Composite Electrode and Lithium-Ion Battery Comprising Same and Method for Producing the Composite Electrode

Abstract

A composite electrode is provided having a collector, the collector is coated with an electrode composition containing an active electrode material, a binding agent, and a conductivity additive such as conductive carbon black. The electrode composition has a concentration gradient along the direction of the electrode thickness in respect of the active electrode material and the conductivity additive, with the concentration gradient of the active electrode material increasing toward the collector, and the concentration gradient of the conductivity additive and the binder decreasing toward the collector. Two different methods of producing the composite electrode are also provided. A lithium-ion battery is further provided which includes a composite electrode having a collector, the collector is coated with an electrode composition containing an active electrode material, a binding agent, and a conductivity additive.

Claims

1. A composite electrode comprising: a collector, the collector is coated with an electrode composition comprising an active electrode material, a binder, and a conductivity additive, wherein the electrode composition has a concentration gradient along the direction of the electrode thickness in respect of the active electrode material, the binder, and the conductivity additive, wherein a concentration gradient of the active electrode material increases in the collector direction, and a concentration gradient of the conductivity additive and a concentration gradient of the binder decreases in the collector direction.

2. The composite electrode according to claim 1, wherein the electrode composition, based on volume, possesses a porosity of 5% to 50%, and has a ratio of the porosity in a near-surface layer to the porosity of a layer near to the collector of 1.2 to 5.

3. The composite electrode according to claim 2, wherein the electrode composition has a ratio of the porosity in a near-surface layer to the porosity of a layer near to the collector of 1.5 to 4.

4. The composite electrode according to claim 2, wherein the electrode composition has a ratio of the porosity in a near-surface layer to the porosity of a layer near to the collector of 1.5 to 2.5.

5. The composite electrode according to claim 1, wherein the conductivity additive is present in the electrode composition in an amount of 1 to 4 wt % and the binder is present in the electrode composition in an amount of 1 to 4 wt %.

6. The composite electrode according to claim 1, wherein the conductivity additive is conductive carbon black.

7. The composite electrode according to claim 1, wherein the electrode composition has a ratio of the weight-based amount of conductivity additive in a layer near to the collector to the weight-based amount of the conductivity additive of a near-surface layer of 1.2 to 5.

8. The composite electrode according to claim 1, wherein the electrode composition has a ratio of the weight-based amount of conductivity additive in a layer near to the collector to the weight-based amount of the conductivity additive of a near-surface layer of 1.5 to 4.

9. The composite electrode according to claim 1, wherein the electrode composition has a ratio of the weight-based amount conductivity additive in a layer near to the collector to the weight-based amount of the conductivity additive of a near-surface layer of 1.5 to 2.5.

10. The composite electrode according to claim 1, wherein the active electrode material is an anode material selected from the group consisting of synthetic graphite, natural graphite, carbon, lithium titanate, and mixtures thereof.

11. The composite electrode according to claim 1, wherein the active electrode material is a cathode material selected from the group consisting of lithium transition-metal oxide, layered oxides, spinels, olivine compounds, silicate compounds, high-energy NCM, and mixtures thereof.

12. The composite electrode according to claim 1, wherein the binder is selected from the group consisting of polyvinylidene fluoride, copolymer of polyvinylidene fluoride and hexafluoropropylene, copolymer of styrene and butadiene, cellulose, cellulose derivatives, and mixtures thereof.

13. The composite electrode according to claim 1, wherein a lithium diffusion coefficient of the active electrode material or of a mixture thereof at room temperature (20° C.) is 1.0×10.sup.−4 cm.sup.2 s.sup.−1 to 1.0×10.sup.−14 cm.sup.2 s.sup.−1 and wherein the gradient of the lithium diffusivity decreases in the collector direction.

14. A lithium-ion battery comprising: two electrodes, a separator, and an electrolyte, wherein at least one of the electrodes is a composite electrode comprising a collector, the collector is coated with an electrode composition comprising an active electrode material, a binder, and a conductivity additive, wherein the electrode composition has a concentration gradient along the direction of the electrode thickness in respect of the active electrode material, the binder, and the conductivity additive, wherein a concentration gradient of the active electrode material increases in the collector direction, and a concentration gradient of the conductivity additive and a concentration gradient of the binder decreases in the collector direction.

