Dual-Functional Electrolyte Additives toward Long-Cycling Lithium-Ion Batteries: Ecofriendly Designed Carbonate Derivatives

Flexible Linker Spacer Length Modulation in Cd-Based Metal-Organic Frameworks: Impact on Polarity and Sequestration Abilities

The heightening concerns over an outbreak of hazardous radioiodine from nuclear waste and carbon dioxide emissions from fossil fuels have restricted access to clean water and air. In this work, three Cd-MOFs (1-3) are self-assembled under environment-friendly conditions using i) a polypyridyl linker spanned by a flexible poly(methylene) spacer, and ii) a bent dicarboxylate linker. With a change in the length of the flexible methylene spacer, the dimensionality of the MOFs is tuned between 3D (1) and 2D (2 and 3). The microscopic images reveal that 1 displays larger particle sizes and a more pronounced morphology compared to 2 and 3. These MOFs show high thermal stability (up to 300 °C) and wettability. A controlled polar feature of 1-3 is utilized to achieve a high uptake capacity of iodine (I2 or I3 -) from water bodies (2.46-2.37 g g-1) and vapor (3.31-2.65 g g-1). With remarkable CO2 uptake by 1-3, the sorbate CO2 is further fixated into market-value products in quantitative conversions and atom economy under room temperature and solvent-free conditions. A comprehensive theoretical support is provided by configurational biased Monte Carlo (CBMC) simulations to reveal the exact locale and binding energies of the sorbates (I2, CO2, and epoxide) toward these MOFs.

Facile construction of heterogeneous dual-ionic poly(ionic liquid)s for efficient and mild conversion of CO2 into cyclic carbonates

In the context of peaking carbon dioxide emissions and carbon neutrality, development of feasible methods for converting CO2 into high value-added chemicals stands out as a hot subject. In this study, P[D+COO-][Br-][DBUH+], a series of novel heterogeneous dual-ionic poly(ionic liquid)s (PILs) were synthesized readily from 2-(dimethylamino) ethyl methacrylate (DMAEMA), bromo-substituted aliphatic acids, organic bases and divinylbenzene (DVB). The structures, compositions and morphologies were characterized or determined by nuclear magnetic resonance (NMR), thermal gravimetric analysis (TGA), infrared spectroscopy (IR), scanning electron microscopes (SEM), and Brunauer-Emmett-Teller analysis (BET), etc. Application of the P[D+COO-][Br-][DBUH+] series as catalysts in converting CO2 into cyclic carbonates showed that P[D+COO-][Br-][DBUH+]-2/1/0.6 was able to catalyze epiclorohydrin-CO2 cycloaddition the most efficiently. This afforded chloropropylene carbonate (CPC) in 98.4% yield with ≥ 99% selectivity in 24 hr under solvent- and additive-free conditions at atmospheric pressure. Reusability experiments showed that recycling of the catalyst 6 times only resulted in a slight decline in the catalytic performance. In addition, it could be used for the synthesis of a variety of differently substituted cyclic carbonates in good to excellent yields. Finally, key catalytic active sites were probed, and a reasonable mechanism was proposed accordingly. In summary, this work poses an efficient strategy for heterogenization of dual-ionic PILs and provides a mild and environmentally benign approach to the fixation and utilization of carbon dioxide.

Perspective on Lewis Acid-Base Interactions in Emerging Batteries

Lewis acid-base interactions are common in chemical processes presented in diverse applications, such as synthesis, catalysis, batteries, semiconductors, and solar cells. The Lewis acid-base interactions allow precise tuning of material properties from the molecular level to more aggregated and organized structures. This review will focus on the origin, development, and prospects of applying Lewis acid-base interactions for the materials design and mechanism understanding in the advancement of battery materials and chemistries. The covered topics relate to aqueous batteries, lithium-ion batteries, solid-state batteries, alkali metal-sulfur batteries, and alkali metal-oxygen batteries. In this review, the Lewis acid-base theories will be first introduced. Thereafter the application strategies for Lewis acid-base interactions in solid-state and liquid-based batteries will be introduced from the aspects of liquid electrolyte, solid polymer electrolyte, metal anodes, and high-capacity cathodes. The underlying mechanism is highlighted in regard to ion transport, electrochemical stability, mechanical property, reaction kinetics, dendrite growth, corrosion, and so on. Last but not least, perspectives on the future directions related to Lewis acid-base interactions for next-generation batteries are like to be shared.

