Nanofibers and Scalable Processes for Energy Storage and Wearable Technology

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1 Nanofibers and Scalable Processes for Energy Storage and Wearable Technology Yong Lak Joo School of Chemical and Biomolecular Engineering Cornell University Cornell Institute of Fashion and Fiber Innovation (CIFFI) Meeting May 17, 2015

Progress in Battery Technology Since 1990, computers have increased rapidly in both speed and power. Improvement of battery technology has stagnated over the past 20 years.

2 Progress in Battery Technology Since 1990, computers have increased rapidly in both speed and power. Improvement of battery technology has stagnated over the past 20 years. Limits of Materials Invention The materials science of rechargeable batteries has changed little in 20 years due to inherent challenges with intercalation chemistry. Improvement Multiple Cell Architecture and Packing Strides have been made to improve the efficiency of packing more materials into the same exterior package. Substrates and Inactive Pieces In addition to improving cell geometry, inactive components such as current collectors, separators, casings, and even binders have been optimized. Nanofiber-based Technology Scalable nanofiber process would result in a meaningful materials upgrade to increase cell-level energy density. 2

3 Rechargeable Li-ion Batteries Li is most electropositive (-3.04 V) and the lightest metal (equivalent weight M = 6.94 g/mol, density = 0.53 g/cm 3 ). Issues and Challenges facing Rechargeable Li Batteries, Nature (2001) No memory effect, low self-discharge rate, and wide operation temp. range

4 Lithium Ion Battery Overview Conventional Li Ion Battery Material Potential Anode Materials Lithium Storage Capacity (mah/g) Volume Change C C 6 Li 372 ~5 % Si SiLi ~420% Pulverization C + xli + charge + xe Li x C discharge discharge Li (1-x) CoO 2 + xli + + xe LiCoO 2 charge Si nanofibers with nanostructures can serve as an excellent Li-ion battery anode

5 Electrospinning: Electrohydrodynamics for Nanofibers Electrospinning uses a strong electric field to accelerate and thin a fluid jet, producing very thin fibers (50 nm 1 m). Process Stages Jet initiation and acceleration in straight line stable jet 1 1 R R ~ R stable_final 0 0 Emergence and propagation of Instability 1 1 R R ~ R whipping_final stable_final stable_final Collection of solidified fibers on grounded collector plate R 1 R 1000 fiber 0 Polymer Solution or Melt HV Grounded Collector Micro pump Stable Jet O t O Whipping Instability (10 )s ; process (10 )s 5

Nanofibers with Hierarchical Structures Useful as non-woven mats with high specific surface area

Can be utilized in integration of length scales Fiber diameter < O(1 m) Nanostructures in Nanofiber

Small (2008) Human Hair 100 m 1 m Electrospun Nanofibers (100 nm dia.

6 Nanofibers with Hierarchical Structures Useful as non-woven mats with high specific surface area Surface area to volume (mass) ratio 1 D (Diameter) Catalysis/Filtration/Membranes/Protective Clothing Can be utilized in integration of length scales Fiber diameter < O(1 m) Nanostructures in Nanofiber Mats Fiber length >> O(1 m) TEM Image of PS-b-PI/ Magnetite Nanofibers Kalra, Joo et al. Small (2008) Human Hair 100 m 1 m Electrospun Nanofibers (100 nm dia.) Surface Area > 10 m 2 /g ~ O(1 nm) ~ O(10 nm) ~ O(100 nm) >> O(1cm) Nanofiber Mat Nanofiber Self-Assembly for NP Placement Functional Nanoparticles (NP) 6

Ceramic or Metal Nanofibers via Water-Based Electrospinning Pure Ceramic, Metal and their Hybrid Nanofibers via Water-based Electrospinning of Their Precursors Heating Mixing Electrospinning Metal or

7 Ceramic or Metal Nanofibers via Water-Based Electrospinning Pure Ceramic, Metal and their Hybrid Nanofibers via Water-based Electrospinning of Their Precursors Heating Mixing Electrospinning Metal or Ceramic Precursor in Polymer Solution Micro Pump Aqueous Polymer Solution with High Metal Precursor Loading (Metal: Polymer = 4:1) Covalent Bonds Induce Homogeneous Metal Precursor Distribution HV Thermal treatment Collector Hansen, Cho, and Joo, Small (2012) 7

Modeling of Viscoelastic Jets in Solution Electrospinning Viscoelastic, non-conducting (PIB/PB) jets Viscoelastic, conducting (PEO/water) jets Initial Jet Carroll and Joo, Phys.

