In-built intermolecular hydrogen bonds enabling stable interfacial chemistry for all-solid-state li metal batteries

All-solid-state lithium batteries (ASSLB), with the conventional flammable organic electrolytes replaced by solid-state ones, promise high energy density and high safety for the next-generation energy storage solution. Among all the candidates, the polymer-based electrolyte draws particular interests owing to their good film-forming ability, ease of scale-up processing and superior adhesion to the electrode surface, generating the milestone concept of lithium polymer electrolyte in the battery history. While polyethylene oxide (PEO)-based electrolytes have been extensively used, the linear structure of PEO with high crystallinity restricts the segmental motion of polymer chains and thus results in unsatisfactory ionic conductivity, especially at low temperatures. Additionally, PEO electrolytes exhibit poor interfacial compatibility with lithium metal as they decompose into a passivation layer that causes the growth of lithium dendrites. The soft nature of PEO with limited mechanical strength are not capable of upholding these dendrites and the battery typically fails at a quite early stage. These shortcomings motivate the search for polymer electrolytes with simultaneously high ionic conductivity, robust mechanical properties, and stable interfaces.

A prevalent strategy to overcome these limitations is to incorporate foreign inorganic nanoparticles, known as fillers, into the parent polymer matrix to form composite structures. These nanosized fillers disrupt the long-range order of polymer chains, expanding the amorphous domains that promote the mobility of Li ions. Although room-temperature conductivities on the order of 1 × 10⁻⁴ S cm⁻¹ can now be reached, the weak ceramic–polymer interface provides only modest mechanical reinforcement, and tensile strengths rarely exceed 1.2 MPa. More importantly, the chemistry of these composites changes little, so interfacial stability against metallic lithium remains poor. Consequently, the design of composite electrolytes with fundamentally new architectures is both timely and critical.

Compared to traditional inorganic fillers, metal-organic frameworks (MOFs), composed of metal clusters and organic linkers, provide a versatile platform for re-engineering electrolyte chemistry at the molecular level. Hereby, we developed a three-in-one composite electrolyte (PCUN) that consists of PEO, Co-doped UiO-66 (CoUiO), and lithium nitrate (LiNO₃). In this system, hydrogen atoms on the PEO chains form strong intermolecular hydrogen bonds with both the μ3-OH oxygen atoms in CoUiO and the nitrate anions, generating a cross-linked network that dramatically suppresses PEO crystallinity. The resulting solution-cast membrane is defect-free, exhibits an ionic conductivity of 5.7×10^-4 S cm^-1 at 25 °C, and possesses a tensile strength of 1.4 MPa, twice that of pristine PEO, while sustaining an ultimate strain of 1293%. When paired with lithium metal, the bimolecular hydrogen-bond-rich interface fosters a solid electrolyte interphase rich in Li₃N and LiF, enabling symmetric cells to cycle stably for 2,000 h without short-circuiting. A prototype all-solid-state lithium-sulfur cell built with this membrane simultaneously delivers high capacity and outstanding stability, underscoring the promise of “three-in-one” polymer electrolytes with in-built intermolecular hydrogen bonds for practical high-energy storage systems.

Other contributors include: Teng Xu, Mengyan Gu, Qin Sun, Zhiyuan Guo, Zijun Li, Mei Yang, Qiuying Xia, Yiren Zhong & Hui Xia from Nanjing University of Science and Technology; and Yiren Zhong from Southeast University.

This work was financially supported by the National Natural Science Foundation of China (Nos. 22272080 (M.Y.) and 52272218 (H.X.)), and the Natural Science Foundation of Jiangsu Province (No. BK20200076 (M.Y.)). Y. Z. acknowledges the Fundamental Research Funds for the Central Universities (No. 2242024k30047).

Brief introduction of NEM research group

The Nano Energy Materials (NEM) Research Group at Nanjing University of Science and Technology was founded in 2011. Today the team comprises six faculty members—three professors and four associate professors—along with more than 50 graduate students. Our core interests are the fundamental science and scalable manufacturing of key materials for:

• All-solid-state thin-film lithium batteries: Developing mass-production routes and 3D architectures that deliver high energy density, intrinsic safety, long cycle life, wide temperature tolerance, low self-discharge, and superior rate capability for self-powered microelectronic systems.

• Next-generation Li⁺/Na⁺ storage and supercapacitors: Designing cost-effective, high-performance electrode and electrolyte materials for both aqueous and organic systems, targeting large-scale deployment in electric vehicles and smart grids.

Website:  http://nem.smse-njust.com/