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V.C Anode Development V.C.1 Nanoscale Composite Hetero-structures: Novel High Capacity Reversible Anodes for Lithium-ion Batteries (U Pitt) Prashant N. Kumta Swanson School of Engineering, Departments of Bioengineering, Chemical and Petroleum Engineering, Mechanical Engineering and Materials Science, University of Pittsburgh, Pittsburgh, PA 15261 Phone: (412)-648-0223; Fax : (412) 624-8069 E-mail: pkumta@pitt.edu Start Date: January 1, 2011 Projected End Date: December 31, 2011 Objectives · Identify new alternative nanostructured anodes to replace synthetic graphite providing higher gravimetric and volumetric energy densities. · Similar or lower irreversible loss (≤15%) in comparison to synthetic graphite. · Similar or better coulombic efficiency (99.9%) in comparison to synthetic graphite. · Similar or better cyclability and calendar life in comparison to synthetic graphite. · Improve the coulombic efficiency, available energy density, rate capability and cycle life of high specific capacity Si based electrodes. · Investigate nano-structured (nc-Si) and amorphous Si (a-Si) based composite or hybrid heterostructured anode. Technical Barriers The important technical barriers of alternative anodes for lithium ion batteries to be used in electrical vehicles or hybrid electrical vehicles are the following: (A) Low energy density (B) Large first cycle irreversible loss (ICL) (25-30%) (C) Inadequate coulombic efficiencies (D) Poor cycle life (D) Poor rate capability (E) Low charge/discharge rates Technical Targets · Synthesize nano-structured (nc-Si) and amorphous Si (a-Si) based composite or hybrid structured anodes using cost effective processing techniques. · Achieve reversible capacity of ~1000-1200 mAh/g. · Reduce first cycle irreversible loss to less than ~15%. · Improve coulombic efficiencies higher than 99.5%. · Improve the rate capability. · Characterize the nano-scale hetero-structures for structure and composition using electron microscopy techniques such as SEM, TEM and HREM. · Investigate the origin and characterize the solid electrolyte interphase (SEI) layer. Accomplishments · Synthesized cost effective chemical and solid state approaches to nanostructured or amorphous Si based composites. · Synthesized binder free electrodes using nanocrystalline Si and vertically aligned carbon nanotube (VACNT) hybrid nanostructures by simple, cost effective two step liquid injection CVD processes directly on INCONEL 600 alloy. · Binder free Si/VACNT heterostructured anode exhibited a specific capacity in excess of ~1500 mAh/g and excellent rate capability. · Identified conductive additives or conductive coatings (CA) on Si/C based anode materials to generate Si/C/CA nanocomposites with improved coulombic efficiency and rate capability. · Synthesized nanocrystalline Si, graphite based nanocomposite (nc-Si/C/) containing additives by high energy mechanical milling exhibiting excellent cyclability (0.1-0.2% capacity loss/cycle), lower irreversible loss and high coulombic efficiency (~99.9%) with a specific capacity exceeding ~800 mAh/g. · Synthesized amorphous Si films directly on Cu-foil by electrochemical reduction of silicon-salts which FY 2011 Annual Progress Report 535 Energy Storage R&D
V.C.1 Nanoscale Composite Hetero-structures: Novel High Capacity Reversible Anodes (U. Pitts) Kumta – U. Pitts exhibit reversible capacity ~1300 mAh/g with excellent stability. · Explored novel thermoplastic (elastomeric) binders to improve the mechanical integrity of the electrode with improved cyclability of Si based composite structure. · The novel Si/C composite and nc-Si/CNT hybrid nanostructures exhibit less than 20% first cycle irreversible loss. Introduction Achieving the DOE-BATT technical targets will require improving the cycling stability, reduced irreversible loss, and improved coulombic efficiency and rate capability of Si based anodes. Hence it is essential to synthesize Si based composites using economical processes exhibiting excellent mechanical properties to endure the large cycling induced volumetric stresses of Li- Si alloys. In 2009, we conducted a systematic investigation of the electrochemical properties of HEMM derived Si/C based composite anodes. These HEMM derived composite anodes synthesized using polymer additives displayed a reversible capacity ~800 mAh/g or higher with a 0.01 0.03% capacity fade per cycle. Scale-up efforts to generate these novel composites are currently in progress; while efforts to further improve the capacities and other important electrochemical properties of these systems are also on-going. In addition, collaborative efforts to understand the SEI layers have been conducted with Dr. Kostecki and Dr. Battaglia at LBNL. Although Si/C based composites exhibiting capacity in excess of ~1000 mAh/g have been generated by HEMM, the system is commercially unsuitable due to high capacity fade of more than 0.2% per cycle. In order to improve the stability of Si/C based composite anodes, carbon nanotubes (CNTs) have been selected over graphite as a matrix. In 2010, a detailed investigation of Si/CNT hybrid structures was reported [1]. The CNTs possess some unparalleled attributes such as good electronic conductivity, high aspect ratio, structural flexibility, and tortuosity. Exploitation of these unique CNT attributes combined with its nano-scale dimensions will enable the generation of a nano-scale conductive network improving the electrical contact between the active Si particles. The Si/CNT hybrid structures exhibit high reversible capacity while also displaying excellent cyclability up to 50 cycles. However, the HEMM derived system exhibited larger than 25% ICL and/or low coulombic efficiency. The CVD derived Si/C nano-composite anode also shows a low coulombic efficiency (~98-99%) albeit a low irreversible loss (8-12%) in contrast. Thus for the Si/C nano-composite anode of capacity higher than ~1000 mAh/g to be commercially viable, the ICL should be lower than 15% and a coulombic efficiency in excess of 99.8%. In this regard, the present work was aimed at reducing the ICL below 20% and improving the coulombic efficiency above 99.8% for HEMM derived or CVD derived nc-Si/C composite by alloying with conductive additives, coating with conductive layers and generating novel microstructures such as hard “core-shell” morphologies. Synthesis of amorphous Si directly on copper foil by electrochemical reduction of silicon salts has also been performed. In addition, studies were also conducted to identify new binders for Si/C composites. PVDF, a commonly used binder in graphite electrodes is not ideal for Si based anodes because of its inability to endure the huge volumetric changes occurring during Li alloying and dealloying. New high strength and elastomeric binders are needed to preserve the mechanical integrity of the electrode. Approach To meet the technical targets, our approach is to explore inexpensive Si and C based composite or hybrid nano-structured electrodes exhibiting 1) an electrochemical potential a few hundred mV above the potential of metallic Li, and 2) a capacity of at least ~1000 mAh/g or higher. To achieve these goals, we focused on exploring novel low cost approaches to generate nano-scale hetero-structures comprising nano-structured Si or amorphous Si and a variety of carbons derived from graphitic carbon as well as CNT. The Si/C composite has been coated or alloyed using various conductive metals as well as a variety of conductive layers to form Si/C/CA nanocomposites with improved rate capability, coulombic efficiency, and structural stability. In order to improve the structural integrity of the Si/C based electrode, which undergoes mechanical disintegration during long term cycling, a preliminary study has been conducted to identify high strength elastomeric binders for Si/C composites electrode. A detailed study of these Si/C based composite anodes has been recently presented at the 2011 DOE annual review. A cost effective simple two-step CVD processes has been employed to synthesize binder free hybrid nc- Si/VACNT nano-structured electrodes on INCONEL 600 alloy. The vertically aligned carbon nanotubes (MWNT) were first synthesized on INCONEL 600 using xylene and ferrocene serving as the carbon and iron catalyst sources, respectively. Deposition of nanostructured Si on VACNTs has been achieved by cracking SiH 4 in the temperature range of 723K-1023K. Under the experimental conditions used, the CNTs grow perpendicular to INCONEL covered with Si nano-clusters deposited directly on VACNT at defined spacing. Si/C composite with conductive additives has been synthesized by HEMM of a mixture of graphite, silicon and additives with suitable polymers. The milled powder was thermally treated at 573K to generate C/Si composite containing the additives. In addition, conducting Energy Storage R &D 536 FY 2011 Annual Progress Report
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V. FOCUSED FUNDAMENTAL RESEARCH Int
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V.A Introduction Duong - DOE, Srini
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V.B Cathode Development V.B.1 First
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V.B.1 First Principles Calculations
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V.B.1 First Principles Calculations
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V.B.2 Cell Analysis, High-energy De
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V.B.3 Olivines and Substituted Laye
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Page 19 and 20: V.B.4 Stabilized Spinels and Nano O
Page 21 and 22: V.B.4 Stabilized Spinels and Nano O
Page 23 and 24: V.B.5 The Synthesis and Characteriz
Page 25 and 26: V.B.5 Synthesis & Characterization
Page 27 and 28: V.B.6 Cell Analysis-Interfacial Pro
Page 29 and 30: V.B.6 Cell Analysis-Interfacial Pro
Page 31 and 32: V.B.7 Role of Surface Chemistry on
Page 39 and 40: V.B.8 Characterization of New Catho
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Page 43 and 44: V.B.9 Layered Cathode Materials (AN
