Preparation and electrochemical characterization of ultrathin WO<Subscript>3−<Emphasis Type="Italic">x</Emphasis></Subscript>/C nanosheets as anode materials in lithium ion batteries

Ultrathin two-dimensional (2D) nanomaterials offer unique advantages compared to their counterparts in other dimensionalities.O-vacancies in such materials allow rapid electron diffusion.Carbon doping often improves the electric conductivity.Considering these merits,the WO3-x/C ultrathin 2D nanomaterial is expected to exhibit excellent electrochemical performance in Li-ion batteries.Here,ultrathin WO3-x/C nanosheets were prepared via an acid-assisted one-pot process.The as-prepared WO3-x/C ultrathin nanosheets showed good electrochemical performance,with an initial discharge capacity of 1,866 mA·h·g-1 at a current density of 200 mA·g-1.After 100 cycles,the discharge and charge capacities were 662 and 661 mA·h·g-1,respectively.The reversible capacity of the WO3-x/C ultrathin nanosheets exceeded those of WO3 and WO3-x nanosheets.The electrochemical testing results demonstrated that WO3-x/C ultrathin nanosheets are promising alternative anode materials for Li-ion batteries.     

Ultrafine Sn nanocrystals in a hierarchically porous N-doped carbon for lithium ion batteries

We report a simple method of preparing a high performance,Sn-based anode material for lithium ion batteries (LIBs).Adding H2O2 to an aqueous solution containing Sn2+ and aniline results in simultaneous polymerization of aniline and oxidation of Sn2+ to SnO2,leading to a homogeneous composite of polyaniline and SnO2.Hydrogen thermal reduction of the above composite yields N-doped carbon with hierarchical porosity and homogeneously distributed,ultrafine Sn particles.The nanocomposite exhibits excellent performance as an anode material for lithium ion batteries,showing a high reversible specific capacity of 788 mAh·g-1 at a current density of 100 mA·g-1 after 300 cycles and very good stability up to 5,000 mA·g-1.The simple preparation method combined with the good electrochemical performance is highly promising to promote the application of Sn based anode materials.     

Understanding of the capacity contribution of carbon in phosphorus-carbon composites for high-performance anodes in lithium ion batteries

Phosphorus has recently received extensive attention as a promising anode for lithium ion batteries (LIBs) due to its high theoretical capacity of 2,596 mAh·g-1.To develop high-performance phosphorus anodes for LIBs,carbon materials have been hybridized with phosphorus (P-C) to improve dispersion and conductivity.However,the specific capacity,rate capability,and cycling stability of P-C anodes are still less than satisfactory for practical applications.Furthermore,the exact effects of the carbon support on the electrochemical performance of the P-C anodes are not fully understood.Herein,a series of xP-yC anode materials for LIBs were prepared by a simple and efficient ball-milling method.6P-4C and 3P-7C were found to be optimum mass ratios of x/y,and delivered initial discharge capacities of 1,803.5 and 1,585.3.mAh.g-1,respectively,at 0.1 C in the voltage range 0.02-2 V,with an initial capacity retention of 68.3％ over 200 cycles (more than 4 months cycling life) and 40.8％ over 450 cycles.The excellent electrochemical performance of the 6P-4C and 3P-7C samples was attributed to a synergistic effect from both the adsorbed P and carbon.     

A new active NaVMoO_6 cathode material for rechargeable Li ion batteries

Brannerite-type NaVMoO6 with vanadium(V5+) and molybdenum(Mo6+) elements in the highest valence states is synthesized by a sol-gel method using Na2CO3, NH4VO3, MoO3 and citric acid reagents. The results of X-ray diffraction(XRD) with Rietveld refinement and X-ray photoelectron spectroscopy(XPS) show that the obtained NaVMoO6 sample is single-phase. Novel electrode material(NaVMoO6) with layered structure is first utilized as cathode material for lithium ion batteries(LIBs). The NaVMoO6 electrode delivers reversible specific capacity of 126.4 mA h g-1 at 5 mA g-1 after 50 cycles. The stable structure of NaVMoO6 is corroborated by ex-situ XRD, suggesting that this material is considered as a prospective cathode for LIBs. This studying enriches the possibilities of molybdenum-based materials as cathodes for LIBs.     

FeSb@N-doped carbon quantum dots anchored in 3D porous N-doped carbon with pseudocapacitance effect enabling fast and ultrastable potassium storage

Potassium-ion batteries(PIBs)are promising ne15t-generation energy storage candidates due to abundant resources and low cost.Sb-based materials with high theoretical capacity(660 mAh·g^-1)and low working potential are considered as promising anode for PIBs.The remaining challenge is poor stability and slow kinetics.In this work,FeSb@N-doped carbon quantum dots anchored in three-dimensional(3D)porous N-doped carbon(FeSb@C/Nc3DC/N),a Sb-based material with a particular structure,is designed and constructed by a green salt-template method.As an anode for PIBs,it exhibits extraordinarily high-rate and long-cycle stability(a capacity of 245 mAh·g^-1 at 3,080 mAh·g^-1 after 1,000 cycles).The pseudocapacitance contribution(83%)is demonstrated as the origin of high-rate performance of the FeSb@C/NС3DC/N electrode.Furthermore,the potassium storage mechanism in the electrode is systematically investigated through ex-situ characterization techniques including ex-situ transmission electron microscopy(TEM)and X-ray photoelectron spectroscopy(XPS).Overall,this study could provide a useful guidance for future design of high-performance electrode materials for PIBs.     

Spinel-layered integrate structured nanorods with both high capacity and superior high-rate capability as cathode material for lithium-ion batteries

Spinel phase LiMn2O4 was successfully embedded into monoclinic phase layeredstructured Li2MrnO3 nanorods,and these spinel-layered integrate structured nanorods showed both high capacities and superior high-rate capabilities as cathode material for lithium-ion batteries (LIBs).Pristine Li2MnO3 nanorods were synthesized by a simple rheological phase method using α-MnO2 nanowires as precursors.The spinel-layered integrate structured nanorods were fabricated by a facile partial reduction reaction using stearic acid as the reductant.Both structural characterizations and electrochemical properties of the integrate structured nanorods verified that LiMn2O4 nanodomains were embedded inside the pristine Li2MnO3 nanorods.When used as cathode materials for LIBs,the spinel-layered integrate structured Li2MnO3 nanorods (SL-Li2MnO3) showed much better performances than the pristine layered-structured Li2MnO3 nanorods (L-Li2MnO3).When charge-discharged at 20 mA·g-1 in a voltage window of 2.0-4.8 V,the SL-Li2MnO3 showed discharge capadties of 272.3 and 228.4 mAh.g-1 in the first and the 60th cycles,respectively,with capacity retention of 83.8％.The SL-Li2MnO3 also showed superior high-rate performances.When cycled at rates of 1 C,2 C,5 C,and 10 C (1 C =200 mA·g-1) for hundreds of cycles,the discharge capacities of the SL-Li2MnO3 reached 218.9,200.5,147.1,and 123.9 mAh·g-1,respectively.The superior performances of the SL-Li2MnO3 are ascribed to the spineMayered integrated structures.With large capacities and superior high-rate performances,these spinel-layered integrate structured materials are good candidates for cathodes of next-generation high-power LIBs.     

Bimetallic zeolitic imidazolate framework-derived substrate-free anode with superior cyclability for high-capacity lithium-ion batteries

Freestanding carbon nanofibers loaded with bimetallic hollow nanocage structures were synthesized.The nanocages inherited the rhombic dodecahedral morphology of the zeolitic imidazolate framework(ZIF)precursors,ZIF-8 and ZIF-67.As anode materials for lithium-ion batteries(LIBs),the bimetallic nanocage-loaded freestanding carbon nanofibers effectively buffered volume expansions and alleviated pulverization through their different reduction and oxidation potentials.The higher capacities of the composite anodes arose via the formation of the Li_xZn alloy and Li₂O by Zn and Co ions,respectively,and the enhanced conductivity conferred by the carbon nanofibers.A synergistic effect of the composite components toward the strong electrochemical performance(688 m A h·g^-1at 1200 m A·g^-1)of the bimetallic nanocage-loaded fibers was demonstrated through the superior long-term stability of the anode(1048 m A h·g^-1after 300 cycles at 100 m A·g^-1),suggesting that the fabricated anode can be a promising material for use in portable LIBs.     

Freestanding hierarchical porous carbon film derived from hybrid nanocellulose for high-power supercapacitors

Nanocellulose is a sustainable and eco-friendly nanomaterial derived from renewable biomass.In this study,we utilized the structural advantages of two types of nanocellulose and fabricated freestanding carbonized hybrid nanocellulose films as electrode materials for supercapacitors.The long cellulose nanofibrils (CNFs) formed a macroporous framework,and the short cellulose nanocrystals were assembled around the CNF framework and generated micro/mesopores.This two-level hierarchical porous structure was successfully preserved during carbonization because of a thin atomic layer deposited (ALD) Al2O3 conformal coating,which effectively prevented the aggregation of nanocellulose.These carbonized,partially graphitized nanocellulose fibers were interconnected,forming an integrated and highly conductive network with a large specific surface area of 1,244 m2·g-1.The two-level hierarchical porous structure facilitated fast ion transport in the film.When tested as an electrode material with a high mass loading of 4 mg·cm-2 for supercapacitors,the hierarchical porous carbon film derived from hybrid nanocellulose exhibited a specific capacitance of 170 F.g-1and extraordinary performance at high current densities.Even at a very high current of 50 A·g-1,it retained 65％ of its original specific capacitance,which makes it a promising electrode material for high-power applications.     

Ordered SnO nanoparticles in MWCNT as a functional host material for high-rate lithium-sulfur battery cathode

Lithium-sulfur battery has become one of the most promising candidates for next generation batteries,and it is still restricted due to the low sulfur conductivity,large volume expansion and severe polysulfide shuttling.Herein,we present a novel hybrid electrode with a ternary nanomaterial based on sulfur-impregnated multiwalled carbon nanotubes filled with ordered tin-monoxide nanoparticles (MWCNT-SnO/S).Using a dry plasma reduction method,a mechanically robust material is prepared as a cathode host material for lithium-sulfur batteries.The MWCNT-SnO/S electrode exhibits high conductivity,good ability to capture polysulfides,and small volume change during a repeated charge-discharge process.In situ transmission electron microscopy and ultraviolet-visible absorption results indicate that the MWCNT-SnO host efficiently suppresses volume expansion during lithiation and reduces polysulfide dissolution into the electrolyte.Furthermore,the ordered SnO nanoparticles in the MWCNTs facilitate fast ion/electron transfer during the redox reactions by acting as connective links between the walls of the MWCNTs.The MWCNT-SnO/S cathode with a high sulfur content of 70 wt.％ exhibits an initial discharge capacity of 1,682.4 mAh·g-1 at 167.5 mA·g-1 (0.1 C rate) and retains a capacity of 530.1 mAh·g-1 at 0.5 C after 1,000 cycles with nearly 100％ Coulombic efficiency.Furthermore,the electrode exhibits the high capacity even at a high current rate of 20 C.     

NaFeTiO4 nanorod/multi-walled carbon nanotubes composite as an anode material for sodium-ion batteries with high performances in both half and full cells

NaFeTiO4 nanorods of high yields (with diameters in the range of 30-50 nm and lengths of up to 1-5 μm) were synthesized by a facile sol-gel method and were utilized as an anode material for sodium-ion batteries for the first time.The obtained NaFeTiO4 nanorods exhibit a high initial discharge capacity of 294 mA·h·g-1 at 0.2 C (1 C =177 mA·g-1),and remain at 115 mA·h·g-1 after 50 cycles.Furthermore,multi-walled carbon nanotubes (MWCNTs) were mechanically milled with the pristine material to obtain NaFeTiO4/MWCNTs.The NaFeTiO4/MWCNTs electrode exhibits a significantly improved electrochemical performance with a stable discharge capacity of 150 mA·h·g-1 at 0.2 C after 50 cycles,and remains at 125 mA·h·g-1 at 0.5 C after 420 cycles.The NaFeTiO4/MWCNTs//Na3V2(PO4)3/C full cell was assembled for the first time;it displays a discharge capacity of 70 mA·h·g-1 after 50 cycles at 0.05 C,indicating its excellent performances.X-ray photoelectron spectroscopy,ex situ X-ray diffraction,and Raman measurements were performed to investigate the initial electrochemical mechanisms of the obtained NaFeTiO4/MWCNTs.     

Rationally designed carbon-coated Fe304 coaxial nanotubes with hierarchical porosity as high-rate anodes for lithium ion batteries

Fe3O4 is a promising high-capacity anode material for lithium ion batteries, but challenges including short cycle life and low rate capability hinder its widespread implementation. In this work, a well-defined tubular structure constructed by carbon-coated Fe3O4 has been successfully fabricated with hierarchically porous structure, high surface area, and suitable thickness of carbon layer. Such purposely designed hybrid nanostructures have an enhanced electronic/ionic conductivity, stable electrode/electrolyte interface, and physical buffering effect arising from the nanoscale combination of carbon with Fe3O4, as well as the hollow, aligned and hierarchically porous architectures. When used as an anode material for a lithium-ion half cell, the carbon-coated hierarchical Fe3O4 nanotubes showed excellent cycling performance with a specific capacity of 1,020 mAh.g^-1 at 200 mA.g^-1 after 150 cycles, a capacity retention of ca. 103%. Even at a higher current density of 1,000 mA·g^-1, a capacity of 840 mAh·g^-1 is retained after 300 cycles with no capacity loss. In particular, a superior rate capability can be obtained with a stable capacity of 355 mAh.g^-1 at 8,000 mA·g^-1. The encouraging results indicate that hierarchically tubular hybrid nanostructures can have important implications for the development of high-rate electrodes for future rechargeable lithium ion batteries （LIBs）.     

Improving the intrinsic electronic conductivity of NiMo04 anodes by phosphorous doping for high lithium storage

Heteroatom doping is one of the most promising strategies toward regulating intrinsically sluggish electronic conductivity and kinetic reaction of transition metal oxides for enhancing their lithium storage.Herein,we designed phosphorus-doped NiMo0₄ nanorods(P-NiMo0₄)by using a facile hydrothermal method and subsequent low-temperature phosphorization treatment.Phosphorus doping played an indispensable role in significantly improving electronic conductivity and the Li+diffusion kinetics of NiMo0₄ materials.Experimental investigation and density functional theory calculation demonstrated that phosphorus doping can expand the interplanar spacing and alter electronic structures of NiMo0₄ nanorods.Meanwhile,the introduced phosphorus dopant can generate some oxygen vacancies on the surface of NiMo0₄,which can accelerate Li+diffusion kinetics and provide more active site for lithium storage.As excepted,P-NiMo0₄ electrode delivered a high specific capacity(1,130 mA·g^-1 at 100 mA·g^-1 after 100 cycles),outstanding cycling durability(945 mA·g^-1 at 500 mA·g^-1 over 200 cycles),and impressive rate performance(640 mA·g^-1at 2,000mA·g^-1)for lithium ion batteries(LIBs).This work could provide a potential strategy for improving intrinsic conductivity of transition metal oxides as high-performance anodes for LIBs.     

Tungsten diselenide nanoplates as advanced lithium/sodium ion electrode materials with different storage mechanisms

Transition-metal dichalcogenides (TMDs) exhibit immense potential as lithium/sodium-ion electrode materials owing to their sandwich-like layered structures.To optimize their lithium/sodium-storage performance,two issues should be addressed:fundamentally understanding the chemical reaction occurring in TMD electrodes and developing novel TMDs.In this study,WSe2 hexagonal nanoplates were synthesized as lithium/sodium-ion battery (LIB/SIB) electrode materials.For LIBs,the WSe2-nanoplate electrodes achieved a stable reversible capacity and a high rate capability,as well as an ultralong cycle life of up to 1,500 cycles at 1,000 mA·g-1.Most importantly,in situ Raman spectroscopy,ex situ X-ray diffraction (XRD),transmission electron microscopy,and electrochemical impedance spectroscopy measurements performed during the discharge-charge process clearly verified the reversible conversion mechanism,which can be summarized as follows:WSe2 + 4Li+ + 4e-←→ W + 2Li2Se.The WSe2 nanoplates also exhibited excellent cycling performance and a high rate capability as SIB electrodes.Ex situ XRD and Raman spectroscopy results demonstrate that WSe2 reacted with Na+ more easily and thoroughly than with Li+ and converted to Na2Se and tungsten in the 1st sodiated state.The subsequent charging reaction can be expressed as Na2Se → Se + 2Na+ + 2e-,which differs from the traditional conversion mechanism for LIBs.To our knowledge,this is the first systematic exploration of the lithium/sodium-storage performance of WSe2 and the mechanism involved.     

TiO2 nanotube branched tree on a carbon nanofiber nanostructure as an anode for high energy and power lithium ion batteries

The inherently low electrical conductivity of TiO2-based electrodes as well as the high electrical resistance between an electrode and a current collector represents a major obstacle to their use as an anode for lithium ion batteries. In this study, we report on high-density TiO2 nanotubes （NTs） branched onto a carbon nanofiber （CNF） ＂tree＂ that provide a low resistance current path between the current collector and the TiO2 NTs. Compared to a TiO2 NT array grown directly on the current collector, the branched TiO2 NTs tree, coupled with the CNF electrode, exhibited -10 times higher areal energy density and excellent rate capability （discharge capacity of -150 mA.h.g-1 at a current density of 1,000 mA·g-1）. Based on the detailed experimental results and associated theoretical analysis, we demonstrate that the introduction of CNFs with direct electric contact with the current collector enables a significant increase in areal capacity （mA·h·cm-2） as well as excellent rate capability.     

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.     

Porous FeS nanofibers with numerous nanovoids obtained by Kirkendall diffusion effect for use as anode materials for sodium-ion batteries

Porous FeS nanofibers with numerous nanovoids for use as anode materials for sodium-ion batteries were prepared by electrospinning and subsequent sulfidation.The post-treatment of the as-spun Fe(acac)3-polyacrylonitrile composite nanofibers in an air atmosphere yielded hollow Fe2O3 nanofibers due to Ostwald ripening.The ultrafine Fe2O3 nanocrystals formed at the center of the fiber diffused toward the outside of the fiber via Ostwald ripening.On sulfidation,the Fe2O3 hollow nanofibers were transformed into porous FeS nanofibers,which contained numerous nanovoids.The formation of porosity in the FeS nanofibers was driven by nanoscale Kirkendall diffusion.The porous FeS nanofibers were very structurally stable and had superior sodium-ion storage properties compared with the hollow Fe2O3 nanofibers.The discharge capacities of the porous FeS nanofibers for the 1st and 150th cycles at a current density of 500 mA.g-1 were 561 and 592 mA.h·g-1,respectively.The FeS nanofibers had final discharge capacities of 456,437,413,394,380,and 353 mA.h.g-1 at current densities of 0.2,0.5,1.0,2.0,3.0,and 5.0 A.g-1,respectively.     

Three-Dimensional Self-assembled Hairball-Like VS4 as High-Capacity Anodes for Sodium-Ion Batteries

Sodium-ion batteries(SIBs)are considered to be attractive candidates for large-scale energy storage systems because of their rich earth abundance and consistent performance.However,there are still challenges in developing desirable anode materials that can accommodate rapid and stable insertion/extraction of Na+and can exhibit excellent electrochemical performance.Herein,the self-assembled hairball-like VS4 as anodes of SIBs exhibits high discharge capacity(660 and 589 mAh g−1 at 1 and 3 A g−1,respectively)and excellent rate property(about 100%retention at 10 and 20 A g−1 after 1000 cycles)at room temperature.Moreover,the VS4 can also exhibit 591 mAh g−1 at 1 A g−1 after 600 cycles at 0°C.An unlike traditional mechanism of VS4 for Na+storage was proposed according to the dates of ex situ characterization,cyclic voltammetry,and electrochemical kinetic analysis.The capacities of the final stabilization stage are provided by the reactions of reversible transformation between Na2S and S,which were considered the reaction mechanisms of Na–S batteries.This work can provide a basis for the synthesis and application of sulfur-rich compounds in fields of batteries,semiconductor devices,and catalysts.     

