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US-12626955-B2 - Electrolytes for low temperature lithium batteries

US12626955B2US 12626955 B2US12626955 B2US 12626955B2US-12626955-B2

Abstract

An electrochemical cell configured to operate at low temperatures includes a cathode comprising a cathode active material, an anode comprising an anode active material, a separator disposed between the cathode and the anode, and an electrolyte. The electrolyte includes a fluorinated cyclic carbonate, a solid electrolyte interphase (SEI)-forming additive salt, a metal fluorophosphate salt, and a fluorinated organic compound.

Inventors

  • Zhengcheng Zhang
  • Mingfu He
  • Qian Liu

Assignees

  • UCHICAGO ARGONNE, LLC

Dates

Publication Date
20260512
Application Date
20230425

Claims (8)

  1. 1 . A method of cycling an electrochemical cell, the method comprising: operating the electrochemical cell at a temperature of about −40° C. to about —20° C.; wherein operating comprises the electrochemical cell having a capacity retention of at least 90% over 300 electrochemical cycles; wherein an electrolyte in the electrochemical cell comprises: a metal fluorophosphate salt, fluorinated cyclic carbonate, a solid electrolyte interphase (SEI)-forming additive salt, where the SEI is a layer of material that forms between the anode and the electrolyte produced by breakdown of electrolyte compounds during electrochemical operation of the electrochemical cell, a fluorinated compound represented by Formula I, Formula II, Formula III, Formula IV, or a mixture of any two or more thereof: wherein: R 1 is a C1-C6 alkyl group; R 2 is a C1-C6 alkyl group; R 3 is F or a fluorinated C1-C5 alkyl group; m is 1, 2, 3, or 4; and n is 1, 2, 3, or 4.
  2. 2 . The method of claim 1 , wherein the electrochemical cell is a lithium secondary battery, the metal fluorophosphate salt is a lithium hexafluorophosphate salt, and the SEI-forming additive salt is lithium difluoro(oxalato)borate (LiDFOB) salt.
  3. 3 . The method of claim 2 , wherein: the lithium secondary battery comprises an anode comprising graphite and a cathode comprising LiNi 0.6 Mn 0.2 Co 0.2 O 2 (NMC622); and operating the lithium secondary battery comprises charging and discharging the lithium secondary battery at a current of C/3 in a voltage window of 2.7 V vs Li/Li + to 4.4 V vs Li/Li + .
  4. 4 . The method of claim 1 , wherein the fluorinated cyclic carbonate is present in the electrolyte in a concentration of about 3% v/v to about 20% v/v.
  5. 5 . The method of claim 1 , wherein the SEI-forming additive salt is present in the electrolyte in a concentration of about 0.03 M to about 0.2 M.
  6. 6 . The method of claim 1 , wherein the fluorinated compound is represented by Formula V, VI, VII, or a mixture of any two or more thereof:
  7. 7 . The method of claim 1 , wherein the fluorinated cyclic carbonate is 4-fluoro-1,3-dioxolan-2-one (FEC).
  8. 8 . The method of claim 1 , wherein the SEI-forming additive salt is difluoro(oxalato)borate (DFOB) salt.

