Roll-to-roll prelithiation of Sn foil anode suppresses gassing and enables stable full-cell cycling of lithium ion batteries

Abstract

Tin foil should have outstanding volumetric capacity as a Li-ion battery anode; however, it suffers from an unacceptable initial coulombic efficiency (ICE) of 10-20%, which is much poorer than that of Si or SnO 2 nanoparticles. Herein, we demonstrate that bare Sn catalyzes liquid electrolyte decomposition at intermediate voltages to generate gas bubbles and Leidenfrost gas films, which hinder lithium-ion transport and erode the solid-electrolyte interphase (SEI) layer. By metallurgically pre-alloying Li to make Li x Sn foil, the lower initial anode potential simultaneously suppresses gassing and promotes the formation of an adherent passivating SEI. We developed a universally applicable roll-to-roll mechanical prelithiation method and successfully prelithiated Sn foil, Al foil and Si/C anodes. The as-prepared Li x Sn foil exhibited an increased ICE from 20% to 94% and achieved 200 stable cycles in LiFePO 4 //Li x Sn full cells at B2.65 mA h cm À2 . Surprisingly, the Li x Sn foil also exhibited excellent air-stability, and its cycling performance sustained slight loss after 12 h exposure to moist air. In addition to LiFePO 4 , the Li x Sn foil cycled well against a lithium nickel cobalt manganese oxide (NMC) cathode (4.3 V and B4-5 mA h cm À2 ). The volumetric capacity of the Li x Sn alloy in the LFP//Li x Sn pouch cell was up to B650 mA h cm À3 , which is significantly better than that of the graphite anode on a copper collector, with a rate capability as high as 3C. Broader contextSelf-supporting tin foil is a high-volumetric-capacity alternative to the graphite LIB anode; however, it shows an exceptionally low initial coulombic efficiency (10-20%), even lower than that of Si and SnO 2 nanoparticles with 410 3 Â contact area with the electrolyte, which is quite strange. Inspired by previous reports that tin catalyzes the decomposition of organic solvents, herein, we proved that bare Sn indeed catalyzes electrolyte decomposition at an intermediate voltage to generate gas bubbles and Leidenfrost films, which cut off the transport of lithium ions and prevent the formation of an adherent SEI. However, when the absolute potential is below 1 V (vs. Li/Li + ), it simultaneously promotes the formation of a solid SEI and mechanical adherence, which can in turn suppress future gassing. Therefore, we developed a roll-to-roll mechanical prelithiation process for tin foil, which lowers its absolute potential before contacting the electrolyte, promotes adherent passivation film formation, and greatly improves its coulombic efficiency and capacity retention so that it can perform well in full cells. Also, the striking air stability of the Li x Sn foil makes it much easier to handle than the bare Li metal anode. Our study provides vital new insights into why self-supporting metallic anodes do not appear to work in LIBs and develops an effective mitigation strategy by cheap and scalable metallurgical prelithiation, which is also applicable to other metallic alloy anode materials.

Sn‐Alloy Foil Electrode with Mechanical Prelithiation: Full‐Cell Performance up to 200 Cycles

“…[18] The Li BCC phase becomes "fluid-like" [18] under mechanical pressure and thus the true contact area between Sn and Li foils is largely increased, greatly accelerating the prelithiation and also making the degree of prelithiation more homogeneous. [12] However, it is worth mentioning that in that previous work the thickness of Li x Sn was ≈100 µm, 25% thicker than the commercial graphite anode of the same areal capacity (≈80 µm thick including copper current collector). [12] However, it is worth mentioning that in that previous work the thickness of Li x Sn was ≈100 µm, 25% thicker than the commercial graphite anode of the same areal capacity (≈80 µm thick including copper current collector).…”

“…Energy Mater. [12] The Li metal spreads like butter on the 3Ag0.5Cu96.5Sn, which is itself also extending. The operation and the influence of pressure on lithiation degree had been explored in our previous work.…”

“…The operation and the influence of pressure on lithiation degree had been explored in our previous work. [12] The Li metal spreads like butter on the 3Ag0.5Cu96.5Sn, which is itself also extending. The alloying and bonding reaction (mechanical prelithiation) occurs simultaneously with the mechanical deformation of the remaining Li BCC and 3Ag0.5Cu96.5Sn phases, until they become one dense layer of 50 µm × 18 cm × 4.5 cm sized Li x 3Ag0.5Cu96.5Sn foil, which is mechanically stable (no huge rolling cracks and can be handled easily without failure) and electronically percolating.…”

“…After prelithiation, the ICE of LiFePO 4 (LFP)//Li x Sn full cell was improved to 94% from 20% and the full cell can deeply cycle 200 times at ≈2.65 mAh cm −2 . [12] However, it is worth mentioning that in that previous work the thickness of Li x Sn was ≈100 µm, 25% thicker than the commercial graphite anode of the same areal capacity (≈80 µm thick including copper current collector). [19] Generally speaking, regardless of electrochemical or mechanical lithiation, we find that the thinner the foil, the less damage tolerant it becomes in subsequent electrochemical cycling.…”

Molecularly Tailored Lithium–Arene Complex Enables Chemical Prelithiation of High‐Capacity Lithium‐Ion Battery Anodes

“…sacrificial Li sources when preparing electrodes has been proposed. [3] However,n anosized additives are difficult to synthesize at larger scale,t ypically require unconventional solvents for the electrode preparation, and inevitably lead to the presence of decomposed products in the electrode, degrading the net energy density.Ana lternative approach is to directly apply Li metal to prelithiate the prepared electrodes.P hysical contact with Li metal can prelithiate the electrode without precise control over the Li dose, [4] whereas building atemporary electrochemical cell allows the delicate control of the Li dose but requires aproblematic re-assembly step for battery fabrication. Some noteworthy progress has been made,s uch as the covering Li foil with ar esistance buffer layer [5] and external shorting of an electrode with Li metal with selected circuit resistance.…”