1 Introduction

2 Overview of first-principles

3 Interaction between electrode materials and polysulfides

3.1 Carbon materials

3.2 Transition metal compounds

3.3 Heterostructure

3.4 MOF and COF

3.5 Other materials

4 Reaction mechanism during charge and discharge

5 Electrolyte

6 Conclusion and outlook

Under the background of "double carbon", the energy structure is facing a profound low-carbon transformation, and it is urgent to develop renewable and clean new energy. Energy storage technology is the key technology to build smart grid and realize the popularization and application of renewable energy, and it is also an important means to stabilize the fluctuation of new energy and reduce the impact of large-scale new energy access on the grid^[1,2]. In addition, with the rapid development of mobile electronic devices, electric vehicles and smart grids, the energy density of traditional lithium-ion batteries is increasingly approaching its theoretical limit, which can not meet the demand of high energy density energy storage exceeding 400 Wh·kg^-1, and the development of new high energy density rechargeable battery technology is urgently needed^[3,4].

Lithium-sulfur batteries are considered to be a promising next-generation high-energy battery technology because of their high theoretical specific capacity (1675 mAh·g^-1) and energy density (2600 Wh·kg^-1) with abundant sulfur reserves, low cost, and environmental friendliness^[5]. However, the insulation of active sulfur and its reduction products, the "shuttle effect" of soluble polysulfide (PS), the slow sulfur reaction kinetics, and the poor cycle stability, serious self-discharge and potential safety hazards caused by the dendrite of lithium anode during charge-discharge process have seriously limited the large-scale application of lithium-sulfur batteries^[6,7]. In order to solve the above problems, researchers have carried out a lot of fruitful work from different perspectives, such as sulfur cathode design, separator modification, electrolyte modification or solid electrolyte^[8⇓~10]. However, there is still a lack of in-depth understanding of the internal electrochemical reaction mechanism of lithium-sulfur batteries and the rational design strategy of electrodes, electrolytes and their interfaces^[11].

Theoretical calculations and simulations have been extended to the fields of chemistry, materials and energy, especially the first-principles calculations based on quantum mechanics, which have unique advantages in clarifying reaction mechanisms, providing new material design strategies and predicting their physical properties^[12,13]. First-principles calculations have also played an important role in studying and solving the key problems of lithium-sulfur batteries. Through the establishment of the calculation model,Simulate the structure and properties of battery materials from the atomic/electronic scale, reveal the complex reaction process and law inside the battery, characterize the structure and energy information of complex intermediate products, visualize the diffusion and decomposition kinetics of molecules/ions,It is of great significance to reveal the reaction mechanism at the electrode-electrolyte interface, provide effective guidance for the screening and design of battery materials, broaden the knowledge and understanding of lithium-sulfur batteries, and promote their development^[14,15]. In this paper, the simulation methods of first-principles calculations are briefly described, and then the important progress in the study of the interaction between electrode materials and polysulfides, the reaction mechanism in the charge-discharge process, and electrolytes for lithium-sulfur batteries based on first-principles calculations is reviewed.Finally, the current challenges and broad prospects of the application of first-principles calculations to lithium-sulfur battery research are prospected.

The first principle is based on quantum mechanics, according to the principle of interaction between atomic nucleus and electron and its basic law of motion, after approximate treatment, the algorithm of solving Schrodinger equation. The commonly used first-principles calculation methods include Hartree-Fork (HF) self-consistent field method, density functional theory (DFT), quasi-particle (GW) approximation, and ab initio molecular dynamics (AIMD), among which HF, DFT, and AIMD are widely used^[16⇓~18].

