SLMP® for Pre-Lithiation and Ultra-Thin Lithium Foil Anode Applications
Authors: Fitch Brian , Yakovleva Marina 
Published: February 2020

Due to low first cycle coulombic efficiency, pre-lithiation techniques are accepted as a necessary enabling technology for high energy anodes such as Si/C composite materials. An independent source of active lithium can be combined electrochemically, chemically or physically with the anode to partially pre-lithiate and reduce first cycle inefficiency therefore increasing cathode utilization. (1) Electrochemical, ex-situ techniques, for example, roll-to-roll electrochemical baths and other techniques, including oversized cathode, lithium rich cathodes, sacrificial salts or in line short circuiting have been proposed. Among the physical techniques are vacuum deposition, sputtering, thermal spraying, and mechanical milling. (1) However, to-date, chemical pre-lithiation techniques have shown the most promise. Specifically, the ex-situ addition of metallic lithium to the anode material. The use of FMC’s advanced material, Lectro® Max Powder (SLMP) has been demonstrated worldwide as an effective and efficient pre-lithiation material. (1),(2),(3) SLMP can deliver capacity close to the theoretical lithium capacity of 3860 mAh/g and, after addition of the electrolyte, reacts with the anode material in-situ, and thus exists in the lithium ion form in the cell. (3) Because of its high capacity, addition of SLMP causes negligible increase in cell mass or volume unlike the case of sacrificial salts or oversized cathode use, which deliver lower capacity per unit mass and leave inactive phases after lithium extraction which might lower overall energy density of the cell. (1) In addition to use as a pre-lithiation agent to enable high energy anode materials SLMP could also be used to fully lithiate anode materials and thus allow the use of new cathode materials. (4)

Most of beyond lithium ion chemistries and next generation lithium ion chemistries will require thin lithium metal anode use to achieve targeted volumetric energy density. Today, production of thin lithium foil involves extrusion of lithium metal followed by rolling to achieve desired thinness, which is complicated and expensive; thus, no commercially viable source of thin foil exists. SLMP-derived thin Li foil offers the possibility of achieving thin foil with width being limited only by the substrate used.
In this work, we show the effectiveness of SLMP in improving the performance of commercially available silicon-based anode material. The anode composition is 85% SiO/C composite material and 15% Polyimide binder. The cathode composition is LiCoO2 (90%) + carbon black (5%) + PVdF (5%). Surface application technique was used to apply SLMP slurry onto the surface of prefabricated SiO electrodes. Single layer pouch SiO/LiCoO2 cells were assembled and 1M LiPF6 /EC+DEC (1:1) was used as the electrolyte. The pouch cells were conditioned at room temperature for 24 hours before the battery test. The pouch cell test protocol was: constant current charge at C/10 to 4.3 V, constant voltage charge at 4.3 V to C/100; constant current discharge at C/10 to 3.0 V. SLMP utilization has been evaluated based on its ability to compensate first cycle irreversible capacity.
Figure 1 below shows the effect of SLMP on first cycle efficiency of SiO/LiCoO2 pouch cells.
One of the important properties of SLMP is its specific capacity. SLMP contains at least 97% metallic lithium which can be fully utilized. To demonstrate this, an electrochemical system has been designed to test SLMP’s capacity, Li/Electrolyte/SLMP+Cu. About 1 mg of SLMP was deposited onto a half-inch Cu disc using a slurry of SLMP. After the solvent was fully evaporated, the electrode was calendered using 12,000 lbs pressure creating SLMP-derived thin Li foil. The electrodes were used to assemble coin cells with lithium foil counter electrode. 1M LiPF6/EC+DEC was used as the electrolyte. The cells were charged at 0.1 mA to 3.0 V.
Figure 2 shows the voltage profiles for the cells comprised of SLMP-derived thin foil. The voltage profiles and the SLMP capacity are reproducible. Close to theoretical lithium capacity can be extracted from the SLMP derived thin foil.
We will also discuss a novel SLMP delivery system which can be used at commercial scale to safely and economically incorporate SLMP into existing LIB systems as well as being used to produce ultra-thin lithium foil for solid state lithium applications.

References

Florian Holtstiege, Peer Bärmann, Roman Nölle, Martin Winter, and Tobias Placke, Pre-Lithiation Strategies for Rechargeable Energy Storage Technologies: Concepts, Promises and Challenges, Batteries 2018, 491), 4

Margret Wohlfahrt-Mehrens, Manuel Weinberger, Novel strategies towards the realization of larger lithium sulfur/silicon pouch cells. Electrochimica Acta, Volume 191, 10, February (2016), p. 124–132.

Y. Li, B. Fitch, Electrochem. Commun., 13, (2011) 664.

K.B. Fitch, M.V. Yakovleva, Y. Li, I. Plitz, A. Skrzypczak, F. Badway, G.G. Amatucci, and Y. Gao, ECS Transaction 2007

Figure 1