KR101876025B1 - Method of manufacturing composite positive electrode for all-solid battery - Google Patents

Abstract

More particularly, the present invention relates to a method of manufacturing a composite anode for a full-solid battery, and more particularly, to a method of manufacturing a composite anode by coating a lithium ion conductive solid electrolyte on a surface of an active material precursor through a vacuum process, The formation of an electrolyte matrix in the composite anode ensures an effective conduction path between the active material particles to minimize the resistance in the electrode and to increase the content of the active material in the composite anode to greatly improve the capacity of the battery. ≪ / RTI >

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a method of manufacturing a composite anode for a solid-

More particularly, the present invention relates to a method of manufacturing a composite anode for a full-solid battery, and more particularly, to a method of manufacturing a composite anode by coating a lithium ion conductive solid electrolyte on a surface of an active material precursor through a vacuum process, The formation of an electrolyte matrix in the composite anode ensures an effective conduction path between the active material particles to minimize the resistance in the electrode and to increase the content of the active material in the composite anode to greatly improve the capacity of the battery. ≪ / RTI >

A pre-solid battery is a battery in which a solid electrolyte is substituted for a liquid electrolyte present in a liquid phase among an anode, an electrolyte, a separator, and an anode material constituting the secondary battery. Conventional secondary batteries (mainly lithium ion secondary batteries) using an organic electrolyte have a property that the electrolyte is volatilized due to an increase in the internal temperature of the battery when an overcharge or an internal short circuit occurs, and there is a risk of fire or explosion .

On the other hand, the entire solid-state battery using the solid electrolyte can greatly improve the safety, and when the ion conductivity is the same, the ion transport rate is three times or more as compared with the liquid electrolyte. Further, since the diffusion rate of lithium ions in the electrolyte is faster than that of the liquid electrolyte, theoretically, high output can be achieved.

However, all solid-state batteries using solid electrolytes are required to have excellent ion transfer paths especially in the anode and cathode electrodes, compared to batteries using conventional liquid electrolytes. In the case of a solid electrolyte using a solid electrolyte, a slurry is generally prepared by mixing the active material and the solid electrolyte powder at the time of electrode formation, and the composite electrode is formed by coating the collector.

In this case, in order to secure the ion conduction path by mixing the solid-solid powder, the fraction of the solid electrolyte in the mixed powder (usually at least 40% by weight) is large, so the electrode resistance is large and the ionic conductivity is relatively low There is a problem that the battery capacity is deteriorated as a result.

In Korean Unexamined Patent Publication No. 2015-0143365, a solid-state electrolyte made of a hydrocarbon-based, fluorine-based or polyester-based polymer is formed on the anode, and a solid electrolyte of a polymer or an inorganic material is formed on the anode. , There is a problem that it is difficult to increase the relative content of the active material due to the large amount of electrolyte used. Also, since the cell structure is complicated by applying a hetero-electrolyte, the process is difficult to implement in the mass production application and the process cost is increased. There is a problem that the resistance of the battery increases due to the polarization due to the difference in conductivity at the hetero-interface.

Therefore, it is necessary to research and develop all-solid-state cells capable of ensuring the capacity of the battery by effectively securing the ion transfer path while reducing the content of the solid electrolyte.

Korea Patent Publication No. 2015-0143365

In order to solve the above problem, instead of the process of applying a conventional heterogeneous electrolyte to a cathode and an anode, a lithium ion conductive solid electrolyte is coated on the surface of an active material precursor with a minimal amount to prepare a composite anode powder, It has been found that an effective conduction path between the active material particles can be ensured to reduce the resistance in the electrode to a minimum and to increase the content of the active material in the composite anode, thereby greatly improving the battery capacity.

Accordingly, it is an object of the present invention to provide a method for manufacturing a composite anode for a full-solid battery in which electrode resistance is minimized while battery capacity is greatly improved.

(A) preparing an active material precursor; (b) coating a surface of the active material precursor with a lithium ion conductive solid electrolyte; (c) drying the active material precursor coated with the lithium ion conductive solid electrolyte to prepare a composite positive electrode powder; (d) casting the composite positive electrode powder on a positive electrode collector to form a composite positive electrode layer; And (e) heat-treating the composite anode layer.

