Unlocking Charge Transfer Limitations for Extreme Fast Charging of Li-Ion Batteries.

Extreme fast charging (XFC) of high-energy Li-ion batteries is a key enabler of electrified transportation. While previous studies mainly focused on improving Li ion mass transport in electrodes and electrolytes, the limitations of charge transfer across electrode-electrolyte interfaces remain underexplored. Herein we unravel how charge transfer kinetics dictates the fast rechargeability of Li-ion cells. Li ion transfer across the cathode-electrolyte interface is found to be rate-limiting during XFC, but the charge transfer energy barrier at both the cathode and anode have to be reduced simultaneously to prevent Li plating, which is achieved through electrolyte engineering. By unlocking charge transfer limitations, 184 Wh kg-1 pouch cells demonstrate stable XFC (10-min charge to 80 %) which is otherwise unachievable, and the lifetime of 245 Wh kg-1 21700 cells is quintupled during fast charging (25-min charge to 80 %).

Quantification of the Dynamic Interface Evolution in High-Efficiency Working Li-Metal Batteries.

Lithium (Li) metal has been considered a promising anode for next-generation high-energy-density batteries. However, the low reversibility and intricate Li loss hinder the widespread implementation of Li metal batteries. Herein, we quantitatively differentiate the dynamic evolution of inactive Li, and decipher the fundamental interplay among dynamic Li loss, electrolyte chemistry, and the structure of the solid electrolyte interphase (SEI). The actual dominant form in inactive Li loss is practically determined by the relative growth rates of dead Li0 and SEI Li+ because of the persistent evolution of the Li metal interface during cycling. Distinct inactive Li evolution scenarios are disclosed by ingeniously tuning the inorganic anion-derived SEI chemistry with a low amount of film-forming additive. An optimal polymeric film enabler of 1,3-dioxolane is demonstrated to derive a highly uniform multilayer SEI and decreased SEI Li+ /dead Li0 growth rates, thus achieving enhanced Li cycling reversibility.

Identifying the Critical Anion-Cation Coordination to Regulate the Electric Double Layer for an Efficient Lithium-Metal Anode Interface.

The persistent efforts to reveal the formation and evolution mechanisms of solid electrolyte interphase (SEI) are of fundamental significance for the rational regulation. In this work, through combined theoretical and experimental model investigations, we elucidate that the electric double layer (EDL) chemistry at the electrode/electrolyte interface beyond the thermodynamic stability of electrolyte components predominately controls the competitive reduction reactions during SEI construction on Li metal anode. Specifically, the negatively-charged surface of Li metal will prompt substantial cation enrichment and anion deficiency within the EDL. Necessarily, only the species participating in the solvation shell of cations could be electrostatically accumulated in proximity of Li metal surface and thereafter be preferentially reduced during sustained dynamic cycling. Incorporating multi-valent cation additives to more effectively drag the favorable anionic SEI enablers into EDL is validated as a promising strategy to upgrade the Li protection performance. The conclusions drawn herein afford deeper understandings to bridge the EDL principle, cation solvation, and SEI formation, shedding fresh light on the targeted regulation of reactive alkali metal interfaces.

Non-Solvating and Low-Dielectricity Cosolvent for Anion-Derived Solid Electrolyte Interphases in Lithium Metal Batteries.

Lithium (Li) metal anodes hold great promise for next-generation high-energy-density batteries, while the insufficient fundamental understanding of the complex solid electrolyte interphase (SEI) is the major obstacle for the full demonstration of their potential in working batteries. The characteristics of SEI highly depend on the inner solvation structure of lithium ions (Li+ ). Herein, we clarify the critical significance of cosolvent properties on both Li+ solvation structure and the SEI formation on working Li metal anodes. Non-solvating and low-dielectricity (NL) cosolvents intrinsically enhance the interaction between anion and Li+ by affording a low dielectric environment. The abundant positively charged anion-cation aggregates generated as the introduction of NL cosolvents are preferentially brought to the negatively charged Li anode surface, inducing an anion-derived inorganic-rich SEI. A solvent diagram is further built to illustrate that a solvent with both proper relative binding energy toward Li+ and dielectric constant is suitable as NL cosolvent.

Designing and Demystifying the Lithium Metal Interface toward Highly Reversible Batteries.

Reversible lithium (Li) plating/stripping is essential for building practical high-energy-density batteries based on Li metal chemistry, which unfortunately remains a severe challenge. In this contribution, it is demonstrated that through the rational regulation of strong Li+ -anion coordination structures in a highly compatible low-polarity solvent, 2-methyl tetrahydrofuran, the Li plating/stripping assisted by a nucleation modulation procedure delivers a remarkably high average Coulombic efficiency under rather demanding conditions (99.7% and 99.5% under 1.0 mA cm-2 , 3.0 mAh cm-2 and 3.0 mA cm-2 , 3.0 mAh cm-2 , respectively). The exceedingly reversible cycling obtained herein is fundamentally correlated with the flattened Li deposition and minimized solid electrolyte interphase (SEI) generation/reconstruction in the customized condition, which notably restrains the growth rates of both dead Li0 (0.0120 mAh per cycle) and SEI-Li+ (0.0191 mAh per cycle) during consecutive cycles. Benefiting from the efficient Li plating/stripping manner, the assembled anode-free Cu|LiFePO4 (2.7 mAh cm-2 ) coin and pouch cells exhibit impressive capacity retention of 43.8% and 41.6% after 150 cycles, respectively, albeit with no optimization on the test conditions. This work provides guidelines into the targeted interfacial design of high-efficiency working Li anodes, aiming to pave the way for the practical deployment of high-energy-density Li metal batteries.

Waterproof lithium metal anode enabled by cross-linking encapsulation.

Lithium (Li) metal is considered as the ultimate anode choice for developing next-generation high-energy batteries. However, the poor tolerance against moist air and the unstable solid electrolyte interphases (SEI) induced by the intrinsic high reactivity of lithium bring series of obstacles such as the rigorous operating condition, the poor electrochemical performance, and safety anxiety of the cell, which to a large extent hinder the commercial utilization of Li metal anode. Here, an effective encapsulation strategy was reported via a facile drop-casting and a following heat-assisted cross-linking process. Benefiting from the inherent hydrophobicity and the compact micro-structure of the cross-linked poly(vinylidene-co-hexafluoropropylene) (PVDF-HFP), the as-encapsulated Li metal exhibited prominent stability toward moisture, as well corroborated by the evaluations both under the humid air at 25 °C with 30% relative humidity (RH) and pure water. Moreover, the encapsulated Li metal anode exhibits a decent electrochemical performance without substantially increasing the cell polarization due to the uniform and unblocked ion channels, which originally comes from the superior affinity of the PVDF-HFP polymer toward non-aqueous electrolyte. This work demonstrates a novel and valid encapsulation strategy for humidity-sensitive alkali metal electrodes, aiming to pave the way for the large-scale and low-cost deployment of the alkali metal-based high-energy-density batteries.