The hydrothermal method is a widely employed technique for producing 2D MoS₂ nanosheets， noted for its simplicity， controllable reaction conditions， and eco-friendliness^[70]. The experimental procedure is illustrated in Fig. 3a^[71]. The resulting nanosheets typically consist of 5~6 stacked layers （Fig. 3b）， providing MoS₂ with high adsorption capacity and a large surface area. By varying the hydrothermal reaction time， the morphology of MoS₂ can be tailored^[72]. Shorter reaction times yield dispersed nanosheets （Fig. 3c， d）， whereas prolonged reaction times result in self-assembled， uniform flower-like structures with increased surface exposure.

The solvothermal method， primarily differs by using organic solvents or non-aqueous systems as the reaction medium. This approach offers notable advantages for synthesizing MoS₂ hybrids， including increased interfacial area， reduced aggregation， and lower energy requirements^[73]. Compared to conventional hydrothermal synthesis， the solvothermal method provides enhanced control over the morphology， crystal structure， and active surface sites of the resulting products^[74-75]. For example， one study employed a solvothermal method with organic solvents to synthesize MoS₂ （Fig. 3e）^[76]， and combined it with polyvinylidene fluoride （PVDF） to create a 1T/2H-phase MoS₂-PVDF nanocomposite membrane. This membrane exhibited excellent structural uniformity， high catalytic reactivity， and remarkable stability， demonstrating outstanding reusability and pollutant degradation efficiency （Fig. 3f）. Typically， the solvothermal process is a one-pot synthesis that facilitates high-pressure growth without requiring additional catalysts， thereby minimizing contamination risks and enhancing product uniformity.

Chemical vapor deposition （CVD） is a widely utilized “bottom-up” synthesis technique for producing high-quality 2D MoS₂ films. This method typically employs molybdenum sources MoO₃^[77]， Mo^[78] or （NH₄）₂MoS₄^[79]， in combination with sulfur powder or H₂S gas as sulfur sources^[80]， under high temperatures ranging from 700~1000 ℃， these precursors react on substrates like Si/SiO₂^[81] and sapphire^[82] to form MoS₂ films. Studies indicate that substrate type and processing temperature significantly influence film structure and integrity. Sitek et al.^[83] systematically studied substrate effects on morphology （Fig. 3g~j）， finding that graphene substrates form thermodynamically stable triangular MoS₂， while SiO₂ substrates produce truncated triangular or circular domains. This highlights how substrate surface properties control nucleation behavior.

Liquid-phase exfoliation （LPE） is a simple， cost-effective， and scalable method for preparing MoS₂ nanosheets. It dissociates bulk MoS₂ into single- or few-layer structures through physical/chemical processes. A typical LPE procedure comprises three stages： solvent dispersion， exfoliation， and product purification （Fig. 4a）^[84]. The process of synthesizing MoS₂ using the LPE method is shown in Fig. 4b^[85]. The exfoliation mechanism relies on 2-MeIm intercalation between MoS₂ layers （Fig. 4c）， with the nanosheets exhibiting aggregation-induced photoluminescence at 420~480 nm and semiconductor properties when formed into films.

Solid-phase exfoliation is one of the earliest "top-down" methods for preparing high-quality 2D MoS₂ nanomaterials. Its principle involves applying external forces to directly peel bulk MoS₂ into few-layer or even monolayer nanosheets. This method is simple to operate， and the resulting materials exhibit high purity and good crystalline integrity， making it widely used for studying the intrinsic properties and device performance of MoS₂. Magda et al.^[86] developed an improved mechanical exfoliation method using chemically enhanced adhesion to produce large-area monolayer MoS₂， addressing limitations of traditional tape-based methods （e.g.， limited productivity and lateral sizes <10 μm）. By leveraging strong interactions between sulfur atoms and gold surfaces， they enhanced adhesion between the bottom MoS₂ layer and underlying gold film. This enabled efficient removal of upper multilayers while leaving monolayers firmly attached to the substrate. In Fig. 4d， e： optical microscopy revealed large， darkest-contrast regions （marked by dashed lines） corresponding to monolayer MoS₂， surrounded by blue multilayer areas. This method extends beyond MoS₂ to other layered materials， generating monolayers spanning hundreds of micrometers.

