ELECTRODE MATERIAL AND LITHIUM-ION ENERGY STORAGE DEVICE HAVING THE ELECTRODE MATERIAL

Abstract

An electrode material and a lithium-ion energy storage device are provided. The electrode material includes at least one material selected from the following structures: a Keplerate-type polyoxometalate containing molybdenum and iron; a Keplerate-type polyoxometalate containing molybdenum and vanadium; a bi-capped Keggin-type polyoxometalate containing vanadium; and a polyoxometalate containing vanadium and a transition metal, wherein the transition metal is nickel, cobalt, iron, or manganese. A lithium-ion energy storage device having the above electrode materials may still maintain higher capacity at higher current density, and may still maintain the original capacity after many cycles.

Claims

1. An electrode material of a lithium-ion capacitor, comprising at least one material selected from the following structures: a Keplerate-type polyoxometalate containing molybdenum and iron; a Keplerate-type polyoxometalate containing molybdenum and vanadium; a bi-capped Keggin-type polyoxometalate containing vanadium; and a polyoxometalate containing vanadium and a transition metal, wherein the transition metal is nickel, cobalt, iron, or manganese.

2. The electrode material of the lithium-ion capacitor of claim 1, wherein the Keplerate-type polyoxometalate containing molybdenum and iron comprises [{Mo.sub.6O.sub.19}⊂{Mo.sub.72Fe.sub.30O.sub.254(CH.sub.3COO).sub.12(H.sub.2O).sub.96}].150H.sub.2O (abbreviated as {Mo.sub.72Fe.sub.30}).

3. The electrode material of the lithium-ion capacitor of claim 1, wherein the Keplerate-type polyoxometalate containing molybdenum and vanadium comprises Na.sub.2K.sub.23{[(Mo.sup.VI)Mo.sup.VI.sub.5O.sub.21(H.sub.2O).sub.3(KSO.sub.4)].sub.12[(V.sup.IVO).sub.30(H.sub.2O).sub.20(SO.sub.4).sub.0.5]}.ca200H.sub.2O (abbreviated as {Mo.sub.72V.sub.30}).

4. The electrode material of the lithium-ion capacitor of claim 1, wherein the bi-capped Keggin-type polyoxometalate containing vanadium comprises M1.sub.xM2.sub.yPV.sub.14O.sub.42, M1 and M2 are cations, x+y=9, x>0, y≥0.

5. The electrode material of the lithium-ion capacitor of claim 1, wherein the polyoxometalate containing vanadium and the transition metal comprises M3.sub.aM4.sub.bNiV.sub.13O.sub.38 or M3.sub.aM4.sub.bMnV.sub.13O.sub.38, M3 and M4 are cations, a+b=9, a>0, b≥0.

6. The electrode material of the lithium-ion capacitor of claim 1, further comprising a conductive additive, a binding agent, or a combination thereof.

7. A lithium-ion capacitor, comprising: a positive electrode; a negative electrode; and an electrolyte located between the positive electrode and the negative electrode, wherein at least one of the positive electrode and the negative electrode contains the electrode material of claim 1.

8. An electrode material of a lithium-ion battery, comprising at least one material selected from the following structures: a Keplerate-type polyoxometalate containing molybdenum and iron; and a polyoxometalate containing vanadium and a transition metal, wherein the transition metal is nickel or manganese.

9. The electrode material of the lithium-ion battery of claim 8, wherein the Keplerate-type polyoxometalate containing molybdenum and iron comprises [{Mo.sub.6O.sub.19}⊂{Mo.sub.72Fe.sub.30O.sub.254(CH.sub.3COO).sub.12(H.sub.2O).sub.96}].150H.sub.2O (abbreviated as {Mo.sub.72Fe.sub.30}).

10. The electrode material of the lithium-ion battery of claim 8, wherein the polyoxometalate containing vanadium and the transition metal comprises M3.sub.aM4.sub.bNiV.sub.13O.sub.38 or M3.sub.aM4.sub.bMnV.sub.13O.sub.38, M3 and M4 are cations, a+b=9, a>0, b≥0.

