Exploiting oleic acid to prepare two-dimensional assembly of Si@graphitic carbon yolk-shell nanoparticles for lithium-ion battery anodes

Carbon coating has been a routine strategy for improving the performance of Si-based anode materials for lithium-ion batteries. The ability to tailor the thickness, homogeneity and graphitization degree of carbon-coating layers is essential for addressing issues that hamper the real applications of Si anodes. Herein, we report the construction of two-dimensional (2D) assemblies of interconnected Si@graphitic carbon yolk-shell nanoparticles (2D-Si@gC) from commercial Si powders by exploiting oleic acid (OA). The OA molecules act as both the surface-coating ligands for facilitating 2D nanoparticle assembly and the precursor for forming uniform and conformal graphitic shells as thin as 4 nm. The as-prepared 2D-Si@gC with rationally designed void space exhibits excellent rate capability and cycling stability when used as anode materials for lithium-ion batteries, delivering a capacity of 1,150 mAh·g⁻¹ at an ultrahigh current density of 10 A·g⁻¹ and maintaining a stabilized capacity of 1,275 mAh·g⁻¹ after 200 cycles at 4 A·g⁻¹. The formation of yolk-shell nanoparticles confines the deposition of solid electrolyte interphase (SEI) onto the outer carbon shell, while simultaneously providing sufficient space for volumetric expansion of Si nanoparticles. These attributes effectively mitigate the thickness variations of the entire electrode during repeated lithiation and delithiation, which combined with the unique 2D architecture and interconnected graphitic carbon shells of 2D-Si@gC contributes to its superior rate capability and cycling performance.

     

High N-doped hierarchical porous carbon networks with expanded interlayers for efficient sodium storage

Sodium-ion batteries (SIBs) have been attracting considerable attention as a promising candidate for large-scale energy storage because of the abundance and low-cost of sodium resources. However, lack of appropriate anode materials impedes further applications. Herein, a novel self-template strategy is designed to synthesize uniform flowerlike N-doped hierarchical porous carbon networks (NHPCN) with high content of N (15.31 at.%) assembled by ultrathin nanosheets via a self-synthesized single precursor and subsequent thermal annealing. Relying on the synergetic coordination of benzimidazole and 2-methylimidazole with metal ions to produce a flowerlike network, a self-formed single precursor can be harvested. Due to the structural and compositional advantages, including the high N doping, the expanded interlayer spacing, the ultrathin two-dimensional nano-sized subunits, and the three-dimensional porous network structure, these unique NHPCN flowers deliver ultrahigh reversible capacities of 453.7 mAh·g⁻¹ at 0.1 A·g⁻¹ and 242.5 mAh·g⁻¹ at 1 A·g⁻¹ for 2,500 cycles with exceptional rate capability of 5 A·g⁻¹ with reversible capacities of 201.2 mAh·g⁻¹. The greatly improved sodium storage performance of NHPCN confirms the importance of reasonable engineering and synthesis of hierarchical carbon with unique structures.

     

2D interspace confined growth of ultrathin MoS2-intercalated graphite hetero-layers for high-rate Li/K storage

Herein,a two-dimensional(2D)interspace-confined synthetic strategy is developed for producing MoS₂intercalated graphite(G-MoS₂)hetero-layers composite through sulfuring the pre-synthesized stage-1 MoCI5-graphite intercalation compound(M0 CI5-GIC).The in situ grown MoS₂nanosheets(3-7 layers)are evenly encapsulated in graphite layers with intimate interface thus forming layer-by-layer MoS₂-intercalated graphite composite.In this structure,the unique merits of MoS₂and graphite components are integrated,such as high capacity contribution of MoS₂and the flexibility of graphite layers.Besides,the tight interfacial interaction between hetero-layers optimizes the potential of conductive graphite layers as matrix for MoS₂.As a result,the G-MoS₂exhibits a high reversible Li+storage of 344 mAh·g^-1even at 10 A·g^-1and a capacity of 539.9 mAh·g^-1after 1,500 cycles at 5 A·g^-1.As for potassium ion battery,G-MoS₂delivers a reversible capacity of 377.0 mAh·g^-1at 0.1 A·g^-1and 141.2 mAh·g^-1even at 2 A·g^-1.Detailed experiments and density functional theory calculation demonstrate the existence of hetero-layers enhances the diffusion rates of Li⁺and K⁺.This graphite interspace-confined synthetic methodology would provide new ideas for preparing function-integrated materials in energy storage and conversion,catalysis or other fields.     

