Self-discharge Process Research Articles

Electrochemical dendrite management via voltage-controlled rearrangement

Abstract The pursuit of advanced energy storage solutions has highlighted the potential of rechargeable batteries with metal anodes due to their high specific capacities and low redox potentials. However, the formation of metal dendrites remains a critical challenge, compromising both safety and operational stability. For zinc-based batteries (ZBs), traditional methods to suppress dendrite growth have shown limited success and often entail performance compromise. Here, we propose a novel strategy termed dendrite rearrangement (DR) that leverages the electrochemical self-discharge process to controllably address the dendrite issues. By temporarily increasing the input voltage within a single cycle, this strategy resets the cell stability without precipitating undesirable side reactions during normal operation. This pioneering technique extends operational lifespans to over three times their original duration, facilitating 80,000 cycles for Zn-ion hybrid capacitors and 3,000 hours for Zn symmetrical cells. Even in scaled-up pouch cells, Ah-level symmetrical cells demonstrate a cumulative capacity nearing 200,000 mAh, significantly surpassing that of reported metal symmetrical cells. Additionally, the electrolytic Zn-MnO2 battery demonstrates a high capacity approaching 10 Ah, setting a new benchmark among reported ZB devices. These results mark a significant advance towards resolving dendrite-related issues in metal anode batteries, paving the way for their sustainable development and potential commercialization.

Effect of Carbonate Solvent Additives in Electrolyte on the Self-Discharge Phenomenon in Organic Electrical Double Layer Capacitors

As a result of industrialization, technological progress, and the growing global population, energy consumption worldwide is skyrocketing. Researchers are thriving to seek high power density storage device to meet these escalating energy demands. Electrical Double Layer Capacitors (EDLCs) also known as a supercapacitor, are energy storage devices that store energy by Coulombic attraction between ions, polarized solvent on the surface of the activated carbon electrodes to form an electric double layer without involving chemical reactions. EDLCs display some remarkable characteristics such as high-power density, ultrafast charge/discharge rates, and long cycle life, surpassing conventional lithium-ion batteries. These features make EDLCs ideal for a wide range of applications, including portable devices, energy backup systems, and electric vehicles.However, the self-discharge effect in EDLCs is a deadly drawback that decrease the shelf life of EDLCs and impeding its practical applications. This phenomenon refers to the spontaneous voltage decay between the electrodes when the capacitor is under open-circuit potential after being charged, leading to a reduction in the stored charge without any external connection. This voltage declination is a complex process therefore, various mechanisms have been proposed to elucidate this phenomenon. There are primarily four mechanisms leading to the self-discharge. First, the internal short-circuit caused by imperfect seal of EDLCs leading to ohmic leakage current. Second, the uneven distribution of pore sizes in activated carbon electrodes leads to a higher resistance for ions to penetrate deeper into the material, resulting in ion accumulation on the surface during short charging times. This accumulation causes an uneven distribution of electron energy in the electrode material. After disconnecting, electrons rearrange to achieve overall energy consistency, while ions gradually redistribute and move into the smaller micropores within the activated carbon electrode. This phenomenon is referred to as charge redistribution effect. Third, Faradic current in EDLCs occurs due to redox reactions, stemming from the decomposition of the electrolyte or chemical reactions involving impurities within the electrolyte. Lastly, during the charging process, ions accumulate at the electrode surface, creating a concentration gradient between the electrodes and the electrolyte. As a result, ions gradually diffuse back into the bulk electrolyte until reaching equilibrium. Addressing self-discharge is paramount in ongoing research efforts.Electrolyte solutions are critical components in EDLCs, providing a medium for ion transport between the electrodes. The electrolyte solution is typically composed of a supporting electrolyte dissolved in a solvent, and the choice of solvent can significantly impact the performance of the device. This study delves into the impact of electrolyte solvent additives in the electrical double layer of EDLCs, leading to varied self-discharge performances. In this report, five commonly-used organic carbonate solvents in EDLCs, were selected to investigate their effects on the self-discharge phenomenon. Cyclic carbonate solvents, such as EC and PC, are known to possess high dielectric constants, high viscosities and high flash points. In contrast, linear carbonates e.g., DEC, DMC, EMC have low viscosities, low dielectric constants and low flash point. By incorporating carbonate solvents into the 1M TEABF4/PC (Tetraethylammonium tetrafluoroborate/propylene carbonate) commercial electrolyte, the performance of five supercapacitors , minimal deviation in electrochemical analyses such as CV and GCD was observed. However, significant differences emerged in EIS, elucidating the varying degrees of self-discharge phenomena. These differences in self-discharge mechanisms across the five EDLCs stemmed from the distinct dielectric constants and molecule sizes of the five solvent additives (i) Low dielectric constant and large molecule size, as seen in DEC (239.4h) and EMC (165.1h), contributed to increased interfacial impedance which effectively prolonging self-discharge compared to commercial one (145.7h). Conversely, the DMC with smaller interfacial resistance initially exhibited lower voltage decline due to reduced charge redistribution effects. However, its rapid ion diffusion process from carbon pores to electrolyte resulted in the fastest self-discharge of DMC (124.7h). (ii) High dielectric EC competes for solvation coordination, reducing interfacial resistance and enhancing intermolecular interaction. This, in turn, leads to the formation of a denser electric double layer (EDL) with EC, therefore decelerating the self-discharge process (205.9h) in EDLCs. In summary, the study emphasizes the significance of solvent additive selection and demonstrates a simple, safe, and cost-effective method to prolonging the self-discharge duration of DEC to more than 1.5 times that of the commercial one, significantly inhibiting the critical self-discharge issue in supercapacitors. Figure 1