8 Modeling of Viscoelastic Jets in Solution Electrospinning Viscoelastic, non-conducting (PIB/PB) jets Viscoelastic, conducting (PEO/water) jets Initial Jet Carroll and Joo, Phys. Fluids (2006) Initial Jet Axisymmetric instability Carroll and Joo, JNNFM (2008) Carroll and Joo, Phys. Fluids (2009) Axisymmetric instability Capillary mode Conducting mode 8

9 Discretized Bead Modeling of Electrospinning Consider a series of discrete beads connected by viscoelastic springs with solvent contribution: Each of beads moves according to Newton s Law: 2 d r m F... 2 v Fst Fg Fa dt very easy to incorporate various forces into the model, such as viscoelastic tension, surface tension, gravity, aerodynamic drag, electromagnetic force 9

10 Application of Model to Initial Jet of PEO/water Conductivity of PEO/water is so high that all the current can theoretically be conducted through the jet. We consider that the electric field interacts with charge within a Debye layer at the jet surface 1mm PEO-2M/water solution, V = 10kV Carroll and Joo, J. App. Phys. (2011) 10

11 Modeling of Whipping Motion during Electrospinning Discrete Modeling of a Model Polymer Jet High Speed Image of PVP/water Jet 11

Typical Profiles of Variables for Entire

10 4 Jet Radius (m) 10-4 Stress (N/m 2 ) 10 3

(m) 10 1 10-4 10-3 10-2 10-1 Contour Length

2 0 10-4 10-3 10-2 10-1 Contour Length (m)

12 Typical Profiles of Variables for Entire Electrospinning Descretized modeling predicts rapid changes in most of key variables (radius, stress, chain orientation, surface charge density, etc.) near the onset of the whipping motion Jet Radius (m) 10-4 Stress (N/m 2 ) Contour Length (m) Contour Length (m) Chain Orientation Factor Contour Length (m) Surface charge density (C/m 2 ) 6 x Contour Length (m) 12

polymeric, metallic and ceramic nanofibers in a single platform with

13 Scalable Nanofiber Manufacturing Process: Gas-assisted Electrospinning Gas-assisted electrospinning process creates polymeric, metallic and ceramic nanofibers in a single platform with higher production rate. Single Nozzle Q = 0.5 ml/min Zhmayev, Cho and Joo, Polymer (2010) 13

14 Gas-assisted Electrospinning: Control of Nanoinclusion Dispersion Combination of strong electric field and high speed air stream in gas-assisted electrospinning (GAES) offers much more effective dispersion of nanoinclusions in polymer, ceramic and metal matrix than conventional electrospinning. Conventional Electrospinning vs. Gas-assisted Electrospinning SiO 2 nanoparticles (33 wt%) in PVA nanofiber E V air 1 m 1 m 14

orientation of graphene nanoribbons (GNRs)

15 Gas-assisted Electrospinning: Control of GNR Dispersion The dispersion and orientation of graphene nanoribbons (GNRs) can greatly be enhanced by gas-assisted electrospinning (GAES). Normalized dispersion area Electrospinning GAES 5.5 [SCFH] GAES 9 [SCFH] GAES 11 [SCFH] GNRs Volume concentration of GNR [%] At 5% GNR (67B) Q air = 0 Q air = 5.5 Q air = 9 Q air = 11 15

Nanofibers in Li-ion Batteries via Water-based Spinning Why nanofibers are able to

gas-assisted water-based electrospinning Nonwoven nanofiber mat control: Shape and

accessible to electrolyte High porosity for separator Compositional control within