15. A method for producing a composite electrode having a collector, the collector is coated with an electrode composition comprising an active electrode material, a binder, and a conductivity additive, the method comprising the steps of: a) combining at least the active electrode material, the binder in solution with a solvent, and the conductivity additive, to form a homogeneous slurry; b) applying the slurry to the collector; c) stripping off the solvent under reduced pressure and/or at elevated temperature, to form a porosity in the slurry; and d) adjusting the porosity by calendering; wherein steps a) to d) are repeated at least once, in the course of which in step a) the electrode composition is modified such that the electrode composition has a concentration gradient along the direction of the electrode thickness in respect of the active electrode material and the conductivity additive, wherein a concentration gradient of the active electrode material increases in the collector direction, and the concentration gradient of the conductivity additive decreases in the collector direction.

16. A method for producing a composite electrode having a collector, the collector is coated with an electrode composition comprising an active electrode material, a binder, and a conductivity additive, the method comprising the steps of: a) combining at least the active electrode material, the binder in solution with a solvent, and the conductivity additive, to form a homogeneous slurry; b) applying the slurry to the collector; c) stripping off the solvent under reduced pressure and/or at elevated temperature, to form a porosity in the slurry; and d) adjusting the porosity by calendering, wherein the electrode composition is modified in step b) by adjusting and utilizing different densities of the electrode material by means of ascending or descending in the slurry, or by utilizing diffusion in the solvent, such that the electrode composition has a concentration gradient along the direction of the electrode thickness in respect of the active electrode material and the conductivity additive, wherein a concentration gradient of the active electrode material increases in the collector direction, and a concentration gradient of the conductivity additive decreases in the collector direction.

Description

WORKING EXAMPLES

[0062] Cell construction principle for all examples:

[0063] Anode: 1% SBR, 2% CMC, 1% Super C45, 96% Hitachi MAG D20.

[0064] Cathode: 4% PVdF Solef® 5130 (from Solvay); 4% Super C45 (from Timcal); 92% NMC111 (from BASF, HED).

[0065] Separator: 25 μm Celgard® 2325. Electrolyte 1 M LiPF.sub.6 in EC:DEC (3:7 v/v). 115 μm packaging with composite aluminum foil from Showa (Japan).

[0066] Anode area: 9.7*7 cm.sup.2; cathode area 9.3*6.6 cm.sup.2.

Example 1

[0067] Areal weight (AW) anode: 7.0 mg/cm.sup.2. AW cathode: 14.0 mg/cm.sup.2. The electrode does not have a graduated design.

Example 2

[0068] Areal weight (AW) anode: 17.5 mg/cm.sup.2. AW cathode: 35.0 mg/cm.sup.2. The electrode does not have a graduated design.

Example 3

[0069] Areal weight (AW) anode: 17.5 mg/cm.sup.2. AW cathode: 35.0 mg/cm.sup.2. Both electrodes have a graduated design according to the invention.

[0070] In this Example, within the cathode, the concentration of conductive carbon black increases from the collector side to the electrode surface from 2-6 percent by weight, and the concentration of the electrode binder increases from 2-6 percent by weight. The concentration of the active material is 94 (current collector) −90 percent by weight (cathode surface). Porosity 30 (current collector side) −36 (cathode surface) percent by volume.

[0071] Within the anode, the concentration of conductive carbon black increases from the collector side to the electrode surface from 0.5-1.5 percent by weight, and the concentration of the two electrode binders, CMC and SBR, is 2-4 percent by weight. The concentration of the active material is 97 (current collector) −95 percent by weight (anode surface). Porosity 30 (current collector side) −36 (anode surface) percent by volume.

[0072] Results of the long-term cycling tests at 1C (CCCV)/1C (CC) under room-temperature conditions:

TABLE-US-00001 TABLE 1 Number of full cycles until 80% Cell example residual capacity is reached Notes 1 500 Electrodes charged to low level with nongraduated design. 2 300 Highly charged electrodes with nongraduated design. 3 500 Highly charged electrodes with graduated design according to the invention.

[0073] Result of Long-Term Cycling:

[0074] The cells with the highly charged electrodes in accordance with a graduated construction according to the present invention exhibit cycling results identical to those of the cells with electrodes charged to a low level. Both cell types, accordingly, also have better cycling stability than cells with highly charged electrodes according to the non-graduated design.

[0075] The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof.