Inhibiting collective cation migration in Li-rich cathode materials as a strategy to mitigate voltage hysteresis.

Lithium-rich cathodes are promising energy storage materials due to their high energy densities. However, voltage hysteresis, which is generally associated with transition metal migration, limits their energy efficiency and implementation in practical devices. Here we reveal that voltage hysteresis is related to the collective migration of metal ions, and that isolating the migration events from each other by creating partial disorder can create high-capacity reversible cathode materials, even when migrating transition metal ions are present. We demonstrate this on a layered Li-rich chromium manganese oxide that in its fully ordered state displays a substantial voltage hysteresis (>2.5 V) associated with collective transition metal migration into Li layers, but can be made to achieve high capacity (>360 mAh g-1) and energy density (>1,100 Wh kg-1) when the collective migration is perturbed by partial disorder. This study demonstrates that partially cation-disordered cathode materials can accommodate a high level of transition metal migration, which broadens our options for redox couples to those of mobile cations.

Promises and Challenges of Next-Generation "Beyond Li-ion" Batteries for Electric Vehicles and Grid Decarbonization.

The tremendous improvement in performance and cost of lithium-ion batteries (LIBs) have made them the technology of choice for electrical energy storage. While established battery chemistries and cell architectures for Li-ion batteries achieve good power and energy density, LIBs are unlikely to meet all the performance, cost, and scaling targets required for energy storage, in particular, in large-scale applications such as electrified transportation and grids. The demand to further reduce cost and/or increase energy density, as well as the growing concern related to natural resource needs for Li-ion have accelerated the investigation of so-called "beyond Li-ion" technologies. In this review, we will discuss the recent achievements, challenges, and opportunities of four important "beyond Li-ion" technologies: Na-ion batteries, K-ion batteries, all-solid-state batteries, and multivalent batteries. The fundamental science behind the challenges, and potential solutions toward the goals of a low-cost and/or high-energy-density future, are discussed in detail for each technology. While it is unlikely that any given new technology will fully replace Li-ion in the near future, "beyond Li-ion" technologies should be thought of as opportunities for energy storage to grow into mid/large-scale applications.

Nano-Sized Structurally Disordered Metal Oxide Composite Aerogels as High-Power Anodes in Hybrid Supercapacitors.

A general method for preparing nano-sized metal oxide nanoparticles with highly disordered crystal structure and their processing into stable aqueous dispersions is presented. With these nanoparticles as building blocks, a series of nanoparticles@reduced graphene oxide (rGO) composite aerogels are fabricated and directly used as high-power anodes for lithium-ion hybrid supercapacitors (Li-HSCs). To clarify the effect of the degree of disorder, control samples of crystalline nanoparticles with similar particle size are prepared. The results indicate that the structurally disordered samples show a significantly enhanced electrochemical performance compared to the crystalline counterparts. In particular, structurally disordered Ni xFe yO z@rGO delivers a capacity of 388 mAh g-1 at 5 A g-1, which is 6 times that of the crystalline sample. Disordered Ni xFe yO z@rGO is taken as an example to study the reasons for the enhanced performance. Compared with the crystalline sample, density functional theory calculations reveal a smaller volume expansion during Li+ insertion for the structurally disordered Ni xFe yO z nanoparticles, and they are found to exhibit larger pseudocapacitive effects. Combined with an activated carbon (AC) cathode, full-cell tests of the lithium-ion hybrid supercapacitors are performed, demonstrating that the structurally disordered metal oxide nanoparticles@rGO||AC hybrid systems deliver high energy and power densities within the voltage range of 1.0-4.0 V. These results indicate that structurally disordered nanomaterials might be interesting candidates for exploring high-power anodes for Li-HSCs.

Dual antibacterial behavior of a curcumin-upconversion photodynamic nanosystem for efficient eradication of drug-resistant bacteria in a deep joint infection.

