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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.

All-solid-state batteries frequently encounter mechanical instability due to the inherent brittleness and low elasticity of inorganic ceramic electrolytes, such as sulfides, oxides, and halides. These electrolytes struggle to accommodate the volumetric fluctuations of positive electrode materials during cycling, potentially leading to performance degradation and premature failure. To address this challenge, we propose a defect-based toughening approach for resilient halide solid electrolytes. By meticulously controlling the cooling rate during synthesis, we successfully increase the defect density within the electrolyte, enhancing its mechanical properties and mitigating the risk of mechanical failure. Mechanical property testing, high-resolution transmission electron microscopy characterization, and synchrotron radiation diffraction analysis reveal that the quenched material exhibit not only a higher Young’s modulus, rendering it less susceptible to deformation under stress and a higher capacity for energy absorption before plastic deformation or fracture due to its increased dispersed defect density. Consequently, it demonstrates better adaptability to the volumetric changes associated with the positive electrode material during battery cycling, effectively mitigating strain-induced material behavior. Here we show the effectiveness of defect-enhanced toughening strategies in optimizing the mechanical properties and microstructure of electrolyte materials, thereby enhancing the overall integrity of solid-state batteries without requiring modifications to their chemical composition. All-solid-state batteries offer high energy density and safety but face interfacial and mechanical challenges. Here, authors present a dispersed defect toughening strategy for halide electrolytes, improving mechanical robustness without sacrificing conductivity, advancing practical use of all-solid-state batteries.

Interfaces are the critical components of all-solid-state batteries, and it is generally believed that high interfacial impedance is the major culprits of battery failure. In this study, the interface impedance has been found not to be a major issue in the batteries comprising Si negative electrode, Li 10 GeP 2 S 12 and Li 10 Si 0.3 PS 6.7 Cl 1.8 electrolytes and LiNi 0.8 Mn 0.1 Co 0.1 O 2 positive electrode. Instead, it is the sustainable interfacial reaction that depletes the active lithium source, causing continuous capacity decay. The interphase layer at the Si/Li 10 Si 0.3 PS 6.7 Cl 1.8 interface comprising nanocrystalline Li 2 S dispersed in an amorphous matrix is thin (with a thickness < 200 nm) and stable, and the battery maintains a good cyclability. In contrast, the interphase layer at the Si/Li 10 GeP 2 S 12 interface is thick with a thickness of 10 μm. Couter-intuitively, despite the thick interfacial layer comprising mainly needle shaped Li 2 S, the interfacial impedance does not increase dramatically, suggesting that interfacial impedance is not the main issue, rather, it is the chemically/electrochemically continuous reaction of negative electrode with Li 10 GeP 2 S 12 that consumes the active lithium source from positive electrode and causes the capacity decay. This study provides atomic-scale interface structures of sulfide based batteries, which have important implications for the design of stable interfaces for high performance batteries. Here, authors use Cryo-FIB and Cryo-TEM to reveal the atomic structures of the sulfide electrolyte/Si electrode interfaces, showing that the continuous lithium-ion consumption during interfacial reaction rather than interface impedance leads to capacity fade and battery failure.

All‐solid‐state (ASS) Na–S batteries are promising for a large‐scale energy‐storage system owing to numerous merits. However, the high conversion reaction barrier impedes their practical application. In this work, the basic mechanism on how Se catalyzes the conversion reaction in the Na–S batteries is unraveled. The sodiation/desodiation of Na–SeS2 nanobatteries are systematically evaluated via in situ transmission electron microscopy (in situ TEM) with a microheating device. The real‐time analyses reveal an amorphous Na–SexSy intermediate phase appears during the direct conversion from SeS2 to Na2S, and a reverse reaction succeeds at 100 °C with a prior formation of Se. The absence of polysulfides and a much lower desodiation temperature in contrast to Na–S nanobatteries demonstrate that the Se incorporation significantly lowers the conversion reaction barrier. According to these findings, the ASS SeS2 batteries using a Na3SbS4 solid electrolyte (SE) are assembled using various SE:C ratios in the composite cathodes to investigate the effect of the ion and electron transport on the electrochemical properties, including the effective transport properties, MacMullin number, and the tortuosity factor. The obtained results in turn confirm the findings from the in situ TEM. These findings are applicable to optimize other S‐based active materials and improve their utilization. Se incorporation lowers the energy barrier in a Na–S battery and thereby catalyzes the reversible conversion reaction. The real‐time transmission electron microscopy discovers an amorphous Na–SexSy intermediate, promoting the transformation from SeS2 to Na2S without the formation of polysulfides. The reverse desodiation accomplishes at a low temperature of 100 °C.