11. The electrode material of the lithium-ion battery of claim 8, further comprising a conductive additive, a binding agent, or a combination thereof.

12. A lithium-ion battery, comprising: a positive electrode; a negative electrode; and an electrolyte located between the positive electrode and the negative electrode, wherein at least one of the positive electrode and the negative electrode contains the electrode material of claim 8.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.

[0022] FIG. 1 is a diagram of the structure of an electrode material of a lithium-ion capacitor according to the first embodiment of the invention.

[0023] FIG. 2 is a diagram of the structure of an electrode material of another lithium-ion capacitor according to the first embodiment of the invention.

[0024] FIG. 3 is a diagram of the structure of an electrode material of another lithium-ion capacitor according to the first embodiment of the invention.

[0025] FIG. 4 is a diagram of the structure of an electrode material of another lithium-ion capacitor according to the first embodiment of the invention.

[0026] FIG. 5 is a cross-sectional view of a lithium-ion energy storage device according to the third embodiment of the invention.

[0027] FIG. 6A is a constant current charge and discharge diagram of the lithium-ion half-cell of Experimental example 1 (electrode material {Mo.sub.72Fe.sub.30}) at a current density of 100 mA/g.

[0028] FIG. 6B is a graph of cyclic voltammetry of the lithium-ion half-cell of Experimental example 1 (electrode material {Mo.sub.72Fe.sub.30}) at different scan rates.

[0029] FIG. 6C is a constant current charge and discharge diagram of the lithium-ion half-cell of Experimental example 1 (electrode material {Mo.sub.72Fe.sub.30}) at different current densities.

[0030] FIG. 6D is a bar graph of the ratio between capacitance and intercalation of the lithium-ion half-cell of Experimental example 1 (electrode material {Mo.sub.72Fe.sub.30}) at different scan rates.

[0031] FIG. 7A is a constant current charge and discharge diagram of the lithium-ion half-cell of Experimental example 2 (electrode material {Mo.sub.72V.sub.30}) at a current density of 100 mA/g.

[0032] FIG. 7B is a graph of cyclic voltammetry of the lithium-ion half-cell of Experimental example 2 (electrode material {Mo.sub.72V.sub.30}) at different scan rates.

[0033] FIG. 7C is a constant current charge and discharge diagram of the lithium-ion half-cell of Experimental example 2 (electrode material {Mo.sub.72V.sub.30}) at different current densities.

[0034] FIG. 7D is a bar graph of the ratio between capacitance and intercalation of the lithium-ion half-cell of Experimental example 2 (electrode material {Mo.sub.72V.sub.30}) at different scan rates.

[0035] FIG. 8A is a graph of cycle performance and Coulomb efficiency of the lithium-ion half-cell of Experimental example 3 (electrode material PV.sub.14) at a current density of 1000 mA/g.

[0036] FIG. 8B is a constant current charge and discharge diagram of the lithium-ion half-cell of Experimental example 3 (electrode material PV.sub.14) at different current densities.

[0037] FIG. 8C is a graph of cycle performance of the lithium-ion capacitor of Experimental example 3 (electrode material PV.sub.14) at different current densities.

[0038] FIG. 8D is a graph of cycle performance of the lithium-ion capacitor of Experimental example 3 (electrode material PV.sub.14) at a large current density of 2 A/g.

[0039] FIG. 8E is a graph of power density and energy density of the lithium-ion capacitor of Experimental example 3 (electrode material PV.sub.14).

[0040] FIG. 9A is a graph of cycle performance and Coulomb efficiency of the lithium-ion half-cell of Experimental example 4 (electrode material NiV.sub.13) at current densities of 0.1 A/g and 5 A/g.

[0041] FIG. 9B is a constant current charge and discharge diagram of the lithium-ion half-cell of Experimental example 4 (electrode material NiV.sub.13) at different current densities.

[0042] FIG. 9C is a graph of cycle performance of the lithium-ion capacitor of Experimental example 4 (electrode material NiV.sub.13) at different current densities.

[0043] FIG. 9D is a graph of cycle performance of the lithium-ion capacitor of Experimental example 4 (electrode material NiV.sub.13) at a large current density of 2 A/g.