Electrochemical exfoliation is an efficient， low-cost， and scalable technique for synthesizing MoS₂ nanosheets. Nayak et al. employed cathodic exfoliation （Fig. 4f）^[87]， where Na₂MoO₄ and thiourea were ultrasonically dispersed and adsorbed onto positively charged NiFe layered double hydroxide （LDH） surfaces. Hydrothermal treatment at 210 ℃ for 24 hours formed interwoven heterostructures. Electrostatic interactions built strongly coupled p-n junction interfaces， while simultaneous hydrothermal exfoliation increased surface area and exposed active sites， suppressing material restacking and promoting spatial separation of photogenerated charges. You et al.^[88] developed anodic exfoliation （Fig. 4g） using bulk MoS₂ as the anode and platinum wire as the cathode in a sulfuric acid electrolyte. Initially， a +1 V voltage enabled hydroxyl radicals to attack crystal edges and form defects. Then， increasing voltage to +10 V drove SO₄^2-/OH^- intercalation between layers （Fig. 4h）. Finally， high-pressure gas expansion from embedded ions achieved mechanical exfoliation， yielding mono-/few-layer nanosheets （Table 1）.

Ionic intercalants are various cations or anions that penetrate the spaces between MoS₂ layers， primarily guided by electrostatic interactions with sulfur atom surfaces， resulting in the expansion of interlayer spacing. Sarkar et al.^[34] synthesized MoS₂/r-GO （reduced graphene oxide） composite nanosheets via a one-step hydrothermal method. The composite materials were directly grown on molybdenum foil， eliminating the need for binders and resulting in enhanced mechanical stability and electronic conductivity. In this process， in addition to acting as the sulfur precursor， thiourea decomposed during hydrolysis to generate NH₄⁺ ions， which acted as intercalants （Fig. 5a）. The insertion of NH₄⁺ weakened the interlayer attractions in MoS₂， resulting in an expanded spacing of around 0.95 nm， markedly exceeding the initial ~0.63 nm， which markedly improved the insertion/extraction capability of Na⁺ ions and enhanced the pseudocapacitive reaction efficiency （Fig. 5b）. The use of rGO further improved conductivity and electrochemical stability. As a result， MoS₂/r-GO//Fe₂O₃/MnO₂ asymmetric supercapacitor was constructed， maintaining more than 98% capacitance even after 20 000 charge-discharge cycles （Fig. 5c）.

In addition to using single ions as intercalants， multi-ion intercalation strategies have also been explored. Wang et al.^[89] utilized thiourea as both a reactant and a precursor for intercalants. During the hydrothermal reaction， thiourea was transformed into ammonium thiocyanate （NH₄SCN）， which dissociated into NH₄⁺ and SCN^- ions. These ions were simultaneously intercalated into the interlayer spaces of MoS₂， significantly expanding the interlayer distance to 9.4 Å （Fig. 5d）. This expanded structure enhanced the Na⁺ adsorption capacity and diffusion rate， thereby markedly improving the electrochemical performance. The resulting E-MoS₂ exhibited excellent specific capacitance in a 3-electrode system and demonstrated good cycling stability in a symmetric supercapacitor， retaining 81.7% of its capacity after 3000 cycles. Density functional theory （DFT） calculations further revealed the stable adsorption behavior of NH₄⁺ and SCN^- on the MoS₂ surface and within its interlayers， as well as their role in lowering the diffusion energy barrier for Na⁺ （Fig. 5e， f）， ultimately leading to expanded interlayer spacing and enhanced capacitive performance （Fig. 5g）.

