Biqiong Wang

On rechargeability and reaction kinetics of sodium–air batteries

Rechargeable metal–air batteries are widely considered as the next generation high energy density electrochemical storage devices. The performance and rechargeability of these metal–air cells are highly dependent on the positive electrode material, where oxygen reduction and evolution reactions take place. Here, for the first time, we provide a detailed account of the kinetics and rechargeability of sodium–air batteries through a series of carefully designed tests on a treated commercial carbon material. Surface area and porous structure of the positive electrode material were controlled in order to gain detailed information about the reaction kinetics of sodium–air batteries. The results indicate that discharge capacity is linearly correlated with surface area while morphology of the solid discharge product is strongly dependent on specific surface area and pore size. Furthermore, it was found that the chemical composition of discharge products as well as charging overpotential is affected by discharge reaction rate.

Superior Stable and Long Life Sodium Metal Anodes Achieved by Atomic Layer Deposition

Na-metal batteries are considered as the promising alternative candidate for Li-ion battery beneficial from the wide availability and low cost of sodium, high theoretical specific capacity, and high energy density based on the plating/stripping processes and lowest electrochemical potential. For Na-metal batteries, the crucial problem on metallic Na is one of the biggest challenges. Mossy or dendritic growth of Na occurs in the repetitive Na stripping/plating process with an unstable solid electrolyte interphase layer of nonuniform ionic flux, which can not only lead to the low Coulombic efficiency, but also can create short circuit risks, resulting in possible burning or explosion. In this communication, the atomic layer deposition of Al2 O3 coating is first demonstrated for the protection of metallic Na anode for Na-metal batteries. By protecting Na foil with ultrathin Al2 O3 layer, the dendrites and mossy Na formation have been effectively suppressed and lifetime has been significantly improved. Furthermore, the thickness of protective layer has been further optimized with 25 cycles of Al2 O3 layer presenting the best performance over 500 cycles. The novel design of atomic layer deposition protected metal Na anode may bring in new opportunities to the realization of the next-generation high energy-density Na metal batteries.

Safe and Durable High-Temperature Lithium–Sulfur Batteries via Molecular Layer Deposited Coating

Lithium-sulfur (Li-S) battery is a promising high energy storage candidate in electric vehicles. However, the commonly employed ether based electrolyte does not enable to realize safe high-temperature Li-S batteries due to the low boiling and flash temperatures. Traditional carbonate based electrolyte obtains safe physical properties at high temperature but does not complete reversible electrochemical reaction for most Li-S batteries. Here we realize safe high temperature Li-S batteries on universal carbon-sulfur electrodes by molecular layer deposited (MLD) alucone coating. Sulfur cathodes with MLD coating complete the reversible electrochemical process in carbonate electrolyte and exhibit a safe and ultrastable cycle life at high temperature, which promise practicable Li-S batteries for electric vehicles and other large-scale energy storage systems.

Tailoring interactions of carbon and sulfur in Li-S battery cathodes: significant effects of carbon- heteroatom bonds†

In this study, effects of carbon–heteroatom bonds on sulfur cathodes were investigated. A series of carbon black substrates were prepared using various treatments to introduce nitrogen or oxygen surface species. Our results indicated that nitrogen-doped carbon black significantly improved the electrochemical performance of sulfur cathode materials. Synchrotron-based XPS revealed that the defect sites of nitrogen-doped carbon are favorable for the discharge product deposition, leading to a high utilization and reversibility of sulfur cathodes. Our studies also found that the introduction of oxygen functional groups results in deteriorated performance of Li–sulfur batteries due to the reduced conductivity and unwanted side reactions occurring between sulfur and surface oxygen species.

Unravelling the Role of Electrochemically Active FePO4 Coating by Atomic Layer Deposition for Increased High-Voltage Stability of LiNi0.5Mn1.5O4 Cathode Material

Ultrathin amorphous FePO4 coating derived by atomic layer deposition (ALD) is used to coat the 5 V LiNi0.5Mn1.5O4 cathode material powders, which dramatically increases the capacity retention of LiNi0.5Mn1.5O4. It is believed that the amorphous FePO4 layer could act as a lithium‐ions reservoir and electrochemically active buffer layer during the charge/discharge cycling, helping achieve high capacities in LiNi0.5Mn1.5O4, especially at high current densities.

Inorganic–Organic Coating via Molecular Layer Deposition Enables Long Life Sodium Metal Anode

Metallic Na anode is considered as a promising alternative candidate for Na ion batteries (NIBs) and Na metal batteries (NMBs) due to its high specific capacity, and low potential. However, the unstable solid electrolyte interphase layer caused by serious corrosion and reaction in electrolyte will lead to big challenges, including dendrite growth, low Coulombic efficiency and even safety issues. In this paper, we first demonstrate the inorganic-organic coating via advanced molecular layer deposition (alucone) as a protective layer for metallic Na anode. By protecting Na anode with controllable alucone layer, the dendrites and mossy Na formation have been effectively suppressed and the lifetime has been significantly improved. Moreover, the molecular layer deposition alucone coating shows better performances than the atomic layer deposition Al2O3 coating. The novel design of molecular layer deposition protected Na metal anode may bring in new opportunities to the realization of the next-generation high energy-density NIBs and NMBs.

