Bioinspired design of Na-ion conduction channels in covalent natural frameworks for quasi-solid-state sodium batteries

Materials synthesis and characterization

A COF with a exactly designed pore construction and negatively charged modified inwalls was ready based on a biomimetic design idea (Fig. 1 and Supplementary Fig. 1). The COF with excessive crystallinity and nanoscale pore construction (TPBD) was synthesized via a solvothermal technique²⁹. The powder X-ray diffraction (PXRD) sample of TPBD exhibits a particular 2θ peak at a low angle of three.4°, attributed to the (100) airplane. The broad peak at the next 2θ diploma (~27°) corresponds to the π-π stacking impact of the (001) airplane between COF layers, and the d spacing is calculated to be ~3.29 Å (Supplementary Fig. 2). To imitate the destructive inwalls of organic Na⁺ channels, the destructive (–COOH)-modified COF (TPDBD) was modified by changing the benzidine (BD) with a 4,4’-diamino-[1,1’-biphenyl]−2,2’-dicarboxylic acid (DBD) monomer. To additional improve the negativity of the COF inwalls, the H⁺ of –COOH was exchanged with Na⁺ via a Na-activation course of with 1 mM NaOH, and the pattern was outlined as “TPDBD-CNa”. As a result of elevated repulsion between COF layers after the introduction of –COO^– teams, the diffraction peak of the (001) airplane of TPDBD-CNa decreases to ~26°, and the corresponding d spacing will increase to ~3.39 Å. Furthermore, the –COO^– teams anchored onto the COF have a big steric hindrance impact and disturb the π − π stacking interactions among the many layers (Supplementary Fig. 3), corresponding with a wider interface distribution at a low angle³⁰. Such decrease crystallinity of TPDBD is conducive to quick ion transport via the efficient elimination of grain boundaries^19,31,32,33. The Brunauer‒Emmett‒Teller (BET) floor space and complete pore quantity of TPBD are 281 m² g^–1 and 0.42 cm³ g^–1, respectively, which lower to 74 m² g^–1 and 0.30 cm³ g^–1 for TPDBD because of the introduction of –COO^– teams (Supplementary Fig. 4). After Na-activation, the precise floor and pore quantity of TPDBD-CNa improve once more to 116 m² g^–1 and 0.60 cm³ g^–1 because of the prevention of the formation of protic acid cross-linked oligomers contained in the pores. Apparently, the distances between the adjoining carbonyl purposeful teams anchored on the COF inwalls are measured within the vary of 6.7–11.6 Å, which is analogous to that of the anionic terminal-modified sub-nanostructure ion channels of the cell membrane (Supplementary Fig. 5)^26,27.

In contrast with these of the BD and DBD monomers, the N-H stretching bands of free diamine (3100-3300 cm^–1) within the Fourier remodel infrared (FTIR) spectra of TPBD, TPDBD, and TPDBD-CNa fully disappear, indicating the whole response of amino teams (Fig. 2a and Supplementary Fig. 6). Furthermore, the carbonyl (C = O) peak at 1612 cm^–1 (1,3,5-triformylphloroglucinol (TP) monomer: 1639 cm^–1) broadens, and a C = C peak at 1586 cm^–1, a C = C fragrant ring (Ar) peak at 1450 cm^–1, and a peak of the C − N bond of the linker at 1256 cm^–1 seem, confirming the formation of a COF. As well as, a brand new particular C = O stretching band peak at 1711 cm^–1 (carboxylic acid) seems for TPDBD and TPDBD-CNa, indicating the profitable incorporation of –COO^– teams³³. As proven within the ¹³C cross-polarization magic-angle-spinning (CP-MAS) solid-state nuclear magnetic resonance (NMR) spectra, after the Schiff base response, the precise shift of the C = O peak (∼192 ppm) of the TP monomer fully disappears, and peaks of the keto carbonyl carbon (a) (∼188.3 ppm for TPBD and ∼184.5 ppm for TPDBD) and biphenyl junction (g) (∼127.8 for TPBD and ∼128.8 ppm for TPDBD) seem (Fig. 2b, c). As well as, chemical shifts of the C = O (h) (∼168.2 ppm) and C (i) (∼126.3 ppm) peaks are noticed for TPDBD, additional indicating the profitable incorporation of –COOH teams^21,29. The Raman spectra show distinct scattering bands at ∼1200, 1386, and 1598 cm^–1, indicating the retention of the structural rigidity of the COF all through the synthesis course of (Supplementary Fig. 7).

a FTIR spectra of TPBD, TPDBD, BD, DBD, and TP. b Partial unit buildings of TPBD and TPDBD. c ¹³C CP-MAS solid-state NMR spectra of TPBD, TPDBD, and TP. d XPS C 1s spectra of TPBD, TPDBD, and TPDBD-CNa. e XPS O 1s spectra of TPBD, TPDBD, and TPDBD-CNa. f SEM picture of TPDBD.

