ELECTRODE FOR LITHIUM-ION BATTERY AND LITHIUM-ION BATTERY COMPRISING THE SAME

Abstract

An electrode for a lithium-ion battery is disclosed, which comprises: a collector comprising a nano-twinned copper foil; and a negative electrode material disposed on the collector, wherein the negative electrode material comprises at least one selected from the group consisting of: silicon, silicon nitride, graphite, graphene, carbon nanotubes, carbon nano-fibers and carbon nano-particles. In addition, a lithium-ion battery comprising the aforesaid electrode is also provided.

Claims

1. An electrode for a lithium-ion battery, comprising: a collector comprising a nano-twinned copper foil; and a negative electrode material disposed on the collector, wherein the negative electrode material comprises an active material comprising at least one selected from the group consisting of: silicon, silicon nitride, graphite, graphene, carbon nanotubes, carbon nano-fibers and carbon nano-particles.

2. The electrode of claim 1, wherein the active material comprises silicon and silicon nitride.

3. The electrode of claim 2, wherein a content of the silicon nitride is ranged from 25% to 85% based on a total weight of the silicon and the silicon nitride.

4. The electrode of claim 1, wherein a thickness of the nano-twinned copper foil is ranged from 1 μm to 500 μm.

5. The electrode of claim 1, wherein at least 50% in volume of the nano-twinned copper foil comprises plural twinned grains.

6. The electrode of claim 5, wherein diameters of the plural twinned grains are respectively ranged from 0.1 μm to 50 μm.

7. The electrode of claim 5, wherein thicknesses of the plural twinned grains are respectively ranged from 0.1 μm to 500 μm.

8. The electrode of claim 5, wherein at least a part of the plural twinned grains are connected with each other.

9. The electrode of claim 5, wherein at least a part of the plural twinned grains are fine grains, and lamination directions of plural nano-twins of the fine grains do not have a preferred direction.

10. The electrode of claim 5, wherein at least a part of the plural twinned grains are formed by plural nano-twins stacking along a [111] crystal axis.

11. The electrode of claim 10, wherein an included angle between a lamination direction of the at least a part of the plural twinned grains and a thickness direction of the nano-twinned copper foil is ranged from 0 degree to 60 degrees.

12. The electrode of claim 1, wherein at least 50% of an area of a surface of the nano-twinned copper foil expose (111) surfaces of plural nano-twins.

13. A lithium-ion battery, comprising: a lithium counter electrode; an electrode, comprising: a collector comprising a nano-twinned copper foil; and a negative electrode material disposed on the collector, wherein the negative electrode material comprises an active material comprising at least one selected from the group consisting of: silicon, silicon nitride, graphite, graphene, carbon nanotubes, carbon nano-fibers and carbon nano-particles; a separator disposed between the lithium counter electrode and the electrode; and an electrolyte disposed between the lithium counter electrode and the electrode and disposed at two sides of the separator.

14. The lithium-ion battery of claim 13, wherein the active material comprises silicon and silicon nitride.

15. The lithium-ion battery of claim 14, wherein a content of the silicon nitride is ranged from 25% to 85% based on a total weight of the silicon and the silicon nitride.

16. The lithium-ion battery of claim 13, wherein a thickness of the nano-twinned copper foil is ranged from 1 μm to 500 μm.

17. The lithium-ion battery of claim 13, wherein at least 50% in volume of the nano-twinned copper foil comprises plural twinned grains.

18. The lithium-ion battery of claim 17, wherein at least a part of the plural twinned grains are fine grains, and lamination directions of plural nano-twins of the fine grains do not have a preferred direction.

19. The lithium-ion battery of claim 17, wherein at least a part of the plural twinned grains are formed by plural nano-twins stacking along a [111] crystal axis.

20. The lithium-ion battery of claim 13, wherein at least 50% of an area of a surface of the nano-twinned copper foil expose (111) surfaces of plural nano-twins.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0031] FIG. 1A is a FIB photo of a nano-twinned copper foil prepared in Embodiment 1 of the present disclosure.

[0032] FIG. 1B is an EBSD photo of a nano-twinned copper foil prepared in Embodiment 1 of the present disclosure.

[0033] FIG. 2 is a tensile strength curve of a nano-twinned copper foil prepared in Embodiment 1 of the present disclosure.

[0034] FIG. 3 is an exploded view of a coin-type half-cell according to Embodiment 2 of the present disclosure.

