Development of rechargeable lithium metal battery (LMB) remains a challenge because of uneven lithium deposition during repeated cycles of charge and discharge. Ionic liquids have received intensive scientific interest as electrolytes because of their exceptional thermal and electrochemical stabilities. Ionic liquid and ionic-liquid-nanoparticle hybrid electrolytes based on 1-methy-3-propylimidazolium (IM) and 1-methy-3-propylpiperidinium (PP) have been synthesized and their ionic conductivity, electrochemical stability, mechanical properties, and ability to promote stable Li electrodeposition investigated. PP-based electrolytes were found to be more conductive and substantially more efficient in suppressing dendrite formation on cycled lithium anodes; as little as 11 wt % PP-IL in a PC-LiTFSI host produces more than a ten-fold increase in cell lifetime. Both PP- and IM-based nanoparticle hybrid electrolytes provide up to 10 000-fold improvements in cell lifetime than anticipated based on their mechanical modulus alone. Galvanostatic cycling measurements in Li/Li4 Ti5 O12 half cells using IL-nanoparticle hybrid electrolytes reveal more than 500 cycles of trouble-free operation and enhanced rate capability.

Advances in materials that enable high-energy and safe electrochemical storage are understood to be a critical next step for portable electronic devices and for electric vehicles. Progress in both fi elds requires high-density, reliable and safe storage of electrical energy. Rechargeable lithium ion batteries (LIB), due to their high energy density, low internal resistance and minimal memory effects, are currently the most attractive storage technology; [1][2][3][4] they are expected to dominate the marketplace for the foreseeable future. Two well-known drawbacks of current LIB technology stem from the carbonaceous material used to host lithium in the anode. First, the 6/1 C/Li molar ratio in the anode lowers the anode specifi c capacity by more than one order of magnitude: from 3860 mAh g −1 to around 360 mAh g −1 . [ 5 ] It also limits the choice of cathode to relatively low capacity, lithiated compounds, such as lithiated metal oxides, phosphates, and silicates, and presents a barrier to usage of novel, high-storage capacity cathode chemistries based on un-lithiated materials including oxygen, sulfur, and carbon dioxide. [ 6,7 ] A second, less appreciated drawback arises from the small difference in potential that separates lithium insertion into the host and lithium plating onto the host. [ 8 ] Thus, either an overcharged or too quickly charged lithium ion battery can become a lithium metal battery (LMB), wherein the deposited metallic lithium provides the primary storage material in the anode. This means that notorious safety issues associated with non-uniform electrodeposition on metallic lithium anodes, dendrite formation and potential for catastrophic cell failure by internal short circuits, [ 8 ] which are normally associated with LMBs, are also an important concern for LIBs.Development of electrolyte and separator platforms that permit safe and reliable cycling of lithium batteries that utilize metallic lithium anodes provide a potential solution to both of these problems, and is thus an important scientifi c undertaking. A key requirement of such an electrolyte/separator would be the ability to suppress or eliminate uneven electrodeposition of Li and/or to retard subsequent dendrite formation and proliferation during repeated charge-discharge cycles. [ 9 ] Several strategies have been proposed in the older literature for suppressing/managing lithium dendrite growth in LMBs. The list includes electrode coatings that prevent dendrite-induced short-circuits; [ 10 ] introducing so-called solid electrolyte interface (SEI) additives into the electrolyte, which facilitate electrodeposition of Li, [ 11 ] application of external pressure on the lithium metal electrode to "fl atten" the electrode/electrolyte interface. [ 12 ] Mechanical blocking using solid or solid-like electrolytes with suffi ciently high modulus to prevent growth of any formed dendrites [ 13,14 ] has good theoretical support from the model of Monroe and Newman, which shows that an electrolyte with shear modulus around two times that of lithiu...

Development of rechargeable lithium metal battery (LMB) remains a challenge because of uneven lithium deposition during repeated cycles of charge and discharge. Ionic liquids have received intensive scientific interest as electrolytes because of their exceptional thermal and electrochemical stabilities. Ionic liquid and ionic‐liquid–nanoparticle hybrid electrolytes based on 1‐methy‐3‐propylimidazolium (IM) and 1‐methy‐3‐propylpiperidinium (PP) have been synthesized and their ionic conductivity, electrochemical stability, mechanical properties, and ability to promote stable Li electrodeposition investigated. PP‐based electrolytes were found to be more conductive and substantially more efficient in suppressing dendrite formation on cycled lithium anodes; as little as 11 wt % PP‐IL in a PC‐LiTFSI host produces more than a ten‐fold increase in cell lifetime. Both PP‐ and IM‐based nanoparticle hybrid electrolytes provide up to 10 000‐fold improvements in cell lifetime than anticipated based on their mechanical modulus alone. Galvanostatic cycling measurements in Li/Li4Ti5O12 half cells using IL–nanoparticle hybrid electrolytes reveal more than 500 cycles of trouble‐free operation and enhanced rate capability.

Connecting structure and morphology to bulk transport properties, such as ionic conductivity, in nanostructured polymer electrolyte materials is a difficult proposition because of the challenge to precisely and accurately control order and the orientation of the ionic domains in such polymeric films. In this work, poly(styrene-block-2-vinylpyridine) (PSbP2VP) block copolymers were assembled perpendicularly to a substrate surface over large areas through chemical surface modification at the substrate and utilizing a versatile solvent vapor annealing (SVA) technique. After block copolymer assembly, a novel chemical vapor infiltration reaction (CVIR) technique selectively converted the 2vinylpyridine block to 2-vinyl n-methylpyridinium (NMP + X − ) groups, which are anion charge carriers. The prepared block copolymer electrolytes maintained their orientation and ordered nanostructure upon the selective introduction of ion moieties into the P2VP block and post ion-exchange to other counterion forms (X − = chloride, hydroxide, etc.). The prepared block copolymer electrolyte films demonstrated high chloride ion conductivities, 45 mS cm −1 at 20 °C in deionized water, the highest chloride ion conductivity for anion conducting polymer electrolyte films. Additionally, straight-line lamellae of block copolymer electrolytes were realized using chemoepitaxy and density multiplication. The devised scheme allowed for precise and accurate control of orientation of ionic domains in nanostructured polymer electrolyte films and enables a platform for future studies that examines the relationship between polymer electrolyte structure and ion transport.

Thin film studies of block copolymer electrolytes (BCEs) reveal a strong dependency between the extent of ionic domain connectivity and terminal defect density on ionic conductivity.