Amperex Technology Ltd v. Maxell Ltd

1. Case Identification

• Case #: IPR2021-01442
• Patent #: 9,166,251
• Filed: September 23, 2021
• Petitioner(s): Amperex Technology Limited
• Patent Owner(s): Maxell Holdings, Ltd.
• Challenged Claims: 1-37

2. Patent Overview

• Title: Nonaqueous Electrolyte Battery and Separator
• Brief Description: The ’251 patent describes a separator for a nonaqueous electrolyte battery. The separator features a multilayer structure comprising a heat-shrinkable microporous "shutdown layer" and a "heat-resistant layer" containing specific concentrations and size distributions of fine particles to enhance safety and prevent short circuits at high temperatures.

3. Grounds for Unpatentability

Ground 1: Claims 1, 3-10, 13-30, and 32-37 are obvious over Kasamatsu in view of Katayama.

• Prior Art Relied Upon: Kasamatsu (WO 2006/061936) and Katayama (WO 2007/066768).
• Core Argument for this Ground:
  • Prior Art Mapping: Petitioner argued that Kasamatsu disclosed the fundamental structure of the claimed battery separator, including a heat-resistant layer integrated with a shutdown layer made of thermoplastic resin. Kasamatsu also taught layer thicknesses and materials overlapping with those claimed. However, Kasamatsu did not explicitly disclose the claimed particle concentration (e.g., ≥ 50 vol. %) or the specific particle size distribution (e.g., < 10 vol. % of particles < 0.2 µm and > 2 µm) in the heat-resistant layer. Petitioner asserted that Katayama supplied these missing elements, disclosing a heat-resistant layer with a preferred particle concentration of at least 80 vol. % and a particle size distribution (0.3-0.7 µm) that meets the claimed limitations.
  • Motivation to Combine: Petitioner contended that a person of ordinary skill in the art (POSITA), addressing the known problem of thermal shrinkage and short-circuiting identified in Kasamatsu, would combine its teachings with Katayama. Katayama was said to solve the precise problem identified in Kasamatsu by teaching how to optimize the particle concentration and size distribution to improve heat resistance and prevent short circuits.
  • Expectation of Success: A POSITA would have had a reasonable expectation of success because the combination involved applying Katayama's specific particle composition to Kasamatsu's similar separator design within a predictable lithium-ion battery chemistry.

Ground 2: Claims 1, 4-10, 13, 15-23, 26-27, and 30-35 are obvious over Yoshida in view of Nagayama, Takezawa, and Amagi.

• Prior Art Relied Upon: Yoshida (European Patent No. EP 1,115,166), Nagayama (WO 2006/134833), Takezawa (Application # 2007/0015058), and Amagi (Japanese Patent Publication No. JP 2003/306594).

• Core Argument for this Ground:

  • Prior Art Mapping: Petitioner alleged that Yoshida disclosed the basic separator architecture, including a shutdown layer integrated with a heat-resistant layer containing over 50 vol. % of fine particles. However, Yoshida lacked specificity regarding the particle size distribution, layer thicknesses, and high-temperature electrode materials. Petitioner argued a POSITA would look to other references to optimize Yoshida's design. Amagi was cited for disclosing commercially available alumina particles (AA-03) with the specific size distribution required by the claims. Nagayama was cited for teaching the claimed layer thicknesses and suitable positive electrode materials. Takezawa was cited for disclosing high-capacity positive electrode active materials with heat generation starting temperatures well above the claimed 180°C.
  • Motivation to Combine: A POSITA would combine these references as a matter of routine optimization. Petitioner asserted a POSITA would incorporate Amagi's well-known particle distribution into Yoshida's separator to improve performance. The POSITA would then look to Nagayama for optimal layer thicknesses to enhance energy density and discharge characteristics—a factor Yoshida noted as important but did not detail. Finally, to maximize battery capacity while maintaining safety, the POSITA would incorporate the high-temperature cathode materials taught by Nagayama and further improved by Takezawa.
  • Expectation of Success: Success would be expected as the combination involved simple substitutions of known, compatible components (particles, layer dimensions, electrode materials) to achieve predictable improvements in a standard battery separator design.

• Additional Grounds: Petitioner asserted additional obviousness challenges, including combining Kasamatsu and Katayama with Miyatake (Ground 1B) to teach specific thermal shrinkage ratios. Further grounds combined the Yoshida/Nagayama/Takezawa/Amagi art with Miyatake (Ground 2B) or Katayama (Ground 2C) to teach limitations related to thermal shrinkage or particle concentration, respectively.

4. Key Technical Contentions (Beyond Claim Construction)

• Priority Date Challenge: Petitioner argued the challenged claims were not entitled to their asserted foreign priority dates. It contended that the priority documents failed to disclose the specific claimed particle size distribution (i.e., less than 10 vol. % of particles below 0.2 µm and above 2 µm), instead only providing broad average particle size ranges. This lack of written description support, per Petitioner, established a later effective filing date, making several key prior art references available under 35 U.S.C. §102(b).

5. Arguments Regarding Discretionary Denial

• Petitioner argued that discretionary denial would be inappropriate under both 35 U.S.C. §325(d) and §314(a) (Fintiv factors).
• §325(d): Petitioner contended that the asserted prior art and arguments were new and materially different from those considered by the examiner during prosecution. Specifically, it noted that the Katayama reference relied upon in the petition is distinct from the Katayama '577 application cited by the examiner and teaches the effectiveness of combining the claimed particle concentration and size distribution, which was a key issue during prosecution.
• §314(a) / Fintiv: Petitioner argued that the co-pending district court litigation was in its infancy, with minimal investment and no trial date set. It asserted that the merits of the petition are strong and that other Fintiv factors weighed heavily in favor of institution.

6. Relief Requested

• Petitioner requested the institution of an inter partes review and the cancellation of claims 1-37 of the ’251 patent as unpatentable.