LiF-Rich Electrode-Electrolyte Interfaces Enabled by Bifunctional Electrolyte Additive to Achieve High-Performance Li/LiNi0.8Co0.1Mn0.1O2 Batteries

Commercial Li-ion batteries use LiPF6-based carbonate electrolytes extensively, but there are many challenges associated with them, like dendritic Li growth and electrolyte decomposition, while supporting the aggressive chemical and electrochemical reactivity of lithium metal batteries (LMBs). This work proposes 1,1,1,3,3,3-hexafluoroisopropyl methacrylate (HFM) as a multifunctional electrolyte additive, constructing protective solid-/cathode-electrolyte interphases (SEI/CEI) on the surfaces for both lithium metal anode (LMA) and Ni-rich cathode to solve these challenges simultaneously. The highly fluorinated group (-CF3) of the HFM molecule contributes to the construction of SEI/CEI films rich in LiF that offer excellent electronic insulation, high mechanical strength, and surface energy. Accordingly, the HFM-derived LiF-rich interphases can minimize the electrolyte-electrode parasitic reactions and promote uniform Li deposition. Also, the problems of LiNi0.8Co0.1Mn0.1O2 particles' inner microcrack evolution and the growth of dendritic Li are adequately addressed. Consequently, the HFM additive enables a Li/LiNi0.8Co0.1Mn0.1O2 cell with higher capacity retention after 200 cycles at 1 C than the cell with no additive (74.7 vs 52.8%), as well as a better rate performance, especially at 9 C. Furthermore, at 0.5/0.5 mAh cm-2, the Li/Li symmetrical battery displays supersteadfast cyclic performance beyond 500 h when HFM is present. For high-performance LMBs, the HFM additive offers a straightforward, cost-effective route.

Acid- and Gas-Scavenging Electrolyte Additive Improving the Electrochemical Reversibility of Ni-Rich Cathodes in Li-Ion Batteries

In view of their high theoretical capacities, nickel-rich layered oxides are promising cathode materials for high-energy Li-ion batteries. However, the practical applications of these oxides are hindered by transition metal dissolution, microcracking, and gas/reactive compound formation due to the undesired reactions of residual lithium species. Herein, we show that the interfacial degradation of the LiNi_0.9Co_xMn_yAl_zO₂ (NCMA, x + y + z = 0.1) cathode and the graphite (Gr) anode of a representative Li-ion battery by HF can be hindered by supplementing the electrolyte with tert-butyldimethylsilyl glycidyl ether (tBS-GE). The silyl ether moiety of tBS-GE scavenges HF and PF₅, thus stabilizing the interfacial layers on both electrodes, while the epoxide moiety reacts with CO₂ released by the parasitic reaction between HF and Li₂CO₃ on the NCMA surface to afford cyclic carbonates and thus suppresses battery swelling. NCMA/Gr full cells fabricated by supplementing the baseline electrolyte with 0.1 wt % tBS-GE feature an increased capacity retention of 85.5% and deliver a high discharge capacity of 162.9 mAh/g after 500 cycles at 1 C and 25 °C. Thus, our results reveal that the molecular aspect-based design of electrolyte additives can be efficiently used to eliminate reactive species and gas components from Li-ion batteries and increase their performance.

LiF-Rich Interfaces and HF Elimination Achieved by a Multifunctional Additive Enable High-Performance Li/LiNi0.8Co0.1Mn0.1O2 Batteries

Li-metal batteries (LMBs), especially in combination with high-energy-density Ni-rich materials, exhibit great potential for next-generation rechargeable Li batteries. Nevertheless, poor cathode-/anode-electrolyte interfaces (CEI/SEI) and hydrofluoric acid (HF) attack pose a threat to the electrochemical and safety performances of LMBs due to aggressive chemical and electrochemical reactivities of high-Ni materials, metallic Li, and carbonate-based electrolytes with the LiPF₆ salt. Herein, the carbonate electrolyte based on LiPF₆ is formulated by a multifunctional electrolyte additive pentafluorophenyl trifluoroacetate (PFTF) to adapt the Li/LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811) battery. It is theoretically illustrated and experimentally revealed that HF elimination and the LiF-rich CEI/SEI films are successfully achieved via the chemical and electrochemical reactions of the PFTF additive. Significantly, the LiF-rich SEI film with high electrochemical kinetics facilitates Li homogeneous deposition and prevents dendritic Li from forming and growing. Benefiting from the collaborative protection of PFTF on the interfacial modification and HF capture, the capacity ratio of the Li/NCM811 battery is boosted by 22.4%, and the cycling stability of the symmetrical Li cell is expanded over 500 h. This provided strategy is conducive to the achievement of high-performance LMBs with Ni-rich materials by optimizing the electrolyte formula.

