KR20200013015A - Elemental coating on oxide materials for lithium rechargeable battery - Google Patents

Abstract

The present invention relates to a surface coating method which can obtain a positive electrode active material for a lithium secondary battery with a uniform coating layer using a simple substance material and realize improved cycle properties and high efficiency properties. The surface coating method comprises steps of: mixing a simple substance material with a lithium transition metal oxide; and thermally treating the mixture and forming a coating layer made of a complex of the simple substance material on the surface of the lithium transition metal oxide, wherein the lithium transition metal oxide has an interlayer structure. The positive electrode active material manufactured by the present invention can realize significantly improved lifespan properties and high efficiency properties.

Description

Surface coating method using single element material for oxide of lithium secondary battery {Elemental coating on oxide materials for lithium rechargeable battery}

The present invention relates to a surface coating method for an oxide for a lithium secondary battery, and more particularly, to obtain a cathode active material for a lithium secondary battery having a uniform coating layer formed using a single element material, thereby realizing improved cycle characteristics and high rate characteristics. To a surface coating method.

Lithium secondary batteries have been widely used in small electronic devices such as mobile phones and laptops until recently, but in recent years, the use of electric vehicles and energy storage systems (ESS) has increased rapidly. The development of lithium secondary batteries with improved battery performance has become very important.

Since the positive electrode of the components of the lithium secondary battery most affect the battery performance, the development of a positive electrode active material with high energy density is essential.

On the other hand, lithium cobalt oxide and lithium nickel oxide having a layered structure widely used as a cathode active material for lithium secondary batteries have high theoretical capacities of 274 mAh / g and 275 mAh / g, respectively.

However, lithium cobalt oxide and lithium nickel-based oxide are not only structurally unstable at high voltage but also have a problem in that capacity retention rate is drastically reduced as the cycle progresses due to reaction with the electrolyte at the material surface.

Since the reduction in capacity retention is due to the reaction between the positive electrode active material and the electrolyte as the cycle progresses, a means for suppressing the reaction occurring between the positive electrode active material and the electrolyte is required. In the case of lithium nickel-based transition metal oxides, when nickel is exposed on the surface of the positive electrode active material, phase transition occurs and the capacity retention rate is deteriorated, and thus a coating layer capable of preventing this is required.

To this end, many studies have been made to form a coating layer on the surface of lithium cobalt oxide and lithium nickel-based oxide, the coating layer was formed by a liquid phase method such as atomic layer deposition (ALD), coprecipitation method.

Although the dual atomic layer deposition method has an advantage of finely controlling the thickness of the thin film, it is not suitable for mass production due to the slow growth rate of the thin film, and there is a problem in that the manufacturing cost increases because it requires the use of relatively expensive equipment compared to other manufacturing methods.

In addition, when the coating layer is formed by a liquid phase method such as coprecipitation, there is a problem in that the manufacturing process is complicated because it must go through a process such as washing and drying.

Accordingly, it is necessary to form a uniform coating layer on the surface of lithium cobalt oxide and lithium nickel-based oxide in a simple process without using a liquid phase method such as atomic layer deposition or coprecipitation.

1) Chem. Mater. 2000, 12, 3788-3791

An object of this invention is to provide the coating method of the oxide for lithium secondary batteries which can improve the lifetime characteristic, capacity | capacitance, and capacity retention of a lithium secondary battery.

One aspect of the present invention for solving the above problems is a step of mixing a lithium transition metal oxide of a single element material consisting of phosphorus (P), and the mixture at a temperature at which the phosphorus (P) is sublimed at 250 ~ 600 ℃ Heat-treating, forming a uniform coating layer made of the compound of the single element material on the surface of the lithium transition metal oxide, wherein the lithium transition metal oxide has a layered structure, the material represented by the following [Formula 1] It provides a surface coating method using a single element material for the oxide for lithium secondary batteries.

[Formula 1]

LiNi _1-xyz Mn _x Co _y M _z O ₂

x<1, 0≤y<1, 0≤z<1, 0≤x+y+z≤1)(Wherein M is one or more selected from the group consisting of Mg, Al, Fe, V, Cr, Ti, W, Ta, Na and Mo, 0

x <1, 0≤y <1, 0≤z <1, 0≤x + y + z≤1)

Another aspect of the present invention for solving the above problems is a step of mixing a lithium transition metal oxide with a single element material consisting of phosphorus (P), and the mixture at a temperature at which the phosphorus (P) is sublimated at 250 ~ 600 ℃ Heat-treating, forming a uniform coating layer made of a compound of the single element material on the surface of the lithium transition metal oxide, wherein the lithium transition metal oxide has a layered structure, the material represented by the following [Formula 2] It provides a surface coating method using a single element material for the oxide for lithium secondary batteries.