[0035] FIG. 4 is a diagram showing the cycle life of the lithium-ion batteries prepared in Embodiment 2 and Comparative embodiment 1 of the present disclosure.

[0036] FIG. 5 is a FIB photo of a nano-twinned copper foil prepared in Embodiment 4 of the present disclosure.

DETAILED DESCRIPTION OF EMBODIMENT

[0037] Different embodiments of the present disclosure are provided in the following description. These embodiments are meant to explain the technical content of the present disclosure, but not meant to limit the scope of the present disclosure. A feature described in an embodiment may be applied to other embodiments by suitable modification, substitution, combination, or separation.

[0038] It should be noted that, in the present specification, when a component is described to have an element, it means that the component may have one or more of the elements, and it does not mean that the component has only one of the element, except otherwise specified.

[0039] In the present specification, except otherwise specified, the feature A “or” or “and/or” the feature B means the existence of the feature A, the existence of the feature B, or the existence of both the features A and B. The feature A “and” the feature B means the existence of both the features A and B. The term “comprise(s)”, “comprising”, “include(s)”, “including”, “have”, “has” and “having” means “comprise(s)/comprising but is/are/being not limited to”.

[0040] Moreover, in the present specification, when an element is described to be arranged “on” another element, it does not essentially means that the elements contact the other element, except otherwise specified. Such interpretation is applied to other cases similar to the case of “on”.

[0041] Moreover, in the present specification, a value may be interpreted to cover a range within ±10% of the value, and in particular, a range within ±5% of the value, except otherwise specified; a range may be interpreted to be composed of a plurality of subranges defined by a smaller endpoint, a smaller quartile, a median, a greater quartile, and a greater endpoint, except otherwise specified.

Embodiment 1

[0042] In the present embodiment, the nano-twinned copper foil was prepared by rotary plating. The equipment for the rotary plating comprises an electroplating tank, a cathode and an anode. The nano-twinned copper foil was formed on the cathode after electroplating. A titanium rotary cylinder electrode as the cathode was assembled below the modulated speed rotator (AFM3M, PINE), the anode was the Ti/IrO.sub.2 dimensionally stable anode (DSA), and a 1 L beaker was used as the electroplating tank. In the present embodiment, the nano-twinned copper foil was prepared by rotary plating, but the present disclosure is not limited thereto.

[0043] The plating solution used in the present embodiment was formulated by CuSO.sub.4.Math.5H.sub.2O and de-ionized water. The total amount of 157.23 g of CuSO.sub.4.Math.5H.sub.2O (including 50 g/L of copper ion) was provided, added with additive (provided by Chemleader Corporation) and then 80 g of H.sub.2SO.sub.4 (96%) was added into the plating solution, followed by adding 0.1 ml of hydrochloric acid (12 N). The plating solution was stirred with a stir bar until CuSO.sub.4.Math.5H.sub.2O was dissolved into the solution (0.8 L) well.

[0044] In the present embodiment, a programmed power source (E3633A, Keysight) was used for current output, and the electrodeposition was performed with the direct current and pulse electrodeposition. The electrodeposition area was 5×12 cm.sup.2, the current density was controlled in a range from 4 ASD (A/dm.sup.2) to 30 ASD, the electrodeposition temperature was controlled in a range from 6° C. to 50° C., the rotation speed of the modulated speed rotator was 800 rpm, and the electrodeposition was performed at atmospheric pressure.

[0045] In the present embodiment, the electrodeposition was performed at a current density of 11 ASD and a temperature of 25° C., and the nano-twinned copper foil with a thickness of 5 μm was obtained. The surface preferred direction and the micro-structure of the obtained nano-twinned copper foil was analyzed with electron backscatter diffraction (EBSD) and focus ion beam (FIB). FIG. 1A and FIG. 1B are respectively a FIB photo and an EBSD photo of the nano-twinned copper foil prepared in the present embodiment.

[0046] As shown in FIG. 1A, the result obtained by the FIB measurement indicates that most of the grains in the nano-twinned copper foil are formed by twins with high density. 60% or more in volume of the nano-twinned copper foil comprises twinned grains. The included angles between the twin direction of 40% or more of the twinned grains and the thickness direction of the nano-twinned copper foil are ranged from about 0 degree to 30 degrees. The included angles between the twin direction of 40% or more of the twinned grains and the surface of the substrate are range from about 60 degrees to 90 degrees. In addition, 80% or more of the twinned grains in the nano-twinned copper foil have the thickness ranging from about 0.1 μm to about 5 μm.