Organic molecular intercalation can also be employed. Zhang et al.^[90] significantly enhanced the electrochemical performance of 2H-MoS₂ in supercapacitors by introducing polypyrrole （PPy） as an organic intercalant and constructing a MoS₂-PPy@Ti₃C₂T_x MXene heterostructure （Fig. 6a）. It demonstrated that PPy intercalation effectively increased the gap between MoS₂ from 6.5 to 10.3 Å （Fig. 6b~g）， thereby enhancing ion diffusion pathways and exposing more active sites. Meanwhile， MXene served as a highly conductive substrate， further improving charge transfer efficiency and boosting the electrode’s energy storage performance and fast-charging responsiveness （Fig.6h~l）. As a result， the synthesized MoS₂-PPy@Ti₃C₂T_x composite delivered a high charge storage capacity of 265 F·g^-1 along with stable long-term performance， maintaining 94.1% retention over 10 000 charge-discharge cycles （Fig. 6k）. The enhanced performance of the composite stems from multiple synergistic effects. PPy intercalation directly expands the interlayer spacing of MoS₂， exposing more edge active sites. In addition， the PPy connects MoS₂ with MXene， forming continuous conductive pathways while providing additional redox-active sites. Furthermore， surface functional groups （—O， —OH） on MXene form chemical bonds with MoS₂， strengthening interfacial charge transfer.

Polymer intercalants refer to long-chain， flexible polymer molecules that can form stable network structures within the interlayers， enhancing the flexibility and electrochemical stability of the composite material. Upon intercalation， they increase electron/ion transport channels， inhibit the restacking of MoS₂ nanosheets， and improve mechanical stability； if the polymers are conductive， they can also contribute to pseudocapacitance. Lian et al.^[91] successfully constructed a multilayer three-dimensional PPy/MoS₂ intercalated composite by polymerizing pyrrole monomers under acidic conditions and subsequently reacting them hydrothermally with sodium molybdate and thiourea （Fig.7a）. X-ray photoelectron spectroscopy （XPS） characterization confirmed that PPy molecules coordinated with the sulfur atoms of MoS₂ via nitrogen atoms and intercalated into the MoS₂ layers， forming a stable 3D intercalated composite structure （Fig.7b）. Experimental data revealed that this composite delivered a notable capacitance of 895.6 F·g^-1 under 1 A·g^-1， sustained an energy output of 3.774 Wh·kg^-1 even at a high power level of 252.8 kW·kg^-1， and preserved 98% of its original capacitance following 10 000 cycles-markedly surpassing the retention rates of pristine PPy （59.8%） and MoS₂ （74.8%） （Fig. 7c）. This structure takes advantage of the interlayer ion transport channels and pseudocapacitive behavior of MoS₂， while the conductive network of PPy enhances charge transfer efficiency and suppresses volume deformation， thereby significantly improving cycling stability （Fig. 7d）. Other polymer intercalants include polyaniline （PANI）. Wang et al. directly intercalated aniline monomers into exfoliated MoS₂ layers and doped them with dodecylbenzene sulfonic acid （DBSA）， successfully preparing a MoS₂/PANI intercalated composite （Fig. 7e）^[92]. Experimental results showed that the intercalation interaction between MoS₂ and PANI significantly improved the composite’s conductivity and thermal stability. The MoS₂/PANI-38 sample achieved a conductivity of 2.38 S·cm^-1， and its maximum thermal decomposition rate occurred at 353 ℃ （Fig.7f）. Electrochemical evaluation revealed that this composite achieved a capacitance value of 390 F·g^-1 and maintained 86% of its initial performance over 1000 charge-discharge cycles-substantially outperforming pure PANI electrodes， which only delivered 131 F·g^-1 with a 42% retention rate. （Fig.7g， h）. This improvement stems from the combined contributions of MoS₂ electrostatic charge storage and PANI’s redox-based capacitance， alongside the homogeneous distribution and effective charge transport facilitated by the interlayer architecture. The study clearly applied polymer intercalation technology， embedding PANI into MoS₂ layers via in-situ polymerization， thereby regulating the interlayer spacing and microstructure of the composite for performance optimization.

