A Highly-Fluorinated Lithium Borate Main Salt Empowering Stable Lithium Metal Batteries.

Traditional lithium salts are difficult to meet practical application demand of lithium metal batteries (LMBs) under high voltages and temperatures. LiPF6, as the most commonly used lithium salt, still suffers from notorious moisture sensitivity and inferior thermal stability under those conditions. Here, we synthesize a lithium salt of lithium perfluoropinacolatoborate (LiFPB) comprising highly-fluorinated and borate functional groups to address the above issues. It is demonstrated that the LiFPB shows superior thermal and electrochemical stability without any HF generation under high temperatures and voltages. In addition, the LiFPB can form a protective outer-organic and inner-inorganic rich cathode electrolyte interphase on LiCoO2 (LCO) surface. Simultaneously, the FPB- anions tend to integrate into lithium ion solvation structure to form a favorable fast-ion conductive LiBxOy based solid electrolyte interphase on lithium (Li) anode. All these fantastic features of LiFPB endow LCO (1.9 mAh cm-2)/Li metal cells excellent cycling under both high voltages and temperatures (e.g., 80 % capacity retention after 260 cycles at 60 °C and 4.45 V), and even at an extremely elevated temperature of 100 °C. This work emphasizes the important role of salt anions in determining the electrochemical performance of LMBs at both high temperature and voltage conditions.

Interphase Regulation by Multifunctional Additive Empowering High Energy Lithium-Ion Batteries with Enhanced Cycle Life and Thermal Safety.

High energy density lithium-ion batteries (LIBs) adopting high-nickel layered oxide cathodes and silicon-based composite anodes always suffer from unsatisfied cycle life and poor safety performance, especially at elevated temperatures. Electrode /electrolyte interphase regulation by functional additives is one of the most economic and efficacious strategies to overcome this shortcoming. Herein, cyano-groups (-CN) are introduced into lithium fluorinated phosphate to synthesize a novel multifunctional additive of lithium tetrafluoro (1,2-dihydroxyethane-1,1,2,2-tetracarbonitrile) phosphate (LiTFTCP), which endows high nickel LiNi0.8 Co0.1 Mn0.1 O2 /SiOx -graphite composite full cell with an ultrahigh cycle life and superior safety characteristics, by adding only 0.5 wt % LiTFTCP into a LiPF6 -carbonate baseline electrolyte. It is revealed that LiTFTCP additive effectively suppresses the HF generation and facilitates the formation of a robust and heat-resistant cyano-enriched CEI layer as well as a stable LiF-enriched SEI layer. The favorable SEI/CEI layers greatly lessen the electrode degradation, electrolyte consumption, thermal-induced gassing and total heat-releasing. This work illuminates the importance of additive molecular engineering and interphase regulation in simultaneously promoting the cycling and thermal safety of LIBs with high-nickel NCMxyz cathode and silicon-based composite anode.

Self-Standing Single-Ion Borate Salt-Based Polymer Electrolyte for Lithium Metal Batteries.

Polymer electrolytes (PEs) with excellent flexibility and superior compatibility toward lithium (Li) metal anodes have been deemed as one of the most promising alternatives to liquid electrolytes. However, conventional lithium bis(trifluoromethanesulfonyl)imide (LiTFSI)-based dual-ion PEs suffer from a low Li ion transference number and notorious Li dendrite growth. Here, a single-ion conducting polyborate salt without any fluorinated groups, polymeric lithium dihydroxyterephthalic acid borate (PLDPB), is presented for addressing the issues of Li metal batteries. Owing to a nearly immovable bulky anion and the presence of a rigid benzene structure, the PLDPB@poly(ethylene oxide) (PEO) PE exhibits an ultrahigh Li ion transference number (0.94) and excellent mechanical strength, which could significantly restrict the growth of Li dendrites. Postmortem analysis reveals that a fluorine-free solid electrolyte interphase (SEI) enriched with B-O and benzene-containing species is formed on the surface of the Li metal anode, thereby facilitating elimination of excessive parasitic reactions and simultaneously suppressing the formation of Li dendrites. Consequently, the LiFePO4/Li cells with PLDPB@PEO PEs show an improved long-term cycling performance and high capacity retention (90.0%) and Coulombic efficiency (99.9%) after 500 cycles. This work may inspire new ideas to boost the development of single-ion conducting salts for dendrite-free Li metal batteries.

Highly Oxidative-Resistant Cyano-Functionalized Lithium Borate Salt for Enhanced Cycling Performance of Practical Lithium-Ion Batteries.