X-ray photoelectron spectroscopy (XPS) was carried out to investigate the floor chemical states of TPBD, TPDBD, and TPDBD-CNa (Fig. second, e). As proven within the C 1s and O 1s XPS spectra of TPBD, the C = O peak is attributed to the keto carbonyl group, indicating the profitable synthesis of the COF-TPBD framework. For TPDBD, particular C = O (286.41 eV) and HO–C = O (288.41 eV) peaks within the C 1s spectrum and O = C–OH (a, 533.43 eV), O = C–OH (b, 532.30 eV), and C = O (531.23 eV) peaks within the O 1s spectrum are noticed³⁴. Furthermore, the O content material of TPDBD is larger than that of TPBD (Supplementary Desk 1), demonstrating the profitable incorporation of carboxylic acid (–COOH) teams within the TPDBD framework. Equally, the binding energies of C = O (286.48 eV) and NaO–C = O (288.66 eV) within the C 1s spectrum and people of O = C–ONa (a, 533.18 eV), O = C–ONa (b, 531.97 eV), and C = O (531.06 eV) within the O 1s spectrum, in addition to the Na 1s peak at 1071.64 eV, point out the profitable change of H⁺ with Na⁺ in TPDBD-CNa (Supplementary Fig. 8). The scanning electron microscopy (SEM) and transmission electron microscopy (TEM) pictures of TPDBD present stacked nanosheets with micrometric and submicrometric morphologies (Fig. 2f and Supplementary Figs. 9 and 10), which is helpful for interfacial contact and compatibility between electrodes and electrolyte³⁵. The power dispersive spectroscopy (EDS) pictures present that C, N, O, and Na are uniformly distributed in TPBD, TPDBD, and TPDBD-CNa (Supplementary Figs. 11–13).

The thermogravimetric evaluation (TGA) profile of TPDBD exhibits a decomposition temperature of 274 °C (43% weight reduction). The primary stage of weight lack of TPDBD-CNa is principally attributable to the decomposition of –COO^– at 264 °C, and the second stage begins at ~308 °C because of the collapse of the framework (46% weight reduction). The addition of NaTFSI improves the thermal stability, and TPDBD-CNa-NaTFSI and TPBD-NaTFSI exhibit decomposition at ~380 and 410 °C with 62 and 60% weight reduction as much as 780 °C, respectively (Supplementary Fig. 14). Furthermore, the precise floor and pore sizes of TPDBD-CNa-NaTFSI and TPBD-NaTFSI lower to 18 m² g^–1 and 0.07 cm³ g^–1, 18 m² g^–1 and 0.08 cm³ g^–1 (Supplementary Fig. 15). The PXRD patterns of TPBD-NaTFSI and TPDBD-CNa-NaTFSI show the robust attribute peaks of NaTFSI and weak small-angle diffraction peaks, indicating the environment friendly incorporation of Na salt into the COF channels (Supplementary Fig. 16)^36,37. The FTIR and Raman spectra of TPBD-NaTFSI and TPDBD-CNa-NaTFSI additional affirm the presence of NaTFSI (Supplementary Figs. 17 and 18). A blue shift in TPBD-NaTFSI and TPDBD-CNa-NaTFSI Raman spectra is noticed in contrast with that of the NaTFSI resolution, indicating the formation of cation/anion associations and quick Na⁺ transport channels in COF-NaTFSI^37,38,39. The ²³Na MAS NMR spectra of TPDBD-CNa-NaTFSI and TPBD-NaTFSI every exhibit two particular indicators centered at –21.67 ppm (peak 1) and –42.36 ppm (peak 2) and –30.77 ppm (peak 1) and –42.39 ppm (peak 2), comparable to Na⁺ in NaTFSI and Na-coordinated COFs (Supplementary Fig. 19). Furthermore, elemental evaluation (EA) and inductive coupled plasma (ICP) emission spectroscopy measurements confirm that the Na contents of TPDBD-CNa-NaTFSI and TPBD-NaTFSI are 5.46 wt.% and three.07 wt.%, respectively (Supplementary Desk 1). Additional EDS elemental mappings illustrate the profitable introduction of Na salt into the COFs (Supplementary Fig. 20).

Biomimetic Na⁺ channels

As a result of destructive inwalls embellished with –COO^– teams, the zeta potentials of TPDBD and TPDBD-CNa are –61.1 and –58.2 mV, a lot decrease than that of TPBD (–42.1 mV), which is helpful for the separation of Na⁺ and TFSI^– (Fig. 3a and Supplementary Fig. 21). The dissociation of NaTFSI in COFs can also be confirmed by DFT calculations (Fig. 3b). As proven within the cost distribution mappings, the C = O and –COO^– teams of TPDBD and TPDBD-COO^– present a darkish pink shade distribution, indicating extra electronegative websites, which is advantageous for Na⁺ adsorption. Within the optimized coordination construction, the bond size between Na⁺ and TFSI^– will increase after the introduction of –COO^–, indicating the dissociation of Na⁺ and TFSI^– (Fig. 3c, d and Supplementary Fig. 22). The negatively charged TPDBD-CNa inwalls can successfully seize Na⁺ and electrostatically repulse TFSI^–, consequently facilitating speedy Na⁺ switch when utilized in QSSEs. It’s value noting that the sub-nanostructured ion channels with extra negatively charged websites (–COO^–) are just like the biomimetic Na channels of the cell membrane (Fig. 3e).