When comparing the three organic ion intercalation methods， the MoS₂/PANI system achieves enhanced conductivity of 2.38 S·cm^-1 through dodecylbenzene sulfonic acid （DBSA） doping. However， this remains notably lower than the MXene-based composite approach， where Ti₃C₂T_x contributes ultrahigh conductivity （150 000 S·m^-1） in the MoS₂-PPy@Ti₃C₂T_x structure. For the PPy/MoS₂ hydrothermal method， though conductivity wasnot directly measured， the uneven PPy coating thickness （25~66 nm） may cause localized resistance variations. These conductivity differences directly correlate with rate capability： the MXene composite maintains 57.6% capacity at 20 A·g^-1， while the PPy/MoS₂ system sustains high energy density （3.774 Wh· kg^-1） even at 252.8 kW·kg^-1 power density. Regarding structural stability， PPy/MoS₂ exhibits superior cycling retention primarily due to covalent N—S bonding between polypyrrole’s nitrogen atoms and sulfur in MoS₂ interlayers， coupled with PPy’s three-dimensional network effectively absorbing ion-insertion stress. Conversely， the MoS₂/PANI system relies on weaker electrostatic interactions. Repeated expansion/contraction of PANI chains during lithiation/delithiation leads to only 86% capacity retention. The MXene composite demonstrates 94.1% retention but faces oxidation susceptibility of terminal functional groups during high-voltage cycling. In summary， while PPy intercalation offers optimal stability， inconsistent coating thickness risks localized stress concentration； the MXene strategy provides unmatched conductivity yet carries unquantified long-term corrosion risks at multi-phase interfaces； and though the PANI approach is cost-effective， electrolyte contamination from degradation byproducts remains a concern.

By adjusting the reaction conditions， MoS₂ nanosheets can be microscopically arranged in a radial or layer-by-layer unfolding manner， ultimately forming flower-like 3D structures. These structures consist of numerous MoS₂ nanosheets with outward-facing edges， presenting an open and loose morphology. Compared to conventional dense layered stacks， this configuration provides increased accessible surface regions and a greater number of electrochemically active regions. For example， Chen et al.^[94] synthesized a 3D flower-like MoS₂/NiCo（OH）₂CO₃ （MoS₂/NiCoHC） composite and applied it to supercapacitors. In Fig. 8a， utilizing MoS₂ nanospheres as initial templates through a solvothermal approach， NiCoHC thin layers spontaneously organized into a 3D flower-like architecture. The morphology was systematically characterized by SEM （Fig.8b）. Experiments revealed that MoS₂ nanospheres acted as nucleation agents to induce the surface growth and assembly of NiCoHC nanosheets into 3D flower-like particles. This architecture notably expanded the accessible surface region， and a large number of surfactant sites are provided through NiCoHC nanosheets， and sulfur atoms at the edge of MoS₂ nanospheres act as additional redox sites， synergistically improving the reaction interface and improving the overall charge storage capacity. Under charge-discharge evaluation， the MoS₂/NiCoHC hybrid exhibited impressive storage capability， reaching 583 C·g^-1 （1296 F·g^-1） at 1 A·g^-1， and maintained 94.3% of its capacity after 2000 cycles （Fig. 8c）. The resulting hybrid device further demonstrated outstanding energy storage capabilities. The authors further used kinetic analysis and impedance spectroscopy to demonstrate that the 3D flower-like structure promoted charge transport and ion diffusion while ensuring long-term cycling stability. Liu et al.^[95] investigated a 3D sandwich-structured MoS₂/C@RGO hybrid fabricated through a combination of molecular self-organization and hydrothermal treatment， where uniformly distributed MoS₂ layers were anchored onto reduced graphene oxide （RGO） along with in situ-formed carbon nanoparticles （Fig.8d）. Among them， RGO provides a high-conductive network in-plane， greatly reducing charge transfer resistance， and MoS₂ provides pseudocapacitor active sites. Supramolecular self-assembly realizes the directional growth of MoS₂ on the RGO surface， forming strong interface bonding. This sandwich structure （RGO-MoS₂-carbon particles） forms a three-layer role of “conductive-active-buffering”. Such a distinctive three-dimensional framework suppressed MoS₂ and RGO aggregation， improved conductivity， enlarged electrolyte accessibility， and promoted ion transport and exposure of active electrochemical sites （Fig.8e~g）. Wei et al.^[96] studied the electrochemical performance enhancement of self-assembled flower-like MoS₂ nanomaterials used as supercapacitor electrode materials. Through a simple one-pot hydrothermal reaction， 1T-phase MoS₂ nanosheets were self-assembled into 3D nanoflower structures. In Fig. 8h， i， this nanoflower framework exhibited a more stable structure and superior charge transport channels compared to discrete nanosheets. In KCl electrolyte， it achieved a specific capacitance of 483 F·g^-1 at 0.5 A·g^-1， while in KOH electrolyte， the activated battery-type charge storage mechanism led to an outstanding capacitance of 1120 F·g^-1. After 2000 cycles， the nanoflower electrodes retained 94% and 96% of their capacities in KCl and KOH electrolytes， respectively， significantly outperforming the nanosheet electrodes （Fig.8j， k）.