[0047] Furthermore, as shown in FIG. 1B, the result obtained by the EBSD measurement indicates that the diameters of the twinned grains measured on the surface of the nano-twinned copper foil of the present embodiment are ranged from about 0.5 μm to 3 μm. In addition, about 50% of the twinned grains measured on the surface of the nano-twinned copper foil are formed by stacking nano-twins along a [111] crystal axis (±15 degrees), and this indicates that the nano-twinned copper foil of the present embodiment has a (111) preferred direction.

[0048] A tensile test was performed on the nano-twinned copper foil of the present embodiment. Before the tensile test, the nano-twinned copper foil was cut into a bone-shape by the punch machine to form the standard specimen for the tensile test. Herein, a tensile tester for measuring the characteristics of the metal sheet (AGS-X 10 N˜10 kN, SHIMADZU) was used to perform the tensile test. The strain rate during the stretching at room temperature was controlled at 4.17×10.sup.−3 s.sup.−1. The original tensile data was recorded by the load unit, Newton (N), and was converted into the stress unit, megapascals (MPa) in consideration of the thickness and the width of the test specimen.

[0049] FIG. 2 is a tensile strength curve of the nano-twinned copper foil prepared in the present embodiment. The result shown in FIG. 2 indicates that the tensile strength of the nano-twinned copper foil (5 μm) prepared in the present embodiment can be as high as 800 MPa. This result indicates that the nano-twinned copper foil prepared in the present embodiment has high strength. In addition, when the nano-twinned copper foil of the present embodiment was annealed at 100° C. for 1 hour, the tensile strength of the annealed nano-twinned copper foil was almost unchanged. This result indicates that the nano-twinned copper foil prepared in the present embodiment has high thermal stability.

[0050] In other embodiments of the present disclosure, the nano-twinned copper foils with different tensile strength (ranging from 400 MPa to 850 MPa) can be prepared by adjusting the current density (ranging from 4 ASD to 30 ASD) and the temperature (ranging from 6° C. to 50° C.) during the electrodeposition.

Embodiment 2

[0051] FIG. 3 is an exploded view of a coin-type half-cell of the present embodiment. The coin-type half-cell comprises: an upper case 11, a battery gasket and spring 12, a negative electrode 13, a separator 14, a lithium counter electrode 15 and a bottom case 16. In the present embodiment, the nano-twinned copper foil (5 μm) prepared in Embodiment 1 was used as the collector, and then a negative electrode material was applied onto the collector, followed by punching into the circular shape to obtain the negative electrode 13 of the lithium-ion battery. Then, the negative electrode 13 was assembled with other components to form the coin-type half-cell of the present embodiment.

[0052] In the present embodiment, the active material comprised in the negative electrode material was a mixture of silicon (crystallized Si) and silicon nitride, wherein the content of the silicon nitride was about 50% based on the total weight of the silicon and the silicon nitride. In other embodiments of the present disclosure, the content of the silicon nitride may be ranged from 25% to 85% based on the total weight of the silicon and the silicon nitride. In addition, the negative electrode material may further comprise a conductive agent and an adhesive agent. In the present embodiment, the conductive agent was super P, the adhesive agent was sodium poly-acrylate (Na-PAA), and a weight ratio of the active material, the conductive agent and the adhesive agent was 70:20:10 (wt %).

[0053] Furthermore, in the present embodiment, the used separator 14 was a polypropylene/polyethylene multi-layer separator. The electrolyte comprised 1 M of LiPF.sub.6 (in ethylene carbonate/diethyl carbonate (EC/DEC) with a volume ratio of 1:1) and 5 wt % of fluoroethylene carbonate (FEC). The lithium counter electrode 15 was a lithium foil.

Comparative Embodiment 1

[0054] The coin-type half-cell of the present comparative embodiment is similar to that shown in Embodiment 2, except that the collector used herein was a rolled copper foil.

[0055] The coin-type half-cells prepared in Embodiment 2 and Comparative embodiment 1 were tested by the charge and discharge test to understand the influence of the nano-twinned copper foil on the efficiency of the lithium-ion battery. Herein, the charge and discharge test was performed with different currents of 0.5, 1, 2, 3 and 5 A/g, and the voltage range was 0.01-1.2 V. The results are shown in the following Table 1.

