KR102455642B1 - Cathode Active Material for Lithium Secondary Battery - Google Patents

Abstract

The present invention provides a lithium secondary battery cathode active material comprising a core including a lithium composite metal oxide, and a coating layer disposed on the core and including an amorphous phase, wherein the amorphous phase is a mixture of lithium oxide, boron oxide and phosphorus It is characterized in that it contains an oxide.

Description

Cathode Active Material for Lithium Secondary Battery

The present invention provides a positive electrode for a lithium secondary battery comprising a core including a lithium composite metal oxide, and a coating layer positioned on the core, wherein the coating layer includes an amorphous phase containing a mixture of lithium oxide, boron oxide and phosphorus oxide It relates to the active material.

Lithium secondary batteries have advantages such as high energy density and voltage, low self-discharge rate, and semi-permanent characteristics that can be charged and discharged and can be used repeatedly, and are used in various fields such as mobile devices, energy storage systems, and electric vehicles.

However, as the lithium secondary battery is repeatedly charged and discharged due to the use of the device or device to which it is applied, the structural instability increases as the lithium ion insertion and desorption process is repeated, and this results in a change in the structure of the oxide and deterioration of lifespan characteristics. There is a problem, and such a phenomenon may occur particularly seriously during high-temperature driving.

Accordingly, there are various examples of coating a metal oxide on the surface of the positive electrode active material in order to solve these problems.

However, in general, the coating layer formed on the surface of the active material is formed in a crystallized state, and as a result, the crystallized coating layer may not be properly coated on the core surface or a uniform surface coating may not be achieved, and such a coating layer is used in lithium secondary batteries. The longer this is, the more difficult it may be to perform a role as a coating layer.

As such, it may be difficult for the prior art positive electrode active material to exhibit a desired level of characteristics through the introduction of a coating layer, and there is a high need for developing a new positive electrode active material capable of solving this problem.

An object of the present invention is to solve the problems of the prior art as described above and the technical problems that have been requested from the past.

After repeated in-depth research and various experiments, the inventors of the present application have developed a new positive electrode active material including a coating layer containing an amorphous phase, and this positive electrode active material is a mixture of lithium oxide, phosphorus oxide and boron oxide in the form of a coating layer. Including the amorphous phase containing the, it is uniformly coated while preventing the decrease in the binding force to the core, and it is confirmed that the cycle and capacity characteristics of the lithium secondary battery can be improved, and especially the high temperature characteristics can be improved, and the present invention came to complete.

Accordingly, the positive active material for a lithium secondary battery according to the present invention includes a core including a lithium composite metal oxide, and a coating layer positioned on the core and including an amorphous phase, wherein the amorphous phase is a mixture of lithium oxide, boron oxide and phosphorus oxide.

The positive active material for a lithium secondary battery according to the present invention includes an amorphous phase including lithium oxide, boron oxide and phosphorous oxide in the form of a mixture in the coating layer, thereby forming a uniform coating on the surface of the core, lithium secondary The cycle and capacity characteristics of the battery can be improved, and in particular, high-temperature characteristics can be improved.

In one specific example, the lithium composite metal oxide may include one or more transition metals and may have a layered crystal structure usable at high capacity and high voltage, and specifically, may be a material represented by the following Chemical Formula 1.

Li[Li _x M _1-xy D _y ]O _2-a Q _a (1)

In the above formula, M is one or more transition metal elements stable in tetracoordinate or hexacoordinate, D is one or more elements selected from alkaline earth metals, transition metals, and nonmetals as a dopant, Q is one or more anions, 0≤x≤ 0.1, 0≤y≤0.1, 0≤a≤0.2.

For reference, when D is a transition metal, the transition metal defined for M is excluded from these transition metals.

In one preferred embodiment, M is at least two elements selected from the group consisting of Ni, Co and Mn, and D is Al, W, Si, V, B, Ba, Ca, Zr, Ti, Mg, Ta, It is at least one element selected from the group consisting of Nb and Mo, and Q may be at least one element selected from F, S, and P.