Carbon-based 3D framework composites involve integrating layered materials such as MoS₂ with 3D porous carbon structures （e.g.， graphene aerogels， CNT networks， carbon foams， or rGO）. This strategy constructs a stable conductive support network that effectively suppresses the interlayer restacking of MoS₂ induced by van der Waals forces during intercalation. Simultaneously， it improves the overall architecture’s available active surface and ion transport pathways. Tiwari et al.^[97] developed MoS₂@CNT heterostructure by combining chemical vapor deposition and physical vapor deposition techniques， enabling precise control over the electrode’s microstructure. This heterostructure forms an open porous network through the synergy between the 3D conductive CNT scaffold and vertically grown MoS₂ nanosheets （Fig. 9a）. Such architecture not only shortens the ion and electron diffusion paths but also broadens the MoS₂ gallery distance to 0.63 nm （Fig. 9b）， providing more intercalation sites for Na⁺ ions. The robust mechanical properties and excellent electrical performance of CNTs effectively suppress volume expansion and structural deformation of MoS₂ during charge/discharge cycles. The CNT network thus offers both mechanical support and improved electron transport for MoS₂. Contact angle measurements further revealed that MoS₂ coating alters the originally superhydrophobic CNT surface （154°， Fig. 9c） to a hydrophilic one （49.2°， Fig. 9d）， thereby enhancing electrolyte infiltration. Electrochemical tests demonstrated that the MoS₂@CNT electrode exhibits a high areal capacitance of 337 mF·cm^-2 at a scan rate of 5 mV·s^-1. In symmetric devices， a capacitance of 131 mF·cm^-2 and a cycling stability of 97.6% were achieved （Fig. 9e，f）. These results confirm the critical role of 3D carbon frameworks in modulating structural stability， conductivity， and ion transport kinetics of 2D materials. Guan et al.^[98] investigated a core-shell structured MoS₂@C/CNTs composite as a supercapacitor electrode. In Fig.9g， few-layer MoS₂ nanosheets were integrated with CNTs and carbon interlayers through a hydrothermal method followed by carbonization， forming a coaxial nanocable structure. CNTs served as the conductive backbone， coated with PEDOT：PSS to create a stable interface. Glucose and CTAB were introduced to facilitate in situ carbonization within the MoS₂ interlayers and on its surface， resulting in carbon intercalation structures. This design increased the gap between MoS₂ layers to 0.72 nm （Fig. 9h，i）， enhancing both electron transport and ion diffusion pathways. Moreover， the carbon layers effectively suppressed MoS₂ volume expansion and improved structural integrity. Electrochemical tests revealed that the material delivered 335 F·g^-1 at 1 A·g^-1 and maintained 127% of its initial capacitance after 40 000 cycles， indicating outstanding durability over extended cycling （Fig 9j~l）. CNT is the basis of core conductivity， PEDOT：PSS performs interface regulation， and carbon interpolation MoS₂ forms the electron transmission gradient. The three work together to break through the bottleneck that traditional materials cannot have both “high capacity-long life”.

