Multifunctional phase-change composites for green electromagnetic interference shielding and thermal response prepared under the guidance of an impedance matching strategy†

Jie He ^ab, Jiaozu Wu ^b, Chul B. Park ^bc, Pengjian Gong *^b, Chaobo Liang *^d and Guangxian Li ^b
aSchool of Aeronautics and Astronautics, Sichuan University, Chengdu 610065, China
^bState Key Laboratory of Polymer Materials Engineering, College of Polymer Science and Engineering, Sichuan University, Chengdu 610065, China. E-mail: pgong@scu.edu.cn
^cMicrocellular Plastics Manufacturing Laboratory, Department of Mechanical and Industrial Engineering, University of Toronto, Toronto M5S 3G8, Canada
^dKey Laboratory of Functional Nanocomposites of Shanxi Province, School of Materials Science and Engineering, North University of China, Taiyuan 030051, P.R. China. E-mail: lcb@nuc.edu.cn

First published on 1st August 2024

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1. Introduction

With the advent of the 5G era, the upgrading of electronic devices and the proliferation of antennas, electromagnetic interference (EMI) between devices is increasing, posing great dangers to the human body and electronic devices.^1–4 At the same time, with an increase in frequency, the power consumption of electronic devices also increases.^5–8 As a result, their own heat accumulation becomes serious. Therefore, it has become a current need to produce a material with both green EMI shielding and energy dissipation properties. Green means that few or no electromagnetic waves are reflected back into the environment. At the same time, as little external energy as possible is used to cool equipment. Conventional homogeneous EMI shielding materials frequently necessitate the incorporation of a substantial quantity of conductive fillers to achieve optimal EMI shielding performance.^9,10 This approach inevitably compromises the mechanical properties of the material and increases the cost. Additionally, due to the high electrical conductivity of the material's surface, the mismatch with air impedance results in significant secondary electromagnetic wave reflection.^11–13

The homogeneous conductive network is transformed into an impedance-matched gradient conductive network, thereby enabling the dissipation of electromagnetic waves along the conductive gradient structure. This increases the electromagnetic wave transmission path within the material, allowing for the complete dissipation of electromagnetic energy. This approach simultaneously addresses the incompatibility between high efficiency EMI shielding effectiveness (SE) and low electromagnetic wave reflection. For instance, Xu et al. used reduced graphene oxide by modification of iron tetraoxide (r-GO@Fe₃O₄) and silver-modified zinc oxide (T-ZnO/Ag) as conductive fillers, in conjunction with a water-soluble polyurethane (WPU) matrix.¹⁴ The electromagnetic gradient structure of the WPU composite film resulted in an EMI SE of 87 dB, while the reflectivity (R) was reduced to 0.39. Duan et al. rationally designed an impedance matching layer of iron–cobalt particles deposited on reduced graphene oxide (FeCo@r-GO)/WPU and an Ag-coated expanded polymer bead (EBAg)/WPU conductive shielding layer.¹⁵ In the X-band, the EBAg/FeCo@r-GO/WPU composite foam achieved an EMI SE of 84.8 dB with an R value of 0.08. Meanwhile, in our previous work, integrated silicon dioxide/carbon nanotubes/polyimide–silver nanowires/cellulose nanofiber (SiO₂/CNTs/PI–AgNW/CNF) composites demonstrated an EMI SE of 110 dB with an R value of 0.2.¹⁶ Many researchers have made significant progress in multilayer asymmetric shielding materials.^10,17,18 However, the heat generated by high-frequency and high-power electronic equipment cannot be dealt with by a single EMI shielding property.

Encouragingly, phase-change materials (PCMs) store and release energy by switching between their own solid–liquid states. At the same time, PCMs provide intelligent thermal management by constantly changing their states as the external temperature changes. In addition, polyethylene glycol's (PEG) non-toxic and non-corrosive properties have earned it an excellent reputation in thermal management. However, PEG's own characteristics of poor thermal stability and low thermal conductivity make it difficult to use alone in thermally managing electronic devices. Thermal conductivity determines the rate at which thermal energy is stored and released, and phase-change enthalpy determines the ability to store energy. In order to improve the thermal conductivity of PEG composites, much research has been conducted on the addition of thermally conductive particles, such as metals (Cu),¹⁹ carbon materials (graphene, carbon nanotubes),²⁰ inorganic particles (boron nitride, aluminium oxide, silicon carbide),²¹ and so on. However, the excess filler reduces the percentage of PEG in the composite, resulting in a significant reduction in the enthalpy change capability of the materials. The use of high-temperature carbonized aerogels as the backbone of PEG is a good way to reduce the influence of PEG by the percentage of filler. The thermal conductivity of composites can be significantly increased while the enthalpy change capability can be maintained.