[0044] FIG. 9E is a graph of power density and energy density of the lithium-ion capacitor of Experimental example 4 (electrode material NiV.sub.13).

DESCRIPTION OF THE EMBODIMENTS

[0045] The invention provides an electrode material of a lithium-ion energy storage device that provides the lithium-ion energy storage device with excellent performance in both power density and energy density, wherein even at a higher current density, higher capacity is still maintained, and after many cycles, the original capacity is still maintained.

[0046] In the following, embodiments are provided to describe actual implementations of the invention.

[0047] In the first embodiment, an electrode material of a lithium-ion capacitor includes at least one material selected from the following structures: a Keplerate-type polyoxometalate containing molybdenum and iron; a Keplerate-type polyoxometalate containing molybdenum and vanadium; a bi-capped Keggin-type polyoxometalate containing vanadium; and a polyoxometalate containing vanadium and a transition metal, wherein the transition metal is nickel, cobalt, iron, or manganese.

[0048] In the first embodiment, the Keplerate-type polyoxometalate containing molybdenum and iron is, for example, [{Mo.sub.6O.sub.19}⊂{Mo.sub.72Fe.sub.30O.sub.254(CH.sub.3COO).sub.12(H.sub.2O).sub.96}].150H.sub.2O (abbreviated as {Mo.sub.72Fe.sub.30}), and the structure diagram thereof is shown in FIG. 1. Although it is difficult to see the location of each element from FIG. 1, it may be obtained that the electrode material has a very large molecular structure. The Keplerate-type polyoxometalate containing molybdenum and iron may be synthesized by a solution method. A large amount of product may be obtained with only solution mixing. The synthesis method is simple and the output speed is extremely fast, and the particle size of the resulting {Mo.sub.72Fe.sub.30} is about several hundred nanometers, such as 100 nm to 200 nm. Since {Mo.sub.72Fe.sub.30} belongs to nano-grade particles and has high surface area, it facilitates desorption performance, making such electrode material preferable for lithium-ion capacitors (LICs). It may be found through experimental verification that when this polyoxometalate is made into an electrode material and placed at the negative electrode of a lithium-ion energy storage device, very high capacity performance may be achieved in the voltage range of 0.01 V to 3 V vs. Li/Li.sup.+, and higher capacity may still be maintained even at higher current density, and the original capacity may still be maintained after many cycles.

[0049] In the first embodiment, the Keplerate-type polyoxometalate containing molybdenum and vanadium is, for example, Na.sub.2K.sub.23{[(Mo.sup.VI)Mo.sup.VI.sub.5O.sub.21(H.sub.2O).sub.3(KSO.sub.4)].sub.12[(V.sup.IVO).sub.30(H.sub.2O).sub.20(SO.sub.4).sub.0.5]}.ca200H.sub.2O (abbreviated as {Mo.sub.72V.sub.30}), and the structure diagram thereof is shown in FIG. 2. Although it is difficult to see the location of each element from FIG. 2, it may be obtained that the electrode material has a very large molecular structure. The Keplerate-type polyoxometalate containing molybdenum and vanadium is also synthesized by a solution method. The synthesis method is simple and the output speed is extremely fast. The particles of the resulting {Mo.sub.72V.sub.30} are also very small, about <10 μm. The Keplerate-type polyoxometalate containing molybdenum and vanadium also has very high capacity performance in the voltage range of 0.01 V to 3 V vs. Li/Li.sup.m, and may still maintain higher capacity even at higher current density, and may still maintain the original capacity after many cycles.

