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Dendrite formation during electrodeposition while charging lithium metal batteries compromises their safety. Although high-shear-modulus (Gs) solid-ion conductors (SICs) have been prioritized to resolve the pressure-driven instabilities that lead to dendrite propagation and cell shorting, it is unclear whether these or alternatives are needed to guide uniform lithium electrodeposition, which is intrinsically density-driven. Here, we show that SICs can be designed within a universal chemomechanical paradigm to access either pressure-driven dendrite-blocking or density-driven dendrite-suppressing properties, but not both. This dichotomy reflects the competing influence of the SIC's mechanical properties and the partial molar volume of Li+ ([Formula: see text]) relative to those of the lithium anode (GLi and VLi) on plating outcomes. Within this paradigm, we explore SICs in a previously unrecognized dendrite-suppressing regime that are concomitantly 'soft', as is typical of polymer electrolytes, but feature an atypically low [Formula: see text] that is more reminiscent of 'hard' ceramics. Li plating (1 mA cm-2; T = 20 °C) mediated by these SICs is uniform, as revealed using synchrotron hard X-ray microtomography. As a result, cell cycle life is extended, even when assembled with thin Li anodes (~30 µm) and either high-voltage NMC-622 cathodes (1.44 mAh cm-2) or high-capacity sulfur cathodes (3.02 mAh cm-2).

Conversion reaction electrodes offer a high specific capacity in rechargeable batteries by utilizing wider valence states of transition metals than conventional intercalation-based electrodes and have thus been intensively studied in recent years as potential electrode materials for high-energy-density rechargeable batteries. However, several issues related to conversion reactions remain poorly understood, including the polarization or hysteresis during charge/discharge processes. Herein, Co3O4 in Na cells is taken as an example to understand the aforementioned properties. The large hysteresis in charge/discharge profiles is revealed to be due to different electrochemical reaction paths associated with respective charge and discharge processes, which is attributed to the mobility gap among inter-diffusing species in a metal oxide compound during de/sodiation. Furthermore, a Co3O4–graphene nanoplatelet hybrid material is demonstrated to be a promising anode for Na rechargeable batteries, delivering a capacity of 756 mAh g−1 with a good reversibility and an energy density of 96 Wh kg−1 (based on the total electrode weight) when combined with a recently reported Na4Fe3(PO4)2(P2O7) cathode.

With the demand for high-energy-storage devices, the rechargeable metal-oxygen battery has attracted attention recently. Sodium-oxygen batteries have been regarded as the most promising candidates because of their lower-charge overpotential compared with that of lithium-oxygen system. However, conflicting observations with different discharge products have inhibited the understanding of precise reactions in the battery. Here we demonstrate that the competition between the electrochemical and chemical reactions in sodium-oxygen batteries leads to the dissolution and ionization of sodium superoxide, liberating superoxide anion and triggering the formation of sodium peroxide dihydrate (Na2O2·2H2O). On the formation of Na2O2·2H2O, the charge overpotential of sodium-oxygen cells significantly increases. This verification addresses the origin of conflicting discharge products and overpotentials observed in sodium-oxygen systems. Our proposed model provides guidelines to help direct the reactions in sodium-oxygen batteries to achieve high efficiency and rechargeability.

Nanoporous carbon, including redox-active functional groups, can be a promising active electrode material (AEM) as a positive electrode for lithium-ion batteries owing to its high electrochemical performance originating from the host-free surface-driven charge storage process. This study examined the effects of the nanopore size on the pseudocapacitance of the nanoporous carbon materials using nanopore-engineered carbon-based AEMs (NE-C-AEMs). The pseudocapacitance of NE-C-AEMs was intensified, when the pore diameter was ≥2 nm in a voltage range of 1.0~4.8 V vs Li+/Li under the conventional carbonate-based electrolyte system, showing a high specific capacity of ~485 mA·h·g−1. In addition, the NE-C-AEMs exhibited high rate capabilities at current ranges from 0.2 to 4.0 A·g−1 as well as stable cycling behavior for more than 300 cycles. The high electrochemical performance of NE-C-AEMs was demonstrated by full-cell tests with a graphite nanosheet anode, where a high specific energy and power of ~345 Wh·kg−1 and ~6100 W·Kg−1, respectively, were achieved. [ABSTRACT FROM AUTHOR]