The electrochemical activity of MoS₂ primarily originates from the sulfur atoms located at the edge sites， while the basal planes exhibit low activity due to their intrinsically low surface reactivity and poor electrical conductivity. Metal doping has emerged as an effective strategy to improve the electrochemical performance of MoS₂， typically achieved by introducing a controlled number of dopants during the synthesis of precursors. The type and concentration of dopants can significantly influence the resulting electrochemical behavior. Among various metal doping approaches， transition metal doping is one of the most representative. Transition metals possess unfilled d orbitals， which can accept lone pair electrons， enabling them to alter the electronic structure of MoS₂. Introducing dopant elements from the transition metal group effectively boosts electrical transport properties， promotes the formation of additional reactive edge sites， and can also stimulate the activity of the inert basal planes， thus markedly enhancing the electrochemical behavior. It has been demonstrated that the incorporation of transition metal ions such as Cu， Ni， Mo， and Fe into the MoS₂ lattice effectively modulates its activity. Vikraman et al.^[107] investigated the regulation of active sites in MoS₂ nanostructures via transition metal doping to enhance their performance in hydrogen evolution reaction （HER） and supercapacitor applications. As shown in Fig. 10a， Ni， Cu， and Fe were successfully doped into MoS₂ matrices through a chemical precipitation method to address issues such as low conductivity and limited active site availability. Structural characterization and electrochemical testing revealed that the doped MoS₂ nanostructures exhibited significant morphological changes： the introduction of transition metals expanded the interlayer spacing and facilitated the formation of vertically aligned nanosheet arrays， while concurrently altering the charge distribution to enhance the accessibility of catalytically active regions （Fig. 10b，c）. Specifically， Cu-doped MoS₂ achieved an impressive capacitance value of 353 F·g^-1 and maintained 94% of its initial capacity over prolonged cycling， attributed to the enlarged active interface and the presence of a porous framework （Fig. 10d， e）. Through Fe/Ni doping， MoS₂ is transformed from semiconductor phase （2H） to metal phase （1T）， and the proportion of 1T phase is increased： the conductivity of the metal phase is higher than that of the 2H phase， which accelerates charge transfer at the electrode interface， Fe doping exposes more edge sites， Cu doping triggers lattice distortion， and experiments combine atom doping with microstructure regulation to achieve a significant improvement in electrochemical performance.

The doping concentration is a crucial factor influencing the electrochemical performance of MoS₂. Singha et al.^[108] investigated the effect of various Mn doping levels on the nanoflower morphology of MoS₂ and its performance in supercapacitors. By adjusting the Mn doping concentration， four types of samples were synthesized： undoped MoS₂ （S-Ⅰ）， low Mn-doping （S-Ⅱ）， medium Mn-doping （S-Ⅲ）， and high Mn-doping （S-Ⅳ） （Fig.10f）. The results demonstrate that an appropriate level of Mn doping in the S-Ⅱ sample significantly enhanced the electrochemical activity. Structural characterizations， such as XRD and TEM， revealed that Mn doping expanded the interlayer spacing of MoS₂ from 0.63 nm to 0.76 nm and increased the specific surface area and porosity. These changes provided more electrochemically active sites， facilitating enhanced adsorption and diffusion of electrolyte ions （Fig.10g，h）. However， excessive Mn doping， as in the S-Ⅳ sample， resulted in a performance decline due to pore blockage and a reduced proportion of Mn³⁺ species. Electrochemical testing showed that the S-Ⅱ sample exhibited the highest specific capacitance in 0.5 M Na₂SO₄ electrolyte and maintained excellent cycling stability， retaining 77% of its capacity after 5000 cycles （Fig.10i~l）.

