Rechargeable Batteries

Transcription

1 Nanomaterial approaches to enhance lithium ion batteries Potential Environmental Benefits of Nanotechnology: Fostering Safe Innovation-Led Growth July 17 th, 2009 Brian J. Landi Assistant Professor of Chemical Engineering and Sustainability NanoPower Research Laboratories (NPRL) Golisano Institute for Sustainability (GIS) Rochester Institute of Technology

2 Rechargeable Batteries Recent Economic Trends (source: Aarkstore Enterprise) Rechargeable batteries, also known as storage batteries, are a continuing strong market, with worldwide sales of $36 billion in The rechargeable battery market will rise to $51 billion by In the US, lead-acid battery technology continues to head rechargeable battery sales with a rechargeable battery market share of 79% in The portable rechargeable battery market, of which lithium-ion has a 75% share, is the fastest growing segment of the rechargeable battery market, showing world market growth of 20% in 2008.

3 Advantages of Lithium Ion Portable Energy Challenge: Energy demand exceeds supply Increase Energy Density (carry more) Fast Recharge (refill often) Device Energy Efficiency (use wisely) Advantages of Lithium Ion Higher Energy and Power Density Higher Cell Voltage (2 to 3X over Ni-X) High charge rates available Low Self discharge rate (1-5%/month) Chemistry is form factor dependent (flexible design) Life can exceed tens of thousands cycles Side note: ZPower has reported that Silver Zinc technology has higher energy density than Li ion

4 Energy Density vs. Power Density Energy (J or Wh) is the ability to do work (currency) Power (J/s or W) is the rate energy is consumed (spending) Power/Energy ratio relates to battery application Lithium ion batteries are generally optimized either for high energy (e.g. for the consumer laptop or cellphone market where longer runtimes are a premium) or for high power (e.g. for the power tool or hybrid vehicle market where brief, high power pulses are a premium).

5 Demands for Rechargeable Batteries Consumer Electronics Grid and Renewable Energy Storage Altairnano and A123 Systems have independently developed 2MW power units for demonstration of utility-grade energy storage as a replacement for lead acid batteries. Automotive HEV: P/E = >15 PHEV: P/E = 3-10 EV: P/E = <3 Source: US DOE Industry Considerations -Battery size (energy density) -Number of units -Cell form factorsfe management

6 Considerations for Vehicles Battery Size and Cost (today: $1000+/kWh) HEV:1-2 kwh, PHEV: 5-15 kwh, EV: 40+ kwh Safety battery abuse from overcharge, physical damage, or high temperature; high voltage ( V) concerns Policy Incentives if economics are only driver, then it directly competes with oil: Electric vehicle with a $10,000 battery requires oil to exceed $125/barrel to equal 5 year total cost of ownership in a Volkswagen Golf 1.6 driven 15,000 km annually source: Boston Consulting Model for ownership buy electric vehicle, lease electric vehicle, or battery exchange (better place model) Manufacturing and battery design

7 Battery Manufacturing for Vehicles Today cells ~3.3 Billion cells in 2008 The Tesla Roadster battery pack (53 KWh-375 V) is comprised of about cells; pack has a mass of about 450kg. Source: Tesla Motors In the near future Battery design for safety, performance, and end-of-life Global Investment in Manufacturing United States: American Recovery and Reinvestment Act of 2009 authorized $2 billion in grants for manufacturers of advanced battery systems and components Germany: Lithium Ion Battery 2015 $650M for 1M PHEV cars by 2020 Japan: Next Generation Vehicle Battery Program China: National High Tech R&D Program

8 Mechanism and Components of Li + Components Anode (negative) active material, binder, substrate, additives Cathode (positive) active material, binder, substrate, additives Electrolyte Lithium salt in mixed carbonate solvents; additives for overcharge, SEI regulation Separator - porous polyolefin Solid-Electrolyte Interface (SEI) is a surface film that generally establishes between an electrode and electrolyte and serves as a passivation layer to allow diffusion of Li+ but restricts additional solvent reduction

9 Active Materials Comparison Electrode Capacity: set by intrinsic materials properties and method of fabrication (i.e. coating thickness, active material loading, etc.) Battery voltage: set by anode/cathode materials and is derived from the electrochemical potential difference Li 4 Ti 5 O 12 has a lithium ion potential of 1.5 V vs. Li/Li + for intercalation Battery Energy Density (Wh): is the product of capacity (Ah) and average voltage (V) - the discharge profile is critical

