Li metal deposition and stripping in a solid-state battery via Coble creep.

Solid-state lithium metal batteries require accommodation of electrochemically generated mechanical stress inside the lithium: this stress can be1,2 up to 1 gigapascal for an overpotential of 135 millivolts. Maintaining the mechanical and electrochemical stability of the solid structure despite physical contact with moving corrosive lithium metal is a demanding requirement. Using in situ transmission electron microscopy, we investigated the deposition and stripping of metallic lithium or sodium held within a large number of parallel hollow tubules made of a mixed ionic-electronic conductor (MIEC). Here we show that these alkali metals-as single crystals-can grow out of and retract inside the tubules via mainly diffusional Coble creep along the MIEC/metal phase boundary. Unlike solid electrolytes, many MIECs are electrochemically stable in contact with lithium (that is, there is a direct tie-line to metallic lithium on the equilibrium phase diagram), so this Coble creep mechanism can effectively relieve stress, maintain electronic and ionic contacts, eliminate solid-electrolyte interphase debris, and allow the reversible deposition/stripping of lithium across a distance of 10 micrometres for 100 cycles. A centimetre-wide full cell-consisting of approximately 1010 MIEC cylinders/solid electrolyte/LiFePO4-shows a high capacity of about 164 milliampere hours per gram of LiFePO4, and almost no degradation for over 50 cycles, starting with a 1× excess of Li. Modelling shows that the design is insensitive to MIEC material choice with channels about 100 nanometres wide and 10-100 micrometres deep. The behaviour of lithium metal within the MIEC channels suggests that the chemical and mechanical stability issues with the metal-electrolyte interface in solid-state lithium metal batteries can be overcome using this architecture.

Thermally Aged Li-Mn-O Cathode with Stabilized Hybrid Cation and Anion Redox.

Though low-cost and environmentally friendly, Li-Mn-O cathodes suffer from low energy density. Although synthesized Li4Mn5O12-like overlithiated spinel cathode with reversible hybrid anion- and cation-redox (HACR) activities has a high initial capacity, it degrades rapidly due to oxygen loss and side-reaction-induced electrolyte decomposition. Herein, we develop a two-step heat treatment to promote local decomposition as Li4Mn5O12 → 2LiMn2O4 + Li2MnO3 + 1/2 O2↑, which releases near-surface reactive oxygen that is harmful to cycling stability. The produced nanocomposite delivers a high discharge capacity of 225 mAh/g and energy density of over 700 Wh/kg at active-material level at a current density of 100 mA/g between 1.8 to 4.7 V. Benefiting from suppressed oxygen loss and side reactions, 80% capacity retention is achieved after 214 cycles in half cells. With industrially acceptable electrolyte amount (6 g/Ah), full cells paired with Li4Ti5O12 anode have a good retention over 100 cycles.

Self-Perpetuating Carbon Foam Microwave Plasma Conversion of Hydrocarbon Wastes into Useful Fuels and Chemicals.

White wastes (unseparated plastics, face masks, textiles, etc.) pose a serious challenge to sustainable human development and the ecosystem and have recently been exacerbated due to the surge in plastic usage and medical wastes from COVID-19. Current recycling methods such as chemical recycling, mechanical recycling, and incineration require either pre-sorting and washing or releasing CO2. In this work, a carbon foam microwave plasma process is developed, utilizing plasma discharge to generate surface temperatures exceeding ∼3000 K in a N2 atmosphere, to convert unsorted white wastes into gases (H2, CO, C2H4, C3H6, CH4, etc.) and small amounts of inorganic minerals and solid carbon, which can be buried as artificial "coal". This process is self-perpetuating, as the new solid carbon asperities grafted onto the foam's surface actually increase the plasma discharge efficiency over time. This process has been characterized by in situ optical probes and infrared sensors and optimized to handle most of the forms of white waste without the need for pre-sorting or washing. Thermal measurement and modeling show that in a flowing reactor, the device can achieve locally extremely high temperatures, but the container wall will still be cold and can be made with cheap materials, and thus, a miniaturized waste incinerator is possible that also takes advantage of intermittent renewable electricity.

Fluorine-donating electrolytes enable highly reversible 5-V-class Li metal batteries.