Fast and stable K-ion storage enabled by synergistic interlayer and pore-structure engineering

Carbon-based material has been regarded as one of the most promising electrode materials for potassium-ion batteries (PIBs). However, the battery performance based on reported porous carbon electrodes is still unsatisfactory, while the in-depth K-ion storage mechanism remains relatively ambiguous. Herein, we propose a facile “in situ self-template bubbling” method for synthesizing interlayer-tuned hierarchically porous carbon with different metallic ions, which delivers superior K-ion storage performance, especially the high reversible capacity (360.6 mAh·g⁻¹@0.05 A·g⁻¹), excellent rate capability (158.6 mAh·g⁻¹@10.0 A·g⁻¹) and ultralong high-rate cycling stability (82.8% capacity retention after 2,000 cycles at 5.0 A·g⁻¹). Theoretical simulation reveals the correlations between interlayer distance and K-ion diffusion kinetics. Experimentally, deliberately designed consecutive cyclic voltammetry (CV) measurements, ex situ Raman tests, galvanostatic intermittent titration technique (GITT) method decipher the origin of the excellent rate performance by disentangling the synergistic effect of interlayer and pore-structure engineering. Considering the facile preparation strategy, superior electrochemical performance and insightful mechanism investigations, this work may deepen the fundamental understandings of carbon-based PIBs and related energy storage devices like sodium-ion batteries, aluminum-ion batteries, electrochemical capacitors, and dual-ion batteries.

     

Flower-like NiCo2S4 nanosheets with high electrochemical performance for sodium-ion batteries

A three-dimensional flower-like NiCo₂S₄ formed by two-dimensional nanosheets is synthesized by a facile hydrothermal method and utilized as the anode for sodium-ion batteries. Studies have shown that materials can achieve the best performance under the ether-based electrolyte system with voltage ranging from 0.3 to 3 V, which could effectively avoid the dissolution of polysulfides and over-discharge of the material. Here, sodium storage mechanism and charge compensation behaviors of this ternary metal sulfide are comprehensively investigated by ex situ X-ray diffraction. Moreover, ex situ Raman spectra, ex situ X-ray photoelectron spectroscopy and transmission electron microscopy measurements are used to related tests for the first time. Additionally, quantitative kinetic analysis unravels that sodium storage partially depends on the pseudocapacitance mechanism, resulting in good specific capacity and excellent rate performance. The initial discharge capacity is as high as 748 mAh·g⁻¹ at a current density of 0.1 A·g⁻¹ with the initial coulomb efficiency of 94%, and the capacity can still maintain at 580 mAh·g⁻¹ with the Coulomb efficiency close to 100% after following 50 cycles. Moreover, by the long cycle test at a high current density of 2 A·g⁻¹, the capacity can still reach at 376 mAh·g⁻¹ after over 500 cycles.

     

Dandelion-Like Bi2S3/rGO hierarchical microspheres as high-performance anodes for potassium-ion and half/full sodium-ion batteries

Sodium-ion batteries (SIBs) and potassium-ion batteries (PIBs) have been considered as attractive alternatives for next-generation battery systems, which have promising application potential due to their earth abundance of potassium and sodium, high capacity and suitable working potential, however, the design and application of bi-functional high-performance anode still remain a great challenge up to date. Bismuth sulfide is suitable as anode owing to its unique laminar structure with relatively large interlayer distance to accommodate larger radius ions, high theoretical capacity and high volumetric capacity etc. In this study, dandelion-like Bi₂S₃/rGO hierarchical microspheres as anode material for PIBs displayed reversible capacity, and 206.91 mAh·g⁻¹ could be remained after 1,200 cycles at a current density of 100 mA·g⁻¹. When applied as anode materials for SIBs, 300 mAh·g⁻¹ could be retained after 300 cycles at 2 A·g⁻¹ and its initial Coulombic efficiency is as high as 97.43%. Even at high current density of 10 A·g⁻¹, 120.3 mAh·g⁻¹ could be preserved after 3,400 cycles. The Na₃V₂(PO₄)₃@rGO//Bi₂S₃/rGO sodium ion full cells were successfully assembled which displays stable performance after 60 cycles at 100 mA·g⁻¹. The above results demonstrate that Bi₂S₃/rGO has application potential as high performance bi-functional anode for PIBs and SIBs.