Description

GOVERNMENT RIGHTS The United States Government has rights in this invention pursuant to Contract No. DE-AC02-06CH11357 between the U.S. Department of Energy and UChicago Argonne, LLC, representing Argonne National Laboratory. FIELD The present technology is generally related to rechargeable electrochemical cells, and more specifically is related to operating rechargeable electrochemical cells at low temperatures. BACKGROUND Lithium-ion batteries (LIBs) are exploited in many portable electronics because of high energy density and high power density (lending long operation time) and cyclability (lending long life span). Moreover, LIBs are now being used widely in electric vehicles. However, the adoption of LIB technology has been constrained by the poor performance of conventional LIBs at low temperatures (i.e from about 0° C. to about −50° C.). This poor performance impacts the ability to use LIBs in certain regions and/or seasons. Therefore, there is need to develop LIBs with adequate low temperature performance. SUMMARY One of the reasons for the poor performance of conventional LIBs at low temperature is a result of the conventional electrolyte. Conventional electrolytes typically include a large amount ethylene carbonate (EC) solvent, which impairs LIB performance at low temperature. At room temperature, EC helps facilitate the formation of a stable solid-electrolyte-interphase (SEI) layer. At low temperatures, LIBs with EC-based electrolytes suffer from sharp drops in capacity and rate capability and severe degradation at low temperatures. Furthermore, electrolytes containing a high proportion of EC tend to freeze at low temperatures below −20° C. because EC has a high melting point (34° C.). To address the problem of EC freezing, tertiary or quaternary carbonate systems with a low portion of EC have been proposed, but these systems still suffered from poor rate capability at low temperatures. In one aspect, an electrochemical cell is provided comprising a cathode comprising a cathode active material; an anode comprising an anode active material; a separator disposed between the cathode and the anode; and an electrolyte. The electrolyte comprises a fluorinated cyclic carbonate; a solid electrolyte interphase (SEI)-forming additive salt, where the SEI is a layer of material that forms between the anode and the electrolyte produced by breakdown of electrolyte compounds during electrochemical operation of the electrochemical cell; a metal fluorophosphate salt; and a fluorinated compound represented by Formula I, Formula II, Formula III, Formula IV or a mixture of any two or more thereof: In any of the compounds represented by Formula I, II, III, or IV, R1 is a C1-C6 alkyl group; R2 is a C1-C6 alkyl group; R3 is F or a fluorinated C1-C5 alkyl group; m is 1, 2, 3, or 4; and n is 1, 2, 3, or 4. In some embodiments, the fluorinated cyclic carbonate may be present in the electrolyte in a concentration of about 3% v/v to about 20% v/v. The fluorinated cyclic carbonate may be present in the electrolyte in a concentration of about 5% v/v to about 15% v/v. The SEI-forming additive salt may be present in the electrolyte in a concentration of about 0.03 M to about 0.2 M. The SEI-forming additive salt may be present in the electrolyte in a concentration of about 0.05 M to about 0.15 M. The fluorinated compound may be represented by Formula V: The fluorinated compound may be represented by Formula VI: The fluorinated compound may be represented by Formula VII: The fluorinated cyclic carbonate may be 4-fluoro-1,3-dioxolan-2-one (FEC). The fluorinated cyclic carbonate may be 4,5-difluoro-1,3-dioxolan-2-one (DFEC). The SEI-forming additive salt may be a difluoro(oxalato)borate (DFOB) salt. The electrochemical cell may be a lithium secondary battery, the metal fluorophosphate salt may be a lithium hexafluorophosphate salt, and the SEI-forming additive salt may be a lithium difluoro(oxalato)borate salt (LiDFOB). R1 may be —CH3, —CH2CH3, —CH2CH2CH3, or —CH2CH2CH2CH3. R2 may be —CH3, —CH2CH3, —CH2CH2CH3, or —CH2CH2CH2CH3. R3 may be —F, —CF3, —CH2F, —CHF2, —CH2CF3, or —CH2CF2H. In an aspect, a method of cycling an electrochemical cell is provided. The method comprises operating the electrochemical cell at a temperature of about −40° C. to about −20° C.; wherein operating comprises the electrochemical cell having a capacity retention of at least 90% over 300 electrochemical cycles. The electrolyte in the electrochemical cell includes any of the electrolytes disclosed here. In some embodiments, the electrochemical cell may be a lithium secondary battery. The lithium secondary battery may include an anode comprising graphite and a cathode comprising LiNi0.6Mn0.2Co0.2O2 (NMC622). Operating the lithium secondary battery may include charging and discharging the lithium secondary battery at a current of C/3 in a voltage window of 2.7 V vs Li/Li+ to 4.4 V vs Li/Li+. In an aspect, an electrolyte is provided. The electrolyte includes a