Lithium metal has gravimetric capacity ∼10× that of graphite which incentivizes rechargeable Li metal batteries (RLMB) development. A key factor that limits practical use of RLMB is morphological instability of Li metal anode upon electrodeposition, reflected by the uncontrolled area growth of solid-electrolyte interphase that traps cyclable Li, quantified by the Coulombic inefficiency (CI). Here we show that CI decreases approximately exponentially with increasing donatable fluorine concentration of the electrolyte. By using up to 7 m of Li bis(fluorosulfonyl)imide in fluoroethylene carbonate, where both the solvent and the salt donate F, we can significantly suppress anode porosity and improve the Coulombic efficiency to 99.64%. The electrolyte demonstrates excellent compatibility with 5-V LiNi0.5Mn1.5O4 cathode and Al current collector beyond 5 V. As a result, an RLMB full cell with only 1.4× excess lithium as the anode was demonstrated to cycle above 130 times, at industrially significant loading of 1.83 mAh/cm2 and 0.36 C. This is attributed to the formation of a protective LiF nanolayer, which has a wide bandgap, high surface energy, and small Burgers vector, making it ductile at room temperature and less likely to rupture in electrodeposition.

Uniformizing the lithium deposition by gradient lithiophilicity and conductivity for stable lithium-metal batteries.

The practical application of lithium metal batteries is hindered by the poor reversibility and large volume change caused by the uncontrollable dendritic growth and the highly reactive surface. In this work, favorable Li deposition is achieved by generating gradient lithiophilicity and conductivity in an Ag-decorated graphene/holey graphene film (G-HGA). Dendrite-free Li metal is deposited on the G-HGA matrix, which greatly reduces the surface area and suppresses the side reaction between the electrolyte and the dendritic Li. The average Li-metal plating-stripping coulombic efficiency (CE) on the G-HGA matrix maintains ∼98.7% over 350 cycles, compared to a worse average CE (∼97.3%) with the bare Cu matrix, only for less than 100 cycles. A full cell constructed by using LiFePO4 and prelithiated G-HGA exhibits excellent rate capability and a high capacity retention of 99.6% for 175 cycles at a low negative to positive capacity ratio of 1.13. This advanced design can inspire further development of high-energy and long-lived Li-metal batteries.

Acid-in-Clay Electrolyte for Wide-Temperature-Range and Long-Cycle Proton Batteries.

Proton conduction underlies many important electrochemical technologies. A family of new proton electrolytes is reported: acid-in-clay electrolyte (AiCE) prepared by integrating fast proton carriers in a natural phyllosilicate clay network, which can be made into thin-film (tens of micrometers) fluid-impervious membranes. The chosen example systems (sepiolite-phosphoric acid) rank top among the solid proton conductors in terms of proton conductivities (15 mS cm-1 at 25 °C, 0.023 mS cm-1 at -82 °C), electrochemical stability window (3.35 V), and reduced chemical reactivity. A proton battery is assembled using AiCE as the solid electrolyte membrane. Benefitting from the wider electrochemical stability window, reduced corrosivity, and excellent ionic selectivity of AiCE, the two main problems (gassing and cyclability) of proton batteries are successfully solved. This work draws attention to the element cross-over problem in proton batteries and the generic "acid-in-clay" solid electrolyte approach with superfast proton transport, outstanding selectivity, and improved stability for room- to cryogenic-temperature protonic applications.

Dense All-Electrochem-Active Electrodes for All-Solid-State Lithium Batteries.

The energy density presents the core competitiveness of lithium (Li)-ion batteries. In conventional Li-ion batteries, the utilization of the gravimetric/volumetric energy density at the electrode level is unsatisfactory (<84 wt% and <62 vol%, respectively) due to the existence of non-electrochemical active parts among the 3D porous electrodes, including electrolytes, binders, and carbon additives. These are regarded as indispensable and irreducible components of the electronic and ionic transport network. Here, a dense "all-electrochem-active" (AEA) electrode for all-solid-state Li batteries is proposed, which is entirely constructed from a family of superior mixed electronic-ionic-conducting cathodes, to minimize the energy density gap between the accessible and theoretical energy density at the electrode level. Furthermore, with the ionic-electronic-conductive network self-supported from the AEA cathode, the dense hybrid sulfur (S)-based AEA electrode exhibits a high compacted filling rate of 91.8%, which indicates a high energy density of 777 W h kg-1 and 1945 W h L-1 at the electrode level based on the total cathodes and anodes when at 70 °C.

Low-Density Fluorinated Silane Solvent Enhancing Deep Cycle Lithium-Sulfur Batteries' Lifetime.

The lithium metal anode (LMA) instability at deep cycle with high utilization is a crucial barrier for developing lithium (Li) metal batteries, resulting in excessive Li inventory and electrolyte demand. This issue becomes more severe in capacity-type lithium-sulfur (Li-S) batteries. High-concentration or localized high-concentration electrolytes are noted as effective strategies to stabilize Li metal but usually lead to a high electrolyte density (>1.4 g mL-1 ). Here we propose a bifunctional fluorinated silane-based electrolyte with a low density of 1.0 g mL-1 that not only is much lighter than conventional electrolytes (≈1.2 g mL-1 ) but also form a robust solid electrolyte interface to minimize Li depletion. Therefore, the Li loss rate is reduced over 4.5-fold with the proposed electrolyte relative to its conventional counterpart. When paired with onefold excess LMA at the electrolyte weight/cell capacity (E/C) ratio of 4.5 g Ah-1 , the Li-S pouch cell using our electrolyte can survive for 103 cycles, much longer than with the conventional electrolyte (38 cycles). This demonstrates that our electrolyte not only reduces the E/C ratio but also enhances the cyclic stability of Li-S batteries under limited Li amounts.

