MgAl Saponite as a Transition-Metal-Free Anode Material for Lithium-Ion Batteries

Abstract

Transition-metal compounds (oxides, sulfides, hydroxides, etc.) as lithium-ion battery (LIB) anodes usually show extraordinary capacity larger than the theoretical value due to the transformation of LiOH into Li2O/LiH. However, there has rarely been a report relaying the transformation of LiOH into Li2O/LiH as the main reaction for LIBs, due to the strong alkalinity of LiOH leading to battery deterioration. In this work, layered silicate MgAl saponite (MA-SAP) is applied as a −OH donor to generate LiOH as the anode material of LIBs for the first time. The MA-SAP maintains a layered structure during the (dis)charging process and has zero-strain characteristic on the (001) crystal plane. In the discharging process, Mg, Al, and Si in the saponite sheets become electron-rich, while the active hydroxyl groups escape from the sheets and combine with lithium ions to form LiOH in the “caves” on sheets, and the LiOH continues to decompose into Li2O and LiH. Consequently, the MA-SAP delivers a maximum capacity of 536 mA h·g–1 at 200 mA·g–1 with a good high-current discharging ability of 155 mA h·g–1 after 1000 cycles under 1 A·g–1. Considering its extremely low cost and completely nontoxic characteristics, MA-SAP has great application prospects in energy storage. In addition, this work has an enlightening effect on the development of new anodes based on extraordinary mechanisms.

Low Volume‐Expansion, Insertion‐Type Layered Silicate Hierarchical Structure For Superior Storage Of Li, Na, K

“…In the Fourier transform infrared (FTIR) spectra of four samples (Figure 1b), the characteristic absorption of layered silicate is always observable, demonstrating they maintain the basic structure of saponite. [ 28–33,34 ] Furthermore, specific absorption peaks of PPy at 1540 cm −1 (C = C), 1450 cm −1 (C‐N), 1185 cm −1 (N‐H or C‐H) and 785 cm −1 (α‐α linked pyrrole ring) in PPy@C/SAP show successful coating of PPy. [ 32–35 ] Detail FTIR peaks attribution of saponite was listed in Table S1 (Supporting Information).…”

“…[ 36,37 ] According to the empirical formula ω G = 1581.6 + 11/(1 + n 1.6 ) (ω G is the location of G band, n is the number of graphene layers), the number of carbon layers in C/SAP or PPy@C/SAP is calculated as 1.29, which substantially meets the thickness requirements of single‐layer graphene (the existence of defects and low graphitization degree make the thickness slightly larger). [ 30 ]…”

“…When using the formula Log( i ) = Log( a )+ b ·Log( v ) to fit peak currents and scanning rate, large b values are gained where i , v , a , b is current, scanning rate and two parameters, separately (Figure 9c). [ 28–30 ] The four selected peaks have b values (0< b <1) of 0.94, 0.80, 0.81, 0.97, pointing out they are almost surface controlled. As a result, this material has a large pseudocapacity ratio of 85.4% at 1.0 mV s −1 based on the formula i = k 1 v + k 2 v 1/2 where k 1 , k 2 are two dynamic parameters and k 1 v is pseudocapacity current.…”

“…Taking the thickness of the laminates (≈1 nm) into account, the thickness of the interlayer carbon layer is ≈0.44 nm, which is close to that of the single-layer graphene (0.36 nm). [30,31] To directly verify the formation of superlattice structure, the C/SAP sample was etched by HCl and LiF to dissolve the silicate host layer. The residual graphene-like carbon layer was observed by atomic force microscope (AFM) (Figure S1, Supporting Information).…”

“…The glucose/SAP was synthesized by self‐intercalation of glucose into SAP in the hydrothermal process. [ 30 ] First, 0.6 g SAP was dispersed into 20 mL de‐ion water in an ultrasonic bath. When a transparent colloid of SAP with obvious Tyndall effect is formed, 1.8 g glucose was added in and then the mixture was reacted at 180 °C for 3 h. The brown product was washed by water and alcohol to remove residual glucose.…”