a Zeta potential values of assorted COFs. b Electrostatic potential mappings of TPBD, TPDBD, and TPDBD-COO⁻ (the white, blue, grey, and pink spheres denote hydrogen, nitrogen, carbon, and oxygen, respectively). c Optimized coordination buildings between NaTFSI and TPDBD and TPDBD-COO⁻ (the white, blue, purple, grey, and pink spheres denote hydrogen, nitrogen, sodium, carbon, and oxygen, respectively). d Bond lengths between NaTFSI and TPBD, TPDBD and TPDBD-COO⁻. e Schematic illustration of the bionic channel in TPDBD-CNa (the pink spheres denote oxygen, and cyan sticks denote the covalent natural framework).

MD simulations had been used to know the Na⁺ transport mechanism of the biomimetic COF with sub-nanometer-sized zones constructed by the adjoining –COO^– teams and COF inwalls. The distribution modes of Na⁺ and TFSI⁻ in TPBD, TPDBD, and TPDBD-CNa are proven in Fig. 4a. Schematic diagrams of COF-NaTFSI are proven in Fig. 4b and Supplementary Fig. 23. The Na⁺ density distribution maps of TPBD-NaTFSI present that almost all Na ions are uniformly distributed throughout your complete pore, and few Na ions are adsorbed on carbonyl teams derived from enol-to-keto tautomerism (Fig. 4c). After the introduction of –COOH, further Na ions are adsorbed onto the negatively charged inwalls of TPDBD-NaTFSI (Fig. 4d). After the Na activation of TPDBD-CNa-NaTFSI, sub-nanoscale zones constructed by the adjoining –COO^– teams and COF inwalls are noticed. Na ions are centrally distributed on the edge zones, whereas the TFSI^– anions are repulsively confined into the middle of the COF channels (Fig. 4e). Every impartial sub-nanometer zone, as within the Na⁺ channel of the cell membrane, is helpful for selective Na⁺ transport. Certainly, the Na⁺ diffusion velocity on the edge zones is larger than that within the middle websites because of the development of quick Na⁺ migration pathways, as within the ion channels of the cell membrane (Fig. 4f). Determine 4g exhibits the imply sq. displacement (MSD) of Na⁺ over time in three sorts of buildings. The self-diffusion coefficients (D_TPBD-NaTFSI ~ 0.085, D_TPDBD-NaTFSI ~ 0.143, and D_{TPDBD-CNa-NaTFSI} ~ 0.239 (10⁸ Ų ns^–1)) had been calculated from the slope of the MSD averaged over the trajectories of particular person Na⁺ particles⁴⁰. The most important D_{TPDBD-CNa-NaTFSI}, indicating the very best Na⁺ transport effectivity, was calculated for TPDBD-CNa, suggesting that the (–COO^–)-based biomimetic channels can improve Na⁺ transport effectivity alongside the sub-nanometer-sized zones. The interplay power between –COO^– (–4 kcal mol^–1)/–COOH (–22 kcal mol^–1) and Na⁺ within the COF was calculated, and the most important interplay power between carbonyl teams and Na⁺ promotes the adsorption of Na⁺ within the sub-nanometer zones (Fig. 4h). The correct distribution of cost and area round COF inwalls endows the biomimetic channel with excessive Na⁺ conduction efficiency.

a Distribution modes of Na⁺ and TFSI⁻ in TPBD, TPDBD, and TPDBD-CNa (the purple and pink spheres and cyan ovals denote sodium, oxygen, and TFSI⁻, respectively, and the cyan sticks denote the covalent natural framework). b Schematic of the MD simulations of TPDBD-CNa-NaTFSI (the white, blue, cyan, pink, yellow, purple, and pink spheres denote hydrogen, nitrogen, carbon, fluorine, sulfur, sodium, and oxygen, respectively). Na⁺ density mappings (the pink areas point out the very best likelihood of Na⁺) of TPBD-NaTFSI (c), TPDBD-NaTFSI (d), and TPDBD-CNa-NaTFSI (e). f Na⁺ velocities on the edge and middle of the TPDBD channel. g MSD outcomes of Na⁺ over time in three sorts of COFs. h Interplay power between –COOH/–COO⁻ teams and Na⁺ in TPDBD.

