Flexible Li-ion Batteries Research Articles

Electrospun free-standing N-doped C@SnO2 anode paper for flexible Li-ion batteries

Electrochemically active SnO2 materials are prospective alternatives for graphite toward better flexible LIBs. However, significant volume changes and structural pulverization restrict the cycling stability and high capacity of SnO2. Here, we report a binder and conductive additive free core-shell N-doped carbon @SnO2 hybrid paper by a subtle coaxial-electrospinning method. Core-shell N-doped C@SnO2 fibers not only offer rapid ionic transport and sufficient buffer space for the volume expansion during the Li insertion and extraction reactions, but also enable high flexibility against both compression and bending deformation. As an anode for LIBs, the hybrid materials delivered a large initial capacity of 1799 mAhg−1 with capacity retention of 729 mAhg−1 after 100 cycles at a current rate of 390.5 mAg−1. More importantly, flexible N-doped C@SnO2 fabrics exhibit excellent electrochemical performance even after a rough treatment, suggesting a facile strategy for the fabrication of electrochemically stable electrodes for flexible LIBs.

In-situ growth of 1T/2H-MoS2 on carbon fiber cloth and the modification of SnS2 nanoparticles: A three-dimensional heterostructure for high-performance flexible lithium-ion batteries

Flexible lithium ion batteries are important for wearable electronic devices. Herein, 1T/2H phase MoS2 nanosheets are grown on carbon fiber cloth, and the ultra-small SnS2 nanoparticles are anchored in the surface of MoS2 nanosheets uniformly. We fabricate the hierarchical nanostructures via a hydrothermal method then water bath process. During in-situ growth of 1T/2H phase MoS2, urea is used as the surfactant and NH4+ (produced by urea and ammonium molybdate tetrahydrate) is acted as insertion guest ions to stabilize 1T phase MoS2. The synergistic effects between MoS2 nanosheets and SnS2 nanoparticles can improve structural stability of the electrode and significant enhance the transport of Li ions and electrons, thereby ameliorate the electrochemical properties. When applied as a binder-free, flexible Li-ion battery anode, it exhibits admirable cycling stability and excellent rate performance. Due to the presence of 1T phase MoS2 and uniform distribution of ultra-small SnS2 nanoparticles on MoS2 nanosheets, the SnS2/MoS2/carbon fiber cloth composites maintain 1294 mA h g−1 when cycling at 100 mA g−1 after 120 cycles. A highly flexible battery based on SnS2/MoS2/carbon fiber cloth and LiCoO2 is fabricated, demonstrating excellent mechanical flexibility and cycling stability.

Free-Standing Sandwich-Type Graphene/Nanocellulose/Silicon Laminar Anode for Flexible Rechargeable Lithium Ion Batteries.

Freely deformable and free-standing electrodes together with high capacity are crucial to realizing flexible Li-ion batteries. Herein, a lamellar graphene/nanocellulose/silicon (GN/NC/Si) film assembled by interpenetrated GN nanosheets is synthesized via a facile vacuum-assisted filtration approach accompanied by the covalent cross-linking effect of glutaraldehyde. The hybrid film consists of the highly conductive GN matrix as an effective current collector, hydroxylated silicon nanoparticles (Si NPs) embedded uniformly within GN interlayer and NC as adhesive to cross-link GN and Si NPs. When applied as anode, the GN/NC/Si film exhibits a high reversible capacity of 1251 mA h g-1 at 100 mA g-1 after 100 cycles and superior rate capability. More importantly, in the stress-strain test, this film represents robust mechanical strength, which not only provides good flexibility but also accommodates volume change of Si during cycling. By coupling with lithium cobalt oxide as the cathode, the full cell successfully powers a light-emitting diode, even bended and folded, indicating the deformation-tolerant GN/NC/Si film electrode for flexible Li-ion batteries. Therefore, the design of layered nanocomposites will offer the possibility closer to the application of flexible batteries.

