Durability of high-energy throughput batteries is a prerequisite for electric vehicles to penetrate the market. Despite remarkable progresses in silicon anodes with high energy densities, rapid capacity fading of full cells with silicon–graphite anodes limits their use. In this work, we unveil degradation mechanisms such as Li+ crosstalk between silicon and graphite, consequent Li+ accumulation in silicon, and capacity depression of graphite due to silicon expansion. The active material properties, i.e. silicon particle size and graphite hardness, are then modified based on these results to reduce Li+ accumulation in silicon and the subsequent degradation of the active materials in the anode. Finally, the cycling performance is tailored by designing electrodes to regulate Li+ crosstalk. The resultant full cell with an areal capacity of 6 mAh cm−2 has a cycle life of >750 cycles the volumetric energy density of 800 Wh L−1 in a commercial cell format.

No abstract

The electrochemical behaviors of a silicon thin-film electrode in organic lithium salt solution were explored with focus on irreversible reactions of the first lithium charge and discharge cycling by using electrochemical quartz crystal microbalance ͑EQCM͒ combined with various electrochemical techniques. A considerable increase in mass of the silicon electrode was observed during lithium charging even before lithium absorption into the electrode, which is ascribed to the buildup of electrolyte reduction products on the silicon surface. Galvanostatic charge-discharge experiments combined with ac impedance spectroscopy demonstrate a significant overpotential growth and an aggravating capacity for the lithium charge and discharge cycling, and suggest they are due to the sedimentation of electrolyte reduction product. Additives containing alkoxy silane functional groups were evaluated as a passivation agent for lithium rechargeable batteries utilizing a silicon anode. The presence of additives in electrolyte suppressed the mass accumulation to the silicon electrode caused by irreversible electrolyte reductions and improved the electrode for cycle life. Electrochemical analyses associated with EQCM as a function of the number of alkoxy functional groups of the additives illustrate that the silicon electrode is passivated by chemical reaction of the alkoxy silane functional group of the additives with hydroxyl groups at the electrode/electrolyte interface, and this passivation improves the cycle life.Silicon as a negative electrode for lithium-ion batteries has been attracting significant interest because of its high specific capacity. 1-6 Silicon reacts with lithium to form Li 4.4 Si alloy, showing theoretical capacity of 4200 mAh/g. Capacity retention is the most important issue for utilizing the silicon-based negative electrode. 1,2,4 It has been generally accepted that the limited cycle life of the silicon electrode is ascribed to severe volume changes of the electrode. 5,6 Many researchers have focused on the structural modification of the silicon electrode to prolong the cycle life of the electrode. 3,4,6 In crystalline silicon, intermetallic phases are formed during lithium charging, leading to inhomogeneous volume expansions which can cause cracking and pulverization of the silicon-lithium alloy. 3,5 Reversible lithium cycling with little capacity loss is possible for amorphous silicon thin film in which the homogeneous volume expansion occurs. 5 To suppress the volume expansion during lithium charging, the silicon particle of the fine grain size uniformly distributed within a less active matrix, like graphite, has been proposed. 7 Organic lithium salt solution reduces electrochemically on the silicon electrode to form a solid electrolyte interphase layer on the electrode because the lithiation potential of the silicon electrode is far lower than 1.0 V Li/Li + . However, few studies on the interface between silicon electrode and organic electrolyte have been conducted. Unlike graphite electrode, it is reasonab...

Since the early nineties there have been a number of reports on the experimental development of Mg electrolytes based on organo/amide-magnesium chlorides and their transmetalations. However, there are no theoretical papers describing the underlying operating mechanisms of Mg electrolytes, and there is no clear understanding of these mechanisms. We have therefore attempted to clarify the operating mechanisms of Mg electrolytes by studying the characteristics of Mg complexes, solvation, chemical equilibrium, Mg-deposition processes, electrolyte-oxidation processes, and oxidative degradation mechanism of RMgCl-based electrolytes, using ab initio calculations. The formation and solvation energies of Mg complexes highly depend on the characteristics of R groups. Thus, changes in R groups of RMgCl lead to changes in the equilibrium position and the electrochemical reduction and oxidation pathways and energies. We first provide a methodological scheme for calculating Mg reduction potential values in non-aqueous electrolytes and electrochemical windows. We also describe a strategy for designing Mg electrolytes to maximize the electrochemical windows and oxidative stabilities. These results will be useful not only for designing improved Mg electrolytes, but also for developing new electrolytes in the future.

No abstract