Zhengxi Zhang

Polymer electrolytes based on dicationic polymeric ionic liquids: application in lithium metal batteries

Polymeric ionic liquids (PILs) have stirred up great interest for their potential applications as electrolyte hosts in lithium metal batteries (LMBs) because of their desirable performance. In this work, PIL-based gel polymer electrolytes applied in lithium metal batteries (LMBs) at low–medium temperatures (25 °C, 30 °C and 40 °C) are first reported. A novel imidazolium-tetraalkylammonium-based dicationic polymeric ionic liquid, poly(N,N,N-trimethyl-N-(1-vinlyimidazolium-3-ethyl)-ammonium bis(trifluoromethanesulfonyl)imide) is successfully synthesized, and its structure and purity are confirmed by 1H NMR, FTIR and elemental analysis. Subsequently, the ternary gel polymer electrolytes are prepared by blending the as-synthesized dicationic PIL as the polymer host with 1,2-dimethyl-3-ethoxyethyl imidazolium bis(trifluoromethanesulfonyl)imide (IM(2o2)11TFSI) ionic liquid and LiTFSI salt in different weight ratios. The PIL-LiTFSI-IM(2o2)11TFSI electrolytes reveal low glass transition temperatures around −54 °C and high thermal stability to about 330 °C. Moreover, the ternary gel polymer electrolytes show good ion conductivity around 10−4 S cm−1 at low–medium temperatures, high electrochemical stability and good interfacial stability with lithium metal. Particularly, the Li/LiFePO4 cells assembled with polymer electrolytes at a rate of 0.1 C are able to deliver discharge capacities of about 160 mA h g−1, 140 mA h g−1 and 120 mA h g−1 at 40 °C, 30 °C and 25 °C, respectively, with excellent capacity retention, as well as exhibiting acceptable rate capability. These findings reveal that dicationic PIL-based electrolytes have great potential for use as safe electrolytes in LMBs.

Synthesis of SnO2/Sn@carbon nanospheres dispersed in the interspaces of a three-dimensional SnO2/Sn@carbon nanowires network, and their application as an anode material for lithium-ion batteries

In this work, a peculiar nanostructure of SnO2/Sn@carbon nanospheres dispersed in the interspaces of a three-dimensional SnO2/Sn@carbon nanowires network composite (denoted as SnO2/Sn@C) has been successfully fabricated by a facile strategy and confirmed by scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy, X-ray diffraction, laser Raman spectroscopy, Brunauer–Emmett–Teller method, energy dispersive X-ray spectrometry, and X-ray photoelectron spectroscopy characterization, illustrating the combination of the nanospheres and the 3-dimensional nanowires network. This architecture effectively withstands the volume change and restricts the agglomeration of SnO2/Sn during the cycling process. Moreover, the SnO2/Sn distributed in carbon matrix and the SnO2/Sn@carbon nanospheres dispersed in interspaces of three-dimensional SnO2/Sn@carbon nanowires network facilitate electron and ion transport throughout the electrode. As a result, this composite exhibits excellent performance as a potential anode material for lithium ion batteries and delivers a reversible capacity of 678.6 mA h g−1 at 800 mA g−1, even after 500 cycles.

Facile template-free preparation of hierarchical TiO2 hollow microspheres assembled by nanocrystals and their superior cycling performance as anode materials for lithium-ion batteries

The design and fabrication of hierarchical TiO2 hollow structures assembled by nanosized building blocks have been proven to be an effective strategy for significantly improving the electrochemical performance of TiO2-based anodes for lithium-ion batteries, which can be attributed to the increased surface lithium storage. Herein, uniformly distributed hierarchical anatase TiO2 hollow microspheres assembled by nanocrystals with an average size of 10–20 nm (denoted as TiO2 HMs) have been successfully prepared via a facile template-free one-pot hydrothermal process. The possible formation mechanism of TiO2 HM is also investigated by time-dependent and ammonium fluoride (NH4F) concentration-dependent experiments. Moreover, our strategy is simpler than other generally template-involved methods as it effectively avoids the tedious preparation and removal process of templates, and the time-consuming heating treatment for crystallization. As a promising anode material for lithium-ion batteries, TiO2 HMs exhibit excellent electrochemical performances in terms of high capacity, ultra-long cycling stability and good rate capability. After 1000 cycles, a capacity of 150.7, 129.9 and 104.5 mA h g−1 is retained at 1, 5 and even 20 C, respectively. The peculiarly hierarchical hollow structure should be responsible for the excellent performances.

Double-shelled support and confined void strategy to improve the lithium storage properties of SnO2/C anode materials for lithium-ion batteries

As promising anode materials for lithium-ion batteries, SnO2 materials have triggered significant research efforts due to their high theoretical capacity. However, their practical applications are impeded by their poor cycle life, which is caused by structural pulverization and large volume changes during cycling. Thus, the development of strategies to improve the cycling performance of SnO2 anodes is indispensable. Herein, a peculiar nanostructured SnO2/C composite (denoted as SnO2@DSC) with a double-shelled carbon support and confined void is fabricated, in which SnO2 is quasi confined in the void-space between two shells. It is suggested that the as-prepared SnO2@DSC has two unique advantages: on the one hand, SnO2 is quasi encapsulated into the confined void between two shells, huge volume change is largely buffered and its electrical connectivity is guaranteed, because even if SnO2 detaches from the outer shell, it can be immobilized again in the interior shell; on the other hand, the structural integrity of the electrode could be guaranteed by virtue of the dual-support of mechanically flexible double-shelled hollow carbon nanospheres. As a result, the as-prepared SnO2@DSC exhibited an excellent cycling performance, delivering a high reversible capacity of 838.2 mA h g−1 at 200 mA g−1 even after 500 cycles.

