A Polymer Lithium-Oxygen Battery

Room-Temperature Solid-State Polymer Electrolyte in Li-LiFePO4 , Li-S and Li-O2 Batteries

A solid polymer electrolyte has been developed and employed in lithium-metal batteries of relevant interest. The material includes crystalline poly(ethylene glycol)dimethyl ether (PEGDME), LiTFSI and LiNO3 salts, and a SiO2 ceramic filler. The electrolyte shows ionic conductivity more than 10-4  S cm-1 at room temperature and approaching 10-3  S cm-1 at 60 °C, a Li+ -transference number exceeding 0.3, electrochemical stability from 0 to 4.4 V vs. Li+ /Li, lithium stripping/deposition overvoltage below 0.08 V, and electrode/electrolyte interphase resistance of 400 Ω. Thermogravimetry indicates that the electrolyte stands up to 200 °C without significant weight loss, while FTIR spectroscopy suggests that the LiTFSI conducting salt dissolves in the polymer. The electrolyte is used in solid-state cells with various cathodes, including LiFePO4 olivine exploiting the Li-insertion, sulfur-carbon composite operating through Li conversion, and an oxygen electrode in which reduction and evolution reactions (i. e., ORR/OER) evolve on a carbon-coated gas diffusion layer (GDL). The cells operate reversibly at room temperature with a capacity of 140 mA h g-1 at 3.4 V for LiFePO4 , 400 mA h g-1 at 2 V for sulfur electrode, and 500 mA h g-1 at 2.5 V for oxygen. The results suggest that the electrolyte could be applied in room-temperature solid polymer cells.

Recent Advances in Rechargeable Metal-CO2 Batteries with Nonaqueous Electrolytes

This review article discusses the recent advances in rechargeable metal-CO2 batteries (MCBs), which include the Li, Na, K, Mg, and Al-based rechargeable CO2 batteries, mainly with nonaqueous electrolytes. MCBs capture CO2 during discharge by the CO2 reduction reaction and release it during charging by the CO2 evolution reaction. MCBs are recognized as one of the most sophisticated artificial modes for CO2 fixation by electrical energy generation. However, extensive research and substantial developments are required before MCBs appear as reliable, sustainable, and safe energy storage systems. The rechargeable MCBs suffer from the hindrances like huge charging-discharging overpotential and poor cyclability due to the incomplete decomposition and piling of the insulating and chemically stable compounds, mainly carbonates. Efficient cathode catalysts and a suitable architectural design of the cathode catalysts are essential to address this issue. Besides, electrolytes also play a vital role in safety, ionic transportation, stable solid-electrolyte interphase formation, gas dissolution, leakage, corrosion, operational voltage window, etc. The highly electrochemically active metals like Li, Na, and K anodes severely suffer from parasitic reactions and dendrite formation. Recent research works on the aforementioned secondary MCBs have been categorically reviewed here, portraying the latest findings on the key aspects governing secondary MCB performances.

Criteria for evaluating lithium-air batteries in academia to correctly predict their practical performance in industry

Although the market share for Li-ion batteries (LiBs) has continuously expanded, the limited theoretical energy density of conventional LiBs will no longer meet the advanced energy storage requirements. Lithium-air batteries (LABs) are potential candidates for next-generation rechargeable batteries because of their extremely high theoretical energy density. However, the reported values for the actual energy density of LABs are much lower than those for LiBs, mainly due to the excess amount of electrolyte in the cell. In the present review article, the practical energy density is estimated for the representative LABs reported in academia, and the critical factors for improving the energy density of LABs are summarized. The criteria for evaluating LABs in laboratory-based experiments are also proposed for accurately predicting the performance of practical cells in industry.

Transition of the Reaction from Three-Phase to Two-Phase by Using a Hybrid Conductor for High-Energy-Density High-Rate Solid-State Li-O2 Batteries

Solid-state Li-O₂ batteries possess the ability to deliver high energy density with enhanced safety. However, designing a highly functional solid-state air electrode is the main bottleneck for its further development. Herein, we adopt a hybrid electronic and ionic conductor to build solid-state air electrode that makes the transition of Li-O₂ battery electrochemical mechanism from a three-phase process to a two-phase process. The solid-state Li-O₂ battery with this hybrid conductor solid-state air electrode shows decreased interfacial resistance and enhanced reaction kinetics. The Coulombic efficiency of Li-O₂ battery is also significantly improved, benefiting from the good contact between discharge products and electrode materials. In situ environmental transmission electron microscopy under oxygen was used to illustrate the reversible deposition and decomposition of discharge products on the surface of this hybrid conductor, visually verifying the two-phase reaction.

Exploring PVFM-Based Janus Membrane-Supporting Gel Polymer Electrolyte for Highly Durable Li-O2 Batteries

Electrolyte is the key to constructing the ionic transport paths and O₂ gas diffusion routes in the cathode as well as maintaining the electrode interfacial stability in view of the complex chemistry of Li-O₂ batteries. A novel poly(vinyl formal) (PVFM)-based Janus membrane, which is prepared via coating multiwalled carbon nanotubes (MWCNTs) on the porous side of the cross-linked PVFM membrane, has been proposed herein to achieve membrane-supporting gel polymer electrolyte (GPE) for Li-O₂ batteries. Within Li-O₂ batteries, the dense side of PVFM-based Janus membrane demonstrates a good compatibility with lithium metal anode, while the other side with MWCNTs coating reserves much more solvent on the surface, assisting the cathode to form enlarged electrolyte-wetted interface. Moreover, the comparative studies indicate that PVFM-based Janus membrane also can provide a conductive pathway, modulate the morphology of the discharge products, and produce accommodation space for the products. So, the Li-O₂ batteries containing PVFM-based Janus membrane-supporting GPE not only demonstrate significantly improved discharge capacity and cycling stability, i.e., 150 times at 1000 mAh g^-1 capacity limitation, but also a narrow voltage gap of 0.90 V and an excellent rate performance up to 1000 mA g^-1.