Effects of current collectors on the self-discharge rates of supercapacitors with aqueous electrolyte

Current collectors play an important role in supercapacitors, impacting not only their electrochemical properties such as rate performance and cycling stability but also their self-discharge processes. In this study, we investigate the self-discharge behaviors of activated carbon supercapacitors with various current collectors, including titanium (Ti) foil, nickel (Ni) foil, 316 stainless steel (SS) foil, and graphite paper (GP), in an aqueous electrolyte. Our findings reveal that at a relatively low charging voltage of 0.8 V, supercapacitors with different current collectors exhibit similar decays in open circuit voltages (OCVs) after 12 h, indicating comparable self-discharge rates. However, at higher charging voltages, SS-based supercapacitors exhibit significantly faster self-discharge compared to Ti, Ni, and GP. Particularly at 1.6 V, the 12-h voltage retention rates decrease from over 60 % for Ti, Ni, and GP supercapacitors, to 46 % for SS supercapacitors. Analysis of the self-discharge mechanism suggests that increased side Faradaic reactions occurring at higher charging voltages in SS-based supercapacitors contribute to the accelerated self-discharge process compared to Ti, Ni, and GP supercapacitors.

NiFe2O4@NiCo2O4 hollow algae-like microspheres enabled by Mott-Schottky for electrochemical energy storage

Designing hybrid structure of transition metal oxides (TMOs) with controlled morphology can adjust the electronic structure and create more kinetics reactions. Herein, a new kind of NiFe2O4@NiCo2O4 nanocomposite was synthesized with one pot hydrothermal route. The unique hollow algae-like microspheres with plenty nanowires and the synergistic effect factors promote high electroactive sites and generate a built-in electric field. The constituted Mott-Schottky heterostructure creates strong interfacial interaction, paves the way for the electrolyte ions diffusion and results high charges transfer abilities by reducing the energy barriers in the heterointerfaces. As cathode material, the NiFe2O4@NiCo2O4 presents satisfactory specific capacity of 996C·g−1 at 0.5 A·g−1 and maintains ultrahigh capacity retention of 81 % at 30 A·g−1 with marvellous stability of only 6 % loss during 20,000 cycles. Interestingly, asymmetric hybrid supercapacitor device based NiFe2O4@NiCo2O4//active carbon (AC) provides tremendous energy density of 117.6 Wh·kg−1 at 438 W·kg−1 power density. What’s more, all-solid-state device offers ultra-low self-discharge process of 9.5 % through 24 h. Therefore, the combination of NiFe2O4@NiCo2O4 to form Mott-Schottky heterojunction was a promising strategy to develop electrode material with high energy storage performance.

