Conducting polymers such as poly(3-hexylthiophene) (P3HT) can be used to convey electronic charge in battery electrodes. The electronic conductivity of P3HT (and other electronically conducting polymers) is potential-dependent. The main advance in this work is to quantify the effect of this potential dependency on battery performance. The discharge characteristics of a battery consisting of a cathode with LiFePO4 particles in a poly(3-hexylthiophene)-b-poly(ethylene oxide) (P3HT-PEO) copolymer matrix that conveys electrons and ions to the active particles, a polystyrene-b-poly(ethylene oxide) (PS-PEO) copolymer electrolyte layer, and a lithium metal anode were examined by experiments and macro-homogeneous modeling; lithium bis (trifluoromethanesulfonyl) imide was the salt in the cathode and the electrolyte. By comparing the model predictions with experiments, we conclude that the electronic conductivity of the polymer in the cathode is significantly lower than that obtained from measurements in the absence of active particles. The potential-dependent conductivity is manifested in the shape of the discharge curve wherein the slope increases continuously with capacity. The model provides insight into the underpinnings of the observed rate-dependency of electrode capacity, thereby guiding the design of the next generation of electrodes.

Syndiotactic polypropylene-b-poly(ethylene oxide)-b-syndiotactic polypropylene (PEOP) triblock copolymers were synthesized and solid polymer electrolytes were prepared by mixing with lithium bis(trifluoromethane) sulfonimide (LiTFSI) salt. PEOP formed strongly-segregated morphologies in the absence and presence of LiTFSI. LiTFSI inhibited poly(ethylene oxide) crystallization without affecting polypropylene crystallinity. The conductivity exhibited a non-monotonic dependence on molecular weight (Mn) with a maximum near 20 kg/mol. In contrast, polystyrene-b-poly(ethylene oxide) electrolytes exhibit conductivity increasing monotonically with Mn, up to a plateau in the high-Mn limit. This suggests that non-conducting semi-crystalline microphases interfere with conducting pathways, while non-conducting amorphous microphases formed well-connected conducting pathways. © 2014 Published by Elsevier B.V.

Hybrid nanostructured materials comprising block copolymers, nanoparticles, and lithium salts have the potential to serve as electrolytes in non- flammable rechargeable lithium batteries. Here we show that the addition of functionalized nanoparticles, at an optimized concentration, into lamellar block copolymer electrolytes, results in an increase in ionic conductivity. This is due to the occurrence of a lamellar-to-bicontinuous phase transition, driven by the addition of nanoparticles. The magnitude of the increase in conductivity is consistent with a simple model that accounts for the morphology of the conducting channels. The conductivity of the optimized hybrid electrolyte is only 6% lower than that of an idealized nanostructured electrolyte with perfectly connected conducting pathways and no dead ends. (Graph Presented).

A significant limitation of rechargeable lithium-ion batteries arises because most of the ionic current is carried by the anion, the ion that does not participate in energy-producing reactions. Single-ion-conducting block copolymer electrolytes, wherein all of the current is carried by the lithium cations, have the potential to dramatically improve battery performance. The relationship between ionic conductivity and morphology of single-ion-conducting poly(ethylene oxide)-b-polystyrenesulfonyllithium(trifluoromethylsulfonyl)imide (PEO-PSLiTFSI) diblock copolymers was studied by small-angle X-ray scattering and ac impedance spectroscopy. At low temperatures, an ordered lamellar phase is obtained, and the "mobile" lithium ions are trapped in the form of ionic clusters in the glassy polystyrene-rich microphase. An increase in temperature results in a thermodynamic transition to a disordered phase. Above this transition temperature, the lithium ions are released from the clusters, and ionic conductivity increases by several orders of magnitude. This morphology-conductivity relationship is very different from all previously published data on published electrolytes. The ability to design electrolytes wherein most of the current is carried by the lithium ions, to sequester them in nonconducting domains and release them when necessary, has the potential to enable new strategies for controlling the charge-discharge characteristics of rechargeable lithium batteries.

Most of the work on Lithium-sulfur (LiS) batteries use liquid electrolytes that have limited stability when coupled with Li metal anodes. We have studied LiS batteries with a solid block copolymer electrolyte which exhibits improved stability against Li anodes. The electrolyte comprises a polystyrene-b-poly(ethylene oxide) (SEO) copolymer doped with a Li salt. Hollow carbon nanospheres impregnated with sulfur were used to build a composite cathode. Two types of sulfur-impregnated functionalized carbon nanospheres were used: One with carboxylic acid groups and the other with short lithium poly(4-styrenesulfonyl(trifluoromethylsulfonyl)imide) (PSTFSI-Li) chains. Cells with Li2S8 dissolved in the SEO based electrolyte served as the baseline. After cycling, the reason for capacity fade was determined by imaging the batteries using synchrotron hard X-ray microtomography. It is generally assumed that LiS cells fail due to dissolution of polysulfide into the liquid electrolyte, i.e., the main problems related to the cathode. In our all-solid cells, failure was primarily due to delamination of the Li foil from the polymer electrolyte layer. Delamination is also observed at the sulfur cathode. It is likely that the large changes in volume of the active materials during cycling induce delamination in all-solid LiS cells.

