IEST SEMS Characterization Solutions Enable Groundbreaking Research: Pressure-Free Silicon-based Anode Achieves 1000 Stable Cycles in All-Solid-State Batteries

A sSilicon-based anode all-solid-state battery (ASSB) operating without external pressure has been demonstrated for the first time at a practical scale, achieving 1,000 stable cycles at 2.5 mA cm⁻² with a capacity retention of 54.9% and a minimal volume expansion of only 14.5% — setting a new record for pressure-free silicon-based ASSBs. The breakthrough, published in Nature Communications (2025) by Xiamen University, relies on a Li₂₁Si₅/Si–Li₂₁Si₅ bilayer composite anode that homogenizes the electric field at the solid-solid interface, enabling stable lithium-ion transport without the 10–250 MPa external pressure conventionally required to maintain electrode–electrolyte contact. Material characterization for this research was performed in part using IEST SEMS series solid electrolyte characterization equipment, acknowledged by the authors in the published paper.

1. Research Summary

A research team led by Chen Songyan and Wang Mingsheng from Xiamen University has published a significant advance in silicon-based anode materials for all-solid-state batteries in Nature Communications, titled “Silicon-based all-solid-state batteries operating free from external pressure” (Nat Commun 16, 1013, 2025). First author Dr. Zhang Zhiyong designed and constructed a Li₂₁Si₅/Si–Li₂₁Si₅ bilayer composite anode that enables stable ASSB operation without external pressure — overcoming a fundamental barrier in solid-state battery engineering.

The battery achieved 1,000 cycles at 2.5 mA cm⁻² with a capacity retention rate of 54.9% and a volume expansion of only 14.5%, establishing a new performance record for pressure-free silicon-based ASSBs. To characterize the bilayer anode’s microstructure, interfacial chemistry, surface potential, and lithium-ion states, the research team employed SEM, XRD, XPS, AFM, and SSNMR, supported by COMSOL Multiphysics simulations. Material characterization was performed using IEST SEMS series solid electrolyte characterization instruments — acknowledged by the authors in the published paper.

Figure 1. Structural characterization and surface potential of the Li₂₁Si₅/Si-Li₂₁Si₅ anode.

2. Key Performance Data: Pressure-Free Silicon-Based All-Solid-State Batteries

The Li₂₁Si₅/Si–Li₂₁Si₅ bilayer anode enables the following verified electrochemical performance in all-solid-state batteries without external mechanical pressure:

3. The Challenge: The “Pressure Dilemma” in All-Solid-State Batteries

The fundamental problem: silicon undergoes dramatic volume expansion (up to ~300%) during lithium intercalation, which disrupts the critical solid-solid contact at the electrode–electrolyte interface in all-solid-state batteries. Conventional approaches require applying substantial external pressure — typically 10–250 MPa for oxide electrolyte systems, 1–10 MPa for sulfide electrolytes — to maintain this contact throughout cycling. For silicon anodes specifically, the large volumetric change makes pressure management particularly complex: the optimal pressure at the start of cycling diverges significantly from the pressure state after hundreds of cycles.

This “pressure dilemma” — the requirement for high, carefully controlled external mechanical load — is one of the primary barriers to practical ASSB integration into electric vehicles and portable electronics, where applying and maintaining hundreds of MPa across a battery pack is mechanically impractical and adds significant system complexity and weight.

4. The Solution: Li₂₁Si₅/Si–Li₂₁Si₅ Bilayer Composite Anode

To overcome this barrier, the Xiamen University team designed a novel Li₂₁Si₅/Si–Li₂₁Si₅ bilayer composite anode fabricated via an integrated cold-pressing and sintering process. The two-layer architecture addresses the pressure requirement through material design rather than external constraint:

• Top Li₂₁Si₅ layer (mixed ionic-electronic conductor, MIEC): homogenizes the interfacial electric field and guides uniform lithium-ion flux across the anode–electrolyte interface, preventing the localized current concentration that drives dendrite formation and interface failure.
• Bottom Si–Li₂₁Si₅ layer (3D conductive network): facilitates ionic and electronic transport throughout the anode volume while effectively dissipating the mechanical stress generated by silicon’s volume expansion — converting what would be destructive localized stress into distributed, manageable deformation.

A key intrinsic feature of this design is a spontaneous self-pre-lithiation effect: lithium migrates from the Li₂₁Si₅ phase to surrounding Si particles during assembly, enhancing initial ionic conductivity and structural integrity before the first charge cycle.

5. Electrochemical Performance Without External Pressure

The bilayer silicon-based anode enables all-solid-state batteries to operate without applied stack pressure while delivering practically relevant performance across all key metrics (see Table 1 above for complete data summary). The combination of 97 ± 0.7% initial Coulombic efficiency, 10 mA cm⁻² critical current density, and 1,000-cycle stability at 2.5 mA cm⁻² in the absence of external pressure represents a significant advance over prior silicon ASSB designs, which typically required pressure to maintain interface integrity and showed substantially faster capacity fade under pressure-free conditions.