Insights into self-discharge processes of Al-graphite batteries

Aluminum graphite dual ion batteries (AGDIB) have been widely explored thanks to abundant electrode materials, a long cycle life and high power density. However, the shelf life of AGDIBs is so far barely understood. This work's detailed self-discharge investigations allow the quantification of capacity losses for up to 4 weeks, confirm a deintercalation mechanism by Raman spectroscopy and X-ray diffraction, and furthermore give insight to influence factors. While a cell employing typical materials such as a natural graphite cathode, Mo current collector and AlCl3/[EMIm]Cl=1.5 ionic liquid electrolyte exhibits a capacity loss of 10 % in 24 h, this value can be significantly reduced to 3 % in 24 h when using a glassy carbon current collector and AlCl3/Et3NHCl=1.5 electrolyte instead. Iron impurities within the electrolyte do not affect battery capacities or self-discharge, since it is deposited on the Al anode within the battery soon after assembly. In general, the instability of the current collector material, gas evolution due to electrolyte oxidation at high cell potentials, and cationic electrolyte species greatly influence the self-discharge independently. Electrolyte speciation changes directly related to self-discharge processes are revealed by IR spectroscopy.

Faradaic and Non-Faradaic Self-Discharge Mechanisms in Carbon-Based Electrochemical Capacitors.

Electrochemical capacitors (ECs) play a crucial role in electrical energy storage, offering great potential for efficient energy storage and power management. However, they face challenges such as moderate energy densities and rapid self-discharge. Addressing self-discharge necessitates a fundamental understanding of the underlying processes. This review sets itself apart from other reviews by focusing on the basic principles of self-discharge processes in carbon-based ECs, particularly examining the nature of the process and the involvement of redox reactions. This study delineates the potential conditions for various self-discharge processes and proposes plausible criteria for differentiation, complemented by mathematical modeling. Additionally, the model selection, curve fitting, and effective tuning methods are explored to control self-discharge processes.

Constructing bilayer heterogeneous organogel electrolytes of Lewis acidic/basic polymers to suppress self-discharge of supercapacitors

Flexible supercapacitors with fast charging rate, long cyclic lifetime and high power density, but often suffer from their rapid self-discharge process, which remains a big challenge for their widely commercial application. Here, we for the first time report a bilayer heterogeneous organogel electrolyte (BHOE) consisting of a layer of Lewis acidic polymer (LAP) and a layer of Lewis basic polymer (LBP), to develop high-performance flexible supercapacitors with slow self-discharge process. The existing strong coordination interaction between the charged LAP (or LBP) and its counter anions (or cations) can effectively restrict the diffusion of ions accumulated on/in the electrodes into or throughout the bilayer electrolyte, which endowed the charged BHOE-based supercapacitor with slow self-discharge time (9.7 h) from its open-circuit voltage to the half, more than ten times longer than those (0.9 h) of devices based homogeneous LAP or LBP electrolytes. Furthermore, the BHOE-based supercapacitor possessed high capacitance retention up to 95 % after thousands of folding cycles, suggesting excellent mechanical flexibility. This study provides a novel strategy to build high-performance flexible supercapacitors with slow self-discharge, which is great meaningful for their practical application in the near future.

Heterostructured MoO3@CoWO4 nanobelts towards high electrochemical performances via oxygen vacancies generation

Heterostructured nanomaterials tend to have a high proportion of oxygen vacancies (VO) due to the presence of heterogeneous interfaces. Herein, a new kind of heterostructured MoO3@CoWO4 nanobelts was successfully evaluated as fascinating cathode material. SEM and TEM analysis indicated that the MoO3 nanobelts were fully blanketed with CoWO4 nanodots. The generation of Vo species was confirmed by XPS and EPR data. By profiting both synergistic and Vo generation effects, MoO3@CoWO4 electrode displayed an excellent capacitance of 246 mAh·g−1 (1966 F·g-1at 0.5 A·g−1) with high-rate capability of 174 mAh·g−1 (1394 F·g−1 at 30 A·g−1) as well as superb stability of 94 % (over 15,000 cycles). Notably, all-solid-state device delivered a good energy value of 63.1 Wh·kg−1 at 375 W·kg−1. Interestingly, the supercapacitor device showed super-low self-discharge comportment of only 12.1 % during 24 h. Importantly, the generation of the VO defects could control the ions diffusion process and lead a sharp decrease in the self-discharge process.

