Electrolyte Regulation in Stabilizing the Interface of a Cobalt-Free Layered Cathode for 4.8 V High-Voltage Lithium-Ion Batteries.

The cobalt-free layered oxide cathode of LiNi0.65Mn0.35O2 is promising for high-energy-density lithium-ion batteries (LIBs). However, under high-voltage conditions, severe side reactions between the Co-free cathode and electrolyte, as well as grain boundary cracks and pulverization of particles, hinder its practical applications. Herein, an electrolyte regulation strategy is proposed by adding fluoroethylene carbonate (FEC) and LiPO2F2 as electrolyte additives in carbonate-based electrolytes to address the above issues. As a result, a homogeneous and dense organic-inorganic hybrid cathode electrolyte interface (CEI) film is formed on the cathode surface. The CEI film consists of C-F, LiF, Li2CO3, and LixPOyFz species, which is proven to be highly conductive and effective in suppressing structure damage and alleviating the interfacial reactions between the cathode and electrolyte. With such a CEI film, the interfacial stability of the Co-free cathode and the high-voltage cycling performance of Li||LiNi0.65Mn0.35O2 are greatly improved. A reversible capacity of 155.1 mAh g-1 and a capacity retention of 81.3% over 150 cycles are attained at a 4.8 V charge cutoff voltage with the tamed electrolyte, whereas the cell without the additives only retains 76.1% capacity retention. Therefore, our work demonstrates the synergistic effect of FEC and LiPO2F2 in stabilizing the interface of Co-free cathode materials and provides an alternative strategy for the electrolyte design of high-voltage LIBs.

Regenerated Graphite Electrodes with Reconstructed Solid Electrolyte Interface and Enclosed Active Lithium Toward >100% Initial Coulombic Efficiency.

Solid electrolyte interface (SEI) is arguably the most important concern in graphite anodes, which determines their achievable Coulombic efficiency (CE) and cycling stability. In spent graphite anodes, there are already-formed (yet loose and/or broken) SEIs and some residual active lithium, which, if can be inherited in the regenerated electrodes, are highly desired to compensate for the lithium loss due to SEI formation. However, current graphite regenerated approaches easily destroy the thin SEIs and residue active lithium, making their reuse impossible. Herein, this work reports a fast-heating strategy (e.g., 1900 K for ≈150 ms) to upcycle degraded graphite via instantly converting the loose original SEI layer (≈100 nm thick) to a compact and mostly inorganic one (≈10-30 nm thick with a 26X higher Young's Modulus) and still retaining the activity of residual lithium. Thanks to the robust SEI and enclosed active lithium, the regenerated graphite exhibited 104.7% initial CE for half-cell and gifted the full cells with LiFePO4 significantly improved initial CE (98.8% versus 83.2%) and energy density (309.4 versus 281.4 Wh kg-1), as compared with commercial graphite. The as-proposed upcycling strategy turns the "waste" graphite into high-value prelithiated ones, along with significant economic and environmental benefits.

Air-Stable Li2S Cathodes Enabled by an In Situ-Formed Li+ Conductor for Graphite-Li2S Pouch Cells.

Using Li2S cathodes instead of S cathodes presents an opportunity to pair them with Li-free anodes (e.g., graphite), thereby circumventing anode-related issues, such as poor reversibility and safety, encountered in Li-S batteries. However, the moisture-sensitive nature of Li2S causes the release of hazardous H2S and the formation of insulative by-products, increasing the manufacturing difficulty and adversely affecting cathode performance. Here, Li4SnS4, a Li+ conductor that is air-stable according to the hard-soft acid-base principle, is formed in situ and uniformly on Li2S particles because Li2S itself participates in Li4SnS4 formation. When exposed to air (20% relative humidity), the protective Li4SnS4 layer maintains its components and structure, thus contributing to the enhanced stability of the Li2S@Li4SnS4 composite. In addition, the Li4SnS4 layer can accelerate the sluggish conversion of Li2S because of its favorable interfacial charge transfer, and continuously confine lithium polysulfides owing to its integrity during electrochemical processes. A graphite-Li2S pouch cell containing a Li2S@Li4SnS4 cathode is constructed, which shows stable cyclability with 97% capacity retention after 100 cycles. Hence, combining a desirable air-stable Li2S cathode and a highly reversible Li-free configuration offers potential practical applications of graphite-Li2S full cells.

Demystifying the Salt-Induced Li Loss: A Universal Procedure for the Electrolyte Design of Lithium-Metal Batteries.

Lithium (Li) metal electrodes show significantly different reversibility in the electrolytes with different salts. However, the understanding on how the salts impact on the Li loss remains unclear. Herein, using the electrolytes with different salts (e.g., lithium hexafluorophosphate (LiPF6), lithium difluoro(oxalato)borate (LiDFOB), and lithium bis(fluorosulfonyl)amide (LiFSI)) as examples, we decouple the irreversible Li loss (SEI Li+ and "dead" Li) during cycling. It is found that the accumulation of both SEI Li+ and "dead" Li may be responsible to the irreversible Li loss for the Li metal in the electrolyte with LiPF6 salt. While for the electrolytes with LiDFOB and LiFSI salts, the accumulation of "dead" Li predominates the Li loss. We also demonstrate that lithium nitrate and fluoroethylene carbonate additives could, respectively, function as the "dead" Li and SEI Li+ inhibitors. Inspired by the above understandings, we propose a universal procedure for the electrolyte design of Li metal batteries (LMBs): (i) decouple and find the main reason for the irreversible Li loss; (ii) add the corresponding electrolyte additive. With such a Li-loss-targeted strategy, the Li reversibility was significantly enhanced in the electrolytes with 1,2-dimethoxyethane, triethyl phosphate, and tetrahydrofuran solvents. Our strategy may broaden the scope of electrolyte design toward practical LMBs.

