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V.C.6 Advanced Binder for Electrode Materials (LBNL) Gao Liu Enviornmental Energy Technologies Division Lawrence Berkeley National Laboratory Berkeley, CA 94720 Phone: (510) 486-7207; Fax: (510) 486-8619 E-mail: gliu@lbl.gov Start Date: October 2010 Projected End Date: September 2012 Objectives · Develop new conductive polymer binder materials to enable Si material in Li-ion negative electrode. Si has the highest Li-ion storage capacity at 4200 mAh/g. However, major issues presvent Si material from being used as negative electrode material in Li-ion cells, including limited life and low coulombic efficiency. The goal of this project is to develop negative electrode binder materials to improve the cycling performance of the Si-based electrode, and compatable with current Li-ion manufacturing process. · Commercial Si particles come with different surface chemistries. The interface between the Si particle and conductive binders plays a critical role for the charge transport. The surfaces native to the Si particles are characterized and modified to improve charge transport at the interface. Technical Barriers This project addresses the following technical barriers from the Energy Storage section of the Vehicle Technologies Program Multi-year Research, Development and Demonstration Plan: · Calendar and cycle life · Energy density · Cost Technical Targets Relevant USABC goals EV · $150/kWh · 230 Wh/dm 3 · 1000, 80% capacity, discharge cycles · 10-year system life PHEV 40-mile · $220/kWh · 193 Wh/dm 3 · 2750, 75%-capacity, discharge cycles +80,000 HEV cycles · 15-year system life Accomplishments · Synthesized a class of conductive polymer binders for Si materials with good electronic conductivity and good adhesion. · The conductive polymer binder enables high capacity cycling of Si particles without conductive additives in the electrode. · Correlated Si nanoparticle surface chemistry to their electrochemical performance. · Developed processes to modify Si nanoparticle surface to improve their electrochemical performance. Introduction Achieving the DOE energy, cycle life and cost targets will require materials of higher capacity and/or voltage and improved coulombic efficiency. High capacity Si based anode material has the potential to fulfill the energy density requirements for EV/PHEV applications. However, full capacity cycling of Si results in significant capacity fade due to a large volume change during Li insertion and removal. Decreasing the particle size to nanometer scale can be an effective means of accommodating the volume change; however, nanoparticle has large specific surface area, which makes the material prone to oxidation to form insulating SiO 2 layer. It is also challenging to make electric connections to all the Si nanoparticles in the electode by using similar size acetylene black nanoparticles. The repeated volume change of Si nanoparticles during cycling can lead to repositioning of the particles in the electrode matrix and result in particle dislocation from the conductive matrix. This dislocation of particles causes the rapid fade of the electrode capacity during cycling. In order to address this issue, Si/conductive polymer composite electrodes were developed. This new electrode can be fabricated with the current Li-ion manufacturing processes. We developed a new class of electric conductive binder materials, which provide improved binding force to the Si surface to help maintain FY 2011 Annual Progress Report 555 Energy Storage R&D
V.C.6 Advanced Binder for Electrode Materials (LBNL) Liu – LBNL good electronic connectivity throughout the electrode. The electrodes made with these binders have significantly improved the cycling capability of Si. Approach Use functional polymer design and synthesis to develop new conductive polymers with proper electronic properties, strong adhesion and improved flexibility to provide electric pathways in the electrode, and to accommodate large volume change of the Si alloy active material during lithium insertion and removal. The rational design of binder is assisted with advanced diagnostic techniques such as XAS at Advance Light Sources and with advanced molecular computation at National Energy Reseearch Secientific Computing Center – both are DOE national user facilities. Results Conductive Polymer Binder with Tailored Electronic Properties. We developed new conductive polymers through a combination of material synthesis, X- ray spectroscopy, density functional theory, and battery cell testing (Figure V - 88). Contrasting other polymer binders, the tailored electronic structure of the new polymer enables lithium doping under the battery environment. The polymer thus maintains both electric conductivity and mechanical integrity during the battery operation. dope the polymer to achieve adequent electronic conductivity. Mechanically, it is also crucial that the polymer is intimately adhered to Si particle surface. Both electrical and mechanical integrity of the electrodes will then be maintained throughout the battery operation The molecular structures of the developed polymers, PFFO and PFFOMB are based on polyfluorene (PF)-type polymers (Figure V - 88) Two key functional groups, carbonyl C=O and methylbenzoic ester -PhCOOCH 3 (MB), were introduced for tailoring the LUMO electronic states and for improving the polymer adhesion respectively, as elaborated below. In order to achieve a properly tailored electronic structure, we have extensively applied synchrotron based soft x-ray absorption spectroscopy (XAS) on a series of polymers to monitor the unoccupied conduction states. XAS provides a simple but direct probe of the excitations of core level electrons to the unoccupied states, i.e., the lowest-energy XAS peaks directly correspond to the LUMO states. Figure V - 89 shows the XAS data collected on three selected PF type polymers and the traditionally used p-type PAN. It is evident that the carbonyl groups in PFFO and PFFOMB generate a new LUMO state at 284.7eV in XAS (blue arrow), much lower than that of the PF (black arrow) and PAN (purple arrow). The additional MB units in PFFOMB do not change the low energy position of this LUMO. Therefore, the carbonyl is the key function group that lowers the LUMO energy level. Figure V - 88: Molecular structure of conductive polymer binder. The technical challenge stems from the reducing enviroment when the Si anode is lithiated. For example, the typically used p-type polyaniline (PAN) conductive polymer will not stay p-doped below 1 V (Li/Li + ), therefore losing electronic conductivity when used in the Si anode, which is operated between 0.01 V–1 V (Li/Li + ). In order to solve the crucial problem on electric connectivity of the binder, we focus on developing polymer binders that could be cathodically (n-type) doped for high electronic conductivity under the reducing environment for anodes. Our strategy for accomplishing the goal is to tailor the energy levels of the polymer conduction state, i.e., the lowest unoccupied molecular orbital (LUMO), so that the electrons could cathodically Figure V - 89: Carbon- 1s XAS spectra collected on a series of polymers. Performance of Si/Conductive Polymer Composite Electrode. A commercial Si material was used to fabricate electrodes with the PFFOMB conductive binders. The Si material is NOT carbon coated. A standard slurry making process was used to fabricate all the composite Si/conductive binder electrodes. Figure V - 90 presents the performance of the PFFOMB/Si based anode that is cast with a Si to polymer weight ratio of 2:1. The electrodes based on PAN and polyvinylidine difluoride (PVDF) Energy Storage R &D 556 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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V.B.4 Stabilized Spinels and Nano O
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V.B.4 Stabilized Spinels and Nano O
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V.B.5 The Synthesis and Characteriz
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V.B.5 Synthesis & Characterization
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V.B.6 Cell Analysis-Interfacial Pro
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V.B.6 Cell Analysis-Interfacial Pro
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V.B.7 Role of Surface Chemistry on
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Page 39 and 40: V.B.8 Characterization of New Catho
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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 and 70: V.B.14 New Cathode Projects (LBNL)
Page 71 and 72: V.C.1 Nanoscale Composite Hetero-st
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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
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Page 117 and 118: V.C.12 Silicon Clathrates for Anode
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Page 121 and 122: V.C.13 Wiring Up Silicon Nanopartic
Page 123 and 124: V.C.13 Wiring Up Silicon Nanopartic
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Page 137 and 138: 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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