A Web‐like Three‐dimensional Binder for Silicon Anode in Lithium‐ion Batteries

Si anode is of paramount importance for advanced energy‐dense lithium‐ion batteries (LIBs). However, the large volume change as well as stress generates during its lithiation‐delithiation process poses a great challenge to the long‐term cycling and hindering its application. Herein this work, a composite binder is prepared with a soft component, guar gum (GG), and a rigid linear polymer, anionic polyacrylamide (APAM). Rich hydroxy, carboxyl, and amide groups on the polymer chains not only enable intermolecular crosslinking to form a web‐like binder, A2G1, but also realize strong chemical binding as well as physical encapsulating to Si particles. The resultant electrode shows limited thickness change of merely 9% on lithiation and almost recovers its original thickness on delithiation. It demonstrates high reversible capacity of 2104.3 mAh g−1 after 100 cycles at a current density of 1800 mA g−1, and in constant capacity (1000 mAh g−1) test, it also shows a long life of 392 cycles. Therefore, this soft‐hard combining web‐like binder illustrates its great potential in the future applications.


Introduction
[3][4] Currently, LIBs based on graphite anode have almost got their maximum energy density of about 300 Wh kg −1 , while it is still hard to meet the market demand.[7] Besides, it is also an earth abundant material which makes it easily available.However, Si particles exhibit dramatic volume change ( > 300%) during the lithiation-delithiation process, causing a series of drawbacks. [8,9][12] Up to now, several strategies are being adopted to address these issues, such as microstructure optimization of Si particles to suppress its pulverization, [13][14][15][16] preparing composite materials (most typically, Si/graphite, or short as Si/C) to buffer the electrode level volume change, [15,17,18] choosing appropriate electrolytes to stabilize the SEI (such as glyme-based electrolytes, [19] nonflammable localized high-concentration electrolytes, [20] etc.).Among which binder is no doubt a convenient and effective approach as it can not only guarantee the electrode structure integrity, [21,22] but also interact with the electrolyte and thus to influence the SEI component. [23,24]In this consideration, many novel binders are developed in the past decade.
Typically, there exists abundant -OH groups and trace SiO 2 on the Si nanoparticles, which makes it possible to realize strong hydrogen binding effect with those binders with hydroxyl, carboxyl, or similar groups with [23][24][25][26][27][28] on which strong adhesion, good dispersion ability, [29] or even self-healing [30,31] is achieved.For example, Yushin's group found that polyacrylic acid (PAA) could increase the cycle stability of the nanosized Si electrode for its rich carboxyl group, which not only enhanced the adhesion, but also contributed in ion transportation and SEI formation. [23]They also reported that the cell performance can be further enhanced by using sodium alginate (SA) as binder due to its optimal hydroxyl and carboxyl-rich structure. [25]uar gum (GG) was used in Sun's work and demonstrated better performances in nanosized Si electrode than that of SA, and the author attributed it to the stronger interaction force with Si as well as the -CH 2 CH 2 O-(EO)-like Li + transport ability of GG. [26] Focused on the molecular formula, these binder optimizations have greatly enhanced cycle stability of Si electrodes, while the physical structure may also greatly influence the adhesion and thus the electrochemical performances.The pioneer work of Messersmith's group illustrated reversible strong adhesion inspired by mussels (chemical binding) and geckos (physical nanoadhesive), the geckel nanoadhesive is less surface selective, which makes it less dependent on surface chemicals such as -OH or SiO 2. [32] Choi and coworkers developed a sliding chain-structured PR-PAA binder which contains different functional groups, carboxyl for adhesion, EO for ion conducting, and αcyclodextrin (α-CD) for stress dissipation. [28]This binder can even Si anode is of paramount importance for advanced energy-dense lithium-ion batteries (LIBs).However, the large volume change as well as stress generates during its lithiation-delithiation process poses a great challenge to the longterm cycling and hindering its application.Herein this work, a composite binder is prepared with a soft component, guar gum (GG), and a rigid linear polymer, anionic polyacrylamide (APAM).Rich hydroxy, carboxyl, and amide groups on the polymer chains not only enable intermolecular crosslinking to form a web-like binder, A2G1, but also realize strong chemical binding as well as physical encapsulating to Si particles.The resultant electrode shows limited thickness change of merely 9% on lithiation and almost recovers its original thickness on delithiation.It demonstrates high reversible capacity of 2104.3 mAh g −1 after 100 cycles at a current density of 1800 mA g −1 , and in constant capacity (1000 mAh g −1 ) test, it also shows a long life of 392 cycles.Therefore, this soft-hard combining web-like binder illustrates its great potential in the future applications.
enable the long-term work of micro-sized Si, which highlighted the feasibility of microstructure design in binder for Si.
