Inactive lithium (Li) formation is the immediate cause of capacity loss and catastrophic failure of Li metal batteries. However, the chemical component and the atomic level structure of inactive Li have rarely been studied due to the lack of effective diagnosis tools to accurately differentiate and quantify Li + in solid electrolyte interphase (SEI) components and the electrically isolated unreacted metallic Li 0 , which together comprise the inactive Li. Here, by introducing a new analytical method, Titration Gas Chromatography (TGC), we can accurately quantify the contribution from metallic Li 0 to the total amount of inactive Li. We uncover that the Li 0 , rather than the electrochemically formed SEI, dominates the inactive Li and capacity loss. Using cryogenic electron microscopies to further study the microstructure and nanostructure of inactive Li, we find that the Li 0 is surrounded by insulating SEI, losing the electronic conductive pathway to the bulk electrode. Coupling the measurements of the Li 0 global content to observations of its local atomic structure, we reveal the formation mechanism of inactive Li in different types of electrolytes, and identify the true underlying cause of low Coulombic efficiency in Li metal deposition and stripping. We ultimately propose strategies to enable the highly efficient Li deposition and stripping to enable Li metal anode for next generation high energy batteries. Main Text:To achieve the energy density of 500 Wh/kg or higher for next-generation battery technologies, Li metal is the ultimate anode, because it is the lightest metal on earth (0.534 g cm -3 ), delivers ultra-high theoretical capacity (3860 mAh g -1 ), and has the lowest negative electrochemical potential (-3.04 V vs. SHE) 1 . Yet, Li metal suffers from dendrite growth and low Coulombic efficiency (CE) which have prevented the extensive adoption of Li metal batteries (LMBs) 2-4 . Since the first demonstration of a Li metal battery in 1976 5 , tremendous effort has been made in preventing dendritic Li growth and improving CE, including electrolyte engineering 6-9 , interface protection 10 and substrate architecture 11 . While dense Li can be achieved without any dendrites during the plating process, the stripping process will eventually dominate the CE thus the reversibility of Li metal anode.The formation of inactive Li, also known as "dead" Li, is the immediate cause of low CE, short cycle life and violent safety hazard of LMBs. It consists of both (electro)chemically formed Li + compounds

Micro- and nanoscale robots that can effectively convert diverse energy sources into movement and force represent a rapidly emerging and fascinating robotics research area. Recent advances in the design, fabrication, and operation of micro/nanorobots have greatly enhanced their power, function, and versatility. The new capabilities of these tiny untethered machines indicate immense potential for a variety of biomedical applications. This article reviews recent progress and future perspectives of micro/nanorobots in biomedicine, with a special focus on their potential advantages and applications for directed drug delivery, precision surgery, medical diagnosis and detoxification. Future success of this technology, to be realized through close collaboration between robotics, medical and nanotechnology experts, should have a major impact on disease diagnosis, treatment, and prevention.

Artificial micromotors, operating on locally supplied fuels and performing complex tasks, offer great potential for diverse biomedical applications, including autonomous delivery and release of therapeutic payloads and cell manipulation. Various types of synthetic motors, utilizing different propulsion mechanisms, have been fabricated to operate in biological matrices. However, the performance of these man-made motors has been tested exclusively under in vitro conditions (outside the body); their behavior and functionalities in an in vivo environment (inside the body) remain unknown. Herein, we report an in vivo study of artificial micromotors in a living organism using a mouse model. Such in vivo evaluation examines the distribution, retention, cargo delivery, and acute toxicity profile of synthetic motors in mouse stomach via oral administration. Using zinc-based micromotors as a model, we demonstrate that the acid-driven propulsion in the stomach effectively enhances the binding and retention of the motors as well as of cargo payloads on the stomach wall. The body of the motors gradually dissolves in the gastric acid, autonomously releasing their carried payloads, leaving nothing toxic behind. This work is anticipated to significantly advance the emerging field of nano/micromotors and to open the door to in vivo evaluation and clinical applications of these synthetic motors.

Advances in bioinspired design principles and nanomaterials have led to tremendous progress in autonomously moving synthetic nano/micromotors with diverse functionalities in different environments. However, a significant gap remains in moving nano/micromotors from test tubes to living organisms for treating diseases with high efficacy. Here we present the first, to our knowledge, in vivo therapeutic micromotors application for active drug delivery to treat gastric bacterial infection in a mouse model using clarithromycin as a model antibiotic and Helicobacter pylori infection as a model disease. The propulsion of drug-loaded magnesium micromotors in gastric media enables effective antibiotic delivery, leading to significant bacteria burden reduction in the mouse stomach compared with passive drug carriers, with no apparent toxicity. Moreover, while the drug-loaded micromotors reach similar therapeutic efficacy as the positive control of free drug plus proton pump inhibitor, the micromotors can function without proton pump inhibitors because of their built-in proton depletion function associated with their locomotion.

Soft robots have garnered interest for real-world applications because of their intrinsic safety embedded at the material level. These robots use deformable materials capable of shape and behavioral changes and allow conformable physical contact for manipulation. Yet, with the introduction of soft and stretchable materials to robotic systems comes a myriad of challenges for sensor integration, including multimodal sensing capable of stretching, embedment of high-resolution but large-area sensor arrays, and sensor fusion with an increasing volume of data. This Review explores the emerging confluence of e-skins and machine learning, with a focus on how roboticists can combine recent developments from the two fields to build autonomous, deployable soft robots, integrated with capabilities for informative touch and proprioception to stand up to the challenges of real-world environments.