Safe Li-ion batteries enabled by completely inorganic electrode-coated silicalite separators†
The recent development of salt-concentrated electrolytes with fire-retarding solvents has paved the route to resolve the safety concerns of electrolytes in Li-ion batteries. However, these salt-concentrated electrolytes have an inherently high viscosity and low wettability on commercially dominant polymeric separators, which inhibits them from filling the pores of separators and electrodes leading to performance issues in the battery. Here we report electrode (cathode)-coated zeolite (silicalite) separators synthesized using a scalable blade-coating process. These separators show a much higher wettability and electrolyte uptake towards these electrolytes due to their higher surface energy and intra-particle micropores, resulting in a uniform Li-ion concentration gradient. The zeolite separator also has a much higher porosity (80%) than the PP (39%) separator resulting in a higher electrolyte loading and hence upgraded electrochemical performance. These coated zeolite separators when used in full cells with salt-concentrated electrolytes demonstrate a 15% higher charge retention in long-term cycling and lower charge transfer and SEI resistance compared to the PP separator, as a result of a more uniform lithium ion concentration profile. Moreover, with 1C-rate cycling, the silicalite separator realizes about 20% higher capacity than the PP separator, while losing about 11% of its capacity as compared to the 25% capacity lost by the PP separator, post 50 cycles. The combination of non-combustible, highly electrolyte wettable and industrially scalable zeolite separators combined with a fire-retarding electrolyte provides an effective approach for developing high performance and safe Li-ion batteries.