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High Conductivity Single-ion Cross-linked Polymers for Lithium Batteries and Fuel Cells

Lawrence Berkeley National Laboratory

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Cross-linked comb-branch structure.The molecular structures are infinitely variable in order to provide optimum properties for both bulk membranes and composite electrodes (MEAs).
Cross-linked comb-branch structure.The molecular structures are infinitely variable in order to provide optimum properties for both bulk membranes and composite electrodes (MEAs).

Technology Marketing SummaryJohn Kerr and co-workers at Berkeley Lab have developed single-ion cross-linked comb-branched polymer electrolytes with high conductivity for use as membranes in lithium batteries, fuel cells, and electrochromic windows. Solid polymer electrolyte separators are used in lithium batteries instead of common organic solvents because (1) they are non-volatile, (2) they inhibit the growth of dendrites, the tiny metallic snowflake structures in lithium metal electrodes that lead to battery failure, and (3) they can be used in very thin films thereby improving the power performance of the battery and increasing the energy density. DescriptionSolid polymer electrolytes have been improved by the creation of single-ion polymer conductors. Single ion conductors, transference number of one, avoid the development of concentration gradients that result in low voltage upon discharge and irreparable damage on charge because the anion is immobilized by covalently connecting it to the polymer comb. Until now, lithium single ion polymer conductors have been plagued with low conductivity, reactivity to lithium, poor cathode compatibility, and mechanical stiffness that leads to poor processing properties. Kerr’s new cross-linked polymer electrolytes based on trifluoromethylsulfonylmethide, sulfonate, and fluoroalkylsulfonate and imide anions overcome these limitations.

The controllable method of preparation results in a material that has uniformly excellent mechanical and ion transport properties that appear to be unaffected by the cross-linking density. This allows density to be varied to suit the application. The cross-linked materials achieve much higher lithium ion conductivities than other cross-linked polymers (10-5 S/cm at ambient temperatures) and yet also inhibit dendrite growth due to the mechanical properties. The side chains of the comb-branched structures are long enough to allow for maximum segmental motion so that the polymer can effectively penetrate between the electrode particles and adhere to electrode surfaces while maintaining the amorphous nature that facilitates high ion mobility. This overcomes many of the problems involved in the preparation of good composite electrode structures.

The capabilities, materials, and principles used for developing these polymer electrolytes for lithium batteries can be adapted to develop polymer films for fuel cells and electrochromic windows. Kerr’s group is investigating the use of new proton solvating functions on comb branch polyether polyelectrolyte materials to provide water-free membranes that can operate at high temperatures for fuel cells.
Benefits
  • High lithium ion conductivity (10-5 S/cm at ambient temperatures)
  • No concentration polarization, i.e. the transference number is one
  • Clean grafting and cross-linking chemistry leaves no reactive residues
  • Materials have uniform, reproducible mechanical properties and electrochemical stability
  • Polymer backbone and cross-link density and flexibility may be adapted to tune the transport and mechanical properties
  • Innovative solution to lithium mobility problems promises even higher conductivity
  • Easy preparation
Applications and Industries
  • Lithium metal polymer and lithium polymer batteries
  • PEM fuel cells
  • Electrochromic windows
  • Electroseparations
More InformationPUBLICATIONS:

Sun, X. and Kerr, J..Synthesis and Characterization of Network Single Ion ConductorsBased on Comb-Branched Polyepoxide Ethers and Lithium
Bis(allylmalonato)borate. Macromolecules, Vol. 39, No. 1, 2006. Pg 362-372.

Sun, X. and Kerr, J..Synthesis and Characterization of Network Single Ion ConductorsBased on Comb-Branched Polyepoxide Ethers and Lithium
Bis(allylmalonato)borate. Macromolecules, Vol. 37, No. 14, 2004. Pg 5133-5135.
Patents and Patent Applications
ID Number
Title and Abstract
Primary Lab
Date
Patent 6,956,083
Patent
6,956,083
Single ion conductor cross-linked polymeric networks
Single ion conductors comprising polymer electrolytes prepared by grafting a salt compound onto a comb-branch polymer or dendrimer are disclosed having superior properties.
Lawrence Berkeley National Laboratory 10/18/2005
Issued
Patent 7,101,643
Patent
7,101,643
Polymeric electrolytes based on hydrosilyation reactions
New polymer electrolytes were prepared by in situ cross-linking of allyl functional polymers based on hydrosilation reaction using a multifunctional silane cross-linker and an organoplatinum catalyst. The new cross-linked electrolytes are insoluble in organic solvent and show much better mechanical strength. In addition, the processability of the polymer electrolyte is maintained since the casting is finished well before the gel formation.
Lawrence Berkeley National Laboratory 09/05/2006
Issued
Technology Status
Technology IDDevelopment StageAvailabilityPublishedLast Updated
IB-1553, 1554 DevelopmentAvailable06/18/201007/28/2010

Contact LBL About This Technology

To: Shanshan Li<ipo@lbl.gov>