“One Stone Two Birds” Strategy of Synthesizing the Battery Material Lithium Sulfide: Aluminothermal Reduction of Lithium Sulfate

Abstract

Lithium sulfide (Li 2 S) is a critical material for clean energy technologies, i.e., the cathode material in lithium−sulfur batteries and the raw material for making sulfide solid electrolytes in all-solidstate batteries. However, its practical application at a large scale is hindered by its industrial production method of reducing lithium sulfate with carbon materials at high temperatures, which emits carbon dioxide and is time-consuming. We hereby report a method of synthesizing Li 2 S by thermally reducing lithium sulfate with aluminum. Compared with the carbothermal method, this aluminothermal approach has several advantages, such as operation at lower temperatures, completion in minutes, no emission of greenhouse gases, and valuable byproducts of aluminum oxide (Al 2 O 3 ). The home-made Li 2 S demonstrates competitive performance in battery tests versus the commercial counterpart. Moreover, using the byproduct Al 2 O 3 to coat the cathode side of the separator can enhance the battery's capacity without influencing its rate capability. Thus, this "one stone two birds" method has great potential for practical applications of developing Li−S batteries.

A Green Method of Synthesizing Battery-Grade Lithium Sulfide: Hydrogen Reduction of Lithium Sulfate

“…In practical applications, the exhaust gas can be cleaned up with alkaline or metal salt solutions, not causing trouble to the environment . Additionally, two sets of low material cost methods (metathesis via LiX-Na 2 S and metallothermal reduction of Li 2 SO 4 ) cannot find sustainable ways to regenerate the needed precursors directly or indirectly. ,, Therefore, among all known methods for Li 2 S production as summarized in Table S2, this hydrogen-reduction method overall seems the most friendly to the environment.…”

“…Learning from the carbothermal strategy, we have recently developed two metallothermal methods for producing Li 2 S by using Mg and Al as reductants, respectively (eqs and ). , The nice things are that both reactions can run at lower temperatures (500–600 °C), finish within shorter periods (a few minutes), and have zero amounts of harmful byproducts (MgO and Al 2 O 3 are valuable). But they also have three shortcomings: (a) the reactions release an extensive amount of heat, and the explosive manner will be difficult to handle for large-scale production; (b) the byproducts are also solids, still requiring multiple steps of purification treatments; and (c) the values of byproducts can only be realized by integrating with the downstream industries, although they are useful chemicals in general.…”

Making the Unfeasible Feasible: Synthesis of the Battery Material Lithium Sulfide via the Metathetic Reaction between Lithium Sulfate and Sodium Sulfide

“…Additionally, we compare the pros and cons of this metathetic solution method with several representative methods of making Li 2 S in the literature (Table S4). The carbothermal method utilizes cheap and abundant raw materials, but it needs high reaction temperatures and has a large amount of CO 2 emission. , The magnesiothermic method and the aluminothermic method conducted at lower reaction temperatures have shorter durations and have no carbon emissions but cannot easily manage the intense heat release. The advantages of ball milling methods are that they are simple and have no liquid wastes, but their disadvantages are low conversion yields, low product purity, and low reproducibility .…”

“…Recently, we have developed two CO 2 -free methods for making battery-grade Li 2 S: (1) metallothermic reduction of Li 2 SO 4 , and (2) metathetic reaction between lithium salts (LiX, X = Cl, Br, I, and NO 3 ) , and sodium sulfide (Na 2 S). Both methods are thermodynamically spontaneous under standard conditions, with the actual operating temperature at 550 °C for the former and 25 °C for the latter.…”