In lithium batteries, a porous separator filled with an electrolyte is placed in between the electrodes. Properties of the separator such as porosity and wettability strongly influence the conductivity of the electrolyte-separator composite. This study focuses on three commercial separators: a single layer polypropylene (Celgard 2500), a trilayer polypropylene-polyethylene-polypropylene (PP-PE-PP), and a porous polytetrafluoroethylene (PTFE). Electron microscopy was used to characterize the pore structure, and these experiments reveal large differences in pore morphology. The separators were soaked in both carbonate- and perfluoropolyether-based electrolytes. The conductivity of the neat electrolytes (σ0) varied from 6.46 × 10-6 to 1.76 × 10-2 S cm-1. The porosity and wettability of the separator affect the electrolyte uptake that in turn affect the conductivity of electrolyte-separator composites. The conductivity of the electrolyte-separator composites (σ) was found to follow a master equation, σ = 0.51·σ0·φc3.2±0.2, where φc is the volume fraction of the electrolyte in each separator.

We report on the synthesis and characterization of a series of microphase-separated, single-ion-conducting block copolymer electrolytes. Salty nanoparticles comprising silsesquioxane cores with covalently bound polystyrenesulfonyllithium (trifluoromethylsulfonyl)imide (PSLiTFSI) chains were synthesized by nitroxide-mediated polymerization. Hybrid electrolytes were obtained by mixing the salty nanoparticles into a microphase-separated polystyrene-b-poly(ethylene oxide) (SEO) block copolymer. Miscibility of PSLiTFSI and poly(ethylene oxide) (PEO) results in localization of the nanoparticles in the PEO-rich microphase. The morphology of hybrid electrolytes was determined by scanning transmission electron microscopy. We explore the relationship between the morphology and ionic conductivity of the hybrid. The transference number of the electrolyte with the highest ionic conductivity was measured by dc polarization to confirm the single-ion-conducting character of the electrolyte. Discharge curves obtained from lithium metal-hybrid electrolyte-FePO4 batteries are compared to the data obtained from the batteries with a conventional block copolymer electrolyte.

The presence and role of polysulfide radicals in the electrochemical processes of lithium sulfur (Li-S) batteries is currently being debated. Here, first-principles interpretations of measured X-ray absorption spectra (XAS) of Li-S cells are leveraged with an ether-based electrolyte. Unambiguous evidence is found for significant quantities of polysulfide radical species (LiS3, LiS4, and LiS5), including the trisulfur radical anion S3-, present after initial discharge to the first discharge plateau, as evidenced by a low energy shoulder in the S K-edge XAS below 2469 eV. This feature is not present in the XAS of cells at increased depth of discharge, which, by our analysis, exhibit increasing concentrations of progressively shorter polysulfide dianions. Through a combination of first-principles molecular dynamics and associated interpretation of in situ XAS of Li-S cells, atomic level insights into the chemistries are provided that underlie the operation and stability of these batteries. Calculated and measured sulfur K-edge X-ray absorption spectra (XAS) and schematic of a lithium-sulfur (Li-S) cell with ether-based electrolyte are reported. The XAS is obtained through the lithium anode probing the electrolyte beyond it. The signature of polysulfide radicals is found as a low-energy shoulder below 2469 eV after discharging to 2.25 V. This feature disappears at greater depths of discharge.

Despite high ionic conductivities, current inorganic solid electrolytes cannot be used in lithium batteries because of a lack of compliance and adhesion to active particles in battery electrodes as they are discharged and charged. We have successfully developed a compliant, nonflammable, hybrid single ion-conducting electrolyte comprising inorganic sulfide glass particles covalently bonded to a perfluoropolyether polymer. The hybrid with 23 wt% perfluoropolyether exhibits low shear modulus relative to neat glass electrolytes, ionic conductivity of 10(-4) S/cm at room temperature, a cation transference number close to unity, and an electrochemical stability window up to 5 V relative to Li(+)/Li. X-ray absorption spectroscopy indicates that the hybrid electrolyte limits lithium polysulfide dissolution and is, thus, ideally suited for Li-S cells. Our work opens a previously unidentified route for developing compliant solid electrolytes that will address the challenges of lithium batteries.

Solid block polymer electrolytes are promising candidates for the development of high energy density rechargeable lithium metal based batteries. All solid-state batteries comprising lithiummetal negative electrode and lithium iron phosphate (LiFePO4) composite positive electrode were assembled. A polystyrene-b-poly(ethylene oxide) (SEO) copolymer doped with a lithium salt was used as the electrolyte. After cycling the batteries, the reason for capacity fade and failure was determined by imaging the batteries using synchrotron hard X-ray microtomography. These experiments revealed partial delamination of the lithium foil and the block copolymer electrolyte layer. The void volume between the foil and electrolyte layer obtained after 40 to 90 cycles is comparable to volume change in the battery during one cycle. A simple model to account for the effect of delamination on current density in the battery is presented. Capacity fade and battery failures observed in our experiments are consistent with this model. No evidence of lithium dendrite formation was found. In contrast, cycled lithium-lithium symmetric cells with the same polymer electrolyte at the same current density failed due to dendrite formation. No evidence of delamination was found in these cells.