Electrolyte-Induced Morphology Evolution to Boost Potassium Storage Performance of Perylene-3,4,9,10-tetracarboxylic Dianhydride.

Organic materials have attracted extensive attention for potassium-ion batteries due to their flexible structure designability and environmental friendliness. However, organic materials generally suffer from unavoidable dissolution in aprotic electrolytes, causing an unsatisfactory electrochemical performance. Herein, we designed a weakly solvating electrolyte to boost the potassium storage performance of perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA). The electrolyte induces an in situ morphology evolution and achieves a nanowire structure. The weakly dissolving capability of ethylene glycol diethyl ether-based electrolyte and unique nanowire structure effectively avoid the dissolution of PTCDA. As a result, PTCDA shows excellent cycling stability (a capacity retention of 89.1% after 2000 cycles) and good rate performance (70.3 mAh g-1 at 50C). In addition, experimental detail discloses that the sulfonyl group plays a key role in inducing morphology evolution during the charge/discharge process. This work opens up new opportunities in electrolyte design for organic electrodes and illuminates further developments of potassium-ion batteries.

High-efficiency Lithium Metal Stabilization and Polysulfide Suppression in Li-S Battery Enabled by Weakly Solvating Solvent.

Lithium-sulfur batteries (LSBs) are considered a highly promising next-generation energy storage technology due to their exceptional energy density and cost-effectiveness. However, the practical use of current LSBs is hindered primarily by issues related to the "shuttle effect" of lithium polysulfide (LiPS) intermediates and the growth of lithium dendrites. In strongly solvating electrolytes, the solvent-derived solid electrolyte interphase (SEI) lacks mechanical strength due to organic components, leading to ineffective lithium dendrite suppression and severe LiPS dissolution and shuttling. In contrast, the weakly solvating electrolyte (WSE) can create an anion-derived SEI layer which can enhance compatibility with lithium metal anode, and restricting LiPS solubility. Herein, a WSE consisting of 0.4 Ð¼ LiTFSI in the mixture of 1,4-dioxane (DX):dimethoxymethane (DMM) is designed to overcome the issues associated with LSB. Surface analyses confirmed the formation of a beneficial SEI layer rich in LiF, enabling homogeneous lithium deposition with an average Coulombic efficiency CE exceeding 99% over 100 cycles. Implementing the low-concentration WSE in Li||SPAN cells yielded an impressive initial specific capacity of 671 mAh g-1. This research highlights the advantages of WSE and offers the pathway for cost-effective electrolyte development, enabling the realization of high-performance LSBs.

Regulating Ion-Dipole Interactions in Weakly Solvating Electrolyte towards Ultra-Low Temperature Sodium-Ion Batteries.

Sodium-ion batteries (SIBs) are recognized as promising energy storage devices. However, they suffer from rapid capacity decay at ultra-low temperatures due to high Na+ desolvation energy barrier and unstable solid electrolyte interphase (SEI). Herein, a weakly solvating electrolyte (WSE) with decreased ion-dipole interactions is designed for stable sodium storage in hard carbon (HC) anode at ultra-low temperatures. 2-methyltetrahydrofuran with low solvating power is incorporated into tetrahydrofuran to regulate the interactions between Na+ and solvents. The reduced Na+-dipole interactions facilitate more anionic coordination in the first solvation sheath, which consistently maintains anion-enhanced solvation structures from room to low temperatures to promote inorganic-rich SEI formation. These enable WSE with a low freezing point of -83.3 °C and faster Na+ desolvation kinetics. The HC anode thus affords reversible capacities of 243.2 and 205.4 mAh g-1 at 50 mA g-1 at -40 and -60 °C, respectively, and the full cell of HC||Na3V2(PO4)3 yields an extended lifespan over 250 cycles with high capacity retention of ~100 % at -40 °C. This work sheds new lights on the ion-dipole regulation for ultra-low temperature SIBs.

