Langyuan Wu

Self-supported electrodes of Na2Ti3O7 nanoribbon array/graphene foam and graphene foam for quasi-solid-state Na-ion capacitors

There is an urgent need but it is still a huge challenge to integrate high energy and power density with high safety in a single energy storage device. Addressing this issue largely depends on design of new energy storage systems with novel electrode architectures. Herein, a novel electrochemical energy storage device called a quasi-solid-state Na-ion capacitor (QSS-NIC) is designed based on a 3D self-supported Na2Ti3O7 nanoribbon array/graphene foam (NTO/GF) anode and graphene foam (GF) cathode, and a Na-ion conducting gel polymer as the electrolyte and separator, without any binders, conducting additives or metal current collectors. Benefiting from the unique 3D self-supported cathode and anode, the GF//NTO/GF configuration achieves a high energy density of 70.6 W h kg−1 and high power density of 4000 W kg−1 on the basis of the mass of both electrodes, and a prominent cycling stability over 5000 cycles (capacitance retention ∼73.2%). This work successfully demonstrates a proof of concept of QSS-NIC as a high performance energy storage device based on two self-supported electrodes, which could provide a feasible approach to bridge the performance gap between capacitors and Na-ion batteries.

Highly stable lithium ion capacitor enabled by hierarchical polyimide derived carbon microspheres combined with 3D current collectors

Lithium ion capacitors (LICs), which combine the merits of both lithium ion batteries and supercapacitors, have recently attracted considerable attention. However, LICs generally use different materials and synthesis routes for the cathode and anode, resulting in a complicated process and high production cost, from an energy storage device perspective. In addition, the current collector interface structure design plays a key role in the electrochemical process. Herein, we have designed and fabricated a novel LIC with similar-symmetric architecture in both electrodes. The nitrogen-doped porous carbon microspheres (NPCM) derived from the hierarchical assembly of polyimide nanosheets as the anode material showed excellent lithium storage properties. The cathode material (NPCM-A) obtained by the activation of NPCM led to an ultrahigh specific surface area (2007 m2 g−1) and excellent capacitance characteristics. Benefiting from the unique superstructure and 3D porous array current collectors, the novel LIC achieved a high energy density of 95.08 W h kg−1 and could retain 48.2 W h kg−1 even at a high power density of 15 kW kg−1 on the basis of mass of both electrodes. Moreover, the LIC achieved 80.1% capacity retention after 5000 ultra-long cycles, corresponding to fading of 0.004% per cycle.

Li4Ti5O12 Anode: Structural Design from Material to Electrode and the Construction of Energy Storage Devices

Spinel Li4 Ti5 O12 , known as a zero-strain material, is capable to be a competent anode material for promising applications in state-of-art electrochemical energy storage devices (EESDs). Compared with commercial graphite, spinel Li4 Ti5 O12 offers a high operating potential of ∼1.55 V vs Li/Li+ , negligible volume expansion during Li+ intercalation process and excellent thermal stability, leading to high safety and favorable cyclability. Despite the merits of Li4 Ti5 O12 been presented, there still remains the issue of Li4 Ti5 O12 suffering from poor electronic conductivity, manifesting disadvantageous rate performance. Typically, a material modification process of Li4 Ti5 O12 will be proposed to overcome such an issue. However, the previous reports have made few investigations and achievements to analyze the subsequent processes after a material modification process. In this review, we attempt to put considerable interest in complete device design and assembly process with its material structure design (or modification process), electrode structure design and device construction design. Moreover, we have systematically concluded a series of representative design schemes, which can be divided into three major categories involving: (1) nanostructures design, conductive material coating process and doping process on material level; (2) self-supporting or flexible electrode structure design on electrode level; (3) rational assembling of lithium ion full cell or lithium ion capacitor on device level. We believe that these rational designs can give an advanced performance for Li4 Ti5 O12 -based energy storage device and deliver a deep inspiration.