Anode For Lithium-ion Capacitors Research Articles

Experimental and theoretical investigation of silicon-based carbon composite electrode for high performance Li-ion capacitors

Lithium-ion capacitors (LICs) have garnered significant attention in recent years due to their ability to overcome the shortcomings of lithium-ion batteries (LIBs) and supercapacitors (SCs). Silicon (Si) stands out as a superior anode material for LICs due to its compelling attributes, including a high theoretical specific capacity (4200 mAh/g) and a low de-lithiation potential. Nevertheless, the inherent challenges of Si, such as low electrical conductivity and significant volume expansion (300 %), contribute to low electrochemical performance. To address this issue, a conductive carbon layer is introduced on Si using a simple and scalable approach. The resulting architecture, known as carbon-encapsulated Si (Si/C), not only improves electrical properties by enhancing Li+ diffusion but also mitigates volume expansion, leading to enhanced capacity and cyclic stability. Theoretical findings based on density functional theory (DFT) support these enhancements, confirming improved interactive properties at an atomic scale, including low binding energy and accelerated charge transfer kinetics (higher valence charge transfer) between the Si/C electrode and Li ions. As a result, the ‘binder-free’ and flexible Si/C electrode exhibits a notable initial discharge capacity (3450 mAh/g at 0.05 C) with improved rate capability (3010 mAh/g at 0.1 C). When employed as an anode in LICs, the Si/C electrode exhibits outstanding performance, boasting a large energy density (222.29 Wh/kg), high power density (25 kW/kg), and superior cyclic stability (81.3 % over 10,000 cycles). These findings highlight the potential of the Si/C electrode as a formidable candidate for advanced energy storage applications.

A universal strategy for producing 2D functional carbon-rich materials from 2D porous organic polymers for dual-carbon lithium-ion capacitors

Two-dimensional (2D) carbon materials have attracted enormous attention, but the complicated synthesis methods, inhomogeneous structure and uncontrollable properties still limit their use. Here we report a universal protocol for fabricating a series of heteroatom-doped 2D porous polymers, including pyrrole and indole as nitrogen-dopant sources, and 3,4-ethoxylene dioxy thiophene as a sulfur-dopant source by a simple chemical crosslinking reaction. This bottom-up strategy allows for the large-scale synthesis of functionalized ultrathin carbon nanosheets with a high heteroatom doping content and abundant porosity. Consequently, the obtained N-doped carbon-rich nanosheets (NCNs) sample has a specific capacity of 573.4 mAh g−1 at 5 A g−1 as an anode for lithium-ion capacitors (LICs), and the optimized sample has a specific capacitance of 100.0 F g−1 at 5 A g−1 when used as a cathode for a LIC. A dual-carbon LIC device was also developed that had an energy density of 168.4 Wh kg−1 at 400 W kg−1, while maintaining outstanding cycling stability with a retention rate of 86.3% after 10 000 cycles. This approach has the potential to establish a way for the precise synthesis of substantial amounts of 2D functionalized carbon nanosheets with the desired structure and properties.

Binder-free boron-doped Si nanowires toward the enhancement of lithium-ion capacitor

Lithium-ion capacitors (LICs) are next-generation electrochemical storage devices that combine the benefits of both supercapacitors and lithium-ion batteries. Silicon materials have attracted attention for the development of high-performance LICs owing to their high theoretical capacity and low delithiation potential (∼0.5 V versus Li/Li+). However, sluggish ion diffusion has severely restricted the development of LICs. Herein, a binder-free anode of boron-doped silicon nanowires (B-doped SiNWs) on a copper substrate was reported as an anode for LICs. B-doping could significantly improve the conductivity of the SiNW anode, which could enhance electron/ion transfer in LICs. As expected, the B-doped SiNWs//Li half-cell delivered a higher initial discharge capacity of 454 mAh g−1 with excellent cycle stability (capacity retention of 96% after 100 cycles). Furthermore, the near-lithium reaction plateau of Si endows the LICs with a high voltage window (1.5–4.2 V), and the as-fabricated B-doped SiNWs//AC LIC possesses the maximum energy density value of 155.8 Wh kg−1 at a battery-inaccessible power density of 275 W kg−1. This study provides a new strategy for using Si-based composites to develop high-performance LIC.

A high-rate and ultrastable anode for lithium ion capacitors produced by modifying hard carbon with both surface oxidation and intercalation

A high-rate and ultrastable anode for lithium ion capacitors produced by modifying hard carbon with both surface oxidation and intercalation

The effects of doped phosphorus on the electrochemical performance of hard carbon anode for lithium ion capacitors

Heteroatom is a practical tactic to improve the ability of carbon materials to store lithium ions. In this research, a series of hard carbon with different phosphorus species and contents were simply prepared by annealing the mixture of phytic acid and starch. By studying the phosphorus functional groups species and electrochemical performance of phosphorus-doped carbon, the relation of phosphorus species, phosphorus atoms contents and the Li-storage performance of samples have been closely related. In this context, the high content of phosphorus atoms not means a high specific capacity and the phosphorus-doped hard carbon will produce a higher specific capacity when the doping content of phosphorus atoms ranges around 1.8 %. As to the effect of phosphorus functional groups species on the electrochemical performance of hard carbon, the Li-ions may be stored more efficiently with the higher proportion of CP bonds in phosphorus functional groups species. In this regard, the understanding of how phosphorus functional groups species affect electrochemical performance on hard carbon will help better understand the effect of phosphorus doping on hard carbon anode for lithium ion storage. Meanwhile, it also will provide some insights and support for the application of phosphorus-doped electrodes.

Hierarchical SnO2@PC@PANI composite via in-situ polymerization towards next-generation Li-ion capacitor by limiting alloying process with high energy, wide temperature performance, and cyclability

Lithium-ion capacitors (LICs) are promising electrochemical energy storage devices with hybridization of the battery-type anode and capacitive-type cathode, bringing high energy density and high power density simultaneously in a single device. We report the extraction of activated carbon from the palmyra fruit, in-situ polymerization with polyaniline (PANI), and the making of different composite formulations with SnO2 to be used as anode for LIC with palmyra fruit-derived activated carbon (PC) as the cathode. The SnO2@PC@PANI electrode is restricted to 1 V vs. Li, which allows only the alloying reaction and eliminates the conversion process. An in-situ impedance study is performed to validate the formation and depletion of the solid electrolyte interface over the battery-type electrode upon cycling. Prior to the fabrication of the LIC, the SnO2@PC@PANI is electrochemically pre-lithiated. The fabricated LIC with balanced mass loadings exhibits a mesmerizing electrochemical performance with a maximum energy density of ∼175 Wh kg–1 at room temperature. The possibility of LIC in different climatic conditions is also analyzed by testing its electrochemical performance in different temperature conditions.

Dehalogenation produces graphene wrapped carbon cages as fast-kinetics and large-capacity anode for lithium-ion capacitors

The sluggish kinetics of battery-type anode limits the realization of high capacitance especially at elevated charge-discharge rates for lithium-ion capacitors (LICs). In this work, graphene wrapped carbon cages (GxPy) are obtained via a facile physical-confined pyrolysis approach from graphene oxide (GO)/polyvinylidene fluoride (PVDF), which exhibits great promise as a fast and large-capacity anode for LICs. The thermal degradation process analysis reveals that carbon cages with abundant mesopores derived from the dehalogenation of PVDF are formed spontaneously due to the HF releasing in the pyrolysis process with the aid of physical confined GO template. Hollow carbon cages could ameliorate the Li+ transport path, while 2D graphene serves as a conducting bridge connecting the isolated carbon cages to minimize the barrier of charge transfer. As a result, a LIC pouch-cell based on GxPy hierarchical carbon anode demonstrates high energy density and superior power density, as well as remarkable cycle life. This study may open a unique avenue for designing fast and large-capacity carbon anode and push the development of high-performance LICs.

Self-supported graphene oxide encapsulated chalcopyrite electrode for high-performance Li-ion capacitor

The combination of lithium-ion batteries and supercapacitors makes lithium-ion capacitors (LICs) the ideal energy storage device for commercial applications. However, the high performance of LICs is restricted due to various shortcomings such as low electrode specific capacity and sluggish reaction kinetics. Additionally, the undesirable ‘polysulfide-diffusion’ effect in the cost-effective metal sulfide-based electrodes results in high capacity degradation. Therefore, developing novel strategies to surmount these drawbacks is of prime importance for the development of high-performance LICs. Herein, a novel composite material with the unique architecture of graphene oxide (GO) encapsulation on the chalcopyrite (CuFeS2) microspheres is fabricated as an anode for LIC. Compared to the traditional binder-based approach for electrode fabrication, the anode is fabricated using a ‘binder-free’ approach to enable the exposure of high-density electroactive sites. As a result, the fabrication of a ‘self-standing’ flexible electrode is obtained that finds numerous applications in wearable technology systems. Detailed electrochemical analysis reveals the enhanced reaction kinetics of the composite electrode along with the improved specific capacities and rate capabilities. The unique architecture of the GO encapsulation not only prevents the structural collapse of the chalcopyrite microspheres but also suppresses the polysulfide diffusion, resulting in higher cyclic stability. The role of such carbon encapsulation is studied in detail using experimental studies and is strongly supported by theoretical calculations based on density functional theory (DFT) for the first time. The calculated binding energy and charge transfer confirmed the improved interactive features of Li ions with the composite electrode in terms of enhanced binding energy and higher valence charge transfer. Additionally, the favorable binding energy of Li2S and Li2S4 polysulfides to the composite electrode than the pristine CFS electrode reflects restricted polysulfide diffusion, resulting in outstanding cyclic stability. The assembled LIC device based on the composite electrode displays a large energy density of 192.33 Wh/kg, a high power density of 14,280 W/kg, and excellent cyclic stability of >90 % for 10,000 cycles, outperforming most of the reported metal sulfide-based LICs.

A high-rate and ultrastable anode for lithium ion capacitors produced by modifying hard carbon with both surface oxidation and intercalation

Due to the difference of energy storage mechanisms between the anode and cathode materials, the power density or rate performance of a lithium-ion capacitor is greatly limited by its anode material. Hard carbon is a promising anode material for lithium ion capacitors, and its modification is an important way to improve the electrochemical performance of lithium-ion capacitors. A commercial hard carbon from Kuraray Inc was modified by oxidation followed by intercalation with ZnCl2 (ZnCl2―OHC). The reversible capacity of a half-cell prepared using this material was 257.4 mAh·g−1 at 0.05 A·g−1, which is obviously higher than the unmodified one (172.5 mAh·g−1). The capacity retention of a full cell prepared using ZnCl2―OHC as the anode and activated carbon as the cathode reached 43.3% when the current density increased from 0.1 to 10 A·g−1, which is more than twice that of the untreated hard carbon. After 5 000 charge-discharge cycles at 1 A·g−1, the capacity retention of the full cell was about 98.4%. The modification of hard carbon by surface oxidation and intercalation is therefore a promising way to improve its anode performance for lithium ion capacitors.

High performance Li-ion capacitor based on novel carbon-coated chalcogenide anode

Lithium-ion capacitors (LICs) exhibit the combined advantages of lithium-ion batteries and supercapacitors. Till now, the development of efficient LICs with high energy-power densities with high cyclic stability is restricted due to the limited performance of the electrode in terms of low capacity and sluggish reaction kinetics. Developing a novel electrode that overcomes these existing drawbacks is one of the possible strategies to enhance electrochemical performance. In this work, the superior Li-ion storage capability of highly interconnected Cu2SnS3 (CSS) nanospheres encapsulated in the carbon nanotubes (CNTs) framework as an efficient anode for LIC is demonstrated. Benefiting from the combined charge storage mechanisms of the CSS (alloying + conversion) and the CNTs (insertion), an exceptional high electrochemical performance in terms of high energy density (158.77 Wh/kg) and high power density (12,500 W/kg) with superior cyclic stability for 10,000 cycles is obtained from the fabricated LIC device. The key factors attributed to the improved electrochemical performance are studied in detail using experimental results, comprehensive characterization techniques and are strongly supported by the relevant simulated models based on theoretical calculations. The plausible binding characteristics of the Li-ion and the valence charge transfer in the electrodes are evaluated using first-principle density functional theory (DFT).

Multilayered graphene endowing superior dispersibility for excellent low temperature performance in lithium-ion capacitor as both anode and cathode

Constructing all-graphene symmetric Lithium-ion capacitor (LIC) with high energy and power density has recently gained widespread attention. Here, O-doping multilayered porous graphene (OMG) with micron-size served as both cathode and anode for LIC was prepared via a simple and easily large-scale air thermal treatment method. By rational controlling the reaction temperature and time in the air, the obtained OMG nano-sheets possess high specific surface areas, abundant nano-pores channels, enlarged graphene-interlayers spacing, good conductivity and superior dispersibility. As anode, OMG delivered high average capacity (247 mA h g−1 at 1.0 A g−1), excellent rate capability (138 mA h g−1 at 10 A g−1) and long-term cycling performance (83% capacity retention for 10,000 cycles). As cathode, OMG showed large average capacity (196 mA h g−1 at 1.0 A g−1), superior rate performance (155 mA h g−1 at 10 A g−1) and outstanding cyclic stability (increasing capacity for 7000 cycles). The assembled all-graphene symmetric OMG//OMG LIC exhibited an excellent rate capability (70.7%), high energy density of 131.6 W h kg−1 at 2272 W kg−1 and high energy density of 87.3 W h kg−1 even at a higher power density of 21660 W kg−1 coupled with ultralong cycling stability (96.8% capacity retention for 5000 cycles). More importantly, OMG//OMG still exhibit excellent low-temperature electrochemical properties (98.5 W h kg−1 at 1130 W kg−1 and 94.2% capacity retention under −30 °C), indicating a great application prospect in the next generation energy storage devices for LIC.

The Full-Cell Design of a Li-Ion Capacitor Using a Sn-Ni Alloy As an Anode

Lithium-ion capacitors (LIC) is composed of a capacitors-type cathode and battery-type anode. Thus, LIC has been considered as a favorable electrochemical energy storage device to bridge the lithium-ion batteries (LIB) and supercapacitors.1 We have reported that the synthesis of Sn-Ni alloy by electrodeposition in aqueous solution and its electrochemical behaviors as an anode for LIB and LIC.2,3 Through the above reports, we confirmed that the LIC consisting of Sn-Ni anode shows higher energy and power density than graphite anode based LIC because of high theoretical capacity of Sn (997 mAh g-1). Herein, the material characterization of Sn-Ni alloy was carried out. Besides, full-cell performances of LIC were tested and compared depending on with/without cell optimization.The Sn-Ni alloy is synthesized by electrodeposition using aqueous electrolyte consisting of Tin(II) chloride dihydrate and Nickel(II) chloride. The material characteristics of Sn-Ni alloy were examined by field emission scanning electron microscopy, X-ray diffraction, glow discharge optical emission spectroscopy, and inductively coupled plasma analysis. The electrochemical performances of Sn-Ni anode and LIC full-cell were tested using alf- and full-cell.The Sn-Ni alloy synthesized by electrodeposition has Ni3Sn4 phase which affects the reversible reaction of Sn-Ni alloy as an anode during lithiation/de-lithiation.2 For that reason, Sn-Ni alloy shows a good discharge performance as an anode for LIC (Fig. 1(a)). The in-depth chemical properties of Sn-Ni alloy was examined by GDOES (Fig. 1(b)). The region from the surface to around 6.9 μm shows that the Sn and Ni are mixed. After that, Cu peak corresponding to the Cu substrate was increased, resulting in an intermediate layer consisting of Sn, Ni, and Cu. The Cu signal after 29.4 μm is relatively higher than Sn and Ni, implying that only Cu substrate was presented. This result indicates that the Sn and Ni are mixed from top of Sn-Ni alloy to middle of film with a thickness of approximately 29. 4 μm.Full-cell optimization of LIC was conducted by mass balancing between cathode and anode. It was confirmed that LIC with cell optimization shows improved energy density and power density compared to LIC without cell optimization. Also, LIC consisting of Sn-Ni anode have higher energy and power density than LIC assembled using graphite anode (Fig.1 (c)). Through the above discussion, we believe that this report provides a blueprint for high-performance LIC with Sn-Ni alloy anode.(Figure 1)Fig. 1 (a) XRD patterns, (b) GDOES curves of Sn-Ni alloy, and (c) Ragone plot of LIC. Acknowledgement This work is partially supported by Advanced Low Carbon Technology Research and Development Program of the Japan Science and Technology Agency (JST-ALCA, JPMJAL1008).

Reaction Mechanism Exploration of Binary Oxide Bi2Mo3O12@Ti3C2 Composite As Anode for Li-Ion Capacitor

Metal oxides as pseudocapacitive materials are widely explored as anode for lithium ion capacitors, owing to their high volumetric and gravimetric lithium storage capacities. We present studies on reaction mechanism of binary Bi2Mo3O12 oxide as an anode for lithium storage. In-situ synchrotron XRD measurements are performed on this exotic material to elucidate lithium storage behaviors, coupled with voltage resolved CVs and ex-situ XPS analyses. Synergistic effect is believed to be the factor on improving electrochemical performance of the binary metal oxide anode instead of simple combination of two single components. The Bi2Mo3O12 anode undergoes an initial irreversible conversion reaction resulting in metallic Bi and Li2MoO4 on electrochemical discharge down to 0.01 V vs. Li+/Li. During successive cycling, the two components reversibly uptake and release lithium ions through alloying/de-alloying and intercalation/de-intercalation reactions by forming Li3Bi alloy and Li2+xMoO4. Cycling stability of the Bi2Mo3O12 anode is considerably enhanced by in-situ composition of Ti3C2 MXene. The Bi2Mo3O12@Ti3C2 composite anode exhibits 227 mAh/g capacity upon prolonged 1000 cycles at 2.5 A/g high charge/discharge rate in the voltage range of 3.0 - 0.01 V. This performance indicates the Bi2Mo3O12@Ti3C2 composite can be a potential candidate as anode for Li-ion capacitors.

Copper niobate nanowires immobilized on reduced graphene oxide nanosheets as rate capability anode for lithium ion capacitor

Binary metal niobium oxides can offer a higher specific capacity compared to niobium pentoxide (Nb2O5) and thus are ideal anode candidates for lithium ion capacitors (LICs). However, their lower electronic conductivity limits their ability to achieve high energy and power densities. In this paper, one-dimensional (1D) copper niobate (CuNb2O6) nanowires are successfully prepared by electrospinning technology and then immobilized on two-dimensional (2D) reduced graphene oxide (rGO) nanosheets to form a unique 1D nanowire/2D nanosheet CuNb2O6/rGO structure. The 1D/2D CuNb2O6/rGO electrode exhibits a high specific capacity of 312.2 mAh g−1 at 100 mA g−1 as the anode of LICs. The proposed Li+ storage mechanism of the CuNb2O6 anode involves CuNb2O6 decomposition into lithium niobate (Li3NbO4) and copper (Cu) during the initial lithium insertion process. The intercalation-type Li3NbO4 will further serve as the host to Li+ and the inactive Cu phase will act as a conductive network for electron transportation. Furthermore, the energy density of the assembled CuNb2O6/rGO//activated carbon (CuNb2O6/rGO//AC) device could achieve a value as high as 92.1 Wh kg−1 and could thus be considered as a possible alternative electrode material for high energy and power LICs.

Reduced graphene oxide decorated with crystallized cobalt borate nanoparticles as an anode in lithium ion capacitors

To improve the lithium storage properties of anode in lithium ion capacitors (LICs), reduced graphene oxide (rGO) decorated with crystallized cobalt borate nanoparticles (Co-B/rGO) was prepared by an in-situ growth method. Microstructural characterizations demonstrate that crystallized Co-B nanoparticles not only act as an effective electron transfer bridge between rGO nanosheets but also provide more active sites for lithium storage. As a result, LIC based on Co-B/rGO anode exhibited stable cycling performance with a capacitance retention of 75% after 2000 cycles at 2000 mA g−1, and high energy and power density. Thus, Co-B/rGO can be a promising anode material for LICs.

In situ anchoring MnO nanoparticles on self-supported 3D interconnected graphene scroll framework: A fast kinetics boosted ultrahigh-rate anode for Li-ion capacitor

Lithium ion capacitors (LICs) are deemed to be an ideal complement between lithium-ion batteries and supercapacitors. However, the sluggish kinetics that leads to a poor rate capability of Faradaic insertion anodes remains a handicap. Herein, a self-supported architecture is designed by combining an interconnected graphene scroll (GS) framework with in situ formed well-distributed MnO nanoparticles (NPs) for an advanced LIC anode. In this architecture, the inner-connected tubular GS framework plays a multifunctional role: serving as an electron transport bridge like “highways”, providing a favorable ion transport pathway as well as accommodating the volume expansion and maintaining the structural stability of MnO. Benefiting from the stable structure, highly localized charge-transfer and low energy diffusion barrier, the as-built anode exhibits an ultrahigh-rate behavior (203 mAh g−1 at 20 A g−1) and robust cycling stability (759 mAh g−1 after 1000 cycles at 2 A g−1). When evaluated as a self-supported anode for LIC, the LIC delivers a high energy density of 179.3 Wh kg−1, a high power density of 11.7 kW kg−1, and a capacity retention of 80.8% after 5000 cycles. Moreover, the corresponding soft-packaged LIC keeps stable electrochemical performances at various bending states. All these features manifest the potential of the architecture for application in advanced energy storage devices.

Aerosol-assisted preparation of N-doped hierarchical porous carbon spheres cathodes toward high-stable lithium-ion capacitors

Lithium-ion capacitors (LICs) are gradually emerging as one of the most indispensable hybrid energy storage devices. However, it is one main challenge to evade the mismatch of electrochemical kinetics and specific capacity between cathode and anode in LICs. Herein, we have proposed an efficient strategy to prepare the nitrogen-doped hierarchical porous carbon spheres (NHPCS) as cathode, which is synthesized by a simple aerosol-spraying pyrolysis using the low-cost phenolic resin as carbon source without any other catalyst or hard template. The NHPCS exhibits porous nanospheres structure with an appropriate nitrogen doping level (3.65 at.%). Benefitting from the two-pronged strategy of N-doped feature and nanostructure engineering, NHPCS achieves a high specific capacity of 74 mAh g−1 at a current density of 0.1 A g−1 and remains 86.5% of initial capacity even being subjected to a high rate of 50-fold. Furthermore, a high-performance LIC has been developed by coupling NHPCS cathode and hard carbon anode, which delivers a maximum energy density of 151 Wh kg−1 and excellent cycle stability (96.3% capacity retention after 3000 cycles). Significantly, such designed porous carbon could not only be convenient for scalable production, but also be served for many other energy storage devices. We have presented a larger-scale spray pyrolysis strategy to prepare nitrogen-doped hierarchical porous carbon spheres (NHPCS). A high-stable lithium-ion capacitor has been constructed by coupling NHPCS cathode with hard carbon anode, which exhibits a maximum energy density of 151 Wh kg−1 and capacity retention of 96.3% over 3000 cycles, showing great potential for the next-generation energy storage application.

