A Shuttle-Free Solid-State Cu-Li Battery Based on a Sandwich-Structured Electrolyte.

Cu-Li batteries leveraging the two-electron redox property of Cu can offer high energy density and low cost. However, Cu-Li batteries are plagued by limited solubility and a shuttle effect of Cu ions in traditional electrolytes, which leads to low energy density and poor cycling stability. In this work, we rationally design a solid-state sandwich electrolyte for solid-state Cu-Li batteries, in which a deep-eutectic-solvent gel with high Cu-ion solubility is devised as a Cu-ion reservoir while a ceramic Li1.4 Al0.4 Ti1.6 (PO4 )3 interlayer is used to block Cu-ion crossover. Because of the high ionic conductivity (0.55 mS cm-1 at 25 °C), wide electrochemical window (>4.5 V vs. Li+ /Li), and high Cu ion solubility of solid-state sandwich electrolyte, a solid-state Cu-Li battery demonstrates a high energy density of 1 485 Wh kgCu -1 and long-term cyclability with 97 % capacity retention over 120 cycles. The present study lays the groundwork for future research into low-cost solid-state Cu-Li batteries.

Locally Fluorinated Electrolyte Medium Layer for High-Performance Anode-Free Li-Metal Batteries.

Low cycling Coulombic efficiency (CE) and messy Li dendrite growth problems have greatly hindered the development of anode-free Li-metal batteries (AFLBs). Thus, functional electrolytes for uniform lithium deposition and lithium/electrolyte side reaction suppression are desired. Here, we report a locally fluorinated electrolyte (LFE) medium layer surrounding Cu foils to tailor the chemical compositions of the solid-electrolyte interphase (SEI) in AFLBs for inhibiting the immoderate Li dendrite growth and to suppress the interfacial reaction. This LFE consists of highly concentrated LiTFSI dissolved in a fluoroethylene carbonate and/or succinonitrile plastic mixture. The CE of Cu||LiNi0.8Co0.1Mn0.1O2 (NCM811) AFLB increased to a high level of 99% as envisaged, and the cycling ability was also highly improved. These improvements are facilitated by the formation of a uniform, dense, and LiF-rich SEI. LiF possesses high interfacial energy at the LiF/Li interface, resulting in a more uniform Li deposition process as proved by density functional theory (DFT) calculation results. This work provides a simple yet utility tech for the enhancement of future high-energy-density AFLBs.

Constructing robust polymer/two-dimensional Ti3C2TX solid-state electrolyte interphase via in-situ polymerization for high-capacity long-life and dendrite-free lithium metal anodes.

We constructed an artificial polymer/two-dimensional Ti3C2TX (MXene) solid electrolyte interphase (SEI) on a Li metal surface via an in-situ polymerization strategy. The polymer layer provides excellent interface contact and outstanding adaptability for the volume expansion of Li metal, decreasing interface impedance. On the other hand, the two-dimensional MXene with a low Li nucleation energy barrier is beneficial for uniform Li deposition and restraint of interfacial side reactions. In this work, a dense and durable MXene-integrated SEI between the Li metal anode and solid-state electrolyte (SSE) interface is constructed to render the Li/SSE/Li cell to maintain a stable polarization voltage of approximately 50 mV at a capacity of 0.50 mAh cm-2 for over 1000 h. It enables the Li/SSE/LiFePO4 cell to deliver a capacity of 130.1 mAh g-1 at 1C with a capacity retention of 91.4% after 900 cycles. Therefore, we believe that this facile in-situ polymerization method for constructing a layer of polymer/MXene SEI at the interface between Li metal anodes and SSE can promote the practical applications of Li metal batteries.

Efficient capture and conversion of polysulfides by zinc protoporphyrin framework-embedded triple-layer nanofiber separator for advanced Li-S batteries.

