Metal–Organic Framework Enabling Poly(Vinylidene Fluoride)‐Based Polymer Electrolyte for Dendrite‐Free and Long‐Lifespan Sodium Metal Batteries

Sodium dentrite formed by uneven plating/stripping can reduce the utilization of active sodium with poor cyclic stability and, more importantly, cause internal short circuit and lead to thermal runaway and fire. Therefore, sodium dendrites and their related problems seriously hinder the practical application of sodium metal batteries (SMBs). Herein, a design concept for the incorporation of metal–organic framework (MOF) in polymer matrix (polyvinylidene fluoride‐hexafluoropropylene) is practiced to prepare a novel gel polymer electrolyte (PH@MOF polymer‐based electrolyte [GPE]) and thus to achieve high‐performance SMBs. The addition of the MOF particles can not only reduce the movement hindrance of polymer chains to promote the transfer of Na+ but also anchor anions by virtue of their negative charge to reduce polarization during electrochemical reaction. A stable cycling performance with tiny overpotential for over 800 h at a current density of 5 mA cm−2 with areal capacity of 5 mA h cm−2 is achieved by symmetric cells based on the resulted GPE while the Na3V2O2(PO4)2F@rGO (NVOPF)|PH@MOF|Na cell also displays impressive specific cycling capacity (113.3 mA h g−1 at 1 C) and rate capability with considerable capacity retention.

types of MOFs (e.g., Zr, Mn, Co, Mg, etc.) have been used successively as the sole or main material for separators in lithium-sulfur or -metal batteries over the past few years [21][22][23][24][25] and have shown remarkable results in surface modification of conventional separators such as Celgard, [26][27][28] bacteria cellulose, [29,30] glass fiber, [31] etc. to achieve inhibition of polysulfide shuttle and lithium dendrite growth.For instance, Hao et al. developed a functional Celgard separator by coating with Tibased MOF to successfully regulate the transport behavior of ions. [26]urther, the use of MOFs as novel fillers for the previously mentioned polymer matrixes is also feasible [32] and shows unique effects in modulating ion transport and other key electrochemical kinetic behaviors.For example, Zhang et al. reported a Zr-based MOF-PVA composite membrane and found that anions are adsorbed and anchored by the open metal sites of MOF particles, resulting in a high lithium ion transference number. [22]Analogously, activated HKUST-1 MOF particles were shown to be a multifunctional additive to modify PEO electrolytes which could improve the interfacial compatibility between electrode and electrolyte. [33,34]Another HKUST-1 MOF-based separator was investigated as an ionic sieve to alleviate the shuttle problem of soluble polysulfides by Bai et al. [35] All of the above cases highlight the ability of MOFs-based separators (or electrolytes) to improve electrochemical performance, but most of them focus only on lithium-based batteries or PEO matrix with low room temperature ionic conductivity and barren high voltage stability, while little efforts, especially at room temperature as well as intrinsic improvement mechanisms, have been devoted to stabilizing metal anodes in SMBs to achieve long-span life at higher current densities.
In light of this, a MOF-modified GPE for dendrite-free SMBs was designed, i.e., the HKUST-1 MOF was introduced into the classical PH matrix with acceptable voltage stability and room temperature ionic conductivity to make GPE by absorbing traditional organic electrolytes (hereinafter referred to as PH@MOF).Meanwhile, its composition was modulated and the intrinsic improvement mechanism was explored.It was shown that the introduction of MOF particles could not only promote the uptake of LEs and enhance the diffusion kinetics of sodium ions but also reduce the polarization by repulsing anions.Specifically, the ion transference number (from 0.42 to 0.64), ionic conductivity (from 9.11 × 10 −5 to 2.52 × 10 −4 S cm −1 ), and electrochemical stability window (from 4.54 to 4.73 V) are significantly increased.Benefiting from prolonging the nucleation time of sodium dendrites thus to inhibit its growth, the PH@MOF GPE-based cells exhibit impressive long-cycle stability.The related design concepts and beneficial properties are shown in Figure 1.It is expected that this work may broaden the prospects for achieving high-performance dendrite-free SMBs.

