In comparison to Li-ion batteries, Na-ion batteries offer the benefits of low cost, good low-temperature performance, and safety, attracting great attention in the cost- and reliability-sensitive applications. With high capacity and low cost, Prussian blue-like materials (PBAs) stand as promising cathode materials for Na-ion batteries. However, the presence of crystalline water within their structure induces fast performance decay of the battery, serving as a critical bottleneck limiting their application. This work reports a facile thermal treatment strategy to effectively remove crystalline water from PBAs cathode materials, improving capacity retention from 73% to 88% after 340 cycles. The in-situ analysis uncovers that the initial loss of Coulombic efficiency of PBAs cathode is a result of its irreversible transformation from a trigonal form to cubic phase during the charging and discharging process. This issue can be addressed by introducing of Na₂C₂O₄ to compensate the irreversible Na loss in the cathode. On this basis, a high-performance quasi-solid-state Na-ion battery is built by pairing a low-water-content PBAs cathode with Na₂C₂O₄ additive and a hard carbon (HC) anode within a poly(ethylene glycol) diacrylate (PEGDA)-based quasi-solid-state electrolyte with high ionic conductivity and electrochemical stability. This battery exhibits the specific capacities ranging from 58 to 105 mAh·g^-1 at current densities from 20 to 500 mA·g^-1, capable of sustaining stable cycling for over 200 cycles. This study underscores the significant improvement in stability and capacity of PBAs cathode materials by the efficient removal of crystalline water in them.

With rapid development of lithium ion batteries (LIB) and sodium ion batteries (SIB), hard carbon (HC) as new anode material has earned much attention. Besides its rich precursor sources and low cost, HC has higher Li⁺ storage capacity and better rate performance than graphite for LIB. Furthermore, it is also recognized as the most commercially potential anode material for SIB. However, low initial Coulombic efficiency is a common issue for HC. In addition, it is believed that the specific capacity can be further improved with the clarification of the Li/Na ion storage mechanism. In recent years, many researches on electrochemical mechanism have been conducted with some model assumptions proposed for better understanding the mechanism. This review introduced the structures and preparation approaches of HC as well as its application in LIB and SIB. The advantages, especially in fast charging, coating and other subdivision were discussed, and the different modification strategies such as pore structure design, doping, optimizing interface between electrode and electrolyte were summarized, aiming at the increase of capacity and the improvement of Coulombic efficiency of batteries.

MXenes with two-dimensional layered structure are widely used in the field of potassium ion supercapacitors because of their excellent electrical properties and adjustable surface functional groups, but their limited dual-capacitor storage capacity severely retards the application of MXenes materials in electrode materials. In this work, the strategy of “Lewis acid molten salt pre-etching + liquid phase etching + in situ hydrothermal recombination” was used to prepare the Ti₃C₂-based heterojunction with Ti₃C₂ as matrix and MnO₂ coated surface to improve the storage of potassium ions in electrode materials. The connection mode, electrical properties and the change of potassium adsorption law at Ti₃C₂-based heterojunction interfaces were studied by using the first principles calculation method based on density functional theory. The results show that the maximum adsorption capacity of potassium ions in the constructed Ti₃C₂-based heterojunction is about 3 times that of Ti₃C₂. The presence of Ti-O-H-O connecting channel increases the number of free electrons in MnO₂, causing Ti₃C₂-based heterojunction exhibiting excellent electrical properties. The electrochemical test results of the three-electrode system show that, at a current density of 1 A·g^-1, Ti₃C₂-based heterojunction can provide 431 F·g^-1 specific capacitance which is much higher than 128 F·g^-1 of bare Ti₃C₂. At a voltage sweep rate of 100 mV·s^-1, the contribution of pseudocapacitance is up to 89%. In addition, the Ti₃C₂-based heterojunction exhibits lower electrochemical impedance, which improves the potassium ion transport rate and electron transfer rate. Therefore, this study demonstrates that the electrochemical performance of Ti₃C₂ matrix can be improved by constructing Ti₃C₂-based heterojunction, and the corresponding energy storage mechanism can provide a theoretical basis for the design of other MXenes-based electrode materials.