The practical application of Lithium-sulfur (Li-S) batteries is significantly inhibited by (i) the notable 'shuttle effect' of lithium polysulfides (LiPS), (ii) the corrosion of the lithium interface, and (iii) the sluggish redox reaction kinetics. The functional separator in the Li-S battery has the potential to provide the perfect solution to these problems. Herein a triple-layer multifunctional PVDF-based nanofiber separator, which contains GoTiN/PVDF layer on the top and bottom and ZnTPP/PVDF layer on the middle, is designed. The polarity and porous structure of this multifunctional separator can greatly improve the wettability of electrolytes and enhance the transportation of Li+. With the zinc-based porphyrin framework (ZnTPP) structure, this separator has a strong chemisorption and LiPS conversion ability, which greatly prevent the 'shuttle effect'. Consequently, the designed multilayer separator showed excellent electrochemical performance. As a result, the cell with GoTiN@ZnTPP@GoTiN nanofiber membrane displayed an initial discharge capacity of 1180 mAh/g with a benign capacity retention of 65.9% at 0.5C and high coulombic efficiency of more than 98.5% after 100 cycles. Even at 2C, it can still release a capacity of 798 mAh/g. Moreover, the remarkable capacity of 591 mAh/g could be achieved with a high sulfur load of 5.76 mg/cm2 under a current density of 0.1C. Based on these merits, this novel and scalable multifunctional separator is a promising candidate to replace the conventional PP separator for advanced Li-S batteries to deal with various challenges.

Realizing High-Performance Li-S Batteries through Additive Manufactured and Chemically Enhanced Cathodes.

Numerous efforts are made to improve the reversible capacity and long-term cycling stability of Li-S cathodes. However, they are susceptible to irreversible capacity loss during cycling owing to shuttling effects and poor Li+ transport under high sulfur loading. Herein, a physically and chemically enhanced lithium sulfur cathode is proposed to address these challenges. Additive manufacturing is used to construct numerous microchannels within high sulfur loading cathodes, which enables desirable deposition mechanisms of lithium polysulfides and improves Li+ and e- transport. Concurrently, cobalt sulfide is incorporated into the cathode composition and demonstrates strong adsorption behavior toward lithium polysulfides during cycling. As a result, excellent electrochemical performance is obtained by the design of a physically and chemically enhanced lithium sulfur cathode. The reported electrode, with a sulfur loading of 8 mg cm-2 , delivers an initial capacity of 1118.8 mA h g-1 and a reversible capacity of 771.7 mA h g-1 after 150 cycles at a current density of 3 mA cm-2 . This work demonstrates that a chemically enhanced sulfur cathode, manufactured through additive manufacturing, is a viable pathway to achieve high-performance Li-S batteries.

Insight into the Microstructure and Ionic Conductivity of Cold Sintered NASICON Solid Electrolyte for Solid-State Batteries.

Li1.3Al0.3Ti1.7(PO4)3 (LATP) is a popular solid electrolyte used in solid-state lithium batteries due to its high ionic conductivity. Traditionally, the densification of LATP is achieved by a high-temperature sintering process (about 1000 °C). Herein, we report the compaction of LATP by a newly developed cold sintering process and post-annealing. LATP pellets are first densified at 120 °C and then annealed at 650 °C, yielding an ionic conductivity of 8.04 × 10-5 S cm-1 at room temperature and a relative density of 93% with a low activation energy of 0.37 eV. High-resolution transmission electron microscopy of the cold sintered pellets is investigated as well, showing that the particles are interconnected with some nanoprecipitates at the grain boundaries. Such nanocrystalline-enriched grain boundaries are beneficial for lithium-ion transportation, which leads to higher ionic conductivity of the cold sintered sample. This new sintering process can direct new horizons for development of all solid-state batteries due to its simplicity.

Unveiling the Interfacial Instability of the Phosphorus/Carbon Anode for Sodium-Ion Batteries.

