Organic hydrogen peroxide-driven low charge potentials for high-performance lithium-oxygen batteries with carbon cathodes

Reducing the high charge potential is a crucial concern in advancing the performance of lithium-oxygen batteries. Here, for water-containing lithium-oxygen batteries with lithium hydroxide products, we find that a hydrogen peroxide aqueous solution added in the electrolyte can effectively promote the decomposition of lithium hydroxide compounds at the ultralow charge potential on a catalyst-free Ketjen Black-based cathode. Furthermore, for non-aqueous lithium-oxygen batteries with lithium peroxide products, we introduce a urea hydrogen peroxide, chelating hydrogen peroxide without any water in the organic, as an electrolyte additive in lithium-oxygen batteries with a lithium metal anode and succeed in the realization of the low charge potential of ∼3.26 V, which is among the best levels reported. In addition, the undesired water generally accompanying hydrogen peroxide solutions is circumvented to protect the lithium metal anode and ensure good battery cycling stability. Our results should provide illuminating insights into approaches to enhancing lithium-oxygen batteries

Singlet oxygen is not the main source of electrolyte degradation in lithium–oxygen batteries

The lithium–air (oxygen) battery could offer significant improvements in gravimetric energy density compared to lithium-ion technology. A major barrier to realising this goal is the oxidative degradation of the electrolyte solution and the carbon at the positive electrode. Recently, the lithium–oxygen field has been focused on the formation of singlet oxygen within the cell, its impact as a major source of degradation, and strategies to mitigate this. Here we have investigated the reactivity of components within the lithium–oxygen cell by exposure to photochemically generated singlet oxygen. We find no significant reaction between the singlet oxygen and tetraglyme, lithium bis(trifluoromethanesulfonyl)imide, or carbon, standard electrode components, and confirm that singlet oxygen is not the major source of degradation in the lithium–oxygen battery. Our studies bring into question the need for strategies to mitigate the impact of singlet oxygen in the cell and highlight the need to refocus on the discovery of electrolyte solutions with stability against lithium peroxide

A High Capacity Gas Diffusion Electrode for Li–O2 Batteries

The very high theoretical specific energy of the lithium–air (Li–O2) battery (3500 Wh kg−1) compared with other batteries makes it potentially attractive, especially for the electrification of flight. While progress has been made in realizing the Li–air battery, several challenges remain. One such challenge is achieving a high capacity to store charge at the positive electrode at practical current densities, without which Li–air batteries will not outperform lithium-ion. The capacity is limited by the mass transport of O2 throughout the porous carbon positive electrode. Here it is shown that by replacing the binder in the electrode by a polymer with the intrinsic ability to transport O2, it is possible to reach capacities as high as 31 mAh cm−2 at 1 mA cm−2 in a 300 µm thick electrode. This corresponds to a positive electrode energy density of 2650 Wh L−1 and specific energy of 1716 Wh kg−1, exceeding significantly Li-ion batteries and previously reported Li–O2 cells. Due to the enhanced oxygen diffusion imparted by the gas diffusion polymer, Li2O2 (the product of O2 reduction on discharge) fills a greater volume fraction of the electrode and is more homogeneously distributed

Decoupling, quantifying, and restoring aging-induced Zn-anode losses in rechargeable aqueous zinc batteries

The search for batteries beyond Li-ion that offer better performance, reliability, safety, and/or affordability has led researchers to explore a diverse array of candidates. The advantages of Zn-ion batteries reside in zinc’s relatively low reactivity, raising the prospect of a rechargeable battery with a simple aqueous electrolyte and a cheaper, safer option to the organic electrolytes that must be paired with reactive lithium. However, water still reacts with the zinc in corrosion reactions. These consume zinc, lowering the battery’s capacity, and generate gas that accumulates in the sealed cell. We diagnose the contribution of corrosion to performance decay in zinc batteries and reveal the critical role of gas accumulation in deactivating large sections of electrode, which cripples cell performance. Fortunately, electrodes can be reactivated by removal of the gas, demonstrating the importance of designing future cells that either prevent gas formation or facilitate its safe release

Revealing the role of fluoride‐rich battery electrode interphases by operando transmission electron microscopy

The solid electrolyte interphase (SEI), a complex layer that forms over the surface of electrodes exposed to battery electrolyte, has a central influence on the structural evolution of the electrode during battery operation. For lithium metallic anodes, tailoring this SEI is regarded as one of the most effective avenues for ensuring consistent cycling behavior, and thus practical efficiencies. While fluoride-rich interphases in particular seem beneficial, how they alter the structural dynamics of lithium plating and stripping to promote efficiency remains only partly understood. Here, operando liquid-cell transmission electron microscopy is used to investigate the nanoscale structural evolution of lithium electrodeposition and dissolution at the electrode surface across fluoride-poor and fluoride-rich interphases. The in situ imaging of lithium cycling reveals that a fluoride-rich SEI yields a denser Li structure that is particularly amenable to uniform stripping, thus suppressing lithium detachment and isolation. By combination with quantitative composition analysis via mass spectrometry, it is identified that the fluoride-rich SEI suppresses overall lithium loss through drastically reducing the quantity of dead Li formation and preventing electrolyte decomposition. These findings highlight the importance of appropriately tailoring the SEI for facilitating consistent and uniform lithium dissolution, and its potent role in governing the plated lithium's structure

The role of an elastic interphase in suppressing gas evolution and promoting uniform electroplating in sodium metal anodes †

