Jang-Hoon Park

A polymer electrolyte-skinned active material strategy toward high-voltage lithium ion batteries: a polyimide-coated LiNi0.5Mn1.5O4 spinel cathode material case

A facile approach to the surface modification of spinel LiNi0.5Mn1.5O4 (LNMO) cathode active materials for high-voltage lithium ion batteries is demonstrated. This strategy is based on nanoarchitectured polyimide (PI) gel polymer electrolyte (GPE) coating. The PI coating layer successfully wrapped a large area of the LNMO surface via thermal imidization of 4-component (pyromellitic dianhydride/biphenyl dianhydride/phenylenediamine/oxydianiline) polyamic acid. In comparison to conventional metal oxide-based coatings, distinctive features of the unusual PI wrapping layer are the highly continuous surface coverage with nanometre thickness (∼10 nm) and the provision of facile ion transport. The nanostructure-tuned PI wrapping layer served as an ion-conductive protection skin to suppress the undesired interfacial side reactions, effectively preventing the direct exposure of the LNMO surface to liquid electrolyte. As a result, the PI wrapping layer played a crucial role in improving the high-voltage cell performance and alleviating the interfacial exothermic reaction between charged LNMO and liquid electrolyte. Notably, the superior cycle performance (at 55 °C) of the PI-wrapped LNMO (PI-LNMO) was elucidated in great detail by quantitatively analyzing manganese (Mn) dissolution, cell impedance, and chemical composition (specifically, lithium fluoride (LiF)) of byproducts formed on the LNMO surface.

Facile fabrication of nanoporous composite separator membranes for lithium-ion batteries: poly(methyl methacrylate) colloidal particles-embedded nonwoven poly(ethylene terephthalate)

Highly-ordered nanoparticle arrangements have drawn substantial attention as an ideal starting template for the preparation of micro- and nanostructured porous materials. In the present study, by exploiting the concept of these unusual colloidal structures, we demonstrate facile fabrication of novel nanoporous composite separator membranes for high-safety and high-power lithium-ion batteries. This is based on the introduction of close-packed poly(methyl methacrylate) (PMMA) colloidal particle arrays to a poly(ethylene terephthalate) (PET) nonwoven support. Herein, the nanoparticle arrangement, driven by the self-assembly of PMMA colloidal particles provides a highly-ordered nanoporous structure, i.e. well-connected interstitial voids formed between the close-packed PMMA nanoparticles, in the composite separator membrane. The nonwoven PET serves as a mechanical support to mitigate the thermal shrinkage of the nonwoven composite separator membrane. Performance benefits of the nonwoven composite separator membrane, as compared to a commercialized polyethylene (PE) separator membrane, are elucidated in terms of thermal shrinkage, liquid electrolyte wettability, and ionic transport. Based on comprehensive characterization of the nonwoven composite separator membrane, the effect of the nanoporous structure on the electrochemical performance, such as self-discharge, discharge capacity, discharge C-rate capability, and cyclability of cells is investigated.

A novel ion-conductive protection skin based on polyimide gel polymer electrolyte: application to nanoscale coating layer of high voltage LiNi1/3Co1/3Mn1/3O2 cathode materials for lithium-ion batteries

A new and facile approach for the surface modification of high-voltage LiNi1/3Co1/3Mn1/3O2 cathode active materials is demonstrated. This strategy is based on polyimide (PI) gel polymer electrolyte (GPE)-directed nanoscale wrapping. The PI coating layer successfully wraps a large area of the LiNi1/3Co1/3Mn1/3O2 surface via thermal imidization of (pyromellitic dianhydride/oxydianiline) polyamic acid. Salient features of the PI wrapping layer are the highly continuous surface coverage with nanometre thickness (∼10 nm) and the facile ion transport through the nanoscale layer. Based on a sound understanding of the nanoarchitectured PI wrapping layer, its influence on the cell performance and thermal stability of high-voltage LiNi1/3Co1/3Mn1/3O2 is investigated as a function of charge cut-off voltage (herein, 4.6 and 4.8 V). The anomalous PI wrapping layer substantially improves the high-voltage cycling performance and alleviates the interfacial exothermic reaction between delithiated LiNi1/3Co1/3Mn1/3O2 and liquid electrolyte. These results demonstrate that the PI wrapping layer effectively prevents the direct exposure of the LiNi1/3Co1/3Mn1/3O2 surface to liquid electrolytes that are highly vulnerable to electrochemical decomposition at high charge voltage conditions, thus behaving as a novel ion-conductive protection skin that mitigates the unwanted interfacial side reactions.