As a competitive anode material for sodium-ion batteries (SIBs), a commercially available red phosphorus, featured with a high theoretical capacity (2596 mA h g-1) and a suitable operating voltage plateau (0.1-0.6 V), has been confronted with a severe structural instability and a rapid capacity degradation upon large volumetric change. In particular, the fundamental determining factors for phosphorus anode materials are yet poorly understood, and their interfacial stability against ambient air has not been explored and clarified. Herein, a high-performance phosphorus/carbon anode material has been fabricated simply through ball-milling the carbon black and red phosphorus, delivering a high reversible capacity of 1070 mA h g-1 at 400 mA g-1 after 200 cycles and a superior rate capability of 479 mA h g-1 at 3200 mA g-1. More importantly, we first reveal the significance of inhibiting the exposure of phosphorus/carbon electrode materials to air, even for a short period, for achieving a good electrochemical performance, which would sharply decrease the reversible capacities. With the assistance of synchrotron-based X-ray techniques, the formation and accumulation of insulating phosphate compounds can be spectroscopically identified, leading to the decay of electrochemical performance. At the same time, these passivation layers on the surface of electrode were found to occur via a self-oxidation process in ambient air. To maintain the electrochemical advantages of phosphorus anodes, it is necessary to inhibit their contact with air through a rational coating or an optimal storage condition. Additionally, the employment of a fluoroethylene carbonate (FEC) additive facilitates the decomposition of the electrolyte and favors the formation of a robust solid electrolyte interphase layer, which may suppress the side reactions between the active Na-P compounds and the electrolyte. These findings could help improve the surface protection and interfacial stability of phosphorus anodes for high-performance SIBs.

Promoting the Transformation of Li2 S2 to Li2 S: Significantly Increasing Utilization of Active Materials for High-Sulfur-Loading Li-S Batteries.

Lithium-sulfur (Li-S) batteries with high sulfur loading are urgently required in order to take advantage of their high theoretical energy density. Ether-based Li-S batteries involve sophisticated multistep solid-liquid-solid-solid electrochemical reaction mechanisms. Recently, studies on Li-S batteries have widely focused on the initial solid (sulfur)-liquid (soluble polysulfide)-solid (Li2 S2 ) conversion reactions, which contribute to the first 50% of the theoretical capacity of the Li-S batteries. Nonetheless, the sluggish kinetics of the solid-solid conversion from solid-state intermediate product Li2 S2 to the final discharge product Li2 S (corresponding to the last 50% of the theoretical capacity) leads to the premature end of discharge, resulting in low discharge capacity output and low sulfur utilization. To tackle the aforementioned issue, a catalyst of amorphous cobalt sulfide (CoS3 ) is proposed to decrease the dissociation energy of Li2 S2 and propel the electrochemical transformation of Li2 S2 to Li2 S. The CoS3 catalyst plays a critical role in improving the sulfur utilization, especially in high-loading sulfur cathodes (3-10 mg cm-2 ). Accordingly, the Li2 S/Li2 S2 ratio in the discharge products increased to 5.60/1 from 1/1.63 with CoS3 catalyst, resulting in a sulfur utilization increase of 20% (335 mAh g-1 ) compared to the counterpart sulfur electrode without CoS3 .

Mitigating the Interfacial Degradation in Cathodes for High-Performance Oxide-Based Solid-State Lithium Batteries.

Solid-state lithium batteries (SSLBs) are the promising next-generation energy storage systems because of their attractive advantages in terms of energy density and safety. However, the interfacial engineering and battery building are of huge challenges, especially for stiff oxide-based electrolytes. Herein, we construct SSLBs by a cosintering method using Li3BO3 as a sintering agent to bind the cathode materials LiNi0.6Mn0.2Co0.2O2 (NMC) and solid-state electrolytes Li6.4La3Zr1.4Ta0.6O12. Small NMC primary particles are compared with large secondary particles to study the effects on interfacial adhesion, mechanical retention, internal resistance evolution, and electrochemical performance. Our results reveal that the interfacial resistance decreases during charging and increases during discharging, resulting in an overall increase in the interfacial resistance after one cycle. The main reason is attributed to the microcracks induced by the volumetric changes of NMC during the electrochemical process. The mechanical degradations at the interfaces accumulated upon cycling can cause capacity decay and low Coulombic efficiency. The SSLB constructed from small NMC primary particles shows regulation of particle distribution, mitigation in local volumetric change, and alleviation in mechanical degradation at the interfaces, leading to smaller resistance change and better electrochemical performance. The findings shed lights on designing SSLBs with good mechanical retention and electrochemical performance.

