Interphase Regulation And Electrode Structure Design Of Lithium-Based Dual-Ion Batteries

To develop electrochemical energy storage systems of the next generation with improved performance,lower cost,and less environmental impact.In recent years,scientists have invented several novel battery systems and optimized them extensively.Dual-ion batteries（DIBs）stand in stark contrast to conventional battery systems whose cations migrate between the cathode and anode.Instead of just preserving the neutrality of the electrolyte,the anions of DIBs in the electrolyte are also incorporated into the electrode reaction.Typical DIBs have a relatively high energy density due to their high operating potential（higher than 4.5 V）.Moreover,the cathode materials of DIBs are mostly constituted of graphite,amorphous carbon,etc.,which have the benefits of cheap cost and reduced environmental pollution.The material of the anodes can consist of a range of alkali metals with low electrode potential and high specific capacity.The batteries with graphite and lithium metal as the cathode and anode materials（LG-DIBs）have been the subject of the most research among the numerous DIBs with different cathode and anode combinations.However,DIBs are still in their infancy and need to be combined with a large number of mechanistic investigations to clarify fundamental scientific questions,which requires a clear and promising research target.Nonetheless,much prior research has focused on the de-/intercalation process of anions in graphite under various solvation conditions,with relatively few investigations into the cathode and anode electrolyte interphases（CEI,AEI）of LG-DIBs.Despite the greater working voltage and energy density of LG-DIBs in comparison to other types of DIBs,there are still three major issues:one is the deactivation of graphite owing to anion de-/intercalation and electrolyte decomposition at high potentials.Due to the limited reversibility of lithium metal deposition and stripping,dendrite growth is the second issue.In other words,both the cathode and anode of LG-DIBs have significant interphase issues.In addition,because the electrode structure of LG-DIBs still has disadvantages such as aluminum current collector corrosion and excessive self-weight,as well as excessive lithium metal usage,LG-DIBs will have severely restricted application potential.Therefore,LG-DIB electrode structures require further development.This paper explores the mechanism of the interphases in battery operation through interface modification and structure design,paired with a range of characterization techniques,and creates a more feasible LG-DIBs electrode structure in light of the concerns identified in the preceding research.This research focuses mostly on the following four aspects:（1）By creating a solid-state electrolyte interface（SEI）protective layer on the surface of the graphite cathode,the cycle stability of LG-DIBs with 1 mol L^-1 Li PF₆-EMC as the electrolyte is greatly enhanced.Under the conditions of upper cut-off voltage of 5.0 V and current density of 200 m A g^-1,the test reveals that the specific capacity of artificial SEI modified graphite（SMG）is approximately 84.5 m A h g^-1,which is much greater than that of unmodified graphite（UMG）of 75.2 m A h g^-1.In addition,SMG has much greater cycle stability than UMG at different cutoff voltages.In contrast,the UMG battery fails after just180 cycles.In addition,X-ray photoelectron spectroscopy（XPS）,high-resolution transmission electron microscopy（HRTEM）,scanning electron microscopy（SEM）,and in-situ X-ray diffraction（XRD）revealed that the artificial SEI protective layer can significantly stabilize the electrode/electrolyte interface and progressively construct the optimal anion migration path.（2）Al₂O₃ was precisely and uniformly coated on commercial mesocarbon microspheres（MCMB）utilizing a wet chemical technique with aluminum sulfate as the aluminum source.Repeated washing eliminated the soluble contaminants adsorbed on the graphite surface following Al₂（SO₄）₃ hydrolysis,hence preventing the formation of by-products during the coating process.The Al₂O₃-coated MCMB（AOCM）demonstrates an ultra-long cycling life in the LG-DIB test,with 82.3%capacity retention after 1000 cycles.The low electronic conductivity of the Al₂O₃ coating layer can not only mitigate the catalytic decomposition of the electrolyte at high potentials due to the inherent high electronic conductivity of graphite,but it can also regulate the chemical composition of CEI to produce organic-based,more flexible CEI.Also,the Al₂O₃ coating layer makes the process of de-/intercalation between graphite layers more orderly without changing the kinetics of anion transport,which helps to keep the graphite crystal structure intact to some extent.（3）A two-pronged approach was employed to further enhance the interfacial stability of LG-DIBs using interface modification techniques for AEI and CEI,respectively.A three-dimensional carbon skeleton was constructed on the surface of the lithium metal anode to form an AEI with a more stable structure and composition.The carbon skeleton uniformized the interfacial electric field distribution and induced the uniform deposition of Li⁺,inhibiting the growth of lithium dendrites and reducing the volume expansion caused by the AEI repeatedly rupturing and regenerating.For the CEI of graphite,the previously mentioned wet chemical method is still used to create an electrochemically inert coating layer,which inhibits the decomposition of the electrolyte and forms a thinner CEI,ensuring that the graphite cathode can be cycled structurally intact.This two-pronged strategy permits LG-DIBs to have a longer cycle life in a wide temperature range,ranging from-25℃ to 40℃.For example,after 2700cycles at 25℃,LG-DIBs retain 80%of their original capacity(200 m A g^-1).（4）Electrode structure design issues in LG-DIBs,such as aluminum current collector corrosion,excessive self-weight,and improper usage of lithium metal anode,impede their development.For this purpose,a design concept for an integrated electrode structure is offered.By mixing single-walled carbon nanotubes（SWCNTs）with graphite,a self-supporting composite electrode（GSC）without an aluminum current collector was created to construct a three-dimensional conductive network around the graphite cathode.While avoiding the difficulties of aluminum current collector corrosion and active material peeling,the loading of active materials is still guaranteed,resulting in a significant reduction in the overall mass of the electrode.A self-supporting Li@CC composite electrode was constructed employing carbon cloth（CC）formed through the carbonization of waste masks as a Li metal carrier,successfully suppressing the formation of Li dendrites and mitigating Li metal volume expansion during deposition-stripping.Importantly,the management of the amount of lithium metal anode is achieved,and waste caused by lithium foil misuse is diminished.Self-supporting Li@CC//GSC full cells are proposed as a unique LG-DIBs electrode structure design.The built-in Li@CC//GSC full cells retain 80%of their initial capacity after 300 cycles.