Cathode Electrolyte Interphase-Forming Additive for Improving Cycling Performance and Thermal Stability of Ni-Rich LiNixCoyMn1-x-yO2 Cathode Materials

High-capacity Ni-rich LiNi_xCo_yMn_1-x-yO₂ (NCM) has been investigated as a promising cathode active material for improving the energy density of lithium-ion batteries (LIBs); however, its practical application is limited by its structural instability and low thermal stability. In this study, we synthesized tetrakis(methacryloyloxyethyl)pyrophosphate (TMAEPPi) as a cathode electrolyte interphase (CEI) additive to enhance the cycling characteristics and thermal stability of the LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811) material. TMAEPPi was oxidized to form a uniform Li⁺-ion-conductive CEI on the cathode surface during initial cycles. A lithium-ion cell (graphite/NCM811) employing a liquid electrolyte containing 0.5 wt % TMAEPPi exhibited superior capacity retention (82.2% after 300 cycles at a 1.0 C rate) and enhanced high-rate performance compared with the cell using a baseline liquid electrolyte. The TMAEPPi-derived CEI layer on NCM811 suppressed electrolyte decomposition and reduced the microcracking of the NCM811 particles. Our results reveal that TMAEPPi is a promising additive for forming stable CEIs and thereby improving the cycling performance and thermal stability of LIBs employing high-capacity NCM cathode materials.

Multifunctional Electrolyte Additive for Bi-electrode Interphase Regulation and Electrolyte Stabilization in Li/LiNi0.8Co0.1Mn0.1O2 Batteries

Rechargeable lithium metal batteries (LMBs) with high energy densities can be achieved by coupling a lithium metal anode (LMA) and a LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811) cathode. Nevertheless, Li dendrite growth on the LMA surface and structural collapse of the NCM811 material, closely tied with the fragile cathode-/solid-electrolyte interphases (CEI/SEI) and corrosive hydrogen fluoride (HF), seriously deteriorate their performances. Herein, trimethylsilyl trifluoroacetate (TMSTFA) as a multifunctional electrolyte additive is proposed for regulation of the CEI/SEI films and elimination of HF. For one thing, the TMSTFA-derived CEI film rich in C-O species is conductive to Li⁺ transport and structural stability of NCM811 materials, and the TMSTFA-derived SEI film mainly consisting of inorganics (Li₂CO₃ and LiF) and organics (C-O and O-C═O species) can significantly promote Li⁺ homogeneous deposition and impede the Li dendrite growth. For another thing, the undesired reactions of the solvents and LiPF₆ salt are effectively retarded by the TMSTFA additive. Consequently, in the presence of TMSTFA, the capacity retention of Li/NCM811 cell is increased by 17% after 200 cycles at 1C, and the lifespan of symmetrical Li/Li cells is prolonged beyond 600 h at 0.5 mA cm^-2.

Multifunctional Electrolyte Additive Stabilizes Electrode-Electrolyte Interface Layers for High-Voltage Lithium Metal Batteries

A lithium metal anode and high nickel ternary cathode are considered viable candidates for high energy density lithium metal batteries (LMBs). However, unstable electrode-electrolyte interfaces and structure degradation of high nickel ternary cathode materials lead to serious capacity decay, consequently hindering their practical applications in LMBs. Herein, we introduced N,O-bis(trimethylsilyl) trifluoro acetamide (BTA) as a multifunctional additive for removing trace water and hydrofluoric acid (HF) from the electrolyte and inhibiting corrosive HF from disrupting the electrode-electrolyte interface layers. Furthermore, the BTA additive containing multiple functional groups (C-F, Si-O, Si-N, and C═N) promotes the formation of LiF-rich, Si- and N-containing solid electrolyte interfacial films on a lithium metal anode and LiNi_0.8Mn_0.1Co_0.1O₂ (NMC811) cathode surfaces, thereby improving the electrode-electrolytes interfacial stability and mitigating the capacity decay caused by structural degradation of the layered cathode. Using the BTA additive had tremendous benefits through modification of both anode and cathode surface layers. This was demonstrated using a Li||NMC811 metal battery with the BTA electrolyte, which exhibits remarkable cycling and rate performances (122.9 mA h g^-1 at 10 C) and delivers a discharge capacity of 162 mA h g^-1 after 100 cycles at 45 °C. Likewise, this study establishes a cost-effective approach of using a single additive to improve the electrochemical performance of LMBs.