Suppressing Electrode Crosstalk and Prolonging Cycle Life in High‐Voltage Li Ion Batteries: Pivotal Role of Fluorophosphates in Electrolytes

Abstract

High-voltage Li ion batteries are compromised by lower cycle life due to enhanced degradation of cathode material, for example LiNi 0.5 Co 0.2 Mn 0.3 O 2 (NCM523). Crucial part is the initiated electrode crosstalk, that is transition metal (TM) dissolution from the cathode and subsequent deposition on the anode, as it forces formation of high surface area lithium, capacity losses and risk of Li dendrite penetration, finally leading to an abrupt end-of-life (= rollover failure). Hence, suppression of this failure cascade is the pivotal strategy to prolong cycle life. A pragmatic approach was presented: the electrolyte manipulation towards formation/presence of fluorophosphates, as they effectively suppressed electrode crosstalk through TM scavenging. Either, they could be intrinsically formed, e. g. by elimination of ethylene carbonate (EC) solvent (= EC-free electrolyte), or simply externally added, e. g. using (good-soluble) lithium difluorophosphate electrolyte additive. Their effectiveness was demonstrated for conventional ECbased and EC-free electrolytes at limiting conditions (4.5 and 4.6 V, respectively). In parallel to supportive approach combinations (e. g. coating), also destructive combinations were highlighted, that is approaches, which even decrease the fluorophosphate content, e. g. vinylene carbonate additive in EC-free electrolytes. Finally, by demonstrating the value of (concentration-optimized) fluorophosphates, appropriate benchmark electrolyte formulations for high-voltage LIBs were discussed.

Lithium Difluorophosphate: A Boon for High Voltage Li Ion Batteries and a Bane for High Thermal Stability/Low Toxicity: Towards Synergistic Dual Additives to Circumvent this Dilemma

“…50 cycles [62] . In line with reported findings, the use of lithium difluoro phosphate (LiDFP) results in best capacity retentions when compared with the the typical electrolyte additives vinylene carbonate (VC) and fluoroethylene carbonate (FEC) and is consequently regarded as electrolyte additive for enabling high voltage application of Li‐ion batteries [50,55] …”

“…Besides their well‐known beneficial impact on interfacial properties, [51–53] the lithium difluorophosphate (LDFP) additive is able to suppress electrode crosstalk via scavenging TMs before they can reach and damage the anode, finally prolong the cycle life; in particular at high voltage (>4.3 V) [54] . Consequently, LiDFP can be reasonably regarded as one of the SOTA electrolyte additives in current electrolyte formulations in LIBs also for high voltage applications [51–53,55] …”

Regulating Dynamic Electrochemical Interface of LiNi0.5Mn1.5O4 Spinel Cathode for Realizing Simultaneous Mn and Ni Redox in Rechargeable Lithium Batteries

“…The 2 m EC‐free DMC electrolyte showed better reduction stability than an EC‐free EMC‐based electrolyte (Figures S20, S22, and S23, Supporting information), while previous studies used EMC‐based electrolytes to improve the high‐voltage performances of LIBs. [ 55–57 ]…”

“…The 2 m EC-free DMC electrolyte showed better reduction stability than an EC-free EMC-based electrolyte (Figures S20, S22, and S23, Supporting information), while previous studies used EMC-based electrolytes to improve the highvoltage performances of LIBs. [55][56][57] In summary, the simple modification of electrolyte formulation, including solvent composition and salt concentration, substantially affects the stability of the LNMO cathodes when cycled within a WVR. We believe that search for better electrolytes to achieve practically viable cycle life will be an essential topic for further studies.…”

Assessment of the calendar aging of lithium-ion batteries for a long-term—Space missions

“…Non-etheless, there are design decisions and components that may significantly influence the LIBs' storage life (Geisbauer et al, 2020). For instance, the selection of an appropriate electrolyte as a crucial component to limit the capacity degradation during storage (Klein et al, 2022). Electrolytes are created by dissolving lithium salts in solvents and operate as ionic charge carriers (Xu and Angell, 2002).…”