Herein, we designed a composite binder, A2G1, based on the intermolecular interactions between the soft GG and rigid anionic polyacrylamide (APAM).APAM is a commonly used flocculant in water purification due to its strong electrostatic force as well as capture effect of the linear molecular chain. [33]In this work, it was used as the backbone for GG, and a web-like structure was obtained as shown in Scheme 1, the soft GG is loosely packed among the APAM branches, chemical binding and the web structure could encapsulate the Si particles effectively.During the lithiation process, the GG chains are unfolded simultaneously so that to keep the strong adhesion.As a result, the electrode shows limited volume change during charge/discharge and delivers a high specific capacity of 2104.3 mAh g −1 at current density of 1800 mAh g −1 after 100 cycles.

Results and Discussion
The scanning electron microscopy (SEM) image and X-ray diffraction (XRD) of nano Si are shown in Figure S1, Supporting Information.GG is a polysaccharide extracted from the seeds of Cyamopsis tetragonolobus, consisting of linear chains of (1 → 4)-β-D-mannopyranosyl units with α-D-galactopyranosyl units attached through (1 → 6) linkages, rich in hydroxyl. [26]APAM is an anionic polymer with various amide and carboxyl groups. [33,34]The molecular formula and corresponding solution pictures of GG and APAM are shown in Figure S2, Supporting Information.Obviously, GG solution is thick and has weak liquidity due to the rich -OH groups on the molecular chain, which lead to intense inter and intra-hydrogen bonds even in the water solution.APAM solution is thin and has strong liquidity even if its molecular weight is quite high, which may be due to the strong electrostatic force hindered the chain from agglomeration.The A2G1 solution shows moderate viscosity and certain wiredrawing effect (Figure S4a, Supporting Information).The solution is then coated into a film and dried.The GG film is soft, as shown in Figure S3, Supporting Information.APAM film is too brittle to form a flexible film.Meanwhile, the A2G1 film is flexible and foldable as shown in Figure S4b, Supporting Information.AFM test was performed on those films and the result is shown in Figure S5, Supporting Information.It can be noted that GG and APAM exhibit the lowest and highest young's modulus, respectively.Meanwhile, the A2G1 presents a moderate value distributed in two regions, which is clearly a sign of the complex between GG and APAM, indicating the formation of the rigid-soft skeleton.
To study the interactions between GG and APAM, GG, APAM, and A2G1 were tested by FTIR as shown in Figure 1a.For GG, the peak at around 3440, 2924, 1654, 1435, 1155, 1068, and 1005 cm −1 are ascribed to the O-H stretching, C-H stretching, O-C-O stretching, -CH 2 stretching, C-OH, CH 2 -OH, and C-O-C asymmetric vibration, respectively.For APAM, the peak located at around 3440, 3193, 2940.9, 1691, 1618, 1562, 1454, 1404, 1323, and 1176 cm −1 is corresponding to the O-H/N-H stretching, asymmetric stretching of -NH 2 , C-H stretching, C=O stretching, N-H bending, N-H in plane deformation, -CH 2 vibration, COO − vibration, C-N stretching and C-O vibration, respectively.After mixing the two polymers, the absorption peaks of -C-H, -CH 2 , -CH 2 OH of A2G1 shared by both shift to 2929, 1454, and 1082 cm −1 , indicating that a chemical interaction occurred.The absorption peak of C-OH of A2G1 from GG shift to lower wavenumbers of 1149 cm −1 .In the meantime, the absorption peaks of -NH 2 asymmetric stretching, -C=O vibration, -N-H bending, -N-H in plane, COO − vibration, C-N stretching from APAM shift to 3195, 1670, 1610, 1546 cm −1 , 1410, and 1327 cm −1 , respectively.The shift of these peaks is ascribed to the formation of intermolecular hydrogen bonds, electrostatic interaction, and ion-dipolar interactions between GG and APAM. [35,36]As shown in Figure 1c, XRD was also conducted to verify the interactions between GG and APAM.Consistent with the FTIR results, the new broad peak between 14.9°and 26.4°in the A2G1 patterns proves the formation of hydrogen bond and iondipole interactions between GG and APAM.From Figure S6, Supporting Information, the absorption peak at 4.79 ppm originates from D 2 O solvent.The peaks at 1.60 and 2.2 ppm on the APAM spectrum can be assigned the -CH 2 -(a) and -CH-(b) groups, respectively.After mixing with GG, the peak positions of -CH 2 -(a) and -CH-(b) shifted to 1.56 and 2.15 ppm, respectively, which also proves the interaction between APAM and GG.
