Elimination of Fluorination: The Influence of Fluorine-Free Electrolytes on the Performance of LiNi_1/3Mn_1/3Co_1/3O₂/Silicon–Graphite Li-Ion Battery Cells

Abstract

In the quest for environmentally friendly and safe batteries, moving from fluorinated electrolytes that are toxic and release corrosive compounds, such as HF, is a necessary step. Here, the effects of electrolyte fluorination are investigated for full cells combining silicon–graphite composite electrodes with LiNi 1/3 Mn 1/3 Co 1/3 O 2 (NMC111) cathodes, a viable cell chemistry for a range of potential battery applications, by means of electrochemical testing and postmortem surface analysis. A fluorine-free electrolyte based on lithium bis(oxalato)borate (LiBOB) and vinylene carbonate (VC) is able to provide higher discharge capacity (147 mAh g NMC –1 ) and longer cycle life at C/10 (84.4% capacity retention after 200 cycles) than a cell with a highly fluorinated electrolyte containing LiPF 6 , fluoroethylene carbonate (FEC) and VC. The cell with the fluorine-free electrolyte is able to form a stable solid electrolyte interphase (SEI) layer, has low overpotential, and shows a slow increase in cell resistance that leads to improved electrochemical performance. Although the power capability is limiting the performance of the fluorine-free electrolyte due to higher interfacial resistance, it is still able to provide long cycle life at C/2 and outperforms the highly fluorinated electrolyte at 40 °C. X-ray photoelectron spectroscopy (XPS) results showed a F-rich SEI with the highly fluorinated electrolyte, while the fluorine-free electrolyte formed an O-rich SEI. Although their composition is different, the electrochemical results show that both the highly fluorinated and fluorine-free electrolytes are able to stabilize the silicon-based anode and support stable cycling in full cells. While these results demonstrate the possibility to use a nonfluorinated electrolyte in high-energy-density full cells, they also address new challenges toward environmentally friendly and nontoxic electrolytes.

Aging and Charge Compensation Effects of the Rechargeable Aqueous Zinc/Copper Hexacyanoferrate Battery Elucidated Using In Situ X-ray Techniques

“…of ∼532 eV originates from C=O, hydrated species such as absorbed H 2 O (zeolitic or coordinating) in CuHCF, or organic OH species from the PVA binder. 48 , 53 , 54 We allocate the peak at ∼533 eV to C–O or SO species from ZnSO 4 ; 48 , 49 , 55 , 56 however, we could not distinguish between these species within the two envelopes. After 200 cycles, we do not observe any major changes in the O 1s spectrum, except for an increase in the overall peak area, which is confirmed as an increase in the relative O content by ∼5% ( Table S5 ).…”

Future Material Developments for Electric Vehicle Battery Cells Answering Growing Demands from an End-User Perspective

“…which has slightly lower solubility and conductivity in conventional carbonate solvents, but features good electrochemical performance below 4.2 V vs. Li/Li + [141]. Examples of LiBOB-based electrolytes in high-energy-density LIBs (Si-graphite and NCM111) have been reported featuring improved performance to that of LiPF 6 -based electrolytes at low current rates (85% capacity retention after 200 cycles at C/10) but still limited at high current rates (60% capacity retention after 300 cycles at C/2) [142]. Despite the general belief that the utmost requirement of the solid electrolyte interphase (SEI) is to be fluorinated [143], it has also been proven that an O-rich SEI is also able to passivate a silicon-graphite composite anode and provide good electrochemical performance in full cells with NMC111.…”

Designing Boron‐Based Single‐Ion Gel Polymer Electrolytes for Lithium Batteries by Photopolymerization

“…On the other hand, the use of boron‐based molecules, either as additives or primary salts, has become popular in electrolyte development, [ 10 ] as these have shown a positive effect on the formation of more stable solid electrolyte interphase (SEI) layers on the negative electrode surface and improved electrochemical performance in LIBs cyclability tests. [ 11 ] For example, Shim et al.…”

“…Researches also proved that the anionic immobility decreases the overpotential generated by anionic concentration gradients and slows down the dendritic growth rate on the negative electrode during the charge-discharge cycles of lithium metal batteries. [7][8][9] On the other hand, the use of boron-based molecules, either as additives or primary salts, has become popular in electrolyte development, [10] as these have shown a positive effect on the formation of more stable solid electrolyte interphase (SEI) layers on the negative electrode surface and improved electrochemical performance in LIBs cyclability tests. [11] For example, Shim et al [12] developed a series of semi-interpenetrated polymeric networks (IPNs) containing polyvinylidene fluoride (PVDF) and boron-based trimethacrylate crosslinkers with different lengths of their ethylene oxide (EO) chains, which exhibited excellent ability as anion-trapping groups when combined with liquid electrolytes based on LiTFSI salt and organic carbonates, obtaining t Li + values ranging from 0.4 to 0.8.…”