In addition, the lithium composite metal oxide may have a crystal structure other than a layered structure, and examples of such a crystal structure include, but are not limited to, a spinel structure and an olivine structure.

The core may have an average particle diameter (D50) of, for example, 1 to 50 μm, but is not particularly limited.

Since the lithium composite metal oxide forming the core of the composition may be prepared by a method known in the art, a description thereof will be omitted herein.

One of the features of the present invention is that an amorphous phase including lithium oxide, boron oxide, and phosphorus oxide in the form of a mixture is included in the coating layer.

Due to this, as can be seen from the subsequent experimental results, a peak is not found in the vicinity of any one of 33.5, 56, 27.5, and 20.5 of 2theta (degree) of X-ray diffractiometry. .

As will be described later, lithium oxide, boron oxide, and phosphorus oxide included in the amorphous phase may be attached to the surface of the core at a low sintering temperature for surface treatment of the core, which is a lithium composite metal oxide. In this process, lithium oxide can act as a coating agent and help the process of boron oxide and phosphorus oxide adhere to the core.

The coating layer may include a composition of Formula 2 below.

αB _x O _y -βP _v O _w -γLi ₂ O (2)

In the above formula, the conditions of α+β+γ=1, 0.35≦x/y≦0.75, and 0.2≦v/w≦0.67 are satisfied, and α, β, and γ may be set on a weight basis.

As a non-limiting example, Chemical Formula 2 may be expressed as αB ₂ O ₃ -βP ₂ O ₅ -γLi ₂ O.

Li ₂ O may improve the meltability or moldability of the coating layer by lowering the high-temperature viscosity of the glassy oxide. In addition, Li ₂ O has excellent lithium ion conductivity and does not react with an electrolyte solution and hydrogen fluoride derived from an electrolyte solution during charging/discharging. Such Li ₂ O may be formed by oxidizing a lithium compound added before firing, or may be added as Li ₂ O itself, or LiOH, Li ₂ CO ₃ , etc. present on the surface of a lithium composite metal oxide as a core. It may be derived from the same lithium-containing component.

The lithium oxide is an amorphous phase in an amount of 2 parts by weight or less, preferably 0.01 to 2 parts by weight, more preferably 0.1 to 1 parts by weight, particularly preferably 0.1 to 0.5 parts by weight, based on 100 parts by weight of the lithium composite metal oxide as the core. can be included in

If the content of lithium oxide is too small, there is a problem in that it is difficult to achieve a uniform coating as described above. On the contrary, if the content of lithium oxide is too large, the coating thickness itself becomes thick, which is not preferable because there may be a problem that acts as a resistance in the battery.

In one specific example, the boron oxide may be B ₂ O ₃ and/or B ₂ O ₅ , preferably B ₂ O ₃ .

The boron oxide may exist as an ion conductor, and may easily form an amorphous phase, thereby improving coating formability together with lithium oxide.

The boron oxide is 2 parts by weight or less, preferably 0.1 to 2 parts by weight, more preferably 0.1 to 1 parts by weight, particularly preferably 0.1 to 0.5 parts by weight based on 100 parts by weight of the lithium composite metal oxide as the core. can be included in

If the content of boron oxide is too small, it may be difficult to achieve the effect as described above, and if it is too large, it is not preferable because it acts as a resistor on the surface and there may be a problem of capacity reduction.

In one specific example, the phosphorus oxide may be P ₂ O ₅ .

The phosphorus oxide cannot react with the transition metal in the manufacturing process of the lithium composite metal oxide, which is the core, and can reduce the amount of lithium remaining on the surface of the core and contribute to the surface coverage effect. may be

The phosphorus oxide may be included in the amorphous phase in an amount of 2 parts by weight or less, preferably 0.01 to 1 parts by weight, and more preferably 0.01 to 0.5 parts by weight based on 100 parts by weight of the lithium composite metal oxide as the core. If the content of phosphorus oxide is too small, it may be difficult to achieve reduction of residual lithium by-products and uniform coating as described above. .