Solid Electrolyte, Flexible Li-ion Fiber Batteries for Compliant Energy Storage and Wearable Applications

In my talk, I would present advances in fabrication of the solid electrolyte-based flexible li-ion fiber batteries, as well as their numerous potential applications in compliant energy storage and wearable devices. In particular, I would detail fabrication of the fiber-shaped lithium ion batteries assembled by twisting a cathode filament together with an anode filament. The cathode filament is fabricated by depositing a LiFePO4 (LFP)-composite layer onto a steel-filled polyester conductive thread (SPCT). As anode filaments, we propose several scenarios including a Li4Ti5O12 (LTO)-composite coated SPCT (dip-and-dry deposition), a tin-coated SPCT (PVD deposition) as well as a bare tin wire. An electrolyte composite layer consisting of LiPF6 and polyethylene oxide is then deposited onto both the anode and cathode filament before the battery assembly. To characterize the electrochemical and mechanical properties of the proposed batteries, we performed charge-discharge tests with different C-rates, electrical impedance tests and mechanical bending tests. The fabrication of the proposed LIBs is simple and cost-effective, as compared to the fiber-shaped LIBs using carbon nanotube fibers. Moreover, the reported LIBs are well suitable for the wearable applications as they feature all-solid electrodes and electrolyte, unlike the majority of other currently existing LIBs that utilize liquid organic solution-based electrolytes that may cause leakage and cause safety concerns. Among other advantages of the proposed LIB are light weight, ease of fabrication, high specific capacitance, high energy density, and good durability.

SnO2 Nanowires on Carbon Nanotube Film as a High Performance Anode Material for Flexible Li-ion Batteries

Today, Li-ion batteries (LIBs) are the most common rechargeable batteries used in electronic devices. SnO2 with theoretical specific capacity of 782 mAh/g is among the best anode materials for LIBs. In this report, Three-dimensional SnO2 nanowires (NWs) on carbon nanotube (CNT) thin film (SnO2 / CNT) is fabricated using a combination of vacuum filtration and thermal evaporation techniques. The resulting 3D heterostructure SnO2/CNT was characterized by X-ray diffraction, transmission electron microscopy (TEM) and scanning electron microscopy (SEM). This fabricated SnO2/CNT electrode has been tested as a flexible and binder-free anode for LIB, which exhibits high initial discharge/charge capacity of 4.8/2.25 mAh/cm2 at a current density of 0.25 A/g, much larger than discharge/charge capacity of bare CNT film (2.2/0.3 mAh/cm2). Relatively high areal capacity of 1.23 mAh/cm2 has been achieved for the fabricated LIB with SnO2/CNT electrode after 20 cycles, proposing this material as a high performance flexible LIB anode material.

Facile synthesis of porous FeCo2O4 nanowire arrays on flexible carbon cloth with superior lithium storage properties

In this work, one-dimensional (1D) needle-like porous FeCo2O4 nanowire arrays on flexible carbon cloth (CC) are successfully fabricated by a facile synthesis route and investigated as anode material for lithium ion batteries (LIBs). X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), and X-ray photoelectron spectroscopy (XPS) have been applied to characterize the materials. The 1D FeCo2O4 nanowires provide a large surface area and enough space to accommodate volume changes. Besides, taking advantages of good conductivity from the CC substrate and the synergistic effect between Co and Fe ions, the integrated FeCo2O4 nanowire arrays/CC electrodes exhibits prominent lithium-storage performance with high reversible capacity of about 2101 mAh g−1 at 100 mA g−1 and outstanding capacity retention of 97.1% from 2 to 200 cycles, and retains high rate capacity of 876 mAh g−1 at 2 A g−1. Even cycled at higher current density of 1 A g−1, FeCo2O4 nanowire arrays/CC electrode still maintains stable reversible capacity of 1013.8 mAh g−1 after 350 cycles, corresponding to 78.3% of the second discharge capacity. Therefore, FeCo2O4 nanowire arrays/CC could be considered to be a promising candidate as anode material for flexible Li-ion batteries and future stretchable/bendable electronic devices.

