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1. In situ formation of a multicomponent inorganic-rich SEI layer provides a fast charging and high specific energy Li-metal battery

   https://doi.org/10.1039/C9TA05063A  

   Sun, Ho-Hyun; Dolocan, Andrei; Weeks, Jason A.; Rodriguez, Rodrigo; Heller, Adam; Mullins, C. Buddie (July 2019, Journal of Materials Chemistry A)

   The performance of the rechargeable Li metal battery anode is limited by the poor ionic conductivity and poor mechanical properties of its solid-electrolyte interphase (SEI) layer. To overcome this, a 3 : 1 v/v ethyl methyl carbonate (EMC) : fluoroethylene carbonate (FEC) containing 0.8 M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and 0.2 M lithium difluoro(oxalate)borate (LiDFOB) dual-salts with 0.05 M lithium hexafluorophosphate (LiPF 6 ) was tested to promote the formation of a multitude of SEI-beneficial species. The resulting SEI layer was rich in LiF, Li 2 CO 3 , oligomeric and glass borates, Li 3 N, and Li 2 S, which enhanced its role as a protective yet Li + conductive film, stabilizing the lithium metal anode and minimizing dead lithium build-up. With a stable SEI, a Li/Li[Ni 0.59 Co 0.2 Mn 0.2 Al 0.01 ]O 2 Li-metal battery (LMB) retains 75% of its 177 mA h g −1 specific discharge capacity for 500 hours at a coulombic efficiency of greater than 99.3% at the fast charge–discharge rate of 1.8 mA cm −2 . 

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2. Improved Performance of Silicon-Containing Anodes with Organic Solvent-Solubilized Lithium Nitrate

   https://doi.org/10.1149/1945-7111/acdd26  

   Rynearson, Leah; Jayawardana, Chamithri; Yeddala, Munaiah; Lucht, Brett L. (June 2023, Journal of The Electrochemical Society)

   Three different organic solvents (dimethylacetamide (DMAc), dimethylformamide (DMF), and dimethyl sulfoxide (DMSO)) were used to improve the solubility of LiNO 3 in a standard carbonate-based electrolyte with lithium difluoro(oxalato)borate (LiDFOB) as the salt. Together, the LiDFOB and organic-solvent solubilized LiNO 3 preferentially reduce on the surface of silicon-containing anodes to create an SEI rich in oxalates, nitrate decomposition species, and B-F species. The improved stability of the SEI throughout the first 100 cycles results in silicon and silicon/graphite composite anodes with better capacity retention than observed with standard electrolytes or fluoroethylene carbonate (FEC) containing electrolytes. This study demonstrates the feasibility of the use of non-traditional electrolyte solvents in the improvement and optimization of lithium ion-battery electrolytes. 

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3. High Performance Tin-coated Vertically Aligned Carbon Nanofiber Array Anode for Lithium-ion Batteries

   https://doi.org/10.1557/adv.2018.520  

   Pandey, Gaind P.; Jones, Kobi; Brown, Emery; Li, Jun; Meda, Lamartine (January 2018, MRS Advances)

   ABSTRACT This study reports a high-performance tin (Sn)-coated vertically aligned carbon nanofiber array anode for lithium-ion batteries. The array electrodes have been prepared by coaxial sputter-coating of tin (Sn) shells on vertically aligned carbon nanofiber (VACNF) cores. The robust brush-like highly conductive VACNFs effectively connect high-capacity Sn shells for lithium-ion storage. A high specific capacity of 815 mAh g -1 of Sn was obtained at C/20 rate, reaching toward the maximum value of Sn. However, the electrode shows poor cycling performance with conventional LiPF 6 based organic electrolyte. The addition of fluoroethylene carbonate (FEC) improve the performance significantly and the Sn-coated VACNFs anode shows stable cycling performance. The Sn-coated VACNF array anodes exhibit outstanding capacity retention in the half-cell tests with electrolyte containing 10 wt.% FEC and could deliver a reversible capacity of 480 mAh g -1 after 50 cycles at C/3 rate. 

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4. Co-intercalation-free ether electrolytes for graphitic anodes in lithium-ion batteries

   https://doi.org/10.1039/D2EE01489K  

   Ma, Peiyuan; Mirmira, Priyadarshini; Eng, Peter J.; Son, Seoung-Bum; Bloom, Ira D.; Filatov, Alexander S.; Amanchukwu, Chibueze V. (November 2022, Energy & Environmental Science)

   Carbonate-based electrolytes are widely used in Li-ion batteries but are limited by a small operating temperature window and poor cycling with silicon-containing graphitic anodes. The lack of non-carbonate electrolyte alternatives such as ether-based electrolytes is due to undesired solvent co-intercalation that occurs with graphitic anodes. Here, we show that fluoroethers are the first class of ether solvents to intrinsically support reversible lithium-ion intercalation into graphite without solvent co-intercalation at conventional salt concentrations. In full cells using a graphite anode, they enable 10-fold higher energy densities compared to conventional ethers, and better thermal stability over carbonate electrolytes (operation up to 60 °C) by producing a robust solvent-derived solid electrolyte interphase (SEI). As single-solvent–single-salt electrolytes, they remarkably outperform carbonate electrolytes with fluoroethylene carbonate (FEC) and vinylene carbonate (VC) additives when cycled with graphite–silicon composite anodes. Our molecular design strategy opens a new class of electrolytes that can enable next generation Li-ion batteries with higher energy density and a wider working temperature window. 

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5. In Situ Engineering of Inorganic‐Rich Solid Electrolyte Interphases via Anion Choice Enables Stable, Lithium Anodes

   https://doi.org/10.1002/adma.202305645  

   Weeks, Jason_A; Burrow, James_N; Diao, Jiefeng; Paul‐Orecchio, Austin_G; Srinivasan, Hrishikesh_S; Vaidyula, Rinish_Reddy; Dolocan, Andrei; Henkelman, Graeme; Mullins, C_Buddie (December 2023, Advanced Materials)

   Abstract The discovery of liquid battery electrolytes that facilitate the formation of stable solid electrolyte interphases (SEIs) to mitigate dendrite formation is imperative to enable lithium anodes in next‐generation energy‐dense batteries. Compared to traditional electrolyte solvents, tetrahydrofuran (THF)‐based electrolyte systems have demonstrated great success in enabling high‐stability lithium anodes by encouraging the decomposition of anions (instead of organic solvent) and thus generating inorganic‐rich SEIs. Herein, by employing a variety of different lithium salts (i.e., LiPF_6,LiTFSI, LiFSI, and LiDFOB), it is demonstrated that electrolyte anions modulate the inorganic composition and resulting properties of the SEI. Through novel analytical time‐of‐flight secondary‐ion mass spectrometry methods, such as hierarchical clustering of depth profiles and compositional analysis using integrated yields, the chemical composition and morphology of the SEIs generated from each electrolyte system are examined. Notably, the LiDFOB electrolyte provides an exceptionally stable system to enable lithium anodes, delivering >1500 cycles at a current density of 0.5 mAh g⁻¹and a capacity of 0.5 mAh g⁻¹in symmetrical cells. Furthermore, Li//LFP cells using this electrolyte demonstrate high‐rate, reversible lithium storage, supplying 139 mAh g_(LFP)⁻¹at C/2 (≈0.991 mAh cm⁻², @ 0.61 mA cm⁻²) with 87.5% capacity retention over 300 cycles (average Coulombic efficiency >99.86%). 

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