Lithium difluoro(oxalato) borate (LiDFOB) has been widely investigated in lithium-ion batteries (LIBs) owing to its advantageous thermal stability and excellent aluminum passivation property. However, LiDFOB tends to suffer from severe decomposition and generate a lot of gas species (e.g., CO2 ). Herein, a novel cyano-functionalized lithium borate salt, namely lithium difluoro(1,2-dihydroxyethane-1,1,2,2-tetracarbonitrile) borate (LiDFTCB), is innovatively synthesized as a highly oxidative-resistant salt to alleviate above dilemma. It is revealed that the LiDFTCB-based electrolyte enables LiCoO2 /graphite cells with superior capacity retention at both room and elevated temperatures (e.g., 80 % after 600 cycles) with barely any CO2 gas evolution. Systematic studies reveal that LiDFTCB tends to form thin and robust interfacial layers at both electrodes. This work emphasizes the crucial role of cyano-functionalized anions in improving cycle lifespan and safety of practical LIBs.

A Novel Potassium Salt Regulated Solvation Chemistry Enabling Excellent Li-Anode Protection in Carbonate Electrolytes.

In lithium-metal batteries (LMBs), the compatibility of Li anode and conventional lithium hexafluorophosphate-(LiPF6 ) carbonate electrolyte is poor owing to the severe parasitic reactions. Herein, to resolve this issue, a delicately designed additive of potassium perfluoropinacolatoborate (KFPB) is unprecedentedly synthesized. On the one hand, KFPB additive can regulate the solvation structure of the carbonate electrolyte, promoting the formation of Li+ FPB- and K+ PF6 - ion pairs with lower lowest unoccupied molecular orbital (LUMO) energy levels. On the other hand, FPB- anion possesses strong adsorption ability on Li anode. Thus, anions can preferentially adsorb and decompose on the Li-anode surface to form a conductive and robust solid-electrolyte interphase (SEI) layer. Only with a trace amount of KFPB additive (0.03 m) in the carbonate electrolyte, Li dendrites' growth can be totally suppressed, and Li||Cu and Li||Li half cells exhibit excellent Li-plating/stripping stability upon cycling. Encouragingly, KFPB-assisted carbonate electrolyte enables high areal capacity LiCoO2 ||Li, LiNi0.8 Co0.1 Mn0.1 O2 (NCM811)||Li, and LiNi0.8 Co0.05 Al0.15 O2 (NCA)||Li LMBs with superior cycling stability, showing its excellent universality. This work reveals the importance of designing novel additives to regulate the solvation structure of carbonate electrolytes in improving its interface compatibility with the Li anode.

Cathode Electrolyte Interphase (CEI) Endows Mo6 S8 with Fast Interfacial Magnesium-Ion Transfer Kinetics.

Magnesium (Mg) metal secondary batteries have attracted much attention for their high safety and high energy density characteristics. However, the significant issues of the cathode/electrolyte interphase (CEI) in Mg batteries are still being ignored. In this work, a significant CEI layer on the typical Mo6 S8 cathode surface has been unprecedentedly constructed through the oxidation of the chloride-free magnesium tetrakis(hexafluoroisopropyloxy)borate (Mg[B(hfip)4 ]2 ) salt under a proper charge cut-off voltage condition. The CEI has been identified to contain Bx Oy effective species originating from the oxidation of [B(hfip)4 ]- anion. It is confirmed that the Bx Oy species is beneficial to the desolvation of solvated Mg2+ , speeding up the interfacial Mg2+ transfer kinetics, thereby improving the Mg2+ -storage capability of Mo6 S8 host. The firstly reported CEI in Mg batteries will give deeper insights into the interface issues in multivalent electrochemical systems.

Leakage-Proof Electrolyte Chemistry for a High-Performance Lithium-Sulfur Battery.

Electrolyte leakage is a severe safety concern in lithium batteries. With highly volatile 1,2-dimethoxyethane as solvent, the leakage related hazards are more pronounced in lithium-sulfur (Li-S) batteries. To address this concern, a leakage-proof electrolyte is delicately designed through functionalizing the commercial electrolyte by Li6 PS5 Cl-grafted poly(ethyl cyanoacrylate), which can interact readily with the aluminum-plastic packing through hydrogen bond to immobilize the electrolyte. The moisture from ambient can also catalyze a further polymerization of the macromolecules to seal the leaking points and thereby to solve the leakage issue, endowing Li-S batteries superior safety even in an artificial cut pouch cell. With a bare S loading of 4.9 mg cm-2 , the battery can deliver good endurance owing to the suppressed polysulfide shuttle by its polar groups. This work enlightens the design of leakage-proof electrolyte and makes a milestone for high performance Li-S batteries.

