High-entropy oxides based on transition metals, such as Mg0.2Co0.2Ni0.2Cu0.2Zn0.2O (TM-HEO), have recently drawn special attention as potential anodes in lithium-ion batteries due to high specific capacity and cycling reversibility. However, the lithiation/delithiation mechanism of such systems is still controversial and not clearly addressed. Here, we report on an operando XAS investigation into TM-HEO-based anodes for lithium-ion cells during the first lithiation/delithiation cycle. This material showed a high specific capacity exceeding 600 mAh g–1 at 0.1 C and Coulombic efficiency very close to unity. The combination of functional and advanced spectroscopic studies revealed complex charging mechanisms, developing through the reduction of transition-metal (TM) cations, which triggers the conversion reaction below 1.0 V. The conversion is irreversible and incomplete, leading to the final collapse of the HEO rock-salt structure. Other redox processes are therefore discussed and called to account for the observed cycling behavior of the TM-HEO-based anode. Despite the irreversible phenomena, the HEO cubic structure remains intact for ∼60% of lithiation capacity, so proving the beneficial role of the configuration entropy in enhancing the stability of the HEO rock-salt structure during the redox phenomena.

The transition to a circular economy vision must handle the increasing request of metals required to satisfy the battery industry; this can be obtained by recycling and feeding back secondary raw materials recovered through proper waste management. Here, a novel and green proof‐of‐concept was developed, based on deep eutectic solvents (DESs) to fully and easily recover valuable metals from various cathode active materials, including LiMn2O4, LiNi0.5Mn1.5O4, and LiNi0.8Co0.2O2. DES composed of choline chloride and lactic acid could leach Li, Mn, Co, and Ni, achieving efficiency of 100 % under much milder conditions with respect to the previous literature. For the first time, to our best knowledge, a two‐step approach was reported in the case of LiNi0.8Co0.2O2 for selective recovery of Li, Co, and Ni with high yield and purity. Furthermore, other cathode components, namely aluminum current collector and binder, were found to be not dissolved by the proposed DES, thus making a simple separation from the active material possible. Finally, this strategy was designed to easily regenerate and reuse the leaching solvents for more than one extraction, thus further boosting process sustainability.

An improved lifetime can be achieved by exploiting higher intrinsic durability of the materials, or by repairing the deteriorated component and restoring its original properties. Indeed, in the last years, several attempts to improve the lifetime of widespread devices (prosthetics, batteries, solar cells, lighting devices, etc.) were reported. [4-8] However, traditional techniques (welding, gluing, patching) need in situ application of fresh healing materials, and are not applicable to many modern complex devices that require disassembly and targeted operations well beyond the expertise of the final user. Moreover, repair by specialized personnel may be impossible or unsustainable from an economic point of view. To overcome these problems, a radically new strategy that can pave the way for more durable materials is emerging: the concept of selfhealing (SH). [9] This term refers to those smart materials that can automatically restore some, or all, of their functions after having suffered of an external damage that degraded their original properties. This usually has to do with autonomous recovery of physical cracks, but may include a wider range of features prolonging the lifetime of a material/ device, which space from anticorrosion to bactericidal properties. [10,11] By tailoring an appropriate response of the system, it becomes possible to design a material that can respond to various external perturbations and accommodate their eventual disturbance. The idea at the base of this approach is usually defined as biomimetic, since it takes inspiration from nature and mimic it in solving complex technological problems. [12] During the years, many different materials or technologies, naively depicted in Figure 1a, have taken inspiration from nature (as Velcro tape which mimics tiny hooks on bur fruits, naturally ventilated facades that mime termites' mounds, hydrophobic lotus-leaf coatings, and iridescent or adhesive surfaces respectively inspired by butterflies and geckos) and self-healing is not an exception. [13-15] In fact, in nature many organisms are capable of healing damages and of restoring their functionalities: skin, bones, plants, and other living systems can sense any failure and reconstruct the injured biological part which recovers its original functionalities. [16-18] Since these features lengthen the life of natural living beings, analog mechanisms can be exploited in artificial self-healing materials to benefit the Major improvements in stability and performance of batteries are still required for a more effective diffusion in industrial key sectors such as automotive and foldable electronics. An encouraging route resides in the implementation into energy storage devices of self-healing features, which can effectively oppose the deterioration upon cycling that is typical of these devices. In order to provide a comprehensive view of the topic, this Review first summarizes the main self-healing processes that have emerged in the multifaceted field of smart materials, classifying them on the basis of t...