Nanofiber 16 Anode Nanofiber Separator Nanofiber Cathode Flexibility of material

16 Nanofibers in Li-ion Batteries via Water-based Spinning Why nanofibers are able to overcome lithium-ion battery issues: Low cost, high throughput manufacturing based on gas-assisted water-based electrospinning Nonwoven nanofiber mat control: Shape and porosity control Highly conductive interconnected network Many reaction sites accessible to electrolyte High porosity for separator Compositional control within each nanofiber: Excellent dispersion control and uniformity Consistent performance Nanofiber 16 Anode Nanofiber Separator Nanofiber Cathode Flexibility of material morphology Allows for many form factors of battery (button, coin, cylindrical, pouch, and prismatic cells) 16

Anodes Based on Si rich Carbon Hybrid Nanofibers Si Nanoparticle PVA+ Si NPs

Electrospinning Anode Li-ion battery Carbon Nanofiber Backbone Accommodation

carbon fibers exhibit a better capacity retention than Si NPs, but has a

17 Anodes Based on Si rich Carbon Hybrid Nanofibers Si Nanoparticle PVA+ Si NPs Electrospinning solution Carbonization Gas-Assisted, Water-based Electrospinning Anode Li-ion battery Carbon Nanofiber Backbone Accommodation of Lithium within Silicon Carbon Nanofiber Half cell performance Si rich carbon fibers exhibit a better capacity retention than Si NPs, but has a room for improvement. Si NP/C fibers 1 Si NPs 17 1 Kim and Joo, et al., ChemElctroChem (2014) 17

Functionalization of hexadecyl-group: good dispersion ability in electrospinning solution

18 Graphene Nanoribbons (GNR) in Si Rich Carbon Fibers Carbon fiber Si NPs ACS Nano (2012) 6, 4231 Graphene nanoribbons (GNRs): unzipped from multi-wall carbon nanotubes by chemicals Functionalization of hexadecyl-group: good dispersion ability in electrospinning solution (up to 12 mg/ml) GNR/Si/C fibers: GNRs can prohibit the pulverization and SEI formation for Si NPs 18

Graphene Nanoribbons (GNR) in Si Rich Carbon Fibers Inclusion of GNRs in the Si rich carbon nanofiber anode greatly improves capacity retention as well as rate

19 Graphene Nanoribbons (GNR) in Si Rich Carbon Fibers Inclusion of GNRs in the Si rich carbon nanofiber anode greatly improves capacity retention as well as rate capability. at 0.1C GNR/Si NP/C fibers 2 Si NP/C fibers 1 Si NPs 1.Kim and Joo, et al., ChemElctroChem (2014) 2.Kim, Chakrapani, Joo, et al. Nano Energy (2015, in press) 19

Direct Deposit of GNR/Polymer Hybrid Nanofibers for LIB Anode Direct

collector (by-passing carbonization, sonication, vacuum mixing,

) GNRs in Binder Polymer (PVA, PAA, PVDF, etc.

GNR/Si NPs Dispersed in Polymer Nanofiber GNR/Si NPs/polymer

step process - High capacitance due to large surface area and thin

20 Direct Deposit of GNR/Polymer Hybrid Nanofibers for LIB Anode Direct incasing of Si NPs in GNRs in one-step electrospinning to current collector (by-passing carbonization, sonication, vacuum mixing, blading, calendaring, etc.) GNRs in Binder Polymer (PVA, PAA, PVDF, etc.) Solution + Si NPs HV Syringe pump High speed gas stream Si NPs GNR/Si NPs Dispersed in Polymer Nanofiber GNR/Si NPs/polymer Nanofiber Mat on Metal (Al or Cu) Current Collector Advantages - One step process - High capacitance due to large surface area and thin thickness - Effective electron transfer due to high conductivity of GNR - Incorporation of Si NPs in GNR for higher capacity Electrodes for Li-Ion Batteries 20

FT IR analysis of Hybrid Si Anodes Before heat treatment The PVA polymer in hybrid assemblies has several bonds of O H, C H, C H 2 and C O before modification of heat treatment (Figure a) After heat

