Solvation Engineering via Fluorosurfactant Additive Toward Boosted Lithium-Ion Thermoelectrochemical Cells.

Lithium-ion thermoelectrochemical cell (LTEC), featuring simultaneous energy conversion and storage, has emerged as promising candidate for low-grade heat harvesting. However, relatively poor thermosensitivity and heat-to-current behavior limit the application of LTECs using LiPF6 electrolyte. Introducing additives into bulk electrolyte is a reasonable strategy to solve such problem by modifying the solvation structure of electrolyte ions. In this work, we develop a dual-salt electrolyte with fluorosurfactant (FS) additive to achieve high thermopower and durability of LTECs during the conversion of low-grade heat into electricity. The addition of FS induces a unique Li+ solvation with the aggregated double anions through a crowded electrolyte environment, resulting in an enhanced mobility kinetics of Li+ as well as boosted thermoelectrochemical performances. By coupling optimized electrolyte with graphite electrode, a high thermopower of 13.8 mV K-1 and a normalized output power density of 3.99 mW m-2 K-2 as well as an outstanding output energy density of 607.96 J m-2 can be obtained. These results demonstrate that the optimization of electrolyte by regulating solvation structure will inject new vitality into the construction of thermoelectrochemical devices with attractive properties.

Prolonging the Cycle Stability of Anion Redox P3-Type Na0.6Li0.2Mn0.8O2 through Al2O3 Atomic Layer Deposition Surface Modification.

Sodium-ion batteries (SIBs) are becoming an alternative option for large-scale energy storage systems owing to their low cost and abundance. The lattice oxygen redox (LOR), which has the potential to increase the reversible capacity of materials, has promoted the development of high-energy cathode materials in SIBs. However, the utilization of oxygen anion redox reactions usually results in harmful lattice oxygen release, which hastens structural deformation and declines electrochemical performance, severely hindering their practical application. Herein, a ribbon-ordered superstructured P3-type Na0.6Li0.2Mn0.8O2 (NLMO) cathode with a uniform Al2O3 coating through atomic layer deposition (ALD) was synthesized. The cycling stability and rate capability of the materials were improved by a proper thickness of the Al2O3 layer. Differential electrochemical mass spectrometry (DEMS) results clearly suggest that the Al2O3 coating can inhibit the CO2 release caused by the highly active surface of the NLMO material. Moreover, the results of transmission electron microscopy (TEM) and etching X-ray photoelectron spectroscopy (XPS) show that the Al2O3 coating can effectively prevent electrolyte and electrode side reactions and the dissolution of Mn. This surface engineering strategy sheds light on the way to prolong the cycling stability of anionic redox cathode materials.

Enabling giant thermopower by heterostructure engineering of hydrated vanadium pentoxide for zinc ion thermal charging cells.

Flexible power supply devices provide possibilities for wearable electronics in the Internet of Things. However, unsatisfying capacity or lifetime of typical batteries or capacitors seriously limit their practical applications. Different from conventional heat-to-electricity generators, zinc ion thermal charging cells has been a competitive candidate for the self-power supply solution, but the lack of promising cathode materials has restricted the achievement of promising performances. Herein, we propose an attractive cathode material by rational heterostructure engineering of hydrated vanadium pentoxide. Owing to the integration of thermodiffusion and thermoextraction effects, the thermopower is significantly improved from 7.8 ± 2.6 mV K-1 to 23.4 ± 1.5 mV K-1. Moreover, an impressive normalized power density of 1.9 mW m-2 K-2 is achieved in the quasi-solid-state cells. In addition, a wearable power supply constructed by three units can drive the commercial health monitoring system by harvesting body heat. This work demonstrates the effectiveness of electrodes design for wearable thermoelectric applications.

High-voltage lithium-metal batteries enabled by ethylene glycol bis(propionitrile) ether-LiNO3 synergetic additives.

The employment of Li metal anodes is a key to realizing ultra-high energy batteries. However, the commercialization of lithium metal batteries (LMBs) remains challenging partially due to the thermodynamic instability and competitive oxidative decomposition of the solvent. Herein, a bi-functional electrolyte for stabilizing the interfaces of both the Li metal anode and LiCoO2 (LCO) cathode is designed by introducing lithium nitrate (LiNO3) through Ethylene Glycol Bis(Propionitrile) Ether (DENE). For the anode, the C8H12N2O2-LiNO3 coordination-solvation contributes to forming a stable Li3N-enhanced solid electrolyte interphase (SEI), which increases the average Li coulombic efficiency (CE) up to 98.5%. More importantly, in situ electrochemical dilatometry further reveals that the highly reversible behavior and a low volume expansion of lithium deposition are related to the stable Li3N-enhanced SEI. The designed electrolyte enables the Li‖LCO cell to achieve an average CE of 99.2% and a high capacity retention of 88.2% up to 4.6 V after 100 cycles. This work provides a strategic guidance in developing high-voltage Li‖LCO batteries with dual electrolyte additives.

