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This article reports the thermal runaway mechanism of a 25-Ah large-format lithium-ion battery without internal short circuit induced by Joule heat. In this condition, chemical crosstalk is believed to be the mechanism. Specifically, cathode-produced oxygen is consumed by the anode with great heat generation. This finding is important for better design of LIBs to avoid thermal runaway via the optimization of all battery components.

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The proper choice of nonprecious transition metals as single atom catalysts (SACs) remains unclear for designing highly efficient electrocatalysts for hydrogen evolution reaction (HER). Herein, reported is an activity correlation with catalysts, electronic structure, in order to clarify the origin of reactivity for a series of transition metals supported on nitrogen‐doped graphene as SACs for HER by a combination of density functional theory calculations and electrochemical measurements. Only few of the transition metals (e.g., Co, Cr, Fe, Rh, and V) as SACs show good catalytic activity toward HER as their Gibbs free energies are varied between the range of –0.20 to 0.30 eV but among which Co‐SAC exhibits the highest electrochemical activity at 0.13 eV. Electronic structure studies show that the energy states of active valence dz2 orbitals and their resulting antibonding state determine the catalytic activity for HER. The fact that the antibonding state orbital is neither completely empty nor fully filled in the case of Co‐SAC is the main reason for its ideal hydrogen adsorption energy. Moreover, the electrochemical measurement shows that Co‐SAC exhibits a superior hydrogen evolution activity over Ni‐SAC and W‐SAC, confirming the theoretical calculation. This systematic study gives a fundamental understanding about the design of highly efficient SACs for HER.

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Sodium-ion batteries are promising alternatives to lithium-ion batteries for large-scale applications. However, the low capacity and poor rate capability of existing anodes for sodium-ion batteries are bottlenecks for future developments. Here, we report a high performance nanostructured anode material for sodium-ion batteries that is fabricated by high energy ball milling to form black phosphorus/Ketjenblack-multiwalled carbon nanotubes (BPC) composite. With this strategy, the BPC composite with a high phosphorus content (70 wt %) could deliver a very high initial Coulombic efficiency (>90%) and high specific capacity with excellent cyclability at high rate of charge/discharge (∼1700 mAh g(-1) after 100 cycles at 1.3 A g(-1) based on the mass of P). In situ electrochemical impedance spectroscopy, synchrotron high energy X-ray diffraction, ex situ small/wide-angle X-ray scattering, high resolution transmission electronic microscopy, and nuclear magnetic resonance were further used to unravel its superior sodium storage performance. The scientific findings gained in this work are expected to serve as a guide for future design on high performance anode material for sodium-ion batteries.

The development of highly reversible multielectron reaction per redox center in sodium super ionic conductor-structured cathode materials is desired to improve the energy density of sodium-ion batteries. Here, we investigated more than one-electron storage of Na in NaVCr(PO). Combining a series of advanced characterization techniques such as ex situ V solid-state nuclear magnetic resonance, X-ray absorption near-edge structure, and in situ X-ray diffraction, we reveal that V/V and V/V redox couples in the materials can be accessed, leading to a 1.5-electron reaction. It is also found that a light change on the local electronic and structural states or phase change could be observed after the first cycle, resulting in the fast capacity fade at room temperature. We also showed that the irreversibility of the phase changes could be largely suppressed at low temperature, thus leading to a much improved electrochemical performance.

P2-type sodium nickel manganese oxide-based cathode materials with higher energy densities are prime candidates for applications in rechargeable sodium ion batteries. A systematic study combining in situ high energy X-ray diffraction (HEXRD), ex situ X-ray absorption fine spectroscopy (XAFS), transmission electron microscopy (TEM), and solid-state nuclear magnetic resonance (SS-NMR) techniques was carried out to gain a deep insight into the structural evolution of P2-Na0.66Ni0.33-xZnxMn0.67O2 (x = 0, 0.07) during cycling. In situ HEXRD and ex situ TEM measurements indicate that an irreversible phase transition occurs upon sodium insertion-extraction of Na0.66Ni0.33Mn0.67O2. Zinc doping of this system results in a high structural reversibility. XAFS measurements indicate that both materials are almost completely dependent on the Ni(4+)/Ni(3+)/Ni(2+) redox couple to provide charge/discharge capacity. SS-NMR measurements indicate that both reversible and irreversible migration of transition metal ions into the sodium layer occurs in the material at the fully charged state. The irreversible migration of transition metal ions triggers a structural distortion, leading to the observed capacity and voltage fading. Our results allow a new understanding of the importance of improving the stability of transition metal layers.