Synthesis of Deliquescent Lithium Sulfide in Air

Abstract

In the field of lithium–sulfur batteries (LSBs) and all-solid-state batteries, lithium sulfide (Li2S) is a critical raw material. However, its practical application is greatly hindered by its high price due to its deliquescent property and production at high temperatures (above 700 °C) with carbon emission. Hereby, we report a new method of preparing Li2S, in air and at low temperatures (∼200 °C), which presents enriched and surprising chemistry. The synthesis relies on the solid-state reaction between inexpensive and air-stable raw materials of lithium hydroxide (LiOH) and sulfur (S), where lithium sulfite (Li2SO3), lithium thiosulfate (Li2S2O3), and water are three major byproducts. About 57% of lithium from LiOH is converted into Li2S, corresponding to a material cost of ∼$64.9/kg_Li2S, less than 10% of the commercial price. The success of conducting this water-producing reaction in air lies in three-fold: (1) Li2S is stable with oxygen below 220 °C; (2) the use of excess S can prevent Li2S from water attack, by forming lithium polysulfides (Li2S n ); and (3) the byproduct water can be expelled out of the reaction system by the carrier gas and also absorbed by LiOH to form LiOH·H2O. Two interesting and beneficial phenomena, i.e., the anti-hydrolysis of Li2S n and the decomposition of Li2S2O3 to recover Li2S, are explained with density functional theory computations. Furthermore, our homemade Li2S (h-Li2S) is at least comparable with the commercial Li2S (c-Li2S), when being tested as cathode materials for LSBs.

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

“…Afterward, XPS (X-ray photoelectronic spectroscopy) was used to characterize the product. 16 As shown in Figure 2C for the S 2p spectrum, the signal of Li 2 S is expectedly strong with the doublet peaks centered at 160.3 and 161.6 eV, respectively. Besides, two sets of doublet peaks centered at 161.7/162.9 and 167.2/168.4 eV, which can be assigned to Li 2 S 2 and Li 2 S 2 O 3 , respectively.…”

“…The existence of Li 2 S 2 is easy to understand because its formation from the reaction between Li 2 S and S (eq 14) is spontaneously favorable. 16 As Li 2 S 2 O 3 is known to fully decompose into Li 2 S and SO 3 at 700 °C (eq 15), 16 its existence in the XPS sample cannot be concomitant in the original product because the synthetic temperature was 800 °C. Then, Li 2 S 2 O 3 should be from the surface oxidation of Li 2 S 2 by oxygen (eq 16) in the environment during the sample preparation period.…”

“…10 As a result, the commercially supplied battery-grade Li 2 S (c-Li 2 S) is too expensive (>$3000/kg) to afford real applications. 16 Therefore, the Li 2 S production industry has to be reshaped. 17 Currently, there are several methods for synthesizing Li 2 S, mainly including the carbothermal reduction method, the solution method, and the ball milling method.…”

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

“…Lithium sulfide (Li 2 S) has received ever-increasing attention in recent years − because it is a key material for two types of advanced batteries: lithium–sulfur (Li–S) batteries , and all-solid-state lithium batteries (ASSLBs). , It can be directly used as the cathode material for Li–S batteries and serves as a raw material for synthesizing sulfide solid electrolytes (SSEs) for ASSLBs . Both systems are advantageous over the current lithium ion batteries (LIBs) due to their higher energy density and better safety. , Their potential applications in electric vehicles and smart grids will require a huge amount of Li 2 S. , However, currently, the commercial battery-grade Li 2 S is very expensive (>$3000/kg) , and not easy to produce at a large scale. , The major synthesis methods include carbothermal reduction of lithium sulfate (Li 2 SO 4 ), solution-phase reactions between lithium and sulfur compounds, − and the ball milling of lithium (hydride) and sulfur. , Among them, the carbothermal reduction approach is the most prevailing one (eq ) normalL normali 2 SO 4 + 2 normalC → normalL normali 2 S + 2 normalC normalO 2 ; .25em Δ G normalr , normalm θ ≈ prefix+ 119 .25em k J / m o l where carbon can be in the inorganic or organic form. Because eq is thermodynamically unfavorable under standard conditions (Δ G θ r,m > 0 kJ/mol), , it has to be performed at high temperatures around 700 °C …”

Na2S Cathodes Enabling Safety Room Temperature Sodium Sulfur Batteries

“…[5][6][7] Recently, the increasing demands for electric vehicles and energy storage systems have significantly elevated the cost of lithium salts. [8][9][10] Additionally, the new emerging applications usually require battery technologies characterized by low cost and high energy density. Nevertheless, the increased prices and uneven distribution of lithium resources could potentially pose risks in the supply chain.…”