zirconia pot of a planetary ball mill (planet type ball mill P-5, manufactured by Fritsch), mixed at 25 to 70 ° C. for 240 minutes, and dried. Got. The obtained composite particles B had an average particle size of 2 μm and a tap density of 0.91 g / cm ³ .

[Test Example 1]
Using the composite particles obtained in Example 1 and Comparative Example 1, a positive electrode of a lithium ion secondary battery was produced. The composite obtained in Example 1 and Comparative Example 1, ketjen black (conductive agent), and polyvinylidene fluoride (binding agent) were mixed at a weight ratio of 80:10:10, and this was mixed with N-methyl. -2-Pyrrolidone was added and sufficiently kneaded to prepare a positive electrode slurry. The positive electrode slurry was applied to a current collector made of an aluminum foil having a thickness of 20 μm using a coating machine, and vacuum dried at 80 ° C. for 12 hours. Thereafter, it was punched into a disk shape of φ14 mm and pressed at 16 MPa for 2 minutes using a hand press to obtain a positive electrode.

Next, a coin-type lithium ion secondary battery was constructed using the positive electrode. A lithium foil punched to φ15 mm was used for the negative electrode. As the electrolytic solution, a solution obtained by dissolving LIPF ₆ at a concentration of 1 mol / l in a mixed solvent in which ethylene carbonate and ethyl methyl carbonate were mixed at a volume ratio of 1: 1 was used. As the separator, a known one such as a polymer porous film such as polypropylene was used. These battery components were assembled and housed in a conventional manner in an atmosphere with a dew point of −50 ° C. or lower to produce a coin-type lithium secondary battery (CR-2032).

  A charge / discharge test at a constant current density was performed using the manufactured lithium ion secondary battery, and a charge / discharge capacity was measured. The charging conditions at this time were constant current and constant voltage charging with a current of 0.1 CA (20 mA / g) and a voltage of 4.8 V, and the discharging conditions were constant current discharging with a current of 0.1 CA and a final voltage of 2.5 V. All temperatures were 30 ° C.

  From the above results, the composite particle A obtained in Example 1 is extremely uniform and has reduced voids as compared to the composite particle B obtained in Comparative Example 1. Therefore, the tap density It can be seen that the secondary battery using the same exhibits excellent battery properties. On the other hand, although the composite particle B obtained in Comparative Example 1 is a fine particle, it does not contain a sufficient amount of conductive carbon and has many voids, so that the tap density is reduced, and the battery physical properties are reduced. This is thought to have caused a decline.

Claims (1)

(1-z) Li ₂ MnO ₃ .zLiMO ₂ (z satisfies 0.25 ≦ z ≦ 0.75, and M represents a transition metal element of Ni, Mn, and Co). After mixing the manganese composite oxide and the conductive carbon, in a closed vessel equipped with an impeller rotating at a peripheral speed of 25 to 40 m / s, a processing temperature of 10 to 50 ° C. and a processing time are applied while applying compressive force and shearing force. The manufacturing method of the lithium excess manganese complex oxide type positive electrode active material which passes through the process mixed in 10 to 60 minutes.