Functionalized interfacial cover design toward pure silicon anode for high power density lithium–ion capacitor

A hybrid PEMFC/supercapacitor device with high energy and power densities based on reduced graphene oxide/Nafion/Pt electrode

Although batteries have been successfully employed in light-duty vehicles (hybrid and fully electric cars), batteries still find it is hard to satisfy power-hungry platforms such as trucks, trams, and buses. Conventional lithium ion batteries (LIB) could provide power density less than 3 kW/kg with relatively moderate energy density. On the other side, supercapacitors (SCs) that are known to provide power density of more than 10 kW/kg have a very low energy density of less than 1 Wh/kg and thus, SCs could not be used solely as energy storage. However, employing anode from LIB and electrode from SC together in a single system would benefit both high energy and power density, which system is-so called lithium ion capacitor (LIC). To date, so many attempts have been done to investigate the best anode material combination with activated carbon (AC) to obtain high performance LIC. The anode materials that are commonly utilized in LIB such as graphite, hard carbon, Li4Ti5O12 (LTO), Fe3O4, SnO2, and silicon based material have been extensively studied for LIC. Graphite that is known as an ubiquitous anode material in LIBs provided relatively high energy density of c.a. 100 Wh/kg and maximum power density of less than 2 kW/kg in LIC. Among all, LTO application was found to be the least desirable material for LIC since it provided relatively low maximum energy and power density, which was merely less than 40 Wh/kg and 2 kW/kg, respectively, due to its low conductivity and high voltage plateau at around 1.5 V. Grphene has been used to reinforce rate capability of Fe3O4 and it demonstrated promising energy density as high as 86 Wh/kg. However, the maximum power density of the enhaced electrode material was only 2.6 kW/kg. Higher power LIC can be achieved by harnessing hard carbon anode material, which displayed maximum power density of about 50 kW/kg. However, the high power density of hard caron in LIC was compensated by extremely low energy density of less than 2 Wh/kg. Herein, we investigate the electrochemical performance of LIC by using silicon oxycarbide (SiOC) as the anode and the AC from biomass (Zalacca salacca) peels as the cathode to provide massive power while maintaining the energy density relatively high. SiOC showed an outstanding rate capability performance indicated by relatively high discharge capacity of over than 200 mAh/g at current density of 80 A/g. The excelent rate capability was attributed to the fast lithium diffusion in SiOC, which was represented by high lithium diffusion coefficient (DLi+) of 5.1 × 10-6 cm2/s. Meanwhile, the AC derived from biomass is promising since its surface area (c.a. 2600 m2/g) and capacitance (163.7 F/g) was significantly higher than that of commercial AC. Combination of SiOC and AC derived from Zalacca salacca in a single unit of LIC could be used to provide a massive power density of 155kW/kg while maintained relatively high energy density of 25 Wh/kg. Moreover, the resulting LIC demonstrated highly stable cycle retention at high C-rate. After reaching equilbrium state, the cycle retention of LIC at 50C was 99.4% after more than 40,000 cycles. At higher C-rate of 100C, the cycle retention of the LIC was 99% even after more than 75,000 cycles. The present study indicates that LIC design based on SiOC and AC from Zalacca salacca peels is suitable for energy storage in high-duty platforms such as trucks, trams, and buses.

Developing dielectric capacitors with both a high power density and a high energy density for application in power electronics has been a long-standing challenge. Glass-ceramics offer the potential of retaining the high relative permittivity of ceramics and at the same time of exhibiting the high dielectric breakdown strength and fast charge/discharge rate of glasses, thus producing concurrently high power and energy densities in a single material. In this work, glass-ceramics are fabricated to achieve simultaneously high power and energy densities, high efficiency, and thermal stability by tuning the glass crystallization process via a suitable nucleating agent and a high oxygen partial pressure. Under the same practical charge-discharge test conditions, the as-prepared glass-ceramics combine the high energy density of ceramics and ultrafast discharge rate of glasses, producing the highest power density among glass- and ceramic-based dielectric materials. This work demonstrates the significant potential of achieving both high power and energy densities in glass-ceramics by optimizing the glass crystallization process.

Lithium-Ion Batteries receive growing attention because of their potentially high energy and power density, which are important requirements for automobile applications. Reports agreed that the positive electrode is hereby the performance limiting cell component. NxMyCz (nickel manganese cobalt spinel) is one of the most promising cathode materials, both due to its rather high operating voltage and to either high power or energy density [1]. Hereby, a compromise between high power (thin layers and, i.e., high porosity) and high energy density (thick layers and, i.e., low porosity) has to be reached, in particular for automotive applications. This demands for an extended understanding of the interplay between microstructure parameters and chemical stoichiometry of NMC cathodes on cell performance characteristics. In this study, two NMC - cathodes recovered from commercial high energy and high power cells are analyzed (i) by SEM and X-ray tomography and (ii) by Electrochemical Impedance spectroscopy (EIS). By evaluating the impedance spectra measured at 0 to 40°C and at SOC 0 to SOC 100 by the distribution function of relaxation times (DRT) [2], a physically motivated transition line model [3] was established. The microstructure parameters required for a quantitative analysis of the electrochemical loss processes were obtained by X-ray tomography data. Additionally, the exact composition is determined by energy dispersive X-ray spectroscopy (EDX) investigations The results confirm, that a NMC electrode custom tailored for high energy density is rather thick (70 µm) and made of large low-porous agglomerates of primary particles, as described in [4]. The significant difference between the NMC cathode of a high energy and a high power cell however is not, as expected, a significantly higher porosity, but a sophisticated combination of small carbon black particles and elongated carbon black fibers, enabling high discharge currents. The tortuosity of the electrode pores, which represent the transport pathways for the liquid electrolyte, is low for the high power cell, which raises the effective electrolyte conductivity significantly, when compared to the high energy cell [4]. Furthermore the high power cell features a special compound of two different NxMyCz active materials. By including all the results from EIS, DRT, X-ray tomography and EDX, an evaluation of the influence of composition and microstructure on performance characteristics of the NxMyCz cathodes will be presented.

Novel Na0.5Bi0.5TiO3 based, lead-free energy storage ceramics with high power and energy density and excellent high-temperature stability

The growing demands for electrochemical energy storage systems is driving the exploration of novel devices, with lithium-ion capacitors (LICs) emerging as a promising strategy to achieve both high energy density and fast charge capability. However, the low capacitance of commercial activated carbon (AC) cathode based on anion absorption/desorption limits LIC applications. Herein, commercial graphite is proposed as the cathode to construct an innovative AC (−)//graphite (+) system. The graphite cathode functions as anion hosting, allowing reversible intercalation/de-intercalation of anions into/from its interlayers. The as-designed AC (−)//graphite (+) full cell achieves stable cycling with 90.6% capacity retention after 200 cycles at 0.1 A g−1 and a prolonged lifespan with 87.5% capacity retention after 5000 cycles at 0.5 A g−1 with the upper cut-off voltage of 5.0 V, yielding a high average Coulombic efficiency (CE) of 99.3%. Moreover, the full cell exhibits a high energy density (>200 Wh kg−1) and power density of 7.7 kW kg−1 (calculated based on active mass in both electrodes). These performances exceed most LICs based on anions absorption/desorption on the surface of AC cathodes. This work explores an effective electrode revolution with the assistance of anion intercalation/de-intercalation chemistry for developing novel LICs with high energy and power densities.

Li ion battery (LIB) and electrochemical capacitor (EC) are considered as the most widely used energy storage systems (ESSs) because they can produce a high energy density or a high power density, but it is a huge challenge to achieve both the demands of a high energy density as well as a high power density on their own. A new hybrid Li ion capacitor (HyLIC), which combines the advantages of LIB and Li ion capacitor (LIC), is proposed. This device can successfully realize a potential match between LIB and LIC and can avoid the excessive depletion of electrolyte during the charge process. The galvanostatic charge-discharge cycling tests reveal that at low current, the HyLIC exhibits a high energy density, while at high current, it demonstrates a high power density. Ragone plot confirms that this device can make a synergetic balance between energy and power and achieve a highest energy density in the power density range of 80 to 300 W kg−1. The cycle life test proves that HyLIC exhibits a good cycle life and an excellent coulombic efficiency. The present study shows that HyLIC, which is capable of achieving a high energy density, a long cycle life and an excellent power density, has the potential to achieve the winning combination of a high energy and power density.

With the battery-type anode and capacitor-type cathode, lithium-ion capacitors (LICs) are expected to exhibit both high energy and high power density but suffer from the mismatch of the electrode reaction kinetics and capacity. Herein, to alleviate the mismatch between the two electrodes and synergistically enhance the energy/power density, we design a method of microwave irradiation reduction to prepare graphene-based electrode material (MRPG/CNT) with fast ion/electron pathway. The three-dimensional structure of CNT intercalation to graphene inhibits the restacking of graphene sheets and improves the conductivity of the electrode material, resulting a rapid ion and electron diffusion channel. Due to its specific properties, MRPG/CNT materials can be used as both anode and cathode electrodes of LICs at the same time. As anode, MRPG/CNT shows a high capacity of 1200 mAh g-1 as well as high rate performance. As cathode, MRPG/CNT displays a high capacity of 108 mAh g-1 and the capacity retention of 100% after 8000 cycles. Coupling the prelithiated MRPG/CNT anode with MRPG/CNT cathode gives a full-graphene-based symmetric LIC, which achieves a high energy density of 232.6 Wh kg-1 at 226.0 W kg-1, 111.2 Wh kg-1 at the ultrahigh power density of 45.2 kW kg-1, and superior capacity retention of 86% after 5000 cycles. The structure design of this electrode provides a new strategy for alleviating the mismatch of LIC electrodes and constructing high-performance symmetrical LICs.

Ru oxide supercapacitors with high loadings and high power and energy densities

Recent advancements in an electrification of transportation sectors and adoption of renewable energies have increased a demand for energy storage devices with both high power density and energy density as current technologies including Li-ion battery (LIB) and electrical double layer capacitor (EDLC) can deliver either high energy or high power density. To bridge the gap between LIB and EDLC, Li-ion capacitors (LICs) was proposed by Amatucci in 2011[1] by employing a LIB-type electrode as an anode and a EDLC-type electrode as a cathode in carbonate based organic electrolytes containing Li-salts. Li-ions are stored in anode via intercalation process and anions are stored on cathode surface via adsorption. LIC is promised to combines the advantages of two entities by delivering high energy density, high power density, long cycle life, and low self-discharge.[2,3] However, the main challenge in LIC is the disparity in charge storage kinetics arising from the different charge storage mechanism in anode and cathode. To increase Li-ion kinetics in LIB-type electrode, many electrode-engineerings including nanostructuring active materials[4], making composites with carbonaceous nanomaterials[5–8], and utilizing electronically conductive sulfides[9] and nitrides[10] showed promising results. However, in spite of the considerable number of studies focusing on increasing power density of LIB-type electrode, only a few reports investigate the effects of electrolytes on the LIC performances.[11,12] The influences of anions in electrolytes on the LIC performance are indisputable as charge storage of the EDLC-type cathode sololy depends on the anion-adsorptions. Herein, this study explores the roles of different anions in Li-salts, including lithium hexfluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), and lithium bis(trifluoromethanesulfonyl)imide (LiC2F6NO4S2, LiTFSI), on the LIC performance. The prepared electrolytes were tested in a LIC consists of spinel lithium titanate anode (Li4Ti5O12, LTO) and activated carbon cathode (AC). The present study aims to highlight the important parameters to be considered when designing an optimized electrolyte system for LIC applications. [1] G.G. Amatucci, F. Badway, A. Du Pasquier, T. Zheng, J. Electrochem. Soc. 148 (2001) A930 [2] K. Naoi, S. Ishimoto, J. Miyamoto, W. Naoi, Energy Environ. Sci. 5 (2012) 9363 [3] W. Zuo, R. Li, C. Zhou, Y. Li, J. Xia, J. Liu, Adv. Sci. 4 (2017) 1 [4] L. Kong, C. Zhang, J. Wang, W. Qiao, L. Ling, D. Long, Sci. Rep. 6 (2016) 21177 [5] H. Kim, M.-Y. Cho, M.-H. Kim, K.-Y. Park, H. Gwon, Y. Lee, K.C. Roh, K. Kang, Adv. Energy Mater. 3 (2013) 1500 [6] J. Wang, H. Li, L. Shen, S. Dong, X. Zhang, RSC Adv. 6 (2016) 71338 [7] L. Yan, X. Rui, G. Chen, W. Xu, G. Zou, H. Luo, Nanoscale. 8 (2016) 8443 [8] Q. Wang, Z.H. Wen, J.H. Li, Adv. Funct. Mater. 16 (2006) 2141 [9] K. Kato, F.N. Sayed, G. Babu, P.M. Ajayan, 2D Mater. 5 (2018) 25016 [10] R. Wang, J. Lang, P. Zhang, Z. Lin, X. Yan, Adv. Adv. Funct. Mater. 25 (2015) 2270 [11] T. Zhang, B. Fuchs, M. Secchiaroli, M. Wohlfahrt-mehrens, S. Dsoke, Electrochim. Acta. 218 (2016) 163 [12] S. Liu, S. Liu, K. Huang, J. Liu, Y. Li, D. Fang, H. Wang, Y. Xia, J. Solid State Electrochem. 16 (2012) 1631