After mixing nano Si with A2G1, the characteristic peak at 3440, 2929, 1670 cm −1 shift to lower wavenumbers due to the formation of intermolecular hydrogen bond between A2G1 and -OH groups of nano Si particles (Figure 1b).In addition, XPS was also used to study the interaction between A2G1 and Si as shown in Figure 1d, the Si 2p spectra of Si can be resolved into two peaks corresponding to Si-Si at 98.6 eV and Si-O at 102.5 eV.After mixing with A2G1, the peak of Si-O shifted to 103.2 eV, indicating a strong interaction between them.
To investigate the binder effect on the mechanical stability of the electrode film, we conducted 180°peeling test for Si@GG, Si@APAM, and Si@A2G1 electrodes (Figure S7, Supporting Information).Si@GG shows the best adhesion with copper foil, followed by Si@A2G1, and finally Si@APAM.We believe that the strong adhesion between Si@GG electrode sheet and copper foil is since GG contains a large number of hydroxyl groups.The content of functional groups in APAM binder is lower than that in GG, resulting in lower peeling force.The adhesion of Si@A2G1 electrode is between Si@GG and Si@APAM.Then, we explore the performance of nano Si electrodes with different binders through a series of electrochemical tests.The cycling performance of electrodes employing different binders at a current density of 0.36 A g −1 in the initial three Scheme 1. Stabilization mechanism of the electrode using the web-like binder, A2G1.
Energy Environ.Mater.2024, 7, e12482 2 of 7 cycles and 1.8 A g −1 in the following cycles were compared in Figure 2a and Figure S8, Supporting Information.The Si@A2G1 electrode exhibits superior cycling stability; it delivers the highest specific capacity of 2104.3 mAh g −1 after 100 cycles.The specific capacities of other electrodes are 612.6 (GG), 1437.4 (APAM), 1785 (A3G1), 1405.9 (A1G1), 1400 (A1G2), and 1344.8 mAh g −1 (A1G3), respectively.In addition, Si@GG and Si@A2G1 show high initial capacity of 3257.7 and 3398.8 mAh g −1 , respectively, while Si@APAM electrode only displays 2647.1 mAh g −1 .The corresponding initial coulombic efficiencies (ICE) of Si@GG, Si@APAM, and Si@A2G1 are 83.85%,83.42%, and 86.33%, respectively, suggesting that the Li + is more completely inserted and extracted during the lithiation and delithiation process in Si@A2G1 electrode, as shown in Figure S9, Supporting Information. [37]Figure 2b presents the long-term cycle performance of Si@GG, Si@APAM, and Si@A2G1 electrodes with a constant capacity of 1000 mAh g −1 at 1.8 A g −1 .The Si@A2G1 electrodes show a duration of 392 cycles, while the Si@GG and Si@APAM electrodes only maintain 99 and 162 cycles, respectively.Figure 2c depicts the rate performance of the Si electrode with different binders at progressively increased current densities.The Si@A2G1 electrode delivers the best rate capability with a high capacity of 966 mAh g −1 even under 10.8A g −1 , while Si@GG and Si@APAM electrodes only display 225 and 21 mAh g −1 .Furthermore, the cycling performance of electrodes at a high current density of 3.6 A g −1 was also tested (Figure 2d).The Si@A2G1 electrode delivers an outstanding cycling stability and maintains the capacity of 2262.4 mAh g −1 after 50 cycles.
