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Amidst growing energy demands and the advancement of new energy technologies, there is an increasing need for rechargeable batteries with higher energy densities and longer cycle lives. Recently, single-phase solid-solution high-entropy oxides (HEOs), known for their multi-component complex composition, have gained significant attention in the field of lithium-ion batteries. The entropy-stabilising effect of these materials contributes to their high structural and cycling stability, making HEOs promising candidates as next-generation electrode materials for lithium-ion batteries. This review summarises current research on HEOs in their roles as anode, cathode, and solid-state electrolyte materials, including the synthetic methods and characterization techniques employed to develop these high-entropy oxides. Furthermore, this paper critically examines existing research challenges and potential mechanisms and anticipates the future application of high-entropy oxides in lithium-ion battery technologies. • Current research on HEOs as anode, cathode, and solid-state electrolyte. • The synthetic methods and characterization techniques of HEOs. • Existing research challenges and potential mechanisms of HEOs. [ABSTRACT FROM AUTHOR]

With the rapid development of flexible electronic devices, flexible lithium-ion batteries are widely considered due to their potential for high energy density and long life. Anode materials, as one of the key materials of lithium-ion batteries, need to have good flexibility, an excellent specific discharge capacity, and fast charge–discharge characteristics. Carbon fibers are feasible as candidate flexible anode materials. However, their low specific discharge capacity restricts their further application. Based on this, N-doped carbon nanofiber anodes with microporous, mesoporous, and macroporous structures are prepared in this paper. The hierarchical and heterogeneous porosity structure can increase the active sites of the anode material and facilitate the transport of ions, and N-doping can improve the conductivity. Moreover, the N-doped flexible carbon nanofiber with a porous structure can be directly used as the anode for lithium-ion batteries without adding an adhesive. It has a high first reversible capacity of 1108.9 mAh g−1, a stable cycle ability (954.3 mAh g−1 after 100 cycles), and excellent rate performance. This work provides a new strategy for the development of flexible anodes with high performance. [ABSTRACT FROM AUTHOR]

Due to the rapid development of bendable electronic products, it is urgent to prepare flexible anode materials with excellent properties, which play a key role in flexible lithium-ion batteries. Although carbon fibers are excellent candidates for preparing flexible anode materials, the low discharge specific capacity prevents their further application. In this paper, a hierarchical porous and silicon (Si)/nitrogen (N) co-doped carbon nanofiber anode was successfully prepared, in which Si doping can improve specific capacity, N doping can improve conductivity, and a fabricated hierarchical porous structure can increase the reactive sites, improve the ion transport rate, and enable the electrolyte to penetrate the inner part of carbon nanofibers to improve the electrolyte/electrode contacting area during the charging–discharging processes. The hierarchical porous and Si/N co-doped carbon nanofiber anode does not require a binder, and is flexible and foldable. Moreover, it exhibits an ultrahigh initial reversible capacity of 1737.2 mAh g−1, stable cycle ability and excellent rate of performance. This work provides a new avenue to develop flexible carbon nanofiber anode materials for lithium-ion batteries with high performance. [ABSTRACT FROM AUTHOR]

Recycling high-valuable metal elements (such as Li, Ni, Co, Al and Cu elements) from scrapped lithium ion batteries can bring significant economic benefits. However, recycling and reusing anode material has not yet attracted wide attention up to now, due to the lower added-value than the above valuable metal materials and the difficulties in regenerating process. In this paper, a novel regeneration process with significant green advance is proposed to regenerate anode material recycled from scrapped Li-ion batteries for the first time. After regenerated, most acetylene black (AB) and all the styrene butadiene rubber (SBR), carboxymethylcellulose sodium (CMC) in recycled anode material are removed, and the surface of anode material is coated with pyrolytic carbon from phenolic resin again. Finally, the regenerated anode material (graphite with coating layer, residual AB and a little CMC pyrolysis product) is obtained. As expected, all the technical indexs of regenerated anode material exceed that of a midrange graphite with the same type, and partial technical indexs are even closed to that of the unused graphite. The results indicate the effective regeneration of anode material recycled from scrapped Li-ion batteries is really achieved. [ABSTRACT FROM AUTHOR]

A new green recycling process (named as direct regeneration process) of cathode material mixture from scrapped LiFePO 4 batteries is designed for the first time. Through this direct regeneration process, high purity cathode material mixture (LiFePO 4 + acetylene black), anode material mixture (graphite + acetylene black) and other by-products (shell, Al foil, Cu foil and electrolyte solvent, etc.) are recycled from scrapped LiFePO 4 batteries with high yield. Subsequently, recycled cathode material mixture without acid leaching is further directly regenerated with Li 2 CO 3 . Direct regeneration procedure of recycled cathode material mixture from 600 to 800 °C is investigated in detail. Cathode material mixture regenerated at 650 °C display excellent physical, chemical and electrochemical performances, which meet the reuse requirement for middle-end Li-ion batteries. The results indicate the green direct regeneration process with low-cost and high added-value is feasible. [ABSTRACT FROM AUTHOR]