Selenium (Se) is considered as a new generation energy storage material of lithium-selenium (Li-Se) battery due to its high volume specific capacity (3253 mAh·cm^-3) and high electronic conductivity (1×10^-5 S·m^-1). To address the problems of volume expansion, fast capacity decay, and low utilization of active materials during its charging-discharging process, a ZIF-L derived nitrogen-doped nanosheets/selenium (Se@NC/CC) flexible self-supported composite electrode is designed in this study for lithium-selenium battery by growing two-dimensional zinc-based metallic organic framework (ZIF-L) on carbon cloth (CC). The rich microporous structure in the nitrogen-doped carbon nanosheets can effectively alleviate the volume expansion during the reaction process, and the doping of heteroatoms N helps to adsorb Li₂Se and reduce the loss of active substances. In particular, it is found that there is strong chemical bonding between Se and C in the Se@NC/CC electrode, which also helps to reduce the loss of active materials and improve the performance. Electrochemical results show that the initial discharge specific capacity of the Se@NC/CC electrode is 574 mAh·g^-1 at a current density of 0.5C (1.0C=675 mAh·g^-1), demonstrating a high initial discharge specific capacity. At a current density of 2.0C, the initial discharge specific capacity is 453.3 mAh·g^-1, which maintains at 406.2 mAh·g^-1 after cycling for 500 cycles and it also displays excellent rate performance compared to literature. Such a flexible self-supported selenium cathode designed in this study provides a new research route on the design of selenium host materials for advanced alkali metal-selenium batteries.

Rechargeable zinc-ion batteries (ZIBs) have captured significant attention as promising solutions for large-scale energy storage. They offer advantages such as low cost, inherent safety, high specific energy, and eco-friendliness. Though numerous breakthroughs have been achieved in the development of cathodes, anodes and electrolytes, ZIBs are still far behind for practical application due to the lack of advanced materials. In the realm of ZIBs, two-dimensional (2D) MXenes have emerged as a fascinating candidate, leveraging their exceptional properties such as high richness, customizability, and unique physiochemical attributes. This review aims to provide a concise overview of advancements in MXene application for ZIBs, encompassing multiple synthesis routes, properties, morphological and structural characteristics, as well as various chemistries employed. Furthermore, detailed elucidation is provided on the recent progress in MXene-based cathodes, anodes, and electrolytes/separators for ZIBs, indicating the great potential of MXenes for achieving high-performance ZIBs. Strategies to enhance the performance of MXene-based ZIBs are also highlighted, including ion-intercalation adjustment, surface modification, heteroatoms doping, and layer spacing widening. Lastly, the review discusses the current challenges and future prospects for MXene-based ZIBs, paving the way for further research and development in this exciting field.

Supercapacitors, distinguished by their unique advantages, including high power performance, stable cycling behavior, and excellent safety, emerge as highly promising energy storage devices in the fields of new energy vehicles and mobile electronic applications. However, the issue of relatively low energy density continues to constrain their practical applications. To enhance electrochemical activity, CoS nanosheets were deposited onto ZnCo₂O₄-ZnO microspheres coated with carbon (ZCO-ZO@C@CoS) using a facile solvothermal method, calcination treatment, and electrochemical deposition reaction. Carbon layer not only promoted electron transport to enhance electrical conductivity, but also improved the stability of the structure. The open network space formed between CoS nanosheets facilitated rapid ion transport. Additionally, CoS nanosheets possessed abundant electroactive sites, enabling rapid reversible redox reactions. The co-effect of nanowires of the core-shell structure, the carbon layer, and the outer nanosheets effectively enhanced the overall electrochemical performance. Consequently, ZCO-ZO@C@CoS exhibited a specific capacitance of 1944 F·g^-1 (972.0 C·g^-1) at 1.5 A·g^-1, with an initial capacity retention of 75% after 10000 cycles at high current density of 20 A·g^-1. The asymmetric supercapacitor device, comprising ZCO-ZO@C@CoS (positive electrode) and activated carbon (negative electrode), also demonstrated excellent specific capacitance, high-rate performance, and exceptional cycling stability, indicating significant potential for practical applications.

