Boyang Liu

Negating interfacial impedance in garnet-based solid-state Li metal batteries

Garnet-type solid-state electrolytes have attracted extensive attention due to their high ionic conductivity, approaching 1 mS cm-1, excellent environmental stability, and wide electrochemical stability window, from lithium metal to ∼6 V. However, to date, there has been little success in the development of high-performance solid-state batteries using these exceptional materials, the major challenge being the high solid-solid interfacial impedance between the garnet electrolyte and electrode materials. In this work, we effectively address the large interfacial impedance between a lithium metal anode and the garnet electrolyte using ultrathin aluminium oxide (Al2O3) by atomic layer deposition. Li7La2.75Ca0.25Zr1.75Nb0.25O12 (LLCZN) is the garnet composition of choice in this work due to its reduced sintering temperature and increased lithium ion conductivity. A significant decrease of interfacial impedance, from 1,710 Ω cm2 to 1 Ω cm2, was observed at room temperature, effectively negating the lithium metal/garnet interfacial impedance. Experimental and computational results reveal that the oxide coating enables wetting of metallic lithium in contact with the garnet electrolyte surface and the lithiated-alumina interface allows effective lithium ion transport between the lithium metal anode and garnet electrolyte. We also demonstrate a working cell with a lithium metal anode, garnet electrolyte and a high-voltage cathode by applying the newly developed interface chemistry.

Conformal, Nanoscale ZnO Surface Modification of Garnet-Based Solid-State Electrolyte for Lithium Metal Anodes

Solid-state electrolytes are known for nonflammability, dendrite blocking, and stability over large potential windows. Garnet-based solid-state electrolytes have attracted much attention for their high ionic conductivities and stability with lithium metal anodes. However, high-interface resistance with lithium anodes hinders their application to lithium metal batteries. Here, we demonstrate an ultrathin, conformal ZnO surface coating by atomic layer deposition for improved wettability of garnet solid-state electrolytes to molten lithium that significantly decreases the interface resistance to as low as ∼20 Ω·cm2. The ZnO coating demonstrates a high reactivity with lithium metal, which is systematically characterized. As a proof-of-concept, we successfully infiltrated lithium metal into porous garnet electrolyte, which can potentially serve as a self-supported lithium metal composite anode having both high ionic and electrical conductivity for solid-state lithium metal batteries. The facile surface treatment method offers a simple strategy to solve the interface problem in solid-state lithium metal batteries with garnet solid electrolytes.

3D‐Printed, All‐in‐One Evaporator for High‐Efficiency Solar Steam Generation under 1 Sun Illumination

Using solar energy to generate steam is a clean and sustainable approach to addressing the issue of water shortage. The current challenge for solar steam generation is to develop easy-to-manufacture and scalable methods which can convert solar irradiation into exploitable thermal energy with high efficiency. Although various material and structure designs have been reported, high efficiency in solar steam generation usually can be achieved only at concentrated solar illumination. For the first time, 3D printing to construct an all-in-one evaporator with a concave structure for high-efficiency solar steam generation under 1 sun illumination is used. The solar-steam-generation device has a high porosity (97.3%) and efficient broadband solar absorption (>97%). The 3D-printed porous evaporator with intrinsic low thermal conductivity enables heat localization and effectively alleviates thermal dissipation to the bulk water. As a result, the 3D-printed evaporator has a high solar steam efficiency of 85.6% under 1 sun illumination (1 kW m-2 ), which is among the best compared with other reported evaporators. The all-in-one structure design using the advanced 3D printing fabrication technique offers a new approach to solar energy harvesting for high-efficiency steam generation.

Toward garnet electrolyte–based Li metal batteries: An ultrathin, highly effective, artificial solid-state electrolyte/metallic Li interface