As such, the special combination of lithium oxide, boron oxide, and phosphorus oxide in the coating layer is based on excellent coating properties and reduction of residual lithium by-products by the interaction of the respective oxides, thereby improving the cycle characteristics, capacity characteristics, etc. of the secondary battery, and especially the high temperature characteristics. can act to improve.

In one specific example, the thickness of the coating layer may be 0.01 to 1 μm, preferably 0.01 to 0.5 μm, and if the thickness of the coating layer is too thin, it is difficult to expect improvement of the desired properties in the present invention, and vice versa It is undesirable because it may act as a factor that hinders the movement of lithium and may increase the resistance in the battery.

In addition, the coating layer is preferably coated by 40% or more based on the surface area of the core, more preferably 90% or more, particularly preferably 100%, based on the surface area of the core, to improve the performance of the lithium secondary battery desired in the present invention. can

The present invention also provides a method for manufacturing the positive electrode active material. Specifically, the manufacturing method according to the present invention comprises boron-containing powder and phosphorus-containing powder, or boron-containing powder as a coating raw material in lithium composite metal oxide powder for core. Mixing the powder, the phosphorus-containing powder and the lithium-containing powder, and firing in an atmosphere containing oxygen in a temperature range at which the amorphous coating layer is formed may be included.

According to an embodiment of the manufacturing method of the present invention, the core and coating raw materials for the production of the positive electrode active material may be mixed in a powder state rather than a solvent-based mixing such as slurry, suspension, solution, etc., and then calcined, and the solvent Since it is not used, it is possible to prevent the coating raw materials from reacting to form a crystalline phase, and can bring about improvement in manufacturing processability and cost reduction.

The boron-containing powder may be boron oxide (eg, B ₂ O ₃ ) itself to be included in the coating layer, but may also be other boron compounds that can be converted into boron oxide through oxidation in some cases. Examples of such other boron compounds include, but are not limited to, H ₃ BO ₃ , HBPO ₄ and the like.

The phosphorus-containing powder may be a phosphorus oxide (eg, P ₂ O ₅ ) itself to be included in the coating layer, but may also be other phosphorus compounds that can be converted into phosphorus oxide through oxidation in some cases. Examples of such other phosphorus compounds include, but are not limited to, (NH ₄ )H ₂ PO ₄ , (NH ₄ ) ₂ HPO ₄ , (NH ₄ ) ₃ PO ₄ , and the like. In the case of (NH ₄ )H ₂ PO ₄ , since it has a low melting point, it is melted on the surface of the core during firing and then oxidized and solidified again to form a coating layer.

The lithium-containing powder may be lithium oxide itself to be included in the coating layer, but may also be other lithium compounds that can be converted into lithium oxide through oxidation in some cases. Examples of such other lithium compounds include, but are not limited to, LiOH, Li ₂ CO ₃ , LiNO ₃ , Li ₂ SO ₄ , and the like.

Here, the lithium oxide of the amorphous coating layer may be derived from a lithium-containing component present on the surface of the lithium composite metal oxide powder, which is the core. It can also be fired.

The temperature range at which the amorphous coating layer is formed may vary somewhat depending on the type and content condition of the raw material. range, preferably from 150°C to 500°C, more preferably from 200°C to 500°C. If the sintering temperature is too low, adhesion of oxides to the surface of the core may be deteriorated. Conversely, if the sintering temperature is too high, it is not preferable because the coating layer is crystallized and uniform coating on the surface of the core may be difficult.

Firing times may range from approximately 2 to 20 hours.

Coating raw materials such as boron-containing powder and phosphorus-containing powder have an average particle diameter of about 0.01 to 5 μm so that they can be uniformly adsorbed to the surface of the core without aggregation between the particles when mixed with the core for the production of the positive electrode active material. It may be desirable to change to an amorphous phase while being partially or entirely melted during the firing process to form a coating layer having a previously defined thickness.

When calcination is performed under the conditions as described above, a coating layer including an amorphous phase containing lithium oxide, boron oxide and phosphorus oxide in the form of a mixture is formed, thereby increasing the coating area and uniformity, thereby increasing the surface coating of the core. Scalability can be increased.

Therefore, in the present invention, the coating layer is uniformly coated on the surface of the active material due to excellent moldability, and the phenomenon that the coating material is separated from the active material and exists separately or agglomerate can be suppressed, and the amount of residual lithium on the surface of the active material is reduced and the surface By providing a coverage effect, capacity characteristics and high rate characteristics of the lithium secondary battery may be increased, and in particular, cycle characteristics and resistance characteristics at high temperatures may be improved.

The present invention also provides a lithium secondary battery including the positive electrode active material. Since the configuration and manufacturing method of the lithium secondary battery are known in the art, a detailed description thereof will be omitted in the present invention.

As described above, the cathode active material according to the present invention includes a coating layer containing a specific amorphous phase on the surface of the core, thereby reducing the amount of lithium by-product remaining on the surface of the core while reducing the amount of lithium by-products remaining on the surface of the core. As a result, the cycle and capacity characteristics of the lithium secondary battery are improved, and in particular, high-temperature characteristics can be improved.

1 is an X-ray diffraction analysis graph for the positive active materials of Examples 1 and 2;

Hereinafter, the present invention will be described in more detail with reference to some embodiments, but the scope of the present invention is not limited thereto.

[Example 1]

(Production of positive electrode active material)

Lithium composite metal oxide (Li(Ni _0.90 Co _0.06 Mn _0.04 ) _0.9955 Ti _0.00075 Zr _0.00075 Al _0.003 O ₂ ) After washing with distilled water and drying in an oven, 100 parts by weight of H ₃ BO ₃ , (NH ₄ ) ₂ HPO ₄ is mixed with a dry mixer, and then heat-treated at 300° C. for 10 hours under O ₂ atmosphere, and a coating layer comprising an amorphous phase containing lithium oxide, boron oxide and phosphorus oxide (approximately 0.01 ~ 0.1 ㎛ range) was prepared a positive active material formed.

Lithium oxide is produced by oxidation of lithium by-product remaining on the surface of lithium composite metal oxide, and the content of lithium compound remaining on the surface of lithium composite metal oxide before heat treatment is approximately 0.3 to 0.6 when measured by acid/base neutralization titration method. It was a weight part, and it was confirmed that about 0.1 to 0.25 parts by weight of lithium oxide (Li ₂ O) was formed by oxidation by heat treatment.

(Manufacture of anode)

The positive active material prepared above, Super-P as a conductive material, and PVdF as a binder were mixed in N-methylpyrrolidone as a solvent at a ratio of 96.5:1.5:2 (weight ratio) to prepare a positive electrode active material paste. A positive electrode active material paste was applied on an aluminum current collector, dried at 120° C., and rolled to prepare a positive electrode.

(Manufacture of lithium secondary battery)

An electrode assembly was prepared by using Li metal as the positive electrode and the negative electrode prepared above, and a porous polyethylene film as a separator was interposed therebetween, and after placing the electrode assembly inside the battery case, the electrolyte was injected into the interior of the battery case. A lithium secondary battery was prepared by injection. At this time, as the electrolyte, lithium at a concentration of 1.0M in an organic solvent in which vinylene carbonate (VC 2wt%) is added to ethylene carbonate/dimethyl carbonate/diethyl carbonate (mixed volume ratio of EC/DMC/DEC = 1/2/1) Hexafluorophosphate (LiPF ₆ ) dissolved therein was used.

[Example 2]

Under the same conditions as in Example 1, except that 0.29 parts by weight of H ₃ BO ₃ and 0.09 parts by weight of (NH ₄ ) ₂ HPO ₄ were mixed, a positive active material, a positive electrode, and a lithium secondary battery were respectively prepared.

[Example 3]

Under the same conditions as in Example 1, except that the heat treatment temperature was set to 500° C., a positive active material, a positive electrode, and a lithium secondary battery were prepared, respectively.

[Example 4]

Under the same conditions as in Example 1, except that the heat treatment temperature was set to 200° C., a positive active material, a positive electrode, and a lithium secondary battery were prepared, respectively.