Optimizing Li-ion Solvation in Gel Polymer Electrolytes to Stabilize Li-Metal Anode.

Gel polymer electrolytes (GPEs) have potential as substitutes for liquid electrolytes in lithium-metal batteries (LMBs). Their semi-solid state also makes GPEs suitable for various applications, including wearables and flexible electronics. Here, we report the initiation of ring-opening polymerization of 1,3-dioxolane (DOL) by Lewis acid and the introduction of diluent 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether (TTE) to regulate electrolyte structure for a more stable interface. This diluent-blended GPE exhibits enhanced electrochemical stability and ion transport properties compared to a blank version without it. FTIR and NMR proved the effectiveness of monomer polymerization and further determined the molecular weight distribution of polymerization by gel permeation chromatography (GPC). Experimental and simulation results show that the addition of TTE enhances ion association and tends to distribute on the anode surface to construct a robust and low-impedance SEI. Thus, the polymer battery achieves 5 C charge-discharge at room temperature and 200 cycles at low temperature -20 °C. The study presents an effective approach for regulating solvation structures in GPEs, promoting advancements in the future design of GPE-based LMBs.

Rational design of covalent organic frameworks with high capacity and stability as a lithium-ion battery cathode.

A two-dimensional covalent organic framework (NTCDI-COF) with rich redox active sites, high stability and crystallinity was designed and prepared. As a cathode material for lithium-ion batteries (LIBs), NTCDI-COF exhibits excellent electrochemical performance with an outstanding discharge capacity of 210 mA h g-1 at 0.1 A g-1 and high capacity retention of 125 mA h g-1 after 1500 cycles at 2 A g-1. A two-step Li+ insertion/extraction mechanism is proposed based on the ex situ characterization and density functional theory calculation. The constructed NTCDI-COF//graphite full cells can realize a good electrochemical performance.

Nitrogen-doped carbon encapsulating Fe7Se8 anode with core-shell structure enables high-performance sodium-ion capacitors.

With the associated advantages of low costs and abundant resources, sodium-ion capacitors (SICs) present a suitable means for large-scale energy storage. However, their practical application is still significantly limited by the sluggish electrochemical reaction kinetics of battery-type anodes. Herein, the nitrogen-doped carbon-encapsulated Fe7Se8 nanorods (Fe7Se8@NC) with a core-shell structure were prepared via an in-situ self-polymerization and carbonization-selenization approach, which improves ion transport and maintains the structural stability of the nanorods. The designed Fe7Se8@NC nanorods exhibit desirable rate capability with a capacity of 290.7 mAh/g at 10 A/g and long-term cyclability with 84.6 % retention over 6000 cycles at 5 A/g. Moreover, research has shown that the diffusion dynamics of Na+ is improved in ether-based electrolytes and that the irreversible reactions at low voltages can be inhibited by a high discharge cut-off voltage. Furthermore, we demonstrated the specific sodium storage mechanism and excellent electrochemical reversibility of the Fe7Se8@NC electrode through in-situ and ex-situ characterization techniques. As expected, the assembled SICs with the Fe7Se8@NC anode and active carbon cathode deliver prominent energy/power densities and an ultra-long cycle life over 5000 cycles, shedding new light on the design of transition metal dichalcogenides as anode materials for advanced energy storage systems.

Zinc ion thermal charging cell for low-grade heat conversion and energy storage.

Converting low-grade heat from environment into electricity shows great sustainability for mitigating the energy crisis and adjusting energy configurations. However, thermally rechargeable devices typically suffer from poor conversion efficiency when a semiconductor is employed. Breaking the convention of thermoelectric systems, we propose and demonstrate a new zinc ion thermal charging cell to generate electricity from low-grade heat via the thermo-extraction/insertion and thermodiffusion processes of insertion-type cathode (VO2-PC) and stripping/plating behaviour of Zn anode. Based on this strategy, an impressively high thermopower of ~12.5 mV K-1 and an excellent output power of 1.2 mW can be obtained. In addition, a high heat-to-current conversion efficiency of 0.95% (7.25% of Carnot efficiency) is achieved with a temperature difference of 45 K. This work, which demonstrates extraordinary energy conversion efficiency and adequate energy storage, will pave the way towards the construction of thermoelectric setups with attractive properties for high value-added utilization of low-grade heat.