Conducting Polymer-Skinned Electroactive Materials of Lithium-Ion Batteries: Ready for Monocomponent Electrodes without Additional Binders and Conductive Agents

Rapid growth of mobile and even wearable electronics is in pursuit of high-energy-density lithium-ion batteries. One simple and facile way to achieve this goal is the elimination of nonelectroactive components of electrodes such as binders and conductive agents. Here, we present a new concept of monocomponent electrodes comprising solely electroactive materials that are wrapped with an insignificant amount (less than 0.4 wt %) of conducting polymer (PEDOT:PSS or poly(3,4-ethylenedioxythiophene) doped with poly(styrenesulfonate)). The PEDOT:PSS as an ultraskinny surface layer on electroactive materials (LiCoO2 (LCO) powders are chosen as a model system to explore feasibility of this new concept) successfully acts as a kind of binder as well as mixed (both electrically and ionically) conductive film, playing a key role in enabling the monocomponent electrode. The electric conductivity of the monocomponent LCO cathode is controlled by simply varying the PSS content and also the structural conformation (benzoid-favoring coil structure and quinoid-favoring linear or extended coil structure) of PEDOT in the PEDOT:PSS skin. Notably, a substantial increase in the mass-loading density of the LCO cathode is realized with the PEDOT:PSS skin without sacrificing electronic/ionic transport pathways. We envisage that the PEDOT:PSS-skinned electrode strategy opens a scalable and versatile route for making practically meaningful binder-/conductive agent-free (monocomponent) electrodes.

Multifunctional semi-interpenetrating polymer network-nanoencapsulated cathode materials for high-performance lithium-ion batteries

As a promising power source to boost up advent of next-generation ubiquitous era, high-energy density lithium-ion batteries with reliable electrochemical properties are urgently requested. Development of the advanced lithium ion-batteries, however, is staggering with thorny problems of performance deterioration and safety failures. This formidable challenge is highly concerned with electrochemical/thermal instability at electrode material-liquid electrolyte interface, in addition to structural/chemical deficiency of major cell components. Herein, as a new concept of surface engineering to address the abovementioned interfacial issue, multifunctional conformal nanoencapsulating layer based on semi-interpenetrating polymer network (semi-IPN) is presented. This unusual semi-IPN nanoencapsulating layer is composed of thermally-cured polyimide (PI) and polyvinyl pyrrolidone (PVP) bearing Lewis basic site. Owing to the combined effects of morphological uniqueness and chemical functionality (scavenging hydrofluoric acid that poses as a critical threat to trigger unwanted side reactions), the PI/PVP semi-IPN nanoencapsulated-cathode materials enable significant improvement in electrochemical performance and thermal stability of lithium-ion batteries.

Fast sintering of silver nanoparticle and flake layers by infrared module assistance in large area roll-to-roll gravure printing system.

We present fast sintering for silver (Ag) nanoparticle (NP) and flake layers printed using roll-to-roll (R2R) gravure printing. An infrared (IR) sintering module was applied to an R2R system to shorten the sintering duration of an R2R gravure-printed Ag layer. IR sintering of the conductive layer was improved by optimising the process condition. After printing of the Ag NP and Ag flake layers, additional IR sintering was performed in the R2R system. The lowest sheet resistance obtained in the Ag NP layer was 0.294 Ω/□, the distance between the substrate and lamp was 50-mm long, the IR lamp power was 500 W, and the sintering time was 5.4 s. The fastest sintering of 0.34 Ω/□ was achieved with 50-mm distance, 1,000-W IR lamp power, and 1.08-s sintering time. In the Ag flake layer, the lowest sheet resistance obtained was 0.288 Ω/□ with a 20-mm distance, 1,000-W IR lamp power, and 10.8-s sintering time. Meanwhile, the fastest sintering was obtained with a 3.83 Ω/□ sheet resistance, 20-mm distance, 1000-W IR lamp, and 1.08-s sintering time. Thus, the IR sintering module can easily be employed in an R2R system to obtain excellent layer sheet resistance.

