Inorganic Oxide-Based "Hydrophobic-Hydrophilic-Hydrophobic" Separators Systems for Long-Life Zinc-Ion Batteries.

Hydrogen reduction reaction (HER) and corrosion limit the long-life cycle of zinc-ion batteries. However, hydrophilic separators are unable to prevent direct contact between water and electrodes, and hydrophobic separators have difficulty in transporting electrolytes. In this work, an inorganic oxide-based "hydrophobic-hydrophilic-hydrophobic" self-assembled separator system is proposed. The hydrophobic layer consists of a porous structure, which can isolate a large amount of free water to avoid HER and corrosion reactions, and can transport electrolyte by binding water. The middle hydrophilic layer acts as a storage layer consisting of the GF separator, storing large amounts of electrolyte for proper circulation. By using this structure separator, Zn||Zn symmetric cell achieve 2200 h stable cycle life at 5 mA cm-2 and 1mAh cm-2 and still shows a long life of 1800 h at 10 mA cm-2 and 1mAh cm-2. The assembled Zn||VO2 full cell displays high specific capacity and excellent long-term durability of 60.4% capacity retention after 1000 cycles at 2C. The assembled Zn||VO2 pouch full cell displays high specific capacity of 172.5mAh g-1 after 40 cycles at 0.5C. Changing the inorganic oxide materials, the hydrophobic-hydrophilic-hydrophobic structure of the separators still has excellent performance. This work provides a new idea for the engineering of water-based battery separators.

Three-in-One Zinc Anodes Created by a Large-scale Two-Step Method Achieving Excellent Long-Term Cyclic Reversibility and Thin Electrode Integrity.

Practical aqueous zinc-ion batteries require low-cost thin zinc anodes with long-term reversible stripping/depositing. However, thin zinc anodes encounter more severe issues than thick zinc, such as dendrites and uneven stripping, resulting in subpar performance and limited lifetimes. Here, this work proposes a three-in-one zinc anode obtained by a large-scale two-step method to address the above issues. In a three-in-one zinc anode, the copper foil as an inactive current collector solves the gradual reduction of the active area when only the pure zinc as an active current collector. This work develops an automatic electroplating device that can continuously deposit a zinc layer on a conducting foil to meet the demand for zinc-coated copper foils. The sodium carboxymethylcellulose (CMC)-zinc fluoride (ZnF2) protective layer prevents direct contact between zinc and separator, and provides a uniform and sufficient supply of zinc ions. The CMC-ZnF2-coated copper foil performs up to 3000 reversible zinc deposition/stripping cycles with a cumulative capacity of 6 Ah cm-2 and an average Coulombic efficiency of 99.94%. The Zn||ZnVO cell using the three-in-one anode achieved a high capacity retention of over 70% after 15 000 cycles. The proposed three-in-one anode and the automatic electroplating device will facilitate industrialization of practical thin zinc anodes.

200 MPa cold isostatic pressing creates surface-microcracks in a Zn foil for scalable and long-life zinc anodes.

The Zn anode suffers from severe dendrite growth and side reactions, which restrict its development in the realm of large-scale energy storage. Herein, in this study, we propose a method to create surface-microcracks in a Zn foil by 200 MPa cold isostatic pressing. The proposed pressing method can avoid the surface tip effect of Zn, and creates a subtly surface-microcracked zinc structure, providing more zinc ion transport channels, thereby effectively alleviating the dendrite growth and side reactions during the repeated Zn plating and stripping. Benefiting from these advantages, the 200 MPa Zn‖Zn symmetric cell can achieve a long cycle life (1525 h) of 1 mA h cm-2 at 2 mA cm-2. The 200 MPa Zn‖VO2 full cell can still maintain a capacity of 110 mA h g-1 after 1000 cycles at 0.1 A g-1. In addition, assembled pouch cells also show excellent cycling stability. The proposed cold isostatic pressing method is compatible with large-scale production applications and provides an effective strategy for realizing high-performance zinc anodes for zinc-ion batteries.

Modulation of the Oxidation End-Product Toward Polysulfides-Free and Sustainable Lithium-Pyrite Thermal Batteries.

The FeS2 has abundant reserves and a high specific capacity (894 mAh g-1 ), commonly used to fabricate Li-FeS2 primary batteries, like LiMx -FeS2 thermal batteries (working at ≈500 °C). However, Li-FeS2 batteries struggle to function as rechargeable batteries due to serious issues such as pulverization and polysulfide shuttling. Herein, highly reversible solid-state Li-FeS2 batteries operating at 300 °C are designed. Molten salt-based FeS2 slurry cathodes address the notorious electrode pulverization problem by encapsulating pulverized particles in time with e- and Li⁺ flow conductors. In addition, the solid electrolyte LLZTO tube serves as a hard separator and fast Li+ channel, effectively separating the molten electrodes to construct a liquid-solid-liquid structure instead of the solid-liquid-solid structure of LiMx -FeS2 thermal batteries. Most importantly, these high-temperature Li-FeS2 solid-state batteries achieve FeS2 conversion to Li2 S and Fe at discharge and further back to FeS2 at charge, unlike room-temperature Li-FeS2 batteries where FeS and S act as oxidation products. Therefore, these new-type Li-FeS2 batteries have a lower operating temperature than Li-FeS2 thermal batteries and perform highly reversible electrochemical reactions, which can be cycled stably up to 2000 times with a high specific capacity of ≈750 mAh g-1 in the prototype batteries.

