Chun Fang

Low-Cost and High-Performance Hard Carbon Anode Materials for Sodium-Ion Batteries

As an anode material for sodium-ion batteries (SIBs), hard carbon (HC) presents high specific capacity and favorable cycling performance. However, high cost and low initial Coulombic efficiency (ICE) of HC seriously limit its future commercialization for SIBs. A typical biowaste, mangosteen shell was selected as a precursor to prepare low-cost and high-performance HC via a facile one-step carbonization method, and the influence of different heat treatments on the morphologies, microstructures, and electrochemical performances was investigated systematically. The microstructure evolution studied using X-ray diffraction, Raman, Brunauer–Emmett–Teller, and high-resolution transmission electron microscopy, along with electrochemical measurements, reveals the optimal carbonization condition of the mangosteen shell: HC carbonized at 1500 °C for 2 h delivers the highest reversible capacity of ∼330 mA h g–1 at a current density of 20 mA g–1, a capacity retention of ∼98% after 100 cycles, and an ICE of ∼83%. Additionally, the sodium-ion storage behavior of HC is deeply analyzed using galvanostatic intermittent titration and cyclic voltammetry technologies.

High valence Mo-doped Na3V2(PO4)3/C as a high rate and stable cycle-life cathode for sodium battery

NASICON-structure Na3V2(PO4)3 (NVP) is a potential cathode material for sodium ion battery, which is still confronted with low rate performance because of its poor conductivity. To address this problem, high-valance Mo6+ ion was introduced into NVP. The crystal structure, electrochemical performances, sodium ion diffusion kinetics and ion transfer mechanism of high valence Mo-doped Na3−5xV2−xMox(PO4)3/C (0 < x < 0.04) were investigated. X-ray diffraction, electron microscopy and XPS data confirmed high purity NASICON phosphate phases. The Na ion diffusion process was identified through CV measurement, which clearly shows rapid sodium ion transportation in the Mo-doped NASICON materials. Moreover, DFT calculations proved that Na ion diffusion is promoted by Mo doping. Benefiting from the superior Na ion kinetics, Na2.9V1.98Mo0.02(PO4)3 exhibited a performance of 90 mA h g−1 at 10C and preserved 83.5% of the original capacity after 500 cycles. Our studies demonstrate that high-valence Mo doped Na3V2(PO4)3/C is a promising cathode material for sodium ion batteries with super-high rate capability and stable cycle life.

A P2-Type Layered Superionic Conductor Ga-Doped Na2Zn2TeO6 for All-Solid-State Sodium-Ion Batteries

Here, a P2-type layered Na2 Zn2 TeO6 (NZTO) is reported with a high Na+ ion conductivity ≈0.6×10-3  S cm-1 at room temperature (RT), which is comparable to the currently best Na1+n Zr2 Sin P3-n O12 NASICON structure. As small amounts of Ga3+ substitutes for Zn2+ , more Na+ vacancies are introduced in the interlayer gaps, which greatly reduces strong Na+ -Na+ coulomb interactions. Ga-substituted NZTO exhibits a superionic conductivity of ≈1.1×10-3  S cm-1 at RT, and excellent phase and electrochemical stability. All solid-state batteries have been successfully assembled with a capacity of ≈70 mAh g-1 over 10 cycles with a rate of 0.2 C at 80 °C. 23 Na nuclear magnetic resonance (NMR) studies on powder samples show intra-grain (bulk) diffusion coefficients DNMR on the order of 12.35×10-12  m2  s-1 at 65 °C that corresponds to a conductivity σNMR of 8.16×10-3  S cm-1 , assuming the Nernst-Einstein equation, which thus suggests a new perspective of fast Na+ ion conductor for advanced sodium ion batteries.

A new layered titanate Na2Li2Ti5O12 as a high-performance intercalation anode for sodium-ion batteries

Currently, it is a great challenge to find suitable electrode materials for sodium-ion batteries (SIBs) with large capacity, long cycle life, and high rate capability. Herein, we report a new layered titanate, Na2Li2Ti5O12 (NLT), derived from K2Li2Ti5O12 (KLT) via an ion-exchange method as a SIB anode material. KLT is prepared by a low-temperature solid-state reaction and then transformed into NLT by replacing potassium with sodium in a NaCl solution at room temperature. NLT provides a sodium-ion intercalation voltage at ∼0.5 V versus Na/Na+ and a reversible capacity of 175 mA h g−1 at a current density of 100 mA g−1. It also shows a high sodium-ion diffusion coefficient of 3.0 × 10−10 cm2 s−1, ensuring a high rate capability. For NLT, extremely high discharging rate capability is achieved with a capacity of more than 80 mA h g−1 at a 60 second full discharge and even with 70 mA h g−1 at a 34 second charge. Kinetics analysis based on cyclic voltammogram reveals a typical sodium-ion intercalation behavior in NLT. Furthermore, the first-principle calculation shows a lower migration energy barrier for sodium ions in NLT than that in other layered titanates. These results suggest that NLT is a very promising anode material for high-performance SIBs, especially for fast-charging stable SIBs.

Porous carbon adsorption layer enabling highly reversible redox-reaction of a high potential organic electrode material for sodium ion batteries

Organic compounds have been utilized in rechargeable batteries as electrode materials on account of their designable structures and reversible redox properties. However, most of them suffer from problems with dissolution resulting in poor electrochemical performance. In this work, we adapt a sodium salt of tetracyanoquinodimethane (NaTCNQ) to work as a high redox potential cathode material in sodium ion batteries (SIBs). A porous carbon coated separator is demonstrated to be an adsorption layer and prevents the dissolved active material from migrating to the anode side. The NaTCNQ cell assembled with a carbon layer containing 5% activated carbon (AC) exhibits a higher initial capacity and greatly improved cycling stability. Using a conductive adsorption layer in organic redox batteries is a promising pathway to develop high performance organic electrode materials for SIBs.

Porous NaTi2(PO4)3/C hierarchical nanofibers for ultrafast electrochemical energy storage

NaTi2(PO4)3 (NTP) with a sodium superionic conductor three-dimensional (3D) framework is a promising anode material for sodium-ion batteries (SIBs) because of its suitable potential and stable structure. Although its 3D structure enables high Na-ion diffusivity, low electronic conductivity severely limits NTPs practical application in SIBs. Herein, we report porous NTP/C nanofibers (NTP/C-NFs) obtained via an electrospinning method. The NTP/C-NFs exhibit a high reversible capacity (120 mA h g-1 at 0.2 C) and a long cycling stability (a capacity retention of ∼93% after 700 cycles at 2 C). Furthermore, sodium-ion full cells and hybrid sodium-ion capacitors have also been successfully assembled, both of which exhibit high-rate capabilities and remarkable cycling stabilities because of the high electronic/ionic conductivity and impressive structural stability of NTP/C-NFs. The results show that the nanoscale-tailored NTP/C-NFs could deliver new insights into the design of high-performing and highly stable anode materials for room-temperature SIBs.

New P2-Type Honeycomb-Layered Sodium-Ion Conductor: Na2Mg2TeO6

A novel solid sodium-ion conductor, Na2Mg2TeO6 (NMTO) with a P2-type honeycomb-layered structure, has been synthesized for the first time by a simple solid-state synthetic route. The conductor of NMTO exhibits high conductivity of 2.3 × 10-4 S cm-1 at room temperature (RT) and a large electrochemical window of ∼4.2 V (versus Na+/Na). The conductor is remarkably stable, both in the ambient environment and within its metallic Na anode. This facile sodium-ion conductor displays potential for use in all-solid-state sodium-ion batteries (SS-SIBs).