How Lithium Difluorophosphate (LiDFP) Improves Battery Performance?

Lithium difluorophosphate (LiDFP, LiPO₂F₂) serves as a crucial component in electrolyte formulations for lithium batteries, where it enhances both performance and stability when pairing with challenging electrode materials like high-voltage cathodes and lithium metal anodes. The growing need for high-energy-density batteries makes LiDFP essential for improving cycling stability, rate performance, and battery lifespan. This research examines LiDFP's functionality and advantages as well as its limitations in lithium battery applications while reviewing current developments and prospective improvements.

Catalog	Name
OFC24389251	lithium difluorophosphate

What is lithium difluorophosphate, and how does it improve battery performance?

As an electrolyte additive, LiDFP stands out because it promotes the development of stable solid electrolyte interphase (SEI) and cathode electrolyte interphase (CEI) layers that help protect electrodes. These interfaces play an essential role in securing electrode materials throughout cycling processes while minimizing electrolyte degradation and corrosion, especially in aggressive battery chemistry.

The SEI and CEI layers play crucial roles in maintaining electrode performance and durability, especially during operations at high voltages and elevated temperatures. The SEI layer develops on the anode of traditional lithium-based batteries, while the CEI layer develops on the cathode. These protective layers prevent unwanted electrolyte reactions at the electrode surface while enhancing battery stability through electrode material degradation limitation. Electrolyte integration with LiDFP strengthens these protective layers and enhances their ability to stabilize the electrode/electrolyte interface.

Fig.1 Based on the comparison of the morphology observed with SEM, LiDFP contributes to the formation of thin and dense SEI/CEI^[1].

The initial purpose of adding LiDFP to lithium-based battery electrolytes was to prevent the breakdown of lithium hexafluorophosphate (LiPF₆), which is a frequently used salt in these electrolytes. The breakdown of LiPF₆ results in the creation of harmful substances like HF, which leads to significant harm to battery parts. The reaction that produces LiDFP from LiPF₆ decomposition becomes minimized through LiDFP addition, which results in improved electrolyte stability and stops the emission of dangerous gases.

How does lithium difluorophosphate enhance different electrode materials?

When LiDFP is paired with aggressive electrode materials, its beneficial impact on battery performance becomes especially apparent. The application of LiDFP has shown to improve both cycling stability and rate capability across diverse cathode and anode materials.

Electrode Material	Effect of LiDFP
LiNi0.5Mn1.5O4 (LNMO)	Enhanced cycling stability and rate performance.
LiNixMnyCo1-x-yO2 (NMC)	Improved charge retention and reduced impedance.
LiMn2O4	Higher efficiency in high-voltage conditions.
LiCoO2	Extended lifespan and stability under stress.
Li Metal	Protection from dendrite growth and electrolyte degradation.
Si and Si@C	Enhanced cycling stability due to improved SEI formation.

LiDFP performs multiple functions that include but are not limited to stabilizing the electrode/electrolyte interface. The material protects aluminum current collectors from corrosion when exposed to electrolytes containing lithium bis(fluorosulfonyl)imide (LiFSI) or lithium bis(trifluoromethylsulfonyl)imide (LiTFSI). The protective effect provided by LiDFP improves battery lifespan under demanding operating conditions.

What are the challenges and improvements for LiDFP usage?

Numerous challenges exist when using LiDFP in lithium-based batteries despite its potential advantages. The main obstacles in the application of LiDFP pertain to its solubility characteristics along with the elasticity properties of the resulting SEI/CEI and the consistency in forming interfacial layers.

Overcoming LiDFP's Low Solubility

LiDFP demonstrates limited solubility within common electrolyte solvents, including carbonates, which presents a major drawback. The limited solubility of LiDFP limits its use because elevated concentrations create more viscous electrolytes that degrade battery functioning. Scientists have tested different solvents other than carbonates to raise LiDFP solubility and improve its performance. The process of generating LiDFP through the in situ decomposition of LiPF6 represents a further research avenue that operates independently of solubility constraints.

Fig.2 LiDFP was formed in situ by adding Li₂CO₃ to the standard electrolyte (STD) at a temperature of 40 °C^[1].

Enhancing Elasticity of LiDFP-Derived SEI/CEI

LiDFP-derived SEI/CEI contains abundant inorganic elements such as Li₃PO₄ and LiF, which provide strength but fail to handle the volume changes during battery cycling, particularly in silicon (Si) electrodes. The SEI/CEI elasticity is increased through the introduction of organic co-additives, including fluoroethylene carbonate (FEC), vinylene carbonate (VC), and difluoroethylene carbonate (DiFEC). When co-additives decompose and polymerize, they generate a uniform organic layer, which moderates the stiffness of inorganic materials to create an SEI/CEI structure that maintains both strength and flexibility.

Uniform Precipitation of LiDFP

The uniform deposition of LiDFP on electrode surfaces remains a critical obstacle for consistent SEI/CEI formation. The new method created by researchers utilizes fluoroether as an antisolvent to reduce carbonate solvent-Li⁺ interactions, which results in an even distribution of LiDFP precipitation on electrodes. The technique enhances both the reproducibility and efficiency of LiDFP integration within the electrolyte to achieve reliable interfacial layer effectiveness.

LiDFP serves as an essential component in lithium battery technology. The development of battery technologies will lead to broader applications of LiDFP in aggressive electrode materials and high-performance chemistries, which will advance the creation of efficient and durable energy storage systems. Alfa Chemistry leads the way in producing advanced electrolyte additives like LiDFP to address the needs of contemporary energy storage technologies. For more information, please contact me.

Reference

1. Wang A., et al. (2023). "Lithium Difluorophosphate as a Widely Applicable Additive to Boost Lithium-Ion Batteries: a Perspective." Advanced Functional Materials. 33(8), 2211958.