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.

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:

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:

For interface reaction phase equilibrium: x_A A + x_BB → x_CC + x_DD + x_EE +…. The volume change rate V_c induced by the interfacial reaction can be calculated by

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 (V_c < -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 V_c 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.

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 (V_c < -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.

Lithium-ion batteries (LIBs) are widely used in electric vehicles and electronic devices due to their high energy density and long cycle life. The migration rate of lithium ions in cathode materials significantly affects the rate performance of LIBs. Previous studies showed that there were certain differences in the migration energy of lithium ions in LiCoO₂ materials at different concentrations of lithium vacancies, which could be due to the different interlayer distances caused by different concentrations of lithium vacancies. The construction of individual lithium vacancies in different supercells can lead to different concentrations of lithium vacancies, which in turn affects the parameters of the unit cell. In addition, the synergistic migration effect between lithium ions also lead to a decrease in the energy barrier for lithium-ion migration. This paper was to use first-principles calculations to investigate the effects of lithium vacancy concentration and synergistic migration on the lithium-ion migration energy in layered materials (i.e., LiCoO₂, LiNiO₂) and spinel material (i.e., LiMn₂O₄).

First principles calculations in this work were conducted using the DS-PAW package, which is based on the density functional theory (DFT) framework and the projector augmented wave (PAW) approach. The basis set is in the form of plane waves, and the cutoff energy is set to be 500 eV. The Monkhorst-Pack scheme was used to integrate the Brillouin zone. The calculations for the models of the Li_1-xCoO₂ and Li_1-xNiO₂ in supercells of 2×2×1, 3×3×1, and 4×4×1 were performed using the k-point meshes of 5×5×2, 3×3×2, and 2×2×2, respectively. The calculations for the models of the Li_xMn₂O₄ and Li_xTi₂O₄ in supercells of 1×1×1, 2×2×1, and 3×3×1 were performed using the k-point meshes of 3×3×3, 2×2×3, and 1×1×3, respectively. The exchange-correlation interactions were treated with Perdew-Burke-Ernzerhof (PBE) functional within the generalized gradient approximation (GGA) formalism. The strong correlation effects of the 3d electrons were considered by using the GGA+U method, with effective U value (U_eff) of 4.91, 5.00, and 3.50 eV for Co, Ni, and Mn, respectively. All atomic positions and cell parameters were relaxed using the conjugate gradient method until the maximum force on each atom was less than 0.03 eV/Å. The energy convergence criterion for the self-consistent field (SCF) loop was set to 10^-5 eV. The activation barriers for Li-ion migration were determined through the climbing image nudged elastic band (CI-NEB) method, and the convergence criterion for the forces on the transition state images was set to 0.1 eV/Å.

The results show that in LiCoO₂ material, the lithium-ion migration energy for the 2×2×1 supercell is significantly smaller than that of other supercells by using the CI-NEB method to calculate the lithium-ion migration energy barrier. This is because the 2×2×1 supercell of LiCoO₂ has a higher concentration of lithium vacancies, which can increase the interlayer distance and decrease in the lithium-ion migration energy. In addition, there are still some differences in the energy for lithium ion migration when different supercells of LiCoO₂ have the same interlayer distance. The synergistic migration effect of lithium ions can lead to a decrease in the energy for lithium ion migration when there are more lithium ion migration pathways in the LiCoO₂ supercell when LiCoO₂ is expanded to the same size. Also, the same pattern in LiNiO₂ material occurs.

The results show that the higher the concentration of lithium vacancies in spinel materials is, the smaller the energy for lithium ion migration will be, after applying the same treatment to spinel materials LiMn₂O₄ and LiTi₂O₄. Unlike layered materials, however, the synergistic migration effect of lithium ions in spinel materials does not have a significant impact on the energy for lithium ion migration. This is because the interaction between transition metals and lithium ions has a certain hindering effect on lithium ion migration when lithium ions migrate in spinel materials.

