Phase Control on Surface for the Stabilization of High Energy Cathode Materials of Lithium Ion Batteries.

The development of high energy electrode materials for lithium ion batteries is challenged by their inherent instabilities, which become more aggravated as the energy densities continue to climb, accordingly causing increasing concerns on battery safety and reliability. Here, taking the high voltage cathode of LiNi0.5Mn1.5O4 as an example, we demonstrate a protocol to stabilize this cathode through a systematic phase modulating on its particle surface. We are able to transfer the spinel surface into a 30 nm shell composed of two functional phases including a rock-salt one and a layered one. The former is electrochemically inert for surface stabilization while the latter is designated to provide necessary electrochemical activity. The precise synthesis control enables us to tune the ratio of these two phases, and achieve an optimized balance between improved stability against structural degradation without sacrificing its capacity. This study highlights the critical importance of well-tailored surface phase property for the cathode stabilization of high energy lithium ion batteries.

Controlling the Reaction of Nanoparticles for Hollow Metal Oxide Nanostructures.

Hollow nanostructures of metal oxides have found broad applications in different fields. Here, we reported a facile and versatile synthetic protocol to prepare hollow metal oxide nanospheres by modulating the chemical properties in solid nanoparticles. Our synthesis design starts with the precipitation of urea-containing metal oxalate, which is soluble in water but exists as solid nanospheres in ethanol. A controlled particle hydrolysis is achieved through the heating-induced urea decomposition, which transforms the particle composition in an outside-to-inside style: The reaction starts from the surface and then proceeds inward to gradually form a water-insoluble shell of basic metal oxalate. Such a reaction-induced solubility difference inside nanospheres becomes highly efficient to create a hollow structure through a simple water wash process. A following high temperature treatment forms hollow nanospheres of different metal oxides with structural features suited to their applications. For example, a high performance anode for Li-ion intercalation pseudocapacitor was demonstrated with the hollow and mesoporous Nb2O5 nanospheres.

Controlling the Compositional Chemistry in Single Nanoparticles for Functional Hollow Carbon Nanospheres.

Hollow carbon nanostructures have inspired numerous interests in areas such as energy conversion/storage, biomedicine, catalysis, and adsorption. Unfortunately, their synthesis mainly relies on template-based routes, which include tedious operating procedures and showed inadequate capability to build complex architectures. Here, by looking into the inner structure of single polymeric nanospheres, we identified the complicated compositional chemistry underneath their uniform shape, and confirmed that nanoparticles themselves stand for an effective and versatile synthetic platform for functional hollow carbon architectures. Using the formation of 3-aminophenol/formaldehyde resin as an example, we were able to tune its growth kinetics by controlling the molecular/environmental variables, forming resin nanospheres with designated styles of inner constitutional inhomogeneity. We confirmed that this intraparticle difference could be well exploited to create a large variety of hollow carbon architectures with desirable structural characters for their applications; for example, high-capacity anode for potassium-ion battery has been demonstrated with the multishelled hollow carbon nanospheres.

Crystallization-induced self-hollowing of molybdenum sulfide nanoparticles and their potential in sodium ion batteries.

A self-hollowing process was demonstrated for the creation of hollow MoS2 nanospheres starting from their amorphous solid precursor, which were spontaneously transformed into a hollow structure during the rearrangement of crystal lattices initiated by a high-temperature treatment, forming hollow-structured materials favorable for their application in sodium ion batteries.

Surface Zn doped LiMn2O4 for an improved high temperature performance.

A surface doping strategy is demonstrated for the stabilization of LiMn2O4, which is achieved by the surface solid reaction between the LiMn2O4 particle and its ZnO nanoshell. The surface treated sample shows a much improved high temperature performance with evidently suppressed Mn dissolution.

Construction of Uniform Cobalt-Based Nanoshells and Its Potential for Improving Li-Ion Battery Performance.

Surface cobalt doping is an effective and economic way to improve the electrochemical performance of cathode materials. Herein, by tuning the precipitation kinetics of Co2+, we demonstrate an aqueous-based protocol to grow uniform basic cobaltous carbonate coating layer onto different substrates, and the thickness of the coating layer can be adjusted precisely in nanometer accuracy. Accordingly, by sintering the cobalt-coated LiNi0.5Mn1.5O4 cathode materials, an epitaxial cobalt-doped surface layer will be formed, which will act as a protective layer without hindering charge transfer. Consequently, improved battery performance is obtained because of the suppression of interfacial degradation.

Controlled formation of uniform nanoshells of manganese oxide and their potential in lithium ion batteries.

Uniform nanoshells of manganese oxides have been successfully prepared by controlling their growth kinetics in solution. The prepared manganese oxides show promising electrochemical performance when used as an anode material in lithium ion batteries.

Controlled formation of uniform CeO2 nanoshells in a buffer solution.

Uniform CeO2 nanoshells were successfully prepared by using buffer solution as a unique growth medium. The application of this methodology to construct a yolk-shell structured Au@CeO2 nanocatalyst shows improved performance for the catalytic CO oxidation.