Key Takeaways & Executive Findings
- •• • Achieved an initial coulombic efficiency (ICE) of 81.4% and a charge transfer resistance (Rct) of 16.4 Ω after 200 cycles, representing a 64% reduction, indicating enhanced interfacial kinetics and stability. • • Delivered a high reversible capacity of 1719.3 mAh g−1 at 0.2 C after 200 cycles and 823.8 mAh g−1 at 0.5 C after 500 cycles, demonstrating excellent long-term cycling stability. • • The molten salt electrolysis synthesis achieved a current efficiency of 68.12% and specific energy consumption of 12.76 kWh kg−1, with an estimated electricity cost of 1154.69 USD ton−1, which is only 20% of commercial Si/C anode prices, offering a significant cost advantage for scalable production. • • The hierarchical design with porous crystalline-amorphous silicon core and MgSiN2-derived Li3N-rich SEI effectively mitigates volume expansion and ensures fast Li+ diffusion (D Li+ = 1.72×10−11 cm2 s−1), addressing the ICE-cycle life trade-off.
Abstract
Silicon anodes offer an ultrahigh theoretical capacity (4200 mAh g−1) but suffer from >300% volumetric expansion during cycling and unstable solid electrolyte interphase (SEI) formation, leading to rapid capacity fading. Here, we design a hierarchical composite p-cSi@aSi@MgSiN2@C featuring a porous crystalline-amorphous silicon core (p-cSi@aSi), an in-situ MgSiN2 transition layer, and an outer nitrogen-doped carbon shell. The 3D interconnected pores accommodate volume expansion, while amorphous silicon enables isotropic lithiation-induced strain, eliminating crystalline phase transition barriers. The MgSiN2 layer transforms into a tough Li3N-rich SEI with ultra-fast ion channels, and the carbon shell provides mechanical confinement and electronic conductivity. This synergistic interface engineering achieves an initial coulombic efficiency (ICE) of 81.4%, a charge transfer resistance of 16.4 Ω after 200 cycles (64% reduction), and a Li+ diffusion coefficient of 1.72×10−11 cm2 s−1. The anode delivers 1719.3 mAh g−1 at 0.2 C after 200 cycles and 823.8 mAh g−1 at 0.5 C after 500 cycles. The molten salt electrolysis synthesis achieves a current efficiency of 68.12% and specific energy consumption of 12.76 kWh kg−1, with an estimated electricity cost of 1154.69 USD ton−1, only 20% of commercial Si/C anodes. This work resolves the ICE-cycle life trade-off and provides a scalable, cost-effective approach for next-generation high-energy batteries.
1. Introduction
Silicon anodes have long been considered the most promising candidate to replace graphite in lithium-ion batteries due to their theoretical specific capacity of 4200 mAh g−1, nearly ten times that of graphite (372 mAh g−1). However, their commercial viability is hindered by severe volumetric changes (300–400%) during charge-discharge cycles, which cause particle cracking and fragmentation. This structural degradation leads to irreversible lithium trapping and continuous reformation of the solid electrolyte interphase (SEI), consuming lithium and electrolyte, and accelerating capacity fade. Additionally, silicon's low intrinsic electrical conductivity (~10−3 S cm−1) further limits rate capability and overall performance. These intertwined failure modes have prevented silicon anodes from achieving both high initial coulombic efficiency (ICE) and long cycle life, a trade-off that remains unresolved in conventional designs.
This work addresses these bottlenecks through a synergistic interface engineering strategy. By constructing a porous crystalline-amorphous silicon core (p-cSi@aSi), the material accommodates volume expansion via 3D interconnected pores and avoids the crystalline-to-amorphous phase transition that causes irreversible lithium loss. The in-situ formed MgSiN2 transition layer transforms into a Li3N-rich SEI with high ionic conductivity and mechanical toughness, while the outer nitrogen-doped carbon shell provides electronic pathways and structural confinement. This design not only stabilizes the SEI but also enhances lithium-ion transport, achieving an ICE of 81.4% and a capacity retention of 1719.3 mAh g−1 after 200 cycles at 0.2 C. Furthermore, the molten salt electrolysis synthesis method offers a scalable and cost-effective route, with an estimated electricity cost of only 1154.69 USD ton−1, representing a 20% cost of commercial Si/C anodes. This integrated approach provides a practical solution to the ICE-cycle life dilemma, paving the way for next-generation high-energy lithium-ion batteries.
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Xintao Wu, Haoxiang Wu, Siwei Jiang, Yazecheng Liu, Peng Hu, Tao Zhang, Liuli Yao, Peng Dong, Wei Xiao, Yingjie Zhang, Zhongren Zhou (2026). Toward efficient and stable lithium storage: molten salt electrolysis-constructed amorphous Si-dominant anodes with synergistic interfaces. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-025-3951-4
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Frequently Asked Questions
What is the failure mechanism of the MgSiN2-derived SEI under prolonged cycling, and how does it maintain interfacial stability?
The MgSiN2 layer undergoes in-situ transformation to form Li3N and Li-Mg alloy during lithiation. Li3N acts as a fast ionic conductor, while the Li-Mg alloy provides elasticity, resulting in a tough and stable SEI that accommodates volume changes without cracking. This is evidenced by the low charge transfer resistance (16.4 Ω after 200 cycles) and stable capacity retention over 500 cycles.
How does the porous crystalline-amorphous silicon structure mitigate volume expansion and improve ICE compared to pure crystalline silicon?
The porous structure provides void spaces to buffer volume expansion, while the amorphous silicon phase undergoes isotropic lithiation, avoiding the anisotropic strain and phase transition barriers of crystalline silicon. This reduces irreversible lithium loss, contributing to the high ICE of 81.4%.
What are the scalability and cost implications of the molten salt electrolysis synthesis method for commercial production?
The synthesis achieves a current efficiency of 68.12% and specific energy consumption of 12.76 kWh kg−1. Using industrial electricity prices in Yunnan Province (0.09 USD kWh−1), the estimated electricity cost is 1154.69 USD ton−1, which is only 20% of the market price of commercial Si/C anodes, indicating significant cost advantages for scale-up.
How does the nitrogen-doped carbon shell contribute to the electrochemical performance beyond providing mechanical confinement?
The nitrogen-doped carbon shell enhances electronic conductivity and facilitates Li+ transport, as indicated by the high Li+ diffusion coefficient (1.72×10−11 cm2 s−1). It also prevents direct contact between silicon and electrolyte, reducing side reactions and SEI overgrowth, thereby improving cycling stability.
What is the specific capacity retention at high current densities, and how does it compare to state-of-the-art silicon anodes?
The anode delivers 823.8 mAh g−1 at 0.5 C after 500 cycles, demonstrating excellent high-rate capability and long-term stability. This performance is competitive with advanced silicon anodes, while the cost-effective synthesis and high ICE make it a promising candidate for practical applications.
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