The calculation results indicated that in layered materials like LiCoO₂ and LiNiO₂, the lower the concentration of lithium vacancies was, the smaller the interlayer distance would be, thus increasing the activation barrier for lithium-ion migration. The migration energy barriers for lithium ions within the 3×3×1 and 4×4×1 supercells of LiCoO₂ were similar, indicating that the energy barriers derived from these supercells could be considered as a representative of the migration energy barriers in the stoichiometric ratio of LiCoO₂. The synergistic migration effect of lithium ions in layered materials reduced migration energy, while the synergistic migration effect of lithium ions in spinel materials was not significant.

Zinc-air batteries have a significant promise for next-generation energy storage due to their low cost, high safety, high theoretical capacity, and abundant availability. Recently, we reported a new rechargeable zinc-air battery based on zinc peroxide chemistry. Compared to conventional zinc-air batteries, this neutral zinc-air battery exhibits higher reversibility and stability, making it a more promising candidate for secondary zinc-air batteries. However, the low energy efficiency of neutral zinc-air batteries remains a challenge. And the mechanism of these neutral zinc-air battery reactions is still unclear. In this work, we systematically investigated the reaction pathways of neutral zinc-air reaction by first-principles calculations.

Density Functional Theory calculations based on a software package named VASP was employed with PAW potentials and the PBE functional. The vdW interactions were corrected by the Grimme's D3 method. The k-point mesh was generated by the Monkhorst-Pack scheme via Pymatgen with MPRelaxSet settings. A cutoff energy of 520 eV was utilized within a convergence criterion of 10^-5 eV for self-consistent calculations. The convergence criterion for ionic relaxation was set to be 0.02 eV/Å. The calculations were performed by a slab model with a thickness of approximately 10 Å and a vacuum layer of greater than 15 Å.

There is a clear linear scaling relationship among the adsorption strengths of O*, ZnO₂*, and ZnO₄* in neutral zinc-air reactions. This relationship constrains the freedom in catalyst design, making it difficult to optimize all intermediate adsorption strengths simultaneously. Breaking this linear scaling relationship will be a focus of future research. The rate-determined step for both the four-electron and two-electron reactions in Ag (111) is the first electron transfer. A weaker ZnO₄* adsorption makes the first reaction barrier as high as 0.78 eV at 1.2 V (vs. Zn/Zn²⁺). This result indicates that even with this metal catalyst, the discharge voltage of neutral zinc-air batteries remains smaller than that of alkaline batteries due to the limitation of linear scaling relationships.

Among various catalysts, Pt (111) exhibits a lowest reaction barrier, indicating that Pt maintains a high catalytic activity in Zn²⁺-involved ORR processes. Conversely, the surface reactivity of Ru (111) and Co (001) catalyst surfaces is significantly greater than that of Ag (111), where over-strong ZnO₄* adsorption makes the second electron transfer the rate-determined step. Meanwhile, the energy barrier of four-electron pathway is notably lower than that of two-electron transfer pathway, showing that the Ru (111) and Co (001) catalyst can favor a four-electron transfer reaction and form ZnO discharge products.

The optimal O* adsorption free energy is found to be around -6 eV based on the linear scaling relationships. And Ag (111) and Pt (111) have relatively appropriate O* adsorption strengths. The neutral zinc-air catalytic activity of Ag and Pt can be further improved via increasing the d-band center. In addition, the calculations also reveal that catalysts with a strong reactivity favor a four-electron transfer pathway.

The theoretical calculation results showed that linear scaling relationships still had true among various adsorption intermediates in neutral zinc-air reactions. Oxygen adsorption strength and overpotential followed the Sabatier principle, indicating that a moderate strength (i.e., ΔG_O* ~ -6 eV) yielded an optimal catalytic activity. Among numerous catalysts, Ag and Pt exhibited an optimal surface reactivity with a high theoretical catalytic activity. Furthermore, employing catalysts with a strong surface reactivity, such as Co and Ru, represented a potential approach to achieve non-protonic four-electron zinc-air batteries.