A Lithium-Air Battery Stably Working at High Temperature with High Rate Performance

Driven by the increasing requirements for energy supply in both modern life and the automobile industry, the lithium-air battery serves as a promising candidate due to its high energy density. However, organic solvents in electrolytes are likely to rapidly vaporize and form flammable gases under increasing temperatures. In this case, serious safety problems may occur and cause great harm to people. Therefore, a kind of lithium-air that can work stably under high temperature is desirable. Herein, through the use of an ionic liquid and aligned carbon nanotubes, and a fiber shaped design, a new type of lithium-air battery that can effectively work at high temperatures up to 140 °C is developed. Ionic liquids can offer wide electrochemical windows and low vapor pressures, as well as provide high thermal stability for lithium-air batteries. The aligned carbon nanotubes have good electric and heat conductivity. Meanwhile, the fiber format can offer both flexibility and weavability, and realize rapid heat conduction and uniform heat distribution of the battery. In addition, the high temperature has also largely improved the specific powers by increasing the ionic conductivity and catalytic activity of the cathode. Consequently, the lithium-air battery can work stably at 140 °C with a high specific current of 10 A g^-1 for 380 cycles, indicating high stability and good rate performance at high temperatures. This work may provide an effective paradigm for the development of high-performance energy storage devices.

A Direct Alcohol Fuel Cell Driven by an Outer Sphere Positive Electrode

Molecular oxygen, the conventional electron acceptor in fuel cells poses challenges specific to direct alcohol fuel cells (DAFCs). Due to the coupling of alcohol dehydrogenation with the scission of oxygen on the positive electrode during the alcohol crossover, the benchmark Pt-based air cathode experiences severe competition and depolarization losses. The necessity of heavy precious metal loading with domains for alcohol tolerance in the state of the art DAFC cathode is a direct consequence of this. Although efforts are dedicated to selectively cleave oxygen, the root of the problem being the inner sphere nature of either half-cell chemistry is often overlooked. Using an outer sphere electron acceptor that does not form a bond with the cathode during redox energy transformation, we effectively decoupled the interfacial chemistry from parasitic chemistry leading to a DAFC driven by alcohol passive carbon nanoparticles, with performance metrics ∼8 times higher than Pt-based DAFC-O₂.

Relevant Features of a Triethylene Glycol Dimethyl Ether-Based Electrolyte for Application in Lithium Battery

Triethylene glycol dimethyl ether (TREGDME) dissolving lithium trifluoromethanesulfonate (LiCF₃SO₃) is studied as a suitable electrolyte medium for lithium battery. Thermal and rheological characteristics, transport properties of the dissolved species, and the electrochemical behavior in lithium cell represent the most relevant investigated properties of the new electrolyte. The self-diffusion coefficients, the lithium transference numbers, the ionic conductivity, and the ion association degree of the solution are determined by pulse field gradient nuclear magnetic resonance and electrochemical impedance spectroscopy. The study sheds light on the determinant role of the lithium nitrate (LiNO₃) addition for allowing cell operation by improving the electrode/electrolyte interfaces and widening the voltage stability window. Accordingly, an electrochemical activation procedure of the Li/LiFePO₄ cell using the upgraded electrolyte leads to the formation of stable interfaces at the electrodes surface as clearly evidenced by cyclic voltammetry, impedance spectroscopy, and ex situ scanning electron microscopy. Therefore, the lithium battery employing the TREGDME-LiCF₃SO₃-LiNO₃ solution shows a stable galvanostatic cycling, a high efficiency, and a notable rate capability upon the electrochemical conditions adopted herein.

A Unique Hybrid Quasi-Solid-State Electrolyte for Li-O2 Batteries with Improved Cycle Life and Safety

In the context of the development of electric vehicle to solve the contemporary energy and environmental issues, the possibility of pushing future application of Li-O2 batteries as a power source for electric vehicles is particularly attractive. However, safety concerns, mainly derived from the use of flammable organic liquid electrolytes, become a major bottleneck for the strategically crucial applications of Li-O2 batteries. To overcome this issue, rechargeable solid-state Li-O2 batteries with enhanced safety is regarded as an appealing candidate. In this study, a hybrid quasi-solid-state electrolyte combing a polymer electrolyte with a ceramic electrolyte is first designed and explored for Li-O2 batteries. The proposed rechargeable solid-state Li-O2 battery delivers improved cycle life (>100 cycles) and safety. The feasibility study demonstrates that the hybrid quasi-solid-state electrolytes could be employed as a promising alternative strategy for the development of rechargeable Li-O2 batteries, hence encouraging more efforts devoted to explore other hybrid solid-state electrolytes for Li-O2 batteries upon future application.