The thickness of the Si anodes using different binders before cycling, after the first lithiation (fully discharged to 0.01 V at a current density of 360 mA g −1 ), and after the first delithiation (fully charged to 2.0 V under the same current density) was measured by SEM, as shown in Figure 3.It can be observed that the original thicknesses of the electrode are 27.4,24.1, and 26.2 μm, respectively.Then, the electrodes were fully discharged at 0.1C rate, and the lithiation process leads to an increase in thickness to 50.71, 36.21, and 28.62 μm for Si@GG, Si@APAM, and Si@A2G1 electrodes, respectively.The corresponding volume expansion rate is 85%, 50%, and 9%, respectively.The electrode thickness shrinks to 30.04, 24.55, and 26.5 μm after delithiation for Si@GG, Si@APAM, and Si@A2G1, respectively.The cross-sectional SEM images of Si@GG, Si@A-PAM, and Si@A2G1 after 100 cycles were measured at the delithiated state (Figure 3jl).It can be noted that the thickness change of Si@GG, Si@APAM, and Si@A2G1 is 204.96%,109.58%, and 54.19%, respectively.Obviously, the volume changes of Si@A2G1 are significantly smaller than that of Si@GG and Si@APAM electrodes, and its no significant crack appears on the Si@A2G1 electrode.This result implies that the A2G1 binder is more effective to suppress the dramatic volume changes of the Si electrodes compared to the GG and APAM.
In order to further understand the outstanding electrochemical performance of Si@A2G1 electrode, the interfacial interactions of electrodes employ GG, APAM, or A2G1 as binder were investigated by the EIS, as shown in Figure 4a-c.Figure 4d displays the equivalent circuit of the Nyquist plots, where R b , R I1 , R I2, and R ct are corresponding to the bulk resistance, interfacial resistance between Li or Si electrode and electrolyte, and the charge transfer resistance, respectively. [38,39]The fitting parameters are summarized in Table S1, Supporting Information.Si@GG electrode presents a relatively small and stable R b , while the R I2 and R ct have a large and unstable increase, which origins from the severe pulverization of nano Si particles and overgeneration of SEI leading to the degradation of electrolyte.Consistent with the crosssectional SEM of Si@GG shown in Figure 3, GG cannot effectively endure the volume changes of nano Si.The above problems result in the sharp capacity decline of Si@GG electrode.Different from the Si@GG electrode, the EIS of Si@APAM and Si@A2G1 electrode exhibits a trend of gradual decrease from 3 to 25 cycles and is relatively stable with the increase in the number of cycles.This implies the formation of a stable electrochemical environment of the Si@APAM and Si@A2G1 electrodes.However, the Si@APAM electrode possesses the largest R b , which may result from the strong electrostatic attraction of the carboxyl group toward Li + that interrupt the charge transfer process, and further lead to lower reversible capacity as shown in Figure 2. Employing A2G1 as binder is beneficial to inhibit the volume changes of nano Si particles and ensure the long cycle stability of the electrode.It can be noted that although the Si@A2G1 electrode shows a high R ct value in the initial stage (which may also attribute to the APAM component), it decreased in the following cycles and stabilized owing to the soft and Li + conductive GG component.Therefore, we attribute the advantages of the A2G1 binder to the synergy of soft GG and rigid skeleton of APAM.
X-ray photoelectron spectroscopy is an effective method to study the tiny changes of the composition of Si surface.We used the XPS measurement to deeply study the composition of SEI layer of Si@GG, Si@APAM, and Si@A2G1 electrodes after 100 cycles, as shown in  [40] The amide group on APAM is the only source of C-N, while it shows a higher intensity in Si@A2G1 than that of Si@APAM, which implies that the Si@APAM may be covered by a thicker SEI.Besides, the O-C=O group could be assigned to the carboxyl group on APAM or the Li 2 CO 3 in SEI, and it shows the highest intensity in Si@GG, in which no APAM is used, therefore, the thickest SEI was formed on this electrode, which is in coincidence with the high interfacial resistance in EIS test.This result is further proved by the O1s spectra in Figure 5b, where the C=O peak is higher than the others.The P 2p spectra also prove the adverse effect of GG as shown in Fig- ure 5c.The peaks located at 134 and 137 eV could be assigned to Li x PF y and Li x PF y O z , respectively. [41,42]Si@GG electrode exhibits the highest content of Li x PF y and Li x PF y O z , indicating that the electrolyte is severely decomposed during the cycle.In addition, the electrode shows the peaks located around 685 and 687 eV are corresponding to LiF and Li x PF y in the F 1 s spectra (Figure 5d). [43]The highest content of LiF of Si@A2G1 electrodes indicates that Si@A2G1 is beneficial for the formation of stable SEI films and leads to an excellent electrochemical performance.