10 Li+ Battery Development There are many possible combinations of active materials for the anode, cathode, and electrolyte that are used in commercial lithium ion batteries each combination will affect performance (i.e. voltage, energy density, cyclability, etc.) Anode Graphite MCMBs Li 4 Ti 5 O 12 Electrolyte LiPF 6 Carbonates Additives Silicon Tin Nanotubes Solid Electrolyte Ionic Liquids LiBOB, LiTFSI Cathode Metal Oxides Iron Phosphate Mixed Oxides High Voltage Phosphates Layered Oxides Source: US DOE Variation in relative constituents will alter performance and energy density (by mass and volume)

11 Challenges with Li+ Today Fabrication &Processing Cell Design &Form Factor Variations in Performance MCMB Copper 50 mm Aluminum LiCoO 2 50 mm Coating Thickness Binder concentration Conductive additives Particle surface area Cylindrical vs. Prismatic Container materials Safety components Reality: Manufacturing Design affects Energy Density, Power Density, Cost, Cyclability, Safety Outcome: Some batteries are good for certain applications, others are not

12 Properties of Nanomaterials Imitating Nature Enhancement of light collection on the cornea of a night-flying moth 1 mm Source: Vukusic and Sambles, 2003 Nanomaterials can have unique quantum confinement properties that are particle size dependent Physical Surface area/interfacial energy from high surface to volume ratio van der Waals forces

13 Advantages of Nano in Lithium Ion Small particle size decreases electron diffusion parameters (benefit: high rate capability; detriment: need for percolation to current collector) High surface area allows active material to absorb lithium ions more effectively (benefit: higher capacity; deteriment: increased SEI) Small particle size may accommodate crystalline expansion of lattice (benefit: improved cyclability; detriment: lattice crystallinity) Nanotubes and nanowires can enhance electrical percolation and mechanical properties by entanglement Doped LiFePO 4 = 165 mah/g* Altairnano nano-li titanate Electrovaya SuperPolymer Nanomaterials offer the potential to create a unique lithium ion battery with both high energy and power density

14 Recent Nanomaterial Research Silicon and Germanium Nanowires LiMn 2 O 4 Nanowires Capacity >1000 mah/g Directed growth Higher Rate capability over conventional materials Potential Limitation: conventional slurry on metal current collector

15 Carbon Nanotubes Carbon nanotubes can be envisioned as a rolled up graphene sheet into a seamless cylinder. The role-up vector will determine the so-called chirality of the single wall carbon nanotube, which relates to whether the structure will be metallic or semiconducting. Single Wall Multi-Wall Single Wall Bundle High conductivity Nanoscale porosity Electrochemical and thermal stability High tensile strength/young s modulus

16 Carbon Nanotubes for Li + batteries 1 Overview of potential uses CNTs can be used as a conductive additive material which increases capacity, improves cyclability, enhances rate capability and mechanical toughness due to percolation network Review Article in the June 2009 Issue 2 CNTs can be fabricated into freestanding electrodes Anode lithium ion storage Predicted LiC 2 = 1116 mah/g, 3X improvement over graphite maximum of LiC 6 =372 mah/g Active material support for ultra high capacity semiconductors and electrical percolation pathways

17 Free-Standing Carbon Nanotubes Electrodes CNT Advantages Increased specific capacity Zero voltage SOC Increased DOD High temperature no binder Comparable C-rates Flexible Geometries Semiconductor Support CNT free-standing electrodes offer a constant capacity as a function of thickness which can dramatically improve the usable electrode capacity in a full battery, particularly in a high power battery design.

18 Raman Intensity (a.u.) Potential Environmental Benefits of Nanotechnology: Fostering Safe Innovation-Led Growth Battery Capacity Improvements Si-SWCNTs 145% SWCNTs % % 35% (a) MWCNTs Raman Shift (cm -1 (b) 5 nm CNT free-standing electrodes have the potential to more than double the state-of-the-art battery capacity with proper design and density.

19 Challenges going forward Nanomaterial Challenges Ongoing technical research is necessary Manufacturing/Costs are not available or competitive Purification of materials requires technical expertise and energy intensive Lack of knowledge for environmental and health risks Lithium Ion Challenges Bulk Powder Paper August 2006, Sony recalled all battery packs sold to Dell over a multi-year period March 2008, LG Chemical experienced a factory fire Concern for battery safety (e.g. electrolyte flammability) Environmental effects of constituent materials

20 Acknowledgements Dr. Ryne P. Raffaelle Dr. Cory D. Cress Matt Ganter Roberta DiLeo Chris Schauerman Jack Alvarenga U.S. Government