Optimizing Electrolyte Additive Loadings in NMC532/Graphite Cells: Vinylene Carbonate and Ethylene Sulfate

Abstract

A matrix of LiNi0.5Mn0.3Co0.2O2/graphite cells filled with 1.33 molal LiPF6 in EC:EMC:DMC (ethylene carbonate: ethyl methyl carbonate: dimethyl carbonate) (25:5:70 by volume) electrolyte and different weight percentages of vinylene carbonate (VC) and ethylene sulfate (DTD) electrolyte additives underwent prolonged charge-discharge cycling at 20 °C and 40 °C. The volume of gas produced during formation and cycle testing was measured. The impedance spectra of the cells before and after cycling was measured. After testing, the electrolyte was extracted for study by nuclear magnetic resonance spectroscopy (NMR) and gas chromatography/mass spectroscopy (GC-MS) to determine what changes in electrolyte composition had occurred. Some cells had their negative electrodes studied by scanning micro-X-ray fluorescence to quantify the amount of transition metals that transferred from the positive electrode to the negative electrode during the testing. Cells containing 1% VC or 2% VC with an additional 1% DTD by weight had the best capacity retention and lowest impedance growth. NMR and GC-MS suggest that these additive combinations promote increased electrolyte salt consumption which may represent a source of lithium to replenish the lithium inventory. Only a small amount of transition metals (0.03% or less) originating from the positive electrode active material was found on the negative electrode after testing. Most cells had over 1500 cycles at both 20 °C and 40 °C conditions.

Solution NMR of Battery Electrolytes: Assessing and Mitigating Spectral Broadening Caused by Transition Metal Dissolution

“…NMR investigation of degradation species in lithium-ion battery electrolyte solutions is typically performed ex situ (i.e., samples are from model experiments or from post-mortem cells). These experiments are generally performed by (i) mixing electrolyte solutions with (or extracting them into) deuterated solvents including dimethyl sulfoxide- d 6 (DMSO), − CD 3 CN, − CDCl 3 , − tetrahydrofuran- d 8 , − and acetone- d 6 ; or (ii) using electrolyte solutions neat ,− or diluted with/extracted into dimethyl carbonate − or ethyl methyl carbonate (EMC) . In case (ii), deuterated solvents are incorporated into, but are physically separated from, the sample (e.g., via use of a solvent capillary).…”

“…In case (ii), deuterated solvents are incorporated into, but are physically separated from, the sample (e.g., via use of a solvent capillary). NMR analysis has also been performed on dissolved solids, such as precipitates formed in electrolyte solutions and surface films on electrodes, with solvents including D 2 O, − DMSO- d 6 , − C 6 D 6 , acetone- d 6 , DCl in D 2 O, and EMC, while CD 3 CN has been found not to dissolve solid electrolyte interphase (SEI) components . In some cases, researchers rinse cell parts with solvents to extract the remaining electrolyte solution, but others do the same in order to dissolve surface films, so the difference between solution NMR of solutions and solution NMR of dissolved solids is not always clear.…”

Bioinspired Thermal Runaway Retardant Capsules for Improved Safety and Electrochemical Performance in Lithium‐Ion Batteries

“…[50] The addition of VC to the electrolyte enhances for LIB capacity retention. [51] However, a trade-off between capacity retention and the cell interfacial resistance was found when VC was added to the electrolyte. [52] Lim et al prepared VC microcapsules successfully by solvent exchange, which allows VC to diffuse through the microcapsule shell at an elevated temperature.…”

“…[ 50 ] The addition of VC to the electrolyte enhances for LIB capacity retention. [ 51 ] However, a trade‐off between capacity retention and the cell interfacial resistance was found when VC was added to the electrolyte. [ 52 ] Lim et al.…”

Key Advances of High-voltage Solid-state Lithium Metal Batteries Based on Poly(ethylene oxide) Polymer Electrolytes

“…为解决目前液态锂离子电池存在的潜在安全隐 患 [11][12][13][14] , 科研人员提出了使用固态聚合物电解质替代液 态碳酸酯电解质的方法 [6,[15][16][17][18][19][20][21] . 其中, 聚环氧乙烷(PEO) 固态聚合物电解质 [22] 是最经典的固态聚合物电解质体 系, 具有优异的可塑性, 可以被制作成不同的形状从而 满足特殊应用领域的差异化需求; 与此同时, PEO 固态 聚合物电解质与锂金属负极界面相容性好 [23][24] .…”