Results and Discussion
The MOF here as a classical and stable material consists of Cu ions and versatile 1,3,5-benzenetricarboxylate (BTC) 3− organic ligands with three oriented coordination modes and different binding sites, [36,37] as shown in the inset of Figure 2a.The XRD pattern shows that the characteristic peaks of the as-prepared MOF are the same as previously reported. [35,38]The FTIR analysis demonstrates the stretching characteristics of C=C on the benzene ring at 1618 and 1374 cm −1 , while the asymmetric and symmetric vibrational characteristics of C=O are shown at 1445 and 1551 cm −1 , respectively, further confirming the successful synthesis of the target MOF (Figure 2b). [39]In addition, the N 2 adsorption-desorption curve of the MOF exhibits typical microporous structure characteristic without hysteresis loop, corresponding to a specific surface area of 1109.7 m 2 g −1 and a pore volume of 0.59 cm −3 g −1 (Figure S1, Supporting Information).It can be seen that the MOF particles have the inherent advantages of high specific surface area and high porosity and have great potential as a carrier or host for LEs to improve the organic electrolyte absorption rate and safety.PH, as a semi-crystalline copolymer, inherits the crystal unit of PVDF and amorphous monomer of HFP, which ensures good mechanical properties as well as certain electrolyte adsorption ability, and is a good separator or skeleton for sodium-based batteries. [15,40]The digital photographs of the pristine PH matrix at different MOF contents (3, 6, 9, 12, 14, 17 wt.%)are given in Figure S2 (Supporting Information), and it is obvious that the color of the membrane gradually becomes darker as the content increases.Electrolyte uptake, ionic conductivity, and electrochemical stability window were used as evaluation indicators to optimize the addition amount of MOF, as shown in Figures S3, S4, and Table S1 (Supporting Information).For a more intuitive comparison, LE based on the Clegard separator was tested under the same conditions.When the amount of MOF is <9 wt.%, the electrolyte uptake (Figure 2d, Table S1, Supporting Information) and ionic conductivity (Figure 2e, Table S1, Supporting Information) are positively correlated with the MOF content.Optimally, with the aid of 9 wt.%MOF, the electrolyte uptake and ionic conductivity of PH@MOF are 202.2% and 2.52 × 10 −4 S cm −1 , respectively, much better than those of PH (only 123.9% and 9.11 × 10 −5 S cm −1 ).When the MOF content exceeds 9 wt.%, the corresponding indexes lose their competitive advantages probably due to the clumped MOF particles but are still higher than those without MOF, e.g., at additions up to 17 wt.%, the relevant parameters still reach 172.1% and 1.02 × 10 −4 S cm −1 , respectively (Table S1, Supporting Information).These results indicate that the electrolyte uptake is positively correlated with the ionic conductivity, which is similar to what was previously reported in the literature and also validates the porous nature of MOF. [34]Slightly differently, the electrochemical stability window gradually increases with increasing MOF content, i.e., from 4.54 V without MOF to 4.73 V at 9 wt.% and 4.82 V at 17 wt.%(Figure 2f and Figure S4, Supporting Information), which can be attributed to the high stability of MOFs. [41]And further Zeta potential results show that the MOF particles have a negative potential reaching −10.97 mV (Table S2, Supporting Information), implying that MOF can repulse anions by electrostatic forces to avoid the oxidation reaction at the anode electrolyte interface, thereby improving high voltage stability and reducing electrochemical polarization, which offers the possibility of matching high-voltage cathodes to develop higher energy density batteries. [42]Based on the above analysis,  and c) FESEM image and relevant EDS mappings of MOF.d) Electrolyte uptake results of LE, PH, and PH@MOF-9% GPEs.Inserts are the digital photos of the skeleton of these GPEs.e) EIS results of LE, PH, and PH@MOF-9% GPEs.Insert is the bar chart of their ion conductivities.f) LSV curves of LE, PH, and PH@MOF-9% GPEs.Insert is the bar chart of their electrochemical stability window.FESEM image of g) PH@MOF matrix, h) the corresponding cross-sections of each matrix, and i) PH@MOF GPE.
a sample with MOF content of 9 wt.% (hereinafter referred to as PH@MOF) was selected as a research object to further explore more advantages of MOF for GPE.And LSV was also carried out to further investigate the stability at the potential range close to Na + /Na of PH@MOF GPE.It can be seen in Figure S5 (Supporting Information) that the PH@MOF GPE exhibits the stability down to 0 V (vs Na + /Na) in the cathodic scan indicating its exceptional electrochemical stability.
