KR101383360B1 - Positive active material for lithium ion capacitor and preparation method thereof - Google Patents

Abstract

The present invention relates to a lithium ion capacitor having excellent capacity characteristics and high energy density. In particular, a lithium composite metal oxide having a large initial irreversible capacity as a lithium source for a carbon-based material applied as a positive electrode active material and a lithium ion for improving energy density The present invention relates to a cathode active material for a lithium ion capacitor using a lithium composite metal oxide having a high reversibility in the operating potential region of a capacitor as a cathode additive, a method of manufacturing the same, and a lithium ion capacitor including the same.
According to the present invention, lithium can be doped to the cathode in an electrochemical manner without using metallic lithium, and the capacity characteristics of the lithium ion capacitor and the safety of the lithium doping process can be significantly improved.

Description

Cathode active material for lithium ion capacitor and manufacturing method thereof {POSITIVE ACTIVE MATERIAL FOR LITHIUM ION CAPACITOR AND PREPARATION METHOD THEREOF}

The present invention relates to a lithium ion capacitor having excellent capacity characteristics and high energy density. More specifically, the present invention uses a specific lithium composite metal oxide as a positive electrode additive in a carbon-based material that is applied as a positive electrode active material, and a positive electrode active material for a lithium ion capacitor, which is further electrochemically doped with lithium and further improves energy density. It relates to a manufacturing method.

With the proliferation of small portable electronic devices, new secondary batteries such as nickel-metal hydride batteries, lithium secondary batteries, super capacitors, and lithium ion capacitors have been actively developed.

Among these, a lithium ion capacitor (LIC) is a new concept of a secondary battery system combining the high power / long life characteristics of an existing electric double layer capacitor (EDLC) and the high energy density of a lithium ion battery.

Electrical double layer capacitors that use physical adsorption reactions of electrical charges in electrical double layers have limited application to a variety of applications because of their low energy density, despite their excellent output and lifetime characteristics. As a means of solving the problems of the electric double layer capacitor, a hybrid capacitor having an improved energy density using a material capable of inserting and desorbing lithium ions as a positive electrode or a negative electrode active material has been proposed. Lithium ion capacitors have been proposed that use a carbon-based material that can be used to insert and detach lithium ions as a negative electrode active material.

For example, as shown in FIG. 1, an electric double layer capacitor exhibits excellent output characteristics using adsorption and desorption of electric charge using an activated carbon material having a large specific surface area symmetrically on the anode and the cathode, but has a low energy density (E _a). Has the disadvantage of In contrast, hybrid capacitors use a high-capacity transition metal oxide as the anode material to increase capacity (E _b ), and lithium-ion capacitors use carbon-based materials that enable reversible insertion and desorption of lithium ions into the cathode material. It is characterized by improving the density (E _d ) performance.

Among them, the lithium ion capacitor may improve performance of energy density compared to other hybrid capacitors due to the property of using a material capable of inserting and desorbing lithium ions at a low reaction potential as a negative electrode active material. In particular, the lithium ion capacitor can be pre-doped the lithium ion with high ionization tendency in the negative electrode to significantly lower the potential of the negative electrode, the cell voltage is also possible to implement a high voltage of 3.8 V or more improved significantly compared to the 2.5 V of the conventional electric double layer capacitor Energy density can be improved compared to other hybrid capacitors.

Looking at the reaction mechanism of the lithium ion capacitor constituting the negative electrode using a carbon-based material doped with lithium ions, the electrons are transferred to the carbon-based material of the negative electrode during charging, and the carbon-based material becomes negatively charged. The lithium ions inserted into the carbonaceous material of the negative electrode and, conversely, the lithium ions inserted into the carbonaceous material of the negative electrode are released during discharge, and the negative ions are again adsorbed to the positive electrode. By using such a reaction mechanism, it is possible to realize a lithium ion capacitor having a high energy density by controlling the doping amount of lithium ions at the cathode. In addition, the lithium ion capacitor is a system that combines the energy storage capacity of the lithium ion battery with the output characteristics of the capacitor. The lithium ion capacitor adopts a material capable of expressing both functions at the same time. Is a future battery system that expands to the level of lithium ion batteries.

However, such a lithium ion capacitor requires a lithium doping process for the insertion and desorption reaction of lithium as well as the electrochemical adsorption and desorption reaction. In order to realize such a lithium ion capacitor, a conventional technique of doping lithium to a negative electrode is a metal laminated by the potential difference between the negative electrode and the metal lithium only by laminating metal lithium on the electrode and then adding an electrolyte to short the negative electrode and the metal lithium. Lithium is melted into the cathode. However, in the case of doping lithium through an electrical short by laminating metal lithium on the electrode, it is difficult to control the amount of lithium doped to the negative electrode, and it is difficult to secure safety due to the lithium metal generated in the doping process. Therefore, there is a problem that is difficult to apply to mass production.

Therefore, there is a need for research on the development of materials and processes for manufacturing lithium ion capacitors, which exhibit excellent output characteristics and lifetime characteristics along with higher energy density as well as excellent capacitor characteristics when used at high power, and are secured to be suitable for mass production.

The present invention is to provide a cathode active material for a lithium ion capacitor can be doped with lithium in an electrochemical manner without using metal lithium, and can further improve the capacitor capacity and energy density.

The present invention also provides a method of manufacturing the cathode active material for a lithium ion capacitor.

The present invention also provides a lithium ion capacitor including the cathode active material.

The present invention provides a cathode active material for a lithium ion capacitor including a first lithium composite metal oxide represented by Chemical Formula 1, a second lithium composite metal oxide represented by Chemical Formula 2, and a carbon-based material.

[Chemical Formula 1]

Li _a M ¹ _b O _c

(2)

Li _d M ² _e O _f

Wherein,

a, b, c, d, e, and f represent 0 <a≤6, 0 <b≤3, 0 <c≤4, 0 <d≤2, 0 <e≤3, and 0 <f≤4, respectively. Satisfied,

M ¹ is one or more selected from the group consisting of Mo, Fe, and Co,

M ² is at least one member selected from the group consisting of Mn, Ti, Ru, Ir, Pt, Sn, and Zr.

The present invention also a) a first lithium composite metal oxide precursor represented by the following formula (3) by mixing and heat-treating a transition metal compound containing at least one selected from the group consisting of a lithium compound and Mo, Fe, and Co Generating; b) reducing the first lithium composite metal oxide precursor represented by Formula 3 to produce a first lithium composite metal oxide represented by Formula 1 below; c) a second lithium composite metal represented by the following Chemical Formula 2 by mixing and thermally treating a transition metal compound containing at least one selected from the group consisting of a lithium compound and Mn, Ti, Ru, Ir, Pt, Sn, and Zr Producing an oxide; And d) mixing the first lithium composite metal oxide and the second lithium composite metal oxide with a carbonaceous material.

[Chemical Formula 1]

Li _a M ¹ _b O _c

(2)

Li _d M ² _e O _f

(3)

Li _{a '} M ^1' _{b '} O _c'

Wherein,

a, b, and c satisfy 0 <a≤6, 0 <b≤3, 0 <c≤4, respectively,

d, e, f satisfy 0 <d ≦ 2, 0 <e ≦ 3, 0 <f ≦ 4, respectively,

a ', b', and c 'satisfy 0 <a'≤6, 0 <b'≤3, and 1 <c'≤5, respectively.

M ¹ and M ^{1 '} are each one or more selected from the group consisting of Mo, Fe, and Co,

M ² is at least one member selected from the group consisting of Mn, Ti, Ru, Ir, Pt, Sn, and Zr.

The present invention also provides a lithium ion capacitor including the cathode active material.

Hereinafter, a cathode active material for a lithium ion capacitor and a method of manufacturing the same, and a lithium ion capacitor including the same according to a specific embodiment of the present invention will be described in detail. It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit and scope of the invention as defined by the appended claims.

In addition, throughout this specification, "comprising" or "containing ", unless specifically stated, refers to including any and all components (or components) Can not be interpreted as excluding.

