Assessing the roles of mechanical cracks in Ni-rich layered cathodes in the capacity decay of liquid and solid-state batteries.

Cracks are ubiquitous in Ni-rich layered cathodes upon cycling in liquid electrolyte-lithium-ion batteries (LELIBs); however, their roles in the capacity decay are unclear. Furthermore, how cracks affect the performance of all solid-state batteries (ASSBs) has not been explored yet. Herein, cracks are created by mechanical compression in the pristine single crystal LiNi0.8Mn0.1Co0.1O2 (NMC811) and their roles in the capacity decay in solid-state batteries are asserted. These mechanically created fresh cracks are predominantly along the (003) planes with minor cracks along the planes slanted to the (003) planes, and both types of cracks contain little or no rock-salt phase, which is in sharp contrast to the chemomechanical cracks in NMC811 where rock-salt phase formation is ubiquitous. We reveal that mechanical cracks cause a significant initial capacity loss in ASSBs but little capacity decay during the subsequent cycling. In contrast, the capacity decay in LELIBs is principally governed by the rock salt phase and interfacial side reactions and thus does not result in an initial capacity loss, but a severe capacity decay during cycling.

Design of Ion Channel Confined Binary Metal Cu-Fe Selenides for All-Climate, High-Capacity Sodium Ion Batteries.

Exploring special anode materials with high capacity, stable structure, and extreme temperature feasibility remains a great challenge in secondary sodium based energy systems. Here, a bimetallic Cu-Fe selenide nanosheet with refined nanostructure providing confined internal ion transport channels are reported, in which the structure improves the pseudocapacitance and reduces the charge transfer resistance for making a significant contribution to accelerating the reaction dynamics. The CuFeSe2 nanosheets have a high initial specific capacity of 480.4 mAh g-1 at 0.25 A g-1 , showing impressively excellent rate performance and ultralong cycling life over 1000 cycles with 261.1 mAh g-1 at 2.5 A g-1 . Meanwhile, it exhibits a good sodium storage performance at extreme temperatures from -20 °C to 50 °C, supporting at least 500 cycles. Besides, the CuFeSe2 ||Na3 V2 (PO4 )3 /C full cell delivers a high specific capacity of 168.5 mAh g-1 at 0.5 A g-1 and excellent feasibility for over 600 cycles long cycling. Additionally, the Na+ storage mechanisms are further revealed by ex situ X-ray diffraction (XRD) and in situ transmission electron microscopy (TEM) techniques. A feasible channelized structural design strategy is provided that inspires new instruction into the development of novel materials with high structural stability and low volume expansion rate toward the application of other secondary batteries.