Lithium-metal batteries (LMBs), as next-generation high-energy-density battery technologies, have attracted considerable attention due to their theoretical energy density (i.e., approximately 3860 mA·h/g), which far exceeds that of conventional lithium-ion batteries (LIBs). This makes LMBs highly promising for applications in electric vehicles, portable electronic devices, and other fields. Compared to conventional LIBs with a theoretical capacity of 372 mA·h/g for graphite anodes, LMBs can offer a longer battery life or a higher energy output, thus addressing the energy density bottleneck faced by the existing energy storage technologies. As a result, LMBs are widely regarded as an important direction for the future development of battery technologies. However, despite the significant advantages of LMBs in terms of energy density, the use of lithium metal anodes still has some challenges. Some issues like dendrite growth and instability of the solid electrolyte interphase (SEI) severely restrict their practical application. It is thus critical to suppress lithium dendrite growth and improve the stability of SEI.

Although the existing studies propose the use of artificial interphase layers to optimize the stability and safety of lithium metal anodes, there is a lack of systematic theoretical guidance, particularly in terms of how to regulate the composition and structure of the interphase layer. This study was to construct functional artificial interphase layers on the lithium metal anode surface by molecular self-assembly techniques. This study also regulated the SEI performance via utilizing self-assembled molecules with varying fluorine contents, thus enhancing the stability and safety of lithium metal anodes and providing a theoretical basis for future interface layer design in lithium metal batteries.

This study used the density functional theory (DFT) and ab initio molecular dynamics (AIMD) simulations to systematically investigate the interaction and structural evolution of self-assembled molecules with different fluorine contents on lithium metal surfaces. The focus was to clarify how fluorine-terminated molecular structures could affect the performance of the organic-inorganic composite artificial interphase layer.

The calculations were performed by a Vienna Ab-initio Simulation Package (VASP) based on the density functional theory. The VASP employs the projector-augmented wave (PAW) method and the Perdew-Burke-Ernzerhof (PBE) functional within the generalized gradient approximation (GGA). All the calculations used Γ-point centered Brillouin zone sampling to ensure accuracy. The PAW method was used for electron-ion interactions with an energy cutoff of 450 eV. Convergence criteria for energy and force were set at 1×10^-4 eV and 0.05 eV/Å, respectively. The van der Waals interactions were determined by the DFT-D3 method. The density of states (DOS), charge differential density, and Bader charge distribution were calculated to characterize an interfacial electronic behavior. Organic-inorganic composite interphase layers were constructed by the molecular models with varying fluorine termini (i.e., F₁∶C₉H₁₉F, F₃∶C₉H₁₇F₃), and the molecular adsorption behavior was analyzed by coverage gradient models to evaluate the adsorption stability through formation energy calculations. The AIMD simulations were conducted to explore the dynamic behavior of the interphase layer. The 20 ps simulations were performed at 300 K (Nosé-Hoover thermostat) with one time step of 1 fs. Lithium ion diffusion coefficients were calculated via mean square displacement (MSD), and the structural characteristics of the interphase layer were analyzed via radial distribution functions (RDF) and coordination numbers.

This study systematically reveals the regulatory mechanisms of fluorine-terminated self-assembled molecules on lithium metal anode interphase layers based on theoretical calculations and dynamic simulations. On the Li(100) lithium metal surface, higher fluorine content molecules (F₃∶C₉H₁₇F₃) exhibit stronger interfacial binding capabilities. The fluorine groups at the molecule heads react with lithium to form LiF as molecular coverage increases, significantly reducing the system formation energy and thereby enhancing the stability and density of the interphase layer. At a high coverage, the fluorine atoms at the heads of F₃ molecules reactwith lithium to form an amorphous LiF layer with a thickness of 6.2 Å (compared to 3.8 Å for the F₁ system), substantially inhibiting interfacial structural relaxation. The DOS analysis indicates that in the LiF layer formed by the F₃ system, Li-F orbitals overlap significantly at -7.5 eV, indicating a strong ionic bonding. The interfacial electrostatic potential is lower for the F₃ system (-4.87 eV), and the thicker LiF layer formed by F₃ molecules results in a a wider negative potential region, and more conducive to lithium ion intercalation/extraction. Lithium ion diffusion dynamics analysis shows that the interphase layer formed by trifluorinated molecules is more stable based on the AIMD simulations with a thickness of 6.2 Å and a lithium ion diffusion coefficient of 4.76×10^-6 cm²/s, indicating a superior lithium ion transport performance. In contrast, the interphase layer formed by monofluorinated molecules has a lithium ion diffusion coefficient of 1.37×10^-5 cm²/s, showing a relatively inferior lithium ion transport performance.