In the present invention, the term "lithium ion capacitor" refers to the use of different asymmetric electrodes for the positive electrode and the negative electrode so that one pole uses a high capacity electrode material and the opposite pole uses a high output electrode material to improve the capacitance characteristics. The secondary battery system. Such lithium ion capacitors generally use carbon-based materials, such as graphite, hard carbon, soft carbon, etc., which have a large capacity as a negative electrode material and can insert and detach lithium ions. In addition to electrochemical adsorption and desorption reactions, lithium has a feature of improving energy density per unit weight because of the use of lithium insertion and desorption reactions at low potentials. In particular, as shown in FIG. 1, the lithium ion capacitor has a high reaction potential of 4.2V while the electric double layer capacitor and the hybrid capacitor have a reaction potential of about 3.0V, and have a high capacity characteristic (E _d ). It is characterized by expressing the energy density.

However, as described above, the lithium ion capacitor requires a lithium doping process for insertion and desorption of lithium as well as an electrochemical adsorption and desorption reaction, and a doping method of laminating an existing metal lithium on an electrode to electrically short it. It is difficult to control the amount of silver lithium doped to the negative electrode, and it is difficult to maintain safety due to lithium metal generated in the doping process.

Accordingly, the present invention adds a specific positive electrode additive as a lithium source to the carbon-based material applied as the positive electrode active material, thereby stably doping lithium to the negative electrode to significantly improve the doping efficiency and safety, suitable for mass production It is possible to obtain a process improvement effect that ensures excellent safety.

Particularly, as a result of the experiments of the present inventors, as a lithium ion capacitor is manufactured using a cathode active material including a lithium composite metal oxide having predetermined characteristics as a cathode additive, an excellent capacitor characteristic when used at high power, and excellent output with high energy density. It has been shown that it shows the characteristics and lifespan, and can replace the doping process using lithium metal, thereby ensuring excellent process safety.

Accordingly, according to one embodiment of the present invention, a cathode active material for a lithium ion capacitor including a cathode additive having predetermined characteristics is provided. The cathode active material for a lithium ion capacitor includes a specific cathode additive, that is, a first lithium composite metal oxide represented by the following Chemical Formula 1, and a second lithium composite metal oxide represented by the following Chemical Formula 2 in the carbon-based material.

[Chemical Formula 1]

Li _a M ¹ _b O _c

(2)

Li _d M ² _e O _f

Wherein,

a, b, c, d, e, and f represent 0 <a≤6, 0 <b≤3, 0 <c≤4, 0 <d≤2, 0 <e≤3, and 0 <f≤4, respectively. Satisfied,

M ¹ is one or more selected from the group consisting of Mo, Fe, and Co,

M ² is at least one member selected from the group consisting of Mn, Ti, Ru, Ir, Pt, Sn, and Zr.

The positive electrode active material for a lithium ion capacitor of the present invention uses a specific positive electrode additive (the first lithium composite metal oxide) having a large initial irreversible capacity to a carbon-based material to be used as the positive electrode active material in order to provide lithium ions to the negative electrode in an electrochemical manner. Doping improves processability and safety by replacing lithium metal in the existing lithium ion doping method, and at the same time, a specific reversible positive electrode additive (the second lithium composite metal oxide) in the operating potential region of the lithium ion capacitor It is characterized in that to further improve the capacity and energy density of the capacitor.

First, the lithium metal used as a lithium source for doping lithium to the existing negative electrode, the first lithium composite metal oxide as a positive electrode additive to be a lithium source in the present invention is represented by the formula (1). In particular, the first lithium composite metal oxide of the present invention is characterized by a large initial capacity and irreversible capacity, it is possible to effectively and efficiently do the lithium electrochemically to the negative electrode of the lithium ion capacitor.

In Formula 1 of the first lithium composite metal oxide, a, b, and c are 0 <a ≦ 6, 0 <b ≦ 3, and 0 <c ≦ 5, preferably 1 ≦ a ≦ 5, 0 <b ≦ 1, and 0 <c≤4, more preferably 1≤a≤2, 0 <b≤1, and 0 <c≤3 (or a = 2, b = 1, c = 3) Can be.

In addition, the metal component M1 forming an oxide together with lithium in the first lithium composite metal oxide may be Mo, Fe, Co, or the like. The Mo, Fe, Co and the like correspond to the transition metal, the positive electrode additive containing such a transition metal is a transition metal oxide. The Mo, Fe, Co and the like has an advantage that can more effectively induce the insertion and desorption of lithium electrochemical in crystal structure. The first lithium composite metal oxide may have a crystal structure such as Rhombohedral, Monoclinic, Orthorhombic, or the like.

In addition, the first lithium composite metal oxide has a characteristic of inserting or detaching lithium ions in a voltage range of 0V to 5V, preferably 2V to 5V, and more preferably 2.3V to 5V. In particular, the lithium composite metal oxide has a large initial irreversible capacity to supply lithium ions to the cathode in an electrochemical manner without using metal lithium.

Accordingly, the first lithium composite metal oxide has an initial charge / discharge efficiency (Q _E ) of 50% or less or 0% to 50%, preferably 40% or less or 0% to 40%, more according to Formula 1 below. Preferably 30% or less, or 0% to 30%.

[Equation 1]

Q _E = (Q _D / Q _C ) × 100

Wherein,

Q _E represents the initial charge and discharge efficiency of the first lithium composite metal oxide,

Q _D represents discharge capacity (mAh / g) at Li / Li + cut-off at a discharge voltage of 2.3 V,

Q _C represents the charge capacity (mAh / g) at Li / Li + cut-off at a charge voltage of 4.7 V.

As shown in FIG. 4, the initial charge / discharge efficiency (Q _E ) of the first lithium composite metal oxide is a constant current or constant voltage method by an electrochemical method under a half cell condition of lithium as a counter electrode, and a voltage of 2.3. Discharge capacity per unit weight of the positive electrode active material at Li / Li + cut-off at V (Q _D , mAh / g) and at the voltage 4.7 V of the positive electrode active material at Li / Li + cut-off The charging capacity per unit weight (Q _C , mAh / g) can be measured and calculated according to the above formula (1).

Here, the discharge capacity per unit weight (Q _D ) based on the total weight of the lithium composite metal oxide at Li / Li + cut-off at a voltage of 2.3 V of the first lithium composite metal oxide is 135 mAh / g or less or 0 to 135 mAh / g, preferably 110 mAh / g or less or 0 to 110 mAh / g, more preferably 85 mAh / g or less or 0 to 85 mAh / g. In addition, the charging capacity (Q _C ) per unit weight for the total weight of the first lithium composite metal oxide at a Li / Li + cut-off at a voltage of 4.7 V of the first lithium composite metal oxide is 200 mAh / g or more, Preferably 230 mAh / g or more, more preferably 250 mAh / g or more or 250 to 700 mAh / g, and in some cases 700 mAh / g or less, 500 mAh / g or less, or 300 mAh / g It may be as follows.

The initial charge / discharge efficiency (Q _E ) of the first lithium composite metal oxide and the discharge capacity (Q _D , mAh / g) at a Li / Li + cut-off at a voltage of 2.3 V and Li / at a voltage of 4.7 V In Li + cut-off, the charging capacity (Q _C , mAh / g) is preferably maintained in the range described above in terms of capacity.

In addition, as the lithium composite metal oxide, at least one selected from the group consisting of Li ₂ MoO ₃ , Li ₅ FeO ₄ , and Li ₆ CoO ₄ may be used.

Meanwhile, the cathode active material of the present invention includes a second lithium composite metal oxide represented by Chemical Formula 2 together with the first lithium composite metal oxide as a cathode additive serving as a lithium source. The second lithium composite metal oxide corresponds to a high capacity transition metal oxide having high reversibility in the operating potential region of the lithium ion capacitor, and may improve the limit of energy density per volume having a conventional lithium ion capacitor and further improve the energy density. have.