In this work, three-dimensional carbonized Ni-MOF/reduced graphene (Ni@C/r-GO) aerogel skeletons were prepared by freeze-drying and high-temperature carbonization. Subsequently, AgNW–polyimide (PI) films were prepared by scratch coating. Finally, PEG was impregnated under vacuum to obtain carbonized Ni-MOF/reduced graphene oxide/silver nanowire–polyimide@polyethylene glycol (Ni@C/r-GO/AgNW–PI@PEG) phase-change multifunctional composites. In the abovementioned composites, the 1.5 mm low-conductive impedance matching layer of Ni@C/r-GO-300 exhibits an impedance matching characteristic that allows for the majority of electromagnetic waves to enter the material. Meanwhile, the 3.5 mm dissipation layer of Ni@C/r-GO-600 dissipates a portion of the electromagnetic waves within the material, while the remaining electromagnetic waves are absorbed and reflected by the highly conductive shielding layer of AgNW–PI. The assembled composite exhibits an EMI SE of up to 62.3 dB in the X-band with an ultra-low R of 0.04, which are beyond the values observed in the majority of green EMI shielding composites. In addition, heat from high-temperature objects is transferred through the highly thermally conductive AgNW–PI membrane to the long-channel Ni@C/r-GO backbone. The three-dimensional thermally conductive network rapidly transfers heat to the entire amount of PEG for energy storage and release. The thermally responsive EMI shielding composites have a promising future in thermal management of artificial intelligence and portable electronic devices as well as in battery heat dissipation packaging.

2. Experimental section

2.1. Synthesis of polyamidoacetic acid (PAA)

The preparation process of the Ni-MOF and silver nanowires (AgNW) is shown in detail in the ESI.†

2.2. Preparation of Ni@C/r-GO aerogels

A GO dispersion of 100 mg (10 mg ml⁻¹) and Ni-MOF dispersion of 30 mg (10 mg ml⁻¹) were, respectively, sonicated for 30 min. Then a certain amount of PAA powder was dissolved in the GO dispersion in the presence of a small amount of TEA (m_PAA/m_TEA = 10:1), and the sonicated MOF dispersion was added to the above GO/PAA dispersion to form a homogeneous solution. A certain amount of the homogeneous solution was poured into a custom-made PTFE mould and freeze-dried at −72 °C for 48 h to obtain Ni-MOF/GO aerogels. Ni-MOF/GO aerogels were thermally imidized at 100 °C, 200 °C, and 300 °C for 1 h under a nitrogen atmosphere, respectively, followed by carbonization at 400 °C, 500 °C, 600 °C, and 700 °C for 2 h to obtain Ni@C/r-GO aerogels, which were named Ni@C/r-GO-400, Ni@C/r-GO-500, Ni@C/r-GO-600, and Ni@C/r-GO-700. For example, the combined Ni@C/r-GO-300 and Ni@C/r-GO-600 aerogels were named Ni@C/r-GO-300-600. The Ni@C/r-GO-200 aerogel was prepared by carbonizing Ni@C/r-GO aerogels at 100 °C for 1 h and 200 °C for 2 h under a nitrogen atmosphere. The Ni@C/r-GO-300 aerogel was prepared by carbonizing Ni@C/r-GO aerogels at 100 °C, 200 °C, and 300 °C for 1 h under a nitrogen atmosphere, respectively.

2.3. Preparation of Ni@C/r-GO/AgNW–PI@PEG

First, a certain quantity of PAA was dissolved in water to prepare a solution with a mass fraction of 5%. Second, 30 wt% and 50 wt% dispersions of AgNW were, respectively, added to and stirred thoroughly into the PAA solution, and then an AgNW–PI film of about 100 μm was prepared using a coating machine. The prepared impedance matching and dissipation layers made from Ni@C/r-GO and the reflection layer of AgNW–PI film were assembled from top to bottom and then filled with PEG resulting in the Ni@C/r-GO/AgNW–PI@PEG composite being obtained. Otherwise, the composite without the AgNW–PI film was named Ni@C/r-GO@PEG.

