Conventional liquid electrolyte-based lithium-ion batteries have achieved a great commercial success. However, their energy density has theoretical limits, and safety concerns such as electrolyte leakage and thermal runaway remain. Replacing liquid electrolytes with inorganic, nonflammable solid electrolytes can significantly enhance battery safety and potentially enable the application of lithium metal anode in all-solid-state batteries (ASSBs), thereby further improving the energy density. Recent development on solid electrolyte materials has advanced rapidly, with significant improvements in ionic conductivity. Among them, halide electrolytes exhibit a high oxidative stability (i.e., ~4 V) and an excellent compatibility with high-voltage cathodes. However, cations (e.g., Zr4+, Al3+, In3+, Y3+) in the electrolyte reduce when halide electrolytes come into contact with lithium metal, forming metallic or alloy phases. These electronically conductive phases could cause continuous electrolyte decomposition, ultimately leading to battery failure. To improve interfacial stability, some strategies such as electrolyte doping, introducing interfacial buffer layers, and employing bilayer solid electrolyte structures are implemented to suppress interfacial reactions. However, the selection of buffer layer materials remains limited to a few commonly used compounds, and the degradation mechanisms at the lithium metal/halide electrolyte interface are still unclear in the atomic scale. This study was to employ theoretical calculations to systematically analyze the interfacial reaction between halide electrolytes and lithium metal, including the electronic conductivity of interfacial reaction products and the effects of volume changes.
Methodes
The reaction phase equilibria between two contacting solid materials could be constructed by the Pymatgen (Python Materials Genomics) module. Based on enthalpy data retrieved from the Materials Project (MP) database, the interfacial reaction energy was calculated to predict the thermodynamic stability of different materials. This approach is widely used to study the interfacial stability between electrolytes and electrodes in batteries. The fundamental principle is to conceptualize two contacting materials, A and B, as a pseudo-binary system:
where x is the mole fraction of component A. The total energy of the pseudo-binary interfacial system can be described as the sum of the energies of components A and B, each weighted by their respective mole fractions:
ΔEinterface(cA,cB, x) ＝ xE(cA) + (1 - x)E(cB)
The interfacial reaction energy is described as the reaction energy of the pseudo-binary interfacial system minus the decomposition energies of components A and B:
where Eeq, interface is the interfacial reaction energy of the pseudo-binary interfacial system; ED(cA) and ED(cB) are the decomposition energies of components A and B, respectively; ED can be obtained by searching the chemical space of all elements of the components and constructing the phase diagram. N is the total number of atoms involved in the reaction. The molar percentage of the electronically conductive phase in the interfacial products is calculated and used as a descriptor for the electronic conductivity of the interphase layer after constructing the reaction phase equilibrium between A and B. The higher the molar percentage is, the stronger the electronic conductivity of the interface layer will be.
For interface reaction phase equilibrium: xAA + xBB → xCC + xDD + xEE +…. The volume change rate Vc induced by the interfacial reaction can be calculated by
where x is the stoichiometric number of different components in the phase equilibrium; v is the volume of the reactant and product per unit molecule.
Results and discussion
The properties of interphases formed between Li-metal and solid electrolyte play a crucial role in the performance of all-solid-state batteries (ASSBs). If the interphase layer exhibits a mixed electronic and ionic conductivity (MIEC), continuous electrolyte decomposition will occur during battery cycling, thus leading to an increased interfacial resistance and an accelerated performance degradation. The complex interfacial reactions generate various interphases, whose volumes may change relative to the reactants (lithium metal and electrolyte). If the interphase layer undergoes volume shrinkage, interfacial separation may occur, exacerbating the inhomogeneous distribution of the interfacial electric field and current. It promotes lithium dendrite nucleation and growth at the interface. The calculation results indicate that the CPP of the interphase layer between halide electrolytes and Li-metal exceeds 9%, leading to the formation of MIEC, which can accelerate electrolyte decomposition during cycling. In addition, the volume shrinkage of interfacial interphase layer (Vc < -17.4%) can also further intensify interfacial separation and dendrite growth. Therefore, optimizing electrolyte composition to reduce interfacial reactivity as well as minimizing CPP and Vc are critical for improving ASSB performance. Based on these interfacial reaction characteristics, selecting coating materials that effectively suppress interfacial reactivity, form a passivating interphase, and exhibit minimal volume changes can significantly enhance the interfacial stability between the Li-metal anode and the electrolyte.
