On November 21, 2023, SK nexilis Co., Ltd. (“SKn”) sued Solus Advanced Materials Co., Ltd. (“Solus”) and various Volta Energy Solutions entities in the United States District Court for the Eastern District of Texas. SK nexilis Co., Ltd. v. Solus Advanced Materials Co., Ltd., Case No. 2:23-cv-00539-JRG-RSP, Dkt. No. 1 (E.D. Tex. Nov. 21, 2023). According to the amended complaint, SKn and Defendants are competitors in the market for supplying battery copper foils for use in electrical vehicle batteries. Dkt. No. 9 at ¶ 10. SKn alleges infringement of U.S. Patent Nos. 9,457,541 (“the ’541 Patent”), 10,480,090 (“the ’090 Patent), 10,811,689 (“the ’689 Patent”), 11,346,014 (“the ’014 Patent”), and 11,591,706 (“the ’706 Patent”). Id., Dkt. No. 9 at ¶ 2.
SKn lists as accused products “battery copper foils including standard battery copper foil (BF-PLSP), high-elongation battery copper foil (SR-PLSP), and high-strength battery foil (HTS-PLSP) products. Dkt. No. 9 at ¶ 9.
Dkt. No. 9-2 at 5 (excerpt of Solus’ website in 2023).
In late September and early October of 2024, Solus petitioned for inter partes review of the five asserted patents. Solus Advanced Materials Co., Ltd. v. SK nexilis Co., Ltd., IPR2024-01460, Paper 2 (PTAB Sept. 20, 2024); Solus Advanced Materials Co., Ltd. v. SK nexilis Co., Ltd., IPR2024-01461, Paper 2 (PTAB Sept. 20, 2024); Solus Advanced Materials Co., Ltd. v. SK nexilis Co., Ltd., IPR2024-01462, Paper 2 (PTAB Sept. 20, 2024); Solus Advanced Materials Co., Ltd. v. SK nexilis Co., Ltd., IPR2024-01463, Paper 2 (PTAB Sept. 20, 2024); Solus Advanced Materials Co., Ltd. v. SK nexilis Co., Ltd., IPR2025-00005, Paper 2 (PTAB Oct. 4, 2024).
These five patents relate to an electrolytic copper foil used in the anode of lithium secondary batteries. The electrolytic copper foil is made with a rotational anode drum by electroplating, resulting in a foil with a shiny surface and a matte surface. See, e.g., the ’090 patent at 4:22-27. The SKn patents describe certain conditions that the electrolytic copper foil should satisfy to yield optimal battery performance.
The electrode of the ’090 patent includes a current collector 110 and an active material layer 120. The ’090 patent at 62-65. The ’090 patent specifies that the current collector 110 is an anode current collector, and thus the active material layer 120 uses anode active material. Id. at 4:7-10.
The ’090 patent, Fig. 1 (annotated).
The current collector 110 includes an electrolytic copper foil 111 having a thickness of 3 to 20 µm and a tensile strength of 30 to 60 kgf/mm2, and a protective layer 112 disposed on the electrolytic copper foil 111. The ’090 patent at 4:11-21. According to the ’090 patent, the protective layer 112 may be formed by anticorrosion treatment of the electrolytic copper foil 111. Id. at 5:65-6:6. This anticorrosion treatment prevents corrosion, improves heat resistance, and enhances adhesive strength to the active material layer 120, thus inhibiting deterioration in charge/discharge efficiency of secondary batteries. Id. at 6:6-11.
The ’090 patent specifies that the active material layer 120 and the protective layer 112 need not be on both surfaces of the current collector 110. Id. at 3:65-4:2; id. at 4:19-21.
The ’090 patent states that, using a rotational anode drum by electroplating, the electrolytic copper foil 111 is formed with a shiny surface 111a and a matte surface 111b. The ’090 patent at 4:22-27. According to the ’090 patent, as the roughness on the shiny and matte surfaces decrease, deterioration in charge/discharge efficiency of the secondary battery would also decrease. Id. For optimal capacity maintenance of the secondary battery, the ’090 patent suggests, for both the shiny and matte surfaces 111a, 111b, a ten-point mean roughness RzJIS of 2µm or less, id. at 4:61-64, and a peak count roughness Rpc of 10 to 100, id. at 5:43-45.
