Large-Scale Nanofiber Manufacturing| Addressing the interface issues of all-solid-state lithiumbatteries by ultra-thin composite solid-state electrolytecombined with the integrated preparation technology

Prof. Fan Lizhen at USTB InfoMat: Integrated Electrode-Electrolyte Preparation Process Solves Interface Issues in Solid-State Batteries

Research Background:
With increasing demands for safety, energy density, and charging capability in future energy storage technologies, interface engineering in solid-state lithium batteries (SSLBs) is receiving growing attention. However, polymer/ceramic interface compatibility, severe agglomeration of ceramic particles, and discontinuous ionic conduction at electrode/electrolyte interfaces severely limit Li+ transport in SSLBs, hindering their application and large-scale manufacturing.

To address this, Prof. Fan Lizhen's team at the University of Science and Technology Beijing designed an integrated electrode-electrolyte preparation process for solid-state batteries using electrospinning combined with solution casting technology to enhance cathode-electrolyte interface contact. They introduced a 3D nanofiber-reinforced composite electrolyte where LLZO nanoparticles dispersed in PAN nanofibers form continuous 3D lithium-conducting pathways, demonstrating excellent electrochemical performance. The research was published in InfoMat under the title "Addressing the interface issues of all-solid-state lithium batteries by ultra-thin composite solid-state electrolyte combined with the integrated preparation technology."

Content Summary:
The team proposed an integrated electrode-electrolyte preparation process for solid-state batteries using electrospinning and solution casting methods. Incorporating LLZO into PAN nanofibers facilitates the formation of continuous lithium-ion transport channels. Additionally, nitrogen (N) from PAN, fluorine (F) from LiTFSI, and oxygen (O) from PEO and SN can combine with lithium, promoting stable SEI formation at the lithium metal-electrolyte interface.The resulting electrolyte, with a thickness of ~16 μm, features a self-supporting structure from the ceramic (LLZO) and polymer (PAN) phases. This continuous interface enables multiphase-coupled lithium-ion transport, while the in-situ formed SEI passivation layer effectively suppresses lithium dendrite formation and growth.

Figure 1. Continuous integrated manufacturing process of 3D LLZO-PAN battery and its interfacial integrated structure.

As shown in Figure 2, SEM images of the polymer-ceramic nanofiber skeleton surface reveal three-dimensional interconnected channels that effectively promote polymer phase penetration and integration, thereby enabling continuous multiphase ionic conduction within the ultrathin SSE membrane. The PAN fibers have a diameter of approximately 500 nm, with the number of nanoparticles inside the nanofibers increasing with ceramic content. The ceramic particles are uniformly distributed within the PAN nanofibers, forming tightly connected three-dimensional conductive self-supporting networks.In contrast, LLZO particles outside PAN fibers (LLZO-PAN) exhibit more aggregated secondary particles, which hinder the formation of continuous conductive networks and result in lower ionic conductivity. After mixing PEO solution with SN, the resulting gel permeates the fiber network to form a 3D LLZO-PAN electrolyte with a thickness of only 16 μm.

Figure 2. Physicochemical properties of 3D LLZO-PAN electrolyte.

As shown in Figure 3, the 3D LLZO-PAN electrolyte demonstrates a room-temperature conductivity of 2.9×10−4 S cm−1, twice that of LLZO-PAN electrolyte. This conductivity enhancement can be attributed to the highly uniform dispersion of LLZO within PAN fibers. The homogeneous LLZO ceramic matrix network reduces the energy barrier for Li+ migration and promotes ion transport within the 3D LLZO-PAN electrolyte. Nano-sized LLZO serves as an ion-conductive filler while simultaneously reducing the crystallinity of the 3D LLZO-PAN electrolyte and enhancing Li+ transport across abundant inorganic-organic phase boundaries.

Figure 3. Electrochemical performance and ion transport mechanism of 3D LLZO-PAN electrolyte.

As shown in Figure 4, the lithium dendrite suppression capability of the composite solid electrolyte was evaluated by assembling Li||Li symmetric cells. The 3D LLZO-PAN electrolyte maintains stable cycling for 1500 hours at a current density of 0.2 mA cm−2. X-ray photoelectron spectroscopy (XPS) characterization of the post-cycled lithium metal interface confirmed the presence of Li3N and LiF in the Li 1s and N 1s spectra of 3D LLZO-PAN. Both Li3N and LiF are excellent electronic insulators that can prevent side reactions that consume active electrolyte components at the interface.

Figure 4. Lithium metal stability of 3D LLZO-PAN.

As shown in Figure 5, the stability of the composite electrolyte with high-voltage cathodes and lithium metal was verified by assembling NCM||Li coin cells. Test results demonstrate that the integrated 3D LLZO-PAN battery exhibits excellent rate capability and cycling stability, with significantly reduced interfacial transfer resistance, confirming the effectiveness of the integrated design in improving cathode contact and reducing internal battery resistance. Even after prolonged cycling, the interfacial contact in integrated 3D LLZO-PAN batteries remains tight, highlighting the persistent strong adhesion at the interface.

Figure 5. Performance of integrated 3D LLZO-PAN Li||NCM811 full cell.

Conclusion:

In summary, we propose an integrated electrode-electrolyte preparation process to address interface issues in solid-state batteries, introducing a three-dimensional nanofiber-reinforced framework as the composite solid electrolyte. The nanofiber-reinforced skeleton and polymer matrix, through the adhesion enabled by electrospinning and solution casting techniques, provide sustained ionic conduction and intimate contact with the cathode. Using integrated ultrathin 3D LLZO-PAN films, the assembled SSLBs can deliver a high energy density of 345.8 Wh kg−1. This work presents a new strategy for processing electrolyte membranes and high-energy-density SSLBs. Our method can be extended to design solid-state batteries for other organic-inorganic composite SSE systems. This work proposes a novel strategy for processing electrolyte membranes and high-energy-density SSLBs, which can be extended to the design of solid-state batteries for other organic-inorganic composite SSE systems.