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Polymer electrolytes have the potential to enable rechargeable lithium (Li) metal batteries. However, growth of nonuniform high surface area Li still occurs frequently and eventually leads to a short-circuit. In this study, a single-ion conducting polymer gel electrolyte is operated at room temperature in symmetric Li||Li cells. We use X-ray microtomography and electrochemical impedance spectroscopy (EIS) to study the cells. In separate experiments, cells were cycled at current densities of 0.1 and 0.3 mA cm

Next-generation electrolytes for lithium batteries must be able to conduct ions at sufficiently high current densities; yet this regime is rarely studied directly. The limiting current density of an electrolyte quantifies the highest possible rate of ion transport under an applied dc potential. Herein, we report on the limiting current density in twelve nanostructured polystyrene-block-poly(ethylene oxide) (PS-b-PEO, or SEO) copolymer electrolytes. We find that the limiting current at a given salt concentration increases systematically with increasing volume fraction of the PEO block (φEO). In contrast, the effective-medium theory, commonly used to analyze conductivity in block copolymer electrolytes, predicts that limiting current is independent of φEO. To resolve this conundrum, the ionic conductivity, the mutual diffusion coefficient of the salt, and the steady-state current fraction of the block copolymer electrolytes were measured. These measurements enable predictions of limiting current with no adjustable parameters using the concentrated solution theory. We found quantitative agreement between experimentally measured limiting current densities and predictions based on the concentrated solution theory. This work sheds light on how to reliably measure and predict limiting current density in composite electrolytes.

A promising approach for enabling rechargeable batteries with significantly higher energy densities than current lithium-ion batteries is by deploying lithium metal anodes. However, the growth of l...

Hybrid organic-inorganic block copolymer electrolytes are of interest to enable batteries containing lithium metal anodes. The conductive block is a standard polymer electrolyte of poly(ethylene oxide) and the mechanically rigid block is an inorganic poly(acryloisobutyl polyhedral oligomeric silsesquioxane) polymer. In this paper, we compare a poly(acryloisobutyl polyhedral oligomeric silsesquioxane)-b-poly(ethylene oxide)-b-poly(acryloisobutyl polyhedral oligomeric silsesquioxane) (POSS-PEO-POSS) triblock copolymer and a poly(ethylene oxide)-b- poly(acryloisobutyl polyhedral oligomeric silsesquioxane) (PEO-POSS) diblock copolymer mixed with lithium bis(trifluoromethanesulfonyl)imide salt. We have experimentally measured the limiting current density in lithium symmetric cells containing hybrid organic-inorganic electrolytes at 90 °C. The cells were polarized at a large range of applied current density. The diblock copolymer electrolyte exhibited a clear plateau in cell potential at all current densities below the limiting current density. At low applied current density, the triblock copolymer electrolyte also exhibited a clear plateau in cell potential. At currents approaching the limiting current density, the triblock copolymer electrolyte exhibited an underdamped potential profile. The cell potential did not reach a plateau at current densities above the limiting current in both systems. The diblock and triblock copolymer electrolytes were fully characterized using electrochemical methods to determine the ionic conductivity, cation current fraction, salt diffusion coefficient, and open circuit voltage as a function of salt concentration. Cell potential and salt concentration as functions of position in the cell at various current densities were calculated using Newman's concentrated solution theory. The theoretical limiting current density was calculated to be the current density at which salt is depleted at the cathode. We see quantitative agreement between experimental measurements and theoretical predictions for the limiting current density in the diblock copolymer electrolyte which has an ordered structure at all salt concentrations, while the experimental limiting current density is lower than the theoretical prediction for the triblock copolymer electrolyte, which exhibits a disordered morphology at high salt concentrations.

There is a growing demand for higher energy density lithium batteries. One approach for addressing this demand is enabling lithium metal anodes. However, nucleation and growth of electronically conductive protrusions, which cause short circuits, prevent the use of this technology with liquid electrolytes. The use of rigid solid electrolytes such as polystyrene-b-poly(ethylene oxide) electrolytes is one solution. An additional requirement for practical cells is needed to use electrolytes with high salt concentration to maximize the flux of lithium ions in the cell. The first systematic study of the effect of salt concentration on the morphology of electrodeposited lithium through a rigid block copolymer electrolyte is presented. The nature, areal density, and morphologies of defective lithium deposits created during galvanostatic cycling of lithium-lithium symmetric cells were determined using hard X-ray microtomography. Cycle life decreases rapidly with increasing salt concentration. X-ray microtomography reveals the presence of multiglobular protrusions, which are nucleated at impurity particles at low salt concentrations; here, the areal density of defective lithium deposits was independent of salt concentration. At the highest salt concentration, this density increases abruptly by a factor of about 10, and defects were also nucleated at locations where no impurities were visible.