In Formula 2 of the second lithium composite metal oxide, d, e, and f are 0 <d ≦ 2, 0 <e ≦ 3, and 0 <f ≦ 4, preferably 1 ≦ d ≦ 2, 0 <e ≦ 2, and 0 <f ≦ 3, more preferably d = 2, e = 1, f = 3. That is, the second lithium composite metal oxide may be more preferably represented by the following formula (4).

[Chemical Formula 4]

Li ₂ M ² O ₃

In the formula, M ² is at least one member selected from the group consisting of Mn, Ti, Ru, Ir, Pt, Sn, and Zr.

In addition, the metal component M ² forming the oxide together with lithium in the second lithium composite metal oxide may be Mn, Ti, Ru, Ir, Pt, Sn, Zr, or the like. The Mn, Ti, Ru, Ir, Pt, Sn, Zr and the like correspond to a transition metal, the positive electrode additive containing such a transition metal is a transition metal oxide. The Mn, Ti, Ru, Ir, Pt, Sn, and Zr has the advantage of more effectively inducing the insertion and desorption of the electrochemical lithium in the operating potential region of the lithium ion capacitor in the crystal structure. The second lithium composite metal oxide may have a crystal structure such as Rhombohedral, Monoclinic, Orthorhombic, or the like.

The second lithium composite metal oxide has a property of reversibly inserting or detaching lithium ions in a voltage range of 1V to 5V, preferably 2V to 5V, and more preferably 2.5V to 5V. In particular, the second lithium composite metal oxide is characterized by high reversibility in the operating potential region of the lithium ion capacitor to improve the energy density limit per volume of the lithium ion capacitor according to the conventional lithium metal doping and further improve the energy density. Have

Accordingly, the second lithium composite metal oxide has a charge / discharge efficiency (Q _{E ′} ) of 50% or more or 50% to 100%, preferably 60% or more under a 2.3V to 4.7V potential according to Formula 2 below. More preferably 70% or more.

[Equation 2]

Q _{E '} = (Q _D' / Q _{C '} ) × 100

Wherein,

Q _{E ′} represents charge and discharge efficiency under a 2.3V to 4.7V potential of the second lithium composite metal oxide.

Q _{D '} represents discharge capacity (mAh / g) at Li / Li + cut-off at a discharge voltage of 2.3 V,

Q _{C ′} represents the charge capacity (mAh / g) at Li / Li + cut-off at a charge voltage of 4.7V.

As shown in FIG. 4, the charge / discharge efficiency (Q _{E ′} ) under the 2.3 V to 4.7 V potential of the second lithium composite metal oxide is a constant current by an electrochemical method under a half cell condition with lithium as a counter electrode. Or in a constant voltage manner, the discharge capacity per unit weight of the positive electrode active material (Q _{D ′} , mAh / g) when the Li / Li + cut-off is performed at a voltage of 2.3 V and the Li / Li + cut-off at a voltage of 4.7 V ( During cut-off, the charge capacity per unit weight of the positive electrode active material (Q _{C ′} , mAh / g) may be measured and calculated according to Formula 2.

Here, the discharge capacity per unit weight (Q _{D '} ) relative to the total weight of the lithium composite metal oxide at Li / Li + cut-off at a voltage of 2.3 V of the lithium composite metal oxide is 100 mAh / g or more or 100 to 300 mAh / g, preferably 130 mAh / g or more, more preferably 150 mAh / g or more. Further, the charge capacity per unit weight (Q _{C ′} ) relative to the total weight of the lithium composite metal oxide at Li / Li + cut-off at a voltage of 4.7 V of the lithium composite metal oxide is preferably 150 mAh / g or more, preferably 170 mAh / g or more, more preferably 200 or more mAh / g or 200 to 300 mAh / g, and in some cases may be less than 200 mAh / g.

Charge and discharge efficiency (Q _{E ′} ) and discharge capacity (Q _{D ′} , mAh / g) at Li / Li + cut-off at 2.3 V under the 2.3 V to 4.7 V potential of the lithium composite metal oxide; In Li / Li + cut-off at a voltage of 4.7 V, the charging capacity (Q _{C ′} , mAh / g) is preferably maintained in the range described above in terms of capacity.

In addition, the lithium composite metal oxide may be selected from the group consisting of Li ₂ MnO ₃ , Li ₂ TiO ₃ , Li ₂ RuO ₃ , Li ₂ IrO ₃ , Li ₂ PtO ₃ , Li ₂ SnO ₃ , and Li ₂ ZrO ₃ . More than one species can be used.

As described above, the positive electrode active material for a lithium ion capacitor of the present invention uses a specific first lithium composite metal oxide and a second lithium composite metal oxide as a positive electrode additive to a carbon-based material applied as the positive electrode active material, thereby forming a lithium ion capacitor. The energy density per volume can be improved and the safety of the doping process can be achieved simultaneously.

That is, as shown in FIG. 2, the conventional lithium ion capacitor laminates lithium metal on an electrode to form a lithium source for transferring lithium ions to the cathode through an electrical short circuit. However, the lithium ion capacitor of the present invention, as shown in Figure 3, by adding a specific positive electrode additive, such as Li ₂ MoO ₃ and Li ₂ RuO ₃ to the positive electrode active material to use as a lithium source, a separate lithium metal laminate It is characterized in that it can effectively transfer lithium ions to the cathode without forming a layer and improve the capacity and energy density of the capacitor.

On the other hand, the carbon-based material used as the positive electrode active material for lithium ion capacitor of the present invention refers to activated carbon having a large specific surface area, the specific surface area of 500 m ² / g or more, preferably 700 m ² / g or more, more preferably It may be more than 1,000 m ² / g or 1,000 to 3,000 m ² / g, in some cases may be less than 2,500 m ² / g, 2,000 m ² / g or less. The carbon-based material may be used at least one of activated carbon, activated carbon and metal oxide composite, activated carbon and conductive polymer composite, and among these, activated carbon is preferable for the conductive aspect.

The positive electrode active material for a lithium ion capacitor according to the present invention has a composition in which a positive electrode additive, that is, the lithium composite metal oxide is mixed together as a lithium source of a negative electrode material to a carbon-based material. In particular, the cathode active material for a lithium ion capacitor according to the present invention may include 0.5 to 49.5 wt% of the first lithium composite metal oxide, 0.5 to 49.5 wt% of the second lithium composite metal oxide, and 50 to 99 wt% of the carbonaceous material. Can be. Preferably, 1 to 34% by weight of the first lithium composite metal oxide, 1 to 34% by weight of the second lithium composite metal oxide, and 65 to 98% by weight of the carbonaceous material, and more preferably, the first 1.5 to 18.5 wt% of the lithium composite metal oxide, 1.5 to 18.5 wt% of the second lithium composite metal oxide, and 80 to 97 wt% of the carbonaceous material. Here, the first lithium composite metal oxide, the second lithium composite metal oxide, and the carbon-based material are 0.5 wt% or more, 0.5 wt% or more, and 99 wt% or less, respectively, so as to effectively dope lithium to the negative electrode. It may be included, and in terms of ensuring excellent conductivity may be included in each of 49.5% by weight or less, 49.5% by weight or less, and 50% by weight or more.

The weight ratio of the two positive electrode additives, that is, the weight ratio of the first lithium composite metal oxide to the second lithium composite metal oxide is 90:10 to 10:90, preferably 80:20 to 20:80, more preferably. May be from 70:30 to 30:70. The first lithium composite metal oxide and the second lithium composite metal oxide may be used in a weight ratio of 90:10 or more in terms of improving negative electrode doping capacity, and may be used in a weight ratio of 10:90 or less in terms of improving energy density.

On the other hand, the first lithium composite metal oxide and the second lithium composite metal oxide may be uniformly mixed throughout the carbon-based material or locally mixed only in part depending on the amount added to the carbon-based material.

The weight ratio of the total weight of the first lithium composite metal oxide and the second lithium composite metal oxide to the carbonaceous material is 10:90 to 90:10, preferably 15:85 to 85:15, and more preferably 20:80 to 80:20. The weight ratio of the carbon-based material to the total weight of the first lithium composite metal oxide and the second lithium composite metal oxide may be 10:90 or more in terms of energy density improvement, and 90:10 or less in terms of power density improvement. .

