Realizing High Capacity and Zero Strain in Layered Oxide Cathodes via Lithium Dual-Site Substitution for Sodium-Ion Batteries.

Sodium-ion batteries have garnered unprecedented attention as an electrochemical energy storage technology, but it remains challenging to design high-energy-density cathode materials with low structural strain during the dynamic (de)sodiation processes. Herein, we report a P2-layered lithium dual-site-substituted Na0.7Li0.03[Mg0.15Li0.07Mn0.75]O2 (NMLMO) cathode material, in which Li ions occupy both transition-metal (TM) and alkali-metal (AM) sites. The combination of theoretical calculations and experimental characterizations reveals that LiTM creates Na-O-Li electronic configurations to boost the capacity derived from the oxygen anionic redox, while LiAM serves as LiO6 prismatic pillars to stabilize the layered structure through suppressing the detrimental phase transitions. As a result, NMLMO delivers a high specific capacity of 266 mAh g-1 and simultaneously exhibits the nearly zero-strain characteristic within a wide voltage range of 1.5-4.6 V. Our findings highlight the effective way of dual-site substitution to break the capacity-stability trade-off in cathode materials for advanced rechargeable batteries.

Tuning Interphase Chemistry to Stabilize High-Voltage LiCoO2 Cathode Material via Spinel Coating.

Cathode electrolyte interphases (CEIs) are critical to the cycling stability of high-voltage cathodes for batteries, yet their formation mechanism and properties remain elusive. Here we report that the compositions of CEIs are largely controlled by abundant species in the inner Helmholtz layer (IHL) and can be tuned from material aspects. The IHL of LiCoO2 (LCO) was found to alter after charging, with a solvent-rich environment that results in fragile organic-rich CEIs. By passivated spinel Li4 Mn5 O12 coating, we achieve an anion-rich IHL after charging, thus enabling robust LiF-rich CEIs. In situ microscopy reveals that LiF-rich CEIs maintain mechanical integrity at 500 °C, in sharp contrast to organic-rich CEIs which undergo severe expansion and subsequent voids/cracks in the cathode. As a result, the spinel-coated LCO exhibits a high specific capacity of 194 mAh g-1 at 0.05 C and a capacity retention of 83 % after 300 cycles at 0.5 C. Our work sheds new light on modulating CEIs for advanced lithium-ion batteries.

Boosting the Kinetics and Stability of Zn Anodes in Aqueous Electrolytes with Supramolecular Cyclodextrin Additives.

The hydrophobic internal cavity and hydrophilic external surface of cyclodextrins (CDs) render promising electrochemical applications. Here, we report a comparative and mechanistic study on the use of CD molecules (α-, ß-, and γ-CD) as electrolyte additives for rechargeable Zn batteries. The addition of α-CD in aqueous ZnSO4 solution reduces nucleation overpotential and activation energy of Zn plating and suppresses H2 generation. Computational, spectroscopic, and electrochemical studies reveal that α-CD preferentially adsorbs in parallel on the Zn surface via secondary hydroxyl groups, suppressing water-induced side reactions of hydrogen evolution and hydroxide sulfate formation. Additionally, the hydrophilic exterior surface of α-CD with intense electron density simultaneously facilitates Zn2+ deposition and alleviates Zn dendrite formation. A formulated 3 M ZnSO4 + 10 mM α-CD electrolyte enables homogenous Zn plating/stripping (average Coulombic efficiency ∼ 99.90%) at 1 mA cm-2 in Zn|Cu cells and a considerable capacity retention of 84.20% after 800 cycles in Zn|V2O5 full batteries. This study provides insight into the use of supramolecular macrocycles to modulate and enhance the interface stability and kinetics of metallic anodes for aqueous battery chemistry.

Building Homogenous Li2 TiO3 Coating Layer on Primary Particles to Stabilize Li-Rich Mn-Based Cathode Materials.

Li-rich Mn-based oxides (LRMOs) are promising cathode materials for next-generation lithium-ion batteries (LIBs) with high specific energy (≈900 Wh kg-1 ) because of anionic redox contribution. However, LRMOs suffer from issues such as irreversible release of lattice oxygen, transition metal (TM) dissolution, and parasitic cathode-electrolyte reactions. Herein, a facile, scalable route to build homogenous and ultrathin Li2 TiO3 (LTO) coating layer on the primary particles of LRMO through molten salt (LiCl) assisted solid-liquid reaction between TiO2 and Li1.08 Mn0.54 Co0.13 Ni0.13 O2 is reported. The prepared LTO-coated Li1.08 Mn0.54 Co0.13 Ni0.13 O2 (LTO@LRMO) exhibits 99.7% capacity retention and 95.3% voltage retention over 125 cycles at 0.2 C, significantly outperforming uncoated LRMO. Combined characterizations of differential electrochemical mass spectrometry, in situ X-ray diffraction, and ex situ X-ray photoelectron spectroscopy evidence significantly suppressed oxygen release, phase transition, and interfacial reactions. Further analysis of cycled electrodes reveals that the LTO coating layer inhibits TM dissolution and prevents the lithium anode from TM crossover effect. This study expands the primary particle coating strategy to upgrade LRMO cathode materials for advanced LIBs.