Successful prevention of lithium dendrite growth would enable the use of lithium metal as an anode material in next-generation rechargeable batteries. Mechanically stiff block copolymer electrolytes have been shown to prolong the life of lithium metal cells by partially suppressing lithium dendrite growth. However, impurity particles that are invariably present in the lithium metal nucleate electrodeposition defects that eventually lead to short circuits. In this study, we use X-ray tomography to study the morphology of electrodeposited lithium in symmetric cells containing a block copolymer electrolyte. An "electrochemical filtering" treatment was performed on these cells to reduce the concentration of impurity particles near the electrode-electrolyte interface, and cells were cycled to determine the effects of the treatment on lifetime. Depending on the treatment details, the average charge passed before failure was improved by 30-400%. For a cell in which the treatment was most effective, the cycle life was increased by more than an order of magnitude, and the measured number of deposition defects per area was negligible. Other treated cells, however, in which the treated lithium was imperfect, had a higher number of deposition defects per area compared to control cells. A majority of the deposition defects in treated cells were confined within the electrodes. In contrast, most of the deposition defects seen in the control cells were protrusions that invaded the electrolyte phase. The increased lifetime in these imperfectly treated cells was not due to a reduction in the number of deposition defects per area, but rather due to the differences in defect morphology. These results motivate the development of deposition defect- and impurity-free lithium metal electrodes.

The formation of dendrites and other protrusions on lithium metal anodes is a subject of continued interest due to the potential to incorporate these anodes in next-generation rechargeable batteries with increased energy densities. Solid polymer electrolytes show improved stability against lithium metal compared to liquid carbonate electrolytes. We have studied the effect of salt concentration on the formation of protrusions formed on electrodeposited lithium through a rigid block copolymer electrolyte, polystyrene-block-poly(ethylene oxide) (PS-b-PEO or SEO), in a lithium‑lithium symmetric cell. The cell lifetime decreases by a factor of 100 when salt concentration is increased by a factor of 5. Our main objective is to understand the reason for this observation. We show that this decrease is not due to a salt-induced change of the morphology of the block-copolymer electrolyte, nor is it due to a salt-induced change of mechanical properties. We use an approach based on Newman's concentrated solution theory to fully characterize ion transport in the block-copolymer electrolyte, and report the conductivity, salt diffusion coefficient, cation transference number, and thermodynamic factor. Neither cell lifetime nor protrusion density in failed cells correlate with any of these electrochemical parameters. However, the electrochemical parameters can be used to predict salt concentration profiles in our symmetric cells. We posit that an important parameter in protrusion growth is the magnitude of the salt concentration gradient, ∆. We observe a direct correlation between ∆ and lithium protrusion growth.

Author(s): Gribble, DA; Frenck, L; Shah, DB; Maslyn, JA; Loo, WS; Mongcopa, KIS; Pesko, DM; Balsara, NP | Abstract: The limiting current is an important transport property of an electrolyte as it provides an upper bound on how fast a cell can be charged or discharged. We have measured the limiting current in lithium-lithium symmetric cells with a standard polymer electrolyte, a mixture of poly(ethylene oxide) and lithium bis(trifluoromethane) sulfonamide salt at 90°C. The cells were polarized with increasing current density. The steady-state cell potential was a smooth function of current density until the limiting current was exceeded. An abrupt increase in cell potential was taken as an experimental signature of the limiting current. The electrolyte mixture was fully characterized using electrochemical methods to determine the conductivity, salt diffusion coefficient, cation transference number, and thermodynamic factor as a function of salt concentration. We used Newman’s concentrated solution theory to predict both cell potential and salt concentration profiles as functions of position in the cell at the experimentally applied current density. The theoretical limiting current was taken to be the current at which the calculated salt concentration at the cathode was zero. We see quantitative agreement between experimental measurements and theoretical predictions for the limiting current. This agreement is obtained without resorting to any adjustable parameters.

Author(s): Maslyn, JA; Mcentush, KD; Harry, KJ; Frenck, L; Loo, WS; Parkinson, DY; Balsara, NP | Abstract: Lithium metal is a high-energy-density battery electrode material, but the largely irreversible growth of lithium protrusions on an initially planar electrode during cycling makes it unsuitable for incorporation into a commercial battery. In this study, a lithium electrode with globular protrusions was stripped electrochemically, and the local morphology of the electrode as a function of time was determined by hard X-ray tomography. We demonstrate that globules are preferentially stripped compared to a planar electrode in our system, which incorporates a nanostructured block copolymer electrolyte. We report current density at the electrode as a function of micron-scale position and time. The local current density during the electrode healing process calculated from a reference frame at the electrode/electrolyte interface provides insight into the driving forces responsible for selective stripping of the globule. These results imply the possibility of discharging protocols that may return a lithium electrode to its initial planar state.