Strategy to change the wettability of the solid-state electrolyte against Li and reduce interface resistance. Solid-state batteries are a promising option toward high energy and power densities due to the use of lithium (Li) metal as an anode. Among all solid electrolyte materials ranging from sulfides to oxides and oxynitrides, cubic garnet–type Li7La3Zr2O12 (LLZO) ceramic electrolytes are superior candidates because of their high ionic conductivity (10−3 to 10−4 S/cm) and good stability against Li metal. However, garnet solid electrolytes generally have poor contact with Li metal, which causes high resistance and uneven current distribution at the interface. To address this challenge, we demonstrate a strategy to engineer the garnet solid electrolyte and the Li metal interface by forming an intermediary Li-metal alloy, which changes the wettability of the garnet surface (lithiophobic to lithiophilic) and reduces the interface resistance by more than an order of magnitude: 950 ohm·cm2 for the pristine garnet/Li and 75 ohm·cm2 for the surface-engineered garnet/Li. Li7La2.75Ca0.25Zr1.75Nb0.25O12 (LLCZN) was selected as the solid-state electrolyte (SSE) in this work because of its low sintering temperature, stabilized cubic garnet phase, and high ionic conductivity. This low area-specific resistance enables a solid-state garnet SSE/Li metal configuration and promotes the development of a hybrid electrolyte system. The hybrid system uses the improved solid-state garnet SSE Li metal anode and a thin liquid electrolyte cathode interfacial layer. This work provides new ways to address the garnet SSE wetting issue against Li and get more stable cell performances based on the hybrid electrolyte system for Li-ion, Li-sulfur, and Li-oxygen batteries toward the next generation of Li metal batteries.

Three-dimensional bilayer garnet solid electrolyte based high energy density lithium metal–sulfur batteries

To simultaneously address the challenges of chemical/physical short circuits and electrode volume variation, we demonstrate a three-dimensional (3D) bilayer garnet solid-state electrolyte framework for advanced Li metal batteries. The dense layer is reduced in thickness to a few microns and still retains good mechanical stability, thereby enabling the safe use of Li metal anodes. The thick porous layer acts as a mechanical support for the thin dense layer which serves as a host for high loading of cathode materials and provides pathways for continuous ion transport. Results show that the integrated sulfur cathode loading can reach >7 mg cm−2 while the proposed hybrid Li–S battery exhibits a high initial coulombic efficiency (>99.8%) and high average coulombic efficiency (>99%) during the subsequent cycles. This electrolyte framework represents a promising strategy to revolutionize Li-metal batteries by transitioning to all-solid-state batteries and can be extended to other cathode materials.

A carbon-based 3D current collector with surface protection for Li metal anode

Lithium metal is considered the ideal anode material for Li-ion-based batteries because it exhibits the highest specific capacity and lowest redox potential for this type of cells. However, growth of Li dendrites, unstable solid electrolyte interphases, low Coulombic efficiencies, and safety hazards have significantly hindered the practical application of metallic Li anodes. Herein, we propose a three-dimensional (3D) carbon nanotube sponge (CNTS) as a Li deposition host. The high specific surface area of the CNTS enables homogenous charge distribution for Li nucleation and minimizes the effective current density to overcome dendrite growth. An additional conformal Al2O3 layer on the CNTS coated by atomic layer deposition (ALD) robustly protects the Li metal electrode/electrolyte interface due to the good chemical stability and high mechanical strength of the layer. The Li@ALD-CNTS electrode exhibits stable voltage profiles with a small overpotential ranging from 16 to 30 mV over 100 h of cycling at 1.0 mA·cm–2. Moreover, the electrodes display a dendrite-free morphology after cycling and a Coulombic efficiency of 92.4% over 80 cycles at 1.0 mA·cm–2 in an organic carbonate electrolyte, thus demonstrating electrochemical stability superior to that of planar current collectors. Our results provide an important strategy for the rational design of current collectors to obtain stable Li metal anodes.

Encapsulation of Metallic Na in an Electrically Conductive Host with Porous Channels as a Highly Stable Na Metal Anode

Room-temperature Na ion batteries (NIBs) have attracted great attention because of the widely available, abundant sodium resources and potentially low cost. Currently, the challenge of the NIB development is due primarily to the lack of a high-performance anode, while the Na metal anode holds great promise considering its highest specific capacity of 1165 mA h/g and lowest anodic potential. However, an uneven deposit, relatively infinite volume change, and dendritic growth upon plating/stripping cycles cause a low Coulombic efficiency, poor cycling performance, and severe safety concerns. Here, a stable Na carbonized wood (Na-wood) composite anode was fabricated via a rapid melt infusion (about 5 s) into channels of carbonized wood by capillary action. The channels function as a high-surface-area, conductive, mechanically stable skeleton, which lowers the effective current density, ensures a uniform Na nucleation, and restricts the volume change over cycles. As a result, the Na-wood composite anode exhibited flat plating/stripping profiles with smaller overpotentials and stable cycling performance over 500 h at 1.0 mA/cm2 in a common carbonate electrolyte system. In sharp comparison, the planar Na metal electrode showed a much shorter cycle life of 100 h under the same test conditions.