As described above, the positive electrode additive according to the present invention, that is, the first lithium composite metal oxide of Formula 1 and the second lithium composite metal oxide of Formula 2 may be electrochemically doped with lithium to the carbon-based negative electrode active material. In addition, the doped lithium ions contribute to the capacitor characteristics, thereby lowering the cell voltage, thereby significantly improving the capacity and energy density of the lithium ion capacitor.

On the other hand, according to another embodiment of the present invention, a method of manufacturing a cathode active material for the lithium ion capacitor is provided. The method of manufacturing a cathode active material for a lithium ion capacitor includes a) a first compound represented by the following Chemical Formula 3 by mixing and heat-treating a transition metal compound containing at least one selected from the group consisting of a lithium compound and Mo, Fe, and Co. Generating a lithium composite metal oxide precursor; b) reducing the first lithium composite metal oxide precursor represented by Formula 3 to produce a first lithium composite metal oxide represented by Formula 1 below; c) a second lithium composite metal represented by the following Chemical Formula 2 by mixing and thermally treating a transition metal compound containing at least one selected from the group consisting of a lithium compound and Mn, Ti, Ru, Ir, Pt, Sn, and Zr Producing an oxide; And d) mixing the first lithium composite metal oxide and the second lithium composite metal oxide with a carbonaceous material.

[Chemical Formula 1]

Li _a M ¹ _b O _c

(2)

Li _d M ² _e O _f

(3)

Li _{a '} M ^1' _{b '} O _c'

Wherein,

a, b, c are 0 <a≤6, 0 <b≤3, 0 <c≤5, respectively, preferably 0≤a≤5, 0 <b≤2, and 0 <c≤5, more preferably Preferably 0 ≦ a ≦ 5, 0 <b ≦ 1, and 0 <c ≦ 4.

In addition, in Formula 2, d, e, and f satisfy 0 <d ≦ 2, 0 <e ≦ 3, and 0 <f ≦ 4, respectively, preferably 1 <d ≦ 2, 0 <e ≦ 2, 0 <f≤3, more preferably d = 2, e = 1, f = 3. In Formula 3, a ', b', and c 'are respectively 0 <a'≤6, 0 <b'≤3, 1 <c'≤5, preferably 0≤a'≤5, 0 <b' 2, 0 <c '≦ 4, more preferably 0 ≦ a' ≦ 5, 0 <b '≦ 1, 0 <c' ≦ 4.

Wherein M ¹ and M ^{1 ′} are each one or more selected from the group consisting of Mo, Fe, and Co, and M ² is selected from the group consisting of Mn, Ti, Ru, Ir, Pt, Sn, and Zr 1 or more types.

In the method of manufacturing a cathode active material for a lithium ion capacitor according to the present invention, a first lithium composite metal oxide and a precursor thereof, a second lithium composite metal oxide, and a carbon-based material as a cathode active material are described above with reference to the cathode active material for a lithium ion capacitor. As applicable.

In step a), the first lithium composite metal oxide precursor of Chemical Formula 3 is a lithium compound such as Li ₂ CO ₃ , LiOH, Li, MoO ₃ , MoO ₂ , (NH ₄ ) ₆ Mo ₇ O ₂₄ 4H ₂ 0, The transition metal compounds such as MoS ₂ , Mo, FeO, Fe ₂ O ₃ , Fe ₃ O ₄ , Fe, CoO, Co, etc. may be mixed to prepare a heat treatment process. At this time, the lithium compound and Mo, Fe, Co itself and the transition metal compound containing the same, the exponential value a, b, c, a ', b', c ' Can be mixed in a molar ratio taking into account, for example, 2: 1 to 7: 1, preferably, 2: 1 to 5: 1, more preferably, 2: 1 to 4: 1. . In addition, the heat treatment process after mixing the lithium compound and the composite metal compound may be carried out at 400 to 1,000 ℃, preferably 500 to 900 ℃, more preferably 500 to 800 ℃, and also, the composite with the lithium compound The heat treatment process for the metal compound may be carried out for 0.5 to 20 hours, preferably 1 to 15 hours, more preferably 2 to 10 hours. The heat treatment process for the lithium compound and the composite metal compound may be performed in an oxygen or air atmosphere.

The step of reducing the first lithium composite metal oxide precursor of Formula 3 in step b) may be performed by heat treatment at 500 to 1,000 ℃, preferably 700 to 900 ℃, more preferably 700 to 800 ℃. In addition, the heat treatment process may be performed for 2 to 50 hours, preferably 5 to 30 hours, more preferably 10 to 20 hours. By maintaining the temperature and time of the heat treatment process, it is possible to effectively convert the first lithium composite metal oxide precursor of Formula 3 to the first lithium composite metal oxide of Formula 1.

In addition, the reducing process of the first lithium composite metal oxide precursor may be performed in an inert atmosphere such as argon (Ar) gas or nitrogen (N ₂ ). In addition, the inert gas part may further include hydrogen (H ₂ ), etc., and is preferably performed under the condition that 5% or less of H ₂ is included in view of improving overall process efficiency.

Through this reduction process, the first lithium composite metal oxide of Chemical Formula 1 having the characteristics as described above may be generated.

In step c), the second lithium composite metal oxide having Formula 2 may be a lithium compound such as Li ₂ CO ₃ , LiOH, Li, and the like, and MnO, Mn, TiO ₂ , Ti, RuO ₂ , Ru, IrCl ₃ , IrO ₂ , Transition metal compounds such as PtCl ₄ , PtCl ₂ , PtO ₂ , Pt (C ₅ H ₇ O ₂ ) ₂ , Pt / C, SnO ₂ , Sn, ZrO ₂ , Zr may be mixed and prepared by a heat treatment process. At this time, the lithium compound and Mn, Ti, Ru, Ir, Pt, Sn, and Zr itself and the transition metal compound containing the same, the molar ratio in consideration of the index values d, e, f, etc. in the second lithium composite metal oxide to be finally produced Can be mixed, for example, in a molar ratio of 2: 1 to 3: 1, preferably 2: 1 to 2.5: 1, more preferably 2: 1 to 2.3: 1.

In addition, the heat treatment process after mixing the lithium compound and the composite metal compound may be carried out at 500 to 1,000 ℃, preferably 700 to 900 ℃, more preferably 700 to 800 ℃, the heat treatment process is 2 For 50 hours, preferably 5 to 30 hours, more preferably 10 to 20 hours. The heat treatment process for the lithium compound and the composite metal compound may be performed in an oxygen or air atmosphere. By maintaining the heat treatment process temperature and time, it is possible to effectively produce the second lithium composite metal oxide of the formula (2).

In the method of manufacturing a cathode active material for a lithium ion capacitor according to the present invention, step d) of mixing the first lithium composite metal oxide and the second lithium composite metal oxide with a carbonaceous material may be performed by various physical mixing methods. . In this case, the carbon-based material as the first lithium composite metal oxide, the second lithium composite metal oxide, and the positive electrode active material may be mixed at 0.5 to 49.5 wt%, 0.5 to 49.5 wt%, and 50 to 99 wt%, respectively. In addition, it may be preferably mixed with 1 to 34% by weight of the first lithium composite metal oxide, 1 to 34% by weight of the second lithium composite metal oxide, and 65 to 98% by weight of the carbonaceous material. More preferably, 1.5 to 18.5 wt% of the first lithium composite metal oxide, 1.5 to 18.5 wt% of the second lithium composite metal oxide, and 80 to 97 wt% of the carbonaceous material may be mixed.

On the other hand, according to another embodiment of the present invention, a lithium ion capacitor including the cathode active material for the lithium ion capacitor is provided. The lithium ion capacitor forms a separate lithium metal layer by using a specific first lithium composite metal oxide having a large initial irreversible capacity and a second lithium composite metal oxide having a high reversibility as an anode additive in an operating potential region of the lithium ion capacitor. It is characterized in that it can effectively transfer lithium ions to the negative electrode without having to. As a result, the lithium ion capacitor according to the present invention can improve the process safety due to the generation of lithium metal by doping lithium ions to the cathode in an electrochemical manner, and at the same time, it is possible to secure an effect of further improving the capacity and energy density of the capacitor. have.

