Composition regulation of polyacrylonitrile-based polymer electrolytes enabling dual-interfacially stable solid-state lithium batteries

The polyacrylonitrile (PAN) is an attractive matrix of polymer electrolytes owing to its wide electrochemical window and strong coordination with Li salts. However, the PAN-based electrolytes undergo severe interfacial problems from both cathode and anode sides, including uneven ionic transfer induced by high rigidity of dry PAN-based polymer, as well as inferior stability against Li-metal anode. Herein, the composition regulation of PAN-based electrolytes is proposed by introducing succinonitrile (SN) plastic crystal and LiNO3 salt for the construction of interfacially stable solid-state lithium batteries. The plastic nature of SN enables the rapid ionic transfer in electrolytes, along with the establishment of conformally interfacial contacts. Meanwhile, a stable solid-electrolyte-interface (SEI) layer consisting of Li3N and LiNO2 is in-situ formed at Li/electrolyte interface, contributing to the inhibition of uncontrol reactions between PAN and Li-metal. Consequently, the resultant Li symmetric cell delivers an extended critical current density of 1.7 mA cm-2 and an outstanding cycling lifespan of 700 h at 0.1 mA cm-2. Moreover, the corresponding solid-state LiNi0.6Co0.2Mn0.2O2/Li full cell shows an initial discharge capacity of 161 mAh/g followed by an outstanding capacity retention of 88.7 % after 100 cycles at 0.1C. This work paves the way for application of PAN-based electrolytes in the field of solid-state batteries by facile composition regulation.

Adjusting Li+ Solvation Structures via Dipole-Dipole Interaction to Construct Inorganic-Rich Interphase for High-Performance Li Metal Batteries

Practical applications of lithium metal batteries are limited by unstable solid electrolyte interphase (SEI) and uncontrollable dendrite Li deposition. Regulating the solvation structure of Li+ via modifying electrolyte components enables optimizing the structure of the SEI and realizing dendrite-free Li deposition. In this work, it is found that the ionic-dipole interactions between the electron-deficient B atoms in lithium oxalyldifluoro borate (LiDFOB) and the O atoms in the DME solvent molecule can weaken the interaction between the DME molecule and Li+, accelerating the desolvation of Li+. On this basis, the ionic-dipole interactions facilitate the entry of abundant anions into the inner solvation sheath of Li+, which promotes the formation of inorganic-rich SEI. In addition, the interaction between DFOB- and DME molecules reduces the highest occupied molecular orbital energy level of DME molecules in electrolytes, which improves the oxidative stability of the electrolytes system. As a result, the Li||Li cells in LiDFOB-containing electrolytes exhibit an excellent cyclability of over 1800 h with a low overpotential of 18.2 mV, and the Li||LiFePO4 full cells display a high-capacity retention of 93.4% after 100 cycles with a high Coulombic efficiency of 99.3%.

Electrode-Electrolyte Interfacial Chemistry Modulation for Ultra-High Rate Sodium-Ion Batteries

Sodium-ion batteries capable of operating at rate and temperature extremes are highly desirable, but elusive due to the dynamics and thermodynamics limitations. Herein, a strategy of electrode-electrolyte interfacial chemistry modulation is proposed. The commercial hard carbon demonstrates superior rate performance with 212 mAh g^-1 at an ultra-high current density of 5 A g^-1 in the electrolyte with weak ion solvation/desolvation, which is much higher than those in common electrolytes (nearly no capacity in carbonate-based electrolytes). Even at -20 °C, a high capacity of 175 mAh g^-1 (74 % of its room-temperature capacity) can be maintained at 2 A g^-1 . Such an electrode retains 90 % of its initial capacity after 1000 cycles. As proven, weak ion solvation/desolvation of tetrahydrofuran greatly facilitates fast-ion diffusion at the SEI/electrolyte interface and homogeneous SEI with well-distributed NaF and organic components ensures fast Na⁺ diffusion through the SEI layer and a stable interface.

