Rechargeable lithium-sulfur batteries.

Electrolytes and interphases in Li-ion batteries and beyond.

Flexible solid-state supercapacitors (FSSCs) are frontrunners in energy storage device technology and have attracted extensive attention owing to recent significant breakthroughs in modern wearable electronics In this study, we review the state-of-the-art advancements in FSSCs to provide new insights on mechanisms, emerging electrode materials, flexible gel electrolytes and novel cell designs The review begins with a brief introduction on the fundamental understanding of charge storage mechanisms based on the structural properties of electrode materials The next sections briefly summarise the latest progress in flexible electrodes (ie, freestanding and substrate-supported, including textile, paper, metal foil/wire and polymer-based substrates) and flexible gel electrolytes (ie, aqueous, organic, ionic liquids and redox-active gels) Subsequently, a comprehensive summary of FSSC cell designs introduces some emerging electrode materials, including MXenes, metal nitrides, metal–organic frameworks (MOFs), polyoxometalates (POMs) and black phosphorus Some potential practical applications, such as the development of piezoelectric, photo-, shape-memory, self-healing, electrochromic and integrated sensor-supercapacitors are also discussed The final section highlights current challenges and future perspectives on research in this thriving field

Towards flexible solid-state supercapacitors for smart and wearable electronics

Ni-rich layered oxides and Li-rich layered oxides are topics of much research interest as cathodes for Li-ion batteries due to their low cost and higher discharge capacities compared to those of LiCoO2 and LiMn2O4. However, Ni-rich layered oxides have several pitfalls, including difficulty in synthesizing a well-ordered material with all Ni3+ ions, poor cyclability, moisture sensitivity, a thermal runaway reaction, and formation of a harmful surface layer caused by side reactions with the electrolyte. Recent efforts towards Ni-rich layered oxides have centered on optimizing the composition and processing conditions to obtain controlled bulk and surface compositions to overcome the capacity fade. Li-rich layered oxides also have negative aspects, including oxygen loss from the lattice during first charge, a large first cycle irreversible capacity loss, poor rate capability, side reactions with the electrolyte, low tap density, and voltage decay during extended cycling. Recent work on Li-rich layered oxides has focused on understanding the surface and bulk structures and eliminating the undesirable properties. Followed by a brief introduction, an account of recent developments on the understanding and performance gains of Ni-rich and Li-rich layered oxide cathodes is provided, along with future research directions.

Nickel-Rich and Lithium-Rich Layered Oxide Cathodes: Progress and Perspectives

The ever-growing demand for advanced rechargeable lithium-ion batteries in portable electronics and electric vehicles has spurred intensive research efforts over the past decade. The key to sustaining the progress in Li-ion batteries lies in the quest for safe, low-cost positive electrode (cathode) materials with desirable energy and power capabilities. One approach to boost the energy and power densities of batteries is to increase the output voltage while maintaining a high capacity, fast charge–discharge rate, and long service life. This review gives an account of the various emerging high-voltage positive electrode materials that have the potential to satisfy these requirements either in the short or long term, including nickel-rich layered oxides, lithium-rich layered oxides, high-voltage spinel oxides, and high-voltage polyanionic compounds. The key barriers and the corresponding strategies for the practical viability of these cathode materials are discussed along with the optimization of electrolytes and other cell components, with a particular emphasis on recent advances in the literature. A concise perspective with respect to plausible strategies for future developments in the field is also provided.

High-voltage positive electrode materials for lithium-ion batteries

Advanced electrolytes with unique functions such as in situ formation of a stable artificial solid electrolyte interphase (SEI) layer on the anode and the cathode, and the improvement in oxidation stability of the electrolyte have recently gained recognition as a promising means for highly reliable lithium-ion batteries with high energy density. In this review, we describe several challenges for the cathode (spinel lithium manganese oxide (LMO), lithium cobalt oxide (LCO), lithium nickel cobalt manganese oxide (NCM), spinel lithium manganese nickel oxide (LNMO), and lithium-rich layered oxide (Li-rich cathode))-electrolyte interfaces and highlight the recent progress in the use of oxidative additives and high-voltage solvents in high-performance cells.

