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Over the past decades, Li-ion battery (LIB) has turned into one of the most important advances in the history of technology due to its extensive and in-depth impact on our life. Its omnipresence in all electric vehicles, consumer electronics and electric grids relies on the precisely tuned electrochemical dynamics and interactions among the electrolytes and the diversified anode and cathode chemistries therein. With consumers' demand for battery performance ever increasing, more and more stringent requirements are being imposed upon the established equilibria among these LIB components, and it became clear that the state-of-the-art electrolyte systems could no longer sustain the desired technological trajectory. Driven by such gap, researchers started to explore more unconventional electrolyte systems. From superconcentrated solvent-in-salt electrolytes to solid-state electrolytes, the current research realm of novel electrolyte systems has grown to unprecedented levels. In this review, we will avoid discussions on current state-of-the-art electrolytes but instead focus exclusively on unconventional electrolyte systems that represent new concepts. [ABSTRACT FROM AUTHOR]

The electrochemical stability window of solid electrolyte is overestimated by the conventional experimental method using a Li/electrolyte/inert metal semiblocking electrode because of the limited contact area between solid electrolyte and inert metal. Since the battery is cycled in the overestimated stability window, the decomposition of the solid electrolyte at the interfaces occurs but has been ignored as a cause for high interfacial resistances in previous studies, limiting the performance improvement of the bulk-type solid-state battery despite the decades of research efforts. Thus, there is an urgent need to identify the intrinsic stability window of the solid electrolyte. The thermodynamic electrochemical stability window of solid electrolytes is calculated using first principles computation methods, and an experimental method is developed to measure the intrinsic electrochemical stability window of solid electrolytes using a Li/electrolyte/electrolyte-carbon cell. The most promising solid electrolytes, Li10GeP2S12 and cubic Li-garnet Li7La3Zr2O12, are chosen as the model materials for sulfide and oxide solid electrolytes, respectively. The results provide valuable insights to address the most challenging problems of the interfacial stability and resistance in high-performance solid-state batteries. [ABSTRACT FROM AUTHOR]

Abstract: Equilibrium potential hysteresis of electrode materials refers to the phenomenon that discharge equilibrium potential is lower than charge equilibrium potential. It is induced by the strain accommodation energy of phase transformation. Taking LiFePO4 as an example, the equilibrium potential hysteresis and accommodation energy of two LiFePO4 with different particle sizes were characterized using galvanostatic intermittent titration technique (GITT), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS) methods. The LiFePO4 sample with 40nm particle size has lower accommodation energy than that of 100nm LiFePO4, which is due to a narrower miscibility gap and smaller potential hysteresis of 40nm LiFePO4 comparing to 100nm LiFePO4. The phase transformation of LiFePO4 occurs only at potential levels above delithiation (charge) equilibrium potential and below lithiation (discharge) equilibrium potential. No phase transformation occurs when charge/discharge is limited in the potential hysteresis range, i.e. LiFePO4 behaves like a solid solution in the potential hysteresis range. A reliable EIS can only be obtained when it is performed at the center of potential hysteresis and the potential amplitude does not exceed the range of equilibrium potential hysteresis. The analysis on strain accommodation and potential hysteresis of LiFePO4 cathodes during Li ion insertion/extraction is also suitable for other phase transformation electrodes. [ABSTRACT FROM AUTHOR]

Lithium-ion capacitors, as a hybrid electrochemical energy storage device, realize high specific energy and power density within one device, thus attracting extensive attention. Here, hierarchically porous Li 3 VO 4 /C nanocomposite is prepared by a solvo-thermal reaction, followed with a post-annealing process. This composite has macropores at the center and mesopores in the wall, thus effectively promoting electrolyte penetration and structure stability upon cycling simultaneously. Compared to mesoporous Li 3 VO 4 , the enhanced rate capability and specific capacity of hierarchically porous Li 3 VO 4 /C indicate the synergistic effect of mesopores and macropores. Inspired by these results, this composite is coupled with mesoporous carbon (CMK-3) for lithium-ion capacitors, generating a specific energy density of 105 Wh kg −1 at a power density of 188 W kg −1 . Even if the power density increases to 9.3 kW kg −1 , the energy density still remains 62 Wh kg −1 . All these results demonstrate the promising potential of hierarchically porous Li 3 VO 4 in lithium ion capacitors. [ABSTRACT FROM AUTHOR]

Abstract: A patterned 3D Si anode is fabricated by physical vapor deposition of n-type Si on a self-assembled TMV1cys-structured nickel current collector. The combination of the large surface area conferred by the virus-enabled 3D Ni/TMV1cys current collector with the high electric conductivity of n-type Si rods results in excellent cyclic stability and rate capability for the core-shell n-type Si/Ni/TMV1cys anodes. Electrochemical impedance spectroscopy reveals that the high electronic conductivity of n-type Si significantly reduces charge transfer resistance, thus even at high current densities the capacity of the n-type Si is increased to almost 630mAh/g compared to undoped Si. [Copyright &y& Elsevier]