3. Results and discussion

3.1. Preparation of Ni@C/r-GO/AgNW–PI@PEG composites

In order to reduce the reflection of electromagnetic waves from the EMI shielding material, the impedance matching layer, the dissipation layer and the reflection layer were assembled together according to the impedance matching principle. The prepared Ni@C/r-GO/AgNW–PI@PEG composites are shown in Fig. 1a–c. First, the low dielectric impedance matching layer Ni@C/r-GO-300, the mediator dielectric dissipation layer Ni@C/r-GO-600 and the high dielectric reflection layer AgNW–PI were bonded with the help of viscous PAA solution to obtain Ni@C/r-GO/AgNW–PI. Finally, the PEG solution was encapsulated in Ni@C/r-GO/AgNW–PI by impregnation under vacuum to obtain the Ni@C/r-GO/AgNW–PI@PEG composite. The infrared spectra of PAA and PI are shown in Fig. S1.† Following gradient temperature imidization, PI showed four peaks at 1782 cm⁻¹, 1718 cm⁻¹, 1369 cm⁻¹, and 715 cm⁻¹. These peaks correspond to the asymmetric stretching vibration of CO, the symmetric stretching vibration of CO, the stretching vibration of C–N, and the bending vibration of CO, respectively,²² which proves the successful transformation of PAA. Previous research demonstrates that in the thermogravimetric assessment of PI, the temperature was elevated to 700 °C, yet the carbonized PI retained 53.6% residue, suggesting that it could serve as a suitable support for the Ni@C and r-GO skeleton.¹⁶ As the carbonization temperature increased, the volumetric shrinkage of Ni@C/r-GO reached 40%, and the density decreased to as low as 25.92 mg cm⁻³ (Fig. S2†), enabling the Ni@C/r-GO-X aerogels to easily balance on a strand of Setaria herb (Fig. S3†). In the composites, r-GO acts as a carbon skeleton with pore sizes in the range of 20–60 μm. Large pores lead to an overall low specific surface area of the aerogel. As the carbonization temperature step increases, the pore diameter of Ni@C increases and the specific surface area decreases further (Table S1†). Due to the low magnetic Ni@C addition, the maximum saturation magnetization of the aerogel was 11.68 emu g⁻¹ at a carbonization temperature of 700 °C (Fig. S4†). In addition, our prepared nanofillers have good dispersion and hydrophilicity to facilitate the close connection of fillers in the aerogel skeleton (Fig. S5†). Fig. S6† illustrates that the Ni-MOF synthesized via the hot-solvent approach has a complete spherical structure with an average diameter of 3.4 μm, whereas the AgNW show an aspect ratio of 300. Differently shaped materials were embedded in the skeleton to form a three-dimensional conductive network, which is capable of forming more heterogeneous interfaces.²³ It can be seen from the XRD pattern that the Ni@C peaks at 44.5°, 51.8°, and 76.4° belong to the (111), (200), and (220) crystal faces, respectively. Additionally, GO exhibits a clear (100) crystal face at 11.08°. Moreover, AgNW show peaks at 37.8°, 44.1°, 64.3°, and 77.4° assigned to the (111), (200), (311), and (222) crystal faces, respectively, reflecting the successful preparation of nanofillers (Fig. S7†).²⁴

3.2. Structural characterization of Ni@C/r-GO/AgNW–PI aerogels

Fig. 2 illustrates the structure of the electromagnetic module of Ni@C/r-GO/AgNW–PI. The impedance-matching layer, designated Ni@C/r-GO-300, is shown in Fig. 2a, while Fig. 2d displays the electromagnetic wave dissipation layer Ni@C/r-GO-600. Finally, the AgNW–PI film represents the electromagnetic wave shielding layer, as shown in Fig. 2g. The vertical growth of ice crystals results in the formation of elongated channel structures in both Ni@C/r-GO-300 and Ni@C/r-GO-600, thus maintaining the direction of electromagnetic wave propagation. Fig. 2b and e illustrate the top views of Ni@C/r-GO-300 and Ni@C/r-GO-600, respectively. It can be observed that GO forms an interconnected three-dimensional conductive network, which is conducive to the multiple reflection of the incident electromagnetic waves. Further magnification reveals that the Ni-MOF adheres to the GO surface, thereby effectively increasing the heterogeneous interface. The higher carbonization temperature Ni@C/r-GO-600 compared to Ni@C/r-GO-300 revealed the partial fracturing of the GO skeleton (Fig. 2c and f). As illustrated in Fig. 2g, the AgNW are intertwined and distributed throughout the 18 μm PI film, suggesting that the AgNW–PI film possesses a superior conductive network, resulting in the shielding layer having enhanced reflective properties (Fig. 2h and i).

3.3. EMI shielding performance of single-layer aerogels

To further verify the reliability of the prepared Ni@C/r-GO/AgNW–PI aerogels based on impedance matching in terms of their EMI shielding performance, the electromagnetic parameters of each layer were investigated separately. As shown in Fig. 3a–c, the conductivity and shielding effectiveness of the AgNW–PI shielding layer increase with the increasing content of AgNW: the EMI SE reaches 58.9 dB and the reflected power coefficient (R) is as high as 0.98 when the content of AgNW reaches 50%, which results in serious secondary contamination of electromagnetic waves. To optimize the impedance matching, we introduced an electromagnetic wave dissipation layer and impedance matching layer. The electromagnetic wave dissipation performance depends on the complex permittivity (ε_r = ε′ − jε′′) and complex permeability (μ_r = μ′ − jμ′′). The electromagnetic wave absorption performance is represented by R_L:

	(1)

	(2)

Z_in is the incident impedance, R_L is the reflection loss, μ_r is the complex permeability, ε_r is the complex permittivity, f is the incident frequency, d is the sample thickness, and c is the speed of light. The attenuation coefficient (α) represents the attenuation ability of the absorber with respect to electromagnetic waves:

	(3)

where α, f, c, ε′, ε′′, μ′and μ′′ represent the attenuation coefficient, the frequency, the speed of light, the real part and the imaginary part of the dielectric constant and the real part and the imaginary part of permeability, respectively. To further evaluate the EM wave dissipation capability of the Ni@C/r-GO-X dissipative layer, the reflection loss (R_L) and effective absorption bandwidth (EAB) of the aerogels at 2–18 GHz were calculated based on the tested EM parameters (Fig. S8†), while the EM wave absorption performance is detailed in Fig. 3d–f (eqn (1) and (2)). The R_L of Ni@C/r-GO-600 with a thickness of 3.5 mm was −48.9 dB at 10.02 GHz (Fig. 3e). In contrast, Ni@C/r-GO-700 exhibits a smaller R_L of −15.1 dB at 9.62 GHz when the thickness is 3 mm (Fig. 3f). Fig. S9† illustrates that Ni@C/r-GO-500 and Ni@C/r-GO-600 exhibit superior impedance matching compared to Ni@C/r-GO-700. Additionally, the attenuation coefficient (α) of Ni@C/r-GO-600 is larger than that of Ni@C/r-GO-500 (eqn (3)). This implies that Ni@C/r-GO-600 maximizes the dissipation of the electromagnetic waves. Meanwhile, the 3D and 2D contour plots are shown in Fig. S10,† where the black line area corresponds to an R_L value below −10 dB, indicating that 90% of the electromagnetic waves are absorbed. The EAB values of Ni@C/r-GO-500, Ni@C/r-GO-600, and Ni@C/r-GO-700 in the range of 2–18 GHz at a thickness of 3–4.5 mm are 4.88 GHz (7.82 GHz–12.7 GHz), 5.3 GHz (8.06 GHz–13.36 GHz), and 4.8 GHz (7.8 GHz–12.6 GHz) (Fig. 3d–f), respectively. In conclusion, all Ni@C/r-GO-X samples perfectly cover the X-band (8.2 GHz–12.4 GHz). Considering the maximum EAB and R_L values, the Ni@C/r-GO-600 aerogel with a thickness of 3.5 mm was finally selected as the electromagnetic wave dissipation layer.

Fig. 3g and Fig. S11† demonstrate that as the carbonization temperature of the dissipation layer Ni@C/r-GO-X increases, the conductivity of the aerogels also increases, resulting in an elevated EMI SE. The conductivity and EMI SE of the Ni@C/r-GO aerogel reached 0.92 S m⁻¹ and 9.69 dB at 700 °C. In order to investigate the shielding mechanism of the Ni@C/r-GO-X aerogel, the average reflection shielding effectiveness (SE_R) and average absorption shielding effectiveness (SE_A) were calculated for Ni@C/r-GO-500, Ni@C/r-GO-600, and Ni@C/r-GO-700. The SE_R values of Ni@C/r-GO-500, Ni@C/r-GO-600, and Ni@C/r-GO-700 are 1.20 dB, 1.56 dB, and 2.81 dB, respectively. These values are below the critical SE_R value of 3.01 dB.²⁵ Concomitantly, the corresponding average R values are 0.24, 0.30 and 0.48, respectively.

In order to enhance the impedance matching of the Ni@C/r-GO-600 dissipation layer with air, an impedance matching layer with lower conductivity and complex permittivity was introduced to further reduce the electromagnetic wave reflection (Fig. S12 and S13†). The conductivities of Ni@C/r-GO-200, Ni@C/r-GO-300, and Ni@C/r-GO-400 are 0.01 S m⁻¹, 0.023 S m⁻¹, and 0.043 S m⁻¹, respectively. Their average SE_R values are 0.28 dB, 0.34 dB, and 1.04 dB, respectively, in comparison to the high value of Ni@C/r-GO-700, while the average R values are much lower at 0.06, 0.07 and 0.22, respectively (Fig. 3j and k). This can be attributed to the diminished conductivity and dielectric parameters of the aerogels, as evidenced by the impedance of the impedance matching layer being closer to that of air (Fig. S14†). This facilitates the passage of electromagnetic waves, thereby reducing reflections from the material's surface.²⁶ The average R values of Ni@C/r-GO-200 and Ni@C/r-GO-300 are close to each other, but the average absorptivity (A) of Ni@C/r-GO-300 (0.20) is higher than that of Ni@C/r-GO-200 (0.13), which is more favorable for energy attenuation inside the composite. The experimental results of broadband R for dissipation and impedance matching layers with optimal carbonization temperatures are effectively verified by simulations, which are in high agreement with the simulations (Fig. 3i and l).