Li2Se as a Cathode Prelithiation Additive for Lithium-Ion Batteries.

In conventional lithium-ion batteries (LIBs), active lithium (Li) ions, which function as charge carriers and could only be supplied by the Li-containing cathodes, are also consumed during the formation of the solid electrolyte interphase. Such irreversible Li loss reduces the energy density of LIBs and is highly desired to be compensated by prelithiation additives. Herein, lithium selenide (Li2Se), which could be irreversibly converted into selenide (Se) at 2.5-3.8 V and thus supplies additional Li, is proposed as a cathode prelithiation additive for LIBs. Compared with previously reported prelithiation reagents (e.g., Li6CoO4, Li2O, and Li2S), the delithiation of Li2Se not only delivers a high specific capacity but also avoids gas release and incompatibility with carbonate electrolytes. The electrochemical characterizations show that with the addition of 6 wt % Li2Se to the LiFePO4 (LFP) cathodes, a 9% increase in the initial specific capacity in half Li||LFP cells and a 19.8% increase in the energy density (based on the total mass of the two electrodes' materials) could be achieved without sacrificing the other battery performance. This work demonstrates the possibility to use Li2Se as a high-efficiency prelithiation additive for LIBs and provides a solution to the high-energy LIBs.

Zinc-Contained Alloy as a Robustly Adhered Interfacial Lattice Locking Layer for Planar and Stable Zinc Electrodeposition.

Stable zinc (Zn)/electrolyte interface is critical for developing rechargeable aqueous Zn-metal batteries with long-term stability, which requires the dense and stable Zn electrodeposition. Herein, an interfacial lattice locking (ILL) layer is constructed via the electro-codeposition of Zn and Cu onto the Zn electrodes. The ILL layer shows a low lattice misfit (δ = 0.036) with Zn(002) plane and selectively locks the lattice orientation of Zn deposits, enabling the epitaxial growth of Zn deposits layer by layer. Benefiting from the unique orientation-guiding and robustly adhered properties, the ILL layer enables the symmetric Zn||Zn cells to achieve an ultralong life span of >6000 h at 1 mA cm-2 and 1 mAh cm-2 , a low overpotential (65 mV) at 10 mAh cm-2 , and a stable Zn plating/stripping for >90 h at an ultrahigh Zn depth of discharge (≈85%). Even with a limited Zn supply and a high current density (8.58 mA cm-2 ), the ILL@Zn||Ni-doped MnO2 cells can still survive for >2300 cycles.

Electrochemical Reactivation of Dead Li2 S for Li-S Batteries in Non-Solvating Electrolytes.

The use of non-solvating, or as-called sparingly-solvating, electrolytes (NSEs), is regarded as one of the most promising solutions to the obstacles to the practical applications of Li-S batteries. However, it remains a puzzle that long-life Li-S batteries have rarely, if not never, been reported with NSEs, despite their good compatibility with Li anode. Here, we find the capacity decay of Li-S batteries in NSEs is mainly due to the accumulation of the dead Li2 S at the cathode side, rather than the degradation of the anodes or electrolytes. Based on this understanding, we propose an electrochemical strategy to reactivate the accumulated Li2 S and revive the dead Li-S batteries in NSEs. With such a facile approach, Li-S batteries with significantly improved cycling stability and accelerated dynamics are achieved with diglyme-, acetonitrile- and 1,2-dimethoxyethane-based NSEs. Our finding may rebuild the confidence in exploiting non-solvating Li-S batteries with practical competitiveness.

Solvation and Interfacial Engineering Enable -40 °C Operation of Graphite/NCM Batteries at Energy Density over 270 Wh kg-1.

Li-ion batteries (LIBs) that can operate under low temperature (LT) conditions are essential for applications in orbital missions, subsea areas, and electric vehicles. Unfortunately, severe capacity loss is witnessed due to tremendous kinetic barriers that emerge at LT. Herein, to surmount such kinetic limitations, a low dielectric environment is tamed throughout the bulk electrolyte, which efficaciously brought the Li+ desolvation energy down to 30.76 kJ mol-1 . At the meantime, the adoption of sodium cations (Na+ ) is proposed as a hetero-cation additive, and a Li-Na hybrid and fluoride-rich interphase is further identified via preferential reduction of Na+ -(solvent/anion) clusters, which is found to efficiently facilitate Li+ migration through the LiF/NaF grain boundaries. Based on a N/P ratio of 1.1, the graphite/LiNi0.5 Co0.2 Mn0.3 O2 (NCM) full cell (cathode loading of ≈18.5 mg cm-2 ) delivers a capacity as high as 125.1 mAh g-1 under -20 °C with prolonged cycling to 100 cycles. Finally, a 270 Wh kg-1 graphite/NCM pouch cell is assembled, which affords a discharge capacity of 108.7 mAh g-1 under -40 °C during the initial cycles. With an eye to both fundamental and practical aspects, this work will propel additional advancements and allow LIBs to fill more roles under extreme operation temperatures than ever before.