“Advanced Materials” – Team of Zhuang Xiaodong from Shanghai Jiao Tong University: Porous and Loose Li–Al Alloy Anode Applied in Sulfide All-Solid-State Batteries

In August 2024, the team led by Zhuang Xiaodong at Shanghai Jiao Tong University published a paper online in the journal Advanced Materials (impact factor > 27.4) titled “A Porous Li–Al Alloy Anode toward High-Performance Sulfide-Based All-Solid-State Lithium Batteries.” The study developed a porous Li–Al alloy anode that exhibited excellent electrochemical performance in sulfide-based all-solid-state batteries.

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Research Background

Sulfide-based all-solid-state batteries (ASSBs) hold the potential to address the current challenges of low energy density and safety concerns in commercial lithium-ion batteries. The key lies in the development of high-performance solid electrolytes. Among the currently developed solid electrolytes, including polymers, oxides, sulfides, and halides, sulfide solid electrolytes (SSEs) have attracted significant attention from both academia and industry due to their extremely high room-temperature ionic conductivity. One of the challenges that needs to be addressed for SSE-based ASSBs is the compatibility between SSEs and lithium metal anodes (LMAs). Adding an artificial interfacial layer between the SSE and LMA can partially solve this problem, but the process is complex, costly, and introduces additional interfaces that increase battery impedance. Alternatively, replacing the LMA with an alloy anode with high specific capacity and a low voltage platform is a relatively feasible solution. The widely studied Li–In alloy anode has low capacity and high cost, making it suitable only for laboratory verification. The Li–Si alloy anode has low electronic conductivity and insufficient rate performance. However, the Li–Al alloy anode offers a suitable combination of specific capacity, voltage platform, electronic conductivity, and cost, making it a promising candidate for practical applications. Despite this, research on the Li–Al alloy anode is currently insufficient, and its performance indicators need further improvement.

Research Question

Recently, Professor Xiaodong Zhuang’s research group at Shanghai Jiao Tong University developed a porous and loose Li–Al alloy anode (LiAl-p) through a simple mechanical mixing and cold pressing technique, and applied it to sulfide-based all-solid-state batteries (as shown in Figure 1). Compared to the dense Li–Al alloy anode (LiAl-d), LiAl-p exhibits significantly smaller volume changes during lithium extraction/insertion (66% vs 17%) (as shown in Figure 2). In situ Raman spectroscopy and molecular dynamics simulations revealed that the Li–Al alloy anode has high chemical/electrochemical stability with the SSE, and the residual oxygen-containing groups on the surface of the Li–Al alloy react with the SSE to form a stable SEI (as shown in Figure 3). Symmetrical cells based on LiAl-p demonstrated a record-breaking critical current density (6.0 mA cm−2) and lithium extraction/insertion stability (5000 hours) (as shown in Figure 4). Surface composition (TOF SIMS) and internal structure (FIB-SEM, XCT) analyses of the cycled LiAl-p revealed that a robust SEI rich in lithium-containing inorganics formed on its surface, while the porous structure effectively mitigated volume effects and suppressed pulverization (as shown in Figure 5). Finally, an all-solid-state battery based on LiAl-p and NCM811 was constructed, achieving an initial specific capacity of 200 mAh g−1 at 0.1 C, with a capacity retention rate of 83% after 1800 cycles at 1 C. The highest areal capacity of this full battery reached 11.9 mAh cm−2, surpassing the highest areal capacity reported for sulfide-based all-solid-state batteries based on LMA and alloy anodes (as shown in Figure 6).

Figure 1: Schematic diagrams of LiAl-p and LiAl-d (a, b); XCT reconstructed 3D images (c, d); and FIB-SEM images (e, f).

Figure 2: Lithium extraction/insertion curves of LiAl-p/d electrodes (a). Cross-sectional SEM images of LiAl-p/d electrodes in their original state, after lithium extraction, and after lithium insertion (b-g).

Figure 3: In situ Raman spectra of the LiAl-p and SSE interface (a). Molecular dynamics simulation theoretical calculations at the LiAl-p and SSE interface (b-i).

Figure 4: Critical current density of LiAl-p symmetrical cells (a) and comparison with reported values (b). Long-term lithium extraction/insertion cycling of LiAl-p/d symmetrical cells (c), and EIS spectra at different cycling stages (d, e).

Figure 5: Characterization of LiAl-p after cycling: TOF SIMS spectra (a) and 3D reconstruction image (b). FIB-SEM images of LiAl-p and LiAl-d after cycling (c, d) and XCT images (e, f). Schematic diagram of structural changes in LiAl-p/d during cycling (g).

Figure 6: Performance characterization of LiAl-p/d|NCM811 full cells: Charge/discharge curves (a), dQ/dV curves (b), in situ pressure change curves (c), rate performance curves (d), long-cycle cycling curves (e), high-loading charge/discharge curves of the cathode (f, g), and comparison with reported values (h).

Research Summary

In this study, researchers used mechanical pressing to produce two types of Li–Al alloy anodes. Notably, the porous alloy anodes exhibited significantly superior room-temperature electrochemical performance compared to the dense alloy anodes, achieving unprecedented levels. These porous anodes demonstrated a record-breaking critical current density of 6.0 mA cm⁻² and a cycle life of 5000 hours in symmetric cells. In full cells, they maintained 83% capacity after 1800 cycles and achieved the highest areal capacity of 11.9 mAh cm⁻². Using a range of analytical techniques, including XPS, TOF-SIMS, in situ Raman spectroscopy, cross-sectional SEM, FIB-SEM, XCT measurements, and DFT calculations, several key factors contributing to the excellent performance of the porous LiAl-p anodes were identified: i) Enhanced stability of the Li–Al alloy with SSE, ii) Formation of a stable SEI through the reaction of surface oxygen species on LiAl-p with SSE, iii) Porous structure accommodating volume changes while maintaining structural integrity. This research provides insights that could inspire the design of ultra-stable alloy anodes and corresponding all-solid-state lithium batteries. Future considerations could include engineering SEIs with Li⁺ conductivity and electronic insulation using organic, inorganic, or composite materials, as well as designing alloy anodes with specialized structures such as nanoparticles, nanosheets, nanowires, and porous architectures.
Original link: https://10.1002/adma.202407128

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