3.4. EMI shielding performance of the assembled aerogels

Based on impedance matching, the optimal combination is 1.5 mm Ni@C/r-GO-300 as the impedance matching layer, 3.5 mm Ni@C/r-GO-600 as the dissipation layer, and AgNW–PI with 50 wt% AgNW as the shielding layer. As shown in Fig. 4a–b, the EMI SE of the assembled aerogel reaches 62.3 dB. The SE_R and R values are only 0.17 dB and 0.04, respectively, which implies that 96% of the electromagnetic waves are absorbed, surpassing the majority of green EMI shielding materials with low R values. Besides, the simulation results shown in Fig. 4c demonstrate good agreement with the experimental results. CST simulations can therefore be used to predict the R values of multilayer shielding materials. The aforementioned impedance matching guideline aerogel has been demonstrated to achieve high EMI SE and negligible R compared to conventional foams, films, and composites, which has rarely been reported in the literature (Fig. S15 and Table S4†). The electromagnetic wave shielding performance was further verified in the experiment. Specifically, when the Ni@C/r-GO/AgNW–PI composite aerogel was positioned close to a Tesla coil, the small light was turned off, otherwise the small light is illuminated when the composite aerogel is removed. The Tesla coil device thoroughly clarified that the Ni@C/r-GO/AgNW–PI composite aerogel has an excellent EMI SE on electromagnetic waves (Fig. S16†). Fig. 4d depicts the EMI shielding mechanism of the assembled aerogel. First, the impedance matching layer Ni@C/r-GO-300 has good impedance matching properties, resulting in a significant reduction of surface reflection. Then, the electromagnetic waves pass through the dissipation layer Ni@C/r-GO-600, and the entry of the electromagnetic waves is facilitated by the long vertical channels. Thus, (I) the three-dimensional r-GO backbone provides continuous conductive loss capability, and the large specific surface area of r-GO is more favorable for electron migration and hopping;^27,28 (II) through eddy current loss and natural resonance, the co-existing Ni@C magnetic particles can move the EAW to lower frequencies; (III) the large number of heterogeneous interfaces between r-GO and Ni@C induces charge generation. This enhances the polarization capability of the material. Finally, when residual electromagnetic waves reach the highly conductive shielding reflection layer of AgNW–PI, they will be absorbed and reflected, and the electromagnetic waves undergo “absorption–reflection–re-absorption” processes.

To visualize the energy consumption of the Ni@C/r-GO/AgNW–PI composite aerogel, CST software was employed to simulate the electromagnetic field radiation (Fig. S17†). The electromagnetic energy decay can be inferred from the current density and energy loss density.²⁹ As illustrated in Fig. 5a–c, the higher current densities of Ni@C/r-GO-600/AgNW–PI and Ni@C/r-GO-300600/AgNW–PI in comparison with that of AgNW–PI can be attributed to the fact that the low R allows electromagnetic waves to enter the interior of the material gradually and to be fully dissipated within the material. The energy loss density cloud diagrams in Fig. 5d–f illustrate that the assembled aerogel exhibits the highest energy loss. This is evidenced by the observation that the electromagnetic waves initially pass through the impedance matching layer Ni@C/r-GO-300, and then gradually decrease the energy consumption at the dissipation layer Ni@C/r-GO-600. Finally, the energy is further dissipated in the AgNW–PI shielding layer. The dissipation layer Ni@C/r-GO-600 exhibits the strongest electromagnetic energy dissipation, which can be attributed to the “absorption–reflection–re-absorption” design concept of the multilayer structure. This enables the dissipation layer Ni@C/r-GO-600 to undergo two electromagnetic energy dissipation processes successively.

3.5. Phase transition behaviors and thermal properties of Ni@C/r-GO/AgNW–PI@PEG

PCMs possess the capacity to absorb and release heat during the phase-transition process.^30–33 Therefore, they can serve as reversible energy storage media to maintain the stability and durability of electronic devices.^34–36 In Fig. 6a, the phase-transition schematic of Ni@C/r-GO/AgNW–PI@PEG illustrates the heat-transfer and phase-transition mechanisms. The thermal conductivity of Ni@C/r-GO@PEG increased with increasing carbonization temperature up to 0.62 W (m K)⁻¹. With the introduction of AgNW, the thermal conductivity of AgNW–PI reached an impressive value of 82.5 W (m K)⁻¹ (Fig. S18†). The heat from the high-temperature object is transferred from bottom to top to the whole Ni@C/r-GO skeleton through the highly thermally conductive AgNW–PI film, and Ni@C/r-GO with its long vertical channels enables the heat to be rapidly transferred to the PEG, resulting in the storage and dissipation of heat. Fig. 6b displays the DSC curves of pristine PEG, Ni@C/r-GO-300@PEG and Ni@C/r-GO-600@PEG. The melting enthalpy and crystallization enthalpy of pristine PEG are 173.67 J g⁻¹ and 167.73 J g⁻¹, respectively. When compared to PEG, Ni@C/r-GO-300@PEG has a melting enthalpy of 158.49 J g⁻¹ and a crystallization enthalpy of 150.38 J g⁻¹. Meanwhile, Ni@C/r-GO-600@PEG exhibits a melting enthalpy of 158.94 J g⁻¹ and a crystallization enthalpy of 150.73 J g⁻¹ (Tables S2 and S3†), indicating partial enthalpy loss due to the introduction of Ni@C/r-GO aerogels. The PEG loading ratio (λ) and enthalpy efficiency (η) represent the phase-transition capacity of PCMs:

	(4)

	(5)

where λ, η, ΔH_m-PCM, ΔH_c-PCM, ΔH_m-PEG, ΔH_c-PEG and W_PEG represent the PEG loading ratio, the enthalpy efficiency, the melting enthalpy and the crystallization enthalpy of PCMs, the melting enthalpy and the crystallization enthalpy of PEG and the mass ratio of PEG in the PCMs, respectively. λ and η values of Ni@C/r-GO-300@PEG and Ni@C/r-GO-600@PEG are presented in Fig. 6c, which were calculated according to eqn (4) and (5).^8,30,37 The results indicate that the λ and η values of Ni@C/r-GO-300@PEG are 90.47% and 97.28%, respectively, and those of Ni@C/r-GO-600@PEG are 90.71% and 96.29%, respectively. These phenomena indicate that the carbonization temperature has essentially no effect on λ and η. The temperature variation of the Ni@C/r-GO/AgNW–PI@PEG composites was monitored further using infrared thermal images. The autonomous temperature regulation capability of Ni@C/r-GO/AgNW–PI@PEG was investigated by comparing with Ni@C/r-GO@PEG (without the reflection layer). The real-time temperatures of the two samples during both warm-up and cool-down were recorded and are presented in Fig. 6d and e. A temperature plateau region appeared in both samples at the same time, which was attributed to the phase-transition energy storage of the PEG slowing down the temperature rise and fall.¹⁶ Additionally, the infrared thermal images presented in Fig. 6f indicate a prolonged time for Ni@C/r-GO/AgNW–PI@PEG to reach its equilibrium temperature, reducing the energy required for cooling. Surprisingly, electronic devices dissipate heat by storing energy through PCMs. As shown in Fig. S19,† the PCM composites were integrated into a 20 W LED chip device. After operating for 120 seconds, the surface temperature of the LED chip was increased to as high as 70.8 °C. In contrast, the temperatures of Ni@C/r-GO@PEG and the Ni@C/r-GO/AgNW–PI@PEG composites were maintained at 65.1 °C and 64.3 °C, respectively, indicating that such PCMs have good thermal management capability for electronic devices.

Thermal stability is a crucial parameter for evaluating the long-term energy storage and release of PCMs.^38–42 To study the thermal stability of the composite PCMs, Ni@C/r-GO/AgNW–PI@PEG, Ni@C/r-GO-300@PEG and Ni@C/r-GO-600@PEG were placed in an oven at 80 °C and subjected to 50 heating and cooling cycles, and the phase-transition behaviors of Ni@C/r-GO-300@PEG and Ni@C/r-GO-600@PEG were recorded by DSC at every 10th cycle. Interestingly, Ni@C/r-GO-300@PEG and Ni@C/r-GO-600@PEG showed a temperature change of less than 2 °C after 50 heating and cooling cycles, and the η value decreased by a maximum of 2.61% (Fig. S20 and S21†). Further heating and cooling cycles at 80 °C showed that the composite PCMs maintain long-term thermal cycling stability (Fig. 5g). Fig. S22† reveals the excellent encapsulation ability exhibited by PEG in the Ni@C/r-GO-X aerogel.

4. Conclusions

In conclusion, based on the principle of impedance matching and the rational assembly of the impedance matching layer, the dissipation layer and the reflection layer, we prepared Ni@C/r-GO/AgNW–PI@PEG green EMI shielding and energy storage materials. The impedance matching layer Ni@C/r-GO-300 reduces the reflection of electromagnetic waves from the material's surface, the dissipation layer Ni@C/r-GO-600 provides excellent electromagnetic wave dissipation capability, and the reflection layer AgNW–PI ensures that the electromagnetic waves are reflected back into the material. The Ni@C/r-GO/AgNW–PI@PEG composite achieves an EMI shielding performance of 62.3 dB with an ultra-low R value of 0.04. In CST simulations, the intrinsic mechanism of electromagnetic energy loss within the material is revealed by the energy loss density cloud maps. Instead, heat is transferred from bottom to top through the highly thermally conductive AgNW–PI membrane to the Ni@C/r-GO backbone with long vertical channels for energy storage and dissipation. The η value of Ni@C/r-GO/AgNW–PI@PEG reaches more than 96.29% and the PCMs demonstrate good stability after 50 heating and cooling cycles. Therefore, the composites prepared on the basis of impedance matching will accelerate the use of EMI shielding materials for the thermal management of artificial intelligence and portable electronic devices as well as battery heat dissipation packaging.

