Electrified Vehicles for Personal Transportation, the Role of - PowerPoint PPT Presentation

Electrified Vehicles for Personal Transportation, the Role of Surface Coatings, and the Use of Thin Films for Electrode Characterization GM Mark Verbrugge (speaker) and Xingcheng Xiao University of Kentucky Rutooj Deshpande, Juchuan Li, Yang-Tse Cheng Molecular Engineering & Sciences Symposium, University of Washington, WA, 18 September 2012

Outline � Automotive context � Why do LiIon cells fail? � The use of thin-film surface coatings to 1. enhance lithium ion electrode performance (particularly life) – positives and negatives 2. characterize and understand active material behavior – stress evolution and solute (Li) diffusion � Summary

EM ERGING VS. M ATURE M ARKETS – GLOBAL COMP ARISON: 2010 Source: GM Economics & Trade; IMF; U.S . Census Bureau/ Haver Analystics

TOP 10 MARKETS BY NEW VEHICLE SALES IN 2011 20 2011 Sales (M) Emerging Markets 39.5 15 Mature Markets 36.5 � ������� Vehicle Sales (M) World Total 76.0 China Growth (%) 10 vs. 2010 vs. 2005 vs. 2000 2% 325% 854% 5 0 China EU U.S. Japan Brazil India Russia Canada S. Korea Australia 2000 2005 2009 2010 2011

PERSONAL MOBILITY MUS T BE REINVENTED FOR THE 21 st CENTURY 9 1.4 World Population Vehicle Parc 8 1.2 7 World Population (Billion) 1.0 Vehicle Parc (Billion) 6 0.8 5 4 0.6 3 0.4 2 0.2 1 0 0.0 1980 1990 2000 2010 2020 2030 Data from U.S. Census Bureau and GM Global Market & Industry Analysis Data from U.S. Census Bureau and GM Global Market & Industry Analysis

Future vehicles will use alternative energy sources Future vehicles will use alternative energy sources like bio-fuel, grid electricity, and hydrogen like bio-fuel, grid electricity, and hydrogen Hydrogen Fuel Cell Improved Improved Displace Displace Main challenges Vehicle Fuel Vehicle Fuel Petroleum Petroleum Economy & Economy & • Higher kWh/kg Battery Electric Emissions Emissions Vehicles (E-Rev) & kWh/m 3 • Lower cost Hybrid Electric Vehicles (including Plug-In HEV) IC Engine and Transmission Improvements Time Time Petroleum (Conventional & Alternative S ources) Alternative Fuels (Ethanol, Bio-diesel, CNG, LPG) Electricity (Conventional & Alternative S ources) Energy Energy Diversity Diversity Hydrogen

STOP-START SYSTEMS STOP-START SYSTEMS Electric Starter Auxiliary Motor Pump ~ 0.5 kWh battery

eAssist™ eAssist™ ROLLOUT ROLLOUT 2012 BUICK REGAL 2013 CHEVROLET MALIBU ~ 1 kWh battery

2-MODE RWD HYBRIDS 2-MODE RWD HYBRIDS ~ 2 kWh battery

CHEVROLET VOLT PERFORMANCE CHEVROLET VOLT PERFORMANCE � The Volt proves electric driving can be spirited � The Volt proves electric driving can be spirited � Top Speed – 100 mph � Top Speed – 100 mph – Torque – 273 lb.-ft. – Torque – 273 lb.-ft. � 0-60 mph in less than � 0-60 mph in less than – Quarter mile in less than – Quarter mile in less than 9 seconds 9 seconds 17 seconds 17 seconds Main challenges • Higher kWh/kg & kWh/m 3 • Lower cost 16 kWh battery

Why do LiIon cells fail? What do surface coatings have to do with cell life?

Electrode potentials Conventional lithium ion Newer lithium ion V Electrochemical reaction 1.35 NiOOH +H 2 O + e- = Ni(OH) 2 + OH � 1 Li 1-x MO 2 + xLi + + xe � = LiMO 2 (M: Ni, Co, Mn) Lithium ion conventional stability window ~ 1.35 V 0.4 FePO 4 + Li + + e � = LiFePO 4 0 H + + e � = 0.5H 2 ~ 2.5 V ~ 1.2 V ~ 4 V ~ 3.3 V O 2 + 2H + + 2e � = 2H 2 O Very stable potential -1.5 Li 4 Ti 5 O 12 + 3Li + + 3e � = Li 7 Ti 5 O 12 window, but lower energy density -2.9 C 6 + Li + + e � = LiC 6 -3 Li + + e � = Li � By changing an electrode voltage, new electrolytes can be employed with improved stability. � For traction applications, conventional lithium ion cells still dominate…lower utilization for improved durability & abuse tolerance.

