Tris(pentafluorophenyl) borane-containing electrolytes for electrochemical reversibility of lithium peroxide-based electrodes in lithium-oxygen batteries

Tris(pentafluorophenyl) borane (TPFPB) is evaluated as an additive for improving electrochemical performance of lithium peroxide (Li2O2)-based electrodes. It is found that TPFPB significantly reduced the charge potential of Li2O2-based electrodes during the first charge process and improved reversible capacity during cycling without adding air (or O-2) to the cell. To confirm the effect of TPFPB on electrolyte decomposition, the surface chemistry of Li2O2-based electrodes cycled in electrolytes with and without TPFPB was investigated.close7

Stabilizing dimensional changes in Si-based composite electrodes by controlling the electrode porosity: An in situ electrochemical dilatometric study

Abstract: A porosity-controllable Si-based composite electrode was fabricated in the present study. Poly(methyl methacrylate) (PMMA), which possesses the unique thermal property of unzipping, was utilized as a pore-forming agent during electrode fabrication. PMMA-treated electrodes presented relatively low volume expansion and little deformation during lithiation. The cyclic dilation behavior of PMMA-treated electrodes was investigated by applying an in situ electrochemical dilatometric method, and enhanced dimensional reversibility during cycling was observed. The dilation behavior was closely related to the electrochemical performance, and PMMA-treated electrodes exhibited improved capacity retention and low impedance change during cycling. The newly generated pores in the PMMA-treated electrode can accommodate the volumetric expansion of Si-based active materials, which suppresses electrode deformation and the breakdown of the electrical network. The porosity plays an important role in Si-based electrodes. Thus, controlling the porosity through PMMA-treatment can be an effective way for the application of Si-based composite electrodes for advanced lithium-ion batteries.close9

Importance of uniformly redistributing external pressure on cycling of pouch-type Li-metal batteries

Li-metal anode (LMA) is considered promising for overcoming the energy density limit of current Li-ion batteries. However, LMAs in large-scale cells are limited by uneven and excessive anode swelling, owing to the notorious buildup of a highly porous passivation ("dead" Li) layer. To demonstrate the impact of the pressure environment on the LMA swelling behavior and cycling stability, the distribution of the actual stack pressure was visualized in pouch cell platforms using pressure-sensitive films. If the stack pressure is not uniform, pouch cell failure occurs regardless of how high the applied pressure is. Conformal stack pressure assisted by the modified pressure setup with force redistributing pads enabled stable cycling even at a lower external pressure. By correlating with the thickness distribution of the "dead" Li layer over the LMA surfaces after cycling, it is suggested that a uniform stack pressure is crucial for mitigating anode swelling and the stable cycling of Li metal pouch cells.FALS

A highly resilient mesoporous SiOx lithium storage material engineered by oil-water templating

Mesoporous silicon-based materials gained considerable attention as high-capacity lithium-storage materials. However, the practical use is still limited by the complexity and limited number of available synthetic routes. Here, we report carbon-coated porous SiOx as high capacity lithium storage material prepared by using a sol-gel reaction of hydrogen silsesquioxane and oil-water templating. A hydrophobic oil is employed as a pore former inside the SiOx matrix and a precursor for carbon coating on the SiOx. The anode exhibits a high capacity of 730 mAh g−1 and outstanding cycling performance over 100 cycles without significant dimensional changes. Carbon-coated porous SiOx also showed highly stable thermal reliability comparable to that of graphite. These promising properties come from the mesopores in the SiOx matrix, which ensures reliable operation of lithium storage in SiOx. The scalable sol-gel process presented here can open up a new avenue for the versatile preparation of porous SiOx lithium storage materials

Hydrogen silsequioxane-derived Si/SiOx nanospheres for high-capacity lithium storage materials

Si/SiOx composite materials have been explored for their commercial possibility as high-performance anode materials for lithium ion batteries, but suffer from the complexity of and limited synthetic routes for their preparation. In this study, Si/SiOx nanospheres were developed using a nontoxic and precious-metal-free preparation method based on hydrogen silsesquioxane obtained from sol-gel reaction of triethoxysilane. The resulting Si/SiOx nanospheres with a uniform carbon coating layer show excellent cycle performance and rate capability with high-dimensional stability. This approach based on a scalable sol-gel reaction enables not only the development of Si/SiOx with various nanostructured forms, but also reduced production cost for mass production of nanostructured Si/SiOx

Dendrite-Free Polygonal Sodium Deposition with Excellent Interfacial Stability in a NaAlCl₄–2SO₂ Inorganic Electrolyte

Room-temperature Na-metal-based rechargeable batteries, including Na–O₂ and Na–S systems, have attracted attention due to their high energy density and the abundance of sodium resources. Although these systems show considerable promise, concerns regarding the use of Na metal should be addressed for their success. Here, we report dendrite-free Na-metal electrode for a Na rechargeable battery, engineered by employing nonflammable and highly Na⁺-conductive NaAlCl₄·2SO₂ inorganic electrolyte, as a result, showing superior electrochemical performances to those in conventional organic electrolytes. We have achieved a hard-to-acquire combination of nondendritic Na electrodeposition and highly stable solid electrolyte interphase at the Na-metal electrode, enabled by inducing polygonal growth of Na deposit using a highly concentrated Na⁺-conducting inorganic electrolyte and also creating highly dense passivation film mainly composed of NaCl on the surface of Na-metal electrode. These results are highly encouraging in the development of room-temperature Na rechargeable battery and provide another strategy for highly reliable Na-metal-based rechargeable batteries

Controlled Ag-driven superior rate-capability of Li4Ti5O12 anodes for lithium rechargeable batteries

The morphology and electronic structure of a Li4Ti5O12 anode are known to determine its electrical and electrochemical properties in lithium rechargeable batteries. Ag-Li4Ti5O12 nanofibers have been rationally designed and synthesized by an electrospinning technique to meet the requirements of one-dimensional (1D) morphology and superior electrical conductivity. Herein, we have found that the 1D Ag-Li4Ti5O12 nanofibers show enhanced specific capacity, rate capability, and cycling stability compared to bare Li4Ti5O12 nanofibers, due to the Ag nanoparticles (\u3c5 \u3enm), which are mainly distributed at interfaces between Li4Ti5O12 primary particles. This structural morphology gives rise to 20% higher rate capability than bare Li4Ti5O12 nanofibers by facilitating the charge transfer kinetics. Our findings provide an effective way to improve the electrochemical performance of Li4Ti5O12 anodes for lithium rechargeable batteries. [Figure not available: see fulltext.] 2013 Tsinghua University Press and Springer-Verlag Berlin Heidelberg