Claim 1 of the ’090 patent recites:
An electrolytic copper foil for a secondary battery, the electrolytic copper foil comprising:
a first surface; and
a second surface opposite to the first surface,
wherein each of the first and second surfaces has a peak count roughness Rpc of 10 to 100,
wherein the peak count roughness Rpc of each of the first and second surfaces is an average of peak count roughness Rpc values measured at randomly-selected three points,
the peak count roughness Rpc of each point is the number of effective peaks which rise above an upper criteria line of 0.5 μm per unit sampling length of 4 mm in a surface roughness profile obtained according to steel-iron test schedule (SEP 1940), and
there is at least one valley deeper than a lower criteria line of −0.5 μm between adjacent ones of the effective peaks.
According to the ’689 patent, one type of conventional lithium secondary batteries uses anodes made of electrolytic copper foil applied with composite active material. The ’689 patent at 1:54-58. These composite active materials expand under heat during charge/discharge, causing the electrolytic copper foil to break. Id. at 1:59-63. The copper foil itself is also vulnerable to curling or wrinkling. Id. at 1:63-2:3.
Addressing the problems discussed above, the purported invention of the ’689 patent is an anode of a lithium secondary battery that uses an electrolytic copper foil 110. The ’689 patent at 2:7-11; id. at 4:40-67. The electrolytic copper foil 110 includes a copper layer 111 having a matte surface MS and a shiny surface SS, and protective layers 112a, 112b on the respective surfaces MS, SS. Id. at 5:1-7.
The ’689 patent, Fig. 1 (annotated).
According to the ’689 patent, the copper layer 111 may be formed on a rotating negative electrode drum by electroplating. The surface that touches the rotating negative electrode drum forms the shiny surface SS, and the opposite surface forms the matte surface MS. The ’689 patent at 5:17-20.
According to the ’689 patent, the protective layers 112a, 112b prevent corrosion of the copper layer 111, improve heat resistance of the copper layer 111, and increase adhesion strength between the copper layer 111 and the active material layers 120a and 120b to maintain the charge/discharge efficiency of the secondary battery. The ’689 patent at 5:26-33.
More importantly, the ’689 patent states that, for optimal secondary battery performance, the electrolytic copper foil 110 should have the following qualities. First, the ’689 patent states that the electrolytic copper foil 110 should maintain a coefficient of thermal expansion in the range of 16 to 22 µm/(m°C). The coefficient of thermal expansion is measured by using a thermochemical analyzer (TMA) while heating the electrolytic copper coil 110 from 30°C to 190°C at a speed of 5°C/min. The ’689 patent at 5:34-40.
Second, the ’689 patent states that the electrolytic copper foil 110 should have a tensile strength of21 to 36 kgf/mm2. Tensile strength is measured by heat treating the electrolytic copper foil 110 at a temperature of 190°C for 1 hour. The ’689 patent at 6:1-4.
Third, the ’689 patent states that the electrolytic copper foil 110 should have a weight deviation of 5% or less. Weight deviation is calculated from measuring the weight of a 5cm×5cm samples at 3 points arranged in a traverse direction (TD) of the electrolytic copper foil 110. The ’689 patent at 6:16-30.
Fourth, the ’689 patent states that the electrolytic copper foil 110 should have an elongation of 3 to 10% at room temperature (25±15°C). The ’689 patent at 6:37-40. Fifth, the ’689 patent states that the electrolytic copper foil 110 have a thickness of 4 to 30µm. Id. at 6:54-55.
Sixth, the ’689 patent states that the electrolytic copper foil 110 should have surfaces S1 and S2 with a peak count (PC) in the range of 3 to 92. Peak count is measured based on the number of effective peaks that rise above a 0.5µm upper criteria line per 4mm unit sample length in a surface roughness profile obtained according to U.S. standard ASME B46.1-2009. Id. at 7:43-64.