[Comparative Example 1]

Under the same conditions as in Example 1, except that heat treatment was performed without mixing H ₃ BO ₃ and (NH ₄ ) ₂ HPO ₄ , a positive electrode active material, a positive electrode, and a lithium secondary battery were respectively prepared.

[Comparative Example 2]

Under the same conditions as in Example 1, except that the heat treatment temperature was set to 600° C., a positive active material, a positive electrode, and a lithium secondary battery were prepared, respectively.

[Comparative Example 3]

Under the same conditions as in Example 1, except that the heat treatment temperature was set to 700° C., a positive active material, a positive electrode, and a lithium secondary battery were prepared, respectively.

[Comparative Example 4]

(NH ₄ ) ₂ HPO ₄ was not mixed, and only H ₃ BO ₃ was mixed in an amount of 0.4 parts by weight, and under the same conditions as in Example 1, a positive electrode active material, a positive electrode, and a lithium secondary battery were respectively prepared.

[Example 5]

A positive active material, a positive electrode, and a lithium secondary battery were respectively prepared under the same conditions as in Example 1, except that H ₃ BO ₃ was not mixed and only (NH ₄ ) ₂ HPO ₄ was mixed in an amount of 0.3 parts by weight.

[Experimental Example 1]

XRD using Cu (Kα ray) for the positive active materials prepared in Examples 1 and 2 in order to confirm the presence of crystalline phases of lithium oxide, boron oxide and phosphorus oxide contained in the positive electrode active material according to an embodiment of the present invention Diffraction measurements were made, and the results are shown in FIG. 1 .

The XRD diffraction measurement conditions are as follows.

- Target: Cu (Kα ray) graphite monochromator

- slit: divergence slit = 1 degree, receive slit = 0.1 mm, scatter slit = 1 degree

- Measuring zone and step angle/measuring time: 10.0 degrees < 2θ < 80 degrees, 2 degrees / 1 minute (=0.1 degrees 3/sec), where 2θ (Theta) represents the diffraction angle.

Referring to FIG. 1, the positive active materials of Examples 1 and 2 are near 33.5 and 56 peaks corresponding to crystalline Li ₂ O in the XRD diffraction measurement results, and near 27.5 peaks corresponding to crystalline B ₂ O ₃ , and , It can be confirmed that the peak is not found in the vicinity of 20.5, which is a peak corresponding to crystalline P ₂ O ₅ .

Accordingly, in the cathode active material according to an embodiment of the present invention, it may be determined that the coating layer is formed in an amorphous phase in which Li ₂ O, B ₂ O ₃ and P ₂ O ₅ are not a crystalline phase.

[Experimental Example 2]

For the lithium secondary batteries prepared in Examples 1 to 4 and Comparative Examples 1 to 5, respectively, 0.1C charging and 0.1C discharge were performed twice by cutting off 2.5V during discharge after 4.3V charging in a room temperature atmosphere. , its results are shown in Table 2 below.

Then, in order to evaluate the high-temperature life characteristics, 0.5C charge and 1.0C discharge are repeatedly performed with 3.0V cut-off during discharge after 4.3V charge at 45°C, and discharge capacity at 30 cycles, 40 cycles, and 50 cycles is shown in Table 3 below in comparison with the discharge capacity in 1 cycle, respectively.

Referring to Tables 2 and 3, the lithium secondary batteries of Examples 1 to 4 according to the present invention have higher overall discharge capacity and higher discharge efficiency than Comparative Example 1 in which a coating layer is not formed, and have excellent cycle characteristics under high temperature conditions. In particular, it can be confirmed that the DCIR (Direct Current Internal Resistance) characteristics related to the lifespan of the secondary battery are remarkably excellent.

This is that, in the case of the active material of the embodiments according to the present invention, as the heat treatment for forming the coating layer proceeds at a relatively low temperature, lithium oxide, boron oxide and phosphorus oxide included in the coating layer are uniformly formed on the surface of the active material as an amorphous phase, and lithium ions It is believed that this is because the movement of the metal is promoted and the lithium ion conductor is improved.