[0050] In the first embodiment, the bi-capped Keggin-type polyoxometalate containing vanadium includes M1.sub.xM2.sub.yPV.sub.14O.sub.42 (abbreviated as PV.sub.14), M1 and M2 are cations, x+y=9, x>0, y≥0. In an embodiment, M1 may be lithium, sodium, or potassium, M2 may be hydrogen, and M1 and M2 are different. For example, a bi-capped Keggin-type polyoxometalate containing vanadium, such as Na.sub.7H.sub.2PV.sub.14O.sub.42 has a structure shown in FIG. 3. The difference between bi-capped Keggin-type and general Keggin-type lies in the different elements in the structure. Keggin-type is mainly polyoxometalate based on Mo or W. The bi-capped Keggin-type polyoxometalate containing vanadium may be synthesized by a solution method, so the synthesis method thereof is simple and the output speed is extremely fast. The particle size of the resulting PV.sub.14 is about 5 μm to 10 μm. The bi-capped Keplerate-type polyoxometalate containing vanadium also has very high capacity performance in the voltage range of 0.01 V to 3 V vs. Li/Li, and may still maintain high capacity even at high current density, and may still maintain the original capacity after many cycles.

[0051] In the first embodiment, the polyoxometalate containing vanadium and the transition metal includes M3.sub.aM4.sub.bNiV.sub.13O.sub.38 (abbreviated as NiV.sub.13) or M3.sub.aM4.sub.bMnV.sub.13O.sub.38 (abbreviated as MnV.sub.13), M3 and M4 are cations, a+b=9, a>0, b≥0. In an embodiment, M3 may be lithium, sodium, or potassium, M4 may be hydrogen, and M3 and M4 are different. For example, the polyoxometalate containing vanadium and the transition metal, such as Na.sub.7NiV.sub.13O.sub.38 or Na.sub.7MnV.sub.13O.sub.38, has a structure shown in FIG. 4. The polyoxometalate containing vanadium and the transition metal may be synthesized by a solution method, so the synthesis method thereof is simple and the output speed is extremely fast. The particle size of the resulting NiV.sub.13 and MnV.sub.13 is about 5 μm to 10 μm. The polyoxometalate containing vanadium and the transition metal also has high capacity performance in the voltage range of 0.01 V to 3 V vs. Li/Li.sup.+, and may still maintain high capacity even at high current density, and may still maintain higher capacity after many cycles.

[0052] In the first embodiment, the electrode material may further include a conductive additive, a binding agent, or a combination thereof. The conductive additive is, for example, natural graphite, artificial graphite, carbon black, acetylene black, carbon fiber, metal powder, metal fiber, or conductive ceramic material. The binding agent may adopt a currently existing binding agent.

[0053] In the second embodiment, an electrode material of the lithium-ion battery of the invention includes at least one material selected from the following structures: a Keplerate-type polyoxometalate containing molybdenum and iron; and a polyoxometalate containing vanadium and a transition metal, wherein the transition metal is nickel, cobalt, iron, or manganese. The Keplerate-type polyoxometalate containing molybdenum and iron and the polyoxometalate containing vanadium and the transition metal of the second embodiment are as described in the first embodiment (as shown in FIG. 1 and FIG. 4) and are therefore not repeated herein. Moreover, the Keplerate-type polyoxometalate containing molybdenum and iron and the polyoxometalate containing vanadium and the transition metal have a large amount of transition metal to transfer electrons, and therefore facilitate the intercalation/deintercalation of lithium ions, and are suitable for electrode materials of lithium-ion batteries.

[0054] FIG. 5 is a cross-sectional view of a lithium-ion energy storage device according to the third embodiment of the invention. Referring to FIG. 5, a lithium-ion energy storage device 500 includes at least a positive electrode 502, a negative electrode 504, and an electrolyte 506, wherein the electrolyte 506 is located between the positive electrode 502 and the negative electrode 504, and the electrolyte 506 may be liquid, colloidal, molten salt, or solid electrolyte. At least one of the positive electrode 502 and the negative electrode 504 includes the electrode material in the above embodiments, and may be made by mixing the electrode material, a conductive additive, and a binding agent into a slurry and coating the slurry on a metal plate (not shown). However, the invention is not limited thereto. In an embodiment, if the lithium-ion energy storage device 500 is a lithium-ion capacitor, then at least one of the positive electrode 502 and the negative electrode 504 contains the above Keplerate-type polyoxometalate containing molybdenum and iron, the above Keplerate-type polyoxometalate containing molybdenum and vanadium, the above bi-capped Keggin-type polyoxometalate containing vanadium, the above polyoxometalate containing vanadium and the transition metal, or a combination of the above materials. In another embodiment, if the lithium-ion energy storage device 500 is a lithium-ion battery, then at least one of the positive electrode 502 and the negative electrode 504 contains the Keplerate-type polyoxometalate containing molybdenum and iron, the polyoxometalate containing vanadium and the transition metal, or a combination of the above materials.

