Pilot-Plant Production of High-Performance Silicon Nanowires by Molten Salt Electrolysis of Silica

Abstract

Silicon nanowires are a kind of promising negative electrode material for lithium-ion batteries. However, the existing production technologies can hardly meet the demands of silicon nanowires in quality and production ability. In this paper, silicon nanowires are successfully prepared by molten salt electrolysis in a pilot-plant. The pilot-plant was successfully operated for 14 months with a current efficiency of 80.3% and an electrolysis energy consumption of 12.8 kW h/kg-Si. The obtained silicon nanowires as a negative electrode material show a specific discharge capacity of 3095 mA h/g and a coulombic efficiency of 89.7% in the first charge–discharge cycle at a rate of 0.1 C in coin-type cell tests and a capacity retention of 83.4% after 250 cycles at a rate of 1 C in pouch cell tests when mixed with graphite.

Template‐Free Electrochemical Formation of Silicon Nanotubes from Silica

“…[43] Constant-voltage electrolysis is conducted, with the cell voltage between the solid cathodes and graphite anode being at 2.2-2.6 V to avoid the formation of Ca-based alloys. [31][32][33][34][35][36][37][38][39][40][41] The cathode potential (versus Ag/AgCl) was monitored in one case during constant-voltage electrolysis at a cell voltage of 2.2 V ( Figure S1, Supporting Information), which shows that the cathode potential (versus Ag/AgCl) during the two-electrode-electrolysis process is consistent with that in the CV curves in Figure 2a, further verifying the preferential reduction of AgCl and formation of Ag-Si.…”

“…In comparison with recently reported Si nanostructures prepared by the same molten salt electrolysis method, the Si-NT@Ag shows an obvious superiority in capacity at similar cycling number and charge/discharge rate. [11,41] Specially, the Si-NT@Ag also shows comparable/superior performance with Si nanostructures prepared by some other methods. [1,2,8,10,12,19,22,26] Even so, substantial improvement for the battery performance is needed before evaluation for a full cell.…”

“…[31][32][33][34][35][36][37][38][39][40][41] However, the solid-solid conversion from SiO 2 to Si makes the nucleation-growth process of Si hardly tunable, therefore construction of hollow Si nanostructure by molten salt electrolysis of silica is an insurmountable challenge. [31][32][33][34][35][36][37][38][39][40][41] As for coating a conductive buffer layer on the surface of Si nanostructures, carbon is commonly used as the candidate. [12][13][14][15][16] However, the unpleasant SiC is readily generated during molten salt electrolysis, therefore making the in situ coating strategy far from expectations.…”

“…The electrode kinetics for molten salt electrolysis of solid silica for Si extraction is governed by ohmic polarization and mass transfer of/through the solid cathode. [31][32][33][34][35][36][37][38][39][40][41] Electrolysis of SiO 2 -AgCl for Si formation ranks among the highest performance in terms of current efficiency (74%, Figure 4m) and energy consumption (12.1 kW h kg Si −1 , Figure 4m). This energyconsumption value is even lower than that of industrial production of metallurgical-grade silicon (>20 kW h kg Si −1 ), [41] promising future industrial production of Si nanotubes.…”

“…Of note, molten salt electrolysis, which is widely adopted for production of metals in industry, has been verified to be adaptable for large-scale production of silicon nanomaterials. [31][32][33][34][35][36][37][38][39][40][41] Compared with the conventional CVD method which uses toxic SiH 4 /SiCl 4 as raw materials and suffers from low production yield, [12,[17][18][19][20][21][22][23][24][25][26][27][28] the molten salt electrolysis strategy with a high production yield herein uses affordable SiO 2 as the starting material and shows a promise for practical production of Si nanotubes.…”