This study used the DFT and AIMD simulations to systematically explore the interaction processes of self-assembled molecules with varying fluorine contents on lithium metal surfaces, and investigate the regulatory effects of fluorine-terminated groups on the performance of the organic-inorganic composite artificial interphase layer. The introduction of fluorine-terminated groups optimized the electronic structure of lithium metal, promoted lithium ion diffusion, and effectively inhibited electron transmission to the organic molecular layer, thereby enhancing an interphase layer stability. Increasing fluorine content enhanced the ionic nature of Li-F bonds, significantly reducing lithium vacancy formation energy and bonding strength, and improving lithium ion migration capability in the interphase layer. The interphase layers formed by trifluorinated self-assembled molecules had thicker structures, higher lithium ion diffusion coefficients, and exhibited a superior stability. This research elucidated the regulatory mechanisms of fluorine-terminated self-assembled molecules on lithium metal anode interphase layers in the atomic scale, providing a theoretical foundation for the design of high-performance lithium anode interphase layers based on molecular engineering, and extended the application prospects of self-assembly technology in the field of energy storage.

As pivotal components in modern energy storage systems, lithium-ion batteries remain constrained by inherent limitations in safety and energy density associated with conventional liquid electrolytes. All-solid-state lithium-ion batteries represent a promising technological pathway to synergistically enhance both energy density and intrinsic safety through the implementation of non-flammable solid-state electrolytes. However, the fundamental trade-off between ionic conductivity and chemical stability persists as a critical challenge in solid-state electrolyte development. The existing material systems exhibit some distinct limitations, i.e., sulfide-based solid-state electrolytes (e.g., Li₁₀GeP₂S₁₂) demonstrate a superior ionic conductivity (~10^-2 S/cm), but suffer from pronounced hygroscopic and oxidative instability, and oxide-based counterparts (e.g., Li₇La₃Zr₂O₁₂) display exceptional environmental stability with inadequate ionic conduction performance. This challenge leads to extensive research into oxysulfide electrolyte systems that combine advantageous characteristics of both material classes through chemical composition. Recent researches on LiAlSO-based materials reveal that enhanced lithium-ion concentration and isoelectronic substitution of Al with Li-Be groups can significantly improve an ionic conductivity. However, the inherent biotoxicity of beryllium substantially elevates synthesis costs and complicates manufacturing processes. To address this limitation, this work was to propose a novel Li₂MgSO electrolyte system for replacing beryllium with the homologous element magnesium. This study also investigated the structural stability, electronic characteristics, and lithium-ion transport mechanisms via utilizing the crystal structure prediction program (CALYPSO) and density functional theory (DFT) calculations. The complementary anion/cation substitution experiments could elucidate composition-property relationships, providing a theoretical foundation for developing cost-effective, high-performance solid-state electrolytes.

The crystal structure of Li₂MgSO was predicted by the CALYPSO method with the particle swarm optimization algorithm. The total energy calculations and geometry optimizations were performed using the Vienna Ab initio Simulation Package (VASP) within the framework of density functional theory (DFT). The projector augmented wave (PAW) approach was used to describe the core-valence electron interaction. The generalized gradient approximation in the parameterization of Perdew, Burke, and Ernzerhof was used to describe the exchange-correlation potential. The plane-wave energy cut-off was set to 500 eV. The geometric structures were fully relaxed until the residual force on each atom was less than 0.02 eV·Å^-1, and the energy converged to less than 10^-5 eV. The hybrid density functional calculation, which was more accurate for electronic band structure calculations, was used to calculate the electronic density of states. The phonon spectrum calculations were carried out based on density-functional perturbation theory, and the phonon dispersion relations and thermodynamic properties were derived by a software named PHONOPY. Bond Valence Site Energy (BVSE) was used to model the possible diffusion channels of Li ions in Li₂MgSO. The migration barriers of Li ions were obtained by the climbing image nudged elastic band (CI-NEB) method. Ab initio molecular dynamics (AIMD) simulations were further employed to investigate the ion transport properties of Li₂MgSO. The simulations were conducted in the canonical ensemble (NVT) using a Nosé-Hoover thermostat at different spanning temperatures (i.e., 800-1600 K). Each simulation lasted for 40 000 steps with one time step of 1 fs.