A periprosthetic joint infection (PJI) with methicillin-resistant Staphylococcus aureus (MRSA) is a catastrophic deep joint infection for patients who have had joint replacement surgery. To efficiently eradicate the MRSA, curcumin-upconversion nanoparticles (curcumin-UCNPs) were synthesized by binding the curcumin onto UCNPs, which could produce singlet oxygen under near infrared (NIR) irradiation. Dual antibacterial behavior induced by the curcumin-UCNP itself and induced by photodynamic therapy were demonstrated. Nearly 100% MRSA was eradicated using curcumin-UCNPs under the NIR irradiation because of the dual antibacterial behavior in vitro. Furthermore, a MRSA-induced PJI model was constructed using Sprague Dawley rats. The NIR could penetrate the rats' knee joint tissue well and activated the curcumin-UCNPs to perform photodynamic therapy, which exhibited a good antibacterial effect in the deep joint tissue (1 cm) and about 80% of MRSA was eradicated in vivo. Blood tests and histopathological examinations revealed that the inflammation was also significantly relieved because of the eradication of MRSA in the curcumin-UCNPs-NIR group. Compared with traditional treatments, this research may provide a new therapy for PJI.

Conductive framework of inverse opal structure for sulfur cathode in lithium-sulfur batteries.

As a promising cathode inheritor for lithium-ion batteries, the sulfur cathode exhibits very high theoretical volumetric capacity and energy density. In its practical applications, one has to solve the insulating properties of sulfur and the shuttle effect that deteriorates cycling stability. The state-of-the-art approaches are to confine sulfur in a conductive matrix. In this work, we utilize monodisperse polystyrene nanoparticles as sacrificial templates to build polypyrrole (PPy) framework of an inverse opal structure to accommodate (encapsulate) sulfur through a combined in situ polymerization and melting infiltration approach. In the design, the interconnected conductive PPy provides open channels for sulfur infiltration, improves electrical and ionic conductivity of the embedded sulfur, and reduces polysulfide dissolution in the electrolyte through physical and chemical adsorption. The flexibility of PPy and partial filling of the inverse opal structure endure possible expansion and deformation during long-term cycling. It is found that the long cycling stability of the cells using the prepared material as the cathode can be substantially improved. The result demonstrates the possibility of constructing a pure conductive polymer framework to accommodate insulate sulfur in ion battery applications.

A general method of fabricating flexible spinel-type oxide/reduced graphene oxide nanocomposite aerogels as advanced anodes for lithium-ion batteries.

High-capacity anode materials for lithium ion batteries (LIBs), such as spinel-type metal oxides, generally suffer from poor Li(+) and e(-) conductivities. Their drastic crystal structure and volume changes, as a result of the conversion reaction mechanism with Li, severely impede the high-rate and cyclability performance toward their practical application. In this article, we present a general and facile approach to fabricate flexible spinel-type oxide/reduced graphene oxide (rGO) composite aerogels as binder-free anodes where the spinel nanoparticles (NPs) are integrated in an interconnected rGO network. Benefiting from the hierarchical porosity, conductive network and mechanical stability constructed by interpenetrated rGO layers, and from the pillar effect of NPs in between rGO sheets, the hybrid system synergistically enhances the intrinsic properties of each component, yet is robust and flexible. Consequently, the spinel/rGO composite aerogels demonstrate greatly enhanced rate capability and long-term stability without obvious capacity fading for 1000 cycles at high rates of up to 4.5 A g(-1) in the case of CoFe2O4. This electrode design can successfully be applied to several other spinel ferrites such as MnFe2O4, Fe3O4, NiFe2O4 or Co3O4, all of which lead to excellent electrochemical performances.

Formation mechanism of LiFePO4 sticks grown by a microwave-assisted liquid-phase process.

A time-dependent study on the formation of LiFePO4 with olivine-type structure is presented. The material is synthesized through a non-aqueous route in benzyl alcohol assisted by microwave radiation. The LiFePO4 forms with an anisotropic morphology of microscale stick-like particles. The detailed structure of these particles and their evolution with reaction time is revealed by transmission electron microscopy; a 3D reconstruction of a particle by electron tomography provides insight into the formation mechanism of these sticks. Without applying a thermal post-annealing treatment or a carbon coating, the electrochemical behavior of the LiFePO4 microsticks is assessed for the preparation of cathodes in lithium-ion batteries.