The purpose of this study was to understand the electrochemical behavior of the interface between porous electrodes and electrolytes of lithium-ion batteries. We propose a new analytical approach that is a combination of the transmission line model theory for cylindrical pores and electrochemical impedance spectroscopy using symmetric cells. Mathematical model and experimental impedance behavior results agree with each other. By mathematically fitting the experimental impedance plots, the individual internal resistance components of the actual porous electrode/electrolyte interface could be described as the following four parameters: electric resistance (R e ), electrolyte bulk resistance, (R sol ), ionic resistance in pores (R ion ), and charge-transfer resistance for lithium intercalation (R ct ). In actual electrodes, the R ion obtained in this study is a characteristic parameter of the porous electrode/electrolyte interface that is important to consider for thick electrodes.

To understand the relationship between the specific energy and power of lithium (Li)-ion batteries, the dependence of the internal resistance of porous electrodes with high loading weight on thickness was systematically investigated. The ionic resistance in pores (Rion) and chargetransfer resistance for Li intercalation (Rct) normalized per unit electrode geometric area were assessed using a combination of electrochemical impedance spectroscopy with symmetric cells and the transmission line model for cylindrical pores. The changes of Rion and Rct and their magnitude show opposite trends with respect to electrode thickness. For thin electrodes, Rion is lower than Rct. The specific power decreases slightly as the electrodes become thicker because the total internal resistance is predominantly affected by the charge-transfer resistance, and there is no delay of the response in the depth direction. In contrast, for thick electrodes, Rion is higher than or approximately equal to Rct, so there is a delay of the reaction in the depth direction. As a result, the power of the battery is dramatically reduced because the total internal resistance is strongly influenced by both Rion and Rct.

As advanced negative electrodes for powerful and useful high-voltage bipolar batteries, an intercalated metal-organic framework (iMOF), 2,6-naphthalene dicarboxylate dilithium, is described which has an organic-inorganic layered structure of π-stacked naphthalene and tetrahedral LiO4 units. The material shows a reversible two-electron-transfer Li intercalation at a flat potential of 0.8 V with a small polarization. Detailed crystal structure analysis during Li intercalation shows the layered framework to be maintained and its volume change is only 0.33%. The material possesses two-dimensional pathways for efficient electron and Li(+) transport formed by Li-doped naphthalene packing and tetrahedral LiO3C network. A cell with a high potential operating LiNi(0.5)Mn(1.5)O4 spinel positive and the proposed negative electrodes exhibited favorable cycle performance (96% capacity retention after 100 cycles), high specific energy (300 Wh kg(-1)), and high specific power (5 kW kg(-1)). An 8 V bipolar cell was also constructed by connecting only two cells in series.

On/off switchable electronic conduction occurs in intercalated metal-organic framework formed by chemical lithiation and heating.

We have found that the specific capacity of a Li-intercalated metal-organic framework (iMOF) electrode material, 2,6-naphthalene dicarboxylate dilithium, can be increased by narrowing the distance between naphthalene layers via ordering. The increase in specific capacity can be attributed to formation of more efficient electron and ion pathways in the framework.