The composite positive electrode for a full-solid battery according to the present invention can be produced by coating a lithium ion conductive solid electrolyte on the surface of an active material precursor through a vacuum process to prepare a composite positive electrode powder and then heat treating the composite positive electrode powder to form an electrolyte matrix in the composite positive electrode, It is possible to secure an effective conduction path between the particles to minimize the resistance in the electrode and increase the content of the active material in the composite anode, thereby greatly improving the battery capacity.

1 is a cross-sectional view of a composite anode powder in which a lithium ion conductive solid electrolyte is thinly coated on the surface of an active material precursor according to the present invention.
2 is a cross-sectional view schematically showing the composite anode layer prepared in the embodiment of the present invention before and after the heat treatment.
3 is an electron micrograph of a lithium ion conductive solid electrolyte-coated active material precursor prepared in an embodiment of the present invention.
FIG. 4 is an electron micrograph of a lithium ion conductive solid electrolyte-coated active material precursor prepared in Comparative Example 2 of the present invention. FIG.
5 is a photograph showing the composite anode layer prepared in Comparative Example 1 (left) and Example (right) of the present invention.
6 is a graph showing the impedance analysis results of the composite anode fabricated in the embodiment (solid line) and the comparative example 1 (dotted line) of the present invention.
7 is a graph showing the capacity characteristics of the battery using the composite anode manufactured in Comparative Example 1 of the present invention.
8 is a graph showing the capacity characteristics of the battery using the composite anode fabricated in the embodiment of the present invention.

Hereinafter, the present invention will be described in more detail with reference to one embodiment.

(A) preparing an active material precursor; (b) coating a surface of the active material precursor with a lithium ion conductive solid electrolyte; (c) drying the active material precursor coated with the lithium ion conductive solid electrolyte to prepare a composite positive electrode powder; (d) casting the composite positive electrode powder on a positive electrode collector to form a composite positive electrode layer; And (e) heat-treating the composite anode layer.

In the present invention, there is a major technical feature in manufacturing a composite anode using a functional powder in which a solid electrolyte material is coated on the surface of an active material in place of a mixed powder of an active material and a solid electrolyte, thereby increasing the fraction of the active material, There is an advantage of simplifying the mixing process. Further, by coating the surface of the active material with a small amount of solid electrolyte to form an electrode, the content of the active material in the composite anode can be increased to improve the battery capacity.

According to a preferred embodiment, the active material precursor used in the step (a) is _{LiCoO 2, LiNi 1/3 Co} 1/3 Mn 1/3 O 2, LiMn ₂ O ₄ can be used, and LiNi _{0 .8} Co _{0 .15} at least one member selected from the group consisting of Al _{0 .05} O _2. Such active material precursors exhibit deterioration in performance at temperatures of about 900 DEG C or higher in an interlayer structure material or an oxide which is a spinel structure material. As the surface treatment material of the active material precursor, it is preferable to use a material having a low melting point of 900 캜 and a high ion conductivity in a lithium ion conductive solid electrolyte (oxide).

1 is a cross-sectional view of a composite anode powder in which a lithium ion conductive solid electrolyte is thinly coated on the surface of an active material precursor according to the present invention. As shown in FIG. 1, the surface of the active material precursor is thinly coated with a lithium ion conductive solid electrolyte having a low melting point.

In order to form a composite anode having such a structure, it is important to select the material of the solid electrolyte coated on the surface of the active material precursor. Specifically, the solid electrolyte should have a melting point within a temperature range at which the active material is not damaged. In addition, it should have good contact with the surface of the active material, and it is preferable to use one having a high lithium ion conductivity for the ion conduction effect.

According to a preferred embodiment of the present invention, in the step (b), the lithium ion conductive solid electrolyte is a lithium phosphate (Li-PO) oxide, lithium borate (Li-BO) Based oxide or a mixture thereof. Specifically, the lithium phosphate (Li-PO) -based oxide has a melting point of about 800 Lt; 0 > C or higher, and lithium borate (Li-BO) Lt; 0 > C. Li ₃ PO _{4 ,} Li ₃ BO ₃ or a mixture thereof may be preferably used. The Li ₃ PO ₄ has a melting point of about 837 ° C and the Li ₃ BO ₃ has a melting point of about 650 ° C, which is a solid electrolyte material suitable for the present invention. However, in the case of the Li-Si-O-based oxide, the melting point is 1200 ℃ least (Li ₂ SiO ₃ 1201 ° C.), which is much higher than the melting point of the active material (about 900 ° C.), which is not suitable for the present invention.

