Artificial Solid Electrolyte Interphase-Protected Li_xSi Nanoparticles: An Efficient and Stable Prelithiation Reagent for Lithium-Ion Batteries

Abstract

Prelithiation is an important strategy to compensate for lithium loss in lithium-ion batteries, particularly during the formation of the solid electrolyte interphase (SEI) from reduced electrolytes in the first charging cycle. We recently demonstrated that LixSi nanoparticles (NPs) synthesized by thermal alloying can serve as a high-capacity prelithiation reagent, although their chemical stability in the battery processing environment remained to be improved. Here we successfully developed a surface modification method to enhance the stability of LixSi NPs by exploiting the reduction of 1-fluorodecane on the LixSi surface to form a continuous and dense coating through a reaction process similar to SEI formation. The coating, consisting of LiF and lithium alkyl carbonate with long hydrophobic carbon chains, serves as an effective passivation layer in the ambient environment. Remarkably, artificial-SEI-protected LixSi NPs show a high prelithiation capacity of 2100 mA h g(-1) with negligible capacity decay in dry air after 5 days and maintain a high capacity of 1600 mA h g(-1) in humid air (∼10% relative humidity). Silicon, tin, and graphite were successfully prelithiated with these NPs to eliminate the irreversible first-cycle capacity loss. The use of prelithiation reagents offers a new approach to realize next-generation high-energy-density lithium-ion batteries.

Challenges and Recent Progress in the Development of Si Anodes for Lithium‐Ion Battery

“…A continuous and uniform artificial SEI coating consisting of Li alkyl carbonate and LiF with long hydrophobic carbon chains is formed on the surface of Li x Si nanoparticles by using 1-fluorodecane. [57] The coated Li x Si nanoparticles showed improved air stability at a low-humidity level (<10% relative humidity). Furthermore, ambient air stable LiSiO anode is demonstrated with low-cost SiO and SiO 2 starting materials.…”

Pre-Lithiation Strategies for Rechargeable Energy Storage Technologies: Concepts, Promises and Challenges

“…For this reason, Zhao et al also presented the formation of an artificial SEI upon Li x Si particles in order to improve their stability [102]. Therefore, they used 1-fluorodecane, which was reduced by Li x Si and, thereby, formed a homogeneous and dense coating layer around the NPs.…”

“…A disadvantage could be the long reaction time, because the sample, which was used for the stability study, was stirred for 5 days in molten Li metal [104]. LixSi-Li2O (core-shell) 1310 91% (1 day in dry air) 67% (5 days in dry air) 5% (6 h in ≈40% RH) [32,105] LixSi (core-shell, artificial SEI) 2100 92% (5 days in dry air) 76% (6 h in 10% RH) [102] Li4.4Si@LixNySiz (core-shell) 2808 - [103] LixSi/Li2O (composite, based on SiO) 2120 91% (5 days in dry air) 58% (6 h in ≈40% RH) [104] LixSi/Li2O (composite, based on SiO2) 1543 - [104] LixSn-Li2O (core-shell) 910 93% (5 days in dry air) 45% (6 h in ≈40% RH) [105] LixSn/Li2O (composite, based on SnO2) 695 56% (6 h in ≈40% RH) [105] LixGe-Li2O (core-shell) 1335 93% (5 days in dry air) 70% (6 h in ≈40% RH) [105] LixGe/Li2O (composite, based on GeO2) 892 85% (6 h in ≈40% RH) [105] Recently, also other group IV elements (Sn, Ge) and their corresponding oxides were used as precursors for the pre-lithiation agent synthesis [105]. DFT calculations showed that the binding energy of Ge-Li (−2.98 eV) and Sn-Li (−2.15 eV) is higher than the binding energy of Si-Li (−0.8 eV), leading to the assumption that the LixZ and LixZ/Li2O particles (Z = Sn or Ge) show an enhanced stability than LixSi-Li2O and LixSi/Li2O particles, respectively [105].…”

Advances in the Application of Silicon and Germanium Nanowires for High‐Performance Lithium‐Ion Batteries

“…[52] As an alternative to using SLMP, Zhao and co-workers have developed a prelithiation agent based on passivated Li x Si NPs. [53,54] The NPs are synthesized through heating of a stoichiometric mixture of Si NPs and Li metal before passivation is performed through the reduction of 1-fluorodecane on the surface to form an artificial SEI layer. When used to prelithiate a Si electrode, the method has been shown to increase the initial C.E.…”

“…value significantly from 76.1% up to 96.8%. [53] A stated disadvantage to such methods is that these prelithiation agents are not stable in polar solvents traditionally used in Li-ion anode slurry processing, an issue that is conveniently avoided should a similar method be used to prelithiate a binder-free NW anode architecture.…”