Na⁺ conduction properties

A big grain boundary impedance can hinder the sensible ion conductivity and the high-efficiency utilization of solvent in QSSEs, that are important features for producing high-performance Na-based cells. As proven in Supplementary Fig. 24, a small quantity of PC solvent might be quickly adsorbed into the COF membrane. The thermal stability of TPBD-NaTFSI and TPDBD-CNa-NaTFSI with a small quantity of PC additive was investigated by TGA (Supplementary Fig. 25). As a result of confinement results of the COF, ~9 wt.% PC solvents have a tendency to connect to the inside of the COF and decompose extra slowly than pure solvent and glass fiber/solvent. MD simulation exhibits that the PC molecules are uniformly adsorbed and infiltrated on the TPDBD-CNa skeletons and aggregated on the TPBD floor, indicating that the well-designed biomimetic COF is helpful for the uniform wettability of PC on the grain boundaries (Supplementary Fig. 26a, b). The high-efficiency utilization of PC can enhance the electrode/electrolyte interface compatibility and cut back the interfacial impedance between particles. Beneath the electrical area, together with Na⁺ transport, some PC molecules are confined into the sub-nanochannels because of the excessive interplay power between TPDBD-CNa and the PC solvent, which may successfully stop PC volatilization and additional promote Na⁺ conductivity (Supplementary Fig. 26c–e and Supplementary Notice 1). The configurations of the corresponding QSSEs after 20 cycles in a Na|QSSE|Na symmetric cell had been measured by FTIR spectroscopy (Fig. 5a). The TPDBD-CNa-QSSE reveals stronger PC-Na⁺ interactions (720 and 1403 cm⁻¹) and extra concentrated TFSI⁻ (787 cm⁻¹) than the TPBD-QSSE, demonstrating a stronger electrolyte aggregation impact⁴¹. As proven within the optimized configuration (Fig. 5b), the Na–O bond size of NaTFSI within the QSSEs turns into longer, indicating that PC can successfully dissociate Na⁺ and TFSI⁻. Determine 5c reveals a schematic diagram of the PC, Na⁺, and TFSI⁻ distributions within the QSSEs.

a FTIR spectra of the ready TPDBD-CNa-QSSE, TPBD-QSSE, and PC solvent (cycled COF movies in Na||Na cells over 20 cycles at 0.02 mA cm⁻² and 25 ± 1 °C). b Na–O bond lengths in PC-Na and PC-NaTFSI. c Schematic diagram of the PC, Na⁺, and TFSI⁻ distributions in TPDBD-CNa (the white, blue, grey, cyan, yellow, purple, and pink spheres denote hydrogen, nitrogen, carbon, fluorine, sulfur, sodium, and oxygen, respectively). d Arrhenius plot of the ionic conductivity of TPDBD-CNa-QSSE and TPBD-QSSE. e Present-time curves of the Na|TPDBD-CNa-QSSE|Na symmetric cell (inset exhibits the EIS at preliminary and regular states and corresponding equal circuit mannequin). f Comparability of the standard efficiency of reported Li⁺/Na⁺ SSEs (the numerical values and testing temperature for the ionic conductivities offered in Supplementary Desk 4).

Electrochemical impedance spectroscopy (EIS) measurements of pellets had been carried out from −40 to 100 °C to review the Na⁺ conduction properties of the QSSEs. The Ti|TPDBD-CNa-NaTFSI|Ti symmetric cell with out solvent can not work correctly beneath 100 °C because of the weak contact between the COF and titanium sheet (Supplementary Fig. 27). The Na⁺ conductivity of the TPDBD-CNa-QSSE is 1.30 × 10⁻⁴ S cm^–1 at 25 ± 1 °C, larger than that of the TPBD-QSSE (9.06 × 10⁻⁵ S cm^–1, 25 ± 1 °C), and even at a low temperature of –40 °C, the TPDBD-CNa-NaTFSI can nonetheless ship an ionic conductivity of 8.98 × 10⁻⁶ S cm^–1 (Fig. 5d, Supplementary Figs. 28 and 29, Supplementary Desk 2, and Supplementary Notice 2). The tendency of accelerating conductivity is in keeping with the self-diffusion coefficients measured by MSD calculations (Fig. 4g). Because the temperature will increase, the Arrhenius plots exhibit a proportional improve within the logarithmic ionic conductivity, and the corresponding activation power (Ea) values of the TPDBD-CNa-QSSE and TPBD-QSSE are 0.204 eV and 0.230 eV, respectively. Benefiting from the exact cost design of the biomimetic Na⁺ channel, the TPDBD-CNa-QSSE exhibits a bigger t_Na+ of 0.90 than the TPBD-QSSE (0.74), suggesting a greater ion migration functionality (Fig. 5e, Supplementary Fig. 30, Supplementary Desk 3, and Supplementary Notice 3). The ion transport performances reported are well-positioned in comparison with the SSE state-of-the-art (Fig. 5f and Supplementary Tables 4 and  5)^{20,22,23,24,35,42,43,44}. Such sub-nanometer-sized zones might be considered biomimetic Na⁺ switch channels and might successfully promote the Na⁺ transport effectivity directionally alongside the oxygen atoms. Furthermore, solvent molecules might be confined within the sub-nanoscale channels in QSSEs to cut back volatilization. The leaping switch mode of Na⁺ from one carboxylic/carbonyl place to the following unoccupied web site beneath a given voltage might be considered a form of pendular Na⁺ transport mechanism, leading to a excessive Na⁺ conduction efficiency (Supplementary Fig. 31).