Summary: role of surface layers on + and � Conventional lithium ion Newer lithium ion V Electrochemical reaction 1.35 NiOOH +H 2 O + e- = Ni(OH) 2 + OH � 1 Li 1-x MO 2 + xLi + + xe � = LiMO 2 (M: Ni, Co, Mn) Lithium ion conventional stability window ~ 1.35 V 0.4 FePO 4 + Li + + e � = LiFePO 4 0 H + + e � = 0.5H 2 ~ 2.5 V ~ 1.2 V ~ 4 V Solvent oxidation on Pt ~2.1 V vs Li ~ 3.3 V O 2 + 2H + + 2e � = 2H 2 O 1.3 V -1.5 Li 4 Ti 5 O 12 + 3Li + + 3e � = Li 7 Ti 5 O 12 Solvent reduction on negative ~0.8 V vs Li -2.9 C 6 + Li + + e � = LiC 6 -3 Li + + e � = Li � Underscores the importance of protective surface coatings, be they formed in situ or ex situ • Disruption of the protective surface coating (e.g., due to dilation, crack propagation, etc.) is deleterious to cell life

Negative electrode

Li + + B + e - � Li • Solvent reduction at ~0.8V vs Li on first cycle • Then ~100% Coulombic efficiency • Next slide for more detail

Formation of the SEI…solvent reduction (ethylene carbonate) Li 2 CO 3 + H 2 C=CH 2 Inorganic Gassing H 2 C CH 2 layer (ethylene) 2Li + + 2e � + O O + H 2 C=CH 2 [Li(OCOO)CH 2 ] 2 Gassing C Organic layer (ethylene) Li + + 2e � = Li V cell ~ � Li ~ ln( SOC ) O LiCH 2 CH 2 (OCOO)Li (Calendar life influence) Organic layer � Example reactions only…many others contribute to the formation of the solid electrolyte layer • For computed IR spectra of surface species in an EC electrolyte, see S. Matsuta, T. Asada, and K. Kitaura. J. Electrochem. Soc . 147(2000)1695-1702…dimers found to be lowest energy • Experimental FTIR data indicates predominance of for [Li(OCOO)CH 2 ] 2 EC and EC+DEC systems with 1M LiPF 6 , see C. R. Yang, Y. Y. Wang, C. C. Wan, J. Power Sources , 72(1998)66.

Positive electrode

The use of surface coatings to enhance lithium ion electrode performance - first, negative electrodes

Synthetic SEI approach, Al 2 O 3 over Li x Si

The use of surface coatings to enhance lithium ion electrode performance - positive electrodes

Commercial electrodes, primary vs secondary particles, composition analyses. FIBS analysis of NCM + LiMn 2 O 4

FIBS & imaging: cathode 3D.avi

SEM Mn map F map image NCM + LiMn 2 O 4 Co map C map S map O map and carbon conductive additive weak x-rays shadowed region Ni map K map C map NCM: Li(Ni x Co y Mn z )O 2 weak x-rays shadowed region

Synthetic SEI approach, “Al 2 O 3 ” over Li x CO 2

The utility of thin films for materials characterization and understanding 1. Mechanical behavior 2. Diffusion analyses

Si Patterns Pattern size 40 x 40 µm 2 Pattern size 17 x 17 µm 2 Gap: 15 µm Gap: 10 µm The crack spacing is around 5 to 10 microns, comparable to the pattern with 2000 mesh size. • Can the gaps provide necessary stress relaxation? • How large of a pad size can be accommodated? Pattern size 7 x 7 µm 2 Gap: 7 µm Related Si island works

Cycling results and the influence of Si pad size • Lithiation voltage lowered from 0.5 to 0.01 V Representative voltage responses

In-situ Stress Wafer curvature � � � � Measurement Click to edit Master title style Click to edit Master title style Click to edit Master title style 1 d d cos � � � 0 � � with MOSS system � � R d 2 L 0 ( M ultibeam O ptical S tress S ensors ) • Click to edit Master text styles Stoney Equation 1 • Second level � f � � in-plane film stress 2 h M H R f f s s 6 h f film thickness • Third level M s substrate biaxial modulus H s substrate thickness • Fourth level R substrate radius of curvature • Fifth level See Janssen et al., “Celebrating the 100th anniversary of the Stoney equation for film stress: 29 29 29 Developments from polycrystalline steel strips to single crystal silicon wafers,” Thin Solid Films 29 9/24/2012 29 517 (2009) 1858–1867.

Comparison of 50 nm thick Si samples: continuous film vs. 7x7 µm 2 pattern Patterned Sample Continuous Film 2 nd & 3 rd Cycle Stress Voltage (V) vs Li/Li+ recovered onset of flow No evidence Note stress ordinate scales differ of flow • See also: S. K. Soni, B. W. Sheldon, X. Xiao and A.Tokranov, “Thickness effects on the lithiation of amorphous silicon thin films,” Scripta Materialia 64 (2011) 307–310.

Solid We seek the minimum crack spacing L cr that does not allow an extra crack to be formed in between mechanics the existing cracks. Below this minimum crack spacing, the stress in the lithiated Si film can not reach its plastic yield stress and therefore no strain localization in the film can take place to form an additional crack. !! h = 0.1 � m

We just discussed the utility of thin film to characterize and understand the mechanical behavior of active materials Next: utility of thin films to assess solute (Li) diffusion in host (Si) materials

• Thin-film (100 nm) electrode (lithiated Si) • Small potential step excitation: linearize about the open-circuit potential and linearize about solute (Li) final concentration. • Electrochemical Biot number B : lone dimensionless group…diffusion over kinetic resistance. Short time solution Long time solution

Short time comparison Long time comparison