Self-Discharge Processes in Symmetrical Supercapacitors with Activated Carbon Electrodes.

The self-discharge of an electric double-layer capacitor with composite activated carbon electrodes and aqueous electrolyte (1 M MgSO4) was studied in detail. Under a long-term potentiostatic charge (stabilization), a decrease in the discharge capacity was observed in the region of voltages exceeding 0.8 V. The self-discharge process consists of two phases. In the initial phase, the cell voltage drop is due to the charge redistribution inside electrodes. During the main phase, the charge transfer between the electrodes determines the voltage drop. The optimal stabilization time of the self-discharge was found to be 50 min at 1.4 V. Hydrophilization of the negative electrode occurred during long-term polarization due to the formation of epoxy functional groups.

(Digital Presentation) Self-Discharge Study of Carbon-Based Supercapacitors with Tunable Pore Size

Electrochemical double-layer capacitors (EDLCs), as a major type of energy storage devices besides rechargeable batteries such as lithium-ion batteries, holds excellent properties such as high power density and ultra-long cycling stability[1-3]; however, its fast self-discharge process has become the major issue that impedes its development and application. Even though research on EDLCs’ self-discharge has demonstrated that the fast self-discharge rate can be tuned even repressed through modifying certain structural properties of electrodes or electrolytes[4-9], to the end of realizing full control over the self-discharge process requires unveiling the fundamental relation between structural parameters (i.e., the pore structure, the surface functionalities, the electrolytic ion size and shape, and etc.) and the self-discharge performance.Carbon, due to its superior chemical stability, high surface area, natural abundance, etc.[4,10], has become one of the main types of electrode materials under extensive research interest for developing advanced EDLCs. Herein, we focus on tuning the pore size, one of the major structural properties of carbon materials relating to its electrochemical performance, to study its effects on self-discharge process and to learn how to construct the optimal pore structure with respect to certain application requirements.In this work, porous carbon materials with designed pore structure are prepared via soft-template method to analyse the self-discharge performance. Through investigating the effects of pore size, as the single variable, on the self-discharge process, as well as on the micro-electrochemical process on the electrode/electrolyte interface, underlying mechanism between pore size and the self-discharge performance has been constructed. These findings should provide guidance on how to locate the optimal pore size for a chosen electrolyte and to realize control over self-discharge, which will serve as solid references for designing the next-generation EDLCs with high performance and controllable self-discharge rates. Reference [1] X. Chen, R. Paul, L. Dai, Natl. Sci. Rev., 2017, 4(3), 453-489.[2] G. Wang, L. Zhang, J. Zhang, Chem. Soc. Rev ., 2012, 41, 797-828.[3] Y. Liu, Y. Shen, L. Sun, J. Li, C. Liu, W. Ren, F. Li, L. Gao, J. Chen, F. Liu, Y. Sun, N. Tang, H. Cheng, Y. Du, Nat. Commun., 2016, 7, 10921.[4] Q. Zhang, C. Cai, J.W. Qin, B.Q. Wei, Nano Energy., 2014, 4, 14-22.[5] T. Tevi, H. Yaghoubi, J. Wang, A. Takshi, J. Power Sources., 2013, 241, 589-596.[6] L. Chen, H. Bai, Z. Huang, L. Li, Energy Environ. Sci., 2014, 7, 1750-1759.[7] G. Shul, D. Bélanger, Phys. Chem. Chem. Phys., 2016, 18, 19137-19145.[8] M. Xia, J. Nie, Z. Zhang, X. Lu, Z.L. Wang, Nano Energy., 2018, 47, 43-50.[9] J. Menzel, E. Frackowiak, K. Fic, Electrochimica Acta, 2020, 332, 135435.[10] D.P. Dubal, O. Ayyad, V. Ruiz, P. Gomez-Romero, Chem. Soc. Rev., 2015, 44, 1777–1790. Figure 1

