Duc Tung Ngo

Mass-scalable synthesis of 3D porous germanium–carbon composite particles as an ultra-high rate anode for lithium ion batteries

Electrode materials with three-dimensional (3D) mesoporous structures possess superior features, such as a shortened solid-phase lithium diffusion distance, a large pore volume, full lithium ion accessibility, and a high specific area, which can facilitate fast lithium ion transport and electron transfer between solid/electrolyte interfaces. In this work, we introduce a facile synthesis route for the preparation of a 3D nanoarchitecture of Ge coated with carbon (3D-Ge/C) via a carbothermal reduction method in an inert atmosphere. 3D-Ge/C showed excellent cyclability: almost 86.8% capacity retention, corresponding to a charge capacity of 1216 mA h g−1 even after 1000 cycles at a 2C-rate. Surprisingly, the high average reversible capacity of 1122 mA h g−1 was maintained at a high charge rate of 100C (160 A g−1). Even at an ultrahigh charge rate of 400C (640 A g−1), an average capacity of 429 mA h g−1 was attained. Further, the full cell composed of a 3D-Ge/C anode and an LiCoO2 cathode exhibited excellent rate capability and cyclability with 94.7% capacity retention over 50 cycles. 3D-Ge/C, which offers a high energy density like batteries as well as a high power density like supercapacitors, is expected to be used in a wide range of electrochemical devices.

Uniform GeO2 dispersed in nitrogen-doped porous carbon core–shell architecture: an anode material for lithium ion batteries

Germanium oxide (GeO2), which possesses great potential as a high-capacity anode material for lithium ion batteries, has suffered from its poor capacity retention and rate capability due to significant volume changes during lithiation and delithiation. In this study, we introduce a simple synthetic route for producing nanosized GeO2 anchored on a nitrogen-doped carbon matrix (GeO2/N–C) via the sol–gel method followed by a calcination process in an inert argon atmosphere. The GeO2/N–C showed superior electrochemical performance over pure GeO2; almost 91.8% capacity retention of 905 mA h g−1 was shown after 200 cycles at the rate of C/2. Interestingly, even at a high rate of 20C, a specific capacity of 412 mA h g−1 was retained. This unique anode performance of GeO2/N–C is derived from the effective combination of nano-size GeO2 and its uniform distribution in a nitrogen-doped carbon matrix. Herein, the nitrogen doped-carbon matrix not only strengthens the structure but also promotes the lithium diffusion in the GeO2/C–N material. Further, the adaptability of GeO2/N–C as an anode in a full cell configuration in combination with the LiCoO2 cathode was demonstrated by exhibiting high specific capacity and good cyclability.

Simple synthesis of highly catalytic carbon-free MnCo2O4@Ni as an oxygen electrode for rechargeable Li-O2 batteries with long-term stability.

An effective integrated design with a free standing and carbon-free architecture of spinel MnCo2O4 oxide prepared using facile and cost effective hydrothermal method as the oxygen electrode for the Li–O2 battery, is introduced to avoid the parasitic reactions of carbon and binder with discharge products and reaction intermediates, respectively. The highly porous structure of the electrode allows the electrolyte and oxygen to diffuse effectively into the catalytically active sites and hence improve the cell performance. The amorphous Li2O2 will then precipitate and decompose on the surface of free-standing catalyst nanorods. Electrochemical examination demonstrates that the free-standing electrode without carbon support gives the highest specific capacity and the minimum capacity fading among the rechargeable Li–O2 batteries tested. The Li-O2 cell has demonstrated a cyclability of 119 cycles while maintaining a moderate specific capacity of 1000 mAh g−1. Furthermore, the synergistic effect of the fast kinetics of electron transport provided by the free-standing structure and the high electro-catalytic activity of the spinel oxide enables excellent performance of the oxygen electrode for Li-O2 cells.

Composite Gel Polymer Electrolyte Based on Poly(vinylidene fluoride-hexafluoropropylene) (PVDF-HFP) with Modified Aluminum-Doped Lithium Lanthanum Titanate (A-LLTO) for High-Performance Lithium Rechargeable Batteries

A composite gel polymer electrolyte (CGPE) based on poly(vinylidene fluoride-hexafluoropropylene) (PVDF-HFP) polymer that includes Al-doped Li0.33La0.56TiO3 (A-LLTO) particles covered with a modified SiO2 (m-SiO2) layer was fabricated through a simple solution-casting method followed by activation in a liquid electrolyte. The obtained CGPE possessed high ionic conductivity, a large electrochemical stability window, and interfacial stability-all superior to that of the pure gel polymer electrolyte (GPE). In addition, under a highly polarized condition, the CGPE effectively suppressed the growth of Li dendrites due to the improved hardness of the GPE by the addition of inorganic A-LLTO/m-SiO2 particles. Accordingly, the Li-ion polymer and Li-O2 cells employing the CGPE exhibited remarkably improved cyclability compared to cells without CGPE. In particular, the CGPE as a protection layer for the Li metal electrode in a Li-O2 cell was effective in blocking the contamination of the Li electrode by oxygen gas or impurities diffused from the cathode side while suppressing the Li dendrites.