[Formula 2]

Li [Li _k Ni _x Mn _y Co _z M _w ] O ₂

k<1, 0≤x<1, 0≤y<1, 0≤z<1, 0≤w<1, 0<k+x+y+z+w≤1)(Wherein M is one or more selected from the group consisting of Al, Fe, V, Cr, Ti, W, Ta, Na and Mo, and 0

k <1, 0≤x <1, 0≤y <1, 0≤z <1, 0≤w <1, 0 <k + x + y + z + w≤1)

The present invention relates to a compound between elements forming a single element material and a lithium transition metal oxide on the surface of a positive electrode active material consisting of a lithium transition metal oxide using a method of heat treatment using a single element material composed of one element such as phosphorus (P). To form a coating layer consisting of, according to this method can be formed a uniform coating layer on the surface of the positive electrode active material.

The positive electrode active material having the coating layer formed as described above suppresses side reactions and phase transitions with the electrolyte at high voltage, thereby improving discharge capacity retention characteristics, life characteristics, and high rate characteristics of the battery.

In addition, the method according to the present invention not only reduces the process cost by heat treatment at a lower temperature than the conventionally developed coating process, there is an advantage that the process is simple and suitable for mass production.

1 is a coating process diagram of a positive electrode active material according to a preferred embodiment of the present invention.
Figure 2 shows the XRD pattern of the positive electrode active material according to Comparative Example 1 and Example 2 of the present invention.
3 is an XPS graph of the positive electrode active material according to Comparative Example 1 and Example 2 of the present invention ((a) Ni 2p, (b) O 1s, (c) S 2p).
4 is a graph showing charge and discharge characteristics of a battery to which a positive electrode active material coated with a sulfur compound according to Comparative Example 1 and Example 2 of the present invention.
5 is a graph showing the life characteristics of a battery to which the positive electrode active material coated with a sulfur compound according to Comparative Example 1 and Example 2 of the present invention.
Figure 6 is a graph showing the charge and discharge characteristics of a battery to which the positive electrode active material coated with a phosphorous compound according to Comparative Example 2 and Example 4 of the present invention ((a) Comparative Example 2, (b) Example 4).

The singular forms used to describe the embodiments of the present invention are intended to include the plural forms as well, unless the phrases clearly indicate the opposite. And the meaning of includes specific characteristics, areas, integers, steps, actions. Specific elements, regions, integers, steps, actions that embody elements and / or components. It does not exclude the presence or addition of elements, components and / or groups.

Unless defined otherwise, all terms including technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. In addition, commonly used terms defined in advance are not to be interpreted in an ideal or very formal sense unless further interpreted and defined as having a meaning consistent with the related technical literature and the presently disclosed contents.

The method of manufacturing a cathode active material according to the present invention includes mixing a single element material with a lithium transition metal oxide, and heat treating the mixture to form a coating layer of the compound of the single element material on the surface of the lithium transition metal oxide. It includes, the lithium transition metal oxide is characterized in that it has a layered structure.

The lithium transition metal oxide may be, preferably, a material represented by the following [Formula 1].

[Formula 1]

LiNi _1-xyz Mn _x Co _y M _z O ₂

(Wherein M is at least one member selected from the group consisting of Mg, Al, Fe, V, Cr, Ti, W, Ta, Na and Mo, 0 ≦ x <1, 0 ≦ y <1, 0≤z <1, 0≤x + y + z≤1)

In addition, the lithium transition metal oxide may be a lithium rich (Li-rich or Li-excess) transition metal oxide, preferably, may be a material represented by the following [Formula 2].

[Formula 2]

Li [Li _k Ni _x Mn _y Co _z M _w ] O ₂

(Wherein M is at least one member selected from the group consisting of Mg, Al, Fe, V, Cr, Ti, W, Ta, Na and Mo, and 0 ≦ k <1, 0 ≦ x <1, 0 ≦ y < 1, 0≤z <1, 0≤w <1, 0 <k + x + y + z + w≤1)

In addition, the single element material may preferably include sulfur (S) or phosphorus (P), but is not necessarily limited thereto. The single element material may be coated on the surface of the positive electrode active material with a single element material, and the electrolyte may be used at a high voltage. If it can function to suppress the side reaction or phase transition of may not be particularly limited.