The morphologies of the pristine PH and PH@MOF matrixes are shown in Figure 2g and Figure S6 (Supporting Information), respectively.Both matrixes have similar porous, indicating that the MOF particles are uniformly dispersed in the PH matrix, which is supported by further elemental distributions on the surface (Figure S7, Supporting Information) and in the cross-section (Figure S8, Supporting Information).It should be noted that this porosity is most likely due to the rapid volatilization of N, N-dimethylformamide solvent during the preparation process.Compared to the former, the latter shows a denser porosity due to the presence of MOF, which ensures adequate and rapid penetration and large adsorption of the LEs.Thanks to the small size of the MOF particles, there is no significant difference in thickness of the two matrixes (95.5 μm for PH and 95.3 μm for PH@MOF, Figure 2h).When the PH@MOF matrix is immersed in the electrolyte to form a GPE, the interaction-induced swelling causes the inherent pores to almost disappear, indicating that such matrix has the effect of preserving the liquid (FESEM image was observed in a high vacuum environment, Figure 2i).
From the XRD patterns of PH and PH@MOF matrix, there are two specific diffraction peaks at 18.5°and 20.3°, corresponding to the (100) and (110) crystallographic planes of the α-crystalline phase in PVDF (Figure 3a). [43]In particular, the intensity and half-peak width of both peaks in the PH@MOF matrix are reduced, indicating that the addition of MOF particles disturbs the regularity of the polymer molecular chain to some extent, thus promoting the reduction of the crystalline phase and irregular crystal orientation.Differential scanning calorimetry (DSC) analysis (Figure 3b) shows the melting temperature (T m ) of the PH@MOF matrix (155 °C) is slightly lower than that of the PH matrix (159 °C), and the same trend is observed for the melting enthalpy (ΔH m ) proportional to the crystallinity (46.9 J g −1 for PH matrix and 39.9 J g −1 for PH@MOF matrix, Figure S9, Supporting Information), suggesting that the presence of MOF particles improves the disordered nature of the polymer, which is consistent with the XRD results.Also, these results indicate that the polymer chains move more easily in the PH@MOF GPE, i.e., the sodium ions migrate more efficiently.The functional groups in the PH@MOF matrix were confirmed by FTIR (Figure 3c).The characteristic peaks of the PH matrix all appear in the spectrum of the PH@MOF matrix, indicating that the addition of MOF particles has no effect on the functional group structure of the pristine polymer.The peaks at 1401, 1230, 1167, and 1070 cm −1 can be attributed to the bending vibration of -CH 2 , symmetric and asymmetric stretching of -CF 2 and α-crystalline phase, respectively.While the peaks at 874 and 834 cm −1 represent the amorphous regions of the polymer, [44] the remaining peaks in the PH@MOF matrix can be assigned to the MOF particles.
Figure 3d depicts the ionic conductivity changes of LE, PH, and PH@MOF GPEs in the range of 0-70 °C based on EIS measurements (Figure S10, Supporting Information).Benefiting from the inherent advantages of high porosity and high liquid uptake of MOF particles, the ionic conductivity of the PH@MOF GPE is much higher than that of PH GPE and LE at any temperature.At 30 °C, the ionic conductivity of PH@MOF GPE is about 3.20 × 10 −4 S cm −1 and still reaches 1.12 × 10 −4 S cm −1 at 0 °C, which is higher than that of PH (1.17 × 10 −4 S cm −1 at 30 °C, 4.00 × 10 −5 S cm −1 at 0 °C) and LE (5.60 × 10 −5 S cm −1 at 30 °C, 1.17 × 10 −5 S cm −1 at 0 °C).The activation energy of every system was calculated by fitting the temperature-dependent conductivities curves making use of the Arrhenius formula [45] and the computed results differ little which means they have similar reaction mechanisms. [31]Further activation energy calculations based on the Arrhenius formula show that the activation energy of PH@MOF GPE (0.107 eV) is the lowest among the three, indicating that it has the fastest kinetic behavior.
