Particle velocimetry based on the temporal feature of upconversion luminescent nanocrystals is a newly-raising fluid velocimetry. Exploiting the availability to low flow rate fluid and exempting redundance external calibration (achieving once calibration for all) are highly expected and challenging. Herein, an engineered core–shell nano-probe, NaYF₄:Yb/Ho/Ce@NaGdF₄, was proposed, in which the Ce³⁺ ions were utilized to manipulate the upconversion dynamic of Ho³⁺. Through optimization, a superior sensitive against low-speed flow is achieved, and the external calibrations before each operation can be avoided. Application demonstrations were conducted on a fluid circulation system with controllable flow rate. The fluid velocity was monitored successfully, no matter it is permanent, or cyclically variating (imitating the in vivo arterial blood). Moreover, this velocimetric route is competent in spatial scanning for handling the spatially inhomogeneous velocity field. Such sensing nanomaterial and fluid velocimetric method exhibit promising application potential in human blood velocimetry, industrial control, or environmental monitoring.

The increasing demand for new energy sources has promoted the improvement of the energy storage capacity of lithium-ion batteries (LIBs) that urged the development of higher energy density cathode materials. The enhancement of the classical cathode in the last 30 years has reached a bottleneck, and then the discovery of the lithium-excess disordered materials has greatly expanded the research space of the cathode materials. Compared with the conventional layered oxides, the lithium-excess disordered rock-salt oxides (LEDRXs) with a more stable structure has higher extractable Li⁺ content, even though the inactive high-valent transition metals (TMs) were needed to compensate for the excess Li, which would reduce the total TM redox content. In addition, oxygen redox provides additional electron capacity for the materials, which also causes O loss and results in the subsequent poor cycle performance. Herein, a series of studies about LEDRXs and their targeted modification measures are summarized, including the prospect of the materials, in order to provide ideas for the design of high-performance LEDRXs. Finally, the new discoveries and outlook on future research directions of LEDRX cathode materials for LIBs with higher energy density are given.