A Novel Regulation Strategy of Solid Electrolyte Interphase Based on Anion-Solvent Coordination for Magnesium Metal Anode.

Magnesium (Mg) metal anode is a highly desirable candidate among various high energy density metal anodes, possessing higher volumetric capacity and better safety characteristic compared to lithium metal. However, most Mg salts in conventional Mg electrolytes easily react with Mg metal to form blocking layers, leading to inferior reversibility of Mg plating/stripping. Here, a stable Mg2+ -conducting solid electrolyte interphase (SEI) is successfully constructed on Mg metal anode by regulating the molecular-orbital-energy-level toward an aluminum(III)-centered anion Mg salt through anion-solvent coordination. Of which, the LUMO energy level of perfluorinated pinacolatoaluminate (Al(O2 C2 (CF3 )4 )2 - , abbreviated as FPA) anion has been adjusted by coordinating with solvent molecule (tetrahydrofuran) for facilitating the formation of advantageous SEI. The existence of SEI formed by FPA anion greatly improves the reversibility and long-term stability of Mg plating/stripping process. More importantly, based on this aluminum(III)-centered Mg electrolyte, the Mo6 S8 /Mg batteries can achieve a fantastic cycle performance of 9000 cycles, proving the beneficial effect of SEI on the cycling stability of Mg battery system. These findings open up a promising avenue to construct stable and compatible SEI on Mg metal anode, and lay significant foundations for the successful development of rechargeable Mg metal batteries.

A Stable Solid Electrolyte Interphase for Magnesium Metal Anode Evolved from a Bulky Anion Lithium Salt.

Rechargeable magnesium (Mg) metal batteries are a promising candidate for "post-Li-ion batteries" due to their high capacity, high abundance, and most importantly, highly reversible and dendrite-free Mg metal anode. However, the formation of passivating surface film rather than Mg2+ -conducting solid electrolyte interphase (SEI) on Mg anode surface has always restricted the development of rechargeable Mg batteries. A stable SEI is constructed on the surface of Mg metal anode by the partial decomposition of a pristine Li electrolyte in the electrochemical process. This Li electrolyte is easily prepared by dissolving lithium tetrakis(hexafluoroisopropyloxy)borate (Li[B(hfip)4 ]) in dimethoxyethane. It is noteworthy that Mg2+ can be directly introduced into this Li electrolyte during the initial electrochemical cycles for in situ forming a hybrid Mg2+ /Li+ electrolyte, and then the cycled electrolyte can conduct Mg-ion smoothly. The existence of this as-formed SEI blocks the further parasitic reaction of Mg metal anode with electrolyte and enables this electrolyte enduring long-term electrochemical cycles stably. This approach of constructing superior SEI on Mg anode surface and exploiting novel Mg electrolyte provides a new avenue for practical application of high-performance rechargeable Mg batteries.

Differentiated Lithium Salt Design for Multilayered PEO Electrolyte Enables a High-Voltage Solid-State Lithium Metal Battery.

Low ionic conductivity at room temperature and limited electrochemical window of poly(ethylene oxide) (PEO) are the bottlenecks restricting its further application in high-energy density lithium metal battery. Herein, a differentiated salt designed multilayered PEO-based solid polymer electrolyte (DSM-SPE) is exploited to achieve excellent electrochemical performance toward both the high-voltage LiCoO2 cathode and the lithium metal anode. The LiCoO2/Li metal battery with DSM-SPE displays a capacity retention of 83.3% after 100 cycles at 60 °C with challenging voltage range of 2.5 to 4.3 V, which is the best cycling performance for high-voltage (≥4.3 V) LiCoO2/Li metal battery with PEO-based electrolytes up to now. Moreover, the Li/Li symmetrical cells present stable and low polarization plating/stripping behavior (less than 80 mV over 600 h) at current density of 0.25 mA cm-2 (0.25 mAh cm-2). Even under a high-area capacity of 2 mAh cm-2, the profiles still maintain stable. The pouch cell with DSM-SPE exhibits no volume expansion, voltage decline, ignition or explosion after being impaled and cut at a fully charged state, proving the excellent safety characteristic of the DSM-SPE-based lithium metal battery.