Successful prevention of lithium dendrite growth would enable the use of lithium metal as an anode material in next-generation secondary batteries. Mechanically stiff solid polymer electrolytes have been shown to prolong the life of lithium metal cells by partially suppressing lithium dendrite growth. A series of diblock copolymers of high modulus and molecular weight were synthesized, and their nanostructures and electrochemical properties were characterized as a function of polymer composition and lithium salt concentration, including measurements of the limiting current. X-ray tomography was used to observe lithium metal plating and cycling through these solid polymer electrolyte membranes under a range of electrochemical conditions. Insight into the interplay between electrochemical and mechanical properties, polymer microstructure, and lithium electrodeposition morphology will aid in the design of next-generation electrolytes.

In a society increasingly concerned by its impact on the environment and the urgent issue of climate change, there is great demand for an energy storage device with higher energy density and power capability (especially for electric vehicles and power grid). The use of the high energy density lithium metal anode jointly with a solid polymer electrolyte could enable the development of large-scale battery applications. Yet, dendritic lithium formation leading to short circuit currently limits its practical applications. Therefore, understanding the fundamentals of dendrite nucleation and growth is necessary to design robust battery systems. In this work, the nucleation and growth of lithium dendrite is studied in function of salt concentration in lithium-lithium symmetric cells in a rigorous manner. Complete electrochemical characterization of a solid block copolymer polystyrene-polyethylene oxide mixed with lithium salt (LiTFSI) will be presented, as well as the cell lifetime under galvanostatic cycling. We have discovered an unexpected relationship between cell lifetime and salt concentration. X-ray micro-tomography was used to underpin the relationship between salt concentration and dendrite nucleation and morphology.

Today the environment is a major society concern and the polluting fossil energy consumption, more and more expensive, is a drag on our economy, thereby the development of alternative transportation such as electric or hybrid vehicles, has become a key need for a sustainable long term development[1]. The increase of energy density necessary to promote this future revolution imposes to develop “new” chemistries for both the active electrode materials and electrolyte[2],[3]. However, for high scale applications a safety issue comes from the liquid electrolytes as they embedded organic solvents that can likely leak or generate flammable reactions. The use of a solid polymer electrolyte (SPE) could solve most of the safety issues encounter with liquid electrolyte. However, the development of SPE has been hampered by two hurdles i/ the inability to design a SPE that has both a high ionic conductivity and good mechanical properties3 and ii/ the motions of lithium ions carry only a small fraction of the overall ionic current which leads during battery operation to the formation of strong concentration gradient with highly noxious effects like favored dendritic growth[4] and limited energy density, especially when power increases. In this context, we are developing nanostructured multifunctional block copolymer electrolytes (BCE), B-A-B comprising a central A block based on poly(ethylene oxide) (PEO) that brings ionic conductivity and a B block that brings other functionalities like mechanical properties, electrochemical stability, increase of transport number etc. We will present our approach in improving the performances of BCEs starting from neutral BCEs like PS-POE-PS[5],[6] laden with a lithium salt to the single-ion BCEs (SIEL) comprising grafted lithium trifluoromethanesulfonylimide (TFSILi)[7] on the B block. Especially, we analyse the impact of the BCEs architecture (composition (ie proportion of PEO), chemistries of the A (linear vs comb PEO) and B (nature of the anions and of the main chain) blocks) on the physical properties such as the morphology, the thermodynamic transitions, the mechanic stability and the ion transport. At last, the impact of transport properties (binary vs single-ion) and mechanical properties on the lithium dendritic growth is also analysed thanks to X-ray micro-tomography. At last, for a complete analysis, the results obtained with several prototypes of batteries will also be presented. [1] J. Tollefson, Nature, 456, 2008, 436-440 [2] F. Cheng, J. Liang, Z. Tao, J. Chen, Advanced Materials, 23, 2011, 1695-1715 [3] M. Armand, J-M Tarascon, Nature, 451, 2008, 652-657 [4] J-N Chazalviel, Physical Review A, 42, 1990, 7355-7367 [5] E. Beaudoin, T. N. T. Phan, M. Robinet et al., Langmuir 2013, 29, 10874−10880 [6] R. Bouchet, T. N. T. Phan, E. Beaudoin et al., Macromolecules 2014, 47, PP2659-2665 [7] R. Bouchet, A. Aboulaich, S. Maria et al. Nature Materials, 12, 2013, 452–457.

