Copper-coordinated cellulose ion conductors for solid-state batteries

Abstract

While solid-state batteries are tantalizing for achieving improved safety and higher energy density, solid ion conductors currently available fail to satisfy the rigorous requirements for battery electrolytes and electrodes. Inorganic ion conductors allow fast ion transport, but their rigid and brittle nature prevents good interfacial contact and impedes device integration and stability.Conversely, flexible polymeric ion conductors provide better interfacial compatibility and mechanical tolerance, but suffer from inferior ionic conductivity (< 10 −5 S cm −1 at room temperature) due to the coupling of ion transport with the polymer chain motion 1-3 . In this work, we report a general design strategy for achieving one-dimensional (1D), high-performance polymer solid-state ion conductors through molecular channel engineering, which we demonstrate via Cu 2+ -coordination of cellulose nanofibrils. The cellulose nanofibrils by themselves are not ionic conductive; however, by opening the molecular channels between the cellulose chains through Cu 2+ coordination we are able to achieve a Li-ion conductivity as high as 1.5×10 −3 S cm −1 at room temperature-a record among all known polymer ion conductors. This improved conductivity is enabled by a unique Li + hopping mechanism that is decoupled from the polymer segmental motion. Also benefitted from such decoupling, the cellulose-based ion conductor demonstrates multiple advantages, including a high transference number (0.78 vs. 0.2-0.5 in other polymers 2 ), low activation energy (0.19 eV), and a wide electrochemical stability window (4.5 V) that accommodate both Li metal anode and high-voltage cathodes. Furthermore, we demonstrate this 1D ion conductor not only as a thin, high-conductivity solid-state electrolyte but also as an effective ion-conducting additive for the solid cathode, providing continuous ion transport pathways with a low percolation threshold, which allowed us to utilize the thickest LiFePO4 solidstate cathode ever reported for high energy density. This approach has been validated with other 3 polymers and cations (e.g., Na + and Zn 2+ ) with record-high conductivities, offering a universal strategy for fast single-ion transport in polymer matrices, with significance that could go far beyond safe, high-performance solid-state batteries.

Acid‐in‐Clay Electrolyte for Wide‐Temperature‐Range and Long‐Cycle Proton Batteries

“…Based on our experiments (Figure 1), we see that: 1) Since there are many more types of natural materials with abundant internal surfaces (like clays and woods [ 25 ] ) than the materials studied in this work, it is reasonable to conjecture that more solid proton electrolytes with superfast proton conductivity and special properties can be synthesized by integrating proton carriers (water and acids) into the hydrophilic networks. The suppression of first‐order freezing transition and the associated drastic drop in proton conductivity down to −82 °C is one of the benefits of this approach.…”

Foldable Solid‐State Batteries Enabled by Electrolyte Mediation in Covalent Organic Frameworks

“…However, transport of lithium ions in SPEs mainly occurs with the segmental relaxation of polymer chains, which results in a low Li + conductivity (<10 −5 S cm −1 ) at room temperature (RT) and inferior cationic transference number t + , generally 0.2-0.4. [3][4][5][6] Filling the SPEs with a ceramic singleion conductor (SIC) is a practical strategy to promote Li + conductivity. Such polymerceramic composite electrolytes (CPEs) could alleviate brittleness associated with the solid-solid contact of ceramic electrolytes, which generally causes poor interfacial Li + transport and dendrite proliferation along grain boundaries.…”

“…However, transport of lithium ions in SPEs mainly occurs with the segmental relaxation of polymer chains, which results in a low Li + conductivity (<10 −5 S cm −1 ) at room temperature (RT) and inferior cationic transference number t + , generally 0.2–0.4. [ 3–6 ]…”

Current international research into cellulose as a functional nanomaterial for advanced applications

“…In the meantime, how to rationally control the chemical and physical properties of nanocellulose to further enhance the electrochemical performance of devices needs to be considered at a scaled-up level [454]. In addition, most of the development of nanocellulose research in batteries and supercapacitors in the past few decades has been limited to sizes no smaller than the elementary fibril level, while the fundamental science and technologies at the molecular level of nanocellulose deserve further exploration [455]. All in all, the emerging applications of nanocellulose are of obvious benefits to energy storage toward carbon neutrality, but more efforts are needed to overcome existing shortcomings of technologies enabled by nanocellulose.…”