Commercially available carbon cloths (CCs) are promising candidates to construct flexible and wearable electronics. Herein, post‐treated CCs are employed to construct flexible supercapacitors (SCs). CCs are first activated in KOH solution and subsequently thermally annealed, resulting in their unique porous microstructure and a wide potential window up to 2.2 V. Using these binder‐ and current‐collector‐free CCs as the capacitor electrodes, a high‐performance and flexible electrical double‐layer capacitor is constructed. In 1 m KOH aqueous solution, its specific capacitance of as high as 1 967.0 mF cm−2 is obtained at a current density of 30 mA cm−2. Moreover, it exhibits excellent capacitance retention and delivers both high energy density (e.g., 93.38 W h kg−1 at a power density of 3 890 W kg−1) and high power density (e.g., 12 850 W kg−1 at an energy density of 12 W h kg−1). Such binder‐free, easy‐assembling, scalable flexible SCs are thus promising for miniaturized electronic industries in the future.

We develop zirconium-templated NiO/NiOOH nanosheets on nickel foam and polypyrrole-embedded in exfoliated carbon fiber cloth as complementary electrodes for an asymmetric battery-type supercapacitor device. We achieve high volumetric energy and power density by the modification of commercially available current collectors (CCs). The modified CCs provide the source of active material, actively participate in the charge storage process, provide a larger surface area for active material loading, need no additional binders or conductive additives, and retain the ability to act as the CC. Nickel foam (NF) CCs are modified by use of a soft-templating/solvothermal treatment to generate NiO/NiOOH nanosheets, where the NF is the source of Ni for the synthesis. Carbon-fiber cloth (CFC) CCs are modified by an electrochemical oxidation/reduction process to generate exfoliated core-shell structures (ECFC). Electropolymerization of pyrrole into the shell structure produces polypyrrole embedded in exfoliated core-shell material (PPy@rECFC). Battery-type supercapacitor devices are produced with NiO/NiOOH@NF and PPy@rECFC as positive and negative electrodes, respectively, to demonstrate the utility of this approach. Volumetric energy densities for the full-cell device are in the range of 2.60-4.12 mWh cm-3 with corresponding power densities in the range of 9.17-425.58 mW cm-3. This is comparable to thin-film lithium-ion batteries (0.3-10 mWh cm-3) and better than some commercial supercapacitors (<1 mWh cm-3).1 The energy and power density is impressive considering that it was calculated using the entire cell volume (active materials, separator, and both CCs). The full-cell device is highly stable, retaining 96% and 88% of capacity after 2000 and 5000 cycles, respectively. These results demonstrate the utility of directly modifying the CCs and suggest a new method to produce high volumetric energy density and power density storage devices.

An ultra-high voltage viologen/Br2 flow battery was designed based on a novel two-electron viologen derivative, a highly-conductive and low-cost porous polyolefin membrane, and an effective complexing agent, making the battery one of the most stable two-electron viologen-based flow batteries with superior energy and power density at the same time.

All nanocarbon Li-Ion capacitor with high energy and high power density

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).