In addition, the single element material may preferably include sulfur (S) or phosphorus (P), but is not necessarily limited thereto. The single element material may be coated on the surface of the positive electrode active material with a single element material, and the electrolyte may be used at a high voltage. If it can function to suppress the side reaction or phase transition of may not be particularly limited.

In addition, the single element material is sulfur (S), the formation of the coating layer is heat-treated the mixture to a temperature at which the sulfur (S) is sublimated sulfur (S) reacts with the lithium transition metal oxide to form a compound. You can do that. In this case, the raw material of the single element material may be at least one selected from red phosphorus, white phosphorus, violet phosphorus, and black phosphorus.

In addition, mixing of the single element material and the lithium transition metal oxide may be performed by directly mixing using a mortar, at least one of a ball mill, a planetary ball mill, and a high energy ball mill. can do.

In addition, the mixing method is a method of directly mixing using a mortar and pestle, ball mill, planetary ball mill and high energy ball mill, such as a method of uniformly mixing the single-element material and the positive electrode active material is not limited Can be used without.

In addition, the step of mixing the single element material and the lithium transition metal oxide, the weight ratio of the single element material and the positive electrode active material, when the weight ratio of the single element material to the total weight of the single element material and the lithium transition metal oxide exceeds 10% It is preferable to mix in the range of more than 0% to 10% or less, because the residue that fails to react increases or the amount of the active material decreases to lower the total capacity of the battery.

In addition, when the heat treatment temperature is less than 150 ° C., the coating layer may not be uniformly formed. If the heat treatment temperature is higher than 600 ° C., sulfur (S) or phosphorus (P) may react with the positive electrode active material to change the crystal structure of the positive electrode active material. It is preferable to heat-treat in the temperature range of 150 degreeC or more and 600 degrees C or less as it can. On the other hand, when the single element material is phosphorus (P), since the phosphorus (P) is less reactive than sulfur (S), it is more preferable to heat-treat at a temperature range of 250 ° C to 600 ° C higher temperature.

In addition, in order to form a uniform coating layer, the heat treatment time is preferably 2 hours or more, and if the heat treatment time is too long, energy costs may be excessively required, so heat treatment is preferably performed for 24 hours or less.

In addition, the heat treatment atmosphere may vary depending on the type of the positive electrode active material. In particular, the nickel molar ratio is full when the transition is 50% by metal basis, because a side reaction on the surface during prolonged contact with air can be up to be degraded, argon (Ar), nitrogen (N _2), helium contained in the positive electrode active material ( Heat treatment in an inert gas atmosphere, such as He), hydrogen (H ₂ ), or a mixture thereof, is preferable since it can form a uniform surface coating layer.

Coating of positive electrode active material

Example 1

Through the process shown in Figure 1, using a sulfur (S) to prepare a cathode active material for a lithium secondary battery coated with a sulfur compound on the surface of the nickel-based lithium transition metal oxide.

First, 400 mg of nickel-based lithium transition metal oxide (NMC811 powder, LiNi _0.8 Mn _0.1 Co _0.1 O ₂ (Umicore)) and 4 mg of sulfur (S) (Sigma Aldrich) were mixed in a mortar.

Next, the mixture was subjected to a heat treatment process at 250 ° C. for 4 hours under an Ar gas atmosphere.

Through this process, a cathode active material for a lithium secondary battery made of a nickel-based lithium transition metal oxide coated with a sulfur compound was produced.

Example 2

Except that the heat treatment temperature was changed to 300 ℃, a positive electrode active material for a lithium secondary battery made of a nickel-based lithium transition metal oxide LiNi _0.8 Mn _0.1 Co _0.1 O ₂ coated with a sulfur compound in the same manner as in Example 1.

Example 3

Except that the heat treatment temperature was changed to 350 ℃ to prepare a positive electrode active material for a lithium secondary battery made of a nickel-based lithium transition metal oxide LiNi _0.8 Mn _0.1 Co _0.1 O ₂ coated with a sulfur compound in the same manner as in Example 1.

Example 4

Using a phosphorus (P) to prepare a cathode active material for a lithium secondary battery coated with a phosphorus compound on the surface of the lithium rich transition metal oxide.