(Invited) Advanced Aqueous Electrolytes for Li-ion Batteries

Current technologies for electric vehicles and other applications require high energy, power density, and long cycle life. However, the energy density and safety of current batteries still need to be improved to satisfy these requirements. Typical Li-ion batteries consist of organic electrolytes that are toxic, flammable, and pose significant safety concerns in the events of thermal runaway and improper operation and handling. In recent years, we have explored advanced materials for Li-ion, Na-ion, Zn-ion and Mg-ion batteries that address these key challenges. A new revolutionary concept of an aqueous electrolyte for Li-ion batteries, termed water-in-salt electrolyte, has been developed, extending the electrochemical voltage stability window of aqueous electrolytes to >4.0V and significantly enhancing the energy density. Use of the water-in-salt gel electrolytes, a robust flexible Li-ion battery that can be cut open, exposed to air, and continue to operate despite the mechanical damage has been demonstrated.

Cross-Linked Poly(vinylidene fluoride-co-hexafluoropropene) (PVDF-co-HFP) Gel Polymer Electrolyte for Flexible Li-Ion Battery Integrated with Organic Light Emitting Diode (OLED).

Here, we fabricate poly(vinylidene fluoride-co-hexafluoropropene) (PVDF-co-HFP) by electrospinning for a gel polymer electrolyte (GPE) for use in flexible Li-ion batteries (LIBs). As a solvent, we use N-methyl-2-pyrrolidone (NMP), which helps produce the cross-linked morphology of PVDF-co-HFP separator, owing to its low volatility. The cross-linked PVDF-co-HFP separator shows an uptake rate higher than that of a commercialized polypropylene (PP) separator. Moreover, the PVDF-co-HFP separator shows an ionic conductivity of 2.3 × 10−3 S/cm at room temperature, comparable with previously reported values. An LIB full-cell assembled with the PVDF-co-HFP-based GPE shows capacities higher than its counterpart with the commercialized PP separator, confirming that the cross-linked PVDF-co-HFP separator provides highly efficient ionic conducting pathways. In addition, we integrate a flexible LIB cell using the PVDF-co-HFP GPE with a flexible organic light emitting diode (OLED), demonstrating a fully flexible unit of LIB and OLED.

Halide Ion Intercalated Electrodeposition Synthesis of Co3O4 Nanosheets with Tunable Pores on Graphene Foams as Free-Standing and Flexible Li-Ion Battery Anodes

Soft portable electronics has grabbed the attention of manufacturing industry. One of the issues is the flexible energy sources with high energy density, high operating voltage, and long lifetime. Flexible lithium ion batteries could be the solution. However, the conventional electrode production process is paste casting which contains binder, conductive additive, and substrates with no capacities and limits the flexibility of lithium ion batteries. Herein, we promote the electrode preparation by halide ion intercalated electrodeposition of Co(OH)2 nanosheet precursors on graphene foams. The Co3O4/graphene foam electrodes, the final product, exhibit good flexibility and mechanical strength. Meanwhile, by regulation of the ratio of Br– and Cl–, specific surface areas, pore volumes, pore diameters, and specific capacities can be modified with the highest specific capacity of 790 mA h g–1 after 100 cycles at a current density of 0.1 C in the voltage range of 0.2–3.0 V. Furthermore, because of the similar par...

Implanting a solid Li-ion battery into a triboelectric nanogenerator for simultaneously scavenging and storing wind energy

Wind energy scavenging and storage usually can be achieved by utilizing two different separated units, such as a triboelectic nanogenerator and a Li-ion battery with need of being periodically charged. Here, we report a new strategy of implanting a flexible solid Li-ion battery (SLB) into a triboelectic nanogenerator (TENG) for simultaneously scavenging and storing wind energy into chemical energy to achieve a self-charging system. The fabricated TENG can deliver an output voltage of about 135V and an output current of about 12μA, which can be utilized to effectively charge the SLB in the triboelectric vibration film of TENG. The SLB can be easily charged from 1.5V to 3.5V in about 55s by using a transformer and a rectifier to connect the TENG. This research provides a new route of energy scavenging and storage devices for self-charging systems.