     

A polyimide cathode with superior stability and rate capability for lithium-ion batteries

Organic-based electrode materials for lithium-ion batteries (LIBs) are promising due to their high theoretical capacity, structure versatility and environmental benignity. However, the poor intrinsic electric conductivity of most polymers results in slow reaction kinetics and hinders their application as electrode materials for LIBs. A binder-free self-supporting organic electrode with excellent redox kinetics is herein demonstrated via in situ polymerization of a uniform thin polyimide (PI) layer on a porous and highly conductive carbonized nanofiber (CNF) framework. The PI active material in the porous PI@CNF film has large physical contact area with both the CNF and the electrolyte thus obtains superior electronic and ionic conduction. As a result, the PI@CNF cathode exhibits a discharge capacity of 170 mAh·g⁻¹ at 1 C (175 mA·g⁻¹), remarkable rate-performance (70.5% of 0.5 C capacity can be obtained at a 100 C discharge rate), and superior cycling stability with 81.3% capacity retention after 1,000 cycles at 1 C. Last but not least, a four-electron transfer redox process of the PI polymer was realized for the first time thanks to the excellent redox kinetics of the PI@CNF electrode, showing a discharge capacity exceeding 300 mAh·g⁻¹ at a current of 175 mA·g⁻¹.

     

Supersaturated bridge-sulfur and vanadium co-doped M0S2 nanosheet arrays with enhanced sodium storage capability

The low specific capacity and sluggish electrochemical reaction kinetics greatly block the development of sodium-ion batteries (SIBs). New high-performance electrode materials will enhance development and are urgently required for SIBs. Herein, we report the preparation of supersaturated bridge-sulfur and vanadium co-doped MoS₂ nanosheet arrays on carbon cloth (denoted as V-MoS_2+x/CC). The bridge-sulfur in MoS₂ has been created as a new active site for greater Na⁺ storage. The vanadium doping increases the density of carriers and facilitates accelerated electron transfer. The synergistic dual-doping effects endow the V-MoS_2+x/CC anodes with high sodium storage performance. The optimized V-MoS_2.49/CC gives superhigh capacities of 370 and 214 mAh·g⁻¹ at 0.1 and 10 A·g⁻¹ within 0.4−3.0 V, respectively. After cycling 3,000 times at 2 A·g⁻¹, almost 83% of the reversible capacity is maintained. The findings indicate that the electrochemical performances of metal sulfides can be further improved by edge-engineering and lattice-doping co-modification concept.

     

VO2·0.2H2O nanocuboids anchored onto graphene sheets as the cathode material for ultrahigh capacity aqueous zinc ion batteries

Aqueous Zinc-ion batteries (ZIBs), using zinc negative electrode and aqueous electrolyte, have attracted great attention in energy storage field due to the reliable safety and low-cost. A composite material comprised of VO₂·0.2H₂O nanocuboids anchored on graphene sheets (VOG) is synthesized through a facile and efficient microwave-assisted solvothermal strategy and is used as aqueous ZIBs cathode material. Owing to the synergistic effects between the high conductivity of graphene sheets and the desirable structural features of VO₂·0.2H₂O nanocuboids, the VOG electrode has excellent electronic and ionic transport ability, resulting in superior Zn ions storage performance. The Zn/VOG system delivers ultrahigh specific capacity of 423 mAh·g⁻¹ at 0.25 A·g⁻¹ and exhibits good cycling stability of up to 1,000 cycles at 8 A·g⁻¹ with 87% capacity retention. Systematical structural and elemental characterizations confirm that the interlayer space of VO₂·0.2H₂O nanocuboids can adapt to the reversible Zn ions insertion/extraction. The as-prepared VOG composite is a promising cathode material with remarkable electrochemical performance for low-cost and safe aqueous rechargeable ZIBs.

     

Improved Na storage and Coulombic efficiency in TiP2O7@C microflowers for sodium ion batteries

Ti-based anode materials in sodium ion batteries have attracted extensive interests due to its abundant resources,low toxicity,easy synthesis and long cycle life.However,low Coulombic efficiency and limited specific capacity affect their applications.Here,cubic-phase TiP₂O₇is examined as anode materials,using in-situ/ex-situ characterization techniques.It is concluded that the redox reactions of Ti4⁺/Ti³⁺and Ti³⁺/Ti⁰consecutively occur during the discharge/charge processes,both of which are highly reversible.These reactions make the specific capacity of TiP₂O₇even higher than the case of TiO2 that only contains a simple anion,0^2-.Interestingly,Ti species participate only one of the redox reactions,due to the remarkable difference in local structures related to the sodiation process.The stable discharge/charge products in TiP₂O₇reduce the side reactions and improve the Coulombic efficiency as compared to T i02.These features make it a promising Ti-based anode for sodium ion batteries.Therefore,TiP₂O₇@C microflowers exhibit excellent electrochemical performances,?109 mAh·g^-1after 10,000 cycles at 2 A·g^-1,or 95.2 mAh·g^-1at 10 A·g^-1.The results demonstrate new opportunities for advanced Ti-based anodes in sodium ion batteries.     

Graphitic nanorings for super-long lifespan lithium-ion capacitors

Porous graphitic carbon nanorings (PGCNs) are proposed by smart catalytic graphitization of nano-sized graphene quantum dots (GQDs). The as-prepared PGCNs show unique ring-like morphology with diameter around 10 nm, and demonstrate extraordinary mesoporous structure, controllable graphitization degree and highly defective nature. The mechanism from GQDs to PGCNs is proven to be a dissolution-precipitation process, undergoing the procedure of amorphous carbon, intermediate phase, graphitic carbon nanorings and graphitic carbon nanosheets. Further, the relationship between particles size of GQDs precursor and graphitization degree of PGCNs products is revealed. The unique microstructure implies PGCNs a broad prospect for energy storage application. When applied as negative electrode materials in dual-carbon lithium-ion capacitors, high energy density (77.6 Wh·kg⁻¹) and super long lifespan (89.5% retention after 40,000 cycles at 5.0 A·g⁻¹) are obtained. The energy density still maintains at 24.5 Wh·kg⁻¹ even at the power density of 14.1 kW·kg⁻¹, demonstrating excellent rate capability. The distinct microstructure of PGCNs together with the strategy for catalytic conversion from nanocarbon precursors to carbon nanorings opens a new window for carbon materials in electrochemical energy storage.

     

A phenazine anode for high-performance aqueous rechargeable batteries in a wide temperature range

Aqueous rechargeable batteries are a possible strategy for large-scale energy storage systems. However, limited choices of anode materials restrict their further application. Here we report phenazine (PNZ) as stable anode materials in different alkali-ion (Li⁺, Na⁺, K⁺) electrolyte. A novel full cell is assembled by phenazine anode, Na_0.44MnO₂ cathode and 10 M NaOH electrolyte to further explore the electrochemical performance of phenazine anode. This battery is able to achieve high capacity (176.7 mAh·g^?1 at 4 C (1.2·Ag^?1)), ultralong cycling life (capacity retention of 80% after 13,000 cycles at 4 C), and excellent rate capacity (92 mAh·g^?1 at 100 C (30 A·g^?1)). The reaction mechanism of PNZ during charge—discharge process is demonstrated by in situ Raman spectroscopy, in situ Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) calculations. Furthermore, the system is able to successfully operate at wide temperature range from ?20 to 70 °C and achieves remarkable electrochemical performance.

     

A combination of hierarchical pore and buffering layer construction for ultrastable nanocluster Si/SiOx anode

Porous Si can be synthesized from diverse silica (SiO₂) via magnesiothermic reduction technology and widely employed as potential anode material in lithium ion batteries. However, concerns regarding the influence of residual silicon oxide (SiO_x) component on resulted Si anode after reduction are still lacked. In this work, we intentionally fabricate a cauliflower-like silicon/silicon oxide (CF-Si/SiO_x) particles from highly porous SiO₂ spheres through insufficient magnesiothermic reduction, where residual SiO_x component and internal space play an important role in preventing the structural deformation of secondary bulk and restraining the expansion of Si phase. Moreover, the hierarchically structured CF-Si/SiO_x exhibits uniformly-dispersed channels, which can improve ion transport and accommodate large volume expansion, simultaneously. As a result, the CF-Si/SiO_x-700 anode shows excellent electrochemical performance with a specific capacity of ~1,400 mA·h·g⁻¹ and a capacity retention of 98% after 100 cycles at the current of 0.2 A·g⁻¹.

     

Rational design of novel ultra-small amorphous Fe2O3nanodots/graphene heterostructures for all-solid-state asymmetric supercapacitors

Constructing graphene-based heterostructures with large interfacial area is an efficient approach to enhance the electrochemical performance of supercapacitors but remains great challenges in their synthesis.Herein,a novel ultra-small amorphous Fe₂O₃nanodots/graphene heterostructure(a-Fe₂O₃NDs/RGO)aerogel was facilely synthesized via excessive metal-ion-induced self-assembly and subsequent calcination route using Prussian blue/graphene oxide(PB/GO)composite aerogel as precursors.The deliberately designed a-Fe₂O₃NDs/RGO heterostructure offers a highly interconnected porous conductive network,large heterostructure interfacial area,and plenty of accessible active sites,greatly facilitating the electron transfer,electrolyte diffusion,and pseudocapacitive reactions.The obtained a-Fe₂O₃NDs/RGO aerogel could be used as flexible free-standing electrodes after mechanical compression,which exhibited a significantly enhanced specific capacitance of 347.4 F·g^-1at 1 A·g^-1,extraordinary rate capability of 184 F·g^-1at 10 A·g^-1,and decent cycling stability.With the as-prepared a-Fe₂O₃NDs/RGO as negative electrodes and the Co₃O₄NDs/RGO as positive electrodes,an all-solid-state asymmetric supercapacitor(a-Fe₂O₃NDs/RGO//Co₃O₄NDs/RGO asymmetric supercapacitor(ASC))was assembled,which delivered a high specific capacitance of 69.1 F·g^-1at 1 A·g^-1and an impressive energy density of 21.6 W·h·k·g^-1at 750 W·k·g^-1,as well as good cycling stability with a capacity retention of 94.3%after 5,000 cycles.This work provides a promising avenue to design high-performance graphene-based composite electrodes and profound inspiration for developing advanced flexible energy-storage devices.     

Physical activation of graphene: An effective,simple and clean procedure for obtaining microporous graphene for high-performance Li/S batteries

Graphene nanosheets are a promising scaffold to accommodate S for achieving high performance Li/S battery. Nanosheet activation is used as a viable strategy to induce a micropore system and further improve the battery performance. Accordingly, chemical activation methods dominate despite the need of multiple stages, which slow down the process in addition to making them tiresome. Here, a three-dimensional (3D) N-doped graphene specimen was physically activated with CO₂, a clean and single step process, and used for the preparation of a sulfur composite (A-3DNG/S). The A-3DNG/S composite exhibited outstanding electrochemical properties such as an excellent rate capability (1,000 mAh·g⁻¹ at 2C), high reversible capacity and cycling stability (average capacity ~ 800 mAh·g⁻¹ at 1C after 200 cycles), values which exceed those measured in chemically activated graphene. Therefore, these results support the use of physical activation as a simple and efficient alternative to improve the performance of carbons as an S host for high-performance Li-S batteries.

     

Infiltrating lithium into carbon cloth decorated with zinc oxide arrays for dendrite-free lithium metal anode

Lithium metal anode for batteries has attracted extensive attentions, but its application is restricted by the hazardous dendritic Li growth and dead Li formation. To address these issues, a novel Li anode is developed by infiltrating molten Li metal into conductive carbon cloth decorated with zinc oxide arrays. In carbonate-based electrolyte, the symmetric cell shows no short circuit over 1,500 h at 1 mA·cm⁻², and stable voltage profiles at 3 mA·cm⁻² for ∼ 300 h cycling. A low overpotential of ∼ 243 mV over 350 cycles at a high current density of 10 mA·cm⁻² is achieved, compared to the seriously fluctuated voltage and fast short circuit in the cell using bare Li metal. Meanwhile, the asymmetric cell withstands 1,000 cycles at 10 C (1 C = 167 mAh·g⁻¹) compared to the 210 cycles for the cell using bare Li anode. The excellent performance is attributed to the well-regulated Li plating/stripping driven from the formation of LiZn alloy on the wavy carbon fibers, resulting in the suppression of dendrite growth and pulverization of the Li electrode during cycling.