A Novel Organic "Polyurea" Thin Film for Ultralong-Life Lithium-Metal Anodes via Molecular-Layer Deposition.

Metallic Li is considered as one of the most promising anode materials for next-generation batteries due to its high theoretical capacity and low electrochemical potential. However, its commercialization has been impeded by the severe safety issues associated with Li-dendrite growth. Non-uniform Li-ion flux on the Li-metal surface and the formation of unstable solid electrolyte interphase (SEI) during the Li plating/stripping process lead to the growth of dendritic and mossy Li structures that deteriorate the cycling performance and can cause short-circuits. Herein, an ultrathin polymer film of "polyurea" as an artificial SEI layer for Li-metal anodes via molecular-layer deposition (MLD) is reported. Abundant polar groups in polyurea can redistribute the Li-ion flux and lead to a uniform plating/stripping process. As a result, the dendritic Li growth during cycling is efficiently suppressed and the life span is significantly prolonged (three times longer than bare Li at a current density of 3 mA cm-2 ). Moreover, the detailed surface and interfacial chemistry of Li metal are studied comprehensively. This work provides deep insights into the design of artificial SEI coatings for Li metal and progress toward realizing next-generation Li-metal batteries.

High-Performance and Recyclable Al-Air Coin Cells Based on Eco-friendly Chitosan Hydrogel Membranes.

Aluminum-air batteries are a promising power supply for electronics due to their low cost and high energy density. However, portable coin-type Al-air batteries operating under ambient air condition for small electronic appliances have rarely been reported. Herein, coin cell-type Al-air batteries using cost-effective and eco-friendly chitosan hydrogel membranes modified by SiO2, SnO2, and ZnO have been prepared and assembled. The Al-air coin cell employing chitosan hydrogel membrane containing 10 wt % SiO2 as a separator exhibits better discharge performance with a higher flat voltage plateau, longer discharge duration, and higher power density than the cells using a chitosan hydrogel membrane containing SnO2 or ZnO. Moreover, we also demonstrate that the presented Al-air coin cell can be recycled by a series of eco-friendly procedures using food-grade ingredients, resulting in recycled products that are environmentally safe and ready for reuse. The Al-air coin cell adopting a recycled cathode from a fully discharged Al-air coin cell using the above-mentioned procedure has shown comparable performance to cells assembled with a new cathode. With these merits of enhanced electrochemical performance and recyclability, this new Al-air coin cell with modified chitosan hydrogel membrane can find wide applications for powering portable and small-size electronics.

High Capacity, Dendrite-Free Growth, and Minimum Volume Change Na Metal Anode.

Na metal anode attracts increasing attention as a promising candidate for Na metal batteries (NMBs) due to the high specific capacity and low potential. However, similar to issues faced with the use of Li metal anode, crucial problems for metallic Na anode remain, including serious moss-like and dendritic Na growth, unstable solid electrolyte interphase formation, and large infinite volume changes. Here, the rational design of carbon paper (CP) with N-doped carbon nanotubes (NCNTs) as a 3D host to obtain Na@CP-NCNTs composites electrodes for NMBs is demonstrated. In this design, 3D carbon paper plays a role as a skeleton for Na metal anode while vertical N-doped carbon nanotubes can effectively decrease the contact angle between CP and liquid metal Na, which is termed as being "Na-philic." In addition, the cross-conductive network characteristic of CP and NCNTs can decrease the effective local current density, resulting in uniform Na nucleation. Therefore, the as-prepared Na@CP-NCNT exhibits stable electrochemical plating/stripping performance in symmetrical cells even when using a high capacity of 3 mAh cm-2 at high current density. Furthermore, the 3D skeleton structure is observed to be intact following electrochemical cycling with minimum volume change and is dendrite-free in nature.