Physical analysis of self-discharge mechanism for supercapacitor electrode for hybrid electric energy storage system

Self-discharge is a spontaneous process that has considerable adverse effects on the performance of supercapacitors. In order to quantitatively investigate the contribution of self-discharge mechanism, this paper proposed a theoretical self-discharge model for carbon electrode of supercapacitors based on electric double layer theory. Three physical contributions, i.e., side reactions, ion diffusion, and ohmic leakage, were investigated. In addition, self-discharge measurement of carbon electrode was performed to validate such theoretical model. The results indicated that the potential drop due to side reactions was negligible throughout the self-discharge process in all cases. In addition, ion diffusion dominated for low initial potential and short holding time, accounting for 50%–80% of self-discharge. On the other hand, ohmic leakage dominated for high initial potential and long holding time. Furthermore, the potential drop due to ion diffusion increased monotonously with time while the potential drop due to ohmic leakage remained constant throughout the self-discharge. Moreover, the potential drop due to ohmic leakage increased with the increase in holding time, which compensated for the decreasing potential drop due to ion diffusion. This could explain the fact that the total electrode potential decay during the self-discharge was independent of holding time. Finally, dimensional analysis was performed to predict self-discharge. Time constants of side reactions, ion diffusion, and ohmic leakage were derived. Overlapping dimensionless electrode potential versus dimensionless time indicated that such dimensional analysis was generally applicable to predict self-discharge of carbon-based supercapacitors at a given initial potential and time.

Nickel cobalt sulfide composite nanosheet anchored on rGO as effective electrode for quasi-solid supercapacitor

A solid supercapacitor based on inorganic/organic composite electrolyte has great promise as a fresh wave of energy storage structure in building engineering owning to its inherent mechanical robustness. Unfortunately, the limited capacity and energy density of these supercapacitors are still challenging. Here, rGO/NixCoyS electrodes were fabricated by in-situ growth on nickel foam (NF). The edge sulfur-enriched NixCoyS nanosheets were equally anchored on rGO surface, increasing the number of electrochemical active sites, accelerating ion diffusion and improving the electrical conductivity. The morphology and electrochemical behavior of the rGO/NixCoyS composite are remarkably affected by the Ni to Co molar ratio. It turned out that the rGO/NixCoyS composite with a Ni to Co molar ratio of 1:1 (rGO/Ni1Co1S) exhibited a high capacitance of 4.55 F cm−2 at 1 mA cm−2. Subsequently, a novel quasi-solid supercapacitor was assembled using rGO/Ni1Co1S cathode, rGO/Fe2O3 anode as well as inorganic/organic composite solid electrolyte. The device achieved a high energy density of 3.6 μWh cm−2 at a power density of 163.2 μW cm−2, and moderate self-discharge (SDC) process, outperforming those of earlier reported structural devices. The practical application demonstration proves the feasibility of ternary rGO/Ni1Co1S electrode combined with inorganic/organic composite solid electrolyte in building energy storage field.

Regulating the synergy coefficient of composite materials for alleviating self-discharge of supercapacitors

Supercapacitor is an efficient energy storage device, yet its wider application is still limited by self-discharge. Currently, various composite materials have been reported to have improved inhibition on self-discharge, while the evaluation of the synergistic effect in composite materials is challenging. Herein, pairs of intercalation type pseudocapacitive niobium oxides are pre-lithiated and coupled to construct conjugatedly configured supercapacitors, within which the cathode and anode experience identical reaction environment with single type of charge carrier, thus providing ideal platform to quantify the synergistic effect of composite materials on the self-discharge process. By using titanium dioxide as the stabilizer, we have compared how the modes of forming composite would influence the self-discharge performance of the active composite materials with similar ratio of the constituent materials. Specifically, core@shell Nb2O5@TiO2 composite using TiO2 as the shell shows significantly higher synergy coefficient (µ = 0.61, defined as the value that evaluates the synergistic effect between composite materials, and can be quantified using the overall performance of the composite, performance of individual component as well as the ratio of the component.) than other control group samples, which corresponds to the highest retained energy of 63% at 100 h. This work is expected to provide a general method for quantifying the synergistic effect and guide the design of composite materials with specific mode of forming the composite.