In particular, the lithium ion capacitor of the present invention includes a cathode including a cathode active material; An anode including a negative electrode active material; And a separator between the positive electrode and the negative electrode, wherein the negative electrode may be supplied with lithium ions only from the positive electrode.

At this time, "receiving only lithium ions from the positive electrode" is, as shown in Figure 3, a separate lithium ion supply layer for supplying lithium ions to the negative electrode, for example, included in the negative electrode or on the negative electrode A separate lithium metal layer stacked (coated or laminated) is not included in the capacitor, and the negative electrode may mean that only lithium ions derived from the lithium composite metal oxide included in the positive electrode active material are supplied.

The lithium ion capacitor of the present invention may include a carbon-based negative electrode active material reversibly inserting or detaching lithium ions in the voltage range of 0V to 5V.

According to the present invention, a lithium ion capacitor including a cathode active material including the first lithium composite metal oxide and the second lithium composite metal oxide and a carbon-based anode active material that reversibly inserts or desorbs lithium ions is formed, thereby forming lithium on the negative electrode. Characterized in that to effectively doping. However, when the first lithium composite metal oxide or the like according to the present invention is applied as a positive electrode additive to a hybrid capacitor using a conventional activated carbon negative electrode which is not a negative electrode active material of a lithium ion capacitor (positive electrode: activated carbon + Li ₂ MoO ₃ , negative electrode: Activated carbon), due to the large initial irreversible nature of the positive electrode additive itself may cause a problem that the capacity and life performance of the capacitor is significantly reduced. In addition, when the second lithium composite metal oxide or the like according to the present invention is applied as a positive electrode additive to the hybrid capacitor or the like (anode: activated carbon + Li ₂ RuO ₃ , negative electrode: activated carbon), the reversible lithium ion (Li + ), Due to the insertion and desorption properties, the effect of improving energy density may occur.

Meanwhile, the lithium ion capacitor according to the present invention has a charge / discharge capacity measured by an electrochemical method of 50 F / g or more, preferably 70 F / g or more, more preferably 100 F / g or more or 100 to 800 F /. It may exhibit excellent performance of g, and in some cases, may represent 750 F / g or less and 700 F / g or less.

As described above, the lithium ion capacitor according to the present invention uses a lithium composite metal oxide having a large initial irreversible capacity in a positive electrode active material to electrochemically dope lithium into a negative electrode, thereby providing a lithium metal electrode or a lithium metal as a separate lithium source. It can be prepared without using.

Hereinafter, a specific example of a cathode active material for a lithium ion capacitor and a method of manufacturing a lithium ion capacitor using the same according to the present invention will be described in detail.

And a method of manufacturing the positive electrode active material for a lithium ion capacitor according to the invention the second step of synthesizing a first step, and a ready-Li ₂ MoO Li ₂ MoO ₃ was treated reducing the ₄ precursor to prepare a Li ₂ MoO ₄ precursor, Li _And a fourth step of synthesizing ₂ RuO ₃ and a fourth step of mixing a Li ₂ MoO ₃ and a carbon-based material to form a cathode active material.

First, a first step of preparing a Li ₂ MoO ₄ precursor is more specifically, a first step of mixing Li ₂ CO ₃ and MoO ₃ in a 1: 1 molar ratio, and a mixture of Li ₂ CO ₃ and MoO ₃ Heat treatment at 400 to 1000 ° C. for 1 to 6 hours in air to form a Li ₂ MoO ₄ precursor. In this case, step 1-2 may be performed in the air.

Next, the second step is a 2-1 step of uniformly mixing 10 wt% or less of Super-P in Li ₂ MoO ₄ through mechanical milling, and 10% or less of a mixture of Li ₂ MoO ₄ and Super-P. The _second step of synthesizing Li ₂ MoO ₃ by heat treatment at 500 ~ 1000 ℃ 10 to 30 hours in an Ar atmosphere containing H ₂ gas of. At this time, the mixing step according to the mechanical milling in the step 2-1 may proceed for about 30 minutes. As the mechanical milling means, for example, a mortar, a ball mill, a vibration mill, a satellite ball mill, a tube mill, a rod mill, a jet mill, a hammer mill, or the like can be used. In addition, the reducing atmosphere according to step 2-2 may be performed under an Ar ₂ atmosphere containing 5-10% of H ₂ gas.

Further, the third step of synthesizing Li ₂ RuO ₃ is more specifically, the 3-1 step of mixing Li ₂ CO ₃ and RuO ₂ in a 1: 1 molar ratio, and a mixture of Li ₂ CO ₃ and RuO ₂ And heat treating at 500 to 1000 ° C. for 10 to 30 hours in air to synthesize Li ₂ RuO ₃ . In this case, step 3-2 may be performed in air.

In the fourth step, Li ₂ MoO ₃ and Li ₂ RuO ₃ synthesized in the second and third steps are mixed with a carbon-based material to form a cathode active material for a lithium ion capacitor. In this case, the cathode active material for a lithium ion capacitor may be formed by mixing 3 to 50 wt% of Li ₂ MoO ₃ , 3 to 30 wt% of Li ₂ RuO ₃ , and 60 to 94 wt% of the carbonaceous material. Preferably to mix with Li ₂ MoO _{3 3} ~ 30% by _{weight, Li 2 RuO 3 3 ~ 10} % by weight, 60-94% by weight of the carbon-based material. The electrochemical lithium doping may be performed in a voltage range of 5V or less.

In order to evaluate the lithium doping characteristics and capacity characteristics of the positive electrode active material for a lithium ion capacitor using the positive electrode additive according to the present invention, a lithium ion capacitor was manufactured as follows.

At this time, as described above, 92 wt% of the positive electrode active material and binder PVdF prepared according to a specific example of the present invention was 8 wt%, and a slurry was prepared using NMP as a solvent. The slurry was applied to an aluminum mesh having a thickness of 20 µm (Al mesh), dried, compacted in a press, and dried for 16 hours at 120 ° C. in a vacuum to prepare an electrode with a disc having a diameter of 12 mm. As the counter electrode, a lithium metal foil punched to a diameter of 12 mm was used, and a PP film was used as the separator. As the electrolyte solution, a mixture solution of 3: 7 of 1M LiPF ₆ EC / DMC was used. After the electrolyte was impregnated into the separator, the separator was sandwiched between the working electrode and the counter electrode, and a case of a stainless steel (SUS) product was manufactured as a test cell for electrode evaluation, that is, a non-aqueous lithium ion capacitor half cell.

Here, when applied as a full cell, as the negative electrode active material, crystalline or amorphous carbon such as artificial graphite, natural graphite, graphitized carbon fiber, graphitized mesocarbon microbead, petroleum coke, resinous plastic, carbon fiber, pyrolytic carbon, etc. At least one of the materials may be used.

The positive electrode additive reversibly inserts or detaches lithium ions in a voltage range of 5 V or less, and is applicable to a lithium ion capacitor to which a non-aqueous electrolyte is driven in a voltage range of 5 V or less.

On the other hand, the production of the positive electrode plate is l kind commonly used in the powder of the positive electrode active material containing the positive electrode additive according to the present invention, if necessary, conductive agent, binder, thickener, filler, dispersant, ion conductive agent, pressure enhancer, etc. Or 2 or more types of addition components are added, and it slurry-pastes with suitable solvents, such as water and an organic solvent. The slurry or paste thus obtained is coated and dried on an electrode support substrate using a doctor blade method or the like, and then pressed using a rolling roll or the like is used as the positive electrode plate.

The binder may be, for example, a rubber binder such as styrene butadiene rubber (SBR), a fluorine resin such as polyethylene tetrafluoride, polyvinylidene fluoride (PVdF, polyvinylidene fluoride), polypropylene, polyethylene, or the like. Thermoplastic resin, acrylic resin, etc. can be used. The amount of the binder may vary depending on the electrical conductivity of the cathode active material, the electrode shape, etc., but may be used in an amount of 2 to 40 parts by weight based on 100 parts by weight of the cathode active material.

