Optimization Study of Low Viscosity Ester-Based Co-solvents on Fast Charging Performance of Sodium Ion Batteries
The team led by Sathiya Mariyappan at the École Polytechnique recently published research titled "Practicality of Methyl Acetate as a Co-solvent for Fast Charging Na-ion Battery Electrolytes" in the journal Electrochimica Acta. This study systematically explores the improvement effects of low viscosity ester-based co-solvents on sodium ion battery electrolytes, achieving a breakthrough where 18650-type sodium ion batteries can charge to 84% SOC within 10 minutes, providing important references for the development of fast charging technology in sodium ion batteries.
Research Background and Significance
With the accelerated transition of global energy structures, electrochemical energy storage technologies are facing unprecedented development opportunities. Due to its abundant raw material resources and low cost advantages, sodium ion batteries are seen as a promising complementary technology to lithium-ion batteries. Particularly in applications such as large-scale energy storage and low-speed electric vehicles, sodium ion batteries demonstrate significant economic advantages.
However, existing sodium ion batteries still have notable shortcomings in fast charging performance. This is mainly due to technical bottlenecks such as insufficient ionic conductivity and poor interfacial stability within electrolyte systems. Traditional sodium ion battery electrolytes often exhibit severe polarization phenomena and capacity decay during high-rate charge-discharge cycles. Therefore, optimizing electrolyte engineering to enhance fast charging performance while ensuring cycling stability has become a key focus area for current research.
The Mariyappan team innovatively employed low viscosity ester compounds as co-solvents and systematically studied their impact mechanisms on the physical-chemical properties and electrochemical performance of electrolytes. This research not only provides specific optimization schemes for electrolyte formulations but also establishes structure-performance relationships between electrolyte components design and battery performance, offering theoretical guidance for subsequent studies.
Design and Characterization of Electrolyte Formulations
The research team selected methyl acetate (MA) and ethyl acetate (EA) as model co-solvents; by adjusting their proportions (4%-20%) in traditional carbonate-based electrolytes, they prepared a series of modified electrolytes. Systematic physical property tests revealed that adding 20% MA increased ionic conductivity from 13.65 mS/cm at 25°C to 15.2 mS/cm; under -10°C conditions it improved from 7.07 mS/cm to 9.8 mS/cm—this significant enhancement is primarily attributed to MA's low viscosity characteristics reducing ionic migration resistance.
Notably, although MA's dielectric constant is relatively low (6.68), experimental results indicate that moderate reductions in dielectric constants can actually help reduce ionic association effects—challenging conventional notions linking high dielectric constants directly with high conductivities—and revealing the importance of solvent structure regulation through systematic temperature-dependent studies which established quantitative relationship models between electrolyte composition-physical parameters-conductivity supporting theoretical foundations for electrolyte engineering design.
Systematic Evaluation Of Electrochemical Performance
Interfacial Stability Optimization
Using Na3V2(PO4)2F3(NVPF)/hard carbon(HC) full cell systems,the research team systematically evaluated electrochemical performances with ester-containing co-solvent electrolytes.Initial tests found that simply adding MA/EA resulted in decreased first-week efficiency indicating increased side reactions at interfaces.To address this issue,a multifunctional additive system containing0 .5 %NaODFB ,3 %VC ,3 %SN,and0 .2 %TMSPI was developed successfully reducing irreversible interfacial reactions by over40 %.Through comparative analysis across different temperatures,research showed that this additive system effectively suppressed decomposition rates under elevated temperatures.At55 °C conditions,electrolyte with additives maintained15 percentage points higher capacity retention than control groups.Notably,introductionofMAco-solvent slightly reduced thermal stability yet brought more pronounced improvementsinfast-charging capabilities reflecting balanced design principles regarding overallperformance evaluation considerations.. n Low Temperature Performance Breakthrough nIn0 °Clow-temperature environments,electrolyte containing20%MA exhibited exceptional performance advantages.Comparedto traditionalelectrolytestheirpolarization voltage dropped35%,effectively alleviating sodiu nucleation phenomena observedunderlowtemperature.Differentialcapacityanalysis(dQ/dV )revealedthatadditionofMAsignificantlyenhancedde solvation kineticsfor sodiummakingcharge transferresistance decreasefrom75 .28Ωto33 .45Ω.Theteamproposeddual explanationsregardingthemechanismsofMA:Ononehand,itimprovedbulkphaseionicconductivityensuringadequatesodium supply.Onanother hand,MAmayparticipateinsolvent reorganization processesreducinginterfacede solvationenergy barriers.This synergistic effect enabledmodifiedelectrolyteto maintaingoodinterface stabilitieswhilesignificantly enhancingiontransport efficienciesatlowtemperatures.. n ### Practical Verification Using18650 Batteries To validate laboratory findings’practicality,theresearchteamfabricatedcommercial-specification18650cylindricalbatteries.Testresults indicatedthatthebatteryusing20%MA+additive-electrolyteachieved84%SOCchargingcapacitywithin10minutesandretained97 .5%capacityafter100cycles.Thisperformanceindexfar exceededtraditionalelectrolyticsystems.Inhigh-temperature(45 °C)circular testing,theadvantagesofmodifiedelectrolyticsystems becameevenmoreapparent.After25cyclesitscapacityretentionwashigherby2 .7percentagepointscomparedtothecontrolgroupandend-of-charge driftphenomenonwaseffectivelysuppressed.These outcomesconfirmtheuniquevalueofMAsol ventintheimprovementoftotalbatteryperformancesettingfoundationsforitspracticalapplications... n ### Conclusion And OutlookThisstudyachievedbreakthroughsinfast-chargingperformanceofsodiumionbatteriesvia comprehensiveoptimizationstrategies.LowviscosityMAco-sovent’sintroductionallowedthe18650batterytoacquire10-minutechargingcapabilitywithoutsignificant sacrificesinotherperformances.Suchoutcomesclearlyremoveimportanttechnicalobstaclesfacingapplicationsofsodiumionbatteriesspecificallyinelectricvehiclesandlarge-scalestoragefields.Futurestudiescould furtherexplore:(1)Developingnewmulti-functionalco-soventsystemstooptimizeperformancesoverbroader temperature ranges;(2)Investigatingdeepersolvency-controlmechanismsontheelectrode/electrolytedesigns;(3)Advancingmass-productionprocessesformodifiedelectrolites.Withtheseadvancements,sodium-ionbatteriesshowpromisefindingoptimalbalancebetweenperformance&costmakingthemviableoptionsnext-generationenergy-storagetechnologies.