According to a preferred embodiment of the present invention, in the step (b), the surface of the active material precursor may be coated with a lithium ion conductive solid electrolyte using a vacuum evaporator. However, the surface treatment method of the active material is not limited thereto.

According to a preferred embodiment of the present invention, the coating amount of the lithium ion conductive solid electrolyte in step (b) may be 2 to 10% by weight based on the precursor of the active material, and the coating thickness may be 15 to 100 nm. If the coating amount is less than 2% by weight, the surface of the active material powder can not be completely covered. If the amount of the lithium ion conductive solid electrolyte is more than 10% by weight, the solid electrolyte layer There is a problem that it acts as a large resistance layer of electron transfer.

Also, if the coating thickness is less than 15 nm, the amount of solid electrolyte dissolved in the heat treatment process is too small and it is difficult to form an electrolyte matrix having effective ion conductivity. If the coating thickness is more than 100 nm, if the amount of the solid electrolyte is too large, the amount of the active material becomes relatively small, so that it is difficult to form a high energy density and consequently there is a problem that the electron conduction is adversely affected. Preferably, the coating thickness is 50 to 70 nm. For example, when the density of the active material is 5 g / cm ³ (LiCoO ₂ = 5.1 g / cm ³ ) and the density of the lithium borate solid electrolyte is 2 g / cm ³ (Li ₃ BO ₃ = 2.16 g / cm ³ ) , When a lithium borate oxide is coated to a thickness of 100 nm on the surface of an active material having an average radius of 2.5 占 퐉, the weight ratio of the active material to the solid electrolyte is 95: 5 by weight. Considering this point, the thickness of the surface coating layer is preferably adjusted to 15 to 100 nm.

According to a preferred embodiment of the present invention, the step (b) may be carried out at a pressure of 10 to 1 × 10 ^-4 Pa for 6 to 10 hours. Specifically, the step (b) the internal reaction chamber primarily made to a vacuum of less than 10 ^-4 Pa, then an argon (Ar) or nitrogen (N ₂₎ pressure of the gas after injecting 10 ~ 1x10 ^-4 Pa . ≪ / RTI >

According to a preferred embodiment of the present invention, drying in step (c) may be performed at a temperature of 250 to 350 ° C for 10 to 14 hours. Specifically, in the step (c), the surface of the active material precursor may be coated with a lithium ion conductive solid electrolyte and then dried to produce a composite positive electrode powder. If the drying temperature is lower than 250 ° C, there is a possibility that deterioration of the active material and deterioration of the solid electrolyte characteristics due to residual moisture may occur due to incomplete drying.

According to a preferred embodiment of the present invention, the composite anode powder dried in step (d) may be cast on a cathode current collector, and then the density of the casting electrode may be increased by a cold uniaxial pressing method at a pressure of 130 to 160 MPa.

According to a preferred embodiment of the present invention, the heat treatment in the step (e) may be performed at a temperature of 600 to 800 ° C. for 4 to 6 hours. Specifically, when the heat treatment temperature is lower than 600 ° C., the solid electrolyte does not dissolve and the matrix formation reaction does not occur. If the heat treatment temperature is higher than 800 ° C., the active material deteriorates or the surface of the active material Coating layer damage may occur. A suitable heat treatment temperature is a temperature higher than the melting point of the solid electrolyte. Also, in the step (e), the lithium ion conductive solid electrolyte coated on the surface of the active material precursor of the composite anode may be melted through heat treatment to form an electrolyte matrix in the composite anode. Here, the lithium ion conductive solid electrolyte is preferably a solid electrolyte material having a melting point within the temperature stable range of the active material.