During charging and discharging, the presence of an internal electric field will induce the migration of anions (e.g., ClO 4− ) and cations (e.g., Na + ) between the positive (cathode) and negative (anode) electrodes, so the conductivity of the LE is controlled by both anions and cations.However, only the charge transfer borne by sodium ions can reflect the unique charge and discharge characteristics of traditional batteries.A low sodium ion transference number (t Na þ ) means that more anions accumulate on the electrode surface leading to increased concentration polarization and thus increased overpotential, which not only limits the increase of energy and power density but also intensifies the formation of sodium dendrites. [46]Therefore, efforts should be made to improve the t Na þ along with the improved conductivity.The polarization curves based on LE, PH, and PH@MOF GPEs are shown in Figure 3e and Figure S11 (Supporting Information), respectively.It can be seen that the curve based on PH@MOF GPE is smoother, implying better interface stability.Quantitative comparison reveals that the t Na þ based on PH@MOF GPE is as high as 0.64, which is much higher than that based on LE (0.25) and PH (0.42) GPE (Figure 3f, Table S3, Supporting Information).These results further indicate that optimization of sodium ion migration efficiency can indeed be achieved by introducing MOF particles to leverage their repulsive forces.49][50][51][52] In addition to these important properties mentioned above, mechanical properties, thermal stability, and electrolyte wettability are also key indicators to assess the performance of GPEs.Excellent mechanical properties can ensure that the separator or matrix will not be punctured even in the presence of sodium dendrites.The stress-strain characteristics of PH and PH@MOF matrixes are compared in Figure 3g.It is clear that the PH@MOF matrix can withstand higher tensile strength (14.17 MPa for PH and 21.68 MPa for PH@MOF) due to the inherited flexibility of the PH matrix and the rigidity of the MOF particles, suggesting its higher safety.Furthermore, a comparison of the thermal stability of the different matrixes at 150 °C for 3 h is shown in Figure 3h.Obviously, the Celgard membrane shrinks almost completely due to its lower melting point, while the PH and PH@MOF matrixes do not change much in size, except for a slight change in color.More brutal thermal stability tests with an open flame show that the shape of the PH@MOF matrix could still be maintained (Figure S12, Supporting Information), i.e., it appears to be noninflammable, probably because the metal ions in the MOF particles promote the process of char formation as reported [53,54] which means the PH@MOF membrane can maintain the shortest time at burning state when it is burned with open flame.In general, the broad compatibility of a polymer matrix with electrolytes can be preliminarily evaluated by wettability.For commonly used electrolytes or organic solvents, the contact angle of the PH@MOF (e.g., 40  3i).
To proof these expectations, sodium plating/stripping behaviors in symmetric cells with different electrolytes were investigated at a current density of 5 mA cm −2 with an areal capacity of 5 mA h cm −2 (Figure 4a).Specifically, the polarization voltage of the symmetric cell based on LE shows an increasing trend with cycling and an obvious short circuit appears at about 85 h which could be caused by sodium dendrites (Figure 4b).For the symmetric cell assembled with PH GPE, although no significant short circuit occurs, its hysteresis voltage fluctuates drastically during the first ~140 h and stabilizes around ~70 mV during subsequent cycles.Of particular note is that the symmetric cell based on the PH@MOF GPE shows attractive stability and impressively low hysteresis voltage (~50 mV) over 800 h.The enlarged profiles in the 130-150 h interval (Figure 4c) and the intuitional hysteresis voltage trend comparison for the first 100 cycles of three different electrolytes (Figure 4d) again prove that Na|PH@MOF GPE|Na has a very stable cycling performance.The electrochemical impedance spectroscopy (EIS) results before and after cycling (100 cycles) can further elucidate the reasons for the differences in the hysteresis voltages of the two systems (Figure S13, Table S5, Supporting Information).It is worth mentioning that the cell based on PH@MOF GPE can achieve smaller polarization voltage and longer stable lifetime (up to 1000 h) at a current density of 1 mA cm −2 with an areal capacity of 1 mA h cm −2 (Figures S14 and S15, Supporting Information).Plating/stripping cycles at different current densities (0.2, 0.5, 1, and 2 mA cm −2 , Figure 4e) show that, in addition to the obvious advantage of ultra-low overpotential, the cell based on PH@MOF GPE remains stable as expected upon abrupt transfer to higher current densities, further indicating the presence of MOF particles can indeed effectively inhibit the formation of sodium dendrites.Specifically, the symmetric cell based on PH@MOF GPE successively exhibits stable Na plating/stripping at different current densities while for the PH-based symmetric cell, short circuits caused by sodium dendrites occur at 1 mA cm −2 after 120 h cycling which can match to the phenomenon of the sudden increasing voltage.Moreover, the polarization voltage of Energy Environ.Mater.2024, 7, e12511 PH-based symmetric cells in the following cycling regains stability which can be attributed to dissolution of dendrites.And notably, the maximum withstand current density of PH@MOF GPE is better than most of the GPEs reported so far (Table S6, Supporting Information). [12,20,34,48,55,56]ompared to symmetric cells based on LE and PH GPE, that of based on PH@MOF GPE shows its absolute superiority.To be more precise about the influence of PH@MOF GPE on sodium metal anode, ex-situ FESEM was employed to observe the surface morphology of sodium metal after the plating/ stripping process for 100 h at 2 mA cm −2 and 2 mA h cm −2 .Figure 5a presents the morphology of sodium metal based on LE.The accumulation of "dead Na" and moss-like dendrites forms a rough layered interface, which is consistent with the unstable electrochemical behavior of symmetric cell.In contrast, the surface morphology of  sodium metal based on PH GPE is slightly improved, but there are still furrows and crisscross cracks (Figure 5b) while that based on PH@MOF GPE is dense and uniform (Figure 5c), indicating the uniform deposition process.