Relating to the linear sweep voltammetry (LSV) measurement, an electrochemical stability window of 5.32 V was noticed for the TPDBD-CNa-QSSE, which is wider than that of the TPBD-QSSE (4.39 V, Fig. 6a), indicating that the biomimetic Na⁺ channels with –COO⁻ teams endow the QSSE with a stronger antioxidant property and better decomposition potential. To disclose the soundness of the QSSE on the molecular degree, the optimized buildings and highest-occupied/lowest unoccupied molecular orbitals (HOMO/LUMO) of TPBD and TPDBD had been decided by DFT calculations (Fig. 6b). It must be famous {that a} decrease HOMO power signifies that it’s more durable to lose electrons, comparable to the next oxidation potential. As a result of introduction of electron-withdrawing –COOH teams, TPDBD exhibits a decrease HOMO power (–5.31 eV) than TPBD (–4.83 eV), indicating the stronger antioxidant property of the TPDBD-CNa-QSSE^36,45. Furthermore, the band hole (E_g) of TPDBD is decided to be 2.17 eV, bigger than that of TPBD (1.90 eV), additional implying that the COF modified with –COO⁻ teams has higher electron insulation, which is most well-liked for QSSEs. Furthermore, UV‒vis absorption spectra (Supplementary Fig. 32) had been used to check the absorption edge and band hole of TPBD (2.15 eV), TPBD-NaTFSI (2.12 eV), TPDBD (2.38 eV), TPDBD-CNa (2.35 eV), and TPDBD-CNa-NaTFSI (2.34 eV)⁴⁶. The altering pattern noticed within the UV‒vis spectra (band hole order: TPBD < TPDBD) is in keeping with the DFT calculations.

a LSV profiles of SS|TPBD-QSSE|Na and SS|TPDBD-CNa-QSSE|Na uneven cells. b Calculated HOMO and LUMO values of TPBD and TPDBD primarily based on DFT calculations. c Price efficiency of Na plating/stripping for Na|QSSE|Na at 25 ± 1 °C and 0.01, 0.03, 0.04, 0.1, 0.2, 0.5, 0.6, and 0.8 mA cm⁻². d Na plating/stripping of Na|QSSE|Na at a present density of 0.01 mA cm⁻² and 25 ± 1 °C for 900 h and a pair of h per cycle (the inset exhibits the time-division plating/stripping curves).

Na plating/stripping plots of the Na|QSSE|Na symmetric cells are displayed in Fig. 6c. Roughly 9 wt.% solvent (PC with 5% fluoroethylene carbonate (FEC)) was added to infiltrate the interface, as FEC can passivate the Na floor and enhance the interface stability. In contrast with TPBD-QSSE (unstable above 0.1 mA cm⁻²), TPDBD-CNa-QSSE reveals decrease polarization and extra secure Na plating/stripping with none signal of short-circuiting. The polarization voltages are ±50, ±75, ±110, ±150, ±180, ±224, ± 450, and ±700 mV at 0.01, 0.03, 0.04, 0.10, 0.2, 0.5, 0.6, and 0.8 mA cm⁻², respectively. Determine 6d describes the long-term interfacial stability between the electrolyte and Na steel electrode utilizing the Na||Na symmetric cell at 0.01 mA cm⁻² for two h per cycle. The TPBD-QSSE and TPDBD-CNa-QSSE each exhibit secure Na plating/stripping conduct over 900 h with none irreversible fluctuation of overpotential. The TPDBD-CNa-QSSE exhibits a decrease voltage plateau of ~62 mV in comparison with the TPBD-QSSE (from 73 to 93 mV from 400 to 900 h). The symmetric cell with the TPDBD-CNa-QSSE at 0.05 mA cm⁻² reveals regular Na insertion/extraction processes for over 450 h with out apparent fluctuation of potential (Supplementary Fig. 33). To confirm the practicality of the ready QSSEs at low temperatures, Na plating/stripping at 0, –5, –10, –15, –20, and –25 °C and symmetric cell operations at 0 °C had been carried out (Supplementary Fig. 34a). Because the temperature is lowered from 0 to –20 °C, the Na|TPDBD-CNa-QSSE|Na symmetric cell exhibits low overpotential and secure voltage profiles beneath 10 μA cm⁻². When the temperature is additional lowered to –25 °C, irregular voltage fluctuations emerge, which might be ascribed to unstable Na plating/stripping and the formation of useless Na (i.e., Na steel areas which might be electronically disconnected from the present collector)^47,48. Nonetheless, because of the absence of biomimetic sub-nanochannels, the voltage irregularity of the Na|TPBD-QSSE|Na symmetrical cell seems at a comparatively low temperature of –10 °C. Furthermore, Supplementary Fig. 34b exhibits that comparatively secure voltage curves had been obtained for over 550 h with out overpotential fluctuation at 0 °C, additional indicating that the bioinspired ionic channel design is helpful for uniform Na⁺ deposition/stripping. A small quantity of PC additive was confined contained in the TPDBD-CNa-QSSE, assuaging interface facet reactions attributable to self-decomposition and thus facilitating extra secure and higher-current-density Na plating/stripping cycles.