Page 49 and 50: V.B.10 Development of High Energy C
Page 51 and 52: V.B.10 Development of High Energy C
Page 53 and 54: V.B.11 Crystal Studies on High-ener
Page 59 and 60: V.B.12 Developing Materials for Lit
Page 65 and 66: V.B.13 Studies on the Local SOC and
Page 67 and 68: V.B.13 Studies on the Local SOC and
Page 69: V.B.14 New Cathode Projects (LBNL)
Page 73 and 74: V.C.1 Nanoscale Composite Hetero-st
Page 75 and 76: V.C.2 Interfacial Processes - Diagn
Page 81 and 82: V.C.3 Search for New Anode Material
Page 83 and 84: V.C.4 Nano-structured Materials as
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Page 87 and 88: V.C.5 Development of High Capacity
Page 89 and 90: V.C.5 Development of High Capacity
Page 91 and 92: V.C.6 Advanced Binder for Electrode
Page 93 and 94: V.C.6 Advanced Binder for Electrode
Page 95 and 96: V.C.7 Three-Dimensional Anode Archi
Page 97 and 98: ARGONNE2_CDJ403T me Pro ile V.C.7 T
Page 99 and 100: V.C.8 Metal-Based High-Capacity Li-
Page 101 and 102: V.C.8 Metal-Based High-Capacity Li-
Page 103 and 104: V.C.9 New Layered Nanolaminates for
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Page 107 and 108: V.C.10 Atomic Layer Deposition for
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Page 111 and 112: V.C.11 Synthesis and Characterizati
Page 113 and 114: V.C.11 Polymer-Coated Layered SiOx-
Page 115 and 116: V.C.12 Synthesis and Characterizati
Page 117 and 118: V.C.12 Silicon Clathrates for Anode
Page 119 and 120: V.C.12 Silicon Clathrates for Anode
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V.C.13 Wiring Up Silicon Nanopartic
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V.C.13 Wiring Up Silicon Nanopartic
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V.C.14 Hard Carbon Materials for Hi
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V.C.14 Hard Carbon Materials for Hi
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V.D.1 Polymer Electrolytes for Adva
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V.D.1 Polymer Electrolytes for Adva
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V.D.2 Interfacial Behavior of Elect
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V.D.2 Interfacial Behavior of Elect
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V.D.3 Molecular Dynamics Simulation
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V.D.3 Molecular Dynamics Simulation
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V.D.4 Bi-functional Electrolytes fo
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V.D.4 Bi-functional Electrolytes fo
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V.D.5 Advanced Electrolyte and Elec
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V.D.6 Inexpensive, Nonfluorinated (
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V.D.6 Nonfluorinated (or Partially
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V.D.7 Development of Electrolytes f
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V.D.8 Sulfones with Additives as El
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V.D.8 Sulfones with Additives as El
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V.D.9 Long-lived Polymer Electrolyt
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V.E Cell Analysis, Modeling, and Fa
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V.E.1 Electrode Fabrication and Fai
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V.E.2 Modeling-Thermo-electrochemis
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V.E.2 Thermo-electrochemistry, Capa
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V.E.3 Intercalation Kinetics and Io
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V.E.4 Mathematical Modeling of Next
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V.E.5 Analysis and Simulation of El
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V.E.5 Analysis and Simulation of El
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V.E.6 Investigation of Critical Par
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V.E.6 Investigation of Critical Par
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V.E.7 Predicting/Understanding New
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V.E.8 New Electrode Designs for Ult
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V.E.8 New Electrode Designs for Ult
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V.E.9 In Situ Electron Spectroscopy
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V.E.9 In situ Electron Spectroscopy
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V.F.1 Energy Frontier Research Cent
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V.F.1 Energy Frontier Research Cent
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V.F.2 Novel In Situ Diagnostics Too
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V.F.2 Novel In Situ Diagnostics Too
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V.G Integrated Lab-Industry Researc
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