Mesoporous, Three-Dimensional Wood Membrane Decorated with Nanoparticles for Highly Efficient Water Treatment

Wood, an earth-abundant material, is widely used in our everyday life. With its mesoporous structure, natural wood is comprised of numerous long, partially aligned channels (lumens) as well as nanochannels that stretch along its growth direction. This wood mesostructure is suitable for a range of emerging applications, especially as a membrane/separation material. Here, we report a mesoporous, three-dimensional (3D) wood membrane decorated with palladium nanoparticles (Pd NPs/wood membrane) for efficient wastewater treatment. The 3D Pd NPs/wood membrane possesses the following advantages: (1) the uniformly distributed lignin within the wood mesostructure can effectively reduce Pd(II) ions to Pd NPs; (2) cellulose, with its abundant hydroxyl groups, can immobilize Pd NPs; (3) the partially aligned mesoporous wood channels as well as their inner ingenious microstructures increase the likelihood of wastewater contacting Pd NPs decorating the wood surface; (4) the long, Pd NP-decorated channels facilitate bulk treatment as water flows through the entire mesoporous wood membrane. As a proof of concept, we demonstrated the use and efficiency of a Pd NPs/wood membrane to remove methylene blue (MB, C16H18N3ClS) from a flowing aqueous solution. The turnover frequency of the Pd NPs/wood membrane, ∼2.02 molMB·molPd-1·min-1, is much higher than the values reported in the literature. The water treatment rate of the 3D Pd NPs/wood membrane can reach 1 × 105 L·m-2·h-1 with a high MB removal efficiency (>99.8%). The 3D mesoporous wood membrane with partially aligned channels exhibits promising results for wastewater treatment and is applicable for an even wider range of separation applications.

Garnet Solid Electrolyte Protected Li-Metal Batteries

Garnet-type solid state electrolyte (SSE) is a promising candidate for high performance lithium (Li)-metal batteries due to its good stability and high ionic conductivity. One of the main challenges for garnet solid state batteries is the poor solid-solid contact between the garnet and electrodes, which results in high interfacial resistance, large polarizations, and low efficiencies in batteries. To address this challenge, in this work gel electrolyte is used as an interlayer between solid electrolyte and solid electrodes to improve their contact and reduce their interfacial resistance. The gel electrolyte has a soft structure, high ionic conductivity, and good wettability. Through construction of the garnet/gel interlayer/electrode structure, the interfacial resistance of the garnet significantly decreased from 6.5 × 104 to 248 Ω cm2 for the cathode and from 1.4 × 103 to 214 Ω cm2 for the Li-metal anode, successfully demonstrating a full cell with high capacity (140 mAh/g for LiFePO4 cathode) over 70 stable cycles in room temperature. This work provides a binary electrolyte consisting of gel electrolyte and solid electrolyte to address the interfacial challenge of solid electrolyte and electrodes and the demonstrated hybrid battery presents a promising future for battery development with high energy and good safety.

Enabling High-Areal-Capacity Lithium–Sulfur Batteries: Designing Anisotropic and Low-Tortuosity Porous Architectures

Lithium-sulfur (Li-S) batteries have attracted much attention due to their high theoretical energy density in comparison to conventional state-of-the-art lithium-ion batteries. However, low sulfur mass loading in the cathode results in low areal capacity and impedes the practical use of Li-S cells. Inspired by wood, a cathode architecture with natural, three-dimensionally (3D) aligned microchannels filled with reduced graphene oxide (RGO) were developed as an ideal structure for high sulfur mass loading. Compared with other carbon materials, the 3D porous carbon matrix has several advantages including low tortuosity, high electrical conductivity, and good structural stability, which make it an excellent 3D lightweight current collector. The Li-S battery assembled with the wood-based sulfur electrode can deliver a high areal capacity of 15.2 mAh cm-2 with a sulfur mass loading of 21.3 mg cm-2. This work provides a facile but effective strategy to develop 3D porous electrodes for Li-S batteries, which can also be applied to other cathode materials to achieve a high areal capacity with uncompromised rate and cycling performance.