Bentonite is an abundant, cheap and readily available natural clay mineral, with montmorillonite (MMT) as its main mineral composition. MMT possesses excellent ion exchange, adsorption and ion transport properties due to its unique two-dimensional layered nanostructure, abundant pore structure, and high specific surface area. Moreover, it also possesses excellent thermal, chemical and mechanical stabilities. In recent years, MMT has attracted extensive attention in the field of electrochemical energy storage owing to the above excellent characteristics, especially the inherent fast ion (Li⁺, Na⁺, Zn²⁺, etc.) transport properties. Thus, the bentonite-based functional materials have been widely applied to the key components (i.e., electrodes, polymer electrolytes, and separators) of electrochemical energy storage devices and show good application prospects. In this review, the structure and physicochemical properties of bentonite are firstly introduced, and then the research progress of bentonite-based functional materials in the field of electrochemical energy storage, mainly including metal anodes, lithium-sulfur battery cathodes, solid/gel polymer electrolytes, and polymer separators, is comprehensively summarized. On the basis of these facts, the ion transport promotion mechanism of bentonite-based functional materials during the process of electrochemical energy storage is elaborated. Finally, the current problems and challenges faced by application of bentonite-based materials in electrochemical energy storage devices are pondered, and the possible future research directions are prospected. This review provides useful guidance for the design and development of bentonite-based electrochemical energy storage functional materials.

Sodium-ion batteries are economical and environmentally sustainable energy storage batteries. Among them, β-NaMnO₂, a promising sodium-ion cathode material, is a manganese-based oxide with a corrugated laminar structure, which has attracted significant attention due to its structural robustness and relatively high specific capacity. However, it has short cycle life and poor rate capability. To address these issues, Ti atoms, known for enhancing structural stability, and Cu atoms, which facilitate desodiation, were doped into β-NaMnO₂ by first-principles calculation and crystal orbital Hamilton population (COHP) analysis. β-NaMn_0.8Ti_0.1Cu_0.1O₂ exhibits a notable increase in reversible specific capacity and remarkable rate properties. Operating at a current density of 0.2C (1C = 219 mA·g^-1) and within a voltage range of 1.8-4.0 V, the modified material delivers an initial discharge capacity of 132 mAh·g^-1. After charge/discharge testing at current densities of 0.2C, 0.5C, 1C, 3C, and 0.2C, the material still maintains a capacity of 110 mAh·g^-1. The doping of Ti atoms slows down the changes in the crystal structure, resulting in only minimal variation in the lattice constant c/a during the desodiation process. Mn and Cu engage in reversible redox reactions at voltages below 3.0 V and around 3.5 V, respectively. The extended plateau observed in the discharge curve below 3.0 V signifies that Mn significantly contributes to the overall battery capacity. This study provides insights into modifying β-NaMnO₂ as a cathode material, offering experimental evidence and theoretical guidance for enhancing battery performance in Na-ion batteries.

