lithium difluorophosphate

• Catalog: OFC24389251
• CAS: 24389-25-1
• Category: Fluorinated Metal Phosphates
• Synonyms: Phosphorodifluoridic Acid, Lithium Salt (1:1)

• InChI Key: InChI=1S/F2HO2P.Li/c1-5(2,3)4;/h(H,3,4)
• Isomeric SMILES: YSNLHLJYEBEKMC-UHFFFAOYSA-N
• Canonical SMILES: [Li].OP(=O)(F)F

• Molecular Formula: LiPO2F2
• Molecular Weight: 107.91
• Appearance: White powder

• Hydrogen Bond Donor Count: 1
• Hydrogen Bond Acceptor Count: 4
• Rotatable Bond Count: 0
• Exact Mass: 108.98422603
• Monoisotopic Mass: 108.98422603
• Topological Polar Surface Area: 37.3Ų
• Heavy Atom Count: 6
• Formal Charge: 0
• Complexity: 62

Catalog	Purity	NMR
OFC24389251A	98%	Confirm to structure

Case Study

Lithium Difluorophosphate as an Electrolyte Additive for NMC/Graphite Batteries

Martinez AC, et al. Electrochimica Acta, 2022, 426, 140765.

This case study explores the role of Lithium Difluorophosphate (LDFP) in NMC/graphite-based cells, focusing on its effects on the solid electrolyte interphase (SEI) and the cathode electrolyte interphase (CEI).
LDFP is unique in that it is not electrochemically active within the typical operating voltage range of 0-4.3 V for NMC/graphite cells. This inactivity means LDFP does not directly participate in the formation of enhanced SEI or CEI layers through typical reduction or oxidation reactions. Despite this, LDFP influences the composition and properties of these interphases indirectly.
Mechanism of Action
During the first charge of the battery, the electrolyte carbonate solvents are reduced, forming classic lithium carbonate and alkyl carbonates in the SEI. This is a standard process in lithium-ion batteries. However, in the presence of LDFP, a unique reaction occurs: the fluorine atoms in the solvents are nucleophilically replaced by RO- and its derivatives. This reaction leads to the precipitation of additional lithium fluoride (LiF) and organofluorolithium phosphate compounds in the SEI.
Effects on SEI and CEI
The formation of these F- and P-based compounds, along with LiF, enhances the passivation properties of both the SEI and CEI. These compounds improve the stability of the SEI by preventing its dissolution at elevated temperatures. Moreover, they hinder the dissolution of transition metals (TMs) from the cathode, which can otherwise lead to deleterious crosstalk reactions between the cathode and anode. This improved passivation translates to better capacity retention and overall battery performance.
The composition of the CEI, influenced by LDFP, may include Ni fluorine or organophosphate components, further contributing to the stability of the cathode. These compounds create a robust protective layer that mitigates the degradation processes typically observed in high-energy-density batteries.

Lithium Difluorophosphate as an Additive to Improve the Electrochemical Performance of Lithium-ion Batteries

Zheng X, et al. Journal of Power Sources, 2019, 439, 227081.

This case successfully prepared and evaluated the performance of SiC and LiNi0.5Co0.2Mn0.3O2 electrodes in the presence of lithium difluorophosphate as an electrolyte additive.
Electrolyte preparation
The base electrolyte was a 1.0 M LiPF6 solution dissolved in a 1:1:1 mixture of ethylene carbonate (EC), ethyl methyl carbonate (EMC) and dimethyl carbonate (DMC) by weight. Vinyl fluorocarbonate (FEC) and lithium difluorophosphate (LiPO₂F₂) were added to the base electrolyte. The addition of FEC and LiPO₂F₂ was carried out in an argon-filled glove box, with the water and oxygen levels maintained at ≤1 mg/L to prevent contamination and ensure the purity of the electrolyte mixture.
Electrode preparation
The SiC electrode consisted of 80 wt% SiC600, 10 wt% carbon black and 10 wt% LA133. These materials were mixed in an aqueous solution and the mixture was then coated and pressed onto a copper foil. The coated electrodes were then dried at 100°C for 12 hours.
The LiNi0.5Co0.2Mn0.3O2 electrode contained 80 wt% LiNi0.5Co0.2Mn0.3O2, 10 wt% carbon black and 10 wt% polyvinylidene fluoride (PVDF). The materials were mixed in N-methylpyrrolidone (NMP) solvent, and then the mixture was coated and pressed onto aluminium foil. The electrode was dried at 100°C for 12 hours.
Manufacture of Button Half Cells
Two types of half-cells were assembled: SiC/Li and LiNi0.5Co0.2Mn0.3O2/Li.
SiC/Li half-cells: these cells were constructed using prepared SiC electrodes and lithium metal as counter electrodes.
LiNi0.5Co0.2Mn0.3O2/Li half-cells: these cells are assembled using LiNi0.5Co0.2Mn0.3O2 electrodes and Li metal as the counter electrode.
For each half-cell, 160 µL of electrolyte mixture was added. The electrolyte mixture contains the base LIB124 electrolyte as well as FEC and LiPO₂F₂ additives.
The CT2001A tester was used to evaluate the charge/discharge activity of the cells. The addition of 3% FEC + 2% LiPO₂F₂ to the electrolyte significantly improves the battery cycling performance compared to FEC or LiPO₂F₂ alone.