Graphene has excellent electrical conductivity and becomes a research hotspot of anode materials for sodium ion batteries. However, pure graphene has a low sodium storage capacity and is not conducive to sodium ion intercalation, which limits its application. Element doping can stabilize the interlayer structure and increase the sodium storage capacity. To study the mechanism of sodium storage and improve the performance of sodium storage, the research progress of the first-principles studies on element-doped graphene anode materials are summarized, and the influence of element doping on the physical properties and electrochemical properties is proposed. Also, the research trend of first-principles application in graphene anode doping of sodium ion batteries is expounded from three aspects, i.e., interface reaction mechanism, co-doping strategy, and laboratory to industrial transformation. It is expected to develop new graphene doped anode materials with a better performance to help the application of energy and environmental protection materials.

First-principles calculations provide a theoretical basis for elemental doping in graphene-based sodium-ion anode materials in an atomic scale. Based on the mechanisms including electronic structure modulation, geometric structure evolution, and bonding characteristics changes, a comprehensive analysis is conducted on the effect of doping elements on the physical properties (i.e., adsorption energy, diffusion energy barriers, electrical conductivity, structural integrity) and electrochemical performance (i.e., specific capacity, cycling stability) of graphene. The mechanisms by which doping regulates the physical properties include a) enhanced adsorption capability primarily originates from either change in the electronic structure of graphene induced by the dopant or the introduction of new active sites, and b) categorized as electronically dominant doping or geometrically dominant doping, respectively. The increase or decrease in diffusion energy barriers is mainly influenced by the charge environment and geometric structure. Different dopants significantly affect the electrical conductivity of graphene, with the core mechanism lying in their modulation of the band gap. The structural stability is primarily determined by the size compatibility and bonding strength between the dopant atoms and carbon atoms, reflected in the magnitude of the cohesive energy. For the electrochemical performance, the adsorption capability serves as the cornerstone of discharge specific capacity, the diffusion energy barriers are a key factor for both discharge specific capacity and rate capability, the structural stability forms the foundation of cycling stability, and the electronic conductivity (governed by the band gap) is a dominant factor for overall electrochemical performance.

This review provides the research progress on a comprehensive, first-principles-based examination in elemental-doped graphene as electrode materials for sodium-ion batteries. It examines the governing mechanisms behind the physical properties and electrochemical performance of doped graphene anode materials. The microscopic physicochemical nature of doped graphene's characteristics is revealed via the detailed atomic-scale simulations and analysis.

The first-principles calculations reveal the distinct mechanisms by which different main-group element dopants affect the physical properties of graphene. Nitrogen (N) and boron (B) doping significantly enhance a sodium-ion adsorption capability and a diffusion performance via modifying the electronic structure of graphene, while maintaining a good structural integrity, thus exhibiting excellent overall performance. Sulfur (S) doping optimizes diffusion kinetics via expanding the interlayer spacing, though its adsorption capability and cycling stability require improvement. Fluorine (F) doping enhances adsorption capability via charge transfer mechanisms but suffers from a lower structural stability. Silicon (Si) doping increases the open-circuit voltage, however, its volumetric effect leads to degraded diffusion performance and structural stability.

The electrochemical performance analysis reveals that nitrogen-doped graphene exhibits a balanced performance in terms of specific capacity and capacity retention rate, making it suitable as a high-performance anode material for sodium-ion batteries. Boron-doped graphene achieves the maximum discharge specific capacity, however, its lower capacity retention rate limits its use to scenarios prioritizing a high energy density. Sulfur-doped graphene demonstrates the optimum cycling stability, but its relatively low specific capacity makes it suitable for applications demanding exceptionally long cycle life. Fluorine-doped graphene and silicon-doped graphene require a further performance optimization. Specifically, fluorine-doped graphene suffers from a low specific capacity and a poor capacity retention, limiting its practical viability. Silicon-doped graphene experiences degraded diffusion performance and structural stability due to its volumetric effect, necessitating a further investigation into doping concentration and structural design.

Based on the first-principles calculations, this review delves into the interactions between doped graphene and the electrolyte, predicting the composition and structure of the solid electrolyte interphase (SEI) film. Some strategies are explored to engineer a more stable SEI layer via simulating the SEI formation process, thereby suppressing the electrolyte decomposition and enhancing the cycling stability and safety of batteries.

Based on the research on doped graphene anode materials, novel doping elements and co-doping strategies can be explored to develop sodium-ion battery anodes with an enhanced adsorption capacity, a reduced diffusion energy barriers, and a superior structural stability. Leveraging the first-principles calculations to predict electrochemical performance of emerging dopants, we optimize doping concentrations and atomic configurations to improve electronic conductivity and ion diffusivity, thus propelling the performance enhancement of sodium-ion batteries.

The research on elemental doping of graphene anode materials for sodium-ion batteries synergistically integrates big data analytics, leveraging extensive experimental and computational datasets to identify and predict dopant effects on the material performance. This data-driven approach enables an accelerated translation from laboratory prototypes to industrial-scale production, reducing manufacturing costs and expediting the commercialization of sodium-ion battery technologies. Consequently, it establishes a robust support framework for developing eco-friendly energy materials and their sustainable implementation.

