(Invited) Si Anodes for Li-Ion Batteries: Experimental Studies on Li-Inventory and Pre-Lithiation Approaches

Abstract

Li inventory and pre-lithiation methods for Si-anode containing Li-ion batteries are evaluated via a number of avenues, and are summarized briefly in this abstract. The capacity fade of the Si-graphite electrode was tracked using a capacity over-sized LiFePO4 cathode in a diagnostic cell. With essentially limitless Li inventory the intrinsic capacity fade was monitored over hundreds of cycles, without limitations/complications from Li metal in a half cell. The introduction of lithium inventory to the cell was accomplished in three ways. To date we have (1) investigated in detail the synthesis and electrochemistry of Li5FeO4 as a prelithiation source. Approach #1. We are currently working towards a blended LFO-NMC cathode to understand the cross-reactivity, impedance changes, and capacity changes in the resultant electrode. (2) Introducing lithium inventory to the cell #2. Overlithiated NCM, i.e., Li1+xNCM523O2, was found to be a viable way to introduce lithium to the cathode with minimal weight increase and no residual byproduct. However, we observed that the electrochemical cycling stability of overlithiated NCM is compromised, likely a result of the irreversible anisotropic structural changes. Work is ongoing to assess the nature of the irreversibility and we are developing strategies to minimize its impact. (3) Introducing lithium inventory to the cell #3. We will report that the 5 V spinel cathode, or Li1+xNi0.5Mn1.5O4, could be further lithiated (x>0) via an ammonia-based chemical lithiation reaction. This material was paired with a Si-graphite anode in a full cell. The excess lithium is released during the first charge and accounts for the first cycle irreversible capacity loss. Subsequent cycling only at 3 to 4.7 V shows a higher capacity and similar fade rate compared to the baseline, un-lithiated cathode.