Li+ ion transport

The use of sonochemical methods [75, 76] leads to a core-shell structure, thus forming uniform coating comprising layers of nanoparticles. With this approach, a balance has to be well set because too thick surface layers impede Li-ion transport and thus lead to high electrodes impedance. 

Polypropylene (PP) and polyethylene (PE) microporous separators (e.g. with 20 jxm thickness and 50% porosity) are used for electrically separating the positive electrode and negative electrode. SEM of microporous separator is shown in Figure 12.1.4. As organic solvents are wettable to PP and PE, the solvents can penetrate into such micropores. The pore size of the separator is normally less than 0.5 (tm, in order to ensure that fine active ceramic particles of electrodes do not pass through the separator. A PP/PE/PP layered separator is often used for practical Li-ion batteries because of a shut down effect. When battery temperature approaches tbe melting point of PE (130°C), micropores of only PE are suddenly closed, and the battery reaction coming from Li-ion transportation is stopped by tbe separator. 

Various approaches have been identified to reduce the extent of electrolyte decomposition and irreversible capacity loss at the carbon negative electrode. By adding additives to PC such as CO, N,0, CO, the self-discharge and cycling behavior of the lithiated carbon electrodes has improved. These additives affect the film properties by decreasing the low-frequency impedance, thus permitting a more rapid Li -ion transport. 

Zheng J, Xiao J, Yu X, Kovarik L, Gu M, Omenya F, Chen X, Zhang JG (2012) Enhanced Li ion transport in LiNio sMni 5O4 through control of site disorder. Phys Chem Chem Phys 14 13515-13521... 

Traditionally electrolytes provide effective Li-ion transport between electrodes and work as a charge-transfer medium within sulfur-containing cathodes. Special requirements for electrolytes in Li-S cells include low viscosity and low solubility of sulfur species. A common Li-S electrolyte consists of a Li salt such as lithium triflate (LiCFaSOa), LiTFSl, LiPFs, and LiC104, and a matrix of one or two organic solvents. Based on liquid electrolytes used in Li-S cells, here we divide and discuss them into four categories (1) ether-based electrolytes, (2) carbonate-based electrolytes, (3) ionic liquid-based electrolytes, and (4) other new Uquid systems. 

Mechanical failure of battery materials has been putatively linked to battery performance degradation over time [1, 2]. It has been postulated that mechanical failure of battery active materials (i) increases surface area of active materials subjected to side reactions and consumes active material (which causes capacity loss), (ii) results in loss of electric contact between the active material particles and between active materials and current collectors [3, 4], increasing the internal impedance for charge transfer, and (iii) potentially redistributes active material particles and decreases volume fraction of electrolyte, making the hthium ion (Li-ion) transport become electrolyte phase limited [5-9]. Mechanical failure of... 

During aging at high appUed-voltage electrolyte components oxidation may induce insulating solid deposits, which may reduce the active surface by impairing li-ion transport to the insertion material, or by insulating active... 

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