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Sodium (Na) metal batteries (SMBs) using Na anode are potential “beyond lithium” electrochemical technology for future energy storage applications. However, uncontrollable Na dendrite growth has plagued the application of SMBs. Understanding Na deposition mechanisms, particularly the early stage of Na deposition kinetics, is critical to enable the SMBs. In this context, we conducted in situ observations of the early stage of electrochemical Na deposition. We revealed an important electrochemical Ostwald ripening (EOR) phenomenon which dictated the early stage of Na deposition. Namely, small Na nanocrystals were nucleated randomly, which then grew. During growth, smaller Na nanocrystals were contained by bigger ones via EOR. We observed two types of EOR with one involving only electrochemical reaction driven by electrochemical potential difference between bigger and smaller nanocrystals; while the other being dominated by mass transport governed by surface energy minimization. The results provide new understanding to the Na deposition mechanism, which may be useful for the development of SMB for energy storage applications.

The two biggest promises of solid-state lithium (Li) metal batteries (SSLMBs) are the suppression of Li dendrites by solid-state electrolyte (SSE) and the realization of a high-energy-density Li anode. However, LMBs have not met their expectations due to Li dendrite growth causing short-circuiting. In fact, Li dendrites grow even more easily in SSE than in liquid electrolyte, but the reason for this remains unclear. Here we report in situ transmission electron microscopy observations of Li dendrite penetration through SSE and "dead" Li formation dynamics in SSLMBs. We show direct evidence that large electrochemomechanical stress generates cracks in the SSE and drives Li through the SSE directly. We revealed that fresh Li nucleation sites emerged in every discharge cycle, creating new "dead" Li in the following charging cycle and becoming the dominant Coulombic efficiency decay mechanism in SSLMBs. These results indicate that engineering flaw size and reducing electronic conductivity in SSEs are essential to improve the performance of SSLMBs.

High interfacial resistance and uncontrollable lithium (Li) dendrite are major challenges in solid-state Li-metal batteries (SSLMBs), as they lead to premature short-circuiting and failure of SSLMBs. Here, we report the synthesis of a composite anode comprising a three-dimensional LiCux nanowire network host infiltrated with Li (Li* anode) with low interfacial impedance and superior electrochemical performance. The Li* anode is fabricated by dissolving Cu foil into molten Li followed by solidification. The Li* anode exhibits good wettability with Li6.4La3Zr1.4Ta0.6O12 (LLZTO) and high mechanical strength, rendering low Li*/LLZTO interfacial impedance, homogeneous deposition of Li, and suppression of Li dendrites. Consequently, the Li* anode-based symmetric cells and full cells with LiNi0.88Co0.1Al0.02O2 (NCA), LiFePO4 (LFP), and FeF2 cathodes deliver remarkable electrochemical performance. Specifically, the Li*/LLZTO/Li* symmetrical cell achieves a remarkably long cycle lifetime of 10 000 h with 0.1 mA·cm-2; the Li*/LLZTO/NCA full cell maintains capacity retention of 73.4% after 500 cycles at 0.5C; and all-solid-state Li*/LLZTO/FeF2 full cell achieves a reversible capacity of 147 mAh·g-1 after 500 cycles at 100 mA·g-1. This work demonstrates potential design tactics for an ultrastable Li*/garnet interface to enable high-performance SSLMBs.

The increasing demand for safe and dense energy storage has shifted research focus from liquid electrolyte-based Li-ion batteries toward solid-state batteries (SSBs). However, the application of SSBs is impeded by uncontrollable Li dendrite growth and short circuiting, the mechanism of which remains elusive. Herein, we conceptualize a scheme to visualize Li deposition in the confined space inside carbon nanotubes (CNTs) to mimic Li deposition dynamics inside solid electrolyte (SE) cracks, where the high-strength CNT walls mimic the mechanically strong SEs. We observed that the deposited Li propagates as a creeping solid in the CNTs, presenting an effective pathway for stress relaxation. When the stress-relaxation pathway is blocked, the Li deposition-induced stress reaches the gigapascal level and causes CNT fracture. Mechanics analysis suggests that interfacial lithiophilicity critically governs Li deposition dynamics and stress relaxation. Our study offers critical strategies for suppressing Li dendritic growth and constructing high-energy-density, electrochemically and mechanically robust SSBs.