Bi-layer lithium phosphorous oxynitride/aluminium substituted lithium lanthanum titanate as a promising solid electrolyte for long-life rechargeable lithium–oxygen batteries

Lithium ion conducting membranes are indispensable for building lithium–air (oxygen) batteries employing aqueous and non-aqueous electrolytes for long-term operation. In this report, we present the high performance of non-aqueous lithium–air batteries, in which a bilayer lithium phosphorous oxynitride/aluminium substituted lithium lanthanum titanate solid electrolyte is employed as a protective layer for a lithium metal electrode and free carbon–manganese dioxide as the cathodic catalyst. Aluminium-doped lithium lanthanum titanate (A-LLTO) pellets were prepared using citrate-gel synthesis followed by pelletization and a sintering process. A thin lithium phosphorous oxynitride (LiPON) layer was then deposited on the A-LLTO using the sputtering method, which was used as a protective interlayer for separating A-LLTO ceramics from the Li metal electrode. With a high ionic conductivity of 2.25 × 10−4 S cm−1 and a large electrochemical stability window of 0–5 V, the LiPON/A-LLTO ceramics showed promising feasibility as a stable solid electrolyte for application in Li–O2 batteries. The aprotic Li–O2 cell containing the Li metal electrode protected by LiPON/A-LLTO exhibited excellent charge–discharge cycling stability with a long life span of 128 cycles under the limited capacity mode of 1000 mA h g−1. After the cycling test, the LiPON/A-LLTO ceramics retained a high ion conductivity of 1.65 × 10−4 S cm−1. In addition, with the introduction of LiPON/A-LLTO, the Li dendrite growth and electrolyte decomposition are effectively suppressed.

Insights into degradation of metallic lithium electrodes protected by a bilayer solid electrolyte based on aluminium substituted lithium lanthanum titanate in lithium-air batteries

Lithium (Li) metal can be degraded by factors such as irregular Li stripping, Li dendritic growth, and the growth of a solid electrolyte interphase (SEI) layer, finally leading to the performance deterioration of Li–air batteries. In particular, the operation of the Li–air battery in ambient air remains a considerable challenge due to the possible occurrence of parasitic reactions on Li metal with moisture and other contaminants diffusing from the outside air. In this work, a protected Li electrode (PLE) composed of Li metal covered with a bilayer lithium phosphorous oxynitride (LiPON)/aluminium substituted lithium lanthanum titanate (A-LLTO) solid electrolyte was suggested. The mechanism for the degradation of Li electrodes with and without the LiPON/A-LLTO protection layer was compared using the Li symmetric cell and Li–air cell by investigating the electrochemical performance of cells and the growth of Li dendrites. The Li symmetric cell employing the LiPON/A-LLTO exhibited superior cyclability to the cell without the solid electrolyte due to the effective suppression of Li dendritic growth. Further, the aprotic Li–air cell employing the PLE showed outstanding electrochemical performance when operated in pure oxygen and even in an air atmosphere: a long life span of 128 cycles in oxygen atmosphere and 20 cycles in air atmosphere under the limited capacity mode of 1000 mA h g−1. The obtained excellent performance of the Li–air cell employing the PLE is attributed to the effective suppression of the Li dendrite growth and electrolyte decomposition with the presence of LiPON/A-LLTO. In addition, dense LiPON/A-LLTO completely protected the Li metal electrode from the penetration of oxygen, moisture, and other contaminants which can degrade the Li metal electrode.

Effect of synthesis temperature on the structural defects of integrated spinel-layered Li1.2Mn0.75Ni0.25O2+δ: a strategy to develop high-capacity cathode materials for Li-ion batteries