Regulation of SEI Formation by Anion Receptors to Achieve Ultra-Stable Lithium-Metal Batteries.

Despite high specific capacity (3860 mAh g-1 ), the utilization of Li-metal anodes in rechargeable batteries are still hampered due to their insufficient cyclability. Herein, we report an anion-receptor-mediated carbonate electrolyte with improved performance and can ameliorate the solid electrolyte interphase (SEI) composition comparing to the blank electrolyte. It demonstrates a high average Coulombic efficiency (97.94 %) over 500 cycles in the Li/Cu cell at a capacity of 1 mAh cm-2 . Raman spectrum and molecular modelling further clarify the screening effects of the anion receptor on the Li+ -PF6 - ion coupling that results in the enhanced ion dynamics. The X-ray photoelectron spectroscopy (XPS) distinguishes the disparities in the SEI components of the developed electrolyte and the blank one, which is rationalized by the molecular insights of the Li-metal/electrolyte interface. Thus, we prepare a 2.5 Ah prototype pouch cell, exhibiting a high energy density (357 Wh kg-1 ) with 90.90 % capacity retention over 50 cycles.

Sodium-ion capacitors: Materials, Mechanism, and Challenges.

Sodium-ion capacitors (SICs), designed to attain high energy density, rapid energy delivery, and long lifespan, have attracted much attention because of their comparable performance to lithium-ion capacitors (LICs), alongside abundant sodium resources. Conventional SIC design is based on battery-like anodes and capacitive cathodes, in which the battery-like anode materials involve various reactions, such as insertion, alloying, and conversion reactions, and the capacitive cathode materials usually depend on activated carbon (AC). However, researchers have attempted to construct SICs based on battery-like cathodes and capacitive anodes or a combination of both in recent years. In this Minireview, charge storage mechanisms and material design strategies for SICs are summarized, with a focus on the battery-like anode materials from both inorganic and organic sources. Additionally, the challenges in the fabrication of SICs and future research directions are discussed.

A Heavily Surface-Doped Polymer with the Bifunctional Catalytic Mechanism in Li-O2 Batteries.

The application of conducting polymers (CPs) in energy storage systems is greatly limited by insufficient reversibility and stability. Here, we successfully incorporated functionalized dopants (Fe(CN)63- [FCN] and PO43- ions) in CPs matrixes to achieve a preferable electrochemical performance. A stable cation inserting/expulsing behavior of surface-doped polycarbazole (PCz) is demonstrated in our work, where doping levels and semiconductor properties of PCz are effectively controlled to adjust their redox properties and stability. With carbon nanotube (CNT) films as the substrate, the CNT/PCz:FCN composite is initially adopted as a free-standing catalytic electrode in Li-O2 cells. The molecule-level dispersed FCN dopants on the surface can work as bifunctional redox mediators on the charge-discharge process. Thus, this composite can not only achieve a low charge plateau of 3.62 V and a regular growth of capacities from 1,800 to 4,800 mAh/gCNT, but also maintain the most of charge voltages under 4.0 V for 150 cycles.

Li4 Ti5 O12 Anode: Structural Design from Material to Electrode and the Construction of Energy Storage Devices.

Spinel Li4 Ti5 O12 , known as a zero-strain material, is capable to be a competent anode material for promising applications in state-of-art electrochemical energy storage devices (EESDs). Compared with commercial graphite, spinel Li4 Ti5 O12 offers a high operating potential of ∼1.55 V vs Li/Li+ , negligible volume expansion during Li+ intercalation process and excellent thermal stability, leading to high safety and favorable cyclability. Despite the merits of Li4 Ti5 O12 been presented, there still remains the issue of Li4 Ti5 O12 suffering from poor electronic conductivity, manifesting disadvantageous rate performance. Typically, a material modification process of Li4 Ti5 O12 will be proposed to overcome such an issue. However, the previous reports have made few investigations and achievements to analyze the subsequent processes after a material modification process. In this review, we attempt to put considerable interest in complete device design and assembly process with its material structure design (or modification process), electrode structure design and device construction design. Moreover, we have systematically concluded a series of representative design schemes, which can be divided into three major categories involving: (1) nanostructures design, conductive material coating process and doping process on material level; (2) self-supporting or flexible electrode structure design on electrode level; (3) rational assembling of lithium ion full cell or lithium ion capacitor on device level. We believe that these rational designs can give an advanced performance for Li4 Ti5 O12 -based energy storage device and deliver a deep inspiration.