Lithium metal is considered the ultimate anode material for future rechargeable batteries1,2, but the development of Li metal-based rechargeable batteries has achieved only limited success due to uncontrollable Li dendrite growth3–7. In a broad class of all-solid-state Li batteries, one approach to suppress Li dendrite growth has been the use of mechanically stiff solid electrolytes8,9. However, Li dendrites still grow through them10,11. Resolving this issue requires a fundamental understanding of the growth and associated electro-chemo-mechanical behaviour of Li dendrites. Here, we report in situ growth observation and stress measurement of individual Li whiskers, the primary Li dendrite morphologies12. We combine an atomic force microscope with an environmental transmission electron microscope in a novel experimental set-up. At room temperature, a submicrometre whisker grows under an applied voltage (overpotential) against the atomic force microscope tip, generating a growth stress up to 130 MPa; this value is substantially higher than the stresses previously reported for bulk13 and micrometre-sized Li14. The measured yield strength of Li whiskers under pure mechanical loading reaches as high as 244 MPa. Our results provide quantitative benchmarks for the design of Li dendrite growth suppression strategies in all-solid-state batteries. Lithium whisker growth and mechanical properties can be studied in situ using a combination of two microscopies.

We report real time imaging of the oxygen reduction reactions (ORRs) in all solid state sodium oxygen batteries (SOBs) with CuO nanowires (NWs) as the air cathode in an aberration-corrected environmental transmission electron microscope under an oxygen environment. The ORR occurred in a distinct two-step reaction, namely, a first conversion reaction followed by a second multiple ORR. In the former, CuO was first converted to Cu2O and then to Cu; in the latter, NaO2 formed first, followed by its disproportionation to Na2O2 and O2. Concurrent with the two distinct electrochemical reactions, the CuO NWs experienced multiple consecutive large volume expansions. It is evident that the freshly formed ultrafine-grained Cu in the conversion reaction catalyzed the latter one-electron-transfer ORR, leading to the formation of NaO2. Remarkably, no carbonate formation was detected in the oxygen cathode after cycling due to the absence of carbon source in the whole battery setup. These results provide fundamental unde...

Lithium metal is an ideal anode for next-generation lithium batteries owing to its very high theoretical specific capacity of 3860 mAh g-1 but very reactive upon exposure to ambient air, rendering it difficult to handle and transport. Air-stable lithium spheres (ASLSs) were produced by electrochemical plating under CO2 atmosphere inside an advanced aberration-corrected environmental transmission electron microscope. The ASLSs exhibit a core-shell structure with a Li core and a Li2 CO3 shell. In ambient air, the ASLSs do not react with moisture and maintain their core-shell structures. Furthermore, the ASLSs can be used as anodes in lithium-ion batteries, and they exhibit similar electrochemical behavior to metallic Li, indicating that the surface Li2 CO3 layer is a good Li+ ion conductor. The air stability of the ASLSs is attributed to the surface Li2 CO3 layer, which is barely soluble in water and does not react with oxygen and nitrogen in air at room temperature, thus passivating the Li core.

The modified resin system of 4, 4'-bismaleimidodiphenylmethane ((BDM)/ortho-diallyl bisphenol A(DBA)(BMI)/reactive groups-terminated polyethersulfone (rPESU) (BMI/P)was prepared by melting pre-polymerization. Typical properties (The gelation time, mechanism, phase structure and thermal stability) of the BMI/P resin were systematically investigated, and their origins were discussed. The results show that the addition of rPESU into BMI resin not only significantly improves the impact toughness and the strength, but also effectively improves the thermal stability although the glass transition temperature is reduced slightly. However the reaction rate of BMI/P resin is accelerated and the gelation time is shortened because of the presence of reactive groups. And then, the cured BMI/P resin has a more complex multi-stage phase structure. Those are the difference with the polyethersulfone (PES) without terminated by reactive groups.

The dielectric response of poly(styrene-co-acrylonitrile) (PSAN) thin films fabricated by a solution casting process was investigated in this work. Linear dielectric behavior was obtained in PSAN films under an electric field at frequencies from 100 Hz to 1 MHz and temperature of −50°C to 100°C. The polymer films exhibited an intermediate dielectric permittivity of 4 and low dielectric loss (tan δ) of 0.027. Under 400 MV/m, the energy density of the PSAN films was 6.8 J/cm3, which is three times higher than that of biaxially oriented polypropylene (BOPP) (about 1.6 J/cm3). However, their charge–discharge efficiency (about 90%) was rather close to that of BOPP. The calculated effective dielectric permittivity of the PSAN films under high electric field was as high as 9, which may be attributed to the improved displacement of the cyanide groups (–CN) polarized at high electric fields. These high-performance features make PSAN attractive for high-energy-density capacitor applications.