TABLE-US-00001 TABLE 1 Comparative Embodiment 2 embodiment 1 Delithiation Lithiation Delithiation Lithiation Current rate capacity capacity Current rate capacity capacity (A/g) (mAh/g) (mAh/g) (A/g) (mAh/g) (mAh/g) 0.2 1488.8 1543.1 0.2 1219.9 1260.0 0.5 1396.9 1423.7 0.5 1132.6 1152.6 1 1267.6 1283.2 1 953.3 963.6 2 1058.8 1068.1 2 782.9 789.2 3 927.3 933.8 3 666.3 670.9 5 757.3 761.6 5 488.4 491.3 High rate 50.9% High rate 40.0% retention retention (0.2 A/g current (0.2 A/g current rate/5 A/g rate/5 A/g current rate) current rate)

[0056] As shown in Table 1, the coin-type half-cell using the nano-twinned copper foil as the collector prepared in Embodiment 2 has slightly increased delithiation capacity (the capacity that the lithium ions release from the negative active material during discharging) and lithiation capacity (the capacity that the negative active material uptakes the lithium ions during charging) at low current rate (0.2 A/g). As the current rate was increased to 5 A/g, the delithiation capacity and the lithiation capacity of the coin-type half-cell using the nano-twinned copper foil prepared in Embodiment 2 was about 150% of that of the coin-type half-cell using the rolled copper foil prepared in Comparative embodiment 1.

[0057] In addition, after calculating the high rate retention of the coin-type half-cells of Embodiment 2 and Comparative embodiment 1, the high rate retention of the coin-type half-cell using the nano-twinned copper foil prepared in Embodiment 2 was about 50.9%, which is better than the high rate retention of 40.0% of the coin-type half-cell using the rolled copper foil prepared in Comparative embodiment 1. Thus, using the nano-twinned copper foil as the collector of the negative electrode can effectively improve the efficiency of the lithium-ion battery.

Embodiment 3

[0058] The coin-type half-cell of the present embodiment is similar to that shown in Embodiment 2, except that the silicon and silicon nitride comprised in the negative electrode material of Embodiment 2 was replaced by graphite in the present embodiment.

[0059] The coin-type half-cells prepared in Embodiment 2 and Embodiment 3 were tested by the aforesaid charge and discharge test, to understand the influence of different negative electrode materials on the efficiency of the lithium-ion battery. Herein, 1 C was 0.372 A/g, and the results are shown in the following Table 2.

TABLE-US-00002 TABLE 2 Embodiment 3 Embodiment 2 Delithiation Lithiation Delithiation Lithiation capacity capacity Current rate capacity capacity C rate (mAh/g) (mAh/g) (A/g) (mAh/g) (mAh/g) 0.2 C 348.9 351.4 0.2 1488.8 1543.1 0.5 C 331.2 332.5 0.5 1396.9 1423.7 1 C 275.2 275.8 1 1267.6 1283.2 2 C 207.2 207.5 2 1058.8 1068.1 3 C 146.2 146.4 3 927.3 933.8 5 C 90.4 90.5 5 757.3 761.6 High rate 25.9% High rate 50.9% retention retention (5/0.2) (5/0.2)

[0060] As shown in Table 2, at low current rate, the delithiation capacity (the capacity that the lithium ions release from the negative active material during discharging) and lithiation capacity (the capacity that the negative active material uptakes the lithium ions during charging) of the coin-type half-cell using Si/Si.sub.3N.sub.4 prepared in Embodiment 2 was about 400% of that of the coin-type half-cell using graphite prepared in Embodiment 3. As the C-rate was increased to 5 C (i.e. 1.86 A/g), the delithiation capacity and the lithiation capacity of the coin-type half-cell using Si/Si.sub.3N.sub.4 prepared in Embodiment 2 was about 800% or more of that of the coin-type half-cell using graphite prepared in Embodiment 3. These results indicate that when the nano-twinned copper foil (5 μm) was used as the collector of the lithium-ion battery, the battery using Si/Si.sub.3N.sub.4 as the active material has better performance than the battery using graphite as the active material.

[0061] FIG. 4 is a diagram showing the cycle life of the lithium-ion batteries prepared in Embodiment 2 and Comparative embodiment 1 of the present disclosure. As shown in FIG. 4, the cycle life of the lithium-ion battery using the nano-twinned copper foil is better than that of the lithium-ion battery using the rolled copper foil. After 250 cycles, the capacity retention rates of the lithium ion batteries using the nano-twinned copper foil and the rolled copper foil are respectively 73% and 59% after cycling charging and discharging.