Atomic layer deposition of lithium phosphates as solid-state electrolytes for all-solid-state microbatteries

Atomic layer deposition (ALD) has been shown as a powerful technique to build three-dimensional (3D) all-solid-state microbattery, because of its unique advantages in fabricating uniform and pinhole-free thin films in 3D structures. The development of solid-state electrolyte by ALD is a crucial step to achieve the fabrication of 3D all-solid-state microbattery by ALD. In this work, lithium phosphate solid-state electrolytes were grown by ALD at four different temperatures (250, 275, 300, and 325 °C) using two precursors (lithium tert-butoxide and trimethylphosphate). A linear dependence of film thickness on ALD cycle number was observed and uniform growth was achieved at all four temperatures. The growth rate was 0.57, 0.66, 0.69, and 0.72 Å/cycle at deposition temperatures of 250, 275, 300, and 325 °C, respectively. Furthermore, x-ray photoelectron spectroscopy confirmed the compositions and chemical structures of lithium phosphates deposited by ALD. Moreover, the lithium phosphate thin films deposited at 300 °C presented the highest ionic conductivity of 1.73 × 10(-8) S cm(-1) at 323 K with ~ 0.51 eV activation energy based on the electrochemical impedance spectroscopy. The ionic conductivity was calculated to be 3.3 × 10(-8) S cm(-1) at 26 °C (299 K).

Nanoscale stabilization of Li–sulfur batteries by atomic layer deposited Al2O3

An atomic layer deposited (ALD) Al2O3 coating applied to sulfur cathodes has been studied in this paper. It is demonstrated that the Al2O3 coating improves the cycling stability of Li–sulfur batteries. The underlying mechanism by synchrotron-based X-ray photoelectron spectroscopy was investigated. The coating layer not only protects the polysulfide from dissolution, but also facilitates the utilization of sulfur, demonstrating improved electrochemical performances.

Ultrahigh Rate and Long‐Life Sodium‐Ion Batteries Enabled by Engineered Surface and Near‐Surface Reactions

To achieve the high-power sodium-ion batteries, the solid-state ion diffusion in the electrode materials is a highly concerned issue and needs to be solved. In this study, a simple and effective strategy is reported to weaken and degrade this process by engineering the intensified surface and near-surface reactions, which is realized by making use of a sandwich-type nanoarchitecture composed of graphene as electron channels and few-layered MoS2 with expanded interlayer spacing. The unique 2D sheet-shaped hierarchical structure is capable of shortening the ion diffusion length, while the few-layered MoS2 with expanded interlayer spacing has more accessible surface area and the decreased ion diffusion resistance, evidenced by the smaller energy barriers revealed by the density functional theory calculations. Benefiting from the shortened ion diffusion distance and enhanced electron transfer capability, a high ratio of surface or near-surface reactions is dominated at a high discharge/charge rate. As such, the composites exhibit the high capacities of 152 and 93 mA h g-1 at 30 and 50 A g-1 , respectively. Moreover, a high reversible capacity of 684 mA h g-1 and an excellent cycling stability up to 4500 cycles can be delivered. The outstanding performance is attributed to the engineered structure with increased contribution of surface or near-surface reactions.

Atomic Layer Deposited Lithium Silicates as Solid-State Electrolytes for All-Solid-State Batteries

Development of solid-state electrolyte (SSE) thin films is a key toward the fabrication of all-solid-state batteries (ASSBs). However, it is challenging for conventional deposition techniques to deposit uniform and conformal SSE thin films in a well-controlled fashion. In this study, atomic layer deposition (ALD) was used to fabricate lithium silicate thin films as a potential SSE for ASSBs. Lithium silicates thin films were deposited by combining ALD Li2O and SiO2 subcycles using lithium tert-butoxide, tetraethylorthosilane, and H2O as precursors. Uniform and self-limiting growth was achieved at temperatures between 225 and 300 °C. X-ray absorption spectroscopy analysis disclosed that the as-deposited lithium silicates were composed of SiO4 tetrahedron structure and lithium oxide as the network modifier. X-ray photoelectron spectroscopy confirmed the chemical states of Li in the thin films were the same with that in standard lithium silicate. With one to one subcycle of Li2O and SiO2 the thin films had a composition close to Li4SiO4 whereas one more subcycle of Li2O delivered a higher lithium content. The lithium silicate thin film prepared at 250 °C exhibited an ionic conductivity of 1.45× 10-6 S cm-1 at 373 K. The high ionic conductivity of lithium silicate was due to the higher lithium concentration and lower activation energy.