Novel Zeolitic Electrolyte for Lithium-Ion Batteries and Beyond
1. Background and objectives
One of the major components of batteries, electrolytes act as the ion-conducting media and electronical insulators to carry out redox reactions ((de)lithiation in lithium-ion batteries or lithium stripping/plating in lithium metal batteries) at the electrode surfaces, thereby creating an electrical potential for energy storage. The physical and chemical characteristics of electrolytes thus become essential in determining the energy and power density, device stability, and cost-effectiveness of the batteries. Historically, electrolytes are utilized in the forms of liquid (organic carbonates), solid (ceramics, polymers), or the hybrid thereof (gel polymers). All come with specific pros and cons which have been extensively engineered to meet our needs for technology integration. Though many major breakthroughs have been achieved, including the recently awarded Nobel Prize of the discovery of lithium-ion batteries, state-of-the-art electrolytes still struggle to enable the next battery generations with the goal of complete independence of fossil fuel.
Several remarkable electrolytes have been synthesized at lab scale that show very promising characteristics, especially in ionic conductivities and stability (electrochemical, thermal, mechanical, and dimensional). Regardless of their associated drawbacks, new approaches recently appear to have stalled as scientific publications and patents constantly revolve around old ideas with rare occasions of significant step forward to break inherent thermodynamic limitations in lithium batteries. In other words, a saturated state of ideas seems inevitable. Thus, a new class of electrolyte is crucial for two reasons: open another direction for development to progress and/or collectively resolve the pitfalls in previously reported electrolytes, together to bridge the gap between lithium batteries and fossil fuel in both consumer and socioeconomical impacts.
Zeolitic materials have been extensively utilized in many industries including catalysis, solar energy storage, and biomedical. However, little research attention has been paid to incorporating this class of material in lithium batteries, except for a very preliminary mixing as ceramic nanofiller into polymer electrolytes without much engineering done.[1]
Nanosheet zeolites recently become a hot topic of research for its novel structure of single-unit-cell thickness. With well-defined channel geometry, zeolite nanosheets can facilitate ionic transport efficiently and uniformly (which is critical for even distribution of lithium flux on electrode surface and for preventing formation of lithium dendrites), and simultaneously can act as an electronic insulator thanks to its ceramic nature. Figure 1 depicts the novel concept of a lithium zeolite battery which is not found in any literature. Along with the ultra-light weight and ultra-low volume, the energy density will be greatly improved. The tunable number of nanosheets is speculated to control the cycling behaviors. This concept, if proved working, shall lead to a patent (academic success statement).
One major concern is the electrode-zeolite interface where the two materials are expected to establish poor contact. Nevertheless, this contact can be dramatically improved if the two surfaces can be chemically bonded. This is where bis(diazonium) salt is introduced to bond zeolite nanosheets to the electrode surface covalently and thus creating an intimate contact. The synthesis process to attach zeolite nanosheets to an electrode surface, e.g. graphite, is summarized via the following chain of reactions:
