Graphene Nanoplatelets for Advanced Energy Storage Applications

Abstract

Graphene nanoplatelets (GNPs) represent a promising class of carbon nanomaterials bridging the gap between graphite and monolayer graphene. Their unique combination of high electrical conductivity, large specific surface area, mechanical strength, and chemical stability makes them attractive for advanced energy storage applications. This review summarizes recent developments in the synthesis, functionalization, characterization, and application of GNPs in supercapacitors, batteries, and hybrid systems. The influence of key structural parameters—such as flake thickness, lateral size, surface chemistry, and defect density—on electrochemical performance is discussed, highlighting structure–property correlations. Particular emphasis is placed on scalable production methods, including mechanical, liquid-phase, and electrochemical exfoliation, as well as edge functionalization and heteroatom doping strategies. Comparative analyses show that GNP-based electrodes can significantly improve specific capacitance, conductivity, and cycling stability, especially when used in composites with polymers or metal oxides. The review also addresses current challenges related to aggregation, dispersion, standardization, and environmental impact. Finally, prospects for the development of sustainable, low-emission GNP production and its integration into next-generation energy storage systems are outlined.

1. Introduction

Modern energy systems face an increasing demand for efficient and durable energy storage technologies, driven by the rapid development of electromobility, renewable energy sources, and smart grid concepts. Traditional solutions, such as conventional lithium-ion batteries and supercapacitors, encounter limitations related to energy density, power capability, charging rate, cycle life, and production cost. Consequently, the search for new electrode materials with enhanced properties has become one of the key directions in the development of next-generation energy storage systems.

Among the numerous nanomaterials studied, graphene nanoplatelets (GNPs-also referred to as graphene flakes, few-layer graphene, graphene nanosheets, or graphite nanoplatelets) occupy a special position. GNPs represent an intermediate structure between graphite and monolayer graphene, consisting of several to a dozen atomic layers with a typical thickness of 2–10 nm and lateral dimensions ranging from a few hundred nanometres to several micrometres [1,2]. In contrast to graphene oxide (GO/rGO) and CVD-grown graphene, GNPs combine high electrical and thermal conductivity with a large specific surface area [3], mechanical robustness, and chemical stability [4], while maintaining relatively low production costs and good scalability [5]. This makes them an attractive compromise between structural quality and industrial feasibility.

The specific morphology of GNPs—with wrinkled sheets, high surface development, and irregular edges—facilitates fast ion transport and effective electrode–electrolyte contact, which is crucial for devices such as batteries, supercapacitors, and hybrid systems. Their electrochemical properties can be further tuned through surface functionalization and heteroatom doping, enabling control over defect density, wettability, and surface activity.

Despite extensive research efforts, the literature still shows discrepancies regarding production methods, structural characteristics, and electrochemical performance of GNPs, mainly due to the absence of standardized evaluation protocols and differences in measurement techniques. Therefore, there is a growing need for comprehensive analyses correlating structural, physicochemical, and electrochemical parameters with performance outcomes.

The purpose of this review is to provide an up-to-date overview of the current state of knowledge on graphene nanoplatelets and their applications in advanced energy storage systems. The article discusses the properties of GNPs, their production and functionalization methods, comparative evaluation with other graphene forms, and their applications in supercapacitors, batteries, and hybrid devices. The review concludes with a discussion on the industrial readiness, cost-effectiveness, and future perspectives of GNP-based technologies in the context of modern energy solutions.

2. Properties of Graphene Nanoplatelets

Graphene nanoplatelets (GNPs) exhibit a unique combination of structural, electrical, and surface-related properties that distinguish them from other graphene derivatives and make them particularly promising for advanced energy storage applications. The performance of GNP-based systems strongly depends on the interrelations between their physicochemical parameters—such as the number of layers, defect density, specific surface area, and oxygen content—and their influence on charge storage and transport processes.

Understanding these correlations is crucial for optimizing the utilization of GNPs in batteries, supercapacitors, and hybrid systems. However, to accurately describe the properties of GNPs and compare results obtained in different studies, it is necessary to apply suitable characterization techniques capable of determining their morphological, structural, and electronic parameters.

A thorough understanding of the structure of graphene nanoplatelets serves as the foundation for analyzing their physicochemical, electrochemical, and interfacial properties, which will be discussed in the following subsections.

2.1. Structural and Physicochemical Parameters

Graphene nanoplatelets (GNPs) possess a complex architecture in which both morphological and physicochemical features play a decisive role in shaping their electrochemical performance. Typically, GNPs consist of several to a dozen graphene layers arranged in a cascade-like manner, with an overall thickness ranging from 2 to 10 nm [1]. These platelets display irregular edges and numerous wrinkles, which naturally form to relieve internal strain within ultrathin carbon structures [2]. Their lateral dimensions usually range from several hundred nanometres to a few micrometres. Within the GNP structure, lattice defects are also present, which can increase the number of electroactive sites while simultaneously affecting local electrical conductivity.

In addition to the layered architecture and morphology, key physicochemical parameters include specific surface area (determined by the BET method), oxygen content (C/O ratio), the intensity ratio of D and G bands in Raman spectra (I_D/I_G), and electrical conductivity. A high specific surface area [3], combined with good conductivity and chemical stability [4], facilitates rapid ion transport and efficient charge exchange at the electrode–electrolyte interface. At the same time, low density, high thermal conductivity, and mechanical robustness [5] make GNPs an exceptional material for modern energy storage technologies.

From an electrochemical perspective, maintaining an appropriate balance between high conductivity and structural stability on one hand, and sufficient defect density and surface development on the other, is of paramount importance. These parameters—strongly dependent on synthesis routes and post-treatment conditions-govern the behaviour of GNPs in intercalation, adsorption, and redox processes. Comprehensive characterization thus requires the application of complementary analytical techniques to examine morphology, crystal structure, elemental composition, and electrical properties.

Table 1. Selected morphological parameters of graphene nanoplatelets (GNPs).

Parameter	Definition/What It Describes	Values Reported in the Literature	Reference
Flake thickness/number of layers	Thickness of an individual platelet and the number of stacked atomic layers	3–10 layers [6]; 0.34–100 nm [5]; 2–3 to 12 layers [7]; 2–10 nm [1]; 6–8 nm (18–24 layers) [8]	[1,5,6,7,8]
Lateral size	In-plane (X–Y) dimension of a platelet	5–25 µm (Strem Chemicals) [5]; average 1.3 µm [9]; 25 µm [8]; 0.1–1 µm after 48 h ball milling [2]	[2,5,8,9]
Specific surface area (BET)	Total active surface area available for adsorption	296 m2/g, 470 m2/g and 714 m2/g [9]; 591 m2/g (after thermal exfoliation) [10]; 120–150 m2/g [8]; 698.53 m2/g [11]	[8,9,10,11]
Oxygen content (wt%)	Indicates oxidation level	5.710 wt%, 8.266 wt%, 13.207 wt% (GNPs); graphite—1.169 wt% [9]	[9]
Carbon content (wt%)	Elemental carbon percentage	94.144 wt%, 91.552 wt%, 86.262 wt% (GNPs); graphite—98.831 wt% [9]	[9]
Raman ID/IG ratio	Degree of disorder/defect density in the sp2 structure	0.53, 0.63, 0.81 [9]; 0.20 → 1.77 (after planetary milling) [12]; 0.79–1.50 [2]; 0.26 (GNP) vs. 0.06 (graphite) [13]	[2,8,9,12,13]
Decomposition temperature (TGA)	Thermal stability and purity	≈600 °C, ≈550 °C, ≈450 °C [9]	[9]
Bulk density	Packing density of GNPs	1.98 g/cm3 [12]	[12]
Average pore width	Ion transport capability	62.5 Å (6.25 nm) [10]; 6.22 nm [11]	[10,11]
Interlayer spacing (d002)	Distance between adjacent graphene layers	0.34 nm (17 L), 0.385 nm (4 L) [14]; 0.34–0.40 nm [2]; 0.36, 0.37, 0.37 nm for NS-G/S-G/N-G (vs. 0.89 nm for GO, 0.335 nm for graphite) [4]	[2,4,14]
Contact angle	Surface wettability (hydrophilicity)	42 ± 1° (GNP) vs. 97 ± 1° (graphite) [15]; 23.2°, 34.3°, 77.1°, 81.6° [2]	[2,15]

summarizes selected morphological and physicochemical parameters of graphene nanoplatelets (GNPs) reported in the literature, which are of particular relevance to their performance in electrochemical energy storage applications.

Based on the literature overview summarized in Table 1, graphene nanoplatelets exhibit the following characteristic parameter ranges:

• Flake thickness/number of layers: 0.34–100 nm or 2–24 layers;
• Lateral size: 0.1–25 µm;
• Specific surface area (BET): 120–714 m²/g;
• Oxygen content: 5.710–13.207 wt%;
• Carbon content: 86.262–94.144 wt%;
• Raman I_D/I_G ratio: 0.20–1.77;
• Thermal stability (TGA onset of mass loss): ≈450–600 °C;
• Average pore width: 6.22–6.25 nm;
• Interlayer spacing (d₀₀₂): 0.34–0.40 nm;
• Contact angle: 23.2–81.6°, covering hydrophilic to weakly hydrophobic surfaces depending on functionalization.

These ranges provide a unified reference for evaluating GNP materials produced by different methods and available from various suppliers.

2.2. Characterization Techniques

The determination of structural and physicochemical parameters of graphene nanoplatelets (GNPs) requires the application of appropriate characterization techniques that enable reliable analysis of their morphology, composition, and surface as well as electrical properties. Accurate material characterization is essential not only for evaluating the quality of the obtained nanoplatelets but also for ensuring the reproducibility of synthesis and post-processing procedures.

The use of complementary analytical methods allows for quantitative assessment of key parameters such as flake thickness, lateral size, Raman I_D/I_G ratio, specific surface area, electrical conductivity, and oxygen content. These data form the basis for comparing the outcomes of different production methods and for analysing the correlations between the structural, compositional, and electrochemical properties of GNPs.

Such a comprehensive approach enables the identification of trends and the search for an optimal combination of features that ensures the best balance between conductivity, structural stability, defect density, and specific surface area. Understanding these relationships makes it possible to determine which parameter values are most desirable for applications in batteries, supercapacitors, and hybrid energy storage systems.

Table 2. Selected characterization techniques of graphene nanoplatelets (GNPs) and their relevance for energy storage materials.

Technique	Parameters Characterized by the Technique	Relevance for GNP Analysis in Energy Storage Systems	Examples of Application in Literature
SEM (Scanning Electron Microscopy)	Morphology, shape, flake size, aggregation	Enables evaluation of GNP homogeneity and dispersion within electrodes, which affects conductivity and electrolyte contact.	[2,4,5]
TEM (Transmission Electron Microscopy)	Number of layers, thickness, defects, stacking faults	Determines exfoliation degree and defect density, both crucial for electrical conductivity and cycling stability.	[3,4,9]
AFM (Atomic Force Microscopy)	Thickness and surface topography	Provides accurate measurements of flake height, allowing correlation between thickness, specific capacitance, and ion transport.
Raman Spectroscopy	Number of layers, defect density (ID/IG), sp2 quality	Identifies the degree of disorder and crystallinity, which directly influence electrochemical activity of GNPs.	[2,9,16]
XRD (X-ray Diffraction)	Interlayer spacing (d002), structural order	Reveals the degree of exfoliation and layer ordering, related to electronic conductivity and structural stability.	[2,4]
BET (Brunauer–Emmett–Teller Analysis)	Specific surface area, porosity	Determines the accessible active surface area and number of adsorption sites for ions, essential for supercapacitor performance.	[3]
XPS (X-ray Photoelectron Spectroscopy)	Elemental composition, C/O ratio, functional groups	Enables analysis of surface purity and functionalization, affecting wettability and electrode-electrolyte interface properties.	[2,13,16]
FTIR (Fourier Transform Infrared Spectroscopy)	Chemical bonds, functional groups	Confirms the presence of oxygen-containing or heteroatom functional groups that modify surface activity.	[2,13]
TGA (Thermogravimetric Analysis)	Thermal stability, material purity	Evaluates the presence of organic residues or impurities that may affect electrode stability.	[2,4,9]
EIS (Electrochemical Impedance Spectroscopy)	Internal resistance, charge transfer resistance	Provides insights into ion/electron transport and electrode-electrolyte interface behavior.	[13]
EA (Elemental Analysis)	Elemental composition	Quantifies the bulk carbon, oxygen, and heteroatom content, useful for assessing oxidation and doping levels.	[2,9]
CV (Cyclic Voltammetry)	Redox activity, reversibility, capacitance behaviour	Evaluates charge storage mechanisms and electrochemical reversibility.	[3,13]
GCD (Galvanostatic Charge–Discharge)	Specific capacitance, rate capability, cyclic stability	Measures charge–discharge characteristics and energy efficiency under practical conditions.	[3,13]
Zeta Potential	Surface potential, dispersion stability	Indicates suspension stability of GNPs, relevant for uniform electrode coating formation.	[2]
Laser Diffraction	Flake size distribution	Determines lateral size distribution of GNP flakes in dispersion.	[16]
EDS (Energy-Dispersive X-ray Spectroscopy)	Elemental ratios (C/O), purity	Complements XPS by providing elemental mapping and compositional uniformity.	[13]
Raman R2 parameter (Voigt-fitted 2D band)	Flake thickness classification; identification of sediment-like or graphite-like spectra	Improves detection of thick or incompletely exfoliated platelets that affect electrode uniformity and electrochemical performance.	[17]
Raman NNLS (Non-Negative Least Squares) spectral decomposition	Relative contributions of GNP-like vs. sediment-like spectral components	Enhances sensitivity to unexfoliated or graphitic material, enabling more reliable assessment of GNP batch quality	[17]
SAXS (Small-Angle X-ray Scattering)	Thickness, size	Provides statistically representative dispersion data and high sensitivity to incompletely exfoliated stacks.	[18]
1H NMR relaxometry	Solvent-accessible surface area, degree of exfoliation, changes in surface chemistry	Enables fast, at-line quantification of exfoliation progress and surface area, directly linked to ion-accessible sites, specific capacitance and charge transfer.	[19]

presents Selected characterization techniques of graphene nanoplatelets (GNPs) and their relevance for energy storage materials.

2.3. Quality Control of Industrial Graphene Nanoplatelets

Ensuring the structural quality and batch-to-batch reproducibility of commercial GNPs remains challenging due to the limitations of commonly used characterization techniques. Raman spectroscopy, although widely applied in both research and industry, has reduced sensitivity when measurements rely on spectra averaged over large sampling areas. In heterogeneous GNP powders, such averaging may obscure local variations and lead to an underestimation of thick, graphitic or insufficiently exfoliated material. Several studies have demonstrated that even notable fractions of graphite or sediment can remain undetected under typical Raman protocols, which highlights the need for point-wise spectral analysis and more advanced processing approaches such as NNLS decomposition or R₂-based classification [17].

Complementary techniques capable of probing a statistically meaningful number of platelets are therefore essential for reliable QC. Small-angle X-ray scattering (SAXS) addresses several of these limitations by analysing millions of particles simultaneously and without the drying artefacts inherent to microscopy-based methods such as AFM or TEM. This enables the extraction of full thickness and lateral size distributions directly in dispersion, covering platelet populations from a few layers up to several tens of layers and diameters spanning hundreds to thousands of nanometres. SAXS is particularly sensitive to incompletely exfoliated stacks because the scattered intensity increases rapidly with platelet thickness, making it a powerful tool for detecting graphitic inclusions or aggregation that would otherwise remain unresolved by Raman spectroscopy [18].

Recent industrial evaluations have shown that in-line Raman provides limited sensitivity to exfoliation progress, as its averaged signal is dominated by residual thick, unexfoliated platelets. Conversely, rapid at-line ¹H NMR relaxometry offers robust, surface-area-dependent readouts within minutes and performs reliably under typical production-floor conditions. These results reinforce the need for multi-technique QC workflows that pair point-resolved Raman analysis with statistically representative dispersion-based methods [19].

Together, these findings indicate that robust quality control of industrial GNP products requires combining multiple characterization strategies. High-resolution local probes (Raman, AFM) must be complemented with statistically representative bulk techniques (SAXS, DLS), while Raman-based QC should rely on point-wise analysis and appropriate spectral classification rather than averaging. Such integrated workflows are essential for accurately determining the exfoliation degree, polydispersity and structural homogeneity of GNPs in commercial production environments.

2.4. Structure-Performance Correlation

The physical and chemical parameters of graphene nanoplatelets (GNPs) have a direct impact on their electrochemical behaviour, determining such key characteristics as specific capacitance, electrical conductivity, cycling stability, and power density. Understanding the correlations between structure and performance is crucial for the rational design of GNP-based electrode materials used in batteries, supercapacitors, and hybrid energy storage systems.

Each parameter—such as the number of layers, defect density, specific surface area, oxygen content, or degree of wrinkling—can affect electron and ion transport in different ways, thereby influencing the efficiency of energy storage processes. Optimizing these features requires a deliberate balance between conductivity and defect density, as well as between structural stability and active surface development.

The analysis of structure-property correlations therefore enables the identification of parameters whose increase or limitation leads to the desired electrochemical outcome. Skillful control of these interdependencies constitutes the foundation of material engineering aimed at developing an electrode material as close as possible to the “ideal” energy storage medium-combining high capacity, durability, and efficiency.

Table 3. Correlation between structural parameters of graphene nanoplatelets (GNPs) and their electrochemical performance in energy storage systems.

GNP Parameter	Observation/Correlation with Electrochemical Performance	Type of Energy Storage System	Reference
Flake thickness/number of layers	Fewer layers → improved ion diffusion.	SC	[13]
Lateral size	Larger lateral size → lower ID/IG ratio, S reduced defect density.		[16]
Specific surface area (BET)	Higher surface area → more edges, more defects (both internal and external), increased porosity and oxygen content, increased ID/IG ratio → lower thermal stability, higher reversible and irreversible capacities.	Li-ion	[9]
Interlayer spacing (d002)	Increased interlayer spacing → increased capacity	Li-ion	[14]
Oxygen-containing groups	Presence of oxygen functional groups → faster redox reactions, additional pseudocapacitance.		[13]
Surface energy/wettability	Lower contact angle → faster ion transport.		[2]
Electrolyte type	Aqueous electrolytes → higher ion mobility → increased capacitance.	SC	[13]
Porosity	Mesoporous structure → fast ion transport.		[13]
Zeta potential	Higher zeta potential → better dispersion stability.		[2]

presents correlation between structural parameters of graphene nanoplatelets (GNPs) and their electrochemical performance in energy storage systems.

2.5. Comparison with Other Graphene Forms (GO/rGO/CVD)

Since the discovery of graphene, numerous structural variants have been developed, differing in their physicochemical properties and synthesis methods. The literature most commonly distinguishes three main classes of graphene-based materials: graphene oxide and reduced graphene oxide (GO/rGO), chemical vapor deposition (CVD) graphene, and graphene nanoplatelets (GNPs). Each of these forms exhibits distinct advantages and limitations arising from differences in synthesis route, structural purity, defect density, and scalability (

Table 4. Comparison of properties of graphene nanoplatelets (GNP), graphene oxide/reduced graphene oxide (GO/rGO), and CVD graphene.

Property/Parameter	GO/rGO	GNP	CVD
Characteristic features	ID/IG = 1.06, C/O = 2.4, d002 = 0.89 nm [4]	Intermediate structure between graphite and monolayer graphene; few to tens of layers (2–10 nm); wrinkled morphology and defective edges.	Single graphite layer, 0.34 nm thick, large lateral size [20]
Production cost	Low [21]	Low [2,20]	High [2]
Production scalability	High [21]	High [2,20]	Low [2]
Advantages	High sorption capacity toward radioactive isotopes and metal ions [20]	Lightweight, low-cost, scalable production, high electrical and thermal conductivity [20]	High structural quality, excellent electrical and thermal conductivity.
Limitations	Requires aggressive chemicals [2]	Aggregation, non-uniform morphology, limited standardization.	Difficult mass production, challenging synthesis process [20]

).

Against this background, graphene nanoplatelets represent an attractive compromise between structural quality, production cost, and process simplicity. GNPs combine the relatively high electrical conductivity and chemical stability typical of CVD graphene with the ease and low cost of production characteristic of GO/rGO materials. As a result, GNPs occupy the “technological middle ground,” providing a favourable balance between performance and scalability. This makes them particularly promising for large-scale industrial applications in energy storage systems, where both electrochemical efficiency and manufacturability are critical factors.

3. Production and Functionalization

The properties and commercial potential of graphene nanoplatelets (GNPs) largely depend on the chosen synthesis method. The selection of an appropriate production technique determines key material features such as the number of layers, flake size and shape, defect density, oxygen content, electrical conductivity, and specific surface area.

Modern GNP fabrication methods aim to achieve a balance between high structural quality and economic feasibility. From the quality perspective, critical physicochemical parameters influencing electrochemical performance include the number of layers, purity, homogeneity, defects, and high conductivity. In contrast, from an industrial standpoint, the most important factors are process yield, synthesis time, unit cost, and scalability.

Achieving equilibrium between these aspects remains the main challenge in developing industrial-scale GNP production methods and directly determines their applicability in modern energy storage systems.

3.1. Production Techniques

Over the past decade, a wide range of graphene synthesis methods has been developed, encompassing both bottom-up approaches (e.g., chemical vapor deposition, CVD) and top-down strategies based on exfoliation of precursor materials (

Table 5. Representative production techniques for graphene nanoplatelets (GNPs).

Production Method (Group)	Description/Process Variant	Process Parameters	Properties of Obtained GNPs	Scalability/Cost	Advantages/Limitations	Reference
Mechanochemical exfoliation + edge functionalization	Ball-milling	500 rpm, 48 h; gases: H2, CO2 (dry ice), SO3, CO2 + SO3; steel capsule.	Lateral size: 0.1–1 µm; ID/IG = 0.79–1.50; d002 = 0.34–0.40 nm; functional groups –H, –COOH, –SO3H; highly dispersible in water, DMF, NMP.	High scalability/low cost	Limitations: possible aggregation (strong H-bonding).	[2]
High-pressure airless spray exfoliation (HPE)	Combined intercalation and high-pressure delamination process.	Graphite KS10 (10 g/L); 1 wt% TBA + Antitera/BYK; intercalation 10 days; pressure 2000 psi; 3 cycles; centrifugation 10,000 rpm; drying 60 °C for 24 h; yield 6 g/L.	Flake size 1–3 µm; 5–8 layers; d002 = 0.324 nm; ID/IG = 0.26; high purity and conductivity.	High scalability/low cost	Advantages: environmentally friendly, simple, efficient, produces clean product. Limitations: long intercalation time (10 days), minor edge defects, flake inhomogeneity.	[13]
Electrochemical exfoliation	Graphite foil in (NH4)2SO4 assisted by ultrasonication.	10 V, 60 min, pH 5.3, T = 5 °C; ultrasonics 630 W/15 min; electrolyte (NH4)2SO4 (aq)	Flake thickness 3–5 nm; ζ = −42.2 mV; lateral size 1600–2000 nm.	Potentially scalable/low cost	Advantages: inexpensive, good dispersion stability. Limitations: too low pH → no GNP formation; too high voltage (≥12 V) → anode degradation.	[22]

). In the case of graphene nanoplatelets (GNPs), top-down techniques are predominantly employed, involving the delamination of graphite using various physical, chemical, or electrochemical means.

These methods can be classified according to the dominant exfoliation mechanism:

• Mechanical exfoliation—based on shear forces, cavitation, or centrifugal action;
• Liquid-phase exfoliation (LPE)—delamination of graphite in a solvent with surface energy matched to graphene, assisted by mechanical energy (e.g., ultrasonication or high-shear mixing);
• Chemical or intercalation-assisted exfoliation—introduction of molecules or ions (intercalants) between graphite layers, followed by expansion and separation via heating or mechanical agitation;
• Electrochemical exfoliation—ion intercalation driven by an applied electric potential;
• Thermal or microwave exfoliation—rapid gas expansion within intercalated graphite causing violent layer separation;
• Hybrid methods—combinations of the above mechanisms designed to optimize both quality and yield.

The choice of synthesis method and process parameters-such as solvent type, exfoliation duration and intensity, or the nature of intercalants-directly determines the resulting GNP thickness, specific surface area, defect density, and electrical conductivity. Ultimately, these parameters govern the material’s suitability for electrochemical applications, including batteries, supercapacitors, and hybrid energy storage systems.

3.2. Functionalization Strategies

The functionalization of graphene nanoplatelets (GNPs) represents a crucial step in tailoring their physicochemical properties for specific applications, particularly in energy storage systems. This process aims to improve wettability, dispersion stability, compatibility with other composite components, and to control defect density and surface activity. In practice, functionalization is essential since pristine GNPs exhibit a natural tendency to aggregate due to strong π-π interactions between graphene layers, which hinders their uniform dispersion in polymer matrices, liquid electrolytes, or active materials.

Functionalization techniques can be broadly classified into four main groups:

Covalent functionalization—involves the chemical attachment of atoms or functional groups to the graphene structure through the formation of stable covalent bonds with carbon atoms.

Non-covalent functionalization—utilizes weak physical interactions (van der Waals, electrostatic, or π-π stacking) to adsorb molecules on the graphene surface without disrupting its crystalline lattice.

Heteroatom doping—consists of substituting a portion of carbon atoms with other elements, thereby modifying the electronic and surface properties of the material.

Hybrid or composite functionalization—refers to the integration of GNPs with other materials (metals, metal oxides, polymers, or carbonaceous materials) without significantly altering their basal structure.

The choice of an appropriate functionalization strategy enables targeted modification of GNP parameters—ranging from enhanced electrical conductivity and cycling stability to increased density of electrochemically active sites (

Table 6. Functionalization strategies of graphene nanoplatelets (GNPs).

Functionalization Type	Description/Process Variant	Process Parameters/Conditions	Effect of Functionalization/Change in GNP Properties	Advantages/Limitations	Reference
Covalent (edge functionalization)	Ball-milling + H2 → HGnP (C–H termination at edges)	500 rpm, 48 h, H2 (10 bar)	Improved dispersion compared to pristine graphite.		[2]
Covalent (edge functionalization)	Ball-milling + CO2 → CGnP (–COOH termination)	500 rpm, 48 h, 100 g dry ice per 5 g graphite, CO2 atmosphere	Strong hydrophilicity, lower contact angle.		[2]
Covalent (edge functionalization)	Ball-milling + SO3 → SGnP (–SO3H termination)	500 rpm, 48 h, SO3 atmosphere, dry process	Highest surface polarity, dispersion stability.		[2]
Covalent (edge functionalization)	Ball-milling + SO3 + CO2 → CSGnP (–COOH/–SO3H)	500 rpm, 48 h, stainless steel capsule, dry process	Improved wettability, dispersion stability, high electrochemical activity.	Limitations: tendency to aggregate under high polarity conditions.	[2]
S-doping	Formation of sulfur–graphene composite (GnPs/SWCNT–S)		High reversible capacity (≈650 mAh/g), high efficiency.		[4]
Plasma fluorination (F-GNP)	Plasma-assisted surface functionalization (Haydale HT60 reactor)	50 g GNP; CF4 gas; pressure < 10 mbar; temperature < 100 °C; process carried out using a Haydale HT60 plasma reactor	Increased defect density.	Safe, scalable process.	[16]
Edge carboxylation	Ball milling	500 rpm, 48 h, CO2 atmosphere	Enhanced specific capacitance, improved wettability, larger active surface area.	Advantages: preserved sp2 structure, good conductivity, high electrochemical activity. Limitations: requires defect control.	[23]

). Understanding the mechanisms, effects, and limitations of each approach allows for the rational design of GNP-based structures optimized for use in batteries, supercapacitors, and hybrid energy storage systems.

The data summarized in Table 6 clearly indicate that heteroatom doping and hybrid functionalization with metal oxides play an important role in enhancing the electrochemical performance of graphene nanoplatelets for energy storage applications. Doping alters the electronic structure and increases the density of active sites, while hybrid GNP-metal oxide structures provide additional pseudocapacitive or redox-active contributions and improve interfacial charge transfer. Across the reviewed studies, functionalized GNPs consistently demonstrate improved wettability, higher specific capacitance, enhanced cycling stability and better overall electrode kinetics compared to pristine materials. These effects confirm that controlled functionalization—whether through covalent modification, heteroatom substitution or integration with metal oxides—is a key strategy for optimizing GNP-based electrodes in batteries, supercapacitors and hybrid energy storage systems.

3.3. Industrial Readiness and Commercial Potential

A growing number of companies worldwide are engaged in the industrial-scale production of graphene nanoplatelets (GNPs), offering materials with diverse properties, purity levels, and technological maturity. An analysis of commercially available GNP products allows for an assessment of the current stage of technological development and the identification of directions for further optimization. Knowledge of existing market solutions is particularly valuable for planning large-scale production, as it enables the comparison of laboratory results with commercial benchmarks, evaluation of competitiveness, and selection of the most efficient and proven manufacturing technologies.

