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Lithium is a promising anode material for next-generation highenergy-density rechargeable batteries owing to its high specific capacity, low density, and low electrochemical reduction potential. However, dendrite growth during cycling impedes its practical application and causes safety hazards. Extensive research has been conducted to obtain dendrite-free safe Li anodes with an extended cycle life by electrolyte or anode surface modification. In previous studies, the symmetrical Li/Li cell test was widely applied to evaluate the effect of various Li anode modification methods on the cycle stability and Li deposition overpotential. However, a general criterion has not yet been established to identify the short circuit in Li/Li cells. Some researchers have even made incorrect conclusions based on the Li/Li cycling data. The most common misjudgment is the ignorance of short circuit signals and mixing up of soft short circuit and normal potential decrease caused by electrode activation. In some studies, the fractal voltage signals were attributed to the unstable activation process of the symmetrical cell. Therefore, this study uses an in situ optical cell to demonstrate that a short circuit caused by the contact of dendrites from two opposite electrodes can cause a sudden drop in cell voltage to certain extent. According to the reversibility of the voltage, the short circuit induced by dendrite growth can be classified into unrecoverable hard short circuits and recoverable soft short circuits. Typical short circuit data were summarized and described to establish a rule to determine the different types of short circuits. The voltage profiles provide characteristic signals to distinguish between the soft short circuit, hard short circuit, and cell activation processes in symmetrical cells. Furthermore, this study provides a reference for identifying dendrite growth and cell short circuits, which is important for confirming the practical effect of different modification methods.

Pre-lithiated sulfur materials are promising cathode for lithium-sulfur batteries. The synthesis of lithium sulfide-carbon (Li 2 S-C) composite by carbothermic reduction of lithium sulfate (Li 2 SO 4) is investigated in this study. The relationship between reaction temperature and the consumption of carbon in the carbothermic reduction of Li 2 SO 4 is first investigated to precisely control the carbon content in the resultant Li 2 S-C composites. To understand the relationship between the material structure and the electrochemical properties, Li 2 S-C composites with the same carbon content are subsequently synthesized by controlling the mass ratio of Li 2 SO 4 /carbon and the reaction temperature. Systematic electrochemical analyses and microscopic characterizations demonstrate that the size of the Li 2 S particles dispersed in the carbon matrix is the key parameter determining the electrochemical performance. A reversible capacity of 600 mAh g −1 is achieved under lean electrolyte condition with high Li 2 S areal loading.