The HF method was proposed by HARTREE and FOCK in the 1920s and 1930s. It uses Hartree approximation, Fock approximation, LCAO-MO approximation, etc. To simplify the unsolvable many-particle Schrodinger equation into a solvable single-particle Schrodinger equation^[19]. The history of DFT can be traced back to the 1920s. In the Thomas-Fermi model established by Thomas and Fermi, the energy of the system is expressed as a function of the electron density. In 1964, Kohn proposed the Hohenberg-Kohn theorem, and in 1965, Kohn and Sham established the Kohn-Sham equation, which clarified the exact relationship between the ground state energy and the electron density^[20][21]. Most of the theoretical simulations in the lithium-sulfur battery field are based on DFT calculations without empirical fitting and parameter tuning^[22]. The physical and chemical properties of materials can be obtained by calculating the stable configuration and energy of materials, such as calculating the formation energy or migration energy of material defects to predict the phase stability of new materials; The interaction mechanism was determined by calculating the adsorption of polysulfide molecules on the surface of electrode materials. The catalytic activity of electrode materials was evaluated by calculating the reaction free energy change, lithium ion diffusion and Li₂S decomposition. AIMD came into being with the development of DFT and HF^[23]. Molecules and atoms are always in motion. Molecular dynamics is a computer simulation method based on classical Newtonian mechanics to simulate the micro-dynamic behavior of materials. By solving the motion equations of all particles, the basic processes related to the atomic motion path are simulated in real time. AIMD can be used to study the electrolyte of lithium-sulfur battery, and can also be used to simulate or predict the kinetic process of electrode surface reaction, especially the interfacial reaction between electrode and electrolyte. The structure and properties of electrolyte, ion transport in electrolyte, ion diffusion on the surface of electrode material or at the electrode-electrolyte interface, ionic conductivity, dielectric constant of electrolyte and viscosity are calculated by establishing bulk and interface structure models.

The insulating properties of active sulfur and its discharge end products, as well as the dissolution shuttle of polysulfide intermediates in the electrolyte, lead to rapid capacity decay and reduced cycle life of the battery. A common solution strategy is to compound sulfur with a conductive support (host) to improve its electron/ion conductivity and to limit that polysulfide ion dissolution shuttle to some extent. The ideal sulfur host material should also have the following characteristics: (1) good adsorption of PS to inhibit PS dissolution shuttle; (2) provide good electron and ion transport to improve reaction kinetics; (3) Catalytically promote the kinetics of PS redox reaction to achieve fast charging and discharging. First-principles calculations were used to explore the interaction between PS and electrode materials, combined with experiments to achieve efficient screening, while guiding the prediction of ideal host materials.

Spontaneous disproportionation and interconversion in the electrochemical reaction of lithium-sulfur batteries lead to the equilibrium distribution of LiPS with unknown length and charge state, which hinders the test of complex S-S bonds and intermediate products (polysulfide molecules, polysulfide ions, radicals, etc.), and makes it difficult to study the charge-discharge reaction process and mechanism. In order to determine the formation and evolution of reaction intermediates, various nondestructive characterization techniques such as UV/Vis, Raman, X-ray absorption spectroscopy, X-ray diffraction, nuclear magnetic resonance spectroscopy, and high performance liquid chromatography have been widely used^[96,97]. For example, Pascal et al. Found that there is an almost linear correlation between the XAS peak area ratio and the chain length of LiPS, but there is a serious overlap of XAS peaks in different LiPS^[98]. The first-principles calculation provides a new method for the elucidation of the reaction mechanism and law in the charge-discharge process.

In lithium-sulfur batteries, the discharge end product is Li₂S, and the charge end products are orthorhombic (α-S) and monoclinic (β-S) sulfur. Understanding the electronic structure and energy information of the intermediate and end products is helpful for the design and development of new electrode or electrolyte materials. Kim et al. Calculated the concentration and mobility of defects in the discharge end product Li₂S based on DFT, and then studied the charge transport mechanism^[99]. The results show that the charge transport in the Li₂S is mainly through the positively charged lithium vacancy, and the contribution of electron conduction is negligible. Liu et al. Studied the charging mechanism of Li₂S based on AIMD, and found that the delithiation process of ultra-small Li₂S nanoparticles represented by Li₂₀S₁₀ clusters was an oxidation reaction, but there were reduction and disproportionation reactions locally, and the long-chain LiPS could firmly bind to insoluble S^2- with Li atoms as the medium^[100]. The role of Li₂S₂ in the charge-discharge process is controversial because it is difficult to observe. According to Feng et al., Park et al. And Yang et al., Li₂S₂ as an intermediate is thermodynamically unstable and prone to spontaneous disproportionation to form Li₂S and S^{[101][102][103]}. Feng et al. Found that there are multiple crystal structures with similar energy in Li₂S₂, indicating that they usually appear in the form of mixtures during their formation, which further proves the difficulty of XRD and other crystal structure characterization methods to analyze charge-discharge products^[101]. Paolella et al. First discovered the presence of Li₂S₂ as an unstable transient species using in situ XRD and determined the conditions for its formation: (1) using a nearly saturated 7 M LiTFSI salt in 1,3-dioxolane (DOL)/1,2-dimethoxyethane (DME)^[104]; (2) There is high-order LiPS at the end of charge or at the beginning of discharge. This confirms the high sensitivity of the chemical reactions involved in the charge-discharge process to the internal environment. LiPS is an important intermediate product in the charge-discharge process of lithium-sulfur batteries. However, the existing form of LiPS in the electrolyte has not been clearly elucidated. Zhang's group recently revealed for the first time that LiPS exhibits a tendency to strongly bind additional lithium ions and form cationic clusters (such as Li₃ {{\mathrm{S}}_6}^{+}) in the electrolyte, confirming the existence of cationic LiPS as the main component in the electrolyte of lithium-sulfur batteries, which updates the conventional understanding of lithium-sulfur battery chemistry^[105]. Further, structural information such as bond length, orbital, and charge of cationic LiPS as well as the chemical properties of LiPS-Li⁺ interaction and the solvation structure of cationic LiPS in electrolyte were obtained based on DFT and MD simulations. The effect of LiPS solvation on the charge-discharge process also needs to be fully considered in the theoretical calculation. Liu et al. Analyzed the thermodynamic behavior of LiPS in DOL and DME^[106]. Park et al. Employed van der Waals augmented density functional theory (vdW-DF), quasi-particle method (G₀W₀), and continuum solvation technique to predict the key structural, spectroscopic, electronic, and surface properties of the redox terminal phases α-S, β-S, Li₂S, and Li₂S₂^[102].

