Nanofluidic voidless electrode for electrochemical capacitance enhancement in gel electrolyte

Porous electrodes with extraordinary capacitances in liquid electrolytes are oftentimes incompetent when gel electrolyte is applied because of the escalating ion diffusion limitations brought by the difficulties of infilling the pores of electrode with gels. As a result, porous electrodes usually exhibit lower capacitance in gel electrolytes than that in liquid electrolytes. Benefiting from the swift ion transport in intrinsic hydrated nanochannels, the electrochemical capacitance of the nanofluidic voidless electrode (5.56% porosity) is nearly equal in gel and liquid electrolytes with a difference of ~1.8%. In gel electrolyte, the areal capacitance reaches 8.94 F cm−2 with a gravimetric capacitance of 178.8 F g−1 and a volumetric capacitance of 321.8 F cm−3. The findings are valuable to solid-state electrochemical energy storage technologies that require high-efficiency charge transport.

Contact angles of (a) water and (b) hexane on TALP pellet surface.
Supplementary Fig. 3 a The digital photo of the TALP powders. b SEM image of aggregated TALP particles. c The digital photo of the compacted TALP pellets with different thicknesses and mass loadings. d The SEM image of the cross-sectional surface of the TALP pellet. e The zoomin SEM image of the cross-sectional surface of the TALP pellet showing the sliding of the sheared nanosheets.
Supplementary Fig. 4 a Schematic illustration of the X-ray incident direction and the diffraction intensity as a result of the nanofluidic channel orientation in compacted TALP pellet. b Hypothetical illustration of the relationship between the preferential alignment and the surface contrast under electron beam irradiation. Bright area is attributed to the basal planes of the TALP due to their surface charging and smoothness. Dark area is related to the edge planes of the TALP because of the fast charge conduction.
Supplementary Fig. 5 a A photo of the dry, leak-free solid gel electrolyte membrane. b An illustration of the two-electrode solid-state EC cell. The solid gel electrolyte was directly sandwiched by two TALP pellets. The pellets were neither soaked in liquid electrolyte nor prefilled with gel before cell assembly. Note that the interphase between the nanofluidic TALP electrodes and the gel electrolyte membrane is most likely in hydrated states due to the hydrophilicity of both components. The interfacial affinity readily allows the ions hop forward and backward. After crossing the interphase, the ions can rapidly move around in the gel-free TALP electrodes through the percolating 2D nanofluidic channels. Further enhancement of the solid-state ion kinetics is achievable dependent on the control and improvement of the texture of nanofluidic channels and the gel/TALP interphase chemistry. c An illustration of the two-electrode liquid-state EC cell with flooded liquid electrolyte. Ch arg e D is c h a rg e Charge Supplementary Fig. 8 Equivalent circuit model for TALP pellet electrodes. The cell resistances were divided to four parts: the equivalent serial resistance (ESR), the interfacial ion resistance (R1), the intra-particle ion resistance (R2), and the inter-particle ion resistance (R3). Rate dependence of Supplementary Fig. 9 Cyclic performance of TALP electrode in gel electrolyte (20 mA cm −2 ). All tests for gel electrolyte were conducted in a two-electrode solid state EC cell as illustrated in Fig. 5b.
Where, Cins represents the instantaneous capacitance of the segmental voltage window (dV), I represents the current density applied in GCD test, dt represents the segmental period of discharge, dV represents the corresponding segmental voltage window, tn represents the time data collected (n=1, 2, 3 …), and the Vn represents the voltage data collected (n=1, 2, 3 …).
Herein, we use the discharge curve under current of 1 mA cm -2 of a symmetric TALP cell with gel electrolyte and single electrode mass loading of 10 mg cm -1 to calculate the Cins and Cave.
The plot of C vs. V is shown as the following figure:  (1) and (2). This value deviates negligibly from the value (0.91850 F cm -2 ) calculated by C=I×t/V, where t is the total discharge time and V is the whole discharge voltage window.