XPS experiments had been carried out to review the chemical composition of the stable electrolyte interphases (SEIs) fashioned on the surfaces of the cycled COF-QSSEs and Na electrodes (Fig. 7a, b). The C 1s, O 1s, F 1s, and Na 1s spectra had been used to estimate the coexistence of natural species (C = C/C − C, C = O, C − F) and inorganic species (Na₂CO₃, Na₂O, and NaF) within the SEI layers. As proven in Fig. 7a, in contrast with these for the TPBD-QSSE, the precise peaks of inorganic species improve, and people of natural species lower barely for the TPDBD-CNa-QSSE. The inorganic species are helpful for the development of secure and compact SEI layers, which is conducive to the inhibition of Na dendrite development. Moreover, in contrast with these of TPDBD-CNa-NaTFSI, the binding energies of the RO − C = O and C = O(Na) peaks of TPDBD-CNa-QSSE lower whereas the binding power of the F 1 s peak will increase. These outcomes additional affirm that Na⁺ tends to be distributed in sub-nanometer-sized zones, whereas TFSI⁻ is electrostatically repulsed within the central area, which is in keeping with the MD simulations. To realize extra insights into the SEI composition, the cycled Na anode floor composition of the Na|TPDBD-CNa-QSSE|Na symmetrical cell was additional analyzed by conducting in-depth Ar⁺ sputtering at 0, 40, 100, and 200 nm. As proven within the elemental content material distribution at completely different SEI depths (Supplementary Fig. 35), C and O are the dominant components on the floor, and the atomic proportion of C undergoes a sharper lower than that of O upon sputtering. Because the sputtering depth will increase, the atomic proportion of Na and the Na/C ratio steadily improve, indicating a gradual strategy in the direction of the Na anode floor. The C 1s, O 1s, F 1s, and Na 1s spectra had been used to review the chemical composition of the SEI at completely different depths (Fig. 7b). As proven within the C 1s spectra, natural species, similar to C − C, C = O, RO − C = O, and C − F species, and inorganic species, similar to Na₂CO₃, with fractional contents are noticed within the outer SEI layer. Because the sputtering depth will increase, the height depth of natural species decreases, and the height depth of inorganic species steadily will increase. Such a variation pattern can also be noticed within the O 1s spectra. When the sputtering depth is 100 nm, the C − F peak nearly disappears, and the NaF sign turns into stronger, indicating that the dominant species are inorganic species, similar to NaF and Na₂CO₃, within the interior layer of the SEI. It must be emphasised that C − F species can prohibit Na⁺ transport and NaF species can speed up ion transport via the SEI^49,50. Moreover, the O and F aspect contents stay nearly fixed, indicating the homogeneous distribution of the SEI composition together with the assorted sputtering depths. In conclusion, the SEI movie of the Na anode primarily based on the TPDBD-CNa-QSSE consists of fewer natural carbonates and comprises dense inorganic substances; thus, the SEI has a excessive mechanical power and is helpful for the inhibition of dendrite development^51,52. The floor morphologies of the membrane and Na steel recovered after 20 cycles had been investigated by SEM observations (Fig. 7c–f). The membrane of the cycled Na|TPBD-QSSE|Na cell reveals extra cracks than that of the Na|TPDBD-CNa-QSSE|Na cell. The collected stress/pressure throughout Na stripping/plating processes can speed up interface deterioration, leading to speedy dendrite development. Furthermore, the branching and gathering of Na dendrites are noticed within the Na|TPBD-QSSE|Na cell to a higher diploma than within the Na|TPDBD-CNa-QSSE|Na cell. These outcomes illustrate that the TPDBD-CNa-QSSE reveals good interfacial compatibility with the Na anode and suppresses the expansion of Na dendrites as a consequence of a secure voltage response.

a XPS C 1s, O 1s, F 1s, and Na 1s spectra of the TPDBD-CNa-QSSE/TPBD-QSSE in Na||Na cells over 20 cycles at 0.02 mA cm⁻² and 25 ± 1 °C and TPDBD-CNa-NaTFSI/TPBD-NaTFSI. b XPS C 1s, O 1s, F 1s, and Na 1s depth profiles of cycled Na steel over 20 cycles at 0.02 mA cm⁻² and 25 ± 1 °C in a Na|TPDBD-CNa-QSSE|Na symmetric cell. SEM pictures of cycled membranes of the TPBD-QSSE (c) and TPDBD-CNa-QSSE (d) over 20 cycles at 0.02 mA cm⁻² and 25 ± 1 °C. SEM pictures of the cycled Na steel of the TPBD-QSSE (e) and TPDBD-CNa-QSSE (f) over 20 cycles at 0.02 mA cm⁻² and 25 ± 1 °C.