Phenoxy Radical-Induced Formation of Dual-Layered Protection Film for High-Rate and Dendrite-Free Lithium-Metal Anodes

The uncontrollable dendrite growth of Li metal anode leads to poor cycle stability and safety concerns, hindering its utilization in high energy density batteries. Herein, a phenoxy radical Spiro-O8 is proposed as an artificial protection film for Li metal anode owing to its excellent film-forming capability and remarkable ionic conductivity. A spontaneous redox reaction between the Spiro-O8 and Li metal results in the formation of a uniform and highly ionic conductive organic film in the bottom. Meanwhile, the phenoxy radicals on surface of Spiro-O8 facilitate the decomposition of Li salt upon exposed to the ether electrolyte and lead the formation of LiF film on the top. Arising from the synergistic effects of inner high ionic conductive film and outer rigid film, stable Li plating/stripping can be realized at a high current density (4000 cycles at 10 mA cm^-2 ) and a high areal capacity of 5 mAh cm^-2 for 550 h with an ultrahigh Li utilization rate of 54.6 %. As a proof of concept, this work shows a facile strategy to rationally fabricate dual-layered interfaces for Li metal anodes.

WSe2 Flakelets on N-Doped Graphene for Accelerating Polysulfide Redox and Regulating Li Plating

The practical application of lithium-sulfur batteries is still limited by the lithium polysulfides (LiPSs) shuttling effect on the S cathode and uncontrollable Li-dendrite growth on the Li anode. Herein, elaborately designed WSe₂ flakelets immobilized on N-doped graphene (WSe₂ /NG) with abundant active sites are employed to be a dual-functional host for satisfying both the S cathode and Li anode synchronously. On the S cathode, the WSe₂ /NG with a strong interaction towards LiPSs can act as a redox accelerator to promote the bidirectional conversion of LiPSs. On the Li anode, the WSe₂ /NG with excellent lithiophilic features can regulate the uniform Li plating/stripping to mitigate the growth of Li dendrite. Taking advantage of these merits, the assembled Li-S full batteries exhibit remarkable rate performance and stable cycling stability even at a higher sulfur loading of 10.5 mg cm^-2 with a negative to positive electrode capacity (N/P) ratio of 1.4 : 1.

Reclaiming Inactive Lithium with a Triiodide/Iodide Redox Couple for Practical Lithium Metal Batteries

High-energy-density lithium (Li) metal batteries suffer from a short lifespan owing to apparently ceaseless inactive Li accumulation, which is accompanied by the consumption of electrolyte and active Li reservoir, seriously deteriorating the cyclability of batteries. Herein, a triiodide/iodide (I₃ ^- /I^- ) redox couple initiated by stannic iodide (SnI₄ ) is demonstrated to reclaim inactive Li. The reduction of I₃ ^- converts inactive Li into soluble LiI, which then diffuses to the cathode side. The oxidation of LiI by the delithiated cathode transforms cathode into the lithiation state and regenerates I₃ ^- , reclaiming Li ion from inactive Li. The regenerated I₃ ^- engages the further redox reactions. Furthermore, the formation of Sn mitigates the corrosion of I₃ ^- on active Li reservoir sacrificially. In working Li | LiNi_0.5 Co_0.2 Mn_0.3 O₂ batteries, the accumulated inactive Li is significantly reclaimed by the reversible I₃ ^- /I^- redox couple, improving the lifespan of batteries by twice. This work initiates a creative solution to reclaim inactive Li for prolonging the lifespan of practical Li metal batteries.

Fire-Retardant, Stable-Cycling and High-Safety Sodium Ion Battery

The safety of energy storage equipment has always been a stumbling block to the development of battery, and sodium ion battery is no exception. However, as an ultimate solution, the use of non-flammable electrolyte is susceptible to the side effects, and its poor compatibility with electrode, causing failure of batteries. Here, we report a non-flammable electrolyte design to achieve high-performance sodium ion battery, which resolves the dilemma via regulating the solvation structure of electrolyte by hydrogen bonds and optimizing the electrode-electrolyte interphase. The reported non-flammable electrolyte allows stable charge-discharge cycling of both sodium vanadium phosphate@hard carbon and Prussian blue@hard carbon full pouch cell for more than 120 cycles with a capacity retention of >85 % and high cycling Coulombic efficiency (99.7 %).