To recycle valuable resource and reduce environmental pollution, a green full-solid route is designed to resynthesize LiFePO 4 /C materials from spent lithium-ion batteries for the first time. With this full-solid route, a simple thermal treatment process is employed to purify and homogenize the recycled cathode materials. No waste acid or alkaline liquid is used, which can avoid the secondary environment pollution. Further, the effect of Li 2 CO 3 content on the performances of regenerated LiFePO 4 /C materials is investigated in detail and LiFePO 4 /C materials with high purity and high tap density are resynthesized. Among these resynthesized LiFePO 4 /C materials, the one with Li 2 CO 3 addition amount of 1.4 wt% displays excellent physical, chemical and electrochemical performances in half cell and full cell, meeting the reuse requirement for Li-ion batteries. These results indicate that this green full-solid route with simple-operation, easily large-scale preparation, low-cost and high added-value is a feasible and promising way to recycle scrapped cathodes and reuse them. Image 1 • LiFePO 4 cathode is recycled from scrapped lithium-ion batteries. • A full-solid route is designed to resynthesize LiFePO 4 /C electrode. • This route is green, high recovery rate and low-cost. • Resynthesized LiFePO 4 /C materials display excellent comprehensive performances. [ABSTRACT FROM AUTHOR]

In 2 O 3 , employed as an anode, demonstrates exceptional capacity in lithium-ion batteries (LIBs). Nonetheless, its propensity for significant volume expansion results in internal fracturing and reorganization. Two-dimensional double transition metal carbides and nitrides (MXenes), characterized by unique out-of-plane metal atom ordering, exhibit promising electrical properties due to their chemical versatility and intricate structure. However, MXenes' tendency to aggregate or stack into lamellar structures impedes their practical energy storage application. To address these issues, a hierarchical porous microrods In 2 O 3 @C@Ti 3 C 2 T X (HPMR-In 2 O 3 @C@Ti 3 C 2 T X) composite anode material was synthesized through electrostatic self-assembly of MIL-68 (In) and Ti 3 C 2 T X , followed by carbonization. This synthesis produced continuous one-dimensional microrods with hierarchical porous channels in HPMR-In 2 O 3 @C, offering a substantial specific surface area, numerous Li+ storage sites, and enhanced charge transfer rates. Moreover, the interlayer space within Ti 3 C 2 T X acts as an electrolyte reservoir, facilitating comprehensive electrochemical reactions and accommodating volume changes during charge-discharge cycles. Consequently, the HPMR-In 2 O 3 @C@Ti 3 C 2 T X anode exhibited remarkable properties, including a high initial discharge specific capacity of 1406 mAh g-1 at 0.1 C, outstanding cycling performance, and superior rate performance. This research presents a promising direction for the advancement of high-performance anode materials for lithium-ion batteries. [Display omitted] [ABSTRACT FROM AUTHOR]

• An N-doped graphite layer was first as a coating layer of SnO 2. • Graphene coating can provide conductive network and alleviate volume expansion. • Nitrogen doping can provide active centers and improve interface stability. • SnO 2 @NG displays the outstanding electrochemical performances. Tin dioxide (SnO 2) with multiple electron transport is considered as a potential substitute for graphite due to these advantages of natural abundance, environmental friendliness, and high theoretical capacity. However, the ineluctable volume change and structural crushing limit its practical application. Hence, SnO 2 is coated by an N-doped graphite layer to form the flexible composite anode (SnO 2 @NG), which can provide a conductive network, increase the electronic conductivity, and effectively mitigate the irreversible volume expansion/contraction during the circulation process. Furthermore, the SnO 2 @NG anode shows a high specific capacity and stable cycle performance in lithium-ion batteries (677.7 mAh g−1 after 100 cycles) and sodium-ion batteries (169.7 mAh g−1 after 100 cycles). This excellent electrochemical performance illustrates that SnO 2 @NG has broad application prospects for high-performance energy storage systems. [ABSTRACT FROM AUTHOR]

With the rapid development of electric vehicles and various electronic products, higher energy density lithium-ion batteries are imperative to develop. As one of the key materials for lithium-ion batteries, anode materials with high energy density have become a research focus. Especially, In 2 O 3 has received increasing attention due to its mature preparation technology, environmental protection, low work voltage, and high theoretical lithium storage capacity. However, the poor conductivity and serious volume change during the lithium removal/insertion process of In 2 O 3 anode limit its performance. Based on this, a hierarchical porous nanotube In 2 O 3 (HPNT-In 2 O 3) anode is successfully prepared, in which the continuous one-dimensional nanotube structure of HPNT-In 2 O 3 and abundant porous channels can provide the large specific surface area, accelerate the charge transfer rate, and supply a large number of Li+ storage active site. Moreover, the HPNT-In 2 O 3 anode can maintain a higher reversible specific capacity of 470 mAh g−1 after 180 cycles at 0.1C, improve the cycling performance and rate performance, compared with a granular In 2 O 3 anode. This work provides a new avenue to develop high performance anode materials for lithium-ion batteries. • A hierarchical porous nanotube In 2 O 3 anode is prepared. • The HPNT-In 2 O 3 anode possesses the large specific surface area. • The HPNT-In 2 O 3 anode displays high electrochemical performances. [ABSTRACT FROM AUTHOR]