Silicon-carbon composite materials and compounds combine the high lithium storage performances of silicon with the structural excellence of carbon. However, their complex electrochemical behavior and volume changes during charging and discharging are urgent issues to be addressed. As an effective theoretical tool, first-principles calculation plays a crucial role in predicting, revealing the characteristics of electrode materials and understanding electrochemical mechanisms in atomic scale. In this review, the first-principles calculation methods were summarized, and recent research results on first-principles calculations of typical silicon-carbon composite materials and compounds as lithium-ion battery anode materials were represented. The laws of diffusion kinetics, interface reactions, mechanical properties and thermodynamic stabilities of silicon-carbon anode materials for lithium-ion batteries were proposed. Furthermore, the first-principles calculations for silicon-carbon anode materials in lithium-ion batteries were outlooked based on three perspectives like density functional theory (DFT), algorithm integration and experimental integration. The development of novel silicon-carbon anode materials with superior performances were anticipated, thereby contributing to the development of the new energy sector.

In this review, the first-principles calculation methods and the research progress of the first-principles calculations on typical silicon-carbon anode materials for lithium-ion batteries were elaborated. The diffusion kinetics, interfacial reactions, mechanical properties and thermodynamic stability laws of silicon-carbon anode materials for lithium-ion batteries were revealed.

1) From the perspective of lithium-ion diffusion kinetics, the diffusion mechanism of lithium ions in silicon-carbon anode materials is complex, which is affected by material structure and chemical composition. In silicon/graphite composite materials, lithium ions are prone to first intercalating between graphite layers and then diffusing into silicon, which is regarded as a two-dimensional diffusion. Lithium ions in silicon/carbon nanotube composite materials undergo an one-dimensional diffusion, primarily along the walls or gaps between carbon nanotubes. The two-dimensional structure in silicon/graphene composite materials facilitates a rapid diffusion of lithium ions. Lithium ions in silicon carbide exhibit bulk and interfacial diffusion, which are influenced by charge transfer and electric field effects.

2) From the perspective of interface reaction, the formation of the SEI film is crucial for the performance of silicon-carbon anode materials. Meanwhile, cycle life and efficiency of the batteries are affected by stability and uniformity of SEI film. The volume expansion of silicon in silicon/graphite composite materials can damage the adjacent SEI film, leading to the continued generation of new SEI film. In silicon/carbon nanotube composite materials, more active sites for lithium ions are provided for the unique tubular structure and high specific surface area of carbon nanotubes, making the SEI film more stable. Silicon/graphene composite materials have a layered structure that promotes the uniform dispersion of electrolyte on the surface for the composite materials, resulting in a more uniform SEI film. Silicon carbide has a great hardness and a wear resistance, which enhances its ability to resist mechanical stress during charging and discharging, effectively protecting the SEI film.

3) From the perspective of mechanical properties, different types of carbon materials have different buffering effects on the volume expansion of silicon. Volume expansion problems of silicon are alleviated because of impurities and defect structure of microcrystalline graphite in silicon/graphite composite materials. In silicon/carbon nanotube composite materials, the flexibility of carbon nanotubes helps to withstand greater structural deformation and enhance the structural stability of silicon. In silicon/graphene composite materials, core–shell structures are more conducive to suppressing the volume expansion of silicon. The decrease in electrochemical performance caused by volume expansion is alleviated by the tight interface bonding between silicon carbide and the matrix material, which also helps to improve the fatigue resistance of materials.

4) From the perspective of thermodynamic stability, the thermodynamic stability is assessed through calculations of formation energy, binding energy, reactivity, and changes in free energy. Silicon/graphite composites, benefiting from the layered structure of graphite, exhibit a good thermodynamic stability due to their low formation energy, high binding energy, and low reactivity. Silicon/carbon nanotube composites have a high binding energy due to their unique structure, but their thermodynamic stability is significantly affected by free energy under high-temperature and high-pressure conditions. Silicon/graphene composite materials, leveraging the two-dimensional structure of graphene, have a moderate formation energy and a high binding energy, resulting in a stable thermodynamic performance. Silicon carbide has a high formation energy, and the covalent bonds between silicon and carbon atoms contribute to its high structural stability and good thermodynamic stability.

Conventional DFT method struggles to accurately simulate intermolecular forces due to its lack of description of nonlocal electron correlations, resulting in significant errors in calculating material structural parameters, mechanical properties and energetic properties. To overcome this problem, the van der Waals Density Functional method is introduced. The Becke 86 exchange functional is incorporated by a named optB86b method, enabling effective corrections to the Generalized Gradient Approximation. The excessively strong repulsive interaction of the exchange functional at short distances is reduced, and the accuracy of DFT method is enhanced.

To enhance the computational efficiency of first-principles calculations and have deeper insights into the lithium storage mechanism of silicon–carbon anode materials in lithium-ion batteries, the first-principles calculations and machine learning, phase-field methods, multiscale simulation techniques are integrated. The data analysis and model optimization are accelerated via machine learning. The evolution of microstructures is captured cross phase-field methods. The macroscopic reaction mechanisms of lithium-ion batteries from a microscopic perspective are revealed based on molecular dynamics and finite element analysis. The precision and efficiency of material development are significantly improved via interdisciplinary integration, expanding the application of silicon–carbon anode materials in the field of new energy.

The first-principles calculations and experimental research should be combined due to some factors such as high experimental costs, stringent experimental condition and low data reproducibility. The accuracy of first-principles calculation methods can be validated via comparing computational predictions with experimental results, promoting the coordinated development of theoretical calculations and experimental research. It is expected that this will lead to the development of new silicon-carbon anode materials with a higher specific capacity, a better cycle stability, and a faster charge/discharge rate, facilitating their application in sodium-ion batteries and other fields and bringing greater breakthroughs to the development of the new energy field.