Author contributions

Jie He: methodology, investigation, and writing – original draft. Jiaozu Wu: methodology, software, and supervision. Chul B. Park: data curation and software. Chaobo Liang: methodology and supervision. Guangxian Li: data curation. Pengjian Gong: conceptualization, writing – reviewing and editing, and supervision.

Data availability

All data are in the manuscript and ESI.†

Conflicts of interest

There are no conflicts to declare.

Acknowledgements

This work was supported by the National Natural Science Foundation of China (No. 52203109 and 52073187), the Fundamental Research Program of Shanxi Province (20210302124314), the Open Foundation of China-Belarus Belt and Road Joint Laboratory on Electromagnetic Environment Effect (ZBKF2022020602), the Advanced Research Project on Armament and Equipment (627010205), the NSAF Foundation (No. U2230202), the State Key Laboratory of Polymer Materials Engineering (No. Sklpme2022-2-03), the Project of Sichuan Science and Technology Plan (No. 2024ZHCG0139) and the Programme of Introducing Talents of Discipline to Universities (B13040).

References

1. L. Liang, X. Yang, C. Li, R. Yu, B. Zhang, Y. Yang and G. Ji, Adv. Mater., 2024, 36, 2313939 CrossRef CAS PubMed .
2. B. Zhan, Y. Qu, X. Qi, J. Ding, J. J. Shao, X. Gong, J. L. Yang, Y. Chen, Q. Peng, W. Zhong and H. Lv, Nano-Micro Lett., 2024, 16, 221 CrossRef CAS PubMed .
3. S. Li, J. Luo, J. Wang, Y. Zhu, J. Feng, N. Fu, H. Wang, Y. Guo, D. Tian, Y. Zheng, S. Sun, C. Zhang, K. Chen, S. Mu and Y. Huang, J. Colloid Interface Sci., 2024, 669, 265–274 CrossRef CAS PubMed .
4. C. Liang, H. Qiu, Y. Zhang, Y. Liu and J. Gu, Sci. Bull., 2023, 68, 1938–1953 CrossRef CAS PubMed .
5. C. Liang, Z. Gu, Y. Zhang, Z. Ma, H. Qiu and J. Gu, Nano-Micro Lett., 2021, 13, 181 CrossRef CAS PubMed .
6. C. Liu, X. Duan, W. Zhang, Q. Huo, X. Sui, Y. Liu and C. Liang, Ceram. Int., 2024, 50, 19829–19837 CrossRef CAS .
7. H. Ma, J. Wu, C. Gao, S. He, P. Gong, Q. Shi, Z. Wang, G. Li and C. B. Park, Chem. Eng. J., 2024, 485, 149883 CrossRef CAS .
8. H. Ma, M. Fashandi, Z. Ben Rejeb, P. Buahom, J. Zhao, P. Gong, Q. Shi, G. Li and C. B. Park, J. Mater. Chem. A, 2024, 12, 9627–9636 RSC .
9. R. Hao, Y. Yang, P. He, Y. Liu, G. Zhao and H. Duan, J. Mater. Sci. Technol., 2025, 2026, 317–326 CrossRef .
10. X. X. Wang, Q. Zheng, Y. J. Zheng and M. S. Cao, Carbon, 2023, 206, 124–141 CrossRef CAS .
11. H. Ma, X. Zhang, L. Yang, L. Ma, C. B. Park, P. Gong and G. Li, Carbon, 2023, 205, 159–170 CrossRef CAS .
12. H. Ma, M. Fashandi, Z. B. Rejeb, X. Ming, Y. Liu, P. Gong, G. Li and C. B. Park, Nano-Micro Lett., 2023, 16, 20 CrossRef PubMed .
13. S. Mandal, K. Samanta, K. Manna, S. Kumar and S. Bose, Nanoscale, 2024, 16, 6984–6998 RSC .
14. Y. Xu, Y. Yang, D. X. Yan, H. Duan, G. Zhao and Y. Liu, ACS Appl. Mater. Interfaces, 2018, 10, 19143–19152 CrossRef CAS PubMed .
15. H. Duan, H. Zhu, J. Gao, D. X. Yan, K. Dai, Y. Yang, G. Zhao, Y. Liu and Z. M. Li, J. Mater. Chem. A, 2020, 8, 9146–9159 RSC .
16. J. He, M. Han, K. Wen, C. Liu, W. Zhang, Y. Liu, X. Su, C. Zhang and C. Liang, Compos. Sci. Technol., 2022, 231, 109799 CrossRef .
17. X. X. Wang, H. T. Wu, W. S. Wang, Y. Luo and Y. J. Zheng, Carbon, 2023, 213, 118267 CrossRef CAS .