By analyzing the structure of LiPS, thermal/kinetic behavior, and the energy change before and after the redox reaction, the first-principles calculation was used to study the interconversion process and law of the end products and intermediate products, which provided a theoretical basis for clarifying the charging and discharging mechanism of lithium-sulfur batteries. Wang et al. Studied the Li₂S_x(1≤x≤8) cluster structure and discharge reaction mechanism based on AIMD and DFT: for Li₂S_x(1≤x≤8)), when X = 1 and 6, the most stable configuration is chain^[107]; For X = 2 ~ 5, 7, 8, the most stable configuration is cyclic (Fig. The stability order of 7a);S₈ and Li₂S_x is Li₂S>Li₂S₂>Li₂S₃>Li₂S₄>Li₂S₅>Li₂S₆>Li₂S₇>Li₂S₈>S₈. Assary et al. Calculated the reduction potential of polysulfides and the Gibbs free energy of interconversion of intermediates, proved the existence of polysulfide ions {{\mathrm{S}}_2}^{2-}, {{\mathrm{S}}_3}^{2-}, {{\mathrm{S}}_4}^{2-}, {{\mathrm{S}}_3}^{2-}, and proposed the discharge reaction mechanism of lithium-sulfur batteries based on this (Fig. 7 B)^[108]. S reduction is generally considered to be a S₈→Li₂S₈→Li₂S₆→Li₂S₄→Li₂S₃→Li₂S₂→Li₂S process^[109]. The actual reaction process is very complex, and there is a deviation from the above reaction sequence. Zhou and Cheng et al. Reported a solid-state lithium-sulfur battery based on quasi-intercalation reaction, in which PVDF-HFP-in-LiFSI was used as a polymer electrolyte for Li-SPAN battery. The residual N, N-dimethylformamide (DMF) in the discharge process enhanced the C — S interaction, thus avoiding the formation of Li₂S. The Li₄S₂-PAN,DFT calculation of the final product also showed that DMF could effectively reduce the reaction energy barrier of the rate-determining step in the discharge process of solid-state SPAN^[110]. Our research team explored the reaction mechanism of introducing biological reductant dithiothreitol (DTT) into the middle layer to reduce polysulfide ions, and found that the reaction goes through four steps: DTT deprotonation, S-S bond cleavage, intramolecular proton transfer and cyclization, in which S-S bond cleavage is the rate-determining step^[111]. Reduction of long chain polysulfides to short chains involves → {{\mathrm{S}}_2}^{2-} ^© {{\mathrm{S}}_6}^{2-}, {{\mathrm{S}}_6}^{2-} → {{\mathrm{S}}_4}^{2-} ^© {{\mathrm{S}}_2}^{2-} , {{\mathrm{S}}_4}^{2-} → {{\mathrm{S}}_2}^{2-} ^© {{\mathrm{S}}_8}^{2-}0 and {{\mathrm{S}}_2}^{2-} U →S^2-©S^2- step. The low charge density S² and S³ atoms in {{\mathrm{S}}_8}^{2-} favor S²-S³ cleavage,Therefore, the reduction produces {{\mathrm{S}}_2}^{2-} and {{\mathrm{S}}_6}^{2-}, compared with {{\mathrm{S}}_3}^{2-} and {{\mathrm{S}}_5}^{2-}, {{\mathrm{S}}_2}^{2-} and {{\mathrm{S}}_6}^{2-} as well as U {{\mathrm{S}}_1}^{2-} UN are more favorable {{\mathrm{S}}_7}^{2-}. Based on systematic DFT calculations, Zhang's group constructed a novel electrocatalytic model to reveal the chemical mechanism of sulfur reduction reaction in Li-S batteries by taking heteroatom-doped carbon materials as an example^[112]. By analyzing the mechanisms of symmetric and asymmetric Li₂S₄→Li₂S reduction, it is demonstrated that the adsorption energy of LiS_y·(y=1,2,3) radicals can be used as a key descriptor to predict the activity, reaction path, rate-determining step, and overpotential of electrocatalysts. Researchers usually study the electrochemical reaction mechanism based on the ideal model in vacuum. However, practical factors such as the dielectric constant of the solvent, external magnetic field and electric field also have an important impact on the electrochemical reaction process^{[113,114][115][116]}. According to Cheviri et al., the smaller the dielectric constant of the solvent is, the more favorable it is for the reduction of LiPS and the less favorable it is for the oxidation of LiPS^[113]. Velasco et al. Found that solvents with high dielectric constant can reduce the activation energy of Li — S bond cleavage in Li₂S^[114]. Zhou and Cabot et al. Used cobalt sulfide as a catalyst. Experiments and theoretical calculations showed that the electron spin polarization of Co ions under an external magnetic field could weaken the electron repulsion and enhance the degree of orbital hybridization, thus significantly improving the adsorption strength of LiPS and the reaction kinetics of lithium-sulfur batteries^[115].