Meeting and testing of quasi-all-solid-state Na|QSSEs|Na₃V₂(PO₄)₃/C cells

To show the sensible software of the QSSEs, Na|QSSEs|Na₃V₂(PO₄)₃/C cells had been assembled utilizing a carbon-doped Na₃V₂(PO₄)₃ (NVP/C) constructive electrode, a sodium steel destructive electrode, and the QSSEs (Supplementary Fig. 36). First, NVP/C with a extremely crystalline part (PDF: #53-0018) was ready by a hydrothermal technique (Fig. 8a)^53,54. SEM pictures of NVP/C present a branched morphology consisting of nanometer flakes with a mean thickness of ~40 nm. Such a 3D interconnected construction is helpful for quick Na⁺ diffusion and relieves mechanical stress attributable to Na⁺ insertion/extraction (Fig. 8b and Supplementary Fig. 37). TGA, Raman, and BET analyses affirm the profitable introduction of a hierarchical porous carbon layer into the NVP/C construction (Supplementary Figs. 38–40).

a XRD sample of NVP/C. b SEM picture of NVP/C. c Histograms of the voltage hysteresis beneath completely different particular currents (the error bar represents the usual deviation of the typical voltage of cost/discharge close to 50 mAh g⁻¹). d Cost/discharge voltage profiles of the Na|TPDBD-CNa-QSSE|NVP/C and Na|TPBD-QSSE|NVP/C cells at 12 mA g⁻¹. e CV curves of the Na|TPDBD-CNa-QSSE|NVP/C and Na|TPBD-QSSE|NVP/C cells at 0.1 mV s⁻¹. f Combustion behaviors of the TPDBD-CNa-QSSE. g Combustion behaviors of the solvent-infiltrated fiberglass separator. h Lengthy-cycle stability of the Na|TPDBD-CNa-QSSE|NVP/C cell at 60 mA g⁻¹ (the inset exhibits a photograph of ten 2.5 V LEDs). i Biking efficiency of the Na|TPDBD-CNa-QSSE|NVP/C tiled pouch cell at 12 mA g⁻¹ for 160 cycles. The inset photographs present a LED powered by the QSSE pouch cell in numerous states of “Tiled”, “Folded 90°”, “Fully folded”, “Unfolded”, and “Minimize”.

The speed performances of the Na|TPDBD-CNa-QSSE|NVP/C and Na|TPBD-QSSE|NVP/C cells are proven in Supplementary Fig. 41. When the precise currents are 60, 120, and 240 mA g⁻¹, the precise capacities of the Na|TPDBD-CNa-QSSE|NVP/C cell are 91.8, 87.6, and 82.1 mAh g⁻¹, respectively. Even at the next price of 480 mA g⁻¹, the cell nonetheless delivers a capability of 68.9 mAh g⁻¹, larger than that of the Na|TPBD-QSSE|NVP/C cell (60.1 mAh g⁻¹ at 480 mA g⁻¹). When the precise present decreases to 60 mA g⁻¹, a particular capability of 91.7 mAh g⁻¹ might be obtained, indicating higher reversible traits in comparison with these of the Na|TPBD-QSSE|NVP/C cell (87.38 mAh g⁻¹ at 60 mA g⁻¹). The cost/discharge voltage profiles of the Na|TPBD-QSSE|NVP/C cell present polarization potentials of 164.8, 260.3, 279.9, 346.5, and 590.2 mV from 12 to 480 mA g⁻¹ (Fig. 8c, d and Supplementary Fig. 42). Benefiting from the quick conduction of Na⁺ and good interfacial stability between the QSSE and electrodes, the polarization voltages of the Na|TPDBD-CNa-QSSE|NVP/C cell are 98.7, 127.3, 191.5, 285.2, and 448.7 mV at particular currents of 12, 60, 120, 240 and 480 mA g⁻¹ at a mean voltage of cost/discharge close to 50 mAh g⁻¹, respectively. Such low electrochemical polarization of the Na|TPDBD-CNa-QSSE|NVP/C cell ensures the structural integrity of the interface and maintains a secure voltage plateau throughout the long-term cost/discharge course of. As illustrated within the cyclic voltammetry (CV) profiles (Fig. 8e), a pair of well-defined redox peaks appeared for each electrodes, comparable to the reversible transformation of V³⁺/V⁴⁺ with two Na extraction/insertions following the electrochemical response Na₃V₂(PO₄)₃ ↔ NaV₂(PO₄)₃⁵⁵. The CV curves of the Na|TPDBD-CNa-QSSE|NVP/C cell present a smaller potential hole and bigger present response than these of the Na|TPBD-QSSE|NVP/C cell, indicating quicker Na⁺ diffusion kinetics enhanced by the upper ion/electron conduction. As well as, CV curves had been measured at varied sweep charges to guage the Na⁺ diffusion kinetics of the cells (Supplementary Fig. 43 and Supplementary Notice 4). In contrast with TPBD, the Na|TPDBD-CNa-QSSE|NVP/C cell reveals oxidation and discount peaks which have a comparatively small potential hole between them and improved Na⁺ conduction within the course of of adjusting the sweep velocity. The D_Na⁺ values of the Na|TPDBD-CNa-QSSE|NVP/C cell for peak 1 (anodic) and peak 2 (cathodic) are decided to be 5.77 × 10⁻¹³ and 6.23 × 10⁻¹³ cm² s⁻¹, respectively, that are larger than these of the Na|TPBD-QSSE|NVP/C cell (2.77 × 10⁻¹³ and 1.92 × 10⁻¹³ cm² s⁻¹), akin to these in most beforehand reported works^54,56. Determine 8f, g exhibits the combustion behaviors of the COF-QSSEs. As soon as the ignited TPDBD-CNa-QSSE membrane is moved away from the hearth, the flames shortly extinguish, whereas the fiberglass separator might be ignited and burn with a vibrant flame accompanied by quantity discount, demonstrating the satisfactory flame resistance property of the TPDBD-CNa-QSSE.