Figure 2. Ionic/electronic transport characterization of the Li₂₁Si₅/Si–Li₂₁Si₅ anode for ASSBs.

6. Characterization Methods: Multi-Modal Analysis of the Pressure-Free Interface

Establishing the mechanistic basis for the bilayer anode’s pressure-free stability required a multi-scale, multi-modal characterization approach:

• Microstructure and phase composition: SEM, XRD — established morphological integrity and phase distribution before and after cycling.
• Interfacial chemistry: XPS — quantified surface chemical states and interfacial reaction products at the anode–electrolyte boundary.
• Surface potential mapping: AFM (Kelvin probe force microscopy) — visualized the electric field homogenization effect of the Li₂₁Si₅ top layer.
• Lithium-ion local environment: solid-state NMR (SSNMR) — probed the chemical state of lithium in the Li₂₁Si₅ and Si–Li₂₁Si₅ phases, providing atomic-level insight into ion transport pathways.
• Real-time structural evolution: in-situ TEM — visualized silicon particle lithiation and volume change behavior under realistic cycling conditions without applied pressure.
• Multiphysics simulation: COMSOL model parameterized by the above data validated that the bilayer design homogenizes current density and redistributes mechanical stress throughout the anode volume, preventing localized failure.

Figure 3. Structure evolution of the Li₂₁Si₅/Si–Li₂₁Si₅ anode during cycling — demonstrating structural stability without external pressure.

7. Engineering Implications for Pressure-Free All-Solid-State Batteries

This work establishes a pathway toward ASSBs that do not depend on impractically high external mechanical pressure. Key engineering implications for ASSB development and manufacturing:

• Cell and pack simplification: removing the external pressure requirement eliminates the need for spring-loaded compression frames, engineered swelling pads, and pressure management systems — reducing module complexity and enabling thinner, lighter pack designs.
• Scalability indicators: cold-press sintering and composite layering are compatible with existing electrode manufacturing flows. Reproducibility of the pre-lithiation extent, microstructure uniformity, and controlled porosity will be the critical scale-up challenges.
• Rate capability and safety balance: achieving 10 mA cm⁻² critical current density with only 14.5% volume expansion demonstrates that the bilayer design balances fast-charging kinetics with mechanical stability — a combination required for high-energy, fast-chargeable EVs.
• Application scope: pressure-free operation opens ASSB applications in flexible electronics, wearables, and curved-surface devices where stack pressure is structurally incompatible with the device form factor.

Key data from this work: a Li₂₁Si₅/Si–Li₂₁Si₅ bilayer silicon anode in an all-solid-state battery achieved 1,000 cycles at 2.5 mA cm⁻², 54.9% capacity retention, 97 ± 0.7% initial Coulombic efficiency, and only 14.5% volume expansion — without any external applied pressure (versus the 10–250 MPa typically required). The bilayer architecture works by homogenizing electric field distribution (via the MIEC Li₂₁Si₅ top layer) and distributing mechanical stress through a 3D Si–Li₂₁Si₅ network, eliminating the localized failure modes that make conventional silicon ASSBs pressure-dependent.

8. Original Paper

Zhang, Z., Zhang, X., Liu, Y. et al. Silicon-based all-solid-state batteries operating free from external pressure. Nat Commun 16, 1013 (2025).

9. IEST Comprehensive Solid-State Battery Testing Solutions

IEST Instrument provides a comprehensive suite of testing systems for solid-state battery research and development — spanning material-level characterization through full-cell performance evaluation. The product portfolio directly supports the multi-scale characterization workflows used in solid-state battery research, accelerating the development and commercialization of next-generation batteries:

• SEMS series — Multi-dimensional solid electrolyte characterization: integrates controlled pressure (up to 350 MPa), electrochemical impedance spectroscopy (EIS, 0.1 Hz–100 kHz), and real-time mechanical response measurement. Directly applicable to studying pressure-contact relationships in solid electrolytes and composite anodes — the core characterization need in pressure-free ASSB research.
• SWE in-situ swelling analyzers: real-time thickness and force monitoring during cycling, capturing volume expansion dynamics across full charge-discharge cycles — critical for quantifying the 14.5% expansion performance that defines pressure-free silicon anode behavior.
• BPD pressure/temperature distribution mapping: spatial pressure uniformity verification across the electrode area — essential for validating that mechanical load is applied or absent uniformly in ASSB test assemblies.

10. FAQ: Silicon-Based Anodes and Pressure-Free All-Solid-State Batteries