Metals fluorides (MFs) are potential conversion cathodes to replace commercial intercalation cathodes. However, the application of MFs is impeded by their poor electronic/ionic conductivity and severe decomposition of electrolyte. Here, a composite cathode of FeF2 and polymer‐derived carbon (FeF2@PDC) with excellent cycling performance is reported. The composite cathode is composed of nanorod‐shaped FeF2 embedded in PDC matrix with excellent mechanical strength and electronic/ionic conductivity. The FeF2@PDC enables a reversible capacity of 500 mAh g–1 with a record long cycle lifetime of 1900 cycles. Remarkably, the FeF2@PDC can be cycled at a record rate of 60 C with a reversible capacity of 107 mAh g–1 after 500 cycles. Advanced electron microscopy reveals that the in situ formation of stable Fe3O4 layers on the surface of FeF2 prevents the electrolyte decomposition and leaching of iron (Fe), thus enhancing the cyclability. The results provide a new understanding to FeF2 electrochemistry, and a strategy to radically improve the electrochemical performance of FeF2 cathode for lithium‐ion battery applications. Embedding nano‐FeF2 into polymer derived carbon (FeF2@PDC) matrix with excellent mechanical strength and electron/ion conductivity enables in situ formation of a Fe3O4 layer that suppresses the decomposition of the electrolyte and inhibits the formation of a detrimental cathode solid electrolyte interface. The Li‐ FeF2@PDC cell exhibits a remarkable long cycle life of 1900 cycles with a reversible capacity over 500 mAh g‐1 at 0.5 C.

Sulfide electrolyte-based all-solid-state batteries (ASSBs) are potential next generation energy storage technology due to the high ionic conductivity of sulfide electrolytes and potentially improved energy density and safety. However, the performance of ASSBs at/below subzero temperatures has not been explored systematically. Herein, low temperature (LT) performance of LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811)|Li 9.54 Si 1.74 P 1.44 S 11.7 Cl 0.3 (LiSPSCl)|Li 4 Ti 5 O 12 (LTO) ASSBs was investigated. By charging the ASSB to 6 V at −40 °C, a capacity of 100.7 mAh·g −1 at 20 mA·g −1 was achieved, which is much higher than that charged to 4.3 V (4.6 mAh·g −1 ) at −40 °C. Moreover, atomic resolution microscopy revealed that the NCM811 remained almost intact even after being charged to 6 V. In contrast, NCM811 was entirely destructed when charged to 6 V at room temperature. The sharp difference arises from the large internal charge transfer resistance at LT which requires high voltage to overcome. Nevertheless, such high voltage is not harmful to the active material but beneficial to extracting most energy out of the ASSBs at LT. We also demonstrated that thinner electrolyte is favorable for LT operation of ASSBs due to the reduced ion transfer distance. This work provides new strategies to boost the capacity and energy density of sulfide-based ASSBs at LT for dedicated LT applications.

All‐solid‐state (ASS) Na–S batteries are promising for a large‐scale energy‐storage system owing to numerous merits. However, the high conversion reaction barrier impedes their practical application. In this work, the basic mechanism on how Se catalyzes the conversion reaction in the Na–S batteries is unraveled. The sodiation/desodiation of Na–SeS 2 nanobatteries are systematically evaluated via in situ transmission electron microscopy (in situ TEM) with a microheating device. The real‐time analyses reveal an amorphous Na–Se x S y intermediate phase appears during the direct conversion from SeS 2 to Na 2 S, and a reverse reaction succeeds at 100 °C with a prior formation of Se. The absence of polysulfides and a much lower desodiation temperature in contrast to Na–S nanobatteries demonstrate that the Se incorporation significantly lowers the conversion reaction barrier. According to these findings, the ASS SeS 2 batteries using a Na 3 SbS 4 solid electrolyte (SE) are assembled using various SE:C ratios in the composite cathodes to investigate the effect of the ion and electron transport on the electrochemical properties, including the effective transport properties, MacMullin number, and the tortuosity factor. The obtained results in turn confirm the findings from the in situ TEM. These findings are applicable to optimize other S‐based active materials and improve their utilization.