Conclusions
Halide electrolytes exhibited an intrinsic thermodynamic instability with Li-metal, originating from the reduction of metal cations in the electrolyte into metallic and alloy phases, with a CPP ranging from 9% to 20%. The presence of these electronically conductive phases rendered the interphases layer a MEIC, leading to continuous reduction of the electrolyte during battery cycling. Also, the interfacial reaction between Li-metal and Li-MF (M = Zr, Nb, Al, Ga, In, Ge, Sn) resulted in interphase layer that underwent volume contraction, with a volume change rate ranging from -36.2% to -17.4%. This could lead to interface separation and the formation of local voids at the interface, which was experimentally confirmed. These phenomena significantly impacted Li-metal deposition and dendrite growth, further deteriorating the performance of Li-metal ASSBs. Based on the interfacial reaction characteristics between Li-metal and halide electrolytes (Vc < -17.4%, CPP > 9%), high-throughput screening was performed to identify materials that could effectively passivate the interface and mitigate reaction-induced volume changes, thereby enhancing the performance of ASSBs. The screening identified binary materials like Li3N and Li3P, along with the ternary material Li9NS3. These materials were validated to enhance the stability of the Li-metal/electrolyte interface, confirming the scientific validity and effectiveness of the screening criteria.
锂金属高理论容量（3860 mA·h/g）和低还原电位（-3.04 V vs. SHE）的优势使其成为最理想的负极材料。然而，锂金属与电解质之间的界面副反应和枝晶生长导致电池性能快速衰退，阻碍锂金属电池在实际中的应用和推广。采用基于第一性原理计算的热力学相平衡方法对卤化物电解质与锂金属之间的界面副反应的反应能、界面产物以及由界面反应导致的体积变化进行分析。研究表明，卤化物电解质与锂金属之间的界面反应层为具有电子、Li+导通能力的混合导体，从而导致界面反应在全固态电池循环过程中持续发生。此外，电解质与锂金属的界面反应会引起体积收缩，导致锂金属与电解质之间发生界面分离，增大界面阻抗和加剧负极界面电场的集中分布，在Li沉积过程中诱发锂枝晶的成核和生长。根据界面反应特性，筛选可有效降低界面层电子电导和缓解界面分离的材料，有助于提升锂金属全固态电池（ASSBs）的性能。
锂金属高理论容量（3860 mA·h/g）和低还原电位（-3.04 V vs. SHE）的优势使其成为最理想的负极材料。然而，锂金属与电解质之间的界面副反应和枝晶生长导致电池性能快速衰退，阻碍锂金属电池在实际中的应用和推广。采用基于第一性原理计算的热力学相平衡方法对卤化物电解质与锂金属之间的界面副反应的反应能、界面产物以及由界面反应导致的体积变化进行分析。研究表明，卤化物电解质与锂金属之间的界面反应层为具有电子、Li+导通能力的混合导体，从而导致界面反应在全固态电池循环过程中持续发生。此外，电解质与锂金属的界面反应会引起体积收缩，导致锂金属与电解质之间发生界面分离，增大界面阻抗和加剧负极界面电场的集中分布，在Li沉积过程中诱发锂枝晶的成核和生长。根据界面反应特性，筛选可有效降低界面层电子电导和缓解界面分离的材料，有助于提升锂金属全固态电池（ASSBs）的性能。
关键词
锂金属
/
全固态电池
/
卤化物电解质
/
密度泛函理论
/
界面反应
Abstract
收起
Introduction
Conventional liquid electrolyte-based lithium-ion batteries have achieved a great commercial success. However, their energy density has theoretical limits, and safety concerns such as electrolyte leakage and thermal runaway remain. Replacing liquid electrolytes with inorganic, nonflammable solid electrolytes can significantly enhance battery safety and potentially enable the application of lithium metal anode in all-solid-state batteries (ASSBs), thereby further improving the energy density. Recent development on solid electrolyte materials has advanced rapidly, with significant improvements in ionic conductivity. Among them, halide electrolytes exhibit a high oxidative stability (i.e., ~4 V) and an excellent compatibility with high-voltage cathodes. However, cations (e.g., Zr4+, Al3+, In3+, Y3+) in the electrolyte reduce when halide electrolytes come into contact with lithium metal, forming metallic or alloy phases. These electronically conductive phases could cause continuous electrolyte decomposition, ultimately leading to battery failure. To improve interfacial stability, some strategies such as electrolyte doping, introducing interfacial buffer layers, and employing bilayer solid electrolyte structures are implemented to suppress interfacial reactions. However, the selection of buffer layer materials remains limited to a few commonly used compounds, and the degradation mechanisms at the lithium metal/halide electrolyte interface are still unclear in the atomic scale. This study was to employ theoretical calculations to systematically analyze the interfacial reaction between halide electrolytes and lithium metal, including the electronic conductivity of interfacial reaction products and the effects of volume changes.