Therefore, the composite anode for a full-solid battery according to the present invention is formed by coating a surface of an active material precursor with a low-melting-point lithium ion conductive solid electrolyte to form a composite anode powder, and then performing heat treatment at a temperature higher than the melting point of the solid electrolyte, The conductive solid electrolyte may melt during the heat treatment to form an electrolyte matrix within the composite anode. The electrolyte matrix in the composite anode thus formed can secure an effective conduction path between the active material particles, thereby minimizing the resistance in the electrode and greatly improving the capacity of the battery.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited by the following Examples.

Example

5% by weight of Li ₃ BO ₃ as a lithium ion conductive solid electrolyte was added to 95% by weight of LiCoO _{2 as an} active material precursor. Then, argon gas was injected and then coated at a pressure of 4 Pa and 4 RPM for 8 hours to coat LiCoO _{2 on} the surface of Li ₃ BO ₃ to a thickness of 50 to 70 nm. LiCoO ₂ surface-coated with Li ₃ BO ₃ was then dried at 300 ° C. for 12 hours to prepare a composite positive electrode powder. Then, the composite positive electrode powder was cast on a positive electrode current collector, and the density of the casting electrode was improved by a cold uniaxial pressing method at a pressure of 146 MPa. Then, the composite anode layer was heat-treated at a temperature of 700 ° C for 5 hours (temperature rise: 5 ° C / min).

2 is a cross-sectional view schematically showing the composite anode powder prepared in the above example before and after the heat treatment. FIG. 2 shows a composite anode layer composed of a composite anode powder in which a lithium ion conductive solid electrolyte (Li ₃ BO ₃ ) is thinly coated on the surface of an active material precursor (LiCoO ₂ ). The left side of FIG. 2 shows the state before the heat treatment after the surface coating of the active material, and the content of the active material can be relatively increased by containing the minimum amount of the solid electrolyte. On the right side of FIG. 2, the lithium ion conductive solid electrolyte coated on the surface of the active material is melted by heat treatment to form an electrolyte matrix between the active materials. The formed electrolyte matrix may have ionic conductivity and serve to reduce resistance in the electrode.

Comparative Example 1

LiCoO ₂ , an active material precursor, and Li ₃ BO ₃ , a lithium ion conductive solid electrolyte, were each dried in a powder state at a temperature of 300 ° C for 12 hours. Next, all the solid batteries were produced in the same manner as in the above example, except that 70% by weight of LiCoO ₂ powder and 30% by weight of Li ₃ BO ₃ powder were mixed to prepare a composite anode.

Comparative Example 2

All the solid batteries were produced in the same manner as in the above example, except that 99% by weight of LiCoO ₂ as an active material precursor was mixed with 1% by weight of Li ₃ BO ₃ as a lithium ion conductive solid electrolyte.

Comparative Example 3

All the solid batteries were produced in the same manner as in the above example, except that 88 wt% of LiCoO ₂ as an active material precursor was mixed with 12 wt% of Li ₃ BO ₃ as a lithium ion conductive solid electrolyte.

Experimental Example 1

The properties of coating thickness and shrinkage ratio of the composite anode powder prepared in Examples and Comparative Examples 1-3 were confirmed, and the results are shown in FIGS. 3, 4 and 5.

3 is an electron micrograph of the lithium ion conductive solid electrolyte-coated active material precursor prepared in the above embodiment. FIG 3, it was confirmed that the lithium ion conductive solid electrolyte is Li ₃ BO ₃ is a thin coating with a thickness of relatively uniform 50 ~ 70 nm on the surface of LiCoO _2. However, the surface covering ratio of such an active material precursor is not an important parameter. Thereafter, the solid electrolyte coated on the surface of the active material is melted to form an electrolyte matrix through the heat treatment process, and this electrolyte matrix has important significance in securing the conduction path in the composite anode and affecting the electrode resistance.

4 is an electron micrograph of the lithium ion conductive solid electrolyte-coated active material precursor prepared in Comparative Example 2. FIG. As can be seen from FIG. 4, the surface of the active material powder was not coated properly, and the surface was exposed, and it was confirmed that the coating layer was not uniform.

In Comparative Example 3, the lithium ion conductive solid electrolyte was excessively mixed on the surface of the active material, so that the surface was not coated properly, so that the physical properties could not be confirmed.