If necessary, examples of the conductive agent include graphite, carbon black, acetylene black, Ketjen Black, carbon fiber, and metal powder. The amount of the conductive material used varies depending on the electrical conductivity, the electrode shape, and the like of the positive electrode active material, but may be used in an amount of 2 to 40 parts by weight based on 100 parts by weight of the positive electrode active material.

In addition, carboxymethyl cellulose (CMC) may be used as the thickener.

At this time, the electrode support substrate (also referred to as 'current collector') may be made of foil, sheet, mesh or carbon fiber such as copper, nickel, stainless steel, aluminum, or the like.

A lithium ion capacitor is manufactured using the anode prepared as described above. The form of the lithium ion capacitor may be any one of a coin, a button, a sheet, a pouch, a cylinder, a square, and the like. The negative electrode, electrolyte, separator, etc. of the lithium ion capacitor may be selected and used within a range known to be applicable to a conventional lithium secondary battery.

The electrolytic solution may be a non-aqueous liquid electrolyte in which a lithium salt is dissolved in an organic solvent, an inorganic solid electrolyte, a composite material of an inorganic solid electrolyte, and the like, but is not limited thereto.

As the solvent of the non-aqueous liquid electrolyte, a carbonate, an ester, an ether or a ketone can be used. Examples of the carbonate include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC) Propylene carbonate (PC), butylene carbonate (BC), and the like can be used. Examples of esters include butyrolactone (BL), decanolide, valerolactone, mevalonolactone, caprolactone, n-methyl acetate, n-ethyl acetate, n- Propyl acetate and the like can be used. As the ether, dibutyl ether and the like can be used. As the ketone, polymethyl vinyl ketone can be used. The non-aqueous liquid electrolyte according to the present invention is not limited to the kind of the non-aqueous organic solvent.

Examples of the lithium salt of the non-aqueous electrolyte solution include LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiClO ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiAlO ₄ At least one selected from the group consisting of LiAlCl ₄ , LiN (C _x F _{2x +1} SO ₂ ) (C _y F _{2x +1} SO ₂ ), wherein x and y are natural numbers, and LiSO ₃ CF ₃ or Mixtures thereof.

As the separator, a porous film made from polyolefin such as polypropylene (PP) or polyethylene (PE), or a porous material such as nonwoven fabric can be used.

In the present invention, matters other than those described above can be added or subtracted as required, and therefore, the present invention is not particularly limited thereto.

According to the present invention, an electrochemical method is performed by adding a positive electrode additive having a large initial irreversible capacity as a lithium source to a carbon-based material for a positive electrode active material of a lithium ion capacitor and a high reversible positive electrode additive to improve energy density in an operating potential region of the lithium ion capacitor. By doping lithium to the carbon-based negative electrode active material, it is possible to ensure improved charge and discharge capacity of the lithium ion capacitor.

In addition, the doping of lithium using the positive electrode additive according to the present invention has the effect of lowering the potential of the negative electrode to improve the energy density of the lithium ion capacitor, and due to the simple lithium doping process will significantly improve the production efficiency of the lithium ion capacitor. It can be effective.

1 is a schematic diagram showing general charge and discharge characteristics of an electric double layer capacitor (EDLC), a hybrid capacitor, and a lithium ion capacitor (LIC).
2 is a schematic diagram showing a general structure of a conventional lithium ion capacitor (LIC).
3 is a schematic diagram showing the structure of a lithium ion capacitor (LIC) according to the present invention.
Figure 4 is a reference graph for the initial charge and discharge efficiency of the positive electrode additive according to the present invention.
5 is an XRD analysis graph of the positive electrode additives Li ₂ MoO ₃ and Li ₂ RuO ₃ synthesized according to Example 1 of the present invention.
6 is a FESEM and HRTEM photograph of the cathode additives Li ₂ MoO ₃ and Li ₂ RuO ₃ synthesized according to Example 1 of the present invention [a) Li ₂ MoO ₃ , b) Li ₂ RuO ₃ , c) Li ₂ MoO ₃ , d) Li ₂ RuO ₃ , e) Li ₂ MoO ₃ , f) Li ₂ RuO ₃ ].
7 is a graph showing the capacity evaluation results of the lithium ion capacitor according to Examples 1 to 2 and Comparative Examples 1 to 2 of the present invention.
FIG. 8 is a graph illustrating 1,000 cycle life evaluation results of lithium ion capacitors according to Examples 1 and 2 and Comparative Examples 1 and 2 of the present invention.

Hereinafter, the present invention will be described in more detail with reference to the following examples. However, the scope of the present invention is not limited to the following examples.

Example  One

A high-performance cathode active material for a lithium ion capacitor including Li ₂ MoO ₃ and Li ₂ RuO ₃ as an additive for improving energy density was prepared as a lithium source for lithium doping to a cathode of a lithium ion capacitor.

Single phase Li ₂ MoO ₃ and Li ₂ RuO ₃ were synthesized as follows.

First, Li ₂ CO ₃ and MoO ₃ are mixed in a molar ratio of 1: 1, and then the mixture of Li ₂ CO ₃ and MoO ₃ is heat-treated at 600 ° C. for 5 hours in air to form a lithium composite metal oxide precursor Li ₂ MoO ₄ . Synthesized. After mixing 7 parts by weight of Super-P uniformly by mechanical milling with respect to 100 parts by weight of Li ₂ MoO ₄ synthesized as described above, the mixture of Li ₂ MoO ₄ and Super-P was heat-treated at 700 ° C. for 10 hours in an N ₂ atmosphere. A first lithium composite metal oxide Li ₂ MoO ₃ was synthesized.

In addition, after mixing Li ₂ CO ₃ and RuO ₂ in a molar ratio of 1: 1, the mixture of Li ₂ CO ₃ and RuO ₂ was heat-treated at 900 ° C. for 12 hours in air to form a second lithium composite metal oxide precursor Li ₂ RuO ₃ was synthesized.

24.2 wt% of the first lithium composite metal oxide Li ₂ MoO ₃ thus synthesized and 5 wt% of the second lithium composite metal oxide precursor Li ₂ RuO ₃ were mixed with 62.8 wt% of activated carbon having a specific surface area of 1,200 m ² / g to obtain a lithium ion capacitor. A cathode active material for was prepared. At this time, the activated carbon was used having an average particle size of 15 ㎛.

On the other hand, for the first lithium composite metal oxide Li ₂ MoO ₃ and the second lithium composite metal oxide Li ₂ RuO ₃ synthesized by the method as described above, through X-ray diffraction (XRD) analysis as shown in FIG. It was confirmed that it had a crystal structure of Rhombohedral. In addition, the microstructure and shape of the first lithium composite metal oxide Li ₂ MoO ₃ and the second lithium composite metal oxide Li ₂ RuO ₃ were confirmed through FESEM and HRTEM photographs as shown in FIG. 6.

In addition, with respect to the first lithium composite metal oxide Li ₂ MoO ₃ , a half cell made of lithium metal as a counter electrode was fabricated, and the discharge capacity per weight (Q _D ) and the charge capacity per weight (Q _C ) were measured by an electrochemical method. The initial charge and discharge efficiency (Q _E ) was calculated according to the following equation 1.

[Equation 1]

Q _E = (Q _D / Q _C ) × 100

Wherein,

Q _E is the initial charge and discharge efficiency of the lithium composite metal oxide, Q _D is the charge capacity per unit weight of the positive electrode active material (mAh / g) at Li / Li + cut-off at a discharge voltage of 2.3 V Q _C is the charge capacity per unit weight of the positive electrode active material (mAh / g) at the Li / Li + cut-off at a charge voltage of 4.7 V.

At this time, the initial charge and discharge efficiency (Q _E ) of the prepared first lithium composite metal oxide Li ₂ MoO ₃ was 43%, and it was confirmed that the initial irreversible capacity had a large characteristic.