Reversible Solid-Solid Conversion of Sulfurized Polyacrylonitrile Cathodes in Lithium-Sulfur Batteries by Weakly Solvating Ether Electrolytes.

Despite carbonate electrolytes exhibiting good stability to sulfurized polyacrylonitrile (SPAN), their chemical incompatibility with lithium (Li) metal anode leads to poor electrochemical performance of Li||SPAN full cells. While the SPAN employs conventional ether electrolytes that suffer from the shuttle effect, leading to rapid capacity fading. Here, we tailor a dilute electrolyte based on a low solvating power ether solvent that is both compatible with SPAN and Li metal. Unlike conventional ether electrolytes, the weakly solvating ether electrolyte enables SPAN to undergo reversibly "solid-solid" conversion. It features an anion-rich solvation structure that allows for the formation of a robust cathode electrolyte interphase on the SPAN, effectively blocking the dissolution of polysulfides into the bulk electrolyte and avoiding the shuttle effect. What's more, the unique electrolyte chemistry endowed Li ions with fast electroplating kinetics and induced high reversibility Li deposition/stripping process from 25 °C to -40 °C. Based on tailored electrolyte, Li||SPAN full cells matched with high loading SPAN cathodes (≈3.6 mAh cm-2 ) and 50 µm Li foil can operate stably over a wide range of temperatures. Additionally, Li||SPAN pouch cell under lean electrolyte and 5 % excess Li conditions can continuously operate stably for over a month.

Synergy of Weakly-Solvated Electrolyte and Optimized Interphase Enables Graphite Anode Charge at Low Temperature.

Graphite anode suffers from great capacity loss and even fails to charge (i.e. Li+ -intercalation) under low temperature, mainly arising from the large overpotential including sluggish de-solvation process and insufficient ions movement in the solid electrolyte interphase (SEI). Herein, an electrolyte is developed by utilizing weakly solvated molecule ethyl trifluoroacetate and film-forming fluoroethylene carbonate to achieve smooth de-solvation and high ionic conductivity at low temperature. Evolution of SEI formed at different temperatures is further investigated to propose an effective room-temperature SEI formation strategy for low-temperature operations. The synergetic effect of tamed electrolyte and optimized SEI enables graphite with a reversible charge/discharge capacity of 183 mAh g-1 at -30 °C and fast-charging up to 6C-rate at room temperature. Moreover, graphite||LiFePO4 full cell maintains a capacity retention of 78 % at -30 °C, and 37 % even at a super-low temperature of -60 °C. This work offers a progressive insight towards fast-charging and low-temperature batteries.

Bulk bismuth anodes for wide-temperature sodium-ion batteries enabled by electrolyte chemistry modulation.

Sodium ion batteries (SIBs) are considered reliable supplies for next-generation energy devices. However, there is a limited understanding of strategies to prevent the performance deterioration of SIBs under extreme temperature conditions. This study aimed to address this challenge by developing modified electrolyte chemistry to achieve stable wide-temperature SIBs. Weakly Na+-solvating solvent 2-methyltetrahydrofuran (MeTHF) was used to promote the kinetics of Na+ de-solvation. Moreover, 1,2-dimethoxyethane (DME) was introduced as a co-solvent because of the high solubility for Na salts and the coupling reaction mechanism with the Bi electrode. The formulated electrolyte not only endows an anion-dominated NaF-rich solid electrolyte interface (SEI) layer, but also reduces the energy required for the Na+ across the SEI layer (from 291.2 to 89.6 meV). Consequently, Na||Bi half batteries achieve stable cycles at 400 mA g-1 at -20, 20 and 60 °C, respectively. Meanwhile, the extreme operating temperature of the batteries can be extended to -40 and 80 °C, which exceeds those of most current lithium/sodium-based batteries. Furthermore, full batteries employing Na3V2(PO4)3 as the cathode material exhibit stable operation over a wide temperature range of -20 to 60 °C. This electrolyte design strategy presented in this study shows significant promise for enabling wide-temperature SIBs with improved performance.