Compared to Li-ion batteries, Na-ion batteries hold significant advantages and market value for achieving low-cost and large-scale energy storage, thanks to the utilization of cheap and abundant Na resources. However, the use of highly flammable liquid electrolytes with leaky risk raises safety concerns for conventional Na-ion batteries under abuse conditions such as mechanical damage, short-circuiting, and thermal runaway. Limited electrochemical stability of liquid electrolytes also hinders further enhancement of the performance of Na-ion batteries for practical use. This study reports a facile way for the preparation of high-performance gel polymer electrolyte (GPE) by thermal-driven radical in-situ polymerization of dipentaerythritol penta-/hexa-acrylat (DPEPA). This GPE exhibits an ionic conductivity of 1.97 mS·cm^-1, a Na⁺ transference number of 0.66, and a broad electrochemical stability window. The DPEPA displays a lower lowest unoccupied molecular orbit (LUMO) energy level than that of ethylene carbonate (EC) and diethyl carbonate (DEC) solvents, allowing for its preferential decomposition alongside NaPF₆ on the anode surface. This leads to a stable organic-inorganic composite film of solid-state electrolyte interphase, inhibiting the decomposition of electrolyte solvents on the anode surface. The quasi-solid-state Na-ion battery employing Na(Ni _1/3Fe_1/3Mn _1/3)O₂ (NFM) cathode and hard carbon (HC) anode in this GPE exhibits a high capacity retention rate of 92% after 300 stable cycles at a current density of 120 mA·g^-1, while achieving the specific capacities of 99-120 mAh·g^-1 within a wide temperature range of 20-80 ℃. In-situ X-ray diffractometer analysis reveals the highly reversible structural evolution of the NFM cathode during Na storage and the “adsorption-pore-filling” mechanism of Na⁺ storage in the HC anode. All data in this research demonstrates that introducing polymers with low LUMO energy levels proves an effective approach to enhance the electrochemical stability of solid-state Na-ion batteries while improving cell safety.

Silicon sludge, the photovoltaic cutting silicon waste, has become one of the expected raw materials for the key silicon carbon anode materials used in high energy density batteries above 300 Wh·kg^-1 due to its low cost, two-dimensional lamellar structure and ultrahigh specific capacity (4200 mAh·g^-1). However, silicon sludge requires systematic modification because of its challenges such as complex composition, large particle size, poor electrical conductivity, low stability and poor electrochemical performance. This paper systematically reviews the application status and research progress of silicon sludge in lithium-ion batteries. Firstly, the important effects of metal and non-metal impurities on battery performance are summarized, in which metal impurities are normally removed by magnetic separation and acid pickling, and non-metallic impurities are removed by liquid-liquid extraction and heat treatment. Secondly, detailed elucidation about the initial performance and modification methods of the silicon sludge is provided. Concretely, silicon sludge can be nano-sized to reduce expansion by grinding, etching, electrothermal shock, and alloy dealloying, enhance electrical conductivity through doping the intrinsic silicon and doping the carbon layer on the silicon surface, improve stability through the construction of inert layer, conductive layer and functional group, and obtain mechanical support and protection through silicon-carbon composite. Finally, the challenges, development directions and future prospects of silicon-based anode based on silicon sludge are put forward, aiming to provide a reference for converting silicon sludge into treasure and promote the rapid development of high energy density lithium-ion batteries.

FeF₃∙0.33H₂O possesses the characteristics of high theoretical capacity and high voltage, but its electrochemical cycling performance is unsatisfactory due to its poor conductivity and serious volume change during redox reaction, resulting in limited application. In this study, by using the strategies of dopamine self-assembly coating, carbonization, HCl etching and HF fluorination, the yolk-shell structured composite FeF₃∙0.33H₂O@carbon nanoboxes (FeF₃∙0.33H₂O@CNBs) composed of N-doped graphene shell and nanocube FeF₃∙0.33H₂O core was synthesized. Its particle size is about 250 nm and thickness of carbon shell is 30-40 nm. FeF₃∙0.33H₂O@CNBs displays an initial charge-discharge capacity of 208 mAh·g^-1 at a current density of 0.2C(1C=237 mA·g^-1). After 50 cycles, the capacity remains 173 mAh·g^-1, and the capacity attenuation rate per cycle is only 0.3%. In comparison, the initial capacity of bare FeF₃∙0.33H₂O is 112 mAh·g^-1, and after 50 cycles, only 95 mAh·g^-1 reserves, indicating superior cycle performance of FeF₃·0.33H₂O@CNBs. Furthermore, charging and discharging results at 0.1C-1C show that the rate performance is also significantly better than bare FeF₃∙0.33H₂O. It’s due to that N-doped graphene shell prepared by this strategy provides good electron/ion transport performance. At the same time, the carbon shell can not only buffer and inhibit the volume change of the core FeF₃∙0.33H₂O, but also shorten the ion migration distance and improve the Li⁺ migration rate on the electrolyte storage and retention performance of the electrolyte. As a result, the electrochemical performances are better than those of previous literature.