Copper nanowire/multi-walled carbon nanotube composites as all-nanowire flexible electrode for fast-charging/discharging lithium-ion battery

A novel lightweight three-dimensional (3D) composite anode for a fast-charging/discharging Li-ion battery (LIB) was fabricated entirely using one-dimensional (1D) nanomaterials, i.e., Cu nanowires (CuNWs) and multi-walled C nanotubes (MWCNTs). Because of the excellent electrical conductivity, high-aspect ratio structures, and large surface areas of these nanomaterials, the CuNW-MWCNT composite (CNMC) with 3D structure provides significant advantages regarding the transport pathways for both electrons and ions. As an advanced binder-free anode, a CuNW-MWCNT composite film with a controllable thickness (∼600 μm) exhibited a considerably low sheet resistance, and internal cell resistance. Furthermore, the random CuNW network with 3D structure acting as a rigid framework not only prevented MWCNT shrinkage and expansion due to aggregation and swelling but also minimized the effect of the volume change during the charge/discharge process. Both a half cell and a full cell of LIBs with the CNMC anode exhibited high specific capacities and Coulombic efficiencies, even at a high current. More importantly, we for the first time overcame the limitation of MWCNTs as anode materials for fast-charging/discharging LIBs (both half cells and full cells) by employing CuNWs, and the resulting anode can be applied to flexible LIBs. This innovative anode structure can lead to the development of ultrafast chargeable LIBs for electric vehicles.

Shapeable electrodes with extensive materials options and ultra-high loadings for energy storage devices

To meet the increasing demand of flexible and wearable electronic devices, a novel injection molding method is established to prepare flexible electrodes with controllable shapes such as film, bowl, wire, etc. It overcomes the materials limitation for traditional methods and could easily create flexible and shapeable electrodes based on 0-D active materials, even with ultra-high loadings and excellent electrochemical performance. Taking flexible and shapeable S/C electrodes as a model, sulfur loadings 24mgcm−2 based on 30nmS/C particles are, for the first time, successfully achieved. It can deliver ultra-high an areal capacity of 27.1mAhcm−2 and a capacity retention of 64.1% after 100 cycles with low electrolyte to sulfur ratio (E/S) of 5.3µLmg−1. In addition, flexible and shapeable Li-ion battery electrodes based on 17mgcm−2 0-D Li3V2(PO4)3 (LVP) electrode could also be obtained, achieving excellent C-rate performance and cycling stability, which is 94mAhg−1 at 5C and nearly 100% capacity retention at 1C during 100 cycles. The results provided a versatile and universal way to create flexible and shapeable electrodes for a variety of energy storage devices.

Electrospun C/GeO2 paper-like electrodes for flexible Li-ion batteries

Carbon/germanium dioxide (C/GeO2) paper-like self-supporting membranes to be used as binder- and collector-free anodes in flexible Li-ion batteries (LIBs) are synthesised via electrospinning (ES) followed by stabilisation and carbonisation heat treatments. Carbonisation is operated at relatively low temperature (550 °C) in order to keep high nitrogen concentration in the carbonaceous fibre network, which is claimed to be beneficial for Li-ion storage. Regardless of the germanium load in the spinnable solution (2.50–4.25 wt%), α-quartz GeO2 nanoparticles (NPs) encapsulated in highly N-doped (10–16 at%) C fibres are produced. The size of the oxide NPs and the fibre diameter increase with increasing germanium load. Based on the results of the compositional analysis, the specific capacities of the composite fibres are expected to range between 590 and 780 mAh/g. Preliminary results of half-cell tests substantially confirm the expectations, with Coulombic efficiencies of 92–96% at the second charge/discharge cycle.

SnO2@a-Si core–shell nanowires on free-standing CNT paper as a thin and flexible Li-ion battery anode with high areal capacity

Here, we report 3D hierarchical SnO2 nanowire (NW) core-amorphous silicon shell on free-standing carbon nanotube paper (SnO2@a-Si/CNT paper) as an effective anode for flexible lithium-ion battery (LIB) application. This binder-free electrode exhibits a high initial discharge capacity of 3020 mAh g−1 with a large reversible charge capacity of 1250 mAh g−1 at a current density of 250 mA g−1. Compared to other SnO2 NW or its core–shell nanostructured anodes, the fabricated SnO2@a-Si/CNT structure demonstrates an outstanding performance with high mass loading (∼5.9 mg cm−2), high areal capacity (∼5.2 mAh cm−2), and large volumetric capacity (∼1750 mAh cm−3) after 25 cycles. Due to the incorporation of CNT paper as the current collector, the weight and thickness of the total electrode is effectively reduced with respect to the conventional LIB anodes. The fabricated electrode has a total thickness of only 30 μm and considering the total weight of the electrode (active mass + current collector), an initial discharge/charge capacity of 2460/1018 mAh g−1 is obtained. Hence, this thin, lightweight and highly flexible structure is proposed as an excellent candidate for high-performance LIB anode materials, especially in flexible electronics.

