Technical analysis of inactive sulfide inhibiting lithium battery capacity loss

【introduction】

Nowadays, there is an urgent need for sustainable energy to develop and improve a wide range of energy storage capabilities, such as wind and solar energy. Electrochemical energy storage has been widely studied due to its advantages of no pollution, high cycle efficiency and good flexibility. As a kind of electrochemical energy storage, lithium-sulfur battery has a theoretical energy density of 2600 Wh Kg-1, so it is considered to be one of the most promising ones for the next generation of energy storage batteries. However, the battery also has many drawbacks such as low electronic conductivity, sedimentation of polysulfides, volume effects and self-discharge, and the like. In addition, the formation of soluble lithium-containing polysulfides reduces the performance of the battery. A large-sized semi-fluid battery has been designed to improve electrochemical performance. However, in the cycle engineering, the capacity of the battery is drastically reduced due to the formation of a large amount of insoluble sulfide.

[Introduction]

Recently, Professor Cui Wei of Stanford University in the United States reported on Nat. commun. that a method of suppressing battery capacity loss is achieved by adding inexpensive sulfur and heating it by stirring to activate the inactive sulfide. The single cell has a capacity of 0.9 Ah and a volumetric energy density of 95 Wh/L (3M Li2S8), which is about 4 times that of a full vanadium flow battery. And at a high concentration of Li2S8 (5M) volume energy density up to 135 Wh / L. For the first time, the study increased the loading of active materials to 0.125 g/cm3 (approximately 2 g S in a single cell) and achieved excellent performance.

[Graphic introduction]

Figure 1: Schematic diagram of the method

(a) a schematic diagram of the reaction of inactive sulfur and sulfur particles during heating and stirring;

(b) a comparison chart of lithium sheets before and after the reaction;

(c) a comparison chart before and after activation of the lithium sheet;

(d) Schematic diagram of the LPS flow battery system.

Figure 2: Reaction of inactive sulfides with sulfur

(a) Inactive sulfur reacts with metallic lithium in DOL/DME at different reaction times;

(b) a comparison chart of lithium sheets before and after the reaction;

(c) a Raman curve of the lithium sheet before and after the reaction;

(d) electrochemical performance of the lithium sheet under 5 M LPS electrolyte after activation;

(e) Voltage curve of lithium sheet under 5 M LPS electrolyte after activation.

Figure 3: Characterization of inactive sulfides

(ad) XPS test curve before and after activation;

(eh) SEM pictures before and after activation.

Figure 4: Electrochemical performance of LPS cells

(a) cycle performance and efficiency curves of the battery;

(b) Horizontal capacity charge and discharge curve, the cutoff voltage is 2.06V, and the capacity is set to 1000 mAh;

(c) Energy comparison diagrams for different current densities;

(d) EIS comparison curve before and after activation;

(e) a voltage curve before and after activation;

(f) a voltage curve at different concentrations;

(g) Comparison of energy density of different batteries;

【summary】

In this paper, a new method is used to activate the inactive sulfide to increase the cycle and energy density of the battery, and the tank design makes the battery easy to disassemble. Moreover, the activation of sulfur and the replacement of lithium are easily realized industrially, and at the same time, it has the characteristics of low sulfur cost. However, the cost of LITFSI in the electrolyte is very high, accounting for almost half of the cost of the entire battery. Therefore, finding a cheap material to replace LITFSI may be one of the future development directions.