Carbon Nanotubes for High-Performance Lithium …

1 Carbon Nanotubes for High-Performance Lithium -Ion BatteriesCarboPowerDavid Ensling1, Alberto Varzi2, Martin Kreis3, Corina T ubert2, Sebastian Schebesta11 VARTA Microbattery GmbH2 FutureCarbon GmbH3 Zentrum f r Sonnenenergie- und Wasserstoff-Forschung (ZSW)Outline Introduction Project Lithium -Ion Battery Processing Material Evaluation Anode Cathode ConclusionsCarboPower21/31/2012 Evaluation of Carbon Nanotubes (CNT) as conductive agent for next-generation Lithium ion batteries Improved energy density due to smaller amounts of conductive additives Increased power density due to high conductivityCarboPowerFutureCarbonPrepar ation, purification, functionalization and dispersion of CNTsVarta MicrobatterySlurry modification, electrode preparation, test / full cellsZSWC haracterization of raw materials and electrodesCarboPower31/31/2012 CNT Manufacturing and Refinement ProcessesCCVD Process for Base Material Synthesis (Catalytic Assisted Chemical Vapor Deposition)Current Production Capacity.

2 ~ 1 ton per yearShort-term upscaleable to >10 tons per year, depending on demand CarboPower41/31/2012 CNT PropertiesSEM (electrode)TEM- MWCNTs (5 to 9 walls)- average outer diameter: 13 nm- length: 1-100 m- BET: ~ 290 m2/g CNT-Dispersions- Water (CMC-binder)- NMP / NEP (PVDF-binder)CarboPower51/31/2012 Preparation of Electrodes for Lithium -Ion BatteriesCoatingCuttingProcess of components on Al- or Cu-foil (10 20 m) of Electrodes: Active material, LiCoO2, Graphite (90%) Conductive agents, Carbon black, CNTs(5%) Binder, PVDF, CMC (5%)CarboPower61/31/2012 Typical processes during cell fabricationStacking(Winding)TaggingPacki ngFinishingActivatingExample: stacked cell1.

3 Stacking of single electrodes and separator2. Tagging of current collectors3. Packing in Pouch4. Filling with electrolyte5. Formation (first charging)CarboPower71/31 : active anode materialCNT: conductive agent in anode and cathodeGraphiteabxyzLayered TM-OxideComposite electrodes:active material/binder/conductive agentLithium-ion batterySolid-electrolyteinterphase(SEI)C arboPower81/31/2012 Negative Electrodes - MWCNTs as Lithium HostGraphite(BET: ca. 4 m2g-1)01002003004005006000123 E vs. Li/Li+ / VSpecific Capacity / mAh g-1 SEII rrev. loss02004006008001000 1200 1400 1600 18000123 E vs. Li/Li+ / VSpecific Capacity / mAh g-1 MWCNTs(BET: ca.)

4 300 m2g-1)SEII rrev. loss Different insertion mechanism compared to graphite (absence of a charge/dischargeplateau) still unclear due to difficulty in determining the Li storage sites Huge irreversible capacity due toSolid Electrolyte Interphase (SEI) proportional tosurface area!Not suited as active anode material !CarboPower91/31/2012 Negative Electrodes - MWCNTs as Conductive Agent1 CLong-term cycling NMC/CNT vs. Graphite/CNTG raphite Very good cycling stability, butinacceptable initial losses (<1V) Capacity is retained up to 80% after1000 cycles in the potential window 1-3 VLong-term cyclingTiO2/CNTvs. - Electrodes - MWCNTs as Conductive AgentCapacity RetentionSEMCNT /BinderNCMM odelLong-term cycling stability of half cells (NMC vs.

5 Li) MWCNTs avoid the contact loss between the particlesproviding a capacity retention up to 75% after 250 cycles at 2 CCarboPower111/31/2012 Promising results for CNT-cathodes combination with standard anode in full cellExperiment Variation of conductive additives (CNT, Carbon black)Full-cellsAnodeCathodeAGraphiteNMC + Carbon / referenceBGraphiteNMC + more carbonCGraphiteNMC + CNTCBCB++CNTCB = Carbon blackCarboPower121/31/2012 Positive Electrodes - MWCNTs as Conductive AgentRate Capability of full cells (NMC/CNT vs. C)BAC improved rate performance for CNT electrodes only slight improvement with high carboncontent over reference Capacity3C5C8C(A) Reference74%45%14%(B) High Carbon 77%56%22%(C) CNT82%61%36%CarboPower131/31/2012C-rate: C (mA) = Cap.

6 (mAh)/hPositive Electrodes - MWCNTs as Conductive AgentLong-term cycling stability of full cells (NMC/CNT vs. C)BAC better cycling stability for CNT electrodes thanfor reference comparable to high Carbon content electrodes(energy density)Capacity250500750(A) Reference92%89%86%(B) High Carbon 94%91%89%(C) CNT96%93%90%CarboPower141/31/2012 The Strategy: functionalizationImproved particle-particle connection(better dispersibility in polar solvents)Chemical oxidationMWCNTs-COOHCNTs unbundlingpristine MWCNTs(highly agglomerated) furtherimprovetheelectrochemicalperforma nce completely replace common additives withthe lowest CNT amount possibleThe aim was toIn principle use of CNTs result in lower percolationthreshold than Carbon black and/or graphiteIn practice MWCNT shavestrongtendencytoagglomerate leading to poor connection ofthe active materials particlesCarboPower151/31/2012 NCM-based cathodes (~ 10 m)

7 90 wt% active material, 2 wt% Conductive Agent, 8 wt% BinderCarboPower161/31/2012 LiFePO4-based cathodes (~ 500nm)90 wt% active material, 2 wt% Conductive Agent, 8 wt% BinderCarboPower171/31/2012 NCM-based cathodesLiFePO4-based MWCNTs-COOH with MWCNT swith Carbon black E vs. Li/Li+ / VSpecific Capacity / mAh g-1C/D rate: 1C020 40 60 80 100 120 1400204060-Zim / Ohm -ZZreal / Ohmsurface MWCNTs-COOH with MWCNT swith Carbon black E vs. Li/Li+ / VSpecific Capacity / mAh g-1C/D rate: 1C electrochemical performance appears to be affectedby surface passivation reaction improved connection network among the active particles,,however dramatic fade of electrochemical performance MWCNTs-COOH provide an enhanced connectionnetwork among the nano-sized LFP particles thusimproving the capacity for LFP cathodes the electrode kinetics appearsto be mainly dominated by resistivity issuesCarboPower181/31/2012 ConclusionsCathodes Significant increase of long-term cycling stability Improvement of rate capability (power density)

8 Increase of rate capability Increase of long-term cycling stability However, large initial losses for graphite due to SEI formation Stable above 1V vs. Li/Li+( TiO2); Problem with graphiteAnodes More difficult than classic conductive agents ( Carbon black, graphite particles) Use of CNTs requires modification of processingProcessabilityCarboPower191/31 /2012 Comparison CNT as conductive additiveCarboPower201/31/2012consumer,EV Power tools,HEVA utomotive,Grid storageThank you!CarboPower211/31/2012