Excessive emission of greenhouse gases has serious adverse effects on global climate. How to reduce carbon emissions has become a global problem. Supercapacitors have advantages of long cycle life, high power density and relatively low carbon emissions. Developing supercapacitor energy storage is an effective measure to build the reliable future energy system. In recent years, MXene materials have achievedgreat popularity in the field of supercapacitor energy storage applications due to their excellent hydrophilicity, electrical conductivity, high electrochemical stability, and surface chemical tunability. However, the serious self-stacking problem of MXene limits its performance in energy storage. Developing advanced MXene materials is critical for next generation high-performance electrochemical energy storage devices. This paper reviews the research progress of MXene material in the field of supercapacitor energy storage. Firstly, the structure and energy storage properties of MXene are introduced, followed by analysis of the energy storage mechanism of MXene. Secondly, nanoengineering of structure design to improve the performance of MXene electrode is depicted. Thirdly, structure-performance relationship of MXene composite materials and its latest research progress in application of supercapacitor are summarized. Finally, research and development trends of MXene as an electrode for supercapacitor are broadly prospected.

The microreactor was constructed by using the block copolymer (P123)/sodium dodecyl sulfate (SDS) hybrid emulsion. Horseshoe-shaped hollow porous carbon was prepared by hydrothermal carbonization of xylose. The results showed that hydrothermal reaction of xylose occurred at interface between microreactor and solution. Hydrophilicity of PEO (hydrophilic block in P123) decreased at hydrothermal temperature of 160 ℃. Hybrid emulsion was swelled and destroyed gradually because PEO ran into the interior of emulsion. Furthermore, the morphology of microreactor could be regulated by the mass ratio of P123/SDS and the opening angle, and cavity diameter could be controlled by the hydrothermal time. Owing to the open cavity, the capacity of charges and ions was magnified and transport distance was reduced. In addition, specific capacitance and energy density of porous carbons were improved and showed positive correlation with cavity diameter. The horseshoe-shaped hollow porous carbon with largest opening angle (63°), cavity diameter (80 nm) and optimal supercapacitor performance was obtained at a P123/SDS mass ratio of 1.25 : 1 by hydrothermal method for 12 h. In a three-electrode system, the product showed a high specific capacitance of 292 F·g^-1 at a current density of 1 A·g^-1. In a two-electrode system, the product showed an excellent energy density (6.44 Wh·kg^-1), specific capacitance of 185 F·g^-1 at a current density of 0.2 A·g^-1 and outstanding cycling stability (94.83%) after 5000 cycles at a current density of 5 A·g^-1.

Lithium-sulfur batteries (LSBs) have attracted wide attention due to their high energy density, abundant raw material reserves and environmental friendliness. However, the shuttle effect of polysulfides, the large volume expansion during the reaction, and the poor electron conductivity of sulfur greatly limit their practical development. In this work, a ZIF-8 derived flower-like two-dimensional (2D) porous carbon nanosheet/sulfur composite (ZCN-SnS₂-S) combined with SnS₂ nanoparticles is designed as the cathode for LSBs. The unique 2D flower-shaped porous structure not only effectively alleviates the volume expansion during the reaction process, but also provides a fast channel for Li⁺ and electron transport. The presence of heteroatom N further promotes the adsorption of polysulfide. In particular, the polar SnS₂ enhances the chemical adsorption on polysulfides, resulting in excellent electrochemical performance. The ZCN-SnS₂-S electrode exhibits high reversible specific capacity of 948 mAh·g^-1 after 100 cycles at 0.2C (1C=1675 mA·g^-1), demonstrating the capacity retention rate of 83.7%. Even at a high current density of 2C for 300 cycles, it still has a reversible specific capacity of 546 mAh·g^-1.