The application of CALYPSO structural prediction program and first-principles calculations indicates that the ground-state configuration of Li₂MgSO can crystallize in a P 4 2₁m space group symmetry. The phonon dispersion analysis reveals a complete absence of imaginary frequencies, confirming the lattice dynamic stability. Electronic structure characterization discloses a substantial band gap of 4.76 eV, satisfying a critical requirement for solid-state electrolytes via ensuring electrochemical stability against redox reactions. The mechanical property evaluation demonstrates the Young modulus of 66.81 GPa and the Pugh ratio of 1.93, indicative of superior crack propagation resistance and favorable ductile behavior, respectively. The collective computational evidence indicates that Li₂MgSO exhibits a promising potential as a high-performance solid-state electrolyte, achieving an optimal balance in structural stability, wide electrochemical window, and mechanical properties.

The BVSE and CI-NEB calculations reveal that there is a three-dimensional ion transport network in Li₂MgSO, comprising two distinct pathways, i.e., 1) a 2D fast diffusion channel within the ab-plane of LiMgSO layers exhibiting a migration barrier of approximately 0.34 eV, and 2) the interlayers form three-dimensional interconnected channels with a low energy barrier (0.17 eV) through vacancy migration. This unique structure substantially enhances a lithium-ion mobility, thus leading to exceptional ionic transport performance.

The AIMD simulations are used to investigate the ion migration characteristics of Li₂MgSO, Li₂MgSeO, and Li₂ZnSO, yielding the activation energies of 0.68, 0.82 eV, and 0.35 eV for lithium diffusion, respectively. The mean square displacement (MSD) analysis reveals the comparative dynamics, i.e., lithium ions in Li₂MgSeO displayed marginally reduce mobility relative to Li₂MgSO, whereas Li₂ZnSO exhibits a twofold increase in MSD values, indicating a superior ionic migration capability. These findings indicate cation-induced effects as the primary governing mechanism for ion transport in Li₂MgSO systems, providing a strategic guidance for optimizing cationic species to engineer expanded transport channels and enhance ionic conductivity.

The theoretical calculations indicated that Li₂MgSO had the excellent kinetic properties, mechanical stability, and a wide bandgap (4.76 eV). The ion transport kinetics analysis unveiled a unique three-dimensional ionic transport network in Li₂MgSO, comprising interlayer migration channels and two-dimensional in-plane migration pathways, with low migration barriers favorable for rapid lithium-ion transport. From the systematic substitution studies of anions (Se) and cations (Zn), Li₂ZnSO demonstrated the superior lithium-ion migration kinetics, compared to Li₂MgSO and Li₂MgSeO, indicating that lithium-ion migration in Li₂MgSO system could be primarily regulated by cation-induced effects.

Sodium-ion batteries with their abundant resource availability and low cost, show a tremendous potential in energy storage. Sodium-ion batteries emerge as a more economical alternative to lithium-ion batteries, making it highly attractive for large-scale grid energy storage applications. To enhance the competitiveness of sodium-ion batteries, the development of high-energy cathode materials is crucial. As a result, recent efforts are made to explore sodium-ion cathode materials, particularly sodium layered oxides and polyanion compounds. The most extensively studied polyanion sodium-ion cathode materials are vanadium phosphates (i.e., Na₃V₂(PO₄)₃ or NVP) and fluorophosphates (i.e., Na₃V₂(PO₄)₂F₃ or NVPF). NVP with its sodium fast ion conductor (Na-superionic conductor, NASICON) structure is considered as a high-performance sodium-storage cathode material. The related experimental results indicate that the actual specific capacity of pure-phase NVP is lower than theoretical expectations, and its cycling stability is generally poor. Adjusting the composition and structure of NVP through elemental doping is an effective strategy to enhance its cycling reversibility, increase reversible capacity, and improve sodium ion diffusion kinetics. However, some challenges exist in accurately measuring the properties of sodium-ion cathode materials during experiments coupled with high trial-and-error costs and the lack of scientific theoretical guidance. This study was to utilize first-principles calculations to investigate the electronic structure characteristics of mixed polyanions doped with different transition metals, aiming to elucidate the conductivity mechanisms within polyanion systems. In addition, the microscopic processes of sodium ion insertion/extraction during the charge and discharge cycles of polyanion cathode materials were also analyzed via simulating all possible sodium ion migration pathways and calculating the corresponding energy barriers and voltage platforms in an ideally conductive polyanion system.