First-principles calculations are also helpful for the prediction of the charge-discharge voltage plateau. In the experimental study, it is generally believed that the first discharge plateau (2.2 – 2.3 V) corresponds to the reduction of elemental S to Li₂S₄, the second discharge plateau (2.0 – 2.1 V) corresponds to the reduction of Li₂S₄ to Li₂S₂/Li₂S, and the lowest potential plateau is related to the conversion of Li₂S₂ to Li₂S^[107,109]. Based on DFT calculation, Lin et al. Successfully predicted the double-plateau open circuit voltage (OCV) of fully solvated LiPS and the single-plateau OCV of unsolvated LiPS, and correlated the fully solvated, partially solvated and unsolvating LiPS with the C/S positive discharge plateau, respectively, and clarified the mechanism and conditions of the single-plateau discharge curve^[117]. Arneson et al. Studied the lithiation reaction of the S₈(100) and (001) planes and the delithiation reaction of the Li₂S(111) plane based on AIMD, and showed that the intermediate slope region between the two voltage plateaus was caused by the overlap of the two reduction mechanisms due to the local lithium concentration change^[109].

The redox process, law and mechanism of polysulfides in lithium-sulfur batteries are very complex, and the experimental study is challenging, and the theoretical calculation is difficult to simulate the complex reaction environment in the battery, so it needs to be clarified by both experimental and computational means.

Electrolyte plays an important role in lithium-sulfur battery, which is responsible for the positive and negative electrodes and transporting Li⁺, and is one of the key factors affecting the specific capacity and cycle stability^[118]. However, many practical problems such as the solubility and (electro) chemical stability of intermediates, the stability of electrolyte, ionic conduction, and the compatibility between electrolyte and electrode remain to be solved. Clarifying the interactions between lithium metal/ion, polysulfide ion, electrode, electrolyte and other systems is beneficial to the screening and design of new electrolytes. Because of the complexity of the electrochemical system, it is difficult for experimental researchers to disassemble the system into individual parts to study the impact on battery performance. First-principles calculations can help researchers explore the independent parts of the battery and its bulk/interface problems. In this chapter, the application of first-principles calculation in lithium-sulfur battery electrolyte is introduced from three aspects of liquid electrolyte, solid electrolyte and electrolyte additive.