Dendrite generation is accompanied by two key processes: nucleation and growth.For the former, the transference of cations (e.g., Na + ) and anions (e.g., ClO 4− ) is crucial. [46,57]Sand et al. [58] have pointed out that a critical time needs to be satisfied from nucleation to growth of the dendrite, which is called "Sand's Time" and has been widely recognized and applied.When the current density exceeds the limit, the concentration of cations near the anode drops to almost zero within Sand's time, which leads to a local space charge accompanied by a large electric field and a rapid deposition of nuclei.After exceeding this threshold, the growth of dendrite will occur.Therefore, prolonging the nucleation time of dendrite is an effective method to control dendrite nucleation and thus inhibit their growth. [59,60]To sum up, from the point of view of dendrite nucleation and growth mechanism, the nature of dendrite inhibition by PH@MOF GPE suppressing dendrites is based on the regulation of ion transport.The MOFs particles with negative charges further restricted the free transport of anions by strong electrostatic interaction which can facilitate the transfer of sodium ions and thus can prolonge the nucleation time of dendrite.Benefiting from this regulation, a homogeneous Na + flux is realized during Na plating/stripping process.Besides, Figure S16 (Supporting Information) show more details about the surface morphology of sodium metal from different magnification times which all display better surface condition of sodium anode of Na|PH@MOF GPE|Na.These results again prove that the designed PH@MOF GPE successfully realizes the regulation of sodium ion transport behavior and effectively avoids the growth of sodium dendrites.Figure 5d illustrates the Energy Environ.Mater.2024, 7, e12511 plating/stripping process of sodium with different electrolytes and their corresponding morphologies of the sodium anode.
Based on the above analysis, to verify the practicality of the GPE design, SMBs were constructed with sodium metal as the anode and NVOPF (Figures S17 and S18, Supporting Information) as the cathode.As shown in Figure 6a, compared with the SMBs based on LE and PH GPE, the NVOPF|PH@MOF GPE|Na cell can not only exhibit an impressive initial capacity (113.3 mA h g −1 ) but also shows considerable long-term cycle stability over 400 cycles with a capacity retention of 80.4% (91.1 mA h g −1 ).][63][64][65][66] It should be noted that the initial capacities of the NVOPF|LE|Na and NVOPF|PH GPE|Na cells are only 99.2 and 96.5 mA h g −1 with capacity retentions of 53.9% and 69.3% after 400 cycles, respectively.Figure 6b displays the differential capacity curves based on PH@MOF GPE in which the shape and position of the peaks almost keep unchanged, and meanwhile, the trend of curves is in great accordance with the CV curves (Figure S19, Supporting Information), indicating the good reversibility of electrochemical reaction. [67]From the charge and discharge profiles of the three cells at the given 50th cycle (Figure 6c), the cell based on PH@MOF GPE maintains the lowest polarization voltage and higher capacity compared with the other two cells.
The rate capabilities of the three cells were further compared in Fig- ure 6d.,69] To be specific, it delivers a capacity of 39.0 mA h g −1 at 8 C (Figure 6e), while the NVOPF|LE|Na and NVOPF|PH GPE|Na cells can only exhibit poor capacities of 9.0 and 1.0 mA h g −1 (Figure S20, Supporting Information), respectively.The ratios between the actual capacity (C) at corresponding current density and the reference capacity of the three cells were compared in Figure 6f, where the specific discharge capacity at 0.5 C was defined as the reference capacity (C 0.5C ).The cell based on PH@MOF GPE shows higher capacity retention, and its reversible capacity can be significantly recovered to 90.7% (108.5 mA h g −1 ) of the initial discharge capacity when the current density is switched back to 1 C rate while those based on LE and PH GPE can only be recovered to 85.7% (71.1 mA h g −1 ) and 82.2% (78.1 mA h g −1 ), respectively.