Self-discharge kinetics behaviors of the Li-Si anode for thermal batteries: Modeling, quantifying and fitting analysis

Self-discharge has significant influence on the service life of thermal batteries. The kinetics process of self-discharge depends on both the structure evolution and intrinsic property of electrodes. Herein, the kinetics model to quantify the self-discharge degree of the Li-Si anode is constructed according to the structure of thermal cells. Typical operation and preparation parameters, i.e. temperature, discharge current and electrode thickness, are evaluated based on the specially designed combined-discharge scheme. Then the effective diffusion coefficients (Deff) of soluble lithium (Li0) that are affected by the three variables are calculated and fitted. The calculation results consequently confirm self-discharge process of the Li-Si anode can be described by the derived equations exactly, and then the process is demonstrated to be diffusion-controlled. Further, Deff increase at the higher temperature and larger discharge current, while decrease with the increased electrode thickness, which is analyzed by scanning electron microscope and X-ray microcomputed tomography. The entire effects on Deff can be coupled in one fitting expression based on Arrhenius equation, and the apparent activation energies decrease under the larger discharge current and smaller electrode thickness. Finally, the additional experiments were conducted to verify the accuracy of the fitting expression.

Low self-discharge all-solid-state electrochromic asymmetric supercapacitors at wide temperature toward efficient energy storage

Electrochromic asymmetric supercapacitors (EASs) have attracted tremendous attention in recent years because of their potential for next-generation civilian portable and intelligent electronics. However, obtaining all-solid-state EASs with low self-discharge rates and outstanding environmental compatibility remains a crucial challenge. Herein, a high-performance all-solid-state EAS was fabricated based on MnO2 positive electrochromic electrode and WO3 negative electrochromic electrode. The obtained EAS exhibits high power/energy density (991.2 W kg−1/117 Wh kg−1 and 15840 W kg−1/44.3 Wh kg−1), superior electrochemical cycle-life (remains 98.4% of its initial capacity after 2000 continuous cycles even at 60 °C). Significantly, the fabricated EAS can still maintain a stable and reversible color change even in harsh environments where operating temperatures are constantly changing from −20 °C to 60 °C. In addition, the underlying self-discharge process and mechanisms of EASs were comprehensively demonstrated at various temperatures. The diffusion-controlled mechanism dominates in the initial discharging process at high working temperatures (such as 60 °C), while both charge redistribution and diffusion-controlled mechanism contribute equally at lower operating temperatures (such as −20 °C). Impressively, the EAS presents a small voltage loss (all below 18%) within 10 h when operated at extreme temperatures. This work can enlighten and promote the development of low self-discharge electrochromic devices at widely operating temperatures for efficient energy storage.

Effects of electrode mass loading on the self-discharge of supercapacitors

Electrode mass loading is an important device parameter for supercapacitors and its effect on electrochemical properties such as energy density, rate performance, and cycle stability has been widely reported. However, how the self-discharge of supercapacitors varies under different mass loadings has not been examined systematically. In this study, we prepared porous activated carbon (AC) electrodes with a series of mass loadings and investigated their self-discharge behavior. It is found that with the increase in mass loadings, the decay rates of open circuit voltages (OCVs) are reduced substantially. Specifically, when the electrode mass loading increased from 0.6 to 10.6 mg cm−2, the cell OCV decay rate at a charging voltage of 1.6 V dropped from 1.07 to 0.05 mV mF−1 hr−1, indicating much slower self-discharge rates at higher mass loadings. Analysis of the self-discharge mechanism suggests that faradaic reactions are the major self-discharge processes for the supercapacitors after float charging. While the OCV decays due to both activation-controlled and diffusion-controlled faradaic reactions are reduced at high mass loadings, the self-discharge attributing to diffusion-controlled faradaic reactions is more affected due to the deeper pores and longer diffusion paths for electrolyte and reactive species in thicker electrodes.

