No abstract

NASICON-type of solid-state electrolyte, Na3Zr2Si2PO12 (NZSP), is one of the potential solid-state electrolytes for all-solid-state Na battery and Na–air battery. However, in solid-state synthesis, high sintering temperature above 1200 °C and long duration are required, which led to loss of volatile materials and formation of impurities at the grain boundaries. This hampers the total ionic conductivity of NZSP to be in the range of 10–4 S cm–1. Herein, we have reduced both the sintering temperature and time of the NZSP electrolyte by sintering the NZSP powders with different amounts of Na2SiO3 additive, which provides the liquid phase for the sintering process. The addition of 5 wt % Na2SiO3 has shown the highest total ionic conductivity of 1.45 mS cm–1 at room temperature. A systematic study of the effect of Na2SiO3 on the microstructure and electrical properties of the NZSP electrolyte is conducted by the structural study with the help of morphological and chemical observations using X-ray diffraction (XRD), scanning electron microscopy, and using focused ion-beam-time of flight-secondary ion mass spectroscopy. The XRD results revealed that cations from Na2SiO3 diffused into the bulk change the stoichiometry of NZSP, leading to an enlarged bottleneck area and hence lowering activation energy in the bulk, which contributes to the increment of the bulk ion conductivity, as indicated by the electrochemical impedance spectroscopy result. In addition, higher density and better microstructure contribute to improved grain boundary conductivity. More importantly, this study has achieved a highly ionic conductive NZSP only by facile addition of Na2SiO3 into the NZSP powder prior to the sintering stage.

No abstract

All-solid-state lithium metal batteries (ASSLiMB) have been considered as one of the most promising next-generation high-energy storage systems that replace liquid organic electrolytes by solid-state electrolytes (SSE). Among many different types of SSE, NASICON-structured Li1+x Al x Ge2–x (PO3)4 (LAGP) shows high a ionic conductivity, high stability against moisture, and wide working electrochemical windows. However, it is unstable when it is in contact with molten Li, hence largely limiting its applications in ASSLiMB. To solve this issue, we have studied reaction processes and mechanisms between LAGP and molten Li, based on which a failure mechanism is hence proposed. With better understanding the failure mechanism, a thin thermosetting Li salt polymer, P­(AA-co-MA)­Li, layer is coated on the bare LAGP pellet before contacting with molten Li. To further increase the ionic conductivity of P­(AA-co-MA)­Li, LiCl is added in P­(AA-co-MA)­Li. A symmetric cell of Li/interface/LAGP/interface/Li is prepared using molten Li–Sn alloy and galvanically cycled at current densities of 15, 30, and 70 μA cm–2 for 100 cycles, showing stable low overpotentials of 0.036, 0.105, and 0.257 V, respectively. These electrochemical results demonstrate that the interface coating of P­(AA-co-MA)Li can be an effective method to avoid an interfacial reaction between the LAGP electrolyte and molten Li.

The Garnet-type solid electrolyte Li 7 La 3 Zr 2 O 12 (LLZO) showing high ionic conductivity and a wide electrochemical potential window is considered as one of the most promising candidates for solid-state batteries. Among various doping derivatives, the Al-and Ga-doped LLZO electrolytes are intensively studied because of their ability to enhance the stability of the cubic structure and to promote good sinter ability as well. Despite showing great similarities in site preference and sintering behavior, the Al and Ga doping derivatives differ by 1 order of magnitude in total ionic conductivity. Therefore, a comparative study on the doping characteristics of Al and Ga with respect to ionic conductivity and sintering behavior is necessary. Herein, we simultaneously introduced Al and Ga into Li sites (Al x Ga 0.25−x -LLZO) to study their influences on the microstructure and electrochemical properties of LLZO. The results show that Ga doping enables a higher conductivity than Al doping and largely promotes sinter ability at the same time. Compared to Al single doping (Al 0.25 ), Ga-contained compositions (x < 0.25) show significant grain growth. Moreover, a slight inclusion of Ga (Al 0.20 Ga 0.05 ) not only modifies the sintering behavior that results in a microstructure transition from fine grains of Al 0.25 (5−20 μm) to abnormally large grains (several hundred micrometers) but also greatly enhances the conductivity, yielding a value that is 3 times higher. However, further increases in Ga ratio in Al x Ga 0.25−x results in marginal increases in conductivity. The total conductivity reaches a maximum of 1.19 × 10 −3 S cm −1 for Ga single doping (Ga 0.25 ) at room temperature. In addition, Al 0.25 also shows fast ion conducting behavior along the grain boundaries with a conductivity of 8.30 × 10 −4 S cm −1 . Consequently, this study sheds lights on the different doping characteristics between Al and Ga, providing guidance for fine composition engineering of these two promising dopants.

Two-dimensional-layered materials (TDLMs) have gained enormous attention because of their open layered structures and high specific capacities in sodium ion batteries (SIBs). However, effectively suppressing the fast capacity fading and serious volume change in cycling process is still a challenge. Herein, we report reduced graphene oxide-riveted bismuth oxychloride (BiOCl) by inducing interfacial Bi–C bonding as the high-performance anode for SIBs. This new composite structure can deliver an initial charge capacity of 266.6 mA h g–1 at 50 mA g–1 and a cycling stability maintaining 81.7% after 100 cycles, which is much superior to recent data of metal oxyhalide. The excellent charge/discharge cyclability is associated with the strong interfacial coupling that significantly reinforces charge transfer and structural stability of the electrode. At the same time, the remarkable mechanical stretching could mitigate the volume expansion and hence maintain the integrity of BiOCl nanosheets during cycling. The proposed strategy based on constructing strong interfacial coupling through chemical bonding and interlayer engineering may hold great promise for developing TDLMs for next-generation rechargeable batteries.

Owing to several advantages of metallic sodium (Na), such as a relatively high theoretical capacity, low redox potential, wide availability, and low cost, Na metal batteries are being extensively studied, which are expected to play a major role in the fields of electric vehicles and grid-scale energy storage. Although considerable efforts have been devoted to utilizing MXene-based materials for suppressing Na dendrites, achieving a stable cycling of Na metal anodes remains extremely challenging due to, for example, the low Coulombic efficiency (CE) caused by the severe side reactions. Herein, a g-C3N4 layer was attached in situ on the Ti3C2 MXene surface, inducing a surface state reconstruction and thus forming a stable hetero-interphase with excellent sodiophilicity between the MXene and g-C3N4 to inhibit side reactions and guide uniform Na ion flux. The 3D construction can not only lower the local current density to facilitate uniform Na plating/stripping but also mitigate volume change to stabilize the electrolyte/electrode interphase. Thus, the 3D Ti3C2 MXene@g-C3N4 nanocomposite enables much enhanced average CEs (99.9% at 1 mA h cm–2, 0.5 mA cm–2) in asymmetric half cells, long-term stability (up to 700 h) for symmetric cells, and stable cycling (up to 800 cycles at 2 C), together with outstanding rate capability (up to 20 C), of full cells. The present study demonstrates an approach in developing practically high performance for Na metal anodes.

Uniaxial tensile and uniaxial compressive tests for Zr-based bulk metallic glasses (BMGs) were conducted at room and cryogenic temperatures, respectively. It was observed that both the change of macroscopic fracture mode from ductile shear fracture to brittle normal tensile fracture and microscopic fracture feature from micron-scaled vein patterns to nano-scaled dimples with decreasing test temperatures were identified, indicating a significant ductile-to-brittle transition (DBT) behavior. The mechanism of DBT behavior was revealed by the competition between the intrinsic critical shear strength τ0 and critical tensile strength σ0 at different temperatures.