Conclusion
In summary, a MOF-in-polymer GPE with a high sodium ion transference number was designed by introducing MOF particles into the PH polymer matrix for dendrite-free SMBs.On the one hand, the addition of MOF particles not only can absorb more organic electrolytes by virtue of its high porosity, thus improving the ionic conductivity, but also can increase the amorphous region in a polymer matrix which facilitates the movement of polymer chains, thus benefiting the transfer of sodium ion.On the other hand, the MOF particles with a negative charge can repulse the anions due to the repulsive force, promoting the transport of sodium ions.Thus, an impressive and stable sodium plating/stripping cycling performance was exhibited in symmetric cell based on the resulted GPE over 800 h with a tiny overpotential, indicating the addition of MOF particles could promote a uniform sodium deposition.Moreover, the SMB assembled with PH@MOF GPE also shows better performance in terms of specific capacity and capacity retention.The GPE proposed in this work may offer a novel idea for achieving high-performance and dendrite-free SMBs.

Experimental Section
Detailed experimental methods can be found in the Supporting Information.
Figure 2c presents the microstructure and EDS mapping of the prepared MOF particles, revealing their octahedral structures with regular facets and uniform elemental distribution.

Figure 2 .
Figure 2. a) XRD, b) FTIR spectrum,and c) FESEM image and relevant EDS mappings of MOF.d) Electrolyte uptake results of LE, PH, and PH@MOF-9% GPEs.Inserts are the digital photos of the skeleton of these GPEs.e) EIS results of LE, PH, and PH@MOF-9% GPEs.Insert is the bar chart of their ion conductivities.f) LSV curves of LE, PH, and PH@MOF-9% GPEs.Insert is the bar chart of their electrochemical stability window.FESEM image of g) PH@MOF matrix, h) the corresponding cross-sections of each matrix, and i) PH@MOF GPE.

Figure 3 .
Figure 3. a) XRD, b) DSC, and c) FTIR results of PH and PH@MOF matrixes.d) Temperature-dependent conductivities of LE, PH, and PH@MOF GPEs.e) Polarization curve with a 10 mV DC voltage of PH@MOF GPE.Inset shows Nyquist plots before and after polarization along with the fitting circuit.f) Bar diagram for comparison of sodium ion transference numbers.g) Stress-strain curves of PH and PH@MOF matrixes.h) Thermal stability and i) electrolyte contact angle comparison between Celgard, PH, and PH@MOF matrixes.

Figure 4 .
Figure 4. a, b) Voltage-time curves of the symmetric cell with different electrolytes at a current density of 5 mA cm −2 .Insets are the enlarged voltage profiles of c) Na|PH@MOF GPE|Na, and Na|PH GPE|Na at 130-150 h.d) Hysteresis voltage trend diagram based on three different electrolytes at the first 200 cycles.e) Voltage-time curves of the symmetric cells with different electrolytes at different current densities.

Figure 5 .
Figure 5. FESEM image of the Na metal anode after cycling at 2 mA cm −2 for 100 h with different electrolytes: a) LE, b) PH GPE, and c) PH@MOF GPE.d) Schematic illustration of sodium plating/stripping behaviors with different electrolytes.

Figure 6 .
Figure 6.a) Cycling performance of the three cells.b) The relevant capacitance differential curve based on PH@MOF GPE at the first three cycles.c) Comparison of polarization voltage between three systems at 50th cycles.d) Rate performance of the three cells.e) Charge and discharge profiles based on PH@MOF GPE at given current density.f) The ratio between the discharge capacity (C) and the reference capacity (C 0.5C ) at various current densities.Comparison of g) cycling performance and h) rate properties of SMBs with previously reported GPEs.
.63 °in PC, 19.23 °in PC with FEC) matrix is significantly smaller than that of the Celgard (e.g., 68.06 °in PC, 68.51 °in PC with FEC) and PH (e.g., 50.11 °in PC, 24.42 °in PC with FEC) matrixes, indicating that the introduction of MOF particles also facilitates the broadening of the compatibility of the polymer matrix (Figure