Additive-Assisted Novel Dual-Salt Electrolyte Addresses Wide Temperature Operation of Lithium-Metal Batteries.

In this study, self-synthesized lithium trifluoro(perfluoro-tert-butyloxyl)borate (LiTFPFB) is combined with lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) to formulate a novel 1 m dual-salt electrolyte, which contains lithium difluorophosphate (LiPO2 F2 ) additive and dominant carbonate solvents with low melting point and high boiling point. The addition of LiPO2 F2 into this novel dual-salt electrolyte dramatically improves cycleability and rate capability of a LiNi0.5 Mn0.3 Co0.2 O2 /Li (NMC/Li) battery, ranging from -40 to 90 °C. The NMC/Li batteries adopt a Li-metal anode with low thickness of 100 µm (even 50 µm) and a moderately high cathode mass loading level of 10 mg cm-2 . For the first time, this paper provides valuable perspectives for developing practical lithium-metal batteries over a wide temperature range.

A Crosslinked Polytetrahydrofuran-Borate-Based Polymer Electrolyte Enabling Wide-Working-Temperature-Range Rechargeable Magnesium Batteries.

A polymer-based magnesium (Mg) electrolyte is vital for boosting the development of high-safety and flexible Mg batteries by virtue of its enormous advantages, such as significantly improved safety, potentially high energy density, ease of fabrication, and structural flexibility. Herein, a novel polytetrahydrofuran-borate-based gel polymer electrolyte coupling with glass fiber is synthesized via an in situ crosslinking reaction of magnesium borohydride [Mg(BH4 )2 ] and hydroxyl-terminated polytetrahydrofuran. This gel polymer electrolyte exhibits reversible Mg plating/stripping performance, high Mg-ion conductivity, and remarkable Mg-ion transfer number. The Mo6 S8 /Mg batteries assembled with this gel polymer electrolyte not only work well at wide temperature range (-20 to 60 °C) but also display unprecedented improvements in safety issues without suffering from internal short-circuit failure even after a cutting test. This in situ crosslinking approach toward exploiting the Mg-polymer electrolyte provides a promising strategy for achieving large-scale application of Mg-metal batteries.

A promising bulky anion based lithium borate salt for lithium metal batteries.

A new salt of lithium trifluoro(perfluoro-tert-butyloxyl)borate (LiTFPFB) which possesses a bulky fluoroalkoxyl functional group in the borate anion has been synthesized for high energy lithium metal batteries. The presence of the bulky fluoroalkoxyl group in the borate anion of LiTFPFB can facilitate ion dissociation and in situ generate a protective film on the Li anode. As a result, LiTFPFB possesses a dramatically improved ionic conductivity and LiFePO4/Li cells using 1.0 M LiTFPFB/PC electrolyte exhibit improved capacity retention especially upon cycling at elevated temperature (60 °C). Ex situ surface analysis reveals that a protective film is formed on the lithium metal anode, which can inhibit further decomposition of the electrolyte. Furthermore, the LiTFPFB based electrolyte also imparts an excellent cycling performance to LiCoO2/Li metal cells for 500 cycles. The outstanding performance of the LiTFPFB salt demonstrates that it is a very promising baseline salt for next generation lithium metal batteries.

Construction of Large-Area Uniform Graphdiyne Film for High-Performance Lithium-Ion Batteries.

Large-area graphdiyne film is constructed by heat treatment, including thermally induced evaporation and a cross-coupling reaction process. The growth mechanism is proposed based on the observation and characterization that the heating temperature plays an important role in the evaporation of oligomers and in triggering the thermal cross-coupling reaction, whereas the heating duration mainly determines the execution of the thermal cross-coupling reaction. By controlling the heat-treatment process, a graphdiyne film with uniform morphology and good conductivity is obtained. The improved GDY film based electrodes deliver good interfacial contact and more lithium storage sites; thus leading to superior electrochemical performance. A reversible capacity of 901 mAh g-1 is achieved. Specifically, the electrodes exhibit excellent rate performance, with which a capacity of 430 mAh g-1 is maintained at a rate as high as 5 A g-1 . These advantages mean that the uniform graphdiyne film is a good candidate for the fabrication of a flexible and high-capacity electrode material.

High Performance Solid Polymer Electrolytes for Rechargeable Batteries: A Self-Catalyzed Strategy toward Facile Synthesis.

