Transition metal dissolution is one of the major causes of capacity and power fade in lithium-ion batteries employing transition metal oxides in the positive electrode. Accelerated testing was accomplished by introducing transition-metal salts in the electrolyte in order to study the effects of dissolution on performance. It is shown that metal dissolution causes a reduction in capacity and cycle stability in full cells. The SEI layer resistance in the negative electrode of full cells increases with increasing concentration of transition metal salts. The growth of the SEI layer is non-uniform and is believed to be caused by the reduction of transition metal species in the negative electrode leading to an increase in inorganic component of the SEI layer. Consumption of fossil fuels in the transportation sector is one of the leading causes of greenhouse gas emissions (GHG).1 Efforts to develop cleaner and more efficient alternatives to the internal combustion engine running on petroleum fuels, such as fuel cells and batteries, are on the rise to mitigate this problem. Rechargeable lithium-ion (Li-ion) batteries offer high energy and power densities, good cyclic stability, and low rates of self-discharge. These characteristics are essential for applications in hybrid electric vehicles (HEV), plug-in hybrid vehicles (PHEV), and electric vehicles (EV). Dissolution of transition metals from the positive electrode is a concern for lithium-ion batteries, and manganese dissolution is a major reason for capacity fade in spinel electrodes, including LiMn 2 O 4 . 15Although less susceptible than spinel, metal dissolution does occur in NCM electrodes and has been implicated in a rise in impedance and capacity fade with cycling. 4,16 Two main routes by which capacity fading may occur due to dissolution are (i) structural changes to the positive electrode and leading to reduced insertion capacity and (ii) accelerated growth of the SEI layer at the negative electrode and the resulting irreversible Li consumption. 15,[17][18][19][20][21][22] Capacity fade due to the structural changes occurring in the positive electrode during partial dissolution is more likely in spinel electrodes, where the extent of dissolution is high, or at high potentials (overcharge). This large degree of dissolution in spinels may cause shrinkage of the active material, which decreased the effective transport properties and kinetics of the electrode.20,23 The extent of dissolution in different positive electrode materials was compared by Choi and Manthiram, 18 and amount of Mn dissolution is 16 times greater in LiMn 2 O 4 compared to NCM electrodes. They also reported that structural stability is directly related to the extent of dissolution in electrodes. 18Dissolution may also cause a decrease in cell capacity by increased growth and breakdown of the SEI layer 21,22 on the negative electrode. Although dissolution has been studied extensively in spinel electrode materials and its negative effects on cell capacity have been wellestablished, how dissoluti...

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Enhancing the performance of rechargeable lithium (Li)−sulfur (S) batteries is one of most popular topics in a battery field because of their low cost and high specific energy. However, S experiences dissolution during its electrochemical reactions; hence, maintaining its initial capacity is challenging. Protecting the S cathode with a Li ion conducting layer that acts as a barrier for polysulfide transport is an attractive strategy, but formation of such protective layers typically involves significant effort and cost. Here, we report a facile route to form a conformal solid electrolyte layer on S cathodes in situ using a carbonate solvent. The chemically and mechanically stable and Li ion conducting protective layer is formed by inducing electrolyte reduction and polymerization reactions on the cathode surface. The layer serves as a polysulfide's barrier, successfully helping to retain S active material in the carbon pores. In addition, it helps to improve the performance of Li anodes.

Exploring cheap and active non-precious metal catalyst for the oxygen reduction reaction (ORR) is a recent major effort in fuel cells for large-scale applications. Herein, we report electrospun cobalt-carbon nanofiber (Co-CNF) as an efficient catalyst for the ORR together with systematic study on active site formation. The ORR activity of Co-CNF increases with increasing Co content up to approximately 30 wt. %, which exhibits high ORR activity comparable with a commercial Pt/C catalyst in alkaline media. XPS and structural analysis reveals a Co-pyridinic N x bond at the edge plane and Co nanoparticles in the Co-CNFs also increase with increasing Co contents. These sites can behave as the primary and the secondary active site for the ORR according to a dual-site mechanism. The ORR activity of Co-CNF may deteriorate even if only one of these sites is limited. The high ORR activity of the Co-CNF catalysts results from the synergetic effect of dual site formation for the ORR. Figure 4. (a) The ORR activity of Co-CNF catalysts with various Co contents and the commercial Pt/C catalysts. (b) H2O2 yield and the electron transfer number of the 32.2 wt. % Co-CNF catalyst in O2-saturated 0.1 M KOH solution at rotating speed of 1600 rpm. ORR activity of (c) 32.2 wt % Co-CNF and (d) 20 wt% Pt/C measured before and after 10,000 voltage cycling from 0.6 to 1.0 V.

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Although lithium–sulfur (Li–S) batteries have 5–10 times higher theoretical capacity (1675 mAh g–1) than present commercial lithium-ion batteries, Li–S batteries show a rapid and continuous capacity fading due to the polysulfide dissolution in common electrolytes. Here, we propose the use of a sulfur-based cathode material, amorphous MoS3 and reduced graphene oxide (r-GO) composite, which can be substituted for the pure sulfur-based cathodes. In order to enhance kinetics and stability of the electrodes, we intentionally pulverize the microsized MoS3 sheet into nanosheets and form an ultrathin nano-SEI on the surface using in situ electrochemical methods. Then, the pulverized nanosheets are securely anchored by the oxygen functional group of r-GO. As a result, the electrochemically treated MoS3/r-GO electrode shows superior performance that surpasses pure sulfur-based electrodes; it exhibits a capacity of about 900 mAh g–1 at a rate of 5C for 2500 cycles without capacity fading. Moreover, a full-cell battery employing the MoS3/r-GO cathode with a silicon–carbon composite anode displays a 3–5 times higher energy density (1725 Wh kg–1/7100 Wh L–1) than present LIBs.