21 FT IR analysis of Hybrid Si Anodes Before heat treatment The PVA polymer in hybrid assemblies has several bonds of O H, C H, C H 2 and C O before modification of heat treatment (Figure a) After heat treatment After modification, the PVA polymer was removed the bonds of O H, C H, and C H 2 (Figure b) Before heat treatment, the hybrid assemblies anode is not working because of poor electrical conductivity and charge transfer by non conductive PVA polymer. After heat treatment, the hybrid anode is [Not working battery ] [working and stable battery] well working by modifying PVA polymer to improve charge transfer feature 21

22 Directly-deposited Si NP/CNT/PVA Nanofiber Anode Capacity (mah/g) Capacity (mah/g) Electrospinning vs. Gas-Assisted Electrospinning PVA:Si:CNTs = 1:1:0.14 at 0.1C GA-ES ES at 1C Cycle No. Significant improvement in capacity due to better dispersion of Si NPs and CNTs ES GA-ES 22

23 Directly-deposited Si NP/CNT/PVA Nanofiber Anode Half-Cell Performance at 0.5C 2500 at 1C Capacity (mah/g) Capacity (mah/g) Cycle (Numbers) Cycle (Numbers) Direct Deposit of Si NP/CNT/PVA increases the capacity and improves capacity retention, giving over 1500 mah/g after 200 cycles at 1C rate. 23

24 Directly-deposited Si NP/CNT/PVA Nanofiber Anode Capacity (mah/g) Rate Capability Test Hybrid Si anodes 0.1C 0.2C 0.5C 1C 0.5C 1C 1.5C 2C 3C 3C 5C Cycle (Numbers) Z Im (ohms) Impedance Test Z Im (ohms) Before cycling After 50 cycles Z Re (ohms) Decreasing R ct Z Re (ohms) Direct deposit of Si NP/CNT/PVA nanofibers on to a current collector leads to much improve rate capabilities, giving 1,350 mah/g at 2C. Hybrid Si anodes has much reduced charge transport resistance after 50 cycles. 24

25 Directly-deposited CNT/Si NP/PVA Anode Full Cell Performance 100 Capacity retention (%) CNT/Si NP/PVA NF Anode Charge process Discharge process Cycle (Numbers) Capacity retention (%) Cycle (Numbers) Charge process Discharge process Si NP/PVA NF Anode Full cells are made by hybrid Si anode with LiNi 1/3 Mn 1/3 Co 1/3 O 2 show much more stable capacity retention than that using Si NP/PVA anode.

26 Directly-deposited Si NP/GNR/PVA Nanofiber Anode Half-Cell Performance Capacity (mah/g) at 0.5C Cycle No PVA:Si:GNR PVA:Si:CNT The Si/GNR/PVA anode exhibits higher capacity than the Si/CNT/PVA anode (> 500 mah/g) 26

27 Summary: Hybrid Si Anodes via Water based Electrospinning for Li ion Batteries Ceramic and metal oxide nanofibers with tailored nanostructures and polymer nanofiber membranes fabricated by water-based gas-assisted electrospinning have been applied as electrode materials and separators for Li-ion batteries. Si rich carbon (SRC) nanofibers have been fabricated by electrospinning aqueous solution of Si nanoparticles and PVA, followed by thermal treatment, which exhibit high capacity in Li-ion battery anode applications. Incorporation of nanostructured conductive carbon graphene nanoribbon (GNR) into SRC nanofibers lead to higher capacity, better retention and rate capability. To make the process more cost-effective, CNT (or GNR)/Si NP/binder solutions have been directly deposited on the current collector. The resulting nanofiber-based Li-ion batteries exhibit a very high energy density without capacity fading (450 Wh/kg for 100 cycles). 27

Replacing Zn-Air Hearing Aid Batteries Button & Coin Cells Button Cells $30B

cylindrical, 5% pouch) Currently there are few rechargeable coin cells due to

High Capacity Li-ion Zn Air Button Cell 7.