An integrated layered-spinel with a nominal composition of (1 − x)Li1.2Mn0.6Ni0.2O2·xLiMn1.5Ni0.5O4 (0.15 < x < 0.3) was synthesized by a hydrothermal reaction followed by firing at different temperatures. The effects of firing temperature on the phase components, cation disorder, and crystal defects, and their relationship with the electrochemical performance of the cathode material were studied. The sample fired at 650 °C showed the highest capacity of up to 320 mA h g−1 and highest initial coulombic efficiency (98%, 2–4.9 V), but the capacity decreased dramatically to only 55% after 50 cycles. The sample fired at 850 °C showed the slowest activation of the layered phase, requiring up to several dozen cycles. The intermediate firing temperature of 750 °C showed a balance between the activation rate, capacity, initial coulombic efficiency, and cycling stability, with 270 mA h g−1 after 10 cycles and a 99% capacity retention after 50 cycles. All samples showed different rates of the layered-to-spinel phase transformation, which depends on the activation rate. This study reports the relationships between synthesis conditions, structure, and electrochemical performance, providing a strategy to develop high-capacity cathode materials based on the (1 − x)Li1.2Mn0.6Ni0.2O2·xLiMn1.5Ni0.5O4 system.

Facile Synthesis of Si@SiC Composite as an Anode Material for Lithium-Ion Batteries

Here, we propose a simple method for direct synthesis of a Si@SiC composite derived from a SiO2@C precursor via a Mg thermal reduction method as an anode material for Li-ion batteries. Owing to the extremely high exothermic reaction between SiO2 and Mg, along with the presence of carbon, SiC can be spontaneously produced with the formation of Si. The synthesized Si@SiC was composed of well-mixed SiC and Si nanocrystallites. The SiC content of the Si@SiC was adjusted by tuning the carbon content of the precursor. Among the resultant Si@SiC materials, the Si@SiC-0.5 sample, which was produced from a precursor containing 4.37 wt % of carbon, exhibits excellent electrochemical characteristics, such as a high first discharge capacity of 1642 mAh g-1 and 53.9% capacity retention following 200 cycles at a rate of 0.1C. Even at a high rate of 10C, a high reversible capacity of 454 mAh g-1 was obtained. Surprisingly, at a fixed discharge rate of C/20, the Si@SiC-0.5 electrode delivered a high capacity of 989 mAh g-1 at a charge rate of 20C. In addition, a full cell fabricated by coupling a lithiated Si@SiC-0.5 anode and a LiCoO2 cathode exhibits excellent cyclability over 50 cycles. This outstanding electrochemical performance of Si@SiC-0.5 is attributed to the SiC phase, which acts as a buffer layer that stabilizes the nanostructure of the Si active phase and enhances the electrical conductivity of the electrode.

Highly porous coral-like silicon particles synthesized by an ultra-simple thermal-reduction method

Porous Si is considered a potential anode material for next-generation Li-ion batteries (LIBs) because of its high specific capacity, low lithiation/delithiation potential, low cost, and environmental friendliness. In this work, we introduce a simplified Mg-thermal-reduction method for the production of mass-scalable coral-like bulk-Si powder with a high surface area (38 m2 g−1), broad pore-size distribution (2–200 nm), and 3-dimensionally (3D) interconnected Si structure for application in LIBs. The porous, coral-like Si electrode delivered a high reversible capacity of 2451 mA h g−1, corresponding to ∼70% of the theoretical capacity of Si, at a rate of C/10. After 100 cycles, the porous, coral-like Si electrode maintained a capacity of 1956 mA h g−1, corresponding to 79.8% of the initial reversible capacity. Importantly, a reasonably high reversible capacity of 614 mA h g−1 was achieved even at a high rate of 10C. These outstanding results demonstrate that the 3D-networked, porous, coral-like Si powder, synthesized via a NaCl-assisted Mg-thermal-reduction process on a stainless-steel plate over a period of one minute, can be employed as a promising anode material for the next generation of high-energy LIBs.

A self-encapsulated porous Sb–C nanocomposite anode with excellent Na-ion storage performance

In this study, a self-encapsulated Sb-C nanocomposite as an anode material for sodium-ion batteries (SIBs) was successfully synthesised using an SbCl3-citrate complex precursor, followed by a drying and calcination process under an inert N2 atmosphere. When the molar ratio of SbCl3 to citric acid was varied from 1 : 1 to 1 : 4, the Sb-C nanocomposite with a molar ratio of 1 : 3 (Sb-C3) exhibited the highest specific surface area (265.97 m2 g-1) and pore volume (0.158 cm3 g-1). Furthermore, the Sb-C3 electrode showed a high reversible capacity of 559 mA h g-1 at a rate of C/10 and maintained a high reversible capacity of 430 mA h g-1 even after 195 cycles at a rate of 1C. The Sb-C3 electrode exhibited an excellent rate capability of 603, 445, and 357 mA h g-1 at the rates of C/20, 5C, and 10C, respectively. Furthermore, a full cell composed of an Sb-C3 anode and a Na3V2(PO4)3 cathode exhibited good specific capacity and cyclability, making the Sb-C composite a promising anode material for high-performance SIBs.