In addition, with respect to the second lithium composite metal oxide Li ₂ RuO ₃ , a half cell made of lithium metal as a counter electrode was fabricated, and an electrochemical method showed a discharge capacity per weight (Q _D ) and a charge capacity per weight (Q _C ). The charge and discharge efficiency (Q _{E '} ) was calculated under the electric potential of 2.3V to 4.7V according to the following equation (2).

[Equation 2]

Q _{E '} = (Q _D' / Q _{C '} ) × 100

Wherein,

Q _{E '} is the charge / discharge efficiency under the 2.3 V to 4.7 V potential of the second lithium composite metal oxide, and Q _D' is the discharge capacity at the Li / Li + cut-off at the discharge voltage of 2.3 V (mAh). / g), Q _{C '} represents the charge capacity (mAh / g) at Li / Li + cut-off at the charge voltage 4.7V.

At this time, the charging and discharging efficiency (Q _{E '} ) is 70% or more under the 2.3V to 4.7V potential of the manufactured second lithium composite metal oxide Li ₂ RuO ₃ , and has a high reversibility in the operating potential region of the lithium ion capacitor. It confirmed that it has.

Example  2

Lithium ions in the same manner as in Example 1, except that 22.8% by weight of the first lithium composite metal oxide Li ₂ MoO ₃ , 10% by weight of the second lithium composite metal oxide Li ₂ RuO _3, and 59.2% by weight of activated carbon were mixed. A cathode active material for a capacitor was prepared.

Comparative Example  One

A positive electrode for a lithium ion capacitor containing 92% by weight of activated carbon so that a lithium ion capacitor may be manufactured by performing a 60% doping of a cathode capacity in a constant voltage (CV) mode using lithium metal in a conventional manner. An active material was prepared.

Comparative Example  2

Lithium ion in the same manner as in Example 1, except that 25.6% by weight of the first lithium composite metal oxide Li ₂ MoO ₃ and 64.4% by weight of activated carbon were mixed without using the second lithium composite metal oxide Li ₂ RuO ₃ . A cathode active material for a capacitor was prepared.

The compositions of the positive electrode active materials according to Examples 1 and 2 and Comparative Examples 1 and 2 are as shown in Table 1 below.

division Lithium doping source Activated carbon (mg) Li ₂ MoO ₃ (mg) Li ₂ RuO ₃ (mg) Example 1 Li ₂ MoO ₃ 5.085 2.238 0.462 Example 2 Li ₂ MoO ₃ 5.085 2.238 0.981 Comparative Example 1 Li ₂ MoO ₃ 5.085 2.238 - Comparative Example 2 Lithium metal 5.085 - -

Test Example

According to Examples 1 and 2 and Comparative Examples 1 and 2, after manufacturing a half cell lithium ion capacitor using the positive electrode active material in the following manner, battery performance evaluation thereof was performed.

a) lithium ion capacitor manufacturing

First, a slurry was prepared using N-methylpyrrolidone (NMP) as a solvent using 92 wt% of the positive electrode active material and 8 wt% of the binder PVdF according to Examples 1 and 2 and Comparative Examples 1 and 2. The slurry was applied to an aluminum mesh having a thickness of 20 μm, dried and compacted by a press, dried for 16 hours at 120 ° C. in a vacuum to prepare an electrode from a disc of 12 mm in diameter. At this time, the positive electrode plate was produced by coating 92% by weight of the active material (activated carbon + Li ₂ MoO ₃ + Li ₂ RuO ₃ ) NMP solution containing 8% by weight PVDF binder and slurry after coating on an aluminum mesh, hard carbon 80wt % And 10 wt% of a conductive material (super-P) were prepared by coating a Cu mesh after preparing an NMP solution and a slurry including 10 wt% of a PVDF binder.

As the anode, a lithium metal foil punched to a diameter of 12 mm was used, and a polyethylene (PE) film was used as the separator. At this time, the mixed solution which mix | blended ethylene glycol / dimethyl chloride (EC / DMC) of 1M LiPF ₆ at 3: 7 was used as electrolyte solution.

After the electrolyte was impregnated into the separator, the separator was sandwiched between the cathode and the anode, and a case of a stainless steel product was manufactured as a test cell for electrode evaluation, that is, a non-aqueous lithium ion capacitor half cell. It was.

b) capacity assessment of lithium ion capacitors

In Comparative Example 1, lithium metal was doped at 60% of the cathode capacity in CV (constant voltage) mode, and Comparative Examples 2 and 1 and 2 were electrochemically 4.7 V vs. Lithium was doped to the cathode via charging at a constant current of 0.1 C up to Li / Li +. The amount of Li ₂ MoO ₃ shown in Table 1 was fixed in an amount capable of doping the negative electrode to the negative electrode capacity 60% in accordance with Comparative Example 1.

c) life assessment of lithium ion capacitors

As described above, the half-cell lithium ion capacitor manufactured by using the cathode active materials according to Examples 1 and 2 and Comparative Examples 1 and 2, and a constant current of 10 C is applied in a potential region of 1.5 V to 3.9 V for 1000 cycles. Charging and discharging were carried out to evaluate the life of the lithium ion capacitor.

In addition, the capacity evaluation and the life evaluation results of the lithium ion capacitors using the cathode active materials according to Examples 1 and 2 and Comparative Examples 1 and 2 are shown in Table 2 below.

division Capacity evaluation result Life Evaluation Result (1,000 cycles) Charge capacity (mF) Discharge capacity (mF) Charge capacity (mF) Discharge capacity (mF) Example 1 701 652 402 402 Example 2 736 697 414 413 Comparative Example 1 399 386 261 261 Comparative Example 2 611 562 362 362

In addition, graphs of capacity evaluation and 1,000 cycle life of the lithium ion capacitor using the cathode active materials according to Examples 1 and 2 and Comparative Examples 1 and 2 are shown in FIGS. 7 and 8, respectively. Here, FIG. 7 compares the charge and discharge curves of the third cycle after lithium doping after the charge and discharge curves, and it was confirmed that Examples 1 to 2 of Li-ion capacitors including Li ₂ RuO ₃ additionally exhibited improved capacity. In addition, as shown in FIG. 8, it was confirmed that the lithium ion capacitors of Examples 1 to 2 additionally including Li ₂ RuO ₃ maintain high capacity without deterioration of life, and the higher the amount of Li ₂ RuO ₃ , the higher the capacity. It was confirmed that the expression.

Meanwhile, as shown in Table 2, according to the present invention, the first lithium composite metal oxide having a large initial irreversible capacity and the second lithium composite metal oxide having high reversibility in the operating potential region of the lithium ion capacitor are used together. It can be seen that the lithium ion capacitor of 2 has a discharge capacity of 652 mF to 697 mF and a discharge capacity of 402 mF to 413 mF after 1,000 cycles. On the other hand, the lithium ion capacitor of Comparative Example 1 has a discharge capacity of 386 mF, and after 1,000 cycles, it can be seen that the discharge capacity remarkably drops to 261 mF. In addition, the lithium ion capacitor of Comparative Example 2 has a discharge capacity of 562 mF and a discharge capacity of 362 mF after 1,000 cycles, which is superior to that of Comparative Example 1, but is significantly lower than Examples 1 to 2.

Thus, Li ₂ MoO ₃ according to the present invention And Li ₂ RuO ₃ Lithium could be electrochemically doped to the negative electrode carbon-based material using the anode additive of transition metal oxide, and the doped lithium ions contributed to the capacitor characteristics, thereby ensuring improved electrochemical characteristics of the lithium ion capacitor and significantly increasing energy density. It can be seen that it is effective in further increasing.