[0055] In the third embodiment, the lithium-ion energy storage device 500 may further include a separator 508 disposed between the positive electrode 502 and the negative electrode 504, wherein the material of the separator 508 is an insulating material such as polyethylene (PE), polypropylene (PP), or a composite structure formed by the above materials (such as PE/PP/PE or Celgard® 2500).

[0056] Experiments are described below to verify the efficacy of the disclosure. However, the disclosure is not limited to the following content.

<Preparation Example 1> Preparation of {Mo.SUB.72.Fe.SUB.30.}

[0057] 7.7 mmol of FeCl.sub.3.6H.sub.2O was added to a solution containing 12.3 mmol of Na.sub.2MoO.sub.4.2H.sub.2O and 25 ml of H.sub.2O to be mixed and stirred, and then 15 ml of 100% CH.sub.3COOH was added to adjust the pH. The mixture was left to stand for 30 minutes to wait for the material to precipitate, then the material was washed and dried to obtain the product [{Mo.sub.6O.sub.19}⊂{Mo.sub.72Fe.sub.30O.sub.254(CH.sub.3COO).sub.12 (H.sub.2O).sub.96}].150H.sub.2O, with a yield ≈2 g and a particle size of about 100 nm to 200 nm. This preparation method may quickly precipitate the above product without heating or cooling and without the use of chemicals such as ethanol.

<Preparation Example 2> Preparation of {Mo.SUB.72.V.SUB.30.}

[0058] 10 mmol of VOSO.sub.4.5H2O dissolved in 35 ml of water was added to 8 ml of 0.5 M H.sub.2SO.sub.4 solution containing 10 mmol of Na.sub.2MoO.sub.4.2H.sub.2O and mixed and stirred for 30 minutes, then 8.72 mmol of KCl was added and stirred for 30 minutes. After the material was precipitated, the material was filtered and washed with 4° C. deionized water, and then dried to obtain the product Na.sub.2K.sub.23{[(Mo.sup.VI)Mo.sup.VI.sub.5O.sub.21 (H.sub.2O).sub.3(KSO.sub.4)].sub.12[(V.sup.IVO).sub.30(H.sub.2O).sub.20(SO.sub.4).sub.0.5]}.ca200H.sub.2O with a yield of 1.84 g (32.7%) and a particle size of about 2 μm to 3 μm.

<Preparation Example 3> Preparation of PV.SUB.14

[0059] First, 2.25 g of NaVO.sub.3 was dissolved in 12.5 ml of hot water at 100° C., then after filtering and cooling to room temperature, 3.1 ml of 1.5 M H.sub.3PO.sub.4 was added while stirring, then 3 M HNO.sub.3 was poured in to lower the pH from 6.0 to 2.3. The solution was kept in a steam bath at 50° C. and a hot concentrated NaCl solution (5 g in 20 ml water) was slowly added. After cooling to room temperature, brown powder was obtained by adding ethanol (solution with same volume), and then the precipitate was filtered and air-dried to obtain the product Na.sub.7H.sub.2PV.sub.14O.sub.42 with a yield=1 g and a particle size of about 5 μm to 10 μm.

<Preparation Example 4> Preparation of NiV.SUB.13

[0060] First, 31.7 g of NaVO.sub.3 was dissolved in 700 ml of deionized water at 80° C. and stirred, and 20 ml of 1M HNO.sub.3 and 20 ml of 1M NiSO.sub.4 were added to adjust the pH, then the mixture was stirred for 4 hours to wait for the material to precipitate, then the material was filtered at room temperature and crystallized at low temperature at 4° C. After drying, the product Na.sub.7NiV.sub.13O.sub.38 was obtained, with a yield=15 g and a particle size of about 5 μm to 10 μm.