First, 400 mg of Li _1.2 Ni _0.2 Mn _0.6 O ₂ and ₄ mg of phosphorus (P) (Sigma Aldrich) were mixed in a mortar. Next, the mixture was subjected to a heat treatment process at 400 ° C. for 4 hours under an air atmosphere. The heat treated material was recovered.

After the above process, a positive electrode active material for a lithium secondary battery made of a lithium rich transition metal oxide coated with a phosphorus compound was produced.

Comparative Example 1

In Comparative Example 1 of the present invention, a lithium secondary battery positive electrode active material including nickel-based lithium transition metal oxide LiNi _0.8 Mn _0.1 Co _0.1 O ₂ used in Examples 1 to 3 was prepared without forming a separate coating layer.

Comparative Example 2

In Comparative Example 2 of the present invention, a cathode active material for a lithium secondary battery including the same lithium rich transition metal oxide as applied in Example 4 was prepared without forming a separate coating layer.

Structural properties evaluation

X-ray diffraction (XRD) analysis and X-ray photoelectron spectroscopy (XPS) analysis were performed to evaluate the structural characteristics of the positive electrode active materials prepared according to the above Examples and Comparative Examples. 3 is shown.

₂ , it can be seen that the positive electrode active material particles prepared according to Example 2 of the present invention are crystalline LiNi _0.8 Mn _0.1 Co _0.1 O ₂ . That is, no deformation occurred in the crystal structure of the cathode active material during the coating process according to the present invention.

In addition, referring to FIG. 3, NiO was exposed to the surface of the cathode active material of Comparative Example 1, but it was confirmed that NiO was hardly exposed to the surface of the cathode active material coated with sulfur of Example 2. In the case of the positive electrode active material of Example 2, it was confirmed that lithium sulfide and lithium sulfate were formed on the surface thereof.

Manufacturing of coin cell

Using the positive electrode active material prepared according to Examples 1 to 3 and Comparative Example 1 was prepared a coin cell for the electrochemical properties evaluation in the following manner.

First, a slurry was prepared using 80% by weight of a positive electrode active material, 15% by weight of Super-P as a conductive material, and 5% by weight of polyvinylidene fluoride (PVDF) in which N-methyl pyronelidone (NMP) was dissolved as a solvent. .

This slurry was applied to an aluminum foil (Al foil), dried, and dried for 12 hours at a temperature of 130 ° C. in a vacuum atmosphere to prepare a circular positive electrode having a diameter of 8 mm.

In addition, a lithium metal punched to a diameter of 10 mm was used as the cathode, a polypropylene (PP) film was used as the separator, and 1 M of ethylene carbonate / diethyl carbonate (EC / DEC) 1 of LiPF ₆ was used as the electrolyte. Coin cells were prepared using a: 1 v / v mixed solution.

Battery performance evaluation

Evaluation of the charge and discharge characteristics of the battery prepared using the positive electrode active material prepared according to Examples 1 to 3 and Comparative Example 1 was carried out using a constant current method, the charge and discharge voltage range was performed from 2.5V to 4.5V. Initial capacity evaluation was carried out at a current density of 0.1C, calculated as 200 mAh / g of 1C, the life characteristics were carried out at C / 3 at room temperature.

Electrochemical performance evaluation of the lithium secondary battery prepared from the cathode active material according to Examples 1 to 3 and Comparative Example 1 is shown in Figure 4, 5 and Table 1 below.

division Positive electrode active material Early
Discharge capacity
(mAh / g) Discharge capacity after 80 cycles
(mAh / g) Core components coating
Precursor Coating temperature
(℃) Example 1 LiNi _0.8 Mn _0.1 Co _0.1 O ₂ S 250 208.3 123.5 Example 2 LiNi _0.8 Mn _0.1 Co _0.1 O ₂ S 300 228.1 176.8 Example 3 LiNi _0.8 Mn _0.1 Co _0.1 O ₂ S 350 199.3 145.7 Comparative Example 1 LiNi _0.8 Mn _0.1 Co _0.1 O ₂ - - 213.7 68.4

As shown in Table 1, the lithium secondary battery to which the positive electrode active material prepared according to Examples 1 to 3 of the present invention is applied, has a discharge capacity of 123.5mAh / g, 176.8mAh / g, and 145.7mAh / g after 80 cycles, respectively. The lithium secondary battery using the positive electrode active material of Comparative Example 1, in which the coating layer was not formed, had a discharge capacity of 68.4 mAh / g after 80 cycles, which was remarkably lower than that of Examples 1 to 3. In other words, Examples 1 to 3 of the present invention. As a result, the life of the coating layer was improved by more than two times as compared with the absence of the coating layer.