Claims (21)

Initial charge and discharge efficiency (Q _E ) according to the following formula 1 is 50% or less, the first lithium composite metal oxide represented by the formula (1),
A second lithium composite metal oxide having a charge and discharge efficiency (Q _{E ′} ) of 50% or more under a 2.3V to 4.7V potential according to Formula 2, represented by Formula 2 below, and
A cathode active material for a lithium ion capacitor including a carbonaceous material:
[Chemical Formula 1]
Li _a M ¹ _b O _c
(2)
Li _d M ² _e O _f
Wherein,
a, b, c, d, e, and f represent 0 <a≤6, 0 <b≤3, 0 <c≤4, 0 <d≤2, 0 <e≤3, and 0 <f≤4, respectively. Satisfied,
M ¹ is one or more selected from the group consisting of Mo, Fe, and Co,
M ² is one or more selected from the group consisting of Mn, Ti, Ru, Ir, Pt, Sn, and Zr,
[Equation 1]
Q _E = (Q _D / Q _C ) × 100
Wherein,
Q _E represents the initial charge and discharge efficiency of the first lithium composite metal oxide,
Q _D represents discharge capacity (mAh / g) at Li / Li + cut-off at a discharge voltage of 2.3 V,
Q _C is the charge capacity (mAh / g) at Li / Li + cut-off at a charge voltage of 4.7 V,
[Equation 2]
Q _{E '} = (Q _D' / Q _{C '} ) × 100
Wherein,
Q _{E ′} represents charge and discharge efficiency under a 2.3V to 4.7V potential of the second lithium composite metal oxide.
Q _{D '} represents discharge capacity (mAh / g) at Li / Li + cut-off at a discharge voltage of 2.3 V,
Q _{C '} represents charge capacity (mAh / g) at Li / Li + cut-off at a charge voltage of 4.7 V. The method of claim 1,
The first lithium composite metal oxide is an anode active material for lithium ion capacitors having an initial charge and discharge efficiency (Q _E ) of 40% or less according to Formula 1 below:
[Equation 1]
Q _E = (Q _D / Q _C ) × 100
Wherein,
Q _E represents the initial charge and discharge efficiency of the first lithium composite metal oxide,
Q _D represents discharge capacity (mAh / g) at Li / Li + cut-off at a discharge voltage of 2.3 V,
Q _C represents the charge capacity (mAh / g) at Li / Li + cut-off at a charge voltage of 4.7 V. The method of claim 1,
The second lithium composite metal oxide has a charge / discharge efficiency (Q _{E ′} ) of at least 60% under a potential of 2.3 V to 4.7 V according to Formula 2 below: a cathode active material for a lithium ion capacitor:
[Equation 2]
Q _{E '} = (Q _D' / Q _{C '} ) × 100
Wherein,
Q _{E ′} represents charge and discharge efficiency under a 2.3V to 4.7V potential of the second lithium composite metal oxide.
Q _{D '} represents discharge capacity (mAh / g) at Li / Li + cut-off at a discharge voltage of 2.3 V,
Q _{C '} represents charge capacity (mAh / g) at Li / Li + cut-off at a charge voltage of 4.7 V. The method of claim 1,
The first lithium composite metal oxide is at least one selected from the group consisting of Li ₂ MoO ₃ , Li ₅ FeO ₄ , and Li ₆ CoO ₄ active material for a lithium ion capacitor. The method of claim 1,
The second lithium composite metal oxide is one selected from the group consisting of Li ₂ MnO ₃ , Li ₂ TiO ₃ , Li ₂ RuO ₃ , Li ₂ IrO ₃ , Li ₂ PtO ₃ , Li ₂ SnO ₃ , and Li ₂ ZrO ₃ . The positive electrode active material for lithium ion capacitors which are the above. The method of claim 1,
The first lithium composite metal oxide is a positive electrode active material for a lithium ion capacitor to insert or remove lithium ions in the voltage range of 0V to 5V. The method of claim 1,
The second lithium composite metal oxide is a positive electrode active material for lithium ion capacitor (reversible in the operating potential region of the lithium ion capacitor) to reversibly insert or remove lithium ions in the voltage range of 1V to 5V. The method of claim 1,
The carbon-based material has a specific surface area of 500 m ² / g or more, the positive electrode active material for lithium ion capacitors. The method of claim 1,
The carbon-based material is at least one selected from the group consisting of activated carbon, activated carbon and metal oxide composite, activated carbon and conductive polymer composite. The method of claim 1,
0.5 to 49.5 wt% of the first lithium composite metal oxide,
0.5-49.5 wt% of the second lithium composite metal oxide, and
A cathode active material for a lithium ion capacitor comprising 50 to 99% by weight of the carbonaceous material. The method of claim 1,
The weight ratio of the first lithium composite metal oxide: second lithium composite metal oxide is 10:90 to 90:10 positive electrode active material for a lithium ion capacitor. a) mixing and heat-treating a transition metal compound containing at least one selected from the group consisting of a lithium compound and Mo, Fe, and Co to produce a first lithium composite metal oxide precursor represented by Formula 3 below;
b) reducing the first lithium composite metal oxide precursor represented by Formula 3 to produce a first lithium composite metal oxide represented by Formula 1 below;
c) a second lithium composite metal represented by the following Chemical Formula 2 by mixing and thermally treating a transition metal compound containing at least one selected from the group consisting of a lithium compound and Mn, Ti, Ru, Ir, Pt, Sn, and Zr Producing an oxide; And
d) mixing the first lithium composite metal oxide and the second lithium composite metal oxide with a carbonaceous material;
Method for producing a cathode active material for a lithium ion capacitor comprising:
[Chemical Formula 1]
Li _a M ¹ _b O _c
(2)
Li _d M ² _e O _f
(3)
Li _{a '} M ^1' _{b '} O _c'
Wherein,
a, b, and c satisfy 0 <a≤6, 0 <b≤3, 0 <c≤4, respectively,
d, e, f satisfy 0 <d ≦ 2, 0 <e ≦ 3, 0 <f ≦ 4, respectively,
a ', b', and c 'satisfy 0 <a'≤6, 0 <b'≤3, and 1 <c'≤5, respectively.
M ¹ and M ^{1 '} are each one or more selected from the group consisting of Mo, Fe, and Co,
M ² is at least one member selected from the group consisting of Mn, Ti, Ru, Ir, Pt, Sn, and Zr. The method of claim 12,
The heat treatment process of step a) is performed at 400 to 1,000 ° C a method for producing a cathode active material for a lithium ion capacitor. The method of claim 12,
Step b) is a method of manufacturing a positive electrode active material for a lithium ion capacitor to reduce the first lithium composite metal oxide precursor by heat treatment at 500 to 1,000 ℃. The method of claim 12,
The heat treatment process of step c) is carried out at 500 to 1,000 ℃ method for producing a positive electrode active material for lithium ion capacitors. The method of claim 12,
The lithium compound of step a) and c) is at least one selected from the group consisting of Li ₂ CO ₃ , LiOH, and Li, respectively. The method of claim 12,
The transition metal compound of step a) is MoO ₃ , MoO ₂ , (NH ₄ ) ₆ Mo ₇ O ₂₄ 4H ₂ 0, MoS ₂ , Mo, FeO, Fe ₂ O ₃ , Fe ₃ O ₄ , Fe, CoO, And Co at least one selected from the group consisting of positive electrode active material for lithium ion capacitors. The method of claim 12,
The transition metal compound of step c) is MnO, Mn, TiO ₂ , Ti, RuO ₂ , Ru, IrCl ₃ , IrO ₂ , PtCl ₄ , PtCl ₂ , PtO ₂ , Pt (C ₅ H ₇ O ₂ ) ₂ , Pt / C, SnO ₂ , Sn, ZrO ₂ , and a method for producing a positive electrode active material for lithium ion capacitors of at least one selected from the group consisting of Zr. A lithium ion capacitor comprising the positive electrode active material according to any one of claims 1 to 11. 20. The method of claim 19,
A cathode including a cathode active material;
An anode including a negative electrode active material; And
Separator between anode and cathode
The lithium ion capacitor of claim 1, wherein the negative electrode receives lithium ions only from the positive electrode. 20. The method of claim 19,
Lithium ion capacitor comprising a carbon-based negative active material for reversibly inserting or detaching lithium ions in the voltage range of 0V to 5V.

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