Three-Dimensional SiC/Holey-Graphene/Holey-MnO2 Architectures for Flexible Energy Storage with Superior Power and Energy Densities.

Although nanostructured materials have recently enabled a dramatic improvement of the current energy-storage units in portable electronics with enhanced functionality, it is still challenging to provide a cost-efficient solution to attain the ultrahigh energy and power densities of supercapacitors (SCs) since nearly arbitrary electrodes are limited to the thinner porous structure with de facto rather low mass loading (∼1 mg cm-2) because of the huge limitations of pronounced impaired ion transport in subnanometer pores in thicker compact electrodes. In this contribution, we report the fabrication of a macro/mesoporous hybrid hierarchical nanocomposite SiC/holey-graphene/holey-MnO2 (SiC/HG/h-MnO2) with tailored porosity by knitting together the quasi-aligned single-crystalline doped 3C-SiC nanowire array and in situ surface-reduced holey graphene framework into a three-dimensional quasi-ordered structure, which enables the mass growth of ultrathin h-MnO2 nanosheets at approximately practical levels of mass loading. The produced synergistically favorable interconnected porous architecture allows for the highly efficient electron transfer and rapid ion transport up to interior surfaces of the network. Remarkably, the all-solid-state flexible asymmetric supercapacitors (ASCs) made with SiC/HG/h-MnO2 and SiC/graphitic carbon (GC) nanoarrays are mechanically robust and show a high areal capacity (0.32 mWh cm-2) and a high rate capability (280 mW cm-2) at ultrahigh mass loading (6.5 mg cm-2), much higher than most of previous superior SCs in aqueous or gelled electrolytes and thus offer an entirely new prototype of textile-based ASCs, which represents a critical step toward practical applications for various portable electronics.

Sacrificial Poly(propylene carbonate) Membrane for Dispersing Nanoparticles and Preparing Artificial Solid Electrolyte Interphase on Li Metal Anode.

Lithium-metal batteries have been regarded as next-generation high-energy-density candidates beyond lithium-ion batteries. However, the lithium-morphology instabilities accompanied by continuous side reactions with electrolytes inevitably leads to dissatisfactory performances and even safety issues, where the unstable interface between lithium-metal anode and electrolytes has been regarded as the root cause. Artificial solid electrolyte interphase engineering has attracted a lot of attention to stabilize lithium-metal anodes. Here, a novel method with universality is reported to produce the organic-inorganic artificial solid electrolyte interphase. Using poly(propylene carbonate) as a sacrificial matrix, nanoparticles are dispersed on lithium-metal anodes surface uniformly to prepare artificial solid electrolyte interphase, where poly(propylene carbonate) turns into liquid propylene carbonate upon contact with lithium-metal anode. Silicon, Li1.5Al0.5Ge1.5(PO4)3, or Li1.4Al0.4Ti1.6(PO4)3 nanoparticles are coated to suppress lithium-morphology instabilities and demonstrated ∼4 times longer cycle life. Preparing various organic/inorganic artificial solid electrolyte interphase is feasible by introducing various components in the fabrication process of poly(propylene carbonate) membrane, endowing this approach with huge potential in the research of artificial solid electrolyte interphase.

Fast Heat Transport Inside Lithium-Sulfur Batteries Promotes Their Safety and Electrochemical Performance.

Lithium-sulfur batteries are paid much attention owing to their high specific capacity and energy density. However, their practical applications are impeded by poor electrochemical performance due to the dissolved polysulfides. The concentration of soluble polysulfides has a linear relationship with the internal heat generation. The issue of heat transport inside lithium-sulfur batteries is often overlooked. Here, we designed a functional separator that not only had a high thermal conductivity of 0.65 W m-1 K-1 but also alleviated the diffusion of dissolved active materials to the lithium anode, improving the electrochemical performance and safety issue. Lithium-sulfur batteries with the functional separator have a specific capacity of 1,126.4 mAh g-1 at 0.2 C, and the specific capacity can be remained up to 893.5 mAh g-1 after 100 cycles. Pouch Cells with high sulfur loading also showed a good electrochemical performance under a lean electrolyte condition of electrolyte/sulfur (E/S) = 3 µL mg-1.