In addition to transition metals， noble metals and rare earth elements have also been doped into MoS₂ for supercapacitor applications. Shao et al.^[109]， utilized a sequential two-step solvothermal process to synthesize Pt-doped MoS₂ layered structures directly on the surface of carbon cloth （CC）. Compared with undoped pristine MoS₂， the Pt doping significantly enhanced the electrochemical performance. The synthesized Pt-MoS₂ delivered an impressive capacitance value of 250 F·g^-1 under 0.5 A·g^-1， and when operated at 10 A·g^-1， its capacitance doubled compared to unmodified MoS₂， indicating a 100% gain. This performance stemmed from the incorporation of Pt， which optimized the material's electronic and structural characteristics. which， as shown by TEM analyses， reduced the crystallinity of MoS₂ and created more active sites， thereby facilitating charge transport and electrolyte ion diffusion （Fig. 11a~c）. To explore practical applications， an asymmetric flexible supercapacitor （ASC） device was constructed， employing Pt-MoS₂ as the cathode material and activated carbon （AC） as the anode. The configuration and corresponding electrochemical performance are illustrated in Fig. 11d~f， the flexible device was tested under various bending angles， and CV curves remained nearly overlapping with negligible changes in specific capacitance， demonstrating excellent mechanical flexibility and bending stability. These properties make the device highly suitable for flexible electronic applications.

Exploiting the abundant f-orbitals and strong spin-orbit coupling inherent in trivalent rare earth （RE³⁺） ions enables modulation of MoS₂ properties. Their incorporation does the lattice， generating abundant defect sites and expanding interlayer spacing， which widens ion transport pathways， reduces bandgap width， and enhances intrinsic electrical conductivity， all of which contribute to improved energy storage performance. Isacfranklin et al.^[110] investigated the application of Nd and Gd-doped MoS₂ electrode materials for supercapacitors. SEM analysis showed that pristine MoS₂ exhibited spherical nanoparticles， while rare earth doping-particularly with Gd-induced a significant morphological transformation into nanosheet structures （Fig.11g~i）. The sheet-like structure enhanced surface exposure and reduced ion migration distances， leading to a significant improvement in electrochemical performance. Electrochemical testing confirmed that Gd-MoS₂ demonstrated the best performance. Electrochemical impedance spectroscopy （EIS） further revealed that Gd-MoS₂ exhibited the lowest solution resistance （0.292 Ω） and charge transfer resistance （0.796 Ω）， indicating superior conductivity. Moreover， Gd-MoS₂ retained 81.50% of its initial specific capacitance after 5000 charge-discharge cycles， demonstrating excellent cycling stability （Fig.11j，k）. This study clearly demonstrated that rare earth element doping-especially with gadolinium-effectively modulated the morphology of MoS₂ （from spherical to sheet-like structures） and significantly improved its key supercapacitor performance metrics， including specific capacitance， conductivity， and cycle life （Fig.11l）. These improvements are primarily attributed to the strong binding affinity between the rare earth 4f vacant orbitals and functional groups， leading to structural optimization. This offers crucial evidence for developing novel RE-modified metal sulfides as high-performance electrodes.