Methodes
The reaction phase equilibria between two contacting solid materials could be constructed by the Pymatgen (Python Materials Genomics) module. Based on enthalpy data retrieved from the Materials Project (MP) database, the interfacial reaction energy was calculated to predict the thermodynamic stability of different materials. This approach is widely used to study the interfacial stability between electrolytes and electrodes in batteries. The fundamental principle is to conceptualize two contacting materials, A and B, as a pseudo-binary system:
where x is the mole fraction of component A. The total energy of the pseudo-binary interfacial system can be described as the sum of the energies of components A and B, each weighted by their respective mole fractions:
ΔEinterface(cA,cB, x) ＝ xE(cA) + (1 - x)E(cB)
The interfacial reaction energy is described as the reaction energy of the pseudo-binary interfacial system minus the decomposition energies of components A and B:
where Eeq, interface is the interfacial reaction energy of the pseudo-binary interfacial system; ED(cA) and ED(cB) are the decomposition energies of components A and B, respectively; ED can be obtained by searching the chemical space of all elements of the components and constructing the phase diagram. N is the total number of atoms involved in the reaction. The molar percentage of the electronically conductive phase in the interfacial products is calculated and used as a descriptor for the electronic conductivity of the interphase layer after constructing the reaction phase equilibrium between A and B. The higher the molar percentage is, the stronger the electronic conductivity of the interface layer will be.
For interface reaction phase equilibrium: xAA + xBB → xCC + xDD + xEE +…. The volume change rate Vc induced by the interfacial reaction can be calculated by
where x is the stoichiometric number of different components in the phase equilibrium; v is the volume of the reactant and product per unit molecule.
Results and discussion
The properties of interphases formed between Li-metal and solid electrolyte play a crucial role in the performance of all-solid-state batteries (ASSBs). If the interphase layer exhibits a mixed electronic and ionic conductivity (MIEC), continuous electrolyte decomposition will occur during battery cycling, thus leading to an increased interfacial resistance and an accelerated performance degradation. The complex interfacial reactions generate various interphases, whose volumes may change relative to the reactants (lithium metal and electrolyte). If the interphase layer undergoes volume shrinkage, interfacial separation may occur, exacerbating the inhomogeneous distribution of the interfacial electric field and current. It promotes lithium dendrite nucleation and growth at the interface. The calculation results indicate that the CPP of the interphase layer between halide electrolytes and Li-metal exceeds 9%, leading to the formation of MIEC, which can accelerate electrolyte decomposition during cycling. In addition, the volume shrinkage of interfacial interphase layer (Vc < -17.4%) can also further intensify interfacial separation and dendrite growth. Therefore, optimizing electrolyte composition to reduce interfacial reactivity as well as minimizing CPP and Vc are critical for improving ASSB performance. Based on these interfacial reaction characteristics, selecting coating materials that effectively suppress interfacial reactivity, form a passivating interphase, and exhibit minimal volume changes can significantly enhance the interfacial stability between the Li-metal anode and the electrolyte.
Conclusions
Halide electrolytes exhibited an intrinsic thermodynamic instability with Li-metal, originating from the reduction of metal cations in the electrolyte into metallic and alloy phases, with a CPP ranging from 9% to 20%. The presence of these electronically conductive phases rendered the interphases layer a MEIC, leading to continuous reduction of the electrolyte during battery cycling. Also, the interfacial reaction between Li-metal and Li-MF (M = Zr, Nb, Al, Ga, In, Ge, Sn) resulted in interphase layer that underwent volume contraction, with a volume change rate ranging from -36.2% to -17.4%. This could lead to interface separation and the formation of local voids at the interface, which was experimentally confirmed. These phenomena significantly impacted Li-metal deposition and dendrite growth, further deteriorating the performance of Li-metal ASSBs. Based on the interfacial reaction characteristics between Li-metal and halide electrolytes (Vc < -17.4%, CPP > 9%), high-throughput screening was performed to identify materials that could effectively passivate the interface and mitigate reaction-induced volume changes, thereby enhancing the performance of ASSBs. The screening identified binary materials like Li3N and Li3P, along with the ternary material Li9NS3. These materials were validated to enhance the stability of the Li-metal/electrolyte interface, confirming the scientific validity and effectiveness of the screening criteria.
Key words
lithium metal
/
all-solid-state-battery
/
halide electrolyte
/
density functional theory
/
interfacial reaction
Fucheng REN, Feilong WANG, Yilin ZHANG, Shuo WANG.
Interface Degradation Mechanisms between Lithium Metal and Halide Electrolytes and Their Suppression Strategies[J].
Journal of the Chinese Ceramic Society,
2025
, 53
(7)
: 1885
-1892
.
DOI: 10.14062/j.issn.0454-5648.20250005
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