Unlike standardized materials with well-defined specifications, graphene nanoplatelets are not yet covered by unified quality standards. Consequently, individual manufacturers adopt different definitions and nomenclature for key parameters such as flake thickness, lateral size, specific surface area, and electrical conductivity. Therefore, when working with commercial materials, it is essential to verify the actual properties provided by each supplier and determine to what extent they meet the requirements of a specific application. An additional observation is that functionalized GNPs—particularly heteroatom-doped variants—are available only from a very limited number of suppliers, while metal oxide-modified GNPs do not appear to be offered as standard catalogue products. This indicates that most advanced functionalization strategies remain at the research stage and have not yet transitioned into industrial-scale manufacturing.

A comparison of GNP producers and their material parameters helps to illustrate the current industrial capabilities and technological boundaries within the global graphene market (

Table 7. Overview of commercial producers of graphene nanoplatelets (GNPs).

Manufacturer/Supplier	Product Specification	Reference
Strem Chemicals	Flake thickness: 6–8 nm; lateral size: 5, 15, 25 µm.	[5]
Nanografi Nano Technology	Average lateral size ≈ 1.3 µm; specific surface area: 296–714 m2/g; oxygen content: 5–13 wt%.	[9]
First Graphene	Lateral size: 5, 10, 20 µm; specific surface area: 10.7 m2/g; O/C ratio: 0.055, 0.051, 0.040.	[16]
Thomas Swan	Specific surface area: 5.21 m2/g; F/C ratio = 0.22 (after functionalization).	[16]
Versarien	Specific surface area: 26.4 m2/g; F/C ratio = 0.044 (after functionalization).	[16]
XG-Sciences	Specific surface area: 685 m2/g; F/C ratio = 0.190 (after functionalization).	[16]

). Such benchmarking also serves as a valuable reference point for ongoing research focused on optimizing GNP synthesis and functionalization toward energy storage applications.

3.4. Performance Comparison of Commercial GNPs in Applications

Device-level data for commercially supplied or industrially scalable graphene nanoplatelets are limited but provide useful benchmarks for evaluating practical performance in supercapacitors. Ikinci et al. (2024) [8] used XG Sciences M25 GNPs as conductive coatings for structural supercapacitors and reported a specific capacitance of 26.05 mF/g for single-cell devices, alongside ~4% improvement in total capacitance due to better interfacial conductivity.

In a separate study, Chiam et al. (2018) [10] investigated thermally exfoliated GNPs (BET 591 m²/g) as electrode materials in stacked copper-foil supercapacitors. The stacked device achieved 24.64 Wh/kg energy density and 402 W/kg power density, representing a four-fold improvement over the single-cell configuration and significantly outperforming a commercial KEMET reference capacitor. Cycling stability remained high, with ~80% capacitance retention at 3 A/g.

Finally, Banavath et al. (2022) [13] demonstrated that industrially scalable spray-exfoliated GNPs can deliver 86 F/g in aqueous electrolyte at 2 A/g and 26 F/g in organic electrolyte at 6 A/g. Rate capability decreased to ~33–38% at the highest tested currents, while long-term cycling retention remained strong at 90–95% after 5000 cycles.

Together, these studies show that commercial and industrial-scale GNPs can enable stable, moderate-performance supercapacitors, though specific capacitance is typically limited by flake restacking, moderate accessible surface area and polydispersity. These performance trends highlight the need for thinner flakes, controlled surface chemistry and improved dispersion strategies to unlock higher energy storage efficiencies in commercial GNP-based electrodes.

4. Applications in Energy Storage

The physicochemical properties of graphene nanoplatelets (GNPs) enable their effective use in various energy storage systems. Each of these technologies operates through a distinct charge storage mechanism and imposes different requirements on the electrode materials, which in turn determines the optimal role and configuration of GNPs within the system.

To fully exploit the potential of graphene nanoplatelets, it is essential to understand their behaviour under different electrochemical configurations and to evaluate their performance depending on operating conditions and electrolyte characteristics. Such an approach allows for identifying which GNP features—such as electrical conductivity, specific surface area, defect density, or structural stability—are most critical for a given type of energy storage system and how they can be compared and optimized.

The growing demand for efficient and durable energy storage technologies stems from the rapid development of electromobility, renewable energy sources, and modern distributed power systems. Energy storage plays a key role in grid stabilization, harvesting surplus energy from renewables, providing uninterrupted power supply, and improving overall energy utilization efficiency. With advancing technology, there is an increasing need for new materials with enhanced electrochemical characteristics, and graphene nanoplatelets-owing to their combination of high conductivity, large surface area, and chemical stability-stand out as one of the most promising candidates for next-generation energy storage systems.

4.1. Comparative Overview of Energy Storage Technologies

Energy storage systems can be generally divided into three main categories: supercapacitors, electrochemical batteries, and hybrid systems that combine features of both technologies. Each of these systems relies on a different charge storage mechanism—ranging from physical ion adsorption in the electric double layer, through redox reactions, to hybrid processes that merge both mechanisms within composite structures.

These technologies differ in key operational parameters such as specific capacitance, energy density, power density, cycling stability, energy efficiency, and cost per unit capacity. Depending on these properties, systems may be better suited for applications requiring high power and rapid charge/discharge (supercapacitors), high energy density and long-term operation (batteries), or a balanced compromise between the two (hybrid systems).

To accurately assess the potential of graphene nanoplatelets (GNPs) across different electrochemical applications, it is essential to understand the specific advantages and limitations of each energy storage technology.

Table 8. Comparative overview of major energy storage technologies (based on [24,25,26]).