Experimental Example 1

[0061] The product {Mo.sub.72Fe.sub.30} of Preparation example 1 together with the conductive additive Super P® and a binding agent were formulated into a mixture in a weight ratio of 70:20:10. After grinding, the mixture was added into deionized water containing 5 wt % CMC+SBR, then the mixture was stirred evenly and then coated on a copper sheet, and then dried to obtain an electrode sheet. This electrode sheet was made into a half-cell, and 1M LiPF.sub.6 in ethylene carbonate (EC) and diethyl carbonate (DEC) (volume ratio 1:1) was used as an electrolyte for electrochemical specific detection. The results are shown in FIG. 6A to FIG. 6D.

[0062] FIG. 6A is a constant current charge and discharge diagram at a current density of 100 mA/g; FIG. 6B is a graph of cyclic voltammetry at different scan rates; FIG. 6C is a constant current charge and discharge diagram at different current densities; and FIG. 6D is a bar graph of the ratio between capacitance and intercalation at different scan rates. From FIG. 6A, it may be seen that a relatively stable slope is obtained in the voltage range of 0.01 V to 3 V vs. Li/Li.sup.+; and it may be seen from FIG. 6B that the main reaction potential of {Mo.sub.72Fe.sub.30} is always 1 V or less, and therefore {Mo.sub.72Fe.sub.30} is suitable as a negative electrode material, and there is no significant polarization phenomenon even at high scan rate, thus enabling rapid redox reaction. It may be seen from FIG. 6C that high capacity may be achieved at high current density. From FIG. 6D, it may be seen that (absorption and desorption) capacitance is the sole contributor to the very fast rate, so {Mo.sub.72Fe.sub.30} may be used not only for lithium-ion batteries, but is also suitable for lithium-ion capacitors.

Experimental Example 2

[0063] A half-cell was fabricated as in Experimental example 1, but the product of Preparation example 1 was replaced by the product {Mo.sub.72V.sub.30} of Preparation example 2. Then the electrochemical specific detection was also performed, and the results are shown in FIG. 7A to FIG. 7D.

[0064] FIG. 7A is a constant current charge and discharge diagram at a current density of 100 mA/g; FIG. 7B is a graph of cyclic voltammetry at different scan rates; FIG. 7C is a constant current charge and discharge diagram at different current densities; and FIG. 7D is a bar graph of the ratio between capacitance and intercalation at different scan rates. From FIG. 7A, it may also be seen that a relatively stable slope is obtained in the voltage range of 0.01 V to 3 V vs. Li/Li.sup.+; and it may be seen from FIG. 7B that the main reaction potential of {Mo.sub.72V.sub.30} is always 1 V or less, and therefore {Mo.sub.72V.sub.30} is suitable as a negative electrode material, and there is no significant polarization phenomenon even at high scan rate, thus enabling rapid redox reaction.

[0065] From FIG. 7C, high capacities 1200 mA h g.sup.−1, 1175 mA h g.sup.−1, 1150 mA h g.sup.−1, 1100 mA h g.sup.−1 1000 mA h g.sup.−1, and 850 mA h g.sup.−1 are observed at different current densities (50 mA/g, 100 mA/g, 200 mA/g, 500 mA/g, 1000 mA/g, and 2000 mA/g) respectively. Therefore, even at higher current density, high capacity may still be maintained. It may be seen from FIG. 7D that (absorption and desorption) capacitance contributes the most to the faster rate, so {Mo.sub.72V.sub.30} is suitable for lithium-ion capacitors.

Experimental Example 3

[0066] A half-cell was fabricated as in Experimental example 1, but the product of Preparation example 1 was replaced by the product PV.sub.14 of Preparation example 3. Then, the cycle performance and the Coulomb efficiency of the lithium-ion half-cell at a current density of 1000 mA/g were measured to obtain FIG. 8A. It may be seen from FIG. 8A that the capacity remained at about 300 mA h g.sup.−1 without decline even after 500 cycles at a current density of 1000 mA/g.