Benefiting from electrode/electrolyte interface compatibility, the Na|TPDBD-CNa-QSSE|NVP/C cell reveals glorious long-cycle stability at a particular present of 60 mA g⁻¹, and 83.5 mAh g⁻¹ is retained after 1000 cycles, comparable to solely 0.0048% capability decay per cycle (Fig. 8h), which is akin to that of most reported SSE-based batteries (Supplementary Desk 6). Even at the next particular present of 120 mA g⁻¹, 74.1 mAh g⁻¹ is retained after 500 cycles, comparable to 0.0195% capability decay per cycle (Supplementary Fig. 44). The inset {photograph} (Fig. 8h) shows ten 2.5 V light-emitting diode (LED) lights powered by the Na|TPDBD-CNa-QSSE|NVP/C cell, and good brightness was maintained for 12 h. Nonetheless, with out sub-nanochannel confinement solvents, overcharge conduct is noticed throughout the long-term biking of the Na|TPBD-QSSE|NVP/C cell even at a comparatively low particular present of 60 mA g⁻¹ (Supplementary Fig. 45), indicating an unstable interface between the TPBD-QSSE and the Na electrode. To additional affirm the sensible software of the ready QSSEs, the biking stability and price efficiency of the Na|TPDBD-CNa-QSSE|NVP/C cell with excessive cathode mass loadings of lively supplies (2.6 mg cm⁻²) and a skinny Na anode (~100 μm) had been carried out (Supplementary Fig. 46 and Supplementary Notice 5). The great cycle stability and reversibility confirm that the Na|TPDBD-CNa-QSSE|NVP/C cell with a excessive mass loading of the cathode exhibits good price efficiency and long-cycle stability. It must be famous that the Na|TPDBD-CNa-QSSE|NVP/C cell at 0 °C retains 103.1 mAh g⁻¹ after 200 cycles at a particular present of 12 mA g⁻¹ with a coulombic effectivity of 99.4% (Supplementary Fig. 47), confirming the nice biking stability of the QSSE-based cell at decreased temperatures. To research the sensible software of the soft-pack Na|TPDBD-CNa-QSSE|NVP/C cell in versatile digital gadgets (Supplementary Fig. 48), a freestanding movie with a big space, excessive flexibility, and mechanical power was ready and is proven in Supplementary Fig. 49. The bendable Na|TPDBD-CNa-QSSE|NVP/C pouch cell (Supplementary Fig. 50) demonstrates good biking efficiency, retaining 105.6 mAh g⁻¹ after 160 cycles at a particular present of 12 mA g⁻¹ with a coulombic effectivity of 99.5% (Fig. 8i). The inset pictures present that the LED machine can operate beneath completely different bending circumstances, verifying the flexibleness and security of the bendable pouch cell. As well as, the Na|TPDBD-CNa-QSSE|NVP/C cell ship excessive particular energies (calculated on the mass of lively materials within the constructive electrode) of 313.2, 302.0, 288.6, 263.8, and 215.1 Wh kg⁻¹ at 12, 60, 120, 240, and 480 A g⁻¹, respectively (Supplementary Fig. 51).

In abstract, a COF-QSSE with a biomimetic Na⁺ channel design was ready via the development of six sub-nanometer zones by the introduction of –COO⁻ teams into the COF inwalls. Benefiting from the correct dimension of the cavity and carbonyl binding websites, the solvents are confined within the biomimetic sub-nanochannels, and the COF-based QSSE reveals a excessive Na⁺ conductivity of 1.30 × 10⁻⁴ S cm⁻¹ and oxidative stability of as much as 5.32 V (versus Na⁺/Na) at 25 ± 1 °C. DFT calculations and MD simulations revealed that Na⁺ undergoes a pore wall adsorption phenomenon (extremely centralized to the carbonyl group) within the sub-nanochannels, and the –COO⁻ teams anchored on the COF inwalls are helpful for the speedy dissociation of NaTFSI. Furthermore, the electrolyte/electrode interface within the Na plating/stripping experiment is secure for 900 h of biking. When assembled with the NVP/C cathode, Na steel anode, and TPDBD-CNa-QSSE membrane, the SSB exhibits 0.0048% capability decay per cycle over 1000 cycles.