Embodiment 4

[0062] The nano-twinned copper foil of the present embodiment was prepared by the similar process illustrated in Embodiment 1, except for the following differences.

[0063] The plating solution used in the present embodiment comprises CuSO.sub.4.5H.sub.2O (including 50 g/L of copper ion), 100 g of H.sub.2SO.sub.4, HCl (including 50 ppm of chloride ion), and additive (9 ml/L). The rotation speed was 1200 rpm and the current density was 15 ASD. The obtained nano-twinned copper foil has a thickness of 5 μm.

[0064] FIG. 5 is a FIB photo of a nano-twinned copper foil prepared in the present embodiment. As shown in FIG. 5, the nano-twinned copper foil was formed by fine twinned grains without specific directions, and the diameters of the fine twinned grains (i.e. the grain size) were ranged from about 100 nm to about 500 nm.

[0065] The coin-type half-cell of the present embodiment is similar to that shown in Embodiment 2, except that the collector used herein was the 5 μm of the nano-twinned copper foil prepared in the present embodiment, and the active material comprised in the negative electrode material is silicon (crystallized Si) but does not comprise silicon nitride.

Comparative Embodiment 2

[0066] The coin-type half-cell of the present comparative embodiment is similar to that shown in Embodiment 4, except that the collector used herein was a rolled copper foil.

[0067] The coin-type half-cells prepared in Embodiment 4 and Comparative embodiment 2 were tested by the aforesaid charge and discharge test, to understand the influence of the nano-twinned copper foil on the efficiency of the lithium-ion battery. The results are shown in the following Table 3.

TABLE-US-00003 TABLE 3 Comparative Embodiment 4 embodiment 2 Delithiation Lithiation Delithiation Lithiation Current rate capacity capacity Current rate capacity capacity (A/g) (mAh/g) (mAh/g) (A/g) (mAh/g) (mAh/g) 0.2 2574.9 2638.9 0.2 2385.0 2448.6 0.5 2280.4 2334.6 0.5 1899.3 1953.0 1 1864.9 1896.9 1 1430.1 1447.4 2 1457.7 1471.8 2 945.4 946.1 3 1153.8 1159.1 3 543.6 544.7 5 773.6 771.8 5 394.5 395.5 High rate 29.2% High rate 16.2% retention retention (0.2 A/g current (0.2 A/g current rate/5 A/g rate/5 A/g current rate) current rate)

[0068] As shown in Table 3, the coin-type half-cell using the nano-twinned copper foil as the collector prepared in Embodiment 4 has slightly increased delithiation capacity (the capacity that the lithium ions release from the negative active material during discharging) and lithiation capacity (the capacity that the negative active material uptakes the lithium ions during charging) at low current rate (0.2 A/g). As the current rate was increased to 5 A/g, the delithiation capacity and the lithiation capacity of the coin-type half-cell using the nano-twinned copper foil prepared in Embodiment 4 was about 196% of that of the coin-type half-cell using the rolled copper foil prepared in Comparative embodiment 2.

[0069] In addition, after calculating the high rate retention of the coin-type half-cells of Embodiment 4 and Comparative embodiment 2, the high rate retention of the coin-type half-cell using the nano-twinned copper foil prepared in Embodiment 4 was about 29.2%, which is better than the high rate retention of 16.2% of the coin-type half-cell using the rolled copper foil prepared in Comparative embodiment 2. Thus, using the nano-twinned copper foil as the collector of the negative electrode can effectively improve the efficiency of the lithium-ion battery.

[0070] In conclusion, compared to the lithium-ion battery using the rolled copper foil as the collector of the negative electrode, the charge and discharge characteristics and the cycle life of the lithium-ion battery using the nano-twinned copper foil as the collector of the negative electrode can be effective improved. In addition, when the nano-twinned copper foil is used in combination with the silicon-based negative electrode material, the charge and discharge characteristics of the lithium-ion battery can further be improved. In particular, the nano-twinned copper foil of the present disclosure has high strength, and can be resistant to the volume change of the silicon-based negative material during charging and discharging. Therefore, the stability and reliability of the lithium-ion battery can further be improved.

[0071] Although the present disclosure has been explained in relation to its embodiment, it is to be understood that many other possible modifications and variations can be made without departing from the spirit and scope of the disclosure as hereinafter claimed.