[0067] Then, the constant current charge and discharge of the lithium-ion half-cell at different current densities were measured to obtain FIG. 8B. From FIG. 8B, the capacities 550 mA h g.sup.−1, 465 mA h g.sup.−1, 440 mA h g.sup.−1, 410 mA h g.sup.−1 and 365 mA h g.sup.−1 are observed at different current densities (50 mA/g, 100 mA/g, 200 mA/g, 500 mA/g, 1000 mA/g, and 2000 mA/g) respectively. Therefore, even at higher current density, high capacity may still be maintained.

[0068] In addition, the electrode sheet (electrode material PV.sub.14) made according to the method of Experimental example 1, a separator (Celgard® 2500), and an active carbon positive electrode sheet were formed into a lithium-ion capacitor, and 1M LiPF.sub.6 in EC and DEC (volume ratio 1:1) was used as the electrolyte for electrochemical specific detection. The results are shown in FIG. 8C and FIG. 8D.

[0069] It may be seen from FIG. 8C that the capacity may be maintained above a predetermined value at different current densities. From FIG. 8D, it may be seen that the lithium-ion capacitor of Experimental example 3 has good cycle performance at a large current density of 2 A/g.

[0070] The electrochemical performance of PV.sub.14 with commercial activated carbon (YP80F) for the positive electrode is shown in FIG. 8E. At a power density of 89 W kg.sup.1 to 3230 W kg.sup.−1, the energy density is 121 W h kg.sup.−1 to 51 W h kg.sup.−1. Therefore, the lithium-ion capacitor of Experimental example 3 (electrode material PV.sub.14) may take into account the performance of both power density and energy density.

Experimental Example 4

[0071] A half-cell was fabricated as in Experimental example 1, but the product of Preparation example 1 was replaced by the product NiV.sub.13 of Preparation example 4. Then, the cycle performance and the Coulomb efficiency of the lithium-ion half-cell at current densities of 0.1 A/g and 5 A/g were measured to obtain FIG. 9A. Then, the constant current charge and discharge of the lithium-ion half-cell at different current densities were measured to obtain FIG. 9B.

[0072] It may be obtained from FIG. 9A and FIG. 9B that electrode materials including NiV.sub.13 lithium-ion half-cells have high capacity (capacity of 700 mA h g.sup.−1 at current density of 0.1 A/g), fast charge and discharge (capacities of 482 mA h g.sup.−1 and 331 mA h g.sup.−1 at high charge rates of 1 A/g and 5 A/g, respectively), and long cycle stability.

[0073] In addition, the electrode sheet (electrode material NiV.sub.13 made according to the method of Experimental example 1, a separator (Celgard® 2500), and an active carbon positive electrode sheet were formed into a lithium-ion capacitor, and 1M LiPF.sub.6 in EC and DEC (volume ratio 1:1) was used as the electrolyte for electrochemical specific detection. The results are shown in FIG. 9C and FIG. 9D.

[0074] It may be seen from FIG. 9C that the capacity may be maintained above a predetermined value at different current densities. From FIG. 9D, it may be seen that the lithium-ion capacitor of Experimental example 4 has good cycle performance at a large current density of 2 A/g.

[0075] The electrochemical performance of NiV.sub.13 with commercial activated carbon (YP80F) for the positive electrode is shown in FIG. 9E. At a power density of 169 W kg.sup.−1 to 8821 W kg.sup.−1, the energy density is 140 W h kg.sup.−1 to 52 W h kg.sup.−1, and the electrochemical performance thereof is better than Experimental example 3. Therefore, the lithium-ion capacitor of Experimental example 4 (electrode material NiV.sub.13) may also take into account the performance of both power density and energy density.

[0076] Based on the above, the electrode material of the invention has a larger molecular structure and a large amount of transition metal. Therefore, even after many cycles, the structure still does not collapse and may transfer a lot of electrons. Therefore, the lithium-ion energy storage device having the electrode material may meet the needs of high current density and high capacity at the same time. In addition, after many cycles, the volume does not expand and collapse, and may still maintain higher capacity.

[0077] Although the invention has been described with reference to the above embodiments, it will be apparent to one of ordinary skill in the art that modifications to the described embodiments may be made without departing from the spirit of the disclosure. Accordingly, the scope of the disclosure is defined by the attached claims not by the above detailed descriptions.