Spin-polarized DFT calculations were used within the Vienna ab initio simulation package. The projector-augmented wave (PAW) method was applied to solve the ion-electron interactions in a periodic system. The generalized gradient approximation (GGA) with Perdew-Burke-Ernzerhof (PBE) functionals was used to take into consideration of the exchange-correlation interactions in the Kohn-Sham equations. A plane-wave basis set with a cutoff energy of 400 eV was used to expand the Kohn-Sham valence states. A k-point mesh of dimensions of 3 × 3 × 1 was employed for the Brillouin zone integration. For calculating the electronic structure, a Monkhorst-Pack grid of 5 × 5 × 1 was sampled. The self-consistent field convergence criteria were set at 1 ×10^-6 eV. All the structures were sufficiently relaxed until the force at each atom was less than 0.02 eV·Å^-1. The climbing-image nudged elastic band (CI-NEB) was used to calculate the migration energy barrier corresponding to the migration path of Na ions. This is an effective way to find the saddle points of the ion diffusion energy. Five intermediate images were constructed between the initial and final states along the sodium ion diffusion path. The calculation formula of charge and discharge voltage is: V = (E(Na_xMP) +(y-x)E(Na)-E(Na_yMP))/(y-x), where E(Na_yMP), E(Na_xMP) and E(Na) indicate the discharge completion state, charging completion state and the energy of Na atoms, respectively.

The results show that Na₃TiMn(PO₄)₃ and Na₃TiFe(PO₄)₃ have more abundant electronic state near the Fermi level, compared to the original Na₃V₂(PO₄)₃. The conductivity of Na₃TiMn(PO₄)₃ and Na₃TiFe(PO₄)₃ is better than that of the original Na₃V₂(PO₄)₃, accelerating the kinetic process of electron transfer and ion extraction. The electronic structure characteristics of mixed polanion based on iron and manganese are analyzed, and the conductive mechanism of polyanionic system is proved via the first-principles calculations, which is helpful to screen the polanion cathode materials with an ideal conductivity.

The CI-NEB method is used to calculate the three diffusion paths and energy barriers in polanionic cathode materials (i.e., Na₃TiMn(PO₄)₃, Na₃TiFe(PO₄)₃ and Na₃V₂(PO₄)₃). The energy barriers for diffusion paths 1 and 3 of the primitive Na₃V₂(PO₄)₃ are both 0.12 eV. The energy barrier of diffusion path 2 is 0.11 eV, which is better than that of diffusion path 1 and 3. For Na₃TiMn(PO₄)₃ and Na₃TiFe(PO₄)₃, the energy difference between the initial and final state structures is too large (i.e., 0.6 eV) although the energy barrier of the diffusion path 1 is extremely low (i.e., only 0.04 eV), which is not conducive to the cyclic diffusion of sodium ions in the cathode material from the thermodynamic perspective. Sodium at Na1 is not conducive to prolapse, and sodium at Na2 is easier to prolapse during diffusion. The structural characteristics of Na₃MM'(PO₄)₃ and experimental studies both thus indicate that sodium prolapsed at different positions has different effects on the structure. In terms of diffusion paths 2 and 3, the energy difference between the initial and final structures is close to 0, and the corresponding diffusion energy barrier is between 0.12 eV and 0.18 eV, favoring the diffusive transport of sodium ions both thermodynamically and kinetically.

As the charging process proceeds, the voltage gradually increases, while desodium and sodium value decreases. The Na2 position is the first sodium ion effluent, which is consistent with that of the experimental studies. The theoretical calculation shows that the voltage platform of Na₃V₂(PO₄)₃ changes, the structure of Na₃V₂(PO₄)₃ changes in the process of sodium extraction, and the voltage platform of Na₃TiMn(PO₄)₃ and Na₃TiFe(PO₄)₃ is more stable than the voltage platform of original Na₃V₂(PO₄)₃.