Metallic Li is one of the ideal anodes for high energy density lithium-ion battery due to its high theoretical specific capacity, low reduction potential as well as abundant reserves. However, the application of Li anodes suffer from serious incompatibility with traditional organic liquid electrolyte. Herein, a gel complex electrolyte (GCE) with satisfactory compatibility with metallic Li anode was constructed via in situ polymerization. The double lithium salt system introduced into the electrolyte can cooperate with the polymer component, which broadens electrochemical window of the electrolyte to 5.26 V compared to 3.92 V of commercial electrolyte, and obtains a high ionic conductivity of 1×10^-3 S·cm^-1 at 30 ℃ as well. Results of morphology characterization and elemental analysis of Li anode surface show that GCE exhibits obvious protective effect on lithium metal under the condition of double lithium salt system, and volume effect and dendrite growth of Li anode are obviously inhibited. At the same time, the lithium metal full battery, assembled with commercial lithium iron phosphate (LiFePO₄) cathode material, exhibits excellent cycling stability and rate performance. The capacity retention rate of the battery reaches 92.95 % after 200 cycles at a constant current of 0.2C (1C = 0.67 mA·cm^-2) at 25 ℃. This study indicates that the GCE can effectively improve the safety, stability and comprehensive electrochemical performance of lithium-metal battery, which is expected to provide a strategy for universal quasi-solid electrolyte design.

Cycle stability and specific capacity of cathode materials for sodium ion batteries play an important role in achieving their wide application. Based on the strategy of introducing specific heteroelements to optimize the structural stability and specific capacity of cathode materials, O3-Na_0.9Ni_0.5-xMn_0.3Ti_0.2Sb_xO₂ (NMTSb_x, x=0, 0.02, 0.04, 0.06) was prepared by a simple solid-state reaction method, and effects of Sb doping amount on the sodium storage properties of Na_0.9Ni_0.5Mn_0.3Ti_0.2O₂ cathode materials were investigated. The characterization results show that the electrostatic repulsion force between oxygen atoms in the transition metal layer is reduced after Sb doping, while the lattice spacing is expanded, which is conducive to deintercalation of Na⁺. Meanwhile, the strong electron delocalization caused by Sb doping decreases energy of the whole system, leading to a stable structure, more conducive to cyclic charging and discharging. The electrochemical test shows that initial discharge specific capacity of undoped NMTSb₀ is 122.8 mAh·g⁻¹ at 1C(240 mA·g⁻¹), and the capacity retention rate is only 41.5% after 200 cycles. But initial discharge specific capacity of doped NMTSb_0.04 is 135.2 mAh·g⁻¹ at 1C, and the capacity retention rate is up to 70% after 200 cycles. This study shows that Sb doped O3 type Na_0.9Ni_0.5Mn_0.3Ti_0.2O₂ cathode material can significantly improve initial discharge specific capacity and capacity retention rate of sodium ion batteries. Our results suggest that Sb doping strategy might be a useful approach for preparation of high stable sodium ion batteries..

Suffering from strong electrostatic interactions between divalent Zn²⁺ and host framework, molybdenum disulfide exhibits slow reaction kinetics as cathode for aqueous zinc-ion batteries. The narrow layer spacing of MoS₂ is difficulty in accommodating large size insertion of hydrated Zn²⁺, resulting in a lower discharge specific capacity. Here, NH₄⁺ expanded MoS₂-N was prepared by a simple ammonia-assisted hydrothermal. The result showed that the ammonia promoted hydrolysis of thioacetamide to provide reduced S^2- and generated a large amount of NH₄⁺ as intercalating particles. These particles expanded the layer spacing of pristine MoS₂ from 0.62 nm to 0.92 nm, greatly reducing the Zn²⁺ inserting energy barrier (with its charge transfer resistance of MoS₂-N only 35 Ω), and increased the discharge specific capacity to 149.9 mAh·g⁻¹ at the current density of 0.1 A·g^-1, 2 times that of MoS₂ electrode without NH₄⁺ expansion. Consequently, it exhibited a stable discharge capacity of about 110 mAh·g^-1 at the current density of 1.0 A·g^-1 with nearly 100% Coulombic efficiency after 200 cycles. The approach of ammonia-assisted layer expansion proposed in this study enriches the modification strategy to enhance the electrochemical performance of MoS₂ and provides a new idea for subsequent cathode development.