Accelerated Solid Electrolyte Interface Quality Assessment of Lithium - Ion Batteries By Mediator-Enhanced Coulometry

Li-ion batteries (LIBs) offer particularly high performance among rechargeable batteries and are used in a variety of industrial domains. They were primarily used as a power supply for portable devices in the past. In recent years their applications have expanded to encompass stationary energy storage systems and electric vehicles (EVs), driving demand for lower-cost LIBs with even higher performance. Demand for LIBs for use in EVs is growing particularly rapidly as governments around the world fast-track measures to promote automobile electrification1 , 2.The quality of the Solid Electrolyte Interphase (SEI) on the negative electrode of Li-ion batteries has a strong impact on the cycle life so that clear determination of their properties is of essential importance to achieve progress in manufacturing processes3. Many kinds of measurements and tests are necessary at each state of the battery manufacturing process to assure the quality of each process. In addition, measurements and testing are essential in a variety of settings, during not only manufacturing, but also for battery research and finished-product inspections.In this work, a new, cheap and easily-implementable methodology to estimate the electrically-insulating quality of the SEI in LIBs is proposed. First, a redox-mediator is added in the electrolyte after the SEI formation cycle, and the redox mediator leads to an internal self-discharge process that is inversely proportional to the electrically-insulating character of the SEI. Second, a few charge and discharge cycles are applied to the battery and the presence of the redox-mediator provokes a shuttle effect enables by the lack of electrically protecting character of the SEI which consumes charges decreasing the coulombic efficiencies, enhancing the sensibility to the SEI protecting nature.The proposed methodology is probed on lithium iron phosphate batteries in pouch cell configuration with two redox mediators (ferrocene (FC) and methyl phthalimide (PHT)) by evaluating the influence of vinylene carbonate as electrolyte additive in the resulting SEI.We believe that the findings based on the application of this mediator-enhanced coulometry can be used to accurately predict the cyclic behavior of LIBs under extended operating conditions, which is especially relevant for a better comprehension of future industrial needs for battery R&D in cell components and production fields. Acknowledgment The authors acknowledge the financial support by the NanoBat project. NanoBat has received funding from the European Union’s Horizon 2020 research and innovation programme under Grant Agreement no. 861962 References S. Manzetti and F. Mariasiu, Renewable & sustainable energy reviews, 51, 1004–1012 (2015).E. Fan et al., Chemical Reviews (2020).E. Ventosa, Current Opinion in Electrochemistry, 25, 100635 (2021) https://www.sciencedirect.com/science/article/pii/S2451910320301708. Figure 1

A conjugately configured supercapacitor based on pairs of pre-lithiated Nb2O5/TiO2 with optimized retained energy upon aging enabled by suppressed self-discharge

Supercapacitors are advantageous in terms of power density and cycle life, but their wider application is limited by self-discharge. Previous attempts for improving the stability have mainly focused on the specific component (materials, separators or electrolytes) of the device, while the feasibility for mitigating self-discharge through a general device-scale configuration is largely unknown. Herein, we report a symmetric supercapacitor with a conjugated configuration, which consists of a pair of pre-lithiated niobium oxide decorated with evenly distributed titanium dioxide, forming a Lix[(Nb2O5):(TiO2)a] vs. Li2-x[(Nb2O5):(TiO2)a] conjugated configuration. The intercalation type pseudocapacitive Nb2O5 are unique due to their linearly sloped charge/discharge curve like electrochemical double layer capacitances (EDLCs) while the charged ions can be inserted/extracted reversibly from the bulk like batteries. As a result, such conjugated device can store energy like conventional EDLCs, while the self-discharge process is significantly supressed. When further added with suitable amount of titanium dioxide as the stabilizer, the conjugated supercapacitor retained 74% of its energy after aging for 48 h. These results are expected to provide a general guidance for designing materials specifically for constructing conjugated supercapacitors with high initial energy density and alleviated self-discharge.

New Technique for Probing the Protecting Character of the Solid Electrolyte Interphase as a Critical but Elusive Property for Pursuing Long Cycle Life Lithium-Ion Batteries.