Through the SEM pictures of the electrode with different binders after 100 cycles at the current density of 1.8 A g −1 , obvious differences in surface morphology are observed, as shown in Figure 6 and Figure S10, Supporting Information.The incorporated web-like binder ensures the A2G1 electrode stability by effectively integrating the Si particles in the continuous deformation environment. [44]orresponding with the above tests, the surface morphology of Si@A2G1 delivers tremendous superiority.In contrast to the Si@GG and Si@APAM electrodes, which show large or small cracks in the surface after cycling, the Si@A2G1 electrodes retain the most intact surface, with almost no cracks even over a large area (Figure 6c).Further magnifying the electrode surface, the Si@A2G1 electrodes still exhibit smooth and continuous morphology (Figure S10f, Supporting Information).With a higher magnification, as shown in Figure S10g-i, Supporting Information, the Si particles in the Si@GG electrode present severe pulverization (Figure S10g, Supporting Information, red framed), which proves that the soft GG chains could not effectively endure the volume changes of nano Si.The Si@APAM electrode displays intermittent binder network, and large quantities of Si particles are directly exposed, which indicates that the linear APAM cannot guarantee the electrode integrity, as shown in Figure S10h, Supporting Information.On sharp contrast, the Si@A2G1 electrode possesses a continuous binder conductive network without Si pulverization or exposure (Figure S10i, Supporting and Coulombic efficiency of electrodes at a current density of 0.36 A g −1 in the initial three cycles and 1.8 A g −1 in the following cycles.b) Long-term cycle performance of Si@GG, Si@APAM, and Si@A2G1 electrodes at a constant capacity of 1000 mAh g −1 at the current density of 1.8 A g −1 .c) Rate performance of electrodes, current density ranging from 0.36 to 10.8 A g −1 .d) Reversible capacity and Coulombic efficiency of electrodes at a current density of 0.36 A g −1 for the first three cycles and at 3.6 A g −1 for the following cycles.
Energy Environ.Mater.2024, 7, e12482 Information); most of the particles are tightly encapsulated.To observe the structure of the binder more clearly, we further enlarged the magnification as shown in Figure 6d-f.The GG exhibits a soft structure, APAM shows a rigid skeleton structure, while the A2G1 presents a continuous web-like network structure just like illustrated in Scheme 1, and this hard-soft synergistic effect enabled long-term cycle stability of the Si electrodes even under high current density.
We also analyze the porosity of the electrode before and after cycles to further understand its stabilization mechanism.Figure S11, Supporting Information, illustrates the image processing treatment applied to Figure S10af, Supporting Information, the SEM images of electrode before and after cycles through Image J software.Porosities of the fresh electrode were calculated by the equation: [45] Where P c is the porosity obtained by calculation; V is the volume of the electrode without current collector; C is the mass ratio of Si, Super P, or binder in the electrode; ρ stands for the density of each component; and W represents the mass loading of the electrode.
The electrode porosity before the cycle was analyzed by both the equation and image processing treatment (P ip-f ), and the cycled electrode porosity was obtained via Image J (P ip-c ) as summarized in Table S2, Supporting Information.It can be noted that P ip-f is quite close to P c , which testified the feasibility of the software.Porosity of all the fresh electrodes is similar, while after the cycle, it decreased to a lower level for the Si@A2G1 electrode than the others, implying that volume expansion of Si can be largely offset by the porosity shrink when the web-like binder is used.As to the electrodes with GG or APAM, the limited porosity variation cannot offset the volume expansion, thus large thickness change occurred as evidenced in Figure 3, which further lead to continuous capacity decay in the charge/discharge process.

Conclusion
Electrode structure integrity is the perquisite for the long-term cycle stability of Si.Herein this work, a web-like binder A2G1 is designed and prepared via a facile solution mixing method of two eco-friendly watersoluble polymers, GG, and APAM.The soft and Li + conductive GG chains were loosely packed among the rigid APAM branches, the rich hydroxy and carboxyl groups on the molecular chains enabled intense and effective binding with Si.Moreover, the web-like structure could still encapsulate the Si particles on their lithiation and expansion by chain extending.As a result, the Si electrode with A2G1 binder showed limited thickness change on lithiation of merely 9%, much lower than that of GG (85%) and APAM (50%).The electrode also demonstrated impressive cycle stability and rate performance; it showed a high reversible capacity of 2104.3 mAh g −1 after 100 cycles at the current density of 1800 mA g −1 , and 966 mAh g −1 at 10.8 A g −1 , which exhibit the feasibility of this soft-hard combining web-like binder.Cross-sectional SEM images of Si@GG, Si@APAM, and Si@A2G1 electrodes before cycling a-c), after the first lithiation d-f) and delithiation g-i), as well as after 100 cycles, delithiated state j-l).   .SEM images of the Si@GG a, d), Si@APAM b, e), and Si@A2G1 c, f) electrodes after 100 cycles at different magnifications.

