Opportunity
The advancement of solid-state lithium-ion batteries (SSLIBs) is critically hindered by the limited electrochemical stability of conventional solid polymer electrolytes (SPEs) when paired with high-voltage cathode materials. While SPEs offer enhanced safety, mechanical flexibility, and processability compared to liquid electrolytes, most existing polymers, such as poly(ethylene oxide) (PEO) or polyvinylidene fluoride (PVDF), possess insufficient oxidation resistance. This makes them incompatible with aggressive, high-energy-density cathodes like nickel-rich LiNi₀.₈Mn₀.₁Co₀.₁O₂ (NMC811) or high-voltage spinel LiNi₀.₅Mn₁.₅O₄ (LNMO), which operate above 4.5V. When coupled with such cathodes, conventional SPEs undergo oxidative decomposition at the cathode-electrolyte interface. This leads to the release of gases like CO₂, cathode surface reconstruction, dissolution of transition metal ions, and the formation of unstable interphases. Consequently, cells experience rapid capacity fade, poor cycling stability, and increased internal resistance, severely limiting the achievable energy density and long-term performance of SSLIBs. The inability to reliably use high-voltage cathodes with SPEs represents a major bottleneck in developing next-generation batteries with higher energy densities for electric vehicles and advanced electronics.
Technology
This patent introduces a novel PVTF-based solid polymer electrolyte (where PVTF denotes poly (vinylidene fluoride-co-trifluoroethylene-co-chlorotrifluoroethylene)) designed to overcome the oxidation instability of SPEs. The core innovation is a composite electrolyte formulation that dramatically widens the electrochemical window to 5.68V. The technology employs a multi-component strategy. First, it utilizes a PVTF polymer matrix, which computational analysis shows has the lowest highest occupied molecular orbital (HOMO) energy level among common polymers, granting it inherent high oxidation stability. Second, lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt is incorporated to provide high ionic conductivity. Third, and crucially, a sacrificial additive, lithium difluorophosphate (LiDFP), is added. During battery operation, the LiDFP decomposes preferentially at the cathode surface to form a robust, multi-layered cathode-electrolyte interphase (CEI). This CEI has an inner inorganic layer rich in Li₃PO₄ and LiF and an outer organic layer. This engineered CEI acts as a protective barrier, preventing direct contact and continuous parasitic reactions between the aggressive high-voltage cathode (e.g., LNMO) and the polymer electrolyte. It also suppresses transition metal dissolution and cathode surface reconstruction. The resulting PVTF-based SPE with LiDFP (denoted PLSE) achieves an exceptional ionic conductivity of 1.91×10⁻³ S cm⁻¹ at room temperature and a low glass transition temperature below -38°C, ensuring good ion transport and low-temperature performance. This combination of a stable polymer matrix and a self-forming protective interphase enables the stable cycling of high-voltage Li||LNMO solid-state cells.
Advantages
- Achieves an exceptionally wide electrochemical stability window of up to 5.68V, enabling compatibility with high-voltage cathode materials.
- Delivers high ionic conductivity (1.91×10⁻³ S cm⁻¹ at ambient temperature) for improved rate capability.
- Enables long-term cycling stability, with high-voltage cells retaining 75% capacity over 200 cycles at 0.5C.
- Features a low glass transition temperature (< -38°C), promoting good low-temperature performance.
- The in-situ formed CEI layer effectively stabilizes the cathode interface, suppressing side reactions and transition metal dissolution.
- The fabrication process (casting and blade coating) is cost-effective, user-friendly, and suitable for scalable manufacturing compared to complex ceramic electrolyte processes.
- Enhances safety by utilizing a solid polymer electrolyte, eliminating flammable liquid components.
Applications
- High-energy-density solid-state lithium-ion batteries for electric vehicles (EVs).
- Advanced consumer electronics requiring long-lasting, safe, and fast-charging batteries.
- Large-scale stationary energy storage systems for grid support.
- Flexible and wearable energy storage devices.
- Other lithium-based battery systems, such as lithium-sulfur or lithium-oxygen batteries, that could benefit from a wide-voltage-window electrolyte.