Finally, the ’689 patent also states that the surfaces S1 and S2 have a surface roughness (Rz) of 3.5µm or less. The ’689 patent at 7:63-64.
Claim 1 of the ’689 patent recites:
An electrolytic copper foil, which includes a first surface and a second surface opposite the first surface, the electrolytic copper foil comprising:
a copper layer including a matte surface facing the first surface and a shiny surface facing the second surface;
a first protective layer on the matte surface of the copper layer; and
a second protective layer on the shiny surface of the copper layer,
wherein:
a coefficient of thermal expansion of the electrolytic copper foil, which is measured using a thermomechanical analyzer (TMA) while heating the electrolytic copper foil from 30° C. to 190° C. at a speed of 5° C./min, ranges from 16 to 22 μm/(m·° C.),
a tensile strength of the electrolytic copper foil, which is measured after a heat treatment at a temperature of 190° C. for 1 hour, ranges from 21 to 36 kgf/mm2,
a weight deviation of the electrolytic copper foil is 5% or less,
a peak count (Pc) of each of the first and second surfaces of the electrolytic copper foil ranges from 3 to 92, and
each of the first and second surfaces has a surface roughness (Rz) of 3.5 μm or less.
According to the ’014 patent, in conventional lithium ion secondary batteries, the force of adhesion between the negative electrodes and the active material applied to the negative electrodes is suboptimal. Low adhesion force may lead to the active material separating from the current collector, resulting in internal short circuit. The ’014 patent at 1:39-62.
Purporting to address the problem above, the ’014 patent describes an electrolytic copper foil 110 with a copper film 111 sandwiched between two protective layers 112, 113:
The ’014 patent, Fig. 1 (annotated). The ’014 patent specifies that the copper foil 110 has a predetermined thickness of 4 to 30µm, id. at 3:57-58, and that the copper film is formed on a rotary negative electrode drum by electroplating, resulting in a shiny surface 111a and a matte surface 111b, id. at 3:65-4:3.
The ’014 patent states that a secondary battery using the electrolytic copper foil 110 operates optimally when the electrolytic copper foil 110 has the following qualities. First, the ’014 patent states that the electrolytic copper foil 110 should have a binding coefficient (BC) between 1.5 and 9.4. The ’014 patent at 5:22-34. The binding coefficient (BC) is calculated as follows:
The ’014 patent at 4:50-54. The ’014 patent specifies that peak height Rp represents surface roughness, and describes ways to measure each value in the equation. Seeid. at 4:55-5:22.
Second, the ’014 patent states that the electrolytic copper foil 110 should have a crystalline structure with a texture coefficient (TC) of a 220 plane between 0.49 to 1.28. The ’014 patent at 5:65-66. The texture coefficient (TC) is calculated as follows:
The ’014 patent at 5:40-67. The ’014 patent states that the texture coefficient of the (220) plane indicates a ratio of the normalized peak strength of the (220) plane to the average peak strength of the (111), (200), (220), and (311) planes normalized as the peak strength of standard Cu in the X-ray diffraction pattern of the sample. Specifically, I(hkl) represents the XRD diffraction strength of an (hkl) crystal plane of a sample, and I0(hkl) means the diffraction strength of an (hkl) crystal plane of standard copper powder. In the equation above, n indicates the number of diffraction peaks within a specific range of diffraction angles (2θ). Id. at 5:48-64.
Third, the ’014 patent states that the electrolytic copper foil 110 should have a weight deviation in lateral direction of less than 3%. The ’014 patent at 6:10-12; see also id. at 6:26-34 (describing how to calculate weight deviation). Fourth, the ’014 patent states that the electrolytic copper foil 110 have a yield strength of 21 to 49 kgf/mm2 measured at a normal temperature (25±15°C). Id. at 6:35-38; see also id. at 6:44-55 (describing how to measure yield strength). Lastly, the ’014 patent states that the protective layers 112, 113 optionally include a roughening treatment layer. Id. at 6:56-62.