Stabilizing Zinc Electrodes with a Vanillin Additive in Mild Aqueous Electrolytes.

Metallic zinc (Zn) is an attractive anode material to use for building an aqueous battery but suffers from dendritic growth and water-induced corrosion. Herein, we report the use of vanillin as a bifunctional additive in aqueous electrolyte to stabilize the Zn electrochemistry. Computational, spectroscopic, and electrochemical studies suggest that vanillin molecules preferentially absorb in parallel on the Zn surface to homogenize the Zn2+ plating and favorably coordinate with Zn2+ to weaken the solvation interaction between H2O and Zn2+, resulting in a compact, dendrite-free Zn deposition and a stable electrode-electrolyte interface with suppressed hydrogen evolution and hydroxide sulfate formation. In the formulated 2 M ZnSO4 electrolyte with 5 mM vanillin, the Zn anode sustains high areal capacity (10 mAh cm-2 at 1 mA cm-2) and remarkable cycling stability (1 mAh cm-2 for 1000 h) in a Zn|Zn cell and high average Coulombic efficiency (99.8%) in a Zn|Cu cell, significantly outperforming the cells without vanillin. Furthermore, the vanillin additive supports stable operation of full Zn|V2O5 batteries and is readily generalized to a Zn(CF3SO3)2-based electrolyte. This work offers a facile and cost-effective strategy of electrolyte design to enable high-performance aqueous Zn batteries.

Electroless Formation of a Fluorinated Li/Na Hybrid Interphase for Robust Lithium Anodes.

Engineering a stable solid electrolyte interphase (SEI) is one of the critical maneuvers in improving the performance of a lithium anode for high-energy-density rechargeable lithium batteries. Herein, we build a fluorinated lithium/sodium hybrid interphase via a facile electroless electrolyte-soaking approach to stabilize the repeated plating/stripping of lithium metal. Jointed experimental and computational characterizations reveal that the fluorinated hybrid SEI mainly consisting of NaF, LiF, LixPOyFz, and organic components features a mosaic polycrystalline structure with enriched grain boundaries and superior interfacial properties toward Li. This LiF/NaF hybrid SEI exhibits improved ionic conductivity and mechanical strength in comparison to the SEI without NaF. Remarkably, the fluorinated hybrid SEI enables an extended dendrite-free cycling of metallic Li over 1300 h at a high areal capacity of 10 mAh cm-2 in symmetrical cells. Furthermore, full cells based on the LiFePO4 cathode and hybrid SEI-protected Li anode sustain long-term stability and good capacity retention (96.70% after 200 cycles) at 0.5 C. This work could provide a new avenue for designing robust multifunctional SEI to upgrade the metallic lithium anode.

Growing Nanostructured CuO on Copper Foil via Chemical Etching to Upgrade Metallic Lithium Anode.

Metallic lithium is one of the most promising anode materials to build next generation electrochemical power sources such as Li-air, Li-sulfur, and solid-state lithium batteries. The implementation of rechargeable Li-based batteries is plagued by issues including dendrites, pulverization, and an unstable solid electrolyte interface (SEI). Herein, we report the use of nanostructured CuO in situ grown on commercial copper foil (CuO@Cu) via chemical etching as a Li-reservoir substrate to stabilize SEI formation and Li stripping/plating. The lithiophilic interconnected CuO layer enhances electrolyte wettability. Besides, a mechanically stable Li2O- and LiF-rich SEI is generated on CuO@Cu during initial discharge, which permits dense and uniform lithium deposition upon subsequent cycling. Compared with bare Cu, the CuO@Cu electrode exhibits superior performance in terms of Coulombic efficiency, discharge/charge overpotentials, and cyclability. By pairing with the Li-CuO@Cu anodes, full cells with LiFePO4 and LiNi1/3Mn1/3Co1/3O2 cathodes sustain 300 cycles with 98.8% capacity retention at 1 C and deliver a specific capacity of 80 mAh g-1 at 10 C, respectively. This work would shed light on the design of advanced current collectors with SEI modulation to upgrade lithium anodes.