In particular, in the case of Example 2, the initial discharge capacity and the discharge capacity after 80 cycles is also improved compared to Examples 1 and 2, the coating process temperature can be formed at a higher temperature of 275 ~ 325 ℃ can be formed desirable.

Charging and discharging characteristics of the battery to which the cathode active materials according to Example 4 and Comparative Example 2 were applied were performed by using a constant current method, and the charging and discharging voltage range was performed from 2.5V to 4.7V. The first cycle was performed at a current density of 0.05C, with 1C calculated at 300 mAh / g, and 0.3C from the second cycle. As shown in FIG. 6, Example 4 having the phosphorus compound coating layer is superior to the discharge capacity and the lifespan characteristics of the first cycle than Comparative Example 2 in which the phosphorus compound coating layer is not formed.

As described above, according to the method of the present invention, the coating layer capable of improving cycle characteristics, high rate characteristics, and the like can be formed on the surface of the cathode active material without changing the crystal structure during the coating process. .

In addition, in the case of sulfur (S), since the synthesis reaction is performed using sulfur (S) in the sublimed gas phase, a very uniform coating layer can be formed on the surface of the positive electrode active material, thereby suppressing side reactions between the electrolyte solution and the positive electrode active material. In the case of the nickel high content lithium transition metal oxide, the exposure of the nickel oxide to the surface of the positive electrode active material is suppressed to prevent the change of the crystal structure of the positive electrode active material during charge / discharge. Accordingly, the electrical conductivity and the diffusion rate of lithium ions of the positive electrode active material can be improved, thereby improving the characteristics of the battery.

In addition, the method according to the present invention has the advantage that the heat treatment at a lower temperature than the coating process developed in advance, as well as the process is simple and suitable for mass production.

Claims (5)

Mixing a single element material made of phosphorus (P) with a lithium transition metal oxide,
Heat treating the mixture at a temperature of 250 to 600 ° C. at which phosphorus (P) is sublimed, thereby forming a uniform coating layer made of a compound of a single element material on the surface of the lithium transition metal oxide;
The lithium transition metal oxide is a surface coating method using a single element material for the oxide for lithium secondary batteries, which is a material represented by the following [Formula 1] having a layered structure.
[Formula 1]
LiNi _1-xyz Mn _x Co _y M _z O ₂
(Wherein M is one or more selected from the group consisting of Mg, Al, Fe, V, Cr, Ti, W, Ta, Na and Mo, and 0 ≦ x <1, 0 ≦ y <1, 0 ≦ z < 1, 0≤x + y + z≤1) Mixing a single element material made of phosphorus (P) with a lithium transition metal oxide,
Heat-treating the mixture at a temperature of 250 to 600 ° C. at which the phosphorus (P) is sublimed to form a uniform coating layer made of a compound of the single element material on the surface of the lithium transition metal oxide,
The lithium transition metal oxide is a surface coating method using a single element material for the oxide for lithium secondary batteries, which is a material represented by the following [Formula 2] having a layered structure.
[Formula 2]
Li [Li _k Ni _x Mn _y Co _z M _w ] O ₂
(Wherein M is one or more selected from the group consisting of Al, Fe, V, Cr, Ti, W, Ta, Na and Mo, and 0 ≦ k <1, 0 ≦ x <1, 0 ≦ y <1, 0≤z <1, 0≤w <1, 0 <k + x + y + z + w≤1) The method according to claim 1 or 2,
The step of mixing the single element material and the lithium transition metal oxide,
The weight ratio of the single element material to the total weight of the single element material and the lithium transition metal oxide is greater than 0% to 10%, surface coating method using a single element material for the oxide for lithium secondary batteries. The method according to claim 1 or 2,
The raw material of the single element material, red phosphorus (white phosphorus), white phosphorus (white phosphorus), violet phosphorus (violet phosphorus), black phosphorus (black phosphorus) is at least one selected from the manufacturing method of the positive electrode active material for lithium secondary batteries. The method according to claim 1 or 2,
Mixing of the single element material and the lithium transition metal oxide may be performed by directly mixing using a mortar, at least one of a ball mill, a planetary ball mill, and a high energy ball mill. Surface coating method using a single element material for the oxide for lithium secondary batteries.

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