3D nitrogen-doped graphene foam with encapsulated germanium/nitrogen-doped graphene yolk-shell nanoarchitecture for high-performance flexible Li-ion battery

Flexible electrochemical energy storage devices have attracted extensive attention as promising power sources for the ever-growing field of flexible and wearable electronic products. However, the rational design of a novel electrode structure with a good flexibility, high capacity, fast charge–discharge rate and long cycling lifetimes remains a long-standing challenge for developing next-generation flexible energy-storage materials. Herein, we develop a facile and general approach to three-dimensional (3D) interconnected porous nitrogen-doped graphene foam with encapsulated Ge quantum dot/nitrogen-doped graphene yolk-shell nano architecture for high specific reversible capacity (1,220 mAh g−1), long cycling capability (over 96% reversible capacity retention from the second to 1,000 cycles) and ultra-high rate performance (over 800 mAh g−1 at 40 C). This work paves a way to develop the 3D interconnected graphene-based high-capacity electrode material systems, particularly those that suffer from huge volume expansion, for the future development of high-performance flexible energy storage systems.

Facile fabrication of foldable electrospun polyacrylonitrile-based carbon nanofibers for flexible lithium-ion batteries

To enable electrospun polyacrylonitrile-based C nanofibers (CNFs) to be employed as anode materials in flexible Li-ion batteries, it is essential to overcome their frangibility and enhance their flexibility.

Chemical vapor deposition-assisted fabrication of a graphene-wrapped MnO/carbon nanofibers membrane as a high-rate and long-life anode for lithium ion batteries

Novel MnO/CNFs@G membrane by electrospinning and APCVD; this anode with high specific capacity and longest cycling life is of great interest to high energy thin film or flexible Li-ion battery.

Facile synthesis of self-supported Mn3O4@C nanotube arrays constituting an ultrastable and high-rate anode for flexible Li-ion batteries

An anode of self-supported Mn3O4@C nanotube arrays has been fabricated by a simple solution route which shows superior electrochemical performance.

Three-Dimensional Carbon Nanostructures for Advanced Lithium-Ion Batteries

Carbon nanostructural materials have gained the spotlight as promising anode materials for energy storage; they exhibit unique physico-chemical properties such as large surface area, short Li+ ion diffusion length, and high electrical conductivity, in addition to their long-term stability. However, carbon-nanostructured materials have issues with low areal and volumetric densities for the practical applications in electric vehicles, portable electronics, and power grid systems, which demand higher energy and power densities. One approach to overcoming these issues is to design and apply a three-dimensional (3D) electrode accommodating a larger loading amount of active anode materials while facilitating Li+ ion diffusion. Furthermore, 3D nanocarbon frameworks can impart a conducting pathway and structural buffer to high-capacity non-carbon nanomaterials, which results in enhanced Li+ ion storage capacity. In this paper, we review our recent progress on the design and fabrication of 3D carbon nanostructures, their performance in Li-ion batteries (LIBs), and their implementation into large-scale, lightweight, and flexible LIBs.

Flexible Bismuth Selenide /Graphene composite paper for lithium-ion batteries

A flexible Bi2Se3/Graphene (BSG) composite paper has been prepared through a simple vacuum filtration method and a thermal reduction together. The BSG composite paper was directly used as anode electrode for lithium-ion batteries, without using any polymer binders or conduction additives. In contrast to the pure Bi2Se3, the BSG exhibits high reversible lithium ion storage capacities and superior cyclic capacity retention. It proposed that the superior lithium storage performances would be attributed to the special construction of the as-prepared BSG paper, in which the graphene can not only act as conductive network for electrodes, but also act as a frame to alleviate volume expansion or aggregation of Bi2Se3 nanosheets during lithiation/delithiation. The as-prepared BSG paper shows a great potential as an anode materials for flexible Li-ion batteries.