Heterogeneous nucleation of Li3VO4 regulated in dense graphene aerogel for lithium ion capacitors

Achieving both high gravimetric and volumetric rate performances of the anode for lithium ion capacitors (LICs) is still a challenge. Herein, we propose a dense Li3VO4 (LVO)/graphene aerogel (GA) composite as the two active components anode, the crystalline and particle size of LVO can be regulated in the GA that provides abundant heterogeneous nucleation sites to prevent the agglomeration and preferred growth of LVO. The dense LVO/GA exhibits significantly improved electrochemical performances. The gravimetric/volumetric specific capacity can reach up to 84.4 mAh g−1 and 63.3 mAh cm−3 at the very high current density of 16 A g−1, as well as the 85% capacity retention after 5000 cycles at 8 A g−1. This superior performance is contributed from the facilitated diffusion rate of confined LVO clusters in GA, the accelerated electron transport offered by the three dimensional (3D) graphene skeleton that closely surrounds LVO, and the fast electrochemical kinetics boosted by the combined dense structure. The LICs exhibit excellent energy/power densities (maximum 122.2 W h kg−1, 8.8 kW kg−1). We believe that this two active components design demonstrates an unparalleled function that the single active material cannot realize, and provide a promising road propelling the development of high performance LICs.

High-capacity MnCo2O4 supported by reduced graphene oxide as an anode for lithium-ion capacitors

In order to construct lithium-ion capacitors (LICs) possessing superior performance, a two-step solvothermal method was adopted to prepare high-capacity MnCo2O4 supported by reduced graphene oxide (rGO). MnCo2O4 particles were formed at the first step and then at the second step they were coated onto the surface of rGO sheets. The introduction of rGO boosted the electronic conductivity and the specific surface area. Such synthesized MnCo2O4/rGO composite was employed as an anode of lithium-ion batteries. An ultrahigh initial discharge capacity (1657 mAh g‒1, 0.1 A g‒1) was achieved. And after this anode was repetitively charged/discharged at 0.2 A g‒1 for 100 cycles, a high reversible capacity (791 mAh g‒1) was also presented. A LIC was constructed by using this superior-performance MnCo2O4/rGO composite acting as an anode coupled with an activated carbon (AC) cathode. The maximum specific energy and specific power of the MnCo2O4/rGO//AC LIC reached 78.8 Wh kg‒1 and 3.0 kWh kg‒1, respectively. Moreover, for this LIC, at the end of the 1000th cycle, the capacity retention ratio was 76.9%.

Graphene-like nitrogen-doped porous carbon nanosheets as both cathode and anode for high energy density lithium-ion capacitor

Carbon materials have unique stability and controllable structure for all-carbon lithium-ion capacitors (LICs) electrode materials. In this paper, we used chitosan as a carbon source and self-doped nitrogen source, zinc nitrate as a templating agent. Hierarchical porous carbon nanosheets (PCNS) materials with graphene-like structure and abundant nitrogen doping were prepared through a one-step carbonization process. The PCNS materials were used as both capacitor-type cathode and battery-type anode for LICs. Due to the multi-mesoporous and ultrathin nanosheets structure, a large specific surface area (1321.3 m2 g−1) was obtained of PCNS materials, which ensures a high specific discharge capacity of 65.8 mAh g−1 at 3 A g−1 for the capacitor-type cathode. The interconnected graphene-like structure not only provides a large adsorbable area but also reduces the diffusion distannce of ions between the surface of the electrode and electrolyte. When the PCNS materials used as an anode for LIC, it also appeared a high specific discharge capacity of 285.0 mAh g−1 at a big current density of 20 A g−1. Finally, all-carbon symmetric LIC with a broad voltage window of 0.01–4.5 V was constructed successfully. The symmetric LIC shows a high energy density of 146 Wh kg−1 (at a power density of 1125 W kg−1) and an excellent capacity retention rate of 84.5% (10,000 cycles at 5 A g−1).