Poly(ethylene oxide) (PEO)-based solid electrolytes are deemed as the most promising alternatives for solid-state lithium batteries on account of their low cost, good stability against Li metal, and easy large-scale production. However, the instability of PEO against high-voltage cathodes severely limits its application in the fields needing high energy density. In this work, a discontinuous cyclized polyacrylonitrile (cPAN) nanolayer, served as an electron-conducting shell, is partially coated on LiNi_0.6Co_0.2Mn_0.2O₂ (NCM) cathode particles, while an ionic liquid acted as ion-conducting pathway is introduced at NCM/PEO interface, enabling the high compatibility of PEO against high-voltage NCM cathode. The cPAN layer not only physically isolates the direct contact of PEO electrolyte from NCM cathode, but also contributes to the electronic transfer inside the cathode due to the formation of delocalized sp² π bond during coating process. Meanwhile, the mobile ionic liquid with good ionic conductivity fully wets cathodic interface, followed by decomposition into cathode-electrolyte interphase (CEI) of LiF and Li₃N, further restricting the oxidation-failure of PEO electrolyte. By taking the combined strategy, the corresponding solid-state NCM/Li battery delivers an excellent electrochemical performance with a capacity retention of 85.3% after 100 cycles at rate of 0.1C (1C=0.18 A·g^-1) under a cutoff voltage of 4.30 V. This work opens up a new direction to address the interfacial stability issues of PEO-based electrolyte against high-voltage cathodes through surface coating and interface modification.

Si anodes hold immense potential in developing high-energy Li-ion batteries. But fast failure due to huge volume change upon Li uptake impedes their application. This work reports a facile yet low-toxic gas fluorination way for yielding F-doped carbon-coated nano-Si anode materials. Coating of nano-Si with F-doped carbon containing high defects can effectively protect Si from huge volume change upon Li storage while facilitating Li⁺ transport and formation of stable LiF-rich solid electrolyte interphase (SEI). This anode exhibits high capacities of 1540-580 mAh·g^-1 at various current rates of 0.2-5.0 A·g^-1, while retaining >75% capacity after 200 cycles. This method also addresses the issues of high cost and toxicity of traditional fluorination techniques that use fluorine sources such as XeF₂ and F₂.

2022 marks the 110th anniversary of X-ray diffraction (XRD), which is a powerful technique used to find out the nature of materials. Rietveld refinement method, as an important means of extracting material structure information, plays a significant role in establishing the relationship between structure and performance of materials. Cathode materials are a vital part of lithium-ion batteries (LIBs). In-depth understanding of their crystal structure and atomic distribution is extremely helpful to promote the development of cathode materials for LIBs. Cathode materials for LIBs are generally the hosts of lithium. Studies on lithium occupation and transfer are inseparable from a deep understanding of its structural characteristics. This review summarizes XRD Rietveld structure refinement and its application in cathode materials for LIBs. XRD Rietveld structure refinement in synthesis, degradation, and structural modification of cathode materials are analyzed by using several types of typical cathode materials as examples. XRD Rietveld method could provide useful structural information of the cathode materials, including phase ratio in composite and crystallographic parameters (e.g., cell parameters, key atomic occupation, and atomic coordinates). Therefore, exploring structure of cathode materials assisted with XRD Rietveld refinement method is of great significance for the development of high-performance cathode materials for LIBs. Finally, the opportunities and challenges in the field of X-ray diffraction technology in detecting structure of cathode materials for LIBs are prospected.