It is urgent to seek high performance solid polymer electrolytes (SPEs) via a facile chemistry and simple process. The lithium salts are composed of complex anions that are stabilized by a Lewis acid agent. This Lewis acid can initiate the ring opening polymerization. Herein, a self-catalyzed strategy toward facile synthesis of crosslinked poly(ethylene glycol) diglycidyl ether-based solid polymer electrolyte (C-PEGDE) is presented. It is manifested that the poly(ethylene glycol) diglycidyl ether-based solid polymer electrolyte possesses a superior electrochemical stability window up to 4.5 V versus Li/Li+ and considerable ionic conductivity of 8.9 × 10-5 S cm-1 at ambient temperature. Moreover, the LiFePO4/C-PEGDE/Li batteries deliver stable charge/discharge profiles and considerable rate capability. It is demonstrated that this self-catalyzed strategy can be a very effective approach for high performance solid polymer electrolytes.

Hydrogen substituted graphdiyne as carbon-rich flexible electrode for lithium and sodium ion batteries.

Organic electrodes are potential alternatives to current inorganic electrode materials for lithium ion and sodium ion batteries powering portable and wearable electronics, in terms of their mechanical flexibility, function tunability and low cost. However, the low capacity, poor rate performance and rapid capacity degradation impede their practical application. Here, we concentrate on the molecular design for improved conductivity and capacity, and favorable bulk ion transport. Through an in situ cross-coupling reaction of triethynylbenzene on copper foil, the carbon-rich frame hydrogen substituted graphdiyne film is fabricated. The organic film can act as free-standing flexible electrode for both lithium ion and sodium ion batteries, and large reversible capacities of 1050 mAh g-1 for lithium ion batteries and 650 mAh g-1 for sodium ion batteries are achieved. The electrode also shows a superior rate and cycle performances owing to the extended π-conjugated system, and the hierarchical pore bulk with large surface area.

A Delicately Designed Sulfide Graphdiyne Compatible Cathode for High-Performance Lithium/Magnesium-Sulfur Batteries.

Novel sulfur cathodes hold the key to the development of metal-sulfur batteries, the promising candidate of next-generation high-energy-storage systems. Herein, a fascinating sulfur cathode based on sulfide graphdiyne (SGDY) is designed with a unique structure, which is composed of a conducting carbon skeleton with high Li+ mobility and short sulfur energy-storing unites. The SGDY cathode can essentially avoid polysulfide dissolution and be compatible with commercially available carbonate-based electrolytes and Grignard reagent-based electrolytes (all phenyl complex (APC) type electrolytes). Both the assembled Li-S and Mg-S batteries exhibit excellent electrochemical performances including large capacity, superior rate capability, high capacity retention, and high Coulombic efficiency. More importantly, this is the first implementation case of a reliable Mg-S system based on nucleophilic APC electrolytes.

Copper- and iron-catalyzed decarboxylative tri- and difluoromethylation of α,ß-unsaturated carboxylic acids with CF3SO2Na and (CF2HSO2)2Zn via a radical process.

A copper-catalyzed decarboxylative trifluoromethylation of various α,ß-unsaturated carboxylic acids by using a stable and inexpensive solid, sodium trifluoromethanesulfinate (CF(3)SO(2)Na, Langlois reagent), was developed. In addition, an iron-catalyzed difluoromethylation of aryl-substituted acrylic acids by using zinc difluoromethanesulfinate (DFMS, (CF(2)HSO(2))(2)Zn, Baran reagent) via a similar radical process was also achieved.

Unexpected copper-catalyzed aerobic oxidative cleavage of C(sp3)-C(sp3) bond of glycol ethers.

An unexpected Cu-catalyzed oxidative cleavage of the C(sp(3))-C(sp(3)) bond in glycol ethers by using air or molecular oxygen as the terminal stoichiometric oxidant is demonstrated. As a result, the corresponding α-acyloxy ethers and formates of 1,2-ethanediol are formed by direct coupling of carboxylic acids and aldehydes with glycol ethers under the reaction conditions. This method represents the first example of Cu-catalyzed aerobic cleavage of saturated C-C bond in ethers.

Pd(II)-catalyzed dehydrogenative olefination of vinylic C-H bonds with allylic esters: general and selective access to linear 1,3-butadienes.

This work demonstrates a general and efficient method to prepare conjugated dienes by Pd(II)-catalyzed direct olefination of unactivated alkenes with allylic esters and acrylates via vinylic C-H activation. Various aryl and heteroaryl alkenes as well as aliphatic alkenes all give the desired linear 1,3-butadienes with retention of the traditional leaving groups such as OAc and other carboxylic acid ester groups.