Bonding Lithium Metal with Garnet Electrolyte by Interfacial Lithiophobicity/Lithiophilicity Transition Mechanism over 380 °C.

Garnet electrolytes, possessing high ionic conductivity (10-4 -10-3 S cm-1 at room temperature) and excellent chemical/electrochemical compatibility with lithium metal, are expected to be used in solid-state lithium metal batteries. However, the poor solid-solid interfacial contact between lithium and garnet leads to high interfacial resistance, reducing the battery power capability and cyclability. Garnet electrolytes are commonly believed to be intrinsically lithiophilic, and lithiophobic Li2 CO3 on the garnet surface accounted for the poor interfacial contact. Here, it is proposed that the interfacial lithiophobicity/lithiophilicity of garnets (LLZO, LLZTO) can be transformed above a temperature of ≈380 °C. This transition mechanism is also suitable for other materials such as Li2 CO3 , Li2 O, stainless steel, and Al2 O3 . By using this transition mechanism, uniform and even lithium can be strongly bonded no-surface-treated garnet electrolytes with various shapes. The Li-LLZTO interfacial resistance can be reduced to ≈3.6 Ω cm2 and sustainably withstood lithium extraction and insertion for up to 2000 h at 100 µA cm-2 . This high-temperature lithiophobicity/lithiophilicity transition mechanism can help improve the understanding of lithium-garnet interfaces and build practical lithium-garnet solid-solid interfaces.

Gradient Electrolyte Strategy Achieving Long-Life Zinc Anodes.

Aqueous Zn-ion batteries are plagued by a short lifespan caused by localized dendrites. High-concentration electrolytes are favorable for dense Zn deposition but have poor performance in batteries with glass-fiber separators. In contrast, low-concentration electrolytes can wet the separators well, ensuring the migration of zinc ions, but the dendrites grow rapidly. In this work, we propose an electrolyte gradient strategy wherein a zinc-ion concentration gradient is established from the anode to the separator, ensuring that the separator keeps a good wettability in low-concentration areas and the zinc anode achieves dendrite-free deposition in a high-concentration area. By using this strategy in a common electrolyte, zinc sulfate, a Zn||Zn symmetric cell achieves 14 000 ultralong cycles (exceeding 8 months) at 5 mA cm-2 and 1 mAh cm-2 . When the current is further increased to 20 mA cm-2 , the symmetric cell could still run for over 10 000 cycles. Assembled Zn||NVO full cells also demonstrate prominent performance. At a high current of 16 mA cm-2 , the NVO cathode with high loading (8 mg cm-2 ) still has a capacity of 58% after 1200 cycles. Overall, the gradient electrolyte strategy provides a promising approach for practical long-life Zn anodes with the advantages of simple operation and low cost.

Copper Particle-Enhanced Lithium-Mediated Synthesis of Green Ammonia from Water and Nitrogen.

Ammonia (NH3) is one of the most frequently produced chemical products in the world, and it plays an indispensable role in life on Earth. However, its synthesis by the Haber-Bosch (H-B) process is highly energy intensive, resulting in extensive carbon emissions that are unsustainable due to their ability to harm the environment. Herein, we propose a facile and mass-producible strategy for increasing the rate and efficiency of nitrogen fixation through the use of copper particle-catalyzed Li nitridation and a solid electrolyte as a medium to reduce Li salt; the above strategy results in the conversion of water and nitrogen into NH3 through the use of renewable electrical energy at room temperature and atmospheric pressure. Copper particles are uniformly pressed into Li metal by a simple rolling method, and their critical role in accelerating the nitrogen fixation process is revealed by both electrochemical tests and simulations. The nitridation of the Li in the composite is reduced to a few minutes instead of the more than 40 h that are needed for bare Li and N2 at room temperature and atmospheric pressure. Our new method provides three important advantages over the H-B method: (1) the new method can be operated at atmospheric pressure, thereby lowering equipment requirements and increasing security; (2) the use of water instead of fossil fuels as a hydrogen source decreases the consumption of these fuels and the emission of CO2; and (3) the low equipment requirements lead to the ready miniaturization and decentralization of the NH3 synthesizing process, thus promoting the possible use of renewable sources of electricity (e.g., wind or solar energy).

A green and sustainable strategy toward lithium resources recycling from spent batteries.

Recycling lithium from spent batteries is challenging because of problems with poor purity and contamination. Here, we propose a green and sustainable lithium recovery strategy for spent batteries containing LiFePO4, LiCoO2, and LiNi0.5Co0.2Mn0.3O2 electrodes. Our proposed configuration of "lithium-rich electrode || LLZTO@LiTFSI+P3HT || LiOH" system achieves double-side and roll-to-roll recycling of lithium-containing electrode without destroying its integrity. The LiTFSI+P3HT-modified LLZTO membrane also solves the H+/Li+ exchange problem and realizes a waterproof protection of bare LLZTO in the aqueous working environment. On the basis of these advantages, our system shows high Li selectivity (97%) and excellent Faradaic efficiency (≥97%), achieving high-purity (99%) LiOH along with the production of H2. The Li extraction processes for spent LiFePO4, LiNi0.5Co0.2Mn0.3O2, and LiCoO2 batteries is shown to be economically feasible. Therefore, this study provides a previously unexplored technology with low energy consumption as well as high economic and environmental benefits to realize sustainable lithium recycling from spent batteries.