The ’014 patent also describes an alternative embodiment with a negative electrode active material layer 120, the ’014 patent at 76:63-7:18; see also id. at Fig. 2, and the manufacturing apparatus for the electrolytic copper foil, id. at 7:19-9:19; see also id.at Fig. 3.
Claim 1 of the ’014 patent recites:
An electrolytic copper foil having a first surface and a second surface, the electrolytic copper foil comprising:
a first protective layer at the first surface;
a second protective layer at the second surface; and
a copper film disposed between the first and second protective layers, wherein
a binding coefficient of the electrolytic copper foil at the first surface or the second surface, defined as Mathematical Expression 1 below, is 1.5 to 9.4,
(Mathematical Expression 1)
Binding coefficient=Rp/μm+ peak density/30+ amount of attachment of Cr/(mg/m2)
(wherein the Rp (μm) is a peak height measured according to JIS B 0601 (2001) standard, wherein the peak density is a number of peaks per unit length of 4 mm, wherein the peak density is measured according to ASME B46.1 (2009) standard with a peak count level of ±0.5 μm and wherein the amount of attachment of Cr (mg/m2) is measured by dissolving the first surface or the second surface of the electrolytic copper foil (110) with a nitric acid solution to obtain a dissolved solution, diluting the dissolved solution with water to obtain a diluted solution, and analyzing the diluted solution using an atomic absorption spectrometer).
According to the ’706 patent, the purported invention is an electrolytic copper foil 100 that is formed on a rotary negative electrode drum by electroplating. The resulting electrolytic copper foil 100 has a shiny surface (an S surface), which is the surface that is in direct contact with the rotary negative electrode drum during electroplating, and a matte surface (an M surface), which is opposite the shiny surface. The ’706 patent at 3:33-40.
The ’706 patent, Fig. 1 (annotated).
The ’706 patent states that the electrolytic copper foil 100 has a thickness of 4 to 30µm, a controlled surface texture factor, and a controlled surface shape factor to inhibit wrinkles, curls, and tears. The ’706 patent at 3:23-26; id. at 3:41-43.
The ’706 patent represents the controlled surface texture factor as a texture coefficient TC of (220) plane, and states that the optimal texture coefficient TC is within the range of 0.40 to 1.32 on both surfaces of the electrolytic copper foil 100. The ’706 patent at 4:12-13. The texture coefficient (TC) is calculated as follows:
The ’706 patent at 3:50-57. In the equation above, I(hkl) represents the XRD diffraction strength of an (hkl) crystal plane of a sample, and I0(hkl) means the diffraction strength of an (hkl) crystal plane of standard copper powder. Id. at 3:58-63. The ’706 patent states that the texture coefficient is obtained from an X-ray diffraction pattern within a range of diffraction angles 2θ between 30 degrees and 95 degrees, and remarkable crystal planes that are considered are (111), (200), (220), and (311) planes (that is, n=4). Consequently, the texture coefficient of (220) plane indicates the ratio of the peak intensity of (220) plane normalized with the peak intensity of standard Cu to the average peak intensity of (111), (200), (220), and (311) planes normalized with the peak intensity of standard Cu in the X-ray diffraction pattern of the sample. Id. at 3:65-4:8.
The ’706 patent represents the controlled surface shape factor as the difference between the ten-point average roughness Rz over the arithmetical average roughness Ra at the two surfaces of the electrolytic copper foil 100, i.e., |Δ(Rz/Ra)|, and states that the optimal |Δ(Rz/Ra)| is less than 2.42. Id. at 4:22-26. Rz and Ra may be measured according to JIS B 0601(2001) standards. Id. at 4:33-34.
The ’706 patent additionally states that a preferrable embodiment of the electrolytic copper foil 100 has the following characteristics: (1) the electrolytic copper foil 100 should have a difference between the peak density PD of the two surfaces the electrolytic copper foil 100, i.e., |ΔPD|, of 96ea or less, the ’706 patent at 4:36-41, (2) the Rz/Ra at the M surface of the electrolytic copper foil 100 should be within the range of 4.2 to 9.0, id. at 4:42-44, (3) the electrolytic copper foil 100 should have a tensile strength, measured at room temperature (25±15°C), of 30 to 65 kgf/mm2, id. at 4:53-55, (4) the electrolytic copper foil 100 should have an elongation, measured at room temperature, of 3% or more, id. at 5:11-14, and (5), the electrolytic copper foil 100 should have a lateral weight deviation of 5% or less, id. at 5:23-25.