18. X. X. Wang, J. C. Shu, W. Q. Cao, M. Zhang, J. Yuan and M. S. Cao, Chem. Eng. J., 2019, 369, 1068–1077 CrossRef CAS .
19. Y. Y. Xiao, D. Y. Bai, Z. P. Xie, Z. Y. Yang, J. H. Yang, X. D. Qi and Y. Wang, Composites, Part A, 2021, 146, 106420 CrossRef CAS .
20. G. Zhou, L. Li, S. Y. Lee, F. Zhang, J. Xie, B. Ye, W. Geng, K. Xiao, J. H. Lee, S. J. Park, Z. Yang, C. Huang and Y. Zhang, Compos. Sci. Technol., 2023, 243, 110256 CrossRef CAS .
21. J. Wie and J. Kim, Polymers, 2021, 13, 456 CrossRef CAS PubMed .
22. D. Kong, J. Li, A. Guo and X. Xiao, Chem. Eng. J., 2020, 408, 127365 CrossRef .
23. Y. Xiong, L. Xu, C. Yang, Q. Sun and X. Xu, J. Mater. Chem. A, 2020, 8, 18863–18871 RSC .
24. F. Peng, W. Zhu, Y. Fang, B. Fu, H. Chen, H. Ji, X. Ma, C. Hang and M. Li, ACS Appl. Mater. Interfaces, 2023, 15, 4284–4293 CrossRef CAS PubMed .
25. M. Peng and F. Qin, J. Appl. Phys., 2021, 130, 225108 CrossRef CAS .
26. G. Li, S. Ma, Z. Li, Y. Zhang, J. Diao, L. Xia, Z. Zhang and Y. Huang, ACS Nano, 2022, 16, 7861–7879 CrossRef CAS PubMed .
27. G. Fang, C. Liu, M. Xu, X. Zhang, Y. Wu, D. H. Kim and G. Ji, Adv. Funct. Mater., 2024, 2404532,  DOI:10.1002/adfm.202404532 .
28. J. Xiao, B. Zhan, X. Qi, J. Ding, Y. Qu, X. Gong, J. L. Yang, L. Wang, W. Zhong and R. Che, Small, 2024, 2311312,  DOI:10.1002/smll.202311312 .
29. X. Su, M. Han, Y. Liu, J. Wang, C. Liang and Y. Liu, J. Colloid Interface Sci., 2022, 628, 984–994 CrossRef CAS PubMed .
30. R. Shen, M. Weng, L. Zhang, J. Huang and X. Sheng, Composites, Part A, 2022, 163, 107248 CrossRef CAS .
31. C. Wu, L. Zeng, G. Chang, Y. Zhou, K. Yan, L. Xie, B. Xue and Q. Zheng, Adv. Compos. Hybrid Mater., 2023, 6, 31 CrossRef CAS .
32. Z. Guo, F. Lin, J. Qiao, X. Liu, M. Liu, Z. Huang, R. Mi, X. Min, Y. Xu and L. Wang, Nano Energy, 2023, 108, 108205 CrossRef CAS .
33. Z. Jia, C. Chen, Y. Zhou, M. Sultan Irshad, Q. Zhang, T. Jiang, D. Shi and J. You, Chem. Eng. J., 2023, 464, 142583 CrossRef CAS .
34. C. Liang, W. Zhang, C. Liu, J. He, Y. Xiang, M. Han, Z. Tong and Y. Liu, Chem. Eng. J., 2023, 471, 144500 CrossRef CAS .
35. W. Aftab, A. Mahmood, W. Guo, M. Yousaf, H. Tabassum, X. Huang, Z. Liang, A. Cao and R. Zou, Energy Storage Mater., 2019, 20, 401–409 CrossRef .
36. Z. Li, R. He, D. An, H. Chen, R. Tao, Z. Sun, J. Li, Z. Zhang, Y. Liu and C. Wong, Composites, Part A, 2022, 163, 107207 CrossRef CAS .
37. H. Cao, Y. Li, W. Xu, J. Yang, Z. Liu, L. Bai, W. Yang and M. Yang, ACS Appl. Mater. Interfaces, 2022, 14, 52411–52421 CrossRef CAS PubMed .
38. J. Zhang, J. Mu, S. Chen and F. Xu, J. Energy Chem., 2022, 75, 229–239 CrossRef CAS .
39. Y. Liao, J. Li, S. Li and X. Yang, J. Energy Storage, 2022, 52, 104751 CrossRef .
40. J. Cui, W. Li, Y. Wang, H. Yu, X. Feng, Z. Lou, W. Shan and Y. Xiong, Adv. Funct. Mater., 2021, 32, 2108000 CrossRef .
41. C. Yin, L. Weng, Z. Fei, L. Shi and K. Yang, Chem. Eng. J., 2021, 431, 134206 CrossRef .
42. P. Cheng, H. Gao, X. Chen, Y. Chen, M. Han, L. Xing, P. Liu and G. Wang, Chem. Eng. J., 2020, 397, 125330 CrossRef CAS .

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Footnote

† Electronic supplementary information (ESI) available. See DOI: https://doi.org/10.1039/d4nr02654c

This journal is © The Royal Society of Chemistry 2024