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Mechanical cracks produced by mechanical pressure cause significant initial capacity loss but little capacity decay in subsequent cycles in ASSB. In contrast, in LELIBs mechanical cracks do not induce initial capacity loss but produce long lasting capacity decay during cycling.

Selenium (Se), whose electronic conductivity is nearly 25 orders higher than that of sulfur (S) and whose theoretical volumetric capacity is 3254 mAh cm

The very high ionic conductivity of Li

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.

Akin to Li, Na deposits in a dendritic form to cause short circuit in Na metal batteries. However, the growth mechanisms and related mechanical properties of Na dendrites remain largely unknown. He...

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.

Understanding the structural evolution of Li2 S upon operation of lithium-sulfur (Li-S) batteries is inadequate and a complete decomposition of Li2 S during charge is difficult. Whether it is the low electronic conductivity or the low ionic conductivity of Li2 S that inhibits its decomposition is under debate. Furthermore, the decomposition pathway of Li2 S is also unclear. Herein, an in situ transmission electron microscopy (TEM) technique implemented with a microelectromechanical systems (MEMS) heating device is used to study the precipitation and decomposition of Li2 S at high temperatures. It is revealed that Li2 S transformed from an amorphous/nanocrystalline to polycrystalline state with proceeding of the electrochemical lithiation at room temperature (RT), and the precipitation of Li2 S is more complete at elevated temperatures than at RT. Moreover, the decomposition of Li2 S that is difficult to achieve at RT becomes facile with increased Li+ ion conduction at high temperatures. These results indicate that Li+ ion diffusion in Li2 S dominates its reversibility in the solid-state Li-S batteries. This work not only demonstrates the powerful capabilities of combining in situ TEM with a MEMS heating device to explore the basic science in energy storage materials at high temperatures but also introduces the factor of temperature to boost battery performance.

Carbon dioxide (CO2) as a greenhouse gas causes globe warming. Recent studies have shown that CO2 can be harnessed to make an energy storage device through the operation of metal-CO2 batteries. While the Li-CO2 and Na-CO2 batteries showing high capacity and good cycle life have been demonstrated, the possibility of creating a K-CO2 battery has not been realized. Here we report the creation of a K-CO2 battery by using CO2 as the cathode in an advanced aberration corrected environmental transmission electron microscope, and in-situ observation of the discharge and charge processes of the nanobattery. During discharge, K2CO3 was generated in the cathode, which converted back to metal K during charge, and the K-CO2 nanobattery demonstrates a good cyclability. Moreover, it is evident that CO gas was released during discharge and the carbon cathode was consumed continuously during charge. Our study provides a fundamental understanding of the K-CO2 battery, which may aid the designing of K-CO2 based energy storage devices.

Using α-manganese dioxide (α-MnO2) nanowires as the air electrode, a K-O2 nanobattery is assembled in an aberration corrected environmental transmission electron microscope. It is found that the α-MnO2 nanowires are reduced into Mn3O4 and MnO during discharge; meanwhile, KO2 is formed on the surface of the α-MnO2 nanowires.

Lithium metal is considered the ultimate anode material for future rechargeable batteries

Battery safety is critical to the application of lithium-ion batteries, especially for high energy density battery applied in electric vehicles. In this paper, the thermal runaway mechanism of LiNi0.8Co0.1Mn0.1O2 based lithium-ion battery is illustrated. And the reaction between cathode and flammable electrolyte is proved as the trigger of the thermal runaway accident. In detail, with differential scanning calorimeter tests for battery components, the material combination contributing to thermal runaway was decoupled. Characterization with synchrotron X-ray diffraction and transmission electron microscopy with in-situ heating proved that the vigorous exothermic reaction is initiated by the liberated oxygen species. The pulse of highly active oxygen species reacted quickly with the electrolyte, accompanied with tremendous heat release, which accelerated the phase transformation of charged cathode. Also, the mechanism is verified by a confirmatory experiment when the highly active oxygen species were trapped by anion receptor, the phase transformation of the charged cathode was inhibited. Clarifying the thermal runaway mechanism of LiNi0.8Co0.1Mn0.1 based lithium-ion battery may light the way to battery chemistries of both high energy density and high safety.