Finally, the ’706 patent describes an apparatus for manufacturing the electrolytic copper foil 100. The ’706 patent at 5:41-11:22; see also id. at Fig. 2.
Claim 1 of the ’706 patent recites:
An electrolytic copper foil having a first surface and a second surface, wherein
a texture coefficient of (220) plane of the electrolytic copper foil defined by Equation 1 below is 0.4 to 1.32,
a difference (|Δ(Rz/Ra)|) between Rz/Ra at the first surface of the electrolytic copper foil and Rz/Ra at the second surface of the electrolytic copper foil is less than 2.42, and
a difference (|ΔPD|) between a peak density (PD) at the first surface of the electrolytic copper foil and a peak density (PD) at the second surface of the electrolytic copper foil is 96 ea or less.
The ’706 patent at 11:44-12:8.
The ’541 Patent
The ’541 patent, titled “Copper Foil for Current Collector of Lithium Secondary Battery with Improved Wrinkle Characteristics,” describes an electrolytic copper foil with specific characteristics to reduce wrinkle formation for use in lithium secondary batteries. Those characteristics include crystal structure, surface roughness, weight deviation, tensile strength and elongation. The ’541 patent at 3:3-7.
Specifically, the ’541 patent states that the crystalline structure of the copper foil should satisfy the following conditions: (1) a ratio of the sum of texture coefficients of the (111) surface and the (200) surface, to the total sum of texture coefficients of the (111) surface, the (200) surface and the (220) surface, is 60 to 85%, (2) a ratio of the texture coefficient of the (111) surface to the total sum of the texture coefficients of the (111) surface, the (200) surface and the (220) surface should be 18 to 38%, (3) a ratio of the texture coefficient of the (200) surface thereto should be 28 to 62%, and (4) a ratio of the texture coefficient of the (220) surface thereto should be 15 to 40%. The ’541 patent at 3:23-33; see also id. at 3:33-50 (describing how to obtain a crystalline structure that satisfies the conditions above); id. at 3:51-4:19 (describing how to calculate the texture coefficient).
The ’541 patent further states that the surface roughness (Rz) of the copper foil should be 2µm or less, the ’541 patent at 4:20-21, the weight deviation should be 3% or less, id. at 4:26-27, and the copper foil should have a tensile strength of 30 to 40 kgf/mm2, an elongation of 3 to 20%, and a thickness of 1 to 35μm, id. at 4:40-42.
Claim 1 of the ’541 patent recites:
A copper foil for a current collector of a lithium secondary battery,
wherein, in a crystalline structure, a ratio of a sum of texture coefficients of a (111) surface and a (200) surface to a total sum of texture coefficients of the (111) surface, the (200) surface and a (220) surface is 60 to 85%, a ratio of a texture coefficient of the (111) surface to the total sum of texture coefficients of the (111) surface, the (200) surface and the (220) surface is 18 to 38%, a ratio of the texture coefficient of the (200) surface to the total sum of texture coefficients of the (111) surface, the (200) surface and the (220) surface is 28 to 62%, and a ratio of the texture coefficient of the (220) surface to the total sum of texture coefficients of the (111) surface, the (200) surface and the (220) surface is 15 to 40%,
wherein the texture coefficient satisfies the following equation:
wherein I(hkl) represents a measured diffraction intensity with respect to a (hkl) surface, and I0(hkl) represents a standard diffraction intensity of ASTM (American Society of Testing Materials) standard powder-shaped diffraction data,
wherein the copper foil has a weight deviation of 3% or less, and
wherein the copper foil has a tensile strength of 30 to 40 kgf/mm2,
so as to prevent the generation of wrinkles at a surface of the copper foil.