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Recent advances in the electrolytes for interfacial stability of high-voltage cathodes in lithium-ion batteries

In conjunction with electrolyte additives used for tuning the interfacial structures of electrodes, functional materials that eliminate or deactivate reactive substances generated by the degradation of LiPF6 -containing electrolytes in lithium-ion batteries offer a wide range of electrolyte formulation opportunities. Herein, the recent advancements in the development of: (i) scavengers with high selectivity and affinity toward unwanted species and (ii) promoters of ion-paired LiPF6 dissociation are highlighted, showing that the utilization of the above additives can effectively mitigate the problem of electrolyte instability that commonly results in battery performance degradation and lifetime shortening. A deep mechanistic understanding of LiPF6 -containing electrolyte failure and the action of currently developed additives is demonstrated to enable the rational design of effective scavenging materials and thus allow the fabrication of highly reliable batteries.

Scavenging Materials to Stabilize LiPF6 -Containing Carbonate-Based Electrolytes for Li-Ion Batteries.

We report a highly promising organophosphorus compound with an organic substituent, tris(trimethylsilyl)phosphite (TMSP), to improve the electrochemical performance of 5 V-class LiNi0.5Mn1.5O4 cathode materials. Our investigation reveals that TMSP alleviates the decomposition of LiPF6 by hydrolysis, effectively eliminates HF promoting Mn/Ni dissolution from the cathode, and forms a protective layer on the cathode surface against severe electrolyte decomposition at high voltages. Remarkable improvements in the cycling stability and rate capability of high voltage cathodes were achieved in the TMSP-containing electrolyte. After 100 cycles at 60 °C, the discharge capacity retention was 73% in the baseline electrolyte, whereas the TMSP-added electrolyte maintained 90% of its initial discharge capacity. In addition, the LiNi0.5Mn1.5O4 cathode with TMSP delivers a superior discharge capacity of 105 mA h g−1 at a high rate of 3 C and an excellent capacity retention of 81% with a high coulombic efficiency of over 99.6% is exhibited for a graphite/LiNi0.5Mn1.5O4 full cell after 100 cycles at 30 °C.

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A multifunctional phosphite-containing electrolyte for 5 V-class LiNi0.5Mn1.5O4 cathodes with superior electrochemical performance

Raman Spectroscopic and X-ray Diffraction Studies of Sulfur Composite Electrodes during Discharge and Charge

High-capacity Si-embedded anodes and Li-rich cathodes are considered key compartments for post lithium-ion batteries with high energy densities. However, the significant volume changes of Si and the irreversible phase transformation of Li-rich cathodes prevent their practical application. Here we report lithium fluoromalonato(difluoro)borate (LiFMDFB) as an unusual dual-function additive to resolve these structural instability issues of the electrodes. This molecularly engineered borate additive protects the Li-rich cathode by generating a stable cathode electrolyte interphase (CEI) while simultaneously tuning the fluoroethylene carbonate (FEC)-oriented solid electrolyte interphase (SEI) on the Si–graphite composite (SGC) anode. The complementary electrolyte design utilizing both LiFMDFB and FEC exhibited an improved capacity retention of 85%, a high Coulombic efficiency of ∼99.5%, and an excellent energy density of ∼400 W h kg−1 in Li-rich/SGC full cells at a practical mass loading after 100 cycles. This dual-function additive approach offers a way to develop electrolyte additives to build a more favorable SEI for high-capacity electrodes.

Jung-Gu Han

Papers

Recent advances in the electrolytes for interfacial stability of high-voltage cathodes in lithium-ion batteries

Scavenging Materials to Stabilize LiPF6 -Containing Carbonate-Based Electrolytes for Li-Ion Batteries.

A multifunctional phosphite-containing electrolyte for 5 V-class LiNi0.5Mn1.5O4 cathodes with superior electrochemical performance

Raman Spectroscopic and X-ray Diffraction Studies of Sulfur Composite Electrodes during Discharge and Charge

Unsymmetrical fluorinated malonatoborate as an amphoteric additive for high-energy-density lithium-ion batteries