High-performance polymeric ionic liquid–silica hybrid ionogel electrolytes for lithium metal batteries

In this work, a new class of high-performance polymeric ionic liquid–silica hybrid ionogel electrolytes (HIGEs) is developed by a nonaqueous sol–gel route, in which LiTFSI–ionic liquid as the ion conducting phase is immobilized with a hybrid pyrrolidinium-based polymeric ionic liquid and silica matrix. The thermal and electrochemical properties of these HIGEs as well as their application in lithium metal batteries (LMBs) are investigated. It is found that HIGEs reveal excellent thermal stability, good room temperature ionic conductivity, high electrochemical stability, a suitable lithium ion transference number, and potential to suppress Li dendrite formation. In particular, Li/LiFePO4 cells with the as-obtained HIGE at 0.2C rate can deliver a discharge capacity of about 150 mA h g−1 at 25 °C, with excellent capacity retention. Moreover, at 0.5C, 1.0C, and 2.0C, the stable discharge capacities are as high as 138.1 mA h g−1, 120.3 mA h g−1 and 73.8 mA h g−1, respectively. The desirable battery performance can be attributed to the good electrochemical properties of HIGEs and interfacial compatibility between HIGEs and electrodes. These findings show that HIGEs prepared in this work have great potential for application as safe electrolytes in LMBs.

Morphology-engineered and TiO2 (B)-introduced anatase TiO2 as an advanced anode material for lithium-ion batteries

Low capacity and poor rate capability are the critical disadvantages for the practical application of anatase TiO2 anode materials for lithium-ion batteries. In this work, we present an effective and facile strategy for improving the electrochemical performance of anatase TiO2 anode materials for lithium-ion batteries. In our strategy, besides designing a unique nanostructure, the introduction of a second phase, TiO2 (B), is also involved. As a result, the electrochemical properties of the as-prepared TiO2 (TiO2-400) with a hierarchical structure of micro/nanoparticles constructed by ultrafine nanowires with 3–8 nm width and several micrometers (μm) length, in terms of capacity, rate capability and cycling performance are significantly improved. A high reversible capacity of 207.1 mA h g−1 is obtained at 0.2 C after 150 cycles. Even after 1000 cycles, high reversible capacities of 186 and 155.4 mA h g−1 are delivered at 1 C and 10 C, respectively. Moreover, reversible capacities of 142.1 and 140 mA h g−1 can be obtained even at 20C and 25 C, respectively. It is suggested that this excellent electrochemical performance may make TiO2-400 a promising anode material for advanced lithium-ion batteries with high power density and ultra-long life.

Polymeric ionic liquid–ionic plastic crystal all-solid-state electrolytes for wide operating temperature range lithium metal batteries

In developing all-solid-state polymer electrolytes for wide operating temperature range lithium metal batteries, an exciting organic ionic plastic crystal, N-ethyl-N-methylpyrrolidinium bis(fluorosulfonyl)imide (P12FSI), has been introduced into the pyrrolidinium-based polymeric ionic liquid (PIL)/LiTFSI solid system to obtain a novel class of PIL–P12FSI–LiTFSI solid polymer electrolytes (SPEs). Such SPEs reveal flexible mechanical characters, attractive room temperature ionic conductivity above 10−4 S cm−1, and high thermal and electrochemical stability as well as potential to suppress the lithium dendrite growth. Particularly, Li/LiFePO4 cells assembled with the as-obtained SPE exhibit high discharge capacity and excellent cycle life over a broad operating temperature range (25–80 °C) and good rate performance. This significant finding indicates that the SPE system obtained in our work has great potential for use in wide operating temperature range lithium metal batteries.

Rational fabrication of hybrid structure of SnOx sandwiched between TiO2 and carbon based on the complementary merits of SnOx, TiO2 and carbon, and its improved lithium storage properties

In spite of high-profile theoretical capacity, the practical application of SnO2 or Sn anode materials for lithium-ion batteries is severely impeded by poor electric conductivity and structural instability. Herein, a hybrid structure of SnO2/Sn sandwiched between TiO2 and carbon with rich porosity, good electric conductivity and stable structure, denoted as TiO2@SnOx@C, is fabricated based on the complementary merits of SnO2, TiO2 and carbon anode materials. The TiO2@SnOx@C exhibits a good electrochemical performance when used as anode material for lithium-ion battery, delivering a capacity of 629 mA h g−1 at 200 mA g−1 after 300 cycles. Moreover, a reversible capacity of 490.3 mA h g−1 is obtained at 1000 mA g−1 even after 1000 cycles and is much higher than theoretical capacity of graphite (372 mA h g−1). The effectively complementary and synergic effect among structural stability of TiO2, high theoretical capacity of SnOx, and good conductive and flexible ability of carbon should be responsible for the superior electrochemical performance of TiO2@SnOx@C.

Hydrogen titanate constructed by ultrafine nanobelts as advanced anode materials with high-rate and ultra-long life for lithium-ion batteries

Hydrogen titanate (H2Ti3O7) anode materials with desirable electrochemical performance, such as long cycling life and high capacity, have rarely been reported so far. In the present work, as-prepared hydrogen titanate with a particularly hierarchical nanostructure exhibits a breakthrough in electrochemical performance as an anode material for lithium-ion batteries by morphology engineering and heat treatment: 168 mA h g−1 at 16.8 A g−1, meaning that a full charge only needs 40 seconds; 184.8, 176.4 and 156.8 mA h g−1 at 0.168, 1.68 and 10.08 A g−1 after 1000 cycles, respectively; 120 mA h g−1 at 10.08 A g−1 even after 4000 cycles. It is believed that such excellent performance makes hydrogen titanate a promising anode material for advanced lithium-ion batteries with ultra-long life and high power density.