The structure and electronic characteristics of Na₃V₂(PO₄)₃, Ti, Cr, Mn, Fe and other transition group metals were investigated. The density of state electronic structure of Ti, Mn and Ti and Fe substituted Na₃MM'(PO₄)₃ polyanionic sodium ion battery cathode material. The results showed that Na₃TiMn(PO₄)₃ and Na₃TiFe(PO₄)₃ had more abundant electronic states near the Fermi level, the conductivity of Na₃TiMn(PO₄)₃ and Na₃TiFe(PO₄)₃ was better than that of the original Na₃V₂(PO₄)₃, which could effectively enhance the conductivity and accelerate the kinetic process of electron transfer and ion extraction. We calculated three sodium ion diffusion paths, analyzed the three diffusion paths of sodium ion in polyanionic cathode materials (i.e., Na₃TiMn(PO₄)₃, Na₃TiFe(PO₄)₃ and Na₃V₂(PO₄)₃) and the corresponding energy barriers of 0.12-0.18 eV, and explained that the materials Na₃TiMn(PO₄)₃ and Na₃TiFe(PO₄)₃ were thermodynamically and kinetically beneficial. The theoretical calculation further studied the influence of voltage platforms on cathode materials. Based on the electronic structure and ion diffusion path results, Na₃TiMn(PO₄)₃ and Na₃TiFe(PO₄)₃ were selected as NASICON sodium ion cathode materials with a superior comprehensive performance.

This review addresses some challenges faced by four major types of single-phase solid-state electrolytes, i.e., oxides, sulfides, halides, and polymers, in large-scale production and application. These challenges stem from the difficulty of balancing the various performance requirements for commercial feasibility. Oxides offer excellent thermal stability and electrochemical windows but suffer from low ionic conductivity and complex processing requirements. Sulfides provide high ionic conductivity but are prone to air sensitivity and narrow electrochemical windows. Halides, while offering high ionic conductivity and electrochemical stability, face high production costs and poor interface stability with lithium metal anodes. Polymers, known for their flexibility and processability, are limited by low ionic conductivity and poor high-voltage stability.

A concept of SHOP-type composite solid electrolytes is proposed to address these challenges. SHOP-type electrolytes provide a balanced solution that meets the demanding requirements for ASSLBs via combining the benefits of polymer electrolytes (i.e., processing flexibility and low cost) with the advantages of inorganic electrolytes (i.e., high ionic conductivity, thermal stability, and mechanical strength). These materials offer a potential for improved safety, performance, and scalability in large-scale production, making them highly promising for future energy storage systems.

Despite their numerous advantages, the development of SHOP-type electrolytes still faces several key challenges. Future research should focus on optimizing the composition and structure of composite solid electrolytes. Understanding the interactions between inorganic and polymer components will be crucial to achieving the ideal performance characteristics. Also, the compatibility of SHOP electrolytes with lithium metal anodes and high-voltage cathodes must be further explored to improve battery efficiency and longevity. Another critical area of research is the reduction of production costs, which is achieved via selecting sustainable materials and optimizing processing methods. Innovations in fabrication techniques that can lower costs and improve scalability are essential for the widespread adoption of ASSLBs.

Interdisciplinary collaborations also play a vital role in advancing the development of ASSLB technologies. Researchers can overcome the existing barriers and accelerate the transition of ASSLBs from lab-scale to industrial-scale production via integrating insights from materials science, electrochemistry, and engineering. Through continuous innovation and optimization, SHOP-type composite solid electrolytes hold a great promise for enabling the widespread adoption of ASSLBs, driving forward the development of high-energy-density, safe, and long-lasting energy storage systems in the future.

Some significant strides are made in the development of solid-state electrolytes, the challenges remain considerable. SHOP-type composite electrolytes with their potential for balanced performance offer a promising path toward the commercial realization of ASSLBs. With further research and development, these materials can significantly contribute to the advancement of next-generation energy storage technologies.