Although defect-rich MoS₂ retains locally ordered hexagonal arrangements of Mo atoms， it exhibits long-range structural disorder overall， primarily manifested as lattice distortion. This “order within disorder” structural characteristic leads to the presence of numerous intrinsic defects-such as sulfur vacancies， voids， and cracks-throughout the surface and bulk of the material in addition to naturally occurring edge sites. These defects provide extra electrochemically active sites， which contribute to enhanced pseudocapacitive reactions and ion intercalation capability. In particular， sulfur vacancies tailor the local atomic arrangement and electronic environment of MoS₂， promoting enhanced charge transfer and conductivity， thereby significantly augmenting its electrochemical reactivity and overall conductivity. Thus， rationally introducing and regulating such intrinsic defects represents a vital approach to enhancing the energy storage function of MoS₂ as an electrode material. For instance， Wu et al.^[111] synthesized ultrathin MoS₂ nanosheets with abundant structural defects by reacting ammonium heptamolybdate （（NH₄）₆Mo₇O₂₄·4H₂O） and L-cysteine in the presence of 1，6-hexanediamine. Physical characterization clearly confirmed the existence of numerous intrinsic defects， especially those related to sulfur atoms， such as S vacancies or uncoordinated sulfur atoms at the edges. These defects were formed intrinsically during synthesis due to the coordination agent （1，6-hexanediamine） modulating the crystal growth kinetics and inhibiting the perfect lattice ordering of MoS₂， rather than being induced by external dopants （Fig. 12a）. The intrinsic defects exposed a high density of unsaturated sulfur active sites， significantly altering the electronic structure and surface properties of the material. In Fig. 12b~d， this defect-rich MoS₂ exhibited excellent electrochemical performance when used as a supercapacitor electrode， delivering high specific capacitance and outstanding cycling stability. The presence of defects promoted the formation of electric double layers and accelerated ion diffusion， contributing to the superior energy storage behavior.

Defect concentration strongly determines the electrochemical performance of materials. Joseph et al. synthesized two types of MoS₂ samples-high defect density （HDD-MoS₂） and low defect density （LDD-MoS₂） by adjusting the amount of thiourea， and probed defect-mediated changes to lattice symmetry， charge transport， and interfacial reactivity^[112].Structural characterizations revealed that higher defect density led to lattice distortion and increased interlayer spacing， thereby enhancing the intercalation and diffusion of electrolyte ions.

The presence of S vacancies introduces additional electronic states adjacent to the Fermi edge and creates localized spin carriers， which contribute to activating the otherwise inert MoS₂ surface and enhancing its charge transport characteristics. Wang et al.^[113] introduced sulfur vacancies into 2H-phase MoS₂ nanosheets by annealing them at different temperatures under an Ar/H₂ atmosphere. The study demonstrated that incorporating sulfur vacancies markedly enhanced the charge transport efficiency and electrochemical storage capacity of MoS₂. As the annealing temperature increased， the concentration of sulfur vacancies rose， resulting in enlarged interlayer spacing， shortened ion diffusion paths， and enhanced electron mobility， all of which facilitated reversible redox reactions （Fig. 12e~g）. MoS_2-x sample annealed at 700 ℃ exhibited the best performance， achieving a maximum specific capacitance of 142.3 F·g^-1 and excellent cycling stability with 87.1% capacitance retention after 5000 cycles （Fig.12h）. DFT calculations further revealed that sulfur vacancies， particularly sulfur edge vacancies， made significant contributions to enhancing conductivity and capacitance （Fig.12i）， by introducing new electronic states near the Fermi level， increasing carrier density， and strengthening electron transfer capability.

Although defect engineering can significantly improve the electrochemical performance of MoS₂， excessively high defect concentrations can cause multiple structural stability problems. For example， too many sulfur vacancies distort the local lattice structure and create stress concentration. Additionally， defect sites allow electrolytes to penetrate more easily， worsening corrosion of the electrode material. Current methods to create defects in MoS₂ require complex equipment and demanding reaction conditions， making large-scale production difficult. That’s why future research should develop advanced characterization tools that can monitor defect behavior during actual operation， providing real-time insights for designing industrial-grade electrodes.

Studies have shown that moderate interlayer spacing is critical to the capacitive performance of two-dimensional electrode materials. As summarized in Table 2， excessively large interlayer distances can create inactive dead volume within the electrode， thereby reducing the effective specific surface area and ion accessibility. This， in turn， weakens the charge storage density and release efficiency， hinders fast ion transport， and limits the utilization of electrochemically active sites-ultimately leading to a decline in the overall energy storage capacity.