5 is a photograph showing the composite anode layer prepared in Comparative Example 1 (left) and Example (right). As can be seen from FIG. 5, in the case of Comparative Example 1, the solid electrolyte content was 30 wt%, which was much higher than that of the above Example, but the shrinkage rate of the specimen after the high temperature heat treatment exceeding the melting point was lower. On the contrary, in the above example, it was confirmed that the sample shrinkage ratio was superior to Comparative Example 1 even though a small amount of 5 wt% of solid electrolyte was coated on the surface of the active material. As a result, it can be seen that the lithium ion conductive solid electrolyte coated on the surface of the active material is melted during the heat treatment and effectively flows the active material powder, thereby increasing the shrinkage ratio.

Experimental Example 2

In order to confirm the resistance characteristics of the composite anode prepared in the examples and comparative examples, impedance evaluation was performed using an impedance analyzer of Solartron, Inc. The results are shown in FIG.

6 is a graph showing impedance analysis results of the composite anode fabricated in the embodiment (solid line) and the comparative example 1 (dotted line). In FIG. 6, it was confirmed that the electrode resistance was much lower in the example (dotted line) than the comparative example 1 (solid line). It was found that the amount of the solid electrolyte to be added was minimized and the molten solid electrolyte was present between the active materials, thereby shortening the diffusion path of lithium ions, thereby reducing the total electrode resistance.

Experimental Example 3

In order to confirm the capacity characteristics of the composite positive electrode prepared in the above Examples and Comparative Examples, a reversible battery made of lithium metal as a negative electrode was prepared and subjected to charging and discharging tests at 0.25 C at room temperature. The results are shown in FIGS. 7 and 8 .

FIG. 7 is a graph showing the capacitance characteristics of the battery using the composite anode manufactured in Comparative Example 1, and FIG. 8 is a graph illustrating capacitance characteristics of the battery using the composite anode manufactured in the embodiment. As shown in FIGS. 7 and 8, in the case of the embodiment prepared by surface-coating the surface of the active material precursor with the lithium ion conductive solid electrolyte, the capacity characteristic was improved to about twice as much as that of Comparative Example 1 prepared by simple mixing powder Respectively.

Accordingly, it has been confirmed that the composite anode according to the present invention can effectively form an ion conduction path in the electrode by forming a composite anode layer by coating a very small amount of lithium ion conductive solid electrolyte on the surface of the active material.

Claims (8)

(a) preparing an active material precursor;
(b) coating a surface of the active material precursor with a lithium ion conductive solid electrolyte;
(c) drying the active material precursor coated with the lithium ion conductive solid electrolyte to prepare a composite positive electrode powder;
(d) casting the composite positive electrode powder on a positive electrode current collector, and then pressing the composite negative electrode at a pressure of 130 to 160 MPa to form a composite positive electrode layer; And
(e) heat treating the composite anode layer;
Wherein the total weight of the positive electrode and the negative electrode is in the range of 1: 1 to 1: 1.
The method according to claim 1,
Wherein in step (a) electrode active material precursor is _{LiCoO 2, LiNi 1/3 Co} 1/3 Mn 1/3 O 2, LiMn ₂ O ₄ , LiNi _0.8 Co _0.15 Al _0.05 O _2, and the like.
The method according to claim 1,
Wherein the lithium ion conductive solid electrolyte in step (b) is Li ₃ PO _{4 ,} Li ₃ BO _3, or a mixture thereof.
The method according to claim 1,
Wherein the coating amount of the lithium ion conductive solid electrolyte in the step (b) is 2 to 10% by weight based on the active material precursor and the coating thickness is 15 to 100 nm.
The method according to claim 1,
Wherein the step (b) is carried out at a pressure of 10 to 1x10 ^-4 Pa for 6 to 10 hours.
The method according to claim 1,
Wherein the drying in step (c) is performed at a temperature of 250 to 350 ° C for 10 to 14 hours.
The method according to claim 1,
Wherein the heat treatment in the step (e) is performed at a temperature of 600 to 800 ° C for 4 to 6 hours.
The method according to claim 1,
Wherein the lithium ion conductive solid electrolyte coated on the surface of the active material precursor of the composite anode layer is melted by heat treatment to form an electrolyte matrix.

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