Type of System	Charge Storage Mechanism	Typical Parameters	Advantages	Limitations
Supercapacitors (EDLC/pseudocapacitive)	Physical ion adsorption at the electrode/electrolyte interface (EDLC) or fast surface redox reactions (pseudocapacitance).	Efficiency > 90%; discharge time: seconds-hours; energy density: ~5 Wh/kg; power density: 50–100 kW; >106 cycles.	Very high power density, fast charging, high efficiency, long cycle life, thermal stability, and absence of chemical degradation.	Low energy density, high self-discharge, high cost per kWh, integration challenges for long-duration systems.
Lithium-ion batteries (Li-ion)	Intercalation reactions within graphite and metal oxide structures.	Efficiency 85–95%; discharge 1 min–8 h; energy 100–265 Wh/kg (200–400 Wh/L); power 250–340 W/kg; 1000–10,000 cycles; cost 500–2500 USD/kWh.	High energy density and efficiency, low self-discharge, compact design, good rate capability.	Capacity fading over cycles, thermal runaway risk, high cost, limited recyclability.
Sodium-sulphur (Na–S)	Electrochemical conversion between molten Na (anode) and molten S (cathode) through a β-alumina electrolyte.	Efficiency 80–90%; energy density 150–240 Wh/kg; 4500–15,000 cycles; discharge sec–hours; cost 400–500 USD/kWh; life time 10–15 years.	High energy density, high efficiency.	High operating temperature, safety/explosion risk, demanding thermal management and maintenance.
Metal-air batteries (Li–air, Zn–air, Al–air)	Metal oxidation and oxygen reduction from ambient air.	Efficiency 50%; discharge seconds-days; energy 500–10,000 Wh/L; power 0.01 MW; few hundred cycles; cost 10–60 USD/kWh.	Extremely high energy density, inexpensive cathode materials.	Cathode instability, metal precipitation, poor oxygen-reaction reversibility, CO2 and humidity sensitivity.

presents comparative overview of major energy storage technologies.

4.2. Supercapacitors

Supercapacitors are energy storage systems distinguished by their high power density, short charging times, and excellent cycling durability. Depending on the charge storage mechanism, two main types can be identified: electric double-layer capacitors (EDLCs), where energy is stored electrostatically, and pseudocapacitors, in which energy storage occurs through fast surface redox reactions.

Graphene nanoplatelets (GNPs) are employed in supercapacitor electrodes as active materials, conductive additives, or three-dimensional (3D) frameworks enhancing charge transport and the accessibility of active surface sites. Owing to their large specific surface area, high electrical conductivity, and chemical stability, GNPs can significantly improve both specific capacitance and cycling stability of the device. Furthermore, when incorporated into composites with conducting polymers or metal oxides, GNPs enable a synergistic effect that combines electrostatic double-layer capacitance with pseudocapacitive redox behaviour, leading to improved overall energy and power performance.

Selected supercapacitor systems utilizing graphene nanoplatelets are summarized in

Table 9. Selected supercapacitor systems utilizing graphene nanoplatelets (GNPs).

System Type and GNP Role	Electrode Configuration/Composition	Specific Capacitance (F/g)	Cycling Retention (%)	Reference
Symmetric EDLC—GNP‖GNP (organic electrolyte)	Active material: GNP (85 wt%) + carbon black (5 wt%) + PVDF binder (10 wt%); current collector: Toray carbon paper; electrolyte: 1 M TEABF4 in acetonitrile (ACN).	26 F/g @ 6 A/g (8.5 F/g @ 14 A/g).	90% after 5000 cycles; coulombic efficiency 84%.	[13]
Symmetric EDLC—GNP‖GNP (aqueous electrolyte)	Active material: GNP (85 wt%) + carbon black (5 wt%) + PVDF (10 wt%) in NMP; current collector: Toray carbon paper; electrolyte: 1 M Na2SO4 (aqueous); separator: paper filter.	86 F/g @ 2 A/g (32 F/g @ 15 A/g).	95% after 5000 cycles; coulombic efficiency 93%.	[13]

.

4.3. Batteries

Graphene nanoplatelets (GNPs) are utilized in various types of electrochemical batteries owing to their high electrical conductivity, large specific surface area, and chemical stability. In lithium-ion batteries, GNPs serve as conductive additives or electrode modifiers, improving charge transport and cycling stability. In lithium-sulphur systems, they help to mitigate the shuttle effect and stabilize the sulphur structure, while in sodium-ion batteries, they act as an alternative anode material to graphite. In metal-air batteries, GNPs can play a catalytic role, enhancing the activity of oxygen reduction and evolution reactions.

Through these functionalities, graphene nanoplatelets contribute to improved specific capacity, coulombic efficiency, and cycling durability across multiple energy storage chemistries (

Table 10. Selected battery energy storage systems employing graphene nanoplatelets (GNPs).

System Type and GNP Role	Electrode Composition	Specific Capacity [mAh/g]/Cycles	Cycling Retention (%)	Reference
Li-ion (GNP as conductive additive/active anode component)	Graphite (84.5 wt%) + GNP (10 wt%) + Super C65 (1 wt%) + CMC/SBR (4.5 wt%).	505 (1st cycle) → 320 (5th cycle, C/20) → 250 (50th cycle, C/5).	100% coulombic efficiency after 50 cycles.	[9]
Li–S (cathode)—GnPs/SWCNT–S composite	Composite cathode: GnPs/SWCNT–S.	≈650 @ 5 C; 900–800 @ 1–2 C.	75.5% after 300 cycles.	[4]
Li-ion—anode (BrGnP)	Ball-milled graphite with Br2 intercalation.	546.8 @ 0.5 C.	38.5% after 500 cycles.	[27]
Li-ion—anode (FGnP)	Ball-milled graphite with F2 treatment.	650.3 @ 0.5 C.	76.6% after 500 cycles.	[27]
Li-ion—anode (IGnP)	Ball-milled graphite with I2 treatment.	562.8 @ 0.5 C.	81.4% after 500 cycles.	[27]

).

4.4. Hybrid Systems

Hybrid energy storage systems combine the advantages of supercapacitors and batteries, offering both high power density and enhanced energy density. In such systems, graphene nanoplatelets (GNPs) play a key role as conductive scaffolds or composite components, facilitating efficient electron and ion transport.

Table 11. Selected hybrid energy storage systems utilizing graphene nanoplatelets (GNPs).