Ether solvent based electrolytes exhibit excellent performance with sodium battery anodes, outperforming the carbonate electrolytes that are routinely used with the analogous lithium-ion battery. Uncovering the mechanisms that facilitate this high performance for ether electrolytes, and conversely diagnosing the causes of the poor cycling with carbonate electrolytes, is crucial for informing the design of optimized electrolytes that promote fully reversible sodium cycling. An important contributor to the performance difference has been suggested to be the enhanced elasticity of the ether-derived solid–electrolyte interphase (SEI) layer, however experimental demonstration of exactly how this translates to improving the microscopic dynamics of a cycled anode remain less explored. Here, we reveal how this more elastic SEI prevents gas evolution at the interface of the metal anode by employing operando electrochemical transmission electron microscopy (TEM) to image the cycled electrode–electrolyte interface in real time. The high spatial resolution of TEM imaging reveals the rapid formation of gas bubbles at the interface during sodium electrostripping in carbonate electrolyte, a phenomenon not observed for the higher performance ether electrolyte, which impedes complete Na stripping and causes the SEI to delaminate from the electrode. This non-conformal and inflexible SEI must thus continuously reform, leading to increased Na loss to SEI formation, as supported by mass spectrometry measurements. The more elastic ether interphase is better able to maintain conformality with the electrode, preventing gas formation and facilitating flat electroplating. Our work shows why an elastic and flexible interphase is important for achieving high performance sodium anodes

Achieving ultra‐high rate planar and dendrite‐free zinc electroplating for aqueous zinc battery anodes

Despite being one of the most promising candidates for grid-level energy storage, practical aqueous zinc batteries are limited by dendrite formation, which leads to significantly compromised safety and cycling performance. In this study, by using single-crystal Zn-metal anodes, reversible electrodeposition of planar Zn with a high capacity of 8 mAh cm−2 can be achieved at an unprecedentedly high current density of 200 mA cm−2. This dendrite-free electrode is well maintained even after prolonged cycling (>1200 cycles at 50 mA cm−2). Such excellent electrochemical performance is due to single-crystal Zn suppressing the major sources of defect generation during electroplating and heavily favoring planar deposition morphologies. As so few defect sites form, including those that would normally be found along grain boundaries or to accommodate lattice mismatch, there is little opportunity for dendritic structures to nucleate, even under extreme plating rates. This scarcity of defects is in part due to perfect atomic-stitching between merging Zn islands, ensuring no defective shallow-angle grain boundaries are formed and thus removing a significant source of non-planar Zn nucleation. It is demonstrated that an ideal high-rate Zn anode should offer perfect lattice matching as this facilitates planar epitaxial Zn growth and minimizes the formation of any defective regions

Clean electrocatalysis in a Li2O2 redox-based Li–O2 battery built with a hydrate-melt electrolyte

The electrocatalysis of the oxygen reduction reaction and oxygen evolution reaction in nonaqueous Li-O-2 batteries suffers from severe side reactions and high charge potential. Herein, we design an unreported hydrate-melt Li-O-2 battery without use of an unstable organic solvent. Its redox reaction depends on the formation of Li2O2 in high yield (96%) and its full decomposition. The designed battery shows an ultralow charge potential of similar to 3.16 V, a high discharge capacity of 38 mAh cm(-2), and stable cycling ability. After careful comparison of the discharge and charge products by XRD, SEM, Raman, FTIR, NMR, and quantitative titration, the great improvement in performance is attributed to the efficient avoidance of side reactions related to organic solvent degradation, which may be the primary cause of the high charge potential in a nonaqueous Li-O-2 battery. These results should initiate a deep understanding of Li-O-2 batteries and indicate another strategy toward practical Li-air batteries with moisture-proof properties and high safety

A solid-state lithium-ion battery with micron-sized silicon anode operating free from external pressure

Abstract Applying high stack pressure (often up to tens of megapascals) to solid-state Li-ion batteries is primarily done to address the issues of internal voids formation and subsequent Li-ion transport blockage within the solid electrode due to volume changes. Whereas, redundant pressurizing devices lower the energy density of batteries and raise the cost. Herein, a mechanical optimization strategy involving elastic electrolyte is proposed for SSBs operating without external pressurizing, but relying solely on the built-in pressure of cells. We combine soft-rigid dual monomer copolymer with deep eutectic mixture to design an elastic solid electrolyte, which exhibits not only high stretchability and deformation recovery capability but also high room-temperature Li-ion conductivity of 2×10−3 S cm−1 and nonflammability. The micron-sized Si anode without additional stack pressure, paired with the elastic electrolyte, exhibits exceptional stability for 300 cycles with 90.8% capacity retention. Furthermore, the solid Li/elastic electrolyte/LiFePO4 battery delivers 143.3 mAh g−1 after 400 cycles. Finally, the micron-sized Si/elastic electrolyte/LiFePO4 full cell operates stably for 100 cycles in the absence of any additional pressure, maintaining a capacity retention rate of 98.3%. This significantly advances the practical applications of solid-state batteries

Singlet oxygen and dioxygen bond cleavage in the aprotic lithium-oxygen battery

Investigation of lithium-oxygen cells on discharge using a mixture of 16O16O and 18O18O gases, showed that O–O bond cleavage occurs during disproportionation of LiO2 to O2 and Li2O2, detected by the presence of isotopic 16O18O. The formation of singlet oxygen, 1O2, was also monitored during disproportionation. While only 4.5% of oxygen was found to undergo bond cleavage and scrambling of oxygen atoms, more than 40% of the singlet oxygen produced during disproportionation came from the scrambling pathway, making it a major source of singlet oxygen generation in lithium-oxygen batteries. Our results demonstrate that Li2O2 formation occurs predominantly by disproportionation, and by controlling the pathway of this step, it may be possible to suppress 1O2 formation, a species that has been implicated in the degradation of lithium-oxygen batteries