A multiphase sodium vanadium phosphate cathode material for high-rate sodium-ion batteries

The unsatisfactory rate capability and poor cycling stability at high rate of sodium-ion batteries(SIBs) have impeded their practical applications. Herein, a Na₃V₂(PO₄)₃/Na₃V₃(PO₄)₄ multiphase cathode materials for high-rate and long cycling SIBs was successfully synthesized by regulation the stoichiometric ratio of raw materials. The combined experiment and simulation results show that the multiphase materials consisted of NASICON structural phase Na3V2(PO4)3 and layered structure phase Na₃V₃(PO₄)₄, possess abundant phase boundaries. Electrochemical experiments demonstrate that the multiphase materials maintain a remarkable reversible capacity of 69.0 mA h g^-1 even at an ultrahigh current density of 100 C with a high capacity retention of 81.25 % even after 10,000 cycles. Na₃V₂(PO₄)₃/Na₃V₃(PO₄)₄ electrode exhibits a higher working voltage, superior rate capability and better cycling stability than Na₃V₂(PO₄)₃ electrode, which indicates that the introduction of second phase can be an effective strategy for the development of novel cathode materials for SIBs.     

Three-dimensionally ordered,ultrathin graphitic-carbon frameworks with cage-like mesoporosity for highly stable Li-S batteries

Mesoporous carbons have been widely utilized as the sulfur host for lithium-sulfur (Li-S) batteries.The ability to engineer the porosity,wall thickness,and graphitization degree of the carbon host is essential for addressing issues that hamper commercialization of Li-S batteries,such as fast capacity decay and poor high-rate performance.In this work,highly ordered,ultrathin mesoporous graphitic-carbon frameworks (MGFs) having unique cage-like mesoporosity,derived from self-assembled Fe3O4 nanoparticle superlattices,are demonstrated to be an excellent host for encapsulating sulfur.The resulting S@MGFs exhibit high specific capacity (1,446 mAh·g-1 at 0.15 C),good rate capability (430 mAh.g-1 at 6 C),and exceptional cycling stability (～0.049％ capacity decay per cycle at 1 C) when used as Li-S cathodes.The superior electrochemical performance of the S@MGFs is attributed to the many unique and advantageous structural features of MGFs.In addition to the interconnected,ultrathin graphitic-carbon framework that ensures rapid electron and lithium-ion transport,the microporous openings between adjacent mesopores efficiently suppress the diffusion of polysulfides,leading to improved capacity retention even at high current densities.     

Flexible aqueous Ca-ion full battery with super-flat discharge voltage plateau

Recently,multivalent metal-ion batteries have attracted considerable interests on the merits of their natural abundance and multielectron redox property.However,the development of Ca-ion battery is still in their preliminary stage because of the lack of suitable electrode material.The Ca-storage performance of the existing materials is still unsatisfactory with low capacity,poor cyclic stability,as well as sloping discharge profiles,which cannot provide stable energy output.In this work,transition metal oxide Sn-doped In2O3(ITO)has been explored as the aqueous Ca-ion battery anode,which could deliver a high discharge capacity of 71.2 mAh·g^-1 with an ultra-flat discharge voltage plateau.The Ca storage mechanism was revealed to be reversible conversion reaction based on ex-situ X-ray diffraction(XRD),X-ray photoelectron spectroscopy(XPS),and transmission electron microscopy(TEM)characterizations.A flexible aqueous Ca-ion battery was subsequently assembled with zinc hexacyanoferrate(ZnHCF)cathode and ITO anode sandwiched by hydrogel electrolyte,which could deliver a high specific capacity of 75.3 mAh·g^-1 at 0.4 A·g^-1 with a flat output voltage plateau at around 0.8 V.The bendable and flexible Ca-ion battery with decent voltage output will pave the way for the energy storage devices towards practical applications in flexible and wearable electronics.