Polyimide/carbon black composite nanocoating layers as a facile surface modification strategy for high-voltage lithium ion cathode materials

Ion-conductive polyimide (PI)/electron-conductive carbon black (CB) composite nanocoating layers (referred to as “PI/CB coating layers”) are presented as a facile and scalable surface modification strategy for high-voltage lithium ion cathode materials (here, LiCoO2 (LCO) is chosen as a model system). The PI/CB coating layers exhibit a unique synergistic effect (i.e., boosted electronic conduction (from CB networks) in conjunction with suppression of unwanted interfacial side reactions between delithiated LCO and the liquid electrolyte (due to PI nanothin films)), which thus exerts a beneficial influence on the electrochemical performance and thermal stability of high-voltage cells.

Facile surface modification of high-voltage lithium-ion battery cathode materials with electroconductive zinc antimonate colloidal nanoparticles

The high-voltage cell approach has garnered a great deal of attention as a simple and effective way to increase the energy density of lithium-ion batteries. Here, we demonstrate a new class of surface modification based on electroconducitve zinc antimonate (AZO, ZnSb2O6) colloidal nanoparticles as a facile and scalable interface engineering strategy for high-voltage cathode materials. The electroconductive AZO colloidal nanoparticles are directly introduced on the surface of cathode materials via simple one-pot solution coating followed by post heat-treatment, in contrast to traditional surface modification using metal oxide precursors that often requires complex sol–gel reaction and high-temperature calcination. LiCoO2 (LCO) powder is chosen as a model cathode material to explore the feasibility of AZO nanoparticle coatings. A salient feature of the AZO nanoparticle layers, as compared to conventional metal oxides-based coating layers that are electrically inert, is the provision of electronic conduction, which thus boosts the electronic conductivity of LCO powders. This beneficial effect of the AZO nanoparticle layers, in collaboration with their contribution to suppressing unwanted interfacial side reactions between delithiated LCO and liquid electrolytes, enables significant improvement in high-voltage (here, 4.4 V) cell performance (AZO nanoparticle-deposited LCO (AZO–LCO) vs. pristine LCO: capacity retention after 50th cycle = 84% vs. 28%, discharge rate capability (2.0 C/0.2 C) = 78% vs. 55%). The potential application of AZO–LCO in high-voltage cells is also discussed with an in-depth consideration of the variation in AC impedance and electrode polarization of cells during cycling.

Polarity-tuned Gel Polymer Electrolyte Coating of High-voltage LiCoO 2 Cathode Materials

We demonstrate a new surface modification of high-voltage lithium cobalt oxide () cathode active materials for lithium-ion batteries. This approach is based on exploitation of a polarity-tuned gel polymer electrolyte (GPE) coating. Herein, two contrast polymers having different polarity are chosen: polyimide (PI) synthesized from thermally curing 4-component (pyromellitic dianhydride/biphenyl dianhydride/phenylenediamine/oxydianiline) polyamic acid (as a polar GPE) and ethylene-vinyl acetate copolymer (EVA) containing 12 wt% vinyl acetate repeating unit (as a less polar GPE). The strong affinity of polyamic acid for allows the resulting PI coating layer to present a highly-continuous surface film of nanometer thickness. On the other hand, the less polar EVA coating layer is poorly deposited onto the , resulting in a locally agglomerated morphology with relatively high thickness. Based on the characterization of GPE coating layers, their structural difference on the electrochemical performance and thermal stability of high-voltage (herein, 4.4 V) is thoroughly investigated. In comparison to the EVA coating layer, the PI coating layer is effective in preventing the direct exposure of to liquid electrolyte, which thus plays a viable role in improving the high-voltage cell performance and mitigating the interfacial exothermic reaction between the charged and liquid electrolytes.