The formation of a protecting nanolayer, so-called solid electrolyte interphase (SEI), on the negative electrode of Li-ion batteries (LIBs) from product precipitation of the cathodic decomposition of the electrolyte is a blessing since the electrically insulating nature of this nanolayer protects the electrode surface, preventing continuous electrolyte decomposition and enabling the large nominal cell voltage of LIBs, e.g., 3.3–3.8 V. Thus, the protection performance of the nanolayer SEI is essential for LIBs to achieve a long cycle life. Unfortunately, the evaluation of this critical property of the SEI is not trivial. Herein, a new, cheap, and easily implementable methodology, the redox-mediated enhanced coulometry, is presented to estimate the protecting quality of the SEI. The key element of the methodology is the addition of a redox mediator in the electrolyte during the degassing step (after the SEI formation cycle). The redox mediator leads to an internal self-discharge process that is inversely proportional to the protecting character of the SEI. Also, the self-discharge process results in an easily measurable decrease in Coulombic efficiency. The influence of vinylene carbonate as an electrolyte additive in the resulting SEI is used as a case study to showcase the potential of the proposed methodology.

(Digital Presentation) A 2.8V Reversible Sn-Li Battery

Tin (Sn) is a metal that is commonly used in our daily life. With the rapid development of lithium-ion battery in the past decades, Sn and its alloy, such as Sn-Cu[1], and Sn-Ni[2], Sn-Co[3] and Sn-Fe[4] have been used as anode for lithium-ion battery because they can undergo alloying/dealloying process with lithium ions and exhibit high capacity and suitable working voltage of about 0.4 V vs. Li/Li+. Sn can also undergo an oxidation reaction to Sn2+, with an electrode potential of about -0.14 V vs. SHE. It is therefore possible to also use Sn as a cathode material.Herein, we are first to demonstrate a metal-metal battery made up of Sn metal as the cathode and Li metal as the anode in organic electrolyte (see Fig. a). Sn foil and Li foil are simply assembled with 3M LiTFSI in dimethoxyethane/propylene carbonate (DME/PC) electrolyte in an Ar-filled glove box to form a pouch cell. During charging, Sn will give out two electrons and dissolves into the electrolyte as Sn2+, while during discharging, the metal ions will be re-deposited onto the cathode. Thus, the energy is stored in the form of Sn2+ in the electrolyte. The charge-discharge curves in Fig. b show that the operating voltage of the battery is about 2.8 V.Since Sn2+ that is dissolved into the electrolyte from the cathode has higher potential than the Li metal anode, any Sn2+ ions cross-over to the anode will be spontaneously reduced, decreasing the efficiency of the battery. To suppress such self-discharge process, an anion exchange membrane based on poly(ionic liquid) polymer coated on common polypropylene separator is adopted. The Sn-Li battery with the modified separator tested in a current rate of 0.2 mA cm-2 with a capacity limitation of 0.1 mAh cm-2 gives an average Coulombic efficiency about 99.5% and can be cycled for more than 1500 cycles(See Fig. c).We found that the stripping/deposition of Sn on the cathode, and its polarization depend strongly on the type of electrolyte used. With 3M LiTFSI in DME/PC electrolyte, the discharge voltage is lowered by about 0.05 V when the current density is increased from 0.2 mA cm-2 to 1 mA cm-2. More results on the factors affecting the charge-discharge performance of Sn-Li batteries will be discussed at the meeting.[1]X. F. Tan, S. D. McDonald, Q. Gu, Y. Hu, L. Wang, S. Matsumura, T. Nishimura, K. Nogita, Journal of Power Sources 2019, 415, 50.[2]H. Zhang, T. Shi, D. J. Wetzel, R. G. Nuzzo, P. V. Braun, Advanced Materials 2016, 28, 742.[3]J. Yang, J. Zhang, X. Zhou, Y. Ren, M. Jiang, J. Tang, ACS Applied Materials & Interfaces 2018, 10, 35216.[4]Z. Lin, X. Lan, X. Xiong, R. Hu, Materials Chemistry Frontiers 2021, 5, 1185. Figure 1