The most common problem of liquid electrolyte is its instability. DOL/DME is the most commonly used electrolyte system. The spontaneous decomposition and gassing of organic electrolyte during battery cycling lead to battery capacity fading and safety problems. Chen et al. studied the gassing behavior of DOL/DME, and the calculation results showed that DOL was easy to decompose into ethylene and tended to react with lithium metal, and the most favorable reaction path (Fig. 8A, B) was reaction 1 → reaction 3 → reaction 5 → reaction 7, showing an adsorption-reaction mechanism^[119]; DME has good stability. With the increase of DME/DOL ratio, the discharge plateau becomes longer and the discharge capacity increases. In addition, Li is the key to gas evolution, based on which the authors propose that a surface protective film can be plated on the lithium anode to protect the lithium anode. The solid electrolyte interphase (SEI) formed by the reaction of metal Li with the electrolyte affects the battery performance by changing the properties of the electrode. Therefore, the exploration of SEI properties is also a focus of researchers in the battery design process. Kamphaus et al. Reported the process of Li surface reduction of Li₂S₈ in DME electrolyte passivated by commonly used SEI components (Li₂O, Li₂CO₃, LiF, LiOH, and Li₂S),Based on the multiphase interface Li/SEI/Li₂S₈ and DME model, the reduction of Li₂S₈ was observed by AIMD^[120]. The study shows that LiPS is inevitably reduced even if it is covered by a passivation layer, which proves the passivation effect of important SEI components including Li₂S. Camacho-Forero et al. Studied the effect of charged interface on electrolyte decomposition, and found that when the interface was charged, the decomposition degree of Li salt was higher, and determined the reduction mechanism of ether and Li salt solvents: C — O bond cleavage and free radical attack^[121]. Han et al compared the oxidation potential of electrolyte molecules in different solvent environments (Li⁺, lithium salt anion (TFSI^-), lithium salt, pyrene), and found that the oxidation potential of isolated electrolyte molecules was beyond the working voltage range of typical lithium-sulfur batteries.Complexation with different solvents changes the oxidation potential :TFSI^- decreases the oxidation potential of electrolyte molecules by at least 4.7%,Li⁺, which is at least 10.4% higher than that of independent molecules^[122]. Pyrene has a negligible effect on the oxidation potential, and its oxidation trend is different from that of Li⁺ and TFSI^-.

Compared with organic liquid electrolytes, solid electrolytes can greatly reduce the potential safety hazards of batteries^[123]. However, the poor interfacial stability between electrode and solid electrolyte, low ionic conductivity, space charge effect and high interfacial resistance have seriously restricted the development of all-solid-state electrolyte lithium-sulfur batteries^[123⇓~125]. Xu et al. Used acidic carbon nanotube paper (ACNTP) to induce in situ polymerization of DOL/DME solution to prepare solid-state electrolyte, and the ACNTP surface — OH and — COOH provided ideal adsorption sites for LiPS, which effectively suppressed the shuttle effect^[126]. Low lithium ion conductivity is a common problem of electrolytes for solid-state lithium-ion batteries and lithium-sulfur batteries, and there are few theoretical studies on solid-state electrolytes for lithium-sulfur batteries. Shi et al. Studied four Li⁺ migration paths on the surface of rare earth solid electrolyte Li₃HoBr₆, and DFT calculations showed that the four migration paths contributed to the high ionic conductivity together, in which the out-of-plane path was more favorable than the in-plane direct path^[127]. Sun et al. Studied the in situ reduction reaction of S₈ on the polyethylene oxide (PEO) chain of electrolyte, and determined that the main reduction product was —S₄Li based on the energy change of lithiation reaction, and —S₄Li significantly promoted the Li⁺ transport through the interaction with PEO^[128]. In addition, the exploration of the interfacial properties (lattice structure, electronic structure, microscopic interaction mechanism, chemical stability, etc.) between cathode Li₂S and solid-state electrolyte is also of great significance to improve the performance of all-solid-state electrolyte lithium-sulfur batteries^[129,130].