Owing to its high thermal and electrical conductivities, its ductility and its overall non-toxicity 1 – 3 , copper is widely used in daily applications and in industry, particularly in anti-oxidation technologies. However, many widespread anti-oxidation techniques, such as alloying and electroplating 1 , 2 , often degrade some physical properties (for example, thermal and electrical conductivities and colour) and introduce harmful elements such as chromium and nickel. Although efforts have been made to develop surface passivation technologies using organic molecules, inorganic materials or carbon-based materials as oxidation inhibitors 4 – 12 , their large-scale application has had limited success. We have previously reported the solvothermal synthesis of highly air-stable copper nanosheets using formate as a reducing agent 13 . Here we report that a solvothermal treatment of copper in the presence of sodium formate leads to crystallographic reconstruction of the copper surface and formation of an ultrathin surface coordination layer. We reveal that the surface modification does not affect the electrical or thermal conductivities of the bulk copper, but introduces high oxidation resistance in air, salt spray and alkaline conditions. We also develop a rapid room-temperature electrochemical synthesis protocol, with the resulting materials demonstrating similarly strong passivation performance. We further improve the oxidation resistance of the copper surfaces by introducing alkanethiol ligands to coordinate with steps or defect sites that are not protected by the passivation layer. We demonstrate that the mild treatment conditions make this technology applicable to the preparation of air-stable copper materials in different forms, including foils, nanowires, nanoparticles and bulk pastes. We expect that the technology developed in this work will help to expand the industrial applications of copper. High oxidation resistance, without degradation of thermal or electrical conductivity, is achieved in copper using surface modification by a solvothermal or electrochemical treatment with sodium formate and formation of a thin surface coordination layer.

Mn4+-doped red-light-emitting phosphors have become a research hotspot that can effectively enhance photosynthesis and promote morphogenesis in plants. Herein, the red phosphor La3Mg2NbO9:Mn4+ was synthesized through the solid-state reaction method. The effects of adding H3BO3 and a charge compensator R+ (R = Li, Na, K) on the crystal structure, morphology, quantum efficiency, and luminous performance of the La3Mg2NbO9:Mn4+ phosphor were systematically analyzed, respectively. The results showed that adding H3BO3 flux and a charge compensator improved the quantum efficiency and luminescence intensity. The emission intensity of the phosphor was enhanced about 5.9 times when Li+ was used as the charge compensator, while it was enhanced about 240% with the addition of H3BO3 flux. Remarkably, it was also found that the addition of H3BO3 flux and a charge compensator simultaneously improved the thermal stability at 423 K from 47.3% to 68.9%. The prototype red LED fabricated using the La3Mg2NbO9:Mn4+,H3BO3,Li+ phosphor exhibited a perfect overlap with the phytochrome absorption band for plant growth. All of these results indicate that the La3Mg2NbO9:Mn4+,H3BO3,Li+ phosphor has great potential for use in agricultural plant lighting.

In order to break through the limitations of the application of traditional temperature measurement technology, non-contact optical temperature sensing material with good sensitivity is one of the current research hotspots. Herein, a series of Dy3+ and Mn4+ co-doping Mg3Ga2SnO8 fluorescent materials were prepared successfully, and the crystal structure, phase purity, and morphology of the synthesized phosphors were comprehensively investigated, as well as their photoluminescence properties, energy transfer, and high-temperature thermal stability. The two pairs of independent thermally coupled energy levels of Dy3+ ions and Mn4+ ions in Mg3Ga2SnO8 are utilized to realize the dual-mode optical temperature detection with excellent performance. On the one hand, based on the different ionic energy level transitions of 4F9/2→6H13/2 and 2Eg→4A2g responding differently to temperature, two emission bands of 577 nm and 668 nm were chosen to construct the fluorescence intensity ratio thermometry, and the maximum sensitivity of 1.82 %K−1 was achieved at 473 K. On the other hand, based on the strong temperature dependence of the lifetime of Mn4+ in Mg3Ga2SnO8:0.06Dy3+,0.009Mn4+, fluorescence lifetime thermometry was constructed and a maximum sensitivity of 2.75 %K−1 was achieved at 473 K. Finally, the Mg3Ga2SnO8: 0.06Dy3+,0.009Mn4+ sample realizes dual-mode optical temperature measurement with high sensitivity and a wide temperature detection range, indicating that the sample has promising applications in optical temperature measurement.