System Type and GNP Role	Electrode Configuration/Composition	Specific Capacitance or Capacity (mAh/g)	Cycling Retention (%)	Reference
Hybrid Li-S/N system—A-NSG	sulphur and nitrogen co-doped GNP (A-NSG).	≈1000 mAh/g (typical).	Stable over >100 cycles; >99% efficiency.	[4]

lists selected hybrid energy storage systems utilizing graphene nanoplatelets (GNPs).

Integrating GNPs with other materials-such as carbon nanotubes (CNTs), MXene structures, or metal oxides-enables synergistic effects that merge electrostatic double-layer capacitance with redox-based energy storage mechanisms. This approach allows for improved specific capacitance/capacity, enhanced cycling stability, and an optimized balance between energy and power density.

5. Discussion

A review of the literature on graphene nanoplatelets (GNPs) reveals both their high application potential and the numerous challenges that must be overcome to fully exploit this material in advanced energy storage systems. Despite extensive research efforts, there remain significant discrepancies in the reported properties and electrochemical performance, stemming mainly from variations in synthesis methods, material quality, degree of functionalization, and the lack of standardized characterization protocols.

This section discusses key issues such as aggregation and dispersion of GNPs, scalability and production costs, as well as environmental and sustainability aspects. In parallel, it highlights emerging research trends and perspectives focused on improving synthesis, functionalization, and composite design to tailor GNP properties for specific electrochemical applications.

5.1. Aggregation, Dispersion, and Processing Challenges

One of the main obstacles limiting the practical use of GNPs is their natural tendency to agglomerate, driven by strong van der Waals and π-π interactions between layers. This leads to the formation of clusters and a reduction in the effective active surface area, which adversely affects electrical conductivity, ion transport, and electrochemical capacitance.

Maintaining a homogeneous dispersion of GNPs in suspensions, polymer matrices, or electrode composites remains a major technological challenge. Effective strategies to improve dispersion include the use of surfactants, controlled sonication, chemical surface functionalization, and process optimization (e.g., pH, viscosity, mixing energy). The careful selection of these parameters is crucial for obtaining stable dispersions that ensure uniform particle distribution and good adhesion to the current collector.

From the perspective of electrode processing, controlling the degree of GNP aggregation and dispersion has a direct impact on pore structure, conductivity, and charge transfer efficiency in final energy storage devices.

5.2. Cost, Scalability, and Standardization Issues

The industrial development of graphene nanoplatelet (GNP) technology requires achieving a balance between material quality and production cost. Laboratory-scale methods, although capable of producing high-purity GNPs with well-controlled properties, are often too expensive and inefficient for large-scale production. In contrast, industrial approaches such as mechanical or liquid-phase exfoliation offer high scalability, but often at the expense of uniformity and consistency in the final product.

Another critical challenge is the lack of unified standards and characterization protocols for GNPs. Differences in measurement techniques and reporting practices—such as layer number, surface area, or oxygen content—make it difficult to compare results across research groups and manufacturers. The absence of consistent quality benchmarks also leads to variability in specifications reported by commercial suppliers. Recent analyses have shown that averaged Raman spectra can overlook substantial fractions of thick or unexfoliated material, highlighting the need for point-wise spectral evaluation and more advanced classification approaches [17]. Complementary techniques such as SAXS provide statistically representative dispersion-level information by probing large platelet populations without drying artefacts, offering a more reliable basis for quality assessment in industrial settings [18]. Additionally, recent industrial work has demonstrated that fast at-line ¹H NMR relaxometry can deliver surface-area-sensitive feedback within minutes, providing a practical and scalable QC tool that supports real-time monitoring and improved process control [19].

Implementing standardized quality assessment and certification procedures is therefore essential for further market development and for enabling widespread adoption of GNPs in industrial energy storage applications.

5.3. Environmental and Sustainability Aspects

The production of graphene nanoplatelets (GNPs) entails an environmental footprint associated with the consumption of energy, water, and chemical reagents used during exfoliation and functionalization. Minimizing these factors is a key aspect of sustainable GNP technology. Increasing attention is being devoted to green synthesis methods that employ milder processing conditions, environmentally benign solvents, secondary raw materials, and recycling of by-products.

From the application standpoint, incorporating GNPs into energy storage systems can extend device lifetime, enhance efficiency, and reduce dependence on critical raw materials such as cobalt and nickel. Development of scalable, low-emission production routes for graphene is essential to achieving a positive overall environmental balance.

Therefore, the sustainable production and application of GNPs can become an important element of emission-reduction strategies and support the global transition toward a more eco-friendly and resilient energy sector.

6. Conclusions and Outlook

Graphene nanoplatelets (GNPs) have emerged as one of the most promising materials for next-generation energy storage systems, combining high electrical conductivity, large specific surface area, mechanical robustness, and chemical stability with good scalability and cost efficiency. Their intermediate structure between graphite and monolayer graphene enables a unique balance between performance and industrial feasibility, making GNPs attractive for integration into renewable and distributed energy systems.

A comprehensive analysis of recent studies reveals that the structural and physicochemical features of GNPs—such as flake thickness, lateral size, oxygen content, and defect density—directly affect electrochemical behaviour and overall device performance. Optimized few-layer GNPs with controlled surface chemistry show enhanced ion transport, charge transfer kinetics, and long-term stability, enabling improved operation of supercapacitors, Li-ion and Li–S batteries, and hybrid storage systems. These attributes are particularly relevant for renewable energy networks, where fast response times, high power density, and extended cycle life are essential for grid stability and energy management.

Despite their potential, challenges remain in aggregation control, material standardization, and large-scale production. Future development should focus on green, low-emission synthesis routes and interdisciplinary optimization linking materials engineering, electrochemistry, and system-level energy design. The integration of GNP-based storage units into renewable distribution networks—for example, as buffers for solar or wind systems—can substantially improve energy efficiency, reliability, and sustainability.

In this context, graphene nanoplatelets are not only a key material innovation, but also a strategic enabler for the optimization and long-term resilience of renewable energy infrastructures, bridging the gap between advanced nanomaterials research and practical applications in distributed power systems.