The high cost and low ionic conductivity at room temperature limit the development of solid-state electrolytes at this stage. Organic liquids are still the common choice, and electrolyte additives are also a general strategy to alleviate the shuttle effect and improve the performance of electrolytes. Luo et al. Introduced commercial nickel chloride dimethoxyethane adduct (NiDME) as an electrolyte additive^[131]. Because the adsorption energy of NiCl₂ to S₈ is small (0.27 eV), NiCl₂ may be released after charging, and after dissolution, it recombines with DME in the electrolyte to achieve the whole electrochemical catalytic cycle (Figure 8 C). During discharge, the additive can significantly accelerate the conversion of S₈ to Li₂S and reduce the electrolyte demand. Wu et al. Used DFT method combined with energy dispersive X-ray spectroscopy and XPS to study the mechanism of lithium difluorooxalatoborate (LiODFB) as an organic electrolyte additive to improve battery performance^[132]. The oxalyldifluoro (oxalato) borate ion (F₂B[ox]^-) was reduced at 1.6 V to form boroxalate radical (^·B[ox]),F^-, which was gradually eliminated. Boron oxalate radicals may react with DME and DOL at absolute zero, and the final products can promote the formation of SEI on the lithium anode, which not only alleviates the shuttle effect, but also stabilizes the Li surface.

LiNO₃ is often used as an electrolyte additive to protect the Li negative electrode and mitigate redox shuttling and battery self-discharge. Ebadi et al. Calculated the electronic structure of LiNO₃ and its possible decomposition products after reduction on the surface of lithium anode (N₂,Core-level binding energies (BEs) of N 1s XPS for N₂O, LiNO₂, Li₃N, and Li₂N₂O₂),The effect of LiNO₃ was revealed by comparing the experimental values^[133]. The results show that the charge transfer between Li (s) and N (or O) (s, p) and the redistribution of valence electron density caused by orbital hybridization may be the main factors affecting the chemical shift of core level BEs, and the BEs are related to the coordination number of N atom.

The internal environment of the battery is more complex in actual use, such as the pollution and impurities caused by the oxidative decomposition reaction of the electrolyte and the multi-phase interface reaction mechanism of the electrode, electrolyte and intermediate products, which need to be further explored.

With the rapid development of computer technology and the continuous progress of theoretical chemistry, first-principles calculation has become a widely used research tool for researchers. In this paper, we review the important research progress of first-principles calculations on the interaction between electrode materials and polysulfides, the reaction mechanism during charge-discharge process, and electrolytes in lithium-sulfur batteries. In the aspect of polysulfide interaction, the ideal electrode materials were screened out by calculating the electronic structure of electrode materials and their surface polysulfide adsorption, catalysis (S reduction and Li₂S decomposition), (Li⁺) migration and other behaviors. In the aspect of charge-discharge mechanism, the key structural, thermodynamic, spectral, electronic and surface properties of the intermediate and final products were calculated, and the charge-discharge voltage platform and electrochemical performance in the experiment were compared to explore the charge-discharge mechanism from the microscopic point of view. In the aspect of electrolyte, the stability of liquid electrolyte, the interfacial properties and ionic conductivity of solid electrolyte, and the exact role of additives are studied, which provides theoretical guidance for the selection and improvement of electrolyte.

Computational simulation based on first principles saves manpower and material resources, which not only speeds up the experimental process of researchers, but also makes it possible to carry out research that is difficult to implement. The application of first-principles calculation in lithium-sulfur batteries is still in the development stage, especially in the aspects of catalytic redox mechanism and solid-state electrolyte. Due to the limitation of current calculation technology, some calculation results can not accurately and clearly explain the experimental phenomena. Researchers can only speculate on the causal relationship based on the correlation between the calculation results and the experimental phenomena. With the development of computer technology and theoretical chemistry, first-principles calculations are expected to solve more basic scientific problems by combining with experiments: (1) the design of sulfur cathode host materials needs to balance their adsorption and catalytic conversion of polysulfides in order to alleviate the shuttle effect and achieve fast charge and discharge; (2) The establishment of descriptors is helpful to understand the interaction between electrode and polysulfide; (3) Complex multi-step, multi-phase, multi-ion and multi-electron redox reactions caused by various sulfur-containing intermediates require deeper theoretical studies on polysulfide molecules, ions and radicals, as well as comprehensive consideration of solvent effects, pores, steric hindrance and other simulation conditions; (4) Screening and design of liquid electrolyte and exploration of key factors affecting stability, as well as in-depth understanding of composition/component optimization, lithium ion migration path and transport mechanism of solid electrolyte materials; (5) The data processing ability of machine learning methods is powerful, and it plays an increasingly important role in lithium-sulfur battery research, including material component screening, new material design, enriching theoretical models, and improving research and development efficiency^[134,135]. In addition, data-driven machine learning methods have also shown potential applications in battery condition assessment and service life prediction^[136,137].