Figure 5 .
Figure 5.The peaks in C 1 s spectra (Figure 5a) located at 284.8, 286, 286.3, 288, 289, and 289.9 eV can be assigned to C-C, C-N, C-O, C=O, O-C-O, and O-C=O, respectively.[40]The amide group on APAM is the only source of C-N, while it shows a higher intensity in Si@A2G1 than that of Si@APAM, which implies that the Si@APAM may be covered by a thicker SEI.Besides, the O-C=O group could be assigned to the carboxyl group on APAM or the Li 2 CO 3 in SEI, and it shows the highest intensity in Si@GG, in which no APAM is used, therefore, the thickest SEI was formed on this electrode, which is in coincidence with the high interfacial resistance in EIS test.This result is further proved by the O1s spectra in Figure5b, where the C=O peak is higher than the others.The P 2p spectra also prove the adverse effect of GG as shown in Fig-ure 5c.The peaks located at 134 and 137 eV could be assigned to Li x PF y and Li x PF y O z , respectively.[41,42]Si@GG electrode exhibits the highest content of Li x PF y and Li x PF y O z , indicating that the electrolyte is severely decomposed during the cycle.In addition, the electrode shows the peaks located around 685 and 687 eV are corresponding to LiF and Li x PF y in the F 1 s spectra (Figure5d).[43]The highest content of LiF of Si@A2G1 electrodes indicates that Si@A2G1 is beneficial for the formation of stable SEI films and leads to an excellent electrochemical performance.Through the SEM pictures of the electrode with different binders after 100 cycles at the current density of 1.8 A g −1 , obvious differences in surface morphology are observed, as shown in Figure6and FigureS10, Supporting Information.The incorporated web-like binder ensures the A2G1 electrode stability by effectively integrating the Si particles in the continuous deformation environment.[44]Corresponding with the above tests, the surface morphology of Si@A2G1 delivers tremendous superiority.In contrast to the Si@GG and Si@APAM electrodes, which show large or small cracks in the surface after cycling, the Si@A2G1 electrodes retain the most intact surface, with almost no cracks even over a large area (Figure6c).Further magnifying the electrode surface, the Si@A2G1 electrodes still exhibit smooth and continuous morphology (FigureS10f, Supporting Information).With a higher magnification, as shown in FigureS10g-i, Supporting Information, the Si particles in the Si@GG electrode present severe pulverization (FigureS10g, Supporting Information, red framed), which proves that the soft GG chains could not effectively endure the volume changes of nano Si.The Si@APAM electrode displays intermittent binder network, and large quantities of Si particles are directly exposed, which indicates that the linear APAM cannot guarantee the electrode integrity, as shown in FigureS10h, Supporting Information.On sharp contrast, the Si@A2G1 electrode possesses a continuous binder conductive network without Si pulverization or exposure (FigureS10i, Supporting

Figure 2 .
Figure 2. Electrochemical performance of nano Si anodes with different binders.a) Reversible capacityand Coulombic efficiency of electrodes at a current density of 0.36 A g −1 in the initial three cycles and 1.8 A g −1 in the following cycles.b) Long-term cycle performance of Si@GG, Si@APAM, and Si@A2G1 electrodes at a constant capacity of 1000 mAh g −1 at the current density of 1.8 A g −1 .c) Rate performance of electrodes, current density ranging from 0.36 to 10.8 A g −1 .d) Reversible capacity and Coulombic efficiency of electrodes at a current density of 0.36 A g −1 for the first three cycles and at 3.6 A g −1 for the following cycles.

Figure 4 .
Figure 4. Nyquist plots of electrodes based on a) GG, b) APAM, and c) A2G1 binders.d) The equivalent circuit of the Nyquist plots.

Figure 6
Figure 6.SEM images of the Si@GG a, d), Si@APAM b, e), and Si@A2G1 c, f) electrodes after 100 cycles at different magnifications.