In addition, in the case of the active material of the examples of the present invention, in comparison with Comparative Examples 4 and 5 containing only one of boron oxide and phosphorus oxide, good characteristics were exhibited in discharge capacity, discharge efficiency and high temperature characteristics, through which, According to an embodiment of the present invention, it can be seen that the active material including both boron oxide and phosphorus oxide in the coating layer has better properties compared to the active material including only one of the two.

In the case of Comparative Examples 2 and 3, it can be seen that the coating layer includes both boron oxide and phosphorus oxide as in the Examples of the present invention, but the properties are lower than those of Examples of the present invention, which are in Comparative Examples 2 and 3 According to the active material, as the heat treatment for the coating layer formation process proceeds at a relatively high temperature, a crystalline coating layer is formed on the surface of the core, and thus it is judged that it exhibits low performance characteristics.

Those of ordinary skill in the art to which the present invention pertains will be able to make various applications and modifications within the scope of the present invention based on the above contents.

Claims (13)

A core comprising a lithium composite metal oxide; and
a coating layer positioned on the core and including an amorphous phase;
including,
The amorphous phase includes lithium oxide, boron oxide and phosphorus oxide in the form of a mixture,
The coating layer is a cathode active material for a lithium secondary battery, characterized in that it comprises a composition of the following formula 2:
αB _x O _y -βP _v O _w -γLi ₂ O (2)
In the above formula, the conditions of α+β+γ=1, 0.35≦x/y≦0.75, and 0.2≦v/w≦0.67 are satisfied. delete The positive active material for a lithium secondary battery according to claim 1, wherein the coating layer has a composition represented by the following Chemical Formula 3:
αB ₂ O ₃ -βP ₂ O ₅ -γLi ₂ O (3)
In the above formula, the condition of α+β+γ=1 is satisfied. The lithium secondary battery according to claim 1, wherein a peak is not found even in the vicinity of any one of 33.5, 56, 27.5 and 20.5 of 2theta (degree) of X-ray diffractiometry. positive electrode active material. The positive active material for a lithium secondary battery according to claim 4, wherein the X-ray diffraction analysis is performed under the following XRD diffraction measurement conditions:
- Target: Cu (Kα ray) graphite monochromator
- slit: divergence slit = 1 degree, receive slit = 0.1 mm, scatter slit = 1 degree
- Measuring zone and step angle/measurement time: 10.0 degrees < 2θ < 80 degrees, 2 degrees / 1 minute (=0.1 degrees 3/sec), where 2θ (Theta) represents the diffraction angle. The cathode active material for a lithium secondary battery according to claim 1, wherein the core has an average particle diameter in the range of 1 to 50 µm. According to claim 1, In the amorphous phase, based on 100 parts by weight of the core, the content of lithium oxide is 0.01 to 2 parts by weight, the content of boron oxide is 0.1 to 2 parts by weight, and the content of phosphorus oxide is 0.01 to 1 weight part A cathode active material for a lithium secondary battery, characterized in that it is negative. The cathode active material for a lithium secondary battery according to claim 1, wherein the coating layer has a thickness of 0.01 to 1 μm. The positive active material for a lithium secondary battery according to claim 1, wherein the coating layer is coated with a surface area of 40 to 100% based on the surface area of the core. 10. A method for manufacturing a positive electrode active material according to any one of claims 1 and 3 to 9, comprising:
In the lithium composite metal oxide powder for a core, (i) a boron-containing powder and a phosphorus-containing powder are mixed, or (ii) a boron-containing powder, a phosphorus-containing powder and a lithium-containing powder are mixed,
A manufacturing method comprising the step of sintering in an atmosphere containing oxygen in the temperature range at which the amorphous coating layer is formed. 11. The method of claim 10, wherein the lithium composite metal oxide powder, boron-containing powder and phosphorus-containing powder are mixed and fired, and the lithium oxide of the amorphous coating layer is derived from a lithium-containing component remaining on the surface of the lithium composite metal oxide powder. manufacturing method. 11. The method according to claim 10, wherein the temperature range is in the range of 150°C to 500°C. 10. A lithium secondary battery comprising the positive active material according to any one of claims 1 and 3 to 9.

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