Oxygen-deficient ferrates with the cubic perovskite structure SrxY1-xFeO3-d were prepared in air (0.71 ≤ x ≤ 0.91) as well as in N2 (x=0.75 and 0.79) at 1573K. The oxygen content of the compounds prepared in air increases with increasing strontium content from 3-δ=2.79(2) for x=0.75 to 3-δ=2.83(2) for x=0.91. Refinement of the crystal structure of Sr0.75Y0.25FeO2.79 using TOF neutron powder diffraction (NPD) data shows high anisotropic atomic displacement parameter (ADP) for the oxygen atom resulting from a substantial cation and anion disorder. Electron diffraction (ED) and high-resolution electron microscopy (HREM) studies of Sr0.75Y0.25FeO2.79 reveal a modulation along p with G± ~0.4p indicating a local ordering of oxygen vacancies. Magnetic susceptibility measurements at 5-390K show spin-glass behaviour with dominating antiferromagnetic coupling between the magnetic moments of Fe cations. Among the studied compositions, Sr0.75Y0.25FeO2.79 shows the lowest thermal expansion coefficient (TEC) of 10.5 ppm K-1 in air at 298-673K. At 773-1173K TEC increases up to 17.2 ppm K-1 due to substantial reduction of oxygen content. The latter also results in a dramatic decrease of the electrical conductivity in air above 673K. Partial substitution of Fe by Cr, Mn and Ni according to the formula Sr0.75Y0.25Fe1-yMyO3-δ (y=0.2, 0.33, 0.5) leads to cubic perovskites for all substituents with y=0.2. Their TECs are higher in comparison with un-doped Sr0.75Y0.25FeO2.79. Only M=Ni has increased electrical conductivity compared to un-doped Sr0.75Y0.25FeO2.79. Studies of cobalt based perovskites for cathode materials in solid oxide fuel cells.

The electrification of transport is a formidable challenge, however the energy storage possible in Li ion batteries is not sufficient to this purpose. A potential option is Lithium-air battery, first because of their very high energy densities and second because of their low costs. Two different approaches to the development of these batteries are possible: the anhydrous system which uses an organic electrolyte, and the aqueous system which uses an aqueous electrolyte [1]. An advantage of the aqueous system is its safety since toxic or inflammable solvents are not used. In order to protect the negative lithium electrode from the aqueous electrolyte, a thin ceramic water and gas tight membrane is used. The interface between the lithium metal and the ceramic membrane plays an important role in the cycling performance of the aqueous lithium air cell. Nonetheless, the poor or non-chemical stability of most ceramic electrolytes in contact with lithium metal limits the performance. A possible strategy to improve the interface between ceramic electrolyte and lithium metal might be by the use of polymer membranes [2]. This study reports the effect of a polymer membrane between a ceramic electrolyte and lithium metal. Block copolymer electrolytes, such as polystyrene-block-poly (ethylene oxide) copolymer electrolyte (SEO) mixed with lithium bis(trifluoromethanesulfonyl) imide (LiTFSI) salt, were used. The single ion conductor ceramic electrolyte was a Lithium Ion Conducting Glass Ceramic (LICGC) purchased from Ohara Corporation (1 inch X 1 inch 150µm thick). Impedance spectroscopy has been used, so as to study the lithium ion - lithium metal transfer from a lithium ion conducting polymer interface. Furthermore, in order to know if the sandwich polymer-ceramic cell showed an additional interfacial resistance, ionic conductivity experiments using electrochemical impedance spectroscopy were performed. Besides, polarization loss quantification at a lithium ion conducting polymer/single ion conductor interface was studied by DC current measurement by the Srinivasan et al method [3]. Finally, in order to confirm the intimacy of the ceramic and the polymer, the interface between the ceramic and the polymer was studied by synchrotron hard X-Ray micro tomography experiments on symmetric lithium-sandwich polymer-ceramic cells. P.G. Bruce, S. A. Freunberger, L. J. Hardwick, J-M. Tarascon, Nature Materials, 11, 19-29 (2012) G.M. Stone, S.A. Mullin, A.A. Teran, D.T. Hallinan, A.M. Minor, A. Hexemer, N.P. Balsara, Journal of the Electrochemical Society 159(3) A222-A227 (2012) Mehrotra, P. N. Ross, V. Srinivasan, Journal of the Electrochemical Society, 161 (10) A1681-A1690 (2014)

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