This review focuses on the status and challenges of testing and evaluation technologies for all-solid-state batteries (ASSBs). As ASSBs are considered as a promising alternative to conventional lithium-ion batteries due to their enhanced safety and potential for higher energy density, understanding and addressing the unique testing challenges they pose is critical. The review systematically represents the novel characteristics of ASSBs, particularly in terms of ion transport mechanisms, interfacial stability, thermal safety, and environmental adaptability. These characteristics significantly differ from those of liquid-based lithium-ion batteries, presenting new challenges in evaluating their performance, reliability and safety.

The review also analyzes the limitations of existing testing and evaluation systems, which are primarily designed for liquid lithium-ion batteries, and highlights a need for new approaches to meet the specific demands of ASSBs. The discussion emphasizes the necessity of developing a comprehensive testing framework that spans all levels, from materials and interfaces to battery cells, systems, and even vehicles. This comprehensive approach is essential to properly assess ASSBs in terms of their performance, lifecycle, and safety under different environmental conditions.

Furthermore, the review identifies some key challenges arising in the evolution of testing technologies, i.e., the need for more accurate in-situ analysis techniques, the integration of intelligent simulation tools, and the incorporation of data-driven approaches. To address these challenges, the review proposes directions for advancing testing methodologies, such as developing high-resolution, real-time in-situ observation tools to capture dynamic processes, utilizing multi-physics simulations to predict performance under complex conditions, and leveraging machine learning for data analysis and prediction of battery behavior. These advancements can integrate cutting-edge techniques into the testing and evaluation processes, facilitating the transition of ASSBs from laboratory research to commercial applications, and ultimately enabling the broader adoption of solid-state battery technology in various industries.

The advances and limitations of chloride SEs from electrode compatibility and ionic conductivity perspectives are analyzed. To better understand recent development of chloride SEs and inspire further explorations and improvements, a typical annual progress is summarized. Chloride SEs were brought back into the spotlight in 2018 due to the stable cycling of uncoated 4 V class cathode LiCoO₂ enabled by Li₃YCl₆ at room temperature. In 2019, a facile and scalable water-mediated synthetic route based on Li₃InCl₆ was developed to overcome the shortcomings of traditional time-consuming mechanical methods. AIMD simulations on LiScCl_3+x is carried out to systematically explore the influence of lithium content on the structure and Li⁺ diffusivity. Note that the above-mentioned chloride SEs (i.e., Li₃YCl₆, Li₃InCl₆ and Li_xScCl_3+x) all use expensive and low-abundance rare-earth elements, which cause high cost and sustainability concerns. Cost-effective Li₂ZrCl₆ with cheap Zr as a central element is developed. As a breakthrough to the close packing anion sublattice of conventional chloride SEs in 2023, a non-close packing style for superionic conduction was realized via selecting large central cation, i.e., LaCl₃-based SE, or employing partial anion replacement, i.e., LiNbOCl₄. The non-close packing anion sublattice with more distorted sites for a low ion migration barrier can theoretically or experimentally realize a high room-temperature ionic conductivity of over 10 mS/cm, compared to those sulfide superionic conductors.

Although a remarkable progress is made on chloride SEs, several crucial challenges have yet to be resolved. The first is still the insufficient interface stability towards the anode. LaCl₃-based SE and Li₃YBr_5.7F_0.3 can enable the cycling of all-solid-state lithium metal battery without extra interface modifications. The interface stabilization mechanisms are still not thoroughly identified. Meanwhile, the 100 cycles and capacity of around 1 mA·h/cm² are insufficient to meet the demand of practical applications. A deeper understanding of interface evolution, accompanied by an artificial interfacial layer to enhance anode interface stability, is needed. The second is that rare and expensive elements like In, Ta, and Sc are still mostly used for high-performance chloride SEs despite Zr-based chloride SEs. It is important for sustainability perspectives and large-scale production to apply cheap and high-abundance elements like Mg, Ca, Al to construct an ion conductive framework and ensure high ionic conductivity and electrode compatibility. The third is that the atmosphere tolerance of chloride SEs needs enhancement to restrain the ionic conductivity loss during ASSLB fabrication due to their easy reaction or combination with water. It is anticipated that chloride SEs can be pushed from laboratory study towards practical applications via taking the intrinsic advantages of chloride SEs and overcoming their shortcomings.