     

Ni@N-doped graphene nanosheets and CNTs hybrids modified separator as efficient polysulfide barrier for high-performance lithium sulfur batteries

Lithium-sulfur batteries (LSBs) have been regarded as one of the most promising energy storage systems to break through the upper limit of lithium-ion batteries. However, the rampant diffusions of soluble lithium polysulfides (LiPSs) in the electrolyte induced the shuttle effect between anode and cathode, resulting in low sulfur utilization, low energy efficiency and short cycling life. Herein, we prove the rational design and construction of Ni nanoparticles filled in vertically grown N-doped bamboo-like carbon nanotubes (CNTs) on graphene nanosheets (Ni@NG-CNTs) as efficient polysulfide barrier for high-performance LSBs. The unique design integrates graphene nanosheets and CNTs into hierarchical architectures with one-dimensional (1D) CNTs, two-dimensional (2D) ultrathin nanosheets and abundant carbon nanocages. This design provides large surface area for lithium polysulfides (LiPSs) adsorption, accelerates electron transport and enhances electrochemical redox of LiPSs. Benefiting from the unique structural features, the LSBs with the Ni@NG-CNTs as polysulfide barrier keep high reversible specific capacities of 309.1 and 265.0 mAh·g⁻¹ at 5 and 10 C rates after 500 cycles. This work provides a new strategy for constructing self-assembled hybrids of CNTs and graphene nanosheets with abundant carbon nanocages for high-performance LSBs.

     

Composites of graphene and encapsulated silicon for practically viable high-performance lithium-ion batteries

A facile and scalable approach to synthesize silicon composite anodes has been developed by encapsulating Si particles via in situ polymerization and carbonization of phloroglucinol-formaldehyde gel, followed by incorporation of graphene nanoplatelets. As a result of its structural integrity, high packing density and an intimate electrical contact consolidated by the conductive networks, the composite anode yielded excellent electrochemical performance in terms of charge storage capability, cycling life and coulombic efficiency. A half cell achieved reversible capacities of 1,600 mAh·g^?1 and 1,000 mAh·g^?1 at 0.5 A·g^?1 and 2.1 A·g^?1, respectively, while retaining more than 70% of the initial capacities over 1,000 cycles. Complete lithium-ion pouch cells coupling the anode with a lithium metal oxide cathode demonstrated excellent cycling performance and energy output, representing significant advance in developing Si-based electrode for practical application in high-performance lithium-ion batteries.      

Ultrasonication-assisted and gram-scale synthesis of Co-LDH nanosheet aggregates for oxygen evolution reaction

Electrochemical water splitting (EWS) is a highly clean and efficient method for high-purity hydrogen production. Unfortunately, EWS suffers from the sluggish and complex oxygen evolution reaction (OER) kinetics at anode. At present, the efficient, stable, and low-cost non-precious metal based OER electrocatalyst is still a great and long-term challenge for the future industrial application of EWS technology. Herein, we develop a simple and fast approach for gram-scale synthesis of flower-like cobalt-based layered double hydroxides nanosheet aggregates by ultrasonic synthesis, which show outstanding electrocatalytic performance for the oxygen evolution reaction in alkaline media, such as preeminent stability, small overpotential of 300 mV at 10 mA·cm⁻² and small Tafel slope of 110 mV·dec⁻¹.

     

Ultra-stable K metal anode enabled by oxygen-rich carbon cloth

The K metal batteries are emerged as promising alternatives beyond commercialized Li-ion batteries. However, suppressing uncontrolled dendrite is crucial to the accomplishment of K metal batteries. Herein, an oxygen-rich treated carbon cloth (TCC) has been designed as the K plating host to guide K homogeneous nucleation and suppress the dendrite growth. Both density function theory calculations and experimental results demonstrate that abundant oxygen functional groups as K-philic sites on TCC can guide K nucleation and deposition homogeneously. As a result, the TCC electrode exhibits an ultra-long-life over 800 cycles at high current density of 3.0 mA·cm⁻² for 3.0 mA·h·cm⁻². Furthermore, the symmetrical cells can run stably for 2,000 h with low over-potential less than 20 mV at 1.0 mA·cm⁻² for 1.0 mA·h·cm⁻². Even at a higher current of 5.0 mA·cm⁻², the TCC electrode can still stably cycle for 1,400 h.