Currently use Zn Air Button Cells (non rechargeable) Energy Density = 200-250

28 Replacing Zn-Air Hearing Aid Batteries Button & Coin Cells Button Cells $30B market for non-rechargeable batteries 65% of this is button cells (30% cylindrical, 5% pouch) Currently there are few rechargeable coin cells due to unique energy density & form factor requirements. High Capacity Li-ion Zn Air Button Cell 7.8 mm Cathode Separator Anode Hearing Aid Market 10M Hearing aids sold annually Currently use Zn Air Button Cells (non rechargeable) Energy Density = Wh/kg High volumetric restrictions and unique form factors required to fit inside ear. We are develpoing the 1 st viable rechargeable battery for the hearing aid industry

Electrochemical Impedance Spectroscopy (EIS) Test: Thick Cathode EIS results - Cupcake (LiCoO 2 )/Li metal, commercial separators - Using aluminum coated coin cell s cups -LiCoO 2 /Conductive

29 Electrochemical Impedance Spectroscopy (EIS) Test: Thick Cathode EIS results - Cupcake (LiCoO 2 )/Li metal, commercial separators - Using aluminum coated coin cell s cups -LiCoO 2 /Conductive Carbon/PVDF=91/6/3 wt% - Charge-transfer resistance - Diffusion of Li ion C d R s R s Using coin cells C d R ct 200mg Electrode Mass: 68mg Mass-transfer-limited current density For = 150 mm, i d = 4.8 A/m 2 Maximum C rate = q F D c/( /2) d R ct W C d =double layer capacitor R ct =polarization (charge transport) resistor W=Warburg resistor R s =solution resistor Mass diffusion limitation of Li ion into the electrode dc id FDeff FD dx eff D eff =10-13 m 2 /s 2 i ( A/ m ) eff eff 2 2 max ( Ah/ m ) F c / 3600 c ( /2) D h 1 29

30 High Capacity Button Cells Anode, Separator and Cathode Manufacturing via Gas-Assisted Electrospinning 7.8 mm High Capacity Button Cells Capacity: 18 mah 30

implemented in products such as wearable electronics as well as flexible displays.

31 Flexible Electrodes based on Carbon Nanofiber Mat The increasing interest in portable and flexible electronics has led to the development of flexible batteries which can be implemented in products such as wearable electronics as well as flexible displays. High Loading of Sulfur via Mesoporus Carbon Nanofibers for Li-S Cathode Sulfur/Mesoporous Carbon NF Composite

32 Directly Deposited Electrodes via Gas-Assisted Electrospray Flexibility Test bending Folding Back Front No exfoliation observed after multitimes folding, indicating the excellent adhesion of electrode materials. Fold-free electrodes can be achieved by using flexible current collector e.g.carbon cloth

33 Directly Deposited Electrodes via Gas-Assisted Electrospray Electrochemical Performance as Li-ion battery Anode Specific capacity (mah/g) Si NPs/Graphene Oxide Sheets 1A/g Drop Cast Elestrospray Binder-free Electrospray Cycle number Gas-assisted electrospray of aqueous Si NPs/Graphene Oxides solution results in high capacity Li-ion battery anodes which can be applied to flexible batteries. 2 A/g

34 Summary: Small Format Li ion Batteries High capacity small format Li-ion batteries Button cells based on rolled configurations have been developed for hearing aid applications. A target capacity of 15 to 20 mah has been achieved. Prismatic cells for open source hardware and its miniaturized chip applications are being developed. Further material/process development is underway to improve the capacity retention. For flexible batteries Free-standing mesoporous carbon nanofiber mat has been applied as Li-S battery cathode. Si NP/Graphene Oxide has been directly deposited on the electrode via gas-assisted electrospray. 34

35 Acknowledgements Graduate Students: Nate Hansen (Intel) Eddie Zhmayev (Corning) Ghazal Shoorideh Soshana Smith Postdocs: Yong Seok Kim (Samsung) Ling Fei Daehwan Cho Kat Chemelewski Collaborators Jinwoo Lee (PUST) Srinivasan Chakrapani (AZ EM) Funding Joo Research Group 35

LITHIUM ION BATTERIES

LITHIUM ION BATTERIES 1 Electrodes & Jelly roll 2 3 Types of Lithium ion batteries 원형, 원통형, cylindrical 각형, prismatic 폴리머, polymer (pouch type) 4 Materials composing electrodes 5 6 Terminology-1